JP3068340B2 - Concentrator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condensing optical system incorporated in a device for storing or reproducing information using a converged light or a device for optically enlarging a minute object.
For example, the present invention relates to an improvement in an optical head device for irradiating a focused light onto an optical disc as a recording medium and an optical condensing device used in an optical microscope and the like, which are used in an optical filing system.

[0002]

2. Description of the Related Art In an optical disk apparatus, a focused light beam is applied to a recording surface of an optical disk as a recording medium.
The information already recorded on the optical disk is reproduced, and new information is recorded on the optical disk or the information is erased from the optical disk. By the way, today, it is desired to improve the recording density for an optical disk due to an increase in information to be recorded. In this case, in order to increase the recording density in the optical disk device, the beam spot diameter of the light beam used in the optical disk device must be reduced.

On the other hand, it is known that in an optical microscope apparatus, as the magnification ratio increases, the brightness of a beam spot cannot be sufficiently obtained. In this case, the light intensity of the beam spot in the light beam generated from the light source device used for illumination must be increased.

As a method for reducing the beam spot size with respect to the optical disk device and a method for increasing the light intensity of the beam spot with respect to the optical microscope device, there is a method called super-resolution. It has already been proposed.

As a method called super-resolution, a method of shielding a central portion of an opening, that is, a lens or the like, through which a light beam can pass (M. Born and E. Wolf: Princip
lesof Optics = Principles of Optics, Pergamon Press Ltd. Oxf
ord, 1975) and the light beam is divided into two concentric circles,
A method of shifting the phase of an optical beam passing through each region by 180 ° (JEwilkins, Jr .: J. Oct. Soc. Am.,
40 (1950) 22).

[0006]

However, when the above-mentioned method called super-resolution is used, as the beam spot size of the focused light beam becomes smaller, the center beam spot becomes smaller. It is known that the peak intensity at the point (1) greatly decreases, and the intensity of side lobes generated by the periphery of the center beam spot increases.

When the peak intensity decreases, for example,
In an optical disk device, the output of a light source used to record information on an optical disk must be increased.
This causes a secondary problem with respect to the heat exhaustion and miniaturization of the optical disk device.
Further, in the optical microscope, there is a problem that sufficient observation cannot be performed because the image of the object to be observed (including the virtual image for visual observation) becomes dark. On the other hand, when the intensity of the sidelobe is increased, there is a problem that a crosstalk signal from an adjacent track is mixed in reproducing information recorded on the optical disk. Further, in the optical microscope, although the above-mentioned magnification is improved, there is a problem that the contrast of the image of the object to be measured (including the virtual image for visual observation) is greatly reduced.

According to the present invention, in the above-mentioned super-resolution focusing optical system, a central beam spot having a sufficiently small beam spot and a sufficient light intensity can be formed.
It is an object of the present invention to provide a light-collecting element capable of sufficiently reducing the intensity of a side lobe generated around a focused beam spot.

[0009]

SUMMARY OF THE INVENTION The present invention has been made based on the above problem, and information is recorded using focused light.
Reproduction of information or recording of information from a recording medium
Has at least one light emitting point
And a light source that focuses light generated from the one light emitting point.
An objective lens for forming at least one spot by
The spot is located at the desired position on the recording medium.
Spot control mechanism for spot control
Placed in the optical path from the recording light source to the recording medium;
Splits light by passing or reflecting light generated from
Wavefront splits light into regions, and light intensity and phase for each adjacent region
Concentrator that changes at least one of
And a light collecting device. In addition, the present invention uses focused light to transmit information.
Reproduction of information from recorded recording media or information
At least one light emitting point
A light source having a light emitting point, and light generated from the one light emitting point.
Objective for bundling to form at least one spot
The spot and its spot at the desired position on the recording medium.
Spot control mechanism for spot control
And passes or reflects light generated from the light source.
The light in the annular region in the cross section of the light
Partial change in intensity and / or phase
The light condensing element that makes the light from the light source to the recording medium
Ru condenser der which is characterized in that is placed in the road. Still further, according to the present invention , information is recorded using focused light.
Playback or recording of information from a recording medium
Used to do and has at least one light emitting point
A light source and the light generated from the one light emitting point
An objective lens that forms at least one spot and
So that the spot is located at a desired position on the recording medium.
Spot control mechanism for spot control on
Placed in the optical path from the light source to the recording medium,
Pass or reflect the light generated from the source to split the light into wavefronts
At least one of the light intensity and phase for each adjacent area.
Also have a light-collecting element that changes either of them.
In addition, in this light-collecting element,
Ru <br/> light collector der the shape of the boundary line, characterized in that has an elliptical shape. Furthermore, the present invention uses focused light
Playback of information from a recording medium on which information is recorded
Is used to record information and at least one
A light source having a light emitting point, and generated from the one light emitting point
Focusing light to form at least one spot
Together with the spot at a desired position on the recording medium.
Spot control mechanism for spot control
Arranged in the optical path from the light source to the recording medium.
Pass or reflect the light generated from the light source
The light intensity and phase of some light in the light cross section
And a light condensing element that partially changes either
And the condensing element has a lens function.
Function is used to focus the light generated from the one emission point.
To form at least one spot.
It is a light collecting device . Still further, the invention provides a focusing
Of information from a recording medium on which information is recorded using light
Information to an information reproducing device or recording medium for reproduction
Recording / reproducing apparatus for recording at least one
A light source having a light-emitting point;
Focused light to form at least one spot
The objective lens and the spot on the recording medium
For spot control so that
Coil coil and information recorded on the recording medium.
A photodetector that converts the signal into an electric signal for reproduction.
Information playback device or information recording and playback device
Passing or reflecting the light generated from the light source,
For the light in the annular region in the light cross section, the light intensity and position
Collection that partially changes at least one of the phases
An optical element is arranged in an optical path from the light source to the recording medium.
To change the half width of the spot on the recording medium.
An information reproducing apparatus or an information recording / reproducing apparatus .

[0010]

The light- collecting element of the light-collecting device according to the present invention may be a light source.
In the optical path from the light source to the recording medium.
Wavefront splitting of light into three light splitting areas by excessive or reflected
And at least one of light intensity and phase for each adjacent region.
By changing either of them, the central beam spot
The light intensity at the
The lobe is canceled.

[0011]

Further, by defining the light splitting region of the light collecting device in a desired shape, it is possible to provide a light beam having a shape and light intensity optimal for various devices in which the light collecting device is incorporated.

[0013]

FIG. 1 shows a light-collecting element according to an embodiment of the present invention.

The light-condensing element 10 is formed of a transparent acrylic (transparent polycarbonate) or a plastic such as a transparent ABS resin, or a transparent (light beam-permissible) material such as glass. Have been. The light-collecting element 10 has minute irregularities 10a, 10b and 10 formed on at least one of the front surface 10f and the back surface 10r.
c. That is, the light-collecting element 10 includes an annular convex region 10b defined by two substantially concentric circular boundary circles, a circular concave region 10c defined inside the annular convex region 10b, and It has three light beam transmitting regions which are sectioned as peripheral concave regions (that is, the front surface 10f or the back surface 10r itself) 10a defined outside the annular convex region 10b. The surface of the circular concave region 10c and the surface of the peripheral concave region 10a have substantially the same height,
The surfaces 10c and 10a and the surface of the annular convex region 10b are located parallel to each other.

In general, the annular convex region 10b is formed with respect to a parallel plate main body (not numbered) on which the light-collecting element 10 is based.
It is formed by directly transferring (molding) a convex portion having a desired area and thickness by a mold transfer method. Further, it can be formed by a replica forming method using the 2P method or by cutting. Further, as shown in FIG. 4 described later, the phase change or the refractive index change layer 50b may be formed by an optical multilayer film capable of locally changing the phase or the refractive index change by ion replacement. .

For example, when a laser beam is incident on the front surface 10f from the back surface 10r along the Z axis shown in FIG. It can be divided into three wavefronts having characteristics corresponding to the three regions of the peripheral concave region 10a, the annular convex region 10b, and the circular concave region 10c. That is, the laser beam passed through the light condensing element 10 is the first and third light beams passed through the peripheral concave area 10a and the circular concave area 10c having substantially equal optical path lengths. And a second light beam that has passed through an annular convex region 10b having a longer optical path length than the peripheral concave region 10a and the circular concave region 10c.

In this case, by optimizing the distance between the peripheral concave region 10a and the circular concave region 10c and the annular convex region 10b, that is, the amount by which the annular convex region 10b is protruded, Can be shifted by π (+ 2nπ) (where n is an integer) [rad = radian]. Similarly, the phase of the second laser beam and the phase of the third laser beam are set to π.
(+ 2mπ) (where m is an integer and n = m also exists)
It is possible to shift by [rad]. Therefore, the phase difference between the first laser beam and the third laser beam is:
2lπ [rad] (where l is an integer, and l = n = m also exists). Incidentally, a circular shape having substantially the same protrusion amount as the annular convex region 10b, or by forming the annular convex region inside the circular concave region 10c, the region is divided into adjacent regions. It becomes possible to sequentially give a phase difference different by π to the laser beam.

Here, the second and third lasers passed through the annular convex region 10b and the circular concave region 10c.
The annular convex regions are arranged so that the
By defining the area of 10b and the circular concave region 10c,
It is possible to cancel side lobes generated around the center beam spot of the focused laser.

FIG. 2 shows an example of a device using the light-collecting element described with reference to FIG. 1, which is incorporated in an optical disk device for recording information on the optical disk or reproducing information from the optical disk. Is shown.

The optical head device 2 has a cross-sectional beam shape, ie, an elliptical beam spot, and emits divergent light, ie, a ray.
A semiconductor laser light source 12 for generating a beam, a beam spot of the laser beam generated from the laser light source 12 is corrected to be substantially circular, and the laser beam is recorded on a recording medium. That is, a polarizing beam including a beam split surface 16a for guiding the laser beam toward the optical disk 22 and separating the laser beam reflected from the optical disk 22 from the laser beam toward the optical disk 22. The splitter 16, the condensing element 10 described in FIG. 1, and the polarizing beam splitter 16
Laser beam separated through the optical disk
It has a photodetector 28 that converts the information recorded in 22 into an electric signal for reproduction.

The optical head device 2 is provided with the laser light source.
A collimating lens 14 for collimating the divergent laser beam between the polarizing beam splitter 12 and the polarizing beam splitter 16.
A .lambda. / 4 plate 18 for matching the isolation between the light transmitting system and the detecting system between the polarizing beam splitter 16 and the optical disk 22, and the laser beam. Have an objective lens 20 for focusing the light on the recording surface of the optical disk 22, respectively.

The optical head device 2 further includes a laser beam separated between the polarization beam splitter 16 and the photodetector 28 via the polarization beam splitter 16.
A focusing lens 24 for focusing a beam on the detection surface of the photodetector 28, and a laser beam passed through the objective lens 20 is positioned on the optical disk 22 with respect to the laser beam.
Cylindrical for generating a control laser beam for enabling beam spot control called focusing and tracking so that a desired beam spot is focused on a desired position on the upper side. It has a lens 26.

The condensing element 10 is provided, for example, between the objective lens 20 and the optical disk 22 or the laser light source 12.
And the polarizing beam splitter 16. The laser beam generated from the laser light source 12 is converted into a parallel beam via the collimating lens 14, and the beam spot is corrected to a substantially circular shape via the polarizing beam splitter 16. Then, the light is incident on the light-collecting element 10. The laser beam incident on the condensing element 10 is, as already described with reference to FIG. 1, the peripheral concave area 10a and the circular concave area 10c.
First and third light beams that have passed through
Wavefront division is performed on each of the second light beam that has passed through 10b.

The laser beam divided into wavefronts is λ /
The light is converted into circularly polarized light via the four plates 18, is given convergence by the objective lens 20, and is irradiated on the recording surface of the optical disk 22. The laser beam irradiated on the recording surface of the optical disc 22
The beam is reflected on the recording surface of the optical disk 22. At this time, the reflectance is locally changed according to the presence or absence of information recorded on the optical disc 22. The reflected laser beam is applied to the objective lens 20, the λ / 4 plate 18 and the light condensing element.
10 are sequentially passed through again, and the polarization beam splitter is
At the same time, the light is returned to the photodetector 28 via the beam split surface 16a.

The laser beam reflected by the beam splitting surface 16a and guided to the photodetector 28 is converted into an electric signal via the photodetector 28 and output to the signal processing circuit 30. Thus, the information is reproduced as information recorded on the optical disk 22. In the signal processing circuit 30, the foreground
An objective lens control signal for beam spot control called "cussing" and "tracking" is also generated at the same time, and the lens coil 32 is energized in accordance with the objective lens control signal so that the laser beam is transmitted to the optical disk 22. It is focused on a desired beam spot at a desired position above. Below, Figure 1
The principle that the intensity of the side lobe generated around the central beam spot can be reduced and the light intensity at the beam spot can be increased by the condensing element shown in FIG. Will be described.

First, a case where the central region _Ac does not exist in FIG. 1, that is, a light-collecting device (super-resolution device) that divides a circular aperture into two parts will be described. The light-collecting device (hereinafter referred to as apodizer) shown in FIG. 1 defines an apodization, that is, a concentric boundary circle that divides a circular aperture into two, and an amplitude inside the aperture with respect to the energy of the central portion. This is a light-collecting element using a method of changing the distribution of transmittance. The development of this apodizer will be described using the results of simulation by a computer using a quadratic Fourier transform and the results of primary analysis using an algebraic approximation formula. As a method of simulation by a computer, first, the focal length is "F" and the aperture efficiency is "NA".
The square circumscribing the circular aperture of the objective lens defined in the above is divided into 200 × 200 elements, and for each element, a) a laser beam having a uniform intensity distribution, and b)
A laser beam having a center intensity defined by e ^-2 and having a Gaussian distribution in which the beam spot diameter W is 1.25 times as large as the objective lens aperture diameter A = 2F · NA. -Stipulates that Second, the two laser beams are placed inside a concentric boundary circle that divides the circular aperture into two parts.
"0" or "-"
The above apodization is achieved by multiplying by 1 ". The resulting amplitude distribution on the pupil of the objective lens is obtained by a two-dimensional Fourier transform using Simpson's formula, and the respective levels are obtained. The beam spot amplitude distribution in the beam, where the parameters of the beam spot amplitude distribution are changed while changing the radius of the concentric boundary line, that is, c) the half width width reduction ratio, d. )
The peak efficiencies and e) the side lobe strength are obtained to obtain the graphs shown in FIGS. 6 to 17 below.

The half-width reduction ratio, peak efficiency and sidelobe intensity are respectively c) the half-width of a beam spot obtained by using super-resolution or apodization versus the conventional value. Half width at the beam spot obtained by the method of d), d) apodization (here, 2
An apodization light-collecting element, that is, an apodizer, is a light-collecting element having a super-resolution of a light-collecting element having a region structure and having a structure of three or more regions and capable of reducing the sidelobe intensity of the light-condensing spot intensity distribution. )) Versus the light intensity at the center beam spot in the beam spot obtained by the conventional method, the light intensity at the center beam spot in the beam spot obtained by the conventional method, e) the super-resolution or Defined as the sidelobe intensity at the beam spot obtained using apodization versus the light intensity at the central beam spot in the super-resolution or beam spot obtained using apodization. Have been.

FIGS. 18 to 20 show a conventionally known method of shielding the central portion of an opening and a method of dividing an optical beam into two concentrically and dividing an optical beam into respective areas. The results of evaluating the method of shifting the phase by π + 2nπ [rad] by the same evaluation method as the present invention are shown.

As is clear from FIGS. 18 and 19, it has been confirmed that in the conventional method, the peak efficiency decreases rapidly and the sidelobe strength increases as the half width reduction ratio decreases. . In particular, it is recognized that when the phase change structure is used, the peak efficiency increases and the sidelobe strength also increases. These characteristics are similar when the incident intensity is changed. On the other hand, in the method of shielding the central portion from light, there is a problem that the light-collecting efficiency is reduced and the sidelobe strength is increased. 18 and 19,
The half width reduction ratio, peak efficiency, and side lobe strength obtained based on the above conditions are rewritten based on the half width reduction ratio.

Next, in order to alleviate the disadvantage that the light-collecting efficiency is reduced in the super-resolution, a super-resolution element structure having the highest light-collecting efficiency will be considered.

The approximation formulas showing the relationship between the half-width region and the peak efficiency shown in FIGS. 18 and 19 have not been derived so far. Below, under general conditions,
Algebraically derives the condition for the highest light collection efficiency.

The planar structure of the super-resolution element is defined as the shape shown in FIG. 20A, the amplitude transmittance on the outside is 1, and T is on the inside. However, T takes a complex number in the range of | T | ≦ 1, and when taking a negative real value, the phase is π + 2nπ [ra
d] It means that it is shifted. The wavelength of the light incident on the objective lens is λ, and the coordinates on the pupil plane of the objective lens and the coordinates on the condensing plane are represented by (X, Y) and (x, y), and the following equation r = (X ² + Y ² ) ^1/2 / F · NA ‥‥‥ (1) and γ = (X ² + Y ² ) ^1/2 ‥‥‥ (2)

A pupil function indicating the optical structure of the super-resolution element is represented by g (X, Y).

In this case, the normalized spot amplitude distribution G (r) on the condensing surface is expressed by the following equation (3) when light having a uniform intensity distribution is incident on the objective lens.

(Equation 1) Becomes

Further, the following equation ρ = NAγ / λ ‥‥‥ (4) is defined, and when 1 ≧ g (r) ≧ a, g (r) = 1, a
> G (r) ≧ 0 and using g (r) = T,
(5)

(Equation 2) Is transformed.

Further, by deforming using the Bessel function, the following equation (6) is obtained.

(Equation 3) Is obtained.

Here, when the peak efficiency is represented by η, the above equation is obtained.
From (6), the following equation η ^1/2 = 1− (1-T) a ² ‥‥‥ (7) is obtained.

When the value of ρ is small, the following equation
(A1)

(Equation 4) Creating an approximate expression up to the third order terms of the [rho in it a formula G ([rho) by substituting the above equation (6) = π {[1- (1-T) a 2] - (πρ) 2 [1- (1-T) a ⁴ ]} ‥‥‥ (8) is obtained.

Here, assuming that the half-width reduction ratio is χ, the equation satisfying χ and η can be obtained from the above equations (7) and (9) by the following equation η-2 {1- (1-T) / 2χ ² } η ^1/2 + T = 0 ９ (9) is derived.

Accordingly, as a solution of the above equation (9) when η ≧ 0, equation (10)

(Equation 5) Is obtained.

Using the above equation (10), T = 0 and T =
The approximate characteristics of η to χ at −1 have been added to FIG. In this case, the value of η is shown slightly lower,
The above equation (10) generally agrees even when compared with the result of simulation by a computer. Therefore, according to equation (10), at T = 0, χ = 2 ^−1/2
At the time, η = 0 is satisfied. This indicates that at T = 0, χ is not approximately equal to or less than 2 ^−1/2 (that is, χ is always equal to or more than 2 ^−1/2 ). T = -1
In, as χ approaches 0, approximately η = 0 is obtained. Therefore, at T = -1, it is reduced to χ = 0 in principle.

When the above equation (10) is solved for χ, the following equation (11) is obtained.

(Equation 6) Is obtained.

This equation (11) indicates that when T = −1, the value of χ is smallest, that is, when T is −1, χ =
It shows that η is maximum at a constant. When the amount of phase shift is other than π + 2nπ [rad], it has been confirmed by simulation that the peak efficiency η is always smaller than the case where T = −1.

On the other hand, the equation (5) is bi in FIG 18 (a) - the amplitude distribution to produce the light passing through the opening portion P _o of the beam spot amplitude distribution is defined by a radius 1 (FIG. 18 (b) This indicates that S _{i produced} by the light passing through the opening P _i having the radius a is subtracted from S _o ) in FIG. From the above equation (7), if the values of η are equal, T
It can be seen that the value of a at T = -1 is smaller than the value of a at = 0. From this, it can be understood that the half value width of _{Sip at} T = -1 is wider than _{Sim at} T = 0.

From the above results, the super-resolution element (apodizer) formed of two regions, which has the highest light-collecting efficiency, has the light passing inside and the light passing outside. It can be seen that the phase change structure can shift the phase of light by π + 2nπ [rad]. The guideline indicating the upper limit value of the peak efficiency with respect to the reduction ratio of the half width of the beam spot when using an apodizer having a structure that splits the light into a wavefront not only in two regions but also in many regions is given by the above equation (10). )
It is approximately shown by setting T = -1.

Next, a method for reducing the strength of the primary sidelobe will be described.

By devising to extend the number of wavefront divisions of light from two regions to three regions, the relative primary sidelobe intensity can be reduced. Here, after explaining the basic principle for reducing the primary side lobe, the optimum structure taking into account the improvement of the peak efficiency will be described.

By substituting T = -1 into the above equation (6), the following equation (A5) is obtained.

(Equation 7) Applying the condition specified by the following equation, the amplitude distribution near the peak position of the primary sidelobe can be expressed by the following equation (12)

(Equation 8) Indicated by

Here, the peak efficiency η is η = 33.3%
, Then the value of a is given by a
= 0.460. In this case, G (ρ) is ρ = 0.7
2 and takes the minimum value.

At this time, the first term on the right side of the equation (12) is -0.341, and the second term is -0.715. That is, since both the first term and the second term show negative values, it is shown that when the sidelobe strength is increased, there is a synergistic effect. Further, since the direction of the value of the second term is small, the Saidoro - mainly due to increase blanking strength, bi is formed by light passing through the P _i in FIG. 18 (a) - beam spot S _im is larger contribution Is recognized.

Note that the above equation (A5) is
Are sequentially expanded, and the following equations (A2), (A
3) and (A4)

(Equation 9) Required by

That is, the above equation (A2) is obtained by making the above equation (A1) and the coefficient of the low-order term of the tailored sine function coincide with each other. On the other hand, by subjecting the above equation (A1) to macro-phosphorus expansion near Z = 5, the following equation (B1) can be obtained from a known graph.

(Equation 10) Is required.

By using Bessel's differential formula for this equation (B1) and the above equation (A1), the above equation (A1)
3) is obtained. Also, by making the coefficients of the low-order terms of this equation (A3) and the sine function coincide with each other, the above equation is obtained.
(A4) is required. These equations (A2), (A3) and
According to (A4), the above equation (A5) for the above equation (A1)
Is required.

Under the above conditions, when the ratio of the intensity of the primary sidelobe to the intensity of the center beam spot is calculated, it becomes 34.0%, which is a simulation result of 34.4% by a computer. It has been confirmed that they almost match.

Next, an apodizer that can reduce the primary sidelobe strength will be described.

By making the apodizer have a three-region structure and adding a positive term to the equation (12), the primary sidelobe is greatly reduced.

That is, as shown in FIG.
The amplitude transmittance of each region is defined as 1, A, B in order from the outside. The beam spot amplitude distribution when the uniform intensity distribution light is incident on this apodizer is given by the equation (13) from the above equation (3).

[Equation 11] Can be expressed as Here, the approximate expression at ρ = 0.72 is obtained from Expressions (13) and (A5) from Expression (14).

(Equation 12) It is expressed as

On the other hand, when b ≦ 0.8, bsin
Since (3.92b) ≧ 0, by setting B−A> 0, the first term having a positive value can be added to the equation (12).

Next, a three-region apodizer which can not only reduce the sidelobe strength but also obtain a relatively high peak efficiency will be described.

From the above equation (14), as a relational equation relating to the peak efficiency η, the equation η ^1/2 = 1− (1−A) a ² + (BA) b ² ‥‥‥ (15) Be guided.

When ρ is substantially 0, the beam spot amplitude distribution is expressed by ρ in equations (A1) and (14).
With respect to the third order term, the following equation (1
6)

(Equation 13) Is led. Therefore, from the above equations (15) and (16),
Formula (17)

[Equation 14] Is obtained. On the right side of this equation (17), the influence of the change by the fourth power is greater than the change of the values of “1-A” and “BA”. In addition, it is known that it is much more susceptible to a change in the value of a having a value larger than b. Therefore, the largest factor that determines the value of the peak efficiency η is the value of a. From this, the above a
In order to reduce the value of A, it is preferable to define A = -1 for η having a fixed desired value in the above equation (15).

In order to reduce the primary sidelobe strength, it is necessary to increase the value of the first term in the equation (14). As is apparent from the above equation (13), the first term of the above equation (14) is the beam spot amplitude distribution S _{c formed} by the light passing through the opening of radius b shown in FIG. Means As the value of b increases, the relative amplitude value decreases with respect to ρ = 0.72. Therefore, if the value of b is sufficiently reduced by defining the value of BA to be large, the strength of the side lobe is efficiently reduced.

Therefore, in order to sufficiently improve the peak efficiency while reducing the side lobe strength, the phase defined by the condition "A = -1, B = 1" is required. Variable structures are suitable.

Under the above conditions, the peak efficiency η
Is assumed to be η = 33.3%, and the optimum values of “a” and “b” in the apodizer having the phase change structure are obtained, the value of a is approximately 0.71 (this In this case, the value of b is approximately 0.54 from equation (15)).
At this time, from the above equation (14), G (0.71)
Becomes substantially zero.

The following is a result of a simulation using a computer using the two-dimensional Fourier transform and a result of verifying the result of the algebraic approximation.

Here, the value of the boundary circle radius of the outermost shell which has the greatest influence on the peak efficiency η is changed, and the above-mentioned radius reduction ratio and the above-mentioned relative value of the primary sidelobe intensity are respectively obtained. When the uniform intensity distribution light is incident, the value of η is specified, and the value of b with respect to the value of a is obtained from the above equation (15). On the other hand, when light having a Gaussian intensity distribution is incident, the following equation (18) is obtained from the above equation (3) between the above η, a and b.

(Equation 15) Is defined.

In the expression (18), α indicates a radius at which the central intensity energy of the light having the Gaussian intensity distribution becomes e ⁻² . Further, as an expression form relating to the phase type apodizer shifted by π + 2nπ, when setting the incident light amplitude distribution at the opening of the objective lens, the polarity of the amplitude distribution only in the ring-shaped region corresponding to the range from b to a is inverted. ing.

FIGS. 7 and 8 show the beam spot distribution when the light having the uniform intensity distribution and the light having the goose distribution are incident, respectively. As is apparent from the figure, the primary sidelobe is greatly reduced as the value of a increases. This effect has been found to be beneficial whether the incident light is light having a uniform intensity distribution or light having a Gaussian distribution. On the other hand, the reduction in the primary side lobe increases the half-width reduction ratio χ, albeit slightly.

In FIG. 7, the peak efficiency η is expressed as η =
Assuming 33.3%, the value of a when the primary sidelobe is substantially "0" is given by the above equation (14) and
It has been confirmed that the result of the calculation according to (15) substantially coincides with “a = 0.71”. According to FIG. 8, when the peak efficiency η is assumed to be η = 50%, the ratio of the side lobe intensity to the peak efficiency is approximately 5.8%, and the half width reduction rate χ is , 87.5%. In this case, it has been confirmed that the primary sidelobe intensity and the secondary sidelobe intensity are substantially equal.

Next, an apodizer structure having four or more regions will be described.

As described above, in the case of the three-region structure,
It has been confirmed that the primary sidelobe strength decreases as the boundary circle radius a increases, while the secondary sidelobe strength increases. When the primary sidelobe intensity is equal to the secondary sidelobe intensity, the value of the primary and secondary sidelobe intensity is determined by the peak efficiency η.
Has been found to increase with decreasing.

This indicates that it is necessary to reduce the secondary sidelobe strength in a range where the peak efficiency η is small. Therefore, a method for canceling the secondary sidelobe amplitude using light passing through the center of the apodizer with a four-region structure will be described.

The boundary circle radii of the apodizer having the four-region structure are defined as a, b, and c from the outside. In this case, the ratio of the light passing through the opening having the radius c to the sum of the amplitudes of the light passing through the annular opening surrounded by a and b is expressed by the following equation.
(19)

(Equation 16) _Is defined as _Ac obtained from

[0074] Here, assuming a case where the A _c is increased, the half-width reduction rate and the Saidoro - are determined from Deployment - the value of the probe intensity simulator by computer. In this case, the parameters - data of the setting method, peak based on the setting method in three regions structure apodizer already described - the click efficiency η is fixed, the optimal values of a and b for the value of each A _c And for each of the primary, secondary and tertiary sidelobes,
It is defined that the maximum value of each intensity is minimized. Here, when A _c = 0 holds, it goes without saying that the already described three-region structure apodizer is shown.

FIG. 10 shows the calculation results when Gaussian distributed light is incident and the peak efficiency η is 12.5%. As apparent from the figure, in the case of A _c = 0.15, minimum Saidoro - Bed intensity is achieved.

FIG. 11 shows an example of a beam spot light intensity distribution when light having a Gaussian distribution is incident on an apodizer having a four-region structure.

FIGS. 12 to 14 show a four-region structured apodizer having a structure different from that of the apodizer shown in FIGS.

The apodizer shown in FIG.
The light is divided into four regions by concentric boundary circles, and the phases of light passing through regions adjacent to each other are shifted by 180 °. Also, in this four-region structure apodizer, the sum of the amplitudes of the light passing through the annular opening P _p1 sandwiched by the boundary circles of the radii a and b, and the light passing through P _p2 sandwiched by the radii b and c. By defining the apodizer so that the sum of the amplitudes becomes equal, as shown in FIG.
A peak is located at a position similar to the position where the primary sidelobe occurs.
A correction light having a peak can be created on the beam west. That is, the correction light is generated by mutual interference between two adjacent lights.

The size (intensity) of the primary sidelobe reduced by the correction light is given by the following equation (20).

[Equation 17] It is defined by A _p being determined from.

[0080] Figure 13 is a apodizer having the 4 domain structure, when the light having a Gaussian distribution is incident, primary Saidoro to changes in the A _p - change of the probe values - Bed and tertiary Saidoro It is shown. Here,
The value of b was fixed so that the efficiency η = constant. From Figure 13, that A _p is increased, the primary Saidoro - with blanking intensity decreases, tertiary Saidoro - Bed intensity seen that increased. It is needless to say that the range in which A _p is substantially zero corresponds to the two-region structure apodizer described above.

Next, with reference to FIGS. 15 to 17, the effect when the multi-region structure apodizer described above is used will be specifically described.

In FIG. 15, the crosstalk ratio is defined as the ratio of the reproduction signal amount when the longest pit exists only in the adjacent track to the reproduction signal amount when the beam spot exists on the center of the longest pit. , Param the primary sidelobe
The results obtained by calculating the above-mentioned crosstalk ratio when the track pitch is changed are shown as data. In FIG. 15, the unit of the track pitch on the horizontal axis is represented by the magnification of the half radius at the beam spot. As is apparent from the figure, the track pitch is approximately 3 with respect to the half-value radius.
Until doubled, the crosstalk rate is kept low.

FIG. 16 shows the calculation results regarding the crosstalk ratio between the shortest pit rows recorded at sparse intervals and the crosstalk ratio between the longest pit rows.

Here, the track pitch was fixed at 3.875 of the beam spot half-value radius and the shortest pit was circular, and the crosstalk ratio to the primary sidelobe intensity ratio was calculated. That is, the crosstalk amount from the minimum pit is reduced by about 6 [dB] from the crosstalk amount from the longest pit, and even if the pits are on the same adjacent track, they are compared with the longest pits. Therefore, it is confirmed that the minimum pit has less crosstalk.

This means that, as an optical disc device, the average crosstalk amount from adjacent tracks is about -20 [dB].
Also, assuming that the worst-case pit row can be tolerated up to about -18 [dB], the target value for reducing the side lobe obtained from FIG. It is recognized that there is a significant effect.

As described above, a sufficiently focused beam spot can be obtained by using the light-collecting element 10 shown in FIG. 1 and having an uneven shape on the surface. From the results of many computer simulations, it is recognized that the four-region structure, that is, the structure in which two or more pairs of irregularities are arranged is optimal for the irregular shape.

The following is a modification of the light-collecting element capable of providing substantially the same function as the light-collecting element shown in FIG.

FIG. 3 shows an example in which the protruding portion 40b formed in a convex shape by the boundary circle is formed in an elliptical shape. Generally, at the laser beam incident surface 16b of the polarization beam splitter 16 shown in FIG. 2, the beam spot of the laser beam from the laser is corrected from an ellipse to a circle. You.
On the other hand, if the aspect ratio of the laser beam (showing the ellipticity of the cross-sectional intensity distribution isointensity line) is too large, the beam spot is transmitted to the objective lens 20 in a non-circular state. There is a possibility that it will be done.

In this case, the light condensing element 40 shown in FIG.
By forming the boundary line of each region into an elliptical shape corresponding to the elliptical component remaining in the beam spot of the laser beam as described above, the laser beam emitted from the beam splitter 16 is formed.
Can be arranged in a substantially circular shape. That is, according to FIG. 3, the projecting portion 40b is long in the direction corresponding to the long axis direction (Y axis) of the beam spot of the laser beam, and
The direction corresponding to the short axis direction (X axis) of the beam spot of the beam is formed short. Specifically, the protrusion 40b
In the above, the beam spot of the laser beam is narrowed down in the long axis direction (Y axis), and the beam spot of the laser beam is diffused in the short axis direction (X axis). Optical properties are provided. When the aspect ratio (the ratio of the minor axis to the major axis in the ellipse) is relatively small, the ellipse normally combined with the laser beam incident surface 16b of the polarizing beam splitter 16 as described above. The correction function may be omitted.

FIG. 4 shows an example in which an optical multilayer film 50 b for locally changing the phase is formed on a transparent flat plate 50. In this case, the laser beam that has passed through the optical multilayer film is repeatedly subjected to multiple reflections at the interface between the layers, and is given a phase corresponding to each layer. The actual optical path length with respect to the laser beam can be changed by locally changing the configuration of the optical multilayer film 50b by a method such as vapor deposition. Further, the above optical multilayer film
50b includes heavy ions etc. in the glass plate 50,
By changing the refractive index of the glass plate locally by ion replacement by the diffusion phenomenon at high temperature, laser beam
Alternatively, a method of changing the actual optical path length for the system may be used. Further, a light reflecting film may be formed on the front surface 50f, and the laser beam may be made incident on the back surface 50r, reflected on the front surface 50f, and then passed through the back surface 50r again to be emitted into the air. It is possible. Further, instead of providing the phase difference, the optical multilayer film 50b may change the light amount transmittance (in some cases, shield light) to give an annular light amount decrease.

FIG. 5 shows an embodiment different from the light-collecting device shown in FIGS. 1, 3 and 4. This condensing element 60 is a lens of the objective lens 20 shown in FIG.
The convex region 60b is formed in the (curved surface) portion.

More specifically, an annular convex region 60b defined by two substantially concentric boundary circles is formed in the light-collecting element or lens 60, so that the annular convex region 60b is formed. A circular concave region 60c defined inside and a peripheral concave region defined outside the annular convex region 60b.
Three light beam transmitting regions, which are defined as 60a, are formed.

Since the light-collecting element 60 is given a refractive power, ie, a curvature, that can function as a lens, the surface of the circular concave region 60c and the surface of the peripheral concave region 60a are
Formed with substantially the same curvature (height). On the other hand, the surfaces of the concave regions 60c and 60a and the surface of the convex region 60b are formed to have a curvature (not the same) defined so as to obtain the same refractive power.

The annular convex region 60b is easily formed in the same manner as the light-collecting device 10 shown in FIG. For example,
The convex (biconvex) lens body 60 that is the base of the light condensing element 60 is sandwiched by a molding “mold” having a concave portion having a desired area and thickness, and the lens body 60 is pressed while being heated. Thereby, it is easily formed. Also, a replica that creates only the convex part separately and attaches it to the lens body (lamination)
Alternatively, it can be formed by a mold transfer method in which a convex lens body is formed and only convex portions are directly molded on the lens surface. Of course, it can also be formed by cutting.

Thus, the light-collecting element 60 can be moved along the Z-axis like the light-collecting element 10 shown in FIG.
When the laser beam is incident on the surface 60f from r,
This laser beam can be divided into three wavefronts having characteristics corresponding to the three regions of the peripheral concave region 60a, the annular convex region 60b, and the circular concave region 60c. That is, the laser beam passed through the light condensing element 60 is combined with the first and third light beams passed through the peripheral concave region 60a and the circular concave region 60c having substantially equal optical path lengths. The peripheral concave area 60a and the circular concave area
The light beam is split into a second light beam that has passed through an annular convex region 60b having an optical path length longer than 60c.

In this case, as in the first embodiment shown in FIGS. 1, 3 and 4, the peripheral concave region 60a and the circular concave region 60c are located between the annular convex region 60b and the peripheral concave region 60a. By optimizing the distance, that is, the amount by which the annular convex region 60b is projected, the phase of the first laser beam and the phase of the second laser beam are set to π (+ 2nπ) (where n is an integer. ) Shift by [rad = radian]. Similarly, the phase of the second laser beam and the phase of the third laser beam are set to π (+ 2mπ) (however,
m is an integer, and n = m also exists). [rad] can be shifted. Accordingly, the phase difference between the first laser beam and the third laser beam is 2lπ [rad] (where l is an integer and l = n = m also exists).

As described above, also in this embodiment, different phase differences are sequentially given to the laser beams divided for each adjacent region by π. The curvature of the concave regions 60c and 60a and the convex region 60b is concentric by optimizing the light beam incident condition or the angle of the boundary region between the convex region 60b and the concave regions 60c and 60a. It is also possible to specify In this case, it is known that the manufacture of a "mold" used for molding is facilitated.

FIG. 21 shows a modification of the lens shown in FIG. In this example, an optical multilayer film (that is, a phase change or a refractive index change layer or a light transmittance change layer) 70b is provided at a desired position on the refraction surface of the lens 70 in the same manner as the light condensing element shown in FIG. It is formed. Therefore, the lens
It is possible to provide a local change in the refractive index and a phase transition or a change in the amount of transmitted light without making the surface of the 70 uneven. It is needless to say that all the methods disclosed with respect to the light-collecting device of FIG. 4 can be used. FIG. 22 shows another modification of the light-collecting device shown in FIG. In the example shown in FIG. 22, a projection 80b formed in a convex shape by a boundary circle formed in an ellipse is provided on the surface of the lens 80. That is, similarly to the example shown in FIG. 3, the boundary line of each region is formed in the lens 80 in an elliptical shape corresponding to the elliptical component remaining in the beam spot of the laser beam. , (Shown in Figure 2)
The laser beam emitted from the beam splitter 16 can be made substantially circular. That is, according to FIG. 22, the protruding portion 80b is longer in the direction corresponding to the long axis direction (Y axis) of the laser beam spot, and the laser beam beam is longer. The direction corresponding to the short axis direction (X axis) of the spot is formed short. More specifically, the projecting portion 80b narrows the beam spot of the laser beam in the long axis direction (Y axis) and the laser beam in the short axis direction (X axis).
Optical properties are provided that can diffuse the beam spot of the beam. Therefore, by using the lens 80 having the elliptical projection 80b formed thereon, the beam of the laser beam can be obtained.
It is possible to remove the elliptical components remaining in the data spot. As in the example of FIG. 3, when the aspect ratio of the beam spot (the ratio of the short axis to the long axis of the ellipse) is relatively small, the laser beam incident on the polarizing beam splitter 16 is incident. It goes without saying that the elliptical correction function normally combined with the surface 16b may be omitted.

When the light-collecting element of the present invention is used in an optical microscope, the light-collecting element is placed between the objective lens and a position where an image (including a virtual image) of the object to be measured is formed. By arranging, it is possible to improve resolution and obtain a clear image with little interference with surrounding images.

FIG. 23 shows a (third) embodiment which is further different from FIGS. 1, 3 and 4, and FIGS. 5, 21 and 22.

According to FIG. 23, the light-condensing element 90 is divided by substantially parallel first and second boundary lines 90a and 90b, and the convex region 90 protrudes from the plane region 90d.
c. Convex region 90c, ie, boundaries 90a and 90b
Are arranged orthogonally to the direction in which information recorded on the optical disk 22 in FIG. 2, that is, pits (not shown) are arranged (tangents to tracks (not shown)).

According to the light condensing element 90, the convex region 90c
The super-resolution described above occurs between the plane area 90d and the plane area 90d (which exists on both sides of the convex area 90c) separated from the convex area 90c via the boundary lines 90a and 90b.
Therefore, as described above, by optimizing the area ratio between the two planar regions 90d and the convex regions 90c, the light-collecting element 90
The beam spot shape of the laser beam passed through the optical disk 22 (not shown) on the optical disk 22 (in FIG. 2)
Only the book and the pits recorded on this track are covered
Can be limited to the width. In this case, the convex region 90
The shape of the beam spot of the beam passed through c is a shape obtained by cutting both sides of the circular beam spot. Therefore, the width (size) of the beam spot can be set to a size that allows the pits recorded on the track to be reliably read out without reducing the peak level of the light intensity of the beam spot. When the light condensing element 90 is of the phase transition type, the convex region 90c is configured to shift the phase by π + 2nπ [rad] with respect to the two plane regions 90d. It can be easily inferred from the examples. Also, when the light condensing element 90 is of the light amount changing type, it is apparent that the convex region 90c has a lower transmittance than the two planar regions 90d.

This reduces crosstalk from adjacent tracks, which is usually secondary to side lobes that occur around the center beam spot defined by the desired size and light intensity. it can.

FIG. 24 shows a modification of the light-collecting device shown in FIG.

The light-collecting element 92 is divided by substantially parallel first to fourth boundary lines 92a to 92d.
It has three planar regions 92 _{e1 to} 92 _e3 and two convex regions 92 _f1 and 92 _f2 defined between the planar regions. That is, the light-collecting element 92 has a planar area 92 _e1 , a first boundary 92 a, a convex area 92 _f1 , a second boundary 92 _b , and a planar area 92 _e1 .
_e2 , third boundary line 92c, convex region _92f2 , fourth boundary line 92
A light division area in which d and the plane area 92 _e2 are arranged in order is defined. In this case, the plane area 92 _e2 substantially located at the center of the light-collecting element 92 has information recorded on the optical disk 22 in FIG. 2, that is, pits (not shown) arranged in the direction (tangents to tracks (not shown)). Are arranged so as to be orthogonal to.

The plane regions 92 _{e1 to} 92 _e3 are formed so as to provide substantially the same phase to the laser beam incident on the light-collecting element 92. On the other hand, the convex region 92
_f1 and _92f2 have substantially the same phase as the laser beam incident on the light-collecting element 92, and have the above-mentioned planar regions _92e1 to _92e1 .
Π + 2n between the laser beam passed through 92 _e3
It is formed to provide a phase difference of π [rad]. Therefore, the laser beam passed through the light-collecting element 92,
Convex area between first boundary line 92a and second boundary line 92b
92 _f1 and a third boundary line 92c and Re is passed through the convex region 92 _f2 between the fourth boundary line 92d - Zabi - The beam, the second boundary line 92b and the third boundary line 92c Π + 2 with respect to the laser beam passed through the plane area 92 _e2 between
A phase difference of nπ [rad] is given. The laser beam passing through the area outside the first boundary line 92a or the fourth boundary line 92d, that is, the laser beam passing through the plane areas _92e1 and _92e3 , passes through the convex areas _92f1 and _92f2 . Based on the laser beam to be used, a phase difference of π + 2nπ [rad] is further provided. In this case, the planar region 92 _e2 passage has been Le - Zabi - beam phase and the planar region 92 _e1, passed through a 92 _e3 the Le - Zabi - the beam phase is same, of course.

The shape of the beam spot of the laser beam passed through the light condensing element 92 is a shape obtained by cutting both sides of a circular beam spot, and the side beam generated near the central spot. Is provided in a greatly reduced state. Therefore, the width (size) of the beam spot can be set to a size that allows the pits recorded on the track to be reliably read out without reducing the peak level of the light intensity of the beam spot.

FIG. 25 shows a modified example different from the light-collecting device shown in FIGS.

According to FIG. 25, the light-collecting element 94 has a first region 94b divided by a first boundary circle 94a and a second region 94b formed substantially concentrically with the first boundary circle 94a. Second Boundary Circle 94
c, having a second region 94d defined between the second boundary circle 94c and the first boundary circle 94a, and a peripheral region 94e defined outside the second boundary circle 94c. I have.

The first region 94b is formed without any limitation on the light transmittance, and all the incident laser beams are formed.
Through the system. The second region 94d is formed to have a slightly lower light transmittance than the first region 94b, and the third region 94e is formed to have a lower light transmittance than the second region 94d. .

The laser beam passed through the light condensing element 94 is provided with a characteristic that the light intensity distribution decreases substantially uniformly from the center toward the periphery. As a result, the cross-sectional shape of the light intensity distribution (not shown) of the condensed spot on the optical disk is, for example, linearly defined as compared with FIG. 6C or FIG. It is approximated as an equilateral triangle or cone. In this case, the light intensity of the laser beam emitted from the light-collecting element 94 is equal to the semiconductor laser as the light source.
It is roughly proportional to the magnitude of the current input to the device. Therefore, by changing the light intensity of the laser beam through the light condensing element 94 substantially linearly, for example, a multi-valued data is recorded on the recording medium by the laser beam having a plurality of light intensities. The size of the recording mark can be easily changed when recording is performed.

According to FIG. 26, the light-collecting element 96 is divided by first and second boundary lines 96a and 96b arranged non-parallel to each other, and is defined inside the boundary lines 96a and 96b. It has a convex region 96c and first and second planar regions 96d and 96e defined outside the boundaries 96a and 96b. In this light-collecting element 96, boundary lines 96a and 96b
2 is arranged along the direction in which information recorded on the optical disc 22 in FIG. 2, that is, pits (not shown) are arranged (tangents to tracks (not shown)).

According to the light condensing element 96, the beam spot of the laser beam incident on the light condensing element 96 is deformed along a track (not shown) so that one end has a larger radius than the other end. It is converted into a spot having an oblong, ie, water-drop or oval cross section. This is useful for making the shape, particularly the width, of the recording mark or pit recorded on the optical disk uniform. That is, the shape of the beam spot of the laser beam passed through the light-collecting element 96 is
Depends on the inclinations (shapes of the convex regions 96c) and the directions of spread of the boundary lines 96a and 96b, the shape of the beam spot is such that the side corresponding to the leading end of the pit on the optical disc is closer to the trailing end side. By defining the shape of the convex region 96c so as to form a deformed long ellipse having a large radius, the intensity of the laser beam required for forming the pit gradually decreases toward the rear end side of the pit. Can be done.

Therefore, the complicated beam control conventionally used to maintain the pit width constant, for example, 1
When recording one pit, it is not necessary to change the light intensity of the laser beam between the position corresponding to the leading end and the position corresponding to the trailing end of the pit.

FIG. 27 shows a modification of the light-collecting device shown in FIG.

As is clear from the figure, the light condensing element 96 is
The position of the dividing line compared to the condensing element 96 shown in FIG.
96a, 96b and areas 96c, 96 divided through division lines
Substantially the same structure is provided except for the different shapes of d and 96e. Therefore, it goes without saying that it functions substantially the same as the light-collecting element already shown in FIG.

FIG. 28 shows another modification of the light collector shown in FIG.

According to FIG. 28, the light condensing element or lens 100
Are separated by first and second boundary lines 102a and 102b that are substantially parallel as viewed from a plane,
The lens has a concave area 106 cut out from the outer surface area 104 of the lens. That is, the lens 100 has the concave area 1
The first and second outer surface areas 104a and 104b, which are defined to have substantially the same area, and the concave area 106 are provided with the area 06 interposed therebetween. The concave area 106 is arranged so as to be orthogonal to the information recorded on the optical disk 22 in FIG. 2, that is, the direction in which pits (not shown) are arranged (tangents to tracks (not shown)). Also, the surfaces of the concave region 106 and the two external surface regions 104a and 104b are provided with curvatures (not the same) defined so as to obtain mutually equal refractive powers.

According to the light-collecting device 100, the concave region 106
And the super-resolution described above occurs between the concave region 106 and the two external surface regions 104a and 104b separated via the boundary lines 102a and 102b. That is, the concave region 106
, Two outer surface areas 104a and 104
The phase of the laser beam passing through b is π + 2nπ [r
ad] It is shifted. Therefore, as already explained, 2
By optimizing the area ratio between the two outer surface areas 104a and 104b and the concave area 106, the beam spot shape of the laser beam that has passed through the light condensing element 100 is shown in FIG. It is possible to limit the width of only one track (not shown) of the optical disc 22 and the pits recorded on this track to the cover width.

Since the light-collecting element 100 has a predetermined curvature, the laser beam passing through the light-collecting element 100 has a circular beam spot shape. It is defined in a shape with both sides cut, while it is focused to the desired beam spot diameter. Further, it is possible to reduce crosstalk from an adjacent track, which is generated secondarily due to side lobes generated around the center beam spot.

FIG. 29 shows a modification of the light-collecting device shown in FIG.

According to FIG. 29, the light-collecting element 110 is divided by first to fourth boundary lines 112a to 112d which are substantially parallel when viewed from a plane, and the outline of the lens.
It has two convex regions 116a and 116b projecting from 114. The outer shape line 114 of the lens is divided into first to third outer shape surface regions 118a, 118b and 118c via the two convex regions 116a and 116b.
The information recorded on the optical disc 22 in FIG. 2, that is, pits (not shown) are arranged in the second outer surface area 118b located substantially at the center of the light condensing element 110.
(Tangent lines of tracks (not shown)). The phase of the laser beam passing through the two convex regions 116a and 116b is shifted by π + 2nπ [rad] with reference to the second outer surface region 118b. On the other hand, the first and third outer surface areas 118a and 118a located outside the two convex areas 116a and 116b
The phase of the laser beam passed through 118c is π + 2nπ compared to the two convex regions 116a and 116b.
[rad] is shifted. Naturally, the phase of the laser beam passing through the second external surface area 118b and the phase of the laser beam passing through the first and third external surface areas 118a and 118c are the same. Stipulated.

The laser beam passed through the light condensing element 110
The beam spot shape of the beam is a shape obtained by cutting both sides of a circular beam spot, and is provided as a state in which side lobes generated near the center spot are greatly reduced. Accordingly, the width of the beam spot can be reduced without reducing the peak level of the light intensity of the beam spot.
(Size) can be set to a size that allows the pits recorded on the track to be reliably read. Further, since the light-collecting element 110 has a predetermined curvature,
The laser beam passed through the light condensing element 110 is a desired beam.
Focused on the spot diameter.

FIG. 30 shows a modification of the light-collecting device shown in FIG.

The light-collecting element 120 is an example that functions substantially the same as the light-collecting element shown in FIG.
Twenty refraction surfaces are provided with substantially parallel strip-shaped optical multilayer films 122a and 122b as viewed from a plane. Each of the optical multilayer films 122a and 122b is a phase change layer, a refractive index change layer, or a light transmittance change layer, and is formed by the same method as that of the condensing element of FIG. Also, the outline 124 of the lens is
First to third outer surface areas 1 via 22a and 122b
26a, 126b and 126c. As in the other embodiments, the optical multilayer films 122a and 122b have a second outer surface area 126b located substantially at the center of the light condensing element 120 and a tangential direction of a track (not shown). Are arranged so as to be orthogonal to.

According to the light-collecting element 120, similarly to the light-collecting element 110 described above, the laser beam passing through the optical multilayer films 122a and 122b with reference to the second outer surface area 126b is used. The phase is shifted by π + 2nπ [rad]. Also, the first and third outer surface areas 126a and 126c located outside the optical multilayer films 122a and 122b.
The phase of the laser beam passed through the
It is further shifted by π + 2nπ [rad] compared to 122b. Similarly, the phase of the laser beam passing through the second outer surface area 126b and the first and third outer surface areas 1
The phase of the laser beam passed through 26a and 126c is defined identically.

FIG. 31 shows an example of an apparatus using the light-collecting element according to any of the embodiments of the present invention.
Built into the beam printer,
An example as an optical device for irradiating a beam is shown.

The printer 150 includes a semiconductor laser (light source) 152 for generating a laser beam, and the semiconductor laser 152.
Deflecting device 156 for deflecting the laser beam from the photosensitive drum, a photosensitive drum 160 on which an electrostatic latent image corresponding to the laser beam deflected via the deflecting device 156 is formed, and this photosensitive member It has an image output unit (not shown) for visualizing the electrostatic latent image formed on the drum 160 and printing it out on recording paper. In the vicinity of the photoconductor drum 160 and at a position that does not affect the image forming area of the photoconductor drum 160, a laser beam in the main scanning direction described later is provided.
Horizontal sync detector 1 to detect horizontal sync of beam
80 are located.

Between the semiconductor laser 152 and the deflecting device 156, the beam cross-sectional shape of the laser beam from the laser 152 is required when used as a laser beam printer. A pre-deflection optical system 154 for narrowing down to a size to be performed is arranged. Also, the deflection device 156 and the photosensitive drum 1
60 and the photosensitive drum via the deflecting device 156
With respect to the laser beam irradiated to the drum 160 in a substantially straight line, after the laser beam is deflected to form an image on the drum 160 so that the laser beam becomes substantially constant at all positions on the drum 160. Optical system 158 is located.

The pre-deflection optical system 154 includes a collimating lens 162 for converting a divergent laser beam from the laser 152 into a parallel beam, and a collimated lens via the collimating lens 162. A light-collecting element 164 for sufficiently reducing the beam cross-sectional shape of the beam, that is, the size of the beam spot, and having passed through the light-collecting element 164, the beam spot size was sufficiently reduced. A cylindrical lens for causing a laser beam to be perpendicularly incident on the reflecting surface of the deflecting device 156.
166 and so on. As the light-collecting element 164, a super-resolution optical element (FIG. 5, FIG. 21, FIG. 22, etc.) according to the embodiment of the present invention described above is used. The cylindrical lens 166 is provided with a refractive power only in a direction orthogonal to a deflecting direction of the deflecting device 156 (a rotating direction of a reflecting surface described later, that is, generally called a main scanning direction), that is, a sub-scanning direction.

The deflecting device 156 includes a polygonal mirror 1 having a plurality of reflecting surfaces arranged circumferentially and rotatably formed.
68, a motor 170 for rotating the polygon mirror 168 at a desired speed, and the like. Polygonal mirror 168
The shape of the reflecting surface is formed as either a flat surface or an aspheric surface in accordance with the combination with the fθ lens described later.

The post-deflection optical system 158 includes a laser beam that has passed through the first and second fθ lenses 172 and 174 and the second fθ lens 174 that provide desired optical characteristics to the laser beam. Outgoing mirror 176 for bending the beam toward the photosensitive drum 160. First fθ lens 1
Numeral 72 denotes an aspherical fθ lens, which has a refractive power substantially equal to the direction in which the refractive power is given (ie, the sub-scanning direction) with respect to the cylindrical lens 166. The first fθ lens 172 is provided on the photosensitive drum 1 due to the inclination of each reflecting surface of the deflecting device 156.
In addition to reducing the deviation of the laser beam on the photoreceptor drum 60, the position of the laser beam irradiated linearly on the photosensitive drum 160 is determined for each reflection surface of the deflecting device 156. It is used to make it proportional to the rotation angle of each reflection surface. On the other hand, the second fθ lens 174 is a toric lens to which refractive power is given only in the deflecting direction of the deflecting device 156, that is, in the main scanning direction.
In cooperation with 172, the position of the laser beam irradiated linearly on each reflecting surface of the deflecting device 156 on the photosensitive drum 160 is proportional to the rotation angle of each reflecting surface. Let it.

A drive mechanism (not shown) is arranged on the photosensitive drum 160. The photosensitive drum 160 is rotated at a desired speed in a desired direction, that is, in a sub-scanning direction orthogonal to the main scanning direction, via the driving mechanism.

The horizontal synchronization detector 180 passes through the second fθ lens 174 and travels toward the photosensitive drum 160.
A part of the beam is detected and a horizontal synchronizing signal is supplied to a controller (not shown).

When a binary print signal containing image information to be printed out is input via an input device (not shown), a laser beam output from the semiconductor laser 152 in response to the print signal is output. It is turned on / off. This intermittent on /
The laser beam in the off state is the collimating lens 1
After being converted into a parallel beam via 62, it is converted via a condenser 164 into a focused beam having a sufficiently small beam spot. The laser beam that has passed through the light condensing element 164 is guided to a plurality of reflecting surfaces of the polygon mirror 168, and is continuously reflected at a constant angular velocity toward the photosensitive drum 160 with the rotation of each reflecting surface. This reflected laser
The rotation of each reflection surface and the position on the photosensitive drum 160 are proportional to each other via the first and second fθ lenses 172 and 174, and the beam is irradiated onto the photosensitive drum 160 in a substantially linear manner.

Since the laser beam guided to the photosensitive drum 160 is turned on / off as image information, the photosensitive drum 160 is turned on / off, that is, the laser beam is turned on / off. Then, an electrostatic latent image corresponding to the image information is formed.
The electrostatic latent image is developed by supplying a visualizing agent such as toner by a developing device (not shown), and the toner is transferred to recording paper fed from a paper feeding device (not shown). The toner is fixed to the recording paper via a fixing device which is not used, and is printed out as a hard copy. In this case, as described above, since the light condensing element 164 can reduce the beam spot of the laser beam, a fine hard copy with high resolution can be obtained. Further, since the light-collecting element 164 increases the intensity of the laser beam, the polygon mirror 168 in the deflecting device 156 can be rotated at a high speed. Therefore, a printing device having a high printing speed is provided.

[0137]

As described above, according to the present invention, 1) a beam at a position where a light beam from a light source is imaged.
And the side spot
Can be greatly reduced. In this case, the light beam from the light source
Since the light collection efficiency of the light source is sufficiently ensured, it is not necessary to consider a light source having a large size and exhaust heat.

2) Since the structure is simple, the manufacturing cost is reduced.

3) Since the optical system can also be used as an objective lens or a polarizing beam splitter, the entire optical system can be reduced in weight and size.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a light-collecting element (apodizer) according to an embodiment of the present invention.

FIG. 2 is a schematic plan view showing an optical head device into which the light-collecting device shown in FIG. 1 is incorporated.

FIG. 3 is a schematic view showing a modified example of the light-collecting device shown in FIG.

FIG. 4 is a schematic view showing a modification of the light-collecting device shown in FIG. 1;

FIG. 5 is a schematic view showing another embodiment different from the light condensing element shown in FIG. 1;

FIG. 6 is a graph showing a relationship between the three-region structure apodizer shown in FIG. 1 and light collection efficiency.

FIG. 7 is a graph showing characteristics when light having a uniform intensity distribution is incident on the three-region apodizer shown in FIG. 1;

8 is a graph showing characteristics when light having a Gaussian intensity distribution is incident on the three-region structure apodizer shown in FIG.

FIG. 9 is a graph showing a relative intensity between a beam intensity and a side lobe intensity of a center beam spot in an optical beam passing through the three-region structure apodizer shown in FIG.

FIG. 10 shows a state in which the three-region structure apodizer shown in FIG. 1 is transformed into a four-region structure, and light having a Gaussian intensity distribution is incident while changing the ratio between the annular opening and the center opening. The graph which shows the characteristic in the case.

FIG. 11 shows a three-region apodizer shown in FIG. 1 transformed into a four-region structure, and the beam intensity and side lobe of the center beam spot in the light beam passing through the four-region structure apodizer. The graph which shows the relative intensity | strength with intensity | strength.

FIG. 12 shows a four-region structure apodizer different from an apodizer obtained by transforming the three-region structure apodizer shown in FIG. 1 into a four-region structure (only the characteristics are shown in FIGS. 11 and 12), and the light collection efficiency. The graph which shows the relationship.

13 is a graph showing characteristics when light having a Gaussian intensity distribution is made incident on the four-region structure apodizer shown in FIG.

FIG. 14 is a graph showing a relative intensity between a beam intensity and a side lobe intensity of a center beam spot in an optical beam that has passed through the four-region structure apodizer shown in FIG.

FIG. 15 is a graph showing the effect on a reproduction signal when the apodizer of the present invention is incorporated in the optical disk device shown in FIG. 2 (change in crosstalk with respect to the track traveling direction).

FIG. 16 is a graph showing an influence on a reproduced signal when the apodizer of the present invention is incorporated in the optical disk device shown in FIG. 2;

FIG. 17 is a graph showing the influence on a reproduction signal when the apodizer of the present invention is incorporated in the optical disk device shown in FIG. 2 (change in crosstalk in a direction crossing a track).

FIG. 18 is a graph showing characteristics when light having a uniform intensity distribution is incident on a conventionally used super-resolution optical element.

FIG. 19 is a graph showing characteristics when light having a Gaussian intensity distribution is incident on a conventionally used super-resolution optical element.

FIG. 20 is a graph showing a relationship between a conventionally used super-resolution optical element and light-collecting efficiency.

FIG. 21 is a schematic diagram showing a modification of the light-collecting device shown in FIG. 5;

FIG. 22 is a schematic view showing another modification of the light-collecting device shown in FIG. 5;

FIG. 23 is a schematic view showing still another embodiment of the light condensing element shown in FIGS. 1 and 5;

24 is a schematic diagram showing a modification of the light-collecting device shown in FIG.

FIG. 25 is a schematic view showing another modification of the light-collecting device shown in FIG. 23;

FIG. 26 is a schematic diagram showing still another modification of the light-collecting device shown in FIG. 23;

FIG. 27 is a schematic diagram showing still another modification of the light-collecting device shown in FIG. 23;

FIG. 28 is a schematic view showing still another modification of the light-collecting device shown in FIG. 5;

FIG. 29 is a schematic view showing a modification of the light-collecting device shown in FIG. 28;

FIG. 30 is a schematic diagram showing another modification of the light-collecting device shown in FIG. 28;

FIG. 31 is a schematic view showing an example of a printer device in which the super-resolution optical element of the present invention is incorporated.

[Explanation of symbols]

10 ... Light-collecting element (apotizer), 10a ... Peripheral concave area, 10b
... annular convex area, 10c ... circular concave area.

Claims (6)

(57) [Claims] 1. Recording in which information is recorded using focused light
To play back or record information from media
A light source that is used and has at least one light emitting point, and that focuses light generated from the one light emitting point to at least
The objective lens that forms one spot and its spot
So that the slot is positioned at the desired position on the recording medium.
A spot control mechanism for controlling the light, and an
The light generated from the source is passed or reflected , the light is split into three light splitting areas, and the light intensity and intensity are divided for each adjacent area.
Focusing to change at least one of the phases from one another
Condenser, characterized by comprising the element. 2. Recording in which information is recorded using focused light
To play back or record information from media
A light source that is used and has at least one light emitting point, and that focuses light generated from the one light emitting point to at least
The objective lens that forms one spot and its spot
So that the slot is positioned at the desired position on the recording medium.
Equipped with a spot control mechanism for controlling the light, passing or reflecting light generated from the light source,
Light intensity and phase for light in the annular region in light cross section
Light that partially changes at least one of the
An element is arranged in an optical path from the light source to the recording medium.
A light condensing device , characterized in that: 3. Recording in which information is recorded using a focused light
To play back or record information from media
A light source that is used and has at least one light emitting point, and that focuses light generated from the one light emitting point to at least
The objective lens that forms one spot and its spot
So that the slot is positioned at the desired position on the recording medium.
A spot control mechanism for controlling the position of the light source , and a light control mechanism disposed in the optical path from the light source to the recording medium.
The light generated by the light source passes through or reflects
Divide the surface and reduce the light intensity and phase
Equipped with a light-condensing element that changes at least one of them
In addition, each area that splits light into wavefronts in this light-collecting element
The feature is that the shape of the boundary between them is elliptical
Light-collecting device that. 4. A recording in which information is recorded using focused light.
To play back or record information from media
A light source that is used and has at least one light emitting point, and that focuses light generated from the one light emitting point to at least
Also, one spot is formed and the above spot is recorded.
Spot control so that it is located at the desired position on the recording medium
And a spot control mechanism for controlling the position of the light source and the light source from the light source to the recording medium.
The light generated from the light source passes through or reflects
At least one of light intensity and phase for some light in the plane
Equipped with a light-collecting element that partially changes
The light-collecting element has a lens function, and this lens function is used.
Light generated from the one light emitting point
A light condensing device characterized by forming at least one spot . 5. A recording in which information is recorded using focused light.
Information reproducing device or recording for reproducing information from medium
An information recording / reproducing apparatus for recording information on a medium.
Ri, a light source having at least one emission point, the less focus the light generated from the one light-emitting point
An objective lens for forming one spot, and the spot is arranged at a desired position on the recording medium.
And a lens coil for performing spot control so as to reproduce information recorded on the recording medium.
Contact a photodetector for converting into an electric signal, the information reproducing apparatus or information recording and reproducing apparatus equipped with a
There are, passed through or reflect light generated from the light source, the
For the light in the annular region in the light cross section, the light intensity and position
Collection that partially changes at least one of the phases
An optical element is arranged in an optical path from the light source to the recording medium.
To change the half width of the spot on the recording medium.
An information reproducing apparatus or an information recording / reproducing apparatus characterized by the above-mentioned. 6. A method for reducing the half width of a spot on a recording medium.
And the side lobe intensity of the spot is 7% or less
An information reproducing apparatus according to claim 5, wherein
Or an information recording / reproducing device.