JPH0695174B2 - Optical information recording device - Google Patents

Description

The present invention relates to an optical information recording device capable of recording information using laser light.

(Prior Art) Conventionally, various methods of recording information have been developed,
Among them, the information recording performed by using a laser beam is particularly attracting attention.

Among them, signal writing to various discs is performed by using a microfabrication technique using a large laser. As a method of writing a signal to various discs using the laser light, a method of narrowing the laser light into a minute light spot and exposing it to a photosensitive chemical material, a shape of a recording surface by heat of the light spot, There are things that are changing the reflectance. In this case, the precision of the machined surface is 0.
High precision of less than 1 (μm) may be required.

However, the device using this large-sized laser (for example, Ar ⁺ laser) has various problems.

The pointing stability (stability of the emitting position and the emitting angle of the light emitted from the tube of the laser) immediately after turning on the laser is not so good as to meet the requirements of the recording optical system. This state can be understood from the figure showing the measurement result of the pointing stability of the Ar ⁺ laser in FIG.

Since the large laser is incorporated as a part of the optical system, whenever this large laser is adjusted, other optical systems that require precise positional accuracy must be readjusted accordingly. I won't. Regarding this, the life of the laser tube is usually about 1000 to 2000 H, and the laser tube must be replaced before use, and it is completely inconvenient to adjust the optical system each time.

Further, the vibration from the outside causes the optical axis variation, which causes the misalignment of the light spot on the recording surface. This is a technical problem that must be eliminated in order to record information with high precision in the submicron order.

As described above, it is no exaggeration to say that solving the above problems such as requiring a great amount of warm-up time is a problem of the current optical recording technology.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the problems as described above. The purpose of the present invention is to reduce the size of the device and to provide highly accurate and stable information. An optical information recording device capable of recording is provided. Moreover,
The present invention provides an optical information recording apparatus that does not require re-adjustment of an optical system except for optical fluctuations of laser light due to various factors, and greatly reduces the warm-up time of laser.

[Structure of the Invention] (Means for Solving the Problem) The present invention relates to two servo mirrors for reflecting light emitted from a laser oscillator in an arbitrary direction, and two light splitting elements provided behind these servo mirrors. And the rotation control of the two servo mirrors by a position control signal from a photodetector that detects the light split by each light splitting element so that the light is incident on a predetermined position on each of these light splitting elements. To do. Furthermore, the distance between the two servo mirrors (k ₀ ), the distance between the second servo mirror and the first photodetector (k ₂ ) and the distance between the two photodetectors (k ₃ ) are as follows: Is satisfied.

k ₀ <k ₂ k ₃ (Operation) Laser beam emission position by the above configuration. By providing an automatic optical axis correction function that detects and corrects the angle deviation,
The optical axis stability during recording is greatly increased, and readjustment of the optical system due to various factors can be eliminated.

(Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings.
First, the optical system of this embodiment will be described with reference to the basic configuration diagram of the optical information recording apparatus of FIG. In addition, a portion from the Ar ⁺ laser device 1 to the servo mirror 5 in FIG. 1 which is not visible in this figure is shown in FIG. First, the light (for example, 4579Å) emitted from the Ar ⁺ laser device 1 is corrected to the optimum optical axis by the mirror 3 and the two servo mirrors 4 and 5 which form the optical axis correction unit. Here, the two servo mirrors 4 and 5 are one of the features of this embodiment, and will be described in detail later. The beam reflected by the servo mirror 5 is split by the beam splitter 7 into two desired spectral ratios of the information signal and the tracking signal recording beam.

First, the system for the former (information signal recording beam) will be described. One of the lights decomposed by the beam splitter 7 passes through the optical modulator 12 and is subjected to optical intensity modulation by a signal,
The amount of light is controlled. Then, the light emitted from the light modulator 12 passes through the mirrors 13 and 14 and the two convex lenses 15 and
The first collimator optical system including the pinhole 16 and the pinhole 16 magnifies and collimates the light and makes it enter the mirror 18. The light reflected by the mirror 18 is reflected by the half prism 19
Most of the light intensity (eg 96%) is reflected by the beam splitter 36
Part (for example, 4%) is divided into the two-divided photodetector 21 via the convex lens 20. Here, the control signal output from the photodetector 21 is the first
Up and down the first convex lens 15 of the collimator optical system of
Here, the fluctuation of the optical axis is minimized. The beam position servo optical system will be described later in detail.

The other light split by the beam splitter 7 is incident on the half prism 8 as a tracking signal recording beam, where it is further transmitted to the mirror 22.
To the half prism 9 as a control signal. This half mirror 9 or less photo detector 10,11
Will be described later in detail together with the above-mentioned servo mirrors 4 and 5.

The tracking recording beam reflected by the mirror 22 is subjected to light intensity modulation and light amount control by an optical modulator 23, and is incident on a mirror 24. The light reflected by the mirror 24 is converted by the 1/2 entrance plate 25 in the direction of linear deflection from a vertical direction on the surface plate 6 to a horizontal direction,
It is incident on a second (beam expanding) collimator optical system composed of two convex lenses 26, 29 and a pinhole 28 via 26. In addition, through this second collimator optical system,
The light reflected by the mirror 30 is mostly transmitted by the half prism 31, is further reflected by the mirror 35, and enters the deflection beam splitter 36 together with the information signal recording beam as a tracking signal recording beam. Here, the two beams are superposed. The light decomposed (reflected) by the other half prism 31 is incident on the two-divided photodetector 34 via the mirror 32 and the convex lens 33 for detecting the optical axis angular displacement. The control signal output from the photodetector 34 drives the first convex lens 27 of the second collimator optical system, where the optical axis fluctuation of the tracking signal recording beam is minimized. This is similar to the beam position servo optical system in the above-mentioned first collimator optical system, and will be described later in the same manner in detail.

The two beams (for information recording and for tracking signal recording) superimposed in the deflection beam splitter 36 are reflected by a mirror 37, and most of the light amount (for example, 96%) is reflected by a half prism 38 via a moving optical system (not shown). Then, the information signal and the tracking signal are recorded on the recording medium. In this case, it is desirable that the relative position (that is, the relative angle) of the two beams is always kept constant. On the other hand, a part (for example, 4%) of the light amount is reflected here and is reflected by the mirror 39.
The beam that is totally reflected by and is returned by the converging lens 40, and the putter is focused by the objective lens 41 (mirror 42, Huff prism (for example, branch ratio 50%: 50%)) and eyepiece lens 44. It can be seen from above with a shape observation microscope. Also, split by half prism 43 (reflection)
The other light thus formed is observed by the camera 45 in terms of beam shape, two beams (information signal, tracking signal), and
The beam shape of the reflected light from the recording medium is observed, and the setting of the focus position is monitored by the data from the camera 45.

Next, the principle of the above beam position servo optical system will be described with reference to FIG. The same parts as those in FIG. 1 are designated by the same reference numerals. The convex lens 15 is 27, 17 is 29, and 20 is 33.
Then, the phototiter 21 will be explained as if it were the same as 34. The convex lenses 15 and 17 form a beam expander, and the convex lens 20 forms an image of the light passing through the expander on the photodetector PD21. Assuming that the exit angle of the light in the vertical plane is displaced by Δθ, the beam movement amount ΔL on the photodetector PD21 is (F ₁ , f ₂ , and f ₃ are focal lengths of the convex lenses 15 and 17). Therefore, in order to return the position of this light to the position before the movement, it is necessary to move the convex lens 15 in the vertical direction.
The amount of movement of the convex lens 15 at the focal position corresponding to ΔL is f ₁ Δ
θ. Therefore, the photoelectrically converted ΔL is a motor 69 directly connected to the convex lens 15 so that a considerable electric signal becomes zero.
By forming a loop that controls the beam position, the beam position can always be kept constant.

However, it is actually difficult to install the photodetector 21 at a predetermined position when the beam position servo optical system is assembled by this method. This situation is shown in FIG. When the light including the parallel movement component Δl is incident on the desired input light shown by the dotted line, the angle change is not output if the photodetector 21 is installed at a predetermined position.
If the photodetector 21 is installed at the position (the position that is moved forward by Δlp), the parallel translation component Δl above becomes 2
At the 1'position, Error is detected and the motor 69 of FIG. 6 shown above is detected.
Therefore, the convex lens 15 is corrected as an angle correction value.
In other words, in this system, although the parallel movement component is not a problem, the parallel movement component is recognized as an angular displacement and malfunctions.

Therefore, in addition to this beam position servo optical system, the following optical axis correction servos are arranged.

The optical axis correction servo system, which is one of the features of this embodiment, will be described with reference to FIG. FIG. 3 is a diagram showing a hardware configuration for correcting the optical axis of the light emitted from the Ar ⁺ laser device 1. (Note that the mirror 3 is omitted from the drawing for the sake of explanation.) First, the light emitted from the Ar ⁺ laser device 1 is guided by the first servo mirror 4 onto the second servo mirror 5, and The light reflected by the second servo mirror 5 is guided to the half prisms 8 and 9. The first and second servo mirrors 4 and 5 can rotate as indicated by arrows in the figure. The light reflected by the half prism 8 is guided to the first photodetector 10 divided into four parts, and the output of this photodetector 10 is used as a control signal for the two motors 100, 10
Drive 1 The four-divided photodetectors 10 and 11 are already known. For example, the vertical error signal of the first photodetector 10 is detected by the comparison amplifier 104, and the horizontal error signal is detected by the comparison amplifier 105. In response, the motors 100 and 101 of the servo mirror 4 are driven. Similarly, the vertical error signal and the horizontal error signal of the second photodetector 11 are detected by the comparison amplifiers 106 and 107, respectively, and the motors 102 and 103 are driven. What is important in constructing this optical axis correction servo system is that one of the two photodetectors that is closer to the Ar ⁺ laser device 1, that is, the control signal from the first photodetector 10 described above
Of the two servo mirrors, the one closer to the Ar ⁺ laser device 1, that is, the first servo mirror 2 described above must be driven, and the light emitted from the Ar ⁺ laser device 1 has two servo mirrors 4, It must be configured in the order of being incident on the two photodetectors 10 and 11 after passing through 5. According to the experiment conducted by the inventor,
The first photodetector causes the second servo mirror to move to the second servomirror.
If the photodetector detects the control signal for driving the first servo mirror, it diverges somewhere where the light emission position and the angular deviation are corrected.

That is, since the conditions for forming the servo system for optical axis correction are such that the light always passes through two predetermined points, first, (1) the light is incident on the first and second servo mirrors and the first servo mirror. And the second photodetector in that order.

(2) The control signal for rotating the first servo mirror is from the first photodetector.

Is mentioned.

Next, the conditions for the optical axis correction will be further examined with reference to FIGS. 4 and 5. FIG. 4 is a diagram schematically showing the configuration of FIG. The same parts as those described above are given the same numbers. First, the distance from the first servo mirror 4 to the second servo mirror 5 is k ₀ , the first servo mirror 4
To the first photo detector (hereinafter simply referred to as PD ₁ ) 1
The distance from 0 to k ₁ and the distance from the second servo mirror 5 to the second photo detector (hereinafter simply referred to as PD ₂ ) 11 are k.
_Set to ₃ . The coefficients indicating the distances of k _{1 to} k ₃ are variable gain coefficients. Further, the emission angle variable of the light from the Ar ⁺ laser device 1 is Δθ ₀ , the emission position displacement is Δl ₀ , the drive angle displacements of the first and second servo mirrors 4 and 5 are Δθm ₁ and Δθm ₂ , PD ₁ 10
The above angular displacement and positional displacement are respectively Δθ ₂ , Δl ₂ , and the transfer functions of the first and second servo mirrors 4 and 5, respectively. (G ₁ , G ₂ : gain coefficient).

Therefore, the angular displacement and position displacement on PD ₁ 10, PD ₂ 11 are Is.

When this system is the addition point of interest and blocks it is on the PD ₁ 10, PD ₂ 11, becomes as shown in FIG. 5 (a). Therefore, when N ₁ (s) =-Δl ₀ + Δθ ₀ k, N ₂ (s) = Δθ ₀ k ₄ is converted, the result is as shown in FIG. 5 (b). The first servo mirror 4, PD ₁ (10) and the second servo mirror 5, PD ₂ (1
Each control loop of 1) becomes a minor loop and its characteristics can be determined independently. However, as you can see from this figure, this loop has an expanded transfer number of 500 and a combined transfer function.
501 is present, and in order to stabilize the entire closed-loop characteristic, selection of the above conversion gain coefficient (distance between each element) is important.

Output of expanded transfer function 500 from addition point 502 (output E ₁ (s))
The transfer function up to E ₂ (s) is Becomes This steady-state deviation is based on the theorem of the final value, This stability condition is k ₁ k ₃ (1).

Next, the transfer function of the closed loop is (N ₂ (s) = 0.) Summing point 502 is is part of the summing junction on the PD ₁ 10. Also, since the drive change of the servo mirror has a double gain, Is the closed loop stabilization condition.

Therefore, From this, k ₀ <k ₂ (2) is obtained. From the above (1) and (2), k ₀ <k ₂ k ₃ (3) is obtained as the loop stability condition. That is, this equation (3) is
To be the eccentricity of interference and the rotation center of the orthogonal axes, such as a servo mirror and the like for correction is between the second servo mirror 5 first photodetector PD ₁ 10 distance (k ₂₎ of first and second It is optimal for stability that the distance is sufficiently larger than the distance (k ₀ ) between the servo mirrors 4, 5.

As described above, part of the tracking recording beam is classified,
Two 4-division photo detectors detect the position and angle deviation of the light emitted from the Ar ⁺ laser device, and correct the optical axis correction servo system, and the output light of each collimator system is detected by the 2-division photo detector. By the beam position servo system that minimizes the optical axis polarization by driving the first convex lens of each collimator system, the relative position fluctuation of the information signal recording beam and the tracking signal recording required beam described above is ± 0.05. It could be suppressed to less than μm. Up to this point, two beams have been described as an information signal recording beam and a tracking recording beam, but when the target recording medium is, for example, a write-once recording disc, as shown in the disc sectional view of FIG. One of the two beams is used as a beam for forming a guide groove (group) (where information is recorded here) and a beam for recording sector information required for recording within a 1.6 μm pitch. Can be used. The fact that such sector information can be recorded at a normal track pitch interval can minimize the relative position fluctuation of the two beams as shown above.

[Effect of the Invention] According to the present invention, it is possible to connect a spot to a predetermined position with extremely high accuracy without causing a change in the optical axis direction and position of light emitted from a laser oscillator.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an optical information recording apparatus showing an embodiment of the present invention, FIG. 2 is a partial configuration diagram showing an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a schematic diagram showing a characteristic part of the device, FIG. 4 is a schematic diagram showing a characteristic part of the device according to one embodiment of the present invention, and FIG. 5 is related to one embodiment of the present invention. FIG. 6 is a principle diagram of the beam position servo optical system, FIG. 7 is a diagram for explaining problems of the beam position servo optical system, and FIG.
FIG. 9 is a view showing pointing slability, and FIG. 9 is a sectional view of a new write-once type recording disk.

Claims (2)

[Claims] 1. A first servo mirror that reflects light from a laser oscillator in an arbitrary direction, a second servo mirror that reflects light reflected by the first servo mirror in an arbitrary direction, and a second servo mirror. To extract a part of the reflected light of the servo mirror of the first
And a first light splitting element for detecting an incident position of the light on the first light splitting element based on a part of the light split by the first light splitting element.
Of the photodetector, first control means for controlling the rotation of the first servo mirror so that light is incident on a predetermined position on the first photolytic element, A second light splitting element for extracting a part of the light; and a second light splitting element for detecting an incident position of the light on the second light splitting element by a part of the light decomposed by the second light splitting element.
And a position control signal from the second photodetector,
A second control means for controlling the rotation of the second servo mirror, a distance (k ₀ ) between the first servo mirror and the second servo mirror, the second servo mirror and the first servo mirror. the distance between the distance (k ₂₎ and the first photodetector and the second photodetector and the photodetector (k ₃₎ are each be configured satisfy the relation of k ₀ <k ₂ k ₃ An optical information recording device characterized by: 2. The optical information recording apparatus according to claim 1, wherein the first and second photodetectors are divided into four parts.