JP2955382B2 - Optical playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for optically reproducing data recorded on a recording medium in the form of pits.

[0002]

2. Description of the Related Art With the recent information society, the amount of data to be handled tends to increase steadily, and it is desired to provide a system capable of recording and reproducing a large amount of data. In response, there are various optical data processing systems that can record and reproduce data at high density. In this system, data is encoded into optically detectable physical marks and recorded on a recording medium, and data is reproduced by detecting these marks by optical means. An example of such a physical mark is a pit formed on a recording medium. In this case, the analog data is recorded, for example, as pits having various lengths according to the data in the track direction. Also,
Digital data is recorded, for example, as a series of pit strings along a track. One example recorded in this way is a compact disk that is currently widespread. Although this compact disk has spread in the field of music, it has recently begun to be used as a computer memory called a CD-ROM. It has over 1,000 times the storage capacity of the 5.25 "floppy disk used in personal computers.

[0003]

While such an optical data processing system substantially meets the current needs, it has also been improved and improved to record data at higher densities. There is also a need for a new data processing system that is capable of doing so. Due to such demands, research and development of new processing systems are still active. It is an object of the present invention to achieve higher density data recording.

[0004]

As one method for achieving higher-density data recording, a set of pits consisting of a plurality of pits having an interval corresponding to data in the width direction of a recording track is recorded on a recording medium. The data is recorded by forming along the pits, a beam of coherent light is irradiated to the set of pits, and the light diffracted by each pit is formed corresponding to the pit interval of each pit set. It is conceivable to reproduce the original data from the interference pattern. In the interference pattern obtained in this manner, the position of the maximum value or the minimum value depends on the pit interval. For example, the interval between the central maximum value and the primary maximum value decreases as the pit interval increases. Therefore, by detecting the interval between the central maximum value and the primary maximum value using a photodiode or the like, it is possible to read the data encoded and recorded at the pit interval.

[0005] An optical reproducing apparatus according to the present invention comprises a light source for emitting light, means for irradiating light from the light source to a set of pits, and + 1st-order and -1st-order diffracted lights diffracted by the set of pits. Position of the first-order diffracted light that moves in accordance with the pit interval of the set of pits obtained by detecting the photoelectric conversion output from each area of the two-divided photodiode, Means for reproducing data from information, a recording medium having a set of pits composed of a plurality of pits formed at intervals corresponding to the data in the width direction of the recording track, and holding the data in the form of a set of pits Play data from.

[0006]

According to the optical reproducing apparatus of the present invention, the + 1st-order and -1st-order diffracted lights diffracted by the recording medium are two 2nd-order diffracted lights.
Each of the divided photodiodes is irradiated. The positions of the + 1st-order diffracted light and the -1st-order diffracted light move relative to the 0th-order diffracted light according to the pit interval formed corresponding to the data. Therefore, for example, + 1st-order diffracted light and -1
The data recorded on the recording medium can be reproduced by detecting the interval between the next-order diffracted lights. The position information of the first-order diffracted light is obtained by detecting and calculating a photoelectric conversion output corresponding to the amount of light irradiated to each area of the two-divided photodiode, and data is reproduced based on the position information.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

[0008] As shown in FIG.
The laser light emitted from 2 is collimated by a collimating lens 14.
Is changed to a parallel beam, and the beam diameter is limited by the aperture 15. The parallel beam that has passed through the stop 15 passes through the polarization beam splitter 16 and the λ / 4 plate 18 and enters the objective lens 20. The objective lens 20 focuses the parallel beam on the surface of the optical disk 22. The optical disk 22
It has a set of pits composed of a plurality of pits formed at intervals according to the data in the width direction of the recording track. The light applied to the optical disk 22 is diffracted by a set of pits,
As shown in FIG. 2, the + 1st-order diffracted light 30 and the -1st-order diffracted light 32 are reflected in directions different from the 0th-order diffracted light 28 by an angle θ. In the drawing, for the sake of explanation, incident light is shown on the left and reflected light is shown on the right. These diffracted lights 28, 30, 3
2 enters the objective lens 20, is converted into a parallel beam by the objective lens 20, passes through the λ / 4 plate 18, is reflected by the polarization beam splitter 16, and is projected on a detector 26.
As shown in FIG. 3, the detector 26 includes three two-part photodiodes 36, 38, and 40 adjacent to each other.
The two-division photodiodes 36, 38, and 40 are irradiated with diffracted lights 28, 30, and 32, respectively.

When the optical disk 22 is considered as a diffraction grating, the relationship between the light incident on the optical disk 22 and the diffracted light is as follows: α is the incident angle of light, θ is the diffraction angle, λ is the wavelength, and the period of the grating is Where p is sinα−sin θ = n ·
λ / p

## EQU1 ## Here, n is an integer and indicates the order of the diffracted light. In other words, the diffraction angle θ of the diffracted light increases as the period p of the diffraction grating increases, and conversely, the diffraction angle θ increases as the period p decreases. Therefore, the interval between the ± first-order diffracted lights 38 and 40 increases as the pit interval of the set of pits decreases, and the interval between the ± first-order diffracted lights 38 and 40 decreases as the pit interval increases.
Therefore, the original data recorded on the optical disk 22 in correspondence with the pit interval of the set of pits is the ± 1st-order diffracted light 3
Reproduction can be performed by detecting the positions (or movement amounts) of 0 and 32.

In this embodiment, the ± 1st-order diffracted light 3
The positions (or movement amounts) of 8, 40 are detected by the detector 26. That is, in FIG. 3, the output currents of the respective regions 38a and 38b of the two-division photodiode 38 are I (38a),
I (38b), each region 40 of the two-division photodiode 40
Assuming that the output currents of a and 40b are I (40a) and I (40b), respectively, when the pit interval decreases and the ± 1st-order diffracted lights 38 and 40 move outward, the relationship between the output currents becomes I (38a). )> I (38
b) And I (40a) <I (40b). When the pit interval increases and the ± 1st-order diffracted light beams 38 and 40 move inward, the relationship between the output currents is I (38a) <I (38b) and I (40a).
> I (40b).

Accordingly, the position (or the amount of movement) of the ± 1st-order diffracted light can be calculated by using the comparator 42 to determine the difference between I (38a) and I (38b), or using the comparator 44 to calculate I (40a). ) And I (40b)
By detecting the difference between
For example, it is detected as an analog amount using both
Data recorded on the optical disc 22 is reproduced at a high speed corresponding to the interval between a plurality of pits formed in the width direction of the recording track. At this time, the offset control is performed so that the zero-order diffracted light 28 always irradiates the center of the two-division photodiode 36. This offset control is performed by performing feedback control so that the output of the comparator 46 that outputs the light amount difference between the area 36a and the area 36b is always 0.

As described above, the optical reproducing apparatus of the present invention has a small number of elements for detecting the positions of the ± 1st-order diffracted lights, and therefore can rapidly record data encoded at pit intervals and recorded. Can be read.

By the way, the output from each area of the two-divided photodiode contains a considerable amount of noise. The noise components are light amount fluctuation noise such as laser noise and medium noise, and shot noise of the photodiode. Since the light amount fluctuation noise is caused by the fluctuation of the light amount of the light source, its magnitude is proportional to the true light amount at each point of the diffraction pattern, and the phase thereof is also equal. Therefore, the light amount fluctuation noise fluctuates with correlation at each point of the diffraction pattern. On the other hand, since shot noise is random noise, there is no correlation at each point of the diffraction pattern. Assuming that the ratio of the light amount fluctuation noise voltage to the output is r, the actual photoelectric conversion output from each region of the photodiode 38 is I (38a) + rI (38a), I (38b) + rI (38b).
It is represented by Here, I (38a) and I (38b) denote output values excluding light amount fluctuation noise, and rI (38a) and rI (38b) denote light amount fluctuation noise components. Therefore, the differential outputs in these regions are

## EQU1 ## Here, r [I (38a) -I (38
b)] indicates light amount fluctuation noise such as laser noise and medium noise. Here, I (38a) and I (38b) take values in a similar range. For example, as the value of I (38a) increases, the value of I (38b) increases as I (38a) increases. It shows a tendency to decrease. I (38a) −
When the pit interval is such that I (38b) takes a value near 0, the value of the light amount fluctuation noise r [I (38a) -I (38b)] also becomes small. As described above, it is known that this light amount fluctuation noise generally accounts for a large portion of the total noise of the system. Therefore, removing such correlated noise is effective in substantially increasing the S / N and improving the recording density.

Next, a second embodiment of the present invention will be described. FIG. 4 shows the configuration of the detector according to the second embodiment. Most of the configuration of the detector of FIG. 4 is common to the detector of FIG. 3, but the position (or the amount of movement) of the first-order diffracted light uses a subtractor 42, an adder 50, and a divider 51. The difference between the outputs 38a and 38b is obtained from a value obtained by dividing the difference by the sum of the outputs. here,

[0017]

(Equation 1) From this, it can be seen that the correlated noise component is completely canceled.

Next, a third embodiment of the present invention will be described. FIG. 5 is a diagram showing a configuration of the detector according to the third embodiment. In this detector 26, the photodiode 3
The position (or the amount of movement) of the first-order diffracted light is obtained from a value obtained by dividing the output of the photodiode 8b by the output of the photodiode 38b (or vice versa). In this case, the dividing power is

[0019]

(Equation 2)

## EQU2 ## Similarly, the correlation noise component is canceled. Accordingly, the noise component is basically only a random noise component, and the S / N is improved, so that the reproduction resolution can be increased, and as a result, the recording density can be increased.

In the above two detectors, the photodiode 3
Although the description has been made with reference to 8a and 38b, it is needless to say that data can be reproduced using the photodiodes 40a and 40b.

Next, a fourth embodiment of the present invention will be described. FIG. 6 is a diagram showing a configuration of the detector according to the fourth embodiment. This detector utilizes both ± 1st-order diffracted light for data reproduction. That is, the photodiode 38
A is a value obtained by adding the outputs of a and 40a by the adder 60, B is a value obtained by adding the outputs of the photodiodes 38b and 40b by the adder 61, and a calculated value of (AB) / (A + B) is a reproduced value. Is what you want. With this configuration, the correlation noise can be canceled in the same manner as in the above-described detector, and the imbalance of the ± 1st-order diffracted light due to the tracking error can be reduced. There is an advantage that it can be reproduced.

[0023]

According to the present invention, without increasing the size of the detection optical system and without lowering the recording density,
By providing a plurality of pits in a track width direction at intervals corresponding to data, an optical reproducing apparatus capable of reproducing data recorded at a high density on an optical recording medium with high S / N with high accuracy and high speed is provided. You.

[Brief description of the drawings]

FIG. 1 shows a configuration of a reproducing apparatus according to an embodiment of the present invention.

FIG. 2 shows how incident light is diffracted on an optical disk.

FIG. 3 shows a configuration of the detector of FIG.

FIG. 4 is a diagram showing a configuration of a detector according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a detector according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a detector according to a fourth embodiment of the present invention.

[Explanation of symbols]

12: laser diode, 14: collimating lens,
15: stop, 16: polarizing beam splitter, 20: objective lens, 26: detector.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/00 G11B 7/135

Claims (4)

(57) [Claims] 1. An optical system for reproducing data from a recording medium having a set of pits including a plurality of pits formed at intervals corresponding to data in a width direction of a recording track and holding the data in the form of a set of pits. A light source for emitting light, means for irradiating a set of pits with light from the light source, and a two-segment photoreceptor for receiving + 1st-order and -1st-order diffracted light diffracted by the set of pits, respectively. A diode, a calculation output means for calculating and outputting a photoelectric conversion output of each area of the two-divided photodiode, and a first-order diffracted light moving according to a pit interval of a set of pits obtained by an output from the calculation output means. Means for reproducing data from position information. 2. The optical reproducing apparatus according to claim 1, wherein said calculation output means calculates and outputs a difference between photoelectric conversion outputs of respective regions of the two-divided photodiode. 3. The optical reproducing apparatus according to claim 1, wherein said calculation output means calculates and outputs a value of a ratio of a difference between a photoelectric conversion output of each area of the two-divided photodiode and a sum thereof. 4. The optical reproducing apparatus according to claim 1, wherein said calculation output means calculates and outputs a ratio value of a photoelectric conversion output of each area of the two-divided photodiode.