JP2632318B2 - Optical wavelength multiplexing recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical wavelength division multiplexing recording / reproducing apparatus.

[Conventional technology]

FIG. 15 is a block diagram showing a configuration of a conventional optical multiplex recording / reproducing apparatus disclosed in Japanese Patent Publication No. 58-51355, for example, and FIG. 16 is a wavelength spectrum diagram of a medium on which information is recorded. In FIG. 15, light emitted from a wavelength-variable light source 81 such as a laser becomes parallel light by a collimator lens 83, and after being polarized in a predetermined direction by an optical deflector 84, becomes a minute light spot by an objective lens 85. The light projected onto the required storage element 87 on the medium 86 having the multiplex recording / reproducing function and passing through the storage element 87 is detected by the light detector 88 provided on the opposite side of the light source 81 via the medium 86. The storage element 87 to be projected is freely selected by the light deflector 84 polarizing the light spot. Light source 81
Can be changed by a wavelength controller 82 such as a scanner provided outside thereof.

The principle of recording and reproduction by wavelength multiplexing will be described with reference to FIG. FIG. 16 (a) shows an absorption spectrum of the medium 86 before the wavelength multiplex recording, and the medium 86 has a wide spectral characteristic. When light having a light intensity spectrum as shown by a broken line in the same figure is projected on this medium 86, a drop occurs in the absorption spectrum of the projected wavelength as shown in FIG. 16 (b). (Hereinafter simply referred to as a hole). When a hole occurs, it is determined that data "1" has been recorded at this wavelength, and a portion having no hole is data "0". To form a hole at an arbitrary wavelength (in other words, write data "1"), use a wavelength controller
It becomes possible by adjusting the wavelength of the light source 81 to the wavelength at which holes are to be formed by using the light source 82 and further increasing the light intensity of the light source 81 to the light intensity required for recording. As shown in FIG. 16 (b), in order to read a signal from a medium having a spectrum multiplexed and recorded by forming holes with different wavelengths, the light intensity of the light source 81 is fixed and ranges from the wavelength range A to B used for storage. If the medium 86 is scanned at the wavelength, the light detector 88 detects the transmitted light of the medium 86 since the absorbance decreases at the wavelength where holes are generated as shown in FIG. 16 (b). The spectrum of the light intensity as shown in (c) is obtained. Therefore, if the recording position is scanned while changing the wavelength in the wavelength range used for storage at a constant speed, a reproduction signal for each wavelength indicating the presence or absence of a hole is obtained from the output of the photodetector 88, and if the change speed of the wavelength is constant, A time-series reproduced signal of the stored data is obtained.

Further, the number n of holes that can be formed in the absorption spectrum in the wavelength range A to B is schematically represented by the following equation.

In the equation (1), ΔW _I is the bandwidth of the absorption spectrum, and ΔW _H is the width of one hole. Therefore, when the value of ΔW _H decreases, the number n of holes that can be formed increases, but in general, the value of ΔW _H decreases at low temperatures, while ΔW _I is hardly affected by temperature. The number n of holes that can be formed, in other words, the data storage capacity in which one hole corresponds to one bit increases.

[Problems to be solved by the invention]

By the way, in the above disclosed example, no detailed disclosure of the optical system in the apparatus is found, but for multiplex recording / reproduction with a plurality of different wavelengths, these beams of a plurality of different wavelengths are efficiently and reliably collected at one data recording position. You need to light. At present, an optical system generally used for an optical recording / reproducing apparatus for an optical disk such as a compact disk and a video disk is for a single wavelength and a single light source. For example, when a plurality of light sources are used, a plurality of objective lenses are required. However, when a plurality of objective lenses are used, a complicated mechanism and precise control are required to irradiate the converged light beam to the same point on the recording medium, and the optical system becomes large.

Furthermore, when a He-Ne laser is used as a light source, for example, the focused spot diameter is 1 mm, and the information recording density is low.

Further, the objective lens has a problem that chromatic aberrations are generated with respect to a plurality of light beams having different wavelengths, and these cannot be condensed at the same position on the recording medium.

Further, a function of condensing light beams having a plurality of different wavelengths reflected from the recording medium at different required positions in order to simultaneously detect the reflected light by wavelength is indispensable for improving the recording / reproducing efficiency.

In addition, a beam splitter and a 4
Although a one-half wavelength plate is used, if the light source is a semiconductor laser, the current manufacturing technology may cause the oscillation wavelength to vary depending on the individual product, and the operating characteristics may vary depending on temperature, injection current, and the like. There is a problem that it is difficult to match the designated wavelength of the quarter-wave plate, the return light to the semiconductor laser as the light source increases, and the light source becomes unstable, such as disturbing the oscillation wavelength.

The present invention has been made in order to solve such a problem, and prevents an optical system from being enlarged, has a high information recording density, and irradiates a recording medium having a plurality of wavelengths.
It is an object of the present invention to provide an optical wavelength division multiplexing recording / reproducing apparatus capable of simultaneously detecting reflected light for each wavelength to enhance recording / reproducing efficiency and reducing return light to the light source to stabilize the light source.

[Means for solving the problem]

An optical wavelength multiplexing recording / reproducing apparatus according to a first aspect of the present invention emits a plurality of light beams having different wavelengths from a light source, converts the emitted light beams into a parallel light flux, guides the emitted light beams to a predetermined optical path, and transfers the guided parallel light to a recording medium. In an optical wavelength multiplex recording apparatus for multiplexing recording / reproducing or erasing information by condensing irradiation, a light source composed of a plurality of wavelength tunable semiconductor lasers for emitting light beams belonging to a plurality of different wavelength bands, and emitted from each light source A dichroic mirror having a wavelength-dispersive reflectivity that guides the optical path of the light beam in each wavelength band to a predetermined optical path according to the wavelength, and a recording medium using a material that generates photochemical hole burning by directing the light beam guided to the predetermined optical path. A dispersive element for simultaneously dispersing and condensing the reflected light from the recording medium to different positions for each wavelength; and Characterized in that and a detecting element group to detect by the wavelength of light.

An optical wavelength division multiplexing recording / reproducing apparatus according to a second invention is characterized in that a holographic diffraction grating is used as a dispersion element.

An optical wavelength division multiplexing recording / reproducing apparatus according to a third invention is characterized in that a photodiode array is used for a detection element group.

An optical wavelength-division multiplex recording / reproducing apparatus according to a fourth aspect of the present invention is characterized in that it comprises a polarizing element that polarizes the light emitted from the light source for recording / reproduction to the recording medium and the reflected light thereof.

An optical wavelength division multiplexing recording / reproducing apparatus according to a fifth invention is characterized in that the polarizing element comprises a beam splitter and a quarter-wave plate, and the reference wavelength of the phase difference provided by the quarter-wave plate is supplied from a recording / reproducing light source. The wavelength is set to one of the wavelengths to be emitted.

[Action]

According to the device of the present invention, a dichroic mirror having a wavelength dispersion property of a reflectance guides an optical path of a light beam emitted from a light source made of a wavelength-variable semiconductor laser to a predetermined optical path according to a wavelength, and a light beam guided to the predetermined optical path. The light condensing element condenses the light on a recording medium using a material that causes photochemical hole burning, and the dispersive element simultaneously disperses and condenses the reflected light from this recording medium to different positions according to the wavelength. Are detected for each wavelength by the detection element group.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing a configuration of an optical wavelength multiplexing recording / reproducing apparatus according to the present invention (hereinafter, referred to as the present apparatus). In the figure, reference numeral 10 denotes an optical head that emits laser light to record and reproduce information. In the figure, reference numeral 1 denotes a tunable high-power semiconductor laser (hereinafter referred to as LD1) that emits a tunable laser light for data recording and reproduction. 2) a high-power semiconductor laser (hereinafter abbreviated as LD2) that emits a laser beam for data erasing; 3 a low-power semiconductor laser (hereinafter abbreviated as LD3) that emits a laser beam for focusing and tracking; Is a low-power semiconductor laser (hereinafter abbreviated as LD4) that emits a laser beam for focusing, and LD1, LD
LD2, LD3, and LD4 emit laser beams belonging to different wavelength bands, respectively, and LD power control circuits 21, 22, 23, and 24 provided behind LD1, LD2, LD3, and LD4 respectively control the emitted laser power. In addition, the collimating lenses 101, 102, 103, 104 are LD1, LD2, LD3
Then, the output diffused light from the LD 4 is converted into parallel light, and is output to the dichroic mirrors 111, 112, 113, and 114, respectively.

The dichroic mirror 111 transmits light in the wavelength band of LD1, while reflecting light in other wavelength bands including LD2, LD3, and LD4, and the dichroic mirror 112 reflects light in the wavelength band of LD2, LD3, The dichroic mirror 113 reflects light in the wavelength band of the LD3, transmits light in other wavelength bands including the wavelength band of the LD4, and the mirror 114 transmits the light in the other wavelength band including the wavelength band of the LD4. In the wavelength band of The light transmitted or reflected by the dichroic mirror 111 is incident on a deflecting beam splitter (hereinafter abbreviated as PBS) 105. The PBS 105 transmits a part of the incident light and reflects the rest toward a hologram lens 108 described later. The light transmitted through the PBS 105 is a quarter-wave plate 10
6 and the quarter-wave plate 106 shifts the phase of the light in the wavelength band of LD1 by one-fourth of the center wavelength of the wavelength band in the incident light.
The phase of the other wavelength band is emitted as it is to an objective lens (hereinafter, abbreviated as OBL) 107 composed of a combination lens or an integrated shaping lens made of plastics, and the OBL 107 condenses the incident parallel light beam. The holographic lens 108, which is a holographic diffraction grating, condenses incident light at different positions in accordance with the wavelength, and condenses the condensed light on a photodiode array (hereinafter abbreviated as PD array) including a plurality of photodetectors. 109 detects with each light detection element.

In addition, focusing actuators 115a and 115b
Drives the OBL 107 in the optical axis direction, and the tracking actuators 116a and 116b drive the OBL 107 in the direction perpendicular to the optical axis.

Next, a configuration of a control system including a wavelength control system of the optical head 10 will be described. In the figure, reference numeral 25 denotes a head amplifier, which converts an output current from each photodetector of the PD array 109 into a voltage, and outputs this voltage signal to the servo circuit 6, the LD wavelength control circuit 7, and the error correction circuit 26. . LD wavelength control circuit 7
LD1 based on the voltage signal corresponding to the emitted laser wavelength
Control the oscillation wavelength of The servo circuit 6 drives the focusing actuators 115a and 115b and the tracking actuators 116a and 116b based on the voltage signals corresponding to the wavelengths of the LD3 and LD4. The error correction circuit 26, LD1
The error correction of the data is performed for each predetermined unit such as one byte based on the voltage signals corresponding to the respective wavelengths. Further, the system controller 27 manages the flow of the entire control system for controlling recording, reproduction, erasure and the like of information.

Next, a medium on which information is recorded and its driving device will be described. In the figure, reference numeral 5 denotes a disk having a layered recording medium for recording and reproducing information by forming holes using the photochemical hole burning (hereinafter abbreviated as PHB) effect. A hub 31 on which the disk 5 rotates is provided, and the hub 31 includes a clutch. In addition, the cartridge 32 covers the entire disk 5 while keeping an appropriate space, protects the disk 5 from outside, and shields and insulates heat. One surface of the cartridge 32 is provided with a liquid crystal shutter 35 for transmitting external irradiation light when the disk 5 is loaded, and the other surface is provided with a recording medium inside the cartridge 32.
A cooler 33 for cooling to the target temperature for the B recording is provided.

The drive device for the disk 5 is provided with a radiator 34 for radiating heat from the cooler 33 and a disk motor 37 connected to the clutch of the hub 31 to rotate the disk 5 when the disk 5 is loaded. The power supply 36 supplies a voltage or a current to the cooling device 33, the liquid crystal shutter 35, and the radiator 34 when the disk 5 is loaded in the drive device.

The operation of the apparatus of the present invention having the above configuration will be described. When the cartridge 32 containing the disk 5 is loaded, the clutch of the hub 31 is connected to the disk motor 37 and the disk 5 starts rotating. Further, a radiator 34 is mounted on the cooler 33, and a current is supplied from a power supply 36 to cool the inside of the cartridge 32. On the other hand, the liquid crystal shutter 35 is also supplied with a voltage from the power supply 36 and opens the shutter to transmit the irradiation light from the optical head 10 so that recording, reproduction, and erasing can be performed.

Next, LD3 and LD4 are turned on by the LD power control circuit 23 and the LD power control circuit 24 for focusing and tracking. The oscillation wavelengths of LD3 and LD4 belong to different wavelength bands according to the structure of the recording medium of the disk 5 described later. FIG. 2 is a diagram showing emission spectra of the semiconductor lasers LD1, LD2, LD3, and LD4. In the figure, the oscillation wavelength of LD3 belongs to the M1 wavelength band, the oscillation wavelength of LD1 belongs to the M2 wavelength band, the oscillation wavelength of LD2 belongs to the M3 wavelength band, and the oscillation wavelength of LD3 belongs to the M4 wavelength band.

A semiconductor laser can cause laser oscillation at discontinuous longitudinal mode wavelengths at substantially constant intervals in its emission spectrum. The oscillation wavelength changes depending on the temperature, injection current, and the like. If the oscillating wavelength is discontinuous as described above, the change is discontinuous, that is, a so-called longitudinal mode jump.

In the present invention, utilizing this longitudinal mode jump, discontinuous laser oscillation wavelengths generated by increasing the injection current are used for recording 1-bit data.

FIG. 2 shows M2, M3, M1 and M4 to which LD1, LD2, LD3 and LD4 belong.
It shows the oscillation state of the wavelength band, and among these, the oscillation wavelengths used for recording and reproducing information are λ1, λ2,
λ3 ...

The light emitted from the LD 3 is converted into a parallel light by the collimator lens 103 and enters the dichroic mirror 113. The dichroic mirror 113 belongs to the M1 wavelength band because it has a characteristic of reflecting only light in the M1 wavelength band.
Reflects the light of LD3 and dichroic mirror 112 the light path.
Bend at right angles to the direction. The dichroic mirror 112 transmits the light in the M1 wavelength band, and the dichroic mirror 111 has a characteristic of reflecting the light. Therefore, the light that has exited the LD 3 is reflected by the dichroic mirror 113, and the dichroic mirror 1
Transmitted through 12, reflected by dichroic mirror 111, PBS
It is incident on 105 as a parallel ray. The light emitted from the LD 4 is converted into a parallel light beam by the collimator lens 104 and then enters the mirror 114, where the optical path is bent at a right angle toward the dichroic mirror 113. The dichroic mirror 113 and the dichroic mirror 112
Since the light in the M4 wavelength band is transmitted and the dichroic mirror 111 is given a characteristic of reflecting the light, the light exiting the LD 4 is reflected by the mirror 114, transmitted through the dichroic mirror 113 and the dichroic mirror 112, and transmitted through the dichroic mirror 111.
And is incident on the PBS 105 as a parallel light beam.

Since the light from LD3 and LD4 incident on PBS 105 is linearly polarized light having only a P-polarized component with respect to the incident surface of PBS 105, it passes through PBS 105 and is incident on quarter-wave plate 106.
The quarter-wave plate 106 is set so that the phase shift amount of the quarter-wave plate 106 becomes one-quarter wavelength with respect to the oscillation wavelength of LD1, so that the LD3 and LD4 that have exited the quarter-wave plate 106 Is converted into elliptically polarized light instead of completely circularly polarized light, enters the OBL 107, and is condensed on the disk 5 by the OBL 107.

The light reflected from the disk 5 is collected again by the OBL 107 to become parallel rays and returns to the quarter-wave plate 106, and the returned light is again phase-shifted by the quarter-wave plate 106 with respect to the oscillation wavelength of the LD1. Since the phase is shifted so that the shift amount becomes a quarter wavelength, elliptically polarized light, which is close to circularly polarized light,
The light is converted into elliptically polarized light that is close to linearly polarized light having only S-polarized light components with respect to the incident surface of the PBS 105. Therefore, most of the light returned from the disk 5 is reflected by the PBS 105, and its optical path is bent at a right angle toward the hologram lens 108. The hologram lens 108 detects the light detected at different positions of the PD array 109 according to the wavelength. Each light detection element is focused on the element, and each light detection element outputs a current proportional to the intensity of the received light to the head amplifier 25, which converts the output current of each light detection element of the PD array 109 to a voltage. Then, the signal is supplied to the LD wavelength control circuit 7, the servo circuit 6, and the error correction circuit 26.

FIG. 3 shows a schematic sectional structure of the disk 5 and wavelength bands M1, M2,
FIG. 9 is a diagram showing absorption spectra of M3 and M4, wherein a disk 5 has a protective layer 5b for protecting a recording medium 5a, which will be described later, from the outside.
And a first auxiliary layer 51 for focusing and tracking,
A recording / reproducing layer 52 for recording data, a heat generating layer 53 for erasing data in the recording / reproducing layer 52 by heating the recording / reproducing layer 52 by generating heat by laser irradiation, a second auxiliary layer 54 for focusing, and protection; And a recording medium 5a in which reflective film layers 55 that reflect light incident from the layer 5b side are sequentially laminated. Also, a first auxiliary layer 51, a recording / reproducing layer 52, an erasing heat generating layer
53, the second auxiliary layer 54 has a light absorption spectrum as shown in FIG. 3, and the first auxiliary layer 51, the recording / reproducing layer 52, and the second auxiliary layer 54 have an M1 wavelength band and an M2 wavelength band, respectively. , PH at M4 wavelength band
Materials that cause the B phenomenon are used.

The information is recorded on the disk 5 in a spiral or concentric manner. The recording locus is called a track, and the data recording position whose interval is determined by the recording / reproducing accuracy is called a pit. The optical head 10 records and reproduces information while tracking this track, and accesses the required track at high speed across the track.

4 and 5 are schematic diagrams of pits formed in the first auxiliary layer 51 and the second auxiliary layer 54 for use in tracking and focusing.

The first auxiliary layer 51 and the second auxiliary layer 54 belong to pits 45, 45, 45... In which holes having a wavelength λ1 (hereinafter abbreviated as λ1 (M1)) belonging to the M1 wavelength band are formed, and belong to the M4 wavelength band. Pits 46, 46, 46,... Formed with holes at a wavelength λ1 (hereinafter abbreviated as λ1 (M4)), a wavelength λ2 belonging to the M1 wavelength band.
(Hereinafter, abbreviated as λ2 (M1)), pits 47, 47, 47... Formed with holes, and a wavelength λ3 (hereinafter, λ3
(Abbreviated as (M1)), pits 48, 48,
48, pits 49, 49, 49... Formed with holes at a wavelength λ4 (hereinafter abbreviated as λ (M1)) belonging to the M1 wavelength band are provided at predetermined intervals.

That is, the pits 45, 45, 45,.
.. (Not shown) on the tracks 51a, 51b, 51c... (Not shown) and provided at positions corresponding to the data recording pits.
Are also provided at positions corresponding to the data recording pits of the recording / reproducing layer 52 on the trajectory corresponding to the track, and are located between the first auxiliary layer 51 and the second auxiliary layer 54. The pit of the recording / reproducing layer 52 is located at the position. The pits 47, 48 and 49 of the first auxiliary layer 51 are intermediate between the tracks 51a, 51b, 51c... Corresponding to the tracks 52a, 52b, 52c. The pits 47, 48, the pits 48, 49, and the pits 49, 47 are tracks 51a, 51b, and 51c, respectively.

Therefore, if lasers in the M1 wavelength band and the M4 wavelength band are irradiated, the λ1 (M1), λ1 (M4), and λ2 (M
1), λ3 (M1), λ4 (M1), and the first and second auxiliary layers 51, 54 by the output currents of the respective photodetectors of the PD array 109.
The presence or absence of a hole is detected, and changes depending on the irradiation distance. The servo circuit 6 detects the amount of change in the output current and, for example,
When reproducing the information of the track 52b of the second track, λ1 (M
Focusing actuators 115a and 115b so that the output current changes at 1) and λ1 (M4) are equal.
To move the OBL 107 in the optical axis direction to
Focusing on 52, λ3 (M1) and λ4
The tracking actuators 116a and 116b are driven so that the amount of change in the output current in (M1) becomes equal, and the OBL
Move 107 perpendicular to the optical axis and the plane created by the track.
Control is performed such that the light spot condensed by 7 always tracks the track 52b in the recording / reproducing layer 52.

6 and 7 are block diagrams showing a configuration of the servo circuit 6, and FIG. 6 shows a focusing servo circuit,
FIG. 7 shows a tracking servo circuit. In FIG. 6, head amplifiers 25a and 25b convert the output currents of λ1 (M1) and λ1 (M4) into voltages, respectively, and this signal is sent to detectors 61a and 61b, each comprising a band-pass filter and an amplitude detector. Is output. The detectors 61a and 61b extract a frequency (hereinafter referred to as a servo frequency) component determined from the number of rotations of the disk 5 and the intervals between the pits 45, 46, 47, 48 and 49 from the voltage signal, and the amplitude thereof (hereinafter referred to as a reproduction envelope). ) Is detected. Output signals from the detectors 61a and 61b are operational amplifiers.
The signals are output to 63a and 63b and are amplified, but are subtracted by one operational amplifier 63a and added by the other operational amplifier 63b.
The signals from the operational amplifiers 63a and 63b are divided by a division circuit 64a.
The division circuit 64a divides the output of the operational amplifier 63a by the output of the operational amplifier 63b. The result of the division is the phase compensator 6
5a, and the phase compensator 65a compares the division result with the driver amplifier while stabilizing the feedback control loop.
The driver amplifier 66a drives the focusing actuators 115a and 115b based on this signal.

In FIG. 8, λ2 (M1), λ3 (M1) and λ2 (M1)
The output current of 4 (M1) is converted into a voltage by head amplifiers 25c, 25d, and 25e, respectively, and this signal is output to detectors 61c, 61d, and 61e each including a band-pass filter and an amplitude detector. Output signals α, β and γ from detectors 61c, 61d and 61e
Are output to the switches 62a, 62b, 62c, 62d, 62e, and 62f. One of the switches 62a, 62b, 62c, 62d, 62e, and 62f sandwiches a track to be tracked. The output corresponding to the light having the wavelength of the right pit is distributed to the operational amplifiers 63c and 63d. The operational amplifiers 63c and 63d compute and amplify these signals.The operational amplifier 63c computes and amplifies the difference between the output on the left and the output on the right, and the operational amplifier 63d computes and amplifies the sum. Is output to the division circuit 64d, and the division circuit 64b outputs the output of the operational amplifier 63c, that is, the difference, to the operational amplifier 63d.
Divide by the output of d, ie the sum. The result of the division is the phase compensator 65b
The phase compensator 65b stabilizes the feedback control loop and outputs the division result to the driver amplifier 66.
b, and the driver amplifier 66b drives the tracking actuators 116a and 116b based on this signal.

In FIG. 8, the reproduction envelope of the λ1 (M1) pit 45 and the λ1 (M4) pit 46 with respect to the position (X) in the optical axis direction of the OBL 107 and the difference and the calculation result of the sum thereof are calculated. Are shown in correspondence with. FIG. 8A shows a reproduction envelope of the λ1 (M1) pit 45, which is an output signal of the detector 61a in FIG. 8th
The solid line in FIG. 6B shows the reproduction envelope of the λ1 (M4) pit 46, and is the output signal of the detection 61b in FIG.
A broken line indicates a reproduction envelope when light is transmitted without the reflective film layer 55. FIG. 8C shows a result of subtraction of the reproduction envelope shown in FIGS. 8A and 8B, and is an output signal of the operational amplifier 63a in FIG.
FIG. 8D shows the result of addition of the reproduction envelopes shown in FIGS. 8A and 8B, and is an output signal of the operational amplifier 63b. FIG. 8 (e) shows the light condensing corresponding to the position X of the OBL 107 in each of FIGS. 8 (a), 8 (b), 8 (c) and 8 (d) in each layer of the recording medium 5a. This shows the position of the spot. Since the light is reflected by the reflective film layer 55, the position of the condensed spot collected after the reflection is OBL107.
However, even after the focal point reaches the reflective film layer 55, the displacement continues in the direction approaching the disk 5, that is, if (X) monotonically increases, the second auxiliary layer 54 and the first auxiliary layer as indicated by dotted lines again.
It is assumed to pass through 51. FIG. 9 shows the focusing state of the irradiation light at the positions C and D at (X) where the difference signal in FIG. 8 (c) becomes zero.

FIG. 9A shows the light condensing state when (X) is at the position C, that is, when the condensed spot is on the recording / reproducing layer 52.
FIG. 2B shows the light condensing state at the position D in FIG. Therefore, the eighth signal which is the output signal of the operational amplifier 63a
When the difference signal shown in FIG. 9C is positive, the polarity for driving the focusing actuators 115a and 115b is adjusted in a direction to move the OBL 107 closer to the disk 5, that is, in a direction to increase (X). When C has passed C and the difference signal has become negative, the polarity is adjusted in a direction to decrease (X),
When the OBL 107 is driven by the focusing actuators 115a and 115b, the light focusing state shown in FIG. 9A is always achieved. However, since the linear and stable region of the servo loop is a limited range in the vicinity of the position C, some kind of pull-in means is required so that the servo loop is closed within this range. Was
It is enough to use the pull-in method of the focusing servo of the CD player. Further, when (X) approaches the disk 5 beyond the position D, if the difference signal is positive, the OBL 107 is driven in a direction further approaching the disk 5, so that
Detecting this, for example, a means for preventing the OBL 107 from colliding with the disk 5 is required. For this, similarly to the above-described retraction means, for example, if a well-known lens collision prevention system of a CD player is used, Is enough.

FIG. 10 shows the λ2 (M1) pits 47 and λ with respect to the position (Y) in the direction perpendicular to the optical axis of the OBL 107 and the surface formed by the track.
The reproduction envelope of the 3 (M1) pit 48 and the λ4 (M1) pit 49, that is, the pit provided in the middle of each track, and the subtraction result thereof are shown corresponding to the position of the converging spot on the recording medium 5a. FIG. 10 (a) shows a reproduction envelope of the λ2 (M1) pit 47, which is an output signal of the detector 61c in FIG. FIG. 10 (b) shows a reproduction envelope of the λ3 (M1) pit 48, which is an output signal of the detector 61d in FIG. FIG. 10 (c) shows a reproduction envelope of the λ4 (M1) pit 49, which is an output signal of the detector 61e in FIG. FIG. 10 (d) shows the result of subtraction of the reproduction envelope shown in FIGS. 10 (a) and 10 (b), and is the output signal of the operational amplifier 63c in FIG. In the figure,
The position E indicates a position where the subtraction result of the two reproduction envelopes is zero, that is, the output current becomes equal. The operational amplifier 63
Illustration of the output signal of d is omitted. Fig. 10 (e)
Indicates the position of the condensed spot on the first auxiliary layer 51 of the recording medium 5a corresponding to the position (Y) of the OBL 107 in FIGS. 10 (a), (b), (c) and FIG. 10 (d). I have. Therefore, for example, if tracking with the track 51a,
When the difference signal shown in FIG. 10 (d), which is the output signal of the operational amplifier 63c, is positive, the tracking actuator 116
The polarity for driving a and 116b is adjusted so that the OBL 107 moves in the direction of increasing (Y), that is, in the direction of the λ3 (M1) pit 48, and (Y) exceeds the position E, and the difference signal is negative. In this case, if the OBL 107 is driven by the tracking actuators 116a and 116b so as to reduce (Y), the focused spot will always track the track 51a. However, similar to the focusing servo, a linear and stable area as a servo loop is a limited area in the vicinity of the position E, so some kind of pull-in means is required to close the servo loop within this area. It is sufficient to use the well-known CD player tracking servo pull-in method.

Next, a procedure for recording and reproducing information on the target track of the recording / reproducing layer 52 while the target track of the recording / reproducing layer 52 is being tracked by the focused spots of the LD3 and LD4 will be described.

In FIG. 1, the LD 1 is lit by the LD power control circuit 21 with an intensity that does not destroy holes already formed in the recording / reproducing layer 51. The oscillation wavelength of LD1 is λ1 (which belongs to the M2 wavelength band where the PHB phenomenon occurs in the recording / reproducing layer 52 due to the vertical mode jump if the injection current to the wavelength control system of LD1 is changed stepwise, for example, by the LD wavelength control circuit 7. M2) to λ
The intermittent oscillation wavelength is controlled up to 8 (M2), and these wavelengths λ1 to λ8 are used for 8-bit data recording, and multiplex recording is performed with this bit as one unit. The light emitted from the LD 1 is converted into a parallel light by the collimator lens 101 and enters the dichroic mirror 111. Since the dichroic mirror 111 has a property of transmitting light in the M2 wavelength band, the dichroic mirror 111 transmits the light of LD1 belonging to the M2 wavelength band and
The light is incident on the PBS 105 as linearly polarized light having only a P-polarized component with respect to the incident surface of the 105. Therefore, the light from LD1 is
The light is transmitted to the OBL 107 as almost perfectly circularly polarized light by the quarter wavelength plate 106, and is condensed on the disk 5. OBL107
Is a lens that has been subjected to aberration correction so that its chromatic aberration can be ignored in the wavelength band from the M1 wavelength band to the M4 wavelength band, and the light condensing position of the light from LD1 is the condensing position of the light from LD3 and LD4. To match. Therefore, a focused spot of the LD 1 for recording information by forming a hole in the recording / reproducing layer 52 or reading information by reading the presence or absence of a hole also tracks a required track of the recording / reproducing layer 52.

When information is recorded, for example, when recording the 1-byte information of "10010110", the clock T _m is T _1, T _4,
At times T ₆ and T ₇ , the LD power control circuit 21 increases the light emission power of the LD 1 to a level necessary for forming a hole in the recording / reproducing layer 52. As a result, λ1 (M
2), holes are formed in pits of λ4 (M2), λ6 (M2), and λ7 (M2).

The light reflected from the disk 5 is condensed by the OBL 107, becomes parallel rays, and returns to the quarter-wave plate 106. The returned light is again shifted in phase by the quarter-wave plate 106 so that the phase shift amount becomes a quarter wavelength with respect to the oscillation wavelength of the LD1, so that the circularly polarized light is shifted from the circularly polarized light to the incident surface of the PBS 105. Is converted into linearly polarized light having only the S-polarized light component. Accordingly, the light returned from the disk 5 is reflected by the PBS 105, and its optical path is bent at a right angle toward the hologram lens 108,
The hologram lens 108 converts these incident lights into PDs according to the wavelength.
The light is focused on corresponding photodetectors arranged at different positions of the array 109.

FIG. 11 shows the positional relationship between pits and condensed spots on the recording / reproducing layer 52 of the disk 5 and a change in the oscillation wavelength of the LD 1 as a time change of an injection current to the wavelength control system. Eleventh
The vertical axis oscillation wavelength lambda _n, the horizontal axis in FIG. (A) shows an application timing T _m of a pulsed current, noted m = x indicates a non-recording period. Current injected into the wavelength control block LD1 is assumed that periodically changing which and stepwise with respect to the timing clock T _m. In this embodiment, the oscillation wavelength λ _{n of} LD1
Is the oscillation wavelength λ _{n where} n = m, corresponding to the clock T _m
Is controlled to oscillate. In addition, when the focused spot of LD1 is relatively expressed with respect to the rotating disk 5,
1 The position is shown as a solid line and a broken line in FIG. Therefore, as the period from the clock T ₀ until the next T ₀ is equal to the period of the servo frequency, if generating a clock T _m using the PLL circuit, so .lambda.1 (M2) as FIG. 11 (b)
Λ1 (M2) focused spot at pit position
The focused spot of λ8 (M2) coincides with the position of the pit of (M2). If the pit distance of λ1 (M2) between the recording units is set to a distance that does not cause interference in view of the spatial frequency characteristics of the focused spot, the photodetector of the PD array 109 that receives only the λ1 (M2) component without being affected by the waveform interference in a group of output current, .lambda.1 by examining the magnitude of the output current at the timing of the clock T ₁
The presence or absence of a hole can be detected based on the wavelength of (M2). The above holds true for pits from λ2 (M2) to λ8 (M2).

Accordingly, when reproducing information, the error correction circuit 26 converts the output current from the photodetector group corresponding to each wavelength into a voltage, and converts the output current from the photodetector group corresponding to each wavelength into a voltage of “L” or “H”. It latches it at the timing of the clock T _m corresponding to the wavelength, detecting the information of the presence or absence of holes. Furthermore, λ
When the information regarding the presence or absence of a hole in the pits from 1 (M2) to λ8 (M2) is complete, the error correction circuit 26 performs error correction using 8-bit (1 byte) information as one unit. The error correction circuit 26 performs high-speed and high-efficiency error correction using the fact that information is recorded in units of one byte and an error correction code is assigned to each of a plurality of units. To correct.

Next, a method of controlling the LD1 emission wavelength in the device of the present invention will be described. The LD wavelength control circuit 7 sets the oscillation wavelength of LD1 to LD1.
The control is performed by changing the injection current to the wavelength control system. The operation will be described below.

Tracks are divided into units called sectors according to the amount of information that the system is set to handle at one time.
The track number and the sector number are recorded in advance at the head of the sector, and such an area is usually called a header area. The system always reproduces the information in the header area, and accurately records and reproduces the information in the target sector of the target track. In this embodiment, wavelength confirmation information is recorded in advance in this header area in addition to the track number and the sector number. The wavelength confirmation information is a reference wavelength to be a reference for recording / reproducing, and a data recording position x1, x2, x3, x in the header area.
In FIG. 4, the information is recorded by forming holes as shown in FIG. In FIG. 12, holes are located in all pits from λ1 (M2) to λ8 (M2) at position x1, holes are located in pits from λ4 (M2) to λ7 (M2) at position x2, and holes are located at position x3. λ3 (M2), λ4 (M2), λ7 (M2), λ8
A hole is previously formed in the pit of (M2), and a hole is previously formed in the pit from λ2 (M2) to λ5 (M2) at the position x4. The pits with holes are shown as solid lines, and the pits without holes are shown as broken lines. Therefore, assuming that a state with a hole is “1” and a state without a hole is “0”, “11111111” at position x1, “0001110” at position x2, and “0” at position x3.
0110011 "and information" 01111000 "are recorded at position x4. The wavelength confirmation information as described above is
It is repeatedly recorded several times in one header area.
Hereinafter, such a region of the wavelength confirmation information is referred to as a wavelength confirmation region.

FIG. 13 is a block diagram showing a configuration of the LD wavelength control circuit 7. The head amplifier 25 converts the output current of the photodetector corresponding to each wavelength from λ1 (M2) to λ8 (M2) into a voltage and outputs the voltage to the wavelength pattern detection / collation circuit 71. Based on this output signal, the wavelength confirmation information recorded in the wavelength confirmation area is detected, the wavelength confirmation information recorded at the reference oscillation wavelength recorded in the ROM 72 is read, and the two are compared. An UP signal or a DOWN signal for adjusting the injection current is supplied to the injection current pattern generation circuit 73. The injection current pattern generation circuit 73 outputs to the D / A (digital / analog) converter 74 a digital signal for raising or lowering the stepwise injection current pattern to the wavelength control system of the LD 1 based on the applied UP signal or DOWN signal. I do. The D / A converter 74 changes the applied digital signal into a current value and outputs the current value to the wavelength control system of the LD1.

Next, the operation will be described with reference to FIG. First in FIG. 14 (a) the header area, when reproducing the second wavelength confirmation information indicates the oscillation wavelength of LD1 of injection current patterns and their time to LD1 wavelength control system of the clock T _m Although the vertical axis represents the oscillation wavelength lambda _n, the oscillation wavelength is increased by the increase of the injection current i, the vertical axis represents the injected current i at the same time, to the horizontal axis changes the injection current at a predetermined time interval a timing the T _m of emitted clock.

FIG. 14 (c) shows the writing and reading of each data,
This is a reference clock that is issued in order to set the operation timing of transfer and the like. First clock T oscillation wavelength of LD1 for _m when the _{T 1 λ0 (M2), λ1} (M2) when T _2, when the T ₃ λ2 (M2), when T ₄ λ3 (M2), λ4 when the T ₅ (M
2), λ5 (M2 when T _6), λ6 (M2 when T _7), oscillates at .lambda.7 (M2) when T _8.

On the other hand, the output current of the photodetector corresponding to the wavelengths from λ1 (M2) to λ8 (M2) is converted into a voltage by the head amplifier 25 and then sent to the LD pattern control circuit 7 and transmitted to the LD pattern control circuit 7. Is entered. The wavelength pattern detection / comparison circuit 71 always detects the magnitude of all the input voltages, and sets "1" on the assumption that a hole is detected when the voltage decreases. For example, the output current of the light detecting element corresponding to the wavelength of .lambda.1 (M2) when in the position x1 T ₂ is to to "1" passes decreases. Similarly, when the T ₃ λ2 (M2), when T ₄ [lambda] 3
(M2), λ4 (M2) , λ5 (M2) when T ₆ when T _5, T ₇
.Lambda.6 (M2) when the output current of the light detecting element corresponding to the wavelength of .lambda.7 (M2) is reduced when T _8, and respectively "1" passes. Further, at the position x2 is, .lambda.4 when T ₅ (M2),
Λ5 when T ₆ (M2), λ6 when T ₇ (M2), when T ₈ lambda
It is assumed that the output current of the photodetector corresponding to the wavelength of 7 (M2) decreases and “1” is set. In position x3 when the T ₄ lambda
3 (M2), λ4 (M2 ) when T _5, when T ₈ λ7 (M2) the output current of the light detecting element corresponding to the wavelength is reduced in the stand is "1". In position x3 when the T ₃ λ2 (M2),
When T ₄ λ3 (M2), λ4 when T ₅ (M2), when T ₆ lambda
It is assumed that the output current of the photodetector corresponding to the wavelength of 5 (M2) decreases and “1” is set. FIG. 14 (b) is more a detected pattern shown in the table, are made to correspond to the clock the T _m of FIG. 14 (a). After obtaining the first detection pattern of the wavelength confirmation information, that is, the position x1
After detecting the pattern once from x1 to x4, from position x1
4 the value of the same clock T _m in the detection pattern up to x4
Convert to bit code. That is, when the T ₁ "000
0 1000 ", when the T _2" because wavelength confirmation information by made. Reference wavelength 1001 "", when the T ₃ "is recorded as shown in FIG. 12, for example λ1 of (M2) If the signal is reproduced at the wavelength, a time-series signal of "1000" is obtained, and the time-series signal of "1001" is obtained at λ2 (M2). _n (M2) is stored in advance in the ROM 72. The wavelength pattern detection / collation circuit 71 outputs the 4-bit code to the ROM 72 as an address, reads data from the corresponding address of the ROM 72, and outputs the data at each clock _Tm . The actual oscillation wavelength of LD1 is compared with the correct oscillation wavelength (Fig. 14 (d)).
A figure showing the verification results, the wavelength pattern detecting matching circuit 71, the result of the collation, and the relationship between the n clock T _m Timing m and the wavelength lambda _n of _(M2) and m = n + k, k is positive In the case of k k pulse signals, if k is negative k DO pulse signal
The WN pulse signal is sent to the injection current pattern generation circuit 73. In this embodiment, it can be seen from the collation result that the relationship of n of the wavelength λ _n (M2) with respect to the timing m of the clock T _m is m = n + 1. Accordingly, one up pulse signal is sent to the injection current pattern generation circuit 73 as shown in FIG. The injection current pattern generating circuit 73 receives this UP pulse signal and raises the stepwise injection current pattern to the wavelength control system of the LD 1 by one step as a whole. Therefore, from the verification second as shown in Figure No. 14 (a), n timing m the wavelength lambda _{n (M2)} of the clock the T _m coincide.

Next, an operation of erasing information from the target track of the recording / reproducing layer 52 while the focused spots of the LD1, LD3, and LD4 are tracking the target track will be described.

In FIG. 1, the LD 2 is turned on by the LD power control circuit 22. The oscillation wavelength of the LD2 belongs to the M3 wavelength band, which is the absorption wavelength band of the erasing heat generation layer 53 in the disk 5.
The light emitted from the LD 2 is converted into a parallel light by the collimator lens 102 and enters the dichroic mirror 112. Since the dichroic mirror 112 and the dichroic mirror 111 have a property of reflecting light in the M2 wavelength band, the light that has exited LD2 is reflected by the dichroic mirror 112,
PBS1 is further reflected by the dichroic mirror 111 and is linearly polarized light having only a P-polarized component with respect to the incident surface of the PBS 105.
It is incident on 05. Therefore, the light from the LD 2 passes through the PBS 105, becomes elliptically polarized light by the quarter-wave plate 106, enters the OBL 107, and is collected on the disk 5. The optical axis of LD2 is LD1, LD3, L
Because it is shifted slightly parallel to the disk rotation direction forward with respect to D4, and because OBL 107 uses a lens that has been subjected to aberration correction so that its chromatic aberration can be ignored in the wavelength band from M1 wavelength band to M4 wavelength band, The focusing position of light from LD2 is LD1, LD3
And a position preceding the required track by a small distance from the light condensing position of the light from LD4. Therefore, in order to erase the information recorded on the recording / reproducing layer 52, the light-converging spot of the LD2 for causing the erasing heat generating layer 53 provided in close contact with the lower side thereof to generate heat is also provided on the recording / reproducing layer 52. Track required tracks.

When the LD 2 is turned on, most of the light energy is absorbed by the erasing heat generation layer 53 and converted into heat energy. Since the heating layer for erasing 53 is provided in close contact with the recording / reproducing layer 52, the heat generated in the heating layer for erasing 53 is immediately diffused to bring the corresponding pits of the recording / reproducing layer 52 to a temperature required for erasing the hole. To raise. The holes in the recording / reproducing layer 52 are maintained without being destroyed up to a normal storage temperature, for example, up to 100 ° C., but at higher temperatures, the holes disappear due to thermal energy. In this case, if the thermal resistance of the erasing heat generation layer 53 and the power of the LD 2 are optimally selected, the range of thermal diffusion is narrowed, and the holes of the required tracks can be eliminated without erasing the holes of the adjacent tracks. Further, by synchronizing the light emission period of the LD 2 with the servo frequency reproduced from the disk 5, it is also possible to erase information in a predetermined unit, for example, in 1-byte units. Furthermore, since the light-collecting light spot of LD2 always precedes the light-collecting light spot of LD1 on the track, if the distance between the spots and the thermal resistance of the recording / reproducing layer 52 are optimally selected, the light-deletion light of LD2 can be obtained. This enables overwriting by recording with the LD1 recording / reproducing condensing light while erasing with the converging light spot.

〔The invention's effect〕

The device of the present invention uses a dichroic mirror to guide the irradiation light from the light source to a predetermined optical path according to the wavelength, using a light source composed of a plurality of wavelength tunable semiconductor lasers, thereby causing photochemical hole burning. It can be focused on the same position on a recording medium using a material, preventing the optical system from becoming large, achieving high information recording density by multiplex recording using a semiconductor laser, and reflecting light from the recording medium. Can be simultaneously detected for each wavelength, so that the recording and reproducing efficiency of information can be improved. In addition, excellent effects are achieved, such as reducing return light to the light source and stabilizing the oscillation wavelength of the light source.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the device of the present invention, FIG. 2 is a diagram showing an emission spectrum of each semiconductor laser, FIG. 3 is a diagram showing a cross-sectional layer structure of a disc and a disc structure diagram showing an absorption spectrum of each layer. 6 and 7 are block diagrams of the servo circuit of FIG. 1, and FIGS. 8, 9, and 10 are diagrams of FIGS. 6 and 7. Waveform diagram for explaining the operation of the servo circuit, FIG. 11 is a waveform diagram for explaining the operation of the recording / reproducing system, FIG. 12 is a recording format diagram of wavelength confirmation information, and FIG. 13 is a configuration of a semiconductor laser oscillation wavelength control circuit. FIG. 14 is an explanatory diagram of the operation of the wavelength control circuit, FIG. 15 is a block diagram showing the configuration of a conventional optical wavelength multiplexing recording / reproducing apparatus, and FIG. 16 is a diagram showing the wavelength spectrum of a recording medium. It is. 1, 2, 3, 4 ... semiconductor laser, 5 ... disk, 10 ... optical head, 101, 102, 103, 104 ... collimating lens, 105 ...
... PBS, 106 ... Quarter wave plate, 107 ... OBL, 108 ...
Hologram lens, 109 …… PD array, 111,112,113 ……
Dichroic mirror, 114... Mirror In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kyosuke Yoshimoto 8-1-1, Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Inside the Applied Equipment Research Laboratories, Mitsubishi Electric Corporation (72) Satoru Yoshimura 8-1-1, Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1 Inside Mitsubishi Electric Corporation Central Research Laboratory (72) Inventor Mitsuo Maeda 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Central Research Laboratory (56) References JP-A-59-92447 (JP, A)

Claims (5)

(57) [Claims] 1. A multiplex recording / reproducing method in which a plurality of light beams having different wavelengths are emitted from a light source, the emitted light beams are converted into parallel light fluxes, and guided to a predetermined optical path. Alternatively, in an optical wavelength multiplex recording apparatus for erasing, a light source composed of a plurality of tunable semiconductor lasers for emitting light beams belonging to a plurality of different wavelength bands, and an optical path of the light beam of each wavelength band emitted from each light source having a wavelength A dichroic mirror having a wavelength-dispersive reflectivity that guides the light beam to a predetermined optical path, and a light-collecting element that focuses the light beam guided to the predetermined optical path onto a recording medium using a material that causes photochemical hole burning. A dispersive element for simultaneously dispersing and condensing the reflected light from the recording medium to different positions for each wavelength; and a detecting element for detecting, by wavelength, the light dispersed and condensed for each wavelength by the dispersive element. Optical wavelength multiplexing recording and reproducing apparatus characterized by comprising a group. 2. The optical wavelength multiplexing recording / reproducing apparatus according to claim 1, wherein a holographic diffraction grating is used as the dispersion element. 3. The optical wavelength multiplexing recording / reproducing apparatus according to claim 1, wherein a photodiode array is used as the detecting element group. 4. An optical wavelength division multiplexing recording / reproducing apparatus according to claim 1, further comprising a polarizing element for polarizing light emitted from said light source for recording / reproducing to a recording medium and reflected light thereof. apparatus. 5. A polarizing element comprising a beam splitter and a quarter.
5. The optical wavelength division multiplexing recording / reproducing apparatus according to claim 4, wherein the optical wavelength multiplexing recording / reproducing apparatus comprises a wavelength plate, and sets a reference wavelength of a phase difference provided by the quarter wavelength plate to one of wavelengths emitted from a recording / reproducing light source.