JP2001110084A - Optical information recording / reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problem that the reflected light of the luminous flux leaks into a light detector to hurt the AF control and accordingly a recording bit shape is affected to deteriorate the quality of reproducing signals. SOLUTION: A wavelength separating means is prepared between an optical multiplexer 106 an optical detector 120 to transmit the reproducing luminous flux and to reflect the recording luminous flux among those beams which are reflected on an optical card 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical information recording / reproducing apparatus for recording information on an optical information recording medium or reproducing the recorded information.

[0002]

2. Description of the Related Art Various types of recording media for optically recording and reproducing information, such as discs, cards, and tapes, have been known. When information is recorded on these information recording media, irradiation is performed by irradiating a light spot having a power sufficient to cause a shape change, a reflectance change, or a structural change according to the characteristics of the recording medium.
When reproducing recorded information, the information pit array is scanned with a light spot having a constant power enough to prevent recording on the recording medium, and reflected light or transmitted light from the recording medium is detected.
The recorded information is reproduced by performing predetermined signal processing using the obtained detection signal.

An optical head used for recording and reproducing information on such a recording medium is configured to be relatively movable with respect to the recording medium in an information track direction comprising information pits in the information area and in a direction crossing the information track. The relative movement in both directions allows the light spot to access a desired information track and scan the information track. The optical head is provided with a focusing lens for focusing the light beam, and an objective lens is used as the lens. The objective lens is held by the optical head so that it can move independently in the optical axis direction (focus direction) and the direction perpendicular to the optical axis, that is, in the direction perpendicular to the information track of the recording medium (tracking direction). Such an objective lens is held via an elastic member, and the focus and the movement of the objective lens in the tracking direction are generally driven by an actuator utilizing magnetic interaction.

FIG. 3 is a schematic plan view of a write-once optical card. A large number of information tracks 2 and tracking tracks 4 are alternately arranged on the information recording surface of the optical card.
The optical card is provided with a home position 3 which is a reference position for accessing the information track 2. The home position 3 is used as a start position for recording and reproducing information on the optical card inserted into the optical information recording / reproducing apparatus, or as a standby position for a light spot, and is also a retract position for autofocus. Therefore, the same recording layer as the information track is provided at the home position 3 in order to obtain the same light reflectance as the information track. However, the tracking track is not provided because it is not necessary for the function and is a flat surface.

The information tracks 2 are arranged in the order of 2-1 2-2, 2-3,... As shown in FIG. 4, tracking tracks 4-1 and 4 are located adjacent to the information tracks 2 respectively.
-2, 4-3, etc. These tracking tracks are auto-tracking (hereinafter abbreviated as AT) for controlling a light spot so as not to deviate from a target information track during light spot scanning during information recording / reproduction.
Used as a guide for

In such AT control, an optical head detects a deviation (AT error) of a light spot from an information track, and feeds back to a tracking actuator that drives the objective lens in a tracking direction in an AT control circuit, thereby obtaining the objective lens. Is moved in the tracking direction (D direction) so that the light spot does not deviate from the target information track. Also, in order to make the light beam into an appropriately sized spot on the recording surface of the optical card (focusing) when scanning the light spot on the information track at the time of recording / reproducing information, the objective lens is automatically moved with respect to the objective lens. Focus (hereinafter abbreviated as AF) control is performed. In such AF control, the optical head detects a deviation (AF error) of a light spot from a focused state, and feeds back to a focus actuator that moves the objective lens in a focus direction in an AF control circuit, thereby focusing the objective lens. The control is performed such that the light spot is focused on the recording layer of the optical card by moving the light spot in the direction.

Here, in FIG. 4, S1, S2, S3,
S4 indicates a light spot irradiated on the optical card 1. AT control is performed using the light spots of S2 and S3 in which the tracking tracks 4-2 and 4-3 are partially applied. Also, AF control and reproduction of information pits are performed using the light spot of S1, and recording of information pits is performed with the light spot of S4. In the figure, 5-1 to 3 represent information pit strings, and 6-1 to 3 represent track numbers (addresses) arranged on both sides of the information pit strings 5-1 to 5-1. Each information track is provided with a track number indicating which track the position is. Further, the width of the information track 2 which is an information area is wider than the width of the tracking track 4, and the width of the tracking track 2 is about 3 μm according to the standard.
m, the width of the information track 4 is 9 μm, and the width of the information pit is about 3
μm.

FIG. 5 is a block diagram showing an example of an optical system of an optical information recording / reproducing apparatus using an optical card as an information recording medium. In FIG. 5, reference numeral 10 denotes a reproducing semiconductor laser which is a reproducing light source, and reference numeral 11 denotes a recording semiconductor laser which is a recording light source. 12 and 13 are collimator lenses, 14 is a diffraction grating, 15 is a half mirror which is a light splitter, 16 is a dichroic prism which is an optical multiplexer, 17 is an objective lens, 18 is a spherical lens, 19 is a cylindrical lens,
20 is a photodetector. As shown in FIG. 6, the photodetector 20 includes four light receiving elements 20-1 to 20-4 and a light receiving element 20-1.
-5 and 20-6.

The light beam emitted from the reproducing semiconductor laser 10 is a linearly polarized light beam perpendicular to the plane of FIG. 5, is converted into a parallel light beam by the collimator lens 12 and is incident on the diffraction grating 14. Is divided into Of the divided diffracted light, the 0th-order diffracted light is used for information reproduction and AF control.
The two ± first-order diffracted lights are used for AT control. The three diffracted light beams are reflected by the half mirror 15, pass through the dichroic prism 16, and enter the objective lens 17.
The light beam incident on the objective lens 17 is narrowed down to a minute optical spot and focused on the optical card 1. This converged light is converted into minute light spots S2 (+ 1st-order diffracted light) and S1 shown in FIG.
(0th-order diffracted light) and S3 (-1st-order diffracted light). The light spot S1 is used for reproduction and AF control as described above.
2 and S3 are used for AT control.

The position of the spot on the optical card 1 is
As shown in FIG. 4, light spots S2 and S3 are located on two adjacent tracking tracks, and spot S1 is an information track 2 which is an information area between the tracking tracks.
Located on top. Note that the tracking of the light spots S2 and S3 is applied. Specifically, the rotation fine adjustment is performed by rotating the diffraction grating 14 about the optical axis so that desired AT control can be performed. Thus, the light spot is irradiated on the optical card 1, and a part of the light spot is reflected on the optical card surface and enters the objective lens 17. This reflected light is transmitted through the dichroic prism 16 and the half mirror 15 and becomes a spherical lens 18.
Then, the light passes through a sensor lens system including the cylindrical lens 19 and enters the photodetector 20.

On the other hand, the luminous flux emitted from the recording semiconductor laser 11 is a linearly polarized luminous flux parallel to the plane of FIG. 5, converted into a parallel luminous flux by the collimator lens 13, reflected by the dichroic prism 16, and further reflected by the objective lens 17. Card 1
The top is illuminated as a light spot. Information recording is performed by the irradiated light spot. Part of the recording light is reflected by the optical card 1, passes through the objective lens 17, and is reflected by the dichroic prism 16. Here, wavelengths of the semiconductor lasers 10 and 11 and wavelength characteristics of the half mirror 15 and the dichroic mirror 16 will be described. The wavelength of the reproducing semiconductor laser 10 is, for example, 790 nm, and the wavelength of the recording semiconductor laser is 830 nm.

FIG. 7 shows the wavelength characteristics of the half mirror 15. The half mirror 15 transmits about 50% of the P-polarized light component and about 50% of the S-polarized light component and reflects about 50% between 790 nm and 830 nm. FIG. 8 shows the wavelength characteristics of the dichroic prism 16. The dichroic prism 16 almost reflects the 830 nm P-polarized light component and almost transmits the S-polarized light component. The dichroic prism 16 has 7
A 90-nm P-polarized light component and an S-polarized light component are deposited on the film so as to transmit the same. Therefore, light emitted from the recording semiconductor laser 11 having a wavelength of 830 nm is reflected by the optical card 1 and returns to the semiconductor laser 11 again. 790 nm
The light emitted from the reproducing semiconductor laser 10 is reflected by the optical card 1 and travels to the photodetector 20.

FIG. 6 is a circuit diagram showing a signal processing circuit.
In FIG. 6, reference numeral 20 denotes the photodetector in FIG. 5, and as described above, the quadrant light receiving elements 20-1 to 20-4 and the light receiving element 20-5,
20-6. Light spots S1, S2, and S3 on the light receiving surface of each light receiving element indicate reflected light from the optical card. The AT control light spots S2 and S3 are received by the light receiving elements 20-5 and 20-6, respectively, and the AF control and reproduction light spot is received by the four-divided light receiving elements 20-1 to 20-4. The output signals of the light receiving elements 20-5 and 20-6 are output to a subtraction circuit 122, and the subtraction circuit 122 detects the difference to generate an AT control signal. The output signals of the quadrant light receiving elements 20-2 and 20-4 are added to an adder circuit 111.
Thus, the output signals of the light receiving elements 20-1 and 20-3 are added by the adding circuit 112, respectively. Adder circuits 111 and 112
Is subtracted by the subtraction circuit 121 and output as an AF control signal. Also, the adder circuits 111 and 112
Are added by an adder circuit 113, and the sum signal of the four divided light receiving elements is output as an information reproduction signal RF.

The AT control signal is output to an AT control circuit (not shown).
By driving an actuator (not shown), the objective lens 17 is driven.
AT in the tracking direction to perform AT control. Further, an AF control circuit (not shown) drives an AF actuator (not shown) based on the AF control signal, and performs AF control by displacing the objective lens 17 in the focus direction. For reproducing information, a light beam for reproduction is scanned on the track of the optical card while performing AT / AF control, and a predetermined signal processing such as binarization and demodulation is performed in a reproduction circuit (not shown) using the information reproduction signal RF. To reproduce the recorded information. When recording information, the recording data is modulated by a predetermined modulation method, and the recording semiconductor laser 11 is driven according to the obtained recording signal. Then, information recording is performed by scanning a target track with a recording light beam whose intensity is modulated according to a recording signal while performing AT / AF control.

[0015]

What is important in the above-mentioned conventional optical head comprising two light sources is that the reproducing light spot and the recording light spot are focused on the medium surface of the optical card, and That is, the reproduction light spot and the recording light spot are located substantially at the center of the information track. Conventionally, as shown in FIG. 4, a reproducing light spot and a recording spot are made to coincide with each other on a medium surface of an optical card. Further, information is recorded by reflecting light from the recording semiconductor laser 11 by the dichroic prism 16 and irradiating the optical card 1 with the light. At this time, a part of the recording light is reflected by the optical card 1, transmitted through the objective lens 17, further reflected by the dichroic prism 16, and returns to the recording semiconductor laser 11 side.

However, as is clear from the film characteristics of the dichroic prism 16 shown in FIG. 8, the light incident on the dichroic prism 16 is not 100% reflected to the recording semiconductor laser 11 side, and several percent of the light is The light passes through the dichroic prism 16 and further passes through the half mirror 15 due to the film characteristics of the half mirror 15 in FIG. The AF control is performed using the difference signal between the sum signals of the two sets of light receiving elements in the diagonal directions in the four divided light receiving elements. At this time, as shown in FIG. 9, when the recording light spot S4 is incident on the four-division light receiving element in a state substantially coinciding with the reproduction light spot S1, the amount of light received by the four-division light receiving element is larger during recording than during reproduction. Become.

For example, the power of the reproducing light spot on the surface of the optical card 1 is 0.1 mW, the recording power is 10 mW, the reflectivity of the optical card 1 is 20%, the dichroic prism 16
The recording wavelength has a transmittance of 3% and the reproduction wavelength has a transmittance of 97.
%, The transmittance of both the recording and reproducing wavelengths of the half mirror 15 is 5
Assuming 0%, the recording light amount Pw reaching the photodetector and the reproducing light amount Pr are as follows: Pw = 10 mW × 0.2 × 0.03 × 0.5 = 0.03
mW Pr = 0.1 mW × 0.2 × 0.97 × 0.5 = 0.0
1 mW. That is, recording light about three times the amount of reproduction light enters the photodetector. In this case, it is conceivable to perform gain switching electrically between the reproduction power and the recording power in the AF control to remove the modulation component of the recording light. FIG. 10 shows a signal processing circuit having gain switching circuits 131 to 134. Each gain switching circuit switches a gain for amplifying an output signal of the light receiving element in accordance with the gain switching signal, and corrects the gain to a constant level signal. The recording signal may be used as the gain switching signal. However, adding such a gain switching circuit leads to complication of an electric circuit and an increase in cost.

It is extremely difficult to make the centers of the reproducing light spot and the recording light spot coincide with each other in a stable manner. As shown in FIG. The displacement of the spot S4 always occurs.
The position of the four-divided light receiving element is adjusted for the reproducing light spot S1, and in this state, the recording light spot S4 is adjusted.
Is shifted from the intersection of the four division lines, the balance of the light reception amounts of the four division light receiving elements is lost. In the AF control, the control is performed so that the difference signal between the two sets of diagonal sum signals of the four-division light receiving elements becomes zero. Therefore, the focus point of each spot by the objective lens is shifted from the medium surface by the influence of the recording light spot, Each spot on the medium surface is in a defocused state. That is, an offset occurs in the AF direction. FIG. 11B shows a light spot on the photodetector surface when each spot is in a defocused state. Therefore, when this defocus state occurs, there is a problem that the shape of the recording pit is affected at the time of recording, and the quality of a reproduced signal is deteriorated at the time of reproduction.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an optical information recording / reproducing apparatus capable of preventing recording light flux from leaking into a photodetector and stably recording and reproducing information. The purpose is to provide.

[0020]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reproducing light source and a recording light source having different wavelengths from each other.
A half mirror that reflects a part of the reproducing light beam emitted from the reproducing light source to the recording medium side, transmits the reproducing light beam reflected from the half mirror, and reflects the recording light beam emitted from the recording light source; An optical multiplexer for multiplexing the reproducing light beam and the recording light beam onto the recording medium and irradiating the recording medium with light; and a light detection device provided on the opposite side of the half mirror from the recording medium side to detect light reflected by the recording medium. A recording device for recording information by irradiating a recording light beam from the recording light source onto a recording medium, irradiating the recording medium with a reproduction light beam from the reproducing light source, and detecting the light with the photodetector. In an optical information recording / reproducing apparatus that reproduces recorded information based on the obtained signal, a reproducing light flux of reflected light from the recording medium is transmitted between the optical multiplexer and a photodetector, and the recording light flux is Set a wavelength separation means to reflect It was achieved by an optical information recording and reproducing apparatus, characterized in that.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a first embodiment of the invention.
It is a figure showing composition of an embodiment. FIG. 1 shows only the optical system (optical head) of the optical information recording / reproducing apparatus. The optical card 1 shown in FIG. 3 is used as a recording medium. In FIG. 1, reference numeral 100 denotes a semiconductor laser for reproduction, and 101 denotes a semiconductor laser for recording. The wavelength of the reproducing semiconductor laser 100 is 790 nm, and the wavelength of the recording semiconductor laser 101 is 830 nm. Also, 102 and 10
3 is a collimator lens, 104 is a diffraction grating, 105 is a half mirror, 106 is a dichroic mirror which is an optical multiplexer, 107 is an objective lens, 108 is a spherical lens, 10
9 is a cylindrical lens, and 120 is a photodetector.
The photodetector 120 is, as shown in FIG.
-1 to 20-4 and light receiving elements 20-5 and 20-6.

Here, the surface P of the optical multiplexer 106 on the side of the photodetector 20 and the surface Q of the half mirror 105 on the side of the optical card 1 are each formed of a wavelength separating film that transmits a reproduction light beam and reflects a recording light beam. A certain dichroic mirror film is formed. The film characteristics of each wavelength separation film are the same as those shown in FIG.
97% of the wavelength of the reproducing light beam is transmitted, and 3% of the wavelength of the recording light beam.
It has the property of transmitting (the remaining 97% is reflected). The characteristics of the half mirror 105 are the same as those shown in FIG. 7, and have a characteristic of transmitting 50% at the wavelength of both the recording and reproducing light beams.

A light beam emitted from the reproducing semiconductor laser 100 is collimated by a collimator lens 102, and then divided by a diffraction grating 104 into three light beams (0th-order diffracted light and ± 1st-order diffracted light). The split light flux enters the objective lens 107 via the half mirror 105 and the dichroic mirror 106, is narrowed down by the objective lens 107, and is irradiated on the optical card 1 as light spots S1, S2, and S3 as shown in FIG. Is done. The light spot S1 is used for reproduction and AF control, and the light spots S2 and S3 are used for AT control. The light beam emitted from the recording semiconductor laser 101 is collimated by a collimator lens 103.
After being collimated by, the light is reflected by the dichroic mirror 106 and enters the objective lens 107. Then, it is stopped down by the objective lens 107, and is irradiated as a light spot S4 on the optical card 1 as shown in FIG. The light spot S4 is used for recording information.

The light beam reflected from the optical card 1 is applied to the objective lens 107, the dichroic mirror 106, the spherical lens 1
08, photodetector 1 through cylindrical lens 109
Detected at 20. In this case, the recording light beam is reflected by the half mirror 105 and the dichroic mirror 106,
Since the wavelength separation film that transmits the reproduction light beam is formed, the amount of the recording light beam incident on the photodetector 120 can be significantly reduced. The output of each light receiving element of the photodetector 120 is processed by the signal processing circuit of FIG.
An AF control signal is generated. AT, AF during recording / reproduction
AT control and AF control are performed based on the control signal.

When recording information, the optical head and the optical card 1 are relatively moved in the track direction by a mechanism (not shown), and the recording semiconductor laser 101 is driven in accordance with the recording signal, so that the intensity-modulated recording is performed. Information is recorded by scanning the light spot S4 on the information track. When information is to be reproduced, the optical head and the optical card 1 are similarly moved in the track direction to scan the reproduction light spot S1 from the reproduction semiconductor laser 100 on the information track. At this time, the reflected light from the optical card 1 is detected by the photodetector 120, and the output of the light receiving elements 20-1 to 20-4 is processed by the signal processing circuit of FIG. Further, the recorded information is reproduced by performing predetermined signal processing using the information reproduction signal RF.

Next, the light amounts of the reproducing light beam and the recording light beam incident on the photodetector 120 of this embodiment will be described.
The reproducing power on the optical card surface is 0.1 mW, the recording power is 10 mW, the reflectance of the optical card 1 is 20%, the transmittance of the recording / reproducing light flux of the half mirror 105 is 50%, and the transmittance of the recording light flux of the dichroic mirror 106 is Is 3%, and the transmittance of the reproducing light beam is 97%. This is exactly the same as the condition in the conventional case of FIG. Further, assuming that the transmittance of the recording light flux of the wavelength separation film formed on the half mirror 105 and the dichroic mirror 106 is 3% and the transmittance of the reproducing light flux is 97%, the reproducing light flux reaches the photodetector 120. The light quantity Pr and the reaching light quantity Pw of the recording light beam are as follows: Pw = 10 mW × 0.2 × 0.03 × 0.03 × 0.05 × 0.03 = 2.7 × 10 ⁻⁵ mW Pr = 0.1 mW × 0.2 × 0.97 × 0.97 × 0.5 × 0.97 = 9.13 × 10 ⁻³ mW. Therefore, the ratio of the reaching light amount Pw of the recording light beam to the reaching light amount Pr of the reproducing light beam is Pw / Pr = 0.003, and the recording light beam reaching the photodetector 120 is about 0.3% of the reproducing light beam. is there. This amount is an amount that does not cause any problem in the AF control operation at the time of recording.

In the above embodiment, the wavelength separation film for reflecting the recording light beam is formed on the dichroic mirror 106 and the half mirror 105. However, the present invention is not limited to this.
For example, the surface of the half mirror 105 on the photodetector 120 side (the surface facing the surface Q in FIG. 1) or the spherical lens 108
Alternatively, it may be provided on the surface of the cylindrical lens 109.
Even in that case, the same effect can be obtained. Further, the wavelength separation film may be provided on either one of the half mirror 105 and the dichroic mirror 106.

FIG. 2 is a diagram showing the configuration of the second embodiment of the present invention. In the first embodiment, the wavelength separation films are formed on the surfaces P and Q. However, since each surface is opposed to the optical card surface, the recording light flux reflected on the surfaces P and Q is transmitted through the optical multiplexer 1.
97% is reflected by the dichroic mirror film in 06,
3% is incident on the optical card side. Further, the light reflected by the optical multiplexer 106 generates a lot of stray light due to internal reflection of the optical multiplexer. In the configuration of the first embodiment, there is no influence of these stray lights. However, since the influence of the stray lights is different due to an increase in the recording power due to the improvement in the recording sensitivity or the recording speed of the recording medium, unnecessary stray lights should be removed. desirable. Also,
The half mirror 105 and the dichroic mirror 106 according to the first embodiment are obtained by bonding two triangular prisms, and one triangular prism is polished on three sides, which is expensive. The second embodiment solves these problems.

In the second embodiment, as shown in FIG.
Half mirror 2 instead of half mirror 105
05, a plate-like half mirror 206 is used instead of the dichroic mirror 106. The half mirror 205 reflects the light beam for reproduction from the semiconductor laser 100 for reproduction,
The dichroic mirror 206 transmits the reproducing light beam, reflects the recording light beam from the recording semiconductor laser 101, and
It combines two light beams and has the same function as that of FIG. The difference from the first embodiment is that the half mirror and the dichroic mirror are each formed in a plate shape. On the surface of the half mirror 205 on the side opposite to the half mirror surface and on the surface of the dichroic mirror 206 on the side opposite to the dichroic surface, a wavelength separation film is formed, which transmits the reproduction light beam and reflects the recording light beam. Other configurations are the same as those in FIG.

As described above, in this embodiment, since the plate-like half mirror 205 and the dichroic mirror 206 are used, in addition to the effects of the first embodiment, the problem of stray light can be solved and the cost can be reduced. it can. Further, the wavelength separation film is composed of the half mirror 205 and the dichroic mirror 20.
6 may be provided. In the first and second embodiments, the wavelength of the semiconductor laser for reproduction is set to 790.
Although the wavelength of the semiconductor laser for recording is 830 nm, the invention is not limited thereto. For example, if the reproduction wavelength is 79
0 nm and the recording wavelength may be 650 nm. However, it is necessary to change the characteristics of the dichroic mirror and the like according to the reproduction wavelength and the recording wavelength.

[0031]

As described above, according to the present invention, a wavelength separating means for reflecting a recording light beam and transmitting a reproducing light beam is provided between an optical multiplexer and a photodetector. The recording light flux leaking into the device can be significantly reduced, the AF control can be performed stably without being affected by the recording light flux at the time of recording, information can be accurately recorded, and high-quality reproduction can be performed at the time of reproduction. A signal can be obtained. Further, by merely providing the wavelength separation means, the recording and reproducing operations can be easily stabilized without requiring a complicated circuit such as a gain switching circuit.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a plan view of the optical card.

FIG. 4 is a diagram showing a light spot on an optical card.

FIG. 5 is a diagram showing an optical system of a conventional optical card recording / reproducing apparatus.

FIG. 6 is a diagram showing a signal processing circuit of a conventional optical card recording / reproducing apparatus.

FIG. 7 is a diagram illustrating a wavelength characteristic of the half mirror 15 of FIG. 5;

8 is a diagram illustrating a wavelength characteristic of the dichroic mirror 16 in FIG.

FIG. 9 is a diagram showing a positional relationship between a reproduction light spot and a recording light spot on a four-divided photodetector.

FIG. 10 is a diagram illustrating a signal processing circuit having a gain switching circuit.

FIG. 11 is a diagram showing a state in which a reproducing light spot and a recording light spot are incident on a four-divided photodetector with a shift, and a state in which each light spot is in a defocused state on a medium surface.

[Explanation of symbols]

 Reference Signs List 1 optical card 100 semiconductor laser for reproduction 101 semiconductor laser for recording 102, 103 collimator lens 104 diffraction grating 105, 205 half mirror 106, 206 dichroic mirror 107 objective lens 108 spherical lens 109 cylindrical lens 120 photodetector

Claims (6)

[Claims] 1. A reproducing light source and a recording light source having different wavelengths from each other, a half mirror for reflecting a part of a reproducing light beam emitted from the reproducing light source toward a recording medium, and a reproducing mirror reflected from the half mirror. An optical multiplexer that transmits the light beam for use, reflects the light beam for recording emitted from the light source for recording, multiplexes the light beam for reproduction and the light beam for recording, and irradiates the recording medium, and the recording medium side of the half mirror. Is provided on the opposite side, and includes a photodetector that detects light reflected by the recording medium, and records information by irradiating a recording light beam from the recording light source onto the recording medium, and the reproduction light source An optical information recording / reproducing apparatus that irradiates a recording medium with a reproduction light beam from the optical disc and reproduces recorded information based on a signal detected by the photodetector, wherein the recording is performed between the optical multiplexer and the photodetector. Light reflected from the medium An optical information recording / reproducing apparatus comprising a wavelength separating means for transmitting a reproducing light beam and reflecting a recording light beam. 2. The optical information recording / reproducing apparatus according to claim 1, wherein the half mirror is made of a plate-like glass, and has a half mirror surface formed on one surface thereof. 3. The optical multiplexer is made of a sheet glass,
2. The optical information recording / reproducing apparatus according to claim 1, wherein a dichroic mirror surface is formed on one surface thereof. 4. The half mirror is made of a plate-like glass whose one surface is a half mirror surface, the optical multiplexer is made of a plate-like glass whose one surface is a dichroic surface, and a surface opposite to the half mirror surface. 2. The optical device according to claim 1, further comprising a wavelength separating unit that reflects a recording light beam and transmits a reproduction light beam on at least one of the surfaces opposite to the dichroic surface. Information recording and reproducing device. 5. The optical information recording / reproducing apparatus according to claim 1, wherein said wavelength separating means is provided in at least one of said half mirror and said optical multiplexer. 6. The optical information recording / reproducing apparatus according to claim 1, wherein said wavelength separating means is a dichroic mirror film.