JPH04265535A - Optical waveguide recording medium reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide recording medium reproducing device in which the modulation frequency of a reference light is changed to have a wide band by providing a waveguide light delay reflection element generating a surface elastic wave in the propagating direction of incident light. CONSTITUTION:A waveguide type light wave delay reflection device 37 is adopted in an optical waveguide recording medium reproducing device. The device 37, which is provided with an electrode (transducer) 101 generating the surface wave on a waveguide 100 guiding light, serves to propagate the surface elastic wave in the light propagating direction of the light waveguide 100. A laser beam is guided to the lightwaveguide 100, high frequency drive current which is demodulated in a burst-like form and generates the surface elastic wave is made to flow to the electrode 101, and the shift in light frequency and the phase delay in time of the reference light which permits the information to be reproduced by means of the interaction between the laser beam and the surface elastic light are realized. Thus, the phase shift several times as large as a wavelength can be given by the delay reflection device 37, and the information can be read out through a long waveguide 100.

Description

[Detailed description of the invention]

0001

[Technical field] The present invention relates to an optical storage medium, in particular, a refractive index discontinuity portion that generates reflected guided light having a plurality of different amplitudes and phase delays by guiding a laser beam (generally referred to as a low-coherent light beam). Using an optical waveguide storage medium having an optical waveguide, a laser beam is guided through the medium, and a part of the reflected guided light and the laser beam with shifted Doppler frequency are optically heterodyne detected, and the recorded information is converted into a time-series signal. The present invention relates to an optical waveguide storage medium reproducing device that reproduces waveforms.

0002

BACKGROUND OF THE INVENTION Conventional optical storage media include optical discs in which a plurality of low light reflectance recesses are arranged in a line as recorded information on a flat reflective film with high light reflectance formed on the surface of a disk substrate as a recording film. In this optical storage medium, a laser beam is focused and irradiated onto a row of recesses, and the difference in the amount of light reflected from the reflective film and the recesses is detected as recorded information. Other optical storage media include
There is also a magneto-optical disk in which information is recorded by forming a plurality of minute magnetization reversal regions in an array on a uniaxial magnetic anisotropic recording film. In this optical storage medium, the difference in rotation angle of the plane of polarization of the reflected light from the magnetization reversal region array is detected as recorded information.

[0003] In these optical storage media, since reproduction is performed using reflected light from a recessed portion or a row of magnetization reversal regions serving as a recording portion, there is a limit to the areal density of such recording portions. When reproducing these optical storage media, the focal point of the laser beam is moved in the optical axis direction in order to follow the surface deflection of the optical storage medium, but this requires focusing for each recording section. Furthermore, since the optical reflectance of the reflected light and the rotation angle of the polarization plane are very small, the signal-to-noise ratio of the detected optical signal is low. Furthermore, since the time-series signal is reproduced only by moving the column of recording units, the access time for reproduction and recording is limited by the moving speed of the optical storage medium.

The optical waveguide storage medium and its reproducing apparatus disclosed in Japanese Patent Laid-Open No. 2-210627 have been developed to solve these problems. Furthermore, as a reproducing device for an optical waveguide storage medium, one having a Michelson interferometer type optical heterodyne detection optical system has been proposed. Such a reproducing device includes a collimation lens that converts the emitted laser beam from a light source into a parallel beam, a half mirror that splits the laser beam guided onto the optical waveguide storage medium, and a cup of one of the split laser beams on the optical waveguide storage waveguide. An objective lens is used to make the laser beam ring, a movable mirror is used to give a phase shift and a frequency shift to the other part of the split laser beam and use it as a reference beam, and the beam is reflected by the refractive index discontinuity created on the optical waveguide and returns again. The sensor is composed of a photodetector that interferes with the signal light and the reference light and heterodyne detects the optical output.

In such an optical waveguide storage medium reproducing device, a movable mirror is used as a means for imparting a phase shift and frequency modulation to the split laser beam for heterodyne detection, so there is a limit to the modulation frequency and the information density is limited. Improvement has been hindered. Furthermore, due to the presence of the mirror drive section, it is difficult to miniaturize and reliability of the reproduction optical system.

[0006]

OBJECTS OF THE INVENTION The present invention has been made in view of this difficulty, and it is an object of the present invention to provide a miniaturized optical waveguide storage medium reproducing device that can widen the modulation frequency of reference light.

[0007]

[Structure of the Invention] The optical waveguide recording medium reproducing device of the present invention includes:
It has an optical waveguide having an optical coupling part for introducing a laser beam, and a plurality of refractive index discontinuities arranged in the optical waveguide, and the shape and relative position of the refractive index discontinuities are information to be recorded. An apparatus for reproducing recorded information from a variable optical waveguide recording medium, the apparatus comprising: a light emitting means for generating a laser beam; a dividing means for dividing the laser beam into two to generate first and second light beams; a reference light generating means that receives one light beam and modulates it by applying a frequency shift to generate a reference light; an irradiation means that guides a second light beam to the optical coupling section; and a second light beam that is reflected by the refractive index discontinuity section. a light superimposing means for superimposing the reflected signal light whose amplitude and phase are modulated and returns through the optical coupling section and the previous reference light to form interference light; and a light detection means for photoelectrically converting the interference light to generate an electrical output. and the reference light generating means has an optical waveguide extending along the optical axis of the first light beam and a surface acoustic wave disposed near the optical waveguide and generates a surface acoustic wave in the optical propagation direction of the optical waveguide. The device is characterized in that it has a waveguide optical delay reflection element having a surface acoustic wave electrode that generates a waveform, and intermittent high-frequency power is supplied to the surface acoustic wave electrode.

[0008]

According to the present invention, there can be obtained an optical waveguide storage medium reproducing device having a heterodyne detection optical system in which the modulation frequency of the reference light is widened.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating the principle of the present invention. First, in FIG. 1(a), the optical waveguide storage medium 1 has a structure in which a core optical waveguide 31 through which light is guided is formed on a substrate 32 forming a cladding having a refractive index lower than that of the core. Air or other cladding is present on the upper boundary surface of the core 31. The end face of the core 31 is an optical coupling part 30 that introduces the laser beam into the core. A plurality of refractive index discontinuities 34 are arranged and recorded in the elongation direction on the upper boundary surface of the inner surface of the core. The refractive index discontinuity portion 34 generates reflected guided light having various amplitudes and phases (i.e., amplitude and phase) based on a complex reflectance based on the relative position and shape from the optical coupling portion 30 on the end face with respect to the incident guided light of the laser beam. This is a minute recess that generates a modulated signal light. The shape and position of the refractive index discontinuities 34 are recorded to obtain a predetermined complex reflectance depending on the information to be stored. The concave portion of the refractive index discontinuity portion 34 may be an embedded portion. If air or cladding is used, the refractive index of the embedded portion being smaller than the refractive index of the core, the shape of the refractive index discontinuity portion 34 may be, for example, a semicircle or a cladding. It is an anti-elliptical embedded type, and its size is a fraction of the wavelength of light to several times the wavelength of light. As for the constituent materials, for example, the core 31 is made of polycarbonate which is transparent to light, and the cladding is made of a polymeric material such as polymethyl methacrylate having a lower refractive index. In this way, the optical waveguide storage medium 1 has at least the optical coupling part 3
0, a core 31, a substrate 32, and a refractive index discontinuous portion 34.

Specifically, as shown in FIG. 2, in the optical waveguide storage medium 1, a plurality of channel type ridge optical waveguides 31 each having an end face of an optical coupling part 30 are arranged in parallel on a substrate 32, and the optical waveguides are arranged in parallel on a substrate 32. There is also one in which a plurality of minute refractive index discontinuities 34, in which a plurality of reflected guided light beams with different amplitudes and phases are generated within the core, are arranged in accordance with the information to be recorded. Although this embodiment is explained as a ridge type waveguide, in the case of a channel type waveguide such as a strip type or a buried type, such a refractive index discontinuity portion 34 may be provided in the core or cladding of the optical waveguide. The same effect can be obtained.

As shown in FIG. 1(a), the optical waveguide storage medium reproducing apparatus of the present invention uses an SLD (Super Luminescensor) as a light emitting means for generating a laser beam.
A light emitting element 35 such as a broadband wavelength oscillation laser diode or a broadband wavelength oscillation laser diode is used to divide the laser beam into two parts.
and a half mirror (beam splitter) 36 as a splitting means for generating a second light beam, and a guide as a reference light generating means for receiving the first laser beam and modulating it by applying a Doppler frequency shift to it to generate a reference light. The wave path light delay reflection element 37, the objective lens 42 as an irradiation means for guiding the second laser beam to the optical coupling section 30, and the reflected signal light and reference light returned by the refractive index discontinuity section 34 are superimposed to produce interference light. It has a half mirror 36 as a light superimposing means, and a photodetector 39 as a light detection means that photoelectrically converts the interference light to generate an electrical output.

A laser beam emitted from a light emitting element 35 disposed opposite to the optical coupling section 30 of the optical waveguide storage medium 1 is converted into a substantially parallel beam by a collimation lens 41 and divided into two by a half mirror 36 . One of the first laser beams traveling straight is focused by the objective lens 42 and guided from the optical coupling section 30, and a part of it is transmitted through the plurality of refractive index discontinuities 34.
This results in a plurality of reflected waveguide lights having different amplitudes and phases, which become signal lights returning from the optical coupling section 30. Figure 1 (
As shown in a), the refractive index discontinuities 34 are a, b, c,
When the information to be recorded is recorded at the position d, the shape and relative position of each refractive index discontinuity portion 34 are determined according to the information to be recorded (explained as analog information in the figure). By arranging a plurality of refractive index discontinuities 34 in the refractive index discontinuous portion 31, it is possible to create modulated signal light having different amplitude and phase information as a function of its shape and propagation distance. The other second laser beam split and reflected by the half mirror 36 is focused by the lens 43 onto the optical coupling portion of the waveguide optical delay reflection element 37, and becomes a reference light that returns after being subjected to Doppler frequency shift. These signal beams and reference beams are multiplexed by a half mirror 36, condensed by a lens 44, and then detected by a photodetector 3.
Optical heterodyne interference is input to 9. The input light is photoelectrically converted into an electrical signal, which passes through a frequency filter 40,
As shown in FIGS. 1(b) and 1(c), an electrical output I(t) in a time-series signal waveform is obtained in response to an optical input Iin of a constant intensity of a laser beam from the light emitting element 35.

As shown in FIG. 3, a waveguide optical delay reflection element 3
7 includes an optical waveguide 100 that extends along the optical axis of one of the laser beams split by the half mirror 36, and an optical waveguide 100 that is disposed near the optical waveguide and generates a surface acoustic wave in the optical propagation direction of the optical waveguide. It has a surface acoustic wave electrode 101. The surface acoustic wave electrode 101 is a pair of comb-shaped electrodes 101 arranged with the optical waveguide 100 in between, as shown in FIG. 4(a).
The surface acoustic wave radiation axes A and B of each comb-shaped electrode are arranged as a and 101b so that they intersect on the optical waveguide. Alternatively, as shown in FIG. 4(b), the surface acoustic wave electrode is a comb-shaped electrode 101c placed on the optical waveguide 100 so that the surface acoustic wave radiation axis C of the comb-shaped electrode coincides with the extension direction of the optical waveguide. may be placed in The waveguide optical delay reflection element 37 uses a substrate 102 of GaAs, SiO2 or T.
made of eO2, and a channel type optical waveguide 100 is placed on it.
It is created by diffusing Ti, Rb, etc. When intermittent high-frequency power is supplied to these surface acoustic wave electrodes, propagation of the surface acoustic waves creates lattice-like stripes with a refractive index that changes at wavelength intervals in the optical waveguide, or uneven wrinkles on the surface. occurs, and this propagates. The guided light in the optical waveguide generates reflected light by the propagating diffraction grating, but since the reflecting surface is moving, the reflected light is given a phase and frequency by the Doppler effect depending on the moving speed. This reflected light is used as reference light.

As described above, in this embodiment, the conventional movable mirror for generating reference light is abolished, and instead, a waveguide type element is used as a light wave delay and reflection device. This waveguide-type light wave delay reflection element has an electrode (transducer) that generates a surface acoustic wave near the waveguide through which light is guided.
It is set so that surface acoustic waves propagate in the light propagation direction of the optical waveguide. In order to guide light that is to become a reference light through such an optical waveguide and generate a surface acoustic wave, a burst-like modulated high frequency wave is applied to the electrode.

Furthermore, if this waveguide type optical wave delay reflection element is used, in the pickup section of a waveguide recording medium reproducing device, an optical path branching mirror and a coupling to the optical waveguide recording medium can be installed on the same substrate on which the element is formed. coupler for
Photodetectors can also be integrated. Like the conventional optical delay reflection device using a movable mirror, it can be miniaturized, and it provides a phase shift several times the laser beam wavelength λ compared to the conventional optical delay reflection device using a movable mirror. It is also possible to read information from.

The principle of the playback device will be explained below. Each frequency component of the laser beam from the light-emitting element 35 is simultaneously reflected by one refractive index discontinuity and receives a constant amplitude and a phase delay proportional to the propagation distance, and the reference beam and Doppler frequency shifted corresponding to the phase delay are generated. have a finger in the pie. At that time, each frequency component becomes in phase, forming one pulse having an amplitude that is the sum of the amplitudes of each frequency component. The reflected component from the next refractive index discontinuity whose phase is further delayed interferes with the reference light given the temporally delayed Doppler shift frequency generated by the waveguide-type light wave delay reflection element, and then form a pulse. Here, in the orthogonal coordinate xyz shown in FIG. 1(a), if the z-direction of extension of the optical waveguide 31 is vertical and the y-direction perpendicular to this is horizontal, each pulse width is equal to the z-axis direction of the refractive index discontinuity. Each amplitude depends on the size of the refractive index discontinuity in the x-axis and y-axis directions, respectively.

[0017] Thus, due to the configuration of the optical waveguide recording medium reproducing apparatus, a plurality of refractive index discontinuities (indicated by a, b, c, and d in FIG. 1(a)) recorded on the optical waveguide recording medium corresponds to the time-series signal electrical output (Fig. 1(c)
), a', b', c', and d' correspond to each other)
, is played. Each pulse has a Nyquist sampling shape of sin(F)/F, and the signal waveform is a series of these. F is the emission spectrum width of the light emitting element 35,
It is a function of the speed of the diffraction grating of the propagating surface acoustic wave, the refractive index dispersion of the optical waveguide, and the length and position of the refractive index discontinuity in the optical waveguide medium. By appropriately selecting these values, the signal modulation frequency can be set from several KHz to several tens of MHz. The width of each pulse can also be set from several tens of milliseconds to several tens of nanoseconds. The light emitting element 35 does not necessarily require a semiconductor laser with a narrow spectrum width; rather, a semiconductor light emitting element that emits low coherent light with a wide spectrum width allows the modulation frequency to be set higher. In addition, by optical heterodyne interferometry, these time-series signal waveforms are
It can be reproduced with a high signal-to-noise ratio of 104.

FIG. 5 specifically shows an optical waveguide storage medium and a reproducing device. The optical waveguide storage medium 50 is a laminated drum-type three-dimensional optical disk made by arranging a large number of plate-like bodies 51 of the channel-type ridge optical waveguide storage medium 1 described above and winding them into a drum shape. In addition to the above-mentioned components, the optical waveguide storage medium reproducing device further includes a condensing lens 42 for coupling to the optical disk optical waveguide installed in the focus actuator, a beam splitter 52 for taking out a part of the reflected light beam for tracking, It has a concave lens 53 that separates the tracking laser beam, and tracking photodetectors 54 and 55. Both ends in the long axis direction of the elliptical cross section of the laser beam from the light emitting element 35 are applied to the clad end face with the core end face optical coupling part in between, and the reflected light is used as a tracking laser beam. Photodetector 54,5
5 captures the tracking laser beam with high sensitivity and high signal-to-noise ratio by optical heterodyne detection. Further, according to the error detection between the two, the focusing microlens 42 and the like are moved in the optical axis direction to focus on the optical coupling part of the optical waveguide, and the pickup head 56 of the optical reproducing device follows the surface deflection of the three-dimensional optical disk 50. I'm letting you do it.

Furthermore, as shown in FIG. 6, in the pickup section of the waveguide recording medium reproducing device, a collimation grating 41a and a grating 36a as an optical path branching mirror are provided on the same substrate on which the waveguide type light wave delay reflection element 37 is formed. A grating coupler 42a for coupling to the optical waveguide recording medium 50 is formed, and the SL
It can also be integrated together with D35a and photodetector 39a.

In this example, a plate-like body in which optical waveguides each having a rectangular cross section of 2×2 μm and a waveguide length of 10 mm are embedded and juxtaposed in a 3.2 μm thick cladding at 2 μm intervals is used.
Rolled and laminated into a drum shape, tracking pitch width 3.2μ
m three-dimensional optical disks 50 are formed. The length of the recorded refractive index discontinuity in the z-axis direction is 10 to 30 μm, x
The depth in the axial direction is 0.1-0.5 μm, the width in the y-axis direction is approximately 0.7 μm, and an average of 500 such discontinuities are recorded for each optical waveguide. Since the optical reflectance of each of the refractive index discontinuities is at most 10-6 to 10-8, even with these reflection losses, the attenuation rate of the final returning laser beam is 1.
It is about 0%. In the figure, the cross section of each optical waveguide is opened at the lower end surface of the three-dimensional optical disk 50, and serves as an optical coupling section. A polycarbonate protective film with a thickness of 2 mm is attached to the surface of the optical coupling portion, and the degree of optical coupling is increased by matching the refractive index of the optical waveguide. In addition, the end face of the optical waveguide is similarly protected,
At the same time, the light propagating through the optical waveguide is allowed to escape. Such a three-dimensional optical disc 50 has a diameter of 8 inches, and the stored information is reproduced while rotating like a compact disc (CD).

The optical waveguide storage medium reproducing device is constructed as explained in the section [Structure of the Invention]. The laser beam from the light emitting element 35 is guided to the optical waveguide storage medium 51, a part of which returns as a signal reflection laser beam whose amplitude and phase are modulated, and the other laser beam is guided to the waveguide optical delay reflection element 37. The signals go back and forth, are combined by a half mirror 36, and pass through an iris 58 that allows only the signal light to pass.
Optical heterodyne detection is performed by the photodetector 39, and after passing through the frequency filter 40, from the electrical output terminal 57, I(
Obtain the electrical output of the time-series signal waveform shown in t). A reproduced signal from one optical waveguide storage medium is temporarily stored in a buffer memory and transferred at an arbitrary clock time. After reading out the information stored in one optical waveguide, the information stored in the optical waveguide of the next channel is sequentially read out by rotating the stereoscopic optical disk 50 and tracking the optical reproducing device head 56.

The specifications of this embodiment are, for example, typically, an emission center wavelength of 1.3 μm and an emission spectrum width of approximately 2×10 1
A 2 Hz SLD was used as the light emitting element 35, an acoustic modulation frequency of 355 MHz was used, and an optical waveguide with a refractive index dispersion of 0.14 was used with an average length and relative position of the refractive index discontinuity of 20 μ.
In the case of the optical waveguide storage medium of this embodiment recorded at m, a storage/reproduction frequency of about 30 MHz can be achieved. At this time, the minimum pulse width is about 35 nanoseconds. The light output of the light emitting element 35 is about 1 mW, and the signal-to-noise ratio of the optical heterodyne interference output based on the reflected light from each of the refractive index discontinuities and the reference light is as large as 104. When converted into a digital amount, the total storage capacity is 500 times that of the current compact disk (1 Gbyte: gigabyte), the mechanical access time per bit is 1/500, and the bit cycle time is approximately 14 times faster.

In this embodiment, an example was explained in which the memory section of the optical waveguide storage medium is composed of long and short refractive index discontinuous parts, and an analog signal is stored and reproduced. It is clear that if the presence or absence of these refractive index discontinuities is recorded at regular intervals, it is possible to store and reproduce digital signals. Furthermore, although an embodiment has been described in which the optical waveguide storage medium is formed into a three-dimensional disk, it is also possible to realize a structure in which the optical waveguide storage medium is arranged side by side on a tape or in a card type and stacked. Further, in this embodiment, the optical waveguide length was set to 10 mm, but the optical waveguide length as a storage medium can be made longer or shorter depending on the required memory capacity.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
As a reference light generation means in an optical waveguide storage medium reproducing device having a heterodyne detection optical system, an optical waveguide extending along the optical axis of an incident laser beam and a surface elastic material disposed near the optical waveguide in the optical propagation direction of the optical waveguide are used. An optical waveguide storage medium reproducing device has a waveguide optical delay reflection element having a surface acoustic wave electrode that generates waves, and intermittent high-frequency power is supplied to the surface acoustic wave electrode, thereby widening the modulation frequency of the reference light. A device is obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the principle of an optical waveguide storage medium reproducing device of the present invention.

FIG. 2 is a perspective view of an optical waveguide storage medium according to the present invention.

FIG. 3 is a perspective view of a waveguide optical delay reflection element according to the present invention.

FIG. 4 is a plan view of a waveguide optical delay reflection element according to the present invention.

FIG. 5 is a schematic diagram of an optical waveguide storage medium reproducing apparatus according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of another embodiment of an optical waveguide storage medium reproducing device head according to the present invention.

[Explanation of symbols]

30... Optical waveguide coupling portion 31... Optical waveguide core 32... Optical waveguide cladding (substrate) 34... Refractive index discontinuity portion 35... Light emitting element 36... Half mirror 37... Waveguide optical delay Reflection element 39... Photodetector 40... Frequency filters 41 to 44... Lens 50... Laminated drum type three-dimensional optical disk 51... Optical waveguide storage medium 52... Beam splitter 53... Concave lenses 54, 55... Tracking Photodetector 56...Optical reproducing device head 57...Electric output terminal 58...Iris 100...Optical waveguide 101...Surface acoustic wave electrodes 101a, 101b, 101c...Comb-shaped electrode 102...
…substrate

Claims (9)

[Claims] 1. An optical waveguide having an optical coupling part for introducing a laser beam, and a plurality of refractive index discontinuities arranged in the optical waveguide, and the shape and relative position of the refractive index discontinuities are different. A device for reproducing recorded information from an optical waveguide recording medium serving as a variable of information to be recorded, comprising a light emitting means for generating a laser beam, and a first for dividing the laser beam into two.
and a splitting means for generating a second light beam, a reference light generation means for receiving the first light beam and modulating it by applying a frequency shift to generate a reference light, and guiding the second light beam to the optical coupling section. a light superimposing means for superimposing the reference light on the reflected signal light that is reflected by the refractive index discontinuity portion, modulated in amplitude and phase, and returned via the optical coupling portion to form interference light; and a light detection means for photoelectrically converting light to produce an electrical output, the reference light generation means being
A waveguide optical delay reflection element having an optical waveguide extending along the optical axis of a light beam and a surface acoustic wave electrode disposed near the optical waveguide and generating a surface acoustic wave in the optical propagation direction of the optical waveguide. 1. An optical waveguide recording medium reproducing device, comprising: an optical waveguide recording medium reproducing device, characterized in that the surface acoustic wave electrode is supplied with intermittent high frequency power. 2. The optical waveguide recording according to claim 1, wherein the amplitude and delay time of the reflected signal light are detected as a time-series electric signal by detecting a beat output component from the light detection means. Media playback device. 3. The surface acoustic wave electrodes are a pair of comb-shaped electrodes placed between the optical waveguides, and the surface acoustic wave electrodes are arranged so that surface acoustic wave emission axes of the comb-shaped electrodes intersect on the optical waveguide. Claim 1 or 2 characterized in that
The optical waveguide recording medium reproducing device described above. 4. The surface acoustic wave electrode is a comb-shaped electrode arranged on the optical waveguide, and the surface acoustic wave radiation axis of the comb-shaped electrode is arranged to coincide with the extending direction of the optical waveguide. 3. The optical waveguide recording medium reproducing apparatus according to claim 1, further comprising: an optical waveguide recording medium reproducing apparatus. 5. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the light emitting means includes a superluminescent diode or a broadband wavelength oscillation laser diode. 6. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the dividing means includes a half mirror or a beam splitter. 7. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the irradiation means has an objective lens. 8. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the light superimposing means includes a half mirror or a beam splitter. 9. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the photodetecting means includes a photodetector.