JPH04265533A - Optical waveguide recording medium reproducing device - Google Patents

Abstract

PURPOSE:To reduce the size of the reproducing optical system of an optical waveguide recording medium reproducing device by using an SLD (superluminescent diode) provided with an active area having an outgoing light end face and with a diffraction grid which is arranged on the side facing the outgoing end face of the active area and the intervals of which are gradually increased as a light source. CONSTITUTION:In the optical system reading recorded information out of an optical waveguide recording medium 1 and reproducing it, a diffraction grid 11 whose pitch is demodulated to the other end than a laser emitting end face 10 of an SLD35 of the light source is provided to modulate the frequency of emitting light and to shift the phase between the respective frequency bands. By providing the diffraction grid 11 whose pitch is demodulated to the side other than the light emitting end face 10 of the SLD35, the frequency of the emitting light can be superimposed to allow the delay of a group speed to be caused between the light of the respective oscillated frequencies.

Description

[Detailed description of the invention]

0001

[Technical Field] The present invention relates to an optical storage medium, particularly an optical waveguide storage medium having an optical waveguide provided with a refractive index discontinuity that generates reflected guided light having a plurality of different amplitudes and phase delays by guiding a laser beam. The present invention relates to an optical waveguide storage medium reproducing device that uses a laser beam to guide a laser beam, detects interference between a part of the reflected guided wave light and the laser beam, and reproduces recorded information as a time-series signal waveform.

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 an object of the present invention is to provide an optical waveguide storage medium reproducing apparatus having a miniaturized reproducing optical system.

[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 for receiving one light beam and reflecting it as a reference light; an irradiation means for guiding a second light beam to the optical coupling section; The light emitting means includes a light superimposing means for superimposing the reflected signal light returning through the coupling part and the reference light to form interference light, and a light detection means for photoelectrically converting the interference light to generate an electrical output, and the light emitting means is characterized in that it includes a superluminescent diode having an active region having an emitting light end face, and a diffraction grating disposed on a side of the active region opposite to the emitting light end face, the distance between each of which is gradually increased.

[0008]

According to the present invention, an optical waveguide storage medium reproducing device having a compact reproducing optical system can be obtained.

[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), in the optical waveguide storage medium reproducing apparatus of the present invention, an SLD (Supe
The light emitting element 35 is a superluminescent diode (luminescent diode). Furthermore, the optical waveguide storage medium reproducing device includes a half mirror (beam splitter) 36 as a splitting means that splits the laser beam into two and generates first and second light beams, and a half mirror (beam splitter) 36 that receives the first laser beam and generates a reference light. A fixed mirror 37 as a reference light generating means, and an objective lens 4 as an irradiation means for guiding the second laser beam to the optical coupling section 30.
2, a half mirror 36 as a light superimposing means that superimposes the reflected signal light and reference light returned by the refractive index discontinuity portion 34 to form interference light, and a photodetector that photoelectrically converts the interference light and generates an electrical output. It has a photodetector 39 as a means.

Here, the light emitting element 35 of the SLD, which is generated by frequency modulating the laser beam itself, has an active layer 5 at the bonded portion of the bonded substrates 3 and 4 sandwiched between the electrodes 1 and 2, as shown in FIG. It is a semiconductor laser device with a striped double heterostructure in which is embedded an active region having an emitting light end face 10 and a diffraction grating 11 disposed on the side opposite to this emitting light end face at the rear of the figure. be.

As shown in the partial cross-sectional plan view along the interface of the active layer in FIG. 4(a), the diffraction grating 11
Alternatively, the grooves are arranged in parallel along the extending direction of the active layer 5 in contact with the joint portion of the active layer 5, and the intervals between the grooves gradually increase. As shown in the partial cross-sectional view along the active layer in FIG. Then, the guided light having a wavelength corresponding to the interval between the grooves 11 is Bragg-reflected, giving a shift in frequency and phase, and acting as a reflection region that returns to the output light end face. Therefore, the emitted laser beam becomes light with multiple longitudinal modes. Semiconductor laser elements in which reflective regions are periodically arranged with grooves arranged at equal intervals, overlapping the active region or on both sides of the active region in the extending direction, are classified as distributed feedback (DFB) or distributed reflection type (DBR).
) These are known as lasers, but these obtain single mode light.

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 part 30, and a part of it has a plurality of different amplitudes and phases due to the plurality of refractive index discontinuities 34. The reflected waveguide light becomes the signal light that returns from the optical coupling section 30. As shown in FIG. 1(a), the refractive index discontinuity portion 34 is
, c, d, the shape and relative position of each refractive index discontinuity portion 34 is determined according to the information to be recorded (in the figure, explained as analog information). By arranging a plurality of refractive index discontinuities 34 in the optical waveguide 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 reflected by the fixed mirror 37 as a reference beam and returns to the half mirror 36. These signal lights and reference lights are multiplexed by a half mirror 36, and a lens 44
The light is focused and input into the photodetector 39 as a result of optical homodyne interference. The input light is photoelectrically converted and becomes an electric signal through a frequency filter 40, and as shown in FIGS. Electrical output of signal waveform I(t)
is obtained.

As described above, in this embodiment, in an optical system for reading and reproducing recorded information from an optical waveguide recording medium,
A pitch-modulated diffraction grating is provided on the side other than the laser beam emitting end face of a superluminescent diode (SLD) as a light source, thereby modulating the frequency of the oscillated light and shifting the phase between each frequency band. By providing a pitch-modulated diffraction grating on the side of the SLD that is not the light-emitting end face, the frequencies of the oscillated lights are superimposed, and it is also possible to cause a group velocity delay between the lights of each oscillation frequency.

Specifically, the spectrum of a laser beam from an SLD equipped with a diffraction grating in which each of the above spacings is gradually increased is light in which a phase difference occurs between the spectral bands of multiple longitudinal modes. . That is, for example, Vr and Vr
It has a phase difference tm with respect to light having a frequency of -1. If such a laser beam is used in a reproducing optical system of an optical waveguide storage medium reproducing device, the electric field amplitude E of the light can be described as shown in the following equation 1.

[0017]

[Math 1]

At this time, the electric field of the interference light between the reference light on the photodetector and the return signal light from the optical waveguide coupling part of the optical waveguide storage medium when reading the optical waveguide storage medium is expressed by the following equation 2. to

[0019]

[Math 2]

[0020] I can write. Equation 2 is still an incoherent superposition of wide-range spectra, and the pit train reproduction signal is detected as a pulse train subjected to exponential amplitude modulation. Thus, with the configuration of the optical waveguide recording medium reproducing device, the plurality of refractive index discontinuities (indicated by a, b, c, and d in FIG. 1(a)) recorded on the optical waveguide recording medium can be This corresponds to the electrical output of the sequence signal (in FIG. 1(c), a', b', c', and d' correspond to each other) and is reproduced. Since the light source 35 uses a light source with a phase shift between the wide spectrum bands as described above, the modulation frequency can be set higher than an optical system using a semiconductor laser with a narrow spectrum width.

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 waveguide installed in the focus actuator, a beam splitter 52 for taking out a part of the reflected beam for tracking, and a beam splitter 52 for tracking. a concave lens 53 that separates the laser beam, and a tracking photodetector 54,
It has 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. The photodetectors 54 and 55 capture the tracking laser beam with high sensitivity and high signal-to-noise ratio even in optical homodyne detection. Furthermore, according to the error detection between the two, the condensing 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 three-dimensional optical disk 5
The optical reproducing device head 56 is made to follow the surface runout of 0.

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 reflected laser beam whose amplitude and phase are modulated, and the other laser beam goes back and forth through the fixed mirror 37 and returns. , is multiplexed by a half mirror 36, passes through an iris 58 that allows only the interference light to pass, and is then sent to a photodetector 3.
9 performs optical detection, passes through a frequency filter 40, and obtains an electrical output of a time-series signal waveform shown by I(t) in FIG. 1(c) from an electrical output terminal 57. 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.

In the above embodiment, optical homodyne detection using the fixed mirror 37 was used as a reference light generating means in the reproduction optical system.
If, for example, an acousto-optic modulator that performs optical frequency modulation on the reference light is used instead of 7, optical heterodyne detection can be performed and a similar effect can be obtained. In this embodiment, an example was explained in which the memory part of the optical waveguide storage medium is configured with refractive index discontinuities of different lengths and shorts, and an analog signal is stored and reproduced. It is clear that by recording the presence or absence of those refractive index discontinuities, it is possible to store and reproduce digital signals. In addition, although an example in which an optical waveguide storage medium is formed into a three-dimensional disk has been described,
It is also possible to arrange them on tape or in a card form and stack them. Furthermore, in this example, the optical waveguide length is 10 m.
Although the length of the optical waveguide, which is the storage medium, can be made longer or shorter depending on the required memory capacity.

[0025]

[Effects of the Invention] As explained above, according to the present invention,
As a light source in the reproduction optical system, a superluminescent diode having an active region having an emitting light end face and a diffraction grating arranged on a side of the active region opposite to the emitting light end face and whose spacing between each grating gradually increases is used. Therefore, the reproducing optical system of the optical waveguide storage medium reproducing device can be miniaturized.

[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 superluminescent diode according to the invention.

FIG. 4 is a diagram illustrating a diffraction grating along the active layer of the superluminescent diode 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.

[Explanation of symbols]

1, 2... Electrodes 3, 4... Bonding substrate 5... Active layer 10... Outgoing light end face 11... Diffraction grating 30... Coupling portion 31 of optical waveguide... Core 32 of optical waveguide... Clad (substrate) 34...Refractive index discontinuity portion 35...Light emitting element 36...Half mirror 37...Fixed mirror 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... Electrical output terminal 58... Iris

Claims (6)

[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 reflecting it as a reference light, an irradiation means for guiding the second light beam to the optical coupling part, and the refractive index inverter. a light superimposing means for superimposing the reference light on the reflected signal light that is reflected by the continuous section, modulated in amplitude and phase, and returned via the optical coupling section to form interference light; and a light superimposition means for photoelectrically converting the interference light to produce an electrical output. the light emitting means has an active region having an emitting light end face, and a diffraction grating disposed on a side of the active region opposite to the emitting light end face, the distance between each of which gradually increases. An optical waveguide recording medium reproducing device comprising a superluminescent diode. 2. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the reference light generating means has a fixed mirror. 3. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the dividing means includes a half mirror or a beam splitter. 4. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the irradiation means has an objective lens. 5. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the light superimposing means includes a half mirror or a beam splitter. 6. The optical waveguide recording medium reproducing apparatus according to claim 1, wherein the photodetecting means includes a photodetector.