JP2008262122A - Shift register type optical memory apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a shift register function with a simple configuration in an optical buffer memory which temporarily stores optical signal, without converting the signal into an electrical signal. <P>SOLUTION: A laser array arranged a plurality of bistable semiconductor lasers in a matrix form of m x m is used. The output light of the bistable semiconductor lasers excluding the bistable semiconductor laser of the last row forms an optical path, in such a manner that the output light is inputted perpendicular to the bistable semiconductor laser of the row adjacent to one. As a result, the information recorded in the bistable semiconductor lasers can be sent successively to the adjacent rows. An optical isolator is arranged within the optical path, in order to prevent the light from returning in the backward direction. Furthermore, the timing to transfer the information of light to the adjacent row is controlled by a space optical modulator arranged within the optical path. A system comprising combining a mirror array and half mirror can be utilized adequately as the optical system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical buffer memory that temporarily stores an optical signal without converting it into an electrical signal. Specifically, the present invention relates to an optical buffer memory using a bistable semiconductor laser having a shift register function.

In next-generation optical fiber communication, a buffer memory capable of temporarily storing an optical signal without converting it into an electrical signal is required. For example, in the future, it is expected that a photonic packet network that performs route control of IP (Internet Protocol) packets with optical signals will be realized, but in order to avoid collision of output ports in a photonic IP router Needs to temporarily hold the optical IP packet. That is, an optical buffer memory is required in the photonic IP router.
As a method for temporarily storing an optical signal without converting it into an electrical signal, an optical buffer memory using a fiber delay line is conventionally known. However, there is a problem that fine timing control of reading is difficult.

  Accordingly, in order to solve this problem, an optical buffer memory using a bistable semiconductor laser has been developed and disclosed (see, for example, Non-Patent Document 1). However, this has a problem that the optical input / output unit becomes complicated as the number of bits increases. Accordingly, an optical buffer memory having a shift register configuration has been developed as a technique for solving this problem. For example, Non-Patent Document 2 discloses a configuration using an individual bistable semiconductor laser, an optical isolator, an optical gate, and a polarizer as an optical buffer memory with a shift register function using a bistable semiconductor laser.

JP 2003-337355 A ([0049]-[0056], FIG. 6, FIG. 7) Mori, Sato, Kawaguchi, “2-bit optical buffer memory using a polarization bistable surface-emitting semiconductor laser”, Society Conference of IEICE, C-3-28, p.150, 2006. H. Kawaguchi, T. Mori, Y. Sato and Y. Yamayoshi, "Optical buffer memory using polarization-bistable vertical-cavity surface-emitting lasers", Japanese Journal of Applied Physics, vol. 45, no. 34, p. L894 , 2006.

  However, in the optical buffer memory with a shift register function, when the bistable semiconductor laser, the optical gate, etc. are composed of individual elements as described above, a large number of elements are required to record multi-bit data, There was a problem of a large-scale configuration.

  Therefore, a configuration has been devised in which a large number of polarization bistable surface emitting semiconductor lasers are integrated in a two-dimensional array, and light is input and output spatially in parallel. Patent Document 1 shows an example of an optical buffer memory with a shift register function using a laser array in which such bistable semiconductor lasers are integrated on a two-dimensional plane.

  However, in an optical buffer memory using a conventional two-dimensional laser array as disclosed in Patent Document 1, in order to prevent the propagation of light in the reverse direction when transferring the output light of a laser to another laser It is necessary to make light incident obliquely, and a decrease in light input efficiency has been a problem. On the other hand, in order to increase the light input efficiency, it is desirable to make vertical light incident, but in order to prevent the propagation of light in the reverse direction, it is necessary to use an optical isolator. However, it has been structurally difficult to insert an optical isolator because bidirectional light is interlaced. Furthermore, there has been a problem that the geometric shape is limited in order to collect light with a reflector.

The shift register type optical memory device according to the present invention, which has been made to solve the above problems,
In an optical memory device that records an optical signal input as a time series signal bit by bit in each bistable semiconductor laser and reads the recorded optical signal as a time series signal at a predetermined timing.
a) a laser array in which a plurality of bistable semiconductor lasers are arranged in an m × n matrix;
b) a shift register optical system that forms an optical path so that the output light of the bistable semiconductor laser excluding the bistable semiconductor laser in the last column is vertically input to the bistable semiconductor laser in the adjacent column in the laser array;
c) an optical isolator arranged so that only forward output light passes on the optical path formed by the shift register optical system;
d) a spatial light modulator disposed on an optical path formed by the shift register optical system;
It is characterized by having.

In the shift register type optical memory device of the present invention, the shift register optical system is
A mirror array comprising at least n-1 mutually parallel mirror elements, each mirror element corresponding to output light from each row of bistable semiconductor lasers except the last row of bistable semiconductor lasers in said laser array;
A plurality of plane mirrors;
Half mirror,
It is preferable to comprise.

According to the shift register type optical memory device of the present invention, the following excellent effects can be obtained.
By using a laser array in which bistable semiconductor lasers are integrated in a two-dimensional array, multi-bit data can be recorded / reproduced with a simple configuration.
The shift register optical system realizes a configuration in which the output light of the bistable semiconductor laser is sequentially input to the bistable semiconductor lasers in adjacent columns. Thus, the shift register function can be provided to the optical memory device with a simple configuration.
Since the optical path is formed so that the input light is vertically input to the bistable semiconductor laser, high light input efficiency can be obtained. In addition, this makes it possible to reduce the interval between the bistable semiconductor lasers, thereby enabling further integration of the bistable semiconductor lasers.
-By disposing an optical isolator on the optical path, it is possible to avoid the problem that the output light of the adjacent bistable semiconductor laser propagates in the opposite direction when light enters the adjacent bistable semiconductor laser. .
-It is not necessary to provide an optical isolator or a spatial light modulator separately, and the overall configuration is simple, so that the cost can be reduced. Low operating power.

  Embodiments of a shift register type optical memory device according to the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a shift register type optical memory device 1 according to the present invention. The shift register type optical memory device 1 includes an input light conversion unit 2, a first lens array 3, a second lens array 4, a third lens array 9, and a plurality of bistable semiconductor lasers arranged in an m × n matrix. Laser array 5, optical isolator 6, spatial light modulator 7, polarizer 8, optical modulator array 10, output light converter 11, mirror array 20, first plane mirror 21, second plane mirror 22, half mirror 23 is included.

In the laser array 5, a plurality of bistable semiconductor lasers are arranged in an m × n matrix. In FIG. 1, it is assumed that a total of 16 bistable lasers are arranged in a 4 × 4 matrix with rows in the left-right direction and columns in the depth direction. In the following, the leftmost column in FIG. 1 is referred to as the first column, then the second column, and so on. Also, the foremost line is called the first line, then the second line, and so on. In this specification, “bistable laser” is abbreviated as “laser” as appropriate.
As is conventionally known (see, for example, Non-Patent Document 2), a bistable semiconductor laser retains laser polarization when there is no external light input, and laser oscillation occurs when light is input from the outside. It has a characteristic that the polarization is switched. Therefore, it can be used as an optical memory that handles binary information using 0 ° polarized light and 90 ° polarized light.

  In the example shown in FIG. 1, the shift register optical system is configured by the mirror array 20, the first plane mirror 21, the second plane mirror 22, and the half mirror 23. By the shift register optical system, the output light of the bistable semiconductor laser excluding the bistable semiconductor laser in the last column in the laser array 5 is vertically input to the bistable semiconductor laser in one column adjacent to the laser array 5. An optical path is formed. Basically, the mirror array 20, the first plane mirror 21, the second plane mirror 22, and the half mirror 23 all rotate the light traveling direction by 90 °. The half mirror 23 partially transmits light and partially reflects light.

  The mirror array 20 includes n-1 (4-1 = 3 in the example of FIG. 1) parallel mirror elements (first mirror element 20-1, second mirror element 20-2, third mirror element 20). -3), each mirror element receives the output light from the bistable semiconductor laser in each column of the laser array 5 and reflects it. That is, the first mirror element 20-1 reflects only output light from the bistable semiconductor laser constituting the first row, and the second mirror element 20-2 only outputs light from the bistable semiconductor laser in the second row. The third mirror element 20-3 reflects the output light from the bistable semiconductor laser in the third row. In addition, the mirror array 20 reflects light from the lower direction in FIG. 1 to the left, but the second mirror element 20-2 is arranged above the first mirror element 20-1, The third mirror element 20-3 is disposed above the second mirror element 20-2. Due to the arrangement of the mirror elements, output light from lasers in a certain row is sequentially input perpendicularly to lasers in adjacent rows.

  The shift register type optical memory device 1 receives three types of optical signals, that is, input signal light, set light, and reset light. The input signal light is an optical signal modulated with digital data. The set light is an optical pulse indicating a bit to be recorded in the input signal light, and the reset light is an optical pulse for resetting the polarization of the laser. The input signal light and the set light are 90 ° polarized and the reset light is 0 ° polarized and input to the input light conversion unit.

An example of the configuration of the input light conversion unit 2 is shown in FIG. The input light conversion unit 2 is a device for spatially separating an optical signal input as a time series signal with a time delay by one bit. Here, for simplicity, only 4-bit signals (injection lights a to d) are considered. The input signal light is first divided into two by the optical demultiplexer a, and one is input to the optical delay device a having a time delay of 2 bits. Each light is further divided into two by an optical demultiplexer b and an optical demultiplexer c, one of which is input to an optical delay b and an optical delay c having a time delay of 1 bit. Accordingly, the input signal light is branched into four, and the injected light c, the injected light b, and the injected light a have a time delay of 1 bit, 2 bits, and 3 bits, respectively, with respect to the injected light d. On the other hand, the set light and the reset light are multiplexed by the optical multiplexer e, and then branched into four by the optical demultiplexer d, the optical demultiplexer e, and the optical demultiplexer f, respectively. It is combined with the input signal light by an optical multiplexer b, an optical multiplexer c, and an optical multiplexer d.
The input light conversion unit 2 shown in FIG. 2 is entirely composed of a planar light circuit (PLC), but is not limited to this. As shown in FIG. It is also possible to configure an optical delay device using an optical fiber delay line. It is also possible to use PLC and optical fiber together.

  The injection light a, injection light b, injection light c, and injection light d output from the input light conversion unit 2 are converted into parallel light by the first lens array 3. Next, the mirror array 20 passes through a part without the mirror or avoids the mirror array, is reflected by the first flat mirror 21, the flat mirror 22, and the half mirror 23, and is condensed by the second lens array 4 and is collected by the laser array 5. Are input to the first row of lasers. Injection light a, injection light b, injection light c, and injection light d are respectively input to the first, second, third, and fourth rows of lasers in the first column of the laser array.

A method for shifting data (0 ° polarized light or 90 ° polarized light) recorded in each column of the laser array to the next column will be described.
The output light of the laser in the first column of the laser array is converted into parallel light by the second lens array 4, passes through the half mirror 23, passes through the optical isolator 6 from the bottom to the top, and is input to the spatial light modulator 7. The optical isolator 6 is an element that passes light in one direction and does not pass light in the reverse direction. In this case, it is arranged so that light passes from the bottom to the top (forward direction) in FIG. In this specification, the direction in which light should travel is called the forward direction.
The spatial light modulator 7 is an element capable of controlling on / off (transmission / blocking) of light only in a part of the plane. For example, it is possible to control such that only the output light from the laser in the first column in the laser array 5 is transmitted and the output light from other columns is not transmitted but blocked. As the spatial light modulator 7, a liquid crystal display or a magneto-optical effect can be used.
When the spatial light modulator 7 corresponding to the first column of the laser array 5 is turned on, the output light of the first column laser passes through the spatial light modulator 7 and is reflected by the mirror of the mirror array 20. The light is reflected by the one plane mirror 21, the second plane mirror 22, and the half mirror 23 so as to rotate by 90 °, collected by the second lens array 4, and overwritten on the second row of lasers in the laser array 5. Similarly, the output light of the second row laser is input to the third row laser, and the output light of the third row laser is input to the fourth row laser. Here, for example, the output light of the laser in the third row is reflected to the left by the half mirror 23 and the light propagating in the direction opposite to the arrow in FIG. 1 is input to the optical isolator 6 from above, so that the optical isolator 6 does not pass through and is not input to the laser in the second row.

A method for outputting data recorded in the last column (fourth column in this embodiment) will be described.
The output light of the laser in the fourth row is converted into parallel light by the second lens array 4 and passes through the half mirror 23, the optical isolator 6, and the spatial light modulator 7 (passing through the optical isolator 6 and the spatial light modulator 7). In other words, the light beam passes through a part of the mirror array 20 that does not have a mirror or avoids the mirror array 20 and is input to the polarizer 8. The polarizer 8 is an element that passes only a polarized light component in a specific direction, and is here arranged to pass 90 ° polarized light and not 0 ° polarized light. As a result, only when the oscillation polarization of the laser in the fourth row is 90 °, the light passes through the polarizer 8 and is collected by the third lens array 9 and input to the optical modulator array 10.

The configuration of the optical modulator array 10 and the output light conversion unit 11 is shown in FIG. The laser output light of the first row, second row, third row, and fourth row of the fourth column of the laser array is laser output light a, laser output light b, laser output light c, and laser output light d, respectively. . Each laser output light is input to an optical modulator a, an optical modulator b, an optical modulator c, and an optical modulator d, and is intensity-modulated. As the optical modulator, a Mach-Zehnder optical modulator using a lithium niobate (LiNbO ₃ ) crystal, an electroabsorption optical modulator using a semiconductor, or the like can be preferably used. The output light from the optical modulator array 10 is input to the output light conversion unit 11. The optical modulator output light b and the optical modulator output light d are respectively input to an optical delay device a and an optical delay device b having a time delay of 1 bit, and are optically modulated by the optical multiplexer a and the optical multiplexer b. Output light a and optical modulator output light c. The latter is input to an optical delay c having a time delay of 2 bits, and the former and the latter are combined by an optical combiner c and output signal light. Is output as As a result, output signal light in which pulses are arranged in time series in the order of the optical modulator output light a, the optical modulator output light b, the optical modulator output light c, and the optical modulator output light d is obtained. In FIG. 4, four optical modulators and an output light conversion unit are integrated in the PLC. However, the present invention is not limited to this, and optical multiplexing by individual optical modulators and optical fiber couplers as shown in FIG. It is also possible to configure with an optical delay device using an optical fiber delay line, and it is also possible to use a PLC and an optical fiber in combination.

  In the above embodiment, the case where a laser array of 4 rows and 4 columns is used is described, but the present invention is not limited to this, and a laser array of any number of rows and columns can be used. The number of rows and columns need not necessarily be equal. Specifically, when an m × n-bit optical buffer memory is configured using a laser array of m rows and n columns, the input light conversion unit 2 is divided into m, the number of lenses of the first lens array 3 is m, The number of lenses of the two-lens array 4 is m × n, the number of divisions of the spatial light modulator 7 is n, the number of mirrors of the mirror array is n−1, the number of lenses of the third lens array 9 is m, the light modulator array 10 The number of optical modulators may be m, and the output light conversion unit may be m multiplexed.

  In general, a spatial light modulator is difficult to perform high-speed modulation. For this reason, in this embodiment, an optical modulator array 10 which is a high-speed optical modulator is prepared separately from the spatial light modulator 7, and the output light of the fourth column laser is modulated. Thereby, it is possible to output a modulation signal that is faster than the internal optical transfer. If the modulation speed of the output signal light may be equal to or lower than that of the spatial light modulator 7, the light modulator array 10 can be omitted and the output light can be modulated in the fourth column of the spatial light modulator 7. is there.

  The output signal light is required to have as much optical power as possible, and since there is optical loss in the optical modulator array 10 and the output light conversion unit 11, high laser output light power is required. On the other hand, in order to reduce the power consumption, it is necessary to reduce the power consumption of the laser by operating the laser with as little optical power as possible. Therefore, by setting the optical power of the laser that outputs light to the outside (in this embodiment, the fourth row laser) to be large, and setting the other lasers to a small optical power that is necessary for internal optical transfer. It is possible to achieve both high output signal light power and low power consumption operation.

In general, a semiconductor laser can operate at a higher speed when the optical power is increased. Therefore, in order to record a high-speed input signal, it is necessary to increase the optical power of the laser. On the other hand, in order to reduce the power consumption, it is necessary to reduce the power consumption of the laser by operating the laser with as little optical power as possible. Therefore, since the optical power of the laser in the first column for recording the input signal is set large, and the internal optical transfer can be performed at a low speed of 1 / m of the input signal, other lasers are set to a small optical power. High-speed input signal recording and low power consumption operation can be achieved at the same time. It is also possible to set the laser that records the input signal and the laser that outputs light to the outside with a large optical power, and the other lasers with a small optical power.
In order to increase the optical power, the laser injection current may be increased.

  In the shift register type optical memory device according to the present invention, since the injection light having the same wavelength is input to the laser in the first column, it is necessary to match the wavelength of each laser constituting the first column with the wavelength of the injection light. Since the output light of the first row laser is input to the second row laser and is repeated until the last row in the same manner, it is necessary to match the wavelengths of all lasers with the wavelengths of the injection light. However, it is difficult to produce a completely uniform laser array, and in an actual laser array, a slight shift occurs in the wavelength of each laser. Therefore, it is preferable to adjust the wavelength by using the fact that the wavelength of the semiconductor laser varies depending on the temperature and arranging a heater in the vicinity of each laser and adjusting the temperature of each laser as shown in FIG. When the wavelength shift of the laser in the vicinity of the laser array is small and the wavelength is gradually changed, the number of heaters is smaller than the number of lasers as shown in FIG. About one). As the heater, it is also possible to use a semiconductor pn junction diode in addition to the resistor.

Next, the operation of the optical buffer memory with a shift register function will be described with reference to the timing chart of FIG. The input signal light is an optical signal modulated with 16-bit data from b ₀ to b ₁₅ . The input signal light is converted into a signal having a different timing by 1 bit like the delayed input signal lights a, b, c, and d by the optical delay unit of the input light conversion unit, and combined with the set light and the reset light and injected. Like light a, b, c, d. Injected light a has the same timing as b _{0 of the} input signal light and the set light. Similarly, injected lights b, c, and d have the same timings of b ₁ , b ₂ , b _{3 of the} input signal light and the set light, respectively. Match. The input optical power to the laser is such that each of the input signal light and the set light is lower than the polarization switching threshold of the laser, and higher than the laser polarization switching threshold when the input signal light and the set light are combined. Set to. When the injection lights a, b, c, and d are input to the lasers in the first, second, third, and fourth rows of the laser array, first, the oscillation polarization of all the lasers in the first column is reduced to 0 by the first reset light. The oscillation polarization of the laser is switched to 90 ° only when the input signal light and the set light are input to the laser at the same time. As a result, b ₀ , b ₁ , b ₂ , and b ₃ of the input signal light are recorded as the oscillation polarization states of the lasers in the _first , _second , _third , and fourth rows, respectively. That is, when b ₀ is “1”, the laser in the first column and the first row is 90 ° polarized, and when b ₀ is “0”, it is 0 ° polarized.

When there is no injection light, these oscillation polarizations are maintained, so that the laser output in the first column continues to oscillate with polarization corresponding to b _0-3 . When the first column of the spatial light modulator 7 is turned on, the output light of the first column laser is input to the second column laser, and the oscillation polarization state of the first column laser is transferred to the second column laser. The As a result, the laser output in the second column becomes oscillation polarization corresponding to b _0-3 . After the transfer, the next data b _4-7 is recorded on the laser in the first column. Similarly, when the second column of the spatial light modulator 7 is turned on, the laser output of the third column becomes oscillation polarization corresponding to b _0-3 , and when the third column of the spatial light modulator 7 is turned on, The laser output in the fourth column is oscillation polarization corresponding to b _0-3 . When the 90 ° polarization component of the laser output in the fourth row is extracted by the polarizer 8 and is pulsed by the optical modulator, the light modulator output light corresponding to b _0-3 is obtained. Then, the optical delay unit of the output light conversion unit converts each bit into a signal having a different timing, such as the delayed light modulator output lights a, b, c, and d, and is combined to be the same bit pattern b ₀ as the input signal light. , B ₁ , b ₂ , b ₃ output signal light. B ₁₅ from b ₄ is recorded / reproduced in the same manner.

In the above description, the case where the number of bits that can be recorded in the optical buffer memory is 16 bits and the number of bits of the input signal light is 16 bits has been described. If the number of bits of the input signal light is larger than the number of bits that can be recorded in the optical buffer memory, it can be recorded in the optical buffer memory on the principle that recording is performed when the set light and the input signal light are simultaneously input to the laser. It also has a function to extract and record only the number of bits. Therefore, it is not necessary to cut out only the number of bits that can be recorded by an optical switch or the like. Conversely, when the number of bits of the input signal light is smaller than the number of bits that can be recorded in the optical buffer memory, there is no problem because “0” is automatically recorded and reproduced for the remaining bits.
In the above embodiment, data “1” is assigned to 90 ° polarization and data “0” is assigned to 0 ° polarization. However, the present invention is not limited to this. Conversely, data “1” is assigned to 0 ° polarization. It goes without saying that even if assigned, it can operate as an optical buffer memory.

[Write method after erasure]
Two methods are conceivable as a method for realizing a shift register function for transferring data recorded in a bistable semiconductor laser to another bistable semiconductor laser. One is the above-described overwrite method, and the other is the post-erase write method.
The post-erase write type shift register type optical memory device further includes a reset light input unit for inputting reset light to a bistable semiconductor laser other than the first column of the laser array, and light formed by the shift register optical system. A polarizer is provided on the road.
Preferably, the mirror element of the mirror array in the above-described overwrite method is a half mirror, and further includes a reset light input unit that inputs reset light to a bistable semiconductor laser other than the first column of the laser array, and the reset light input unit It is preferable that the optical path of the reset light output from the laser beam is superimposed on the optical path formed by the shift register optical system by passing through each mirror element that is a half mirror.

Hereinafter, an example of the shift register type optical memory device of the post-erase writing method will be described.
FIG. 8 is an overall configuration diagram of another configuration (write after erase method) of the shift register type optical memory device 1 according to the present invention. The first reset light input to the input light conversion unit 2 is the same as the overwrite light of the overwrite method. The first spatial light modulator 31 has a function similar to that of the overwrite-type spatial light modulator 7, but may be modulated only with respect to 90-degree polarized light. The optical isolator 6 has a function similar to that of the overwrite type optical isolator, but may be configured to prevent propagation in the reverse direction only for 90 ° polarized light. Input signal light, set light, input light conversion unit 2, first lens array 3, first plane mirror 21, second plane mirror 22, half mirror 23, second lens array 4, laser array 5, third lens array 9 The optical modulator array 10, the output light conversion unit 11, and the output signal light are the same as those of the overwrite type shift register type optical memory device shown in FIG.
Further, the input signal light, the set light, and the first reset light are input to the input light conversion unit 2, and the injection light a, injection light b, injection light c, and injection light d output from the input light conversion unit 2 are laser arrays. The process up to the point where the laser beam is input to the first column of No. 5 is the same as the overwriting method described above.

  In FIG. 8, the injection light a, the injection light b, the injection light c, and the injection light d pass through the second spatial light modulator 32, but the injection light a and the injection light b of the second spatial light modulator 32. The portions corresponding to the injection light c and the injection light d are always in a transmissive state. The second reset light is 0 ° polarized continuous light. The second reset light emitted from the end face of the optical fiber spreads at a certain angle and is collimated by the lens 33. In FIG. 8, the propagation of the second reset light is depicted by lines corresponding to the second reset light demultiplexing unit 43 for each laser of the laser array 5, but actually the light propagates continuously and propagates. As shown in FIG. 11A, the second spatial light modulator 32 is an element capable of controlling transmission / reception of light for each portion corresponding to a column of the laser array, and is only for 0-polarized light. It may be modulated. A portion corresponding to the first row (injected light a to d) of the second spatial light modulator 32 is provided with a modulator similar to that of the second row or the like, and is always in a transmission state, or is transparent without providing a modulator. This is an area. Alternatively, the second spatial light modulator 32 can be arranged so that the injected light propagates avoiding the second spatial light modulator 32. Thereby, the injection light d is input from the injection light a to the first column of the laser.

  The half mirror array 30 is composed of a half mirror element 30-1, a second half mirror element 30-2, and a third half mirror element 30-3, which are a plurality of half mirrors parallel to each other, and the arrangement of the half mirror array 30 is of the overwriting method described above. Similar to the mirror array 20. The second reset light transmitted through the second spatial light modulator 32 is transmitted through the half mirror element of the half mirror array 30, reflected by the first plane mirror 21 and the second plane mirror 22, and then reflected by the half mirror 23. Then, the light is condensed by the second lens array 4 and inputted to lasers other than the first row of the laser array 5.

  The laser output light of the laser array 5 becomes parallel light in the lens array 4, passes through the half mirror 23, and is input to the polarizer 8. The polarizer 8 is an element that transmits 90 ° polarized light and blocks 0 ° polarized light. Therefore, when the oscillation polarization of the laser is 90 °, the laser output light passes through the polarizer 8, passes through the optical isolator 6 from the bottom to the top, and the first spatial light modulator 31 applies each column of the laser array 5. Transmission / blocking is controlled. When the oscillation polarization of the laser is 0 °, the light is blocked by the polarizer 8 and is not input to the optical isolator or the first spatial light modulator 31. Therefore, the optical isolator 6 and the first spatial light modulator 31 are polarized by 90 °. The configuration of the optical isolator 6 and the first spatial light modulator 31 is simplified as compared with the overwriting method that needs to function only for light of 0 ° and 90 ° polarized light. can do. As described above, the optical isolator and the spatial light modulator need only act on the polarized light passing through the polarizer 8.

  The light that has passed through the first spatial light modulator 31 is reflected by the half mirror elements of the half mirror array 30, reflected by the first plane mirror 21 and the second plane mirror 22, and then reflected by the half mirror 23. The light is condensed by the lens array 4 and input to the bistable semiconductor laser in the right column adjacent to the laser array 5. The structure in which the laser output light is input to one of the adjacent lasers is the same as in the overwriting method. The light propagating in the direction opposite to the arrow in FIG. 8 does not pass through the optical isolator 6 in the case of 90 ° polarization, and does not pass through the polarizer 8 in the case of 0 ° polarization. Is never entered. The output light of the laser in the fourth row, which is the last row, becomes parallel light by the second lens array 4, passes through the half mirror 23, the polarizer 8, the optical isolator 6, and the first spatial light modulator 31, and then the half mirror array 30. Then, the light passes through a portion having no half mirror element or avoids the half mirror array 30 and is collected by the third lens array 9 and input to the light modulator array 10. As a result, only when the oscillation polarization of the laser in the fourth column is 90 °, it passes through the polarizer 8 and is input to the optical modulator array 10.

  In the post-erase write shift register type optical memory device, as in the case of the overwrite type shift register type optical memory device, the input optical conversion unit 2 can be composed of PLC, optical fiber, or a combination of both, The device array 10 and the output light conversion unit 11 can be configured by PLC, optical fiber, or a combination of both. In this embodiment, the case where the laser array 5 of 4 rows and 4 columns is used has been described. However, the present invention is not limited to this, and it is of course possible to use a laser array having an arbitrary number of rows and columns. .

In the post-erase write type shift register type optical memory device, the optical modulator array 10, which is a high-speed optical modulator, is provided separately from the first spatial light modulator 31, so that it is faster than internal optical transfer. A modulated signal is output. If the modulation speed of the output signal light may be equal to or lower than the speed of the first spatial light modulator 31, the light modulator array 10 is omitted and the output light is modulated by the fourth column of the first spatial light modulator 31. It is also possible.
Further, in the shift register type optical memory device of the post-erase write method, similarly to the above-described shift register type optical memory device of the overwrite method, the optical power of the first column laser for recording the input signal is set large. Other lasers may be set to a small optical power. Of course, it is possible to set the lasers in the row for recording the input signal and the lasers in the row to output light to the outside with high optical power, and the other lasers with low optical power.
Furthermore, similarly to the overwriting method, a heater can be provided in the laser array 5 as shown in FIG.

  Even when the number of bits of the input signal light is larger or smaller than the number of bits that can be recorded in the optical buffer memory, there is no problem as in the overwriting method. In the above embodiment, “1” of data is assigned to 90 ° polarization and “0” of data is assigned to 0 ° polarization. However, the present invention is not limited to this. Conversely, “1” of data is assigned to 0 ° polarization. And the first reset light and the second reset light can be operated as an optical buffer memory in the same manner even when the 90 ° polarization is used.

In the above description, as a method of distributing the second reset light to each laser, a method of making the light emitted from the optical fiber and spread as shown in FIG. There is also a method of branching according to the number of (n × m). 9A and 9B are configuration examples of a reset light demultiplexing unit provided for branching one light into 4 rows and 4 columns. FIG. 9A is a top view and FIG. 9B is a side view. The reset light demultiplexing unit is provided in the shift register type optical memory device in place of the second spatial light modulator 32 and the lens 33, and includes a first reset light demultiplexing unit 41 and a reset light demultiplexing lens array 42. And a second reset light demultiplexing unit 43.
The first reset optical demultiplexing unit 41 includes three optical demultiplexers, ie, optical demultiplexers 41-a, 41-b, and 41-c, and receives four second reset lights (reset light). (rs-a, reset light rs-b, reset light rs-c, reset light rs-d).
The reset light demultiplexing lens array 42 is provided in a subsequent stage (light traveling direction) of the first reset light demultiplexing unit 41, and converts the light demultiplexed by the first reset light demultiplexing unit 41 into parallel light. .

As shown in FIG. 9 (b), the second reset light demultiplexing unit 43 is provided further downstream of the reset light demultiplexing lens array 42, and includes three half mirrors HM1, HM2, HM3, and three mirrors M1, M2. , M3. As shown in FIG. 9 (a), these mirrors and half mirrors are all of a length that can reflect all the light demultiplexed by the first reset light demultiplexing unit 41 (in FIG. 9 (a)). The length of the reset light is set to be 45 ° with respect to the traveling direction of the input reset light.
The half mirror HM1 is provided in the traveling direction of the second reset light input from the reset light demultiplexing lens array 42. Here, the reset light rs-a, which is one of the second reset lights demultiplexed into four by the first reset light demultiplexing unit 41, is considered as an example with reference to FIG. 9B.

A half mirror HM2 is provided behind the half mirror HM1. Half of the input reset light rs-a is transmitted through the half mirror HM1 to become reset light rs-a1 and travels backward (to the left in FIG. 9B), and half is reflected to reset light. It becomes rs-a2 and proceeds downward.
Next, half of the reset light rs-a1 is transmitted through the half mirror HM2 and travels backward as reset light rs-a3, and half is reflected and travels downward as reset light rs-a4.
A mirror M2 is provided below the half mirror HM2, and the reset light rs-a4 reflected without passing through the half mirror HM2 is reflected by the mirror M2, and the lower part of the reset light rs-a3 is reflected in the subsequent stage. Proceed toward.
Further, a mirror M1 is provided below the half mirror HM1, and the reset light rs-a2 reflected without passing through the half mirror HM1 travels backward by the mirror M1, and behind the mirror M1. It reaches the half mirror HM3 provided. Half of the reset light rs-a2 is transmitted through the half mirror HM3 to become the reset light rs-a5 and proceeds to the subsequent stage. The light reflected without passing through the half mirror HM3 proceeds downward as reset light rs-a6, but is reflected leftward by the mirror M3 provided below the half mirror HM3 and proceeds to the subsequent stage.
Input the reset by making the interval between the half mirror HM2 and the mirror M2, the interval between the half mirror HM3 and the mirror M3 equal, and making the interval between the half mirror HM1 and the mirror M1 twice the interval between the half mirror MH2 and the mirror M2. The reset light rs-a3, rs-a4, rs-a5, and rs-a6, which are light beams obtained by demultiplexing the light rs-a by 1/4, are also sent to the subsequent stage at equal intervals.
In this way, one light is demultiplexed into 4 × 4 = 16 by the reset demultiplexing unit.

  The operation of the post-erase write method will be described with reference to the timing chart shown in FIG. The process from the input signal light to the laser output in the first column is the same as that in the above-described overwrite method (FIG. 7). When data is transferred from the first column to the second column, first, the second column of the second spatial light modulator 32 is turned on, and 0 ° -polarized reset light is applied as shown in “Reset light of the second column”. Input to the second row laser and reset the second row laser output to 0 ° polarization. Thereafter, the first row of the first spatial light modulator 31 is turned on, and 90 ° polarized light is emitted only when the first row laser is 90 ° polarized as shown in “Output of first row spatial light modulator”. Input to the second row of lasers. Thus, only when each laser in the first row is 90 ° polarized, the oscillation polarization of each laser in the second row is switched to 90 °. As a result, the oscillation polarization state of the first row laser is transferred to the second row laser. After the transfer, the next data is recorded in the first column. Similarly, the second column data is transferred to the third column, and the third column data is transferred to the fourth column. When the 90 ° polarization component of the laser output in the fourth column is extracted by the polarizer 8, pulsed by the optical modulator array 10, added with a delay by the output light conversion unit 11, and combined, as in the overwrite method. The recorded data is played back.

[How to record data continuously]
FIG. 10 (a) shows an example of division corresponding to a laser array column of a spatial modulator (an example showing an independently operable portion). The above-described shift register type optical memory device and post-erase write method The present invention can be applied to both shift register type optical memory devices. However, in this configuration, the first row of data is recorded in the first row of lasers, and the transfer of the next new row of data can be recorded in the first row only after the transfer is performed. There is a time during which recording cannot be performed between recording one column of data and the next column of data. In order to solve this problem and continuously record data, in the spatial light modulator, a portion (one row) corresponding to the output light of each column of the bistable semiconductor laser on the laser array is divided into a plurality of locations (blocks). ). As a result, before the recording of all the data for one column is completed, the data for the already recorded blocks can be transferred to prepare for the recording of the next data. FIG. 10B shows an example in which one row is divided into two blocks, the first half and the second half. In this case, data is transferred to the fourth column in the order of the first half and the second half. In addition, only the first column may be divided and the second and subsequent columns may not be divided as shown in FIG.

First, a method of continuously recording data in an overwrite type shift register type optical memory device having the overall configuration as shown in FIG. 1 will be described with reference to the timing chart of FIG. The spatial light modulator 7 is divided into four columns as in the example shown in FIG. 10C, and the first column is further divided into two.
The input signal light is an optical signal modulated with 16-bit data from b ₀ to b ₁₅ that are temporally continuous. By changing the input light conversion unit as shown in the example shown in FIG. 12, for example, the timing of the set light and the reset light in the first half (injection light a and injection light b) and the second half (injection light c and injection light d) is changed. Different by 2 bits. With respect to the input signal light, the injection light a and the injection light c are delayed by 1 bit, the injection light b and the injection light d are not delayed, and the timings indicated by the delayed input signal lights a, b, c, and d are reached. Thus, the injection lights a, b, c, and d match the timings of the set light with b ₀ , b ₁ , b ₂ , and b _{3 of the} input signal light, respectively, and the injection lights c and d are from the injection lights a and b. However, the timing of the set light and the reset light is delayed by 2 bits. When the injection lights a, b, c, and d are respectively input to the lasers in the first, second, third, and fourth rows of the laser array, b ₀ and b ₁ are recorded in the first half of the first column, and 2 bits B ₂ and b ₃ are recorded in the _second half of the first row with a delay of minutes. When the first half of the first row of the spatial light modulator is turned on, the output light of the first half laser of the first row is input to the first half laser of the second row, and the oscillation polarization state of the first half laser of the first row is 2 The first half laser of the second row is transferred to the laser, and the first half laser output of the second row becomes the oscillation polarization corresponding to b _0-1 . Thereafter, the first half of the first column is reset, and the next data (b ₄ and b ₅ ) are recorded in the first half of the first column. If only 2 bits of a time delay to turn on the second half of the first column of the spatial light modulator, the laser output of the second half of the second column is the oscillation polarization corresponding to b _2-3 in the same manner. Thereafter, the second half of the first column is reset, and the next data (b ₆ and b ₇ ) is recorded in the second half of the first column. If the second row of the spatial light modulator is turned on within the time when b _0-1 and b _2-3 coexist in the second row laser, b _0-1 and b _2-3 are simultaneously turned into the third row laser. The laser output in the third column becomes oscillation polarization corresponding to b _0-3 . When the third column of the spatial light modulator is turned on, the laser output in the fourth column becomes oscillation polarization corresponding to b _0-3 . With b _{0-3 in the} fourth column, b _{4-7 in the} third column, b _{8-11 in} the second column, and b _{12-15 in the} first column, the time until reproduction is waited. At the time of reproduction, as shown in FIG. 14, when the subsequent data is sequentially transferred, the laser output in the fourth column is switched in the order of b _4-7 , b _8-11 , b _{12-15 at} a 4-bit time interval. . The 90 ° polarization component of the laser output in the fourth row is extracted by the polarizer 8, pulsed by the optical modulator, and the delayed light modulator output light a, b, c, d by the optical delay unit of the output light conversion unit. is converted to the timing of different signals bit by bit, it is multiplexed, b ₁₅ are reproduced from the b ₀ consecutive similar to the input signal light.

  As described above, it is possible to record data continuously by dividing one column of the spatial light modulator into the first half and the second half and operating them at different timings. Here, one column is divided equally into two parts, the first half and the second half. However, the present invention is not limited to this, and it is possible to divide into three or more divisions when there are many rows. Is also possible. In the above example, the second and subsequent columns are transferred without being divided. However, the present invention is not limited to this, and the entire column of the spatial light modulator may be divided and transferred to the final column.

Next, a method of continuously recording data in the shift register type optical memory device of the post-erase write method having the overall configuration as shown in FIG. 8 will be described with reference to the timing chart of FIG. The first spatial light modulator 31 is divided into four columns as in the example shown in FIG. 10C, and the first column is further divided into two.
Also in this case, the input light conversion unit 2 is changed as shown in FIG. 12, as in the case where data is continuously recorded in the above-described overwrite type shift register type optical memory device. Then, from the input signal light input to the laser output in the first column, the same operation as the above-described overwriting method is performed.

When data is transferred from the first column to the second column, first, the second column of the second spatial light modulator 32 is turned on, and 0 ° -polarized reset light is applied as shown in “Reset light of the second column”. Input to the second row laser and reset the second row laser output to 0 ° polarization. Thereafter, the first half of the first row of the first spatial light modulator 31 is turned on, and only when the first half of the first row of lasers is 90 ° -polarized as shown in “Output of the first half of the first spatial light modulator”. 90 ° polarized light is input to the first half of the second row of lasers. Thereafter, the second half of the first column of the first spatial light modulator 31 is turned on, and only when the second half laser of the first column is 90 ° -polarized as shown in “Second-half spatial light modulator output”. 90 ° polarized light is input to the second half of the second row of lasers. As a result, only when each laser in the first row is 90 ° polarized, the oscillation polarization of each laser in the second row is switched to 90 °. As a result, the oscillation polarization state of the first row laser is transferred to the second row laser. When data is transferred from the second column to the third column, the third column of the second spatial light modulator 32 is turned on, and 0 ° -polarized reset light is output as shown in “Reset light of the third column”. The laser beam in the third row is input, and the laser output in the third row is reset to 0 ° polarization. After that, the second column of the first spatial light modulator 31 is turned on, and 90 ° polarized light is emitted only when the second column laser is 90 ° polarized as shown in the “second column spatial light modulator output”. The laser beam is input to the third row laser, and the oscillation polarization state of the second row laser is transferred to the third row laser. Similarly, when data is transferred up to the fourth column and the subsequent data is sequentially transferred as shown in the timing chart of FIG. 15, the laser output of the fourth column is b _4-7 and b ₈ at 4-bit time intervals. _-11 and b _12-15 in this order. When the 90 ° polarization component of the laser output in the fourth row is extracted by the polarizer 8, pulsed by the optical modulator, added with a delay by the output light conversion unit, and combined, continuous data from b ₀ to b ₁₅ is obtained. Played.

  As described above, continuous data can be recorded by dividing one row of the first spatial light modulator 31 into the first half and the second half and operating them at different timings. In this embodiment, one column is equally divided into two parts, the first half and the second half. However, of course, the present invention is not limited to this, and when there are a large number of rows, it can be divided into three or more parts. It is also possible to divide. Further, as shown in FIG. 11 (c), it is possible to divide the second column of the second spatial light modulator 32 and reset the laser of the second column in the first half and the second half. Further, all the columns of the first spatial light modulator 31 are divided as shown in FIG. 10B, and all the columns of the second spatial light modulator 32 are divided as shown in FIG. It is also possible to perform reset and transfer by dividing the first half into the second half up to the column.

  The shift register type optical memory device according to the present invention has been described above with specific examples, but it is obvious that these are only examples. In other words, improvements and changes may be made as appropriate within the spirit of the present invention.

1 is an overall configuration diagram of a shift register type optical memory device 1 according to the present invention. The figure which shows an example of a structure of an input light conversion part. The figure which shows the other example of a structure of an input light conversion part. The figure which shows the structural example of an optical modulator array and an output light conversion part. The figure which shows the other structural example of an optical modulator array and an output light conversion part. The structural example in the case of providing a heater in a laser array. 4 is a timing chart showing the operation of the shift register type optical memory device according to the present invention. The whole block diagram of the other structure of the shift register type | mold optical memory device 1 which concerns on this invention. It is a structural example of the reset light demultiplexing part provided in order to branch one light into 4 rows 4 columns, (a) Top view, (b) Side view. It is a figure which shows the example of a division | segmentation of a spatial light modulator, (a) The example of a division corresponding to the row | line | column of a laser array, (b) The example which divides | segments one row into two blocks, (c) The example which divides | segments only the 1st row. It is a figure which shows the example of a division | segmentation of a 2nd spatial light modulator, (a) The example of a division corresponding to the row | line | column of a laser array, (b) The example which divides | segments one row into two blocks, (c) Dividing only the 1st row | line Example. The figure which shows the other structural example of an input light conversion part. 6 is a timing chart for explaining the operation of the shift register type optical memory device of the post-erase write method. 6 is an example of a timing chart when data is continuously recorded in an overwrite type shift register type optical memory device. 6 is an example of a timing chart in the case where data is continuously recorded in a shift register type optical memory device using a post-erase writing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Shift register type optical memory device 2 ... Input light conversion part 3 ... 1st lens array 4 ... 2nd lens array 5 ... Laser array 6 ... Optical isolator 7 ... Spatial light modulator 8 ... Polarizer 9 ... 3rd lens array 10 Optical modulator array 11 Output light conversion unit 20 Mirror array 20-1 First mirror element 20-2 Second mirror element 20-3 Third mirror element 21 First plane mirror 22 Second plane Mirror 23 ... Half mirror 30 ... Half mirror array 30-1 ... First half mirror element 30-2 ... Second half mirror element 30-3 ... Third half mirror element 31 ... First spatial light modulator 32 ... Second space Optical modulator 33 ... lens 41 ... first reset light demultiplexing unit 42 ... reset light demultiplexing lens array 43 ... second reset light demultiplexing unit

Claims (11)

In an optical memory device that records an optical signal input as a time series signal bit by bit in each bistable semiconductor laser and reads the recorded optical signal as a time series signal at a predetermined timing.
a) a laser array in which a plurality of bistable semiconductor lasers are arranged in an m × n matrix;
b) a shift register optical system that forms an optical path so that the output light of the bistable semiconductor laser excluding the bistable semiconductor laser in the last column is vertically input to the bistable semiconductor laser in the adjacent column in the laser array;
c) an optical isolator arranged so that only forward output light passes on the optical path formed by the shift register optical system;
d) a spatial light modulator disposed on an optical path formed by the shift register optical system;
A shift register type optical memory device. The shift register optical system is
A mirror array comprising at least n-1 mutually parallel mirror elements, each mirror element corresponding to output light from each row of bistable semiconductor lasers except the last row of bistable semiconductor lasers in said laser array;
A plurality of plane mirrors;
Half mirror,
The shift register type optical memory device according to claim 1, comprising: Furthermore, a reset light input unit for inputting reset light to a bistable semiconductor laser other than the first row of the laser array,
The shift register type optical memory device according to claim 1, wherein a polarizer is provided on an optical path formed by the shift register optical system. The mirror element of the mirror array is a half mirror,
Further, a reset light input unit that inputs reset light to a bistable semiconductor laser other than the first column of the laser array is provided, and the optical path of the reset light output from the reset light input unit passes through the half mirror. The shift register type optical memory device according to claim 2, wherein the shift register type optical memory device is superimposed on an optical path formed by the shift register optical system.   5. The shift register type optical memory device according to claim 3, wherein the optical isolator and the spatial light modulator act only on light having a predetermined polarization state. An optical modulator that operates at a higher speed than the spatial light modulator and modulates the intensity of light is provided on the optical path of the output light of the bistable semiconductor laser of the last column in the laser array. Item 6. The shift register optical memory device according to any one of Items 1 to 5.   7. The shift according to claim 1, wherein in the laser array, the optical power of the bistable semiconductor laser in the first row and / or the last row is larger than the optical power of other bistable semiconductor lasers. Register type optical memory device.   8. One or a plurality of heaters capable of individually adjusting the temperature for adjusting the wavelength of the bistable semiconductor laser are arranged in the plane of the laser array. The shift register type optical memory device described.   9. The spatial light modulator can operate independently for each portion corresponding to the output light of each column of a bistable semiconductor laser on the laser array. Shift register type optical memory device.   In the part where the spatial light modulator corresponds to the output light of each column of the bistable semiconductor laser on the laser array, only the part corresponding to the first line or all the parts are further divided into a plurality of regions. The shift register type optical memory device according to claim 1, wherein each portion is operable independently. The shift register type optical memory device according to claim 10,
An optical signal recording method in a shift register type optical memory device, wherein an optical signal is continuously recorded by operating a plurality of locations corresponding to the first row of the spatial light modulator at different timings.

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