JP4368573B2 - Ultrafast optical memory device using a bistable semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrafast optical memory device using a bistable semiconductor laser.
[0002]
[Prior art]
At present, the optical fiber communication system has been developed as a communication transmission system that bears an advanced information society. However, current optical fiber communication systems have not yet fully utilized the light characteristic of a carrier frequency of 200 THz. In order to respond to the increase in information volume in the future, development of a further ultra-high-speed optical communication system is desired, but for this ultra-high speed, an all-optical system that uses light for signal processing is also expected. Has been. In particular, an all-optical packet-based routing technique is required.
[0003]
FIG. 5 is a schematic diagram of a conventional fiber delay line buffer memory.
In this figure, 101 is a packet input, 102 is a first optical switch, 103 is a packet storage device, 104 is a second optical switch, and 105 is a packet output.
However, in the method using such a fiber delay line buffer memory, it is difficult to read out information at the required timing and control for each bit.
[0004]
[Non-Patent Document 1]
Tamura, Yamayoshi, Kawaguchi "All-optical signal processing using ultrafast polarization bistable surface-emitting semiconductor lasers" Science Technology, LQE 2000-42 (August 2000)
[0005]
[Non-Patent Document 2]
Yamayoshi, Kawaguchi, "All-optical ultra-high-speed DEMUX using polarization bistability of surface-emitting semiconductor lasers", PS98-15 (June 1998)
[0006]
[Non-Patent Document 3]
H. Kawaguchi, “Bistable laser diodes and ther application; State of the art,” IEEE J. et al. Selected. Top. Quantum Electron. , 3 (1997) 1254.
[0007]
[Problems to be solved by the invention]
Therefore, the inventors of the present application are provided with a plurality of bistable semiconductor lasers that perform an AND gate operation and a memory operation, and are all-optical without converting an optical signal into an electrical signal. The development of an ultrahigh-speed optical memory capable of recording one bit at a time on a semiconductor laser and reading the recorded signal as a time-series signal at a necessary timing has become an issue.
[0008]
Furthermore, as will be described in detail later, as the number of bits increases, an optical space parallel signal converter that receives an optical time series signal for input and output and an optical time series signal converter that receives an optical parallel signal are required for the number of bits. However, there is a drawback that the apparatus becomes large, and it has been a problem to solve it.
In view of the above situation, the present invention provides an ultrahigh-speed optical memory device using a bistable semiconductor laser that can read out information at a control and necessary timing for each bit and has a shift register function. Objective.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In an ultrahigh-speed optical memory device using a bistable semiconductor laser, an optical branch / delay line to which a time-series first linearly polarized optical signal is input, a half mirror, and a first to the half mirror An optical signal writing means comprising a linearly polarized set light irradiating means and a second linearly polarized reset light irradiating means, and the optical signal writing means converts the time-series optical signals into spatially parallel signals. The first linearly polarized light mode and the second linearly polarized light mode whose polarization directions are orthogonal to each other are set as two natural laser oscillation modes, and the optical signal converted into the spatial parallel signal an array having a plurality of bistable semiconductor laser to perform an aND gate operation and memory operation is an aND operation of the set light, the output light from said plurality of bistable semiconductor laser Of these, an analyzer that transmits the first linearly polarized light, an optical gate means that is composed of a saturable absorber to which the first linearly polarized light that has passed through the analyzer is input, and gate light that irradiates the optical gate means A pulse irradiating means and an optical delay / merging line for the read signal light are provided, and provided with an optical signal reading means for reading the optical signal written in the array, without converting the optical signal into an electrical signal. An all-optical type is characterized in that a time-series optical signal is recorded on each bistable semiconductor laser bit by bit, and the recorded signal is read out as a time-series signal in accordance with a required timing.
[0010]
[ 2 ] In the ultrafast optical memory device using the bistable semiconductor laser described in [1], the ultrafast optical memory device reflects output light from each of the plurality of first stage bistable semiconductor lasers. A reflector for inputting to each of the plurality of bistable semiconductor lasers in the second stage, a second optical gate means, a second half mirror, and a second to the second half mirror. Gate light pulse irradiation means, and when the second gate light pulse from the second gate light pulse irradiation means is incident on the second light gate means via the second half mirror, The output light from each of the plurality of bistable semiconductor lasers in the first stage passes through the second optical gate means and is reflected by the reflector, and then the plurality of bistable semiconductor lasers in the second stage. Record by entering each No. is characterized by having a shift register function to be transferred and recorded.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a schematic diagram of an ultrafast optical memory device using a bistable semiconductor laser according to a first embodiment of the present invention.
In this figure, 1 is an ultrafast optical signal (input signal), 1A is a header, 2 is an optical time-series signal / optical space parallel signal converter, 3, 4 and 13 are half mirrors, and 5 is a one-dimensional or two-dimensional signal. Polarized bistable surface emitting semiconductor laser (VCSEL) array, 6 is set light, 7 is reset light, 11 is an analyzer (transmits 0 ° polarized light), 12 is an optical gate element, 14 is a gate light pulse, 15 is light Spatial parallel signal / optical time-series signal conversion device 16 is an ultrafast optical signal (output signal).
[0012]
In the following, a detailed description will be given of signal writing to an ultrafast optical memory using a bistable semiconductor laser and readout of a signal from an ultrafast optical memory using a bistable semiconductor laser.
FIG. 2 shows a signal writing to an ultrahigh-speed optical memory using a bistable semiconductor laser according to the first embodiment of the present invention using an optical branching / delay line for conversion from an optical space parallel signal to an optical time-series signal. It is a schematic diagram to explain.
[0013]
In this figure, 21 is an ultrafast optical signal (input signal), 21A is a header, 22 is an optical branching / delay line, 22A is an input port, 22B is an output port, 23 is a half mirror, and 24 is a one-dimensional or two-dimensional signal. A polarization bistable surface emitting semiconductor laser (VCSEL) array, 25 is set light, and 26 is reset light.
Here, the operation principle of the VCSEL element will be described.
[0014]
In a surface emitting semiconductor laser in which the optical waveguide has a square cross-sectional shape, there are two eigenmodes along the side of the square of the electric field direction. Here, they are called 0 ° mode and 90 ° mode. The optical gain of the surface-emitting semiconductor laser is approximately equal to the two laser oscillation modes, and the two modes are strongly coupled through gain saturation, resulting in bistability. When a short light pulse is incident from the outside, the polarization is switched to the same polarization mode as the incident pulse light, and the switched polarization is maintained even when the incident pulse disappears. Therefore, a polarization bistable optical memory can be realized. Polarization switching speed is as extremely high as 7 ps, which is the world's fastest switching speed for optical bistable elements. Applications such as optical demultiplexing (optical DEMUX) in ultrahigh-speed optical communication and direct conversion of optical RZ signals to optical NRZ signals can be expected.
[0015]
Next, writing of signals to the polarization bistable surface emitting semiconductor laser (VCSEL) array 24 will be described with reference to FIG.
First, by entering a reset light 26 having an electric field perpendicular to the paper surface (referred to as 90 ° light), the oscillation polarization of each polarization bistable surface emitting semiconductor laser (VCSEL) array 24 is perpendicular to the paper surface (90 ° light). ).
[0016]
As shown in FIG. 2, a header 21 </ b> A is added to the ultrafast high-speed optical signal. An optical signal polarized in the plane of the paper (referred to as 0 ° light) enters from the input port 22A of the optical branch / delay line 22, is branched, delayed by a bit interval, and output from each output port 22B. 23 and injected into the VCSEL array 24.
[0017]
Next, when the optical signal that is delayed most by the optical branching / delaying line 22 reaches the VCSEL array 24, the 0 ° -polarized set light 25 is incident on the VCSEL array 24 by the signal from the header 21A. The polarization of the VCSEL array 24 is not switched only by the signal light, but when the set light 25 and the signal light are simultaneously incident, the polarization is switched from 90 ° light to 0 ° light.
[0018]
Therefore, as shown in FIG. 2, when the set light 25 is incident, the “1” and “0” signals injected into the VCSEL array 24 are recorded in the VCSEL array 24 as oscillation polarization.
FIG. 3 is a schematic diagram for explaining reading of signals from the ultrafast optical memory using the bistable semiconductor laser according to the first embodiment of the present invention.
[0019]
In this figure, 27 is a half mirror, 28 is an analyzer, 29 is a saturable absorber, 30 is a gate light pulse, 31 is an optical delay / merging line, 32 is a mirror, and 33 is an ultrafast optical signal (output signal). is there.
The optical signal (record) written as shown in FIG. 2 is read as follows.
[0020]
From the VCSEL array 24, laser oscillation light of 0 ° polarization and 90 ° polarization is emitted continuously (CW) in accordance with “1” and “0” signals. The analyzer 28 allows only 0 ° polarized light to pass through and enters the saturable absorber 29. Next, the gate light pulse 30 enters the saturable absorber 29, and the CW light from the VCSEL array 24 is cut out as pulse light. Next, the optical pulses are arranged in time series by the optical delay / merging line 31 and read out as an ultrafast optical signal (output signal) 33.
[0021]
As described above, memory can be stored in units of optical packets, and data can be read out in units of optical packets when necessary.
According to the above embodiment, it is shown by a detailed computer simulation using a rate equation that an ultrahigh-speed optical memory operation is possible.
It is known from Non-Patent Documents 1 to 3 described above that this analysis method is suitable for analysis of this type of optical memory operation and the result agrees well with the experimental result.
[0022]
FIG. 4 is a diagram showing a simulation result of an ultrafast optical memory using a bistable semiconductor laser according to the first embodiment of the present invention. FIG. 4A shows a time waveform of an ultrafast optical signal (0 °), 4B is a set light (0 °), FIG. 4C is a reset light (90 °), FIG. 4D is a 0 ° polarization component of the memory output, FIG. 4E is a gate light pulse, FIG. 4F shows the read output. The vertical axis indicates optical power (μW), and the horizontal axis indicates time (ps).
[0023]
In the time waveform of the ultrahigh-speed optical signal shown in FIG. 4A, the pulse width of the optical signal is 1 ps, the pulse interval is 5 ps, and the signal transmission speed is 200 Gbit / s. The optical signal power of each channel is 5 μW. The case of 6 channels was analyzed in accordance with the schematic diagrams shown in FIGS. The header 21A having a pulse width of 10 ps is read, 1 ps set light (10 μW) is generated with an appropriate time delay, and set to enter the VCSEL array 24 simultaneously with the signal light of the sixth channel.
[0024]
As a result, as shown in FIG. 4D, the 0 ° polarization component of the memory output is stored as “0” or “1” depending on whether the optical signal is “0” or “1”. At this time, the optical output of the memory is about 500 μW, which is advantageous in that it is 100 times (20 dB) larger than the optical signal.
Next, as shown in FIG. 4E, the absorption of the saturable absorber 29 is saturated with the gate light pulse 30 of about 1 ps and 100 μW, and the signal light is read out as shown in FIG.
[0025]
When the reading of the signal light is finished, as shown in FIG. 4C, the optical memory is reset to a 90 ° signal with the reset light 26 of 1 ps and 20 μW.
Through this series of operations, memory can be stored in units of optical packets and can be read out in units of optical packets when necessary.
Next, a second embodiment of the present invention will be described.
[0026]
FIG. 6 is a schematic diagram of an ultrafast optical memory device using a bistable semiconductor laser showing a second embodiment of the present invention.
In this figure, 201 is a half mirror, 202 is a two-dimensional polarization bistable surface emitting semiconductor laser (VCSEL) array, 203 is an optical gate element, and 204 is a reflector.
[0027]
The apparatus of the present embodiment is obtained by replacing the polarization bistable surface emitting semiconductor laser array 24 shown in the first embodiment with a two-dimensional array 202. An optical time-series signal / optical space parallel signal converter (not shown), Reset light generator (not shown), set light generator (not shown), gate light generator (not shown), analyzer 11, optical gate element 12, and optical space parallel signal / light time series signal converter (not shown) ), And a reflector 204, an optical gate element 203, and a gate light generation device are added to this device.
[0028]
First, as shown in the first embodiment, signal writing to the two-dimensional polarization bistable surface emitting semiconductor laser array 202 will be described. First, by entering reset light having an electric field perpendicular to the paper surface (called 90 ° light), the oscillation polarization of each polarization bistable surface emitting semiconductor laser is reset perpendicular to the paper surface (called 90 ° light). The
A header is added to the ultra-fast time series signal. An optical time-series signal polarized in the paper (referred to as 0 ° light) is converted by an optical time-series signal / optical space parallel signal converter and injected into a different polarization bistable surface emitting semiconductor laser for each bit. Next, when the optical signal reaches the first stage of the VCSEL array 202 (A _{1 to} A _{4 in} FIG. 6), the 0 ° -polarized set light is incident on the VCSEL array 202 by the signal from the header. The polarization of the VCSEL array 202 is not switched only by signal light, but is switched from 90 ° light to 0 ° light when set light and signal light are incident simultaneously. Therefore, when the set light is incident, the “1” and “0” signals injected into the VCSEL array 202 are recorded as the oscillation polarization of the VCSEL.
[0029]
Next, the shift register function will be described with reference to FIGS.
FIG. 7 is a schematic diagram showing the arrangement in more detail for one column of surface emitting semiconductor lasers A ₁ , B ₁ , C ₁ , D ₁ for optical signals.
In the conventional optical packet memory described above, when the number of bits is increased, the number of input / output ports of the optical time-series signal / optical space parallel signal conversion device is required by the number of bits. In the present invention, this problem is solved by providing an optical shift register function for collectively transferring and recording signals recorded in several bistable semiconductor lasers to another bistable semiconductor laser.
[0030]
FIG. 6 shows a conceptual diagram of a shift register using a two-dimensional polarization bistable surface emitting semiconductor laser array composed of a 4 × 4 surface emitting semiconductor laser. According to the operating principle shown in FIG. 1, “1” and “0” signals are recorded as 0 ° and 90 ° oscillating polarizations in A _{1 to} A ₄ , respectively. The outputs of the surface emitting semiconductor lasers A _{1 to} A ₄ are emitted with a diffraction spread of several degrees, and are focused on the surface emitting semiconductor lasers B _{1 to} B ₄ by the reflector 204 disposed on the upper surface. Near the reflector 204, there is disposed an optical gate element 203 through which the output of the surface emitting semiconductor laser is transmitted when a gate light pulse is incident from the outside. If the distance between the surface emitting semiconductor laser and the reflector 204 is 1, the lasing polarization of B _{1 to} B ₄ is A _{1 to} A _{4 when} the gate is opened for a time shorter than 2 l / c (c is the speed of light). By injecting the output, the oscillation polarization becomes the same as each of A _{1 to} A _4, and signals are written and recorded respectively. For example, if l is 5 cm, the gate opening time is 30 ps or less. Next, A _{1 to} A ₄ are reset with reset light having 90 ° polarization, and a new signal is written. Then you open the gate in the gate light, the signal of B ₁ .about.B ₄ is a C ₁ -C _4, signals of A ₁ to A ₄ is recorded is written into B ₁ ~B _4. Reading of the signal can be realized by reading out the CW output of the surface emitting semiconductor laser in the final stage (D _{1 to} D _{4 in} the column in the figure) as described later.
[0031]
FIG. 8 is a timing chart showing the recording of the optical signal surface emitting semiconductor lasers A _{1 to} A _N , and FIG. 9 is a timing chart showing the shift register function, that is, A ₁ to B ₁ , B ₁ to C _1. 4 is a timing chart showing how signals are transferred and recorded from C ₁ to D ₁ .
In ultra-high speed optical memory device with a shift register function according to the present invention, A ₁ ~ by AND gate operation of the number of bits, the set light and the signal light that matches the number of y direction of the surface emitting semiconductor laser shown in FIG. 6 It is recorded on a surface emitting semiconductor laser of A _N. This signal is transferred to B _{1 to} B _N and recorded by the input of the gate light, and then the oscillation polarization of A _{1 to} A _N is reset to 90 ° by the reset light, and the next signal is recorded.
[0032]
Reading of the record is performed as follows. From the last stage (D _{1 to} D _{4 in} FIG. 6) of the VCSEL array 202, laser oscillation light of 0 ° polarization and 90 ° polarization is emitted continuously (CW) in accordance with “1” and “0” signals. The analyzer 11 passes only 0 ° polarized light and enters the optical gate element 12. Next, a gate light pulse is incident on the optical gate element 12, and the CW light from the final stage of the VCSEL array 202 is passed through and cut out as pulse light. Next, optical pulses are arranged in time series by an optical space parallel signal / optical time series signal converter. As described above, memory can be stored in units of optical packets, and data can be read out in units of optical packets when necessary.
[0033]
According to the second embodiment of the present invention, a plurality of bistable surface emitting semiconductor lasers that perform an AND gate operation and a memory operation are provided, and an all-optical type time series light without converting an optical signal into an electrical signal. In an ultrahigh-speed optical memory that can record a signal bit by bit in each bistable semiconductor laser and read out the recorded signal as a time-series signal at the required timing, the recorded signal is transferred from one bistable semiconductor laser to another bistable semiconductor. It has the function of transferring to the laser and recording.
[0034]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0035]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
(1) An optical signal can be routed in units of optical packets without converting an optical signal into an electrical signal, and high speed optical communication can be achieved.
[0036]
(2) A recording signal can be transferred from one bistable semiconductor laser to another bistable semiconductor laser and recorded.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an ultrafast optical memory device using a bistable semiconductor laser according to a first embodiment of the present invention (conceptual diagram of a shift register using a two-dimensional polarization bistable surface emitting semiconductor laser array). .
FIG. 2 is a schematic diagram for explaining signal writing to an ultrafast optical memory using a bistable semiconductor laser according to a first embodiment of the present invention.
FIG. 3 is a schematic diagram for explaining signal reading from an ultrahigh-speed optical memory using a bistable semiconductor laser according to the first embodiment of the present invention.
FIG. 4 is a diagram showing a simulation result of an ultrafast optical memory using a bistable semiconductor laser according to the first embodiment of the present invention.
FIG. 5 is a schematic diagram of a conventional fiber delay line buffer memory.
FIG. 6 is a schematic diagram of an ultrafast optical memory device using a bistable semiconductor laser showing a second embodiment of the present invention.
FIG. 7 is a schematic diagram showing in more detail the arrangement of one row of surface emitting semiconductor lasers A ₁ , B ₁ , C ₁ , D ₁ for optical signals of the second embodiment of the present invention.
FIG. 8 is a timing chart showing recording of surface-emitting semiconductor lasers A _{1 to} A _N of optical signals according to the second embodiment of the present invention.
FIG. 9 is a timing chart showing the state of transfer and recording of optical signal surface emitting semiconductor lasers A ₁ to B ₁ , B ₁ to C ₁ , and C ₁ to D _{1 according} to a second embodiment of the present invention. It is.
[Explanation of symbols]
1,21 Ultrafast optical signal (input signal)
1A, 21A Header 2 Optical Time Series Signal / Optical Space Parallel Signal Conversion Device 3, 4, 13, 23, 27, 201, 205 Half Mirror 5, 24, 202 One-dimensional or two-dimensional polarization bistable surface emitting semiconductor laser ( VCSEL) array 6,25 set light 7,26 reset light 11,28 analyzer (transmits 0 ° polarized light)
12,203 Optical gate element 14,30 Gate optical pulse 15 Optical spatial parallel signal / optical time-series signal converter 16,33 Ultra high-speed optical signal (output signal)
22 Optical Branch / Delay Line 22A Optical Branch / Delay Line Input Port 22B Optical Branch / Delay Line Output Port 29 Saturable Absorber 31 Optical Delay / Merge Line 32 Mirror 204 Reflector

Claims (2)

(A) An optical branch / delay line to which a time-series first linearly polarized optical signal is input, a half mirror, a first linearly polarized set light irradiation means to the half mirror, and a second linearly polarized light Optical signal writing means comprising the reset light irradiation means of
(B) The optical signal writing means converts the time-series optical signal into a spatially parallel signal and writes it bit by bit, and the first linearly polarized light mode and the second linearly polarized light mode whose polarization directions are orthogonal to each other. And an array having a plurality of bistable semiconductor lasers that perform an AND gate operation and a memory operation that are AND operations of the optical signal converted into the spatially parallel signal and the set light. When,
(C) An analyzer that transmits the first linearly polarized light out of the output light from the plurality of bistable semiconductor lasers, and a saturable absorber that receives the first linearly polarized light that has passed through the analyzer. An optical signal for reading an optical signal written in the array , comprising: an optical gate means comprising: a gate light pulse irradiating means for irradiating the optical gate means; and an optical delay / merging line for the read signal light Reading means,
(D) All-optical type without converting optical signals into electrical signals, time series optical signals are recorded on each bistable semiconductor laser one bit at a time, and the recorded signals are read out as time series signals according to the required timing Ultra high-speed optical memory device using a bistable semiconductor laser. 2. The ultrafast optical memory device using the bistable semiconductor laser according to claim 1, wherein the ultrafast optical memory device reflects output light from each of a plurality of bistable semiconductor lasers in a first stage and outputs second light. A reflector for inputting to each of a plurality of bistable semiconductor lasers in a stage, a second optical gate means, a second half mirror, and irradiation of a second gate light pulse to the second half mirror And when the second gate light pulse from the second gate light pulse irradiating means is incident on the second optical gate means via the second half mirror, the first stage Output light from each of the plurality of bistable semiconductor lasers is transmitted through the second optical gate means and reflected by the reflector, and then input to each of the plurality of bistable semiconductor lasers in the second stage. Transfer the recorded signal. It has a shift register function to be finely recorded ultrafast optical memory device using a bistable semiconductor laser according to claim.

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