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WO2025027853A1 - Semiconductor laser and method for generating optical spikes - Google Patents

Semiconductor laser and method for generating optical spikes Download PDF

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Publication number
WO2025027853A1
WO2025027853A1 PCT/JP2023/028453 JP2023028453W WO2025027853A1 WO 2025027853 A1 WO2025027853 A1 WO 2025027853A1 JP 2023028453 W JP2023028453 W JP 2023028453W WO 2025027853 A1 WO2025027853 A1 WO 2025027853A1
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mode
semiconductor laser
optical
section
pulse
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PCT/JP2023/028453
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French (fr)
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Nikolaos-Panteleimon DIAMANTOPOULOS
Shinji Matsuo
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Nippon Telegraph And Telephone Corporation
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1025—Extended cavities
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
    • H01S5/0287—Facet reflectivity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
    • H01S5/06209—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in single-section lasers
    • H01S5/06216—Pulse modulation or generation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
    • H01S5/0651—Mode control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H01S5/125—Distributed Bragg reflector [DBR] lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/16—Semiconductor lasers with special structural design to influence the modes, e.g. specific multimode
    • H01S2301/163—Single longitudinal mode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
    • H01S5/0422—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer
    • H01S5/0424—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer lateral current injection
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
    • H01S5/0651—Mode control
    • H01S5/0653—Mode suppression, e.g. specific multimode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1039—Details on the cavity length

Definitions

  • the present invention relates to a semiconductor laser for generating optical spikes and a method for generating optical spikes.
  • PICs photonic integrated circuits
  • NPL neuromorphic photonics with massive parallelization and wide bandwidth capabilities
  • SiPh silicon photonics
  • this limitation can be alleviated by mimicking the brain processing in the form of spiking neural networks.
  • This class of neural networks is based on spiking neurons that time-integrate the input signal and emit short spike-like pulses just after the energy threshold has been reached. Due to the '1' or '0' output feature, neurons and spiking neural networks are not limited by SNR or noise propagation in the system. As a result, scalability is not limited. Furthermore, due to the event-driven feature, most of the energy is consumed only during the output operations (events), so it attracts attention as an energy-efficient operation.
  • Conventional methods for realizing optoelectronic or all-optical spiking neurons include semiconductor lasers with integrated supersaturated absorbers, optically-injected surface-emitting lasers (VCSELs, vertical-cavity surface-emitting lasers), phase-change materials in micro-rings, electronic-based spike generation, and the like.
  • VCSELs optically-injected surface-emitting lasers
  • vertical-cavity surface-emitting lasers vertical-cavity surface-emitting lasers
  • phase-change materials in micro-rings electronic-based spike generation, and the like.
  • a semiconductor laser according to the present invention includes an active gain section, a mirror section disposed at one end of the active gain section, and an optical feedback section disposed at the other end of the active gain section.
  • Fig. 1 is a schematic diagram showing the configuration of a semiconductor laser according to a first embodiment of the present invention.
  • Fig. 2 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention.
  • Fig. 3 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention.
  • Fig. 4 is a flowchart for describing a method for generating optical spikes according to the first embodiment of the present invention.
  • Fig. 5A is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention.
  • Fig. 5B is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention.
  • Fig. 1 is a schematic diagram showing the configuration of a semiconductor laser according to a first embodiment of the present invention.
  • Fig. 2 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention.
  • Fig. 3 is a diagram for explaining the operation
  • FIG. 5C is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention.
  • Fig. 6A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 6B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 6C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 7A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 7B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 7C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 8A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 8B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 8C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention.
  • Fig. 9A is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention.
  • Fig. 9B is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention.
  • Fig. 9C is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention.
  • Fig. 9D is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of
  • a semiconductor laser 10 according to the present embodiment includes an active gain section 11, a mirror section 12, and an optical feedback section 13, as shown in Fig. 1.
  • the active gain section 11 contains a laser gain medium and is used as an intermediate section.
  • the gain medium is a multi-quantum well (MQW) core made of InGaAsP.
  • MQW multi-quantum well
  • the width of the MQW core may be 0.4 to 1 ⁇ m and the number of well layers may be 3 to 12.
  • the MQW core has a gain peak in the wavelength band of 1.2 to 1.6 ⁇ m.
  • the MQW core may be made of a semiconductor such as InGaAlAs other than InGaAsP.
  • the cladding is a low-refractive index material such as InP or SiO 2 .
  • the mirror section 12 is integrated on one facet (a non-laser-emitting facet) side of the semiconductor laser 10. That is, the mirror section 12 is disposed at one end of the active gain section 11. In order to operate the semiconductor laser 10 efficiently, it is desirable that the mirror section 12 has a high reflectance of 90% or more.
  • the optical feedback section 13 is integrated on the other facet (a laser-emitting facet) side of the semiconductor laser 10. That is, the optical feedback section 13 is disposed at the other end of the active gain section 11.
  • the optical feedback section 13 has a reflective film having a low reflectance of 10% or less on the facet.
  • the side mode frequency is close to the main mode frequency of a laser cavity.
  • the frequency separation (frequency difference) between the side mode and the main mode of the laser cavity is preferably 100 GHz or less.
  • the laser cavity is comprised by a section extending from one end of the active gain section 11 to the laser-emitting facet of the optical feedback section 13.
  • the side mode produced by the optical feedback triggers nonlinear dynamics for spike generation. This occurs when an external energy perturbation is injected in the laser in the form of electrical or optical pulses.
  • a threshold hereafter referred to as the "spiking threshold”
  • the side mode is momentarily excited via the chirping mechanism of the laser (which will be described later).
  • the linewidth enhancement factor in III-V semiconductor lasers operating in a wavelength band of 1.2 to 1.6 ⁇ m is 3 or more in order to obtain a high-chirping effect.
  • the ratio of the cavity quality factor (Q) between the two modes is interchanged according to the bi-modal Q-switching mechanism.
  • the side mode excitation is observed as strong excitation in the output power compared to the average output power of the laser. This strong output power excitation is the optical spike. After this process occurs, the semiconductor laser 10 returns to its steady state.
  • Fig. 2 shows a schematic diagram of mode hopping of the semiconductor laser 10.
  • Fig. 3 shows the bias current versus output power (I-L characteristic) of the semiconductor laser 10.
  • I-L characteristic a mode hopping occurs from the first mode 1 to the second mode 2 when the bias current increases (open circle 153 in the figure).
  • a mode hopping occurs from the second mode 2 to the first mode 1 when the bias current decreases (open circle 151 in the figure).
  • a hysteresis is observed near the bias current range between the direction in which the bias current increases (solid line in the figure) and the direction in which the bias current decreases (dashed line in the figure).
  • the bias current is preferably set in a range where the first mode 1 is stable but close to the mode-hopping range.
  • the operating point may be set in a range where hysteresis occurs in the decreasing direction of the bias current (filled circle 154 in the figure).
  • the spiking threshold depends on the laser structure or the cavity structure. In the present embodiment, it is important that the laser structure provides a large chirp. Therefore, a laser structure with a membrane structure is desirable.
  • the membrane structure has a high optical confinement and thus allows a large chirping effect.
  • a membrane-structured laser is a laser in which a current is injected in a lateral direction (in a plane parallel to the substrate surface, a direction perpendicular to the direction in which light is guided (waveguide direction)).
  • the cavity structure It is also important to design the cavity structure so that the first mode and the second mode are separated by 100 GHz or less. As described above, the first mode and the second mode are produced by the feedback waveguide in the cavity structure. As a result, mode separation is established. Therefore, cavity parameters such as reflectance, length, and grating configuration affect mode separation and affect the spiking threshold.
  • Fig. 4 shows a flowchart diagram for explaining a method for generating optical spikes.
  • Figs. 5A to 5C show schematic diagrams for describing the method for generating optical spikes.
  • the semiconductor laser 10 is biased with a voltage 161 to cause laser oscillation (initial laser oscillation state). That is, the semiconductor laser 10 is operated at the operating point (step S1).
  • electrical pulses 162 are input from the outside (step S2).
  • an electrical input or a combination of multiple electrical inputs is supplied by a bias tee along with a DC bias current.
  • the bias voltage of the laser exceeds the spiking threshold, a mode hopping from the second mode to the first mode occurs, and subsequently, the mode returns from the first mode to the second mode.
  • Optical spikes are generated in this process.
  • an initial laser oscillation state is set (step S1).
  • optical pulses 163 are input from the outside (step S2).
  • the optical pulses 163 are supplied to one facet of the semiconductor laser 10 by an external spiking laser, a modulated laser light, or a combination of multiple optical inputs.
  • the bias voltage of the laser exceeds the spiking threshold, a mode hopping from the second mode to the first mode occurs, and subsequently, the mode returns (recovers) from the first mode to the second mode.
  • Optical spikes are generated in this process.
  • the wavelength of the injected light is desirably detuned from the main mode of the laser cavity by 5 to 20 nm.
  • Both the E/O method and the O/O method in the present embodiment produce a step-like output at the spiking threshold in the laser characteristics, as shown in Fig. 5C.
  • the spiking threshold is indicated by the filled circle164.
  • Fig. 6A shows the simulation results.
  • Fig. 6A shows changes over time of injected current I (171 in the figure), carrier density N (172 in the figure), frequency chirping ⁇ (173 in the figure), mode threshold gain g th (174 in the figure), and photon density S (175 in the figure).
  • the dashed line indicates the spiking threshold.
  • the dashed line indicates the first mode threshold gain g th and the solid line indicates the second mode threshold gain g th .
  • the dashed line indicates the first mode photon density and the dotted line indicates the second mode photon density.
  • the solid line indicates the total photon density of the first mode and the second mode.
  • spike-like pulses pulse width: 50 ps
  • the carrier density N and the frequency chirping ⁇ sharply increase, and subsequently return to the initial value.
  • the second mode threshold gain g th sharply increases, and subsequently returns to the initial value.
  • the first mode threshold gain g th decreases, and subsequently returns to the initial value.
  • the changes in the first mode threshold gain g th and the second mode threshold gain g th are small.
  • the photon density S does not change, and no optical spike is generated.
  • the carrier density N and the frequency chirping ⁇ sharply increase, and subsequently return to the initial value.
  • the second mode threshold gain g th sharply increases, and subsequently returns to the initial value.
  • the first mode threshold gain g th decreases, and subsequently returns to the initial value.
  • Fig. 6B shows the relationship between the peak-to-peak voltage V p-p of the input electrical pulses and the peak-to-average intensity of the optical output of the semiconductor laser 10.
  • the spiking threshold appears when the input V p-p of input electrical pulses with a pulse width of 50 ps is 400 mV.
  • Fig. 6C shows the dependency of modal threshold gain on wavelength shift (frequency chirping).
  • the dashed line indicates the first mode threshold gain g th and the solid line indicates the second mode threshold gain g th .
  • the starting point (that is, steady state) of the first mode and second mode threshold gains at DC are indicated by filled circles.
  • the first mode threshold gain and the second mode threshold gain exhibit different dependencies on wavelength shift. As the wavelength shift changes, the first mode and second mode threshold gains change. When the respective threshold gains become equal, that is, at the intersection of their respective dependencies, the ratio of the first mode threshold gain and the second mode threshold gain is interchanged.
  • An input pulse triggers a deviation of the carrier density N.
  • a frequency chirping ⁇ occurs.
  • time-coupling time-integration
  • the semiconductor laser 10 is useful for simultaneous detection and spiking-based processing in spiking neural networks. Although an example using two electrical pulses has been shown, three or more electrical pulses may be used.
  • the amplitude of each of the plurality of pulses is within a range in which the bias state of the semiconductor laser 10 does not exceed the spiking threshold when the pulses are applied. As a result of the time integration of multiple pulses, the bias condition of the semiconductor laser 10 exceeds the spiking threshold.
  • a plurality of electrical pulses may be input within a time range on the order of 0.01 ns to 0.1 ns.
  • Fig. 7A shows the relationship between the V p-p of the input electrical pulse and the peak-to-average voltage of the optical output measured by the oscilloscope.
  • V p-p 100 mV
  • Fig. 8A shows the relationship between the input optical power and the peak-to-average voltage of the optical output measured by the oscilloscope.
  • the optical output increases sharply when the input power increases from 11.5 dBm to 12 dBm. This indicated that a mode hopping occurred at 11.5 mV, resulting in a spiking threshold of 11.5 mV.
  • Figs. 8B and 8C respectively show optical output waveforms when the input optical power is below the spiking threshold (9 dBm) and above the spiking threshold (12 dBm).
  • the results of time-sweeping two input pulses at input optical powers of 9 dBm and 12 dBm as the optical output waveforms were measured by a sampling oscilloscope.
  • optical spikes were observed at intervals of 200 ps when the input optical power was above the spiking threshold (12 dBm). This is the result of two mode hoppings, that is, the process of a temporary mode hopping and recovery.
  • This optical spike interval (200 ps) corresponds to a spiking rate of 5 GHz.
  • the experimentally obtained spiking rate of 5 to 10 GHz suggests that spiking neuron processing of about 10 GHz can be performed with optical spikes generated using the semiconductor laser 10 according to the present embodiment.
  • optical spikes can be generated at a high rate.
  • a semiconductor laser according to a first example of the present invention will be described with reference to Fig. 9A.
  • a semiconductor laser 20 according to the present example has a configuration based on the DFB laser structure, as shown in Fig. 9A.
  • a DFB section 21 is provided as an active gain section.
  • One end of the DFB section 21 is provided with a high-reflection coating film 221 as a mirror section.
  • a waveguide (hereinafter referred to as a "feedback waveguide") 231 having a low-reflection facet 2311 is provided as an integrated optical feedback section.
  • the length of the DFB section 21 is 50 to 150 ⁇ m and the DFB diffraction grating is designed for single-mode operation.
  • the high-reflection coating film 221 is, for example, a multilayer film of Si and SiO 2 .
  • the feedback waveguide 231 is composed of an InP waveguide.
  • the core width is 0.6 to 1.5 ⁇ m and the length is 100 to 300 ⁇ m.
  • a cladding such as SiO 2 .
  • a semiconductor laser according to a second example of the present invention will be described with reference to Fig. 9B.
  • a semiconductor laser 30 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9B.
  • a DFB section 21 is provided as an active gain section.
  • One end of the DFB section 21 is provided with a first DBR section 222 as a mirror section.
  • a second DBR section (hereinafter referred to as a "feedback DBR") 232 is provided as an integrated optical feedback section.
  • the DFB section 21 is the same as in the first example.
  • the first DBR section 222 of the mirror section is designed to have a Bragg wavelength centered at the main lasing mode of the DFB section 21.
  • This DBR section 222 is composed of an InP waveguide.
  • the core width is 0.6 to 1.5 ⁇ m and the length is 100 ⁇ m or less.
  • it has a cladding such as SiO 2 .
  • the feedback DBR 232 is composed of an InP waveguide.
  • the core width is 0.6 to 1.5 ⁇ m and the length is 100 to 300 ⁇ m. It has a cladding such as SiO 2 .
  • the diffraction grating is designed to have a Bragg wavelength detuning of 1 to 3 nm compared with the main mode of the DFB laser.
  • a semiconductor laser according to a third example of the present invention will be described with reference to Fig. 9C.
  • a semiconductor laser 40 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9C.
  • a DFB section 21 is provided as the active gain section 11.
  • One end of the DFB section 21 is provided with a first DBR section 222 as a mirror section.
  • a feedback waveguide 231 is provided at the other end of the DFB section 21.
  • the DFB section 21 and the feedback waveguide 231 are the same as in the first example, and the first DBR section 222 is the same as in the second example.
  • a semiconductor laser according to a fourth example of the present invention will now be described with reference to Fig. 9D.
  • a semiconductor laser 50 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9D.
  • a DFB section 21 is provided as the active gain section 11.
  • One end of the DFB section 21 is provided with a high-reflection coating film 221 as a mirror section.
  • a feedback DBR 232 is provided at the other end of the DFB section 21.
  • the DFB section 21 and the high-reflection coating film 221 are the same as in the first example, and the feedback DBR 232 is the same as in the second example.
  • optical spikes can be generated at a high rate.
  • an example using an input pulse with a pulse width of 50 ps has been illustrated, but the present invention is not limited to this.
  • An input pulse with a pulse width of 50 ps or greater may be used to generate optical spikes.
  • the width of the input pulse is 50 ps or less. It is desirable that the width of the input pulse is 1 ps or more.
  • Input pulses in the embodiment of the present invention include spike-like pulses (input spikes). Input spikes may be used when laser neurons are used as the intermediate layer of a photonic spiking neural network.
  • a semiconductor laser including: an active gain section; a mirror section disposed at one end of the active gain section; and an optical feedback section disposed at the other end of the active gain section.
  • a method for generating optical spikes including: allowing the semiconductor laser according to any one of Additional Notes 1 to 7 to oscillate with a predetermined bias; and inputting a pulse to the semiconductor laser.
  • the method for generating optical spikes according to Additional Note 7 or 8, further including: measuring the optical spikes to obtain a spiking threshold for the optical spikes; determining the predetermined bias; and determining a magnitude of the pulse, wherein the predetermined bias is a bias immediately before the spiking threshold, and a magnitude of the pulse is determined such that a bias state of the semiconductor laser exceeds the spiking threshold when the pulse is applied.
  • the present invention can be applied to computer systems, communication systems, computer devices, and communication devices.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)

Abstract

The semiconductor laser (10) of the present invention includes an active gain section (11), a mirror section (12) disposed at one end of the active gain section, and an optical feedback section (13) disposed at the other end of the active gain section. During laser oscillation, after a mode hopping from a main mode of a cavity formed from the one end to the other end to another mode according to a pulse input, optical spikes may be output in a process of returning from the other mode to the main mode.　In this way, the present invention can provide a semiconductor laser that generates optical spikes at a high rate.

Description

Semiconductor Laser and Method for Generating Optical Spikes
The present invention relates to a semiconductor laser for generating optical spikes and a method for generating optical spikes.
In recent years, computer processing capacity is increasing due to the development of the application of the latest AI machine learning. However, as processing speeds continue to increase and computer systems become more complex, power consumption and CO2 emissions become significant issues. For low power consumption, neuromorphic hardware accelerators, such as processors that mimic the processing functions of the human brain, have recently been developed.
One promising platform for neuromorphic computing is PICs (photonic integrated circuits) and neuromorphic photonics with massive parallelization and wide bandwidth capabilities (NPL 1).
The application of silicon photonics (SiPh) technology is important in conventional coherent/linear networks, artificial neural networks and reservoir computing networks. However, since SiPh-only PICs do not have gain elements (amplifiers, lasers, and the like), system scalability is limited by a low signal-to-noise ratio due to the propagation and coupling losses in the PIC.
On the other hand, this limitation can be alleviated by mimicking the brain processing in the form of spiking neural networks. This class of neural networks is based on spiking neurons that time-integrate the input signal and emit short spike-like pulses just after the energy threshold has been reached. Due to the '1' or '0' output feature, neurons and spiking neural networks are not limited by SNR or noise propagation in the system. As a result, scalability is not limited. Furthermore, due to the event-driven feature, most of the energy is consumed only during the output operations (events), so it attracts attention as an energy-efficient operation.
Conventional methods for realizing optoelectronic or all-optical spiking neurons include semiconductor lasers with integrated supersaturated absorbers, optically-injected surface-emitting lasers (VCSELs, vertical-cavity surface-emitting lasers), phase-change materials in micro-rings, electronic-based spike generation, and the like.
B.J. Shastri, et al., "Photonics for artificial intelligence and neuromorphic computing," Nat. Photonics, vol. 15, pp. 102-114 (2021), <URL:http:// https://doi.org/10.1038/s41566-020-00754-y>
However, the processing speed of the prior art has been limited to several GHz or less due to the speed limitation of the physical nonlinear processing involved in spike generation.
In order to solve the above problems, a semiconductor laser according to the present invention includes an active gain section, a mirror section disposed at one end of the active gain section, and an optical feedback section disposed at the other end of the active gain section.
According to the present invention, it is possible to provide a semiconductor laser and a method for generating optical spikes that generate optical spikes at a high rate.
Fig. 1 is a schematic diagram showing the configuration of a semiconductor laser according to a first embodiment of the present invention. Fig. 2 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. Fig. 3 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. Fig. 4 is a flowchart for describing a method for generating optical spikes according to the first embodiment of the present invention. Fig. 5A is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention. Fig. 5B is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention. Fig. 5C is a diagram for explaining a method for generating optical spikes according to the first embodiment of the present invention. Fig. 6A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 6B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 6C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 7A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 7B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 7C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 8A is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 8B is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 8C is a diagram for explaining the effects of the semiconductor laser and the optical spike generation method according to the first embodiment of the present invention. Fig. 9A is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention. Fig. 9B is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention. Fig. 9C is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention. Fig. 9D is a schematic diagram showing the configuration of a semiconductor laser according to the first embodiment of the present invention.
<First Embodiment>
A semiconductor laser and an optical spike generation method according to a first embodiment of the present invention will be described with reference to Figs. 1 to 8C.
<Configuration of semiconductor laser>
A semiconductor laser 10 according to the present embodiment includes an active gain section 11, a mirror section 12, and an optical feedback section 13, as shown in Fig. 1.
The active gain section 11 contains a laser gain medium and is used as an intermediate section. The gain medium is a multi-quantum well (MQW) core made of InGaAsP. For example, the width of the MQW core may be 0.4 to 1 μm and the number of well layers may be 3 to 12. The MQW core has a gain peak in the wavelength band of 1.2 to 1.6 μm. The MQW core may be made of a semiconductor such as InGaAlAs other than InGaAsP.
The cladding is a low-refractive index material such as InP or SiO2.
The mirror section 12 is integrated on one facet (a non-laser-emitting facet) side of the semiconductor laser 10. That is, the mirror section 12 is disposed at one end of the active gain section 11. In order to operate the semiconductor laser 10 efficiently, it is desirable that the mirror section 12 has a high reflectance of 90% or more.
The optical feedback section 13 is integrated on the other facet (a laser-emitting facet) side of the semiconductor laser 10. That is, the optical feedback section 13 is disposed at the other end of the active gain section 11. The optical feedback section 13 has a reflective film having a low reflectance of 10% or less on the facet. By the optical feedback, a side mode (first mode 1 described later) in the laser spectrum is produced.
The side mode frequency is close to the main mode frequency of a laser cavity. The frequency separation (frequency difference) between the side mode and the main mode of the laser cavity is preferably 100 GHz or less. Here, the laser cavity is comprised by a section extending from one end of the active gain section 11 to the laser-emitting facet of the optical feedback section 13.
When the frequency of the side mode is close to the frequency of the main mode of the laser cavity, the side mode produced by the optical feedback triggers nonlinear dynamics for spike generation. This occurs when an external energy perturbation is injected in the laser in the form of electrical or optical pulses. When the total injected energy exceeds a threshold (hereafter referred to as the "spiking threshold"), the side mode is momentarily excited via the chirping mechanism of the laser (which will be described later). In addition, for example, it is desirable that the linewidth enhancement factor in III-V semiconductor lasers operating in a wavelength band of 1.2 to 1.6 μm is 3 or more in order to obtain a high-chirping effect.
In this process, the ratio of the cavity quality factor (Q) between the two modes is interchanged according to the bi-modal Q-switching mechanism. The side mode excitation is observed as strong excitation in the output power compared to the average output power of the laser. This strong output power excitation is the optical spike. After this process occurs, the semiconductor laser 10 returns to its steady state.
The details of spike generation will be described below with reference to Figs. 2 and 3.
Fig. 2 shows a schematic diagram of mode hopping of the semiconductor laser 10. When an electrical or optical energy perturbation is injected and the injected energy exceeds the spiking threshold, side mode (first mode) 1 is excited and a mode hopping from second mode 2 to first mode 1 occurs (141 in the figure). After that, the semiconductor laser 10 returns to a steady state (142 in the figure).
Fig. 3 shows the bias current versus output power (I-L characteristic) of the semiconductor laser 10. In this I-L characteristic, a mode hopping occurs from the first mode 1 to the second mode 2 when the bias current increases (open circle 153 in the figure). A mode hopping occurs from the second mode 2 to the first mode 1 when the bias current decreases (open circle 151 in the figure).
A hysteresis is observed near the bias current range between the direction in which the bias current increases (solid line in the figure) and the direction in which the bias current decreases (dashed line in the figure).
In the increasing direction of the bias current (from open circle 151 to open circle 152 in the figure), before mode hopping occurs, a four-wave mixing is observed since both modes experience approximately the same gain (that is, approximately the same Q) in this bias current range where excitation of four-wave mixing side modes occurs (open circle 152 in the figure).
In order to generate spikes, the bias current is preferably set in a range where the first mode 1 is stable but close to the mode-hopping range. For example, as shown in Fig. 3, the operating point may be set in a range where hysteresis occurs in the decreasing direction of the bias current (filled circle 154 in the figure).
At this operating point, when a pulse is applied from the outside while the laser is oscillating in a state in which the second mode 2 is dominant, a mode hopping occurs temporarily from the second mode 2 to the first mode 1. Subsequently, the laser oscillation state returns from the first mode 1 to the second mode 2. Optical spikes are generated during this transition process.
The spiking threshold depends on the laser structure or the cavity structure. In the present embodiment, it is important that the laser structure provides a large chirp. Therefore, a laser structure with a membrane structure is desirable. The membrane structure has a high optical confinement and thus allows a large chirping effect. A membrane-structured laser is a laser in which a current is injected in a lateral direction (in a plane parallel to the substrate surface, a direction perpendicular to the direction in which light is guided (waveguide direction)).
It is also important to design the cavity structure so that the first mode and the second mode are separated by 100 GHz or less. As described above, the first mode and the second mode are produced by the feedback waveguide in the cavity structure. As a result, mode separation is established. Therefore, cavity parameters such as reflectance, length, and grating configuration affect mode separation and affect the spiking threshold.
<Optical spike generation method>
A method for generating optical spikes according to the present embodiment will be described with reference to Figs. 4 and Figs. 5A to 5C. Fig. 4 shows a flowchart diagram for explaining a method for generating optical spikes. Figs. 5A to 5C show schematic diagrams for describing the method for generating optical spikes.
As a first method for generating optical spikes, a method using electrical input pulses or electrical input spikes (E/O method) will be described with reference to Figs. 4 and 5A.
First, the semiconductor laser 10 is biased with a voltage 161 to cause laser oscillation (initial laser oscillation state). That is, the semiconductor laser 10 is operated at the operating point (step S1).
Next, electrical pulses 162 are input from the outside (step S2). As the electrical pulses 162, an electrical input or a combination of multiple electrical inputs is supplied by a bias tee along with a DC bias current.
As a result, the bias voltage of the laser exceeds the spiking threshold, a mode hopping from the second mode to the first mode occurs, and subsequently, the mode returns from the first mode to the second mode. Optical spikes are generated in this process.
As a second method for generating optical spikes, a method using optical input pulses or optical input spikes (O/O method) will be described with reference to Figs. 4 and 5B.
First, as in the E/O method described above, an initial laser oscillation state is set (step S1).
Next, optical pulses 163 are input from the outside (step S2). The optical pulses 163 are supplied to one facet of the semiconductor laser 10 by an external spiking laser, a modulated laser light, or a combination of multiple optical inputs.
As a result, the bias voltage of the laser exceeds the spiking threshold, a mode hopping from the second mode to the first mode occurs, and subsequently, the mode returns (recovers) from the first mode to the second mode. Optical spikes are generated in this process.
Here, the wavelength of the injected light is desirably detuned from the main mode of the laser cavity by 5 to 20 nm.
Both the E/O method and the O/O method in the present embodiment produce a step-like output at the spiking threshold in the laser characteristics, as shown in Fig. 5C. In the figure, the spiking threshold is indicated by the filled circle164.
<Effects>
Effects of the semiconductor laser 10 according to the present embodiment will be described with reference to Figs. 6A to 8C.
To verify the operation of the semiconductor laser 10, simulations were performed using MATLAB software based on laser modeling with two-mode rate equations. Fig. 6A shows the simulation results.
Fig. 6A shows changes over time of injected current I (171 in the figure), carrier density N (172 in the figure), frequency chirping Δν (173 in the figure), mode threshold gain gth (174 in the figure), and photon density S (175 in the figure). At 171 in the figure, the dashed line indicates the spiking threshold. At 174 in the figure, the dashed line indicates the first mode threshold gain gth and the solid line indicates the second mode threshold gain gth. At 175 in the figure, the dashed line indicates the first mode photon density and the dotted line indicates the second mode photon density. The solid line indicates the total photon density of the first mode and the second mode.
When spike-like pulses (pulse width: 50 ps) are supplied in the injected current I and the current value of the pulses exceeds the spiking threshold (t = about 0.25 ns), after about 0.04 ns from the supply of the pulses, the carrier density N and the frequency chirping Δν sharply increase, and subsequently return to the initial value.
In the mode threshold gain gth, the second mode threshold gain gth sharply increases, and subsequently returns to the initial value. The first mode threshold gain gth decreases, and subsequently returns to the initial value.
Subsequently, approximately 0.01 ns after the change in gth, the total photon density S sharply increases, and subsequently returns to the initial value. That is, an optical spike is generated.
When the current value of the pulses supplied in injected current I does not exceed the spiking threshold value (t = about 1 ns), the changes in the carrier density N and frequency chirping Δν are small.
In the mode threshold gain gth, the changes in the first mode threshold gain gth and the second mode threshold gain gth are small.
As a result, the photon density S does not change, and no optical spike is generated.
In the injected current I, when two electrical pulses are supplied with a time interval of about 0.05 ns, and the current value of each pulse does not exceed the spiking threshold (t = about 1.75 ns), after about 0.015 ns from the supply of the second pulse, the carrier density N and the frequency chirping Δν sharply increase, and subsequently return to the initial value.
In the mode threshold gain gth, the second mode threshold gain gth sharply increases, and subsequently returns to the initial value. The first mode threshold gain gth decreases, and subsequently returns to the initial value.
Subsequently, approximately 0.008 ns after the change in gth, the total photon density S sharply increases, and subsequently returns to the initial value. That is, an optical spike is generated.
Fig. 6B shows the relationship between the peak-to-peak voltage Vp-p of the input electrical pulses and the peak-to-average intensity of the optical output of the semiconductor laser 10.
The spiking threshold appears when the input Vp-p of input electrical pulses with a pulse width of 50 ps is 400 mV.
Fig. 6C shows the dependency of modal threshold gain on wavelength shift (frequency chirping). In the figure, the dashed line indicates the first mode threshold gain gth and the solid line indicates the second mode threshold gain gth. In the figure, the starting point (that is, steady state) of the first mode and second mode threshold gains at DC are indicated by filled circles.
The first mode threshold gain and the second mode threshold gain exhibit different dependencies on wavelength shift. As the wavelength shift changes, the first mode and second mode threshold gains change. When the respective threshold gains become equal, that is, at the intersection of their respective dependencies, the ratio of the first mode threshold gain and the second mode threshold gain is interchanged.
An input pulse triggers a deviation of the carrier density N. As a result, a frequency chirping Δν occurs. When the frequency chirping (wavelength shift) is large enough that the first mode and second mode threshold gains intersect at the intersection, a large excitation of the photon dense appears due to a temporal excitation of the first mode.
On the other hand, when the energy of the input pulse is not large enough to cause significant chirping and the first mode and second mode threshold gains do not intersect at the intersection, no excitation of the output photon density is observed.
Also, if two electrical pulses arrive close in time in succession, the combined energy will trigger a spike (event) even if the respective energies do not exceed the spiking threshold. This time-coupling (time-integration) feature in the semiconductor laser 10 is useful for simultaneous detection and spiking-based processing in spiking neural networks. Although an example using two electrical pulses has been shown, three or more electrical pulses may be used.
The amplitude of each of the plurality of pulses is within a range in which the bias state of the semiconductor laser 10 does not exceed the spiking threshold when the pulses are applied. As a result of the time integration of multiple pulses, the bias condition of the semiconductor laser 10 exceeds the spiking threshold. A plurality of electrical pulses may be input within a time range on the order of 0.01 ns to 0.1 ns.
In the above, an example using electrical pulses was shown, but a similar effect can be obtained by using optical pulses.
The effects of the semiconductor laser 10 according to the present embodiment were experimentally verified.
First, experimental results by the E/O method using an electrical input signal will be described. In the experiment, an NRZ (non-return-to-zero) pulse of 10 to 25 GHz was input to the DFB section of the semiconductor laser 10. A DC bias current was supplied by a bias tee together with pulses. The Vp-p of the pulse voltage was varied from 50 to 325 mV. Optical output was measured by a sampling oscilloscope.
Fig. 7A shows the relationship between the Vp-p of the input electrical pulse and the peak-to-average voltage of the optical output measured by the oscilloscope.
When the Vp-p of the input electrical pulse increases from 125 mV to 150 mV, the optical output increases sharply. This indicated that a mode hopping occurred at 125 mV, yielding a spiking threshold of 125 mV.
Figs. 7B and 7C respectively show optical output waveforms when Vp-p is below the spiking threshold (Vp-p = 100 mV) and above the spiking threshold (Vp-p = 300 mV). The results of time-sweeping two input pulses at Vp-p = 100 mV and Vp-p = 300 mV as optical output waveforms were measured by a sampling oscilloscope.
As shown in Fig. 7C, two optical spikes were observed at intervals of 100 ps when Vp-p was above the spiking threshold (Vp-p = 300 mV). This is the result of two mode hoppings, that is, the process of a temporary mode hopping and recovery. This optical spike interval (100 ps) corresponds to a spiking rate of 10 GHz.
From the above, in a state in which the semiconductor laser 10 is biased at a voltage lower than 125 mV (spiking threshold) to cause laser oscillation, by inputting a pulse with a bias voltage exceeding 125 mV (spiking threshold), optical spikes are generated.
Next, experimental results by the O/O method using an optical input signal will be described. In the experiment, laser light from an external laser source was modulated by a Mach-Zehnder modulator and subsequently amplified by an optical amplifier to generate NRZ optical pulses at 10 to 25 GHz. The optical output power of this optical pulse was varied from 9 to 13 dBm and input to the DFB section of the semiconductor laser 10. An optical circulator was used for optical input and measurements. Optical output was measured by a sampling oscilloscope.
Fig. 8A shows the relationship between the input optical power and the peak-to-average voltage of the optical output measured by the oscilloscope.
The optical output increases sharply when the input power increases from 11.5 dBm to 12 dBm. This indicated that a mode hopping occurred at 11.5 mV, resulting in a spiking threshold of 11.5 mV.
Figs. 8B and 8C respectively show optical output waveforms when the input optical power is below the spiking threshold (9 dBm) and above the spiking threshold (12 dBm). The results of time-sweeping two input pulses at input optical powers of 9 dBm and 12 dBm as the optical output waveforms were measured by a sampling oscilloscope.
As shown in Fig. 8C, optical spikes were observed at intervals of 200 ps when the input optical power was above the spiking threshold (12 dBm). This is the result of two mode hoppings, that is, the process of a temporary mode hopping and recovery. This optical spike interval (200 ps) corresponds to a spiking rate of 5 GHz.
From the above, in a state in which the semiconductor laser 10 is biased at a voltage lower than the spiking threshold (voltage corresponding to the optical power of 11.5 dBm) to cause laser oscillation, by inputting an optical pulse so that the total energy injected exceeds the spiking threshold (energy corresponding to the optical power of 11.5 dBm), optical spikes are generated.
Further, as described above, the experimentally obtained spiking rate of 5 to 10 GHz suggests that spiking neuron processing of about 10 GHz can be performed with optical spikes generated using the semiconductor laser 10 according to the present embodiment.
According to the semiconductor laser and the optical spike generation method according to the present embodiment, optical spikes can be generated at a high rate.
A semiconductor laser according to a first example of the present invention will be described with reference to Fig. 9A.
A semiconductor laser 20 according to the present example has a configuration based on the DFB laser structure, as shown in Fig. 9A. A DFB section 21 is provided as an active gain section. One end of the DFB section 21 is provided with a high-reflection coating film 221 as a mirror section. At the other end of the DFB section 21, a waveguide (hereinafter referred to as a "feedback waveguide") 231 having a low-reflection facet 2311 is provided as an integrated optical feedback section.
The length of the DFB section 21 is 50 to 150 μm and the DFB diffraction grating is designed for single-mode operation.
The high-reflection coating film 221 is, for example, a multilayer film of Si and SiO2.
The feedback waveguide 231 is composed of an InP waveguide. The core width is 0.6 to 1.5 μm and the length is 100 to 300 μm. Like the DFB section, it has a cladding such as SiO2.
A semiconductor laser according to a second example of the present invention will be described with reference to Fig. 9B.
A semiconductor laser 30 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9B. A DFB section 21 is provided as an active gain section. One end of the DFB section 21 is provided with a first DBR section 222 as a mirror section. At the other end of the DFB section 21, a second DBR section (hereinafter referred to as a "feedback DBR") 232 is provided as an integrated optical feedback section.
The DFB section 21 is the same as in the first example.
The first DBR section 222 of the mirror section is designed to have a Bragg wavelength centered at the main lasing mode of the DFB section 21. This DBR section 222 is composed of an InP waveguide. The core width is 0.6 to 1.5 μm and the length is 100 μm or less. Like the DFB section 21, it has a cladding such as SiO2.
The feedback DBR 232 is composed of an InP waveguide. The core width is 0.6 to 1.5 μm and the length is 100 to 300 μm. It has a cladding such as SiO2. The diffraction grating is designed to have a Bragg wavelength detuning of 1 to 3 nm compared with the main mode of the DFB laser.
A semiconductor laser according to a third example of the present invention will be described with reference to Fig. 9C.
A semiconductor laser 40 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9C. A DFB section 21 is provided as the active gain section 11. One end of the DFB section 21 is provided with a first DBR section 222 as a mirror section. A feedback waveguide 231 is provided at the other end of the DFB section 21.
The DFB section 21 and the feedback waveguide 231 are the same as in the first example, and the first DBR section 222 is the same as in the second example.
A semiconductor laser according to a fourth example of the present invention will now be described with reference to Fig. 9D.
A semiconductor laser 50 according to the present example has a configuration based on a DBR laser structure, as shown in Fig. 9D. A DFB section 21 is provided as the active gain section 11. One end of the DFB section 21 is provided with a high-reflection coating film 221 as a mirror section. A feedback DBR 232 is provided at the other end of the DFB section 21.
The DFB section 21 and the high-reflection coating film 221 are the same as in the first example, and the feedback DBR 232 is the same as in the second example.
According to the semiconductor lasers according to the first to fourth examples, optical spikes can be generated at a high rate.
In the embodiment of the present invention, an example using an input pulse with a pulse width of 50 ps has been illustrated, but the present invention is not limited to this. An input pulse with a pulse width of 50 ps or greater may be used to generate optical spikes. In order to achieve a processing speed exceeding several GHz, it is desirable that the width of the input pulse is 50 ps or less. It is desirable that the width of the input pulse is 1 ps or more.
Input pulses in the embodiment of the present invention include spike-like pulses (input spikes). Input spikes may be used when laser neurons are used as the intermediate layer of a photonic spiking neural network.
In the embodiments of the present invention, an example of the structure, dimensions, materials, and the like of each component is shown in the configuration of the semiconductor laser, the method for generating the optical spike, and the like, but the present invention is not limited to this. Any device that exhibits the functions and effects of the semiconductor laser and the optical spike generation method may be used.
It should be noted that the present invention is not limited to the above-described embodiment, and it is obvious that many modifications and combinations can be implemented by those skilled in the art within the technical concept of the present invention.
Some or all of the above-described embodiments or examples thereof can also be described in the following additional notes, but are not limited to the following.
(Additional Note 1)
　　　　A semiconductor laser including:
　　　　an active gain section;
　　　　a mirror section disposed at one end of the active gain section; and
　　　　an optical feedback section disposed at the other end of the active gain section.
(Additional Note 2)
　　　　The semiconductor laser according to Additional Note 1, wherein
　　　　during laser oscillation, after a mode hopping from a main mode of a cavity formed from the one end to the other end to another mode according to a pulse input, optical spikes are output in a process of returning from the other mode to the main mode.
(Additional Note 3)
　　　　The semiconductor laser according to Additional Note 2, wherein
　　　　a frequency difference between the main mode and the other mode is 100 GHz or less.
(Additional Note 4)
　　　　The semiconductor laser according to Additional Note 2 or 3, wherein
　　　　the pulse has a width of 1 ps or more and 50 ps or less.
(Additional Note 5)
　　　　The semiconductor laser according to any one of Additional Notes 2 to 4, wherein
　　　　the pulse is an optical pulse, and a wavelength of the optical pulse is detuned from the main mode by 5 nm or more and 20 nm or less.
(Additional Note 6)
　　　　The semiconductor laser according to any one of Additional Notes 1 to 5, wherein
　　　　the active gain section has a DFB laser structure,
　　　　the mirror section is composed of either a high-reflection coating film or a first DBR having a diffraction grating, and
　　　　the optical feedback section is composed of either a waveguide having a low-reflection facet or a second DBR having a diffraction grating.
(Additional Note 7)
　　　　A method for generating optical spikes, including:
　　　　allowing the semiconductor laser according to any one of Additional Notes 1 to 7 to oscillate with a predetermined bias; and
　　　　inputting a pulse to the semiconductor laser.
(Additional Note 8)
　　　　The method for generating optical spikes according to Additional Note 7, wherein
　　　　the pulse is a plurality of temporally successive pulses.
(Additional Note 9)
　　　　The semiconductor laser according to Additional Note 6, wherein
　　　　the second DBR is detuned from the main mode by 1 nm or more and 3 nm or less.
(Additional Note 10)
　　　　The semiconductor laser according to any one of Additional Notes 1 to 6 and 9, wherein
　　　　the active gain section is composed of a membrane-type laser.
(Additional Note 11)
　　　　The method for generating optical spikes according to Additional Note 7 or 8, further including:
　　　　measuring the optical spikes to obtain a spiking threshold for the optical spikes;
　　　　determining the predetermined bias; and
　　　　determining a magnitude of the pulse, wherein
　　　　the predetermined bias is a bias immediately before the spiking threshold, and
　　　　a magnitude of the pulse is determined such that a bias state of the semiconductor laser exceeds the spiking threshold when the pulse is applied.
(Additional Note 12)
　　　　The method for generating optical spikes according to Additional Note 8, wherein
　　　　a time range in which the plurality of pulses are input is 0.01 ns or more and 0.1 ns or less,
　　　　a magnitude of each of the plurality of pulses is in a range in which a bias state of the semiconductor laser does not exceed the spiking threshold when the pulse is applied, and
　　　　a time integration of the plurality of pulses is determined such that the bias state of the semiconductor laser exceeds the spiking threshold.
The present invention can be applied to computer systems, communication systems, computer devices, and communication devices.
10　　　Semiconductor laser
11　　　Active gain section
12　　　Mirror section
13　　　Optical feedback section

Claims (8)

  1. A semiconductor laser comprising:
    　　　　an active gain section;
    　　　　a mirror section disposed at one end of the active gain section; and
    　　　　an optical feedback section disposed at the other end of the active gain section.
  2. 　　　　The semiconductor laser according to claim 1, wherein
    　　　　during laser oscillation, after a mode hopping from a main mode of a cavity formed from the one end to the other end to another mode according to a pulse input, optical spikes are output in a process of returning from the other mode to the main mode.
  3. 　　　　The semiconductor laser according to claim 2, wherein
    　　　　a frequency difference between the main mode and the other mode is 100 GHz or less.
  4. 　　　　The semiconductor laser according to claim 2 or 3, wherein the pulse has a width of 1 ps or more and 50 ps or less.
  5. 　　　　The semiconductor laser according to claim 2 or 3, wherein
    　　　　the pulse is an optical pulse, and a wavelength of the optical pulse is detuned from the main mode by 5 nm or more and 20 nm or less.
  6. 　　　　The semiconductor laser according to claim 1, wherein
    　　　　the active gain section has a DFB laser structure,
    　　　　the mirror section is composed of either a high-reflection coating film or a first DBR having a diffraction grating, and
    　　　　the optical feedback section is composed of either a waveguide having a low-reflection facet or a second DBR having a diffraction grating.
  7. 　　　　A method for generating optical spikes, comprising:
    　　　　allowing the semiconductor laser according to claim 1 to oscillate with a predetermined bias; and
    　　　　inputting a pulse to the semiconductor laser.
  8. 　　　　The method for generating optical spikes according to claim 7, wherein
    　　　　the pulse is a plurality of temporally successive pulses.
PCT/JP2023/028453 2023-08-03 2023-08-03 Semiconductor laser and method for generating optical spikes WO2025027853A1 (en)

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