CN220797411U

CN220797411U - Optical frequency comb source based on self-injection locking

Info

Publication number: CN220797411U
Application number: CN202320968965.4U
Authority: CN
Inventors: 刘午; 周志伟
Original assignee: Hefei Si Zhen Chip Technology Co ltd
Current assignee: Hefei Si Zhen Chip Technology Co ltd
Priority date: 2023-04-26
Filing date: 2023-04-26
Publication date: 2024-04-16
Anticipated expiration: 2033-04-26

Abstract

The application discloses an optical frequency comb source based on self injection locking, which comprises a semiconductor laser, a laser driver, a first waveguide beam splitter, a second waveguide beam splitter and a waveguide filter, wherein the first waveguide beam splitter, the second waveguide beam splitter and the waveguide filter are integrated on an optical chip. The semiconductor laser works in a gain switch mode under the action of the laser driver to output optical pulses, one part of the optical pulses output by the semiconductor laser are output outside the optical chip after being split by the first waveguide beam splitter and the second waveguide beam splitter, and the other part of the optical pulses are processed by the waveguide filter to form self-injection optical signals with specific frequencies, and the self-injection optical signals are fed back and injected into the semiconductor laser to realize self-injection locking of the semiconductor laser and generation of an effective optical frequency comb. In addition, the optical frequency comb source provided by the application can be realized based on a traditional semiconductor laser and a traditional silicon-based chip technology, and is easy to integrate on a chip.

Description

Optical frequency comb source based on self-injection locking

Technical Field

The application belongs to the field of optical frequency comb sources, and particularly relates to an optical frequency comb source based on self-injection locking.

Background

An Optical Frequency Comb (OFC) refers to a spectrum that is spectrally composed of a series of frequency components that are uniformly spaced and have a stable coherent phase relationship. The optical frequency comb is represented by a frequency spectrum sequence with the same frequency interval in the frequency domain, and is represented by an ultrashort pulse sequence in the time domain, wherein the frequency interval in the frequency domain and the pulse width in the time domain strictly follow the Fourier transformation relation. Since the optical frequency comb is distributed in the frequency domain in a shape particularly similar to a comb used in our daily lives, it is visually referred to as an "optical frequency comb", simply referred to as an "optical frequency comb". The optical frequency comb has a plurality of frequency components, and thus can be used as a measuring tool for optical frequencies like a ruler with precise scales, which is the most precise optical frequency measuring tool so far. The optical frequency comb provides an ideal research tool for the fields of optical frequency precision measurement, atomic ion transition energy level measurement, remote signal clock synchronization, satellite navigation and the like. With the rapid development of optical communication technology in recent years, optical frequency combs are also being widely applied to the fields of dense wavelength division multiplexing, multi-wavelength ultrashort pulse generation, optical arbitrary waveform generation and the like.

Optical frequency generation based on mode-locked pulse laser the comb is a conventional optical frequency comb generation scheme. Mode-locked pulse laser refers to a periodically varying pulse generated by locking the phase between the longitudinal modes of the laser, which appears in the frequency domain as a spectrum with a series of longitudinal modes, so that an optical frequency comb can be obtained, and the longitudinal mode spacing of the laser is equivalent to the comb tooth spacing of the optical frequency comb. However, the generation of optical frequency combs based on mode-locked lasers is limited by the laser cavity length, which is typically only a few megahertz to tens of megahertz in its repetition frequency. The optical frequency comb with the frequency interval of tens megahertz can be produced by adopting the optical modulation technology in the mode-locked laser, however, the frequency interval is limited by the photoelectric modulator and the radio frequency signal generator, and along with the frequency rise, the cost of the optical frequency comb is rapidly increased, so that the optical frequency comb is unfavorable for large-scale application.

The microcavity optical frequency comb developed in recent years has congenital advantages in the aspect of repeated frequency, and the defects of the traditional optical frequency comb technology are exactly overcome. The generation of optical frequency combs using microcavity structures is a relatively efficient solution. The microcavity structure can generate large-interval optical frequency combs with intervals of more than 100GHz, noise of the optical frequency combs is small, the signal-to-noise ratio can reach 40dB, and the comb teeth have better coherence. However, the technology for industrially preparing the microcavity is still immature, so that the cost of the optical frequency comb is high, and meanwhile, the microcavity is high in temperature sensitivity and needs to be continuously regulated and controlled, so that the final optical frequency comb device is complex in structure, high in cost, difficult to integrate on a chip and poor in system stability.

Disclosure of Invention

In order to solve the above problems, the application provides an optical frequency comb source based on self-injection locking, which generates an effective optical frequency comb through self-injection and has the advantages of simple structure, stable frequency spectrum and easy on-chip integration. It is specifically the scheme is as follows:

the application discloses an optical frequency comb source based on self injection locking, which comprises a semiconductor laser, a laser driver, a first waveguide beam splitter, a second waveguide beam splitter and a waveguide filter, wherein the first waveguide beam splitter, the second waveguide beam splitter and the waveguide filter are integrated on an optical chip;

the semiconductor laser is operated in a gain-switching mode for outputting optical pulses, the optical pulse is an initial pulse or an optical frequency comb pulse; the laser driver is connected with the semiconductor laser and used for driving the semiconductor laser; the first waveguide beam splitter is used for splitting the optical pulse output by the semiconductor laser, the optical pulse input by the second waveguide beam splitter or the optical pulse input by the waveguide filter, the waveguide filter is used for filtering the received optical pulse and transmitting the filtered optical pulse to the second waveguide beam splitter or the first waveguide beam splitter, and the second waveguide beam splitter is used for splitting the optical pulse input by the first waveguide beam splitter or the optical pulse input by the waveguide filter; the first waveguide beam splitter and the second waveguide beam splitter each comprise a first upper port, a second upper port, a first lower port and a second lower port, the first upper port of the first waveguide beam splitter is connected with the semiconductor laser, the first upper port of the second waveguide beam splitter is connected with the second upper port of the first waveguide beam splitter, and two ends of the waveguide filter are respectively connected with the second lower port of the first waveguide beam splitter and the second lower port of the second waveguide beam splitter.

Preferably, the beam splitting ratio of the first waveguide beam splitter and the beam splitting ratio of the second waveguide beam splitter are both (90+n): (10-N), wherein N is a positive integer less than 10.

Further, the optical frequency comb source further comprises a waveguide attenuator integrated on the optical chip and used for attenuating the intensity of the received optical pulse, and two ends of the waveguide attenuator are respectively connected with the waveguide filter and the second lower port of the second waveguide beam splitter.

Further, the optical frequency comb source further comprises a waveguide delay line integrated on the optical chip, the waveguide delay line is used for carrying out delay processing on received optical pulses, so that the time of transmitting the optical pulses subjected to delay processing to the semiconductor laser is consistent with the time of one optical pulse output by the semiconductor laser, and two ends of the waveguide delay line are respectively connected with the waveguide attenuator and the second lower port of the second waveguide beam splitter.

Preferably, the waveguide attenuator is composed of a third waveguide beam splitter, a first transmission waveguide, a second transmission waveguide, a fourth waveguide beam splitter and a phase modulator, the third waveguide beam splitter and the fourth waveguide beam splitter each comprise a third upper port and a third lower port, two ends of the first transmission waveguide are respectively connected with the third upper port of the third waveguide beam splitter and the third upper port of the fourth waveguide beam splitter, two ends of the second transmission waveguide are respectively connected with the third lower port of the third waveguide beam splitter and the third lower port of the fourth waveguide beam splitter, and the phase modulator is arranged on the second transmission waveguide.

Preferably, the method comprises the steps of, the semiconductor laser is a distributed feedback laser or a distributed Bragg reflection laser.

Preferably, the laser driver comprises a direct current source for generating a direct current bias current, an RF radio frequency signal source for generating a sinusoidal drive signal, and a bias device comprising a feed inductance connected to the direct current source and a blocking capacitance connected to the RF radio frequency signal source, the direct current bias current and the sinusoidal drive signal being injected into the semiconductor laser through the bias device.

Preferably, the waveguide filter is an MZ unequal arm interferometer type filter or a micro-ring resonator type optical filter.

Preferably, the MZ unequal arm interferometer filter is a single stage MZ unequal arm interferometer or is composed of a cascade of a plurality of MZ unequal arm interferometers.

Preferably, the micro-ring resonant cavity type optical filter is composed of an annular waveguide and a coupling straight waveguide connected end to end, wherein the coupling straight waveguide receives the optical pulse and couples the optical pulse to the annular waveguide.

In general, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects:

the application provides an optical frequency comb source based on self injection locking, which comprises a semiconductor laser, a laser driver, a first waveguide beam splitter, a second waveguide beam splitter and a waveguide filter, wherein the first waveguide beam splitter, the second waveguide beam splitter and the waveguide filter are integrated on an optical chip. The semiconductor laser works in a gain switch mode under the action of the laser driver to output optical pulses, one part of the optical pulses output by the semiconductor laser are output outside the optical chip after being split by the first waveguide beam splitter and the second waveguide beam splitter, and the other part of the optical pulses are processed by the waveguide filter to form self-injection optical signals with specific frequencies, and the self-injection optical signals are fed back and injected into the semiconductor laser to realize self-injection locking of the semiconductor laser and generation of an effective optical frequency comb. The self-injection optical signal is formed after the partial optical pulse output by the semiconductor laser is filtered by the waveguide filter, the frequency of the self-injection optical signal is consistent with a certain frequency of the optical pulse output by the semiconductor laser in self-radiation, and after the self-injection optical signal is fed back and injected into the semiconductor laser, the line width of the optical pulse output by the semiconductor laser is greatly narrowed, so that the phase noise of the optical pulse is effectively reduced. After the self-injection optical signal is fed back and injected into the semiconductor laser, each pulse output by the semiconductor laser is based on the self-injection locking effect instead of random spontaneous emission, so that the optical pulses output by the semiconductor laser have the same phase difference, clearer comb lines and distinguishable comb line intervals can be generated, and meanwhile, the comb tooth flatness and the coherence of the generated optical frequency comb are improved. In addition, the optical frequency comb source provided by the application can be realized based on a traditional semiconductor laser and a traditional silicon-based chip technology, and is easy to integrate on a chip.

Drawings

In order to more clearly illustrate the present embodiments or the technical solutions in the prior art, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of an optical frequency comb source based on self-injection locking according to an embodiment of the present application;

FIG. 2 is a schematic structural view of a first waveguide splitter and a second waveguide splitter of the present application;

fig. 3 is a schematic structural diagram of an optical frequency comb source based on self-injection locking according to another embodiment of the present application;

FIG. 4 is a schematic diagram of a waveguide attenuator according to one embodiment of the present application;

fig. 5 is a schematic structural diagram of an optical frequency comb source based on self-injection locking provided in the present application based on fig. 3;

FIG. 6 is a schematic diagram of an optical frequency comb pulse spectrum formed by the present application;

FIG. 7 is a schematic diagram of a laser driver according to the present application;

FIG. 8 is a schematic diagram of the structure of an MZ unequal arm interferometer of the present application;

FIG. 9 is a schematic diagram of a MZ unequal arm interferometer filter in one embodiment of the present application;

fig. 10 is a schematic structural diagram of a micro-ring resonator optical filter according to an embodiment of the present application.

Detailed Description

In order to make the above objects, features and advantages of the present application more comprehensible, embodiments accompanied with figures and detailed description are described in further detail below. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. Based on the embodiments herein, one of ordinary skill in the art will obtain all other embodiments without making any inventive faculty, all falling within the scope of the present application.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.

In order to facilitate understanding and explanation of the technical solutions provided by the embodiments of the present application, the background art of the present application will be described first.

With the rapid development of optical communication technology in recent years, optical frequency combs are increasingly widely applied to the fields of dense wavelength division multiplexing, multi-wavelength ultrashort pulse generation, optical arbitrary waveform generation and the like.

The generation of optical frequency combs based on mode-locked pulse lasers is a conventional optical frequency comb generation scheme. Mode-locked pulse laser refers to a periodically varying pulse generated by locking the phase between the longitudinal modes of the laser, which appears in the frequency domain as a spectrum with a series of longitudinal modes, so that an optical frequency comb can be obtained, and the longitudinal mode spacing of the laser is equivalent to the comb tooth spacing of the optical frequency comb. However, the generation of optical frequency combs based on mode-locked lasers is limited by the laser cavity length, which is typically only a few megahertz to tens of megahertz in its repetition frequency. The optical frequency comb with the frequency interval of tens megahertz can be produced by adopting the optical modulation technology in the mode-locked laser, however, the frequency interval is limited by the photoelectric modulator and the radio frequency signal generator, and along with the frequency rise, the cost of the optical frequency comb is rapidly increased, so that the optical frequency comb is unfavorable for large-scale application.

Based on this, the present application provides an optical frequency comb source based on self-injection locking, as shown in fig. 1, including a semiconductor laser, a laser driver, a first waveguide beam splitter, a second waveguide beam splitter, and a waveguide filter, where the first waveguide beam splitter, the second waveguide beam splitter, and the waveguide filter are integrated on one optical chip.

In one embodiment of the present utility model, when the material of the optical chip is silicon-based silicon dioxide, the semiconductor laser and the laser driver are mixed and integrated with the optical chip by means of a hybrid package. In another embodiment of the present utility model, when the material of the optical chip is a III-V material such as indium phosphide (InP), gallium arsenide (GaAs), the semiconductor laser may be directly integrated on the optical chip.

In the application, the semiconductor laser works in a gain switch mode and is used for outputting optical pulses, and the laser driver is connected with the semiconductor laser and is used for driving the semiconductor laser, and the optical pulses output by the semiconductor laser are initial pulses or optical frequency comb pulses.

Specifically, when the semiconductor laser starts operating under the drive of the laser driver, an initial pulse is output. Under the beam splitting action of the first waveguide beam splitter and the second waveguide beam splitter and the filtering action of the waveguide filter, part of the initial pulse becomes a self-injection optical signal with specific frequency, the self-injection optical signal is fed back and injected into the semiconductor laser, and the semiconductor laser outputs an optical frequency comb pulse based on the self-injection optical signal. The current optical frequency comb pulse is fed back and injected into the semiconductor laser by a part of self-injection optical signals with specific frequencies, and the semiconductor laser continuously outputs the optical frequency comb pulse based on the current self-injection optical signals under the beam splitting action of the first waveguide beam splitter and the second waveguide beam splitter and the filtering action of the waveguide filter. The process is a period reciprocating continuous process, and in summary, each optical frequency comb pulse is generated by self-injection of the optical frequency comb pulse in the previous period.

The first waveguide beam splitter is used for splitting optical pulses output by the semiconductor laser, optical pulses input by the second waveguide beam splitter or optical pulses input by the waveguide filter, the waveguide filter is used for filtering received optical pulses and transmitting the filtered optical pulses to the second waveguide beam splitter or the first waveguide beam splitter, and the second waveguide beam splitter is used for splitting the optical pulses input by the first waveguide beam splitter or the optical pulses input by the waveguide filter; the first waveguide beam splitter and the second waveguide beam splitter each comprise a first upper port, a second upper port, a first lower port and a second lower port, as shown in fig. 2, the first upper port of the first waveguide beam splitter is connected with the semiconductor laser, the first upper port of the second waveguide beam splitter is connected with the second upper port of the first waveguide beam splitter, and two ends of the waveguide filter are respectively connected with the second lower port of the first waveguide beam splitter and the second lower port of the second waveguide beam splitter.

In the application, the light pulse output by the semiconductor laser is transmitted to the first waveguide beam splitter for beam splitting, most of the split light pulse is transmitted to the second waveguide beam splitter for beam splitting, and the other small part of the light pulse is transmitted to the waveguide filter, wherein the small part of the light pulse is named as a reverse light pulse for convenience in distinguishing and representing, and the reverse light pulse is filtered by the waveguide filter and then sequentially fed back and injected into the semiconductor laser through the second waveguide beam splitter and the first waveguide beam splitter; after the light pulse transmitted from the first waveguide beam splitter to the second waveguide beam splitter is split, most of the light pulse is transmitted outside the optical chip, and the other small part of the light pulse is transmitted to the waveguide filter, wherein the small part of the light pulse is named as forward light pulse, the forward light pulse sequentially passes through the waveguide filter and the first waveguide beam splitter and is fed back and injected into the semiconductor laser, and the time when the reverse light pulse and the forward light pulse are transmitted to the semiconductor laser is the same.

Wherein the first and second waveguide splitters may be directional couplers, multimode interferometers (MMI) or MZ interferometers, and one skilled in the art may select different types of splitters as desired. In order to ensure that only a small number of light pulses are self-injected into the semiconductor laser, the beam splitting ratio of the first waveguide beam splitter and the beam splitting ratio of the second waveguide beam splitter are both set to be (90+N): (10-N), wherein N is a positive integer less than 10. That is, the first waveguide beam splitter and the second waveguide beam splitter are capable of directing the input light pulses in accordance with (90+n): (10-N) proportional energy beam splitting to obtain two groups of light pulses after beam splitting. Specifically, the splitting ratio of the first waveguide beam splitter to the second waveguide beam splitter may be 99:1, or 95:5, etc.

The waveguide filter filters the light pulses input thereto so that the center spectral line of the light pulses input thereto is narrower, preferably typically up to less than 100MHz. In order to realize self-injection locking of a semiconductor laser, one of the important conditions is that the wavelength of an optical pulse self-injected into the semiconductor laser is close to the wavelength of an optical pulse that can be emitted by the semiconductor laser, and thus a waveguide filter is provided to filter the self-injected optical pulse. In the present application, the waveguide filter is an MZ unequal arm interferometer type filter or a micro-ring resonator type optical filter.

In the embodiment of the utility model, the semiconductor laser works in a gain switch mode under the action of the laser driver to output optical pulses, most of the optical pulses output by the semiconductor laser are output outside the optical chip after being split by the first waveguide beam splitter and the second waveguide beam splitter, and the other small part of the optical pulses (comprising reverse optical pulses and forward optical pulses) are processed by the waveguide filter to form self-injection optical signals with specific frequencies, and the self-injection optical signals are fed back and injected into the semiconductor laser to realize self-injection locking of the semiconductor laser and generation of an effective optical frequency comb. The small part of light pulse output by the semiconductor laser is filtered by the waveguide filter to form a self-injection light signal, the frequency of the self-injection light signal is consistent with a certain frequency of the light pulse output by the semiconductor laser in spontaneous radiation, and when the self-injection light signal is fed back and injected into the semiconductor laser, the line width of the light pulse output by the semiconductor laser is greatly narrowed, so that the phase noise of the light pulse is effectively reduced. After the self-injection optical signal is fed back and injected into the semiconductor laser, each pulse output by the semiconductor laser is based on the self-injection locking effect instead of random spontaneous emission, so that the optical pulses output by the semiconductor laser have the same phase difference, clearer comb lines and distinguishable comb line intervals can be generated, and meanwhile, the comb tooth flatness and the coherence of the generated optical frequency comb are improved. In addition, the optical frequency comb source provided by the application can be realized based on a traditional semiconductor laser and a traditional silicon-based chip technology, and is easy to integrate on a chip.

In another embodiment of the present utility model, the optical frequency comb source further includes a waveguide attenuator integrated on the optical chip, for attenuating the intensity of the received optical pulse, and two ends of the waveguide attenuator are respectively connected to the waveguide filter and the second lower port of the second waveguide beam splitter, and the optical frequency comb source structure based on this embodiment is shown in fig. 3.

In order to ensure that the self-injection locking of the semiconductor laser is successful, another important condition is that the light intensity of the self-injection light pulse fed back into the semiconductor laser cannot be too high, otherwise the self-injection light pulse will affect the stability of the output light pulse of the semiconductor laser. The waveguide attenuator is thus arranged to attenuate the light intensity of the self-injected light pulse, adjusting the light intensity of the self-injected light pulse.

In an embodiment of the present application, the waveguide attenuator is composed of a third waveguide beam splitter, a first transmission waveguide, a second transmission waveguide, a fourth waveguide beam splitter and a phase modulator, the structure is shown in fig. 4, the third waveguide beam splitter and the fourth waveguide beam splitter each include a third upper port and a third lower port, two ends of the first transmission waveguide are respectively connected with the third upper port of the third waveguide beam splitter and the third upper port of the fourth waveguide beam splitter, two ends of the second transmission waveguide are respectively connected with the third lower port of the third waveguide beam splitter and the third lower port of the fourth waveguide beam splitter, and the phase modulator is disposed on the second transmission waveguide.

Specifically, the beam splitting ratio of the third waveguide beam splitter to the fourth waveguide beam splitter in the waveguide attenuator is 50:50, the phase modulator carries out phase modulation on the optical pulse input to the second transmission waveguide, forms a phase difference with the optical pulse transmitted on the first transmission waveguide, and interference cancellation is achieved after the optical pulse on the second transmission waveguide subjected to phase modulation meets the optical pulse on the first transmission waveguide, so that the intensity attenuation of the optical pulse is realized.

In this embodiment, the specific transmission process of the signal is:

the light pulse output by the semiconductor laser is transmitted to the first waveguide beam splitter for beam splitting, most of the split light pulse is transmitted to the second waveguide beam splitter for beam splitting, the other small part of the light pulse (reverse light pulse) is transmitted to the waveguide filter, the reverse light pulse is filtered by the waveguide filter and then is input to the third waveguide beam splitter of the waveguide attenuator for beam splitting, one group of the split reverse light pulse is input to the first transmission waveguide through the third upper port, the other group of the split reverse light pulse is input to the second transmission waveguide through the third lower port, the phase modulator on the second transmission waveguide phase modulates the group of the reverse light pulse, the reverse light pulse transmitted through the first transmission waveguide and the reverse light pulse on the second transmission waveguide phase modulated meet and combine in the fourth waveguide beam splitter to generate interference cancellation, light intensity attenuation of the reverse light pulse is realized, and the attenuated reverse light pulse is sequentially fed back to the semiconductor laser through the second waveguide beam splitter and the first waveguide beam splitter.

After the light pulse transmitted from the first waveguide beam splitter to the second waveguide beam splitter is split, most of the light pulse is transmitted outside the optical chip, another small part of the light pulse (forward light pulse) is transmitted to the waveguide attenuator, the forward light pulse is input to the fourth waveguide beam splitter of the waveguide attenuator for splitting, one group of forward light pulses after splitting is input to the first transmission waveguide through the third upper port, the other group of reverse light pulses is input to the second transmission waveguide through the third lower port, the phase modulator on the second transmission waveguide carries out phase modulation on the group of forward light pulses, the forward light pulse transmitted through the first transmission waveguide and the forward light pulse on the second transmission waveguide subjected to phase modulation meet and combine in the third waveguide to generate interference cancellation, so that light intensity attenuation of the reverse light pulse is realized, and the attenuated forward light pulse sequentially passes through the waveguide filter and the first waveguide beam splitter for feedback injection to the semiconductor laser.

In another embodiment of the utility model, based on fig. 3, the optical frequency comb source further comprises a waveguide delay line integrated on the optical chip for delay processing of the received optical pulses, the time of transmitting the optical pulse subjected to delay processing to the semiconductor laser is consistent with the time of one optical pulse output by the semiconductor laser, and two ends of the waveguide delay line are respectively connected with the waveguide attenuator and the second lower port of the second waveguide beam splitter, as shown in fig. 5.

The time of injecting the reverse light pulse and the forward light pulse into the semiconductor laser through the delay action of the waveguide delay line is exactly consistent with the time of outputting the light pulse by the semiconductor laser. Specifically, the reverse light pulse is sequentially injected into the semiconductor laser through the waveguide filter, the waveguide attenuator, the waveguide delay line, the second waveguide beam splitter and the first waveguide beam splitter, the forward light pulse is sequentially injected into the semiconductor laser through the waveguide delay line, the waveguide attenuator, the waveguide filter and the first waveguide beam splitter, and the reverse light pulse and the forward light pulse are simultaneously injected into the semiconductor laser. By setting the waveguide delay line, the time from the injection of the light pulse to the arrival of the semiconductor laser corresponds to the time when the semiconductor laser outputs the light pulse.

In this application, the semiconductor laser is preferably a distributed feedback laser or a distributed Bragg reflection laser.

The semiconductor laser has the advantages of small volume, wide wavelength coverage, mature manufacturing process, convenient integration and the like. The semiconductor laser can generate ultrashort optical pulses when working in a gain switch mode, and further, the distributed feedback laser or the distributed Bragg reflection laser has a periodic ripple structure, has a selective effect on a mode, and can realize dynamic single longitudinal mode working. In the application, part of the light pulse generated by the semiconductor laser is processed and then fed back to be injected into the semiconductor laser, so that the self-injection of the light pulse is realized. The resonant cavity of the semiconductor laser has a plurality of oscillation modes and has a wide gain curve. When the self-injected light pulse returns to the resonant cavity of the semiconductor laser, the refractive index of the carrier and medium in the cavity is changed, the oscillation mode during free running is inhibited, the oscillation frequency is changed, the oscillation mode in the resonant cavity consistent with the self-injected light pulse is enhanced, other modes are inhibited due to the mode competition effect, and the laser light pulse is finally output in a single longitudinal mode state, so that the aim of injection locking is fulfilled.

Let the modulation frequency of the semiconductor laser be f ₂ The frequency of the light pulse passing through the waveguide filter is f ₁ . The output initial pulse is coupled to the optical chip, through transmission and processing on the optical chip, a part of initial pulse (self-injection optical pulse) is fed back and injected into the semiconductor laser, the semiconductor laser reaches the self-injection locking state under the injection locking of the self-injection optical pulse, the optical frequency comb pulse is output, each optical frequency comb pulse is generated in the following process by self-injection of the optical frequency comb pulse from the previous period, the formed optical frequency comb pulse spectrum is shown in figure 6, and the center frequency of the spectrum is shown by f ₁ The comb width of the frequency spectrum is determined by the modulation frequency f of the semiconductor laser ₂ And (5) determining.

In this application, the laser driver includes a dc source, an RF radio frequency signal source, and a bias device, the structure is shown in fig. 7, the dc source is used for generating a dc bias current, the RF radio frequency signal source is used for generating a sinusoidal driving signal, the bias device is composed of a feeding inductance and a blocking capacitance, the feeding inductance is connected with the dc source, the blocking capacitance is connected with the RF radio frequency signal source, and the dc bias current and the sinusoidal driving signal are injected into the semiconductor laser through the bias device.

The direct current bias current generated by the direct current source and the sine drive signal generated by the RF signal source are combined in the bias device and then injected into the semiconductor laser, so that the semiconductor laser is driven to periodically generate light pulses. The feed inductor in the bias device is used for adding direct current bias current to prevent sinusoidal driving signals generated by the RF radio frequency signal source from leaking into the direct current source system; the blocking capacitance within the bias is used to input a sinusoidal drive signal, while blocking bias current from being input to the RF radio frequency signal source.

In this application, in particular the MZ unequal arm interferometer filter is a single stage MZ unequal arm interferometer or is composed of a cascade of a plurality of MZ unequal arm interferometers.

The MZ unequal arm interferometer is composed of a first 3dB directional coupler, a transmission short arm, a transmission long arm and a second 3dB directional coupler which are connected, and the structure is shown in figure 8. When the light pulse is input from the port 1, the light pulse is divided into two groups of light signals with the same energy through the first 3dB directional coupler, the phase difference is pi/2, one group of light signals is transmitted along the transmission short arm, the other group of light signals is transmitted along the transmission long arm, the interference of the two groups of light signals at the port 3 is enhanced based on the phase difference brought by the two 3dB directional couplers and the path difference between the transmission short arm and the transmission long arm, the interference of the two groups of light signals at the port 4 is cancelled, according to the setting, the light frequency meeting the specific relation of the wavelength is output from the port 3, the light frequency meeting the specific relation of the other wavelength is output from the port 4, and the light frequency output from the port 4 is set to be abandoned, so that the filtering function is achieved.

In another embodiment, the MZ unequal arm interferometer type filter is composed of a cascade of a plurality of MZ unequal arm interferometers, the port 3 of the current MZ unequal arm interferometer is connected with the port 1 of the next MZ unequal arm interferometer, the structure is as shown in fig. 9, an interference effect is formed on each MZ unequal arm interferometer, and finally the cumulative interference effect achieves the filtering function.

In addition, the waveguide filter in the present application may also use a micro-ring resonator type optical filter, specifically, the micro-ring resonator type optical filter is composed of an annular waveguide and a coupling straight waveguide connected end to end, where the coupling straight waveguide receives an optical pulse and couples the optical pulse to the annular waveguide, and the structure is shown in fig. 10. The light pulse is coupled into the annular waveguide through the coupling straight waveguide, and is transmitted in the annular waveguide in an annular mode and causes resonance under certain conditions. When the phase of light at a specific wavelength around the annular waveguide is in a resonance state when the interference constructive condition is met, the light energy at the resonance state wavelength is balanced with the loss of the annular waveguide and is not output, and the light energy which does not meet the resonance state wavelength cannot store energy in the annular waveguide and is output from a port of the coupling straight waveguide, so that the filtering effect is achieved based on the performance of the micro-annular resonant cavity. In order to achieve better filtering effect, a plurality of micro-ring resonant cavity type optical filters can be cascaded, but the manufacturing difficulty is increased along with the increase of the cascade structure, so that the two-three cascade structure is preferable, and the spectrum modulation of the optical pulse is realized.

Based on the above explanation and illustration of the present application, a semiconductor laser is operated in gain-switching mode to output optical pulses under the action of a laser driver, and under the action of a waveguide beam splitter, and a small part of light pulse is fed back and injected into the semiconductor laser after filtering, attenuation and delay treatment, so that the self injection locking of the semiconductor laser and the generation of an effective optical frequency comb are realized. After filtering by the waveguide filter, the frequency of the optical signal which is automatically injected into the semiconductor laser is consistent with a certain frequency of the optical pulse which is automatically radiated and output by the semiconductor laser, the linewidth of the optical pulse which is output by the semiconductor laser based on the self-injected optical signal is greatly narrowed, and the phase noise of the optical pulse is effectively reduced. After the self-injection optical signal is fed back and injected into the semiconductor laser, each pulse output by the semiconductor laser is based on the self-injection locking effect instead of random spontaneous emission, so that the optical pulses output by the semiconductor laser have the same phase difference, clearer comb lines and distinguishable comb line intervals can be generated, and meanwhile, the comb tooth flatness and the coherence of the generated optical frequency comb are improved. In addition, the optical frequency comb source provided by the application can be realized based on a traditional semiconductor laser and a traditional silicon-based chip technology, and is easy to integrate on a chip.

Various embodiments in this specification are described in terms of steps that are performed in parallel or in a combination of steps that are performed in parallel, each embodiment is mainly described and is different from other embodiments, and the same similar parts among the embodiments are mutually referred.

It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Furthermore, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements, but also includes other elements not expressly listed or inherent to such article or apparatus. Without further limitation, the element defined by the statement "comprising one … …", it is not excluded that additional identical elements are present in an article or device comprising the above-mentioned elements.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The optical frequency comb source based on self injection locking is characterized by comprising a semiconductor laser, a laser driver, a first waveguide beam splitter, a second waveguide beam splitter and a waveguide filter, wherein the first waveguide beam splitter, the second waveguide beam splitter and the waveguide filter are integrated on one optical chip;

the semiconductor laser works in a gain switch mode and is used for outputting optical pulses, and the optical pulses are initial pulses or optical frequency comb pulses; the laser driver is connected with the semiconductor laser and used for driving the semiconductor laser; the first waveguide beam splitter is used for splitting the optical pulse output by the semiconductor laser, the optical pulse input by the second waveguide beam splitter or the optical pulse input by the waveguide filter, the waveguide filter is used for filtering the received optical pulse and transmitting the filtered optical pulse to the second waveguide beam splitter or the first waveguide beam splitter, and the second waveguide beam splitter is used for splitting the optical pulse input by the first waveguide beam splitter or the optical pulse input by the waveguide filter; the first waveguide beam splitter and the second waveguide beam splitter each comprise a first upper port, a second upper port, a first lower port and a second lower port, the first upper port of the first waveguide beam splitter is connected with the semiconductor laser, the first upper port of the second waveguide beam splitter is connected with the second upper port of the first waveguide beam splitter, and two ends of the waveguide filter are respectively connected with the second lower port of the first waveguide beam splitter and the second lower port of the second waveguide beam splitter.

2. The self-injection locking based optical frequency comb source of claim 1, wherein the splitting ratio of the first waveguide splitter and the splitting ratio of the second waveguide splitter are (90+n): (10-N), wherein N is a positive integer less than 10.

3. The self-injection locking based optical frequency comb source of claim 1, further comprising a waveguide attenuator integrated on the optical chip for attenuating the intensity of the received optical pulses, two ends of the waveguide attenuator being connected to the waveguide filter and the second lower port of the second waveguide splitter, respectively.

4. A self-injection locking based optical frequency comb source as claimed in claim 3, further comprising a waveguide delay line integrated on the optical chip for delay processing the received optical pulses so that the time of transmitting the delayed optical pulses to the semiconductor laser coincides with one of the optical pulses output by the semiconductor laser, wherein two ends of the waveguide delay line are respectively connected to the waveguide attenuator and the second lower port of the second waveguide beam splitter.

5. The optical frequency comb source based on self-injection locking according to claim 3, wherein the waveguide attenuator is composed of a third waveguide beam splitter, a first transmission waveguide, a second transmission waveguide, a fourth waveguide beam splitter and a phase modulator, the third waveguide beam splitter and the fourth waveguide beam splitter each comprise a third upper port and a third lower port, two ends of the first transmission waveguide are respectively connected with the third upper port of the third waveguide beam splitter and the third upper port of the fourth waveguide beam splitter, two ends of the second transmission waveguide are respectively connected with the third lower port of the third waveguide beam splitter and the third lower port of the fourth waveguide beam splitter, and the phase modulator is arranged on the second transmission waveguide.

6. A self-injection locking based optical frequency comb source as claimed in any of claims 1 to 5 wherein the semiconductor laser is a distributed feedback laser or a distributed bragg reflection laser.

7. A self-injection locking based optical frequency comb source as claimed in any one of claims 1 to 5 wherein the laser driver comprises a dc source for generating a dc bias current, an RF radio frequency signal source for generating a sinusoidal drive signal, and a biaser consisting of a feed inductance and a blocking capacitance, the feed inductance being connected to the dc source, the blocking capacitance being connected to the RF radio frequency signal source, the dc bias current and the sinusoidal drive signal being injected into the semiconductor laser through the biaser.

8. A self-injection locking based optical frequency comb source as claimed in any one of claims 1 to 5 wherein the waveguide filter is an MZ unequal arm interferometer type filter or a micro-ring resonator type optical filter.

9. The self-injection locking based optical frequency comb source of claim 8, wherein the MZ unequal arm interferometer filter is a single stage MZ unequal arm interferometer or is comprised of a cascade of MZ unequal arm interferometers.

10. The self-injection locking based optical frequency comb source of claim 8, wherein the micro-ring resonator type optical filter is comprised of an annular waveguide and a coupling straight waveguide connected end to end, the coupling straight waveguide receiving and coupling optical pulses to the annular waveguide.