阅读说明：本技术 一种半导体锁模激光器及锁模激光器调谐设置方法 (Semiconductor mode-locked laser and mode-locked laser tuning setting method ) 是由 张璟 于 2019-09-11 设计创作，主要内容包括：本发明公开了一种半导体锁模激光器,包括：第一反射器与第二反射器相对设置；饱和吸收体设置于第一反射器的一侧；半导体增益介质设置于饱和吸收体远离第一反射器的一侧；时延调制器设置于半导体增益介质远离饱和吸收体的一侧；第二反射器设置于时延调制器远离所述半导体增益介质的一侧。本发明还公开了一种半导体激光器的调谐方法。通过本发明提供的半导体锁模激光器及调谐方法,可在不影响锁模激光器正常工作情况下,改变腔体内部的有效光程,以输出重复频率可连续调谐的超窄光脉冲。(The invention discloses a semiconductor mode-locked laser, comprising: the first reflector and the second reflector are arranged oppositely; the saturated absorber is arranged on one side of the first reflector; the semiconductor gain medium is arranged on one side of the saturable absorber far away from the first reflector; the time delay modulator is arranged on one side of the semiconductor gain medium far away from the saturable absorber; the second reflector is arranged on one side of the time delay modulator, which is far away from the semiconductor gain medium. The invention also discloses a tuning method of the semiconductor laser. By the semiconductor mode-locked laser and the tuning method provided by the invention, the effective optical path in the cavity can be changed under the condition that the normal work of the mode-locked laser is not influenced, so that the ultra-narrow optical pulse with the continuously tunable repetition frequency can be output.)

1. A semiconductor mode-locked laser, comprising: the optical fiber amplifier comprises a first reflector, a second reflector, a saturable absorber, a semiconductor gain medium and a time delay modulator;

the saturable absorber is arranged on one side of the first reflector;

the semiconductor gain medium is arranged on one side, far away from the first reflector, of the saturable absorber;

the time delay modulator is arranged on one side, far away from the saturable absorber, of the semiconductor gain medium;

the second reflector is arranged on one side of the time delay modulator, which is far away from the semiconductor gain medium;

the first reflector is arranged opposite to the second reflector.

2. The semiconductor mode-locked laser of claim 1, wherein the delay modulator is comprised of a ring resonator combination and a phase shifter.

3. The semiconductor mode-locked laser according to any one of claims 1 to 2, wherein the first reflector is a total reflection mirror and the second reflector is a half reflection mirror.

4. The semiconductor mode-locked laser of claim 3, wherein the saturable absorber and the semiconductor gain medium are semiconductor amplifiers.

5. The semiconductor mode-locked laser of claim 2, wherein the coupling coefficient is [1,1,1,1 ] when]The time delay of the ring resonant cavity combination is the theoretical maximum value tau_max＝C_RR*n_effC; when the coupling coefficient is [0,0,0, 0%]Time delay is the theoretical minimum, τ_max＝L_S*n_effC, wherein C_RRIs the circumference of a ring-shaped resonant cavity, L_SIs the total length of the lower arm straight waveguide, n_effThe effective refractive index of the waveguide is, and c is the speed of light.

6. The semiconductor mode-locked laser of claim 3, wherein the half-mirror is an active distributed Bragg grating.

7. A tuning setting method of a semiconductor mode-locked laser is characterized in that a saturable absorber is arranged on one side of a first reflector;

arranging a semiconductor gain medium on one side of the saturable absorber far away from the first reflector;

a time delay modulator is arranged on one side of the semiconductor gain medium, which is far away from the saturable absorber;

and arranging a second reflector on one side of the time delay modulator, which is far away from the semiconductor gain medium.

8. The method of claim 7, wherein the time delay modulator is constructed using a ring resonator assembly and a phase shifter.

9. The method of claim 7, wherein the saturable absorber and the semiconductor gain medium are separately constructed using semiconductor amplifiers.

10. The method of tuning a semiconductor mode-locked laser according to any one of claims 7 to 9, wherein the second reflector is constructed using an active distributed bragg grating.

Technical Field

The invention relates to the field of semiconductor lasers, in particular to a semiconductor mode-locked laser and a mode-locked laser tuning setting method.

Background

A semiconductor mode-locking laser (also called a pulse laser), which refers to a multi-longitudinal mode with a random initial phase relationship in a laser cavity, and is adjusted to have a fixed phase difference by a technical means, so as to finally realize the output of a time sequence light pulse with ultra-narrow pulse width and high light intensity, and the frequency domain of the time sequence light pulse is represented as an optical frequency comb with a fixed mode interval. At present, the application range and application prospect of the laser are very wide, and the laser plays an important role in clock recovery, millimeter wave/terahertz signal generation, microwave signal processing and biomedical imaging in high-speed optical communication.

In the technical scheme of the existing laser, the effective optical distance of the laser oscillation cavity is a fixed value, so that the repetition frequency of the laser is a fixed value. This technical drawback limits the use of lasers in numerous scenarios, for example in the specific use of coupled-opto-electronic-oscillation-based microwave signal sources, the non-adjustability of the repetition rate results in the signal source being able to generate only a single-frequency microwave signal; in the optical frequency comb based on the frequency domain characteristic, the interval of the comb is a fixed value, so that only one-time or multi-frequency-multiplication optical frequency comb can be adopted, and the continuously adjustable performance cannot be realized. In addition, in a specific application requiring a precise pulse repetition frequency, due to process errors in the design and manufacture of semiconductor devices, the pulse repetition frequency cannot be accurately controlled to meet design requirements.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, it is an object of the present invention to provide a semiconductor mode-locked laser.

The technical scheme adopted by the invention is as follows:

in a first aspect, the present invention provides a semiconductor mode-locked laser, comprising: the optical fiber amplifier comprises a first reflector, a second reflector, a saturable absorber, a semiconductor gain medium and a time delay modulator;

the first reflector is arranged opposite to the second reflector;

the saturable absorber is arranged on one side of the first reflector;

the semiconductor gain medium is arranged on one side, far away from the first reflector, of the saturable absorber;

the time delay modulator is arranged on one side, far away from the saturable absorber, of the semiconductor gain medium;

the second reflector is arranged on one side of the time delay modulator, which is far away from the semiconductor gain medium.

Further, the time delay modulator is formed by a ring-shaped resonant cavity combination.

Further, the first reflector is a total reflection mirror, and the second reflector is a half reflection mirror.

Further, the saturable absorber and the semiconductor gain medium are semiconductor amplifiers.

Further, when the coupling coefficient is [1,1,1,1 ]]Time delay of the ring resonator is at theoretical maximum tau_max＝C_RR*n_effC; when the coupling coefficient is [0,0,0, 0%]Time delay is the theoretical minimum τ_max＝L_S*n_eff/c。

Further, the half mirror is an active distributed bragg grating.

To this end, a second object of the present invention is to provide a method of tuning a semiconductor laser.

In a second aspect, the present invention provides a tuning method of a semiconductor mode-locked laser, wherein a saturable absorber is disposed on one side of a first reflector;

arranging a semiconductor gain medium on one side of the saturable absorber far away from the first reflector;

a time delay modulator is arranged on one side of the semiconductor gain medium, which is far away from the saturable absorber;

and arranging a second reflector on one side of the time delay modulator, which is far away from the semiconductor gain medium.

Further, the time delay modulator is constructed by utilizing a ring resonator combination.

Further, the saturable absorber and the semiconductor gain medium are respectively constructed by using semiconductor amplifiers.

The invention has the beneficial effects that:

the invention introduces the time delay medium which can be continuously regulated and controlled into the cavity of the laser, so as to change the effective optical path in the cavity under the condition of not influencing the normal work of the laser, and output the ultra-narrow optical pulse with continuously tunable repetition frequency.

The continuous tunable of the pulse repetition frequency of the laser is realized by externally regulating and controlling a time delay medium in the cavity, and the limitation of the existing model in practical application is overcome.

Drawings

FIG. 1 is a block diagram of a semiconductor mode-locked laser system according to an embodiment of the present invention;

FIG. 2 is a block diagram of a semiconductor mode-locked laser system according to an embodiment of the present invention;

FIG. 3 is a time delay structure diagram of a multi-stage ring resonator according to an embodiment of the present invention;

FIG. 4 is a graph of laser output wavelength for an embodiment of the present invention;

FIG. 5 is a graph of the combined delay of the ring resonators according to the embodiment of the present invention;

FIG. 6 is a graph of an output signal versus pulse repetition frequency according to an embodiment of the present invention.

Description of reference numerals: 100. a semiconductor mode-locked laser; 200. a semiconductor mode-locked laser; 1. a first reflector; 2. a second reflector; 3. a saturable absorber; 4. a semiconductor gain medium; 5. a delay modulator; 10. a multimode interference reflector; 20. an active distributed Bragg grating; 30. a first semiconductor amplifier; 40. a second semiconductor amplifier; 51. combining annular resonant cavities; 52. a phase shifter; 511. a first phase shifter; 512. a second phase shifter.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

Referring to fig. 1, fig. 1 is a block diagram of a semiconductor mode-locked laser system according to an embodiment of the present invention. As shown in fig. 1, the semiconductor mode-locked laser system block includes: the device comprises a first reflector 1, a second reflector 2, a saturable absorber 3, a semiconductor gain medium 4 and a time delay modulator 5. The first reflector 1 and the second reflector 2 are arranged oppositely; the saturable absorber 3 is arranged on one side of the first reflector 1; the semiconductor gain medium 4 is arranged on one side of the saturable absorber 3 far away from the first reflector 1; the time delay modulator 5 is arranged on one side of the semiconductor gain medium 4 far away from the saturable absorber 3; the second reflector 2 is arranged on the side of the delay modulator 5 remote from the semiconductor gain medium 4.

Wherein, the first reflector 1 is a total reflector to be used as a cavity reflector; the half mirror of the second reflector 2 serves as a cavity mirror and also as a pulse output port. The first reflector 1 and the second reflector 2 are arranged oppositely to form a resonant cavity of the semiconductor mode-locked laser, and the saturable absorber 3, the semiconductor gain medium 4 and the time delay modulator 5 are respectively arranged in the cavity. When the semiconductor mode-locked laser 100 is operated, both the saturable absorber 3 and the semiconductor gain medium 4 interact to achieve the output of a pulse train. The pulse repetition frequency of the laser is controlled by controlling the time delay medium, and the repetition frequency of the pulse sequence and the time delay in the resonant cavity of the semiconductor laser 100 are in a reciprocal relationship.

Under the condition that the semiconductor mode-locked laser 100 generates large light intensity, the loss of the laser in the resonant cavity caused by the saturable absorber 3 is small; in the case where the semiconductor laser generates a small light intensity, the loss of the laser light in the resonant cavity by the saturable absorber 3 is large. By modulating the loss (Q value) in the laser cavity and pulsing to produce pulse widths on the order of nanoseconds or even tens of picoseconds.

In the initial working state of the semiconductor mode-locked laser 100, the noise fluctuation generated by the semiconductor gain medium 4 is continuously amplified in the resonant cavity, the power loss caused by the saturable absorber 2 is compensated by one of the noise peaks with the maximum power, the loss of other low-power noise in the resonant cavity is greater than the gain, and the power gradually declines to 0 in the oscillation process. When the only noise peak is continuously amplified by the semiconductor gain medium 4, and the saturation power of the saturable absorber 3 is reached, the carriers in the saturable absorber are excited to move from the valence band to the conduction band, the saturable absorber 3 is in a transparent state, and the loss is reduced. In this state, the optical power in the resonant cavity increases sharply to reach the saturation power of the semiconductor gain medium 4, and its gain decreases continuously and is quickly lower than the losses in the cavity. After a period of time, the intensity of light decreases and the saturable absorber and gain medium return to normal, since the loss is greater than the gain. In the above process, the saturable absorber 3 and the semiconductor gain medium 4 gradually undergo slow saturable absorption and form a net gain, and an optical pulse train is generated.

When the semiconductor mode-locked laser 100 works stably, the repetition frequency of the generated pulse and the round-trip time in the cavity of the semiconductor mode-locked laser are in a reciprocal relation, and the pulse repetition frequency can be regulated and controlled by regulating and controlling the time delay modulator 5 in the resonant cavity of the laser 100. In the regulation and control schemes of the plurality of delay modulators 5, the multi-stage cascaded filter is widely applied to all-optical signal processing due to the large delay regulation and control range and strong reconfigurability. The Z variation of the filter frequency response of the multistage cascade can be expressed as:

referring to fig. 2, fig. 2 is a structural diagram of a semiconductor mode-locked laser system according to an embodiment of the present invention. As shown in fig. 2, the first reflector 1 is a multimode interference reflector 10, whose reflectivity is 100%; the second reflector 2 is an active distributed Bragg grating (DBR) 20, and the coupling strength is 50cm^-1Length of L_DBRThe reflectivity is 50-60% when the particle size is 200 mu m. A resonant cavity of the semiconductor mode-locked laser 200 is formed by oppositely disposing the first reflector 1 and the second reflector 2. Different current values are set through the outside to regulate and control the second reflector 2 so as to select different filtering center wavelengths, thereby regulating and controlling the output wavelength of the semiconductor laser.

Under the action of the reverse bias voltage, the first semiconductor amplifier 30 is used as a saturable absorber 3 to modulate the loss in the resonant cavity of the semiconductor mode-locked laser 200 and emit a pulse, and the pulse width generated is in the order of several nanoseconds or even tens of picoseconds. The second semiconductor amplifier 40 is used as a semiconductor gain medium 4 under the action of the injected current to provide gain to the semiconductor laser 200 and to achieve stimulated emission amplification with population inversion and light generation. Wherein the first semiconductor amplifier 30 has a length of 100 μm and the second semiconductor amplifier 30 has a length of 1000 μm. The phase shifter 52 (PS) is an active waveguide with a length of 130 μm, and can inject different current values and cooperate with an active distributed bragg grating, so that the output wavelength of the mode-locked laser can be adjusted in a large range and with high precision.

The time delay reconfigurable ring resonator combination 51 is a 4-stage cascaded ring resonator to construct a flat time delay all-pass filter with continuous tuning. Wherein the circumference of the ring-shaped resonant cavity is C_RRThe total length of the lower arm straight waveguide is L_SThe effective refractive index of the waveguide being n_effAnd c is the speed of light. Selecting a suitable coupling coefficient [ kappa ]₁,κ₂,κ₃,κ₄]And relative phase

In combination, continuous tunability of flat time delay within a certain range can be realized. The tunable range is determined by the annular cavity length. Two limit cases: when the coupling coefficient is [1,1,1,1 ]]Time delay of the ring resonator is at theoretical maximum tau_max＝C_RR*n_effC; when the coupling coefficient is [0,0,0, 0%]When the optical signal passes through the straight waveguide of the lower arm only, the time delay is the theoretical minimum value tau_max＝L_S*n_eff/c。

For example, a reverse bias voltage of-0.7 to-0.8V is set on the first semiconductor amplifier 20 so that it exhibits the operation characteristic of a saturated absorber and absorbs light in the wavelength range from visible light to mid-infrared light; the second semiconductor amplifier 30 is injected with a current to exhibit the operating characteristics of the gain medium, the operating threshold of the semiconductor laser 200 is 25 to 30mA, and the stable state operating current is 50 to 90mA of the threshold.

The optical signal excited by the semiconductor mode-locked laser 200 is a wide-spectrum multi-longitudinal-mode signal, and the wavelength adjustment and control process is a process of selecting different modes. The effective refractive index can be continuously regulated by changing the value of the injection current on the active distributed bragg grating 20, so that the central wavelength of the grating can be continuously regulated. Linear fine tuning of the oscillation time in the resonant cavity is achieved by injecting a current into the phase shifter 52 in the cavity to change its effective refractive index. The central wavelength of the optical frequency comb in the frequency domain can be accurately adjusted within a certain range by simultaneously regulating the active distributed bragg grating 20 and the phase shifter 52. The time delay reconfigurable ring resonator combination 51 constitutes an all-pass filter with a continuously tunable flat time delay whose magnitude and amplitude response are controlled by the coupling coefficient and relative phase.

Since the refractive indexes of the active distributed bragg grating 20 and the phase shifter 52 are both increased after the current is injected, the semiconductor laser 200 only undergoes a blue shift as the injection current is increased, that is, the frequency of the light emitted from the semiconductor laser 200 shifts to the blue end of the electromagnetic spectrum.

In other embodiments, the center wavelength may be tunable by adjusting the coupling coefficients and relative phases of the ring resonators.

In other embodiments, a laser resonator can be constructed by using a large bandwidth multimode interference mirror instead of the active distributed bragg grating 20 on the right end as a half mirror, which can narrow the pulse width of the pulse in the time domain and enlarge the spectral width of the generated optical frequency comb in the frequency domain, including more combs, and the center wavelength of the semiconductor laser 200 is a fixed value.

In other embodiments, the time delay modulator 5 is replaced by introducing a fabry-perot cavity (F-P cavity) or a one-dimensional photonic crystal in the linear cavity of the semiconductor laser 200. The Fabry-Perot cavity is arranged to introduce an oscillation cavity into the semiconductor laser, so that the modulatable time delay is provided; by arranging the one-dimensional photonic crystal to introduce an adjustable time delay medium such as a Bragg waveguide grating into the semiconductor laser, and injecting current from the outside, dispersion can be continuously adjusted and controlled, so that the time delay of a grating group is changed, and continuous adjustability of pulse repetition frequency is realized.

Referring to fig. 3, fig. 3 is a time delay structure diagram of a multi-level ring resonator according to an embodiment of the invention. As shown in fig. 3, each ring resonator is of a single-arm type, the coupling portion is a closed ring resonator formed by connecting two 2X2 symmetric Mach-zehnder interferometers (MZIs), the left and right ports of the upper arm are connected, the cavity includes a tunable first phase shifter 511, and injection is controlled to form a closed ring resonatorCurrent controlling relative phase shift of each ring resonator

The lower arm is a straight waveguide part and comprises a tunable phase shifter 512, and the coupling coefficient is tuned within the range of 0-1 by controlling the injection current of the waveguide. Thus, the Z variation of the frequency response of the N-order ring resonator can be expressed as:

wherein

For relative phase shift, k_nIs the coupling coefficient.

The frequency response of the frequency response can be defined by z-exp (-j2 pi f/f)_FSR) Obtained as exp (-j2 π v), f_FSRIs the free spectral range of the ring laser and v is the normalized frequency. The time delay of the ring resonator cascaded in multiple stages can be obtained by superposing the time delay of each stage, and the total time delay tau (v) of unit ring length can be expressed as:

referring to fig. 4, fig. 4 is a graph of an output wavelength of a mode-locked laser according to an embodiment of the present invention. As shown in FIG. 4, the coupling coefficient combination [ kappa ] is set by setting the ring resonator₁,κ₂,κ₃,κ₄]The combination of the relative phases isIn the form, different time delays are set with different parameters. By changing the time delay, the oscillation time of the laser cavity is continuously tuned, and further the pulse repetition frequency is continuously tuned.

As shown in fig. 4, when the current values on the active distributed bragg gratings 20 are set to 0mA, 1mA, and 2mA, respectively, the semiconductor laser 200 has center wavelengths of 1543.8nm, 1542.9nm, and 1541.2nm, respectively. When the three current values are set for the active distributed bragg grating, the central wavelength at which the semiconductor laser 200 operates is shifted by a small amount of about 0.1nm when the injection current of the phase shifter 52 is 0.5 mA.

Referring to fig. 5, fig. 5 is a graph illustrating a combined delay time of a ring resonator according to an embodiment of the invention. As shown in fig. 5, the ordinate is the group delay and the abscissa is the free spectral range. The pulse signal output by the semiconductor laser is detected by using the photoelectric detector, and as can be seen from the figure, the pulse repetition frequency is different under different time delays for a single frequency signal (pulse repetition frequency) on a frequency domain.

Referring to fig. 6, fig. 6 is a graph illustrating an output signal and a pulse repetition frequency according to an embodiment of the invention. As shown in fig. 6, the ordinate is the output power, and the abscissa is the free spectral range. As can be seen from the figure, the frequency spectrum of the single frequency multiplication (pulse repetition frequency) of the output signal corresponds to different pulse repetition frequencies under different time delays.

In summary, different types of implementation schemes of the mode-locked laser can be selected for specific implementation according to different advantages of the mode-locked laser in high repetition frequency, ultra-narrow bandwidth, time jitter stability and the like. The mode-locked laser designed by the embodiment is mainly used for the specific implementation of the generation and processing of microwave signals, and a passive laser is selected as a design scheme. Passive lasers are used as optical signal sources, and have many applications in photonic generation and processing of microwave signals, and typical schemes are as follows: microwave signal generation based on a coupled photoelectric oscillation system, ranging based on time domain pulse characteristics and optical frequency comb generation based on frequency domain broad spectrum characteristics.

The embodiment of the invention also provides a tuning setting method of the semiconductor mode-locked laser, wherein a saturable absorber 3 is arranged on one side of the first reflector 1; a semiconductor gain medium 4 is arranged on the side of the saturable absorber 3 far away from the first reflector 1; a time delay modulator 5 is arranged on one side of the semiconductor gain medium 4 far away from the saturable absorber 3; a second reflector 2 is arranged on one side of the time delay modulator 5 far away from the semiconductor gain medium 4; constructing a time delay modulator 5 by utilizing the ring resonant cavity combination and the phase shifter; the saturable absorber 3 and the semiconductor gain medium 4 are respectively constructed by a semiconductor amplifier, and the second reflector 2 is constructed by a sub-active distributed bragg grating 20.

The first reflector 1 and the second reflector 2 are oppositely arranged to form a resonant cavity, and the first reflector 1 is a total reflector and is used as a cavity reflector; the half mirror of the second reflector 2 serves as a pulse output port. The first reflector 1 and the second reflector 2 are arranged oppositely to form a resonant cavity of the semiconductor mode-locked laser, and the saturable absorber 3, the semiconductor gain medium 4 and the time delay modulator 5 are respectively arranged in the cavity. When the semiconductor laser 100 is operated, both the saturable absorber 3 and the semiconductor gain medium 4 interact to achieve an output of a pulse train. The pulse repetition frequency of the laser is controlled by controlling the time delay medium, and the repetition frequency of the pulse sequence and the time delay in the resonant cavity of the semiconductor laser 100 are in a reciprocal relationship.

When the semiconductor mode-locked laser 100 is operating stably, the repetition frequency of the generated pulse is inverse to the round-trip time in the cavity_R＝1/T_RThe pulse repetition frequency can be regulated and controlled by regulating and controlling the time delay modulator 5 in the resonant cavity of the cavity 100 of the semiconductor laser. In the regulation and control schemes of the plurality of delay modulators 5, the multi-stage cascaded filter is widely applied to all-optical signal processing due to the large delay regulation and control range and strong reconfigurability. The Z variation of the filter frequency response of the multistage cascade can be expressed as:

referring again to fig. 2, a 4-stage cascaded ring resonator is used as the ring resonator combination 51 to construct a flat time-delay all-pass filter with continuous tuning. Wherein the circumference of the ring-shaped resonant cavity is C_RRThe total length of the lower arm straight waveguide is L_SThe effective refractive index of the waveguide being n_eff. Selecting a suitable coupling coefficient k₁,k₂,k₃,k₄]And relative phase

In combination, continuous tunability of flat time delay within a certain range can be realized. The tunable range is determined by the annular cavity length. Two limit cases: when the coupling coefficient is [1,1,1,1 ]]Time delay of the ring resonator is at theoretical maximum tau_max＝C_RR*n_effC; when the coupling coefficient is [0,0,0, 0%]When the optical signal passes through the straight waveguide of the lower arm only, the time delay is the theoretical minimum value tau_max＝L_S*n_eff/c。

Referring to fig. 3, each ring resonator of the ring resonator assembly is a single-arm type, the coupling portion is a closed ring resonator formed by two 2X2 symmetric Mach-Zehnder interferometers (MZIs), the left and right ports of the upper arm are connected, the cavity includes a tunable phase shifter, and the relative phase shift of each ring resonator is controlled by controlling the injection current

The lower arm is a straight waveguide part and comprises a tunable phase shifter, and the coupling coefficient is tuned within the range of 0-1 by controlling the injection current of the waveguide. Thus, the Z variation of the frequency response of the N-order ring resonator can be expressed as:

the frequency response of the frequency response can be defined by z-exp (-j2 pi f/f)_FSR) Obtained as exp (-j2 π v), f_FSRIs the free spectral range of the ring laser and v is the normalized frequency. The time delay of the ring resonator cascaded in multiple stages can be obtained by superposing the time delay of each stage, and the total time delay tau (v) of unit ring length can be expressed as:

the optical signal excited by the semiconductor mode-locked laser 100 is a wide-spectrum multi-longitudinal-mode signal, and the wavelength adjustment process is a process of selecting different modes. The effective refractive index can be continuously regulated by changing the value of the injection current on the active distributed bragg grating 20, so that the central wavelength of the grating can be continuously regulated. Linear fine tuning of the resonant cavity oscillation time is achieved by injecting a current into the phase shifter 52 within the resonant cavity to change its effective index. The central wavelength of the optical frequency comb in the frequency domain can be accurately adjusted within a certain range by simultaneously regulating the active distributed bragg grating 20 and the phase shifter 52. The annular resonant cavities with reconfigurable time delay are combined to form an all-pass filter, the all-pass filter has continuously tunable flat time delay, and the size and the amplitude response of the time delay are controlled by a coupling coefficient and a relative phase.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.