Mode-locked laser and driving method thereof

Abstract

The present invention relates to the field of semiconductor optoelectronic technology, and provides a mode-locked laser and a driving method thereof, wherein the mode-locked laser comprises: a saturated absorber, an input end waveguide region, a multimode interference coupler, and a plurality of reflection arms of different lengths, each reflection arm comprising an output end waveguide region, a phase control region, and a multimode interference reflector arranged in sequence; wherein the saturated absorber is arranged on one side of the input end waveguide region, the other side of the input end waveguide region is arranged at the input end of the multimode interference coupler, a plurality of output end waveguide regions of different lengths are respectively arranged at a plurality of output ends of the multimode interference coupler, a plurality of reflection arms of different lengths respectively form a plurality of sub-resonant cavities of different cavity lengths with the end face of the saturated absorber, and the sub-resonant cavities of different cavity lengths correspond to different repetition frequencies of mode-locked pulses. The present invention can effectively reduce the nonlinear effect in the pulse evolution process, and realize the output of high-power mode-locked pulses with switchable multiple repetition frequencies.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronic technology, and in particular to a mode-locked laser and a driving method thereof. Background Art

[0002] Ultrashort pulse light sources have important applications in systems such as optical analog-to-digital conversion (ADC), optical fiber communication, and optically generated terahertz wave communication. Mode locking technology is a common method for generating ultrashort pulses. Semiconductor mode-locked lasers are an integrable pulse light source. Since the cavity length of semiconductor mode-locked lasers is shorter than that of solid-state and fiber lasers, they can generate short pulses with a repetition rate of several GHz to hundreds of GHz, and the pulse width can reach the picosecond level. At the same time, they have the advantages of high integration, compact structure, low cost, and easy mass production.

[0003] Traditional mode-locked lasers include a gain region and a saturated absorption (SA) region. The gain region provides the energy required for lasing, and the SA region acts as a switch gate related to light intensity to achieve pulse output. The repetition frequency of the pulse is inversely proportional to the cavity length. The shorter the cavity length, the higher the repetition frequency. However, as the cavity length shortens, the laser distributed mirror loss increases, the threshold is higher, the heat dissipation becomes worse, and it is more susceptible to the Auger effect under high current, and the saturated output power is generally lower.

[0004] With the development of THz technology and ultra-high-speed optical sampling technology, the system has an increasingly strong demand for ultra-high repetition rate light sources, and at the same time, the requirements for pulse power are also getting higher and higher. However, there is a structural contradiction between high repetition rate and high power output for traditional mode-locked lasers. One way to solve this problem is to use collision mode locking. The basic principle is to set the SA zone between two gain zones. When the SA is located at 1 / N of the entire cavity length, a collision mode-locked pulse output N times the fundamental frequency can be formed in the resonant cavity. For example, when N=2, a 2-fold frequency-locked output can be achieved. When N=3, a 3-fold frequency-locked output can be formed. This structure can achieve high repetition rate output with a relatively long cavity length. However, the collision mode-locked structure is a single-mode resonant cavity, and the operating frequency is also fixed, making it difficult to achieve multiple repetition rate outputs.

[0005] In addition, the collision-locked mode laser uses a single-mode waveguide structure, and the energy storage in the resonant cavity is low, which is not conducive to high peak energy output. In order to further increase the saturation power of the collision-locked mode laser, it is necessary to increase the volume of the active region. The usual way is to increase the thickness of the resonant cavity to expand the mode field volume in the resonant cavity. However, this method can only increase the volume of the resonant cavity to a limited extent, resulting in a limited increase in the output power of the collision-locked mode laser. Summary of the invention

[0006] The present invention provides a mode-locked laser and a driving method thereof, which are used to solve the defects that a mode-locked laser with a collision mode-locked structure in the prior art is difficult to output multiple repetition frequencies, and the output power of the collision mode-locked laser is limited due to the limited increase in the volume of the resonant cavity. The present invention can effectively reduce the nonlinear effect in the pulse evolution process and realize high-power mode-locked pulse output with switchable multiple repetition frequencies.

[0007] A mode-locked laser provided by the present invention comprises: a saturated absorber, an input end waveguide region, a multimode interference coupler and a plurality of reflection arms of different lengths, each of the reflection arms comprising an output end waveguide region, a phase control region and a multimode interference reflection mirror arranged in sequence;

[0008] The saturated absorber is arranged on one side of the input end waveguide region, the other side of the input end waveguide region is arranged at the input end of the multimode interference coupler, a plurality of output end waveguide regions of different lengths are respectively arranged at a plurality of output ends of the multimode interference coupler, and the plurality of reflection arms of different lengths respectively form a plurality of sub-resonant cavities of different cavity lengths with the end face of the saturated absorber, and the sub-resonant cavities of different cavity lengths correspond to different repetition frequencies of mode-locked pulses.

[0009] According to a mode-locked laser provided by the present invention, the saturated absorber, the input end waveguide region, the multimode interference coupler, the output end waveguide region, the phase control region and the multimode interference reflector are integrated on the same substrate.

[0010] According to a mode-locked laser provided by the present invention, the saturated absorber, the input end waveguide region, the multimode interference coupler, the output end waveguide region, the phase control region and the multimode interference reflector are all active structures, and have the same material growth structure.

[0011] According to a mode-locked laser provided by the present invention, the material growth structure comprises, from bottom to top, a substrate, a buffer layer, a lower confinement layer, a quantum well layer, an upper confinement layer, an upper cap layer and an ohmic contact layer.

[0012] According to a mode-locked laser provided by the present invention, the substrate is an N-type semiconductor substrate, the buffer layer is an N-type semiconductor buffer layer, the upper cover layer is a P-type semiconductor upper cover layer, and the ohmic contact layer is a P-type semiconductor contact layer.

[0013] According to a mode-locked laser provided by the present invention, the saturated absorber, the input end waveguide region, the multimode interference coupler, the output end waveguide region, the phase control region and the electrode layer of the multimode interference reflector are all arranged on the ohmic contact layer.

[0014] According to a mode-locked laser provided by the present invention, a first electrical isolation groove is provided between the electrode layer of the saturated absorber and the electrode layer of the input end waveguide region, and a second electrical isolation groove is provided between the output end of the multimode interference coupler and the electrode layer of the output end waveguide region, and the first electrical isolation groove and the second electrical isolation groove are both obtained by selectively etching the ohmic contact layer using a selective wet etching process.

[0015] According to a mode-locked laser provided by the present invention, the electrode layer of the input-end waveguide region is connected to the electrode layer of the multimode interference coupler.

[0016] The present invention also provides a driving method for any one of the above-mentioned mode-locked lasers, comprising:

[0017] Applying current to one or more of the output end waveguide regions, the phase control region, and the electrode layers of the multi-mode interference reflector to select one or more sub-resonant cavities;

[0018] Aligning the cavity mode positions of the one or more sub-resonant cavities by finely adjusting the current applied to the phase control region of the one or more sub-resonant cavities in combination with the vernier effect;

[0019] A reverse bias voltage or an external modulation signal is applied to the saturated absorber to make the mode-locked laser work in a mode-locked state, thereby outputting mode-locked pulses with a corresponding repetition frequency.

[0020] The mode-locked laser provided by the present invention comprises: a saturated absorber, an input end waveguide region, a multimode interference coupler and a plurality of reflection arms of different lengths, each reflection arm comprising an output end waveguide region, a phase control region and a multimode interference reflector arranged in sequence; wherein the saturated absorber is arranged on one side of the input end waveguide region, the other side of the input end waveguide region is arranged at the input end of the multimode interference coupler, and a plurality of output end waveguide regions of different lengths are respectively arranged at a plurality of output ends of the multimode interference coupler. On the one hand, the larger cavity structure of the multimode interference coupler is utilized to improve the energy storage capacity and heat dissipation capacity of the cavity of the mode-locked laser, and to increase the saturation energy to reduce the influence of self-phase modulation, thereby effectively improving the output power of the mode-locked laser; on the other hand, a plurality of reflection arms of different lengths respectively form a plurality of sub-resonant cavities of different cavity lengths with the end face of the saturated absorber, and the sub-resonant cavities of different cavity lengths correspond to different mode-locked pulse repetition frequencies, and the mode-locked pulses of the corresponding repetition frequencies can be output by selecting one or more sub-resonant cavities. Therefore, the present invention can effectively reduce the nonlinear effect in the pulse evolution process, and realize the output of high-power mode-locked pulses with switchable repetition frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a schematic diagram of the structure of the mode-locked laser provided by the present invention;

[0023] Figure 2 is a schematic diagram of the material growth structure of the mode-locked laser provided by the present invention;

[0024] Figure 3 It is a schematic structural diagram of the electrode layer and isolation trench of the mode-locked laser provided by the present invention;

[0025] Figure 4 It is a schematic flow chart of the driving method of the mode-locked laser provided by the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Combine the following Figures 1 to 3 The mode-locked laser of the present invention is described.

[0028] Please refer to Figure 1 , Figure 1 Schematic diagram of the structure of the mode-locked laser provided by the present invention. Figure 1 As shown, the mode-locked laser includes: a saturated absorber 1, an input end waveguide region 2, a multimode interference coupler 3, and a plurality of reflection arms of different lengths. Each reflection arm includes an output end waveguide region 4, a phase control region 5, and a multimode interference reflector 6 arranged in sequence. The saturated absorber 1 is arranged on one side of the input end waveguide region 2, the other side of the input end waveguide region 2 is arranged at the input end of the multimode interference coupler 3, and a plurality of output end waveguide regions 4 of different lengths are respectively arranged at a plurality of output ends of the multimode interference coupler 3.

[0029] The multimode interference reflector 6 can form the reflective end face required for laser resonance. Multiple multimode interference reflectors 6 and the saturated absorber 1 together constitute a resonant cavity. Multiple reflective arms of different lengths respectively constitute multiple sub-resonant cavities with different cavity lengths with the end face of the saturated absorber. The sub-resonant cavities with different cavity lengths correspond to different repetition frequencies of the mode-locked pulse.

[0030] The light reflected by different ports of the multimode coupling reflector 6 is coupled into the reverse-biased saturated absorber 1 through the multimode interference coupler 3, so as to form sub-resonant cavities with different cavity lengths.

[0031] The multimode interference coupler 3 can generate optical gain under the excitation of the driving current. The multimode interference coupler 3 has multiple ports, the input port is provided with an input end waveguide area 2, and the multiple output ports are respectively provided with multiple output end waveguide areas 4 of different lengths. The input light is distributed to multiple output single-mode waveguide outputs by using the self-image effect, that is, the input light is divided into multiple equal-intensity single-mode outputs. The multimode interference coupler 3 can increase the volume of the resonant cavity, and use the larger cavity structure of the multimode interference coupler to improve the energy storage capacity and heat dissipation capacity of the mode-locked laser cavity, and increase the saturation energy to reduce the influence of self-phase modulation, thereby effectively improving the output power of the mode-locked laser.

[0032] Under the action of the reverse bias voltage, the saturated absorber 1 can produce saturated absorption of the laser in the resonant cavity to form a pulse output. That is, the saturated absorber 1 can achieve passive mode-locked pulse output under the action of the reverse bias voltage. The saturated absorber 1 can also achieve hybrid mode-locking when an external modulation signal is applied.

[0033] The fine-tuning phase control zone 5 is used to fine-tune the cavity length of the sub-resonant cavity. By fine-tuning the current applied by the phase control zone 5, the cavity membrane position of the sub-resonant cavity is adjusted, and the cavity length of the sub-resonant cavity can be fine-tuned. Combined with the vernier effect, the position alignment of the cavity modes commonly supported in multiple sub-resonant cavities can be achieved. A reverse bias voltage or an external modulation signal is applied to the saturated absorber 1 to make the saturated absorber 1 operate in the saturated absorption mode. At this time, the saturated absorber 1 has a stronger saturation absorption effect on the mode commonly supported by the sub-resonant cavity, that is, it has a higher transmittance to the peak of the commonly supported light mode, and has a stronger absorption for other misaligned modes, so that the entire structure only supports the locking of the aligned mode, that is, the mode-locked laser operates in a mode-locked state, thereby achieving a high-power mode-locked pulse output with a higher repetition rate.

[0034] When a sub-resonant cavity works alone, a mode-locked pulse output corresponding to the repetition frequency of the sub-resonant cavity can be output. When more than two sub-resonant cavities work simultaneously, the pulse repetition frequency is determined by the lowest common multiple of the repetition frequencies of the multiple sub-resonant cavities. In a specific implementation, the number of sub-resonant cavities can be increased by increasing the number of reflection arms of different lengths. The number of sub-resonant cavities working simultaneously is controlled by whether current is applied. By switching the combination of sub-resonant cavities working simultaneously, a mode-locked pulse output with switchable repetition frequencies can be achieved.

[0035] In this embodiment, on the one hand, the larger cavity structure of the multimode interference coupler is used to improve the energy storage capacity and heat dissipation capacity of the mode-locked laser cavity, and the saturation energy is increased to reduce the influence of self-phase modulation, thereby effectively improving the output power of the mode-locked laser; on the other hand, multiple reflection arms of different lengths respectively form multiple sub-resonant cavities with different cavity lengths with the end face of the saturated absorber. The sub-resonant cavities with different cavity lengths correspond to different mode-locked pulse repetition frequencies, and one or more sub-resonant cavities can be selected to output mode-locked pulses with corresponding repetition frequencies. Therefore, this embodiment can effectively reduce the nonlinear effect in the pulse evolution process and realize high-power mode-locked pulse output with switchable multiple repetition frequencies.

[0036] Optionally, the saturated absorber 1, the input end waveguide region 2, the multimode interference coupler 3, the output end waveguide region 4, the phase control region 5 and the multimode interference reflector 6 are integrated on the same substrate.

[0037] Specifically, the saturated absorber 1, the input end waveguide region 2, the multimode interference coupler 3, the output end waveguide region 4, the phase control region 5 and the multimode interference reflector 6 can be integrated on the same substrate through dry etching and butt-joint growth processes.

[0038] The mode-locked laser can operate in the communication band of 1.5μm or 1.3μm. It can also operate in any other band besides the communication band of 1.5μm and 1.3μm by adjusting the semiconductor gain material of the mode-locked laser.

[0039] In this embodiment, the saturated absorber, input waveguide region, multimode interference coupler, output waveguide region, phase control region and multimode interference reflector are integrated on the same substrate, which can eliminate the coupling loss between discrete devices and reduce packaging complexity.

[0040] Optionally, the saturated absorber 1, the input end waveguide region 2, the multimode interference coupler 3, the output end waveguide region 4, the phase control region 5 and the multimode interference reflector 6 are all active structures, and have the same material growth structure.

[0041] Wherein, optionally, Figure 2As shown, the material growth structure includes from bottom to top: substrate 7, buffer layer 8, lower confinement layer 9, quantum well layer 10, upper confinement layer 11, upper cap layer 12 and ohmic contact layer 13. This embodiment is not limited thereto, and other material growth structures may also be used.

[0042] Optionally, the substrate 7 is an N-type semiconductor substrate, for example, an n-InP substrate, or a substrate of other semiconductor materials; the buffer layer 8 is an N-type semiconductor buffer layer, for example, an n-InP buffer layer, or a buffer layer of other semiconductor materials; the upper cover layer 12 is a P-type semiconductor upper cover layer, for example, a p-InP upper cover layer, or an upper cover layer of other semiconductor materials; the ohmic contact layer 13 is a P-type semiconductor contact layer, for example, a p-InGaAs contact layer, or a contact layer of other semiconductor materials.

[0043] In this embodiment, when the input end waveguide region, the multimode interference coupler, the output end waveguide region and the multimode interference reflector are active structures, optical gain can be generated under the excitation of a driving current.

[0044] Alternatively, if Figure 3 As shown, the electrode layers of the saturated absorber 1 , the input end waveguide region 2 , the multimode interference coupler 3 , the output end waveguide region 4 , the phase control region 5 and the multimode interference reflector 6 are all arranged on the ohmic contact layer 13 .

[0045] Among them, the electrode layer 14 is the electrode layer of the saturated absorber 1, the electrode layer 16 is the electrode layer of the output end waveguide area 4, the electrode layer 17 is the electrode layer of the phase control area 5, and the electrode layer 18 is the electrode layer of the multimode interference reflector 6. Optionally, the electrode layer of the input end waveguide area 2 is connected to the electrode layer of the multimode interference coupler 3, that is, the electrode layer 15 is the electrode layer of the input end waveguide area 2 and the multimode interference coupler 3.

[0046] Alternatively, if Figure 3 As shown, a first electrical isolation groove 19 is provided between the electrode layer 14 of the saturated absorber 1 and the electrode layer 15 of the input end waveguide region 2, and a second electrical isolation groove 20 is provided between the output end of the multimode interference coupler 3 and the electrode layer 16 of the output end waveguide region 4. Both the first electrical isolation groove 19 and the second electrical isolation groove 20 are obtained by selectively etching the ohmic contact layer using a selective wet etching process.

[0047] In this embodiment, appropriate current is applied to the electrode layer 15 and the electrode layers of any two reflection arms (i.e., electrode layer 16, electrode layer 17, and electrode layer 18) so that the optical gain in the resonant cavity of the mode-locked laser is greater than the loss in the resonant cavity, thereby providing the gain required for mode locking.

[0048] Based on any one of the mode-locked lasers provided in the above embodiments, a driving method of the mode-locked laser is described in detail below.

[0049] Please refer to Figure 4 , Figure 4 FIG. 1 is a flow chart of a method for driving a mode-locked laser provided by the present invention. Figure 4 As shown, the driving method of the mode-locked laser provided by the present invention may include the following steps:

[0050] Step 401, applying current to one or more output end waveguide regions, phase control regions and electrode layers of a multi-mode interference reflector to select one or more sub-resonant cavities;

[0051] Step 402, aligning the cavity mode positions of one or more sub-resonant cavities by fine-tuning the current applied to the phase control region of one or more sub-resonant cavities and combining the vernier effect;

[0052] Step 403: Apply a reverse bias voltage or an external modulation signal to the saturated absorber to make the mode-locked laser work in a mode-locked state, thereby outputting mode-locked pulses with a corresponding repetition frequency.

[0053] In step 401, in the mode-locked laser, a plurality of multimode interference mirrors 6 and a saturated absorber 1 together form a resonant cavity, and a plurality of reflection arms of different lengths respectively form a plurality of sub-resonant cavities with different cavity lengths with the end face of the saturated absorber. Current is applied to one or more output end waveguide regions, phase control regions, and electrode layers of the multimode interference mirrors, and one or more sub-resonant cavities to be operated can be selected from the plurality of sub-resonant cavities with different cavity lengths.

[0054] For example, if current is applied to the waveguide region, the phase control region, and the electrode layer of the multi-mode interference reflector corresponding to one output end of the sub-resonant cavity 1, the sub-resonant cavity 1 is selected.

[0055] If current is applied to the waveguide regions of the two output ends, the phase control region and the electrode layers of the multi-mode interference reflector corresponding to the sub-resonant cavity 1 and the sub-resonant cavity 2, the sub-resonant cavity 1 and the sub-resonant cavity 2 are selected.

[0056] In step 402, the cavity film position of one or more sub-resonant cavities is adjusted by fine-tuning the current applied by the phase control region 5 of one or more sub-resonant cavities, so that the cavity length of one or more sub-resonant cavities can be fine-tuned. Combined with the vernier effect, the position alignment of the cavity mode supported in one or more sub-resonant cavities can be achieved.

[0057] For example, the cavity mode position of the sub-resonant cavity 1 is aligned by fine-tuning the current applied to the phase control region 5 of the sub-resonant cavity 1 in combination with the vernier effect.

[0058] By fine-tuning the current applied to the phase control region 5 of the sub-resonant cavity 1 and the sub-resonant cavity 2 and combining the vernier effect, the position of the cavity mode supported by the sub-resonant cavity 1 and the sub-resonant cavity 2 is aligned.

[0059] In step 403, a reverse bias voltage or an external modulation signal is applied to the saturated absorber 1, so that the saturated absorber 1 works in the saturated absorption mode. At this time, the saturated absorber 1 has a stronger saturation absorption effect on the mode commonly supported by the sub-resonant cavity, that is, it has a higher transmittance to the commonly supported light mode peak, and has a stronger absorption for other misaligned modes, so that the entire structure only supports the locking of the aligned mode, that is, the mode-locked laser works in the mode-locked state, thereby achieving a high-power mode-locked pulse output with a higher repetition rate.

[0060] When a sub-resonant cavity works alone, a mode-locked pulse output corresponding to the repetition frequency of the sub-resonant cavity can be output. When more than two sub-resonant cavities work simultaneously, the pulse repetition frequency is determined by the lowest common multiple of the repetition frequencies of the multiple sub-resonant cavities. In a specific implementation, the number of sub-resonant cavities can be increased by increasing the number of reflection arms of different lengths. The number of sub-resonant cavities working simultaneously is controlled by whether current is applied. By switching the combination of sub-resonant cavities working simultaneously, mode-locked pulse outputs with different repetition frequencies can be achieved.

[0061] In this embodiment, first, current is applied to the waveguide region, phase control region and electrode layer of the multi-mode interference reflector at the output end of one or more channels, and one or more sub-resonant cavities to be operated can be selected from multiple sub-resonant cavities with different cavity lengths; then, the cavity mode position of one or more sub-resonant cavities is aligned by fine-tuning the current applied to the phase control region of one or more sub-resonant cavities in combination with the vernier effect; finally, a reverse bias voltage or an external modulation signal is applied to the saturated absorber 1, so that the saturated absorber 1 operates in the saturated absorption mode, at which time the saturated absorber 1 has a stronger saturation absorption effect on the mode commonly supported by the sub-resonant cavities, that is, it has a higher transmittance for the peak of the commonly supported optical mode, and has a stronger absorption for other non-aligned modes, so that the entire structure only supports the locking of the aligned mode, that is, the mode-locked laser operates in the mode-locked state, thereby achieving a high-power mode-locked pulse output with a higher repetition frequency. Therefore, this embodiment can effectively reduce the nonlinear effect in the pulse evolution process and achieve a high-power mode-locked pulse output with switchable multiple repetition frequencies.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mode-locked laser, characterized in that: include: A saturated absorber, an input waveguide region, a multimode interference coupler, and a plurality of reflection arms of different lengths, each of the reflection arms comprising an output waveguide region, a phase control region, and a multimode interference reflector arranged in sequence; The saturated absorber is arranged on one side of the input end waveguide region, the other side of the input end waveguide region is arranged at the input end of the multimode interference coupler, a plurality of output end waveguide regions of different lengths are respectively arranged at a plurality of output ends of the multimode interference coupler, the plurality of reflection arms of different lengths respectively form a plurality of sub-resonant cavities of different cavity lengths with the end face of the saturated absorber, and the sub-resonant cavities of different cavity lengths correspond to different repetition frequencies of mode-locked pulses; Aligning the cavity mode positions of the one or more sub-resonant cavities by finely adjusting the current applied to the phase control region of the one or more sub-resonant cavities in combination with the vernier effect; A reverse bias voltage or an external modulation signal is applied to the saturated absorber to make the mode-locked laser work in a mode-locked state, thereby outputting mode-locked pulses with a corresponding repetition frequency.

2. The mode-locked laser according to claim 1, characterized in that: The saturable absorber, the input end waveguide region, the multi-mode interference coupler, the output end waveguide region, the phase control region and the multi-mode interference reflector are integrated on the same substrate.

3. The mode-locked laser according to claim 1, characterized in that: The saturated absorber, the input end waveguide region, the multimode interference coupler, the output end waveguide region, the phase control region and the multimode interference reflector are all active structures, and have the same material growth structure.

4. The mode-locked laser according to claim 3, characterized in that: The material growth structure comprises, from bottom to top, a substrate, a buffer layer, a lower confinement layer, a quantum well layer, an upper confinement layer, an upper cover layer and an ohmic contact layer.

5. The mode-locked laser according to claim 4, characterized in that: The substrate is an N-type semiconductor substrate, the buffer layer is an N-type semiconductor buffer layer, the upper cover layer is a P-type semiconductor upper cover layer, and the ohmic contact layer is a P-type semiconductor contact layer.

6. The mode-locked laser according to claim 4 or 5, characterized in that: The saturated absorber, the input end waveguide region, the multimode interference coupler, the output end waveguide region, the phase control region and the electrode layer of the multimode interference reflector are all arranged on the ohmic contact layer.

7. The mode-locked laser according to claim 6, characterized in that: A first electrical isolation groove is arranged between the electrode layer of the saturated absorber and the electrode layer of the input end waveguide region, and a second electrical isolation groove is arranged between the output end of the multimode interference coupler and the electrode layer of the output end waveguide region. Both the first electrical isolation groove and the second electrical isolation groove are obtained by selectively etching the ohmic contact layer using a selective wet etching process.

8. The mode-locked laser according to claim 6, characterized in that: The electrode layer of the input-end waveguide region is connected to the electrode layer of the multi-mode interference coupler.

9. A method for driving a mode-locked laser according to any one of claims 1 to 8, characterized in that: include: Applying current to one or more of the output end waveguide regions, the phase control region, and the electrode layers of the multi-mode interference reflector to select one or more sub-resonant cavities; Aligning the cavity mode positions of the one or more sub-resonant cavities by finely adjusting the current applied to the phase control region of the one or more sub-resonant cavities in combination with the vernier effect; A reverse bias voltage or an external modulation signal is applied to the saturated absorber to make the mode-locked laser work in a mode-locked state, thereby outputting mode-locked pulses with a corresponding repetition frequency.

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