Semiconductor optical frequency comb laser and method of fabrication

Abstract

The present disclosure provides a semiconductor optical frequency comb laser and a preparation method, and relates to the technical field of semiconductor lasers. The semiconductor optical frequency comb laser comprises: at least one first ridge region and at least one second ridge region; in the case that the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are alternately coupled in series; the width of each second ridge region is less than the width of each first ridge region; wherein the at least one first ridge region is used to provide gain for a light beam; the at least one second ridge region is used to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of semiconductor lasers, and more particularly, to a semiconductor optical frequency comb laser and a preparation method. BACKGROUND

[0002] A pulse mode-locked optical frequency comb (Pulse Mode-Locked Optical Frequency Comb) is a kind of laser that generates a series of ultra-short optical pulses with equal time intervals through a mode-locking mechanism. These pulses exhibit a periodic sequence in the time domain and a series of equally spaced discrete frequency components in the frequency domain, forming a structure similar to a comb. With high coherence and wide frequency coverage, it can be widely used in precision measurement, optical communication, spectroscopy and other fields. However, the existing mode-locked laser system has a complex structure, requires a complex feedback control system and high-precision components, and has a high preparation cost, which is difficult to meet the demand of large-scale production. SUMMARY

[0003] Therefore, the present disclosure provides a semiconductor optical frequency comb laser and a preparation method.

[0004] In one aspect, the present disclosure provides a semiconductor optical frequency comb laser, comprising: at least one first ridge region and at least one second ridge region; in the case where the sum of the number of first ridge regions and the number of second ridge regions is greater than or equal to 3, the first ridge region and the second ridge region are alternately coupled in series; the width of each second ridge region is less than the width of each first ridge region; wherein the at least one first ridge region is configured to provide gain for a light beam; the at least one second ridge region is configured to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb.

[0005] According to an embodiment of the present disclosure, regulating the nonlinear effect of the gain medium comprises: exciting a spatial hole burning effect to generate multiple longitudinal modes by controlling the carrier concentration of the gain medium in the at least one second ridge region; and exciting a four-wave mixing effect in the at least one second ridge region to regulate the frequency spacing between the multiple longitudinal modes.

[0006] According to an embodiment of the present disclosure, regulating the nonlinear effect of the gain medium further comprises: a single electrode, the at least one first ridge region and the at least one second ridge region sharing the single electrode; and regulating the nonlinear effect of the gain medium by causing the gain medium of the at least one second ridge region to undergo optical saturation effect when a positive current injected into the single electrode is greater than a threshold value.

[0007] According to an embodiment of the present disclosure, the method further includes: injecting a positive current into the single electrode; traversing a range of the injected positive current by a preset step size to determine an operating current of the frequency-modulated mode-locked optical frequency comb.

[0008] According to an embodiment of the present disclosure, the semiconductor optical frequency comb laser further includes: at least one transition region, each first ridge region and each second ridge region being coupled in series alternately through one transition region; and a structure for coupling the light beam with gain through the first ridge region to the second ridge region adjacent to the first ridge region.

[0009] According to an embodiment of the present disclosure, each transition region includes a first end and a second end; the first end is connected to each first ridge region correspondingly; the second end is connected to each second ridge region correspondingly; the width of the first end is the same as the width of each first ridge region; and the width of the second end is the same as the width of each second ridge region.

[0010] According to an embodiment of the present disclosure, the total length of the at least one first ridge region is 50%-60% of the remaining cavity length of the semiconductor optical frequency comb laser cavity length minus the total length of the at least one transition region.

[0011] According to an embodiment of the present disclosure, the total length of the at least one second ridge region is 40%-50% of the remaining cavity length of the semiconductor optical frequency comb laser cavity length minus the total length of the at least one transition region.

[0012] According to an embodiment of the present disclosure, the material of the semiconductor optical frequency comb laser includes a group III-V compound semiconductor.

[0013] The second aspect of the present disclosure provides a preparation method of a semiconductor optical frequency comb laser, including: preparing an epitaxial wafer; growing a protection layer on the epitaxial wafer; performing photolithography etching treatment on the protection layer to prepare at least one first ridge region and at least one second ridge region, wherein, in the case that the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are coupled in series alternately; the width of each second ridge region is smaller than the width of each first ridge region; wherein the at least one first ridge region is used to provide gain for a light beam; the at least one second ridge region is used to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb; growing an insulating layer on the surface of the epitaxial wafer containing the at least one first ridge region and the at least one second ridge region; performing photolithography etching on the insulating layer to form an injection window; growing a P-face metal on the surface of the epitaxial wafer containing the injection window; growing an N-face electrode on the surface of the epitaxial wafer away from the P-face metal to obtain the semiconductor optical frequency comb laser.

[0014] The semiconductor optical frequency comb laser provided by the embodiment of the present disclosure has at least the following beneficial effects:

[0015] The single-section structure is formed by alternately coupling each second ridge strip region and the first ridge strip region corresponding to each second ridge strip region in series, which is simple in structure and does not need complex external elements, and can meet the demand of mass production.

[0016] The high nonlinearity effect is realized by the second ridge strip region connected to the first ridge strip region, so that the frequency modulation mode-locked optical frequency comb is outputted, and the mode-locked state can be realized within a certain current range and the period waveform of the time-domain output frequency modulation can be realized in the case of injecting positive current.

[0017] The preparation method of the semiconductor optical frequency comb laser of the present disclosure has simple preparation process, does not need secondary epitaxy, and reduces the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0019] Figure 1 The structure diagram of the semiconductor optical frequency comb laser of the embodiment of the present disclosure is schematically shown;

[0020] Figure 2 The epitaxial structure diagram of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0021] Figure 3 The flowchart of the preparation method of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0022] Figure 4 The time-domain diagram of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0023] Figure 5 The frequency-domain diagram of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0024] Figure 6 The phase diagram of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0025] Figure 7 The length-transmittance relationship diagram of the transition region of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0026] Figure 8 The energy transfer distribution diagram of the semiconductor optical frequency comb laser according to the embodiment of the present disclosure is schematically shown;

[0027] Figure 9 A schematic diagram of a repetition frequency of a semiconductor optical frequency comb laser according to an embodiment of the present disclosure is shown schematically. DETAILED DESCRIPTION

[0028] Embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present disclosure. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. However, it will be apparent to one skilled in the art that one or more embodiments can be practiced without these specific details. In other instances, well-known systems and structures have not been described in detail in order to avoid unnecessarily obscuring the concepts of the present disclosure.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the term "including" "comprising" and the like are meant to be inclusive, but not limiting to the components, steps, operations and / or functions that are described, but that additional or other components, steps, operations, and / or functions can also be utilized.

[0030] All terms used herein, including technical and scientific terms, have the meanings commonly understood by one of ordinary skill in the art unless otherwise defined herein. It should be noted that the terms used herein are defined as having meanings that are consistent with the context of the specification in which the terms are used and should not be interpreted in an overly idealized or overly formal manner.

[0031] In instances where expressions such as "at least one of A, B, and C, etc." are used, in general, it should be interpreted that the meaning is generally as understood by one of ordinary skill in the art (e.g., "a system having at least one of A, B, and C" should include but not be limited to a system that has A alone, a system that has B alone, a system that has C alone, a system that has both A and B, a system that has both A and C, a system that has both B and C, and / or a system that has A, B, and C, etc.).

[0032] In order to achieve stable ultra-short pulse output, the existing pulse mode-locked optical frequency comb is usually provided with an electrical isolation structure to separate the gain region from the saturable absorption region to ensure that there is no unnecessary interaction between the two regions. In this system, a positive bias current is injected into the gain region to provide sufficient inverted population so that the laser can be started and maintained; a reverse bias current is injected into the saturable absorption region to adjust its transmittance characteristics, which helps to lock the mode spacing and stabilize the pulse sequence.

[0033] However, the introduction of an additional electrical isolation structure and a double current source control system increases the complexity of the system, which not only increases the manufacturing cost, but also increases the failure points due to the increase in components. At the same time, since there are multiple variables that need to be precisely controlled, any slight change can cause fluctuations in the output pulse characteristics, affecting the long-term stability and repeatability of the optical frequency comb.

[0034] Based on this, the embodiment of the present disclosure provides a frequency modulation mode-locked optical frequency comb, by setting a single-section structure, the structure is simple, and no complex external elements are needed, which can meet the demand of large-scale production. And by controlling the second ridge region to generate high nonlinear effect, a frequency modulation mode-locked optical frequency comb with good stability is generated, and high-order modes are filtered out to output a stable fundamental mode.

[0035] In the embodiment of the present disclosure, when the injected current is higher than the threshold current, resonance is formed and a spatial hole burning effect is generated, resulting in mode competition and multi-mode output. When the intracavity power is large enough, due to the increase of nonlinear effect, four-wave mixing effect can be excited, which can have an effect similar to optical injection locking, so that the multi-mode output becomes equidistant comb teeth. The population grating caused by the spatial hole burning effect can cause carrier particle number modulation and further cause third-order nonlinear effect, thereby changing the gain and refractive index, so that the multi-mode output in the frequency domain becomes equidistant comb teeth, but the phase of the equidistant comb teeth in the frequency domain is chaotic.

[0036] And both amplitude and frequency can cause equidistant comb teeth, wherein amplitude modulation is to modulate the output power of the laser by changing the amplitude of the injected current; frequency modulation is to modulate the output frequency of the laser by changing the frequency of the injected current.

[0037] But the particle number pulsation is mainly affected by the particle number inversion of amplitude modulation and optical parametric gain. For fast gain medium (carrier gain time T1 is related to intracavity light field intensity, therefore, increasing intracavity light field intensity, quantum well medium can exhibit similar fast gain medium effect), it behaves as parametric loss in a larger frequency range. According to the principle of maximum emission of laser, it can be determined that the amplitude modulation is suppressed, and behaves as frequency modulation.

[0038] At the same time, dispersion and gain curvature can affect the phase-locked mechanism, so that the phase behaves as a chirp property, that is, the derivative of the phase behaves as linear with respect to time.

[0039] Figure 1 The structure diagram of the semiconductor optical frequency comb laser of the embodiment of the present disclosure is schematically shown.

[0040] As Figure 1 shown, the present disclosure provides a semiconductor optical frequency comb laser in one aspect, which comprises at least one first ridge region 1 and at least one second ridge region 2.

[0041] In the case where the sum of the number of the first ridge region 1 and the number of the second ridge region 2 is greater than or equal to 3, the first ridge region 1 and the second ridge region 2 are alternately coupled in series; the width of each second ridge region is less than the width of each first ridge region.

[0042] The at least one first ridge region 1 is configured to provide gain for the light beam.

[0043] The at least one second ridge region 2 is configured to suppress high-order modes in the light beam with gain; and to regulate nonlinear effects of the gain medium by controlling carrier concentration of the gain medium in each second ridge region to generate frequency-modulated mode-locked optical frequency comb.

[0044] In the embodiments of the present disclosure, by setting the at least one first ridge region, the energy density is low and the light saturation effect is weak, high gain can be provided to generate high light field intensity and in-cavity resonant light power. The width of the second ridge region is set to be smaller than that of the first ridge region to ensure that only the fundamental mode can propagate therein, effectively suppressing high-order modes, reducing multi-transverse-mode interference, and improving light beam quality and stability. Meanwhile, the energy density of the second ridge region is high and the light saturation effect is strong, and the second ridge region has high nonlinear effects.

[0045] By adopting the design of alternating coupling and series connection of multiple first ridge regions and second ridge regions, the overall structure is simplified, the use of complex elements is reduced, and the manufacturing and maintenance costs are effectively reduced. Meanwhile, by accurately controlling the carrier concentration of the gain medium in each second ridge region, the nonlinear effects of the gain medium can be optimized to ensure high stability of the frequency interval and low phase noise.

[0046] The number of the first ridge regions and the second ridge regions can be set as needed. Setting multiple first ridge regions can provide higher gain for the light beam. Setting multiple second ridge regions can better filter out high-order modes to output stable fundamental modes, and can also improve nonlinear effects to generate stable frequency-modulated mode-locked optical frequency comb. When the total number of the first ridge regions and the second ridge regions is two, the first ridge regions and the second ridge regions are directly coupled and connected. When the total number of the first ridge regions and the second ridge regions is greater than or equal to three, the first ridge regions and the second ridge regions are alternatingly coupled and connected in series.

[0047] In some possible embodiments, the semiconductor optical frequency comb laser includes two first ridge regions 1 and one second ridge region 2, wherein the two first ridge regions are located at two ends of the second ridge region and are alternatingly coupled and connected with the second ridge region.

[0048] On the basis of the above-mentioned embodiments, the nonlinear effects of the gain medium are regulated by controlling the carrier concentration of the gain medium in the at least one second ridge region to excite spatial hole burning effect to generate multiple longitudinal modes; and exciting four-wave mixing effect in the at least one second ridge region to regulate the frequency interval between the multiple longitudinal modes.

[0049] By precisely controlling the carrier concentration of the gain medium in the second ridge region, effective holes can be formed at specific locations, which suppress the gain of high-order modes, so that only longitudinal modes that can obtain sufficient gain at the hole location can stably oscillate. Therefore, only a few specific longitudinal modes can stably exist and oscillate, forming multiple longitudinal modes. Under high power density, four-wave mixing effect can be excited, which promotes phase locking between different longitudinal modes, so that the frequency difference between adjacent longitudinal modes remains constant.

[0050] On the basis of the above-mentioned embodiment, the method further comprises: the single electrode is shared by the at least one first ridge region and the at least one second ridge region; and the nonlinear effect of the gain medium is regulated by controlling the positive current injected into the single electrode to be greater than a threshold value, so that the gain medium in the at least one second ridge region is subjected to optical saturation effect.

[0051] By controlling the positive current injected into the single electrode to be greater than a threshold value, the gain medium in the second ridge region can be ensured to enter an optical saturation state, the nonlinear effect of the gain medium can be effectively regulated, and the stable oscillation of the multiple longitudinal modes and the high consistency of the frequency interval can be ensured. Specifically, when the injected current exceeds a certain threshold value, the carrier concentration in the gain medium increases sharply, resulting in obvious optical saturation effect. And by adopting the single electrode design, the number of electrodes that need to be independently controlled is reduced, further simplifying the system and reducing the cost.

[0052] On the basis of the above-mentioned embodiment, the method further comprises: injecting a positive current into the single electrode; and traversing the range of the injected positive current with a preset step size to determine the working current of the frequency-modulated mode-locked optical frequency comb.

[0053] In the embodiment of the present disclosure, by traversing the range of the injected positive current and adjusting step by step with a preset step size, the optimal working current of the frequency-modulated mode-locked optical frequency comb can be accurately determined. Under this working current, the optical frequency comb exhibits stable frequency-modulated mode-locked characteristics, and has high frequency interval consistency and low phase noise.

[0054] According to the embodiment of the present disclosure, the semiconductor optical frequency comb laser further comprises: at least one transition region 3, each first ridge region 1 and each second ridge region 2 are alternately coupled in series through one transition region 3; and a device for coupling the light beam after gain in the first ridge region to the second ridge region adjacent to the first ridge region.

[0055] In the embodiments of the present disclosure, by setting at least one transition region, the light beam can be efficiently coupled from the first ridge region to the second ridge region, reducing scattering and reflection, and reducing power loss. Avoiding direct connection between the first ridge region and the second ridge region can cause power loss to increase, transverse mode mismatch, and cannot effectively capture transverse mode energy, which seriously affects the transmission quality of the optical signal and the system performance.

[0056] On the basis of the above-mentioned embodiments, each transition region comprises a first end and a second end; wherein the first end is connected to each first ridge region in correspondence; and the second end is connected to each second ridge region in correspondence.

[0057] The width of the first end is the same as the width of each first ridge region, and the width of the second end is the same as the width of each second ridge region.

[0058] In the embodiments of the present disclosure, by setting the first end of the transition region to have the same width as the first ridge region, it is ensured that the light beam does not have a sudden change when entering the transition region, avoiding unnecessary scattering and reflection. The second end of the transition region has the same width as the second ridge region, ensuring that the light beam can propagate smoothly when entering the second ridge region, avoiding transverse mode mismatch. Inside the transition region, the width gradually decreases from the first end to the second end, forming a smooth gradient structure, which can effectively guide the propagation path of the light beam and reduce energy loss in mode conversion. It should be noted that the length of each transition region can be set as needed, and the longer the length, the more efficient the energy transfer.

[0059] According to the embodiments of the present disclosure, the total length of the at least one first ridge region is 50%-60% of the remaining cavity length after removing the total length of the at least one transition region from the cavity length of the semiconductor optical frequency comb laser.

[0060] In the embodiments of the present disclosure, by accurately limiting the proportion of the total length of the first ridge region set, the mode field area corresponding to the first ridge region can be effectively controlled, so that the laser can operate in the best working state. And by controlling the mode field area, the threshold current of the laser can be adjusted and kept within a reasonable range, which helps to improve the output power, beam quality and stability of the laser. At the same time, the longer first ridge region can reduce the average current injection density, reducing the risk of local overheating and helping to provide system stability

[0061] According to the embodiments of the present disclosure, the total length of the at least one second ridge region is 40%-50% of the remaining cavity length after removing the total length of the at least one transition region from the cavity length of the semiconductor optical frequency comb laser.

[0062] In the embodiments of the present disclosure, by precisely controlling the proportion of the second ridge region, the second ridge region maintains a high nonlinear action and loss balance, avoids the problem that the second ridge region is too long to affect the output power of the laser, and increases the loss and energy consumption. If it is too short, it cannot effectively filter out high-order modes and the spatial hole burning effect and four-wave mixing effect are insufficient, and the multi-longitudinal mode phase locking cannot be achieved.

[0063] According to the embodiments of the present disclosure, the material of the semiconductor optical frequency comb laser includes a III-V compound semiconductor, and the laser is integrally active, which is beneficial to make up for the power loss caused by electrical isolation and etching of the surface grating, and to improve the power of the entire laser. The semiconductor epitaxial material has the advantages of wide gain range and low threshold current, and the use of electrical injection pumping mode is convenient and easy to realize high-precision control.

[0064] According to the embodiments of the present disclosure, a bias generator is further included for generating a radio frequency signal. The radio frequency signal is mixed with the light beam to stabilize the performance of the optical frequency comb.

[0065] Figure 2 The semiconductor optical frequency comb laser epitaxial structure according to the embodiments of the present disclosure is schematically shown.

[0066] Figure 3 The semiconductor optical frequency comb laser preparation method flow chart according to the embodiments of the present disclosure is schematically shown.

[0067] As shown in Figure 2 and Figure 3 , the second aspect of the present disclosure provides a semiconductor optical frequency comb laser preparation method, comprising:

[0068] Step 1: preparing an epitaxial wafer; on the substrate, epitaxially growing a buffer layer, a graded layer, a cladding layer, a graded layer, a periodic unit, a graded layer, a cladding layer, a layer, a cladding layer, a layer, a layer, and a layer to obtain an epitaxial wafer. The periodic unit includes a barrier layer, a quantum well layer, and a barrier layer, and the number of periods of the periodic unit is 5; UID represents undoped.

[0069] Step 2: growing a silicon dioxide protective layer on the prepared epitaxial wafer;

[0070] Step three: performing multiple photolithography etching processes on the protective layer to prepare at least one first ridge region and at least one second ridge region, wherein, in the case that the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are alternately coupled in series; the width of each second ridge region is less than the width of each first ridge region; wherein the at least one first ridge region is used to provide gain for the light beam; the at least one second ridge region is used to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb; the photoresist includes AZ703.

[0071] Step four: after step three is completed, removing the residual silicon dioxide and growing a silicon dioxide insulation layer on the surface of the epitaxial wafer containing the at least one first ridge region and the at least one second ridge region;

[0072] Step five: performing photolithography etching on the insulation layer to expose the epitaxial wafer below the insulation layer;

[0073] Step six: growing P-face metal on the surface of the epitaxial wafer containing the injection window, and using photolithography and etching the metal to image the electrode to form a single electrode;

[0074] Step seven: after performing thinning and polishing on the surface of the epitaxial wafer away from the P-face metal, growing an N-face electrode on the surface.

[0075] Step eight: coating high-reflection film HR and anti-reflection film AR on both ends; and then slicing and cleaving to obtain a semiconductor optical frequency comb laser.

[0076] In the embodiments of the present disclosure, the preparation method of the semiconductor optical frequency comb laser is simple, does not require secondary epitaxy and electron beam lithography, and can be realized by using ordinary optoelectronic processes, thereby reducing the production cost and meeting large-scale production.

[0077] On the basis of the above-described embodiments, the frequency-modulated mode-locked optical frequency comb laser includes two first ridge regions 1 and one second ridge region 2, wherein the two first ridge regions 1 are located at two ends of the second ridge region 2, and the two first ridge regions 1 and the one second ridge region 2 are alternately coupled in series through one transition region 3.

[0078] The etching depth of the first ridge region and the second ridge region can include 1.75 μm, but is not limited thereto.

[0079] The length of the two first ridge regions is L1 = L3 = 460 um, the second ridge length is L2 = 920 um, the transition region length is L5 = 100 um, the total cavity length is 2040 um, the first ridge width is L4 = 10.4 um, and the second ridge width is L4 / 4 = 2.6 um.

[0080] By fixing the prepared frequency-modulated mode-locked optical frequency comb laser on a C-Mount type heat sink, temperature control is performed using a temperature controller to perform characterization tests of multiple performances.

[0081] After the test starts, a single-section single-electrode injection is performed by injecting a positive current, the range of the injected positive current is 0-500 mA, the injected current is scanned in steps of 2 mA, when the laser starts to lase, it is recorded as the threshold current, the current is continuously increased, when the laser enters the mode-locked state, it is recorded as the mode-locked threshold current, the current is continuously increased, and the mode-locked state will experience disappearance and reappearance. The range of the injected current with the mode-locked characteristics is the mode-locked characteristic working area. The frequency modulation characteristics of the optical frequency comb can be measured by the step heterodyne method to verify the characteristics of almost stable in time domain, multi-mode lasing in frequency domain, and phase chirp change.

[0082] Figure 4 A time domain diagram of the semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0083] Figure 5 A frequency domain diagram of the semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0084] Figure 6 A phase diagram of the semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0085] As shown in Figure 4 , the frequency-modulated optical frequency comb of the present embodiment shows obvious periodicity and sharp peaks in the time domain, and has period stability.

[0086] As shown in Figure 5 , in the frequency domain, the frequency shows a linear increasing trend within a position range of 0 to about 6 mm, and the frequency uniformly increases with the increase of the position; at a position of about 6 mm, the frequency shows a significant mutation, the frequency rapidly decreases from close to 0.4 THz to close to -0.5 THz, and then rapidly increases to a value close to 0 THz in a short time; after 6 mm, the frequency again shows a linear increasing trend. It is shown that the output is a multi-longitudinal mode, and the consistency of the interval between the multi-longitudinal modes is consistent.

[0087] As shown in Figure 6 , the phase changes linearly with the position, showing the chirp characteristics of the phase.

[0088] Figure 7A length-transmittance relationship diagram of a transition region of a semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0089] As shown in Figure 7 , the transmittance of the transition region can be adjusted by controlling the length of the transition region, and the energy coupling from the first ridge region to the second ridge region can be better controlled, and the loss can be reduced.

[0090] Figure 8 A schematic diagram of energy transfer distribution of a semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0091] As shown in Figure 8 , the energy distribution diagram of the first ridge region and the second ridge region is given, and Figure 8 It can be known that the energy ratio of the first ridge region to the second ridge region is 3.2:1.

[0092] Figure 9 A schematic diagram of a repetition frequency of a semiconductor optical frequency comb laser according to an embodiment of the present disclosure is schematically shown.

[0093] As shown in Figure 9 , it is shown that single mode lasing and narrow linewidth are obtained under the injection current of 0.7A, and high frequency stability and low noise characteristics are obtained.

[0094] Therefore, the semiconductor optical frequency comb laser of the embodiment of the present disclosure can output a stable repetition frequency and high power, and has the advantages of simple process and low cost. When the laser is given sufficient anomalous dispersion compensation, the pulse can be reproduced in the time domain, and it is further illustrated that the phase curve has a parabolic characteristic. Specifically, since the amplitude modulation is suppressed, the frequency-locked laser cannot exhibit the time-domain pulse. The time-domain pulse requires that the phase between the comb teeth is equal, and the phase between the comb teeth of the frequency-locked laser is chirped. Therefore, a section of anomalous dispersion fiber (i.e. phase chirp with opposite slope) can be added to compensate, so that the phase between the comb teeth is equal, and the pulse is reproduced.

[0095] At the same time, according to the change of the injection current, the peak power of the repetition frequency, the change of the peak wavelength, and the advantages and disadvantages of the spectral characteristics can be observed, and the influence of the temperature and the carrier on the characteristics of the laser can be judged. When the laser is externally injected with a radio frequency signal or light with a frequency equal to the repetition frequency, the mode-locked characteristics and the spectral characteristics can be adjusted to achieve excellent performance of narrower repetition frequency linewidth and flatter spectrum.

[0096] Those skilled in the art can understand that the features recited in various embodiments and / or claims of the present disclosure can be combined and / or integrated in various combinations, even if such combinations or integrations are not expressly recited in the present disclosure. In particular, the features recited in various embodiments and / or claims of the present disclosure can be combined and / or integrated in various combinations without departing from the spirit and teachings of the present disclosure. All such combinations and / or integrations fall within the scope of the present disclosure.

[0097] The above describes embodiments of the present disclosure. However, these embodiments are merely for illustrative purposes, and are not intended to limit the scope of the present disclosure. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be advantageously used in combination. The scope of the present disclosure is defined by the appended claims and their equivalents. Those skilled in the art can make various substitutions and modifications without departing from the scope of the present disclosure, and all such substitutions and modifications shall fall within the scope of the present disclosure.

Claims

1. A semiconductor optical frequency comb laser, characterized by, Comprising: at least one first ridge region and at least one second ridge region; in the case where the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are coupled in series alternately; the width of each of the second ridge regions is less than the width of each of the first ridge regions; wherein the at least one first ridge region is configured to provide gain for a light beam; the at least one second ridge region is configured to suppress high-order modes in the light beam with gain; and by controlling the carrier concentration of the gain medium in each of the second ridge regions to regulate the nonlinear effect of the gain medium, a frequency-modulated mode-locked optical frequency comb is generated; the regulation of the nonlinear effect of the gain medium comprises: by controlling the carrier concentration of the gain medium in the at least one second ridge region to excite a spatial hole burning effect to generate multiple longitudinal modes; and exciting the at least one second ridge region to generate a four-wave mixing effect to regulate the frequency spacing between the multiple longitudinal modes; a single electrode, the at least one first ridge region and the at least one second ridge region share the single electrode; wherein by controlling the positive current injected into the single electrode to be greater than a threshold value, the gain medium of the at least one second ridge region is subjected to optical saturation to regulate the nonlinear effect of the gain medium.

2. The semiconductor optical frequency comb laser of claim 1, wherein, Further comprising: injecting a positive current into the single electrode; traversing the range of the injected positive current by a preset step size to determine the operating current of the frequency-modulated mode-locked optical frequency comb.

3. The semiconductor optical frequency comb laser of claim 1, wherein, Further comprising: at least one transition region, each of the first ridge regions and each of the second ridge regions are coupled in series alternately through one of the transition regions; for coupling the light beam with gain through the first ridge region to the second ridge region adjacent to the first ridge region.

4. The semiconductor optical frequency comb laser of claim 3, wherein, Each of the transition regions comprises a first end and a second end; wherein the first end is connected to each of the first ridge regions correspondingly; the second end is connected to each of the second ridge regions correspondingly; the width of the first end is the same as the width of each of the first ridge regions, and the width of the second end is the same as the width of each of the second ridge regions.

5. The semiconductor optical frequency comb laser of claim 1, wherein, The total length of the at least one first ridge region is 50%-60% of the remaining cavity length after the total length of the at least one transition region is removed from the cavity length of the semiconductor optical frequency comb laser.

6. The semiconductor optical frequency comb laser of claim 5, wherein, The total length of the at least one second ridge region is 40%-50% of the remaining cavity length after the total length of the at least one transition region is removed from the cavity length of the semiconductor optical frequency comb laser.

7. The semiconductor optical frequency comb laser of claim 1, wherein, The material of the semiconductor optical frequency comb laser comprises a group III-V compound semiconductor.

8. A method of fabricating a semiconductor optical frequency comb laser, characterized by, Comprising: preparing an epitaxial wafer; growing a protective layer on the epitaxial wafer; The method comprises: growing an epitaxial wafer containing at least one first ridge region and at least one second ridge region on a substrate; performing photolithography etching on the epitaxial wafer to prepare the at least one first ridge region and the at least one second ridge region, wherein, when the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are coupled in series alternately; the width of each second ridge region is less than the width of each first ridge region; the at least one first ridge region is used to provide gain for a light beam; the at least one second ridge region is used to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb; the regulation of the nonlinear effect of the gain medium comprises: controlling the carrier concentration of the gain medium in the at least one second ridge region to excite a spatial hole burning effect to generate multiple longitudinal modes; and exciting the at least one second ridge region to generate a four-wave mixing effect to regulate the frequency spacing between the multiple longitudinal modes; growing an insulating layer on the surface of the epitaxial wafer containing the at least one first ridge region and the at least one second ridge region; performing photolithography etching on the insulating layer to form an injection window; growing P-face metal on the surface of the epitaxial wafer containing the injection window to form a single electrode, and the at least one first ridge region and the at least one second ridge region share the single electrode; wherein, by controlling the positive current injected into the single electrode to be greater than a threshold value, the nonlinear effect of the gain medium in the at least one second ridge region is regulated by causing optical saturation of the gain medium; growing an N-face electrode on the surface of the epitaxial wafer away from the P-face metal to obtain the semiconductor optical frequency comb laser. The semiconductor optical frequency comb laser comprises: a substrate; an epitaxial wafer containing at least one first ridge region and at least one second ridge region grown on the substrate; a single electrode grown on the surface of the epitaxial wafer containing the at least one first ridge region and the at least one second ridge region; and an N-face electrode grown on the surface of the epitaxial wafer away from the single electrode; wherein, when the sum of the number of the first ridge regions and the number of the second ridge regions is greater than or equal to 3, the first ridge regions and the second ridge regions are coupled in series alternately; the width of each second ridge region is less than the width of each first ridge region; the at least one first ridge region is used to provide gain for a light beam; the at least one second ridge region is used to suppress high-order modes in the light beam with gain; and the nonlinear effect of the gain medium is regulated by controlling the carrier concentration of the gain medium in each second ridge region to generate a frequency-modulated mode-locked optical frequency comb; the regulation of the nonlinear effect of the gain medium comprises: controlling the carrier concentration of the gain medium in the at least one second ridge region to excite a spatial hole burning effect to generate multiple longitudinal modes; and exciting the at least one second ridge region to generate a four-wave mixing effect to regulate the frequency spacing between the multiple longitudinal modes.

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