A tunable semiconductor laser array

Abstract

The present invention discloses a tunable semiconductor laser array. The unit lasers in the array do not have a grating structure and are tunable, and are V-cavity tunable lasers, tunable lasers based on half-wave coupled partial reflectors, or small-size tunable lasers based on polymer imaging couplers; the entire array emits a set of wavelength sequence lasers, the wavelength interval can be designed, each unit laser emits a wavelength, all lasers work at the same time, and the cavity length of each unit laser is slightly different, so that the current required for each unit laser to work at different wavelengths is basically close. The present invention can greatly simplify the complexity of the back-end circuit and the control algorithm, thereby reducing costs, the wavelength sequence is tunable, the wavelength range that can work is expanded, and it can be flexibly applied to occasions with different wavelength sequence requirements; simplify the process, the scope of use is flexible, only one set of tuning circuits is required to control the wavelength tuning of the entire array, low cost, large range, and tunable.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor lasers, and in particular to a tunable semiconductor laser array based on a tunable semiconductor laser solution without a grating structure. Background Art

[0002] The traditional distributed feedback laser (DFB) array, as a mature technology, has stable performance. However, the DFB array requires the production of gratings, and different lasers in the array need to produce gratings with different periods to emit different wavelengths, which greatly increases the complexity of the process and reduces the yield rate. At the same time, the DFB laser is a fixed wavelength laser that is not tunable. The array can only emit a set of designed wavelength sequences. Different wavelength sequence requirements can only produce different DFB arrays, which is not flexible enough.

[0003] The use of tunable laser arrays to form tunable laser arrays can flexibly adapt to different emission wavelength sequence requirements. The main commercial tunable laser solutions currently include: Y-type tunable semiconductor lasers (MG-Y) based on modulated gratings, distributed feedback lasers (SG-DBR) based on sampled gratings, distributed feedback lasers (DS-DBR) based on digital supermode gratings, and external cavity tunable lasers based on silicon photonics technology. Most of them also use grating structures, or even more complex multi-segment gratings and modulated grating structures. In addition, these tunable semiconductor laser solutions include multi-segment structures such as grating areas, gain areas, and phase areas. To achieve single-mode operation and wavelength tuning, electrodes on each area need to be used, and the tuning control algorithm for multi-electrode coordination is complex. The independent control and tuning of each tunable laser in the array increases the complexity of the entire control circuit and greatly increases the cost. The docking process between the silicon photonics part and the active part required for the external cavity tunable laser based on silicon photonics technology is complex, which also increases the cost. Summary of the invention

[0004] In view of the deficiencies of the background art and the prior art, the object of the present invention is to provide a low-cost tunable semiconductor laser array that does not require a grating structure and simplifies the control circuit and the control algorithm.

[0005] The present invention does not require a grating, simplifies the process, has a flexible scope of use, and only requires one set of tuning circuits to control the wavelength tuning of the entire array. It has the potential for further on-chip integration or silicon-optical hybrid integration and is a low-cost, large-range tunable semiconductor laser array solution.

[0006] The technical solution adopted by the present invention is:

[0007] 1. A tunable semiconductor laser array:

[0008] The tunable semiconductor laser array is composed of a plurality of unit laser arrays, wherein the unit lasers are tunable semiconductor lasers without a grating structure, and each unit laser in the array is arranged in parallel, and the number of unit lasers is the same as the number of wavelengths required to be emitted simultaneously.

[0009] The output positions of all unit lasers are aligned on the same side of the array to facilitate output coupling. The spacing between adjacent unit lasers in the array is determined by the output requirements of the application scenario.

[0010] The unit laser used in the array is a tunable laser solution that does not require a grating structure, so the entire array does not require grating production and does not require secondary epitaxy; it does not use a tunable laser solution based on silicon photonics technology to avoid complex docking processes.

[0011] The unit laser comprises two optical resonant cavities with different optical lengths, the two optical resonant cavities are connected by half-wave coupling, the energy between the two optical resonant cavities is coupled by half-wave coupling, and electrodes for current injection are arranged on the two optical resonant cavities;

[0012] The electrode of one of the optical resonant cavities emits light after current is injected. Part of the light returns to the original optical resonant cavity through half-wave coupling, and the other part of the light is incident on the other optical resonant cavity after half-wave coupling. The non-half-wave coupled end of any optical resonant cavity can be used as the output end of the laser to emit laser of the working wavelength.

[0013] The light energy that returns to the original optical resonant cavity from the half-wave coupling is used as the through coupling, and the light energy that enters another optical resonant cavity through the half-wave coupling is used as the cross coupling. The phase difference between the cross-coupled light and the through-coupled light is controlled to be π at the half-wave coupling, and the proportional relationship between the cross-coupling energy and the through-coupling energy is controlled. These two points are used to achieve selective loss of wavelength, which is used to adjust parameters such as the side mode suppression ratio of the unit laser to achieve optimal single-mode performance.

[0014] The two optical resonant cavities with different optical lengths are a long cavity and a short cavity. The length ratio between the long cavity and the short cavity of each unit laser is the same. By setting the lengths of the long cavity and the short cavity of each unit laser to be different, each unit laser emits lasers of different working wavelengths under basically the same current injection.

[0015] By adjusting only the lengths of the long cavity and the short cavity of each unit laser, the working wavelengths of the lasers emitted by each unit laser can be adjusted to be different under substantially the same current injection.

[0016] The unit laser of the present invention realizes wide-range tuning by forming a vernier effect.

[0017] The long cavity and the short cavity each correspond to a set of equally spaced resonant frequencies called a comb spectrum, and there is only one resonant frequency overlap between the comb spectra of the long cavity and the short cavity within the gain spectrum of the quantum well material, and the overlapped resonant frequency is used as the operating wavelength of the unit laser;

[0018] Injecting current into any optical resonant cavity changes its equivalent refractive index, changes its optical length, and causes its corresponding comb spectrum to move, thereby changing the resonant frequency of the two optical resonant cavities that overlap and achieving tuning of the working wavelength.

[0019] The optical resonant cavity corresponding to the shift of the comb spectrum is called a tuned cavity, and the optical resonant cavity in which the comb spectrum does not shift determines the operating wavelength of the laser and serves as a fixed gain cavity.

[0020] Both ends of each optical resonant cavity of the unit laser are provided with deeply etched reflecting surfaces, wherein the deeply etched reflecting surface at the outer end of the optical resonant cavity close to the output end of the unit laser is set as a semi-transmissive and semi-reflective surface, and the other deeply etched reflecting surfaces are set as reflecting surfaces by coating high reflectivity films.

[0021] The deep etched reflective surface refers to a reflective surface whose etching depth exceeds the depth of the quantum well active layer and can completely reflect the waveguide light spot. The deep etched reflective surface has a high reflectivity and can be coated with a high reflectivity film as a reflective mirror of an optical resonant cavity, or as a semi-transmissive and semi-reflective structure for laser output.

[0022] The core function of deeply etching the reflective surface is to accurately define the length of the optical resonant cavity, thereby ensuring that the functions related to the length of the optical resonant cavity in the present invention are accurately implemented.

[0023] The unit lasers constituting the array are V-cavity tunable lasers, tunable lasers based on half-wave coupled partial reflectors, or small-size tunable lasers based on polymer imaging couplers.

[0024] The unit laser is a V-shaped cavity tunable laser, which includes two optical resonant cavities, which are distributed in a V shape, and each optical resonant cavity is mainly composed of a half-wave coupler, a section of curved waveguide, and a section of straight waveguide connected in sequence. The half-wave coupler of the two optical resonant cavities is shared, so that the two optical resonant cavities are coupled and connected through the half-wave coupler; the half-wave coupler is connected to the first deeply etched reflection surface at the end not connected to the curved waveguide, and the straight waveguide of each optical resonant cavity is connected to a respective deeply etched reflection surface at the end not connected to the curved waveguide; the laser is provided with three electrodes, one of which covers the half-wave coupler and a part of the curved waveguides of the two optical resonant cavities, and the other two electrodes respectively cover the remaining part of the curved waveguides and the straight waveguides of the two optical resonant cavities.

[0025] The unit laser is a tunable laser based on a half-wave coupled partial reflector, and the tunable laser based on a half-wave coupled partial reflector comprises two optical resonant cavities and a coupling waveguide, the two optical resonant cavities are distributed along the same straight line, and a coupling waveguide is arranged between the two optical resonant cavities;

[0026] Each optical resonant cavity is mainly composed of a deeply etched reflection surface, a section of optical waveguide, a section of tapered waveguide and a second partial reflector connected in sequence, and the two optical resonant cavities are coupled to each other through a coupling waveguide connected to the respective second partial reflectors; one end of the second partial reflector is connected to the large end of the tapered waveguide, and the width of the second partial reflector is greater than the large end width of the tapered waveguide; the second partial reflector is provided with deeply etched reflection surfaces with a 45-degree cut angle as the second partial reflection surface on both sides of the end surface connected to the coupling waveguide, and the remaining part in the middle of the end surface is connected to the coupling waveguide in the middle; a part of the energy distribution at the end of the second partial reflector of the optical resonant cavity is reflected back to the optical resonant cavity where it is located to form a straight-through coupling, and the other part of the energy is coupled to another optical resonant cavity through the coupling waveguide to form a cross coupling.

[0027] The deep etching reflection surface is to etch a first pit penetrating the quantum well layer on the wafer, and use the plane of the wall of the first pit as the first partial reflection surface;

[0028] The second partial reflective surface is located at the end of the second partial reflector and two second pits are etched on both sides of the symmetrical line where the second partial reflector is located. Each second pit is set to a 45-degree cut angle at a corner close to the end, and the plane of the pit wall with a 45-degree cut angle is used as the second partial reflective surface; and there is a gap distance with a width less than the width of the second partial reflector between the two second pits, and a coupling waveguide is set at the gap distance; the two second pits of the second partial reflective surface of the two optical resonant cavities are shared.

[0029] The unit laser is a small-size tunable laser based on a polymer imaging coupler, and the small-size tunable laser based on a polymer imaging coupler comprises two optical resonant cavities and a deep-etched waveguide, each optical resonant cavity is mainly composed of a first partial reflection surface, a polymer imaging coupler and a second partial reflection surface connected in sequence, the two optical resonant cavities are distributed along the same straight line, and are coupled to each other through a middle deep-etched waveguide connected to the second partial reflection surfaces of each.

[0030] Each optical resonant cavity has two second partial reflection surfaces, which are respectively located on the symmetrical sides of the connection between the end of the polymer imaging type coupler and the middle deeply etched waveguide; the two side parts of one end of the polymer imaging type coupler are connected to the second partial reflection surface, and the remaining part in the middle is coupled and connected to the middle deeply etched waveguide; the two second partial reflection surfaces on both sides constitute a group of total reflection structures; a part of the energy distribution of the end face of the polymer imaging type coupler end of the optical resonant cavity is reflected back to the optical resonant cavity where it is located to form a straight-through coupling, and the other part of the energy is coupled to another optical resonant cavity through the middle deeply etched waveguide to form a cross coupling.

[0031] The first partial reflection surface is a first pit etched on the wafer and penetrating the quantum well layer, and the plane of the pit wall of the first pit is used as the first partial reflection surface;

[0032] The second partial reflection surface is formed by etching two second pits at the end of the polymer imaging coupler and on both sides symmetrically of the straight line where the polymer imaging coupler is located. Each second pit is set to have a 45-degree cut angle at a corner close to the end of the polymer imaging coupler, and the plane of the pit wall with the 45-degree cut angle is used as the second partial reflection surface; and there is a gap distance between the two second pits with a width less than the width of the polymer imaging coupler, and an intermediate deeply etched waveguide is set at the gap distance; the two second pits of the second partial reflection surfaces of the two optical resonant cavities are shared.

[0033] 2. The control method of the tunable semiconductor laser array enables different unit lasers to operate at different wavelengths in the wavelength sequence:

[0034] The optical resonator cavities of the unit lasers in the array have different lengths.

[0035] The optical resonant cavity corresponding to the movement of the comb spectrum is used as the tuning cavity, usually a long cavity, and the optical resonant cavity in which the comb spectrum does not move is used as the fixed gain cavity, usually a short cavity. The fixed gain cavity determines at which wavelengths the laser can work, and then the method is carried out as follows:

[0036] Taking one of the unit lasers as a reference, keeping the length of the fixed gain cavity of the reference unit laser unchanged, slightly adjusting the cavity length of the fixed gain cavity of the remaining unit lasers, usually the cavity length of the short cavity, so that each unit laser can output lasers corresponding to the required working wavelength sequence under basically the same current injection;

[0037] Then, with the goal of making the length ratio between the long and short cavities of each unit laser consistent with the length ratio between the long and short cavities of the reference unit laser, the cavity lengths of the long cavities of all unit lasers are slightly adjusted, so that the length ratio between the long and short cavities of each unit laser is consistent with the length ratio between the long and short cavities of the reference unit laser, so as to ensure that the position of the comb spectrum alignment of the vernier effect does not change relative to the reference unit laser when the same current is injected, and ensure that the working wavelength determined by the short cavity is selected;

[0038] After the cavity length is adjusted in this way, under the condition of substantially the same current injection, the set of operating wavelengths emitted by all unit lasers is the required operating wavelength sequence;

[0039] When the tunable semiconductor laser array emits laser light of a working wavelength sequence, the magnitudes of the corresponding working currents received and injected by all unit lasers are substantially consistent.

[0040] Basically the same current means that the difference between the minimum current and the maximum current injected into each unit laser is 1%.

[0041] The operating wavelength sequence of the tunable semiconductor laser array can be tuned itself. Since the operating currents of different unit lasers are substantially the same, all unit lasers can be tuned synchronously without the need to independently control the tuning of each unit laser. After the operating wavelength of the reference unit laser is tuned to a specific wavelength in the new operating wavelength sequence, the entire array is automatically tuned to the new operating wavelength sequence.

[0042] The tunable laser scheme used in the tunable semiconductor laser array of the present invention does not require a grating structure, nor is it a scheme based on silicon photonics technology that requires end-to-end docking coupling technology. The scheme adopted is to achieve excellent single-mode performance by introducing wavelength selective loss through a half-wave coupler, to achieve a large tuning range through the vernier effect using two optical resonant cavities with different cavity lengths, and to accurately define the cavity length by deeply etching the reflective surface. Including but not limited to V-cavity tunable lasers, tunable lasers based on half-wave coupled partial reflectors, and small-size tunable lasers based on polymer imaging couplers.

[0043] The tunable semiconductor laser array as a whole emits a set of wavelength sequences with specific wavelength intervals. Each unit laser in the array works synchronously, and each unit laser sequentially emits the wavelengths in the wavelength sequence according to the order in the array, and all unit lasers work under the injection of currents of substantially similar magnitude. Because the array is composed of tunable lasers, the wavelength sequence itself can be tuned. All unit lasers can act uniformly under one tuning instruction, without the need for independent tuning control of each unit laser, which simplifies complexity and reduces costs.

[0044] In the tunable semiconductor laser array, the cavity length of the unit laser changes in sequence. The change of cavity length is used to achieve the emission of different wavelengths under similar current injection. A unit laser is selected as a reference, and the reference is usually the starting or ending unit laser in the array. The short cavity length that determines the working wavelength of the laser in the remaining unit lasers is fine-tuned by a difference in sequence, and then the long cavity length is adjusted with the ratio of the long and short cavity lengths of each unit laser consistent with the reference as the goal, so as to ensure that the spectral position of the comb spectrum alignment of the vernier effect does not change, which is equivalent to translating two sets of comb spectrums without changing the overlapping position. At the same time, by designing the degree of cavity length adjustment, the wavelength interval in the wavelength sequence can be designed to meet the needs of inconsistent wavelength intervals. Considering that the cavity length change relative to the reference is very small, usually considering the frequency interval of the wavelength sequence of 100GHz, when the array consists of 16 unit lasers, the cavity length change does not exceed 2.5μm, the cavity length change amplitude is not greater than 1%, and the heating effect caused by current injection has basically no effect, so all unit lasers can work in different wavelengths in the wavelength sequence in sequence under the injection of the same current as the reference. If the wavelength sequence is very long, resulting in a large scale in the array, and the difference in length of the unit lasers emitting the head wavelength and the tail wavelength in the wavelength sequence causes the thermally induced refractive index change caused by current injection to be non-negligible, the current of the unit laser emitting the tail wavelength can be fine-tuned to compensate. The compensation amplitude is related to the square root of the cavity length change amplitude. Considering a frequency interval of 100GHz for the wavelength sequence and an array composed of 40 unit lasers, the cavity length change amplitude is 2%, and the maximum current compensation amplitude is 1%. Relative to the working current size, the working current of all unit lasers can be basically consistent.

[0045] In the tunable laser array, all unit lasers are aligned at the output end, and can be coupled and output through an optical fiber array, or combined and output through an on-chip integrated multimode interference coupler, arrayed waveguide grating (AWG) or etched diffraction grating (EDG) and other combiners. This is conducive to the integration of more other functional devices on the chip, such as modulators and photodetectors. When outputting through an optical fiber array, the array spacing is designed to match the requirements of the optical fiber array. When outputting through an on-chip integrated combiner, the deeply etched reflective surface at the output end of all unit lasers is replaced by a deeply etched groove of a semi-transmissive and semi-reflective structure. The deep etched groove also has an etch depth exceeding the quantum well layer, and has a certain transmittance to couple part of the energy into the rear-end optical waveguide for output.

[0046] Compared with the background technology, the present invention has the following beneficial effects:

[0047] 1. The present invention adopts a tunable laser solution without a grating, which simplifies the process and reduces the cost.

[0048] 2. The present invention uses a method in which the cavity lengths of unit lasers in the array are different, so that each unit laser operates at a current of similar magnitude and emits a different wavelength, which greatly simplifies the control circuit and algorithm and reduces the cost.

[0049] 3. The wavelength sequence emitted by the present invention can be tuned itself, which increases the flexibility of array use.

[0050] 4. The wavelength sequence emitted by the present invention can be designed so that the wavelength interval in the sequence can meet the requirements of application scenarios with inconsistent wavelength intervals.

[0051] In summary, the present invention forms an array by using tunable lasers without a grating structure, and achieves operation at different wavelengths while keeping the operating current substantially the same by changing the cavity length of the unit lasers in the array. At the same time, the array's operating wavelength sequence can be tuned, and all unit lasers in the array do not need independent tuning control, thereby improving the flexibility of the array, greatly simplifying the control circuit, and significantly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of a V-cavity tunable laser.

[0053] Figure 2 It is a schematic diagram of the structure of a tunable semiconductor laser array based on a V-cavity tunable laser array.

[0054] Figure 3 Schematic diagram of a tunable laser based on a half-wave coupled partial reflector.

[0055] Figure 4 It is a schematic diagram of the half-wave coupler structure of a tunable laser based on a half-wave coupled partial reflector.

[0056] Figure 5 It is a schematic diagram of the structure of a tunable semiconductor laser array based on a tunable laser with a half-wave coupled partial reflector.

[0057] Figure 6 Schematic diagram of a small-size tunable laser based on a polymer imaging coupler, including a three-electrode scheme (a) and a two-electrode scheme (b).

[0058] Figure 7 It is a schematic diagram of the structure of a tunable semiconductor laser array of a small-size tunable laser based on a polymer imaging coupler.

[0059] Figure 8 Schematic diagram of the phase and amplitude of the amplitude reflection coefficient correction factor η when the coupling phase is π / 2, where (a) represents the phase and (b) represents the amplitude.

[0060] Fig. 9It is a schematic diagram of the phase and amplitude of the amplitude reflection coefficient correction factor η when the coupling phase is π, where (a) represents the phase and (b) represents the amplitude.

[0061] Fig.10 This is a schematic diagram of the threshold gain difference of each longitudinal mode when the self-coupling coefficient is 0.75 and 0.2.

[0062] Fig.11 This is a graph showing the relationship between the main and secondary mode threshold differences and the normalized cross-coupling coefficient for devices with 4%, 5% and 7% cavity length differences.

[0063] Fig.12 It is a schematic diagram of the vernier effect principle and a schematic diagram of the resonant frequency and free spectrum range of the long cavity and short cavity.

[0064] Fig.13 It is a schematic diagram of the principle of changing the operating wavelength by fine-tuning the cavity length without changing the current.

[0065] Fig.14 This is a schematic diagram of the structure of the tunable semiconductor laser array on-chip integrated application through deep etching grooves and output waveguides, where (a) represents the case of a V-cavity tunable laser in this scenario, (b) represents the case of a tunable laser based on a half-wave coupled partial reflector in this scenario, and (c) represents the case of a small-size tunable laser based on a polymer imaging coupler in this scenario.

[0066] In the figure: half-wave coupler (101), deeply etched reflection surfaces (100, 110, 120), curved waveguides (111, 121), straight waveguides (112, 122), electrodes (102, 113, 123);

[0067] Deeply etched reflection surface (210), optical waveguide (211, 221), second partial reflector (213, 223), tapered waveguide (212, 222), coupling waveguide (231), second partial reflection surface (214, 224), electrodes (201, 215, 225);

[0068] A polymer imaging coupler (311, 321), a first partial reflection surface (310, 320), a second partial reflection surface (312, 322), a middle deep etched waveguide (331), a long cavity electrode (323) or a short cavity electrode (313), and a coupler electrode (301). DETAILED DESCRIPTION

[0069] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0070] The tunable semiconductor laser array of the present invention is composed of a plurality of unit laser arrays, each of the unit lasers is a tunable semiconductor laser without a grating structure, the unit lasers in the array are arranged in parallel, the number of the unit lasers is the same as the number of wavelengths required to be emitted simultaneously, and the number of the unit lasers is determined by the number of wavelengths required to be emitted simultaneously.

[0071] Figure 2 , Figure 5 and Figure 7 The basic structural schematic diagram of the present invention is shown in the figure. The tunable semiconductor laser array is formed by an array of unit lasers therein. Each unit laser is a tunable laser. Usually, the starting or end unit laser in the array is designated as a reference laser. The unit laser adopts a tunable laser solution that does not require a grating structure, and the entire array does not need to introduce a grating; at the same time, the tunable laser solution based on silicon photonics technology is not adopted, avoiding complex end-to-end docking coupling processes and reducing costs. The material used in the present invention is a multi-layer quantum well wafer based on III-V semiconductor compounds, which mainly includes a waveguide layer, a quantum well layer, a lower cladding layer and a substrate from top to bottom.

[0072] The cavity lengths of all unit lasers in the array are different, and they are arranged in parallel, and the deep etched reflective surfaces 120, 220, and 320 at the right light output are aligned. The spacing between all unit lasers in the array is determined by the application, such as matching the output fiber array spacing. The unit laser can be in the form of a V-shaped cavity tunable laser (such as Figure 2 ), tunable lasers based on half-wave coupled partial reflectors (such as Figure 5 ) and small-size tunable lasers based on polymer imaging couplers (such as Figure 7 ). The entire array emits a wavelength sequence with a specific wavelength interval, each unit laser emits a wavelength in the wavelength sequence, and all unit lasers operate at currents of similar magnitude. The manufacturing process of the present invention is simple, requiring only conventional DFB laser process steps and deep etching processes similar to those after removing the grating manufacturing steps.

[0073] Each unit laser comprises two optical resonant cavities with different optical lengths, the two optical resonant cavities are connected by half-wave coupling, and the energy between the two optical resonant cavities is coupled by half-wave coupling, and electrodes for current injection are arranged on the two optical resonant cavities;

[0074] The electrode of one of the optical resonant cavities emits light after current is injected. Part of the light returns to the original optical resonant cavity through half-wave coupling, and the other part of the light is incident on another optical resonant cavity after half-wave coupling. The non-half-wave coupling end of any optical resonant cavity can be used as the output end of the laser to emit the working wavelength.

[0075] The ratio between the electrodes corresponding to the two optical resonant cavities and the optical lengths of the respective optical resonant cavities is consistent with the ratio between the optical lengths of the two optical resonant cavities.

[0076] The light energy coupled back to the original optical resonant cavity from the half-wave is used as the through coupling, the energy coupled back to the original optical resonant cavity from the half-wave is used as the through coupling energy, the light energy entering another optical resonant cavity through the half-wave coupling is used as the cross coupling, and the energy entering another optical resonant cavity through the half-wave coupling is used as the cross coupling energy. At the half-wave coupling point, the phase difference between the cross-coupled light and the through-coupled light is controlled to be π through the half-wave coupler, and the proportional relationship between the cross-coupling energy and the through-coupling energy is controlled. These two points are used to achieve selective loss of wavelength, thereby adjusting parameters such as the side mode suppression ratio of the unit laser to achieve optimal single-mode performance.

[0077] The two optical resonant cavities with different optical lengths are respectively a long cavity and a short cavity. The one with a long optical length is referred to as a long cavity, and the one with a short optical length is referred to as a short cavity. The optical length ratios between the long cavity and the short cavity of each unit laser are the same. By only setting the lengths of the long cavity and the short cavity of each unit laser to be different, while the other parameters and conditions are the same, each unit laser can emit lasers of different working wavelengths under basically the same current injection.

[0078] In a specific implementation, considering that the wavelength sequence interval of the array emission is 100 GHz, if the number of unit lasers is 16 or less, each unit laser receives the same injected current and no compensation is required;

[0079] If the number of unit lasers is 17 to 40, the maximum difference between the injected currents received by the unit lasers is 1%, that is, the difference between the minimum current and the maximum current is 1%.

[0080] The long cavity and the short cavity each correspond to a set of equally spaced resonant frequencies called comb spectra. Within the gain spectrum of the unit laser material, only one resonant frequency overlaps between the two sets of comb spectra of the long cavity and the short cavity, allowing single-mode operation, with the overlapping resonant frequency as the operating wavelength of the unit laser.

[0081] Injecting current into any one of the two optical resonant cavities causes its equivalent refractive index to change, thereby changing its optical length and causing its corresponding comb spectrum to move, while the comb spectrum of the other optical resonant cavity does not move, thereby changing the overlapping resonant frequency of the two optical resonant cavities and achieving tuning of the working wavelength.

[0082] The present invention is a method of using a small refractive index change to make the comb spectrum move slightly to achieve a large change in the working wavelength. This is called the vernier effect, and a large wavelength tuning range can be achieved using a limited refractive index change. Because the comb spectrum frequency interval of the long cavity is smaller, the same refractive index change can make the two groups of comb spectra align at more positions, that is, a larger tuning range can be achieved. Therefore, the long cavity is a tuning cavity, and the short cavity is a fixed gain cavity.

[0083] Deeply etched reflecting surfaces are provided at both ends of each optical resonant cavity of the unit laser, so that the end face of each optical resonant cavity in the optical length direction is defined by the deeply etched reflecting surface, and the optical length of each optical resonant cavity is the optical distance between the deeply etched reflecting surfaces at both ends, wherein the deeply etched reflecting surface at the outer end of the optical resonant cavity close to the output end of the unit laser is set as a semi-transmissive and semi-reflective surface, and the remaining deeply etched reflecting surfaces are set as reflecting surfaces by coating with high reflectivity films.

[0084] In a specific implementation, the unit lasers constituting the array may be one of a V-cavity tunable laser, a tunable laser based on a half-wave coupled partial reflector, or a small-size tunable laser based on a polymer imaging coupler.

[0085] All three laser solutions include a certain form of half-wave coupling to achieve excellent single-mode characteristics, and also include two optical resonant cavities with a certain length difference to achieve a large tuning range using the vernier effect. All three lasers can achieve single-electrode tuning by injecting current through electrodes on the long cavity or short cavity, simplifying the tuning control algorithm, and none of the three requires a grating.

[0086] 1) V-cavity tunable laser:

[0087] like Figure 1 As shown, two optical resonant cavities are included, and the two optical resonant cavities are distributed in a V shape. Each optical resonant cavity is mainly composed of a half-wave coupler 101, a section of curved waveguide 111, 121, and a section of straight waveguide 112, 122 connected in sequence. One end of the curved waveguide 111, 121 is connected to one end of the straight waveguide 112, 122. The half-wave coupler 101 of the two optical resonant cavities shares the same one, so that the two optical resonant cavities are coupled and connected through the half-wave coupler 101; the half-wave coupler 101 is not connected to the curved waveguide 111, 121. One end at which the waveguides 111 and 121 are connected is connected to the first deeply etched reflection surface 100, and the straight waveguides 112 and 122 of each optical resonant cavity are connected to their respective deeply etched reflection surfaces 110 and 120 at the end not connected to the curved waveguides 111 and 121; specifically, the straight waveguide 112 of the short cavity is connected to the second deeply etched reflection surface 110 at the end not connected to the curved waveguide 111, and the straight waveguide 122 of the long cavity is connected to the third deeply etched reflection surface 120 at the end not connected to the curved waveguide 121.

[0088] The laser is provided with three electrodes, wherein one electrode 101 covers the curved waveguides 111, 121 located in the half-wave coupler 101 and a part of the two optical resonant cavities, and the other two electrodes 113, 123 cover the curved waveguides 111, 121 and the straight waveguides 112, 122 located in the remaining parts of the two optical resonant cavities respectively.

[0089] Each of the single deep-etched reflective surfaces 100 , 110 , and 120 is formed by etching a pit on the wafer that penetrates the quantum well layer, with the plane of the pit wall serving as the reflective surface.

[0090] Among the deeply etched reflection surfaces 110 and 120 of the two optical resonant cavities, the second deeply etched reflection surface 110 corresponding to the short cavity is set as a total reflection surface, and the third deeply etched reflection surface 120 corresponding to the long cavity is set as a semi-transparent and semi-reflective surface, which serves as the output end of the unit laser.

[0091] Current is injected into all electrodes, and then the straight waveguides 112, 122 / curved waveguides 111, 121 under the electrodes excite light in the optical resonant cavity. The light propagates back and forth in the optical resonant cavity, and is reflected when it propagates to the deeply etched reflective surface. When it propagates to the half-wave coupler 101, cross-coupling and through-coupling occur.

[0092] 2) Tunable laser based on half-wave coupled partial reflector:

[0093] like Figure 3 and Figure 4 As shown, it includes two optical resonant cavities and a coupling waveguide 231, the two optical resonant cavities are distributed along the same straight line, and the coupling waveguide 231 is arranged between the two optical resonant cavities;

[0094] Each optical resonant cavity is mainly composed of a deeply etched reflecting surface 210, 220, a section of optical waveguide 211, 221, a section of tapered waveguide 212, 222 and a second partial reflector 213, 223 connected in sequence, and the two optical resonant cavities are coupled to each other through a coupling waveguide 231 connecting the respective second partial reflectors 213, 223; the two second partial reflectors 213, 223 and the coupling waveguide 231 together constitute a half-wave coupler.

[0095] One end of the second partial reflector 213, 223 is connected to the large end of the tapered waveguide 212, 222, and the other end is symmetrically provided with second partial reflecting surfaces 214, 224 with a cut angle of 45 degrees on both sides of the axis; the small end of the tapered waveguide 212, 222 is connected to the optical waveguide 211, 221, and the width of the second partial reflector 213, 223 is greater than the width of the large end of the tapered waveguide 212, 222; the second partial reflectors 213, 223 are provided with deep etched reflecting surfaces with a cut angle of 45 degrees on both sides of the end surface connected to the coupling waveguide 231 as the second partial reflecting surfaces 214, 224, and the remaining part in the middle of the end surface is connected to the middle coupling waveguide 231; there are two second partial reflecting surfaces 214, 224, which are respectively located on the symmetrical sides of the connection between the end of the second partial reflector 213, 223 and the coupling waveguide 231.

[0096] Part of the energy in the energy distribution at the end of the second partial reflector 213, 223 of the optical resonant cavity is reflected back to the optical resonant cavity where it is located to form a through coupling, and the other part of the energy is coupled to another optical resonant cavity through the coupling waveguide 231 to form a cross coupling.

[0097] The deep etching of the reflection surfaces 210 and 220 is to etch a first pit on the wafer that penetrates the quantum well layer, and use the plane of the wall of the first pit as the first partial reflection surface;

[0098] The second partial reflective surfaces 214, 224 are formed by etching two second pits at the ends of the second partial reflectors 213, 223 and on both sides symmetrically of the straight line where the second partial reflectors 213, 223 are located. Each second pit is set to have a 45-degree cut angle at a corner near the end, and the plane of the pit wall with the 45-degree cut angle is used as the second partial reflective surface; and there is a gap distance with a width smaller than the width of the second partial reflectors 213, 223 between the two second pits, and a coupling waveguide 231 is set at the gap distance; the two second pits of the second partial reflective surfaces 214, 224 of the two optical resonant cavities are shared, that is, two second pits that penetrate the quantum well layer are etched between the ends of the second partial reflectors 213, 223 of the two optical resonant cavities and on both sides symmetrically of the straight line where the second partial reflectors 213, 223 are located, and each second pit is set to have a 45-degree cut angle at a corner near the ends of the second partial reflectors 213, 223, and the plane of the pit wall with the 45-degree cut angle is used as the second partial reflective surface.

[0099] Of the deeply etched reflection surfaces 210 and 220 of the two optical resonant cavities, one deeply etched reflection surface 210 and 220 is a total reflection surface, and the other deeply etched reflection surface 210 and 220 is a semi-transparent and semi-reflective surface, which serves as the output end of the laser.

[0100] The second partial reflection surfaces 214 and 224 are also deeply etched reflection surfaces, and two deeply etched reflection surfaces with a cut angle of 45 degrees constitute a group of total reflection structures.

[0101] The laser is provided with three electrodes, namely, a coupler electrode 201 located in the middle and a short cavity electrode 215 and a long cavity electrode 225 located on both sides respectively; the coupler electrode 201 simultaneously covers the tapered waveguides 212, 222 and the second partial reflectors 213, 223 and a part of the optical waveguides 211, 221 in the two optical resonant cavities, and the ratio between the optical lengths of the two optical resonant cavities covered by the coupler electrode 201 is consistent with the ratio between the overall optical lengths of the two optical resonant cavities; the long cavity electrode 225 and the short cavity electrode 215 respectively cover the longer optical resonant cavity and the shorter optical resonant cavity and cover the remaining parts of the optical waveguides 211, 221 not covered by the coupler electrode 201, and the length of the optical resonant cavity covered by the long cavity electrode 225 is greater than the length of the optical resonant cavity covered by the short cavity electrode 215.

[0102] Current is injected into all electrodes, and then the long cavity electrode 225 / short cavity electrode 215 / coupler electrode 201 under the electrodes excite light in the optical resonant cavity. The light propagates back and forth in the optical resonant cavity. When it propagates to the coupling waveguide 231, cross coupling and through coupling occur. When it propagates to the deeply etched reflective surface, reflection or semi-transmission and semi-reflection occurs.

[0103] 3) Small-size tunable laser based on polymer imaging coupler:

[0104] like Figure 6 As shown, it includes two optical resonant cavities and an intermediate deeply etched waveguide 331, each optical resonant cavity is mainly composed of respective first partial reflection surfaces 310, 320, aggregate imaging type couplers 311, 321 and second partial reflection surfaces 312, 322 connected in sequence, the two optical resonant cavities are distributed along the same straight line, and are coupled to each other through a section of intermediate deeply etched waveguide 331 connecting respective second partial reflection surfaces 312, 322; a half-wave coupler is formed by two aggregate imaging type couplers 311, 321 and the intermediate deeply etched waveguide 331 coupling the two optical resonant cavities.

[0105] Each optical resonant cavity has two second partial reflection surfaces 312, 322, which are respectively located on the symmetrical sides of the connection between the end of the aggregate imaging coupler 311, 321 and the middle deeply etched waveguide 331; the two side parts of one end of the aggregate imaging coupler 311, 321 are connected to the second partial reflection surfaces 312, 322, and the remaining part in the middle is coupled and connected to the middle deeply etched waveguide 331; the two second partial reflection surfaces 312, 322 on both sides constitute a group of total reflection structures; a part of the energy distribution of the end face of the aggregate imaging coupler 311, 321 of the optical resonant cavity is reflected back to the optical resonant cavity where it is located to form a straight-through coupling, and the other part of the energy is coupled to another optical resonant cavity through the middle deeply etched waveguide 331 to form a cross coupling.

[0106] The first partial reflection surfaces 310 and 320 are first pits etched on the wafer and penetrating the quantum well layer, and the plane of the pit wall of the first pit is used as the first partial reflection surface;

[0107] The second partial reflection surfaces 312 and 322 are formed by etching two second pits at the ends of the polymer imaging couplers 311 and 321 and on both sides of the symmetric lines where the polymer imaging couplers 311 and 321 are located. Each second pit is set at a 45-degree cut angle at a corner close to the ends of the polymer imaging couplers 311 and 321, and the plane of the pit wall with a 45-degree cut angle is used as the second partial reflection surface; and there is a gap distance between the two second pits with a width less than the width of the polymer imaging couplers 311 and 321, and a gap distance is set at the gap distance. The waveguide 331 is deeply etched in the middle; the two second pits of the second partial reflection surfaces 312 and 322 of the two optical resonant cavities are shared, that is, two second pits that penetrate the quantum well layer are etched between the opposite ends of the polymer imaging type couplers 311 and 321 of the two optical resonant cavities and on both sides of the symmetry of the straight line where the polymer imaging type couplers 311 and 321 are located, and each second pit is set to a 45-degree cut angle at a corner close to the end of the polymer imaging type coupler 311 and 321, and the plane of the pit wall with a 45-degree cut angle is used as the second partial reflection surface.

[0108] Of the first partial reflection surfaces 310 and 320 of the two optical resonant cavities, one first partial reflection surface 310 and 320 is a total reflection surface, and the other first partial reflection surface 310 and 320 is a semi-transparent and semi-reflective surface, which serves as the output end of the laser.

[0109] There are two electrode settings for small-size tunable lasers based on polymer imaging couplers:

[0110] First, the laser is provided with two electrodes, namely a short cavity electrode 313 and a long cavity electrode 323, which are respectively located on two sides; the long cavity electrode 323 and the short cavity electrode 313 are respectively covered on the longer optical resonant cavity and the shorter optical resonant cavity.

[0111] The second type, the laser is provided with three electrodes, namely, a coupler electrode 301 located in the middle and a short cavity electrode 313 and a long cavity electrode 323 located on both sides respectively; the coupler electrode 301 covers a part of each of the two optical resonant cavities at the same time, and the ratio between the optical lengths of the two optical resonant cavities covered by the coupler electrode 301 is consistent with the ratio between the overall optical lengths of the two optical resonant cavities; the long cavity electrode 323 and the short cavity electrode 313 respectively cover the longer optical resonant cavity and the shorter optical resonant cavity and cover the remaining part not covered by the coupler electrode 301, and the length of the long cavity electrode 323 covering its corresponding optical resonant cavity is greater than the length of the short cavity electrode 313 covering its corresponding optical resonant cavity.

[0112] Current is injected into all electrodes, and then the long cavity electrode 323 / short cavity electrode 313 / coupler electrode 301 under the electrodes excite light in the optical resonant cavity. The light propagates back and forth in the optical resonant cavity. When it propagates to the middle deeply etched waveguide 331, cross coupling and through coupling occur. When it propagates to the reflective surface, reflection or semi-transmission and semi-reflection occurs.

[0113] When the tunable semiconductor laser array is in operation, it emits a set of lasers with a working wavelength sequence with a specific wavelength interval, and each unit laser emits a laser with a working wavelength. The unit lasers in the array sequentially emit lasers with specific wavelengths in the working wavelength sequence. The working wavelength sequence that the array can emit is not unique in itself, and can be tuned by the synchronous action of all unit lasers in the array.

[0114] When a tunable semiconductor laser array emits a laser of a specific operating wavelength sequence, although all unit lasers in the array operate at different operating wavelengths, the required operating currents injected into the corresponding electrodes of all unit lasers are basically consistent, which can greatly simplify the back-end control circuit and reduce costs. The basically consistent operating current means that the minimum current and maximum current of the same electrode in an array of up to 40 unit lasers at a wavelength interval of 100GHz differ by 1%.

[0115] The wavelength interval in the above working wavelength sequence can be designed, and each unit laser in the array emits one of the wavelengths, and all unit lasers work simultaneously. The cavity length of each unit laser in the array is slightly different, so that the current required by each unit laser when working at different wavelengths is basically similar, which can greatly simplify the complexity of the back-end circuit and the control algorithm, thereby reducing costs. In addition, the wavelength sequence emitted by the entire array itself is tunable, which expands the range of wavelength sequences that can work and can be flexibly applied to occasions with different wavelength sequence requirements.

[0116] In specific implementations, the output of the array can be coupled through fiber array docking, or by introducing deep etched grooves with semi-transmissive and semi-reflective functions at all unit laser output positions to replace the original deep etched reflective surfaces, to integrate array waveguide gratings, etched diffraction gratings and other devices on-chip for combined output, or to integrate devices with more functions.

[0117] The implementation principle of the present invention is as follows:

[0118] The half-wave couplers in the above three tunable laser solutions have the same function, but the three solutions are different in specific implementation forms. The half-wave coupler couples the energy of two optical resonant cavities to form direct-coupled energy and cross-coupled light energy, and controls the energy ratio of the two parts to the optimal value according to parameters such as the cavity length difference between the two optical resonant cavities. At the same time, the half-wave coupler can control the phase difference between the cross-coupled light and the direct-coupled light to be π to introduce wavelength selective loss, hence the name half-wave coupler. By introducing wavelength selective loss to improve the laser mode selection ability, the laser single-mode performance parameters such as the side mode suppression ratio (SMSR) are greatly improved.

[0119] The working conditions required for the half-wave coupler are analyzed based on the threshold equation. The general threshold equation for the tunable laser scheme including the half-wave coupler and two optical resonators is as follows:

[0120] C 11 *r1*r2*e 2*(g+i*k)*ls + C 22 *r1*r2*e 2*(g’+i*k’)*ll -(C 11 *C 22 -C 12 *C 21 )*r1 2 *r2 2 *e 2 *(g+i*k)*ls *e 2*(g’+i*k’)*ll =1 (1.1)

[0121] Where * indicates multiplication, g and k, g' and k' are the gain coefficients and propagation constants in the short cavity and long cavity respectively, subscript 1 indicates a short cavity, and subscript 2 indicates a long cavity. 11 With C 22 are the through coupling coefficients of the energy amplitude from the short cavity back to the short cavity through the half-wave coupler and from the long cavity back to the long cavity through the half-wave coupler, C 12 With C 21are the cross-coupling coefficients of the energy amplitude from the short cavity to the long cavity and from the long cavity to the short cavity through the half-wave coupler, r1 and r2 represent the end face reflection coefficients of the two optical resonant cavities at the non-half-wave coupler ends, ll is the cavity length of the long cavity, and ls is the cavity length of the short cavity. The reference position for calculating the four coupling coefficients is the half-wave coupler 101 and the connection 111, 121 of the two bending waves, i.e. the output position of the half-wave coupler, for the V-cavity tunable laser; for the other two schemes, it is the position just through the second partial reflection surface 214, 224, 312, 322 to the corresponding optical resonant cavity. Due to the symmetry of the optical paths of the two optical resonant cavities, the short cavity is taken as the main analysis target in the subsequent analysis, and the influence of factors such as the extra phase difference of the long cavity and the half-wave coupler on the short cavity is generally manifested as a complex reflection coefficient η. η can be expressed as:

[0122] η = C 11 +C 21 *C 12 *r1*r2*e 2*(g’+i*k’)*ll / (1-C 22 *r1*r2*e 2*(g’+i*k’)*ll ) (1.2)

[0123] According to the symmetry of the long and short cavity structure, it can be considered that C 11 =C 22 =C b , C 12 =C 21 =C x , where C b The through coupling coefficient, C, represents the energy amplitude x represents the cross-coupling coefficient of energy amplitude. Both are amplitude complex coupling coefficients, C b With C x The imaginary difference of reflects the phase difference between the through coupling coefficient and the cross coupling coefficient. Therefore, the amplitude reflection coefficient correction factor η can be simplified as:

[0124] η = C b +C x 2 *r1*r2*e 2*(g’+i*k’)*ll / (1-C b *r1*r2*e 2*(g’+i*k’)*ll ) (1.3)

[0125] Figure 8 and Fig. 9The phase and amplitude of the energy amplitude reflection coefficient correction factor η in two special cases when the phase difference is π / 2 and π are given in the figure. It can be found that when the phase difference between the through coupling coefficient and the cross coupling coefficient is π / 2, the amplitude of η is constant at 1 over a large wavelength range, and there is no loss for any wavelength. This shows that the extra phase difference of the long cavity and the half-wave coupler has no effect on the resonance of the short cavity, and the two optical resonant cavities are completely independent. Such a half-wave coupler does not provide any mode selection function and cannot be applied. Fig. 9 As shown in , when the phase difference between the through coupling coefficient and the cross coupling coefficient is π, η plays a wavelength selective effect, with loss for wavelengths other than the main mode, and the equivalent energy amplitude reflection coefficient of the short cavity close to the half-wave coupler side is a wavelength-dependent comb spectrum with a very narrow bandwidth. The comb spectrum of the reflection coefficient, the resonance spectrum of the short cavity itself, and the gain spectrum of the material work together to ensure the mode selection function of the laser, achieve excellent single-mode performance, and achieve similar single-mode performance with a grating structure without using a grating. It can be seen that the phase difference of π between the through coupling coefficient and the cross coupling coefficient is the first performance indicator of a half-wave coupler that can provide a mode selection mechanism. Because the phase difference is π, it is called a half-wave coupler.

[0126] On the other hand, under the premise that the phase difference between the through coupling coefficient and the cross coupling coefficient is π, improving the proportional relationship between the cross coupling coefficient and the through coupling coefficient can further improve the single-mode performance. The influence of the proportional relationship between the two coupling coefficients on the energy amplitude reflection coefficient correction factor η is mainly reflected in Fig.10 The width of the comb spectrum shown and the contrast that characterizes the degree of its peak height. The SMSR of a laser is a characteristic indicator to measure the single-mode characteristics. It represents the power difference between the main mode and the maximum power side mode near it. Theoretically, it can be characterized by the threshold gain difference between the two modes. The greater the difference in threshold gain between the main mode and the side mode, the better the single-mode performance. Starting from the threshold equation (1.1), considering the usual equal loop gain condition in use (that is, considering g*ls=g*ll), the threshold gain g0 of the main mode is only determined by the end face reflection coefficients r1 and r2 at the non-half-wave coupler ends of the two optical resonators. The half-wave coupler does not introduce any loss to the main mode. The thresholds of other modes can also be solved from the threshold equation. The results are shown in Fig.10 as shown in . Fig.10 The threshold conditions of the main mode and the side mode are calculated in , considering two cases where the through coupling coefficient is 0.75 and 0.2. Since the half-wave coupler has no loss to the main mode, different through coupling coefficients are equivalent to different ratios of the cross-coupling coefficient to the through coupling coefficient. It can be seen that with a larger through coupling coefficient (0.75), that is, a smaller ratio of the cross-coupling coefficient to the through coupling coefficient, the narrower amplitude reflection coefficient correction factor η brings a larger threshold gain difference, about 8cm -1, while the threshold gain difference is only 0.32cm when the through coupling coefficient is 0.2 -1 .

[0127] Next, we consider the relationship between the optimal ratio of the cross-coupling coefficient to the through-coupling coefficient and the cavity length difference. Define the normalized intensity cross-coupling coefficient χ of the half-wave coupler, which better measures the ratio between the cross-coupling and through-coupling:

[0128] χ=|C 21 | 2 / (|C 11 | 2 +|C 21 | 2 )=|C 12 | 2 / (|C 12 | 2 +|C 22 | 2 ) (1.4)

[0129] Fig.11 The relationship between the threshold difference between the main side modes and χ is shown in the calculation of the three cavity length differences of 4%, 5% and 7%. For a specific cavity length difference, there is an optimal χ, at which the threshold difference between the main side modes is the largest, that is, the single-mode performance is the best. The normalized intensity cross-coupling coefficient χ required for different cavity length differences is different. It is calculated that the 7% cavity length difference corresponds to 0.043, the 5% cavity length difference corresponds to 0.023, and the 4% cavity length difference corresponds to 0.015. The larger the cavity length difference is, the greater the ability to achieve a large main side mode threshold difference, and the larger χ is, which also means a larger cross-coupling coefficient and a smaller through-coupling coefficient, which is equivalent to a higher SMSR. The normalized intensity cross-coupling coefficient χ is also an important performance indicator of the half-wave coupler. However, a larger cavity length difference will result in a smaller tuning range, which is a disadvantage, so a compromise between multiple factors is required. The normalized intensity cross-coupling coefficient χ is specially optimized for a specific design (specific cavity length difference). The cavity length difference in the design is usually between 4% and 7%, which is a more appropriate design to balance the SMSR and the tuning range.

[0130] In summary, under the premise of selecting a suitable cavity length difference, the half-wave coupler optimizes the optimal normalized intensity cross-coupling coefficient χ and makes the phase difference between the cross-coupling and the through-coupling π, thereby introducing wavelength selective loss to achieve excellent single-mode performance.

[0131] The three tunable laser schemes adopted in the present invention all include two optical resonant cavities with different cavity lengths, the long one is called a long cavity and the short one is called a short cavity, and the axial length is defined at both ends by deeply etching the reflecting surface. The precise definition of the cavity length during production by deeply etching the reflecting surface, rather than determining the cavity length by the traditional cleavage process, plays a core role in the present invention. The long cavity and the short cavity each correspond to a set of equally spaced resonant frequencies, called comb spectra. The resonant frequency intervals of the two groups of comb spectra are unequal, and the comb spectrum frequency interval corresponding to the long cavity is smaller. Within the gain spectrum range of the laser material, only one resonant frequency of the two groups of comb spectra overlaps, thereby ensuring single-mode operation, and the overlapping resonant frequency is the operating wavelength of the laser.

[0132] The vernier effect refers to the process of injecting current into any optical resonant cavity to move its comb spectrum, so that the overlap position of the two sets of comb spectra changes and the working wavelength is tuned. A larger wavelength change, i.e., the change in the overlap position of the two sets of comb spectra, is achieved through a smaller refractive index change, i.e., the movement of the set of comb spectra that moves. One set of comb spectra moves and aligns with the other set of comb spectra that does not move, and the overlap position changes in turn to tune the wavelength. The cavity in which the comb spectrum moves is called a tuning cavity, and the cavity in which the comb spectrum does not move is called a fixed gain cavity. The fixed gain cavity determines the working wavelength.

[0133] The short cavity length is ls, and its comb resonance frequency interval is:

[0134] Δf s =c / (2*n g *ls) (2.1)

[0135] Where c is the speed of light in a vacuum, n g is the group refractive index of the laser waveguide. The resonant frequency interval of the short cavity is selected according to the needs, generally according to the ITU standard of 100GHz or 200GHz. If a small-size tunable laser solution is used, the resonant frequency interval is very large, and the frequency interval of 400GHz to 800GHz can be designed. The length of the long cavity is ll=ls*(1+α), where α is the percentage of the cavity length difference between the long cavity and the short cavity. Similarly, the resonant frequency and frequency interval of the long cavity can be calculated. The frequency interval is smaller than that of the short cavity. The two sets of comb spectra are as follows Fig.12 As shown in l With f s The distance between the two overlapping positions of the two comb spectra is called the free spectral range (FSR), which represents the size of the laser tuning range and is also expressed by Fig.12 As shown in , the calculation is shown in formula 2.2.

[0136] FSR=(Δf l *Δf s ) / |Δf s -Δfl |=(1+α) / α*Δf l (2.2)

[0137] Where Δf l represents the comb spectrum frequency interval of the long cavity, Δf s Represents the frequency interval of the comb spectrum of the short cavity. By injecting current to change the refractive index of one of the optical resonant cavities, its corresponding comb spectrum can be moved, causing the coincidence frequency to change and wavelength tuning to be achieved. This phenomenon is called the vernier effect. The vernier effect requires only a small change in the refractive index to achieve a large change in wavelength, thereby improving the tuning efficiency. Since the frequency interval in the comb spectrum of the long cavity is smaller, more wavelengths can be aligned after the comb spectrum is moved under the same current, and more wavelengths can be tuned. Therefore, the long cavity is usually a tuning cavity. The short cavity is usually not tuned, and its comb resonance frequency interval determines the frequency interval of the entire laser operating wavelength. The wavelength that the laser can tune occurs on a series of discrete comb frequencies determined by the short cavity. The long cavity moves the comb spectrum of the long cavity to align and select a specific operating wavelength.

[0138] The tunable semiconductor laser array of the present invention emits a wavelength sequence with a specific wavelength interval when in operation, and each unit laser in the array emits a wavelength in the wavelength sequence. By fine-tuning the cavity length of each unit laser, each unit laser can be operated at a different wavelength in the wavelength sequence under an operating current of approximately the same magnitude. First, a unit laser in the array is selected as a reference laser, usually the first or last unit laser in the array, and is properly tuned so that the reference laser emits the starting or ending wavelength in the wavelength sequence under an operating current of an appropriate magnitude. Then, the unit lasers arranged sequentially in the array sequentially emit other wavelengths in the wavelength sequence under an operating current of approximately the same magnitude.

[0139] As mentioned above, the tunable laser solution used in the present invention usually has an operating wavelength selected on the comb spectrum of the short cavity and determined by the short cavity. For the adjusted reference laser operating wavelength, the relationship with the reference laser short cavity length is:

[0140] 2*n g0 *l s0 =m0*λ0 (3.1)

[0141] Among them, n g0 is the group refractive index in the short cavity of the reference laser, l s0 is the short cavity length of the reference laser, λ0 is the operating wavelength of the reference laser, and m0 is the order.

[0142] For any other unit laser, assuming that its operating wavelength is λ1, it also satisfies the following relationship with its short cavity length:

[0143] 2*n g1 *l s1 =m1*λ1 (3.2)

[0144] Where n g1 is the group refractive index in the short cavity, l s1 is the short cavity length, m1 is the order. For the same optical resonant cavity structure, the group refractive index of the two is the same. g0 =n g1 , let the working order of the two be the same m0=m1, then:

[0145] l s0 / l s1 =λ0 / λ1 (3.3)

[0146] The ratio of their working wavelengths is only related to the ratio of their short cavity lengths. Since the difference in their working wavelengths is very small, at a wavelength interval of 100 GHz, the difference between the tail and the head of the wavelength sequence in the array composed of 40 unit lasers is 2%. Therefore, the maximum difference in the short cavity length of the unit laser and the reference laser in the array is also 2%, which is very small overall, and in turn can also ensure that the operation is at the same level.

[0147] Since the tunable laser solution adopted in the present invention uses the vernier effect to select the final operating wavelength, the long cavity length also needs to be adjusted to ensure that the position of the vernier alignment in the two sets of comb spectra does not change.

[0148] For the reference laser, it satisfies:

[0149] 2*n g0 *l s0 =m s0 *λ0 (3.4)

[0150] 2*n g0 *l l0 =m l0 *λ0 (3.5)

[0151] Among them l s0 , l l0 is the cavity length of the short cavity and long cavity of the reference laser, m s0 With m 10 It is the order of the working wavelength λ0 in the short cavity and long cavity of the reference laser.

[0152] For any other unit laser, it satisfies:

[0153] 2*n g1 *l s1 =m s1 *λ1 (3.6)

[0154] 2*n g1 *ll1 =m l1 *λ1 (3.7)

[0155] Among them l s1 , l l1 is the cavity length of the short cavity and long cavity of any other unit laser, m s1 With m 11 It is the order of the operating wavelength λ1 of any unit laser in the short cavity and long cavity of any unit laser.

[0156] It is also assumed that all group refractive indices are consistent due to the same optical resonance strong structure, and the short cavity working order of any other unit laser is m s1 Compared with the reference laser short cavity order m s0 Let the long cavity of any other unit laser work at the order m l1 Compared with the reference laser long cavity order m s1 Consistent, at this time:

[0157] l s1 / l l1 = m s1 / m l1 = m s0 / m l0 = l s0 / l l0 (3.8)

[0158] That is, if the ratio of the length of the long and short cavities of any other unit laser is kept consistent with that of the reference laser, the cursor alignment position in the comb spectrum can be guaranteed not to change, and any other unit laser works at λ1 determined in equation 3.3. Similarly, at a wavelength interval of 100 GHz, the maximum variation of the length of the unit laser relative to the reference laser in the array of 40 unit lasers is also 2%.

[0159] The change of the operating wavelength is achieved by fine-tuning the cavity length of the two optical resonators. This effect is similar to quasi-continuous tuning. The wavelength is tuned by making the two sets of comb spectra of any unit laser move synchronously relative to the two sets of comb spectra of the reference laser and keeping the vernier effect alignment position unchanged, see Fig.13 as shown in . Fig.13 Medium s0 With f l0 is the comb spectrum of the short cavity and long cavity of the reference laser, f0 is the operating frequency corresponding to the operating wavelength λ0 of the reference laser; f s1 With f l1is the comb spectrum of the short cavity and long cavity of any unit laser, f1 is the operating frequency corresponding to the operating wavelength λ1 of the reference laser; Δf is the frequency difference between the two operating wavelengths, which is equivalent to the interval between the two operating wavelengths. Assuming that the reference laser operates at the starting position of the wavelength sequence, and the operating wavelengths of other unit lasers are longer than the operating wavelength of the reference laser, the unit laser cavity length is longer than the reference laser. Since the comb spectrum reflects the resonant frequency, its long and short cavity comb spectrum is shifted to the left relative to the comb spectrum of the reference laser, and the alignment position remains unchanged, ultimately achieving a longer operating wavelength of the unit laser. Δf s0 With Δf l0 is the comb spectrum interval between the short cavity and the long cavity of the reference laser, Δf s1 With Δf l1 is the comb spectrum interval between the short cavity and the long cavity of any unit laser. Due to the change of the cavity length of the unit laser relative to the reference laser, Δf s0 Not equal to Δf s1 , Δf l0 Not equal to Δf l1 , but their differences are still equivalent to the difference in cavity length of the unit laser relative to the reference laser. At a wavelength interval of 100 GHz, the maximum variation in an array of 40 unit lasers is usually Δf s0 With Δf l0 2% of the designed wavelength interval (usually equivalent to Δf s0 ) is very small and can be ignored.

[0160] In the above process, it is necessary to ensure that the only factor that causes the comb spectrum to move is the cavity length, so it can be achieved without changing the injected current. At the same time, since the maximum difference in cavity length between different unit lasers in the array is very small, at a wavelength interval of 100 GHz, the maximum cavity length difference in the array composed of 16 unit lasers is only 1%, and the amplitude of the thermal refractive index change caused by the resistance change can be ignored when the current remains unchanged. Thereby, different unit lasers in the array of the present invention each emit different wavelengths in the wavelength sequence, but work under the same current. If the array scale is very large, the number of unit lasers at a wavelength interval of 100 GHz is greater than 16, reaching 40 or even more, and the cavity length change makes the amplitude of the thermal refractive index change caused by the resistance change cannot be ignored, the current compensation of the tail several unit lasers can be fine-tuned. The purpose of current compensation is to keep the same electrode power consumption consistent. Since the change in cavity length is equivalent to the change in resistance of the corresponding electrode, the current compensation adjustment amplitude is related to the square root of the change in cavity length, which is very small. At a wavelength interval of 100 GHz, when the number of unit lasers is 40, it is only 1%, which meets the requirement that all unit lasers work under approximate current. All unit lasers in the array operate at similar currents, which greatly simplifies the control circuit requirements and the tuning control of the entire array. When the wavelength sequence emitted by the entire array needs to be tuned, the tuning process is basically equivalent to tuning the reference laser. Once the reference laser operating wavelength is tuned in place, the entire array automatically tunes to the new operating wavelength sequence, simplifying the tuning circuit and reducing costs. In addition, from the working principle of the above array, it can be seen that the wavelength interval in the wavelength sequence itself can be designed on demand by changing the cavity length of each unit laser relative to the reference laser, that is, Fig.13 The Δf in the figure can be changed as needed, and even the wavelength interval itself does not necessarily need to be a constant, so the present invention can flexibly adapt to the needs of different scenarios.

[0161] The specific embodiments are as follows: Embodiment 1:

[0162] like Figure 2 As shown, the tunable semiconductor laser array is formed by V-cavity tunable lasers, and the deeply etched reflective surfaces 120 at the long cavity ends of all V-cavity tunable lasers in the array are aligned with each other as light emitting surfaces.

[0163] The basic structure of the unit laser of the V-cavity tunable laser is as follows Figure 1 As shown in , the two optical resonant cavities are distributed in a V-shape, and the half-wave coupler 101 at the bottom of the V-shape couples the two optical resonant cavities.

[0164] A long optical resonant cavity is called a long cavity, and a short optical resonant cavity is called a short cavity.

[0165] Each optical resonant cavity includes a half-wave coupler 101 and a respective curved waveguide 111, 121 and a straight waveguide 112, 122. The end faces of the two optical resonant cavities are deeply etched reflective surfaces 100, 110, 120. Since the two optical resonant cavities share the half-wave coupler 101, there are only three deeply etched reflective surfaces 100, 110, 120. Compared with the traditional cleavage surface, the deeply etched reflective surfaces 100, 110, 120 can accurately control the cavity length of the optical resonant cavity. The deeply etched reflective surfaces 100, 110, 120 have a higher reflectivity of about 0.4 because they pierce the quantum well layer. At the same time, a certain transmittance can be used for output.

[0166] The optical resonant cavity at the bottom of the V-shaped cavity tunable laser is designed as a long cavity, and its end is parallel to the crystal direction and outputs through its deeply etched reflective surface 120. The deeply etched reflective surfaces 100 and 110 for non-output are coated with a high reflectivity film to increase the reflectivity to 0.99, reduce the loss and lower the laser threshold.

[0167] One end of the half-wave coupler 101 is a deeply etched reflective surface 100, and the other end is connected to two sections of curved waveguides 111 and 121. Another function of the deeply etched reflective surface 100 here is to fold the optical path of the half-wave coupler 101 in half, so that the actual half-wave coupler 101 is half the length of the designed value, making the laser more compact. The energy of an optical resonant cavity is transmitted to the half-wave coupler 101 and reflected by the deeply etched reverse surface 100. A part of it returns to itself after passing through the half-wave coupler 101, and the other part enters another optical resonant cavity after passing through the half-wave coupler 101. The part that returns to itself after passing through the half-wave coupler 101 is called through coupling, and the part that enters another optical resonant cavity is called cross coupling.

[0168] The half-wave coupler 101 controls the energy ratio and phase difference of cross coupling and straight-through coupling to be π at its own output position, that is, at the connection between the half-wave coupler 101 and the two curved waveguides 111 and 121, so that it has wavelength selective loss and thus the laser has excellent single-mode performance. The half-wave coupler 101 can be realized by improving a 2*2 directional coupler, or by a polymer imaging coupler developed from a multi-mode interference coupler.

[0169] The polymer imaging coupler here is derived from the N*N multimode interference coupler. By optimizing its input position and compressing its overall size, the image it forms is polymerized and the energy distribution and phase distribution of the output port are adjusted to achieve the cross-coupling and straight-through coupling energy ratio and phase relationship requirements required by the half-wave coupler 101. The design of the half-wave coupler 101 in the V-cavity tunable laser requires simultaneous optimization of the cross-coupling and straight-through coupling energy relationship and the π phase difference. The electrodes 102, 113, and 123 of the V-cavity tunable laser are designed to be three.

[0170] The coupler electrode 102 covers the half-wave coupler 101 and a portion of the long cavity and the short cavity in equal proportion, and is the main gain electrode and direct modulation electrode. The remaining long cavity and short cavity are covered by the long cavity electrode 123 and the short cavity electrode 113, respectively. By injecting current into the long cavity electrode 123 or the short cavity electrode 113, a wide range of wavelength tuning can be achieved through the vernier effect. The V-cavity tunable laser can be tuned by changing only one electrode current, and the tuning control algorithm is simple. Figure 2 The array of V-cavity tunable lasers is shown in the figure, in which the deeply etched reflective surface 120 on the long cavity light-emitting side of all V-cavity tunable lasers in the array is aligned, and the long cavity length and short cavity length of all V-cavity tunable lasers are different. Embodiment 2:

[0171] like Figure 5 As shown, the tunable semiconductor laser array is formed by tunable lasers based on half-wave coupled partial reflectors, and the tunable lasers based on half-wave coupled partial reflectors in the array have long cavity ends with deeply etched reflective surfaces 220 as light emitting surfaces aligned with each other.

[0172] The basic structure of the unit laser of the tunable laser based on half-wave coupled partial reflector is as follows Figure 3 As shown in . Its two optical resonant cavities are also divided into a long cavity and a short cavity, which are distributed in a straight line, coupled by a coupling waveguide in the middle 231, and the long cavity design is located on the right.

[0173] Each optical resonant cavity is mainly composed of a deep etched reflection surface 210, 220, a section of optical waveguide 211, 221, a section of tapered waveguide 212, 222 and a second partial reflector 213, 223. The two second partial reflectors 213, 223 and the coupling waveguide 231 together form a half-wave coupler, such as Figure 4 as shown in .

[0174] The second partial reflectors 213 and 223 are a wide waveguide, one side of which is connected to the tapered waveguide, and the other side is symmetrically axially with two ends of the second partial reflective surfaces 214 and 224 cut at 45 degrees. The second partial reflective surfaces 214 and 224 are also deeply etched reflective surfaces. Two deeply etched reflective surfaces with 45-degree cut angles constitute a group of total reflection structures, and the middle is a coupling waveguide 231 connecting two optical resonant cavities. The second partial reflectors 213 and 223 widen the light field distribution from the tapered waveguides 212 and 222 and divide it into three parts. The two side parts are reflected back to their own optical resonant cavities by the second partial reflective surfaces 214 and 224 to form a straight-through coupling, and the middle part is coupled into another optical resonant cavity by the coupling waveguide to form a cross-coupling. The energy ratio relationship between the cross-coupling and straight-through coupling of the half-wave coupler is determined by the second partial reflectors 213 and 223, and the π phase difference between the cross-coupling and the straight-through coupling is determined by the length of the coupling waveguide 231. The two are optimized separately, which improves the design freedom and reduces the design difficulty. The tapered waveguides 212 and 222 coordinate and match the light field distribution between the optical waveguides 211 and 221 and the second partial reflectors 213 and 223 to reduce losses. The optical waveguides 211 and 221 constrain the output spot size and divergence angle, improve the output quality and match the required cavity length. The two deeply etched reflection surfaces 210 and 220 and the second partial reflection surfaces 214 and 224 accurately define the cavity lengths of the two optical resonant cavities. The deeply etched reflection surface 220 on the long cavity side is used for laser output, and the other deeply etched reflection surface 210 is plated with a high reflectivity film to reduce the laser threshold.

[0175] The electrodes 201, 215, and 225 of the laser are also designed to be three. The coupler electrode 201 covers the complete second partial reflectors 213, 223, the complete tapered waveguides 212, 222, and a portion of the two optical waveguides 211, 221. The ratio of the cavity length of the two optical resonant cavities covered by the coupler electrode 201 is consistent with the ratio of the length of the two optical resonant cavities themselves, and it is also the main gain electrode and direct modulation electrode. The remaining optical waveguides 211 and 221 are respectively covered by the corresponding long cavity electrode 225 and the short cavity electrode 215. The ratio of the long and short cavity lengths covered by the coupler electrode 201 to the total length of the long and short cavities is about 0.6. By injecting current into the long cavity electrode 225 or the short cavity electrode 215, the wavelength can be tuned over a large range through the vernier effect, and a single electrode can also be tuned.

[0176] The laser is characterized by a linear distribution, which is more compact in the longitudinal direction and more suitable for forming a laser array. In addition, there is no curved waveguide in the structure, which partially reduces the laser threshold. Figure 5 The figure shows a tunable laser array based on a half-wave coupled partial reflector, in which the deeply etched reflective surface 220 on the long cavity light-emitting side of all tunable lasers based on a half-wave coupled partial reflector in the array is aligned, and the long cavity length and short cavity length of all tunable lasers based on a half-wave coupled partial reflector are different. Embodiment 3:

[0177] like Figure 7 As shown, the tunable semiconductor laser array is formed by small-size tunable lasers based on polymer imaging couplers, and the small-size tunable lasers based on polymer imaging couplers can adopt two electrode design schemes. The deep-etched reflective surfaces 320 at the long cavity ends of the small-size tunable lasers based on polymer imaging couplers in the array are aligned with each other as light-emitting surfaces.

[0178] The basic structure of the unit laser of a small-size tunable laser based on a polymer imaging coupler is as follows Figure 6 As shown in . Its two optical resonant cavities are also distributed in a straight line, and the long cavity design is located on the right side of the figure. The two optical resonant cavities are composed of their own polymer imaging couplers 311, 321 and first partial reflection surfaces 310, 320 and second partial reflection surfaces 312, 322 at both ends of the polymer imaging couplers 311, 321. The first partial reflection surfaces 310, 320 and the second partial reflection surfaces 312, 322 are all deeply etched reflection surfaces. The second partial reflection surfaces 312, 322 are located on both sides of the ends of the polymer imaging couplers 311, 321 along the light propagation direction, with a 45-degree cut angle. Each end of each polymer imaging coupler 311, 321 has two second partial reflection surfaces 312, 322, and the two constitute a group of total reflection structures. Between the two groups of second partial reflection surfaces 312 and 322 is an intermediate deeply etched waveguide 331 that couples and connects the two optical resonant cavities. The two polymer imaging couplers 311 and 321 and the intermediate deeply etched waveguide 331 that couples and connects the two optical resonant cavities constitute a half-wave coupler.

[0179] The polymerized imaging couplers 311 and 321 in this laser solution are designed based on a 1*N multimode interference coupler with a suitable width and length and specific imaging conditions. The image on the imaging surface is polymerized to a certain extent by means of overall size compression, and the energy distribution of the output end face is adjusted to meet the specific energy distribution requirements. Parts of the energy distribution on both sides of the output end face are reflected back to the original optical resonant cavity through the second partial reflection surface 312 and 322 as straight-through coupling, and the other part is coupled into another optical resonant cavity through the middle deep etched waveguide 331 as cross coupling.

[0180] Different from the V-cavity tunable laser of Example 1, here the polymer imaging couplers 311 and 321 only need to consider the energy distribution of the output end face, without considering the phase relationship. The energy distribution of the output end face determines the energy relationship between the cross coupling and the straight-through coupling. The polymer imaging couplers 311 and 321 are designed to meet the energy ratio relationship between the cross coupling and the straight-through coupling required by the half-wave coupler. The phase relationship between the cross coupling and the straight-through coupling required by the half-wave coupler is met by adjusting the length of the middle deep-etched waveguide 331. Since the polymer imaging couplers 311 and 321 constitute the main body of the optical resonant cavity, and due to the principle factors of the polymer imaging couplers 311 and 321, their length can be designed to 50μm-100μm, a small-sized tunable laser with a channel spacing of 400GHz and above, up to 800GHz, is realized. The deep-etched reflective surface 320 on the right long cavity side is used for output, and the other deep-etched reflective surface 310 is plated with a high reflectivity film to reduce the laser threshold.

[0181] There are two schemes for electrode design. The three-electrode scheme is as follows: Figure 6 As shown in (a), the coupler electrode 301 covers a portion of the two optical resonant cavities. The length ratio of the covered portion is consistent with the overall length ratio of the two optical resonant cavities. It is the main gain electrode and direct modulation electrode. The remaining long cavity and short cavity are covered by the long cavity electrode 323 and the short cavity electrode 313 respectively. The two-electrode scheme is as follows Figure 6 As shown in (b), the long cavity is covered by the long cavity electrode 323, and the short cavity is covered by the short cavity electrode 313. No coupler electrode is required, and the structure is more compact and suitable for applications that do not require modulation. The wavelength can also be tuned over a large range through the vernier effect by injecting current into the long cavity electrode 323 or the short cavity electrode 313, and a single electrode can also be tuned. The laser is characterized by a small size and a more compact structure, which is conducive to subsequent on-chip integration and is suitable for use as an array.

[0182] Figure 7 The tunable laser array of the small-size tunable laser based on the polymer imaging type coupler is shown in the figure, in which the deeply etched reflective surface 320 on the long cavity light-emitting side of all the small-size tunable lasers based on the polymer imaging type coupler in the array are aligned, and the long cavity length and short cavity length of all the small-size tunable lasers based on the polymer imaging type coupler are different. Embodiment 4:

[0183] The output of the tunable semiconductor laser array can be achieved by changing the deep-etched reflective surface at the output end of the unit laser to a deep-etched groove 401, and connecting the output waveguide 402 to the rear end of the deep-etched groove for output. Fig.14 The three tunable laser schemes are described in the figure. The three tunable laser schemes are changed to the case where the groove 401 is deeply etched and connected to the output waveguide 402 output. Fig.14(a) represents the improved structure of the V-cavity tunable laser. Fig.14 (b) represents the improved structure of the tunable laser based on half-wave coupled partial reflector. Fig.14 (c) represents the improved structure of a small-size tunable laser based on a polymer imaging coupler.

[0184] In the small-size tunable laser solution based on a polymer imaging coupler, the output spot size is slightly larger, and a tapered waveguide needs to be added to the front end of the output waveguide 402 for matching. This output method is suitable for on-chip integration, and the output waveguide can directly enter the input end of various combiners for final beam combining and output. The type of combiner can be a multimode interference coupler, an etched diffraction grating, or a commonly used array waveguide grating. The deeply etched groove 401 is also a structure that is engraved through the quantum well layer, and is also a semi-transmissive and semi-reflective structure, and two optical devices can be connected at both ends. The width of the deeply etched groove 401 is relatively narrow, and the interference effect can be used to design it into a high reflectivity form. The reflectivity is higher than the deeply etched surface, which is beneficial to the operation of the laser while having a certain transmittance, and coupling the energy into the output waveguide 402 for output.

[0185] The above design scheme is of a descriptive nature, and any scheme similar to its spirit falls within the scope of protection of this patent.

Claims

1. A tunable semiconductor laser array, characterized in that: The tunable semiconductor laser array is composed of a plurality of unit laser arrays, wherein the unit lasers are tunable semiconductor lasers without a grating structure, and each unit laser in the array is arranged in parallel, and the number of unit lasers is the same as the number of wavelengths required to be emitted simultaneously; The unit laser comprises two optical resonant cavities with different optical lengths, the two optical resonant cavities are connected by half-wave coupling, the energy between the two optical resonant cavities is coupled by half-wave coupling, and electrodes for current injection are arranged on the two optical resonant cavities; The electrode of one of the optical resonant cavities emits light after being injected with current, a part of the light returns to the original optical resonant cavity through half-wave coupling, and another part of the light is incident on another optical resonant cavity after half-wave coupling. The non-half-wave coupled end of any optical resonant cavity is used as the output end of the laser to emit laser light of the working wavelength; The unit lasers constituting the array are small-sized tunable lasers based on polymer imaging couplers; The unit laser is a small-size tunable laser based on a polymer imaging coupler, and the small-size tunable laser based on a polymer imaging coupler comprises two optical resonant cavities and a deep-etched waveguide (331), each optical resonant cavity mainly consisting of respective first partial reflection surfaces (310, 320), polymer imaging couplers (311, 321) and second partial reflection surfaces (312, 322) connected in sequence, the two optical resonant cavities are distributed along the same straight line, and are coupled to each other via a middle deep-etched waveguide (331) connecting respective second partial reflection surfaces (312, 322); Each optical resonant cavity has two second partial reflection surfaces (312, 322), which are respectively located on two symmetrical sides of the connection between the end of the polymer imaging type coupler (311, 321) and the middle deep etched waveguide (331); the two side parts of one end of the polymer imaging type coupler (311, 321) are connected to the second partial reflection surfaces (312, 322), and the remaining part in the middle is coupled to the middle deep etched waveguide (331) in the middle; the two second partial reflection surfaces (312, 322) on both sides form a group of total reflection structures; a part of the energy distribution of the end face of the polymer imaging type coupler (311, 321) of the optical resonant cavity is reflected back to the optical resonant cavity where it is located to form a straight-through coupling, and the other part of the energy is coupled to another optical resonant cavity through the middle deep etched waveguide (331) to form a cross coupling; The polymerized imaging coupler is based on an N*N type multimode interference coupler. By optimizing its input position and compressing its overall size, the image formed is polymerized and the energy distribution of the output port is adjusted, thereby achieving the cross-coupling and through-coupling energy ratio requirements required by a half-wave coupler consisting of two polymerized imaging couplers (311, 321) and an intermediate deep-etched waveguide (331) coupling and connecting two optical resonant cavities.

2. The tunable semiconductor laser array according to claim 1, characterized in that: The light energy coupled back to the original optical resonant cavity from the half-wave is used as the through coupling, and the light energy entering another optical resonant cavity through the half-wave coupling is used as the cross coupling. The phase difference between the cross-coupled light and the through-coupled light is controlled to be π, and the proportional relationship between the cross-coupling energy and the through-coupling energy is controlled to adjust the side mode suppression ratio and other parameters of the unit laser.

3. The tunable semiconductor laser array according to claim 1, characterized in that: The two optical resonant cavities with different optical lengths are a long cavity and a short cavity. The length ratio between the long cavity and the short cavity of each unit laser is the same. By setting the lengths of the long cavity and the short cavity of each unit laser to be different, each unit laser emits lasers of different working wavelengths under basically the same current injection.

4. The tunable semiconductor laser array according to claim 3, characterized in that: The long cavity and the short cavity each correspond to a set of equally spaced resonant frequencies called a comb spectrum, and there is only one resonant frequency overlap between the comb spectra of the long cavity and the short cavity within the gain spectrum of the quantum well material, and the overlapped resonant frequency is used as the operating wavelength of the unit laser; Injecting current into any optical resonant cavity changes its equivalent refractive index, changes its optical length, and causes its corresponding comb spectrum to move, thereby changing the resonant frequency of the two optical resonant cavities that overlap and achieving tuning of the working wavelength.

5. The tunable semiconductor laser array according to claim 1, characterized in that: Both ends of each optical resonant cavity of the unit laser are provided with deeply etched reflecting surfaces, wherein the deeply etched reflecting surface at the outer end of the optical resonant cavity close to the output end of the unit laser is set as a semi-transmissive and semi-reflective surface, and the other deeply etched reflecting surfaces are set as reflecting surfaces by coating high reflectivity films.

6. The control method for a tunable semiconductor laser array according to any one of claims 4 to 5, characterized in that: The optical resonant cavity corresponding to the movement of the comb spectrum is used as the tuning cavity, and the optical resonant cavity in which the comb spectrum does not move is used as the fixed gain cavity, and then the method is carried out in the following manner: Taking one of the unit lasers as a reference, adjusting the cavity lengths of the fixed gain cavities of the remaining unit lasers, so that each unit laser can output lasers corresponding to the required working wavelength sequence under substantially the same current injection; Then, the cavity lengths of the long cavities of all the unit lasers are adjusted so that the length ratio between the long and short cavities of each unit laser is consistent with the length ratio between the long and short cavities of the reference unit laser; After the cavity length is adjusted in this way, under the condition of substantially the same current injection, the set of operating wavelengths emitted by all unit lasers is the required operating wavelength sequence; When the tunable semiconductor laser array emits laser light of a working wavelength sequence, the magnitudes of the corresponding working currents received and injected by all unit lasers are substantially consistent.

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