An integrated external cavity laser and its usage method

Abstract

This invention discloses an integrated external cavity laser and its usage method, relating to the fields of optical communication and photonic integrated devices. The integrated external cavity laser includes a light source module, a coupling module, and an external cavity module. The coupling module couples the optical signal output from the light source module to the external cavity module. The external cavity module splits the optical signal into two paths to adjust the splitting ratio between the two paths. The external cavity module also returns the mode-selected two paths of light to the light source module via the coupling module. The light source module reflects the optical signal returned from the coupling module, so that the light source module, coupling module, and external cavity module form a closed resonant cavity. This invention can narrow the laser linewidth and improve the side-mode rejection ratio under the performance limitations of existing integrated devices.

Description

Technical Field

[0001] This invention relates to the fields of optical communication and photonic integrated device technology, specifically to an integrated external cavity laser and its usage method. Background Technology

[0002] Tunable lasers have important applications in wavelength division multiplexing (WDM) systems and coherent optical communication systems. As an important method for realizing tunable lasers, external cavity lasers have advantages such as a large wavelength tunable range, high side-mode suppression ratio, narrow linewidth, and high temperature stability, and have been widely used.

[0003] In addition to the advantages mentioned above, integrated external cavity lasers also have the advantages of low power consumption and small size of integrated devices. They can be integrated into complex optoelectronic chips as on-chip light sources, and have great scientific research and commercial application value.

[0004] However, due to limitations in the performance of on-chip devices, current integrated external cavity lasers are unlikely to achieve significant improvements in performance such as linewidth and side-mode rejection ratio. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first aspect of this invention provides an integrated external cavity laser that can narrow the laser linewidth and improve the side-mode rejection ratio under the limitation of existing integrated device performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An integrated external cavity laser includes: a light source module, a coupling module, and an external cavity module;

[0008] The coupling module is used to couple the optical signal output by the light source module to the external cavity module;

[0009] The external cavity module is used to split the optical signal into two paths to adjust the splitting ratio between the two paths, and the external cavity module is also used to return the two paths of light after mode selection to the light source module through the coupling module;

[0010] The light source module is also used to reflect the light signal returned by the coupling module, so that the light source module, the coupling module and the external cavity module form a closed resonant cavity.

[0011] In some embodiments, the external cavity module includes:

[0012] A coupling unit, which is connected to the coupling module;

[0013] An adjustable beam splitter module, which is connected to the coupling unit, is used to split the optical signal into two paths and can adjust the beam splitting ratio between the two paths.

[0014] A high-Q resonant cavity module, which is connected to the adjustable beam splitter module, is used to select modes of the two beams and return the selected two beams to the adjustable beam splitter module;

[0015] The adjustable beam splitter module is also used to combine the two beams returned by the high-Q resonant cavity module and return them to the light source module through the coupling unit and the coupling module.

[0016] In some embodiments, the adjustable beam splitter module includes:

[0017] A first multimode interferometer is used to split the optical signal transmitted by the coupling unit into two paths;

[0018] A first waveguide is connected to one path of the first multimode interferometer, and a thermoelectric electrode is provided on the first waveguide;

[0019] The second waveguide is connected to the other path of the first multimode interferometer. The second waveguide is provided with a thermoelectric electrode and is the same length as the first waveguide.

[0020] The second multimode interferometer is connected to the first waveguide and the second waveguide, and inputs the optical signals transmitted in the first waveguide and the second waveguide to the high-Q resonant cavity module, respectively.

[0021] In some embodiments, the high-Q resonant cavity module includes:

[0022] The first upload / download type microring is equipped with a thermal electrode;

[0023] The third waveguide is connected to the second multimode interferometer and is used to couple one optical signal split off from the second multimode interferometer into the first upload / download type micro-ring;

[0024] A fourth waveguide, which cooperates with the third waveguide to enclose the first upload / download type micro-ring, is connected to the second multimode interferometer and is used to couple another optical signal split off from the second multimode interferometer into the first upload / download type micro-ring.

[0025] In some embodiments, the tail ends of the third and fourth waveguides are provided with anti-reflection structures.

[0026] In some embodiments, the high-Q resonant cavity module includes:

[0027] The second upload / download type microring is equipped with a thermal electrode;

[0028] The third upload / download type microring is spaced apart from the second upload / download type microring. The third upload / download type microring is also provided with a thermoelectric electrode, and the ring lengths of the third upload / download type microring and the second upload / download type microring are different.

[0029] The fifth waveguide is connected to the second multimode interferometer and is used to couple one optical signal split off from the second multimode interferometer into the second upload / download micro-ring;

[0030] The sixth waveguide is connected to the second multimode interferometer and is used to couple another optical signal split off from the second multimode interferometer into the third upload / download microring;

[0031] The seventh waveguide, in conjunction with the fifth and sixth waveguides, encloses the second upload / download type microring and the third upload / download type microring.

[0032] In some embodiments, the coupling unit is a pattern converter.

[0033] In some embodiments, the light source module includes a distributed feedback DFB laser, and the DFB laser has a reflective end face.

[0034] In some embodiments, the coupling module is a lens.

[0035] The second aspect of the present invention provides a method for using the above-mentioned integrated external cavity laser, which can narrow the laser linewidth and improve the side-mode rejection ratio under the limitation of existing integrated device performance.

[0036] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0037] A method of using an integrated external cavity laser as described above, the method comprising the following steps:

[0038] The external cavity module is used to adjust the splitting ratio between the two beams to form a PT symmetry broken state;

[0039] The control condition ensures that only one selected mode satisfies the PT symmetry breaking state, so as to concentrate energy on the selected mode;

[0040] By changing the resonant frequency of the external cavity module, the selected mode of the PT symmetry breaking state can be changed.

[0041] Compared with the prior art, the advantages of the present invention are as follows:

[0042] The integrated external cavity laser of this invention includes a light source module, a coupling module, and an external cavity module. The optical signal output from the light source module is coupled into the external cavity module via the coupling module. The optical signal is then split into two equal-length paths by an adjustable beam splitter module, and each path passes through a high-Q resonant cavity module for precise mode selection. The signal then returns to the adjustable beam splitter module, passes through the coupling module, and enters the light source module. It is then reflected again by the reflective end face of the light source module, forming a closed resonant cavity composed of the light source module, coupling module, and external cavity module. The adjustable beam splitter divides this closed resonant cavity into two loops of equal physical length. By adjusting the splitting ratio, the two loops satisfy the PT symmetry breaking condition, enabling further excitation of single modes while suppressing side modes, and achieving narrow-linewidth laser emission from the emission end face of the light source module. The system-on-chip structure designed in this invention is simple, simplifies the structure of off-chip stable systems, and is beneficial for mass production. Attached Figure Description

[0043] Figure 1 This is a structural block diagram of the integrated external cavity laser in an embodiment of the present invention;

[0044] Figure 2 This is a structural block diagram of the external cavity module in an embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of the external cavity module in one embodiment of the present invention;

[0046] Figure 4 This is a schematic diagram of the integrated external cavity laser in an embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the external cavity module in another embodiment of the present invention;

[0048] Figure 6 This is a flowchart of the method for using the integrated external cavity laser in an embodiment of the present invention.

[0049] In the diagram: 1. Light source module; 11. DFB laser; 12. Reflecting end face; 2. Coupling module; 3. External cavity module; 31. Coupling unit; 32. Adjustable beam splitting module; 321. First multimode interferometer; 322. First waveguide; 323. Second waveguide; 324. Second multimode interferometer; 33. High-Q resonant cavity module; 331. First upload / download type microring; 332. Third waveguide; 333. Fourth waveguide; 334. Anti-reflection structure; 335. Second upload / download type microring; 336. Third upload / download type microring; 337. Fifth waveguide; 338. Sixth waveguide; 339. Seventh waveguide; 4. Thermoderm. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] See Figure 1 As shown in the figure, an embodiment of the present invention discloses an integrated external cavity laser, which includes a light source module 1, a coupling module 2 and an external cavity module 3.

[0052] The coupling module 2 is used to couple the optical signal output by the light source module 1 to the external cavity module 3; the external cavity module 3 is used to split the optical signal into two paths to adjust the splitting ratio between the two paths respectively, and the external cavity module 3 is also used to return the two paths of light after mode selection to the light source module 1 through the coupling module 2; the light source module 1 is also used to reflect the optical signal returned by the coupling module 2 so that the light source module 1, the coupling module 2 and the external cavity module 3 form a closed resonant cavity.

[0053] Specifically, the light source module 1 is connected to the coupling module 2, and the coupling module 2 is connected to the external cavity module 3. The external cavity module 3 is a monolithically integrated system-on-a-chip, which can be based on a silicon-based material system, or it can be based on silicon nitride, silicon oxide, lithium niobate thin film, or other material systems commonly used in the field.

[0054] The light source module 1, coupling module 2 and external cavity module 3 can be monolithically integrated using heterogeneous integration technology, or monolithically integrated using hybrid integration technology or other integration technologies commonly used in this field.

[0055] In this embodiment of the invention, the light emitted by the light source module 1 is input into the external cavity module 3 through the coupling module 2. The light selected by the external cavity module 3 returns to the light source module 1 through the coupling module 2. After passing through the reflection unit of the light source module 1, the light is reflected and coupled into the external cavity module 3 through the coupling module 2. This process is repeated, and the light source module 1, the coupling module 2 and the external cavity module 3 constitute a resonant cavity.

[0056] In a specific implementation, the light source module 1 includes a distributed feedback DFB laser 11, and the DFB laser is provided with a reflective end face 12, and the coupling module 2 is a lens.

[0057] The external cavity module 3 can select the mode of the laser by realizing PT (parity-time) symmetry breaking. Combined with the mode selection effect of the high-Q resonator, the mode selection effect is greatly optimized, realizing a narrow bandwidth laser signal and a high side-mode suppression ratio.

[0058] To achieve the above effect, see Figure 2 As shown, the external cavity module 3 includes a coupling unit 31, an adjustable beam splitting module 32, and a high-Q resonant cavity module 33.

[0059] The coupling unit 31 is connected to the coupling module 2; the adjustable beam splitter 32 is connected to the coupling unit 31 and is used to split the optical signal into two paths and adjust the splitting ratio between the two paths; the high-Q resonant cavity module 33 is connected to the adjustable beam splitter and is used to select the mode of the two paths and return the selected two paths to the adjustable beam splitter 32; the adjustable beam splitter 32 is also used to merge the two paths returned by the high-Q resonant cavity module 33 and return them to the light source module 1 through the coupling unit 31 and the coupling module 2.

[0060] The coupling unit 31 is used to couple the light input from the coupling module 2 into the on-chip system and transmit it to the adjustable beam splitter 32. The coupling unit 31 can be implemented using a mode converter or other technologies commonly used in the art.

[0061] The adjustable beam splitting module 32 splits one beam of light input from the coupling unit 31 into two beams, and the splitting ratio between the two beams can be adjusted arbitrarily. This effect can be achieved using an adjustable Mach-Zehnder interferometer (MZI), an adjustable directional coupler, or other methods commonly used in the field.

[0062] The high-Q resonant cavity module 33 includes at least two ports, which can be connected to the two beams split from the tunable beam splitter module 32, respectively. Optionally, the high-Q resonant cavity module 33 can be implemented using a upload / download type microring, or it can be implemented using an integrated phase-shifting Bragg grating or other technologies commonly used in the art.

[0063] In some embodiments, see Figure 3 As shown, the specific structure of the external cavity module 3 includes: a coupling unit 31, a 1×2 first multimode interferometer (MMI) 321, a first waveguide 322, a second waveguide 323, a 2×2 second multimode interferometer 324, a first upload / download type microring 331, a third waveguide 332, a fourth waveguide 333, an anti-reflection structure 334, and a thermoelectric electrode 4.

[0064] Specifically, the first multimode interferometer 321 is used to split the optical signal transmitted by the coupling unit into two paths; the first waveguide 322 is connected to one path of the first multimode interferometer, and the first waveguide is provided with a thermoelectric electrode 4; the second waveguide 323 is connected to the other path of the first multimode interferometer, the second waveguide 323 is also provided with a thermoelectric electrode 4, and the second waveguide 323 is the same length as the first waveguide; the second multimode interferometer 324 is connected to the first waveguide 322 and the second waveguide 323, and inputs the optical signals transmitted by the first waveguide and the second waveguide to the high-Q resonant cavity module 33 respectively.

[0065] The first upload / download type microring 331 is provided with a thermoelectric electrode 4; the third waveguide 332 is connected to the second multimode interferometer 324 and is used to couple one optical signal split off from the second multimode interferometer 324 into the first upload / download type microring 331;

[0066] The fourth waveguide 333 cooperates with the third waveguide 332 to enclose the first upload / download type micro-ring 331. The fourth waveguide 333 is connected to the second multimode interferometer 324 and is used to couple another optical signal split from the second multimode interferometer 324 into the first upload / download type micro-ring 331. In addition, both the third waveguide 332 and the fourth waveguide 333 are provided with anti-reflection structures 334 at their tail ends.

[0067] The following is combined with Figure 4 To describe the working principle of the embodiments of the present invention:

[0068] The light emitted by the DFB laser 11 is focused by a lens (coupling module 2) onto a mode converter (coupling unit 31), and then split into two paths by a 1×2 first multimode interferometer 321. These paths pass through equal-length waveguides (first waveguide 322 and second waveguide 323) with thermoelectrodes 4, and are then split into two paths by a 2×2 second multimode interferometer 324: one path couples clockwise into the first upload / download micro-ring 331 via the third waveguide 332, propagates clockwise within the ring, and then couples clockwise out of the first upload / download micro-ring 331 via the fourth waveguide 333, returning to the second multimode interferometer 324; the other path couples counterclockwise into the first upload / download micro-ring 331 via the fourth waveguide 333, propagates counterclockwise within the ring, and then couples counterclockwise out of the first upload / download micro-ring 331 via the third waveguide 332, returning to the second multimode interferometer 324. Light that is not coupled into the first upload / download microring 331 in the third waveguide 332 and the fourth waveguide 333 will be absorbed by the anti-reflection structure 334 and will not be reflected back into the third waveguide 332, the fourth waveguide 333, or the first upload / download microring 331. The two beams returning to the second multimode interferometer 324 will be reversed and interfered and merged into one beam through the first multimode interferometer 321, and then returned to the DFB laser 11 through the mode converter and lens, reflected by the reflecting end face 12, and the above process will be repeated. At this point, the entire system constitutes a resonant cavity.

[0069] It is worth noting that the first multimode interferometer 321, the thermoelectrode 4, and the second multimode interferometer 324 constitute an adjustable Mach-Zehnder interferometer (MZI) structure. By applying a voltage to the thermoelectrode 4 on the first waveguide 322 and the second waveguide 323, the splitting ratio between the two beams output from the second multimode interferometer 324 can be changed. The two beams split from the second multimode interferometer 324 pass through the micro-loop in clockwise and counterclockwise directions respectively and then return, forming two mutually coupled loops with equal physical lengths. When the splitting ratio is adjusted to generate gain in one loop and loss in the other, according to the PT symmetry principle, the modes in the loops can be represented as follows:

[0070]

[0071] Where ω n It is the eigenfrequency of the nth mode, g n and α n These are the gain and loss in the two loops of the nth mode, respectively, κ n It is the coupling coefficient between the two loops. When the splitting ratio is adjusted to make the gain and loss satisfy g... n =-α n When the above formula is used, it can be rewritten as:

[0072]

[0073] At this point, the PT symmetry condition is satisfied. When the loop gain is greater than the coupling coefficient, i.e., g... n >κ n When PT symmetry is broken, a pair of conjugate amplified and attenuated eigenmodes are generated. The amplified mode gains significantly more than the other modes, thus achieving single-mode lasing. This further narrows the laser linewidth based on the first upload / download microring mode selection. When the control conditions ensure that only one selected mode satisfies the PT symmetry breaking state, energy is concentrated in the selected mode. According to energy conservation, other modes are suppressed, thereby improving the side-mode suppression ratio of the emitted laser. By adjusting the voltage of the thermoelectric electrode 4 applied to the first upload / download microring 331, the resonant frequency of the first upload / download microring 331 can be changed, thus altering the selected mode under PT symmetry breaking and consequently changing the emitted laser frequency, achieving frequency tunability.

[0074] In other words, the adjustable beam splitter 32 in the external cavity module 3 can reduce the laser linewidth through the characteristic of PT symmetry breaking. Combined with the mode selection effect of the high-Q resonant cavity module 33, it can further narrow the laser linewidth. Through mode selection using the PT symmetry breaking characteristic, other modes can be effectively suppressed, improving the side-mode suppression ratio of the laser.

[0075] In other embodiments, see Figure 5As shown, the high-Q resonant cavity module 33 includes a second upload / download type microring 335, a third upload / download type microring 336, a fifth waveguide 337, a sixth waveguide 338, and a seventh waveguide 339.

[0076] The second upload / download type microring 335 is provided with a thermal electrode 4; the third upload / download type microring 336 is arranged at an interval from the second upload / download type microring 335, and the third upload / download type microring 336 is also provided with a thermal electrode 4, and the ring lengths of the third upload / download type microring 336 and the second upload / download type microring 335 are different.

[0077] The fifth waveguide 337 is connected to the second multimode interferometer 324 and is used to couple one optical signal split from the second multimode interferometer 324 into the second upload / download micro-ring 335; the sixth waveguide 338 is connected to the second multimode interferometer 324 and is used to couple another optical signal split from the second multimode interferometer 324 into the third upload / download micro-ring 336; the seventh waveguide 339 cooperates with the fifth waveguide 337 and the sixth waveguide 338 to enclose the second upload / download micro-ring 335 and the third upload / download micro-ring 336. Anti-reflection structures 334 are provided on the fifth waveguide 337, the sixth waveguide 338, and the seventh waveguide 339.

[0078] Understandably, due to the slight difference in ring length between the second upload / download type microring 335 and the third upload / download type microring 336, the free spectrum range of the resonance spectrum after interference can be increased by utilizing the vernier effect through interference between the two microrings. Compared to Figure 3 The external cavity module shown is an example of a design that can significantly improve the frequency tuning range of a laser.

[0079] In summary, the integrated external cavity laser of this invention includes a light source module 1, a coupling module 2, and an external cavity module 3. The optical signal output from the light source module 1 is coupled into the external cavity module 3 via the coupling module 2. The optical signal is then split into two equal-length paths by an adjustable beam splitter module 32, and each path passes through a high-Q resonant cavity module 33 for precise mode selection. The signal then returns to the adjustable beam splitter module 32, passes through the coupling module 2, and enters the light source module 1. It is then reflected again by the reflection end face 12 in the light source module 1, forming a closed resonant cavity composed of the light source module 1, coupling module 2, and external cavity module 3. After beam splitting by the adjustable beam splitter module 32, this closed resonant cavity is divided into two loops of equal physical length. By adjusting the splitting ratio, the two loops satisfy the PT symmetry breaking condition, enabling further excitation of single modes while suppressing side modes, and achieving narrow-linewidth laser emission from the emission end face of the light source module. The on-chip system designed in this invention has a simple structure, simplifies the off-chip stabilization system structure, and is beneficial for large-scale production.

[0080] See Figure 6As shown, this embodiment of the invention also discloses a method for using the above-mentioned integrated external cavity laser, the method comprising the following steps:

[0081] S1. The splitting ratio between the two beams is adjusted using the external cavity module 3 to form a PT symmetry broken state.

[0082] S2. The control condition ensures that only one selected mode satisfies the PT symmetry breaking state, so as to concentrate energy on the selected mode.

[0083] S3. By changing the resonant frequency of the external cavity module 3, the selected mode of the PT symmetry breaking state is changed.

[0084] Specifically, the external cavity module 3 includes the following structure: coupling unit 31, 1×2 first multimode interferometer (MMI) 321, first waveguide 322, second waveguide 323, 2×2 second multimode interferometer 324, first upload / download type microring 331, third waveguide 332, fourth waveguide 333, anti-reflection structure 334 and thermoelectrode 4.

[0085] The first multimode interferometer 321 is used to split the optical signal transmitted by the coupling unit into two paths; the first waveguide 322 is connected to one path of the first multimode interferometer, and the first waveguide is provided with a thermoelectric electrode 4; the second waveguide 323 is connected to the other path of the first multimode interferometer, the second waveguide 323 is also provided with a thermoelectric electrode 4, and the second waveguide 323 is the same length as the first waveguide; the second multimode interferometer 324 is connected to the first waveguide 322 and the second waveguide 323, and inputs the optical signals transmitted by the first waveguide and the second waveguide to the high-Q resonant cavity module 33 respectively.

[0086] The first upload / download type microring 331 is provided with a thermoelectric electrode 4; the third waveguide 332 is connected to the second multimode interferometer 324 and is used to couple one optical signal split off from the second multimode interferometer 324 into the first upload / download type microring 331;

[0087] The fourth waveguide 333 cooperates with the third waveguide 332 to enclose the first upload / download type micro-ring 331. The fourth waveguide 333 is connected to the second multimode interferometer 324 and is used to couple another optical signal split from the second multimode interferometer 324 into the first upload / download type micro-ring 331. In addition, both the third waveguide 332 and the fourth waveguide 333 are provided with anti-reflection structures 334 at their tail ends.

[0088] By applying voltage to the thermoelectrodes 4 on the first waveguide 322 and the second waveguide 323, the splitting ratio between the two beams output from the second multimode interferometer 324 can be changed. The two beams split from the second multimode interferometer 324 pass through the micro-loop in clockwise and counterclockwise directions respectively and then return, forming two mutually coupled loops with equal physical lengths. When the splitting ratio is adjusted so that one loop generates gain and the other loop generates loss, according to the PT symmetry principle, the mode in the loop can be represented as:

[0089]

[0090] Where ω n It is the eigenfrequency of the nth mode, g n and α n These are the gain and loss in the two loops of the nth mode, respectively, κ n It is the coupling coefficient between the two loops. When the splitting ratio is adjusted to make the gain and loss satisfy g... n =-α n When the above formula is used, it can be rewritten as:

[0091]

[0092] At this point, the PT symmetry condition is satisfied. When the loop gain is greater than the coupling coefficient, i.e., g... n >κ n When PT symmetry is broken, a pair of conjugate amplified and attenuated eigenmodes are generated. The amplified mode gains significantly more than the other modes, thus achieving single-mode lasing. This further narrows the laser linewidth based on the first upload / download microring mode selection. When the control conditions ensure that only one selected mode satisfies the PT symmetry breaking state, energy is concentrated in the selected mode. According to energy conservation, other modes are suppressed, thereby improving the side-mode suppression ratio of the emitted laser. By adjusting the voltage of the thermoelectric electrode 4 applied to the first upload / download microring 331, the resonant frequency of the first upload / download microring 331 can be changed, thus altering the selected mode under PT symmetry breaking and consequently changing the emitted laser frequency, achieving frequency tunability.

[0093] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An integrated external cavity laser, characterized in that, include: Light source module, coupling module, and external cavity module; The coupling module is used to couple the optical signal output by the light source module to the external cavity module; The external cavity module is used to split the optical signal into two paths to adjust the splitting ratio between the two paths, and the external cavity module is also used to return the two paths of light after mode selection to the light source module through the coupling module; The light source module is also used to reflect the optical signal returned by the coupling module, so that the light source module, coupling module and external cavity module form a closed resonant cavity; The external cavity module includes: A coupling unit, which is connected to the coupling module; An adjustable beam splitter module, which is connected to the coupling unit, is used to split the optical signal into two paths and can adjust the beam splitting ratio between the two paths. A high-Q resonant cavity module, which is connected to the adjustable beam splitter module, is used to select modes of the two beams and return the selected two beams to the adjustable beam splitter module; The adjustable beam splitter module is also used to combine the two beams returned by the high-Q resonant cavity module and return them to the light source module through the coupling unit and the coupling module; The adjustable beam splitter module includes: A first multimode interferometer is used to split the optical signal transmitted by the coupling unit into two paths; A first waveguide is connected to one path of the first multimode interferometer, and a thermoelectric electrode is provided on the first waveguide; The second waveguide is connected to the other path of the first multimode interferometer. The second waveguide is provided with a thermoelectric electrode and is the same length as the first waveguide. A second multimode interferometer is connected to the first waveguide and the second waveguide, and inputs the optical signals transmitted in the first waveguide and the second waveguide to the high-Q resonant cavity module, respectively. The coupling module is a lens; The optics are split by the adjustable beam splitting module, which divides the closed resonant cavity into two loops of equal physical length. By adjusting the splitting ratio, the two loops satisfy the PT symmetry breaking condition to excite single modes while suppressing side modes.

2. The integrated external cavity laser according to claim 1, characterized in that, The high-Q resonant cavity module includes: The first upload / download type microring is equipped with a thermal electrode; The third waveguide is connected to the second multimode interferometer and is used to couple one optical signal split off from the second multimode interferometer into the first upload / download type micro-ring; A fourth waveguide, which cooperates with the third waveguide to enclose the first upload / download type micro-ring, is connected to the second multimode interferometer and is used to couple another optical signal split off from the second multimode interferometer into the first upload / download type micro-ring.

3. An integrated external cavity laser according to claim 2, characterized in that: The tail ends of the third and fourth waveguides are both equipped with anti-reflection structures.

4. An integrated external cavity laser according to claim 1, characterized in that, The high-Q resonant cavity module includes: The second upload / download type microring is equipped with a thermal electrode; The third upload / download type microring is spaced apart from the second upload / download type microring. The third upload / download type microring is also provided with a thermoelectric electrode, and the ring lengths of the third upload / download type microring and the second upload / download type microring are different. The fifth waveguide is connected to the second multimode interferometer and is used to couple one optical signal split off from the second multimode interferometer into the second upload / download micro-ring; The sixth waveguide is connected to the second multimode interferometer and is used to couple another optical signal split off from the second multimode interferometer into the third upload / download microring; The seventh waveguide, in conjunction with the fifth and sixth waveguides, encloses the second upload / download type microring and the third upload / download type microring.

5. An integrated external cavity laser according to claim 1, characterized in that, The coupling unit is a pattern converter.

6. An integrated external cavity laser according to claim 1, characterized in that: The light source module includes a distributed feedback DFB laser, and the DFB laser has a reflective end face.

7. A method of using the integrated external cavity laser as described in claim 1, characterized in that, The method includes the following steps: The external cavity module is used to adjust the splitting ratio between the two beams to form a PT symmetry broken state; The control condition ensures that only one selected mode satisfies the PT symmetry breaking state, so as to concentrate energy on the selected mode; By changing the resonant frequency of the external cavity module, the selected mode of the PT symmetry breaking state can be changed.

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