An integrated external cavity laser and method of use

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 pump source, a coupling module, and an external cavity module. The coupling module couples the pump light signal output from the pump source to the external cavity module. The external cavity module amplifies the pump light signal and splits it into two paths to adjust the splitting ratio between the two paths. The external cavity module also combines the two split light signals, using part of the combined light signal for output and part for return to be amplified again. This invention provides on-chip gain and increases the output power of the external cavity laser despite the 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] In view of the deficiencies in the prior art, the first aspect of the present invention provides a method that can provide on-chip gain and improve the output power of an external cavity laser under the limitation of the performance of existing integrated devices.

[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 pump source, a coupling module, and an external cavity module;

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

[0009] The external cavity module is used to amplify the pump optical signal and split the amplified optical signal into two paths to adjust the splitting ratio between the two paths. The external cavity module is also used to combine the two optical signals and use part of the combined optical signal for output and part for return for further amplification.

[0010] In some embodiments, the external cavity module includes:

[0011] A coupling unit, which is connected to the coupling module;

[0012] A gain module, which is connected to the coupling unit, is used to amplify the pump optical signal;

[0013] A high-Q resonant cavity module, which is connected to the gain module, is used to filter the pump light signal, output the amplified light signal, and select the laser mode;

[0014] An adjustable beam splitter module, which is connected to the high-Q resonant cavity module, is used to split the amplified optical signal into two paths and adjust the splitting ratio between the two paths.

[0015] The beam combining module, which is connected to the adjustable beam splitter and the gain module, is used to combine the two beams split by the adjustable beam splitter into one beam, input a portion of the combined optical signal back to the gain module, and output the other portion.

[0016] In some embodiments, the high-Q resonant cavity module includes:

[0017] Upload / download type microring, which is equipped with a thermoelectric electrode;

[0018] The first waveguide is connected to the gain module and is used to couple the output of the gain module into the upload / download microring, and the upload / download microring adjusts the resonant wavelength through a thermoelectric electrode to filter the pump light signal.

[0019] The second waveguide, in conjunction with the first waveguide, encloses the upload / download type micro-ring. The second waveguide is connected to the adjustable beam splitter module and is used to couple the amplified optical signal into the adjustable beam splitter module.

[0020] In some embodiments, both the tail ends of the first waveguide and the second waveguide are provided with anti-reflection structures.

[0021] In some embodiments, the adjustable beam splitter module includes:

[0022] A first multimode interferometer is used to split the amplified optical signal transmitted through the second waveguide into two paths.

[0023] The third waveguide is connected to one path of the first multimode interferometer, and the first waveguide is provided with a thermoelectric electrode;

[0024] A fourth waveguide is connected to another path of the first multimode interferometer. The fourth waveguide is provided with a thermoelectric electrode and is the same length as the third waveguide.

[0025] The second multimode interferometer is connected to the third and fourth waveguides and splits the optical signals transmitted in the third and fourth waveguides into two paths again.

[0026] The fifth waveguide is connected to one path of the second multimode interferometer, and a thermoelectric electrode is provided on the fifth waveguide;

[0027] The sixth waveguide is connected to the other path of the second multimode interferometer. The sixth waveguide is provided with a thermoelectric electrode, and the fifth waveguide is the same length as the sixth waveguide.

[0028] In some embodiments, the beam combining module includes a third multimode interferometer and a fourth multimode interferometer;

[0029] The third multimode interferometer is connected to the fifth and sixth waveguides and is used to combine the optical signals output from the fifth and sixth waveguides, and to output part of the combined optical signal and input part of it to the fourth multimode interferometer.

[0030] One input port of the fourth multimode interferometer is connected to the third multimode interferometer, the other input port is connected to the coupling unit, and the output port of the fourth multimode interferometer is connected to the gain module.

[0031] In some embodiments, the coupling unit is a pattern converter.

[0032] In some embodiments, the gain module is an erbium-doped waveguide amplifier.

[0033] In some embodiments, the coupling module is a lens.

[0034] A second aspect of the present invention provides a method for using the above-mentioned integrated external cavity laser, which can provide on-chip gain and increase the output power of the external cavity laser under the limitation of existing integrated device performance.

[0035] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0036] A method of using an integrated external cavity laser as described above, the method comprising the following steps:

[0037] The pump light signal is amplified using the external cavity module, and the amplified light signal is split into two paths. The splitting ratio between the two paths is adjusted to form a PT symmetry broken state.

[0038] The control condition ensures that only one selected mode satisfies the PT symmetry breaking state, so as to concentrate energy on the selected mode;

[0039] By changing the resonant frequency of the external cavity module, the selected mode of the PT symmetry breaking state is changed, thereby changing the wavelength of the emitted light.

[0040] Compared with the prior art, the advantages of the present invention are as follows:

[0041] The integrated external cavity laser of this invention includes a pump source, a coupling module, and an external cavity module. The pump light signal generated by the pump source is coupled into the external cavity module via the coupling module and coupling unit. The pump light signal then enters the gain module, which provides a gain effect on the corresponding wavelength of the light signal. The amplified light signal and the pump light signal simultaneously pass through a high-Q resonant cavity module, where the pump light signal is filtered and the laser mode is selected. The amplified light signal enters an adjustable beam splitter module, which splits the light signal into two equal-length paths. These two paths are then combined into a single path by a beam combiner module and returned to the gain module, thus forming two loops of equal physical length. By adjusting the splitting ratio when splitting into two paths, the two loops satisfy the PT symmetry breaking condition, enabling further excitation of single modes while suppressing side modes. By adjusting the resonant wavelength of the high-Q resonant cavity to align with the characteristic wavelength of the gain module, PT symmetry breaking can be selectively controlled, aligning the excited mode with the resonant wavelength of the high-Q resonant cavity, thereby generating a laser with high output power, narrow linewidth, and high side-mode suppression ratio. Attached Figure Description

[0042] Figure 1 This is a structural block diagram of the integrated external cavity laser in an embodiment of the present invention;

[0043] Figure 2 This is a structural block diagram of the external cavity module in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the external cavity module in one embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the structure of an integrated external cavity laser according to one embodiment of the present invention;

[0046] Figure 5 This is a flowchart of the method for using the integrated external cavity laser in an embodiment of the present invention.

[0047] In the diagram: 1. Pump light source; 2. Coupling module; 3. External cavity module; 31. Coupling unit; 32. Gain module; 33. High-Q resonant cavity module; 331. Upload / download type micro-ring; 332. First waveguide; 333. Second waveguide; 334. Anti-reflection structure; 34. Adjustable beam splitting module; 341. First multimode interferometer; 342. Third waveguide; 343. Fourth waveguide; 344. Second multimode interferometer; 345. Fifth waveguide; 346. Sixth waveguide; 35. Beam combining module; 351. Third multimode interferometer; 352. Fourth multimode interferometer; 36. Output port; 4. Thermodems. Detailed Implementation

[0048] 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.

[0049] See Figure 1 As shown, an embodiment of the present invention discloses an integrated external cavity laser, including a pump source 1, a coupling module 2, and an external cavity module 3.

[0050] The coupling module 2 is used to couple the pump light signal output by the pump light source 1 to the external cavity module 3. The external cavity module 3 is used to amplify the pump light signal and split the amplified light signal into two paths to adjust the splitting ratio between the two paths. The external cavity module 3 is also used to combine the two paths of light and use part of the combined light signal for output and part for return for further amplification.

[0051] Specifically, the pump light source 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 nitride material system, or silicon, silicon oxide, or other material systems commonly used in the field.

[0052] The pump light source 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.

[0053] In this embodiment of the invention, the light emitted by the pump source 1 is input into the external cavity module 3 through the coupling module 2, and the generated laser is emitted from the external cavity module 3. The external cavity module 3 can realize optical amplification and can select the mode of the laser by utilizing PT (parity-time) symmetry breaking. Combined with the mode selection effect of the high-Q resonant cavity, the mode selection effect is greatly optimized, realizing a high-power, narrow-bandwidth, and high side-mode suppression ratio laser signal.

[0054] In a specific implementation, the pump source 1 can be a laser, and the coupling module 2 is a lens.

[0055] See Figure 2 As shown, the external cavity module 3 includes a coupling unit 31, a gain module 32, a high-Q resonant cavity module 33, an adjustable beam splitting module 34, a beam combining module 35, and an output port 36.

[0056] The system comprises the following components: coupling unit 31 connected to coupling module 2; gain module 32 connected to coupling unit 31 for amplifying the pump light signal; high-Q resonant cavity module 33 connected to gain module 32 for filtering the pump light signal, outputting the amplified light signal, and selecting the laser mode; adjustable beam splitter module 34 connected to high-Q resonant cavity module 33 for splitting the amplified light signal into two paths and adjusting the splitting ratio between the two paths; and beam combiner module 35 connected to adjustable beam splitter module 34, gain module 32, and output port 36 for combining the two paths split by adjustable beam splitter module 34 into one, inputting a portion of the combined light signal back to gain module 32, and outputting the other portion from output port 36. Therefore, gain module 32, high-Q resonant cavity module 33, adjustable beam splitter module 34, and beam combiner module 35 form a ring, constituting the main body of the external cavity laser resonant cavity.

[0057] 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 gain module 32. The coupling unit 31 can be implemented using a mode converter or other techniques commonly used in the art. The gain module 32 is used to generate on-chip gain and can be implemented based on erbium-doped waveguide amplifier technology or other techniques commonly used in the art.

[0058] The high-Q resonant cavity module 33 includes an upload / download type micro-ring 331, a first waveguide 332, a second waveguide 333, and an anti-reflection structure 334.

[0059] The upload / download microring 331 is equipped with a thermoelectric electrode 4. A first waveguide 332 is connected to a gain module 32 and couples the output of the gain module 32 into the upload / download microring 331. The upload / download microring 331 adjusts its resonant wavelength via the thermoelectric electrode 4 to filter the pump light signal. A second waveguide 333 cooperates with the first waveguide 332 to enclose the upload / download microring 331. The second waveguide 333 is connected to an adjustable beam splitter 34 and couples the amplified light signal into the adjustable beam splitter 34. Both the first waveguide 332 and the second waveguide 333 have anti-reflection structures at their ends.

[0060] The adjustable beam splitter module 34 splits the light output from the high-Q resonant cavity module 33 into two paths, and the splitting ratio between the two paths can be arbitrarily adjusted. This effect can be achieved using an adjustable Mach-Zehnder interferometer (MZI), an adjustable directional coupler, or other methods commonly used in the art. In this embodiment, the adjustable beam splitter module 34 includes a first multimode interferometer 341, a third waveguide 342, a fourth waveguide 343, a second multimode interferometer 344, a fifth waveguide 345, and a sixth waveguide 346.

[0061] The first multimode interferometer 341 is used to split the amplified optical signal transmitted by the second waveguide 333 into two paths; the third waveguide 342 is connected to one path of the first multimode interferometer 341, and a thermoelectric electrode 4 is provided on the third waveguide 342; the fourth waveguide 343 is connected to the other path of the first multimode interferometer 341, and a thermoelectric electrode 4 is provided on the fourth waveguide 343, and the fourth waveguide 343 is the same length as the third waveguide 342; the second multimode interferometer 344 is connected to the third waveguide 342 and the fourth waveguide 343, and splits the optical signal transmitted by the third waveguide 342 and the fourth waveguide 343 into two paths again; the fifth waveguide 345 is connected to one path of the second multimode interferometer 344, and a thermoelectric electrode 4 is provided on the fifth waveguide 345; the sixth waveguide 346 is connected to the other path of the second multimode interferometer 344, and a thermoelectric electrode 4 is provided on the sixth waveguide 346, and the fifth waveguide 345 is the same length as the sixth waveguide 346.

[0062] The beam combining module 35 combines the two beams split by the adjustable beam splitter 34 into one beam, inputting a portion of it back to the gain module 32 and inputting the other portion to the output port 36. This effect can be achieved using a multimode interferometer, a directional coupler, or other methods commonly used in the art. In this embodiment, the beam combining module 35 includes a third multimode interferometer 351 and a fourth multimode interferometer 352.

[0063] The third multimode interferometer 351 is connected to the fifth waveguide 345 and the sixth waveguide 346, and is used to combine the optical signals output from the fifth waveguide 345 and the sixth waveguide 346. The combined optical signal is used partly for output and partly for input to the fourth multimode interferometer 352. One input port of the fourth multimode interferometer 352 is connected to the third multimode interferometer 351, the other input port is connected to the coupling unit 31, and the output port of the fourth multimode interferometer 352 is connected to the gain module 32.

[0064] The output port 36 is used to emit the generated laser signal from the chip. This can be achieved using a mode converter, a grating, or other methods commonly used by those skilled in the art.

[0065] In some embodiments, see Figure 3 As shown, the specific structure of the external cavity module 3 includes: a mode speckle converter (coupling unit) 31, a 2×1 fourth multimode interferometer 352, an erbium-doped waveguide amplifier (gain module) 32, an upload / download type micro-ring 331, an anti-reflection structure 334, a 1×2 first multimode interferometer (MMI) 341, a 2×2 second multimode interferometer 344, a 2×2 third multimode interferometer 351, a mode speckle converter (emission port) 36, and a thermoelectrode 4.

[0066] The following is based on Figure 4 The working principle of the embodiments of the present invention is described as follows:

[0067] The laser (pump source) 1 emits light with wavelength λ1, which is focused by the lens (coupling module) 2 onto the mode converter (coupling unit) 31. The light is then input to the erbium-doped waveguide amplifier (gain module) 32 through an input port of the fourth multimode interferometer 352, exciting a light signal with wavelength λ2. The light with wavelengths λ1 and λ2 passes through an uplink / downlink microring 331, where the thermoelectrode 4 adjusts the resonant wavelength of the microring 331 to align it with λ2, filtering out λ1. Other light is absorbed by the anti-reflection structure 334. The light signal with wavelength λ2 is split into two equal-length paths by the first multimode interferometer 341. The phase difference between the two paths is changed by the thermoelectrodes 4 on the third waveguide 342 and the fourth waveguide 343. The signal is then split again by the second multimode interferometer 344, and the splitting ratio between the two paths is related to the phase difference caused by the thermoelectrodes 4 on the third waveguide 342 and the fourth waveguide 343. After being tunably split, the two optical signals are fed into the output port 36 via the third multimode interferometer 351, and into the fourth multimode interferometer 352, so that the optical path forms a complete resonant cavity.

[0068] After passing through the second multimode interferometer 344, the resonant cavity splits into two loops with the same physical length but different optical powers and are coupled to each other. When the splitting ratio is adjusted to make one loop generate gain and the other loop generate loss, according to the PT symmetry principle, the modes in the loops can be represented as follows:

[0069]

[0070] 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:

[0071]

[0072] At this point, the PT symmetry condition is satisfied. When the loop gain is greater than the coupling coefficient, i.e., g... n >κ nWhen 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 mode selection of the uplink / downlink microring 331. 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 applied to the thermoelectric electrode 4 on the uplink / downlink microring 331, the resonant wavelength of the uplink / downlink microring 331 can be changed, thus altering the selected mode under PT symmetry breaking and consequently changing the emitted laser wavelength, achieving wavelength tunability. When the adjusted wavelength is aligned with the gain wavelength λ2 of the erbium-doped waveguide amplifier (gain module) 32, the power of the emitted laser can be further increased.

[0073] In summary, the integrated external cavity laser of this invention includes a pump source 1, a coupling module 2, and an external cavity module 3. The pump light signal generated by the pump source 1 is coupled into the external cavity module 3 through the coupling module 2 and coupling unit 31. The pump light signal then enters the gain module 32, which provides a gain effect on the corresponding wavelength of the light signal. The amplified light signal and the pump light signal simultaneously pass through the high-Q resonant cavity module 33, which filters the pump light signal and selects the laser mode. The amplified light signal enters the adjustable beam splitter module 34, which splits the light signal into two equal-length paths. These two paths are then combined into one by the beam combiner module 35 and returned to the gain module 32, thus forming two loops of equal physical length. By adjusting the splitting ratio when splitting into two paths, the two loops satisfy the PT symmetry breaking condition, which can further excite single modes while suppressing side modes. By adjusting the resonant wavelength of the high-Q resonator to align it with the characteristic wavelength of the gain module, PT symmetry breaking can be selectively controlled, aligning the excited mode with the resonant wavelength of the high-Q resonator, thereby exciting a laser with high output power, narrow linewidth, and high side-mode suppression ratio.

[0074] See Figure 5 As 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:

[0075] S1. The pump light signal is amplified using the external cavity module, and the amplified light signal is split into two paths. The splitting ratio between the two paths is adjusted to form a PT symmetry broken state.

[0076] 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.

[0077] S3. By changing the resonant frequency of the external cavity module, the selected mode of the PT symmetry breaking state is changed, thereby changing the wavelength of the emitted light.

[0078] Specifically, the external cavity module 3 includes the following structure: a mode speckle converter (coupling unit) 31, a 2×1 fourth multimode interferometer (MMI) 352, an erbium-doped waveguide amplifier (gain module) 32, an upload / download type microring 331, an anti-reflection structure 334, a 1×2 first multimode interferometer 341, a 2×2 second multimode interferometer 344, a 2×2 third multimode interferometer 351, a mode speckle converter (emission port) 36, and a thermoelectrode 4.

[0079] The laser (pump source) 1 emits light with wavelength λ1, which is focused by the lens (coupling module) 2 onto the mode converter (coupling unit) 31. The light is then input to the erbium-doped waveguide amplifier (gain module) 32 through an input port of the fourth multimode interferometer 352, exciting a light signal with wavelength λ2. The light with wavelengths λ1 and λ2 passes through an uplink / downlink microring 331, where the thermoelectrode 4 adjusts the resonant wavelength of the microring 331 to align it with λ2, filtering out λ1. Other light is absorbed by the anti-reflection structure 334. The light signal with wavelength λ2 is split into two equal-length paths by the first multimode interferometer 341. The phase difference between the two paths is changed by the thermoelectrodes 4 on the third waveguide 342 and the fourth waveguide 343. The signal is then split again by the second multimode interferometer 344, and the splitting ratio between the two paths is related to the phase difference caused by the thermoelectrodes 4 on the third waveguide 342 and the fourth waveguide 343. After being tunably split, the two optical signals are fed into the output port 36 via the third multimode interferometer 351, and into the fourth multimode interferometer 352, so that the optical path forms a complete resonant cavity.

[0080] After passing through the second multimode interferometer 344, the resonant cavity splits into two loops with the same physical length but different optical powers and are coupled to each other. When the splitting ratio is adjusted to make one loop generate gain and the other loop generate loss, according to the PT symmetry principle, the modes in the loops can be represented as follows:

[0081]

[0082] 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:

[0083]

[0084] 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 mode selection of the uplink / downlink microring 331. 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 applied to the thermoelectric electrode 4 on the uplink / downlink microring 331, the resonant wavelength of the uplink / downlink microring 331 can be changed, thus altering the selected mode under PT symmetry breaking and consequently changing the emitted laser wavelength, achieving wavelength tunability. When the adjusted wavelength is aligned with the gain wavelength λ2 of the erbium-doped waveguide amplifier (gain module) 32, the power of the emitted laser can be further increased.

[0085] 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: Pump light source, coupling module and external cavity module; The coupling module is used to couple the pump light signal output by the pump light source to the external cavity module; The external cavity module is used to amplify the pump optical signal and split the amplified optical signal into two paths to adjust the splitting ratio between the two paths. The external cavity module is also used to combine the two optical signals and use part of the combined optical signal for output and part for return for further amplification. The external cavity module includes: A coupling unit, which is connected to the coupling module; A gain module, which is connected to the coupling unit, is used to amplify the pump optical signal; A high-Q resonant cavity module, which is connected to the gain module, is used to filter the pump light signal, output the amplified light signal, and select the laser mode; An adjustable beam splitter module, which is connected to the high-Q resonant cavity module, is used to split the amplified optical signal into two paths and adjust the splitting ratio between the two paths. A beam combining module, which is connected to the adjustable beam splitter and the gain module, is used to combine the two beams split by the adjustable beam splitter into one beam, input a portion of the combined optical signal back to the gain module, and output the other portion. The high-Q resonant cavity module includes: Upload / download type microring, which is equipped with a thermoelectric electrode; The first waveguide is connected to the gain module and is used to couple the output of the gain module into the upload / download microring, and the upload / download microring adjusts the resonant wavelength through a thermoelectric electrode to filter the pump light signal. The second waveguide, in conjunction with the first waveguide, encloses the upload / download type micro-ring. The second waveguide is connected to the adjustable beam splitter module and is used to couple the amplified optical signal into the adjustable beam splitter module. The adjustable beam splitter module includes: A first multimode interferometer is used to split the amplified optical signal transmitted through the second waveguide into two paths. The third waveguide is connected to one path of the first multimode interferometer, and a thermoelectric electrode is provided on the third waveguide; A fourth waveguide is connected to another path of the first multimode interferometer. The fourth waveguide is provided with a thermoelectric electrode and is the same length as the third waveguide. The second multimode interferometer is connected to the third and fourth waveguides and splits the optical signals transmitted in the third and fourth waveguides into two paths again. The fifth waveguide is connected to one path of the second multimode interferometer, and a thermoelectric electrode is provided on the fifth waveguide; The sixth waveguide is connected to the other path of the second multimode interferometer. The sixth waveguide is provided with a thermoelectric electrode, and the fifth waveguide is the same length as the sixth waveguide. The coupling module is a lens; The amplified optical signal enters the adjustable beam splitter and is split into two equal-length paths. The two paths are then combined into one by the beam combining module and returned to the gain module to form two loops of equal physical length. By adjusting the splitting ratio when splitting into two paths, 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: Both the first and second waveguides have anti-reflection structures at their tail ends.

3. An integrated external cavity laser according to claim 2, characterized in that, The beam combining module includes a third multimode interferometer and a fourth multimode interferometer; The third multimode interferometer is connected to the fifth and sixth waveguides and is used to combine the optical signals output from the fifth and sixth waveguides, and to output part of the combined optical signal and input part of it to the fourth multimode interferometer. One input port of the fourth multimode interferometer is connected to the third multimode interferometer, the other input port is connected to the coupling unit, and the output port of the fourth multimode interferometer is connected to the gain module.

4. An integrated external cavity laser according to claim 2, characterized in that, The coupling unit is a pattern converter.

5. An integrated external cavity laser according to claim 1, characterized in that: The gain module is an erbium-doped waveguide amplifier.

6. A method of using the integrated external cavity laser as described in claim 1, characterized in that, The method includes the following steps: The pump light signal is amplified using the external cavity module, and the amplified light signal is split into two paths. The splitting ratio between the two paths is adjusted 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 is changed, thereby changing the wavelength of the emitted light.

Images