An external cavity laser and method of adjustment

Abstract

The application discloses an external cavity laser and a regulating method. The external cavity laser comprises a reflective semiconductor optical amplifier, a converter and an external cavity. The reflective semiconductor optical amplifier is used for generating spontaneous emission light. The converter is used for realizing mutual conversion of the spontaneous emission light and TE polarized light. The external cavity comprises a phase shifter, a nanobeam cavity and a tunable ring mirror arranged in sequence. The TE polarized light is transmitted to the nanobeam cavity after being phase-shifted by the phase shifter, and is transmitted to the tunable ring mirror after being primarily selected in frequency by the nanobeam cavity. The tunable ring mirror makes the TE polarized light return along the original path by dynamically controlling reflectivity. The external cavity laser designed in the application inherits the advantages of high Q value, ultra-small size and high transmittance of the nanobeam cavity, introduces feedback regulation capability, realizes dynamic compensation of gain unevenness, optimizes output power flatness and expands the tuning range.

Description

Technical Field

[0001] This invention relates to an external cavity laser and its adjustment method, belonging to the field of optoelectronic device technology. Background Technology

[0002] CMOS-compatible on-chip optical waveguide technology has driven the development of high integration and miniaturization in lasers. Chip-scale lasers feature wide tuning range, narrow linewidth, ease of large-scale integration, light weight, and low cost, making them widely used in optical communication, sensing, optical detection, and ranging systems. By coupling III-V gain chips with silicon or silicon nitride waveguide platforms, high-performance lasers can be combined with low-loss waveguide platforms.

[0003] The key challenge is to achieve a silicon-based external cavity laser with a wide wavelength tuning range, small size, and dynamic gain compensation capability. A wide wavelength tuning range means the laser can operate over a wider range of wavelengths, covering more communication bands or sensing channels. In wavelength division multiplexing (WDM) systems, a larger tuning range means supporting more independent wavelength channels, thereby increasing communication capacity. In lidar, a wide tuning range enables finer range resolution and multi-target detection. Small size means higher integration and a smaller chip area. In photonic integrated circuits, smaller device size means integrating more functions on a single chip, reducing cost and improving reliability. Gain chips (such as SOA and RSOA) do not have a flat gain across different wavelengths, typically high in the middle and low at the edges. Without compensation, the laser's output power will decrease or even fail to lasing when tuned to a lower gain band. Therefore, dynamic compensation is crucial for maintaining stable output power throughout the tuning range and expanding the practically usable tuning range.

[0004] Currently, the tuning range of monolithically integrated DFB / DBR lasers is usually less than 10nm, which is unsatisfactory in terms of wavelength tuning range and fabrication complexity. External cavity lasers based on cascaded microrings usually require multiple microrings and their tuning electrodes, occupying a large chip area. External cavity lasers based on nanobeam cavities have a fixed reflectivity, cannot be dynamically compensated, and have large fluctuations in output power.

[0005] Therefore, there is an urgent need to develop an external cavity laser that can maintain a compact size while also having a wide tuning range and dynamic gain compensation capability. Summary of the Invention

[0006] The purpose of this invention is to provide an external cavity laser and a tuning method that, while inheriting the advantages of high Q value, ultra-small size and high transmittance of nanocrystal lasers, introduces feedback tuning capability to achieve dynamic compensation for gain unevenness, thereby optimizing output power flatness and expanding the tuning range.

[0007] To achieve the above objectives, the present invention is implemented using the following technical solution.

[0008] In a first aspect, the present invention provides an external cavity laser, comprising: a reflective semiconductor optical amplifier, a transducer, and an external cavity.

[0009] The reflective semiconductor optical amplifier is used to generate spontaneous emission light;

[0010] The converter is used to realize the mutual conversion between spontaneous emission light and TE polarized light;

[0011] The external cavity includes a phase shifter, a nanobeam cavity, and a tunable ring mirror arranged sequentially. The TE polarized light is phase-shifted by the phase shifter and then transmitted to the nanobeam cavity. After initial frequency selection by the nanobeam cavity, it is transmitted to the tunable ring mirror. The tunable ring mirror dynamically adjusts the reflectivity to make the TE polarized light return along its original path. The returned TE polarized light is returned to the reflective semiconductor optical amplifier by the converter. The reflective surface of the reflective semiconductor optical amplifier and the Fabry-Perot resonator formed by the tunable ring mirror form positive feedback, thereby generating laser oscillation. Finally, the laser is output from the output end of the tunable ring mirror.

[0012] Furthermore, the converter includes a mode-spot converter for realizing the mutual conversion between RSOA large mode field beam and single-mode waveguide TE polarized light;

[0013] When the spontaneous emission light is input to the mode converter, the mode converter is used to convert the spontaneous emission light into TE polarized light output;

[0014] When the TE polarized light is input to the mode converter, the mode converter is used to convert the TE polarized light into a light spot output that matches the reflective semiconductor optical amplifier.

[0015] Furthermore, the phase shifter aligns the longitudinal mode position of the resonant cavity with the resonant peak of the nanobeam cavity by adjusting the longitudinal mode position of the resonant cavity, thereby achieving continuous tuning without mode skipping.

[0016] Furthermore, the nanobeam cavity includes a narrow linewidth filter for initial screening of a single longitudinal mode:

[0017] When the wavelength frequency of the optical signal after phase modulation by the phase shifter matches the resonant frequency of the nanocrystal, the phase-modulated optical signal is localized within the nanocrystal and phase accumulation occurs, thereby increasing the optical path length; when they do not match, the phase-modulated optical signal is attenuated or transmitted by the nanocrystal.

[0018] Furthermore, the tunable ring mirror adopts a Sagnac ring structure based on a Mach-Zehnder interferometer (MZI), including two MZI arms, one of which integrates a titanium nitride (TiN) thermoelectrode. The phase difference between the two beams of light input to the two MZI arms is changed through the thermo-optic effect, thereby changing the reflectivity.

[0019] Furthermore, the TE-polarized light returned by the tunable ring mirror can only return to the reflective semiconductor optical amplifier via the converter when the TE polarized light satisfies the resonance condition of the nanocrystal and its round-trip phase matches the phase adjusted by the phase shifter.

[0020] Furthermore, the nanobeam cavity is a one-dimensional photonic crystal nanobeam cavity, composed of a periodic air hole array etched from a nanobeam waveguide, including a rectangular hole array, a tapered gradient hole array, and a reverse tapered gradient hole array, which together constitute a nanobeam FP resonant cavity; the rectangular hole array, the tapered gradient hole array, and the reverse tapered gradient hole array are all periodic structures; the tapered gradient hole array and the reverse tapered gradient hole array have the same period and number of holes, and their air hole duty cycles are gradually distributed along the light propagation direction, resulting in a corresponding gradual change in the radius of the circular holes; the rectangular hole array has a different period and number of holes than the tapered gradient hole array and the reverse tapered gradient hole array, and the air hole duty cycles are fixed, so the length and width of the rectangular holes are fixed accordingly.

[0021] In a second aspect, the present invention provides a method for adjusting an external cavity laser, employing the external cavity laser described in any one of the first aspects, the method comprising:

[0022] By altering the resonant wavelength of the nanobeam cavity through the thermo-optic effect, the resonant peak can be shifted within a preset broadband range.

[0023] Adjusting the reflectivity of the tunable ring mirror: When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier is lower than a first preset threshold, the reflectivity of the tunable ring mirror is increased to compensate for the insufficient gain.

[0024] When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier is higher than the second preset threshold, the reflectivity of the tunable ring mirror is reduced to prevent excessive feedback from causing mode instability or output power fluctuations.

[0025] The above dynamic adjustment method effectively overcomes the problem of uneven gain in reflective semiconductor optical amplifiers, thereby expanding the practically usable tuning range.

[0026] Furthermore, the adjustment method also includes:

[0027] The phase shifter is adjusted synchronously to ensure that the longitudinal mode position of the resonant cavity is aligned with the resonant peak of the nanobeam cavity, thereby achieving continuous tuning without mode skipping.

[0028] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0029] 1. The external cavity laser provided by this invention adopts a structure of cascaded nanocavity and tunable ring mirror, which separates the two functions of wavelength selection and feedback control that are simultaneously performed by the traditional nanocavity. While maintaining the advantages of high Q value, ultra-small size and high transmittance of nanocavity, the external cavity laser introduces dynamic feedback adjustment capability through tunable mirror, so that wavelength selection and feedback control can be optimized independently and without interference, thereby achieving effective compensation for gain unevenness, and ultimately optimizing output power flatness and expanding the tuning range.

[0030] Among them, the high Q value combined with the significant extension of the effective cavity length by the external cavity enables the external cavity laser to obtain a narrow linewidth on the order of thousands; the high transmittance effectively reduces the insertion loss in the external cavity, which is beneficial to reducing the threshold and increasing the output power; the ultra-large free spectral range ensures that there is only one resonance peak in a large wavelength range, thereby guaranteeing the single-mode operation characteristics of the external cavity laser.

[0031] 2. The external cavity laser tuning method provided by the present invention achieves coarse wavelength tuning through a nanocavity, gain compensation through a tunable ring mirror, and fine phase matching through a phase shifter. The three are tuned in synergy to achieve continuous wavelength tuning without mode hopping, effectively avoiding the mode hopping problem caused by the mismatch between the filter peak and the longitudinal mode in traditional methods. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of an external cavity laser according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of a silicon-based one-dimensional photonic crystal nanocavity air hole array for an external cavity laser provided in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of a nitrogen-silicon one-dimensional photonic crystal nanocavity air hole array for an external cavity laser provided according to an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the silicon-based one-dimensional photonic crystal nanocavity transmittance of an external cavity laser provided according to an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the transmittance of a one-dimensional photonic crystal nanocavity of an external cavity laser provided according to an embodiment of the present invention.

[0037] In the figure: 1. Reflective semiconductor optical amplifier; 2. Mode converter; 3. Phase shifter; 4. One-dimensional photonic crystal nanocrystal; 5. Tunable ring mirror; 01. Rectangular aperture array; 02. Tapered aperture array; 03. Reverse tapered aperture array. Detailed Implementation

[0038] It should be noted that:

[0039] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0040] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment introduces an external cavity laser, including:

[0043] The reflective semiconductor optical amplifier 1 is used to generate spontaneous emission light; the reflective semiconductor optical amplifier 1 is connected to a DC power supply.

[0044] The converter is used to realize the mutual conversion between spontaneous emission light and TE polarized light;

[0045] The external cavity includes a phase shifter 3, a nanobeam cavity, and a tunable ring mirror 5 arranged sequentially. The TE polarized light is phase-shifted by the phase shifter 3 and then transmitted to the nanobeam cavity. After initial frequency selection by the nanobeam cavity, it is transmitted to the tunable ring mirror 5. The tunable ring mirror 5 dynamically adjusts the reflectivity to make the TE polarized light return along the original path. The returned TE polarized light returns to the reflective semiconductor optical amplifier 1 via the converter. The reflective surface of the reflective semiconductor optical amplifier 1 and the Fabry-Perot resonator formed by the tunable ring mirror 5 form positive feedback, thereby generating laser oscillation. Finally, the laser is output from the output end of the tunable ring mirror 5.

[0046] In summary, the external cavity laser in this embodiment achieves narrow linewidth, tunable, and stable laser output through the synergistic effect of the reflective semiconductor optical amplifier 1 and the tunable ring mirror 5. Specifically, the reflective semiconductor optical amplifier 1 serves as the gain medium, and its reflective surface, together with the tunable ring mirror 5, constitutes a Fabry-Perot resonant cavity. Mode matching between spontaneous emission light and TE polarized light is achieved through a converter. Combined with precise phase control of the light wave by a phase shifter and preliminary frequency selection by the nanobeam cavity, side modes are effectively suppressed. At the same time, the tunable ring mirror 5 can dynamically adjust the reflectivity, which not only allows for flexible selection of the laser wavelength but also reduces intracavity loss.

[0047] Furthermore, the converter includes a mode converter 2 for realizing the function of beam spot size conversion; when the spontaneous emission light is output from one side, TE-polarized light is output on the right side via the mode converter 2; when the TE-polarized light is input from the right side, a beam spot matching the reflective semiconductor optical amplifier 1 is output on the left side via the mode converter 2. By adapting the beam spot size and mode through the mode converter 2, the connection loss between different devices can be effectively reduced, the efficiency of laser conversion and transmission can be improved, and a better foundation can be provided for subsequent stable laser oscillation, thereby ensuring the power and beam quality of the final output laser.

[0048] Furthermore, the phase shifter 3 aligns the longitudinal mode position of the resonant cavity with the resonant peak of the nanobeam cavity to achieve continuous tuning without mode skipping. During tuning, the reflective semiconductor optical amplifier 1 is first turned on, and its output spontaneous emission light is converted into TE polarized light by the mode converter 2. The light then passes through the phase shifter 3 and the nanobeam cavity in sequence before entering the tunable ring mirror 5. The tunable ring mirror 5 reflects the light wave that meets the resonance condition back along the original path. The reflected light then passes through the nanobeam cavity for frequency selection, the phase of the phase shifter 3 for phase modulation, and the mode of the mode converter 2 for inverse mode conversion before returning to the reflective semiconductor optical amplifier 1, forming laser oscillation in the Fabry-Perot resonant cavity. When it is necessary to tune the laser output wavelength, the reflection parameters of the tunable ring mirror 5 are changed to adjust the output wavelength. At the same time, the phase of the phase shifter is adjusted to keep the longitudinal mode position of the resonant cavity aligned with the resonant peak of the nanobeam cavity, thereby achieving stable output of the target wavelength laser.

[0049] Furthermore, the nanocavity described in this embodiment includes a silicon-based one-dimensional photonic crystal nanocavity filter, which has the advantages of ultra-small size, ultra-large free spectral range, and low insertion loss, and can ensure the initial screening of a single longitudinal mode.

[0050] When the wavelength frequency of the optical signal after phase modulation by the phase shifter 3 matches the resonant frequency of the one-dimensional photonic crystal nanocrystal cavity 4, the phase-modulated optical signal is localized within the one-dimensional photonic crystal nanocrystal cavity 4 and phase accumulation is generated to increase the optical path; when they do not match, the phase-modulated optical signal is rapidly attenuated or transmitted by the one-dimensional photonic crystal nanocrystal cavity 4.

[0051] This embodiment introduces a silicon-based external cavity laser based on SOI material. The silicon-based external cavity laser uses an SOI substrate, wherein the top silicon layer has a thickness of 220 nm, and the upper and lower cladding layers are both silicon dioxide.

[0052] like Figure 2 As shown, the nanobeam cavity is a one-dimensional photonic crystal nanobeam cavity 4, which is composed of a periodic air hole array etched by a nanobeam waveguide. The air hole array includes a rectangular hole array 01, a tapered gradient hole array 02, and a reverse tapered gradient hole array 03, which together constitute a nanobeam FP resonant cavity. The rectangular hole array 01, the tapered gradient hole array 02, and the reverse tapered gradient hole array 03 are all periodic structures. The tapered gradient hole array 02 and the reverse tapered gradient hole array 03 have the same period and number of holes, and their air hole duty cycles are gradually distributed along the light propagation direction, resulting in a corresponding gradual change in the radius of the circular holes.

[0053] Furthermore, the rectangular hole array 01 has a different period and number of holes than the tapered gradient hole array 02 and the reverse tapered gradient hole array 03, and the duty cycle of the air holes is fixed. The length and width of the rectangular holes are correspondingly fixed. The specific parameters are as follows:

[0054] The waveguide width is 700nm. The tapered gradient aperture array 02 contains 12 air holes, and the reverse tapered gradient aperture array 03 also contains 12 air holes. In this embodiment, the holes are circular in shape, with a duty cycle of 0.2 for the central lattice air hole and a duty cycle of 0.1 for the outermost lattice air hole. The period, i.e., the lattice constant, is 343nm. The rectangular aperture array 01 contains 30 air holes with a duty cycle of 0.05. The length of the rectangular holes is 170nm, and the calculated width is approximately 71nm.

[0055] Duty cycle The expression is:

[0056] ;

[0057] in, Where is the radius of the air hole. The spacing between the air holes in a certain direction. The feature width in another vertical direction;

[0058] Starting from the center of the tapered gradient hole array 02 and the reverse tapered gradient hole array 03, the radius of the i-th air hole is... The expression is:

[0059] ;

[0060] in, The number of air holes in a single-sided tapered gradient hole array. The radius of the outermost lattice air hole. denoted as , where is the radius of the air hole in the central lattice.

[0061] Furthermore, such as Figure 4 As shown, this embodiment uses the three-dimensional finite-difference time-domain method to simulate the one-dimensional photonic crystal nanocavity 4. The silicon-based one-dimensional photonic crystal nanocavity filter operates in the wavelength range of 1500-1800 nm. Figure 4 (a) Transmittance with a rectangular aperture array period fixed at 343 nm, and with both tapered and reverse tapered aperture arrays having a period of 323 nm. Figure 4 (b) Transmittance dB plots are shown for rectangular aperture arrays with a fixed period of 343 nm, and for tapered and reverse tapered aperture arrays with a period of 323 nm. The results show that the resonant wavelength of the one-dimensional photonic crystal nanocavity 4 is 1549.49 nm, and the quality factor Q is approximately 1.19 × 10⁻⁶. 3 Transmittance greater than 95%, free spectral range FSR exceeding 150 nm, and side-mode suppression ratio greater than 40 dB; compared with traditional high Q values ​​(>10 5 Compared to nanobeam cavities, the one-dimensional photonic crystal nanobeam cavity 4 in this embodiment maintains high transmittance while significantly reducing insertion loss by lowering the Q value, which is beneficial for reducing the laser threshold and improving tuning stability.

[0062] Furthermore, the optical signal, after initial frequency selection by the one-dimensional photonic crystal nanobeam cavity 4, continues to be transmitted to the tunable ring mirror 5. In this embodiment, the tunable ring mirror 5 adopts a Sagnac ring structure based on MZI, and the size of the Sagnac ring is 485μm×55μm.

[0063] Furthermore, when the TE polarized light returned by the tunable ring mirror 5 satisfies the resonance condition of the one-dimensional photonic crystal nanocrystal cavity 4, and its round-trip phase matches the phase adjusted by the phase shifter 3, the returned TE polarized light can return to the reflective semiconductor optical amplifier 1 via the converter. The high reflectivity surface of the reflective semiconductor optical amplifier 1 and the Fabry-Perot resonant cavity formed by the tunable ring mirror 5 form a stable positive feedback, thereby generating laser oscillation and outputting laser light from the output end of the tunable ring mirror 5.

[0064] This embodiment also introduces an external cavity laser based on a silicon nitride waveguide platform. The silicon-based external cavity laser uses a silicon nitride waveguide platform, wherein the waveguide thickness is 800nm ​​and the upper and lower cladding layers are both silicon dioxide.

[0065] like Figure 3As shown, the nanobeam cavity in this embodiment is a one-dimensional photonic crystal nanobeam cavity 4, which is composed of a periodic air hole array etched by a nanobeam waveguide. The air hole array includes a rectangular hole array 01, a tapered gradient hole array 02, and a reverse tapered gradient hole array 03, which together constitute a nanobeam FP resonant cavity. The rectangular hole array 01, the tapered gradient hole array 02, and the reverse tapered gradient hole array 03 are all periodic structures. The tapered gradient hole array 02 and the reverse tapered gradient hole array 03 have the same period and number of holes, and their air hole duty cycles are gradually distributed along the light propagation direction, resulting in a corresponding gradual change in the radius of the circular holes.

[0066] Furthermore, the rectangular hole array 01 has a different period and number of holes than the tapered gradient hole array 02 and the reverse tapered gradient hole array 03, and the duty cycle of the air holes is fixed. The length and width of the rectangular holes are correspondingly fixed. The specific parameters are as follows:

[0067] The waveguide width is 1200nm. The tapered gradient aperture array 02 contains 23 air holes, and the reverse tapered gradient aperture array 03 contains 23 air holes. Unlike the aperture shape of the silicon-based external cavity laser based on SOI material, the aperture shape of the external cavity laser based on the silicon nitride waveguide platform is elliptical, with the major axis perpendicular to the light propagation direction. The duty cycle of the central lattice air hole is 0.45, the duty cycle of the outermost lattice air hole is 0.12, and the period, i.e. the lattice constant, is 457nm. The major axis radius of the air hole gradually decreases from the center to the outermost edge, while the minor axis radius remains unchanged. The rectangular aperture array 01 has 46 apertures, a duty cycle of 0.12, and a period of 470nm.

[0068] In this embodiment, as Figure 5 As shown, this embodiment uses the three-dimensional finite-difference time-domain method to simulate the one-dimensional photonic crystal nanocrystal cavity 4. The silicon nitride one-dimensional photonic crystal nanocrystal cavity filter operates in the wavelength range of 1500-1700nm, where... Figure 5 (a) Transmittance with a rectangular aperture array period fixed at 470 nm, and with both tapered and reverse tapered aperture arrays having a period of 457 nm. Figure 5 (b) Transmittance dB plots with the period of the rectangular aperture array fixed at 470 nm and the periods of the tapered and reverse tapered aperture arrays both at 457 nm show that the resonant wavelength of the one-dimensional photonic crystal nanobeam cavity 4 is 1550.19 nm and the quality factor Q is approximately 1.19 × 10⁻⁶. 3 Transmittance greater than 90%, free spectral range FSR greater than 98 nm; compared with traditional high Q value (>10 5Compared to nanobeam cavities, the one-dimensional photonic crystal nanobeam cavity 4 in this embodiment maintains high transmittance while significantly reducing insertion loss by lowering the Q value, which is beneficial for reducing the laser threshold and improving tuning stability.

[0069] Furthermore, the optical signal, after initial frequency selection by the one-dimensional photonic crystal nanobeam cavity 4, continues to be transmitted to the tunable ring mirror 5. In this embodiment, the tunable ring mirror 5 adopts a Sagnac ring structure based on MZI, and the size of the Sagnac ring is 1655μm×508μm.

[0070] Example 2

[0071] Based on the external cavity laser of Embodiment 1, this embodiment introduces a method for adjusting an external cavity laser, including:

[0072] By altering the resonant wavelength of the nanobeam cavity through the thermo-optic effect, the resonant peak can be shifted within a preset broadband range.

[0073] Adjusting the reflectivity of the tunable ring mirror 5: When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier 1 is lower than a first preset threshold, the reflectivity of the tunable ring mirror 5 is increased to compensate for insufficient gain.

[0074] When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier 1 is higher than the second preset threshold, the reflectivity of the tunable ring mirror 5 is reduced to prevent excessive feedback from causing mode instability or output power fluctuations.

[0075] Furthermore, in this embodiment, wavelength tuning is achieved by synergistically adjusting the one-dimensional photonic crystal nanocrystal cavity 4 and the tunable ring mirror 5. Specifically, the refractive index of the one-dimensional photonic crystal nanocrystal cavity 4 is changed through the thermo-optic effect, so that its resonance peak moves continuously over a wide spectral range.

[0076] Furthermore, during the tuning process, the phase shifter 3 is adjusted synchronously to ensure that the longitudinal mode of the resonant cavity is always aligned with the resonant peak of the one-dimensional photonic crystal nanobeam cavity 4, thereby achieving continuous tuning without mode skipping.

[0077] Furthermore, the tunable ring mirror 5 is composed of a micro-Zone Inductor (MZI) and a waveguide loop connecting its two output ends. A thermoelectric electrode is integrated on one arm of the MZI. By adjusting the phase difference between the two arms, the beam splitting ratio is changed, thereby achieving dynamic control of the reflectivity. In this embodiment, the thermoelectric electrodes of the one-dimensional photonic crystal nanocavity 4, the MZI, and the phase shifter 3 are simultaneously adjusted according to the target wavelength to achieve the overall function. After the laser is started, the target resonant position to which the one-dimensional photonic crystal nanocavity 4 needs to be tuned is first determined according to the target output wavelength. The heating power required for its thermoelectric electrodes is calculated. Simultaneously, based on the actual gain of the reflective semiconductor optical amplifier 1 at the target wavelength, the reflectivity to which the tunable ring mirror 5 needs to be matched is calculated, and the target heating power of the MZI thermoelectric electrode is obtained. According to the longitudinal mode alignment requirements of the resonant cavity, the target heating power of the phase shifter 3 thermoelectric electrode is calculated. Simultaneously, corresponding power drives are applied to the three thermoelectric electrodes to output a target wavelength laser with stable wavelength and power.

[0078] Based on the high Q-value of the one-dimensional photonic crystal nanocavity 4 and the extension effect of the external cavity on the effective cavity length, the silicon-based external cavity laser in Example 1 can achieve narrow linewidth output in the MHz range. By synergistically adjusting the resonant wavelength of the one-dimensional photonic crystal nanocavity 4 and the reflectivity of the tunable ring mirror 5, a continuous tuning range of more than 150 nm is expected to be achieved. The silicon nitride external cavity laser in Example 1 can also achieve narrow linewidth output in the MHz range and is expected to achieve a continuous tuning range of more than 98 nm, both of which can effectively improve the output power flatness.

[0079] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0080] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0081] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0082] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0083] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. An external cavity laser, characterized in that, include: Reflective semiconductor optical amplifier (1), converter and external cavity, The reflective semiconductor optical amplifier (1) is used to generate spontaneous emission light; The converter is used to realize the mutual conversion between spontaneous emission light and TE polarized light; The external cavity includes a phase shifter (3), a nanobeam cavity, and a tunable ring mirror (5) arranged sequentially. The TE polarized light is phase-shifted by the phase shifter (3) and transmitted to the nanobeam cavity. After initial frequency selection by the nanobeam cavity, it is transmitted to the tunable ring mirror (5). The tunable ring mirror (5) dynamically adjusts the reflectivity to make the TE polarized light return along the original path. The returned TE polarized light returns to the reflective semiconductor optical amplifier (1) through the converter. The reflective surface of the reflective semiconductor optical amplifier (1) and the Fabry-Perot resonator formed by the tunable ring mirror (5) form positive feedback, thereby generating laser oscillation, and finally outputting laser from the output end of the tunable ring mirror (5).

2. The external cavity laser according to claim 1, characterized in that, The converter includes a pattern converter (2); When the spontaneous emission light is input to the mode converter (2), the mode converter (2) is used to convert the spontaneous emission light into TE polarized light output; When the TE polarized light is input to the mode converter (2), the mode converter (2) is used to convert the TE polarized light into a light spot output that matches the reflective semiconductor optical amplifier (1).

3. The external cavity laser according to claim 1, characterized in that, The phase shifter (3) adjusts the longitudinal mode position of the resonant cavity to align with the resonant peak of the nanobeam cavity, thereby achieving continuous tuning without mode skipping.

4. The external cavity laser according to claim 1, characterized in that, The nanobeam cavity includes a narrow linewidth filter for initial screening of a single longitudinal mode: When the wavelength frequency of the optical signal after phase modulation by the phase shifter (3) matches the resonant frequency of the nanocrystal, the phase-modulated optical signal is localized in the nanocrystal and phase accumulation is generated to increase the optical path; when they do not match, the phase-modulated optical signal is attenuated or transmitted by the nanocrystal.

5. The external cavity laser according to claim 1, characterized in that, The tunable ring mirror (5) adopts a Sagnac ring structure based on a Mach-Zehnder interferometer, including two Mach-Zehnder interferometer arms. One of the Mach-Zehnder interferometer arms is equipped with a titanium nitride thermoelectrode. The phase difference between the two beams of light input to the two Mach-Zehnder interferometer arms is changed through the thermo-optic effect, thereby changing the reflectivity.

6. The external cavity laser according to claim 1, characterized in that, When the TE polarized light returned by the tunable ring mirror (5) satisfies the resonance condition of the nanocrystal and its round-trip phase matches the phase adjusted by the phase shifter (3), the returned TE polarized light can be returned to the reflective semiconductor optical amplifier (1) via the converter.

7. The external cavity laser according to claim 1, characterized in that, The nanobeam cavity is a one-dimensional photonic crystal nanobeam cavity (4), which is composed of a periodic air hole array etched by a nanobeam waveguide, including a rectangular hole array (01), a tapered gradient hole array (02), and a reverse tapered gradient hole array (03), which together constitute a nanobeam FP resonant cavity; the rectangular hole array (01), the tapered gradient hole array (02), and the reverse tapered gradient hole array (03) are all periodic structures; The tapered gradient aperture array (02) and the reverse tapered gradient aperture array (03) have the same period and number of apertures, and their air aperture duty cycles are gradually distributed along the light propagation direction, resulting in a corresponding gradual change in the radius of the circular apertures; the rectangular aperture array (01) has a different period and number of apertures than the tapered gradient aperture array (02) and the reverse tapered gradient aperture array (03), and the air aperture duty cycle is fixed, and the length and width of the rectangular apertures are fixed accordingly.

8. A method for adjusting an external cavity laser according to any one of claims 1 to 7, characterized in that, The adjustment method includes: By altering the resonant wavelength of the nanobeam cavity through the thermo-optic effect, the resonant peak can be shifted within a preset broadband range. Adjusting the reflectivity of the tunable ring mirror (5): When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier (1) is lower than a first preset threshold, the reflectivity of the tunable ring mirror (5) is increased to compensate for insufficient gain. When the resonant wavelength is tuned to a band where the gain of the reflective semiconductor optical amplifier (1) is higher than the second preset threshold, the reflectivity of the tunable ring mirror (5) is reduced to prevent excessive feedback from causing mode instability or output power fluctuation.

9. The method for adjusting an external cavity laser according to claim 8, characterized in that, The adjustment method further includes: Synchronously adjust the phase shifter (3) to ensure that the longitudinal mode position of the resonant cavity is aligned with the resonant peak of the nanobeam cavity, thereby achieving continuous tuning without mode skipping.

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