External cavity laser and tuning method thereof

Abstract

The present disclosure relates to an external cavity laser and a tuning method thereof. The external cavity laser comprises a gain chip and a tunable mirror. The tunable mirror comprises a main waveguide, a beam splitter, a first branch waveguide, a first photonic crystal modulator, a second branch waveguide and a second photonic crystal modulator. The beam splitter is used to equally divide the optical signal transmitted by the main waveguide into a first optical signal and a second optical signal, and transmit the first optical signal to the first branch waveguide and the second optical signal to the second branch waveguide. The first photonic crystal modulator is used to tune the first optical signal transmitted by the first branch waveguide. The second photonic crystal modulator is used to tune the second optical signal transmitted by the second branch waveguide. The external cavity laser can ensure the efficient and stable light output of the laser on the basis of realizing the miniaturization and high-speed direct tuning of the laser.

Description

Technical Field

[0001] This disclosure relates to the field of optical communication technology, and in particular to an external cavity laser and its tuning method. Background Technology

[0002] Currently, external cavity lasers are being developed towards smaller size, lower power consumption, and higher speed. This has led to increasing attention being paid to their application in optical communication technology.

[0003] In related technologies, external cavity lasers often use micro-ring resonators (also known as micro-ring modulators) as their external cavity mirrors, thereby enabling high-speed direct modulation of the laser by utilizing the hybrid integration of micro-ring resonators and semiconductor gain chips.

[0004] However, due to the limitations of the free spectral range of the microring, the microring resonator is a narrowband device, requiring precise adjustment and control of its resonance peak to ensure it matches the wavelength of the input light from the light source. Furthermore, if the resonance peak of the microring resonator drifts, its reflectivity to the semiconductor gain chip will also change, making the optical field within the microring resonator unstable and thus affecting the quality of the optical signal after tuning. Summary of the Invention

[0005] Based on this, the present disclosure provides an external cavity laser and its tuning method, which can ensure efficient and stable laser output while achieving laser miniaturization and high-speed direct tuning.

[0006] To achieve the above objectives, some embodiments of this disclosure provide an external cavity laser. The external cavity laser includes a gain chip and a tunable mirror coupled to the gain chip. The tunable mirror includes a main waveguide, a beam splitter, a first branch waveguide, a first photonic crystal modulator, a second branch waveguide, and a second photonic crystal modulator. The main waveguide is coupled to the gain chip and configured to receive an optical signal transmitted by the gain chip. The beam splitter is coupled to the main waveguide and configured to divide the optical signal transmitted by the main waveguide into a first optical signal and a second optical signal. The first branch waveguide is coupled to the beam splitter and configured to receive the first optical signal. The first photonic crystal modulator is disposed beside the first branch waveguide and configured to tune the first optical signal transmitted by the first branch waveguide. The second branch waveguide is coupled to the beam splitter and configured to receive the second optical signal. The second photonic crystal modulator is disposed beside the second branch waveguide and configured to tune the second optical signal transmitted by the second branch waveguide.

[0007] In this embodiment, the gain chip and the tunable mirror together constitute the FP cavity of the external cavity laser. After the gain chip transmits the optical signal to the main waveguide of the tunable mirror, a beam splitter can be used to divide the optical signal transmitted through the main waveguide into a first optical signal and a second optical signal. Then, a first photonic crystal modulator is used to tune the first optical signal, and a second photonic crystal modulator is used to tune the second optical signal. In this way, under the tuning effect of the first and second photonic crystal modulators, and under the effect of beam reflection and beam interference within the FP cavity, the optical signal can be directly and quickly output from the output port of the external cavity laser, thereby realizing high-speed direct tuning of the external cavity laser.

[0008] In some embodiments, the tunable mirror further includes a common waveguide.

[0009] The first photonic crystal modulator is disposed on the side of the first branch waveguide closer to the second branch waveguide, and the second photonic crystal modulator is disposed on the side of the second branch waveguide closer to the first branch waveguide. A common waveguide is disposed between the first and second photonic crystal modulators.

[0010] The common waveguide is configured to: receive a first optical signal tuned by a first photonic crystal modulator and transmit the tuned first optical signal to the resonant cavity of a second photonic crystal modulator for secondary tuning by the second photonic crystal modulator and coupling it to a second branch waveguide; and receive a second optical signal tuned by the second photonic crystal modulator and transmit the tuned second optical signal to the resonant cavity of the first photonic crystal modulator for secondary tuning by the first photonic crystal modulator and coupling it to a first branch waveguide.

[0011] In this embodiment, a common waveguide is located between the first photonic crystal modulator and the second photonic crystal modulator. This common waveguide enables secondary tuning of the first and second optical signals, i.e., push-pull tuning of the first and second optical signals within the FP cavity, thereby maximizing the tuning of the optical signals and ensuring that the tuning of the first and second optical signals has the same optical path (displacement).

[0012] For example, after the optical signals are divided into a first optical signal and a second optical signal, the first photonic crystal modulator and the second photonic crystal modulator can perform anti-phase modulation of the two optical signals. That is, under the action of the same input electrical signal, the resonance peaks of the first photonic crystal modulator and the second photonic crystal modulator shift in opposite directions. Therefore, after the first optical signal and the second optical signal are tuned twice by the first photonic crystal modulator and the second photonic crystal modulator respectively, the change in the resonance peak between the first photonic crystal modulator and the second photonic crystal modulator can cancel the change in beam reflection in the FP cavity during the modulation of the first optical signal and the second optical signal, so as to ensure that the FP cavity has a stable optical reflectivity and a stable optical field. The working state of the gain chip is no longer affected by the modulation signal, thereby ensuring efficient and stable light output of the external cavity laser.

[0013] In some embodiments, the tunable mirror further includes a lower cladding and an upper cladding disposed opposite to each other. A main waveguide, a beam splitter, a first branch waveguide, a first photonic crystal modulator, a second branch waveguide, a second photonic crystal modulator, and a common waveguide are respectively disposed between the lower cladding and the upper cladding.

[0014] In some embodiments, a semiconductor layer is disposed on the upper surface of the lower cladding layer. The tunable mirror further includes a first electrode, a second electrode, and a common electrode disposed on the upper surface of the upper cladding layer. The first electrode, the second electrode, and the common electrode are respectively connected to the semiconductor layer through vias in the upper cladding layer.

[0015] A first photonic crystal modulator is located between the first electrode and the common electrode and is configured to tune the optical signal under the influence of electrical signals provided by the first electrode and the common electrode. A second photonic crystal modulator is located between the second electrode and the common electrode and is configured to tune the optical signal under the influence of electrical signals provided by the second electrode and the common electrode.

[0016] Thus, by providing different voltage signals to the first electrode and the common electrode, the resonant peak of the first photonic crystal modulator can be adjusted using the bias voltage between them. Similarly, by providing different voltage signals to the second electrode and the common electrode, the resonant peak of the second photonic crystal modulator can be adjusted using the bias voltage between them.

[0017] In some embodiments, the orthographic projection shape of the common waveguide on the upper cladding is "U". In this way, while ensuring that the common waveguide can meet the requirements for optical signal transmission, the spatial positions of the components within the tunable mirror can be set more reasonably, which helps to reduce the planar area of ​​the tunable mirror, thereby reducing the overall size of the external cavity laser and improving the optical modulation speed of the external cavity laser.

[0018] Optionally, the common electrode is located in the concave region of the orthographic projection of the common waveguide onto the upper cladding.

[0019] In some embodiments, the tunable mirror further includes a first heating layer and a second heating layer. The first heating layer is disposed on the upper surface of the upper cladding and lies within the orthogonal projection range of the first photonic crystal modulator on the upper cladding. The second heating layer is disposed on the upper surface of the upper cladding and lies within the orthogonal projection range of the second photonic crystal modulator on the upper cladding. Heating the first heating layer causes a change in the effective refractive index of the first photonic crystal modulator, thereby adjusting the resonance peak of the first photonic crystal modulator. Similarly, heating the second heating layer causes a change in the effective refractive index of the second photonic crystal modulator, thereby adjusting the resonance peak of the second photonic crystal modulator.

[0020] Based on this, by using the first heating layer and the second heating layer, the resonance peaks of the first photonic crystal modulator and the second photonic crystal modulator can be independently adjusted to ensure that the resonance peaks of the first photonic crystal modulator and the second photonic crystal modulator are consistent. This compensates for the resonance peak deviation caused by factors such as processing errors, which is beneficial to improving the modulation efficiency of the tunable mirror and ensuring its light reflectivity, so as to further ensure the efficient and stable light output of the external cavity laser.

[0021] In other embodiments, a first branch waveguide extends along a first direction, and a second branch waveguide extends along a second direction; the first and second directions intersect the transmission direction of the main waveguide, respectively, and are symmetrical about the transmission direction of the main waveguide. A first photonic crystal modulator is disposed beside the first branch waveguide along the first direction; a second photonic crystal modulator is disposed beside the second branch waveguide along the second direction.

[0022] The tunable mirror further includes a common waveguide. The common waveguide is disposed on the side of the first photonic crystal modulator away from the first branch waveguide, and on the side of the second photonic crystal modulator away from the second branch waveguide. The common waveguide is configured to: receive a first optical signal tuned by the first photonic crystal modulator and transmit the tuned first optical signal to the resonant cavity of the second photonic crystal modulator for secondary tuning by the second photonic crystal modulator and coupling it to the second branch waveguide; and receive a second optical signal tuned by the second photonic crystal modulator and transmit the tuned second optical signal to the resonant cavity of the first photonic crystal modulator for secondary tuning by the first photonic crystal modulator and coupling it to the first branch waveguide.

[0023] Optionally, the common waveguide includes a straight waveguide.

[0024] The technical effects achievable by the common waveguide in this embodiment are the same as those in some of the foregoing embodiments, and will not be described in detail here.

[0025] In some embodiments, the tunable mirror further includes a first phase shifter and a second phase shifter. The first phase shifter is coupled to a first branch waveguide and configured to adjust the phase of a first optical signal received by the first branch waveguide. The second phase shifter is coupled to a second branch waveguide and configured to adjust the phase of a second optical signal received by the second branch waveguide. Thus, by independently adjusting the phases of the first and second optical signals to maintain phase consistency, phase differences introduced during the transmission of the first and second optical signals due to manufacturing or design errors can be avoided, preventing optical field instability within the FP cavity. This helps ensure efficient and stable laser output.

[0026] In some embodiments, the tunable mirror further includes a wavelength adjuster. The wavelength adjuster is coupled to the main waveguide and configured to adjust the wavelength of the optical signal received by the main waveguide. By adjusting the wavelength of the optical signal received by the main waveguide using the wavelength adjuster, the wavelength of the optical signal transmitted from the gain chip to the main waveguide can be matched with the operating wavelengths of the first and second photonic crystal modulators, ensuring that the operating output (e.g., output power) of the gain chip is not affected by changes in the modulation states of the first and second photonic crystal modulators.

[0027] In some embodiments, the first photonic crystal modulator and the second photonic crystal modulator each include: a photonic crystal modulation structure, or multiple cascaded photonic crystal modulation structures. This allows the optical signal located at its resonance peak after tuning by each photonic crystal modulation structure to enter adjacent or opposite photonic crystal modulation structures, thereby achieving greater tuning of the optical signal and improving the tuning efficiency and quality of the first and second photonic crystal modulators.

[0028] Optionally, the photonic crystal modulation structure includes: a one-dimensional photonic crystal nanobeam cavity structure or a two-dimensional photonic crystal slab structure.

[0029] Optionally, the photonic crystal modulation structure includes: a cylindrical array structure, a herringbone structure, or a hole array structure.

[0030] In some embodiments, the beam splitter includes: a Y-branch waveguide, a 1×2 multimode interference coupler, a 2×2 multimode interference coupler, or a directional coupler with a beam splitting ratio of 50:50.

[0031] On the other hand, some embodiments of this disclosure provide a tuning method for an external cavity laser. The tuning method includes the steps described below.

[0032] The main waveguide receives the optical signal transmitted by the gain chip and transmits the optical signal to the beam splitter.

[0033] The beam splitter divides the optical signal into a first optical signal and a second optical signal, and transmits the first optical signal to the first branch waveguide and the second optical signal to the second branch waveguide.

[0034] The first photonic crystal modulator tunes the first optical signal transmitted through the first branch waveguide.

[0035] The second photonic crystal modulator tunes the second optical signal transmitted through the second branch waveguide.

[0036] In some embodiments, the tuning method for an external cavity laser further includes the following steps.

[0037] The first photonic crystal modulator couples the tuned first optical signal to a common waveguide, which then transmits the tuned first optical signal to the resonant cavity of the second photonic crystal modulator. The second photonic crystal modulator performs secondary tuning on the tuned first optical signal and couples the secondary-tuned first optical signal to the second branch waveguide.

[0038] The second photonic crystal modulator couples the tuned second optical signal to a common waveguide, which then transmits the tuned second optical signal to the resonant cavity of the first photonic crystal modulator. The first photonic crystal modulator performs secondary tuning on the tuned second optical signal and couples the secondary-tuned second optical signal to the first branch waveguide.

[0039] In some embodiments, the tuning method for an external cavity laser further includes the following steps.

[0040] The resonance peak of the first photonic crystal modulator is adjusted by the first heating layer so that the resonance peak of the first photonic crystal modulator is consistent with that of the second photonic crystal modulator.

[0041] The resonance peak of the second photonic crystal modulator is adjusted by the second heating layer so that the resonance peak of the second photonic crystal modulator is consistent with that of the first photonic crystal modulator.

[0042] In some embodiments, the tuning method for an external cavity laser further includes the following steps.

[0043] Before the optical signal is transmitted to the beam splitter through the main waveguide, the wavelength of the optical signal is adjusted by a wavelength modulator so that the wavelength of the optical signal is consistent with the operating wavelength of the first photonic crystal modulator and the operating wavelength of the second photonic crystal modulator.

[0044] In some embodiments, the tuning method for an external cavity laser further includes the following steps.

[0045] Before the first optical signal transmitted through the first branch waveguide is tuned by the first photonic crystal modulator, the phase of the first optical signal is adjusted by the first phase shifter so that the phase of the first optical signal is consistent with the phase of the second optical signal.

[0046] Before the second optical signal transmitted through the second branch waveguide is tuned by the second photonic crystal modulator, the phase of the second optical signal is adjusted by the second phase shifter so that the phase of the second optical signal is consistent with the phase of the first optical signal.

[0047] The tuning method for external cavity lasers provided in this disclosure is applied to the external cavity lasers described in some of the foregoing embodiments. The tuning method can also achieve all the technical effects achievable by the aforementioned external cavity lasers, and will not be detailed here. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the structure of a tunable mirror in an external cavity laser provided in one embodiment;

[0050] Figure 2 This is a schematic diagram of the structure of a tunable mirror in another external cavity laser provided in one embodiment;

[0051] Figure 3 for Figure 2 The diagram shows the tuning path of a first optical signal in a tunable mirror.

[0052] Figure 4 for Figure 3 A schematic diagram of the resonant cavity of the first photonic crystal modulator in the tuning path of the first optical signal shown;

[0053] Figure 5 for Figure 3 A schematic diagram of the resonant cavity of the second photonic crystal modulator in the tuning path of the first optical signal shown;

[0054] Figure 6 for Figure 2 The diagram shows the tuning path of a second optical signal in a tunable mirror.

[0055] Figure 7 for Figure 6 A schematic diagram of the resonant cavity of the second photonic crystal modulator in the tuning path of the second optical signal shown;

[0056] Figure 8 for Figure 6 A schematic diagram of the resonant cavity of the first photonic crystal modulator in the tuning path of the second optical signal shown;

[0057] Figure 9 This is a schematic diagram of a one-dimensional photonic crystal modulation structure provided in one embodiment;

[0058] Figure 10 This is a schematic diagram of a two-dimensional photonic crystal modulation structure provided in one embodiment;

[0059] Figure 11 This is a schematic diagram of the photonic crystal modulation structure provided in one embodiment when a cylindrical array structure is used;

[0060] Figure 12 This is a schematic diagram of the photonic crystal modulation structure provided in one embodiment when a fishbone structure is adopted;

[0061] Figure 13 This is a schematic diagram of a photonic crystal modulation structure provided in one embodiment, when a aperture array structure is used.

[0062] Figure 14 for Figure 2 A schematic cross-sectional view of an adjustable reflector along the AA direction is shown.

[0063] Figure 15 for Figure 2 A schematic cross-sectional view of an adjustable mirror along the BB direction is shown.

[0064] Figure 16 for Figure 2 A schematic cross-sectional view of a tunable mirror along the CC direction is shown.

[0065] Figure 17 for Figure 2 A schematic cross-sectional view of a tunable mirror along the DD direction is shown.

[0066] Figure 18 This is a schematic diagram of the structure of a tunable mirror in another external cavity laser provided in one embodiment;

[0067] Figure 19 This is a schematic diagram of the structure of a tunable mirror in another external cavity laser provided in one embodiment;

[0068] Figure 20 This is a schematic diagram illustrating the optical signal tuning principle of an external cavity laser provided in one embodiment;

[0069] Figure 21This is a schematic diagram of the optical signal tuning principle of another external cavity laser provided in one embodiment;

[0070] Figure 22 This is an optical transmission spectrum of an external cavity laser provided in one embodiment.

[0071] Explanation of reference numerals in the attached figures:

[0072] 100 - External cavity laser, 1 - Gain chip, 2 - Tunable mirror, 21 - Main waveguide

[0073] 22-Wavelength adjuster, 23-Beam splitter, 24-First branch waveguide, 241-First phase shifter

[0074] 25-Second branch waveguide, 251-Second phase shifter, 26-First photonic crystal modulator,

[0075] 261 - First heating layer, 27 - Second photonic crystal modulator, 271 - Second heating layer

[0076] 28 - Common waveguide, 20 - Lower cladding, 30 - Semiconductor layer, 40 - Upper cladding, 50 - Power monitor.

[0077] 60 - Photonic crystal modulation structure, 41 - First electrode, 42 - Second electrode, 43 - Common electrode.

[0078] R1 - Resonant cavity of the first photonic crystal modulator, R2 - Resonant cavity of the second photonic crystal modulator;

[0079] L1 - First optical signal, L2 - Second optical signal, R - Reflected optical signal. Detailed Implementation

[0080] To facilitate understanding of this disclosure, a more complete description will now be given with reference to the accompanying drawings, which illustrate embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0081] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure.

[0082] It should be understood that when a component or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" other components or layers, it may be directly on, adjacent to, connected to, or coupled to other components or layers, or there may be intervening components or layers. Conversely, when a component is referred to as being "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other components or layers, there are no intervening components or layers.

[0083] It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or parts, these elements, components, areas, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, area, layer, or part from another element, component, area, layer, or part. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or part discussed below may be referred to as the second element, component, area, layer, or part.

[0084] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as “below,” “under,” or “below” will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0085] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.

[0086] Embodiments of the invention are described herein with reference to cross-sectional views that serve as schematic diagrams of preferred embodiments (and intermediate structures) of the present disclosure, thus allowing for the expectation of variations in the illustrated shapes due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of the present disclosure should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. The regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of the invention.

[0087] Currently, external cavity lasers are widely used in various technological fields such as military, industry, agriculture, aviation, communications, and medicine due to their advantages such as high efficiency, long lifespan, stable frequency, and wide wavelength tuning range.

[0088] Please see Figure 1 and Figure 2 This disclosure provides an external cavity laser 100 in some embodiments. The external cavity laser 100 is, for example, a silicon-based III / V hybrid integrated laser.

[0089] It should be noted that, Figure 1 and Figure 2 Only the structure of the external cavity feedback element in the external cavity laser 100 is shown. The structures of other components of the external cavity laser 100 can be found in related technologies, and will not be described in detail in this embodiment.

[0090] like Figure 1 and Figure 2 As shown, the external cavity laser 100 includes a gain chip 1 and a tunable mirror 2 coupled to the gain chip 1. The tunable mirror 2 includes a main waveguide 21, a beam splitter 23, a first branch waveguide 24, a second branch waveguide 25, a first photonic crystal modulator 26, and a second photonic crystal modulator 27.

[0091] The main waveguide 21 is coupled to the gain chip 1 and is configured to receive the optical signal transmitted by the gain chip 1.

[0092] Gain chip 1 has a gain dielectric and a high reflectivity. Gain chip 1 is, for example, a reflective semiconductor optical amplifier (RSOA). Main waveguide 21 is, for example, a silicon-based planar waveguide. Gain chip 1 can be coupled to the input port of main waveguide 21 by end-face coupling (including surface vertical coupling) or grating coupling.

[0093] Beam splitter 23 is coupled to main waveguide 21 and is configured to split the optical signal transmitted by main waveguide 21 into a first optical signal and a second optical signal.

[0094] Beam splitter 23 is used to equally divide the optical signal to achieve equal distribution of optical power. Beam splitter 23 can be: a Y-branch waveguide, a 1×2 multi-mode interference coupler (MMI), a 2×2 multi-mode interference coupler, or a directional coupler with a beam splitting ratio of 50:50, etc. This embodiment does not impose any limitations on this; the appropriate option can be selected based on actual needs.

[0095] The first branch waveguide 24 is coupled to the beam splitter 23 and is configured to receive a first optical signal. The first photonic crystal modulator 26 is disposed beside the first branch waveguide 24 and is configured to tune the first optical signal transmitted through the first branch waveguide 24.

[0096] The second branch waveguide 25 is coupled to the beam splitter 23 and is configured to receive the second optical signal. The second photonic crystal modulator 27 is disposed beside the second branch waveguide 25 and is configured to tune the second optical signal transmitted through the second branch waveguide 25.

[0097] The first branch waveguide 24 and the second branch waveguide 25 are, for example, silicon-based planar waveguides.

[0098] The first photonic crystal modulator 26 and the second photonic crystal modulator 27 are formed using photonic crystal materials, which have advantages such as small size, high output power, and small equivalent reflection changes, and are not affected by the free spectral range (FSR). Furthermore, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 each have only one resonance peak within their operating wavelength band, making them less susceptible to inter-mode competition effects. This allows them to have a wider operating wavelength range and facilitates modulation control.

[0099] In this embodiment, a high-reflection side of the gain chip 1 can together with the tunable reflector 2 to form the FP cavity of the external cavity laser 100. The output port of the external cavity laser 100 can be one or more, for example: the output port of the external cavity laser 100 can be the output port Out1 of the first branch waveguide 24 and / or the output port Out2 of the second branch waveguide 24. However, it is not limited to this.

[0100] After the gain chip 1 transmits the optical signal to the main waveguide 21 of the tunable reflector 2, the beam splitter 23 can divide the optical signal transmitted through the main waveguide 21 into a first optical signal and a second optical signal. Then, the first optical signal is tuned by the first photonic crystal modulator 26, and the second optical signal is tuned by the second photonic crystal modulator 27. In this way, under the tuning effect of the first photonic crystal modulator 26 and the second photonic crystal modulator 27, as well as the effect of beam reflection and beam interference within the FP cavity, the optical signal can be directly and quickly output from the output port of the external cavity laser 100, thereby realizing high-speed direct tuning of the external cavity laser 100.

[0101] In one possible implementation, such as Figure 1 As shown, the tunable mirror 2 further includes a first phase shifter 241 and a second phase shifter 251. The first phase shifter 241 is coupled to the first branch waveguide 24 and configured to adjust the phase of a first optical signal received by the first branch waveguide 24. The second phase shifter 251 is coupled to the second branch waveguide 25 and configured to adjust the phase of a second optical signal received by the second branch waveguide 25.

[0102] The structures of the first phase shifter 241 and the second phase shifter 251 can be selected and configured according to actual needs, limited to adjusting the phase of the corresponding optical signal. In this way, by independently adjusting the phases of the first and second optical signals to ensure their phase consistency, it is possible to avoid phase differences introduced during the transmission of the first and second optical signals due to process errors or design errors, which could lead to optical field instability within the FP cavity. This helps ensure efficient and stable laser output.

[0103] In another possible implementation, such as Figure 2 As shown, the first photonic crystal modulator 26 is disposed on the side of the first branch waveguide 24 near the second branch waveguide 25, and the second photonic crystal modulator 27 is disposed on the side of the second branch waveguide 25 near the first branch waveguide 24. The tunable mirror 2 further includes a common waveguide 28 disposed between the first photonic crystal modulator 26 and the second photonic crystal modulator 27. The common waveguide 28 is configured to: receive a first optical signal tuned by the first photonic crystal modulator 26 and transmit the tuned first optical signal to the resonant cavity of the second photonic crystal modulator 27 for secondary tuning by the second photonic crystal modulator 27 and then couple it to the second branch waveguide 25; and receive a second optical signal tuned by the second photonic crystal modulator 27 and transmit the tuned second optical signal to the resonant cavity of the first photonic crystal modulator 26 for secondary tuning by the first photonic crystal modulator 26 and then couple it to the first branch waveguide 24.

[0104] In this embodiment of the disclosure, the structure of the tunable reflector 2 is as follows: Figure 2 As shown.

[0105] Based on this, the tuning path diagram of the first optical signal is as follows: Figure 3 As shown. Accordingly, in this case, the resonant cavity R1 of the first photonic crystal modulator 26 is as follows: Figure 4 As shown, the resonant cavity R1 includes at least a spatial region with optical signal uploading and downloading functions, formed by the first photonic crystal modulator 26, the first branch waveguide 24 (Input), and the common waveguide 28 (Drop Output). The resonant cavity R2 of the second photonic crystal modulator 27 is as follows... Figure 5 As shown, the resonant cavity R2 includes at least a spatial region with optical signal uploading and downloading functions, consisting of a second photonic crystal modulator 27, a common waveguide 28 (Input), and a second branch waveguide 25 (Drop Output).

[0106] Similarly, the tuning path diagram of the second optical signal is as follows: Figure 6 As shown. Accordingly, in this case, the resonant cavity R2 of the second photonic crystal modulator 27 is as follows: Figure 7 As shown, the resonant cavity R2 includes at least a spatial region with optical signal uploading and downloading functions, formed by the second photonic crystal modulator 27, the second branch waveguide 25 (Input), and the common waveguide 28 (Drop Output). The resonant cavity R1 of the first photonic crystal modulator 26 is as follows... Figure 8 As shown, the resonant cavity R1 includes at least a spatial region with optical signal uploading and downloading functions, consisting of a first photonic crystal modulator 26, a common waveguide 28 (Input), and a first branch waveguide 24 (Drop Output).

[0107] In this embodiment, the common waveguide 28 is located between the first photonic crystal modulator 26 and the second photonic crystal modulator 27. The common waveguide 28 enables secondary tuning of the first and second optical signals, i.e., push-pull tuning of the first and second optical signals within the FP cavity. This maximizes the tuning of the optical signals and ensures that the tuning of the first and second optical signals has the same optical path (displacement). For example, after the optical signals are equally divided into the first and second optical signals, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can perform inverse modulation of the two optical signals. That is, under the same input electrical signal, the resonant peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 shift in opposite directions. Therefore, after the first optical signal and the second optical signal are tuned twice by the first photonic crystal modulator 26 and the second photonic crystal modulator 27 respectively, the change in the resonance peak between the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can offset the change in the reflection of the beam in the FP cavity during the modulation of the first optical signal and the second optical signal, so as to ensure that the FP cavity has a stable optical reflectivity and a stable optical field, thereby ensuring the efficient and stable output of the external cavity laser.

[0108] In addition, please see Figure 4 and Figure 5 In some embodiments, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 may each be composed of a single photonic crystal modulation structure 60, or may be composed of multiple cascaded photonic crystal modulation structures 60. Optionally, the photonic crystal modulation structure 60 may be an SOI photonic crystal structure or a SiN photonic crystal structure.

[0109] Optionally, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 are each composed of multiple photonic crystal modulation structures 60 cascaded along the transmission direction of the corresponding waveguide. In this way, the optical signal located at its resonant peak after being tuned by each photonic crystal modulation structure 60 can enter adjacent or opposite photonic crystal modulation structures 60, thereby achieving greater tuning of the optical signal and improving the tuning efficiency and tuning quality of the first photonic crystal modulator 26 and the second photonic crystal modulator 27.

[0110] The photonic crystal modulation structure 60 can be configured in various ways. For example, based on the dimensions of the photonic crystal, the photonic crystal modulation structure 60 can be configured as follows: Figure 9 The one-dimensional photonic crystal nanobeam cavity structure shown; or, as... Figure 10 The diagram shows a two-dimensional photonic crystal planar structure. Based on the shape of the photonic crystal, the photonic crystal modulation structure 60 is, for example, as shown below. Figure 11 The cylindrical array structure shown, such as Figure 12 The fishbone structure shown, or as Figure 13 The aperture array structure shown is not limited to this embodiment.

[0111] Furthermore, the resonant peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 are related to their structures, and the specific design can be selected according to actual needs. The operating wavelengths of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can be selected and set according to the requirements of modulation bandwidth and extinction ratio.

[0112] Please continue reading. Figure 1 and Figure 2 In some embodiments, the tunable mirror 2 further includes a wavelength adjuster 22. The wavelength adjuster 22 is coupled to the main waveguide 21 and configured to adjust the wavelength of the optical signal received by the main waveguide 21. By adjusting the wavelength of the optical signal received by the main waveguide 21 using the wavelength adjuster 22, the wavelength of the optical signal transmitted from the gain chip 1 to the main waveguide 21 can be matched with the operating wavelengths of the first photonic crystal modulator 26 and the second photonic crystal modulator 27. This ensures that the operating output (e.g., output power, wavelength of the output optical signal) of the gain chip 1 is not affected by changes in the modulation state of the first photonic crystal modulator 26 and the second photonic crystal modulator 27.

[0113] Optionally, the wavelength modulator 22 is a phase shifter. The wavelength modulator 22 can adjust the phase of the optical signal received by the main waveguide 21 and adjust the equivalent length of the FP cavity so that the wavelength of the optical signal received by the main waveguide 21 changes.

[0114] To more clearly illustrate the structure of the tunable reflector 2 in the embodiments of this disclosure, the following embodiments are used as examples. Figure 2 The structure shown is an example of its layered structure.

[0115] Please combine Figure 2 , Figure 14 , Figure 15 , Figure 16 and Figure 17 It is understood that the tunable mirror 2 also includes a lower cladding 20 and an upper cladding 40 disposed opposite to each other. The main waveguide 21, beam splitter 23, first branch waveguide 24, first photonic crystal modulator 26, second branch waveguide 25, second photonic crystal modulator 27, and common waveguide 28 are respectively disposed between the lower cladding 20 and the upper cladding 40.

[0116] The lower cladding layer 20 serves as the substrate or insulating carrier for the tunable mirror 2 and can be made of a silicon substrate or a silicon-based substrate. The upper cladding layer 40 is formed of a light-transmitting insulating material, such as light-transmitting resin or silicon dioxide.

[0117] The upper surface of the lower cladding layer 20 is usually provided with a semiconductor thin film. By patterning different regions of the semiconductor thin film and doping with different types of materials, different parts of the semiconductor thin film can be used to form the semiconductor layer 30, the main waveguide 21, the first branch waveguide 24, the first photonic crystal modulator 26, the second branch waveguide 25, the second photonic crystal modulator 27, and the common waveguide 28, respectively.

[0118] For example, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 are respectively formed by PN structures after semiconductor thin film doping. Furthermore, the photon lifetime in the first photonic crystal modulator 26 and the second photonic crystal modulator 27 is related to the tuning quality of their resonant cavities, which can directly affect the modulation bandwidth of the external cavity laser 100. This disclosure does not limit this aspect; modulation can be performed according to actual needs.

[0119] Based on the above embodiments, please refer to Figure 2 and Figure 17 The tunable mirror 2 further includes a first electrode 41, a second electrode 42, and a common electrode 43 disposed on the upper surface of the upper cladding 40. The first electrode 41, the second electrode 42, and the common electrode 43 are respectively connected to the semiconductor layer 30 through vias in the upper cladding 40.

[0120] The first photonic crystal modulator 26 is located between the first electrode 41 and the common electrode 43, and is configured to tune the optical signal under the influence of the electrical signals provided by the first electrode 41 and the common electrode 43. Thus, since the first electrode 41 and the common electrode 43 each provide different voltage signals, the resonant peak of the first photonic crystal modulator 26 can be adjusted using the bias voltage between them.

[0121] The second photonic crystal modulator 27 is located between the second electrode 42 and the common electrode 43, and is configured to tune the optical signal under the influence of the electrical signals provided by the second electrode 42 and the common electrode 43. Thus, since the second electrode 42 and the common electrode 43 each provide different voltage signals, the resonant peak of the second photonic crystal modulator 27 can be adjusted using the bias voltage between them.

[0122] Optionally, the first electrode 41 and the second electrode 42 are grounded. The common electrode 43 is connected to an external voltage terminal to receive the modulated voltage signal. Conversely, it is also permissible to have the common electrode 43 grounded and the first electrode 41 and the second electrode 42 connected to external voltage terminals to receive the modulated voltage signal.

[0123] Optionally, the first electrode 41, the second electrode 42, and the common electrode 43 are made of metallic conductive materials, such as copper, aluminum, tungsten, etc.

[0124] In some embodiments, please continue reading Figure 2The orthographic projection of the common waveguide 28 onto the upper cladding 40 is U-shaped. Thus, while ensuring that the common waveguide 28 can meet the aforementioned optical signal transmission requirements, the spatial positions of the components within the tunable mirror 2 can be set more reasonably. This helps to reduce the planar area of ​​the tunable mirror 2, thereby reducing the overall size of the external cavity laser 100 and ultimately increasing the optical modulation speed of the external cavity laser 100.

[0125] In addition, please see Figure 2 and Figure 18 The U-shaped opening of the common waveguide 28 can face or move away from the beam splitter 23. Figure 18 In the example shown, the transmission of the optical signal in the common waveguide 28 can be referred to Figure 2 In the example, the transmission direction of the common waveguide 28 is opposite to that of the common waveguide 28.

[0126] Optionally, the common electrode 43 is located in the concave region of the orthographic projection of the common waveguide 28 onto the upper cladding 40.

[0127] Please see Figure 2 and Figure 17 In some embodiments, the tunable mirror 2 further includes a first heating layer 261 and a second heating layer 271. The first heating layer 261 is disposed on the upper surface of the upper cladding 40 and is located within the orthographic projection range of the first photonic crystal modulator 26 on the upper cladding 40. The second heating layer 271 is disposed on the upper surface of the upper cladding 40 and is located within the orthographic projection range of the second photonic crystal modulator 27 on the upper cladding 40.

[0128] Here, the first heating layer 261 and the second heating layer 271 can be metal heating layers or silicon heating layers.

[0129] Optionally, the first heating layer 261 and the second heating layer 271 are metal heating layers. In this way, they can be made of the same material as the first electrode 41, the second electrode 42 and the common electrode 43, and can be fabricated in a single patterning process.

[0130] Furthermore, the first heating layer 261 and the second heating layer 271 can be externally connected to a controller for heating under the controller's control. Thus, heating the first heating layer 261 can change the effective refractive index of the first photonic crystal modulator 26, thereby adjusting the resonance peak of the first photonic crystal modulator 26. Similarly, heating the second heating layer 271 can change the effective refractive index of the second photonic crystal modulator 27, thereby adjusting the resonance peak of the second photonic crystal modulator 27.

[0131] Based on this, by using the first heating layer 261 and the second heating layer 271, the resonance peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can be independently adjusted to ensure that the resonance peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 are consistent. This compensates for the resonance peak deviation caused by factors such as processing errors, which is beneficial to improving the modulation efficiency of the tunable mirror 2 and ensuring its light reflectivity, so as to further ensure the efficient and stable light output of the external cavity laser.

[0132] Please refer to [link / reference needed] for further information. Figure 18 In some embodiments, the beam splitter 23 is a 2×2 MMI. Correspondingly, the tunable mirror 2 also includes a power monitoring device 50 coupled to the beam splitter 23. Thus, the power monitoring device 50 can be used to monitor the operating status of the beam splitter 23 in real time to ensure that the beam splitter 23 can equally divide the optical signal transmitted through the main waveguide 21.

[0133] Please see Figure 19 In some other embodiments, the first branch waveguide 24, the second branch waveguide 25, and the common waveguide 28 may also have other configurations.

[0134] For example, a first branch waveguide 24 extends along a first direction, and a second branch waveguide 25 extends along a second direction; wherein the first and second directions intersect the transmission direction of the main waveguide 21, and are symmetrical about the transmission direction of the main waveguide 21. Optionally, the first and second directions are perpendicular to the transmission direction of the main waveguide 21. A first photonic crystal modulator 26 is disposed beside the first branch waveguide 24 along the first direction; a second photonic crystal modulator 27 is disposed beside the second branch waveguide 25 along the second direction. A common waveguide 28 is disposed on the side of the first photonic crystal modulator 26 away from the first branch waveguide 24, and on the side of the second photonic crystal modulator 27 away from the second branch waveguide 25. The common waveguide 28 is, for example, a straight waveguide.

[0135] In this embodiment, the function of the common waveguide 28 and the technical effects it can achieve are the same as in the previous embodiments, and will not be repeated here.

[0136] Based on this, for example, the first electrode 41 can be disposed along a first direction on the side of the first branch waveguide 24 away from the first photonic crystal modulator 26. The second electrode 42 can be disposed along a second direction on the side of the second branch waveguide 25 away from the second photonic crystal modulator 27. The common electrode 43 can be disposed on the side of the common waveguide 28 away from both the first photonic crystal modulator 26 and the second photonic crystal modulator 27. Thus, the first photonic crystal modulator 26 is located between the first electrode 41 and the common electrode 43, and can tune the optical signal under the action of the electrical signals provided by the first electrode 41 and the common electrode 43. The second photonic crystal modulator 27 is located between the second electrode 42 and the common electrode 43, and can tune the optical signal under the action of the electrical signals provided by the second electrode 42 and the common electrode 43.

[0137] Furthermore, the relevant features of the first electrode 41, the second electrode 42, and the common electrode 43 can be found in some of the aforementioned embodiments, and will not be repeated here.

[0138] The structure of the external cavity laser is as described in some of the embodiments above. Some embodiments of this disclosure also provide a tuning method for the external cavity laser, as described below.

[0139] Please see Figure 1 , Figure 2 , Figure 19 , Figure 20 and Figure 21 The tuning method includes the following steps.

[0140] S100, the main waveguide 21 receives the optical signal transmitted by the gain chip 1 and transmits the optical signal to the beam splitter 23.

[0141] S200, the beam splitter 23 divides the above optical signal into a first optical signal L1 and a second optical signal L2, and transmits the first optical signal L1 to the first branch waveguide 24 and the second optical signal L2 to the second branch waveguide 25.

[0142] S300, the first photonic crystal modulator 26 tunes the first optical signal L1 transmitted by the first branch waveguide 24.

[0143] S400, the second photonic crystal modulator 27 tunes the second optical signal L2 transmitted by the second branch waveguide 25.

[0144] In this embodiment, a high-reflection side of the gain chip 1, together with the tunable mirror 2, can form the FP cavity of the external cavity laser 100. After the main waveguide 21 receives the optical signal transmitted by the gain chip 1, the beam splitter 23 can divide the optical signal transmitted by the main waveguide 21 into a first optical signal L1 and a second optical signal L2. Then, the first optical signal L1 is tuned by the first photonic crystal modulator 26, and the second optical signal L2 is tuned by the second photonic crystal modulator 27. In this way, under the tuning effect of the first photonic crystal modulator 26 and the second photonic crystal modulator 27, and under the effect of beam reflection and beam interference within the FP cavity, the optical signal can be directly and quickly output from the output port of the external cavity laser 100, thereby realizing high-speed direct tuning of the external cavity laser 100.

[0145] Depending on the structure of the external cavity laser 100, the specific tuning method will also be different.

[0146] In some embodiments, the structure of the external cavity laser 100 is as follows: Figure 1 As shown. Please refer to [the original text]. Figure 20 The tuning method of the external cavity laser 100 also includes the following steps.

[0147] S210, before the first photonic crystal modulator 26 tunes the first optical signal L1 transmitted through the first branch waveguide 24, the phase of the first optical signal L1 is adjusted by the first phase shifter 241 so that the phase of the first optical signal L1 is consistent with the phase of the second optical signal L2.

[0148] S220, before the second photonic crystal modulator 27 tunes the second optical signal L2 transmitted through the second branch waveguide 25, the phase of the second optical signal L2 is adjusted by the second phase shifter 251 so that the phase of the second optical signal L2 is consistent with the phase of the first optical signal L1.

[0149] This embodiment of the invention independently adjusts the phases of the first optical signal L1 and the second optical signal L2 to ensure their phase consistency. This avoids phase differences introduced during the transmission of the first and second optical signals L1 and L2 due to process or design errors, which could lead to optical field instability within the FP cavity. This, in turn, helps ensure efficient and stable laser output.

[0150] In other embodiments, the external cavity laser 100 is structured as follows: Figure 2 and Figure 19 As shown. Please refer to [the original text]. Figure 21 The tuning method of the external cavity laser 100 also includes the following steps.

[0151] S350, the first photonic crystal modulator 26 couples the tuned first optical signal L1 to the common waveguide 28, and the common waveguide 28 transmits the tuned first optical signal L1 to the resonant cavity of the second photonic crystal modulator 27. The second photonic crystal modulator 27 performs secondary tuning on the tuned first optical signal L1 and couples the secondary-tuned first optical signal L1 to the second branch waveguide 25.

[0152] S450, the second photonic crystal modulator 27 couples the tuned second optical signal L2 to the common waveguide 28, and the common waveguide 28 transmits the tuned second optical signal L2 to the resonant cavity of the first photonic crystal modulator 26. The first photonic crystal modulator 26 performs secondary tuning on the tuned second optical signal L2 and couples the secondary-tuned second optical signal L2 to the first branch waveguide 24.

[0153] In this embodiment, secondary tuning of the first optical signal L1 and the second optical signal L2 can be achieved through the common waveguide 28. This means that push-pull tuning of the first optical signal L1 and the second optical signal L2 within the FP cavity is achieved, thereby maximizing the tuning of the optical signals and ensuring that the tuning of the first optical signal L1 and the second optical signal L2 has the same optical path (displacement). For example, after the optical signals are equally divided into the first optical signal L1 and the second optical signal L2, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can perform inverse modulation of the two optical signals. That is, under the same input electrical signal, the resonant peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 shift in opposite directions. Therefore, after the first optical signal L1 and the second optical signal L2 are tuned twice by the first photonic crystal modulator 26 and the second photonic crystal modulator 27 respectively, the change in the resonance peak between the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can offset the change in the reflection of the beam inside the FP cavity during the modulation of the first optical signal L1 and the second optical signal L2, so as to ensure that the FP cavity has a stable optical reflectivity and a stable optical field, thereby ensuring the efficient and stable output of the external cavity laser.

[0154] In some embodiments, please continue reading Figure 19 and Figure 20 The tuning method for external cavity lasers also includes the following steps.

[0155] S001, the resonance peak of the first photonic crystal modulator 26 is adjusted by the first heating layer 261 so that the resonance peak of the first photonic crystal modulator 26 is consistent with the resonance peak of the second photonic crystal modulator 27.

[0156] S002, the resonance peak of the second photonic crystal modulator 27 is adjusted by the second heating layer 271 so that the resonance peak of the second photonic crystal modulator 27 is consistent with the resonance peak of the first photonic crystal modulator 26.

[0157] Here, there is no order restriction between S001 and S300, or between S002 and S400; that is, either one can be executed first, or both can be executed simultaneously.

[0158] In this embodiment, the first heating layer 261 and the second heating layer 271 can be used to independently adjust the resonance peak of the first photonic crystal modulator 26 and the resonance peak of the second photonic crystal modulator 27, so as to ensure that the resonance peaks of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 are consistent, thereby compensating for the resonance peak deviation caused by factors such as processing errors. This is beneficial to improving the modulation efficiency of the tunable mirror 2, while ensuring its light reflectivity, so as to further ensure the efficient and stable light output of the external cavity laser.

[0159] In some embodiments, please continue reading Figure 19 and Figure 20 The tuning method for external cavity lasers also includes the following steps.

[0160] S110, before the main waveguide 21 transmits the optical signal to the beam splitter 23, the wavelength of the optical signal is adjusted by the wavelength modulator 22 so that the wavelength of the optical signal is consistent with the operating wavelength of the first photonic crystal modulator 26 and the operating wavelength of the second photonic crystal modulator 27.

[0161] Wavelength modulator 22 is, for example, a phase shifter. Wavelength modulator 22 can adjust the phase of the optical signal received by the main waveguide 21, thereby adjusting the equivalent length of the FP cavity, so as to change the wavelength of the optical signal received by the main waveguide 21.

[0162] In this embodiment, the wavelength adjuster 22 is used to adjust the wavelength of the optical signal received by the main waveguide 21, so that the wavelength of the optical signal transmitted from the gain chip 1 to the main waveguide 21 is matched with the operating wavelength of the first photonic crystal modulator 26 and the second photonic crystal modulator 27, thereby ensuring that the operating output (e.g., output power, wavelength of the output optical signal) of the gain chip 1 is not affected by the modulation state changes of the first photonic crystal modulator 26 and the second photonic crystal modulator 27.

[0163] It should be understood that, unless otherwise explicitly stated herein, the execution order of some steps in the tuning method of the external cavity laser 100 described above is not strictly limited. These steps may be executed selectively or in any other order depending on the signal to be modulated by the external cavity laser 100; that is, the execution order of these steps is not necessarily sequential.

[0164] The external cavity laser 100 and its tuning method provided in this disclosure are as described above. After simulation of the external cavity laser 100, the optical transmission spectrum of each signal in the external cavity laser 100 is as follows: Figure 22 As shown. Specifically, Figure 22 Figure (a) shows the transmission spectrum of the first optical signal L1 and the second optical signal L2 in the first state, such as the on state (0) of the laser, and the reflection spectrum of the equivalent reflected light R in the FP cavity. Figure 22 Figure (b) shows the transmission spectrum of the first optical signal L1 and the second optical signal L2 in the second state, for example, the off state of the laser (1), and the reflection spectrum of the equivalent reflected light R in the FP cavity. Figure 22 Figure (c) shows the resonant peak spectrum of the FP cavity in the external cavity laser 100. Figure 22 Figure (d) shows the spectrum of the output optical signal of the external cavity laser 100.

[0165] Thus, from Figure 22 As can be seen, under different states, the external cavity laser 100 can have a stable and uniform narrowband reflection spectrum to ensure the stability of the optical field in the FP cavity, thereby achieving stable and efficient light output from the external cavity laser 100.

[0166] The resonant cavities of the first photonic crystal modulator 26 and the second photonic crystal modulator 27 can only have one resonant peak. After adjusting the wavelength of the optical signal input to the gain chip 1 using the wavelength adjuster 22 to match the operating wavelengths of the first photonic crystal modulator 26 and the second photonic crystal modulator 27, the modulation of the optical signal by the first photonic crystal modulator 26 and the second photonic crystal modulator 27 ensures that the optical signal with the same wavelength as the resonant peak has a much higher reflectivity in the FP cavity than other wavelength optical signals. This makes the optical signal the sole output optical signal of the external cavity laser 100. For example... Figure 22 As shown in Figure (d) in the table.

[0167] Therefore, the first photonic crystal modulator 26 and the second photonic crystal modulator 27 have wavelength selection function, which can effectively modulate the optical signal by the first photonic crystal modulator 26 and the second photonic crystal modulator 27 without affecting the output power of the gain chip 1, thereby accurately modulating the wavelength of the output optical signal of the external cavity laser 100.

[0168] In summary, during the push-pull tuning of the optical signal using the first photonic crystal modulator 26 and the second photonic crystal modulator 27, the beam reflectivity within the FP cavity of the external cavity laser 100 can remain stable. Therefore, after using a constant current to drive the gain chip 1, the optical field within the FP cavity is stable, ensuring that the output optical signal of the external cavity laser 100 is not affected by the dynamic response of the external cavity laser 100.

[0169] Based on this, the stable output of a single-wavelength optical signal from the external cavity laser 100 can be achieved by adjusting the wavelength of the optical signal transmitted through the main waveguide 21 using the wavelength adjuster 22, so that this wavelength is matched and aligned with the operating wavelengths of the first photonic crystal modulator 26 and the second photonic crystal modulator 27. This significantly reduces the wavelength adjustment range of the external cavity laser 100 and simplifies its wavelength control.

[0170] In the description of this specification, the technical features of the above-described embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0171] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An external cavity laser, characterized by, The external cavity laser comprises: a gain chip and a tunable mirror coupled with the gain chip; wherein the gain chip has a high reflection surface, and the high reflection surface and the tunable mirror jointly constitute an F-P cavity of the external cavity laser; the tunable mirror comprises: a main waveguide coupled with the gain chip and configured to receive an optical signal transmitted by the gain chip; a beam splitter coupled with the main waveguide and configured to equally divide the optical signal transmitted by the main waveguide into a first optical signal and a second optical signal; a first branch waveguide coupled with the beam splitter and configured to receive the first optical signal; a first photonic crystal modulator arranged beside the first branch waveguide and configured to tune the first optical signal transmitted by the first branch waveguide; a second branch waveguide coupled with the beam splitter and configured to receive the second optical signal; and a second photonic crystal modulator arranged beside the second branch waveguide and configured to tune the second optical signal transmitted by the second branch waveguide; wherein the tunable mirror further comprises a common waveguide; the common waveguide is configured to receive the first optical signal tuned by the first photonic crystal modulator, transmit the tuned first optical signal into a resonant cavity of the second photonic crystal modulator, and couple the second optical signal tuned by the second photonic crystal modulator to the first branch waveguide after secondary tuning by the second photonic crystal modulator; and receive the second optical signal tuned by the second photonic crystal modulator, transmit the tuned second optical signal into a resonant cavity of the first photonic crystal modulator, and couple the first optical signal tuned by the first photonic crystal modulator to the second branch waveguide after secondary tuning by the first photonic crystal modulator; wherein an output port of the external cavity laser is an output port of the first branch waveguide and / or an output port of the second branch waveguide.

2. The external cavity laser of claim 1, wherein: the first photonic crystal modulator is arranged on a side of the first branch waveguide close to the second branch waveguide, and the second photonic crystal modulator is arranged on a side of the second branch waveguide close to the first branch waveguide; the common waveguide is arranged between the first photonic crystal modulator and the second photonic crystal modulator.

3. The external cavity laser of claim 2, wherein, The tunable mirror further comprises oppositely arranged lower and upper cladding layers; the main waveguide, the beam splitter, the first branch waveguide, the first photonic crystal modulator, the second branch waveguide, the second photonic crystal modulator, and the common waveguide are respectively arranged between the lower and upper cladding layers.

4. The external cavity laser of claim 3, wherein, An upper surface of the lower cladding layer is provided with a semiconductor layer; the tunable mirror further comprises a first electrode, a second electrode, and a common electrode; the first electrode, the second electrode, and the common electrode are respectively arranged on an upper surface of the upper cladding layer and are connected to the semiconductor layer through vias in the upper cladding layer. The first photonic crystal modulator is located between the first electrode and the common electrode and is configured to tune the optical signal under the action of an electrical signal provided by the first electrode and the common electrode. The second photonic crystal modulator is located between the second electrode and the common electrode and is configured to tune the optical signal under the action of an electrical signal provided by the second electrode and the common electrode.

5. The external cavity laser of claim 3 or 4, wherein A normal projection shape of the common waveguide on the upper cladding layer is a "U" shape.

6. The external cavity laser of claim 5, wherein, In the case where the tunable mirror further comprises a common electrode, the common electrode is located in a concave region of the normal projection of the common waveguide on the upper cladding layer.

7. The external cavity laser of claim 3 or 4, wherein, The tunable mirror further comprises: A first heating layer is arranged on the upper surface of the upper cladding layer and located in the range of the normal projection of the first photonic crystal modulator on the upper cladding layer. A second heating layer is arranged on the upper surface of the upper cladding layer and located in the range of the normal projection of the second photonic crystal modulator on the upper cladding layer.

8. The external cavity laser of claim 1, wherein The first branch waveguide extends along a first direction, and the second branch waveguide extends along a second direction; the first direction and the second direction are respectively intersected with the transmission direction of the main waveguide and are symmetric about the transmission direction of the main waveguide; the first photonic crystal modulator is arranged on the side of the first branch waveguide along the first direction; and the second photonic crystal modulator is arranged on the side of the second branch waveguide along the second direction. The common waveguide is arranged on the side of the first photonic crystal modulator away from the first branch waveguide and on the side of the second photonic crystal modulator away from the second branch waveguide.

9. The external cavity laser of claim 8, wherein, The common waveguide comprises a straight waveguide.

10. The external cavity laser of claim 1, wherein, The tunable mirror further comprises: A first phase shifter is coupled with the first branch waveguide and is configured to adjust the phase of the first optical signal received by the first branch waveguide. A second phase shifter is coupled with the second branch waveguide and is configured to adjust the phase of the second optical signal received by the second branch waveguide.

11. The external cavity laser of claim 1, wherein, The tunable mirror further comprises: A wavelength adjuster is coupled with the main waveguide and is configured to adjust the wavelength of the optical signal received by the main waveguide.

12. The external cavity laser of claim 1, wherein, The first photonic crystal modulator and the second photonic crystal modulator each comprise one photonic crystal modulation structure or a plurality of cascaded photonic crystal modulation structures.

13. The external cavity laser of claim 12, wherein, The photonic crystal modulation structure comprises a one-dimensional photonic crystal nanobeam cavity structure or a two-dimensional photonic crystal flat plate structure.

14. The external cavity laser of claim 12, wherein, The photonic crystal modulation structure comprises a cylindrical array structure, a fishbone structure, or a hole array structure.

15. The external cavity laser of claim 1, wherein, The beam splitter comprises a Y-branch waveguide, a 1x2 multimode interference coupler, a 2x2 multimode interference coupler, or a directional coupler with a splitting ratio of 50:

50.

16. A method of tuning an external cavity laser, characterized by, The external cavity laser comprises a gain chip and a tunable mirror coupled with the gain chip; the gain chip has a high reflection surface which, together with the tunable mirror, constitutes an F-P cavity of the external cavity laser; the tunable mirror comprises a main waveguide, a beam splitter, a first branch waveguide, a first photonic crystal modulator, a second branch waveguide, a second photonic crystal modulator and a common waveguide; the tuning method comprises: The main waveguide receives an optical signal transmitted by the gain chip and transmits the optical signal to the beam splitter; The beam splitter equally divides the optical signal into a first optical signal and a second optical signal, transmits the first optical signal to the first branch waveguide, and transmits the second optical signal to the second branch waveguide; The first photonic crystal modulator tunes the first optical signal transmitted by the first branch waveguide; The second photonic crystal modulator tunes the second optical signal transmitted by the second branch waveguide; The first photonic crystal modulator couples the tuned first optical signal to the common waveguide, the common waveguide transmits the tuned first optical signal into a resonant cavity of the second photonic crystal modulator, the second photonic crystal modulator tunes the tuned first optical signal again, and the second photonic crystal modulator couples the twice-tuned first optical signal to the second branch waveguide; The second photonic crystal modulator couples the tuned second optical signal to the common waveguide, the common waveguide transmits the tuned second optical signal into a resonant cavity of the first photonic crystal modulator, the first photonic crystal modulator tunes the tuned second optical signal again, and the first photonic crystal modulator couples the twice-tuned second optical signal to the first branch waveguide; The output port of the external cavity laser is the output port of the first branch waveguide and / or the output port of the second branch waveguide.

17. The tuning method of claim 16, wherein, The tunable mirror of the external cavity laser further comprises a first heating layer and a second heating layer; The tuning method further comprises: Adjusting the resonant peak of the first photonic crystal modulator through the first heating layer so that the resonant peak of the first photonic crystal modulator is consistent with the resonant peak of the second photonic crystal modulator; Adjusting the resonant peak of the second photonic crystal modulator through the second heating layer so that the resonant peak of the second photonic crystal modulator is consistent with the resonant peak of the first photonic crystal modulator.

18. The tuning method of claim 17, wherein, The tunable mirror of the external cavity laser further comprises a wavelength adjuster; The tuning method further comprises: Adjusting the wavelength of the optical signal through the wavelength adjuster before the main waveguide transmits the optical signal to the beam splitter, so that the wavelength of the optical signal is consistent with the working wavelength of the first photonic crystal modulator and the working wavelength of the second photonic crystal modulator.

19. The tuning method of claim 16, wherein, The tunable mirror of the external cavity laser further comprises a first phase shifter and a second phase shifter; The tuning method further comprises: adjusting, by the first phase shifter, a phase of the first optical signal before the first optical signal transmitted by the first branch waveguide is tuned by the first photonic crystal modulator, so that the phase of the first optical signal is consistent with the phase of the second optical signal; adjusting, by the second phase shifter, a phase of the second optical signal before the second optical signal transmitted by the second branch waveguide is tuned by the second photonic crystal modulator, so that the phase of the second optical signal is consistent with the phase of the first optical signal.

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