A hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide

Abstract

The present invention relates to the technical fields of external cavity lasers and lithium niobate photonic waveguides, specifically providing a hybrid integrated external cavity tunable laser based on a lithium niobate photonic waveguide. The laser comprises an end-coupled semiconductor optical amplifier and a photonic chip, wherein the waveguide layer of the photonic chip is made of lithium niobate. The photonic chip includes a phase modulator, a vernier microring filter, and an asymmetric MZI. The phase modulator adjusts the laser phase based on the electro-optic effect of the lithium niobate material; the vernier microring filter adjusts the laser wavelength based on the vernier effect of the vernier microring filter and the electro-optic effect of the lithium niobate material; and the asymmetric MZI suppresses side modes at different laser wavelengths based on the electro-optic effect of the lithium niobate material. A time-varying voltage signal is synchronously applied to the electrodes of the phase modulator, the vernier microring filter, and the asymmetric MZI to achieve wide-bandwidth linear frequency modulation of the laser. The present invention has a simple manufacturing process and a fast tuning response speed. Based on the electro-optic effect of the lithium niobate material, wide-bandwidth linear frequency modulation of the laser is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of external cavity lasers, and in particular relates to a hybrid integrated external cavity tunable laser based on lithium niobate photon waveguide. Background Art

[0002] With the rapid development of new energy vehicles and intelligent driving technologies, and people's increasing awareness of driving safety, new technologies for intelligent driving have emerged in recent years. Frequency-modulated continuous-wave lidar technology has become a highly promising intelligent driving ranging solution due to its advantages such as long measurement distance, high ranging accuracy, and strong anti-interference ability. It uses a laser to emit light with a frequency that changes linearly with time. The light reflected by the object beats the frequency of the laser emitted light. The beat signal is calculated by the detector and computer to obtain the object's distance and speed information.

[0003] The challenge of linear frequency modulation lidar technology lies in generating a laser signal with high linearity and a wide frequency modulation bandwidth. The linearity and frequency modulation bandwidth of the emitted light directly affect the measured distance and accuracy. For long-range ranging, linear frequency modulation lidar technology places high demands on the laser: first, the emitted light must have extremely high linearity; second, the laser modulation bandwidth must be at least in the GHz range; and third, the laser linewidth must be narrow (less than 100 kHz).

[0004] There are currently several laser solutions that can achieve linear frequency modulation:

[0005] For example, the solution of directly modulating the laser using current, but the linearity of the laser modulated by this solution is low, and the externally modulated laser is expensive, large in size, and difficult to process.

[0006] For example, the Chinese invention patent with publication number CN114024193A and publication date of February 8, 2022, and the invention name is "A high-speed linear frequency-modulated external cavity laser based on thin-film lithium niobate". It uses the laser generated by the optical amplifier to change the output wavelength of the external cavity laser through the thermally tuned microring in the lithium niobate narrow-band reflection filter chip. By adding a time-varying voltage to the electrodes of the lithium niobate phase shifter, the refractive index is changed through the electro-optical effect of lithium niobate to achieve the frequency shift of the laser longitudinal mode, and finally output a frequency-modulated continuous wave signal. The thermo-optical effect and electro-optical effect of silicon-based lithium niobate material realize the output of continuously tunable signals, and the overall size is small. However, this solution utilizes the thermo-optical effect of lithium niobate to heat the lithium niobate waveguide through a heater to change the refractive index of the waveguide, thereby achieving modulation. However, it takes time for the heat from the heater to diffuse to the waveguide, and the modulation speed is relatively slow, which will limit the frequency modulation speed of the generated signal and has certain limitations in the generation of fast frequency modulation signals. Applying a time-varying voltage signal to a lithium niobate phase shifter presents challenges such as short phase shifter length and limited frequency-modulated continuous wave (FMCW) signal bandwidth. Furthermore, the use of a single microring results in a low FSR and a limited wavelength tuning range. Furthermore, the use of a Bragg grating as a reflector results in a constant reflectivity, unadjustable output power, and low output power. Furthermore, the use of curved electrodes results in misalignment between the applied electric field and the crystal's extraordinary axis, which reduces the electro-optical response on the TFLN platform and degrades modulation performance.

[0007] Therefore, there is an urgent need to design a high-performance linear frequency modulated laser that can achieve long-distance ranging, with low cost, small size, narrow linewidth, high linearity, fast frequency modulation speed, and large modulation bandwidth. Summary of the Invention

[0008] In view of this, the present invention aims to provide a hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide, which solves the defects of traditional tunable lasers based on thermo-optical effect, such as complex manufacturing process, slow tuning response speed, small linear frequency modulation bandwidth and small wavelength tunable range. By synergistically applying time-varying voltage to the semiconductor optical amplifier (SOA), adjustable coupler, phase modulator, vernier microring filter and asymmetric MZI motor, large-scale linear frequency modulation is achieved, making it applicable to FMCW (frequency modulated continuous wave) long-distance ranging for OPA scanning mode.

[0009] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0010] The present invention provides a hybrid integrated external cavity tunable laser based on lithium niobate photon waveguide, comprising: a semiconductor optical amplifier, and a photonic chip whose waveguide layer is made of lithium niobate material;

[0011] The photonic chip includes:

[0012] A phase modulator comprising a phase modulator waveguide segment and a first electrode. By adjusting the voltage applied to the first electrode, the refractive index of the phase modulator waveguide segment is changed based on the electro-optical effect of the lithium niobate material to achieve laser phase modulation.

[0013] A vernier microring filter includes a first microring filter and a second microring filter of different circumferences, wherein the first microring filter is connected to a second electrode, and the second microring filter is connected to a third electrode. By adjusting the voltage applied to the second electrode and the third electrode, laser wavelength adjustment is achieved based on the vernier effect of the vernier microring filter and the electro-optical effect of the lithium niobate material;

[0014] An asymmetric MZI, which includes two unequal-arm waveguides with a length difference and is connected to a fourth electrode. By adjusting the voltage applied to the fourth electrode, the electro-optic effect of lithium niobate material is used to achieve side mode suppression at different laser wavelengths.

[0015] By synchronously applying a time-varying voltage signal to the first electrode, the second electrode, the third electrode and the fourth electrode, large-bandwidth linear frequency modulation of the laser is achieved.

[0016] Preferably, the semiconductor optical amplifier is a reflective semiconductor optical amplifier, which is used to provide a laser gain medium.

[0017] Preferably, the semiconductor optical amplifier is coupled to the end face of the photonic chip, the coupling end face of the semiconductor optical amplifier and the photonic chip is coated with an anti-reflection film, and the far end face of the semiconductor optical amplifier relative to the photonic chip is coated with an anti-reflection film.

[0018] Preferably, the material layer of the photonic chip includes:

[0019] a substrate layer, the material of which is silicon;

[0020] A waveguide layer provided above the substrate layer is a lithium niobate ridge waveguide, and a cladding layer of silicon dioxide material is provided on both the upper and lower surfaces of the waveguide layer;

[0021] The electrode layer is arranged above the cladding layer on the upper surface of the waveguide layer, and its material is gold.

[0022] Preferably, the phase modulator includes a first phase modulator provided in a front-end waveguide section of the vernier microring filter and a second phase modulator provided in a rear-end waveguide section of the vernier microring filter.

[0023] Preferably, the perimeters of the first microring filter and the second microring filter are both 2000-2500 um, and the difference between their perimeters is 1-10 um.

[0024] Preferably, the first microring filter and the second microring filter are both microring straight racetrack waveguides, the second electrode is arranged above the straight waveguide portion of the first microring filter; the third electrode is arranged above the straight waveguide portion of the second microring filter.

[0025] Preferably, the asymmetric MZI is arranged in the waveguide section between the first microring filter and the second microring filter. By adjusting the voltage applied to the fourth electrode, the refractive index of the waveguide changes based on the electro-optical effect of the lithium niobate material, thereby changing the phase difference between the two unequal arm waveguides, thereby achieving side mode suppression under different wavelength lasers.

[0026] Preferably, it further includes a spot mode converter provided in the waveguide section at the front end of the first phase modulator, the spot mode converter being used to match the gain waveguide light mode size in the semiconductor optical amplifier with the waveguide spot mode size of the photonic chip.

[0027] Preferably, the optical system further comprises a first adjustable coupler provided in the waveguide section between the mode spot converter and the first phase modulator, and a second adjustable coupler provided in the waveguide section at the rear end of the second phase modulator, wherein the first adjustable coupler is connected to a fifth electrode, and the second adjustable coupler is connected to a sixth electrode. By adjusting the voltage applied to the fifth electrode, the coupling coefficient of the first adjustable coupler is changed to control the reflection ratio of the light injected from the semiconductor optical amplifier and the optical power entering the subsequent waveguide;

[0028] The second adjustable coupler and the semiconductor optical amplifier form a Fabry-Perot resonant cavity. By adjusting the voltage applied to the sixth electrode, the coupling coefficient of the second adjustable coupler is changed to control the power of the output laser.

[0029] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0030] This invention provides a hybrid integrated external cavity tunable laser for FMCW lidar ranging using an OPA scanning method. This device utilizes a lithium niobate waveguide phase modulator, a vernier microring filter, and an asymmetric MZI. By synchronously applying a time-varying voltage, the refractive index of the lithium niobate waveguide is directly controlled, changing the laser wavelength and phase, thereby achieving wide-bandwidth linear frequency modulation of the laser. The modulation principle of this invention is based on the electro-optical effect of the lithium niobate material, avoiding the delay caused by the traditional thermo-optical effect. The rapid electro-optical effect of lithium niobate ensures high linearity of the frequency-modulated signal, improves the frequency-modulation response speed, and reduces ranging errors.

[0031] The present invention can dynamically align the longitudinal mode with the filter passband by synchronously adjusting the voltages of the vernier microring filter, asymmetric MZI, phase modulator, and semiconductor optical amplifier. The present invention adopts a combined design of a vernier microring filter and an asymmetric MZI to achieve wide wavelength tuning with a tuning range of >70nm, far exceeding the traditional single microring solution. The side mode suppression ratio is >5dB, which can ensure stable single-mode laser output. The vernier effect is used to expand the bandwidth of a single microring, achieving high-speed refractive index modulation and wide spectral coverage.

[0032] The present invention uses a reflective semiconductor optical amplifier and a lithium niobate photonic chip to form a hybrid integrated external cavity tunable laser in an end-face coupling manner. Compared with traditional tunable lasers, the present invention does not require a complex optical lens system and a mechanical rotation system, nor does it require complex processes such as multi-material bonding and transfer. The present invention only requires traditional photolithography and etching processes, and has the advantages of high process compatibility, low cost, superior device performance, facilitation of coupling packaging and mass production, and flexible design. Compared with traditional external cavity lasers with more discrete components, the external cavity tunable laser of the present invention has the characteristics of high integration, simple manufacturing process, low cost, superior device performance, facilitation of coupling packaging and mass production. Compared with other hybrid integrated external cavity lasers, this embodiment has the advantages of a large tuning range, high linearity, large modulation bandwidth, good scattering performance, and fewer process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 1 is a schematic structural diagram of a hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to an embodiment of the present invention;

[0035] Figure 2 1 is a top view of a hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide provided in accordance with an embodiment of the present invention;

[0036] Figure 3 is a cross-sectional view of a phase modulator provided according to an embodiment of the present invention.

[0037] Reference numerals include:

[0038] Semiconductor optical amplifier 1, anti-reflection film 101, anti-reflection film 102;

[0039] Photonic chip 2, electrode layer a, waveguide layer b, cladding layer c, substrate layer d;

[0040] Mode spot converter 3, first adjustable coupler 401, second adjustable coupler 402, first phase modulator 501, second phase modulator 502, first microring filter 6, asymmetric MZI 7, second microring filter 8, input waveguide 9, output waveguide 10;

[0041] A first electrode a01 , a second electrode a02 , a third electrode a03 , a fourth electrode a04 , a fifth electrode a05 , and a sixth electrode a06 . DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, or methods. In some cases, some operations related to the present invention are not shown or described in the specification. This is to avoid the core part of the present invention being overwhelmed by too much description. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0043] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various orders in the description and the drawings are only for the purpose of clearly describing a certain embodiment and are not intended to be a required order, unless otherwise specified that a certain order must be followed.

[0044] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0045] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0046] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0047] See also Figure 1 and Figure 2In one embodiment of the present invention, a hybrid integrated external cavity tunable laser based on a lithium niobate photonic waveguide is provided, which can be used as a linear frequency modulation integrated light source for an OPA scanning FMCW lidar. Specifically, the tunable laser includes: a semiconductor optical amplifier 1 and a photonic chip 2. The semiconductor optical amplifier 1 forms a laser Fabry-Perot cavity (FP cavity) with the photonic chip 2 through end-face butt coupling. Compared with the traditional multi-material bonding process, the end-face coupling fabrication process has a simpler process flow, higher process compatibility, and lower fabrication cost. In this embodiment of the present invention, the semiconductor optical amplifier 1 is a reflective semiconductor optical amplifier, which provides the gain medium for the laser in the laser. In addition, an anti-reflection film 101 is coated on the coupling end face of the semiconductor optical amplifier 1 and the photonic chip 2. The reflectivity of the anti-reflection film 101 is ≤0.01%. The anti-reflection film 101 can effectively reduce the interference of the end face reflection on the cavity mode; the far end face of the semiconductor optical amplifier 1 relative to the photonic chip 2 is coated with an anti-reflection film 102, that is, the anti-reflection film 102 is coated on the tail of the semiconductor optical amplifier 1. The reflectivity of the anti-reflection film 102 is 10%. The anti-reflection film 102 is used to improve the reflectivity of the laser and also serves as a resonance surface of the laser resonant cavity.

[0048] The photonic chip 2 is located on one side of the anti-reflection film 101. The photonic chip 2 is the core control component of the laser's external cavity and together with the semiconductor optical amplifier 1 constitutes a hybrid integrated external cavity laser. In terms of preparation materials and structure, the material layers of the photonic chip 2 are as follows from bottom to top:

[0049] The substrate layer d is made of silicon and is used to provide mechanical support.

[0050] Waveguide layer b, waveguide layer b is arranged above substrate layer d, waveguide layer b is a ridge waveguide of lithium niobate thin film, the etching depth of the ridge waveguide is 200-300nm, and waveguide layer b is used to realize laser transmission.

[0051] Cladding layers c are grown on the upper and lower surfaces of the waveguide layer b, respectively. The cladding layers c are made of silicon dioxide insulating material and are used to protect the waveguide structure and limit light field leakage.

[0052] The electrode layer a is arranged above the cladding layer c on the upper surface of the waveguide layer b. The electrode layer a mainly includes electrodes of various functional units on the photonic chip 2. The electrode material is gold, and the spacing between adjacent electrodes is 1-5 um (micrometers).

[0053] The photonic chip 2 features wavelength tuning, linear frequency modulation, power regulation, and side-mode suppression. It includes an input waveguide 9 fabricated along the waveguide layer and connected via the waveguides; a spot size converter 3; a tunable coupler; a phase modulator; a vernier microring filter; an asymmetric MZI 7; and an output waveguide 10. The spot size converter 3 is located at the very front end of the waveguide, closest to the semiconductor optical amplifier 1. It matches the gain waveguide template size in the semiconductor optical amplifier 1 with the waveguide spot size of the photonic chip 2, reducing coupling losses. The spot size converter 3 incorporates an inverted tapered waveguide coupler or trident waveguide coupler, optimizing mode overlap efficiency through a gradual transition region. After being processed by the spot size converter 3, light continues to transmit through the input waveguide 9.

[0054] The adjustable coupler includes a first adjustable coupler 401 and a second adjustable coupler 402, wherein the first adjustable coupler 401 is arranged in the rear end waveguide section of the mode spot converter 3. The first adjustable coupler 401 mainly includes its corresponding first adjustable coupler waveguide section and a fifth electrode a05 arranged above it and connected to the lithium niobate waveguide section. By adjusting the voltage applied to the fifth electrode a05, based on the electro-optical effect of the lithium niobate material, the coupling coefficient of the first adjustable coupler 401 can be changed, thereby controlling the reflection ratio of the light injected from the semiconductor optical amplifier 1 and the optical power entering the subsequent waveguide.

[0055] The phase modulator includes a first phase modulator 501 and a second phase modulator 502. The first phase modulator 501 is disposed in the waveguide segment between the first tunable coupler 401 and the vernier microring filter, while the second phase modulator 502 is disposed in the waveguide segment at the rear end of the vernier microring filter. The first and second phase modulators 501 and 502 have identical structures, each including its corresponding phase modulator waveguide segment and a first electrode a01 disposed above the first electrode a01 and connected to the lithium niobate waveguide segment. The same voltage is applied to the first electrodes a01 of the first and second phase modulators 501 and 502. By adjusting the voltage applied to the first electrodes a01 of the first and second phase modulators 501 and 502, an electro-optic effect occurs in the lithium niobate waveguide, thereby changing the refractive index of the lithium niobate waveguide. This changes the optical cavity length of the laser and the longitudinal mode spacing, thereby achieving phase modulation of the light. By applying voltage to the first electrodes a01 of the first and second phase modulators 501 and 502, the phase change of the light can be precisely controlled, thereby achieving frequency modulation of the light. Among them, the optical cavity length of the laser refers to the optical path length traveled by the laser in the resonant cavity in one round trip, which is related to the geometric length and refractive index of the waveguide. When the first electrode a01 applies voltage, the electric field acts on the lithium niobate waveguide, triggering its electro-optical effect, causing the refractive index of the lithium niobate waveguide to change. The change in refractive index causes the optical cavity length to change accordingly. The change in optical cavity length affects the phase accumulation in the laser cavity, thereby realizing phase modulation of the light.

[0056] The vernier microring filter includes a first microring filter 6 and a second microring filter 8. The waveguide segment between the first and second microring filters 6 and 8 is equipped with an asymmetric MZI 7, i.e., an asymmetric Mach-Zehnder interferometer. The first microring filter 6, the asymmetric MZI 7, and the second microring filter 8 are sequentially connected to the rear-end waveguide segment of the first phase modulator 501. The first and second microring filters 6 and 8 are both straight microring racetrack waveguides. The free spectral ranges (FSRs) of the first and second microring filters 6 and 8 differ slightly, and the FSR of the vernier microring filter is greater than the bandwidth of the amplified spontaneous emission spectrum of the semiconductor optical amplifier 1. A second electrode a02 is located above the straight waveguide portion of the first microring filter 6 and connected to the microring waveguide segment. A third electrode a03 is located above the straight waveguide portion of the second microring filter 8 and connected to the microring waveguide segment. This design effectively avoids curved electrodes and reduces manufacturing complexity. The circumference of the first microring filter 6 and the second microring filter 8 ranges from 2000 to 2500 μm, but the circumferences of the two are different, with a circumference difference of 1 to 10 μm. Compared to a single microring design, the vernier effect generated by the circumference difference between the first microring filter 6 and the second microring filter 8 can effectively expand the tuning range. By applying an adjustable voltage to the second electrode a02 and the third electrode a03, an electro-optical effect is generated in the lithium niobate waveguide, causing the resonant peak of the vernier microring filter to redshift. When the transmission peaks of its resonant cavity completely overlap, that is, when the transmittance reaches its maximum value, the set wavelength is lased. By adjusting the voltage applied to the second electrode a02 and / or the third electrode a03, the position of the overlapping transmission peaks can be electrically and precisely adjusted, thereby tuning the lasing wavelength. When laser light enters the first microring filter 6 and the second microring filter 8, light of a specific wavelength resonates within the microrings, forming a specific resonance peak in the transmission or reflection spectrum. By varying the applied voltage, the position of the resonance peak can be adjusted based on the electro-optic effect and, in turn, the refractive index of the microrings, thereby tuning the laser output wavelength. Because the first microring filter 6 and the second microring filter 8 have different circumferences, they can cover different wavelength ranges based on the vernier effect, thereby achieving wide-range wavelength tuning. Testing has shown that the laser designed in this invention achieves a wide wavelength tuning range exceeding 70 nm, meeting the wide tuning range requirements of FMCW lidar.

[0057] In addition, since the vernier microring filter obtained by cascading lithium niobate microrings may exhibit dual-wavelength or multi-wavelength lasing during the microring lasing process, resulting in a small tuning range, a large mode gain difference is required to obtain a sufficiently high side mode suppression ratio. The mode transmission difference between the dominant laser mode and the closest side mode will significantly affect the side mode suppression ratio and the stability of the laser. When the gain difference is too small, the wavelength of the laser will become unstable, and in some cases, multi-mode oscillation may occur. To solve this problem, in addition to adjusting the coupling coefficient, coupling length, and coupling spacing of the resonant cavity, the embodiment of the present invention also adds an asymmetric MZI7, utilizes the asymmetric MZI7 to work in conjunction with the vernier microring filter, and achieves alignment of the transmission peak of the asymmetric MZI7 with the longitudinal mode of the laser by precisely controlling the resonance peak position of the microring. Specifically, the asymmetric MZI7 is composed of two branch waveguides, and a fourth electrode a04 is connected above the two branch waveguides and to the waveguide segment. The two branch waveguides have a length difference, typically 1000-2000 μm, forming two unequal-arm waveguides. When an optical signal enters the asymmetric MZI7, it splits into two light paths, each propagating along an unequal-arm waveguide of different lengths. Due to the different arm lengths, the light travels through these two paths for different lengths, resulting in a phase difference between the two light paths. The two beams of light will overlap at the output of the asymmetric MZI7. Due to the phase difference between the two light paths, interference will occur at the output, allowing light of specific wavelengths to pass while destructively interfering with light of other wavelengths. Due to the periodic transmission spectrum of the MZI7, only the main mode that meets the specific phase conditions can pass through. The side modes, whose wavelengths correspond to the transmission valley of the MZI7, interfere destructively and are suppressed. When targeting lasers of different wavelengths, a voltage is applied to the fourth electrode a04 of MZI7, and the electro-optical effect of lithium niobate is used to change the effective refractive index of the waveguide. The change in refractive index will change the phase difference between the two unequal-arm waveguides, thereby dynamically adjusting the transmission spectrum of MZI7. This enables the laser to increase the mode gain difference (gain difference > 5dB) at different wavelengths, improve the side mode suppression ratio, adapt to the needs of wavelength tuning, and achieve single-mode output with high SMSR.

[0058] A second tunable coupler 402 is provided on the rear-end waveguide segment of the second microring filter 8. The structure and operating principle of the second tunable coupler 402 are similar to those of the first tunable coupler 401. However, the second tunable coupler 402 also serves as a cavity facet of the laser resonant cavity. The second tunable coupler 402 and the anti-reflection film 102 of the semiconductor optical amplifier 1 form a laser Fabry-Perot resonant cavity (FP cavity). Specifically, the second tunable coupler 402 primarily comprises its corresponding second tunable coupler waveguide segment and a sixth electrode a06 disposed above the sixth electrode a06 and connected to the lithium niobate waveguide segment. By adjusting the voltage applied to the sixth electrode a06, the coupling coefficient of the second tunable coupler 402 can be varied based on the electro-optical effect of the lithium niobate material, thereby changing the reflectivity of the second tunable coupler 402 and controlling the optical power of the resonant cavity output light, thereby achieving stable laser output. In the present invention, the second tunable coupler 402 is used to replace a traditional Bragg grating. By varying the voltage applied to the sixth electrode a06, the output power can be adjusted. After being output from the second tunable coupler 402 , the laser light is output along the output waveguide 10 .

[0059] During laser operation, voltage is applied and regulated to the second and third electrodes a02 and a03 of the vernier microring filter. Leveraging the linear electro-optical effect of lithium niobate, the voltage directly alters the waveguide refractive index, thereby varying the laser's effective cavity length and achieving wavelength tunability. The output laser power is then set by appropriately adjusting the voltage at the sixth electrode a06 of the second tunable coupler 402, depending on the desired output laser power. Simultaneously, a triangular waveform-shaped, time-varying voltage signal is applied to the fourth electrode a04 of the semiconductor optical amplifier 1 and the asymmetric MZI 7, achieving wide-bandwidth, high-linear frequency modulation of the output laser.

[0060] As an optional embodiment, the second adjustable coupler 402 may also be replaced by an electrically tunable loop mirror.

[0061] As an optional embodiment, the asymmetric MZI 7 may be replaced by a microring having a size that differs from the circumference of the microrings of the first microring filter 6 and the second microring filter 8 by 50-200 μm.

[0062] As an optional embodiment, the semiconductor optical amplifier 1 and the photonic chip 2 may be connected by photonic lead integration to reduce coupling loss, improve production efficiency, and increase laser output power.

[0063] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this specification shall be included in the scope of protection of this specification.

[0064] The systems, devices, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0065] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0066] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0067] The foregoing description of this specification describes specific embodiments. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different from that described in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order shown or the sequential order to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide, characterized in that: include: Semiconductor optical amplifiers and photonic chips with waveguide layers made of lithium niobate; The photonic chip includes: A phase modulator includes a phase modulator waveguide segment and a first electrode. By adjusting the voltage applied to the first electrode, the refractive index of the phase modulator waveguide segment is changed based on the electro-optical effect of the lithium niobate material to achieve laser phase adjustment. The phase modulator includes a first phase modulator provided in the front-end waveguide segment of the vernier microring filter and a second phase modulator provided in the rear-end waveguide segment of the vernier microring filter. A vernier microring filter comprising a first microring filter and a second microring filter of different circumferences, wherein the first microring filter is connected to a second electrode, and the second microring filter is connected to a third electrode. By adjusting the voltage applied to the second electrode and the third electrode, laser wavelength adjustment is achieved based on the vernier effect of the vernier microring filter and the electro-optical effect of the lithium niobate material; An asymmetric MZI, comprising two unequal-arm waveguides with a length difference, connected to a fourth electrode, achieves side-mode suppression at different laser wavelengths based on the electro-optical effect of lithium niobate by adjusting the voltage applied to the fourth electrode. By synchronously applying a time-varying voltage signal to the first electrode, the second electrode, the third electrode and the fourth electrode, large-bandwidth linear frequency modulation of the laser is achieved.

2. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The semiconductor optical amplifier is a reflective semiconductor optical amplifier, which is used to provide a laser gain medium.

3. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The semiconductor optical amplifier is coupled to the end face of the photonic chip. The coupling end face of the semiconductor optical amplifier and the photonic chip is coated with an anti-reflection film. The far end face of the semiconductor optical amplifier relative to the photonic chip is coated with an anti-reflection film.

4. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The material layer of the photonic chip includes: a substrate layer, the material of which is silicon; A waveguide layer provided above the substrate layer is a lithium niobate ridge waveguide, and a cladding layer of silicon dioxide material is provided on both the upper and lower surfaces of the waveguide layer; The electrode layer is arranged above the upper surface cladding layer of the waveguide layer, and its material is gold.

5. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The perimeters of the first microring filter and the second microring filter are both 2000-2500 um, and the difference between the perimeters thereof is 1-10 um.

6. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The first microring filter and the second microring filter are both microring straight racetrack waveguides. The second electrode is arranged above the straight waveguide portion of the first microring filter; the third electrode is arranged above the straight waveguide portion of the second microring filter.

7. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: The asymmetric MZI is arranged in the waveguide section between the first microring filter and the second microring filter. By adjusting the voltage applied to the fourth electrode, the refractive index of the waveguide changes based on the electro-optical effect of the lithium niobate material, thereby changing the phase difference between the two unequal-arm waveguides, thereby achieving side mode suppression under different wavelength lasers.

8. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 1, characterized in that: It also includes a spot mode converter provided in the front end waveguide section of the first phase modulator, and the spot mode converter is used to match the gain waveguide light mode size in the semiconductor optical amplifier with the waveguide spot mode size of the photonic chip.

9. The hybrid integrated external cavity tunable laser based on lithium niobate photonic waveguide according to claim 8, characterized in that: The optical fiber further comprises a first adjustable coupler provided in the waveguide section between the pattern spot converter and the first phase modulator, and a second adjustable coupler provided in the waveguide section at the rear end of the second phase modulator, wherein the first adjustable coupler is connected to a fifth electrode, and the second adjustable coupler is connected to a sixth electrode. By adjusting the voltage applied to the fifth electrode, the coupling coefficient of the first adjustable coupler is changed to control the reflection ratio of the light injected from the semiconductor optical amplifier and the optical power entering the subsequent waveguide; The second adjustable coupler and the semiconductor optical amplifier form a Fabry-Perot resonant cavity. By adjusting the voltage applied to the sixth electrode, the coupling coefficient of the second adjustable coupler is changed to control the power of the output laser.

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