Heterogeneous integrated tunable laser

Abstract

The invention relates to the technical field of tunable lasers, in particular to a heterogeneous integrated tunable laser, which comprises a silicon nitride photon chip and a lithium tantalate film bonded on the upper surface of the silicon nitride photon chip, and is characterized in that the lithium tantalate film and a silicon nitride waveguide layer are heterogeneously integrated to form a hybrid waveguide; the silicon nitride photon chip is sequentially provided with an annular reflector, a gain chip, a vernier micro-ring filter, a phase modulator and an adjustable annular mirror along a waveguide layer, the annular reflector and the adjustable annular mirror form a resonant cavity, and the refractive index of the mixed waveguide is changed by adjusting voltage applied to an electrode of the vernier micro-ring filter, so that the refractive index of the mixed waveguide is changed. The rapid switching of the output laser wavelength is realized; the refractive index of the mixed waveguide is changed by adjusting the voltage applied to the electrode of the phase modulator, and linear frequency modulation signal output is achieved. The tunable laser overcomes the defects that a traditional tunable laser is low in tuning speed, small in linear frequency modulation bandwidth, small in wavelength adjustable range and the like, and is simple in manufacturing process and low in economic cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunable lasers, and particularly relates to a heterogeneous integrated tunable laser. Background Art

[0002] With the demands of artificial intelligence and big data for information transmission speed and transmission capacity, silicon photonics technology has developed rapidly. Utilizing the characteristics of fast light transmission speed and no additional heat generation, optical chips have received extensive attention. Silicon waveguide optical chips can be produced using the mature silicon CMOS process already in electronic chip manufacturing, with the advantages of low cost, large production volume, and being convenient for optoelectronic integration and co-packaging with electronic chips, and excellent performance. It provides development impetus for optical communication, optical interconnection, and optical sensing.

[0003] However, due to the two-photon absorption characteristic of the silicon waveguide material itself, the transmission loss of the silicon waveguide chip is large, and silicon is a centrosymmetric crystal without linear electro-optic effect, and can only perform optical modulation through the free carrier dispersion effect of silicon, with slow modulation speed and easy distortion under high-speed signals.

[0004] Due to the excessive transmission loss of silicon materials, researchers have proposed using silicon nitride as the transmission waveguide material for optical chips. Compared with silicon materials, silicon nitride materials have low-loss transmission characteristics. However, since silicon nitride is an insulator without linear Pockels electro-optic effect and only has a weak Kerr electro-optic effect. Therefore, the thermo-optic effect is mostly used for modulation during optical modulation, with slow thermo-tuning speed and unable to meet high-speed modulation requirements.

[0005] In recent years, the research on lithium niobate waveguide materials has been in full swing. Thin-film lithium niobate materials are known as the silicon of photonic chips. They have lower transmission loss than silicon waveguides, large electro-optic coefficients, and linear Pockels effects. Since the refractive index of lithium tantalate materials can be directly changed by voltage, lithium niobate modulation can meet high-speed requirements. Currently, high-speed optical modulators are mainly prepared based on lithium niobate materials. However, lithium niobate materials are difficult to etch. Currently, lithium niobate waveguides can only be ridge waveguides, and the etching angle cannot reach 90°. Therefore, due to rough sidewall etching, the lateral scattering loss of lithium niobate is large, unable to achieve the low-loss performance of silicon nitride materials, and it is difficult to prepare with high cost.

[0006] The article titled "Lithium tantalate photonic integrated circuits for volumemanufacturing" published in the journal Nature by Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, Xinru Ji, Junyin Zhang, Terence Blesin, Alisa Davydova, Yang Chen, Kai Huang, Xi Wang, Xin Ou & Tobias J. Kippenberg has demonstrated the feasibility of fabricating high-performance lithium tantalate photonic chips. Like lithium niobate, lithium tantalate is a non-centrosymmetric crystal with a strong linear electro-optic (Pockels) effect. Under the action of an external electric field, its refractive index changes, enabling effective modulation of converting electrical signals into optical signals. The electro-optic properties of lithium tantalate are an important basis for its applications in fields such as optical communication, optical computing, and lidar. The fabrication process of silicon-based lithium tantalate wafers is closer to that of silicon-on-insulator. Therefore, lithium tantalate thin films can be manufactured at low cost and on a large scale, making them valuable for applications. Moreover, lithium tantalate thin films have excellent electro-optic conversion characteristics, temperature characteristics, good thermal conductivity, compatibility with silicon, and lower optical losses than wafer-level lithium niobate. They are new materials urgently needed for the development of new devices in the post-Moore era.

[0007] As a new type of laser solution, heterogeneous integrated high-speed frequency-modulated lasers have important application potential in intelligent driving and lidar technologies. For the requirements of frequency-modulated lidar applications for light sources, the light source is required to have high linearity, high speed, narrow linewidth, and high power. Combining the low-loss advantage of silicon nitride materials and the high-speed linear electro-optic modulation advantage of lithium tantalate materials, and taking advantage of the large production volume of heterogeneous integration process technology, compared with the disadvantages of high requirements for end-face butt coupling and packaging in hybrid integration, it has the advantages of low coupling requirements and small losses. In summary, using heterogeneous integration technology to combine the advantages of low transmission loss of silicon nitride and high-speed linear modulation of lithium tantalate can meet the requirements of OPA-FMCW lidar for integrated frequency-modulated lasers with mass production capacity, small volume, narrow linewidth, high linearity, fast frequency modulation speed, and high power.

[0008] Existing solutions have proposed bonding lithium niobate thin films above silicon waveguide double micro - rings and ring - mirror micro - cavities. A filtering structure is formed through the Vernier effect of two micro - ring filters to obtain a laser with a wide tuning range and a narrow linewidth. Utilizing the advantages of the bonded lithium niobate thin film, such as low loss, strong linear electro - optic effect, and fast modulation speed, the linewidth of the laser can be further compressed, the output laser power can be increased, and high - speed linear frequency modulation can be achieved. However, the following problems still exist in this solution: First, the butt - joint coupling between the gain chip and the heterogeneous integrated silicon nitride - lithium niobate chip has a large technical difficulty, complex manufacturing process, and poor mass - production ability.

[0009] Second, lithium niobate thin - film wafers are currently less used and have a high cost.

[0010] Third, when using a silicon waveguide, due to the two - photon absorption effect of silicon, under the demand of high - power applications, it will affect the power output, with a low tuning speed, a small linear frequency - modulation bandwidth, and a small wavelength - tunable range.

[0011] Fourth, in the case of large - range tuning of the double - micro - ring structure, the mode gain is low, and the side - mode suppression ratio of the output laser is low. Summary of the Invention

[0012] In view of this, the present invention aims to provide a heterogeneous integrated high - power and high - speed tunable laser, which overcomes the defects of the existing technology, such as complex manufacturing process, low tuning speed, small linear frequency - modulation bandwidth, and small wavelength - tunable range, and has the advantages of a wide wavelength - tuning range, high linearity, large modulation bandwidth, narrow linewidth, and high power.

[0013] To achieve the above - mentioned purpose, the technical solution of the present invention is realized as follows: The present invention provides a heterogeneous integrated tunable laser, including: A silicon nitride photonic chip, which includes, connected in sequence along the laser output path: a gain unit, a Vernier micro - ring filter, a phase modulator, and an adjustable ring mirror; And a lithium tantalate thin film covering the upper surface of the silicon nitride photonic chip. The lithium tantalate thin film and the silicon nitride waveguide layer of the silicon nitride photonic chip form a hybrid waveguide through heterogeneous integration; Among them, the phase modulator, the Vernier micro - ring filter, and the adjustable ring mirror are arranged in the hybrid waveguide region. A first electrode of the Vernier micro - ring filter and a second electrode of the phase modulator are provided on the upper surface of the lithium tantalate thin film; By adjusting the voltage applied to the first electrode, based on the electro - optic effect of the lithium tantalate thin film, the wavelength adjustment of the output laser is realized; By adjusting the voltage applied to the second electrode, based on the electro - optic effect of the lithium tantalate thin film, the linear frequency modulation of the output laser is realized.

[0014] Preferably, a third electrode of the tunable ring mirror is further provided on the upper surface of the lithium tantalate thin film. By adjusting the voltage applied to the third electrode, based on the electro-optic effect of the lithium tantalate thin film, the reflection and transmission ratios of the tunable ring mirror to the laser are changed, and the laser output power is adjusted.

[0015] Preferably, the gain unit includes a ring mirror and a gain chip. The ring mirror and the tunable ring mirror form a Fabry-Perot resonator, and the gain chip is used to provide laser gain.

[0016] Preferably, the gain chip is a III-V gain chip, and the III-V gain chip is bonded to the silicon nitride waveguide layer of the silicon nitride photonic chip.

[0017] Preferably, the gain unit includes two gain chips. The two gain chips are designed in parallel, and the same voltage is applied to the two gain chips at the same time to improve the laser gain.

[0018] Preferably, a mode spot converter and a Y-shaped input waveguide are sequentially arranged between the gain unit and the Vernier micro-ring filter. The mode spot converter is used to match the optical mode size of the gain waveguide in the gain unit with the waveguide mode spot size of the Y-shaped input waveguide.

[0019] Preferably, the Vernier micro-ring filter includes three cascaded micro-rings with different circumferences. The first micro-ring and the second micro-ring realize the laser wavelength adjustment based on the Vernier effect, and the third micro-ring is used to narrow the linewidth and improve the side mode suppression ratio.

[0020] Preferably, the third micro-ring is an asymmetric AMZ.

[0021] Preferably, the circumferences of the first micro-ring and the second micro-ring both range from 600 to 800 microns, and the circumference difference between the first micro-ring and the second micro-ring is 5 to 15 microns.

[0022] Preferably, by applying a square wave voltage to the first electrode of the Vernier micro-ring filter, the wavelength switching of the output laser is realized; by applying a triangular wave voltage to the second electrode of the phase modulator, the linear frequency modulation of the output laser is realized.

[0023] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention bonds a III-V gain chip and a lithium tantalate thin film on a partial area of a silicon nitride photonic chip to form a heterogeneous integrated external cavity tunable laser, which has advantages such as a wide wavelength tuning range, high linearity frequency modulation, large modulation bandwidth, narrow linewidth, and high power. Moreover, a hybrid waveguide is formed by heterogeneous integration of the lithium tantalate thin film and the silicon nitride waveguide layer. By applying a square wave voltage and a triangular wave voltage to the electrodes of the Vernier micro-ring filter and the phase modulator, and utilizing the excellent linear electro-optic effect of lithium tantalate, the refractive index of the hybrid waveguide of lithium tantalate and silicon nitride is regulated by voltage. By adjusting the voltage applied to the electrodes of the Vernier micro-ring filter, the refractive index of the hybrid waveguide is changed, realizing rapid switching of the output laser wavelength; by adjusting the voltage applied to the electrodes of the phase modulator, the refractive index of the hybrid waveguide is changed, thereby changing the optical cavity length and the longitudinal mode position, realizing the output of a linear frequency modulation signal. In addition, lithium tantalate has stable chemical properties and a high Curie point, and it can maintain its performance within a large temperature range, effectively improving the reliability and lifespan of the device. Moreover, the dielectric loss of lithium tantalate is relatively low, which can effectively reduce the energy loss during the transmission of the device. Compared with lithium niobate wafers, lithium tantalate materials have been widely applied in the radio frequency field and have the advantage of low wafer cost. The heterogeneous integration of lithium tantalate and silicon nitride can endow the chip with characteristics such as superior performance, diverse functions, small coupling loss, and being conducive to packaging and mass production.

[0024] The laser of the present invention is driven by voltage, which not only realizes a wide wavelength tuning range and high linearity frequency modulation, but also controls the reflection and transmission ratios of the laser by the voltage-controlled tunable ring mirror, thereby realizing the control of the laser power output and increasing the output power range. In addition, by bonding a III-V gain chip on silicon nitride, the chip integration degree is improved, and a dual-gain chip parallel connection design is adopted and coupled through a Y-branch. After applying the same voltage to the two gain chips, the laser gain can be effectively increased, thereby realizing high-power output.

[0025] The present invention heterogeneously integrates a III-V gain chip and a lithium tantalate thin film on a silicon nitride photonic chip through a bonding process. Compared with the existing end-face coupling process, it effectively reduces complex manufacturing steps, significantly improves production efficiency, increases the structural integration degree, and this structure does not rely on a complex optical lens system and a mechanical rotation system, reducing the difficulty and requirements of coupling and packaging, and being conducive to the packaging and mass production of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic structural diagram of a heterogeneous integrated tunable laser provided according to an embodiment of the present invention; Figure 2 is a top view of a heterogeneous integrated tunable laser according to an embodiment of the present invention; Figure 3 is a cross-sectional view of a hybrid waveguide according to an embodiment of the present invention.

[0027] The reference numerals therein include: ring mirror 1, gain chip 2, mode spot converter 3, Y-shaped input waveguide 4, lithium tantalate thin film 5, vernier micro-ring filter 6, first micro-ring 601, second micro-ring 602, third micro-ring 603, phase modulator 7, tunable ring mirror 8, output waveguide 9; electrode a, first electrode a01, second electrode a02, third electrode a03, silicon nitride waveguide layer b, silicon dioxide cladding c, silicon substrate d. Detailed implementation manners

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Similar elements in different embodiments are denoted by related similar element numbers. In the following embodiments, many details are described to enable a better understanding of the present invention. 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, in order to avoid the core part of the present invention being overwhelmed by excessive description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0029] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment, and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0030] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is 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 should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0031] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0032] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0033] Please refer to Figure 1 and Figure 2 , in an embodiment of the present invention, a heterogeneous integrated tunable laser is provided. Through the heterogeneous integration of silicon nitride and lithium tantalate thin film 5, high-power and high-speed tunable laser output is achieved. Specifically, the heterogeneous integrated tunable laser includes a silicon nitride photonic chip and a lithium tantalate thin film 5. The waveguide layer for beam transmission in the silicon nitride photonic chip is a silicon nitride waveguide, and the thickness of the lithium tantalate thin film 5 is 0.2 - 0.5 microns. The lithium tantalate thin film 5 covers the silicon nitride waveguide layer of the silicon nitride photonic chip through a bonding or transfer process, and a hybrid waveguide is formed through heterogeneous integration. As Figure 3 shown, the hybrid waveguide sequentially includes the following material layers from bottom to top: A substrate layer, the material of the substrate layer is silicon, that is, a silicon substrate d, and the silicon substrate d is used to provide mechanical support.

[0034] A silica cladding layer c, which is arranged above the silicon substrate d. The silica cladding layer c is an insulating material and is used to protect the waveguide structure and limit the leakage of the optical field.

[0035] A silicon nitride waveguide layer b is disposed above the silica cladding layer c and mainly serves as a transmission channel for optical signals. The silicon nitride material has a high refractive index and can effectively confine the optical signals to transmit inside it.

[0036] A lithium tantalate thin film 5 is disposed above the silicon nitride waveguide layer b and jointly forms a hybrid waveguide with the silicon nitride waveguide layer b. The lithium tantalate material has a high linear electro-optic effect. The lithium tantalate thin film 5 is bonded to the silicon nitride waveguide layer to form a hetero-integrated structure. In this structure, optical signals are transmitted in the silicon nitride waveguide and are modulated by the lithium tantalate thin film 5 at the same time. When a voltage is applied to the lithium tantalate thin film 5, its refractive index changes, thereby changing the phase modulation and wavelength tuning of the optical signals. The electro-optic effect of the lithium tantalate thin film 5 enables the hybrid waveguide to respond quickly to electrical signals and achieve high-speed modulation of optical signals, meeting the requirements for optical signal modulation in applications such as lidar.

[0037] An electrode layer a is disposed on the upper surface of the lithium tantalate thin film 5. The electrode layer a mainly includes electrodes of each functional unit. The electrode material is gold, and the distance between adjacent electrodes is 1 - 5 micrometers.

[0038] The silicon nitride photonic chip includes, in sequence along the laser emission path: a gain unit, a mode spot converter 3, an input waveguide, a Vernier micro-ring filter 6, a phase modulator 7, a tunable ring mirror 8, and an output waveguide 9, that is, the above units are all disposed on the silicon nitride waveguide layer of the silicon nitride photonic chip. Among them, the gain unit is used to provide a gain medium for the laser, and specifically includes a ring mirror 1 and a gain chip 2. The ring mirror 1 is disposed at the front end of the silicon nitride waveguide and serves as an end face of the resonant cavity of the tunable laser. A Fabry - Perot resonant cavity is formed by the ring mirror 1 and the tunable ring mirror 8 at the rear end. The ring mirror 1 can be a mirror with adjustable reflectivity, or a mirror with fixed reflectivity, or an embedded electrically tunable directional coupler.

[0039] The gain chip 2 uses a group III - V gain chip, and the group III - V gain chip is hetero-integrated on the silicon nitride waveguide layer of the silicon nitride photonic chip through a bonding process or a micro-transfer printing process. The role of the group III - V gain chip is to provide gain for the laser, so that the optical signals are effectively amplified. A mode spot converter 3 is disposed on the silicon nitride waveguide section at the rear end of the gain chip 2, and the mode spot converter 3 is used to adjust the optical mode size of the gain waveguide of the gain chip 2.

[0040] As an alternative embodiment, in order to increase the maximum output power of the laser, the present invention embodiment may also be provided with multiple parallel gain chips 2. Taking the two-path gain design as an example, the gain unit is provided with two ring mirrors 1 and two gain chips 2. On each gain optical path, a ring mirror 1 and a gain chip 2 are connected, and the two gain chips 2 are bonded in parallel to form a parallel design. Mode spot converters 3 are respectively arranged at the rear ends of the two gain chips 2, and the two-path gain is coupled through a Y-shaped input waveguide 4 at the rear ends of the two mode spot converters 3. At this time, the same voltage is applied to the two gain chips 2 simultaneously to increase the laser gain. When setting multiple parallel gain chips 2, its principle and structure are the same as or similar to the above two-path gain. With the above parallel design, without increasing the equivalent length of the gain chip 2, the output power of the laser is increased, and the line width of the laser output by the laser is reduced.

[0041] The vernier micro-ring filter 6, the phase modulator 7, the tunable ring mirror 8 and the output waveguide 9 are all arranged in the hybrid waveguide region, that is, a lithium tantalate thin film 5 covers the upper surface regions of the vernier micro-ring filter 6, the phase modulator 7, the tunable ring mirror 8 and the output waveguide 9 on the silicon nitride photonic chip. After the laser enters the hybrid waveguide through the Y-shaped input waveguide 4, the optical mode exists in both the silicon nitride and lithium tantalate materials at the same time, and the laser is transmitted through the hybrid waveguide of the silicon nitride and lithium tantalate. The vernier micro-ring filter 6 adopts a three-stage cascaded vernier micro-ring design, which includes a first micro-ring 601, a second micro-ring 602 and a third micro-ring 603. Among them, the circumferences of the first micro-ring 601 and the second micro-ring 602 are relatively close. The circumferences of the first micro-ring 601 and the second micro-ring 602 are both in the range of 600-800 microns, and the circumference difference between the two is 5-15 microns. The first micro-ring 601 and the second micro-ring 602 are coupled to each other through a waveguide. A wide wavelength tuning range is achieved through the vernier effect of the circumference difference between the two. The circumference of the third micro-ring 603 is quite different from that of the first micro-ring 601 and the second micro-ring 602, and the value range of its circumference size is 1000-1500 microns.

[0042] On the upper surfaces of the lithium tantalate thin films 5 above the first micro-ring 601, the second micro-ring 602, and the third micro-ring 603, a first electrode a01 is provided. The first electrode a01 is a gold electrode. By applying and adjusting a voltage to the first electrodes a01 corresponding to the first micro-ring 601 and the second micro-ring 602, the electro-optic effect occurs in the lithium tantalate material in the corresponding hybrid waveguides of the first micro-ring 601 and the second micro-ring 602. The refractive index of the lithium tantalate thin film changes, and then the refractive index of the hybrid waveguide changes. Due to the perimeter difference between the first micro-ring 601 and the second micro-ring 602, a Vernier effect will be generated between the two. Based on the Vernier effect, the tuning range can be effectively expanded. By applying an adjustable voltage to the first electrodes a01 corresponding to the first micro-ring 601 and the second micro-ring 602, the electro-optic effect of the lithium tantalate waveguide is promoted, the resonance peak of the laser redshifts, and at the position where the transmission peaks of its resonant cavity completely overlap, that is, when the transmittance reaches the maximum value, the laser emits at the set wavelength. By adjusting the applied voltage, the position of the overlapping transmission peak can be accurately adjusted electrically, and then the lasing wavelength can be tuned to realize the switching of the output laser wavelength of the laser.

[0043] In addition, since dual-wavelength or multi-wavelength lasing may occur during the micro-ring lasing process of the first micro-ring 601 and the second micro-ring 602, resulting in a small tuning range, in order to obtain a sufficiently high side-mode suppression ratio, a large mode gain difference needs to be obtained. 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 be unstable and may cause multi-mode oscillation in some cases. To solve this problem, in the embodiment of the present invention, a third micro-ring 603 is added at the rear ends of the first micro-ring 601 and the second micro-ring 602 to further extend the cavity length, narrow the linewidth, and at the same time increase the mode gain and improve the side-mode suppression ratio. The third micro-ring 603 works in cooperation with the first micro-ring 601 and the second micro-ring 602. By precisely controlling the resonance peak position of the micro-ring, the transmission peak is aligned with the longitudinal mode of the laser. In actual control, by simultaneously applying a square-wave voltage to the three groups of first electrodes a01 corresponding to the Vernier micro-ring filter 6, that is, the three groups of first electrodes a01 corresponding to the first micro-ring 601, the second micro-ring 602, and the third micro-ring 603, the wavelength switching of the output laser is realized, and the side-mode suppression ratio is improved at the same time.

[0044] As an optional embodiment, the third micro-ring 603 can adopt an asymmetric AMZ (Asymmetric Mach-Zehnder Interferometer) interferometer. Through the asymmetric AMZ, the laser can increase the mode gain difference at different wavelengths, improve the side-mode suppression ratio, meet the requirements of wavelength tuning, and realize single-mode output with high SMSR.

[0045] The rear-end hybrid waveguide of the vernier micro-ring filter 6 is provided with a phase modulator 7. On the upper surface of the lithium tantalate thin film 5 above the phase modulator 7, a second electrode a02 is provided, and the second electrode a02 is also a gold electrode. The hybrid waveguide corresponding to the phase modulator 7 is used to guide the transmission of optical signals and is composed of silicon nitride and lithium tantalate. When a voltage is applied to the second electrode a02 corresponding to the phase modulator 7, due to the excellent linear electro-optic effect of lithium tantalate, the change in voltage will cause the effective refractive index of the hybrid waveguide to change. The change in refractive index causes the propagation constant of the optical signal in the hybrid waveguide to change and the optical cavity length to change, thereby realizing the modulation of the phase of the optical signal. In actual control, by applying a triangular waveform voltage to the second electrode a02 corresponding to the phase modulator 7, high linearity laser output is achieved.

[0046] An adjustable ring mirror 8 is provided on the rear-end waveguide of the phase modulator 7. The adjustable ring mirror 8 is the other end face of the laser resonator cavity and forms a Fabry-Perot resonator cavity of the laser with the ring mirror 1. Since the adjustable ring mirror 8 is also provided on the hybrid waveguide, and a third electrode a03 is provided on the upper surface of the lithium tantalate thin film 5 above the adjustable ring mirror 8, and the third electrode a03 is a gold electrode. When a voltage is applied to the third electrode a03, the electro-optic effect occurs in the lithium tantalate in the hybrid waveguide, which further changes the effective refractive index of the hybrid waveguide. The change in refractive index will cause the reflection and transmission ratios of the adjustable ring mirror 8 to the laser to change, that is, the laser output conditions are changed. Therefore, by adjusting the voltage applied to the third electrode a03, the laser output power can be changed. The adjustable ring mirror 8 can also be replaced by an electrically tunable directional coupler with an embedded three-stage cascaded micro-ring.

[0047] After the laser exits from the adjustable ring mirror 8, it enters the output waveguide 9, and the laser output is realized through the output waveguide 9. By simultaneously changing the voltages applied to the vernier micro-ring filter 6 and the phase modulator 7, large-range linear frequency modulation of the laser can be achieved. By changing the voltage applied to the adjustable ring mirror 8, high-power range laser output can be achieved.

[0048] In summary, the above is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0049] The system, device, module or unit illustrated in the above one or more embodiments can be specifically implemented by a computer chip or an entity, or by a product with a certain function. A typical implementation device is a computer. Specifically, the computer can be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0050] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, commodity or device comprising said element.

[0051] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and reference can be made to the corresponding part of the method embodiment for the relevant content.

[0052] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the particular order or sequential order shown to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A heterogeneous integrated tunable laser, characterized in that, Comprising: A silicon nitride photonic chip, which includes, connected in sequence along the laser emission path: a gain unit, a Vernier micro-ring filter, a phase modulator, and an adjustable ring mirror; And a lithium tantalate thin film covering the upper surface of the silicon nitride photonic chip, and a hybrid waveguide is formed by heterogeneous integration of the lithium tantalate thin film and the silicon nitride waveguide layer of the silicon nitride photonic chip; Wherein, the phase modulator, the Vernier micro-ring filter, and the adjustable ring mirror are arranged in the hybrid waveguide region, and a first electrode of the Vernier micro-ring filter and a second electrode of the phase modulator are arranged on the upper surface of the lithium tantalate thin film; By adjusting the voltage applied to the first electrode, based on the electro-optic effect of the lithium tantalate thin film, the wavelength adjustment of the output laser is realized; By adjusting the voltage applied to the second electrode, based on the electro-optic effect of the lithium tantalate thin film, the linear frequency modulation of the output laser is realized.

2. The heterogeneous integrated tunable laser according to claim 1, wherein A third electrode of the adjustable ring mirror is also arranged on the upper surface of the lithium tantalate thin film. By adjusting the voltage applied to the third electrode, based on the electro-optic effect of the lithium tantalate thin film, the reflection and transmission ratio of the adjustable ring mirror to the laser is changed, and the adjustment of the laser output power is realized.

3. The heterogeneous integrated tunable laser according to claim 1, characterized in that, The gain unit includes a ring mirror and a gain chip. The ring mirror and the adjustable ring mirror form a Fabry-Perot resonator, and the gain chip is used to provide laser gain.

4. The heterogeneous integrated tunable laser according to claim 3, wherein Comprising: The gain chip is a III-V gain chip, and the III-V gain chip is bonded to the silicon nitride waveguide layer of the silicon nitride photonic chip.

5. The heterogeneous integrated tunable laser according to claim 3, wherein The gain unit includes: two gain chips. The two gain chips are designed in parallel, and the same voltage is applied to the two gain chips simultaneously to improve the laser gain.

6. The heterogeneous integrated tunable laser according to claim 5, wherein, A mode spot converter and a Y-shaped input waveguide are sequentially arranged between the gain unit and the Vernier micro-ring filter. The mode spot converter is used to match the optical mode size of the gain waveguide in the gain unit with the waveguide mode spot size of the Y-shaped input waveguide.

7. The heterogeneous integrated tunable laser according to claim 1, wherein The Vernier micro-ring filter includes three cascaded micro-rings with different circumferences. Among them, the first micro-ring and the second micro-ring realize the laser wavelength adjustment based on the Vernier effect, and the third micro-ring is used to narrow the line width and improve the side mode suppression ratio.

8. The heterogeneous integrated tunable laser according to claim 7, characterized in that, The third micro-ring is an asymmetric AMZ.

9. The heterogeneous integrated tunable laser according to claim 7, wherein The circumferences of the first micro-ring and the second micro-ring both have a value range of 600 - 800 microns, and the circumference difference between the first micro-ring and the second micro-ring is 5 - 15 microns.

10. The heterogeneous integrated tunable laser according to claim 1, characterized in that, By applying a square wave voltage to the first electrode of the Vernier micro-ring filter, the wavelength switching of the output laser is realized; by applying a triangular wave voltage to the second electrode of the phase modulator, the linear frequency modulation of the output laser is realized.

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