Waveguide external cavity laser

Abstract

The invention provides a waveguide external cavity laser comprising a gain chip used for generating a light source; the passive external cavity chip is used for providing narrowband feedback and comprises a spot size converter, a grating and a waveguide, and the gain chip is coupled with the grating through the spot size converter; the waveguide is used for transmitting an optical signal; the gratings are located on the side face of the waveguide and comprise periodically-arranged etching structures, and the gratings on the two sides of the waveguide are arranged in a staggered mode. Compared with the prior art, the integrated asymmetric lateral coupling grating external cavity narrow linewidth semiconductor laser provided by the invention can output light with a specified wavelength under the condition of no power-on tuning, only one control loop is needed for tuning, and the application requirement of kilohertz level linewidth is met. In addition, while the requirements for high side mode rejection ratio and narrow linewidth laser output are met, the size of the structure machined through the scheme is relatively large, machining can be completed through a low-manufacturing-process technology, and therefore the technology manufacturing cost is lower.

Description

Technical Field

[0001] This application relates to the field of optoelectronic communication and sensing technologies, and more particularly, to a waveguide external cavity laser. Background Art

[0002] In fields such as long-distance fiber sensing, optical interferometric measurement, microwave photonics, and coherent optical communication, the demand for kHz-level narrow linewidth lasers is increasing. Currently, commercially available kHz-level narrow linewidth lasers are mainly solid-state lasers, fiber lasers, and fiber external cavity lasers, which are often bulky and expensive. In contrast, semiconductor lasers integrated with passive external cavity chips - integrated external cavity narrow linewidth semiconductor lasers - have volume and cost advantages and are gradually moving towards commercial applications. To obtain single longitudinal mode laser output with a kHz-level linewidth, integrated external cavity narrow linewidth semiconductor lasers mostly adopt a passive external cavity scheme with two cascaded microrings, and use high-Q microrings and the Vernier effect of the two microrings to obtain a narrowband reflection spectrum. The external cavity design of this laser uses a microring as the core unit device, but the spectrum of the actually processed microring deviates greatly from the design result, and the Vernier effect of the two microrings will amplify this deviation. Therefore, without electrical tuning, the actual output optical wavelength of such lasers deviates greatly from the design value. In addition, this laser requires electrical adjustment of the two microrings, phase shifters, and power splitters, and there are many control loops. For semiconductor lasers using symmetric lateral coupling gratings, due to the small size of the modulation structure of the gratings, the accuracy requirements for processing technology are relatively high. Summary of the Invention

[0003] To at least overcome the above deficiencies in the prior art, the purpose of this application is to provide a waveguide external cavity laser, including: A gain chip for generating a light source; A passive external cavity chip, including a mode spot converter, a grating, and a waveguide, the gain chip is coupled to the grating via the mode spot converter; the waveguide is used for transmitting optical signals; the grating is located on the side of the waveguide and includes periodically arranged etched structures, and the gratings on both sides of the waveguide are arranged with a dislocation.

[0004] In a possible implementation manner, the waveguide external cavity laser further includes a control circuit, and the control circuit is located at the optical signal input end of the passive external cavity chip and is used to control the phase of the waveguide so as to adjust the output wavelength of the waveguide external cavity laser.

[0005] In a possible implementation manner, the gain chip includes opposite first and second end faces, the reflectivity of the first end face is not less than 90%, and the reflectivity of the second end face is not more than 0.05%, and the second end face is coupled to the grating via the mode spot converter.

[0006] In a possible implementation, the coupling manner between the gain chip and the passive external cavity chip is direct butt coupling or lens coupling.

[0007] In a possible implementation, the grating includes a first grating disposed on the first side of the waveguide and a second grating disposed on the second side of the waveguide. The first grating and the second grating include high-order Bragg waveguide gratings with serrated misalignment.

[0008] In a possible implementation, the grating includes a third grating located on the first side of the waveguide and a fourth grating located on the second side of the waveguide. There is a first spacer region between the grating and the waveguide, and the material of the first spacer region includes a low refractive index material; The third grating and the fourth grating are misaligned.

[0009] In a possible implementation, the grating includes a fifth grating located on the first side of the waveguide. There is a second spacer region between the fifth grating and the waveguide, and the material of the second spacer region includes a low refractive index material; The fifth grating includes a protrusion facing the waveguide.

[0010] In a possible implementation, the period of the first grating and the second grating is 3.4 μm, the number of periods is 1000, the modulation depth is 0.3 μm. In the direction parallel to the waveguide, the width of the first grating and the second grating is 0.5 μm, the misalignment amount of the first grating and the second grating is 1.5 μm, and the maximum width of the waveguide is 3.0 μm.

[0011] In a possible implementation, the grating period of the third grating and the fourth grating is 3.4 μm, the number of periods is 1000. In the direction parallel to the waveguide, the width of the third grating and the fourth grating is 0.5 μm, the misalignment amount of the third grating and the fourth grating is 1.2 μm, the maximum width of the waveguide is 1.1 μm, and the distance between the waveguide and the third grating and the fourth grating is 0.6 μm.

[0012] In a possible implementation, the period of the fifth grating is 3.4 μm, the number of periods is 1000. In the direction parallel to the waveguide, the width of the fifth grating is 0.5 μm, the maximum width of the waveguide is 1.1 μm, the distance between the waveguide and the fifth grating is 0.6 μm, and the height of the protrusion in the direction close to the waveguide is 0.15 μm.

[0013] Compared with the prior art, the present application has the following beneficial effects: The present application provides a waveguide external cavity laser. Compared with the prior art, in this solution, the gratings on both sides of the waveguide are misaligned to form an asymmetric lateral coupling grating, which can obtain a narrower laser linewidth. While meeting the requirements of high side mode suppression ratio and narrow linewidth laser output, the size of the processed structure is relatively large, and a low-process technology can be used for processing, so the process manufacturing cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 is a schematic structural diagram of the waveguide external cavity laser provided by the present application; Figure 2 is a schematic diagram of the control circuit of the waveguide external cavity laser provided by the present application; Figure 3 is one of the specific embodiments of the waveguide external cavity laser provided by the present application; Figure 4 is the second specific embodiment of the waveguide external cavity laser provided by the present application; Figure 5 is the third specific embodiment of the waveguide external cavity laser provided by the present application; Figure 6 is the reflection spectrum amplitude and phase of the grating in the third specific embodiment of the waveguide external cavity laser provided by the present application; Figure 7 is the output spectrum of the waveguide external cavity laser provided by the present application.

[0016] Reference numerals: gain chip - 100; passive external cavity chip - 200; waveguide - 201; mode field converter - 202; grating - 203; first grating - 203(a); second grating - 203(b); third grating - 203(c); fourth grating - 203(d); fifth grating - 203(e); control circuit 300; phase shifter - PS. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0018] Accordingly, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0019] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not require further definition and explanation in subsequent drawings.

[0020] In the description of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship in which the product of this application is usually placed during use. It is only for the convenience of describing the present application 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 of the present application. In addition, terms such as "first", "second", etc. are only used for descriptive distinction and cannot be understood as indicating or implying relative importance.

[0021] Furthermore, terms such as "horizontal", "vertical", "hanging", etc. do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0022] In the description of the present application, it should also be noted that unless otherwise clearly defined and limited, the terms "arranged", "installed", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0023] It should be noted that, without conflict, different features in the embodiments of the present application can be combined with each other.

[0024] Through research by the inventors, it is found that current external cavity narrow linewidth semiconductor lasers include integrated dual-micro-ring external cavity narrow linewidth semiconductor lasers using two cascaded micro-rings, planar waveguide grating external cavity lasers using symmetric lateral coupling gratings, etc. In the first technical solution, micro-rings are used as the core unit devices. However, there is a large deviation between the actually processed spectrum of the micro-rings and the design results, and the Vernier effect of the two micro-rings will amplify this deviation. Therefore, it is necessary to electrically adjust the two micro-rings, phase shifters, power splitters, etc., and there are many control loops. In the second solution, since a symmetric lateral coupling grating needs to be used, the reflection spectrum bandwidth of the symmetric lateral coupling grating is larger under the same modulation structure, resulting in a smaller side mode suppression ratio of the laser. At the same time, in order to obtain a higher side mode suppression ratio, the fabricated symmetric lateral coupling grating has a modulation structure with a smaller size and higher processing accuracy requirements, and the manufacturing cost is higher. In addition, a silica planar waveguide is used. Since the thermo-optic coefficient of silica is smaller than that of silicon and silicon nitride, the efficiency of electro-tuning is lower and the power consumption is higher.

[0025] In view of this, please refer to Figure 1 , this application provides a waveguide external cavity laser, including: a gain chip 100 for generating a light source; a passive external cavity chip 200, including a mode spot converter 202, a grating 203, and a waveguide 201. The gain chip 100 is coupled to the grating 203 via the mode spot converter 202; the waveguide 201 is used for transmitting optical signals; the grating 203 is located on the side of the waveguide 201 and includes etched structures arranged periodically, and the gratings 203 on both sides of the waveguide 201 are arranged in a staggered manner.

[0026] In this embodiment, the gain chip 100 and the passive external cavity chip 200 are coupled to form a resonant cavity. The gain chip 100 can be made of a semiconductor material and contains a multi-quantum well or quantum dot structure inside, and can generate optical gain under the condition of external electrical injection. The passive external cavity chip 200 is used to provide narrowband feedback and includes a mode spot converter 202, a waveguide 201, and a grating 203. When the electrical injection reaches the threshold condition, carriers in the gain chip 100 recombine to generate spontaneous emission light, and the photons enter the waveguide 201 of the passive external cavity chip 200 and propagate. At the same time, under the action of the grating 203, the unwanted wavelengths are filtered out, and the light of a specific wavelength is reflected back to the gain chip 100 to form optical feedback. The feedback light is stimulated and amplified in the gain chip 100 to form a laser oscillation, and then a laser with better monochromaticity is output.

[0027] The grating in this embodiment uses an asymmetric lateral coupling grating 203.

[0028] Since the coupling coefficient of the asymmetric lateral coupling grating 203 in this application is approximately expressed by the following formula: Where is the coupling coefficient, is the coupling coefficient of the ordinary Bragg grating, m is the grating order, dL is the misalignment, and Λ is the grating period.

[0029] Therefore, compared with the ordinary symmetric Bragg waveguide grating, the coupling coefficient of the asymmetric lateral coupling grating 203 used in this embodiment is lower, and thus it has a smaller 3dB bandwidth of the reflection spectrum. That is, the side mode suppression ratio of the waveguide external cavity laser provided in this embodiment is relatively high, and the single-mode stability is good; that is, the waveguide external cavity laser in this embodiment has a stronger selectivity for wavelengths and can output laser with a narrower linewidth and higher purity.

[0030] In addition, while meeting the requirements of high side mode suppression ratio and narrow linewidth laser output, the size of the processed structure of the waveguide external cavity laser provided by this solution is relatively large, and low-process technology can be used for processing, so the process manufacturing cost is lower.

[0031] It should be noted that the materials for making the grating and the waveguide include silicon nitride, silicon, silicon dioxide, etc., and different materials can be selected under different size parameters and application scenarios.

[0032] In a possible implementation manner, please refer to Figure 2 , the waveguide external cavity laser further includes a control circuit 300, and the control circuit 300 is located at the optical signal input end of the passive external cavity chip 200, and is used to control the phase of the waveguide 201 so as to adjust the output wavelength of the waveguide external cavity laser.

[0033] In this embodiment, the grating 203 with an asymmetric structure can achieve wavelength tuning by adjusting the parameters of the unilateral grating 203, and can output light with a specified wavelength without electrical tuning. Its tuning only requires a control circuit 300. The control circuit includes a phase shifter PS. The phase shifter PS is located at the optical signal input end of the passive external cavity chip 200, and adjusts the output wavelength of the waveguide external cavity laser by controlling the phase of the waveguide 201, and this waveguide external cavity laser can meet the application requirements of a linewidth at the kHz level.

[0034] In a possible implementation manner, the gain chip 100 includes opposite first and second end faces. The reflectivity of the first end face is not less than 90%, and the reflectivity of the second end face does not exceed 0.05%. The second end face is coupled to the grating 203 via the mode spot converter 202.

[0035] In this embodiment, the first end face is used to enhance the intracavity feedback. By setting the reflectivity of the first end face to be not less than 90%, the maximum amount of light can be fed back to the gain chip 100. The second end face is used to couple with the grating 203. By setting the reflectivity of the second end face to be not more than 0.05%, the reflected light from the second end face can be weakened, making the feedback of the external cavity grating 203 dominant, and enabling more effective screening of light of a specific wavelength, thereby outputting laser with better monochromaticity.

[0036] In a possible implementation manner, the coupling manner between the gain chip 100 and the passive external cavity chip 200 is direct butt coupling or lens coupling.

[0037] In this embodiment, the gain chip 100 and the passive external cavity chip 200 can be directly butt-coupled and directly connected to the second end face of the gain chip 100 through high-precision alignment. Compared with other coupling methods, direct butt coupling has the advantages of simple structure, low cost, and good thermal stability. The gain chip 100 and the passive external cavity chip 200 can also be coupled through a lens. This method uses a lens to adjust the spot size and can solve the problem of mode field mismatch. In contrast, it has higher flexibility and coupling efficiency, but the system complexity and cost are also relatively high. Different coupling methods can be selected to couple the gain chip 100 and the passive external cavity chip 200 in different usage scenarios.

[0038] In a possible implementation manner, the grating 203 includes a first grating 203(a) disposed on the first side of the waveguide 201 and a second grating 203(b) disposed on the second side of the waveguide 201. The first grating 203(a) and the second grating 203(b) include high-order Bragg waveguide 201 gratings 203 with serrated misalignment.

[0039] Please refer to Figure 3 , the first grating 203(a) and the second grating 203(b) include the following dimensional parameters: grating period Λ, number of grating periods , misalignment amount dL of the gratings on both sides of the waveguide, modulation depth dW, and maximum width of the waveguide and total length of the grating .

[0040] In this embodiment, the grating 203 and the waveguide 201 are integrally fabricated, and the structure of the grating 203 is embedded or combined into the waveguide 201. One period length of the first grating 203(a) and the second grating 203(b) includes a first region I, a second region II, a third region III, and a fourth region IV. Among them, in the first region I and the third region III, the waveguide 201 has the grating 203 on only one side, so the effective refractive index is the same, which is the first refractive index; in the second region II, the first grating 203(a) and the second grating 203(b) are aligned, and their effective refractive index is the second refractive index; in the fourth region IV, the waveguide 201 does not have the grating 203 on both sides, and its effective refractive index is the third refractive index.

[0041] To increase the minimum line width of processing and reduce the manufacturing cost, the grating order of the asymmetric lateral coupling grating 203 can be selected as 5, 7, 9, 11 or larger odd numbers.

[0042] Specifically, the following settings can be made for the first grating 203(a) and the second grating 203(b). The period Λ of the first grating 203(a) and the second grating 203(b) is 3.4 μm, the number of periods is 1000, the modulation depth dW is 0.3 μm. In the direction parallel to the waveguide 201, the widths of the first grating 203(a) and the second grating 203(b) are 0.5 μm, the misalignment amount dL of the first grating 203(a) and the second grating 203(b) is 1.5 μm, and the maximum width of the waveguide 201 is 3.0 μm. Optionally, in this embodiment, the material for fabricating the waveguide includes silicon nitride.

[0043] In a possible implementation manner, the grating 203 includes a third grating 203(c) located on the first side of the waveguide 201 and a fourth grating 203(d) located on the second side of the waveguide 201. There is a first spacer region between the grating 203 and the waveguide 201, and the material of the first spacer region includes a low refractive index material, such as silica and other materials; the third grating 203(c) and the fourth grating 203(d) are misaligned.

[0044] Please refer to Figure 4 , the third grating 203(c) and the fourth grating 203(d) include the following dimensional parameters: grating period Λ, number of grating periods , misalignment amount dL of the gratings on both sides of the waveguide, maximum width of the waveguide , grating-to-waveguide spacing Gap, grating width and total length of the grating .

[0045] In this embodiment, the grating 203 and the waveguide 201 are fabricated separately, resulting in better dimensional uniformity of the fabricated waveguide 201. Moreover, since there is no sawtooth structure, the processing tolerance is improved, and a lower-process and lower-cost process solution, such as laser direct writing and contact lithography, can be used.

[0046] The period length of the third grating 203(c) and the fourth grating 203(d) includes a fifth region V, a sixth region VI, a seventh region VII, and an eighth region VIII. In the fifth region V and the seventh region VII, the waveguide 201 has a grating 203 on only one side, so the effective refractive index is the same, which is the fourth refractive index. In the sixth region VI, the third grating 203(c) and the fourth grating 203(d) are aligned, and their effective refractive index is the fifth refractive index. In the eighth region VII, there is no grating 203 on both sides of the waveguide 201, and its effective refractive index is the sixth refractive index.

[0047] Specifically, the following settings can be made for the third grating 203(c) and the fourth grating 203(d). The grating period Λ of the third grating 203(c) and the fourth grating 203(d) is 3.4 μm, and the number of grating periods is 1000. In the direction parallel to the waveguide 201, the widths of the third grating 203(c) and the fourth grating 203(d) are 0.5 μm, the misalignment amount dL of the third grating 203(c) and the fourth grating 203(d) is 1.2 μm, the maximum width of the waveguide 201 is 1.1 μm, and the distance Gap between the waveguide 201 and the third grating 203(c) and the fourth grating 203(d) is 0.6 μm. Optionally, in this embodiment, the material for fabricating the waveguide may include silicon nitride.

[0048] In a possible implementation, the grating 203 includes a fifth grating 203(e) located on the first side of the waveguide 201. There is a second spacer region between the fifth grating 203(e) and the waveguide 201, and the material of the second spacer region includes a low refractive index material, such as silica and other materials. The fifth grating 203(e) includes a protrusion 204 facing the waveguide 201.

[0049] Please refer to Figure 5 , the fifth grating 203(e) includes the following dimensional parameters: grating period Λ, number of grating periods , maximum waveguide width , grating-to-waveguide spacing Gap, protrusion height dd on the grating, grating width and total grating length .

[0050] In this embodiment, the grating 203 and the waveguide 201 are fabricated separately, and the waveguide 201 has a grating structure on only one side, which can avoid the influence of the relative position error between the gratings 203 on both sides.

[0051] In this embodiment, the period length of the fifth grating 203(e) includes a ninth region IX, a tenth region X, an eleventh region XI, and a twelfth region XII. Among them, the ninth region IX and the eleventh region XI are the regions on both sides of the protrusion 204, so the effective refractive indices are the same, which is the seventh refractive index; the tenth region X is the region where the protrusion 204 is located, and its effective refractive index is the eighth refractive index; in the twelfth region XII, there is no grating 203 on both sides of the waveguide 201, and its effective refractive index is the ninth refractive index.

[0052] Specifically, the following settings can be made for the fifth grating 203(e). The period Λ of the fifth grating 203(e) is 3.4 μm, and the number of periods is 1000. In the direction parallel to the waveguide 201, the width of the fifth grating 203(e) is 0.5 μm, the maximum width of the waveguide 201 is 1.1 μm, the distance Gap between the waveguide 201 and the fifth grating 203(e) is 0.6 μm, and the height dd of the protrusion in the direction close to the waveguide 201 is 0.15 μm. Optionally, in this embodiment, the material for fabricating the waveguide may include silicon nitride.

[0053] It should be noted that the grating 203 can be selected as a sub-grating. The period of the sub-grating is less than the wavelength of light, which has high resolution and can be designed in a small size, making it more suitable for miniaturization and integration applications; at the same time, the sub-grating can efficiently control light in a wide wavelength range, thereby reducing losses and improving the performance of the system.

[0054] Please refer to Figure 6 and Figure 7 , the waveguide external cavity laser with an asymmetric lateral coupling grating provided by this application has a linewidth of the order of kHz and a high side mode suppression ratio. Figure 6 are the reflection spectrum amplitude and phase of the asymmetric lateral coupling fifth grating 203(e), and its 3dB bandwidth is less than 0.2 nm, and the spectral side mode suppression ratio is about 10 dB. The output spectrum of the waveguide external cavity laser using the asymmetric lateral coupling grating 203 of this application is as Figure 7 shown. It is calculated that the corresponding linewidth is less than 3 kHz, and the single-mode characteristic of the waveguide external cavity laser is very good, and the side mode suppression ratio is greater than 55 dB.

[0055] In summary, the present application provides a waveguide external cavity laser, comprising: a gain chip 100 for generating a light source; a passive external cavity chip 200 including a mode spot converter 202, a grating 203, and a waveguide 201, wherein the gain chip 100 is coupled to the grating 203 via the mode spot converter 202; the waveguide 201 is used for transmitting an optical signal; the grating 203 is located on the side of the waveguide 201 and includes an etched structure arranged periodically, and the gratings 203 on both sides of the waveguide 201 are arranged in a staggered manner. Compared with the prior art, in this solution, by arranging the gratings 203 on both sides of the waveguide 201 in a staggered manner to form an asymmetric lateral coupling grating, a narrower laser linewidth can be obtained; while meeting the requirements of high side mode suppression ratio and narrow linewidth laser output, the size of the processed structure is relatively large, and a low-process technology can be used for processing, so the process manufacturing cost is lower.

[0056] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0057] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A waveguide external cavity laser, characterized in that, Comprising: A gain chip for generating a light source; A passive external cavity chip, including a mode spot converter, a grating, and a waveguide. The gain chip is coupled to the grating via the mode spot converter; the waveguide is used for transmitting an optical signal; the grating is located on the side of the waveguide and includes periodically arranged etching structures, and the gratings on both sides of the waveguide are arranged with a dislocation.

2. The waveguide external cavity laser according to claim 1, wherein, The waveguide external cavity laser further includes a control circuit located at the optical signal input end of the passive external cavity chip for controlling the phase of the waveguide so as to adjust the output wavelength of the waveguide external cavity laser.

3. The waveguide external cavity laser according to claim 1, characterized in that, The gain chip includes opposite first and second end faces. The reflectivity of the first end face is not less than 90%, and the reflectivity of the second end face is not more than 0.05%. The second end face is coupled to the grating via the mode spot converter.

4. The waveguide external cavity laser according to claim 1, wherein The coupling mode between the gain chip and the passive external cavity chip is direct butt coupling or lens coupling.

5. The waveguide external cavity laser according to claim 1, characterized in that, The grating includes a first grating provided on the first side of the waveguide and a second grating provided on the second side of the waveguide. The first grating and the second grating include a high-order Bragg waveguide grating with a sawtooth dislocation.

6. The waveguide external cavity laser according to claim 1, wherein The grating includes a third grating located on the first side of the waveguide and a fourth grating located on the second side of the waveguide. There is a first spacer region between the grating and the waveguide, and the material of the first spacer region includes a low refractive index material; The third grating and the fourth grating are arranged with a dislocation.

7. The waveguide external cavity laser according to claim 1, wherein The grating includes a fifth grating located on the first side of the waveguide. There is a second spacer region between the fifth grating and the waveguide, and the material of the second spacer region includes a low refractive index material; The fifth grating includes a protrusion facing the waveguide.

8. The waveguide external cavity laser according to claim 5, wherein The period of the first grating and the second grating is 3.4 μm, the number of periods is 1000, the modulation depth is 0.3 μm. In the direction parallel to the waveguide, the width of the first grating and the second grating is 0.5 μm, the dislocation amount of the first grating and the second grating is 1.5 μm, and the maximum width of the waveguide is 3.0 μm.

9. The waveguide external cavity laser according to claim 6, characterized in that, The grating period of the third grating and the fourth grating is 3.4 μm, the number of periods is 1000. In the direction parallel to the waveguide, the width of the third grating and the fourth grating is 0.5 μm, the dislocation amount of the third grating and the fourth grating is 1.2 μm, the maximum width of the waveguide is 1.1 μm, and the distance between the waveguide and the third grating and the fourth grating is 0.6 μm.

10. The waveguide external cavity laser according to claim 7, characterized in that, The period of the fifth grating is 3.4 μm, the number of periods is 1000. In the direction parallel to the waveguide, the width of the fifth grating is 0.5 μm, the maximum width of the waveguide is 1.1 μm, the distance between the waveguide and the fifth grating is 0.6 μm, and the height of the protrusion in the direction close to the waveguide is 0.15 μm.

Images