Waveguide external cavity laser

Abstract

The application provides a waveguide external cavity laser, comprising: a gain chip for generating a light source; a passive external cavity chip for providing narrow-band feedback, comprising a mode spot converter, a grating and a waveguide, the gain chip being coupled with the grating via the mode spot converter; the waveguide being used for transmitting an optical signal; the grating being located at the side of the waveguide and comprising periodically arranged etching structures, the gratings on both sides of the waveguide being arranged in a staggered manner. Compared with the prior art, the application provides an integrated asymmetric side-coupling grating external cavity narrow-line-width semiconductor laser, which can output light of a specified wavelength without electrical tuning, the tuning of which only needs one control loop and meets the application requirement of kilohertz-level line width. In addition, while meeting the requirements of high side mode suppression ratio and narrow-line-width laser output, the size of the structure processed by the application is relatively large, the processing can be completed by using a low-process technology, and therefore the processing cost is lower.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoelectric communication and sensing technology, in particular to a waveguide external cavity laser. BACKGROUND

[0002] In the fields of long-distance fiber sensing, optical interferometry, microwave photonics and coherent optical communication, the demand for kilohertz narrow linewidth lasers is increasing. Currently, the commercial kilohertz narrow linewidth lasers are mainly solid-state lasers, fiber lasers and fiber external cavity lasers. These lasers are often bulky and expensive. In contrast, integrated passive external cavity chip semiconductor lasers, integrated external cavity narrow linewidth semiconductor lasers, have the advantages of small size and low cost, and are gradually moving towards commercial applications. In order to obtain single longitudinal mode laser output with kilohertz linewidth, integrated external cavity narrow linewidth semiconductor lasers mostly use a passive external cavity scheme with two micro-ring cascades, which utilizes the high-Q micro-ring and the vernier effect of the two micro-rings to obtain narrow-band reflection spectrum. The external cavity design of this laser uses a micro-ring as the core unit device. However, the actual processing spectrum of the micro-ring deviates greatly from the design result, and the vernier effect of the two micro-rings amplifies this deviation, so that the actual output wavelength of this kind of laser deviates greatly from the design value without electrical tuning. In addition, this laser needs to adjust two micro-rings, a phase shifter and a power divider, and the control loop is more. The semiconductor laser using a symmetric lateral coupling grating has a smaller modulation structure size of the grating, and has a higher requirement for the precision of the processing technology. SUMMARY

[0003] In order to at least overcome the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a waveguide external cavity laser, comprising:

[0004] A gain chip for generating a light source.

[0005] A passive external cavity chip including a mode spot converter, a grating and a waveguide, the gain chip being coupled with 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 a periodic arrangement of etched structures, and the gratings on both sides of the waveguide are arranged in a staggered manner.

[0006] In a possible implementation, the waveguide external cavity laser further comprises a control circuit, which is located at the input end of the optical signal of the passive external cavity chip, and is used for controlling the phase of the waveguide to adjust the output wavelength of the waveguide external cavity laser.

[0007] In a possible implementation, 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%, wherein the second end face is coupled with the grating via the mode spot converter.

[0008] In a possible implementation, the gain chip and the passive external cavity chip are coupled in a direct butt coupling or a lens coupling manner.

[0009] In a possible implementation, the grating includes a first grating disposed on a first side of the waveguide and a second grating disposed on a second side of the waveguide, and the first grating and the second grating include a high-order Bragg waveguide grating with sawtooth misalignment.

[0010] In a possible implementation, the grating includes a third grating on a first side of the waveguide and a fourth grating on a second side of the waveguide, and the grating and the waveguide have a first spacing region therebetween, and a material of the first spacing region includes a low refractive index material.

[0011] The third grating and the fourth grating are misaligned.

[0012] In a possible implementation, the grating includes a fifth grating on a first side of the waveguide, and the fifth grating and the waveguide have a second spacing region therebetween, and a material of the second spacing region includes a low refractive index material.

[0013] The fifth grating includes a protrusion towards the waveguide.

[0014] In a possible implementation, the first grating and the second grating have a period of 3.4 μm, a number of periods of 1000, a modulation depth of 0.3 μm, a width of 0.5 μm in a direction parallel to the waveguide, a misalignment of 1.5 μm, and a maximum width of the waveguide of 3.0 μm.

[0015] In a possible implementation, the third grating and the fourth grating have a grating period of 3.4 μm, a number of periods of 1000, a width of 0.5 μm in a direction parallel to the waveguide, a misalignment of 1.2 μm, a maximum width of the waveguide of 1.1 μm, and a distance between the waveguide and the third grating and the fourth grating of 0.6 μm.

[0016] In a possible implementation, the fifth grating has a period of 3.4 μm, a number of periods of 1000, a width of 0.5 μm in a direction parallel to the waveguide, a maximum width of the waveguide of 1.1 μm, a distance between the waveguide and the fifth grating of 0.6 μm, and a height of the protrusion in a direction close to the waveguide of 0.15 μm.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] The application provides a waveguide external cavity laser. Compared with the prior art, the application forms an asymmetric lateral coupling grating by staggered arrangement of the gratings on both sides of the waveguide, so that 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 the processing can be completed by using a low processing technology, so that the processing cost is lower. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings required to be called in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Figure 1 A structure schematic diagram of the waveguide external cavity laser provided by the application is provided.

[0021] Figure 2 A schematic diagram of the control circuit of the waveguide external cavity laser provided by the application is provided.

[0022] Figure 3 One of the specific embodiments of the waveguide external cavity laser provided by the application is provided.

[0023] Figure 4 The second specific embodiment of the waveguide external cavity laser provided by the application is provided.

[0024] Figure 5 The third specific embodiment of the waveguide external cavity laser provided by the application is provided.

[0025] Figure 6 The reflection spectrum amplitude and phase of the grating of the third specific embodiment of the waveguide external cavity laser provided by the application are provided.

[0026] Figure 7 The output spectrum of the waveguide external cavity laser provided by the application is provided.

[0027] Figure legend: gain chip-100; passive external cavity chip-200; waveguide-201; mode spot 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

[0028] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present application.

[0030] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0031] In the description of the present application, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower" and the like is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship commonly placed when the product of the present application is used, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only used for differentiation in description and cannot be understood as indicating or implying relative importance.

[0032] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components must be absolutely horizontal or overhanging, 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.

[0033] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0034] It should be noted that, in the case of no conflict, different features in the embodiments of the present application can be combined with each other.

[0035] The inventors have found that current external cavity narrow linewidth semiconductor lasers include integrated double-microring external cavity narrow linewidth semiconductor lasers using two microring cascades, planar waveguide grating external cavity lasers using symmetric side-coupled gratings, etc. In the first technical solution, microrings are used as core unit devices, but the actual processing spectrum of the microring deviates greatly from the design result, and the vernier effect of the two microrings amplifies this deviation, so that two microrings, phase shifters, power dividers, etc. need to be added for electrical adjustment, and the control loop is more. In the second solution, due to the need to use symmetric side-coupled gratings, the reflection spectrum bandwidth of the symmetric side-coupled gratings 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 symmetric side-coupled grating has a smaller size and a higher processing precision requirement for the modulation structure, and the production cost is higher; in addition, the silicon dioxide planar waveguide has a smaller thermal-optical coefficient than silicon and silicon nitride, and the efficiency of electrical tuning is lower and the power consumption is higher.

[0036] Therefore, the present application provides a waveguide external cavity laser, which comprises a gain chip 100 for generating a light source, a passive external cavity chip 200 comprising a mode spot converter 202, a grating 203 and a waveguide 201, the gain chip 100 being coupled with the grating 203 via the mode spot converter 202, the waveguide 201 being used for transmitting an optical signal, the grating 203 being located on the side of the waveguide 201 and comprising a periodic arrangement of etched structures, and the gratings 203 on both sides of the waveguide 201 being arranged in a staggered manner. Figure 1

[0037] In the 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 internally contains a multi-quantum well or quantum dot structure, and can generate optical gain under the condition of external electrical injection. The passive external cavity chip 200 is used to provide narrow-band feedback and comprises a mode spot converter 202, a waveguide 201 and a grating 203. When the electrical injection reaches the threshold condition, the carrier recombination in the gain chip 100 generates spontaneous emission light, and the photons enter the waveguide 201 of the passive external cavity chip 200 and propagate, and at the same time, under the action of the grating 203, the unnecessary wavelengths are filtered out, and the light of a specific wavelength is reflected back to the gain chip 100, forming optical feedback. The feedback light is amplified in the gain chip 100, forming laser oscillation, and then outputting laser with good monochromaticity.

[0038] The grating in the embodiment is an asymmetric side-coupled grating 203.

[0039] The coupling coefficient of the asymmetric side-coupled grating 203 in the present application is approximately expressed as follows:

[0040] ​

[0041] wherein is a coupling coefficient, is a coupling coefficient of a common Bragg grating, m is a grating order, dL is a misalignment amount, and A is a grating period.

[0042] Therefore, compared with a common symmetric Bragg waveguide grating, the coupling coefficient of the asymmetric lateral coupling grating 203 used in the embodiment is lower, and thus the 3dB bandwidth of the reflection spectrum is smaller, that is, the side mode suppression ratio of the waveguide external cavity laser provided in the embodiment is higher, and the single mode stability is better; that is, the waveguide external cavity laser in the embodiment has stronger selectivity for wavelength, and can output laser with narrower line width and higher purity.

[0043] In addition, while meeting the requirements of high side mode suppression ratio and narrow line width laser output, the structure of the waveguide external cavity laser provided in the embodiment has a relatively large size, and can be processed using a low process technology, so that the process manufacturing cost is lower.

[0044] It should be noted that the materials for manufacturing the grating and the waveguide include silicon nitride, silicon, and silicon dioxide, and different materials can be selected in different size parameters and application scenarios.

[0045] In a possible implementation, referring to Figure 2 The waveguide external cavity laser further includes a control circuit 300, the control circuit 300 is located at the light signal input end of the passive external cavity chip 200, and is configured to control the phase of the waveguide 201 to adjust the output wavelength of the waveguide external cavity laser.

[0046] In the embodiment, the grating 203 with the asymmetric structure can realize wavelength tuning by adjusting the parameters of the single-side grating 203, and can output light with a specified wavelength without power tuning. The tuning only needs a control circuit 300, and the control circuit includes a phase shifter PS. The phase shifter PS is located at the light 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. The waveguide external cavity laser can meet the application requirement of kilohertz-level line width.

[0047] In a possible implementation, 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 is not more than 0.05%. The second end face is coupled with the grating 203 via the mode spot converter 202.

[0048] In the embodiment, the first end face is used to enhance the feedback of the inner cavity, and the reflectivity of the first end face is set to be not less than 90%, so that the maximum light feedback can be returned to the gain chip 100. The second end face is used to be coupled with the grating 203, and the reflectivity of the second end face is set to be not more than 0.05%, so that the reflected light of the second end face can be weakened, the feedback of the external cavity grating 203 becomes dominant, the specific wavelength light can be more effectively screened, and then the laser with better monochromaticity can be output.

[0049] In a possible implementation, the gain chip 100 and the passive external cavity chip 200 are coupled in a direct butt coupling or lens coupling manner.

[0050] In the embodiment, the gain chip 100 and the passive external cavity chip 200 can be directly butt coupled, and the second end face of the gain chip 100 is directly connected through high-precision alignment. Compared with other coupling manners, the 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 lens coupling. This manner can adjust the spot size by using a lens, and can solve the mode field mismatch problem. Compared with the other manners, the lens coupling has higher flexibility and coupling efficiency, but the system complexity and cost are also relatively high. In different use scenarios, different coupling manners can be selected to couple the gain chip 100 and the passive external cavity chip 200.

[0051] In a possible implementation, the grating 203 includes a first grating 203(a) arranged on the first side of the waveguide 201 and a second grating 203(b) arranged on the second side of the waveguide 201, and the first grating 203(a) and the second grating 203(b) include high-order Bragg waveguide gratings 203 with sawtooth misalignment.

[0052] Please refer to Figure 3 , the first grating 203(a) and the second grating 203(b) include the following size parameters: grating period Λ, number of grating periods , misalignment amount dL of gratings on both sides of the waveguide, modulation depth dW and maximum width of the waveguide and total length of the grating .

[0053] In this embodiment, the grating 203 and the waveguide 201 are integrated, with the structure of the grating 203 embedded or combined into the waveguide 201. One period 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. In the first region I and the third region III, the waveguide 201 has a 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 its effective refractive index is the second refractive index. In the third region IV, the waveguide 201 has no gratings 203 on either side, and its effective refractive index is the third refractive index.

[0054] To increase the minimum linewidth of the fabrication and reduce manufacturing costs, the grating order of the asymmetric lateral coupling grating 203 can be selected as an odd number such as 5, 7, 9, 11 or larger.

[0055] Specifically, the first grating 203(a) and the second grating 203(b) can be configured as follows: the period Λ of the first grating 203(a) and the second grating 203(b) is 3.4 μm, and the number of periods is... With a modulation depth dW of 1000 and a width of 0.3 μm, the first grating 203(a) and the second grating 203(b) have widths of 0.5 μm in the direction parallel to the waveguide 201, and the misalignment dL between the first grating 203(a) and the second grating 203(b) is 1.5 μm. The maximum width of the waveguide 201 is... The thickness is 3.0 μm. Optionally, in this embodiment, the material used to fabricate the waveguide includes silicon nitride.

[0056] In one possible implementation, the grating 203 includes a third grating 203(c) located on a first side of the waveguide 201 and a fourth grating 203(d) located on a second side of the waveguide 201. The grating 203 and the waveguide 201 have a first gap region. The material of the first gap region includes a low refractive index material, such as silicon dioxide. The third grating 203(c) and the fourth grating 203(d) are staggered.

[0057] 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. The misalignment dL of the gratings on both sides of the waveguide, and the maximum width of the waveguide. , Grating-waveguide spacing Gap, Grating width and the total length of the grating .

[0058] In the embodiment, the grating 203 and the waveguide 201 are not integrated, so that the waveguide 201 is better in uniformity of size after processing, and the processing tolerance is improved because of no sawtooth structure, and a lower process and lower cost process scheme, such as laser direct writing and contact photolithography, can be used.

[0059] One 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. Among them, the waveguide 201 has a grating 203 on only one side in the fifth region V and the seventh region VII, so that the effective refractive index is consistent, which is the fourth refractive index; the third grating 203(c) and the fourth grating 203(d) are aligned in the sixth region VI, and the effective refractive index thereof is the fifth refractive index; and the waveguide 201 has no grating 203 on both sides in the eighth region VII, and the effective refractive index thereof is the sixth refractive index.

[0060] Specifically, the third grating 203(c) and the fourth grating 203(d) can be configured as follows. The grating period Λ of the third grating 203(c) and the fourth grating 203(d) is 3.4 μm, the number of periods N is 1000, in the direction parallel to the waveguide 201, the width of the third grating 203(c) and the fourth grating 203(d) is 0.5 μm, the dislocation 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.

[0061] In a possible implementation, the grating 203 includes a fifth grating 203(e) located on the first side of the waveguide 201, the fifth grating 203(e) has a second spacing region with the waveguide 201, the material of the second spacing region includes a low refractive index material such as silica and the like, and the fifth grating 203(e) includes a protrusion 204 towards the waveguide 201.

[0062] Please refer to Figure 5 , the fifth grating 203(e) includes the following size parameters: grating period Λ, number of grating periods N, maximum width of waveguide W, distance between grating and waveguide Gap, height of protrusion on grating dd, width of grating Wg, and total length of grating L. .

[0063] ​​​​​​In the embodiment, the grating 203 and the waveguide 201 are not integrated, and the waveguide 201 has the grating structure on only one side, so that the influence of the relative position error of the two sides of the grating 203 can be avoided.

[0064] In the embodiment, the length of one period of the fifth grating 203(e) includes the ninth region IX, the tenth region X, the eleventh region XI, and the twelfth region XII. The ninth region IX and the eleventh region XI are regions on both sides of the protrusion 204, and thus the effective refractive index is consistent, being the seventh refractive index; the tenth region X is a region where the protrusion 204 is located, and the effective refractive index thereof is the eighth refractive index; and the twelfth region XII does not have the grating 203 on both sides of the waveguide 201, and the effective refractive index thereof is the ninth refractive index.

[0065] Specifically, the fifth grating 203(e) can be configured as follows. The period Λ of the fifth grating 203(e) is 3.4 μm, the number of periods N is 1000, in the direction parallel to the waveguide 201, the width W of the fifth grating 203(e) is 0.5 μm, the maximum width Wmax 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 the embodiment, the material for manufacturing the waveguide can include silicon nitride.

[0066] It should be noted that the grating 203 can be a sub-grating, the period of which is smaller than the wavelength of light, and the sub-grating has high resolution and can be designed in a small size, and is more suitable for miniaturization and integration applications; at the same time, the sub-grating can efficiently regulate and control light in a wide waveband range, thereby reducing loss and improving the performance of the system.

[0067] Please refer to Figure 6 and Figure 7 The waveguide external cavity laser provided by the present application has a kilohertz-level line width and a high side mode suppression ratio. Figure 6 The amplitude and phase of the reflection spectrum of the asymmetrically side-coupled fifth grating 203(e) are shown in FIG. 6, and the 3dB bandwidth thereof 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 asymmetrically side-coupled grating 203 of the present application is shown in FIG. 7, and the calculated line width corresponding thereto is less than 3 kHz, and the single mode characteristic of the waveguide external cavity laser is good, and the side mode suppression ratio is greater than 55 dB. Figure 7

[0068] ​​​​In summary, the application provides a waveguide external cavity laser, comprising: a gain chip 100 for generating a light source; a passive external cavity chip 200, comprising a mode spot converter 202, a grating 203 and a waveguide 201, the gain chip 100 being coupled with the grating 203 via the mode spot converter 202; the waveguide 201 being used for transmitting an optical signal; the grating 203 being located at the side of the waveguide 201 and comprising a periodic arrangement of etching structures, the gratings 203 on both sides of the waveguide 201 being arranged in a staggered manner. Compared with the prior art, the present application forms an asymmetric lateral coupling grating by arranging the gratings 203 on both sides of the waveguide 201 in a staggered manner, so that 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 the processing can be completed using a low process, so that the process manufacturing cost is lower.

[0069] It should be noted that the relational terms herein such as first and second, and the like, are used solely to distinguish one from another entity or action, without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element preceded by "comprises... " does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0070] The above only describes the preferred embodiments of the application and is not intended to limit the application. The application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A waveguide external cavity laser, characterized in that, include: A gain chip is used to generate a light source; a passive external cavity chip includes a mode converter, a grating, and a waveguide, wherein the gain chip is coupled to the grating via the mode converter; the waveguide is used to transmit 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 staggered to form an asymmetric laterally coupled grating. The coupling coefficient of the asymmetric lateral coupling grating is: ； in k The coupling coefficient; k 0 represents the coupling coefficient of a standard Bragg grating; m is the grating order; dL is the misalignment amount; Λ represents the grating period; The grating order of the asymmetric lateral coupling grating is selected as an odd number such as 5, 7, 9, 11 or larger; The grating includes a first grating disposed on a first side of the waveguide and a second grating disposed on a second side of the waveguide, wherein the first grating and the second grating include a high-order Bragg waveguide grating with staggered sawtooth patterns. Alternatively, the grating includes a third grating located on a first side of the waveguide and a fourth grating located on a second side of the waveguide, with a first gap region between the grating and the waveguide, the first gap region being made of a low refractive index material; the third grating and the fourth grating are staggered. Alternatively, the grating may include a fifth grating located on a first side of the waveguide, the fifth grating having a second spacing region between it and the waveguide, the second spacing region being made of a low-refractive-index material; the fifth grating may include protrusions facing the waveguide.

2. The waveguide external cavity laser according to claim 1, characterized in that, The waveguide external cavity laser also includes a control circuit located at the optical signal input terminal of the passive external cavity chip, which is used to control the phase of the waveguide 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 a first end face and a second end face opposite to each other, the first end face having a reflectivity of not less than 90% and the second end face having a reflectivity of not more than 0.05%, wherein the second end face is coupled to the grating via the mode converter.

4. The waveguide external cavity laser according to claim 1, characterized in that, The gain chip and the passive external cavity chip are coupled by direct docking or lens coupling.

5. The waveguide external cavity laser according to claim 1, characterized in that, The first grating and the second grating have a period of 3.4 μm, a period number of 1000, and a modulation depth of 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 of the first grating and the second grating is 1.5 μm, and the maximum width of the waveguide is 3.0 μm.

6. The waveguide external cavity laser according to claim 1, characterized in that, The third and fourth gratings have a grating period of 3.4 μm and a period number of 1000. In the direction parallel to the waveguide, the width of the third and fourth gratings is 0.5 μm, the misalignment of the third and fourth gratings is 1.2 μm, the maximum width of the waveguide is 1.1 μm, and the distance between the waveguide and the third and fourth gratings is 0.6 μm.

7. The waveguide external cavity laser according to claim 1, characterized in that, The fifth grating has a period of 3.4 μm and a period number of 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. The height of the protrusion in the direction close to the waveguide is 0.15 μm.

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