DFB laser and application thereof

Abstract

The DFB laser comprises a substrate, a quantum well active layer, a grating layer and a waveguide layer which are stacked in sequence, a ridge waveguide is formed on the waveguide layer, the ridge waveguide comprises a vertical waveguide and a trapezoidal waveguide, the vertical waveguide and the trapezoidal waveguide have the same thickness, and the top surface of the vertical waveguide and the top surface of the trapezoidal waveguide are located on the same horizontal plane. The vertical waveguide is perpendicular to the front end face of the DFB laser, the trapezoidal waveguide has an inclined angle relative to the front end face, the trapezoidal waveguide is trapezoidal, the vertical waveguide is rectangular, the lower bottom of the trapezoid is located on the front end face, the upper bottom of the trapezoid is connected with the short side of the rectangle, and the length of the upper bottom of the trapezoid is equal to that of the short side of the rectangle. And the ratio of the length of the lower bottom of the trapezoid to the length of the short side of the rectangle is M which is more than 1 and less than or equal to 4. According to the utility model, the quantity of light reflected back to the laser can be reduced, the output beam quality of the laser can be improved, the divergence angle is reduced, the light intensity density of the light outlet end is reduced, and the reliability is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of semiconductor laser, especially to a DFB laser and its application. BACKGROUND

[0002] Distributed feedback laser (DFB) is a type of laser that achieves optical feedback by periodically modulating the refractive index in the gain medium. DFB lasers are widely used in modern optical communication systems, laser radars, spectral analysis, and gas sensing due to their single-mode output, narrow linewidth, high power stability, and compact structure design, making them indispensable components in these systems.

[0003] Despite the excellent performance of DFB lasers in many applications, their performance is still susceptible to external environmental factors, especially the influence of external reflected light. When external reflected light enters the laser cavity, it will interfere with the internal light field of the laser, causing the following problems: (1) Output power fluctuation: the interference of reflected light can cause instability of the laser output power, affecting the signal transmission quality of the system. (2) Mode transition: external reflected light may cause the laser to transition from single-mode operation to multi-mode state, destroying its single-mode output characteristics. (3) Line width broadening: the feedback effect of reflected light increases the phase noise of the laser, causing the output spectral line width to increase, reducing the spectral purity of the system. (4) Eye diagram distortion: in optical communication systems, the eye diagram of the output signal may be distorted by the interference of reflected light, affecting the reliability and speed of data transmission.

[0004] These problems not only affect the performance of individual DFB lasers, but also may have a negative impact on the transmission quality and stability of the entire optical communication system. Therefore, how to effectively suppress the interference of external reflected light has become one of the key technologies to improve the performance of DFB lasers.

[0005] In order to solve the adverse effects of external reflected light on DFB lasers, the industry has proposed a variety of solutions, but most of these solutions have certain limitations in practical applications.

[0006] One of the traditional solutions is to add an optical isolator inside the packaged device of the DFB laser, which is used to block the feedback of the external reflected light in the laser cavity. Although this method can effectively reduce the interference of reflected light and improve the stability of the laser, it also has the following shortcomings: (1) Cost increase: As an independent optical element, the cost of the optical isolator is relatively high, especially in large-scale optical communication systems, the overall cost is significantly increased. (2) Packaging complexity: The integration of the optical isolator makes the packaging structure of the laser more complex, increasing the manufacturing difficulty and process complexity. (3) Size increase: The integration of the optical isolator may cause the volume of the laser module to increase, which is not conducive to high-density integration and small-size design requirements.

[0007] Another common solution is to interface a section of the coupling waveguide at the end face of the DFB laser, and by designing a specific optical coupling structure, the intensity of the reflected light is reduced, thereby weakening its interference with the operation of the laser. Although this method alleviates the problem of reflected light to some extent, it also has the following challenges: (1) Process complexity: Additional etching and epitaxial interfacing of the waveguide are required during the manufacturing process, increasing the complexity and number of steps of the manufacturing process. (2) Increased manufacturing cost: Complex manufacturing processes not only prolong the production cycle but also increase production costs, which is not conducive to large-scale commercial applications. (3) Stability issues: Due to the involvement of multiple processes, process errors are easily introduced, affecting the precision and stability of the coupling waveguide, and reducing the overall performance of the laser.

[0008] With the rapid development of optical communication networks, especially the high-speed and long-distance transmission requirements for DFB lasers, higher performance is required. Specifically: (1) Higher integration: In order to meet the needs of data centers and fiber communication systems for compact and high-density modules, DFB lasers need to achieve higher integration and small-size design. (2) Lower manufacturing cost: In large-scale commercial applications, how to reduce the manufacturing cost of DFB lasers and improve their cost performance becomes a key competitive force. (3) Higher anti-reflection capability: In order to reduce the dependence on external devices and improve the anti-reflection capability of DFB lasers, it has become a core requirement to improve the overall performance and reliability of the system. (4) Better thermal management performance: The demand for high power density and long-term operation requires DFB lasers to have higher thermal management capabilities to ensure stable operation and extend service life.

[0009] In summary, although the existing technology has made some progress in solving the problem of external reflected light interference of DFB lasers, there are still many shortcomings such as high cost, complex process, large structure size, etc. How to maintain the excellent performance of DFB lasers while simplifying the structure design, reducing the manufacturing cost and improving the anti-reflection capability has become an important direction for current research and industrial development. Practical new type content

[0010] The utility model discloses in order to solve above-mentioned problem provides a kind of DFB laser, by forming the ridge waveguide structure of specific shape in waveguide layer, effectively reduce the light quantity reflected back into laser cavity, while improve the quality of output beam.This design not only reduces the dependence on additional optical isolator, reduces the overall cost and manufacturing complexity of relative docking scheme, also improves the stability and reliability of laser, with significant technical and economic advantages.

[0011] A DFB laser includes a substrate, a quantum well active layer, a grating layer, and a waveguide layer stacked in order. Two spaced grooves are formed on the waveguide layer, and a ridge waveguide is formed between the grooves. The ridge waveguide includes a vertical waveguide and a trapezoidal waveguide. The vertical waveguide and the trapezoidal waveguide have the same thickness, and the top surface of the vertical waveguide and the top surface of the trapezoidal waveguide are in the same plane. The vertical waveguide is perpendicular to the front end surface of the DFB laser, and the trapezoidal waveguide has an inclination angle with respect to the front end surface of the DFB laser. From a top view, the trapezoidal waveguide has a trapezoidal shape, and the vertical waveguide has a rectangular shape. The lower base of the trapezoid is located on the front end surface of the DFB laser, the upper base of the trapezoid is connected to the short side of the rectangle, the length of the upper base of the trapezoid is equal to the length of the short side of the rectangle, and the ratio of the length of the lower base of the trapezoid to the length of the short side of the rectangle is M, where 1 < M ≤ 4.

[0012] Further, from a top view, the trapezoidal waveguide is an isosceles trapezoid.

[0013] Further, the angle of the bottom corner of the trapezoidal waveguide ranges from 60° to 89°.

[0014] Further, the length of the trapezoidal waveguide ranges from 10 μm to 150 μm.

[0015] Further, the thickness of the waveguide layer ranges from 1 μm to 3 μm.

[0016] Further, the DFB laser further includes an N-face electrode, a buffer layer, a lower confinement layer, an upper confinement layer, a passivation layer, and a P-face electrode. The N-face electrode is located on the side of the substrate away from the lower confinement layer. The buffer layer is located between the substrate and the lower confinement layer. The quantum well active layer is located between the lower confinement layer and the upper confinement layer. The passivation layer covers the waveguide layer and forms an opening at the ridge waveguide. The P-face electrode is located on the passivation layer and connected to the ridge waveguide through the opening of the passivation layer.

[0017] Further, the material of the passivation layer is silicon dioxide or silicon nitride.

[0018] Further, the DFB laser further includes an etching stop layer located between the waveguide layer and the grating layer.

[0019] Further, an anti-reflection film is coated on the front end surface of the DFB laser, and a high-reflection film is coated on the rear end surface of the DFB laser.

[0020] Further, the DFB laser is applied to optical communication, laser radar and optical sensing.

[0021] The utility model has the following advantages:

[0022] 1、Reduce the reflection light coupling: effectively reduce the possibility of external reflection light into the laser cavity;

[0023] 2、Improve the beam quality: the mode size of output beam increases, and the divergence angle decreases, which is beneficial to subsequent optical coupling;

[0024] 3、Process and simple structure: the process is consistent with conventional RW type (ridge waveguide) DFB, and the structure does not need complex additional devices, and the integration degree is high. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the structural diagram of the utility model Figure 1 ;

[0026] Figure 2 It is the schematic view of the ridge waveguide of the utility model;

[0027] Figure 3 It is the structural diagram of the utility model Figure 2 ;

[0028] Figure 4 It is the structural diagram of another embodiment of the utility model.

[0029] REFERENCE NUMERALS

[0030] Substrate 1 Buffer layer 2 Lower confinement layer 3 Quantum well active layer 4 Upper confinement layer 5

[0031] Grating layer 6 Waveguide layer 7 Vertical waveguide 71 Trapezoidal waveguide 72

[0032] N-face electrode 91 Passivation layer 8 P-face electrode 92 Anti-reflection film AR 93 Reflection film HR 94 DETAILED DESCRIPTION

[0033] The utility model will be further described in detail below in combination with the drawings and specific embodiments. It needs to be explained here that if the terms "upper", "lower", "inner", "outer" and other orientation or position relationship appear, it is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship of the product of the application when it is usually placed, which is only for the convenience of description, and cannot be understood as the limitation of the utility model. The technical features involved in each embodiment of the utility model described below can be combined with each other as long as they do not conflict with each other.

[0034] The utility model discloses a kind of distributed feedback (DFB) lasers of optimized structure, to improve the performance and reliability of laser. As shown inFigure 1 and Figure 3 As shown in the preferred embodiment of the utility model, it comprises substrate 1, quantum well active layer 4, grating layer 6 and waveguide layer 7 which are stacked in sequence, and each layer plays a key role in the overall structure. The thickness of waveguide layer 7 ranges from 1 μm to 3 μm to optimize the performance of optical waveguide and heat management. The period accuracy error of grating layer 6 is not more than ± 0.2 nm to ensure the accuracy of the working wavelength of the laser.

[0035] On waveguide layer 7, two spaced grooves are formed by precision machining, and in this embodiment, the grooves are formed by etching waveguide layer 7, and the sidewalls of the grooves are perpendicular to substrate 1. The ridges between the grooves form ridge waveguides, as shown in Figure 2 and Figure 3 As shown in the preferred embodiment of the utility model, it comprises substrate 1, quantum well active layer 4, grating layer 6 and waveguide layer 7 which are stacked in sequence, and each layer plays a key role in the overall structure. The thickness of waveguide layer 7 ranges from 1 μm to 3 μm to optimize the performance of optical waveguide and heat management. The period accuracy error of grating layer 6 is not more than ± 0.2 nm to ensure the accuracy of the working wavelength of the laser.

[0036] From the top view, the shape of trapezoidal waveguide 72 presents a trapezoidal shape, and the shape of vertical waveguide 71 presents a rectangular shape. In the specific design, the lower base of the trapezoidal waveguide is located on the front end face of the DFB laser to ensure the effective input and guidance of light energy. The upper base of the trapezoid is in close contact with the short side of the rectangle, and the length a of the upper base of the trapezoid is equal to the length d of the short side of the rectangle, i.e. a = d. The ratio of the length b of the lower base of the trapezoid to the length d of the short side of the rectangle is M, and 1 < M ≤ 4. This geometric proportion design not only ensures the stability of the ridge waveguide, but also optimizes the performance of the laser.

[0037] A section of trapezoidal waveguide is integrated at the output end of the DFB laser, so that the waveguide width gradually expands from the standard size of the active region to a larger size. Moreover, by adjusting the length and expansion angle of the trapezoidal waveguide, the expansion degree of the mode size is controlled to ensure that the coupling efficiency of the reflected light is minimized.

[0038] Further, from the top view, the trapezoidal waveguide 72 is an isosceles trapezoid. Designing the trapezoidal waveguide 72 into an isosceles trapezoidal shape makes the mode more controllable and symmetrical, and is less likely to produce high-order distorted modes. Of course, if there is a special coupling requirement or adjustment requirement of the light output direction, it is also possible to make it into a non-isosceles trapezoidal shape, such as Figure 4 as shown, for example, a right trapezoid, to meet the needs of customers.

[0039] Furthermore, the angle range of the base angle A of the trapezoidal waveguide 72 is 60° to 89°.

[0040] Furthermore, the length c of the trapezoidal waveguide 72 is 10–150 μm. The introduction of the trapezoidal (gradually narrowing) band can reduce the divergence angle, improve the quality of light speed, and reduce the amount of external reflections entering the waveguide.

[0041] Preferably, in this embodiment, the ratio of the length b of the lower base of the trapezoid to the length d of the shorter side of the rectangle is M, where 1.1 ≤ M ≤ 3. For example, a = d = 2 nm, b = 4 nm, and M = 2. In this case, the effects of reducing the divergence angle, improving the quality of light speed, and reducing the amount of external light reflection entering the body are optimal.

[0042] Furthermore, it also includes an N-side electrode 91, a buffer layer 2, a lower confinement layer 3, an upper confinement layer 5, a passivation layer 8, and a P-side electrode 92. The N-side electrode 91 is located on the back side of the substrate 1 (i.e., the side away from the lower confinement layer 3). The buffer layer 2 is stacked on the substrate 1 and is located between the substrate 1 and the lower confinement layer 3. The quantum well active layer 4 is located between the lower confinement layer 3 and the upper confinement layer 5. The passivation layer 8 covers the waveguide layer 7 and forms an opening at the ridge waveguide (i.e., the ridge waveguide metal contact window). The P-side electrode 92 is located on the passivation layer 8 and is connected to the ridge waveguide through the opening of the passivation layer 8.

[0043] Furthermore, the passivation layer 8 is made of silicon dioxide or silicon nitride. The function of the passivation layer 8 is to prevent the influence of environmental moisture on the chip, improve its airtightness, resist moisture and oxidation corrosion, improve ESD level, reduce electrode capacitance, and enhance bandwidth characteristics.

[0044] Furthermore, it also includes an etch stop layer 75, which is located between the waveguide layer 7 and the grating layer 6. The function of the etch stop layer 75 is to prevent the grating layer 6 from being etched during the fabrication of the ridge waveguide and the etching of the waveguide layer 7.

[0045] Furthermore, such as Figure 3 As shown, an anti-reflection film (AR film) is coated on the front end of the DFB laser, and a high-reflection film (HR film) is coated on the rear end. The AR film allows light to be efficiently output from the front end, while the HR film reflects light from the other end, avoiding light energy loss, achieving directional unidirectional laser output, improving optical power utilization, suppressing mode jumps caused by crystal plane reflection, improving the mode stability of the laser, and improving the temperature and linewidth characteristics of the laser.

[0046] The application provides a preparation method of a DFB laser, comprising the following steps: providing a substrate 1, sequentially manufacturing a buffer layer 2, a lower limiting layer 3, a quantum well active layer 4, an upper limiting layer 5 and a grating layer 6 on the substrate 1; manufacturing a grating structure on the grating layer 6; manufacturing an etching stop layer 75 and a waveguide layer 7 on the grating structure; etching two spaced grooves on the waveguide layer 7 to form a ridge waveguide between the grooves, wherein the ridge waveguide comprises a vertical waveguide 71 and a trapezoidal waveguide 72; covering a silicon dioxide layer (i.e. a passivation layer 8) on the waveguide layer 7; and manufacturing a ridge waveguide metal contact window on the waveguide layer 7. The ridge waveguide metal contact window is formed by etching the silicon dioxide layer above the ridge waveguide, a P-face electrode 92 is located on the silicon dioxide layer and connected with the ridge waveguide through the ridge waveguide metal contact window, and an N-face electrode 91 is manufactured on the back of the substrate 1. Therefore, the structure is compatible with the existing process, can be realized by using a conventional semiconductor processing process, is feasible, and will not significantly increase the complexity and cost of chip manufacturing.

[0047] In the case of a conventional vertical waveguide, the external reflected light will return along the original path, with a high spatial overlap and phase matching with the waveguide mode, thus the coupling efficiency is high, resulting in more reflected light entering the laser cavity. The expanded mode size corresponds to a smaller divergence angle, making it more difficult for the reflected light to be recaptured by the waveguide. The present application expands the mode size through the trapezoidal waveguide, resulting in a decrease in the numerical aperture NA:

[0048]

[0049] wherein:

[0050] n eff is the effective refractive index, θ is the divergence angle (half angle), and w is the mode radius.

[0051] The increase in the mode radius w results in a decrease in the NA and the divergence angle θ, making it more difficult for the reflected light to be coupled back into the waveguide fundamental mode with a narrow mode size.

[0052] Through the above structural design, the DFB laser of the present application exhibits significant advantages in multiple aspects. First, the combination of the trapezoidal waveguide 72 and the vertical waveguide 71 effectively reduces the amount of light reflected back into the laser, reducing internal feedback and thus improving the stability and reliability of the laser. Second, the optimized waveguide structure improves the output beam quality of the laser, specifically manifested in the reduction of the divergence angle and the decrease in the light intensity density at the output end. This not only improves the focusing performance of the laser beam, but also reduces the potential damage risk to external equipment and the environment. In addition, the reduced light intensity density enables the laser to better adapt to the demand for high power density in practical applications, prolongs the service life of the equipment, and reduces the negative effects of thermal effects.

[0053] In general, the DFB laser device has the advantages of wide application prospect and market value, and can be applied to optical communication, laser radar, optical sensing and other application fields requiring high-quality laser output.

[0054] The above is only a preferred embodiment of the present application, and does not limit the technical scope of the present application in any way. Any changes or modifications made in accordance with the claims and description of the present application shall fall within the scope of the present application.

Claims

1. A DFB laser characterized by: The DFB laser includes a substrate, a quantum well active layer, a grating layer and a waveguide layer which are stacked in sequence, two spaced grooves are formed on the waveguide layer, a ridge waveguide is formed between the grooves, the ridge waveguide includes a vertical waveguide and a trapezoidal waveguide, the vertical waveguide and the trapezoidal waveguide have the same thickness, and the top surface of the vertical waveguide and the top surface of the trapezoidal waveguide are in the same plane, the vertical waveguide is perpendicular to the front end surface of the DFB laser, and the trapezoidal waveguide has an inclination angle relative to the front end surface of the DFB laser, as viewed from above, the trapezoidal waveguide has a trapezoidal shape, and the vertical waveguide has a rectangular shape, the lower base of the trapezoid is located on the front end surface of the DFB laser, the upper base of the trapezoid is connected to the short side of the rectangle, the length of the upper base of the trapezoid is equal to the length of the short side of the rectangle, and the ratio of the length of the lower base of the trapezoid to the length of the short side of the rectangle is M, wherein 1 < M ≤ 4.

2. The DFB laser of claim 1, wherein: As viewed from above, the trapezoidal waveguide is an isosceles trapezoid.

3. The DFB laser of claim 1, wherein: The bottom angle of the trapezoidal waveguide ranges from 60° to 89°.

4. The DFB laser of claim 1, wherein: The length of the trapezoidal waveguide ranges from 10 μm to 150 μm.

5. The DFB laser of claim 1, wherein: The thickness of the waveguide layer ranges from 1 μm to 3 μm.

6. The DFB laser of claim 1, wherein: The DFB laser further includes an N-face electrode, a buffer layer, a lower confinement layer, an upper confinement layer, a passivation layer and a P-face electrode, the N-face electrode is located on the side of the substrate away from the lower confinement layer, the buffer layer is located between the substrate and the lower confinement layer, the quantum well active layer is located between the lower confinement layer and the upper confinement layer, the passivation layer covers the waveguide layer and forms an opening at the ridge waveguide, and the P-face electrode is located on the passivation layer and connected to the ridge waveguide through the opening of the passivation layer.

7. The DFB laser of claim 6, wherein: The passivation layer is made of silicon dioxide or silicon nitride.

8. The DFB laser of claim 1, wherein: The DFB laser further includes an etching stop layer, which is located between the waveguide layer and the grating layer.

9. The DFB laser of claim 1, wherein: An anti-reflection film is coated on the front end surface of the DFB laser, and a high-reflection film is coated on the rear end surface of the DFB laser.

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