A DFB laser and wafer
By designing vertical and curved waveguide structures and anti-reflection films in DFB lasers and optimizing the tilt angle, the instability problem caused by external reflected light was solved, achieving low-cost and efficient suppression of reflected light and improvement of mode stability.
Patent Information
- Application Number
- CN202422929988.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-11-28
- Estimated Expiration
- 2034-11-29
AI Technical Summary
External reflected light entering the DFB laser cavity causes instability, affecting output power and mode. Traditional optical isolators increase cost and complexity.
Design vertical and curved waveguide structures for DFB lasers, combine anti-reflection and high-reflection films, optimize waveguide tilt angles to reduce reflected light coupling, and employ misaligned waveguide structures to simplify the manufacturing process.
It effectively reduces reflected light coupling, simplifies the process flow, reduces costs, improves the stability and optical power utilization of lasers, and reduces mode switching.
Smart Images
Figure CN223612846U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to semiconductor laser technology field especially relates to a DFB laser and wafer. BACKGROUND
[0002] DFB (Distributed Feedback Laser) laser, namely distributed feedback laser, has become an indispensable key component in modern optical communication systems due to its single-mode output, narrow linewidth, high power stability and compact structure and other advantages. However, the entry of external reflected light into the laser cavity can cause instability, such as output power fluctuation, mode jump, linewidth broadening and the like. These external reflected lights can interact with the optical field inside the laser, interfere with the original working state of the laser, thereby affecting the mode, power and eye diagram of the laser output, and affecting the transmission of the system. Therefore, weakening the entry of external reflection into the waveguide is crucial for maintaining the stable operation of the laser.
[0003] The traditional solution is to add an optical isolator inside the packaged device, thereby avoiding the disturbance of reflected light to the working state of the laser. However, with the rapid popularization and promotion of optical communication networks, higher demands are put forward for the cost of devices, and on the basis of traditional devices, it is required to further remove the isolator to reduce the cost of packaged devices, which requires the laser chip to have higher anti-reflection capability. SUMMARY
[0004] The utility model discloses in order to solve above-mentioned problem, provide a kind of DFB laser and wafer, can play the effect of anti-reflection and remove isolator, and will not significantly increase the complexity and cost of chip manufacturing.
[0005] A kind of DFB laser, including substrate, quantum well active layer, grating layer and waveguide layer stacked in sequence, two spaced recesses are formed on waveguide layer, and ridge waveguide is formed between recess, ridge waveguide includes vertical waveguide perpendicular to the light emitting end face of DFB laser and curved waveguide with inclination angle relative to the light emitting end face of DFB laser, vertical waveguide and curved waveguide are connected, curved waveguide is close to the light emitting end face side of DFB laser, the included angle of curved waveguide inclination angle is 5 ° ~ 35 °, and the length of curved waveguide is 10 μm ~ 150 μm.
[0006] Further, it further includes N electrode, buffer layer, lower limit layer, upper limit layer, passivation layer and P electrode, N electrode is located in the substrate far from the lower limit layer side, buffer layer is located between substrate and lower limit layer, quantum well active layer is located between lower limit layer and upper limit layer, passivation layer covers waveguide layer, and forms opening at ridge waveguide, and P electrode is located on passivation layer and is connected with ridge waveguide through the opening of passivation layer.
[0007] Further, the material of the passivation layer is silicon dioxide or silicon nitride.
[0008] Further, an anti-reflection film is coated on the light emitting end face, and a high reflection film is coated on the other end face far from the light emitting end face.
[0009] Further, an etching stop layer is further included, and the etching stop layer is located between the waveguide layer and the grating layer.
[0010] Further, the length of the curved waveguide is 50-80 μm.
[0011] Further, the ridge waveguide further includes a staggered waveguide structure, and the staggered waveguide is a straight waveguide and an inclined waveguide, the straight waveguide is located on the side close to the light emitting end face of the DFB laser, and the inclined waveguide is located on the other side far from the light emitting end face of the DFB laser.
[0012] Further, the straight waveguide and the vertical waveguide are on the same straight line.
[0013] Further, the curved waveguide is gradually curved along the light emitting direction.
[0014] A wafer, a plurality of DFB laser arrays are arranged, the DFB laser includes a substrate, a lower limiting layer, a quantum well active layer, an upper limiting layer, a grating layer and a waveguide layer which are sequentially stacked, two spaced grooves are formed on the waveguide layer, a ridge waveguide is formed between the grooves, the ridge waveguide includes a vertical waveguide perpendicular to the light emitting end face of the DFB laser and a curved waveguide with an inclination angle relative to the light emitting end face of the DFB laser, the vertical waveguide and the curved waveguide are connected, the curved waveguide is located on the side close to the light emitting end face of the DFB laser, and the included angle of the inclination angle of the curved waveguide is 5-35°; the DFB laser further includes a staggered waveguide structure, the staggered waveguide is a straight waveguide and an inclined waveguide, the straight waveguide is located on the side close to the light emitting end face of the DFB laser, and the inclined waveguide is located on the other side far from the light emitting end face of the DFB laser; along the light emitting direction, at the connection of the adjacent two DFB lasers, the straight waveguide of one DFB laser is connected with the vertical waveguide of the other DFB laser, and the curved waveguide of one DFB laser is connected with the inclined waveguide of the other DFB laser.
[0015] The utility model has the following advantages:
[0016] 1, reduce the reflection light coupling: effectively reduce the possibility of external reflection light into the laser cavity;
[0017] 2, process and simple structure: the process is consistent with conventional RW type (ridge waveguide) DFB, the structure does not need complicated additional device, and the integration degree is high. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 It is the structure diagram of the utility model Figure One ;
[0019] Figure 2 is a top view of the ridge waveguide of the utility model;
[0020] Figure 3 is a local schematic view of the utility model before wafer splitting;
[0021] Figure 4 is a structural schematic view of the utility model Figure Two .
[0022] Reference signs
[0023] Substrate 1 Buffer layer 2 Lower confinement layer 3 Quantum well active layer 4 Upper confinement layer 5
[0024] Grating layer 6 Waveguide layer 7 Vertical waveguide 71 Curved waveguide 72 Straight waveguide 73
[0025] Oblique waveguide 74 Etching stop layer 75 N-face electrode 91 Passivation layer 8 P-face electrode 92
[0026] Anti-reflection film 93 High-reflection film 94. DETAILED DESCRIPTION
[0027] The utility model will be further described 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 when the product of the application is used, which is only for the convenience of description, and cannot be understood as a limitation on 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.
[0028] The utility model discloses a DFB laser, as shown in Figure 1 and Figure 4 The preferred embodiment of the utility model comprises substrate 1, lower confinement layer 3, quantum well active layer 4, upper confinement layer 5, grating layer 6 and waveguide layer 7 which are stacked in sequence, two spaced grooves are formed on the waveguide layer 7 by etching, and a ridge waveguide is formed between the grooves, as shown in Figure 2 The ridge waveguide comprises vertical waveguide 71 and curved waveguide 72, the vertical waveguide 71 is perpendicular to the light-emitting end face of the DFB laser, the curved waveguide 72 has an inclination angle θ relative to the light-emitting end face of the DFB laser, the inclination angle θ specifically refers to the included angle between the tangent at the intersection of the curved waveguide and the normal of the light-emitting end face, the vertical waveguide 71 and the curved waveguide 72 are connected, the curved waveguide 72 is close to the light-emitting end face side of the DFB laser, the included angle of the inclination angle θ of the curved waveguide 72 is 5 ° ~ 35 °, and the curved waveguide 72 makes the coupling efficiency of external reflected light e -(sinθ)2The reflected light is reduced by optimizing the design of the waveguide tilt angle θ.
[0029] The length of the curved waveguide 72 is 10 μm to 150 μm. The curved waveguide 72 is designed to reduce the coupling efficiency of the external reflected light into the waveguide, while maintaining the design of the vertical waveguide 71 to increase the resonance feedback and mode selection effect. Preferably, the length of the curved waveguide 72 is 50 μm to 80 μm. When the tilt angle is fixed, the shorter the curved waveguide 72, the smaller the bending radius, which will result in greater loss. Since the length of the curved waveguide 72 is proportional to the chip size and manufacturing cost, and the feedback and mode selection effect of the vertical waveguide 71 is relatively weak, the length of the curved waveguide 72 needs to be considered and optimized comprehensively.
[0030] Further, it further includes an N-face electrode 91, a buffer layer 2, a passivation layer 8, and a P-face electrode 92. The N-face electrode 91 is located on the back 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 located between the substrate 1 and the lower confinement layer 3. The passivation layer 8 covers the waveguide layer 7 and forms an opening (i.e., a ridge waveguide metal contact window) at the ridge waveguide. The P-face electrode 92 is located on the passivation layer 8 and connected to the ridge waveguide through the opening of the passivation layer 8.
[0031] Further, it further includes an etching stop layer 75 located between the waveguide layer 7 and the grating layer 6. The etching stop layer 75 serves to prevent etching to the grating layer 6 during the process of etching the waveguide layer 7 to form the ridge waveguide.
[0032] Further, an anti-reflection film (AR film for short) is coated on the light-emitting end face, and a high-reflection film (HR film for short) is coated on the other end face away from the light-emitting end face. The AR film allows efficient output of light from the light-emitting end face, and the HR film reflects light from the other end face to avoid loss of light energy, thereby achieving directional unidirectional output of laser, improving the utilization rate of optical power, suppressing mode hopping caused by crystal face reflection, improving the mode stability of the laser, and improving the temperature characteristics and linewidth characteristics of the laser.
[0033] Further, the material of the passivation layer 8 can be silicon dioxide or silicon nitride. The passivation layer 8 serves to improve air tightness, resist water vapor and oxidation corrosion, improve ESD level, reduce electrode capacitance, and improve bandwidth characteristics.
[0034] Further, it further includes a misaligned waveguide structure, which is a straight waveguide 73 and an inclined waveguide 74. The straight waveguide 73 is located on the side of the light-emitting end face of the DFB laser, and the inclined waveguide 74 is located on the other side away from the light-emitting end face of the DFB laser. The waveguides at the HR / AR end are designed to extend, thereby avoiding design failure caused by process deviation.
[0035] Furthermore, the straight waveguide 73 and the vertical waveguide 71 are aligned on the same straight line, which simplifies the manufacturing process and reduces costs.
[0036] Furthermore, the curved waveguide 72 is gradually curved along the light output direction to avoid abrupt changes in the waveguide, which would cause coupling transmission loss and affect device performance.
[0037] This application provides a method for fabricating a DFB laser, comprising: providing a substrate 1, and sequentially fabricating a buffer layer 2, a lower confinement layer 3, a quantum well active layer 4, an upper confinement layer 5, and a grating layer 6 on the substrate 1; fabricating a grating structure on the grating layer 6; fabricating an etch stop layer 75 and a waveguide layer 7 on the grating structure; etching two spaced grooves on the waveguide layer 7, forming a ridge waveguide between the grooves, the ridge waveguide including a vertical waveguide 71, a curved waveguide 72, a straight waveguide 73, and a slanted waveguide 74; covering the waveguide layer 7 with a silicon dioxide layer (i.e., a passivation layer 8); fabricating a ridge waveguide metal contact window on the waveguide layer 7; the ridge waveguide metal contact window being formed by etching the silicon dioxide layer above the ridge waveguide; a P-side electrode 92 located on the silicon dioxide layer and connected to the ridge waveguide through the ridge waveguide metal contact window; and fabricating an N-side electrode 91 on the back side of the substrate 1.
[0038] like Figure 3 As shown (the grooves are not shown in the figure for better illustration), a wafer is provided with an array of multiple DFB lasers. Each DFB laser comprises a substrate 1, a lower confinement layer 3, a quantum well active layer 4, an upper confinement layer 5, a grating layer 6, and a waveguide layer 7, stacked sequentially. Two spaced grooves are etched into the waveguide layer 7, forming a ridge waveguide between the grooves. The ridge waveguide includes a vertical waveguide 71 and a bent waveguide 72. The vertical waveguide 71 is perpendicular to the emitting end face of the DFB laser, and the bent waveguide 72 has an angle relative to the emitting end face of the DFB laser. The vertical waveguide 71 and the bent waveguide 72 are connected, and the bent waveguide 72 is close to... On one side of the emitting end face of the DFB laser, the angle of inclination of the bent waveguide 72 is 5° to 35°. The DFB laser also includes a staggered waveguide structure, consisting of a straight waveguide 73 and an oblique waveguide 74. The straight waveguide 73 is located on one side of the emitting end face of the DFB laser, and the oblique waveguide 74 is located on the other side away from the emitting end face. Along the light output direction, at the connection point of two adjacent DFB lasers, the straight waveguide 73 of one DFB laser is connected to the vertical waveguide 71 of another DFB laser, and the bent waveguide 72 of one DFB laser is connected to the oblique waveguide 74 of another DFB laser. During the cleaving process of the DFB laser, due to limitations in process precision, there are cleaving and cleavage errors. If the bent waveguide or vertical waveguide stops precisely at the end face, and cleavage deviation exists, the waveguide will not extend to the end face, affecting the device's output power, coupling efficiency, phase characteristics, waveguide terminal reflection, cleavage surface reflection, etc., which is a necessary design consideration.
[0039] In the case of a conventional vertical waveguide, the external reflected light will return along the original path, with high spatial overlap and phase matching with the waveguide mode, so the coupling efficiency is high, resulting in more reflected light entering the laser cavity. The utility model discloses a waveguide is designed with the normal of end face an angle θ of curved waveguide, so that the propagation direction of reflected light and the mode propagation direction of waveguide are not identical, leading to the spatial misalignment, and the overlap integral reduces, can reduce the efficiency of external reflected light coupling back waveguide.
[0040] Assuming that the waveguide mode is single mode, the mode field distribution is:
[0041] Ψ wg (x,y,z)=χ(x,y)e iβz
[0042] Wherein: χ (x, y) is the transverse mode distribution. β is the propagation constant of waveguide mode.
[0043] After the external reflected light passes through the end face, the electromagnetic field entering the waveguide can be expressed as:
[0044] Ψ refl (x,y,z)=χ refl (x,y)e i(αx+β’z)
[0045] Wherein: χ refl (x,y) is the transverse mode distribution of reflected light.
[0046] α is the wave number component of reflected light in the x direction.
[0047] β' is the wave number component of reflected light in the z direction.
[0048] Then the coupling efficiency η is:
[0049]
[0050] The inclination angle θ causes the reflected light to have a wave number component in the x direction: α=k0n eff sinθ
[0051] Wherein: k0=2π / λ is the wave number in vacuum, n eff is the effective refractive index of waveguide, and λ is the wavelength of light.
[0052] Assuming that the transverse field distribution of waveguide mode and reflected light is Gaussian distribution, the coupling integral becomes:
[0053]
[0054] Solve the integral of Gaussian function and complex exponential function, and finally the expression of coupling efficiency is obtained after simplifying:
[0055]
[0056] The above derivation and calculation show that:
[0057] The curved waveguide makes the coupling efficiency of the external reflected light decrease in the form of e -(sinθ)2 Therefore, the effect of weakening the reflected light can be achieved by optimizing the reasonable waveguide tilt angle θ.
[0058] 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 be 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 which is perpendicular to a light emitting end face of the DFB laser and a curved waveguide which has an inclination angle with respect to the light emitting end face of the DFB laser, the vertical waveguide and the curved waveguide are connected, the curved waveguide is close to one side of the light emitting end face of the DFB laser, the inclination angle of the curved waveguide is 5°-35°, and the length of the curved waveguide is 10μm-150μm.
2. 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 a side of the substrate which is 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.
3. The DFB laser of claim 2, wherein: The passivation layer is made of silicon dioxide or silicon nitride.
4. The DFB laser of claim 1, wherein: An anti-reflection film is coated on the light emitting end face, and a high reflection film is coated on the other end face which is away from the light emitting end face.
5. 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.
6. The DFB laser of claim 1, wherein: The length of the curved waveguide is 50μm-80μm.
7. The DFB laser of claim 1, wherein: The ridge waveguide further includes a staggered waveguide structure, the staggered waveguide includes a straight waveguide and an inclined waveguide, the straight waveguide is close to one side of the light emitting end face of the DFB laser, and the inclined waveguide is located on the other side which is away from the light emitting end face of the DFB laser.
8. The DFB laser of claim 7, wherein: The straight waveguide and the vertical waveguide are in the same straight line.
9. The DFB laser of claim 1, wherein: The curved waveguide is gradually curved along the light emitting direction.
10. A wafer, characterized by: A plurality of DFB lasers are arranged in an array, each of the DFB lasers 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 which is perpendicular to a light emitting end face of the DFB laser and a curved waveguide which has an inclination angle with respect to the light emitting end face of the DFB laser, the vertical waveguide and the curved waveguide are connected, the curved waveguide is close to one side of the light emitting end face of the DFB laser, the inclination angle of the curved waveguide is 5°-35°, and the length of the curved waveguide is 10μm-150μm; each of the DFB lasers further includes a staggered waveguide structure, the staggered waveguide is a straight waveguide and an inclined waveguide, the straight waveguide is close to one side of the light emitting end face of the DFB laser, and the inclined waveguide is located on the other side which is away from the light emitting end face of the DFB laser; and along the light emitting direction, at the connection between two adjacent DFB lasers, the straight waveguide of one DFB laser is connected to the vertical waveguide of the other DFB laser, and the curved waveguide of one DFB laser is connected to the inclined waveguide of the other DFB laser.