A waveguide structure for reducing the reflectivity of the gain chip cavity surface

Abstract

The present invention provides a waveguide structure for reducing the reflectivity of the cavity surface of a gain chip, comprising a substrate, a ridge waveguide, a first groove and a second groove, wherein the ridge waveguide is located above the substrate and has a front cavity surface; the first groove and the second groove are separately arranged on both sides of the ridge waveguide, the first groove and the second groove both have a tapering region, the width of the tapering region gradually decreases in the direction from the first groove to the front cavity surface, the truncated surface of the first groove forms a first angle with the side wall of the ridge waveguide, the truncated surface of the second groove forms a second angle with the side wall of the ridge waveguide, and the first angle and the second angle are both less than 90°. In the present invention, the first groove and the second groove are both provided with a tapering region to truncate the groove, the angle between the truncated surface of the groove and the side wall of the ridge waveguide is less than 90°, and the photons reflected back by the front cavity surface are reflected again away from the waveguide structure after reaching the truncated surface of the groove, and will not enter the interior of the ridge waveguide to form a resonance effect, thereby reducing the generation of spectral ripples.

Description

Technical Field

[0001] The invention belongs to the technical field of gain chips and relates to a waveguide structure for reducing the reflectivity of a cavity surface of a gain chip. Background Art

[0002] Gain chips, including superluminescent diodes and semiconductor optical amplifiers, are an important light source and are widely used in optical imaging, optical communications, optical sensing and other fields. In these applications, gain chips provide high brightness, wide bandwidth and stable light output. The most important indicator of the gain chip and one of the biggest technical difficulties is that the photons generated by the gain chip cannot be reflected by the cavity surface and resonate in the cavity like ordinary lasers to form mode selection-spectral ripples, because the formation of spectral ripples will seriously interfere with the stability of the spectral frequency in subsequent applications of the product. In order to suppress the intracavity resonance of the gain chip and reduce the spectral ripples, the light-emitting cavity surface needs to achieve a reflectivity of less than 1e-4 at the target wavelength. If only the cavity surface coating method is used to achieve this reflectivity, the film thickness control accuracy usually needs to be controlled within 2nm, which is extremely difficult to achieve for the stability of the coating machine and the yield requirements of the product.

[0003] In order to achieve more effective and stable reduction of the spectral ripple of the gain chip, a common method is to use an inclined angle ridge waveguide / end bent waveguide structure so that most of the photons emitted to the cavity surface cannot be reflected back into the waveguide by the cavity surface like ordinary lasers. However, even if this method is used in conjunction with an anti-reflection film on the cavity surface, it is still difficult to control the cavity surface reflectivity within the requirement, and some scattered photons will still be reflected back into the laser waveguide by the cavity surface.

[0004] Therefore, how to provide a waveguide structure that reduces the reflectivity of the gain chip cavity surface to block the photons scattered back by the cavity surface and prevent them from entering the ridge waveguide to form resonance has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a waveguide structure that reduces the reflectivity of the gain chip cavity surface, so as to solve the problem in the prior art that scattered photons are reflected back by the cavity surface into the laser waveguide to generate resonance.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a waveguide structure for reducing the reflectivity of the gain chip cavity surface, comprising:

[0007] substrate;

[0008] A ridge waveguide, wherein the ridge waveguide is located above the substrate in a vertical direction and has a front cavity surface;

[0009] A first groove and a second groove, in the horizontal direction, the first groove and the second groove are separated and arranged on both sides of the ridge waveguide, wherein the first groove and the second groove both have a gradually tapering area, and the width of the gradually tapering area gradually decreases in the direction from the first groove to the front cavity surface, the gradually tapering area truncation surface of the first groove forms a first angle with the side wall of the ridge waveguide, the gradually tapering area truncation surface of the second groove forms a second angle with the side wall of the ridge waveguide, and the first angle and the second angle are both less than 90°.

[0010] Optionally, the first angle and the second angle are equal.

[0011] Optionally, the first angle and the second angle are not equal.

[0012] Optionally, the distance between the truncation surface of the gradually tapering region of the first groove and the front cavity surface is 10-25 μm, and the distance between the truncation surface of the gradually tapering region of the second groove and the front cavity surface is 10-25 μm.

[0013] Optionally, it also includes an ohmic contact layer and a top electrode metal layer. In the vertical direction, the ohmic contact layer is located above the ridge waveguide, and the top electrode metal layer is located above the ohmic contact layer. In the horizontal direction, an ohmic contact removal area is provided between one end of the ohmic contact layer facing the front cavity surface and the front cavity surface, so that the ohmic contact layer is separated from the front cavity surface by a preset distance.

[0014] Optionally, in the horizontal direction, a top electrode removal area is provided between one end of the top electrode metal layer facing the front cavity surface and the front cavity surface, so that the top electrode metal layer is spaced a preset distance from the front cavity surface.

[0015] Optionally, in the horizontal direction, the distance between the top electrode metal layer and the front cavity surface is not less than 10 μm.

[0016] Optionally, the ridge waveguide has a curved structure at one end of the front cavity surface.

[0017] Optionally, the ridge waveguide is a linear structure, and an extension direction of the ridge waveguide forms an angle with a normal direction of the front cavity surface.

[0018] Optionally, a quantum well region layer is provided between the substrate and the ridge waveguide.

[0019] As described above, in the waveguide structure for reducing the reflectivity of the gain chip cavity surface of the present invention, the first groove and the second groove are both provided with a gradually tapering area to truncate the groove, and the angle between the truncation surface of the groove and the side wall of the ridge waveguide is less than 90°. After the photons reflected back by the front cavity surface reach the truncation surface of the groove, they are reflected again away from the waveguide structure, and will not enter the interior of the ridge waveguide to form a resonance effect, thereby reducing the generation of spectral ripples. In addition, an ohmic contact removal area is provided between one end of the ohmic contact layer facing the front cavity surface and the front cavity surface, so that the ohmic contact layer and the front cavity surface are separated by a preset distance, which can prevent the current from leaking from the top electrode of the ridge waveguide through the ohmic contact layer to the front cavity surface when the device is powered on and working, causing device failure; and a top electrode removal area is provided between one end of the top electrode metal layer facing the front cavity surface and the front cavity surface, so that the top electrode metal layer and the front cavity surface are separated by a preset distance, so as to prevent the deformation of the top electrode metal layer from blocking part of the front cavity surface when the cavity surface is dissociated, causing reflection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The cross-sectional view of the waveguide structure for reducing the reflectivity of the gain chip cavity surface according to the present invention is shown.

[0021] Figure 2 It is a schematic longitudinal cross-sectional view of a waveguide structure for reducing the reflectivity of the gain chip cavity surface according to the present invention.

[0022] Figure 3 It is a schematic diagram showing that the first angle and the second angle are set to be unequal in the waveguide structure for reducing the reflectivity of the gain chip cavity surface of the present invention.

[0023] Figure 4 It is a schematic diagram showing the formation of a top electrode removal region in a top electrode metal layer in a waveguide structure for reducing the reflectivity of a gain chip cavity surface according to the present invention.

[0024] Figure 5 It is a schematic diagram showing that the ridge waveguide in the waveguide structure for reducing the reflectivity of the gain chip cavity surface of the present invention adopts an inclined straight waveguide.

[0025] Component number description

[0026] 1 Substrate

[0027] 2 Ridge waveguide

[0028] 3 Anterior cavity surface

[0029] 4 First groove

[0030] 5 Second groove

[0031] 6 Quantum Well Region

[0032] 7 Ohm contact layer

[0033] 70 ohm contact removal area

[0034] 8 Top electrode metal layer

[0035] 80 Top electrode removal area 80

[0036] 9 Insulation layer

[0037] L1, L2 distance DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0040] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first feature and the second feature are formed in direct contact, and may also include embodiments in which additional features are formed between the first feature and the second feature, such that the first feature and the second feature may not be in direct contact.

[0041] See also Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0042] This embodiment provides a waveguide structure that reduces the reflectivity of the gain chip cavity surface. Figure 1 and Figure 2The waveguide structure for reducing the reflectivity of the gain chip cavity surface includes a substrate 1, a ridge waveguide 2, a first groove 3 and a second groove 4. In the vertical direction (Z direction), the ridge waveguide 2 is located above the substrate 1, and the ridge waveguide 2 has a front cavity surface 3; in the horizontal direction (Y direction), the first groove 3 and the second groove 4 are separately arranged on both sides of the ridge waveguide 2, wherein the first groove 3 and the second groove 4 both have a gradually tapering region, and the width of the gradually tapering region gradually decreases in the direction along the first groove 4 pointing to the front cavity surface 3, the gradually tapering region truncation surface of the first groove 4 forms a first angle θ1 with the side wall of the ridge waveguide 2, and the gradually tapering region truncation surface of the second groove 5 forms a second angle θ2 with the side wall of the ridge waveguide 2, and the first angle θ1 and the second angle θ2 are both less than 90°.

[0043] As an example, in this embodiment, the gain chip adopts a superluminescent diode, the front cavity surface 3 is the light output cavity surface, the first groove 4 and the second groove 5 are both provided with a gradually tapering area to truncate the groove, and the angle between the truncation surface of the groove and the side wall of the ridge waveguide 2 is less than 90°. After the photons reflected back by the front cavity surface 3 reach the groove truncation surface, they are reflected again away from the waveguide structure and will not enter the interior of the ridge waveguide 2 to form a resonance effect, thereby reducing the generation of spectral ripples; that is, the present application blocks a small amount of photons scattered back by the front cavity surface 3 through multiple reflections, so that it cannot enter the interior of the ridge waveguide 2 to form resonance.

[0044] Specifically, in this embodiment, the first angle θ1 is equal to the second angle θ2. In other examples, such as Figure 3 As shown, the first angle θ1 and the second angle θ2 may also be set to be unequal, and may be set according to requirements.

[0045] As an example, the angles of the first angle θ1 and the second angle θ2 can be selectively adjusted according to needs. When the angle becomes smaller, more photons reflected back by the front cavity surface 3 will be scattered out of the waveguide structure, and will not enter the ridge waveguide 2 to form a resonance effect, thereby reducing the generation of spectral ripples; however, reducing the angle formed by the groove cross-section and the side wall of the ridge waveguide 2 will reduce the coupling efficiency of the main mode photons transmitted from the cavity surface into the ridge waveguide 2 to a certain extent, resulting in certain optical losses. Therefore, the angle between the groove cross-section and the ridge waveguide 2 is set according to needs.

[0046] As an example, the distance between the gradually tapering section of the first groove 4 and the front cavity surface 3 is 10-25μm, and the distance between the gradually tapering section of the second groove 5 and the front cavity surface 3 is 10-25μm. The larger the distance between the groove section and the front cavity surface 3, the more photons reflected by the front cavity surface 3 will scatter out of the waveguide structure instead of entering the ridge waveguide 2 to form a resonance effect, thereby reducing the generation of spectral ripples. However, increasing the distance between the groove section and the front cavity surface 3 will cause certain optical losses when photons are transmitted in the ridge waveguide 2. Therefore, the distance between the groove section and the front cavity surface 3 is set according to demand.

[0047] As an example, the substrate 1 includes a silicon substrate, an SOI substrate, a silicon carbide substrate, a sapphire substrate, a gallium nitride substrate or any other suitable substrate, wherein a quantum well region layer 6 is also arranged between the substrate 1 and the ridge waveguide 2, and the quantum well region layer 6 serves as an active region of the device, provides sufficient optical gain, and determines the lasing wavelength of the device and the service life of the device.

[0048] As an example, a waveguide material layer is formed on the quantum well region layer 6 by an epitaxial growth method, and then the waveguide material layer is etched to form the first groove 4 and the second groove 5, and the structure between the first groove 4 and the second groove 5 serves as the ridge waveguide 2. Specifically, the first groove 4 and the second groove 5 can be formed by etching by dry etching or wet etching. If dry etching is used, the etching depth accuracy of the first groove 4 and the second groove 5 is less than or equal to 100nm, that is, the depth accuracy of the ridge waveguide 2 is less than or equal to 100nm, and the side wall verticality of the ridge waveguide 2 is 90°±2°; if wet etching is used, a wet etching stop layer is reserved at a suitable depth in the epitaxial growth stage, and the side wall verticality of the ridge waveguide 2 is required to be 90°±2° in wet etching.

[0049] As an example, an ohmic contact layer 7 and a top electrode metal layer 8 are also included. In the vertical direction (Z direction), the ohmic contact layer 7 is located above the ridge waveguide 2, and the top electrode metal layer 8 is located above the ohmic contact layer 7. In the horizontal direction (X direction), an ohmic contact removal area 70 is provided between one end of the ohmic contact layer 7 facing the front cavity surface 3 and the front cavity surface 3, so that the ohmic contact layer 7 is spaced a preset distance from the front cavity surface 3. The ohmic contact layer 7 is a high P-type doped layer, which is used to form an ohmic contact with the top electrode metal layer 8.

[0050] As an example, an insulating layer 9 is provided at the ohmic contact removal area 70, that is, a portion of the top electrode metal layer 8 is in contact with the ohmic contact layer 7, and another portion of the top electrode metal layer 8 is in contact with the insulating layer 9. In the area close to the front cavity surface 3, the top electrode metal layer 8 is isolated from the ridge waveguide 2 by the insulating layer 9, forming a current blocking structure to prevent the current from leaking from the top electrode of the ridge waveguide 2 through the ohmic contact layer 7 to the front cavity surface 3 when the device is powered on, thereby causing device failure.

[0051] Specifically, in this embodiment, the ohmic contact layer 7 is formed by an epitaxial growth method, and then the local area where the ohmic contact layer 7 contacts the front cavity surface 3 is etched away to form the ohmic contact removal area 70, and the ohmic contact removal area 70 is filled with the insulating layer 9, and then the top electrode metal layer 8 is formed. That is, by removing the high P-type doping layer in the local area of ​​the front cavity surface by etching, leakage can be effectively prevented and the stability and reliability of the device can be improved.

[0052] As an example, the distance L1 between the ohmic contact layer 7 and the front cavity surface 3 is not less than 20 μm to achieve a better current blocking effect.

[0053] As an example, further, Figure 4 As shown, in the horizontal direction (X direction), a top electrode removal area 80 is provided between one end of the top electrode metal layer 8 facing the front cavity surface 3 and the front cavity surface 3, so that the top electrode metal layer 8 is separated from the front cavity surface 3 by a preset distance, so as to prevent the top electrode metal layer 8 from deforming and blocking part of the front cavity surface 3 to cause reflection when the cavity surface is dissociated.

[0054] Specifically, in this embodiment, the distance L2 between the top electrode metal layer 8 and the front cavity surface 3 is not less than 10 μm, so as to meet the precision margin requirement of cavity surface dissociation during device process processing, and prevent the cavity surface from deviating from the top electrode removal area 80 during cavity surface dissociation due to excessive cavity surface dissociation position error.

[0055] As an example, the top electrode metal layer 8 can be manufactured by a metal stripping method. A negative photoresist is used to form a photoresist layer and pattern it. Metal growth and wet stripping are performed based on the patterned photoresist layer to obtain the top electrode metal layer 8. After the negative photoresist is developed, an inverted trapezoidal structure is formed to facilitate subsequent metal stripping. The difference between the upper and lower surfaces of the inverted trapezoidal structure is measured to be between 2μm±0.3μm.

[0056] As an example, in this embodiment, the gain chip adopts a superluminescent diode, one side of the cavity surface is an anti-reflection structure, and the other side of the cavity surface is a high-reflection structure, that is, the ridge waveguide 2 has a curved structure at one end of the front cavity surface 3 to reduce the reflection of photons directed to the front cavity surface 3 back into the waveguide, thereby improving the anti-reflection capability, and the other end of the ridge waveguide 2 is a high-reflection structure, and the other end of the ridge waveguide 2 is a straight structure. In another example, Figure 5 As shown, the gain chip adopts a semiconductor optical amplifier, and the cavity surfaces on both sides are anti-reflection structures. The ridge waveguide 2 is a linear structure, and the extension direction of the ridge waveguide 2 has an angle with the normal direction of the front cavity surface 3 (inclined intersection ridge waveguide) to reduce the reflection of photons incident on the cavity surface back into the waveguide, wherein both ends of the ridge waveguide 2 are provided with a gradually tapering area, and both ends of the ridge waveguide 2 are provided with an ohmic contact removal area 70 and the top electrode removal layer 80.

[0057] In summary, in the waveguide structure for reducing the reflectivity of the gain chip cavity surface of the present invention, the first groove and the second groove are both provided with a gradually tapering area to truncate the groove, and the angle between the truncation surface of the groove and the side wall of the ridge waveguide is less than 90°. After the photons reflected back by the front cavity surface reach the truncation surface of the groove, they are reflected again away from the waveguide structure, and will not enter the interior of the ridge waveguide to form a resonance effect, thereby reducing the generation of spectral ripples. In addition, an ohmic contact removal area is provided between one end of the ohmic contact layer facing the front cavity surface and the front cavity surface, so that the ohmic contact layer and the front cavity surface are separated by a preset distance, which can prevent the current from leaking from the top electrode of the ridge waveguide through the ohmic contact layer to the front cavity surface when the device is powered on and working, causing device failure; and a top electrode removal area is provided between one end of the top electrode metal layer facing the front cavity surface and the front cavity surface, so that the top electrode metal layer and the front cavity surface are separated by a preset distance, preventing the top electrode metal layer from deforming and blocking part of the front cavity surface when the cavity surface is dissociated to bring reflection. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A waveguide structure for reducing the reflectivity of a gain chip cavity surface, characterized in that: include: substrate; A ridge waveguide, wherein the ridge waveguide is located above the substrate in a vertical direction and has a front cavity surface; A first groove and a second groove, in a horizontal direction, the first groove and the second groove are separately arranged on both sides of the ridge waveguide, wherein the first groove and the second groove both have a gradually tapering region, and in a direction from the first groove to the front cavity surface, the width of the gradually tapering region gradually decreases, a truncated surface of the gradually tapering region of the first groove forms a first angle with a sidewall of the ridge waveguide, a truncated surface of the gradually tapering region of the second groove forms a second angle with the sidewall of the ridge waveguide, and the first angle and the second angle are both less than 90°; An ohmic contact layer and a top electrode metal layer, in the vertical direction, the ohmic contact layer is located above the ridge waveguide, and the top electrode metal layer is located above the ohmic contact layer, and in the horizontal direction, an ohmic contact removal area is provided between one end of the ohmic contact layer facing the front cavity surface and the front cavity surface, so that the ohmic contact layer is spaced a preset distance from the front cavity surface.

2. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: The first angle is equal to the second angle.

3. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: The first angle and the second angle are not equal.

4. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: The distance between the truncation surface of the gradually tapering area of ​​the first groove and the front cavity surface is 10-25 μm, and the distance between the truncation surface of the gradually tapering area of ​​the second groove and the front cavity surface is 10-25 μm.

5. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: In the horizontal direction, a top electrode removal area is arranged between one end of the top electrode metal layer facing the front cavity surface and the front cavity surface, so that the top electrode metal layer is spaced a preset distance from the front cavity surface.

6. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 5, characterized in that: In the horizontal direction, the distance between the top electrode metal layer and the front cavity surface is not less than 10 μm.

7. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: The ridge waveguide has a curved structure at one end of the front cavity surface.

8. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to claim 1, characterized in that: The ridge waveguide is a linear structure, and an extending direction of the ridge waveguide forms an angle with a normal direction of the front cavity surface.

9. The waveguide structure for reducing the reflectivity of the gain chip cavity surface according to any one of claims 1 to 8, characterized in that: A quantum well region layer is arranged between the substrate and the ridge waveguide.

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