A vertical-cavity surface-emitting laser and its fiber coupling system

Abstract

This application discloses a vertical-cavity surface-emitting laser (VCSEL) and an optical fiber coupling system. The VCSEL includes a first reflector layer, an oxide layer, and an active layer stacked together. The first reflector layer includes a grating region, which comprises a first grating portion and a second grating portion surrounding the first grating portion. An unoxidized region is formed on the oxide layer, defining a laser emission window located within the orthographic projection range of the first grating portion onto the oxide layer. The VCSEL provided in this application allows external back-reflection interference light sources to refract at the grating region. The emission window partially blocks the refracted light, preventing it from entering the resonant cavity, reducing its impact on the VCSEL's optical field distribution, improving the signal-to-noise ratio, and increasing the transmission rate and distance.

Description

Technical Field

[0001] This application generally relates to the field of optoelectronic technology, and specifically to a vertical cavity surface-emitting laser and an optical fiber coupling system. Background Technology

[0002] With the development of optical communication, semiconductor laser diodes have attracted much attention and development in many fields. Vertical-Cavity Surface-Emitting Lasers (VCSELs) have advantages such as high speed, high integration, and high cost-effectiveness, and are developing rapidly in fields such as short-distance high-speed parallel optical interconnects, Ethernet data communication networks, and data centers. They are one of the new light sources in the field of optical communication.

[0003] In the field of high-speed optical communication, the coupling between lasers and optical fibers is a very important link. During this coupling process, interference from external light will affect the coupling efficiency. Back reflection is generated by any interface or scattering center in the optical network. Back reflection can propagate along the optical path or optical guide and does not need to be emitted from the closest point to the signal source. When the back-reflected optical signal enters the resonant cavity, the change in the resonance condition often causes a large change in the laser output.

[0004] Therefore, finding ways to reduce the impact of interference light has become an urgent problem to be solved in optical coupling. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a vertical cavity surface-emitting laser and fiber coupling system that can improve the laser's anti-interference capability.

[0006] In a first aspect, this application provides a vertical cavity surface-emitting laser, including a first reflector layer, an oxide layer, and an active layer stacked together. The first reflector layer includes a grating region, which includes a first grating portion and a second grating portion disposed around the first grating portion. An unoxidized region is disposed on the oxide layer, which is used to define a laser emission window. The emission window is located within the orthographic projection range of the first grating portion on the oxide layer.

[0007] Furthermore, the phase difference of the first grating portion is less than the phase difference of the second grating portion, and / or the transmission coefficient of the first grating portion is less than the transmission coefficient of the second grating portion, and / or the refractive index of the first grating portion is greater than the refractive index of the second grating portion, and / or the reflectivity of the first grating portion is greater than the reflectivity of the second grating portion.

[0008] Preferably, the grating region comprises a plurality of gratings arranged in a periodic or non-periodic array. Each grating includes a column and a grating slot arranged along the array direction. In the periodic array of gratings, the widths of each grating are equal, and the widths of each column or grating slot are unequal. In the non-periodic array of gratings, the widths of each grating are unequal.

[0009] Preferably, the first grating portion includes a central grating groove and central pillars adjacent to both sides of the central grating groove.

[0010] Preferably, the first grating portion includes a plurality of first grating bodies arranged in a periodic array, and the second grating portion includes a plurality of second grating bodies arranged in a periodic array. The first grating body includes a first grating groove and a first grating bar, and the second grating body includes a second grating groove and a second grating bar. The density of the first grating groove in the first grating portion is less than the density of the second grating groove in the second grating portion.

[0011] Furthermore, the width of the first gate body is greater than the width of the second gate body, the width of the first gate groove is less than the width of the second gate groove, and the width of the first gate bar is greater than the width of the second gate bar.

[0012] Furthermore, the width of the first grid groove is smaller than the width of the first grid bar; the width of the second grid groove is smaller than the width of the second grid bar.

[0013] Furthermore, it also includes a second reflector layer disposed on the side of the active layer away from the oxide layer, wherein the first reflector layer has a first electrode disposed on the side away from the active layer, and the second reflector layer has a second electrode disposed on the side away from the active layer.

[0014] Secondly, this application provides an optical fiber coupling system including a vertical cavity surface-emitting laser as described in any of the above.

[0015] Furthermore, it also includes a total reflection prism configured to receive a laser beam emitted from an exit window and to totally reflect the laser beam onto an optical fiber, wherein the laser beam emitted from the exit window is perpendicular to the direction of the optical fiber.

[0016] The technical solutions provided by the embodiments of this application may include the following beneficial effects:

[0017] The vertical-cavity surface-emitting laser (VCSEL) provided in this application embodiment causes external back-reflection interference light sources to refract at the grating region. The refracted light is partially blocked by the exit window, preventing the backlight from entering the resonant cavity, reducing its impact on the VCSEL's optical field distribution, improving the signal-to-noise ratio, and increasing the transmission rate and distance. Furthermore, by controlling the area of ​​the exit window, the laser's divergence angle is reduced, which helps improve optical coupling efficiency.

[0018] The vertical cavity surface-emitting laser provided in this application embodiment adjusts the refractive index and phase of the grating by designing the grating period and the width of each grating, so as to achieve the effect that external light is difficult to enter the resonant cavity while internal light can be emitted, thereby further improving the anti-interference of the emitted light and further improving the coupling efficiency. Attached Figure Description

[0019] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0020] Figure 1 A schematic diagram of a vertical cavity surface-emitting laser provided for an embodiment of this application;

[0021] Figure 2 A schematic diagram of another vertical-cavity surface-emitting laser provided for an embodiment of this application;

[0022] Figure 3 A schematic diagram of another vertical-cavity surface-emitting laser provided for an embodiment of this application;

[0023] Figure 4 A schematic diagram of another vertical-cavity surface-emitting laser provided for an embodiment of this application;

[0024] Figure 5 A schematic diagram illustrating the working principle of a grating provided for embodiments of this application;

[0025] Figure 6 This is a schematic diagram of the structure of an optical fiber coupling system provided for an embodiment of this application.

[0026] In the picture:

[0027] 1. First reflector layer; 2. Exit window; 3. Grating area; 4. Active layer; 5. Oxide layer; 51. Unoxidized area; 52. Oxidized area; 21. First grating groove; 22. First grating strip; 23. Second grating groove; 24. Second grating strip; 31. First grating section; 32. Second grating section; 6. Second reflector layer; 7. Oxide isolation layer; 8. Current spreading layer; 91. Central grating groove; 92. Central pillar; 10. First electrode; 11. Second electrode; 12. Optical fiber; 13. Total internal reflection prism. Detailed Implementation

[0028] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] Please see details. Figure 1-4 This application provides a vertical cavity surface-emitting laser, including a first reflector layer 1, an oxide layer 5, and an active layer 4 stacked together. The first reflector layer 1 includes a grating region 3, the grating region 3 includes a first grating portion 31 and a second grating portion 32 disposed around the first grating portion 31. An unoxidized region 51 is disposed on the oxide layer 5, the unoxidized region 51 is used to define a laser emission window 2, and the emission window 2 is located within the orthographic projection range of the first grating portion 31 on the oxide layer.

[0031] It should be noted that the vertical-cavity surface-emitting laser in this application uses a high-contrast grating (HCG). An HCG is a grating with a period shorter than the wavelength of light, possessing high reflectivity and transmission focusing capabilities. When light shines on its surface, the grating exhibits the characteristic of not undergoing higher-order diffraction.

[0032] The oxide layer 5 is provided with an unoxidized area 51 and an oxidized area 52 surrounding the unoxidized area 51, the unoxidized area 52 being used to define the exit window 2.

[0033] In specific settings, a wet oxidation process can be used, for example, at a temperature of 430℃, 2L / min of nitrogen gas carries water vapor at a certain temperature for selective wet oxidation. The oxidation depth, that is, the extension depth of the oxide layer 5 in the left and right directions, is controlled by time to form an oxidized zone in the oxide layer 5, and the central part, the part that has not undergone wet oxidation, forms an unoxidized zone.

[0034] In a high-contrast grating vertical-cavity surface-emitting laser with multiple emission regions, the current flowing through each emission region is made uniform by setting an oxide layer 5, resulting in high brightness consistency of the emission regions and improving the quality of the vertical-cavity surface-emitting laser.

[0035] The laser also includes a second reflector layer 6 disposed on the side of the active layer 4 away from the first reflector layer 1. The first reflector layer 1 has a first electrode 10 disposed on the side away from the active layer 4, and the second reflector layer 6 has a second electrode 11 disposed on the side away from the active layer 4.

[0036] The second reflector layer 6 can be a DBR. The second reflector layer may be composed of layers of two materials with different refractive indices, AlGaAs and GaAs; both the substrate and the second reflector layer can be N-type or both P-type.

[0037] It should be noted that, in the embodiments of this application, other layer structures may be provided between the light-emitting layer and the first reflector layer or between the oxide layer and the first reflector layer, such as oxide isolation layer 7 or current spreading layer 8, etc. This application does not limit the specific structure between the layers of the laser.

[0038] The resonant cavity is a necessary and crucial component of a fiber laser. It typically consists of two mirrors, a total reflection mirror and a half reflection mirror, located at opposite ends of the optical path. These mirrors form the resonant cavity through light reflection. Using a high-reflectivity grating as the total reflection mirror in the laser resonant cavity, spontaneous emission oscillates within the cavity, generating stimulated emission that produces laser output.

[0039] For a laser beam located inside the resonant cavity, as it enters a high-refractive-index material from a low-refractive-index material, the light is reflected in the grating region. When the light inside the resonator reaches the grating layer in the forward direction, it exhibits high reflectivity. For a back-reflected beam located outside the resonant cavity, it is refracted as it enters a low-refractive-index material from a high-refractive-index material. When the external light reaches the grating layer, refraction also occurs.

[0040] For height ratio gratings, they have extremely high reflectivity and reflection bandwidth, which can be adjusted by various factors such as substrate refractive index, grating period, duty cycle, etching depth, and morphology.

[0041] In existing technologies, various parameters within the chip need to be adjusted, such as changing the doping concentration of rare-earth ion-doped silica fiber or altering the shape and structure of the grating, to achieve a higher signal-to-noise ratio for the laser. However, in this application, the area of ​​the exit window is adjusted to control the back-reflected light entering the resonant cavity, thereby improving the anti-interference effect. To further enhance the laser's anti-interference capability, this embodiment further adjusts the grating region's configuration, increasing the refraction angle of the back-reflected light entering the first grating section, thus reducing the amount of back-reflected light entering the exit window from the first grating section.

[0042] For example, the phase difference of the first grating portion is less than the phase difference of the second grating portion, and / or, the transmission coefficient of the first grating portion is less than the transmission coefficient of the second grating portion, and / or, the refractive index of the first grating portion is greater than the refractive index of the second grating portion, and / or, the reflectivity of the first grating portion is greater than the reflectivity of the second grating portion.

[0043] In a specific configuration, the grating area consists of multiple gratings arranged in a periodic or non-periodic array, each grating including a column and a grating slot arranged along the array direction.

[0044] like Figure 1 As shown, in the periodically arrayed array of multiple grids, each grid has the same width, while the widths of the columns or the grid slots within the multiple grids are unequal. Figure 1 In this context, the width of each gate is σ; for example... Figure 2 , 3 As shown, the widths of the various gates in the aperiodic array are not equal. Figure 2 , 3 In the diagram, the widths of each grid are σ1, σ2, σ3, and σ4, respectively.

[0045] Additionally, it should be noted that in the quasi-periodic grating layer, the width of each periodic grating groove in the grating layer designed in this invention can be uniform or non-uniform; in the non-periodic grating, the width of each grating in the grating layer designed in this invention can be uniform or non-uniform.

[0046] In this application embodiment, the specific parameters or structure of the grating layer are not limited. However, this application adjusts the reflectivity and reflection phase by adjusting the structural parameters of the grating layer to improve the laser's resistance to external light interference.

[0047] It should be noted that a non-uniform grating is used in the embodiments of this application. The more non-uniform the arrangement of lines on the grating, the wider the angular span of the diffraction order, which results in a lower resolution of the grating and a less obvious diffraction effect.

[0048] A grating, also known as a diffraction grating, is an optical element that uses the principle of multi-slit diffraction to disperse light (decompose it into a spectrum).

[0049] The position of the spectral lines produced by the grating on the screen can be determined by ±kλ = d. The formula is expressed as follows. In the formula, a represents the width of the grating groove, b represents the spacing between the cylinders, φ is the diffraction angle, θ is the angle between the incident direction of light and the normal to the grating plane, k is the spectral order of the bright fringe (k = 0, ±1, ±2...), λ is the wavelength, and a+b is called the grating constant.

[0050] For the height ratio grating HCG of this application, the phenomenon of non-retrogenic higher-order diffraction is adopted, and only the 0th order diffraction exists. The mechanism of transmittance can be explained as follows: Physically, HCG can be regarded as a short planar waveguide array with the propagation direction along the y-axis. The incident light excites multiple modes of the waveguide array. The first two modes play a major role, and the higher-order modes are all in the form of evanescent surface-bound waves below the cutoff condition.

[0051] According to the Bragg phase-matching condition, HCG has three physical parameters that can control the grating's transmittance (or reflectance) and phase: the width of the cylinder, the width of the grating groove, and the thickness of the grating. Incident light can excite modes confined within the waveguide. That is, arbitrary phase distributions of reflected or transmitted light can be achieved by changing the grating structural parameters laterally.

[0052] In specific settings, well-known finite element methods or rigorous coupled-wave analysis can be used to determine parameters such as the refractive index, reflectivity, and phase curve of the grating. For example, grating vision software can be used to convert different patterns into grating line counts, and by utilizing the principle of grating refraction, different patterns can be presented at different angles. Gratings of different specifications will have different refractive effects and refraction angles. This application will not elaborate further on this point.

[0053] By adjusting the grating structure, the grating region can be likened to a plano-concave mirror, such as... Figure 5 As shown, the structure includes a flat surface and a concave surface. The back-reflected light can be considered as incident perpendicular to the grating region. The flat surface corresponds to one side of the back-reflected light source, and the concave surface corresponds to one side of the resonant cavity. The reflected light inside the resonant cavity is concentrated in the region between the first reflector layer and the second reflector layer.

[0054] When light reaches the concave mirror from the resonant cavity, the reflected light is focused light, such as... Figure 5 As shown in (II), light entering from the outside becomes diffused after passing through the concave mirror, as... Figure 5 As shown in (I), this reduces the impact on the laser itself. The grating layer can achieve this by adjusting the period and the width of each grating. Figure 5 The effect of a plano-concave lens.

[0055] In one embodiment, the first grating portion includes a central grating groove 91 and central pillars 92 adjacent to both sides of the central grating groove 91.

[0056] In this embodiment, the area of ​​the exit window is adjusted to control the back-reflected light entering the resonant cavity. It should be noted that the area of ​​the exit window in this application can be less than or equal to the orthogonal projection area of ​​the first grating portion on the oxide layer. However, while satisfying various laser parameters, such as the signal-to-noise ratio, the area of ​​the exit window can be appropriately adjusted. Regardless of the specific configuration, it falls within the inventive concept of this application.

[0057] It should be noted that in the embodiments of this application, the grating section defines the specific position of the grating in the grating region. In some embodiments, for example, if the number of grating slots is even, one of the two grating slots at the center can be selected as the central grating slot. This application does not limit the specific position of the selected grating slot. Furthermore, in some embodiments, for example, if the number of grating slots is odd, one of the grating slots at the center can be selected as the central grating slot.

[0058] In one embodiment, the first grating portion 31 includes a plurality of first grating bodies arranged in a periodic array, and the second grating portion 32 includes a plurality of second grating bodies arranged in a periodic array. The first grating body includes a first grating groove 21 and a first grating bar 22, and the second grating body includes a second grating groove 23 and a second grating bar 24. The density of the first grating groove 21 in the first grating portion 31 is less than the density of the second grating groove 23 in the second grating portion 32.

[0059] In a specific configuration, the width of the first gate body is greater than the width of the second gate body, the width of the first gate groove 21 is less than the width of the second gate groove 23, and the width of the first gate bar 22 is greater than the width of the second gate bar 24. The width of the first gate groove 21 is less than the width of the first gate bar 22; the width of the second gate groove 23 is less than the width of the second gate bar 24.

[0060] In this embodiment, the grating is designed to be sparse and narrow in the middle and dense and wide on both sides. This allows the phase difference to be smaller when external light enters from the middle and larger when it enters from both sides, thus achieving a concave lens effect and reducing the amount of external light entering the active area to achieve a better anti-reflection effect.

[0061] In this embodiment, the external back-reflection interference light source is refracted at the grating region. The refracted light is partially blocked by the exit window, preventing the backlight from entering the resonant cavity, reducing its impact on the VCSEL optical field distribution, improving the signal-to-noise ratio, and increasing the transmission rate and distance. Furthermore, by controlling the area of ​​the exit window, the divergence angle of the laser is reduced, which helps improve optical coupling efficiency.

[0062] In addition, in this embodiment, by designing the period and width of the grating, the refractive index and phase of the grating are adjusted to achieve the effect that external light is difficult to enter the resonant cavity while internal light can be emitted, thereby improving the anti-interference of the emitted light and improving the coupling efficiency.

[0063] Secondly, this application provides an optical fiber coupling system including a vertical cavity surface-emitting laser as described in any of the above.

[0064] Furthermore, it also includes a total reflection prism 13, which is configured to receive the laser beam emitted from the exit window 9 and reflect the laser beam onto the optical fiber 12.

[0065] It should be noted that, Figure 6 The image only shows the case where the optical fiber is perpendicular to the laser. In some embodiments, the exit angle of the laser beam is adjusted so that it corresponds to the position of the optical fiber.

[0066] The laser in this embodiment is applicable not only to cases where the fiber and laser are directly coupled, but also to cases where the fiber is not directly coupled. The back-reflected light can come from any optical element (such as a prism) on the chip's aperture. A prism between the fiber and the VCSEL directs the light.

[0067] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0068] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0069] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for descriptive purposes only and is not intended to limit the invention. Terms such as “set” appearing herein can refer to either a component being directly attached to another component or a component being attached to another component via an intermediary. A feature described in one embodiment herein may be applied, alone or in combination with other features, to another embodiment, unless that feature is not applicable in that other embodiment or is otherwise stated.

[0070] The present invention has been described through the above embodiments; however, it should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the present invention to the described embodiments. Those skilled in the art will understand that many variations and modifications can be made based on the teachings of the present invention, and all such variations and modifications fall within the scope of protection claimed by the present invention.

Claims

1. A vertical-cavity surface-emitting laser, characterized in that, The system includes a first reflector layer, an oxide layer, and an active layer stacked together. The first reflector layer includes a grating region, which includes a first grating portion and a second grating portion disposed around the first grating portion. An unoxidized region is disposed on the oxide layer, which is used to define a laser emission window. The emission window is located within the orthographic projection area of ​​the first grating portion on the oxide layer, and the area of ​​the emission window is less than or equal to the orthographic projection area of ​​the first grating portion on the oxide layer. It also includes a second reflector layer disposed on the side of the active layer away from the oxide layer, wherein the first reflector layer has a first electrode disposed on the side away from the active layer, and the second reflector layer has a second electrode disposed on the side away from the active layer; By adjusting the period and the width of each grating in the grating region, the grating region is made analogous to a plano-concave mirror. The plano-concave mirror includes a plane and a concave surface. The plane is one side corresponding to the back-reflecting light source, and the concave surface is one side corresponding to the resonant cavity. This allows the reflected light inside the resonant cavity to be concentrated in the region between the first reflector layer and the second reflector layer. The grating period of the grating region is less than the wavelength of the back-reflected light source; The phase difference of the first grating portion is less than the phase difference of the second grating portion, and / or the transmission coefficient of the first grating portion is less than the transmission coefficient of the second grating portion, and / or the reflectivity of the first grating portion is greater than the reflectivity of the second grating portion.

2. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The grating region consists of a plurality of gratings arranged in a periodic array. Each grating includes a column and a grating groove arranged along the array direction. The width of each of the plurality of gratings arranged in the periodic array is equal, and the width of each column or the width of each grating groove is unequal.

3. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The first grating section includes a central grating groove and central pillars adjacent to both sides of the central grating groove.

4. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The first grating portion includes a plurality of first grating bodies arranged in a periodic array, and the second grating portion includes a plurality of second grating bodies arranged in a periodic array. The first grating body includes a first grating groove and a first grating bar, and the second grating body includes a second grating groove and a second grating bar. The density of the first grating groove in the first grating portion is less than the density of the second grating groove in the second grating portion.

5. The vertical-cavity surface-emitting laser according to claim 4, characterized in that, The width of the first grid body is greater than the width of the second grid body, the width of the first grid groove is less than the width of the second grid groove, and the width of the first grid bar is greater than the width of the second grid bar.

6. The vertical-cavity surface-emitting laser according to claim 4, characterized in that, The width of the first grid groove is smaller than the width of the first grid bar; the width of the second grid groove is smaller than the width of the second grid bar.

7. An optical fiber coupling system, characterized in that, Including the vertical cavity surface-emitting laser as described in any one of claims 1-6.

8. The fiber optic coupling system according to claim 7, characterized in that, It also includes a total reflection prism, which is configured to receive a laser beam emitted from an exit window and reflect the laser beam onto an optical fiber, wherein the laser beam emitted from the exit window is perpendicular to the direction of the optical fiber.

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