A vertical cavity surface emitting laser
By integrating a near-wavelength grating layer and a second reflector layer into VCSELs to form a polarization-selective hybrid layer, the polarization instability problem of laser emission is solved, enabling low-cost and high-reliability laser manufacturing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG BERXEL PHOTONICS CO LTD
- Filing Date
- 2023-03-31
- Publication Date
- 2026-07-03
AI Technical Summary
Traditional VCSELs suffer from polarization instability in laser emission, and existing technologies make it difficult to manufacture VCSELs with stable polarization, resulting in high production costs.
A polarization-selective hybrid layer is formed by integrating a near-wavelength grating layer with a second reflector layer. The period of the near-wavelength grating is smaller than the wavelength of light in the propagation medium but larger than the wavelength of light in the semiconductor material. A conformal layer and a termination layer are combined to improve the grating etching accuracy and device reliability.
This achieves highly stable and highly polarized laser emission, reduces production costs, simplifies the manufacturing process, and improves device reliability.
Smart Images
Figure CN116404522B_ABST
Abstract
Description
Technical Field
[0001] This disclosure generally relates to the field of optoelectronic device technology, and specifically to a vertical cavity surface-emitting laser. Background Technology
[0002] Vertical cavity surface emitting lasers (VCSELs) have many advantages such as small size, long lifespan and low threshold current, and can be widely used in high-speed optical chips, data centers, structured light and lidar.
[0003] Traditional VCSELs exhibit varying degrees of polarization in their laser emission, depending on device design, manufacturing conditions, and the highly complex modes of spontaneous polarization conversion under diverse operating conditions. Currently, related technologies utilize diffraction gratings and subwavelength gratings to demonstrate VCSELs with stable polarization. However, each of these configurations has specific drawbacks. For instance, diffraction gratings with periods longer than the laser wavelength are easy to manufacture due to their large feature size, but their performance degrades significantly due to higher-order diffraction losses. Subwavelength gratings, on the other hand, require periods shorter than the laser wavelength and are formed using special epitaxial methods, posing significant manufacturing challenges and increasing production costs. Summary of the Invention
[0004] In view of the above-mentioned defects or deficiencies in the related technologies, it is desirable to provide a vertical cavity surface-emitting laser that is simple in structure, easy to manufacture, and inexpensive.
[0005] This disclosure provides a vertical-cavity surface-emitting laser (VCSEL) comprising a substrate layer, a buffer layer, a first reflector layer, a light-emitting layer, a polarization-selective mixing layer, and an electrode layer stacked together. The polarization-selective mixing layer includes a second reflector layer and a near-wavelength grating layer integrated above the second reflector layer. The period of the near-wavelength grating is less than the wavelength of light in the propagation medium and greater than the wavelength of light in the semiconductor material of the VCSEL.
[0006] Alternatively, in some embodiments of this disclosure, the near-wavelength grating is formed by etching a capping layer in the second reflector layer.
[0007] Optionally, in some embodiments of this disclosure, the shape of the region corresponding to the near-wavelength grating includes at least one of polygons and circles.
[0008] Optionally, in some embodiments of this disclosure, the outer surface of the near-wavelength grating is provided with at least one conformal layer.
[0009] Optionally, in some embodiments of this disclosure, when the cumulative thickness of the conformal layer exceeds a preset threshold, a planarization layer is further disposed above the conformal layer, and there is a gap between the planarization layer and the conformal layer.
[0010] Optionally, in some embodiments of this disclosure, the conformal layer and the planarization layer respectively include at least one of a SiN layer, an Al2O3 layer, a TiO2 layer, and a SiO2 layer.
[0011] Optionally, in some embodiments of this disclosure, at least one termination layer is disposed below the near-wavelength grating.
[0012] Optionally, in some embodiments of this disclosure, the bottom of the near-wavelength grating is located above the terminating layer; or, the bottom of the near-wavelength grating penetrates the terminating layer and reaches the interior of the overlay layer in the second reflector layer.
[0013] Optionally, in some embodiments of this disclosure, the termination layer includes at least one of a Si layer, a Ge layer, a GaN layer, an AlGaN layer, a GaAs layer, an AlGaAs layer, an InGaP layer, an InGaAs layer, and an AlAs layer.
[0014] Optionally, in some embodiments of this disclosure, the light-emitting layer includes an active layer and an oxide layer stacked together, the oxide layer including an unoxidized region for emitting laser light and an oxidized region surrounding the unoxidized region.
[0015] As can be seen from the above technical solutions, the embodiments disclosed herein have the following advantages:
[0016] This disclosure provides a vertical cavity surface-emitting laser (VCSEL) that integrates a near-wavelength grating layer with a second reflector layer. The period of the near-wavelength grating is smaller than the wavelength of light in the propagation medium but larger than the wavelength of light in the semiconductor material of the laser, thereby forming a polarization-selective mixing layer of the laser cavity. This enables the emission of highly stable and highly polarized laser light. The structure is simple and easy to manufacture, while the second reflector layer is thinner, reducing production costs. Attached Figure Description
[0017] Other features, objects, and advantages of this disclosure will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:
[0018] Figure 1 This is a schematic diagram of the structure of a vertical cavity surface-emitting laser provided in an embodiment of the present disclosure;
[0019] Figure 2 A schematic diagram of reflectivity, diffraction loss, and phase obtained by RCWA calculation is provided for an embodiment of this disclosure;
[0020] Figure 3 This is a schematic diagram illustrating the setting of one conformal layer, two conformal layers, and multiple conformal layers according to embodiments of this disclosure;
[0021] Figure 4 This is a schematic diagram of another embodiment of the present disclosure with multiple conformal layers;
[0022] Figure 5 This is a schematic diagram illustrating another embodiment of setting multiple conformal layers provided in this disclosure;
[0023] Figure 6 This is a schematic diagram illustrating the setting of one termination layer, two termination layers, and multiple termination layers according to embodiments of the present disclosure;
[0024] Figure 7 This is a schematic diagram illustrating the positional relationship between a near-wavelength grating and a termination layer, provided in an embodiment of this disclosure.
[0025] Figure 8 This is a schematic diagram illustrating the positional relationship between a near-wavelength grating and a termination layer, provided in an embodiment of this disclosure.
[0026] Figure 9 This is a schematic diagram illustrating the relationship between the size of the corresponding region of a near-wavelength grating and the size of the unoxidized region, provided in an embodiment of this disclosure.
[0027] Figure 10 A schematic diagram showing the relationship between the size of the corresponding region of a near-wavelength grating and the size of the unoxidized region, provided in an embodiment of this disclosure;
[0028] Figure 11 A schematic diagram showing the relationship between the size of the corresponding region and the size of the unoxidized region of another near-wavelength grating provided in an embodiment of this disclosure;
[0029] Figure 12 This is a schematic diagram of different shapes of a grating region provided in an embodiment of the present disclosure;
[0030] Figure 13 This is a schematic diagram of a grating element in different orientations provided in an embodiment of the present disclosure;
[0031] Figure 14 This is a schematic diagram of a grating provided in an embodiment of the present disclosure;
[0032] Figure 15 This is a schematic diagram of the unit cell of a grating provided in an embodiment of the present disclosure.
[0033] Figure label:
[0034] 10-Vertical-cavity surface-emitting laser, 11-Substrate layer, 12-Buffer layer, 13-First reflector layer, 14-Emitting layer, 141-Active layer, 142-Oxide layer, 143-Unoxidized region, 144-Oxidized region, 15-Polarization-selective mixing layer, 151-Second reflector layer, 1511-Cover layer, 152-Near-wavelength grating layer, 153-Conformal layer, 154-Planarization layer, 155-Interface, 156-Gap, 157-Termination layer, 16-Electrode layer. Detailed Implementation
[0035] To enable those skilled in the art to better understand the present disclosure, the technical solutions of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present disclosure.
[0036] The terms "first," "second," "third," "fourth," etc. (if present) in this disclosure, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this disclosure described can be implemented in orders other than those illustrated or described herein.
[0037] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or device that includes a series of steps or modules is not necessarily limited to those steps or modules that are explicitly listed, but may include other steps or modules that are not explicitly listed or that are inherent to such process, method, product, or device.
[0038] For ease of understanding and explanation, the following will use... Figures 1 to 15 The vertical cavity surface-emitting laser provided in the embodiments of this disclosure is described in detail.
[0039] Please refer to Figure 1This is a schematic diagram of a vertical-cavity surface-emitting laser (VCSEL) according to an embodiment of this disclosure. The VCSEL 10 includes a stacked substrate layer 11, a buffer layer 12, a first reflector layer 13, a light-emitting layer 14, a polarization-selective mixing layer 15, and an electrode layer 16. The polarization-selective mixing layer 15 includes a second reflector layer 151 and a near-wavelength grating layer 152 integrated above the second reflector layer 151. The period of the near-wavelength grating is smaller than the wavelength of light in the propagation medium (e.g., air) and larger than the wavelength of light in the semiconductor material of the VCSEL 10. Therefore, any losses from higher diffraction orders in the transmission direction are completely eliminated, and losses caused by higher diffraction orders in the reflection direction are minimized by appropriately designing the grating stripe width, gap, and etching depth.
[0040] Optionally, in this embodiment of the present disclosure, the near-wavelength grating is formed by etching the capping layer 1511 in the second reflector layer 151. The advantage of this arrangement is that it eliminates the need to modify existing epitaxial designs, facilitating manufacturing. Furthermore, the vertical-cavity surface-emitting laser 10 can be manufactured alongside conventional vertical-cavity surface-emitting lasers, and both types of devices can be integrated into an array. Additionally, the far field of the vertical-cavity surface-emitting laser 10 can be substantially similar to that of a conventional vertical-cavity surface-emitting laser.
[0041] It should be noted that in this embodiment, the first reflector layer 13 and the second reflector layer 151 can be distributed Bragg reflector (DBR) layers. Further, the reflectivity of the hybrid reflector for light with the desired polarization direction is designed to match the reflectivity of the individual DBR, while the reflectivity for light with a non-desired polarization direction is greater than a threshold and less than the reflectivity for light with the desired polarization direction. The reflectivity difference of the polarization-selective hybrid layer 15 can be any value greater than 0.5, 0.8, 1, 1.5, 2, 3, 5, 10, or 20%, where a greater difference in reflectivity results in a greater degree of laser polarization, and the degree of laser polarization is more stable under various operating conditions such as different laser drive currents and different temperatures. The degree of laser polarization can be greater than 5dB, 7dB, 10dB, 15dB, 20dB, and 30dB. Furthermore, the diffraction loss caused by near-wavelength gratings can be minimized through appropriate design and can be less than 50%, 30%, 20%, 15%, 10%, 7%, 5%, 3%, 2%, 1%, and 0.5%. In summary, the advantage of integrating near-wavelength gratings into laser reflectors is that the performance loss of the laser is at most affected only by the diffraction loss of the grating in the desired polarization direction of the laser; conversely, the diffraction loss of light with non-desired polarization directions has only a minor impact on the laser performance.
[0042] like Figure 2The diagrams shown illustrate reflectivity, diffraction loss, and phase calculated using RCWA (Rigorous Coupled Wave Analysis) according to embodiments of this disclosure, where the desired polarization of the laser is TE mode. For this polarization, the hybrid reflector has enhanced reflectivity and is designed to match the reflectivity of the second reflector layer 151 without a near-wavelength grating, optimizing laser performance such as power, threshold, and slope efficiency. In TE mode, the polarization-selective hybrid layer 15 has a designed low diffraction loss of less than 10%, minimizing its impact on laser performance. The diffraction loss of TM mode light is between 20% and 25%, significantly higher than that of TE mode, but since its reflectivity is lower than that of TE mode and it does not lasing, it has no practical impact on laser performance. For TE and TM light, the one-way phase of the hybrid reflector is close to π and 0, respectively, meaning that a round-trip phase condition of multiples of 2π is satisfied for light in both polarization directions. In summary, the overall phase of the hybrid reflector depends on the DBR layer thickness, the design of the DBR capping layer 1511, and grating parameters such as period, stripe width, gap, and etch depth.
[0043] Optionally, in this embodiment of the present disclosure, at least one conformal layer 153 is provided on the outer surface of the near-wavelength grating. This arrangement has the advantage of improving the reliability and optical characteristics of the vertical-cavity surface-emitting laser 10. For example... Figure 3 The diagrams shown illustrate, respectively, the setting of one conformal layer, two conformal layers, and multiple conformal layers according to embodiments of this disclosure. When the cumulative thickness of the conformal layer 153 exceeds a preset threshold, the gap between the grating and the structure becomes flat. A planarization layer 154 is disposed above the conformal layer 153, wherein the preset threshold can be 0.5 times the height of the grating gap. Further, as... Figure 4 As shown, it illustrates how the perfectly conformal layer 153 bonds along the interface 155 and achieves flatness. And as... Figure 5 As shown, it illustrates how the conformal layer 153 bonds along the interface 155 and forms voids 156 when planarity is achieved. It should be noted that in the embodiments of this disclosure, the conformal layer 153 and the planarization layer 154 can be made of inorganic dielectric materials, such as at least one of SiN, Al2O3, TiO2, and SiO2 layers, and formed by methods such as ALD (Atomic Layer Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition), CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), and sputtering.
[0044] Optionally, in this embodiment of the present disclosure, at least one termination layer 157 is provided below the near-wavelength grating. The termination layer 157 can be used for etching termination or defect propagation termination, thereby not only enhancing the uniformity of the grating etching depth and improving the cross-sectional shape of the grating gap, but also increasing the accuracy of the grating gap etching depth. For example, relative to the material of the termination layer 157 and relative to the material of the cover layer 1511 of the second reflector layer 151, the etching forming the grating gap has a selectivity greater than a threshold level, namely 1.5:1, 2:1, 3:1, 5:1, 10:1, 20:1, 50:1 and 100:1, etc., and also improving the reliability of the vertical cavity surface-emitting laser 10. The termination layer 157 and the capping layer 1511 of the second reflector layer 151 can be formed during the epitaxial growth of the vertical cavity surface-emitting laser 10 using methods such as MOCVD (Metal-organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), and LPE (Liquid Phase Epitaxy). For example... Figure 6 The figures shown are schematic diagrams illustrating the setting of one termination layer, two termination layers, and multiple termination layers according to embodiments of this disclosure. Further, as... Figure 7 As shown, the bottom of the near-wavelength grating is located above the termination layer 157; or as... Figure 8 As shown, the bottom of the near-wavelength grating penetrates the termination layer 157 and reaches the interior of the capping layer 1511 in the second reflector layer 151. It should be noted that in this embodiment, the termination layer 157 can be made of a semiconductor material, such as at least one of Si, Ge, GaN, AlGaN, GaAs, AlGaAs, InGaP, InGaAs, and AlAs layers. Furthermore, the refractive index of the termination layer 157 can be close to or closely match the refractive index of the material constituting the capping layer 1511 of the second reflector layer 151, and the termination layer 157 can have a thickness less than λ / 4, λ / 6, λ / 8, λ / 10, or less than 50 nm, 20 nm, 10 nm, 7 nm, or 5 nm, where λ represents the laser wavelength.
[0045] Optionally, in this embodiment of the present disclosure, the light-emitting layer 14 includes an active layer 141 and an oxide layer 142 stacked together. The oxide layer 142 includes an unoxidized region 143 for emitting laser light and an oxidized region 144 surrounding the unoxidized region 143. For example, the oxide layer 142 may include aluminum material, and the emitted laser light is in the near-infrared range and its polarization direction is parallel to the near-wavelength grating strip. The active layer 141 is a single quantum well layer or a multiple quantum well (MQW) layer, used to emit light when energized. The unoxidized region 143 is a conductive region. After a voltage is applied to the electrodes at both ends of the vertical cavity surface-emitting laser 10, the current is conducted through the unoxidized region 143, while the oxide region 144 is an insulating region used to isolate the current.
[0046] Furthermore, such as Figure 9 As shown, in this embodiment of the present disclosure, the size of the region corresponding to the near-wavelength grating can be larger than the size of the unoxidized region 143, which will result in the polarization of virtually all laser modes of the vertical-cavity surface-emitting laser 10. And as... Figure 10 The size of the region corresponding to the near-wavelength grating shown can be equal to the size of the unoxidized region 143, or as... Figure 11 The size of the region corresponding to the near-wavelength grating shown can be smaller than the size of the unoxidized region 143. In this case, many transverse modes of the vertical-cavity surface-emitting laser 10 are polarized, for example, the fundamental mode is polarized. Based on the relative reflectivity of the grating-equipped and ungrating-equipped regions of the hybrid reflector, when the reflectivity of the hybrid reflector substantially matches the reflectivity of the individual second reflector layer 151, multiple transverse modes can be polarized, while other modes can be unpolarized. When the reflectivity of the hybrid reflector is higher than the reflectivity of the individual second reflector layer 151, multiple polarized modes of the vertical-cavity surface-emitting laser 10 will preferentially emit laser light over multiple unpolarized modes.
[0047] Optionally, in the embodiments of this disclosure, the shape of the region corresponding to the near-wavelength grating includes at least one of polygons and circles. The polygons include, but are not limited to, triangles and quadrilaterals, and the circles include, but are not limited to, perfect circles and ellipses. For example... Figure 12 and Figure 13As shown, the grating region of the hybrid reflector can be designed in various shapes and orientations, such that a specific transverse mode of the vertical-cavity surface-emitting laser 10 is polarized. Based on the relative reflectivity of the grating-equipped and ungrated regions of the hybrid reflector, the vertical-cavity surface-emitting laser 10 preferably emits light in a specific polarized transverse mode, or emits light in a specific polarized transverse mode along with unpolarized light in other transverse modes. The shape and orientation of the grating portion of the hybrid reflector are designed such that the vertical-cavity surface-emitting laser 10 emits laser light in a desired polarization direction within a specific transverse mode, wherein the direction of linearly polarized emission can be controlled by rotation, while circularly polarized light can be controlled by a chiral structure.
[0048] In addition, such as Figure 14 and Figure 15 The figures shown are schematic diagrams of the grating and unit cell of a grating provided in an embodiment of this disclosure. The 2D grating structure can be constructed from... Figure 14 The grid shown is defined and associated with a specific grating element or Figure 15 The unit cells shown are combined. It can be understood that asymmetric grating elements are used to design hybrid reflectors based on 2D gratings that are selective for linearly polarized light, while chiral grating elements are used to design hybrid reflectors based on 2D gratings that are selective for circularly polarized light.
[0049] The vertical cavity surface-emitting laser provided in this disclosure integrates a near-wavelength grating layer with a second reflector layer. The period of the near-wavelength grating is smaller than the wavelength of light in the propagation medium and larger than the wavelength of light in the semiconductor material of the laser, thereby forming a polarization-selective mixing layer of the laser cavity. This enables the emission of highly stable and highly polarized laser light. The structure is simple and easy to manufacture, while the second reflector layer is thinner, reducing production costs.
[0050] It should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and not to limit them; although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this disclosure.
Claims
1. A vertical-cavity surface-emitting laser, characterized in that, The vertical cavity surface-emitting laser includes a substrate layer, a buffer layer, a first reflector layer, a light-emitting layer, a polarization selective mixing layer, and an electrode layer stacked together. The polarization selective mixing layer includes a second reflector layer and a near-wavelength grating layer integrated above the second reflector layer. The period of the near-wavelength grating is less than the wavelength of light in the propagation medium and greater than the wavelength of light in the semiconductor material of the vertical cavity surface-emitting laser. The near-wavelength grating is formed by etching the capping layer in the second reflector layer; The outer surface of the near-wavelength grating is provided with multiple conformal layers; The cumulative thickness of the conformal layer exceeds a preset threshold to make the gap of the grating flat. A planarization layer is also provided above the conformal layer, and there is a gap between the planarization layer and the conformal layer.
2. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The shape of the area corresponding to the near-wavelength grating includes at least one of polygons and circles.
3. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The conformal layer and the planarization layer each include at least one of the following: a SiN layer, an Al2O3 layer, a TiO2 layer, and a SiO2 layer.
4. The vertical-cavity surface-emitting laser according to any one of claims 1 to 3, characterized in that, At least one termination layer is disposed below the near-wavelength grating.
5. The vertical-cavity surface-emitting laser according to claim 4, characterized in that, The bottom of the near-wavelength grating is located above the terminating layer; or, the bottom of the near-wavelength grating penetrates the terminating layer and reaches the interior of the overlay layer in the second reflector layer.
6. The vertical-cavity surface-emitting laser according to claim 4, characterized in that, The termination layer includes at least one of the following: Si layer, Ge layer, GaN layer, AlGaN layer, GaAs layer, AlGaAs layer, InGaP layer, InGaAs layer, and AlAs layer.
7. The vertical-cavity surface-emitting laser according to claim 1, characterized in that, The light-emitting layer includes an active layer and an oxide layer stacked together. The oxide layer includes an unoxidized region for emitting laser light and an oxidized region surrounding the unoxidized region.