Surface emitting laser with photonic crystal cladding with gradually changed structure

Abstract

The invention discloses a surface emitting laser with a photonic crystal cladding with a gradually-changed structure, and relates to the technical field of semiconductor lasers. The surface emitting laser comprises a substrate, a lower distributed Bragg reflector, an n-type cladding, an active region, a p-type spacer layer, a photonic crystal layer, a p contact layer and an upper electrode. The photonic crystal layer comprises a two-dimensional periodic hole array which is divided into a central radiation area, a transition area and a peripheral in-plane limiting area in a plane. A plurality of holes are formed in each unit cell, the lattice constant and the aperture are kept basically constant by only changing the positions of the holes in the unit cells, controllable radiation coupling of a central area and low-loss strong in-plane constraint of a peripheral area can be achieved at the same time through the structure, interface scattering and mode competition are effectively restrained, and the performance of the device is improved. And the single-mode stability, the threshold performance and the manufacturing tolerance of the small-size surface emitting laser are improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a surface-emitting laser with a structurally graded photonic crystal cladding. Background Technology

[0002] Surface-emitting photonic crystal lasers (PCSELs) are a type of surface-emitting semiconductor laser that utilizes a two-dimensional photonic crystal to achieve in-plane coherent oscillation and diffraction in a vertical direction. They can realize single-mode oscillation, narrow divergence angle, high power, and high coherence over large areas, showing great promise for applications in lidar, optical communication, and displays. However, as device size shrinks, in-plane losses increase dramatically, and edge scattering becomes significant, leading to a higher threshold voltage and difficulties in lasing, thus limiting the miniaturization and high-speed performance of PCSELs.

[0003] In existing technologies, a "two-photon crystal structure" is often used to enhance the in-plane feedback of small-sized PCSELs, which involves introducing a bandgap photonic crystal reflection ring around the central oscillation region. However, this method, by changing the aperture, fill factor, or period to form a heterogeneous structure, often introduces abrupt changes in the bandgap structure between the central and cladding regions. These abrupt changes lead to interface scattering and the generation of interface states, causing mode distortion and a decrease in far-field quality. Simultaneously, the bandgap center frequencies of the central and cladding regions are difficult to match precisely, easily leading to mode competition and frequency drift, making them highly sensitive to manufacturing errors and reducing yield. Furthermore, in pursuing strong in-plane confinement, it is often difficult to simultaneously achieve low out-of-plane radiation loss, resulting in a performance trade-off.

[0004] Therefore, there is an urgent need for a new photonic crystal heterostructure design that can enhance in-plane confinement and mode selection capabilities while minimizing interface effects and synergistically optimizing out-of-plane radiation characteristics, thereby improving the performance and manufacturing tolerance of small-sized PCSELs. Summary of the Invention

[0005] The purpose of this invention is to provide a surface-emitting laser with a structurally graded photonic crystal cladding to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides a surface-emitting laser with a structurally graded photonic crystal cladding, comprising, from bottom to top, a lower electrode, a substrate, a lower distributed Bragg mirror, an n-type cladding, an active region, a p-type spacer layer, a photonic crystal layer, a p-contact layer, and an upper electrode; the photonic crystal layer contains a two-dimensional periodic aperture array, which is divided in a plane into a central radiating region, a transition region, and an outer in-plane confinement region; the unit cell of the two-dimensional periodic aperture array contains multiple apertures, and the displacement parameter of the apertures within the unit cell is defined as d, wherein the unit cell of the central radiating region adopts a first displacement parameter d. L The unit cell of the confined region in the outer plane adopts the second displacement parameter d.H , and d L ≠d H The displacement parameter d of the unit cell in the transition region changes from the first displacement parameter d. L Continuously change to the second displacement parameter d H .

[0007] Preferably, the unit cell contains four holes, with the center of the unit cell as a reference point. The four holes are evenly spaced along the circumference of the reference point, and the distance from the center of each hole to the reference point is equal to the distance from the center of the hole to the reference point. d, where 0 < d < a / 2, and a is the lattice constant of the two-dimensional periodic hole array.

[0008] Preferably, the second displacement parameter d H The value range is from 0.48a to 0.52a, and the first displacement parameter d L The value range is from 0.40a to 0.47a.

[0009] Preferably, in the central radiation region, transition region, and outer in-plane confinement region, the aperture r of the two-dimensional periodic aperture array remains constant or varies by less than 10%.

[0010] Preferably, the width of the transition zone is 3a to 20a.

[0011] Preferably, the continuous change of the displacement parameter d in the transition region follows a linear function, a piecewise linear function, a cosine function, a hyperbolic tangent function, or a Gaussian function.

[0012] Preferably, it further includes an n-type spacer layer and a current limiting layer disposed between the n-type cladding and the active region, wherein the n-type spacer layer is located above the current limiting layer.

[0013] Preferably, the current confinement layer is an oxide confinement layer, an ion implantation confinement layer, or a tunnel junction confinement layer.

[0014] Preferably, the two-dimensional periodic aperture array is formed in the photonic crystal layer by surface etching or buried etching processes.

[0015] Preferably, the shape of the central radiation area is circular, square, rectangular, or elliptical, and the outer confinement area is a single-ring or multi-ring structure surrounding the central radiation area.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: The surface-emitting laser with a structurally graded photonic crystal cladding provided by this invention achieves a continuous gradient by adjusting only the spatial distribution of the relative position displacement parameter d of the aperture within the unit cell, using different d values ​​in the central radiating region, transition region, and outer in-plane confinement region, while maintaining the lattice constant and aperture essentially unchanged. This allows for the formation of a low-vertical-loss, high-in-plane-reflection "bandgap" cladding in the outer region, and controllable radiative coupling output in the central region. This design effectively reduces band structure mismatch and geometric abrupt changes between the central and cladding regions, suppresses interface scattering and interface states, improves the device's single-mode stability, far-field quality, and threshold performance, and has a higher tolerance for manufacturing errors. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the planar structure division and unit cell parameters of a two-dimensional photonic crystal according to an embodiment of the present invention; wherein, Figure 1 (a) is a schematic diagram of a two-dimensional photonic crystal planar structure according to an embodiment of the present invention; Figure 1 (b) is a schematic diagram showing the relationship between the mode frequency near the Γ point and the vertical radiation loss (or vertical loss) as a function of d under different unit cell pore displacement parameters d. Figure 1 (c) is a schematic diagram of the cell structure as d changes.

[0019] Figure 2 This is a schematic cross-sectional view of the device according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the numerical simulation results of a two-dimensional finite-difference time-domain (FDTD) method according to an embodiment of the present invention. Figure 3 (a) is a schematic diagram of the two-dimensional photonic crystal planar structure used in the simulation; Figure 3 (b) is the frequency domain response curve obtained at the predetermined monitoring location; Figure 3 (c) is from Figure 3 (b) Schematic diagram of the two-dimensional field distribution (or field strength distribution) corresponding to several resonance peaks selected.

[0021] Figure 4 This embodiment of the invention presents emission spectral data of a device acquired under optical pumping excitation conditions. Wherein, Figure 4 (a) is a schematic diagram of the two-dimensional photonic crystal aperture array of the test sample divided in a plane; Figure 4(b) The effect of aperture displacement parameter partitioning / gradient design on emission peak position, spectral morphology and stability under limited lateral dimensions.

[0022] In the figure: 100, central radiation region; 200, transition region; 300, peripheral in-plane confinement region; 410, p-contact layer; 420, photonic crystal layer; 430, p-type spacer layer; 440, active region; 450, n-type spacer layer; 460, current confinement layer; 470, n-type cladding; 480, lower distributed Bragg mirror; 490, substrate; 510, upper electrode; 520, lower electrode. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] This invention provides a surface-emitting laser with a structurally graded photonic crystal cladding, comprising, from bottom to top, a lower electrode 520, a substrate 490, a lower distributed Bragg mirror 480, an n-type cladding 470, an active region 440, a p-type spacer layer 430, a photonic crystal layer 420, a p-contact layer 410, and an upper electrode 510. The photonic crystal layer 420 includes a two-dimensional periodic aperture array, which is divided in a plane into a central radiating region 100, a transition region 200, and an outer in-plane confinement region 300. Each cell of the two-dimensional periodic aperture array contains multiple apertures, and the displacement parameter of the apertures within the cell is defined as d. The cell of the central radiating region 100 uses a first displacement parameter d. L The unit cell of the in-plane confinement region 300 adopts the second displacement parameter d. H , and d L ≠d H The displacement parameter d of the unit cell in the transition region 200 changes from the first displacement parameter d L Continuously change to the second displacement parameter d H .

[0025] This invention employs a partitioned structure consisting of a central radiating region 100, a transition region 200, and an outer in-plane confinement region 300. Different regions utilize different intracellular hole displacement parameters d, with parameter d continuously and gradually changing in the transition region 200. This allows for the synergistic optimization of the radiative coupling strength in the central region and the in-plane confinement capability in the outer region within the same device. The outer in-plane confinement region 300 uses a specific d... HThe value can significantly reduce the out-of-plane radiation loss of the Γ-point mode, forming an effective in-plane "bandgap mirror," enhancing the in-plane constraint of the optical mode and suppressing higher-order transverse modes. Different d values ​​are used in the central radiation region 100. L The value provides a suitable out-of-plane radiation coupling channel for the target lasing mode, enabling effective vertical emission. The continuous gradient design of the transition region 200 smoothly connects the central and peripheral regions, avoiding strong interface scattering and parasitic interface states introduced by abrupt changes in structural parameters, thereby improving mode purity and far-field quality.

[0026] The scheme is further optimized so that the unit cell contains four holes. With the center of the unit cell as the reference point, the four holes are evenly spaced along the circumference of the reference point, and the distance from the center of each hole to the reference point is 1 / 2. d, where 0 < d < a / 2, and a is the lattice constant of the two-dimensional periodic hole array.

[0027] By employing a four-hole unit cell and defining the displacement parameter d in this manner, the hole position offset can be clearly quantified, facilitating structural design and parameter control. This symmetrical displacement method can systematically change the symmetry of the unit cell, thereby effectively controlling the photonic band structure, especially the coupling and radiation characteristics of modes near the Γ point.

[0028] Further optimize the scheme, the second displacement parameter d H The value range is from 0.48a to 0.52a, and the first displacement parameter d L The value range is from 0.40a to 0.47a.

[0029] By using the outer area d H Setting the anode in the range of 0.48a to 0.52a can achieve extremely low vertical radiation loss of the photonic crystal near the Γ point, thereby maximizing its performance as an in-plane low-loss reflective cladding. This is achieved by adjusting the anode in the central region d... L Setting it within the range of 0.40a to 0.47a can ensure sufficient in-plane feedback while providing enough out-of-plane radiation coupling strength for the target mode, thus facilitating stable surface emission output.

[0030] Further optimization of the scheme: in the central radiation zone 100, the transition zone 200 and the outer in-plane confinement zone 300, the aperture r of the two-dimensional periodic aperture array remains constant or the change ratio is less than 10%.

[0031] By keeping the aperture r essentially constant across all zones, the fill factor in each zone can be kept approximately constant. This minimizes the bandgap center frequency drift caused by geometric changes, reduces band structure mismatch between the central and peripheral regions, thus contributing to the stability of the target lasing mode and improving the device's manufacturing tolerance to etching aperture fluctuations.

[0032] The scheme was further optimized so that the width of the transition zone 200 was 3a to 20a.

[0033] By setting the width of the transition region 200 to several to tens of lattice periods, sufficient space can be provided to achieve a smooth transition of the displacement parameter d. A width that is too narrow may result in insufficient gradation and residual scattering; a width that is too wide may occupy too much of the effective gain region. This width range achieves a good balance between suppressing interface effects and maintaining device compactness.

[0034] Further optimization of the scheme: the continuous change of displacement parameter d in transition zone 200 follows a linear function, a piecewise linear function, a cosine function, a hyperbolic tangent function, or a Gaussian function.

[0035] By employing these mathematical functions to describe the gradient of d, the structure of the transition region can be precisely controlled, and the adaptability of the mode field can be flexibly optimized. For example, cosine or hyperbolic tangent functions can provide a smoother boundary transition, potentially further reducing scattering; designers can select the optimal gradient function form based on simulation results.

[0036] Further optimizations include an n-type spacer layer 450 and a current limiting layer 460 disposed between the n-type cladding layer 470 and the active region 440, with the n-type spacer layer 450 located above the current limiting layer 460.

[0037] By setting a current limiting layer 460, the injected current can be limited to the central region of the device and aligned with the optical mode region. This can improve the current injection efficiency and reduce the threshold current, which is a common auxiliary means to realize high-performance semiconductor lasers.

[0038] Further optimization of the scheme: the current confinement layer 460 can be an oxide confinement layer, an ion implantation confinement layer, or a tunnel junction confinement layer.

[0039] By listing various feasible current-limiting methods, this invention demonstrates the advantages of its core innovation in photonic crystal structure and the strong compatibility between current-limiting methods. This invention does not limit the specific current-limiting mechanism, thus improving the universality and feasibility of the technical solution.

[0040] Further optimization of the scheme involves forming a two-dimensional periodic aperture array in the photonic crystal layer 420 through surface etching or buried etching processes.

[0041] By illustrating the two main fabrication processes for aperture arrays, we can cover different process routes and device structure choices. Surface etching is simple and direct; buried etching followed by regrowth can result in a smoother interface and lower scattering loss. This provides flexibility for actual production.

[0042] The scheme is further optimized so that the shape of the central radiation area 100 is circular, square, rectangular or elliptical, and the outer confinement area 300 is a single ring or multiple ring structure surrounding the central radiation area 100.

[0043] By allowing the central and peripheral regions to have different shapes, it is possible to adapt to the beam shape and symmetry requirements of different application scenarios. For example, circular partitions are beneficial for obtaining circularly symmetrical beams, while square or rectangular partitions may be beneficial for coupling with waveguides or specific arrays. Multi-ring peripheral structures may provide stronger in-plane confinement.

[0044] The surface-emitting laser with a structurally graded photonic crystal cladding provided by this invention first designs the structural parameters of each layer of the vertical cavity (such as the distributed Bragg mirror 480, the active region 440, etc.) based on the target wavelength and material system. The core step lies in the design of the photonic crystal layer 420: determining the lattice constant *a* and aperture *r*; selecting a four-hole unit cell model and defining the displacement parameter *d*; and determining the *d* parameter that achieves low vertical loss through band structure simulation. H The value range (e.g., 0.48a-0.52a) and the d that can achieve moderate radiative coupling L The value range is (e.g., 0.40a-0.47a); in the layout design, the photonic crystal plane is divided into a central radiation region 100, a transition region 200, and an outer in-plane confinement region 300, and a specific d is assigned to each region. L and d H In the transition region 200, the d-value of each unit cell is generated according to a selected gradient function (such as linear gradient); the aperture r is kept constant throughout the region. In terms of fabrication process, each layer is first epitaxially grown on the substrate 490; then, the designed partitioned gradient aperture array pattern is transferred to the photonic crystal layer 420 using electron beam lithography or deep ultraviolet lithography combined with dry etching (such as ICP); optionally, a current confinement layer 460 is fabricated (such as selective oxidation); finally, the upper electrode 510 and the lower electrode 520 are fabricated to complete the packaging and testing.

[0045] Through the above implementation process, the technical effects achieved by this invention are significant: First, by changing only the aperture displacement parameter d, a highly efficient "bandgap mirror" is formed in the outer in-plane confinement region 300, greatly enhancing the in-plane optical field confinement and effectively suppressing multi-transverse mode oscillations, providing a new solution to the problem of insufficient in-plane feedback in small-sized PCSELs. Second, the differentiated d-value design of the central radiation region 100 provides a controllable vertical radiation channel, achieving efficient surface emission output. Most importantly, the continuous gradient of the transition region 200 and the constant aperture design fundamentally weaken the band structure abruptness and geometric abruptness in traditional heterostructures, significantly reducing the risk of interface scattering loss and parasitic interface state generation, making the target lasing mode more stable and the far-field beam quality better. In addition, due to the mild changes in structural parameters and small band structure mismatch, the device exhibits stronger tolerance to unavoidable process deviations such as aperture errors and etching depth fluctuations during manufacturing, which is beneficial to improving production yield and consistency. In summary, this invention features an innovative design at the photonic crystal structure level, providing an effective technical path for realizing high-performance, small-size, and highly reliable surface-emitting lasers.

[0046] Example 1 like Figures 1 to 4 As shown, this embodiment is a surface-emitting semiconductor laser structure integrating a two-dimensional photonic crystal aperture array, which, from top to bottom, includes: an upper electrode 510, a p-contact layer 410, a photonic crystal layer 420, a p-type spacer layer 430, an active region 440, an n-type spacer layer 450, a current confinement layer 460, an n-type cladding layer 470, a lower distributed Bragg reflector 480, a substrate 490, and a lower electrode 520. The two-dimensional photonic crystal aperture array of the device is prepared by surface etching, with a lattice constant of a, an aperture of r, and an etching depth of h, mainly located in the photonic crystal layer 420 and partially located in the p-contact layer 410. Figure 1 As shown in (a), the two-dimensional photonic crystal aperture array is divided in a plane into a central radiating region 100, a transition region 200, and an outer in-plane confinement region 300. The central radiating region 100 is used to provide controllable radiative coupling / emission characteristics for the target mode; the outer in-plane confinement region 300 is used to enhance in-plane confinement (e.g., through bandgap reflection / equivalent reflection cladding) and suppress multiple transverse modes; the transition region 200 is used to smoothly transition the structural parameters between the central radiating region 100 and the outer in-plane confinement region 300, thereby reducing interface scattering and interface states.

[0047] like Figure 1As shown in (c), this invention uses the "relative position displacement parameter d of the intracellular holes" as the main control quantity. With the cell center as a reference, in this embodiment, the cell contains four holes, with the hole centers located at (±d / 2, ±d / 2) or an equivalent fourfold symmetry position, where 0 < d < a / 2, and a is the lattice constant of the two-dimensional periodic hole array. By changing d, the cell symmetry and its coupling / radiation characteristics to modes near the Γ point can be altered, thereby controlling the vertical radiation loss and in-plane confinement capability. In the partitioned structure of this invention: the central radiation region 100 uses the first displacement parameter d = d L The in-plane confinement region 300, which is used to achieve the radiation coupling strength required for the target mode (i.e., stronger out-of-plane coupling or higher vertical radiation), adopts the second displacement parameter d=d. H This is used to reduce vertical radiation loss near the Γ point and enhance in-plane confinement capability; in the transition region 200, d from d L Continuous transition to d H This is to avoid additional scattering caused by geometric abrupt changes.

[0048] To reduce the structural mismatch between the center and the periphery, it is preferable to keep the aperture r basically constant (or change less than a preset ratio) in the central radiation region 100, the transition region 200 and the periphery in-plane confinement region 300, so that the fill factor is basically constant or approximately constant. Figure 1 (b) Examples of changes in d and frequency / vertical loss near the Γ point are given, which can be used to guide d. L With d H The choice is as follows. As an example, not a limitation, d is acceptable. H Located near the parameter range with lower vertical loss (e.g., (0.48–0.52)a), while d L The parameter range is located outside this interval (e.g., (0.40–0.47)a). The width of the transition region 200 can take several unit cell periods (e.g., 3a–20a), and the transition function can be a linear, piecewise linear, cosine, tanh, or Gaussian function.

[0049] like Figure 4 As shown in (a), the two-dimensional photonic crystal aperture array of the test sample is divided into a central radiation region 100, a transition region 200, and an outer in-plane confinement region 300 in the plane. The size of the central radiation region is 25 μm (based on the diameter of the central radiation region), and the total width of the transition region and the outer in-plane confinement region is 21 μm. Overall, it is a small-sized photonic crystal cavity structure. Figure 4As shown in (b), emission spectrum data of the device were acquired under optical pumping excitation conditions to characterize the influence of aperture displacement parameter partitioning / gradient design on the emission peak position, spectral morphology, and stability under limited lateral dimensions. This result illustrates that, under the aforementioned small-size configuration, the structure of this invention can still achieve effective surface emission output from the central radiating region, with in-plane confinement provided by the peripheral in-plane confinement region, thereby helping to suppress undesired modes and improve output mode performance.

[0050] The following is a feasible preparation process (taking GaAs system as an example; other material systems can be replaced with equivalent methods): S1. Epitaxial Growth: A lower distributed Bragg reflector 480, an n-type cladding layer 470, a current confinement layer 460 (optional), an n-type spacer layer 450 (optional), an active region 440 (e.g., multiple quantum wells), a p-type spacer layer 430, a photonic crystal layer 420, and a p-contact layer 410 are sequentially epitaxially grown on the substrate 490. The doping type and thickness of each layer are determined according to the target wavelength and electrical requirements.

[0051] S2. Photonic Crystal Patterning: A hard mask / photoresist layer is formed on the device surface. A two-dimensional hole array pattern is defined using electron beam lithography (EBL) or deep ultraviolet lithography (DUV). The d-partitioning / gradient rules of the central radiation region 100, the transition region 200 and the peripheral in-plane confinement region 300 are implemented in the layout.

[0052] S3. Etching to form a hole array: ICP or RIE etching is used to transfer the hole array to the photonic crystal layer 420. The etching depth h can be set to: partial etching, in which the holes are mainly formed in the photonic crystal layer 420 to reduce the process risk to the active region; or through / deep etching, in which the holes extend to the p-type spacer layer 430 or even deeper to enhance two-dimensional feedback or control radiation coupling.

[0053] After etching, the mask can be removed, and necessary surface cleaning / passivation can be performed.

[0054] S4. Current limiting structure (optional): If an oxidation limiting method is used, the current limiting layer 460 can be wet-oxidized in the laterally exposed area to form an oxidation aperture to limit the current injection area; the current limiting structure can be aligned or approximately aligned with the planar position of the central radiation area 100, but the core innovation of the present invention does not depend on the form of current limiting.

[0055] S5. Metal Electrode and Packaging: An upper electrode 510 (which can be an annular windowed electrode to facilitate light emission) is formed on the upper surface of the device, and a lower electrode 520 is formed on the back side of the substrate. Annealing, dicing and packaging are then completed.

[0056] To verify the impact of the hole displacement partitioning / gradient design of this invention on mode selectivity, two-dimensional FDTD numerical simulation can be used. For example... Figure 3(a) shows the construction of a finite-size photonic crystal planar structure model; the spectral response is obtained through time-domain excitation and Fourier transform, as shown in Figure (a). Figure 3 As shown in (b); and the corresponding two-dimensional mode field distribution is extracted from the main resonance peaks in the spectrum, as shown in (b). Figure 3 As shown in (c), the spatial distribution and radiation characteristics of different peaks corresponding to modes are compared. This simulation can be used to demonstrate that by selecting different values ​​of d in the central radiation region 100 and the outer confinement region 300 and setting a transition region 200, the mode density and the competition relationship between the master modes can be changed, thereby achieving the effects of target mode enhancement and undesired mode suppression.

[0057] Example 2 The differences between this embodiment and Embodiment 1 are as follows: 1. Number and shape of holes in a unit cell: The number of holes in a unit cell is not limited to four holes, but can also be two, six or more holes; the shape of the holes is not limited to circular holes, but can also be elliptical holes, polygonal holes or composite holes, as long as an equivalent "hole displacement parameter d" can be defined and regional differentiation can be achieved.

[0058] 2. Zone shape: The central radiating zone 100 can be circular, square, rectangular, elliptical or polygonal; the outer confined zone 300 can be a single ring or multiple rings surrounding the zone; the transition zone 200 can gradually change radially or along a certain direction.

[0059] 3. Current limiting structure: The current limiting layer 460 can be replaced by ion implantation limiting, tunnel junction limiting or other current limiting structures; the key to this invention is the partitioning / gradient design of the photonic crystal aperture displacement parameter d, rather than the type of current limiting structure.

[0060] 4. Etching Method (Surface Etching / Buried Etching): The photonic crystal aperture array can be formed using either surface etching, where the aperture array is formed from the device surface downwards after epitaxy and located within the photonic crystal layer 420 and its adjacent layers; or buried etching, where the aperture array is first etched into a predetermined layer (e.g., photonic crystal layer 420 or its adjacent waveguide layer), and then buried within the device by regrowth / epitaxy. The etching depth h of the aperture array can be selected based on the trade-off between the target radiative coupling strength and the additional scattering loss, and can be partial or deep etching.

[0061] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface-emitting laser with a structurally graded photonic crystal cladding, characterized in that, The system comprises, from bottom to top, a lower electrode (520), a substrate (490), a lower distributed Bragg mirror (480), an n-type cladding (470), an active region (440), a p-type spacer layer (430), a photonic crystal layer (420), a p-contact layer (410), and an upper electrode (510). The photonic crystal layer (420) contains a two-dimensional periodic hole array, which is divided in a plane into a central radiation region (100), a transition region (200), and an outer in-plane confinement region (300). The unit cell of the two-dimensional periodic hole array contains multiple holes, and the displacement parameter of the holes in the unit cell is defined as d. The unit cell of the central radiation region (100) adopts a first displacement parameter d. L The unit cell of the in-plane confinement region (300) adopts the second displacement parameter d. H , and d L ≠d H The displacement parameter d of the unit cell of the transition region (200) is from the first displacement parameter d. L Continuously change to the second displacement parameter d H .

2. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, The unit cell contains four holes. With the center of the unit cell as a reference point, the four holes are evenly spaced along the circumference of the reference point, and the distance from the center of each hole to the reference point is 1 / 2. d, where 0 < d < a / 2, and a is the lattice constant of the two-dimensional periodic hole array.

3. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 2, characterized in that, The second displacement parameter d H The value range is from 0.48a to 0.52a, and the first displacement parameter d L The value range is from 0.40a to 0.47a.

4. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, In the central radiation region (100), transition region (200), and outer in-plane confinement region (300), the aperture r of the two-dimensional periodic aperture array remains constant or varies by less than 10%.

5. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, The width of the transition region (200) is 3a to 20a.

6. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, The continuous change of displacement parameter d in the transition region (200) follows a linear function, a piecewise linear function, a cosine function, a hyperbolic tangent function, or a Gaussian function.

7. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, It also includes an n-type spacer layer (450) and a current limiting layer (460) disposed between the n-type cladding layer (470) and the active region (440), wherein the n-type spacer layer (450) is located above the current limiting layer (460).

8. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 7, characterized in that, The current confinement layer (460) is an oxide confinement layer, an ion implantation confinement layer, or a tunnel junction confinement layer.

9. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, The two-dimensional periodic aperture array is formed in the photonic crystal layer (420) by surface etching or buried etching processes.

10. The surface-emitting laser with a structurally graded photonic crystal cladding according to claim 1, characterized in that, The central radiation area (100) is circular, square, rectangular or elliptical in shape, and the outer confinement area (300) is a single ring or multiple ring structure surrounding the central radiation area (100).

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