Laser coupling system

Abstract

The present invention relates to a semiconductor laser coupling system. According to an example embodiment, the coupling system can include a surface emitting laser having an emission surface, a superlens integrated at the emission surface of the surface emitting laser for focusing a light beam emitted from the emission surface, and an optical fiber or an on-chip optical waveguide configured to couple with the focused light beam.

Description

Technical Field

[0001] This invention relates generally to the field of optoelectronic devices, and more particularly to a coupling device and system for an integrated superlens surface-emitting laser and an optical fiber / on-chip waveguide, which enables the miniaturization and integration of optical communication devices using semiconductor lasers. Background Technology

[0002] Optical communication is a crucial component of modern communication technology, encompassing fiber optic communication and optical chip communication. Fiber optic communication uses optical fibers as the transmission medium to transmit information in the form of light, offering numerous advantages. First, fiber optic communication boasts high transmission speeds, theoretically reaching the speed of light, far exceeding other communication technologies. Second, it offers large capacity, capable of transmitting massive amounts of information simultaneously, meeting the demands of modern society for high-volume data transmission. Furthermore, fiber optic communication is resistant to electromagnetic interference, ensuring the security and stability of information transmission. Optical chip communication is a more integrated communication method, utilizing on-chip optical waveguides as the light transmission medium.

[0003] Optical communication plays a vital role in many fields, including the internet, telephone communication, and television broadcasting. With the development of new technologies such as 5G and cloud computing, the importance of optical communication will become even more prominent. In optical communication, semiconductor lasers are widely used due to their advantages such as small size, high efficiency, low power consumption, long lifespan, and low cost. Their main function is to transmit and modulate optical signals. Transmitting optical signals is the process of converting electrical signals into optical signals, while modulating optical signals involves changing the intensity, phase, or frequency of the optical signal to transmit information through optical fibers or on-chip optical waveguides.

[0004] Currently, there are two main methods for coupling semiconductor lasers to optical fibers. The first is end-face coupling, where the emitting surface of the semiconductor laser is aligned with the input end of the optical fiber, and the optical signal is directly transmitted from the laser to the fiber. This coupling method is simple, but requires precise alignment, and due to the mode size mismatch between the laser beam and the fiber, the coupling efficiency is usually low. The other method is optical lens coupling, which adds one or more lenses between the semiconductor laser and the optical fiber to improve coupling efficiency. This coupling method is more complex than end-face coupling, but it can achieve even higher coupling efficiency. Figure 1A A schematic diagram of a semiconductor laser coupled to an optical fiber using this coupling method is shown. Figure 1A As shown, the modulated beam is output from the light-emitting surface of the semiconductor laser 101, and a lens group (containing one or more lenses) is provided in the optical path to focus the beam onto the coupling surface of the optical fiber 103.

[0005] In optical chip communication systems, there are two main coupling methods between semiconductor lasers and optical chips: surface coupling and edge coupling. Edge coupling in optical chip systems is similar to coupling semiconductor lasers to optical fibers. Due to mode mismatch, traditional semiconductor lasers, without lens groups, suffer from low efficiency when directly coupled to on-chip waveguides. Figure 1B A schematic diagram of the coupling system after adding a lens is shown. On the other hand, using surface coupling, due to the divergence angle of traditional semiconductor lasers and the second-order diffraction problem of the grating, it is generally necessary to introduce an additional optical fiber and tilt the fiber at a certain angle, such as... Figure 1C As shown.

[0006] However, while introducing lens groups into the coupling system between semiconductor lasers and fiber / on-chip waveguides can improve efficiency, it also introduces alignment and packaging challenges. Lens elements are typically much larger than the semiconductor laser chip, making it difficult to reduce the overall size of the optical module. Furthermore, to achieve the required alignment precision, the packaging process in the development and production of the optical modules' optical components needs to be precise, resulting in packaging costs accounting for a significant portion of the total cost. This, in turn, limits the ability of the coupling system to achieve greater integration and lower cost-effectiveness. Summary of the Invention

[0007] The present invention provides a laser coupling system that can solve one or more of the above-mentioned technical problems.

[0008] According to an exemplary embodiment of this application, a laser coupling system is provided, comprising: a surface-emitting laser having an emitting surface; a superlens integrated at the emitting surface of the surface-emitting laser for focusing a light beam emitted from the emitting surface; and an optical fiber or on-chip waveguide configured to couple with the focused light beam.

[0009] In one exemplary embodiment, the superlens is configured to convert a light beam emitted from the light-emitting surface into a light beam that can match the optical fiber or on-chip optical waveguide.

[0010] In one exemplary embodiment, the optical fiber is a single-mode optical fiber or a multimode optical fiber, and the on-chip optical waveguide is in an edge-coupled or surface-coupled mode.

[0011] In one exemplary embodiment, the emitted light beam is focused at one or more focal points and coupled to one or more optical fibers or on-chip optical waveguides.

[0012] In one exemplary embodiment, the surface-emitting laser includes a photonic crystal surface-emitting laser or a topological cavity surface-emitting laser.

[0013] In one exemplary embodiment, the back surface of the surface-emitting laser is used as the light-emitting surface of the surface-emitting laser, and the superlens includes a nanopillar structure or a nanopore structure formed on the back surface.

[0014] In an exemplary embodiment, the nanopillar structure includes semiconductor materials, insulating materials, metallic materials, organic materials, or transparent conductive materials.

[0015] In an exemplary embodiment, the nanostructure includes one or more of amorphous silicon, titanium dioxide, silicon nitride, silicon oxide, aluminum oxide, and hafnium dioxide; preferably, the nanopillar structure includes amorphous silicon.

[0016] In one exemplary embodiment, the nanopillar structures are arranged in a non-periodic manner, and each nanopillar structure has a height h, a length l, a width s, and a rotation angle θ. Preferably, one or more of the height h, length l, width s, and rotation angle θ of the nanopillar structures are modulated to adjust the phase, intensity, and / or polarization of the beam emitted from the surface-emitting laser.

[0017] In one exemplary embodiment, the length l ranges from 350 nm to 450 nm, and the width s ranges from 100 nm to 250 nm.

[0018] Based on some implementation methods, the coupling system of this application directly integrates a superlens on the emitting surface of a surface-emitting laser. Surface-emitting lasers can provide large-area single-mode lasers, achieving millimeter-scale aperture and watt-level output power. The superlens can control the emitted light field in any degree of freedom, such as phase, polarization, and emission angle, achieving focused output of the emitted beam without a lens. Therefore, this invention provides a possibility for simplifying and miniaturizing fiber / on-chip waveguide communication devices. Compared to traditional lasers that require lens groups for fiber / on-chip waveguide coupling, this invention directly integrates a superlens on the emitting surface of the semiconductor laser, ensuring high coupling efficiency while reducing the lens alignment steps in subsequent packaging processes, simplifying the packaging process, and further reducing device costs.

[0019] The above and other features and advantages of the present invention will become apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. Attached Figure Description

[0020] Figure 1A This is a schematic diagram of an existing semiconductor laser coupled with an optical fiber system.

[0021] Figure 1B-1C This is a schematic diagram of an existing semiconductor laser coupled with an on-chip optical waveguide.

[0022] Figure 2AThis is a schematic diagram of a semiconductor laser coupled to an optical fiber according to an exemplary embodiment of this application.

[0023] Figure 2B-2C This is a schematic diagram of a semiconductor laser coupled to an on-chip optical waveguide according to an exemplary embodiment of this application, wherein the coupling methods are edge coupling and surface coupling.

[0024] Figure 3 This is a schematic diagram of the three-dimensional spatial structure of a coupling system between a semiconductor laser and an optical fiber / on-chip waveguide according to an exemplary embodiment of this application.

[0025] Figure 4A This is a schematic diagram of the layered structure of a semiconductor laser chip module according to an exemplary embodiment of this application.

[0026] Figure 4B This is a schematic diagram of the layered structure of a semiconductor laser chip module according to another exemplary embodiment of this application.

[0027] Figure 5 This is a schematic diagram of a nanopillar structure forming a superlens according to an exemplary embodiment of this application.

[0028] Figure 6 This is a curve showing the relationship between the parameters of the nanopillar structure of the superlens and the control of the phase, wavelength, and transmittance of the emitted beam.

[0029] Figure 7 This is an electron micrograph of the nanopillar structure that forms the superlens.

[0030] Figure 8 This is a schematic diagram of the optical testing installation structure.

[0031] Figure 9 This is a schematic diagram of parameters for optical testing of a device in an exemplary embodiment of this application.

[0032] Figure 10 The tolerance test curves of the coupled system are shown. Detailed Implementation

[0033] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings, the same reference numerals generally represent the same parts or steps. Note that the drawings may not be drawn to scale.

[0034] Figure 2A A schematic diagram of a semiconductor laser coupling system with an optical fiber according to an embodiment of this application is shown. Figure 2AAs shown, the coupling system between the laser and the optical fiber includes a surface-emitting laser 210, which can be a photonic crystal surface-emitting laser (PCSEL), a topological cavity surface-emitting laser (TCSEL), or a vertical cavity surface-emitting laser (VCSEL). Its specific structure will be discussed in detail below. Preferably, the surface-emitting laser 210 is a PCSEL or TCSEL. Compared to a VCSEL, a PCSEL or TCSEL can provide a larger output surface, for example, reaching millimeter-scale aperture. Therefore, integrating a superlens 220 on a single surface-emitting laser 210 allows for manipulation of the output light field in any degree of freedom (polarization, phase, wavelength, etc.) through subwavelength-scale microstructures, and provides a well-coherent light source.

[0035] The superlens 220 (also known as a metasurface) can be directly integrated into the light-emitting surface of the surface-emitting laser 210. For example, micro- and nano-structures can be directly etched into the semiconductor layer of the emitting surface to form a superlens, or an additional superlens layer can be deposited on the light-emitting surface, and micro- and nano-structures can be etched into this superlens layer to form a superlens. Alternatively, micro- and nano-structures can be directly deposited, grown, or epitaxially grown on the light-emitting surface of the surface-emitting laser to form a superlens. In this way, the surface-emitting laser 210 and the superlens 220 form a single chip module.

[0036] As previously described, the superlens 220 can arbitrarily adjust the polarization, phase, wavelength and other parameters of the laser beam. The superlens 220 disclosed herein can focus the beam emitted from the light-emitting surface of the surface-emitting laser 210 through micro-nano structure design, thereby enabling the laser beam output to be coupled into the optical fiber / on-chip waveguide, thus eliminating the need for lens groups, additional tilted optical fibers and complex alignment steps in conventional semiconductor laser and optical fiber coupling systems.

[0037] The optical fiber 230 can be a standard single-mode fiber or a multimode fiber. By adjusting its position, the optical fiber 230 can be coupled to the beam focused by the superlens 220. For example, the coupling end face of the optical fiber can be located at the focusing focal length of the superlens, thereby achieving optical coupling between the laser beam emitted by the laser 210 and the optical fiber 230. In one embodiment, the position of the optical fiber 230 in the optical path direction of the beam can be adjusted by an adjustment device (not shown) to achieve a better or optimal coupling efficiency.

[0038] Figure 2B , 2C This diagram illustrates the structure of a coupling system between a semiconductor laser and an on-chip waveguide according to an embodiment of this application. Figure 2ASimilar to the coupling system shown, the laser-waveguide coupling system also includes a surface-emitting laser 210 with an integrated superlens 220; that is, the surface-emitting laser 210 and the superlens 220 are also formed as a single chip module. The difference lies in that the beam emitted from the emitting surface of the surface-emitting laser 210 is optically coupled to the on-chip optical waveguide 240 after being focused by the superlens 220, including edge coupling. Figure 2B ) and surface coupling method ( Figure 2C This also eliminates the need for lens groups and additional optical fibers in conventional coupling systems. In one embodiment, the on-chip optical waveguide 240 can be adjusted in position along the optical path of the beam to achieve better or optimal coupling efficiency.

[0039] In one embodiment, when the on-chip optical waveguide uses a surface coupling method, the conventional approach generally requires the introduction of additional optical fibers and tilting the fiber angle to increase coupling efficiency (see...). Figure 1B In the application embodiments, such as... Figure 2C As shown, by designing or changing the structure of the integrated superlens 220, the laser beam can be emitted at an angle, thereby enabling fiber-free on-chip coupling and reducing device size and complexity.

[0040] In one embodiment, the on-chip waveguide 240 mainly includes a substrate and a waveguide layer formed thereon, such as a planar waveguide layer or a ridged waveguide layer. This invention does not limit the specific structure of the on-chip waveguide; it is understood that various existing or future-developed on-chip waveguides can be used in conjunction with the chip module of the integrated superlens surface-emitting laser of this application for optical communication.

[0041] Figure 3A schematic diagram of the three-dimensional spatial structure of a semiconductor laser coupled to an optical fiber / waveguide according to an embodiment of this application is shown. As shown, the coupling system mainly includes a surface-emitting laser 210, a superlens 220, and an optical fiber 230 or an on-chip waveguide 240 (side-coupled or surface-coupled). In this embodiment, the surface-emitting laser 210 is, for example, a PCSEL or TCSEL laser with a size of approximately 1 mm × 1 mm, which can achieve an output beam aperture comparable to that of a VCSEL array laser module, while the thickness of the laser module can be reduced to approximately 300 μm. Therefore, the volume of the entire laser module can be reduced by more than an order of magnitude, realizing the planarization and integration of the semiconductor laser source in the laser-optical fiber / waveguide coupling system. The superlens 220 is integrated at the light-emitting surface of the surface-emitting laser 210, for example, on the back side of the surface-emitting laser 210. The superlens 220 includes a nanopillar structure formed on the back side. Multiple nanostructure units are arranged (non-)periodically on the back side of laser 210 and are distributed in a circular pattern. The optical parameters of the material are used to modulate the polarization characteristics and phase of the emitted light to achieve focusing. The focused beam is coupled into optical fiber 230 or on-chip waveguide 240, so that the data carried by the beam can be transmitted via optical pulses through optical fiber 230, or by side coupling or surface coupling and oblique focusing onto on-chip waveguide 240.

[0042] exist Figure 3 In the example, for coupling with fiber 230, the original laser spot 210 is, for example, a vector beam with a diameter of 500 μm. After passing through the superlens 220 integrated on the back, the beam is focused at a focal length of 1.9 mm, with a focused spot size of 10 μm. It is understood that this is merely an example and not a limitation. In practical applications requiring more space, such as when isolators or other components need to be added between the semiconductor laser and the fiber, a larger superlens can be integrated on the back of a surface-emitting laser with a larger mode field area (e.g., 1 mm), resulting in a longer focal length. For edge coupling with on-chip waveguide 240, the original laser spot 210 is, for example, a vector beam with a diameter of 500 μm. After passing through the superlens 220 integrated on the back, the beam is focused at a focal length of 80 μm, with a focused spot size of 500 nm, further reducing the size of the coupling system. Meanwhile, by adjusting the unit size of the superlens, the focused beam can be tilted at a set angle (e.g., 10°) and the focused spot size can be 10μm, thus achieving surface coupling of the on-chip optical waveguide. Compared with the traditional surface coupling method through optical fiber, this method greatly reduces the device size and simplifies the packaging alignment problem.

[0043] Figure 4A This is a schematic diagram of the layered structure of an integrated semiconductor laser chip module according to an exemplary embodiment of the present invention. Figure 4AAs shown, the semiconductor laser module may include a bottom electrode layer 211, a first semiconductor layer 213, an active layer 215, a second semiconductor layer 217, and a top electrode layer 219, which constitute the structure shown in Figure 2 or Figure 3 The surface-emitting laser 210 is shown. The first semiconductor layer 211 and the second semiconductor layer 217 can have different conductivity types. For example, the first semiconductor layer 211 can be an N-type doped semiconductor layer, and the second semiconductor layer 217 can be a P-type doped semiconductor layer, or vice versa, thereby injecting N-type carriers and P-type carriers into the active layer 215, respectively. For a photonic crystal surface-emitting laser (PCSEL), the active layer 215 includes a photonic crystal layer formed therein or in its vicinity (e.g., at the upper or lower surface), which includes a semiconductor material and a spatially periodic structure formed in the semiconductor material by materials of different refractive indices, such as air, wherein the air holes are arranged spatially periodically, resulting in a periodic distribution of the optical refractive index. When light propagates therein, an energy band structure is generated, and the photon frequency in the band gap is forbidden to propagate. This characteristic is used to fabricate a high-efficiency zero-threshold semiconductor laser. For a topological cavity surface-emitting laser (TCSEL), the active layer 215 similarly includes a photonic crystal layer formed therein or nearby (e.g., at the upper or lower surface). The photonic crystal supercell structure is further modulated in two independent dimensions to generate a vortex-like structural change around the cavity center of the photonic crystal cavity, thereby opening the Dirac point in the energy band of the photonic crystal supercell at its equilibrium position. Therefore, it can also be called a topological photonic crystal layer. The specific structure and principle of the topological cavity surface-emitting laser (TCSEL) can be found in the applicant's prior invention patent CN201911035379.9, and will not be described in detail here. For simplicity, in Figure 4A Only the active layer 215 is shown; a separate photonic crystal layer or topological photonic crystal layer is not shown, but it should be understood that a photonic crystal layer or topological photonic crystal layer is formed in or near the active layer 215.

[0044] Continue to refer to Figure 4A The bottom electrode layer 211 and the top electrode layer 219 can be formed of a conductive metal material. To facilitate laser emission, the top electrode layer 219 can be formed as a ring; in other embodiments, the top electrode layer 219 can also be formed as a porous structure or a mesh structure. Alternatively, when the top electrode layer 219 is formed of a transparent conductive material such as IZO or ITO, the top electrode layer 219 can also be formed as a single, continuous layer. Furthermore, the top electrode layer 219 can also include a very thin metal layer, allowing the laser to pass through the top electrode layer 219 for emission.

[0045] It should be understood that Figure 4AOnly the basic layer structures of photonic crystal surface-emitting lasers (PCSELs) and topological cavity surface-emitting lasers (TCSELs) are shown. They can also include various additional layers, such as Bragg reflector layers, buffer layers, protective layers, etc. This invention is not limited to specific structures of PCSELs and TCSELs; rather, various structures of PCSELs and TCSELs can be used as surface-emitting lasers 210 in the semiconductor laser module of this invention. It should be understood that various existing or future-developed TCSELs, as long as they can provide a near-field spot size that meets application requirements, can be applied to the chip module integrating the superlens surface-emitting laser of this application.

[0046] It is also understood that the preferred embodiments of the surface-emitting laser 210 of the present invention have been described above using PCSEL and TCSEL lasers as examples, but the present invention is not limited thereto. The surface-emitting laser 210 can also be selected as a conventional vertical cavity surface-emitting laser (VCSEL) in the art, the structure of which will not be described in detail here.

[0047] exist Figure 4A In the illustrated embodiment, since the top electrode layer 219 is formed in a ring shape, the second semiconductor layer 217 can be considered as the top layer of the surface-emitting laser 210, with its upper surface serving as the light-emitting surface of the surface-emitting laser 210. The superlens 220 can be integrated into the upper surface of the second semiconductor layer 217 (e.g., as the back surface of the surface-emitting laser 210), including a nanopillar structure formed on this surface, which will be described in detail below. In other embodiments, the top layer of the surface-emitting laser 210, i.e., the layer constituting the light-emitting surface, can be other layers, such as other semiconductor layers, or it can be an insulating protective layer, a metal layer serving as the top electrode, etc. In this case, the superlens 220 can be integrated into the upper surface of such a conductor layer, insulating protective layer, or top electrode metal layer. For example, the nanopillar structure of the superlens 220 can be formed by directly photolithography, etching, etc., on the top layer of the surface-emitting laser 210. Only a portion of the depth of the top layer can be etched, or the entire depth of the top layer can be etched without affecting the original function of the top layer.

[0048] Figure 4B This is a schematic diagram of the layered structure of an integrated semiconductor laser chip module according to another exemplary embodiment of the present invention. Figure 4B In the embodiment shown, the structure of the surface-emitting laser 210 is similar to... Figure 4AThe embodiments shown are essentially the same, including a bottom electrode layer 211, a first semiconductor layer 213, an active layer 215, a second semiconductor layer 217, and a top electrode layer 219. Repeated descriptions of these layers will be omitted here. See also... Figure 4B The semiconductor laser module also includes a top layer formed on the surface-emitting laser 210. Figure 4B The superlens layer 212 is located on the second semiconductor layer 217, wherein the nanopillar structure of the superlens 220 is formed in the upper surface of the superlens layer 212. Here, the superlens layer 212 can also be considered as part of the superlens 220. Although Figure 4B This illustration shows only a portion of the thickness of the superlens layer 212 etched to form the nanopillar structure. However, in other embodiments, the entire thickness of the superlens layer 212 can also be etched to form the nanopillar structure, meaning the superlens layer 212 and the nanopillar structure are the same layer. Figure 4B In the illustrated embodiment, the superlens layer 212 is deposited directly on the top layer of the surface-emitting laser 210; in other embodiments, a transparent interlayer may also exist between the superlens layer 212 and the top layer of the surface-emitting laser 210. Here, integrating the superlens 220 into the light-emitting surface of the surface-emitting laser means that the two are in direct or indirect contact, but there are no gaps or openings for beam expansion as in the prior art. The superlens layer 212 may include semiconductor materials, insulating materials, metallic materials, organic materials, or transparent conductive materials, etc., examples of which include, but are not limited to, one or more of amorphous silicon, titanium dioxide, silicon nitride, silicon oxide, aluminum oxide, hafnium dioxide, gold, silver, polyaniline, polypyrrole, polythiophene and poly(p-phenylene), IZO, ITO, etc. In one embodiment, in order to form a good interface with the underlying second semiconductor layer 217 to reduce reflection, the superlens layer 212 may include silicon material, such as amorphous silicon.

[0049] Apart from Figure 4B In addition to forming a superlens layer 212 first and then etching out nanopillar structures to form a superlens 220, in other embodiments, nanopillar structures can also be deposited, grown, or epitaxially grown directly on the light-emitting surface of the surface-emitting laser 210. For example, a sacrificial layer, such as a photoresist layer, can be formed on the light-emitting surface of the surface-emitting laser 210, and openings with desired patterns can be formed therein by processes such as ultraviolet lithography, electron beam lithography, or dry etching to expose the underlying light-emitting surface. Then, nanopillar structures are deposited, grown, or epitaxially grown, and finally the sacrificial layer, such as the photoresist layer, is removed, leaving the superlens 220 formed by the nanopillar structures.

[0050] In some exemplary embodiments, the superlens 220 can be directly formed on the top layer of the surface-emitting laser 210 or on the upper surface of the superlens layer 212 thereon via an etching process. Therefore, the step of forming the superlens 220 can be integrated into the process of forming the surface-emitting laser 210, and then individual surface-emitting lasers 210 can be cut out at the end. This allows for self-aligned formation of the surface-emitting laser 210 and the superlens 220 integrated thereon. In other embodiments, the top layer of the surface-emitting laser 210 can be etched after the surface-emitting laser 210 has been fabricated and individual surface-emitting lasers 210 have been cut out, or a superlens layer can be deposited and etched thereon to prepare the superlens 220. This invention avoids the need to attach a pre-prepared superlens to the surface-emitting laser 210 via a patch method, which is simpler in terms of process. Furthermore, patch bonding incurs additional packaging alignment costs, unnecessary waste in terms of volume and substrate material, and interface reflection problems.

[0051] Refer to the above Figure 4A and Figure 4B In the various embodiments described, a protective layer may also be formed on the superlens 220 to protect the nanopillar structure of the superlens 220. Such a protective layer may be formed of a transparent material and its refractive index may differ from that of the material forming the superlens 220, for example, it may be significantly greater or less than the refractive index of the material forming the superlens 220.

[0052] It should be understood that throughout this application, the nanopillar structure of the superlens 220 also encompasses the formation of nanopores, which can be considered as nanopillars formed in air or a vacuum. For example, a superlens layer 212 can be formed first, and then a nanopore structure can be etched within it. The light modulation principle of nanopores is the same as that of nanopillars, and will not be elaborated here. Therefore, when nanopillars or nanounits are mentioned in this application, they may also include nanopores.

[0053] Figure 5 This is a schematic diagram of the nanopillar structure for forming a superlens 220 according to an exemplary embodiment of the present invention. Figure 5 As shown, the superlens 220 may include rectangular nanopillar structures, but the nanopillar structures may also have other shapes, such as, but not limited to, elliptical. Multiple nanopillar structures may, for example, be arranged in a two-dimensional triangular lattice (e.g., Figure 5 The nanopillars can be arranged in a tetragonal lattice (not shown) or a periodicity of P. Each nanopillar structure can have a height h, a length l, and a width s (as shown in the left figure). Figure 5As shown in the right figure), and may also have a rotation angle θ, which refers to the rotation angle of the nanopillar structure relative to a predetermined reference direction in the two-dimensional plane of the arrangement. One or more of the height h, length l, width s, and rotation angle θ of the nanopillar structure can be modulated to adjust the phase, intensity, and / or polarization of the laser emitted from the surface-emitting laser module, thereby achieving focusing of the laser beam emitted from the laser. In one embodiment, the rectangular nanopillar structure is made of amorphous silicon (a-Si) with a refractive index of 3.34, located on the second semiconductor layer 217 formed in InP. When a beam of light travels along the z-direction (reference direction...), Figure 3 When incident on this nanopillar structure, its emitted light field With the incident light field The relationship can be represented as:

[0054]

[0055] Where t l and t S The transmittance coefficients of light polarized along the l-direction and along the s-direction. Let θ be the rotation matrix, and θ be the angle between the slow axis of the nanopillar and the predetermined x-axis direction (which is the aforementioned rotation angle θ in the XY coordinate system illustrated). In the incident light field E... in Given a specific condition, by selecting parameters l, s, and θ, this nanopillar can absorb any incident light field E under near-lossless conditions. in The emitted light field E is modulated into an arbitrary phase and polarization. out In one embodiment, the photonic crystal surface-emitting laser (PCSEL) and the topological cavity surface-emitting laser (TCSEL) used as the surface-emitting laser 220 are both single-mode lasers with defined incident phase and polarization. Therefore, combining the superlens 220 with the surface-emitting laser 210 can produce an outgoing beam with arbitrary phase and polarization.

[0056] Return to reference Figure 3 Taking a topological cavity surface-emitting laser (TCSEL) as an example, the beam emitted after passing through the resonant cavity is a radially polarized vector beam. To transmit it in, for example, a single-mode fiber 230 or an on-chip waveguide 240, the beam needs to be converted into a beam that can be efficiently matched to the fiber / on-chip waveguide. For example, the radially polarized vector light needs to be converted into linearly polarized light, while simultaneously matching the numerical aperture (NA) and mode field diameter of the single-mode fiber or on-chip waveguide. Therefore, the nanopillar structure of the superlens first needs to be designed to function as a half-wave plate. For example, the angle between the long axis of the nanopillar unit of the superlens structure and the laser polarization direction is... The polar angle between the radial vector polarization and the x-axis, and the transmission phase along the major axis. Transmission phase with short axis direction satisfy: Short-axis transmission phase It can be modulated within the 0-π range, thereby adjusting the output phase of linearly polarized light.

[0057] To prevent higher-order reflections, the arrangement period P of the nanopillar structure should be less than [value missing]. Where n InP Given the refractive index of InP, a period P of, for example, 558 nm is selected. The height h of the nanopillar is 1.5 μm. The length range of the short side s of the rectangle is chosen to be 100 nm to 250 nm, preferably 120 nm to 244 nm, and the range of the long side l is chosen to be 350 nm to 450 nm, preferably 382.7 nm to 438.4 nm. Then, the emission phase at different positions is designed according to the Fourier iteration algorithm. The correspondence between the rectangle parameters, emission intensity, and emission phase is as follows: Figure 6 As shown, its transmittance is basically over 80%, exceeding the 73% transmittance of the InP substrate itself to air, which means that the surface integration of the superlens 220 also acts as an anti-reflection coating.

[0058] The focusing characteristics of the superlens are also affected by the parameters such as s and l of the nanopillar units and the arrangement design of the nanopillars; that is, the focal length f can also be adjusted through the structural design of the nanopillars. Figure 7 This is an electron microscope (SEM) image of the nanopillar structure forming the superlens 220. This example shows a superlens structure obtained by depositing amorphous silicon on an InP substrate (e.g., the second semiconductor layer 217) and then processing it through UV exposure, electron beam lithography, and dry etching. Amorphous silicon was chosen to form the superlens due to a combination of processing difficulty and modulation efficiency considerations. However, in some embodiments, other materials can be used, or the nanopillar structure can be formed directly by etching on the top layer of the surface-emitting laser 210 (e.g., the InP semiconductor layer or the top electrode metal layer). The processing accuracy mainly depends on the etching accuracy. When the superlens 220 is formed in the top electrode metal layer, which is formed as a continuous layer, the top electrode metal layer simultaneously modulates the beam and guides the current, making the current injection more uniform. However, due to the high light absorption rate of the metal, it can affect the transmittance of the emitted beam to some extent.

[0059] like Figure 7 As shown, at a resolution of 1 μm, several adjacent nanopillar structural units in the radial direction of the metasurface have the same rotation angle. Meanwhile, at a resolution of 20 μm, the metasurface as a whole is composed of several annularly arranged nanostructural units, that is, the nanostructural units are arranged to form several circular rings. The radial period in the circular periodic arrangement can be selected as a subwavelength scale, which facilitates the control of the laser beam.

[0060] In this example, refer to Figure 3Taking the coupling of a semiconductor laser and an optical fiber as an example, the focal length f of the superlens is 1.9 mm and the diameter of the focused spot is 10 μm. According to the NA calculation formula (2), the NA of the output spot of the surface-emitting laser 210 with integrated superlens is 0.13. Its spot diameter and NA are comparable to the mode field diameter and NA of the single-mode fiber 230. Therefore, it can be optically coupled well with the fiber 230.

[0061]

[0062] It should be noted that, in this embodiment, a topological cavity surface-emitting laser with a mode field diameter of 500 μm is selected to illustrate the principle of the invention, and the corresponding focal length of the superlens is approximately 1.9 mm. In practical applications requiring larger space, such as when isolators or other components need to be added between the semiconductor laser and the optical fiber, a larger superlens can be integrated on the back of a surface-emitting laser with a larger mode field area (e.g., 1 mm), and a longer focal length can be obtained. Furthermore, in some embodiments, by adjusting the structural parameters of the metasurface, the metasurface can emit multiple focused beams, meaning the emitted beam is focused at multiple focal points, which can be coupled into multiple optical fibers or on-chip waveguides respectively.

[0063] To verify the technical advantages and application prospects of this invention, optical testing can be performed on the fabricated integrated superlens surface-emitting laser coupled to an optical fiber system. In one embodiment, the integrated optical chip can be mounted on a TO (transistor outline) base. Figure 8 A schematic diagram of the optical testing installation structure is shown. As shown in the figure, the TCSEL chip module with integrated superlens is mounted on a TO base. The single-mode optical fiber can be fixed by a clamping device on a three-dimensional displacement stage. The optical fiber and the laser chip are aligned; for example, the distance between the fiber end face and the laser chip can be adjusted to enable optical coupling, i.e., the superlens focuses the beam onto the coupling end face of the optical fiber. It is understood that those skilled in the art can also build a surface-emitting laser and on-chip waveguide coupling system for optical testing.

[0064] In this embodiment, the surface laser chip module with integrated superlens enables device miniaturization. The entire module requires only a single semiconductor chip approximately 100 micrometers thick, with the chip area determined by the diffraction limit and focusing focal length required for the application. In contrast, traditional semiconductor lasers require one or more lenses for coupling with optical fibers / waveguides, with each lens being on the order of millimeters in thickness, resulting in an overall device size also on the order of millimeters. Therefore, compared to traditional modules, the vertical thickness of the laser chip module in this invention is reduced by 1-2 orders of magnitude, and the elimination of traditional lenses also makes the entire device lighter.

[0065] Since lenses are no longer needed, the coupling system of this invention significantly reduces alignment difficulty compared to traditional coupling systems. Aligning and coupling a semiconductor laser to an optical fiber / waveguide is a precise operation, requiring ensuring the laser beam accurately enters the fiber / waveguide. In this process, lenses are used to focus the laser onto the end face of the fiber / waveguide. The general alignment process includes: first, preliminary alignment, where the semiconductor laser is placed in a fixed position, and the lens is placed in front of the laser's optical path, allowing the laser to pass through the lens. Then, the end face of the fiber / waveguide is placed near the focal point of the lens; next, fine alignment is performed, where the laser is turned on, and an optical power meter or photodiode is used to monitor the optical power coupled into the fiber / waveguide. The position of the fiber / waveguide on the three-dimensional displacement stage is then gradually adjusted until the coupled optical power reaches its maximum; finally, optimization alignment is performed, which may require repeated adjustments to the positions of the lens and the fiber / waveguide to achieve optimal coupling efficiency.

[0066] As can be seen, in the traditional coupling methods between semiconductor lasers and optical fibers / waveguides, the lens introduces new alignment uncertainties during the coupling process, complicating the packaging steps and thus increasing the cost of the packaging process. On the other hand, the aligned lens needs to be fixed to a specific location on the device using adhesive, with a tolerance of only sub-micrometers, requiring highly precise fixing equipment. However, with the use of optical devices, the adhesive used to fix the lens position may shift due to uncertainties such as temperature, causing lens displacement, optical path bending, and ultimately, optical device failure.

[0067] Unlike traditional coupling methods, in the design of this invention, a superlens is integrated directly on the back of the surface-emitting semiconductor laser. This reduces the coupling alignment steps of the lens in traditional alignment operations. Then, the best or optimal coupling efficiency can be obtained simply by adjusting the position of the fiber / waveguide. Furthermore, there will be no problem of lens displacement due to high temperature or other reasons. This can greatly reduce the packaging difficulty and reduce the cost of the entire optical module device.

[0068] The advantages of the coupling efficiency of the coupling system integrating a superlens and a surface-emitting laser of the present invention will be explained below.

[0069] Currently, the semiconductor lasers used for 1550nm / 1310nm (wavelength) optical communication are edge-emitting semiconductor lasers (DFBs). The coupling between DFBs and optical fibers / waveguides generally employs a single spherical lens, or a combination of aspherical and cylindrical lenses, depending on the specific application requirements. Single-spherical lenses are often used in applications with lower power requirements. Because the focusing effects of spherical lenses on the major and minor axes of the emitted light from an edge-emitting laser differ, single-spherical lenses can easily lead to mode field mismatch between the focused beam and the intrinsic modes of the optical fiber / waveguide. In single-spherical lens coupling systems, the coupling efficiency from the DFB to the optical fiber is typically only around 20%. In systems with higher power requirements, multi-lens modules can be used; for example, introducing aspherical lenses to correct spherical aberration can achieve a coupling efficiency of 50%. Introducing a three-lens module (two cylindrical lenses and one aspherical lens) can achieve a coupling efficiency of 80%, but as described in the alignment process analysis above, the additional lens group significantly increases alignment difficulty and leads to higher packaging costs.

[0070] Unlike DFB, in this invention, thanks to the excellent beam quality of the surface-emitting laser, a focused beam with nearly 100% matching to the single-mode fiber / waveguide mode field and NA can theoretically be obtained using only a monolithically integrated metasurface lens. Even considering that the metalens may exhibit close to 10% zero-order diffraction during actual fabrication, the final experimental efficiency can theoretically reach approximately 90%. Figure 8 The experimental setup can test the coupling efficiency of the optical chip in this embodiment. For example, a surface-emitting semiconductor laser with integrated superlens is mounted on a TO base, and a single-mode fiber is placed on a triaxial displacement stage for testing. Figure 9 (a) shows the power input-light intensity output (LI) curve of the device. Figure 9 (b) shows the spectrum of the device. By adjusting the center alignment and focal length of the single-mode fiber and the optical chip using a displacement stage, a test efficiency of 50% was finally obtained. This process does not require the introduction of any lenses. Compared with traditional systems that introduce independent lens elements, the coupling process of this embodiment is much simpler.

[0071] Figure 10 The system's tolerance for coupling in the z-axis and xy-axis directions is shown. The coupling efficiency is obtained by moving the fiber along the x / z axis and conducting tests. Figure 10 (a) shows a comparison of tolerance calculations in the x-direction between the coupling system of the present invention and a conventional DFB. Figure 10 (b) shows an experimental and computational comparison of the tolerance tests for both in the x-axis direction. Figure 10(c) shows an experimental and computational comparison of the tolerance tests for both methods in the z-axis direction. It can be seen that, compared to traditional coupling methods, this invention exhibits better coupling tolerance due to the superior beam quality of the surface-emitting laser and the elimination of the need for independent lens elements. Simultaneously, the coupling efficiency between the topological cavity surface-emitting laser (TCSEL) with integrated superlens and the optical fiber is significantly improved. Compared to coupling systems using lenses, this embodiment of the invention significantly reduces the alignment difficulty of the device while ensuring coupling efficiency, making the entire optical device more cost-effective.

[0072] According to the technical solution of this invention, a lensless fiber coupling system is designed and implemented based on a surface-emitting semiconductor laser with integrated superlens. Since no traditional lens is needed, the alignment difficulty during packaging is greatly reduced. Thanks to the integrated design, the device size is reduced in thickness by 1-2 orders of magnitude compared to traditional semiconductor laser and lens module systems. Furthermore, the optical device according to this invention emits a high-quality beam, with a mode field area and NA consistent with single-mode fiber, thereby achieving coupling efficiency superior to traditional single-lens modules.

[0073] Unless the context explicitly requires otherwise, throughout the specification and claims, the words “comprising,” “including,” “comprise,” “including,” etc., shall be interpreted in an inclusive sense, rather than an exclusive or exhaustive sense. That is, they mean “including but not limited to.” The term “connection” as commonly used herein refers to two or more elements that can be directly connected or connected via one or more intermediate elements. Furthermore, when used in this application, the terms “this,” “above,” “below,” and similar terms shall refer to the entire application and not any particular part thereof. Where the context permits, the term “or” refers to a list of two or more items, encompassing all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list.

[0074] Furthermore, unless otherwise specifically stated or otherwise understood in the context in which they are used, the conditional language used herein, such as “can,” “may,” “possibly,” “can,” “for example,” “likely,” “such as,” etc., is generally intended to express that certain embodiments include certain features, elements, and / or states, while other embodiments do not. Therefore, such conditional language is not generally intended to imply that one or more embodiments require features, elements, and / or states in any way, or that one or more embodiments must include logic for making a decision, with or without author input or prompts, that determines whether such features, elements, and / or states are included in or will be performed in any particular embodiment.

[0075] While certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of this disclosure. In fact, the novel facilities, methods, and systems described herein can be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes can be made to the form of the methods and systems described herein without departing from the spirit of this disclosure. For example, although blocks are presented in a given arrangement, alternative embodiments may perform functions similar to different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks can be implemented in a variety of different ways. Any suitable combination of elements and actions of the various embodiments described above can be combined to provide further embodiments. The appended claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of this disclosure.

[0076] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A laser coupling system, comprising: A surface-emitting laser, wherein the surface-emitting laser has a light-emitting surface; A superlens, integrated on the light-emitting surface of the surface-emitting laser, is used to focus the light beam emitted from the light-emitting surface; as well as An optical fiber or on-chip optical waveguide configured to couple with a focused beam of light.

2. The laser coupling system according to claim 1, wherein, The superlens is configured to convert the light beam emitted from the light-emitting surface into a light beam that can match the optical fiber or on-chip optical waveguide.

3. The laser coupling system according to claim 1 or 2, wherein, The optical fiber is a single-mode fiber or a multimode fiber, and / or the on-chip optical waveguide is in an edge-coupled or surface-coupled mode.

4. The laser coupling system according to claim 1 or 2, wherein, The emitted beam is focused at one or more focal points and coupled to one or more optical fibers or on-chip waveguides.

5. The laser coupling system as described in any one of claims 1 to 4, wherein, The surface-emitting laser includes a photonic crystal surface-emitting laser or a topological cavity surface-emitting laser.

6. The laser coupling system according to any one of claims 1 to 5, wherein, The back side of the surface-emitting laser is used as the light-emitting surface of the surface-emitting laser. The superlens includes a nanopillar structure or a nanopore structure formed on the back side.

7. The laser coupling system according to claim 6, wherein, The nanostructures include semiconductor materials, insulator materials, metallic materials, organic materials, or transparent conductive materials.

8. The laser coupling system according to claim 6 or 7, wherein, The nanopillar structure includes one or more of amorphous silicon, titanium dioxide, silicon nitride, silicon oxide, aluminum oxide, and hafnium dioxide. Preferably, the nanopillar structure includes amorphous silicon.

9. The laser coupling system according to any one of claims 5 to 8, wherein, The nanopillar structures are arranged in a non-periodic manner, and each nanopillar structure has a height h, a length l, a width s, and a rotation angle θ. Preferably, one or more of the height h, length l, width s, and rotation angle θ of the nanopillar structures are modulated to adjust the phase, intensity, and / or polarization of the beam emitted from the surface-emitting laser.

10. The laser coupling system according to claim 9, wherein, The length l ranges from 350 nm to 450 nm, and the width s ranges from 100 nm to 250 nm.

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