Coupling system for on-chip light source and photon chip

Abstract

The invention provides a coupling system for an on-chip light source and a photon chip. The coupling system comprises an input light source, a collimating lens, a focusing lens, a reflecting prism and an on-chip grating which are sequentially arranged in the direction of a light path, and an optical waveguide located on the side face of the on-chip grating. The collimating lens is used for primarily shaping emergent light of an input light source into a collimated light beam, the focusing lens is used for focusing the collimated light beam to the on-chip grating, and the collimating lens and the focusing lens are both aspheric plano-convex lenses. According to the system, non-uniformity caused by a large divergence angle of the semiconductor laser is effectively corrected through the aspheric micro lens, output of approximately parallel light beams is achieved, the light beams are accurately focused to the photon chip grating through the aspheric focusing lens subsequently, the coupling efficiency of light energy is greatly improved, and compared with two cylindrical lenses in the prior art, the coupling efficiency of light energy is greatly improved. The design of the focusing lens and the reflector is added, so that the number of optical elements is reduced, and error accumulation is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of on-chip integrated optical biosensor detection, and in particular relates to a coupling system for an on-chip light source and a photonic chip. Background Art

[0002] In the field of on-chip integrated optical biosensing, technological advancements are driving increasing demands for miniaturization and integration of devices. Combining photonic chips with bio-microfluidic chips can help miniaturize detection systems. Although photonic chips have already achieved on-chip manipulation of light transmission and detection, they still require a bulky external light source as an input excitation source. Using a semiconductor on-chip light source can reduce the size of the light source, but due to the inherent asymmetry of the fast and slow axis divergence angles of the semiconductor on-chip light source, two cylindrical lenses, one aligned along the fast and slow axes, are typically used to shape the laser output spot into a parallel beam. This beam is then focused by a lens onto a grating or other subsequent optical elements. Optical systems have numerous components and require high alignment accuracy. The actual assembly process is susceptible to minor errors, resulting in low efficiency.

[0003] Another type of technical solution attempts to use microlens arrays or composite microlens structures to shape the divergent light beam, but these are usually designed based on standard shapes. Standard microlenses (especially spherical microlenses) are often difficult to fully correct and compensate for high-order aberrations when faced with extremely large divergence angles, resulting in a certain divergence in the collimated light beam, thereby limiting the quality of the focused light spot and coupling efficiency.

[0004] Therefore, how to efficiently couple the semiconductor light source chip with the photonic chip to realize the integration of the entire detection system has become the key to reducing the system size and improving the system integration. Summary of the Invention

[0005] The present invention aims to provide a coupling method of an on-chip light source and a photonic chip, which is used to couple the on-chip light source with the photonic chip and realize system integration of a semiconductor laser light source and the photonic chip.

[0006] To achieve the above objectives, the present invention provides a coupling system for an on-chip light source and a photonic chip, comprising an input light source, a collimating lens, a focusing lens, a reflecting prism, and an on-chip grating arranged in sequence along the optical path, and an optical waveguide located on the side of the on-chip grating; the collimating lens is used to preliminarily shape the output light of the input light source into a collimated beam, and the focusing lens is used to focus the collimated beam onto the on-chip grating; both the collimating lens and the focusing lens are aspherical plano-convex lenses.

[0007] A substrate is provided at the bottom of the input light source, the collimating lens, the focusing lens, and the on-chip grating.

[0008] A heat sink is provided between the input light source, the collimating lens, the focusing lens and the substrate.

[0009] A reflective layer is provided between the on-chip grating and the substrate.

[0010] A buffer layer is provided between the reflective layer and the substrate.

[0011] The input light source adopts an integrated semiconductor laser chip.

[0012] The collimating lens corrects the high-order aberrations of the output light of the input light source by optimizing the surface parameters, so that the divergence angle of the collimated light beam in both the fast axis and the slow axis directions is lower than the divergence angle threshold; the aspheric focusing lens ensures that the collimated light beam is focused into a focused light spot coupled with the mode field and the on-chip grating by optimizing the surface parameters.

[0013] The surface parameters of the collimating lens and focusing lens are optimized by the following methods:

[0014] S1: Model the characteristics of the output light of the input light source;

[0015] S2: Obtain the mode field characteristics coupled to the on-chip grating;

[0016] S3: Set the optimization targets of the collimating lens and the focusing lens, and determine the reflection surface angle of the reflection prism;

[0017] S4: Establish a beam propagation model;

[0018] S5: According to the optimization target and the propagation model of the light beam, the surface parameters of the collimating lens and the focusing lens are simulated and iteratively optimized to obtain the surface parameters of the collimating lens and the focusing lens that meet the optimization target.

[0019] For the collimating lens, the optimization goal is to ensure that the divergence angle of the collimated light beam in both the fast and slow axis directions is lower than the divergence angle threshold. For the focusing lens, the optimization goal is to match the focused spot size with the on-chip grating and minimize the wavefront distortion. The reflection surface angle of the reflecting prism is determined based on the incident angle coupled by the matching on-chip grating.

[0020] The coupling system for on-chip light sources and photonic chips of the present invention utilizes aspheric microlenses to effectively correct the non-uniformity caused by the large divergence angle of the semiconductor laser, achieving the output of a nearly parallel light beam, which is then precisely focused onto the photonic chip grating through an aspheric focusing lens, greatly improving the coupling efficiency of light energy. Compared with the design of two cylindrical lenses in the prior art, the design of a focusing lens and a reflector reduces the number of optical components and reduces error accumulation. In addition, according to the characteristics of different input light sources, such as different output light mode field distributions and different wavelengths of different laser chips, the optical path parameters can be optimized in a targeted manner, including optimizing the surface parameters of the collimating lens and the focusing lens, to achieve efficient coupling of the incident light into the grating, with better versatility and flexibility. In addition, the additional reflective layer at the bottom of the grating can reflect more incident light and couple it into the waveguide, thereby improving the coupling efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of a system for coupling an on-chip light source and a photonic chip;

[0022] Figure 2 Schematic diagram of the reflection surface angle of the reflecting prism.

[0023] Figure 3 This is the design diagram for the optical path simulation of the coupling system.

[0024] Figure 4A is the light field distribution diagram of the outgoing light of the incident light source, Figure 4B It is the mode field distribution diagram of the light spot reaching the on-chip grating surface.

[0025] Figure 5 This is the optimization result of the grating coupler coupling efficiency.

[0026] The reference numerals are as follows:

[0027] 101 is a substrate; 201 is a heat sink; 301 is an input light source; 401 is a collimating lens; 501 is a focusing lens; 601 is a reflecting prism; 701 is an on-chip grating; 801 is an optical waveguide; 901 is a reflecting layer; and 902 is a buffer layer. DETAILED DESCRIPTION

[0028] The coupling system for an on-chip light source and a photonic chip of the present invention is mainly based on the following principles:

[0029] By introducing a microlens with an aspheric structure, the semiconductor laser chip's widely diverging light spot is initially shaped, transforming it into a nearly parallel, collimated beam. Subsequently, another optimized aspheric lens is used to focus the collimated beam, forming a focused spot suitable for matching the photonic chip's grating structure. By introducing both an aspheric collimating microlens and an aspheric focusing microlens, this invention reduces the alignment accuracy requirements to a certain extent. This invention can optimize the parameters of various components in the optical path system based on the mode field characteristics of different light sources, thereby improving coupling efficiency.

[0030] like Figure 1 As shown in FIG. 1 , a coupling system for an on-chip light source and a photonic chip according to the present invention includes an input light source 301, a collimating lens 401, a focusing lens 501, a reflecting prism 601, and an on-chip grating 701, which are sequentially arranged along the optical path, and an optical waveguide 801 located on the side of the on-chip grating 701. The on-chip grating 701 is a grating structure provided on the photonic chip and is used to couple incident light into the chip.

[0031] A substrate 101 is located beneath the input light source 301, collimating lens 401, focusing lens 501, and on-chip grating 701. A heat sink 201 is located between the input light source 301, collimating lens 401, focusing lens 501, and substrate 101 to improve heat dissipation. A reflective layer 901 is located between the on-chip grating 701 and substrate 101 to improve coupling efficiency. A buffer layer 902 is located between the reflective layer 901 and substrate 101 to enhance the mechanical strength of the reflective layer 901.

[0032] The heat sink 201 and the input light source 301 are both connected to an external driving circuit to control the light emission and heat dissipation of the input light source 301 .

[0033] The input light source 301 uses an integrated semiconductor laser chip (e.g., an edge-emitting laser or a DFB laser). The characteristic of a semiconductor laser light source chip is that the emitted light has a large divergence angle in the fast axis direction (the fast axis divergence angle reaches 30 degrees), while the slow axis divergence angle is relatively small (about 2-5 degrees), forming an asymmetric large divergence angle spot mode field.

[0034] The collimating lens 401 is used to initially shape the output light of the input light source 301 into a nearly parallel collimated beam. The focusing lens 501 is used to focus the collimated beam onto the on-chip grating 701 (ie, the grating coupling region on the surface of the photonic chip).

[0035] Therefore, if Figure 3As shown, the output light of the input light source 301 passes through the collimating lens 401 and propagates to the focusing lens 501 as parallel light, is focused by the focusing lens 501 to reduce the spot size, and finally passes through the reflecting prism 601 to propagate to the on-chip grating 701, so that the light beam is coupled into the optical waveguide 801 by grating diffraction when passing through the on-chip grating 701. Figure 4A is the light field distribution diagram of the outgoing light of the incident light source, Figure 4B is the mode field distribution diagram of the light spot reaching the surface of the on-chip grating.

[0036] Both the collimating lens 401 and the focusing lens 501 are aspheric plano-convex lenses. The collimating lens 401 uses optimized surface parameters to correct for higher-order aberrations of the output light from the input light source 301, reducing the divergence angle of the output collimated light beam in the fast axis direction. This ensures that the divergence angle of the collimated light beam in both the fast and slow axis directions is below a divergence angle threshold. It is generally believed that the smaller the divergence angle, the better the collimation. For example, the divergence angle threshold can be 1°. The aspheric focusing lens uses optimized surface parameters to ensure that the collimated light beam is focused into a focused spot that couples the mode field with the on-chip grating 701.

[0037] The formula for the surface parameters of the convex surface of an aspheric plano-convex lens is:

[0038]

[0039] Where z(r) is the height of the convex surface of the aspheric plano-convex lens in the direction of the optical axis; r is the radial distance; R is the vertex curvature radius; k is the eccentricity (ellipsoid, parabola, hyperbola, etc.); A n is the high-order aberration correction coefficient.

[0040] The surface parameters of the collimating lens 401 and the focusing lens 501 are optimized by the following methods:

[0041] Step S1: Modeling the characteristics of the output light of the input light source 301;

[0042] Among them, the mode field distribution (Gaussian beam parameters) of the laser output beam is obtained, such as M 2 Factor, fast and slow axis divergence angle.

[0043] Step S2: obtaining the mode field characteristics coupled by the on-chip grating 701;

[0044] The coupled mode field characteristics of the on-chip grating 701 are obtained by measurement or simulation modeling.

[0045] The relationship between the mode field of the light beam and the parameters of the on-chip grating 701 is coupled and matched from two aspects.

[0046] On the one hand, the incident angle of the light beam needs to meet the grating coupling condition, as shown in formula (2):

[0047]

[0048] Among them, n eff is the effective refractive index of the optical waveguide; n in is the refractive index of the incident medium; θ is the incident angle of the light beam; m is the diffraction order (usually ±1); λ is the operating wavelength; and P is the grating period.

[0049] On the other hand, the mode field size is related to the grating area and must meet the following matching conditions:

[0050] w beam =w grating ,

[0051] Among them, w beam is the diameter of the beam mode field, w grating is the effective area width of the grating.

[0052] Therefore, the present invention can adjust the reflecting prism 601 to adjust the incident angle of the light beam. The reflecting prism 601 only changes the propagation direction of the light and does not affect the spot size. A focusing lens 501 is also provided, and the focusing lens 501 is used to further focus the collimated light beam into a smaller spot to facilitate efficient coupling of the grating.

[0053] In addition, the duty cycle and period of the grating affect the grating diffraction angle, which in turn affects the coupling efficiency, and the optimal value needs to be obtained through simulation optimization.

[0054] Step S3: setting the optimization targets of the collimating lens 401 and the focusing lens 501, and determining the reflection surface angle of the reflection prism 601;

[0055] For collimating lens 401, the optimization goal is to ensure that the divergence angle of the collimated light beam in both the fast and slow axes is below the divergence angle threshold. For focusing lens 501, the optimization goal is to ensure that the focused spot size matches the on-chip grating 701 and that the wavefront distortion is minimized, thereby achieving high coupling efficiency. The angle of the reflecting surface of reflecting prism 601 is determined based on the incident angle coupled by on-chip grating 701. This allows focusing lens 501 to coordinate with on-chip grating 701 to meet the mode field characteristics coupled by on-chip grating 701.

[0056] Step S4: establishing a light beam propagation model;

[0057] The propagation model of the light beam uses the Gaussian beam propagation formula or the wave optics model, and is then iteratively optimized in conjunction with the surface parameters of the collimating lens 401 and the focusing lens 501 .

[0058] Step S5: According to the optimization target and the propagation model of the light beam, the surface parameters of the collimating lens 401 and the focusing lens 501 are subjected to software simulation and iterative optimization to obtain the surface parameters of the collimating lens 401 and the focusing lens 501 that meet the optimization target.

[0059] In this embodiment, software such as Zemax, COMSOL, and CodeV are used to perform optical path simulation and curvature optimization of the complete system.

[0060] In summary, the present invention effectively overcomes the problems of high alignment accuracy and many components in traditional optical systems through the following structural innovations, thereby improving the beam coupling efficiency: (1) Simplified structural design: The core optical system only contains two aspheric lenses (collimating lens and focusing lens) and a reflecting prism. The aspheric microlens is used to effectively correct the unevenness caused by the large divergence angle of the semiconductor laser, achieving the output of a nearly parallel beam. Subsequently, the aspheric focusing lens is used to accurately focus the beam onto the photonic chip grating, greatly improving the coupling efficiency of light energy. Compared with the design of two cylindrical lenses, one focusing lens and one reflector in the prior art, the number of optical components is reduced and the error accumulation is reduced. (2) Aspheric lens design: Through the specially designed aspheric curvature, the lens has the ability to correct high-order aberrations and can shape a laser beam with a large divergence angle into a nearly parallel beam, thereby improving the alignment tolerance and reducing the difficulty of system alignment. Based on the characteristics of different input light sources, such as different output light mode field distributions and different wavelengths of different laser chips, the optical path parameters can be optimized specifically, including the surface parameters of the collimating lens and focusing lens, to achieve efficient coupling of the incident light into the grating, with better versatility and flexibility. (3) Grating integrated reflection layer design: Adding a reflection layer to the bottom of the grating improves the coupling efficiency of the light beam into the waveguide, which can reflect and couple more incident light into the waveguide, improving the system coupling efficiency.

[0061] Compared to traditional systems using two cylindrical lenses and a focusing lens, this invention optimizes the optical path design and reduces the number of optical components, resulting in a more compact coupled optical system with improved error tolerance. Furthermore, the aspheric lens offers strong aberration correction capabilities, maintaining high beam shaping and focusing performance even with minor installation errors.

[0062] The present invention is not only applicable to traditional photonic chips such as silicon-based and silicon nitride-based chips, but also to various emerging photonic integration platforms. It can be widely used in multiple fields such as laser communication, optical interconnection, and optical sensing, meeting the various requirements of modern photonic integration technology for high coupling efficiency and miniaturization.

[0063] Experimental results:

[0064] 1.Optimization of optical path parameters:

[0065] Based on the light divergence angle characteristics and emission wavelength of light source 301, optical simulation software is first used to optimize the parameters of each component of the optical path system, including the aspheric collimating lens 401, aspheric focusing lens 501, prism 601, and on-chip grating 701 parameters (including grating period, duty cycle, and incident angle). This ensures that the light spot mode field after passing through the microlens optical path matches the grating size and obtains the best coupling efficiency. A semiconductor laser chip with a fast-axis divergence angle of 30 degrees, a slow-axis divergence angle of 2 degrees, and an operating wavelength of 638nm is used as the optimization object. The optimized collimating lens 401 has a radius of 3.1mm, a center thickness of 2mm, and is made of K9 glass. Specifically, the even-order aspheric parameters corresponding to formula (1) are A4=3.05×10 -4 ,A6=-1.214×10 -5 , A8=7.362×10 -7 The radius of the focusing lens 501 is 2.6 mm, the center thickness is 5.93 mm, and the material is K9 glass. Specifically, the even-order aspheric parameters corresponding to formula (1) are A4 = 2.273 × 10 -4 ,A6=-3.365×10 -5 , A8=9.302×10 -7 The reflecting surface angle θ of the reflecting prism 601 is 40 degrees, and the reflecting surface angle θ is the angle between the reflecting surface and the horizontal plane. Figure 2 As shown, the purpose is to allow the collimated and focused light beam to enter the bottom on-chip grating 701 at a 10-degree tilt angle; the period of the on-chip grating 701 is 440nm, the duty cycle is 0.572, and the optimal tilt angle of the incident light is 10 degrees. Figure 5 As shown, the grating coupling efficiency is approximately 45% at a wavelength of 638nm. The optimized lens assembly optical path achieves a beam shaping transmission efficiency of approximately 26.8%, and a grating coupling efficiency of approximately 45%. Therefore, the total coupling efficiency from the light source to the photonic chip is 12%. Individual components are customized based on these optimized parameters. Precision micromachining, laser processing, or injection molding can be used in the fabrication of aspheric microlenses to achieve high-precision aspheric curvature, ensuring stable and reliable initial beam shaping.

[0066] 2. Light source installation

[0067] The input light source 301 is a semiconductor laser chip, which is mounted on the heat sink 201 in the form of a bare chip, and the light emission and heat dissipation of the input light source 301 are controlled by an external driving circuit.

[0068] 3. Optical component installation

[0069] The prepared optical components, including the collimating lens 401, focusing lens 501, and reflecting prism 601, are sequentially installed and the optical path is adjusted to ensure that the reflected light spot after passing through prism 601 matches the grating size and position to achieve maximum coupling efficiency. Subsequently, a high-precision packaging process is used to secure the relative positions of all components in the coupling system for on-chip light sources and photonic chips. The heat sink 201 utilizes aluminum nitride, a low-thermal expansion material, for rapid heat conduction and stable support. The substrate 101 is made of Invar alloy, a low-thermal expansion material. Thus, the combination of low-thermal expansion materials and high-precision packaging ensures that the system maintains high coupling efficiency and long-term stability under operating temperature and mechanical vibration conditions.

Claims

1. A coupling system for an on-chip light source and a photonic chip, characterized in that: It includes an input light source, a collimating lens, a focusing lens, a reflecting prism and an on-chip grating arranged in sequence along the optical path, as well as an optical waveguide located on the side of the on-chip grating; the collimating lens is used to initially shape the output light of the input light source into a collimated beam, and the focusing lens is used to focus the collimated beam onto the on-chip grating. Both the collimating lens and the focusing lens are aspherical plano-convex lenses.

2. The coupling system for an on-chip light source and a photonic chip according to claim 1, characterized in that: A substrate is provided at the bottom of the input light source, the collimating lens, the focusing lens, and the on-chip grating.

3. The coupling system for an on-chip light source and a photonic chip according to claim 2, characterized in that: A heat sink is provided between the input light source, the collimating lens, the focusing lens and the substrate.

4. The coupling system for an on-chip light source and a photonic chip according to claim 2, wherein: A reflective layer is provided between the on-chip grating and the substrate.

5. The coupling system for an on-chip light source and a photonic chip according to claim 4, characterized in that: A buffer layer is provided between the reflective layer and the substrate.

6. The coupling system for an on-chip light source and a photonic chip according to claim 1, characterized in that: The input light source adopts an integrated semiconductor laser chip.

7. The coupling system for an on-chip light source and a photonic chip according to claim 1, characterized in that: The collimating lens corrects the high-order aberrations of the output light of the input light source by optimizing the surface parameters, so that the divergence angle of the collimated light beam in both the fast axis and the slow axis directions is lower than the divergence angle threshold; the aspheric focusing lens ensures that the collimated light beam is focused into a focused light spot coupled with the mode field and the on-chip grating by optimizing the surface parameters.

8. The coupling system for an on-chip light source and a photonic chip according to claim 7, characterized in that: The surface parameters of the collimating lens and focusing lens are optimized by the following methods: Step S1: Modeling the characteristics of the output light of the input light source; Step S2: obtaining the mode field characteristics coupled to the on-chip grating; Step S3: setting the optimization targets of the collimating lens and the focusing lens, and determining the reflection surface angle of the reflection prism; Step S4: establishing a light beam propagation model; Step S5: According to the optimization target and the propagation model of the light beam, the surface parameters of the collimating lens and the focusing lens are subjected to software simulation and iterative optimization to obtain the surface parameters of the collimating lens and the focusing lens that meet the optimization target.

9. The coupling system for an on-chip light source and a photonic chip according to claim 8, characterized in that: For the collimating lens, the optimization goal is to ensure that the divergence angle of the collimated light beam in both the fast and slow axis directions is lower than the divergence angle threshold. For the focusing lens, the optimization goal is to match the focused spot size with the on-chip grating and minimize the wavefront distortion. The reflection surface angle of the reflecting prism is determined based on the incident angle coupled by the matching on-chip grating.

Images