Optical engine, optical module, optical system and FA structure suitable for optical chip coupling

Abstract

The present invention provides an optical engine, an optical module, and an optical system and FA structure suitable for optical chip coupling. The optical engine includes a laser, a collimating lens, a converging lens, an isolator, and an optical chip arranged in sequence along the optical path. The collimating lens is used to collimate the laser emitted by the laser; the converging lens is used to converge the output light of the collimating lens, and the output light of the converging lens is coupled into the input light coupler of the optical chip after passing through the isolator, and the output light coupler of the optical chip is coupled with the optical fiber array of the FA structure. The FA structure includes an optical fiber array and a pigtail, the pigtail adopts a single-mode optical fiber, and the optical fiber array adopts a small-mode optical fiber. The single-mode optical fiber of the pigtail is fused with the small-mode optical fiber of the optical fiber array, and the end face of the small-mode optical fiber of the optical fiber array is coated with a 56nm-60nm anti-reflection film. The present invention improves the overall system coupling efficiency of the optical engine, greatly reduces the length of the entire optical engine while meeting a high coupling efficiency, and greatly improves the optical output power, return loss and other performances of the silicon photonic solution module.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to an optical engine, an optical module, and an optical system and FA structure suitable for optical chip coupling. Background Art

[0002] In recent years, with the continuous development of optical modules in the field of optical communications, the integration technology of micro-nanoscale information devices with photons as carriers has attracted much attention and has been gradually applied to real-life scenarios. The high-precision optimized integration of optical chips has provided more possibilities for the miniaturization and high-performance design and spatial placement of other optical devices. Among them, how to use optical waveguides to collect external free-space light beam information has become one of the core exploration directions of experts in the field, namely, high-efficiency optical coupling technology based on mode field adaptation.

[0003] According to the design concept of integrated devices inside optical chips, in order to realize multi-channel information transmission, reduce the difficulty of silicon substrate integration and improve optical coupling efficiency, optical chips generally use MMI to achieve one-to-four, one-to-eight and other similar splitting forms, which directly determines the power selection of the laser, and designs different types of end couplers and mode spot converters on the chip to reduce coupling losses in space. However, the loss caused by mode field mismatch cannot be ignored. Among them, the loss caused by the size mismatch between the optical fiber used for optical communication and the mode spot diameter of the optical chip is the most serious.

[0004] The light beam after being transmitted through the optical chip waveguide and processed by the internal modulator still needs to be received by the outside world. Generally, a chip on board packaging solution (Chip on Board) is adopted, and the end face coupler of the multi-channel optical chip is horizontally coupled in the form of a fiber array (FA). However, since single-mode optical fiber is generally used for medium and long-distance transmission in the field of optical communications, its NA is between 0.11 and 0.14, which leads to a limited light receiving range of the FA that is horizontally coupled to the optical chip coupler. In addition, due to the constraints of the mode field matching principle, the alignment of the axes of light is a prerequisite for coupling. The energy loss caused by these factors has always been an important topic of discussion in the early stage of optical development. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes an optical engine, an optical module, and an optical system and FA structure suitable for optical chip coupling.

[0006] The technical solution of the present invention is implemented as follows: The present invention discloses an optical system suitable for coupling with a silicon photonic chip, comprising a collimating lens and a converging lens arranged between a laser and an optical chip, wherein the collimating lens is used to collimate the laser emitted by the laser, and the converging lens is used to converge the output light of the collimating lens.

[0007] In some embodiments, the collimating lens has a numerical aperture NA∈(0.5, 0.65);

[0008] Or / and, the thickness of the collimating lens is t∈(0.7,0.84) mm;

[0009] Or / and, the numerical aperture NA∈(0.17,0.2) of the converging lens;

[0010] Or / and, the thickness of the converging lens is t∈(0.62,0.75) mm;

[0011] Or / and, the NA corresponding to the far-field divergence angle of the laser is always smaller than the NA corresponding to the incident surface of the collimating lens;

[0012] Or / and, the incident surface of the collimating lens is a first aspheric surface, the exit surface of the collimating lens is a second aspheric surface, the curvature radius of the first aspheric surface is (1.416±3%) mm, the curvature radius of the second aspheric surface is (-0.503±3%) mm, the cone coefficient of the first aspheric surface is -38.671, and the cone coefficient of the second aspheric surface is -1.769; the incident surface of the converging lens is a third aspheric surface, the exit surface of the converging lens is a fourth aspheric surface, the curvature radius of the third aspheric surface is (1.194±3%) mm, the curvature radius of the fourth aspheric surface is (-6.417±3%) mm, the cone coefficient of the third aspheric surface is -0.825, and the cone coefficient of the fourth aspheric surface is 18.635.

[0013] In some embodiments, the numerical aperture NA of the collimating lens is 0.6, and the numerical aperture NA of the converging lens is 0.17.

[0014] The optical system suitable for silicon photonic chip coupling of the present invention also includes an isolator located between the converging lens and the photonic chip. The outgoing light of the converging lens is coupled into the light input coupler of the photonic chip after passing through the isolator.

[0015] The present invention also discloses an FA structure suitable for silicon photonic chip coupling, comprising an optical fiber array and a pigtail, wherein the pigtail adopts a single-mode optical fiber, and the optical fiber array adopts a small-mode optical fiber. The single-mode optical fiber of the pigtail is fused with the small-mode optical fiber of the optical fiber array, and the optical fiber end face of the optical fiber array is coated with an anti-reflection film.

[0016] In some embodiments, the small mode optical fiber is a high numerical aperture optical fiber;

[0017] Or / and, the film thickness of the antireflection film is positively correlated with the application range of the working wavelength;

[0018] Or / and, the thickness of the antireflection film is 56nm-60nm, and the working wavelength is 1304.5nm-1317.5nm.

[0019] In some embodiments, the numerical aperture of the small mode optical fiber is 0.28.

[0020] In some embodiments, an angle is set between the optical fiber end face of the optical fiber array and the vertical plane, forming an upper end inclined surface with an angle of 8°±0.1°.

[0021] In some embodiments, the small-mode optical fiber is fixed between the V-groove substrate and the lower cover plate, and a horizontal spacing L along a first direction is provided between the end face of the lower cover plate close to the optical chip and the optical fiber end face of the optical fiber array. The first direction is parallel to the laser emission direction of the laser, and the minimum value of the horizontal spacing L is 0.28 to 0.31 mm.

[0022] The present invention also discloses an optical engine, including an optical chip, a laser and the FA structure as described above, wherein the optical system as described above is arranged between the optical input coupler of the optical chip and the laser, and the optical output coupler of the optical chip is coupled to the optical fiber array of the FA structure.

[0023] In some embodiments, the laser, collimating lens, converging lens, isolator, optical chip and FA structure are all mounted on a substrate, and the center line spacing between the laser light emitting end face and the optical chip light input coupler is 0.01 mm to 0.015 mm.

[0024] The present invention also discloses an optical module, which adopts the optical engine as described above.

[0025] The present invention has at least the following beneficial effects: the dual-lens optical system designed by the present invention can be applied to DFB lasers with fast and slow axis divergence angles of 18° to 27° @ FWHM in the field of optical communications, with an optical simulation coupling efficiency of 83% to 96%, and a practical application coupling efficiency of about 90%. At the same time, the length of the entire optical engine is greatly reduced while meeting a high coupling efficiency, and the shortest optical path length is only 3.7 mm, which not only reduces the manufacturing and processing costs of the tungsten copper substrate and the fiber array, but also frees up a lot of space for the digital analog circuit design and wiring layout in the early stage of PCBA.

[0026] The present invention also proposes a specially designed and practically applied coated small-mode FA, which is not only compatible with the two structural designs of single-mode and small-mode couplers at the output end of the optical chip, but also has a higher end face coupling efficiency than the single-mode FA conventionally used in the industry. At the same time, due to the coating on the end face of the optical fiber, the low return loss phenomenon at the fiber fusion point of the single-mode optical fiber and the small-mode optical fiber is solved. The actual return loss after coating is the same as that of the single-mode optical fiber, which greatly improves the optical output power, return loss and other performances of the silicon photonic solution module.

[0027] After the silicon wafer is cut, there will generally be a 20um to 40um cutting groove left. Correspondingly, there is such a gap between the FA fiber end face and the chip coupler waveguide, which will cause a loss of 6dB to 8dB. Therefore, in this structure, the lower cover plate will be retreated by 0.3mm, and the upper cover plate and the optical fiber will be simultaneously ground into an 8° up and down slope during the manufacturing process. This not only ensures that the optical fiber and the coupler waveguide are in full contact, with a gap of only about 5um, and a coupling efficiency of about 70%, but also due to the effect of the anti-reflection film, the module-level return loss is ultimately 35dB to 40dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of the structure of an optical system suitable for coupling with a silicon photonic chip provided by an embodiment of the present invention;

[0029] Figure 2 This is a diagram for analyzing the physical optics coupling efficiency;

[0030] Figure 3 It is a spot diagram, which is used to analyze the light spot reaching the receiving surface. It mainly analyzes whether the light spot passing through the lens system is within the diffraction limit and the light distribution.

[0031] Figure 4 A schematic diagram of the optical path of an optical system suitable for coupling with a silicon photonic chip provided by an embodiment of the present invention;

[0032] Figure 5 This is an enlarged picture of the light reaching the image plane after being deflected by the isolator, which mainly provides guidance for LD and chip bonding work;

[0033] Figure 6 A schematic diagram of coupling an FA structure suitable for coupling a silicon photonic chip and an optical chip output light coupler provided by an embodiment of the present invention;

[0034] Figure 7 It is a comparison chart of the coupling data of the FA of two structures and the optical couplers of two structures;

[0035] Figure 8 A schematic diagram of the structure of a light engine provided by an embodiment of the present invention;

[0036] Fig. 9 A schematic diagram of a FA structure provided by an embodiment of the present invention;

[0037] Fig.10 This is a comparison chart of the return loss values ​​of the small-mode FA array before and after coating;

[0038] Fig.11 A schematic diagram of the important optical parameter table of the dual-lens system.

[0039] In the accompanying drawings, 1 is a substrate, 2 is an optical chip, 2a is an input light coupler, 2b is an output light coupler of the optical chip, 3 is a collimating lens, 4 is a converging lens, 5 is a laser, 6 is an isolator, 7 is an optical fiber array, 71 is a V-groove substrate, 72 is a lower cover plate, 73 is a small-mode optical fiber, 74 is a bevel, and 8 is a pigtail. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0041] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one", "one" or "the" do not indicate quantity restrictions, but indicate that there is at least one. Similar words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described target changes, the relative positional relationship may also change accordingly.

[0042] In each of the accompanying drawings, identical elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not all drawn to scale. In addition, some well-known parts may not be shown in the drawings.

[0043] Many specific details of the present invention are described below, such as component structures, materials, dimensions, processing techniques and technologies, in order to more clearly understand the present invention. However, as those skilled in the art will appreciate, the present invention may be implemented without following these specific details.

[0044] The present invention discloses a coupling technology of silicon photonic chips and laser diodes in optical modules in the field of optical communications, which involves a double-lens high-efficiency coupling and isolator-assembled anti-reflection compatibility system in which a DFB laser Gaussian beam enters a single-mode and small-mode coupler of a silicon photonic chip. The system length and the working distance between devices can be reasonably adjusted according to the parameters of the optical chip mode spot converter (coupler), and the waveguide of the light output coupler is end-face coupled by using a fiber array with a special structure after internal modulation of the chip, thereby improving the coupling efficiency and the anti-reflection performance of the module, and meeting the relevant technical requirements of the integrated optical chip technology in the field of optical fiber communications.

[0045] Embodiment 1

[0046] like Figure 1 As shown, this embodiment discloses an optical system suitable for coupling with a silicon photonic chip, including a collimating lens 3 and a converging lens 4 arranged between a laser 5 and an optical chip 2, wherein the collimating lens 3 is used to collimate the laser emitted by the laser, and the converging lens 4 is used to converge the output light of the collimating lens.

[0047] The optical system for coupling silicon photonic chips of the present invention also includes an isolator 6 located between the converging lens and the photonic chip. The outgoing light of the converging lens 4 is coupled into the optical coupler 2a of the photonic chip 2 after passing through the isolator 6. Isolator: allows unidirectional light to pass through, provides anti-reflection performance, has an isolation of 35dB, low forward insertion loss, reduces signal interference, and ensures the safety of light transmission. The laser, collimating lens, converging lens, isolator and photonic chip are arranged in sequence along the optical path.

[0048] In some embodiments, the numerical aperture NA∈(0.5, 0.65) of the collimating lens 3, and the thickness t∈(0.7, 0.84) mm of the collimating lens 3; the numerical aperture NA∈(0.17, 0.2) of the converging lens 4; and the thickness t∈(0.62, 0.75) mm of the converging lens 4.

[0049] In some embodiments, the NA corresponding to the far-field divergence angle of the laser is always smaller than the NA corresponding to the incident surface of the collimating lens.

[0050] In some embodiments, the collimating lens includes a lens base, one side of the lens base is provided with an incident surface, and the other side of the lens base is provided with an exit surface. Light is incident from the incident surface of the collimating lens and is emitted from the exit surface of the collimating lens. The converging lens includes a lens base, one side of the converging lens is provided with an incident surface, and the other side of the converging lens is provided with an exit surface. Light is incident from the incident surface of the converging lens and is emitted from the exit surface of the converging lens.

[0051] The incident surface of the collimating lens is a first aspheric surface, the exit surface of the collimating lens is a second aspheric surface, the curvature radius of the first aspheric surface is (1.416±3%) mm, the curvature radius of the second aspheric surface is (-0.503±3%) mm, the cone coefficient of the first aspheric surface is -38.671, and the cone coefficient of the second aspheric surface is -1.769; the incident surface of the converging lens is a third aspheric surface, the exit surface of the converging lens is a fourth aspheric surface, the curvature radius of the third aspheric surface is (1.194±3%) mm, the curvature radius of the fourth aspheric surface is (-6.417±3%) mm, the cone coefficient of the third aspheric surface is -0.825, and the cone coefficient of the fourth aspheric surface is 18.635.

[0052] During the optimization process, in order to correct spherical aberration, improve image quality, and make the beam waist of the light spot closer to the receiving surface, the collimating lens and the converging lens are given appropriate aspheric coefficients, up to the 6th order, so that more light energy can be concentrated on one point.

[0053] The above-mentioned silicon photonics solution uses an external laser, a dual-lens system, and an optical chip coupler structure. It is necessary to reduce the size of the Gaussian beam waist W0 as much as possible through the lens system to concentrate its energy while meeting the mode field radius of the chip coupler. However, since the divergence angle θ of the fast and slow axes of the laser itself is different, and as the current increases, the divergence angle θ will also have a corresponding range of variation, and the beam waist W0 will also change accordingly, the design of the dual lens needs to consider factors such as mode field adaptation, reasonable NA design, defocus and spherical aberration correction.

[0054] The working principle of the upper optical end Lens system of the present invention is analyzed as follows:

[0055] For the mode field parameters (single-mode mode field 9.2um, small-mode mode field 4.8um) of the DFB laser with divergence angle (fast axis 22°~27°, slow axis 18°~22°, FWHM) and the silicon photonic chip coupler 2a, optical simulation software is used to perform tolerance analysis to determine the system length, working distance between devices, and center deviation of the optical axis direction under the best coupling efficiency, and then packaging work is carried out, such as Figure 1 shown.

[0056] The numerical aperture NA value of the collimating lens 3 designed by the present invention is ∈ (0.5, 0.65), and its thickness t∈

[0057] (0.7,0.84)mm, which can meet the fast and slow axis divergence angles of most lasers in the optical communication market, that is, the NA corresponding to the far-field divergence angle of the laser is always smaller than the NA corresponding to the first surface of the first lens. In the collimation and shaping stage, more light will be collected to avoid energy loss. The converging lens 4NA∈(0.17,0.2), t∈

[0058] (0.62, 0.75) mm, the collimating lens 3NA0.6 and the converging lens 4NA0.17 used after the actual mold opening, the optical coupling efficiency of the laser 5 to the chip input optical coupler 2a through the optical system can be 83% to 96%. If the optical chip input (Input) coupler adopts a single-mode structure, that is, the mode field diameter is about 9.2um, the coupling efficiency is as high as 94%. The input adopts a small-mode coupler, and the waveguide XY mode field diameter of the optical chip of the present invention is 4.7um and 4.8um. ​​After adjusting the working distance between each device, the coupling efficiency is about 91% to 92%. Figure 2As shown, the beam waist diameter of the light spot passing through the optical emitting component is 6.4um and 5.3um in the X and Y directions respectively. The laser, optical chip and isolator are mounted on the tungsten copper substrate using silver glue according to the simulation tolerance data. To ensure the tolerance stability of the optical path and lens coupling and the glue thickness of 50um to 70um, the thickness machining tolerance of the part of the substrate that carries the optical system needs to be ±0.01mm. Based on the optical path simulation and the deflection effect of the isolator on light propagation, the center line spacing between the laser light-emitting end face and the silicon photonic chip optical coupler during the mounting process needs to be 0.01mm to 0.015mm to ensure that the light emitted from the optical component can enter the optical coupler normally after being deflected by the isolator. The optical path is as follows Figure 4 , Figure 5 As shown in the figure, during the lens dispensing process, ultraviolet optical glue with low CTE thermal expansion coefficient, linear shrinkage rate less than 0.25%, and short photothermal curing time is used to ensure that the displacement deviation of the lens during the glue curing and baking stages is within the coupling tolerance range, ensuring the normal coupling efficiency of the optical end of the system.

[0059] The optimization work carried out on the dual-lens optical model of the present invention is mainly to perform iterative optimization by setting optical parameters (such as Gaussian angle θ and beam waist radius ω0) of different receiving ends at POP, wherein the use of correlation functions is to optimize the core operation, mainly the reasonable control and definition of operands such as image plane spot size, aberration light constraint, system length, system coupling efficiency, etc., and the key optical parameters such as the curvature radius, thickness, cone coefficient K, aspheric coefficient and working distance between devices of the lens are set as variables, and a series of iterative optimizations are carried out, wherein the variables for optimizing the spot at a certain working length are the lens thickness and the working distance of the device, the aberration is corrected by optimizing the curvature radius, and the cone coefficient K and the aspheric coefficient are used to improve the surface shape. The spot size can be preliminarily optimized based on the spot diagram and centroid. The RMS spot radius of the collimating lens designed in the present invention is about 0.289 mm. The collimating lens is adjusted to achieve a better collimation effect and reduce the energy loss of light. The spot is further focused and reduced by the converging lens. In order to reduce the software optimization time, a program algorithm is written to link the optical software to achieve secondary optical development. The Seidel coefficient is observed to analyze whether aberrations such as spherical aberration and coma are reasonably corrected. The spot diagram can be used to roughly evaluate the shape of the spot that passes through the light emitting component to the image plane under diffraction conditions and whether it is within the diffraction limit. In particular, the light propagation after being deflected by the isolator can directly know the offset and the size of the focused image. Figure 3 As shown in the figure, after being deflected by the isolator, the focal point is 41um away from the vertex of the main optical axis image plane. Although spherical aberration still exists, the overall light energy is within the diffraction limit. The present invention discloses the important optical parameters of the designed and optimized dual lens system, such as Fig.11 shown.

[0060] Embodiment 2

[0061] See also Figure 6 The present invention also discloses a FA structure suitable for silicon photonic chip coupling, including a fiber array 7 and a pigtail 8, wherein the pigtail 8 adopts a single-mode fiber, and the fiber array 7 adopts a small-mode fiber. The single-mode fiber of the pigtail is fused with the small-mode fiber of the fiber array, and the fiber end face of the fiber array (or the entire end face of the fiber array) is coated with an anti-reflection film. The film thickness of the anti-reflection film is generally positively correlated with the application range of the working wavelength. The small-mode fiber end face of the fiber array of this embodiment (or the coupling end face of the fiber array) is coated with an anti-reflection film of 56nm to 60nm, and the working wavelength is 1304.5nm to 1317.5nm.

[0062] As a preferred solution, small mode optical fiber uses high numerical aperture optical fiber, such as UHNA1 small mode optical fiber.

[0063] In some embodiments, the numerical aperture of the small mode optical fiber is 0.28.

[0064] The small-mode optical fiber 73 is fixed between the V-groove substrate 71 and the lower cover 72. In this embodiment, optical glue is used to fix the bare core of the small-mode optical fiber in the V-groove of the V-groove substrate, and then a high-precision fixture is used to combine the lower cover with the V-groove substrate.

[0065] In some embodiments, see Figure 6 The fiber end face of the fiber array or the coupling end face of the fiber array (or the entire head end face of the fiber array) is provided with an angle with the vertical plane, forming an upper end tilt (the side facing the optical chip is the front side, i.e. Figure 6 The right side of the figure shows an inclined surface 74 with an angle of 8°, so that a part of the reflected light enters the optical fiber cladding at a certain angle. The coupling end face of the optical fiber array is the end face coupled to the optical chip.

[0066] In some embodiments, the minimum distance between the head end face of the lower cover plate of the optical fiber array and the optical fiber end face of the optical fiber array is greater than the distance between the light-emitting side end face of the optical chip light coupler and the optical chip end face ( Figure 6 The distance between the optical fiber end face and the coupler waveguide is as short as possible and they are butt-jointed in a horizontal manner.

[0067] In some embodiments, a horizontal spacing L is provided along a first direction between the end face of the lower cover plate close to the optical chip and the optical fiber end face of the optical fiber array. The first direction is parallel to the laser emission direction of the laser, and the minimum value of the horizontal spacing L is 0.28-0.31 mm.

[0068] The working principle of the lower optical end Fiber Array (FA for short) coupling system of the present invention is analyzed as follows: light will have loss during transmission, among which return loss is caused by the discontinuity of the transmission link and the power loss generated by part of the signal reflected back to the signal source during transmission. Therefore, the fiber end face is polished to 8°, so that part of the reflected light enters the fiber cladding at a certain angle to improve the return loss performance. The precise docking between the optical fibers directly determines the coupling efficiency between the chip coupler and the optical fiber. When the wafer is cut, there will be 20um to 40um cutting grooves on the edges of the optical couplers of some chips, which will cause at least 4dB of power loss for the fiber end face coupling, and the re-cutting of the groove will have the risk of damaging the integrated device inside the optical chip. Therefore, the FA designed by the present invention not only grinds the fiber end face by 8° to ensure the fiber return loss, but also the lower cover plate of the FA will retreat 0.3mm to allow the fiber end face to fully contact the optical chip output (Output) coupler to ensure the best mode field matching with the waveguide inside it. Figure 6 As shown, the actual coupling efficiency can be between 74% and 80%.

[0069] Secondly, the silicon photonic chip coupler involved in the present invention mainly has two structures: single-mode and small-mode. The difference between the two lies mainly in the mode field diameter and divergence angle. Since NA is directly related to the divergence angle, if the NA of the output light coupler is too large, the energy of the edge light will be lost outside the field of view of the FA. As the receiving FA, if a small-mode FA with a high numerical aperture NA is used, more light energy from the optical chip will be received within the effective field of view, thereby improving the coupling efficiency. Figure 7 The figure shows the coupling data of two structures of FA and two structures of optical couplers. The figure uses a one-to-four optical chip integrating single-mode and small-mode couplers.

[0070] During the verification process, the FA manufacturing process directly determines the contact state between the multi-channel optical fiber end face and the multi-channel coupler waveguide of the optical chip. Therefore, the pitch tolerance accuracy during the processing must be very strict. According to the industry's FA manufacturing standards, considering the coupling tolerance of the coupler waveguide and the optical fiber, the center pitch tolerance between the V-grooves of the V-groove substrate must be maintained at ±0.0007mm, and the horizontal spacing between the longitudinal V-grooves must also be maintained at ±0.0007mm to ensure that when the multi-channel optical fiber participates in the end-face coupling, there will be no serious loss caused by excessive optical fiber spacing, such as Fig. 9As shown. The main problem in the coupling process of this verification experiment is on the optical fiber of CH2 and CH4. The pitch tolerance of FA on the X and Y axes is too large, which makes the roll angle unable to be adjusted normally. However, through the single-channel coupling operation, it is proved that the coupling of small-mode FA to the couplers of the two structures is not much different. The insertion loss is analyzed to be 0.2dB~0.6dB. However, the optical end is coupled using single-mode FA. The coupling efficiency between single-mode and single-mode is higher than that between single-mode and small-mode, and the difference is 1dB~1.3dB. Therefore, in order to improve the coupling efficiency of the Output and meet the design compatibility of the mode spot converter of the optical chip, a small-mode optical fiber with a high numerical aperture (NA0.28) can be used. At the same time, in order to improve the return loss performance of the entire optical module transmitting end, a layer of anti-reflection (AR) film is coated on the optical fiber end face of the small-mode FA to avoid the problem of poor return loss caused by fiber fusion. The coated small-mode MT-FA proposed and actually applied by the present invention has a pigtail part that is a single-mode optical fiber. After being fused with the high-numerical-aperture small-mode optical fiber, if it is not coated, the return loss of the optical device is only 28dB to 32dB. After coating, the return loss can be as high as 56dB, and the minimum is also 41dB. Fig.10 As shown, it is the return loss value of small mode FA before and after coating.

[0071] Embodiment 3

[0072] The present invention further discloses an optical engine, comprising an optical chip and the FA structure as described in the second embodiment, wherein the light output coupler of the optical chip is coupled to the optical fiber array of the FA structure.

[0073] Embodiment 4

[0074] The present invention further discloses a light engine, comprising an optical chip and a laser, wherein an optical system as described in the first embodiment is arranged between the light input coupler of the optical chip and the laser.

[0075] Embodiment 5

[0076] See also Figure 8 The present invention also discloses an optical engine, including an optical chip, a laser, and the FA structure as described in the second embodiment, wherein an optical system as described in the first embodiment is arranged between the input light coupler of the optical chip and the laser, and the output light coupler of the optical chip is coupled to the optical fiber array of the FA structure.

[0077] In some embodiments, the laser 5, collimating lens 3, converging lens 4, isolator 6, optical chip 2 and FA structure are all mounted on the substrate 1, and the center line distance between the laser light emitting end face and the optical chip light input coupler is 0.01mm to 0.015mm.

[0078] In some embodiments, the substrate 1 is a tungsten copper substrate.

[0079] Embodiment 4

[0080] The present invention further discloses an optical module, which adopts the optical engine described in the third embodiment, the fourth embodiment or the fifth embodiment.

[0081] The optical system and FA structure provided in this application are suitable for high-efficiency coupling of optical chip couplers, which can effectively be compatible with the chip input single-mode coupler (mode field diameter 9.2um) and small-mode coupler (mode field diameter 4.8um) structures at the same time, ensuring that the laser enters the chip end face coupler through the optical system, and the coupling efficiency is 83% to 96% through optical software analysis, and the actual application coupling efficiency is 70% to 80%. It also introduces an analysis method for how to correctly select the best NA optical fiber to improve the horizontal coupling efficiency for the light output coupler of different mode fields of the optical chip, which can directly avoid the loss caused by abnormal device structure and optical parameters, save the device trial and error cost, and provide some feasible suggestions for the early design of the optical chip mode spot converter.

[0082] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An optical system suitable for coupling with a silicon photonic chip, characterized in that: It comprises a collimating lens and a converging lens arranged between the laser and the optical chip, wherein the collimating lens is used to collimate the laser emitted by the laser, and the converging lens is used to converge the outgoing light of the collimating lens; the numerical aperture NA∈(0.5, 0.65) of the collimating lens; the numerical aperture NA∈(0.17, 0.2) of the converging lens; the NA corresponding to the far-field divergence angle of the laser is always smaller than the NA corresponding to the incident surface of the collimating lens; the incident surface of the collimating lens is a first aspheric surface, the exit surface of the collimating lens is a second aspheric surface, the incident surface of the converging lens is a third aspheric surface, and the exit surface of the converging lens is a fourth aspheric surface; The thickness of the collimating lens is t∈(0.7,0.84) mm; The thickness of the converging lens is t∈(0.62,0.75) mm; The radius of curvature of the first aspherical surface is (1.416±3%) mm, the radius of curvature of the second aspherical surface is (-0.503±3%) mm, the cone coefficient of the first aspherical surface is -38.671, and the cone coefficient of the second aspherical surface is -1.769; the radius of curvature of the third aspherical surface is (1.194±3%) mm, the radius of curvature of the fourth aspherical surface is (-6.417±3%) mm, the cone coefficient of the third aspherical surface is -0.825, and the cone coefficient of the fourth aspherical surface is 18.

635.

2. The optical system suitable for coupling with a silicon photonic chip according to claim 1, characterized in that: It also includes an isolator located between the converging lens and the optical chip. The outgoing light of the converging lens is coupled into the light input coupler of the optical chip after passing through the isolator.

3. A light engine, characterized in that: The invention comprises an optical chip, a laser and an FA structure, wherein an optical system as claimed in any one of claims 1 to 2 is arranged between the optical input coupler of the optical chip and the laser, the optical output coupler of the optical chip is coupled with the optical fiber array of the FA structure, the FA structure comprises an optical fiber array and a pigtail, the pigtail adopts a single-mode optical fiber, the optical fiber array adopts a small-mode optical fiber, the single-mode optical fiber of the pigtail is fused with the small-mode optical fiber of the optical fiber array, and the optical fiber end face of the optical fiber array is coated with an anti-reflection film.

4. The light engine according to claim 3, wherein: The laser, collimating lens, converging lens, isolator, optical chip and FA structure are all mounted on the substrate; or / and, The center line distance between the laser light emitting end face and the optical chip light input coupler is 0.01mm to 0.015mm.

5. The light engine according to claim 3, wherein: Small mode fiber uses high numerical aperture fiber; Or / and, the film thickness of the antireflection film is positively correlated with the application range of the working wavelength; Or / and, the thickness of the antireflection film is 56nm-60nm, and the working wavelength is 1304.5nm-1317.5nm.

6. The light engine of claim 3, wherein: An included angle is arranged between the optical fiber end face of the optical fiber array and the vertical plane, forming an inclined plane with an upper end tilted forward by 7.9° to 8.1°.

7. The light engine of claim 3, wherein: The small-mode optical fiber is fixed between the V-groove substrate and the lower cover plate. A horizontal spacing L along a first direction is provided between the end face of the lower cover plate close to the optical chip and the optical fiber end face of the optical fiber array. The first direction is parallel to the laser emission direction of the laser. The minimum value of the horizontal spacing L is 0.28 to 0.31 mm.

8. An optical module, characterized in that: A light engine as described in any one of claims 3 to 7 is used.

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