Method for coupling a distributed feedback laser to an electro-absorption modulator waveguide

Abstract

The application discloses a kind of coupling methods of distributed feedback laser and electro-absorption modulator waveguide, comprising: taking a substrate with electro-absorption modulator and waveguide, form self-alignment microcavity with positioning structure on substrate;Microcavity metal thin film electrode and solder layer are made in self-alignment microcavity;Self-alignment mark is made on distributed feedback laser;Distributed feedback laser is placed in self-alignment microcavity, and the self-alignment high-precision optical coupling of distributed feedback laser and electro-absorption modulator waveguide is completed using reverse solder bonding process.In the application, by making self-alignment microcavity with positioning structure on substrate and making self-alignment mark on distributed feedback laser, DFB and EAM are self-aligned heterogeneous integration on chip, efficient, stable, compact optical coupling is realized, with the advantages of high coupling efficiency, low cost, short cycle, compact structure, is the ideal choice for realizing excellent monochromaticity and high-speed modulation light source.

Description

Technical Field

[0001] The invention belongs to the field of photoelectric modulation, and in particular relates to a coupling method of a distributed feedback laser and an electro-absorption modulator waveguide. Background Art

[0002] With the rapid development of modern communication technology, the demand for high-speed, stable, and efficient fiber-optic communication systems is growing. Distributed feedback lasers (DFBs) and electro-absorption modulators (EAMs), as key components in fiber-optic communication systems, possess excellent monochromaticity and high-speed modulation capabilities, respectively. However, in practical applications in optoelectronic co-packaging, achieving efficient and stable coupling between distributed feedback lasers and EAMs in a smaller size to improve the performance of the entire fiber-optic communication system has always been a research hotspot and difficulty in the industry.

[0003] The coupling between a distributed feedback laser and an EAM is essentially the coupling between their mode fields, that is, the degree of matching between their mode fields. The higher the matching degree, the higher the coupling efficiency. During the coupling process, the light emitted by the distributed feedback laser is coupled to the input of the EAM to achieve optical signal modulation. Currently, there are various coupling methods for distributed feedback lasers and EAMs, but all have some shortcomings. For example, directly connecting the output end of the distributed feedback laser to the input end of the EAM may lead to large coupling losses due to the possible mismatch between the mode field distribution of the distributed feedback laser and the EAM. By adding a lens (such as a spherical lens, aspherical lens, etc.) between the distributed feedback laser and the EAM, the light emitted by the distributed feedback laser is collimated and focused to better match the mode field of the EAM. Although lens coupling can significantly improve the coupling efficiency, it increases the complexity and cost of the system and occupies a large space, which is not conducive to optoelectronic co-packaging applications. The output of the distributed feedback laser is connected to the input end of the EAM through an optical fiber. This fiber coupling has the advantages of high flexibility and low transmission loss, but there are influences such as fiber loss and dispersion, and it also occupies a large space, which is not suitable for optoelectronic co-packaging applications. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a coupling method between a distributed feedback laser and an electro-absorption modulator waveguide.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for coupling a distributed feedback laser to an electro-absorption modulator waveguide comprises the following steps:

[0007] A substrate is provided on which an electroabsorption modulator and a waveguide are formed;

[0008] forming a self-aligned microcavity with a positioning structure at a position corresponding to the input coupling end face of the waveguide on the substrate, wherein the shape and size of the self-aligned microcavity are adapted to the shape and size of the distributed feedback laser;

[0009] Fabricating a microcavity metal thin film electrode at a position below the laser metal thin film electrode in the self-aligned microcavity, and fabricating a solder layer on the microcavity metal thin film electrode;

[0010] Making a self-alignment mark on the distributed feedback laser, wherein the shape of the self-alignment mark matches the shape of the positioning structure, so as to facilitate positioning of the distributed feedback laser and align the distributed feedback laser with the waveguide of the electro-absorption modulator;

[0011] A distributed feedback laser is placed in the self-aligned microcavity, wherein the output end of the distributed feedback laser is automatically aligned with the input coupling end face of the waveguide under the limiting effect of the positioning structure;

[0012] The self-aligned high-precision optical coupling between the distributed feedback laser and the electro-absorption modulator waveguide is achieved by using a flip-chip bonding process.

[0013] Furthermore, the self-aligned microcavity is formed by photolithography and ICP etching on the input coupling end face of the waveguide after the electro-absorption modulator and waveguide of the distributed feedback laser are manufactured on the substrate.

[0014] Furthermore, the positioning structure is used to position the distributed feedback laser in the vertical direction and in each horizontal direction.

[0015] Furthermore, the distributed feedback laser has a first side surface and a second side surface arranged opposite to each other, and the positioning structure includes at least two first support pillars arranged at positions corresponding to the first side surface of the distributed feedback laser in the self-aligned microcavity and at least two second support pillars arranged at positions corresponding to the second side surface of the distributed feedback laser;

[0016] The self-alignment mark includes at least two first side positioning grooves arranged on the first side of the distributed feedback laser and at least two second side positioning grooves arranged on the second side of the distributed feedback laser; the first side positioning grooves correspond to the first support pillars one-to-one, and the second side positioning grooves correspond to the second support pillars one-to-one, and the first side positioning grooves and the second side positioning grooves are both half-through grooves etched on the bottom surface of the distributed feedback laser.

[0017] Furthermore, a SiN film is deposited on the surfaces of the first support pillar and the second support pillar, and the height of the first support pillar and the second support pillar and the height difference between the first support pillar and the second support pillar are compensated by controlling the thickness of the SiN film.

[0018] Furthermore, the thickness of the solder layer is adapted to the distance between the metal film electrode of the laser and the metal film electrode of the microcavity after the distributed feedback laser is placed in the self-aligned microcavity.

[0019] Furthermore, the microcavity metal film electrode is a metal film formed by a PECVD process, and a typical material thereof is Ti / Pt / Au.

[0020] Furthermore, the solder layer includes a barrier layer disposed on the microcavity metal film electrode and a multilayer solder film disposed on the barrier layer.

[0021] Furthermore, the barrier layer includes a Pt metal film layer disposed on the microcavity metal film electrode and a Ti metal film layer disposed on the Pt metal film layer.

[0022] Furthermore, the solder film includes a Sn solder film layer and an Au solder film layer, and the number of layers of the solder film is determined according to the required thickness of the solder layer.

[0023] In this invention, a self-aligned microcavity with a positioning structure is formed on the substrate used to fabricate the electro-absorption modulator and waveguide, and a self-alignment mark is fabricated on the distributed feedback laser. The matching of the positioning structure and the self-alignment mark enables self-aligned, high-precision optical coupling between the distributed feedback laser and the electro-absorption modulator's waveguide. This provides an on-chip heterogeneous integration method for DFB and EAM in optoelectronic co-packaging applications, achieving efficient, stable, and compact optical coupling. This method boasts high coupling efficiency, low cost, short cycle time, and compact structure, making it an ideal choice for achieving excellent monochromaticity and high-speed modulated light sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0025] Figure 1 This is a flow chart of an embodiment of a method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to the present invention.

[0026] Figure 2 Schematic diagram of the structure of the self-aligned microcavity and waveguide on the substrate.

[0027] Figure 3Schematic diagram of the structure of the solder layer.

[0028] Figure 4 A top view of the distributed feedback laser placed in the self-aligned microcavity.

[0029] Figure 5 for Figure 4 A-A' sectional view in the figure.

[0030] The accompanying drawings in this specification are numeraled as follows:

[0031] Self-aligned microcavity-100; first support pillar-110; second support pillar-120; microcavity metal film electrode-130;

[0032] Distributed feedback laser-200; first side positioning groove-210; second side positioning groove-220; laser metal thin film electrode-230;

[0033] Solder layer 300 ; barrier layer 310 ; Pt metal thin film layer 311 ; Ti metal thin film layer 312 ; solder film 320 ; Sn solder thin film layer 321 ; Au solder thin film layer 322 ; substrate 900 ; anti-reflection film 910 ; waveguide 920 . DETAILED DESCRIPTION

[0034] The following describes the implementation of the present invention through specific examples. The illustrations provided in the following embodiments are only used to schematically illustrate the basic concept of the present invention. The following embodiments and features in the embodiments may be combined with each other unless there is any conflict.

[0035] See also Figure 1 , Figure 1 This is a flow chart of an embodiment of a method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to the present invention. The distributed feedback laser 200 is typically an InP-based distributed feedback laser, used to provide a high-power, wavelength-locked laser source for a silicon-based electro-absorption modulator. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to this embodiment includes the following steps:

[0036] S100. A substrate 900 is obtained. An electro-absorption modulator and a waveguide 920 are formed on the substrate 900. The input coupling end face of the waveguide 920 is provided with an anti-reflection film 910. The substrate 900 is generally a silicon-based substrate. The waveguide 920 can be fabricated on the substrate 900 using a deep silicon etching method to provide an input optical path for the electro-absorption modulator. The anti-reflection film 910 can be deposited on the input coupling end face of the waveguide 920 using a sputtering method to reduce the reflected light energy at the coupling interface of the waveguide 920.

[0037] S200, please refer toFigure 2 A self-aligned microcavity 100 with a positioning structure is formed on the substrate 900 at a position corresponding to the input coupling end face of the waveguide 920. The shape and size of the self-aligned microcavity 100 are compatible with the shape and size of the distributed feedback laser 200. That is, the shape and size of the self-aligned microcavity 100 are determined by the shape and size of the distributed feedback laser 200, so that the distributed feedback laser 200 can be easily placed in the self-aligned microcavity 100. In this embodiment, the self-aligned microcavity 100 is formed at the input coupling end face of the waveguide 920 by photolithography and ICP etching after the electro-absorption modulator and waveguide 920 of the distributed feedback laser 200 are fabricated on the substrate 900.

[0038] The positioning structure is used to limit the distributed feedback laser 200 so that the distributed feedback laser 200 is aligned with the waveguide 920 of the electro-absorption modulator. The positioning structure generally positions the distributed feedback laser 200 in the vertical direction and in each horizontal direction. In this embodiment, the distributed feedback laser 200 has a first side surface and a second side surface that are arranged opposite to each other. The positioning structure includes two first support columns 110 arranged at positions corresponding to the first side surface of the distributed feedback laser 200 in the self-aligned microcavity and two second support columns 120 arranged at positions corresponding to the second side surface of the distributed feedback laser 200. Of course, the positioning structure can also include more than two first support columns 110 and more than two second support columns 120. The shapes of the first support columns 110 and the second support columns 120 are generally the same.

[0039] S300, please refer to Figure 3 A microcavity metal thin film electrode 130 is formed at a position below the laser metal thin film electrode 230 in the self-aligned microcavity 100, and a solder layer 300 is formed on the microcavity metal thin film electrode 130. The laser metal thin film electrode 230 is generally a metal thin film whose typical material is Ti / Pt / Au. The microcavity metal thin film electrode 130 can be manufactured using the following manufacturing method:

[0040] A metal film, typically made of Ti / Pt / Au, is first deposited on the bottom surface of the self-aligned microcavity 100 using a PECVD process. The excess Ti / Pt / Au metal film is then etched away using photolithography and metal etching processes. The remaining Ti / Pt / Au metal film forms the microcavity metal film electrode 130. Of course, since the laser metal film electrode 230 has a large area, multiple microcavity metal film electrodes 130 can be fabricated on the bottom surface of the self-aligned microcavity 100 to increase connection reliability.

[0041] The thickness of the solder layer 300 is adapted to the distance between the laser metal thin film electrode 230 and the microcavity metal thin film electrode 130 after the distributed feedback laser 200 is put into the self-aligned microcavity 100, so that the laser metal thin film electrode 230 contacts the solder layer 300 after the distributed feedback laser 200 is put into the self-aligned microcavity 100, and the laser metal thin film electrode 230 and the microcavity metal thin film electrode 130 are firmly welded after the reverse soldering is completed.

[0042] The solder layer 300 can include a barrier layer 310 disposed on the microcavity metal thin film electrode 130 and a multilayer solder thin film 320 disposed on the barrier layer 310. The barrier layer 310 is used to limit the shape of the solder thin film 320 after the solder thin film 320 is melted. In the embodiment, the barrier layer 310 includes a Pt metal thin film layer 311 disposed on the microcavity metal thin film electrode 130 and a Ti metal thin film layer 312 disposed on the Pt metal thin film layer 311. Each of the solder thin films 320 includes a Sn solder thin film layer 321 and an Au solder thin film layer 322, and the number of layers of the solder thin film 320 is determined according to the required thickness of the solder layer 300. The method for manufacturing the multilayer solder thin film 320 is as follows:

[0043] The Sn solder thin film layer 321 and the Au solder thin film layer 322 are alternately evaporated by an electron beam, the excess Sn solder thin film layer 321 and the Au solder thin film layer 322 are removed by a photolithography etching process, and the multilayer solder thin film 320 is formed after heat treatment.

[0044] Since the depth of the waveguide 920 on the substrate 900 usually reaches nearly 10 μm, the photoresist used in the photolithography process for manufacturing the microcavity metal thin film electrode 130 and the solder layer 300 needs to be thick, such as AZ2035 type photoresist, which can realize a 6 μm thick resist pattern, so as to facilitate the growth of the metal thin film and the gold-tin solder and the stripping of the photoresist.

[0045] S400, a self-aligned mark is manufactured on the distributed feedback laser 200. The self-aligned mark can be formed by a front etching process. The shape of the self-aligned mark is adapted to the shape of the positioning structure, so as to limit the distributed feedback laser 200 and align the distributed feedback laser 200 with the waveguide 920 of the electro-absorption type modulator. Of course, the self-aligned mark can be manufactured first, and then the positioning structure is formed in the self-aligned microcavity 100 according to the shape of the self-aligned mark.

[0046] The self-alignment mark includes two first side positioning grooves 210 arranged on the first side of the DFB laser 200 and two second side positioning grooves 220 arranged on the second side of the DFB laser 200; the first side positioning grooves 210 and the first support columns 110 correspond to each other one by one, and the second side positioning grooves 220 and the second support columns 120 correspond to each other one by one. The first side positioning grooves 210 and the second side positioning grooves 220 are both half-through grooves etched on the bottom surface of the DFB laser 200, so as to support the DFB laser 200 after the first support columns 110 and the second support columns 120 respectively abut against the upper groove walls of the first side positioning grooves 210 and the second side positioning grooves 220.

[0047] S500, please refer to Figure 4 and Figure 5 The DFB laser 200 is placed in the self-alignment microcavity 100, and the output end of the DFB laser 200 is automatically aligned with the input coupling end face of the waveguide 920 under the limiting action of the positioning structure. Of course, due to the errors in the manufacturing process, the shape and position of the first support column 110 and the second support column 120 may not be matched with the shape and position of the first side positioning groove 210 and the second side positioning groove 220 to high precision. At this time, a Si N thin film (not shown in the figure) can be deposited on the surface of the first support column 110 and the second support column 120, and the height of the first support column 110 and the second support column 120 and the spacing between the first support column 110 and the second support column 120 are compensated by controlling the thickness of the Si N thin film, so that the first support column 110 and the second support column 120 are matched with the first side positioning groove 210 and the second side positioning groove 220 to high precision after the Si N thin film is deposited.

[0048] S600, the self-alignment high-precision optical path coupling of the DFB laser 200 and the waveguide 920 of the electro-absorption modulator is completed by using the inverted solder bonding process. This step generally includes the following processing steps: chip positioning of the DFB laser 200, heating of the solder layer 300, high-precision mounting, cooling and solidification, etc. by using a high-precision inverted solder bonding device, and the welding process curve can be optimized in combination with a welding jig and a welding heating mode. These are all conventional process methods in the prior art, and will not be described here.

[0049] In this embodiment, a self-aligned microcavity 100 with a positioning structure is formed on the substrate 900 on which the electro-absorption modulator and waveguide 920 are fabricated, and a self-alignment mark is formed on the distributed feedback laser 200. The alignment of the positioning structure and the self-alignment mark achieves self-aligned, high-precision optical coupling between the distributed feedback laser 200 and the electro-absorption modulator waveguide 920. This provides an on-chip heterogeneous integration method for DFB and EAM co-packaging applications, achieving efficient, stable, and compact optical coupling. This method offers the advantages of high coupling efficiency, low cost, short cycle time, and compact structure, making it an ideal choice for achieving excellent monochromaticity and high-speed modulated light sources.

[0050] The above embodiments merely represent preferred embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for coupling a distributed feedback laser to an electro-absorption modulator waveguide, characterized in that: The following steps are involved: A substrate is provided on which an electroabsorption modulator and a waveguide are formed; forming a self-aligned microcavity with a positioning structure at a position corresponding to the input coupling end face of the waveguide on the substrate, wherein the shape and size of the self-aligned microcavity are adapted to the shape and size of the distributed feedback laser; Fabricating a microcavity metal thin film electrode at a position below the laser metal thin film electrode in the self-aligned microcavity, and fabricating a solder layer on the microcavity metal thin film electrode; Making a self-alignment mark on the distributed feedback laser, wherein the shape of the self-alignment mark is adapted to the shape of the positioning structure, so as to limit the distributed feedback laser and align the light outlet of the distributed feedback laser with the waveguide of the electro-absorption modulator; A distributed feedback laser is placed in the self-aligned microcavity, wherein the output end of the distributed feedback laser is automatically aligned with the input coupling end face of the waveguide under the limiting action of the positioning structure; The self-aligned high-precision optical coupling between the distributed feedback laser and the electro-absorption modulator waveguide is achieved using a flip-chip bonding process. The distributed feedback laser has a first side surface and a second side surface that are arranged opposite to each other, and the positioning structure includes at least two first support pillars arranged at positions corresponding to the first side surface of the distributed feedback laser in the self-aligned microcavity and at least two second support pillars arranged at positions corresponding to the second side surface of the distributed feedback laser; The self-alignment mark includes at least two first side positioning grooves provided on the first side of the distributed feedback laser and at least two second side positioning grooves provided on the second side of the distributed feedback laser; the first side positioning grooves correspond to the first support pillars one-to-one, and the second side positioning grooves correspond to the second support pillars one-to-one, and the first side positioning grooves and the second side positioning grooves are both half-through grooves etched on the bottom surface of the distributed feedback laser; A SiN film is also deposited on the surfaces of the first support pillar and the second support pillar, and the heights of the first support pillar and the second support pillar and the height difference between the first support pillar and the second support pillar are compensated by controlling the thickness of the SiN film.

2. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 1, wherein: The self-aligned microcavity is formed on the input coupling end face of the waveguide by photolithography and ICP etching after the electro-absorption modulator and the waveguide are manufactured on the substrate.

3. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 1, wherein: The positioning structure is used to position the distributed feedback laser in the vertical direction and in each horizontal direction.

4. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 1, wherein: The thickness of the solder layer is adapted to the distance between the metal film electrode of the laser and the metal film electrode of the microcavity after the distributed feedback laser is placed in the self-aligned microcavity.

5. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 1, wherein: The microcavity metal film electrode is a metal film formed by a PECVD process, and the typical material is Ti / Pt / Au.

6. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 1, wherein: The solder layer comprises a barrier layer arranged on the microcavity metal film electrode and a multilayer solder film arranged on the barrier layer.

7. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 6, wherein: The barrier layer comprises a Pt metal film layer arranged on the microcavity metal film electrode and a Ti metal film layer arranged on the Pt metal film layer.

8. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide according to claim 7, wherein: The solder film includes a Sn solder film layer and an Au solder film layer, and the number of layers of the solder film is determined according to the required thickness of the solder layer.

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