Coupling method of distributed feedback laser and electric absorption type modulator waveguide

Abstract

The invention discloses a method for coupling a distributed feedback laser and an electric absorption type modulator waveguide, which comprises the following steps of: taking a substrate with an electric absorption type modulator and a waveguide, and forming a self-alignment microcavity with a positioning structure on the substrate; manufacturing a microcavity metal film electrode and a solder layer in the self-aligned microcavity; making a self-alignment mark on the distributed feedback laser; the distributed feedback laser is placed in the self-alignment microcavity, and self-alignment high-precision optical path coupling of the distributed feedback laser and the electric absorption type modulator waveguide is completed by adopting a back-off welding bonding process. In the invention, the self-alignment microcavity with a positioning structure is manufactured on the substrate and the self-alignment mark is manufactured on the distributed feedback laser to carry out self-alignment on-chip heterogeneous integration on the DFB and the EAM, so that efficient, stable and compact optical path coupling is realized, and the device has the advantages of high coupling efficiency, low cost, short period and compact structure; the method is an ideal choice for realizing excellent monochromaticity and a 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 (DFB) and electro-absorption modulators (EAM) are key components in fiber-optic communication systems, with excellent monochromaticity and high-speed modulation capabilities, respectively. However, in practical applications in the field of optoelectronic co-packaging, how to achieve 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 the distributed feedback laser and the EAM is essentially the coupling between the mode fields of the two, that is, the matching degree between the mode fields of the two. The higher the matching degree, the higher the coupling efficiency. In the coupling process, the light emitted by the distributed feedback laser is mainly coupled to the input end of the EAM to achieve the modulation of the optical signal. At present, there are various coupling methods between the distributed feedback laser and the EAM, but they all have some shortcomings. For example, directly connecting the output end of the distributed feedback laser to the input end of the EAM. Since the mode field distribution of the distributed feedback laser and the EAM may not match, direct coupling may lead to large coupling losses. 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 optical fiber coupling has the advantages of high flexibility and low transmission loss, but there are influences such as optical 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 with 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 film electrode at a position below the laser metal film electrode in the self-aligned microcavity, and fabricating a solder layer on the microcavity metal 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 limit the distributed feedback laser and align the distributed feedback laser with the waveguide of the electro-absorption modulator;

[0011] The distributed feedback laser is placed in the self-aligned microcavity, and 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 path coupling between the distributed feedback laser and the electro-absorption modulator waveguide is achieved by using the 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] Further, 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;

[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 supporting pillars one-to-one, and the second side positioning grooves correspond to the second supporting 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 column and the second support column, and the height of the first support column and the second support column and the height difference between the first support column and the second support column 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 the present invention, a self-aligned microcavity with a positioning structure is formed on a substrate for making an electro-absorption modulator and a waveguide, and a self-alignment mark is made on a distributed feedback laser, and the self-alignment high-precision optical path coupling of the distributed feedback laser and the waveguide of the electro-absorption modulator is achieved through the mutual matching of the positioning structure and the self-alignment mark. Thus, a DFB and EAM on-chip heterogeneous integration method is provided for the field of optoelectronic co-packaging applications, and efficient, stable and compact optical path coupling is achieved, which has the advantages of high coupling efficiency, low cost, short cycle and compact structure, and is 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 The figure 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' section view.

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

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

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

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

[0034] The following describes the implementation methods 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 without conflict.

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

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

[0037] S200, please refer to Figure 2 A self-aligned microcavity 100 with a positioning structure is formed at a position on the substrate 900 corresponding to the input coupling end face of the waveguide 920. The shape and size of the self-aligned microcavity 100 are adapted to 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 as to facilitate the placement of the distributed feedback laser 200 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 methods after the electro-absorption modulator and waveguide 920 of the distributed feedback laser 200 are manufactured 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 the position 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 the position corresponding to the second side surface of the distributed feedback laser 200. Of course, the positioning structure may 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, see Figure 3 , a microcavity metal film electrode 130 is fabricated at a position below the laser metal film electrode 230 in the self-aligned microcavity 100, and a solder layer 300 is fabricated on the microcavity metal film electrode 130. The laser metal film electrode 230 is generally a metal film whose typical material is Ti / Pt / Au. The microcavity metal film electrode 130 can be fabricated by the following fabrication method:

[0040] First, a metal film of typical material Ti / Pt / Au is deposited on the bottom surface of the self-aligned microcavity 100 by a PECVD process, and then the excess Ti / Pt / Au metal film is etched away by a photolithography and metal etching process, and the remaining Ti / Pt / Au metal film forms a microcavity metal film electrode 130. Of course, since the area of ​​the laser metal film electrode 230 is relatively large, a plurality of microcavity metal film electrodes 130 can be made on the bottom surface of the self-aligned microcavity 100 to increase the reliability of the connection.

[0041] The thickness of the solder layer 300 is adapted to the spacing between the laser metal film electrode 230 and the microcavity metal film electrode 130 after the distributed feedback laser 200 is placed in the self-aligned microcavity 100, so that after the distributed feedback laser 200 is placed in the self-aligned microcavity 100, the laser metal film electrode 230 and the solder layer 300 are in contact, and the laser metal film electrode 230 and the microcavity metal film electrode 130 are firmly welded after the flip-flop welding is completed.

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

[0043] The Sn solder film layer 321 and the Au solder film layer 322 are formed by electron beam alternating layered evaporation, and the redundant Sn solder film layer 321 and the Au solder film layer 322 are removed by photolithography and etching process, and a multilayer solder film 320 is formed after heat treatment.

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

[0045] S400, a self-alignment mark is made on the distributed feedback laser 200, and the self-alignment mark can be formed by a front etching process; the shape of the self-alignment 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 modulator. Of course, the self-alignment mark can also be made first, and then the positioning structure is formed in the self-alignment microcavity 100 according to the shape of the self-alignment mark.

[0046] The self-alignment mark includes two first side positioning grooves 210 arranged on the first side of the distributed feedback laser 200 and two second side positioning grooves 220 arranged on the second side of the distributed feedback laser 200; the first side positioning grooves 210 correspond to the first support pillars 110 one by one, and the second side positioning grooves 220 correspond to the second support pillars 120 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 distributed feedback laser 200, so that the first support pillars 110 and the second support pillars 120 can respectively abut against the upper groove walls of the first side positioning grooves 210 and the second side positioning grooves 220 to support the distributed feedback laser 200.

[0047] S500, please refer to Figure 4 and Figure 5 , the distributed feedback laser 200 is placed in the self-aligned microcavity 100, and the output end of the distributed feedback laser 200 is automatically aligned with the input coupling end face of the waveguide 920 under the limiting effect of the positioning structure. Of course, due to the possible errors in the manufacturing process, the shape and position of the first support column 110 and the second support column 120 cannot meet the high-precision adaptation requirements with the shape and position of the first side positioning groove 210 and the second side positioning groove 220. At this time, a Si N film (not shown in the figure) can also 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 distance between the first support column 110 and the second support column 120 are compensated by controlling the thickness of the Si N film, so that the first support column 110 and the second support column 120 can achieve high-precision matching with the first side positioning groove 210 and the second side positioning groove 220 after the Si N film is deposited.

[0048] S600, using flip-chip bonding process to complete the self-aligned high-precision optical path coupling of the distributed feedback laser 200 and the waveguide 920 of the electro-absorption modulator. This step generally includes using high-precision flip-chip bonding equipment to complete the distributed feedback laser 200 chip positioning, solder layer 300 heating, high-precision mounting, cooling and curing, and other processing steps, and can be combined with welding fixtures and welding heating methods to optimize the welding process curve. These are all conventional process methods in the current technology and will not be described in detail here.

[0049] In this embodiment, a self-aligned microcavity 100 with a positioning structure is formed on a substrate 900 for making an electro-absorption modulator and a waveguide 920, and a self-alignment mark is made on a distributed feedback laser 200, and self-alignment high-precision optical path coupling of the distributed feedback laser 200 and the waveguide 920 of the electro-absorption modulator is achieved through the mutual matching of the positioning structure and the self-alignment mark. Thus, a method for on-chip heterogeneous integration of DFB and EAM is provided for the field of optoelectronic co-packaging applications, and efficient, stable and compact optical path coupling is achieved, which has the advantages of high coupling efficiency, low cost, short cycle and compact structure, and is an ideal choice for achieving excellent monochromaticity and high-speed modulated light sources.

[0050] The above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached 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 film electrode at a position below the laser metal film electrode in the self-aligned microcavity, and fabricating a solder layer on the microcavity metal film electrode; 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 limit the distributed feedback laser and align the light outlet of the distributed feedback laser with the waveguide of the electro-absorption modulator; The distributed feedback laser is placed in the self-aligned microcavity, and 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; The self-aligned high-precision optical path coupling between the distributed feedback laser and the electro-absorption modulator waveguide is achieved by using the flip-chip bonding process.

2. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 1, characterized in that: 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 the waveguide are manufactured on the substrate.

3. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 1, characterized in that: 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 as claimed in claim 1, characterized in that: 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 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 supporting pillars one-to-one, and the second side positioning grooves correspond to the second supporting 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.

5. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 4, characterized in that: A SiN film is also deposited on the surfaces of the first supporting pillar and the second supporting pillar, and the heights of the first supporting pillar and the second supporting pillar and the height difference between the first supporting pillar and the second supporting pillar are compensated by controlling the thickness of the SiN film.

6. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 4, characterized in that: 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.

7. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 1, characterized in that: The microcavity metal film electrode is a metal film whose typical material is Ti / Pt / Au formed by PECVD process.

8. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 1, characterized in that: The solder layer comprises a barrier layer arranged on the microcavity metal film electrode and a multilayer solder film arranged on the barrier layer.

9. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 8, characterized in that: 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.

10. The method for coupling a distributed feedback laser to an electro-absorption modulator waveguide as claimed in claim 9, characterized in that: 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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