CN112068245B

CN112068245B - Stray light deflector, optical chip and manufacturing method thereof

Info

Publication number: CN112068245B
Application number: CN202010997251.7A
Authority: CN
Inventors: 杜炳政; 朱晓田; 李特尔·布兰特·埃弗雷特; 戴维森·罗伊·理查德; 王翔; 李伟恒; 张强
Original assignee: Qxp Technologies Inc; Zhuhai Qixin Photoelectric Technology Co Ltd
Current assignee: Advanced Optoelectronics Chongqing Co ltd
Priority date: 2020-09-21
Filing date: 2020-09-21
Publication date: 2021-08-10
Anticipated expiration: 2040-09-21
Also published as: CN112068245A

Abstract

The invention discloses a stray light deflector, an optical chip and a manufacturing method thereof. The chip is provided with the groove based on a gray scale etching mode, the groove wall of the groove is plated with the metal reflecting layer capable of reflecting stray light with different wavelengths to the external space to form the stray light deflector, the stray light with different wavelengths, different modes and different angles of the optical chip can be effectively removed, and the method has the advantages of simple process steps, flexible layout and low cost.

Description

Stray light deflector, optical chip and manufacturing method thereof

Technical Field

The invention relates to an optical waveguide device, in particular to a stray light deflector, an optical chip and a manufacturing method thereof.

Background

An optical chip, a photonic chip or an integrated optical waveguide chip is one of the key device structures in the fields of 5G optical communication, optical calculation and the like. The laser, the optical fiber and the optical detector can be directly connected and interacted with the optical chip through different coupling modes. Common coupling modes are shown in fig. 1 and are divided into two types: end-coupling and grating coupling. The signal light source is output from a laser 01 or an optical fiber 02, enters the optical chip loop 05 through an input waveguide 04 in the optical chip 03 for optical signal processing, and is transmitted to the optical detector 07 through a port of the output waveguide 06 after the optical signal processing is finished.

In the interactive processing process of the optical chip 03, the laser 01 and the optical fiber detector 07, two types of coupling loss inevitably exist: coupling losses and on-chip losses. The coupling loss is caused by the fact that when the laser 01 or the optical fiber 02 is coupled with the optical chip 03, there is an inevitable optical loss, so that part of the light enters the region outside the waveguide of the optical chip. This portion of the light that enters the region outside the waveguide is referred to as scattered light, as shown in FIG. 2. Similarly, the on-chip loss is light that is processed by a signal in the optical chip, and scattered light inevitably exists in each waveguide of the chip.

Any loss of scattered light on the optical chip is not limited by the optical waveguide, and can propagate in any direction in the chip. A part of the scattered light may enter the optical detector and the optical chip monitor, and the part of the scattered light (i.e., the stray light) that is not processed by the optical loop is also converted into an electrical signal by the optical detector and the optical chip monitor. This means that these scattered light will generate background noise and cross-talk and interfere with the recognition rate of the normally processed useful light signal. These disturbances will degrade the performance of the optical system and the performance of the optical chip, resulting in reduced optical assembly and chip performance and yield.

To solve the above-mentioned problem of stray light crosstalk, some solutions have been proposed in the art:

chinese patent, publication No. CN1290354A, entitled a method for absorbing stray light of an integrated optical circuit, which adopts a doping region disposed in a chip to absorb stray light, but this method has a complicated process flow and high cost for disposing the doping region in the optical chip.

Chinese patent, publication No. CN108037564A, entitled scattering light deflector, which uses a reflection unit with high refractive index and low refractive index arranged alternately in a periodic or quasi-periodic structure in an optical chip to treat stray light, but this approach still has the following problems:

1. wavelength selectivity, mode selectivity and transmission direction selectivity are natural properties of the reflecting element (see end of this paragraph for specific analysis). While the mode and direction of the scattered light in the chip waveguide loop are uncertain. Therefore, stray light with larger bandwidth, more modes and multi-directional scattering inevitably needs to be cascaded with a multi-period photonic crystal structure to complete the diversion or shielding of the scattered light. According to the calculation method described in the document [ Fink Y.A direct Omnidirective Reflector [ J ]. science.1998,282(5394): 1679-. Taking a photonic band gap of a multilayer film period of the one-dimensional photonic crystal as an example, fig. 3 is a structure diagram and parameters of the one-dimensional photonic crystal, and n0, n1 and n2 are respectively medium 1, medium 2 and

medium

3, 3 different refractive indexes of materials; h1 and h2 are thicknesses of the medium 1 and the medium 2, a is h1+ h2, and a is the periodic thickness of the photonic crystal; the wavevector is k, the direction parallel to the direction of the periodic alignment of the crystals is y, and the direction perpendicular to the direction of the periodic alignment of the crystals is x.

Fig. 4 (a) is a band gap diagram in which the one-dimensional photonic crystal structure has a refractive index of n 0-1, n 1-2.2, n 2-1.7, and a thickness ratio of h2/h 1-2.2/1.7, respectively, and fig. 4 (B) is a band gap diagram in which the refractive index of n 0-1, n 1-4.6, n 2-1.6, and the thickness ratio of h2/h 1-1.6/0.8, respectively. In fig. 4, (a) and (B) have white reflection bands, and the horizontal axis represents the wave vector in the x direction; the vertical axis represents frequency in units of (2 π c/a). Since the filling materials and filling ratios of (a) and (B) in fig. 4 are different, the band gaps are greatly different, which indicates that the reflection band (or reflection band) of the photonic crystal is related to the refractive index of the material and the filling ratio (i.e., the thickness ratio). From the unit of the vertical axis frequency 2 π c/a, it can be seen that the photonic crystal reflection band (or reflection band) is affected by the photonic crystal period width. Further, the reflection band gaps corresponding to different ky on the horizontal axis are also different, indicating that the photonic crystal reflection band (or reflection band) is mode-dependent on the light propagation direction.

As can be seen from the above description, wavelength selectivity, mode selectivity, and direction selectivity respectively cause that some wavelengths of stray light, some non-set modes of stray light, and some non-set angles of stray light cannot be deflected or filtered well, so that a broadband, multi-mode, or multi-directional deflector structure needs to be covered by multi-stage cascade, which inevitably results in a large deflector structure size, occupies a space of a chip functional region, or a high-performance photonic crystal diverter cannot be placed in a chip functional region with limited space.

2. In order to ensure that the reflection unit performs reflection processing on stray light with various wavelengths, the reflection unit needs a strict etching line width and size (according to the above photonic crystal bandgap analysis, the etching line width and size have a close relationship with the reflection wavelength), which brings a great process challenge. For example, the diameter of a photonic crystal hole working in a C wave band in a Si optical chip with the thickness of a 220nm core layer is approximately 80 nm-200 nm, and the width of a strip-shaped periodic structure is approximately 80 nm-200 nm. . In addition, after the etching of the holes or the stripe-shaped periodic structures, the filling of the corresponding refractive index material is required. While small size holes/trenches impose high requirements on the filling process. The filling defects will change the refractive index of the filled region and further affect the performance of the reflective element, including the operating wavelength, the reflection efficiency.

3. In the above manner, the stray light is still confined to the waveguide core layer for propagation after being diverted, and is likely to be transmitted back into the laser loop as a return loss component (or transmitted to the detector as a noise component), which cannot be predicted by the designer.

Disclosure of Invention

The invention aims to provide a stray light deflector which has large bandwidth, is insensitive to mode and scattering direction, is easy to realize in process, can reflect all stray light out of an external space from an optical chip, avoids the problem that residual light is bound on a waveguide layer to be propagated, and can be possibly transmitted back to the inside of a laser loop to become return loss components or transmitted to a detector to become noise components and the like.

Meanwhile, the invention also provides an optical chip using the stray light deflector and a manufacturing method thereof.

The specific technical scheme of the invention is as follows:

the invention provides a stray light deflector, which comprises a groove arranged on an optical chip, wherein two side groove walls of the groove are provided with an inclined surface, and the inclined surface is plated with a metal reflecting layer which can completely reflect stray light with different wavelengths, different modes and different angles to an external space from the opening end of the groove; the length, width and depth of the groove are all in micron or submicron level.

Further, the inclined surface is a straight inclined surface or a curved inclined surface.

Furthermore, the groove is made by adopting a grey etching process of a CMOS or a mechanical etching process.

Furthermore, the metal reflecting layer is made of gold, copper or aluminum.

The invention provides an optical chip, which comprises an input waveguide, an output waveguide, at least one optical signal transmission waveguide and/or at least one sensitive area; two stray light deflectors are arranged on two sides of the input waveguide and used for reflecting stray light output by the input waveguide out of the groove.

Furthermore, two stray light deflectors are arranged on two sides of the output waveguide of the optical chip and used for reflecting stray light output by the input waveguide out of the groove.

Furthermore, one side or two sides of the optical signal transmission waveguide of the optical chip are provided with the stray light deflectors which are used for reflecting stray light output by the optical signal transmission waveguide out of the groove.

Further, each sensitive area of the optical chip is surrounded by a plurality of stray light deflectors as described above.

The invention provides a manufacturing method of the optical chip, which is characterized by comprising the following steps of:

step 1: sequentially manufacturing a lower coating layer, a waveguide layer and an upper coating layer on the base layer in a deposition or growth mode, thereby forming an optical chip body;

step 2: forming a groove on the optical chip body by adopting a CMOS gray scale etching mode, wherein one of two groove walls of the groove is an inclined plane;

and step 3: plating a metal reflecting material on the optical chip body so as to form a stray light deflector for reflecting stray light with different wavelengths to an external space from the opening end of the groove;

and 4, step 4: and removing the metal reflecting materials in other areas on the optical chip body except the inclined surface, so as to form a metal reflecting layer on the inclined surface of the groove, and finishing the optical chip.

Compared with the prior art, the invention has the beneficial effects that:

1. the chip is provided with the groove based on the gray scale etching mode, the groove wall of the groove is plated with the metal reflecting layer capable of reflecting stray light with different wavelengths to the external space to form the stray light deflector, compared with the existing reflecting unit, the stray light deflector is simple in implementation process, the problem that when the existing reflecting unit is adopted to reflect the stray light, the stray light is still bound to the waveguide core layer after being turned, and finally is randomly transmitted and transmitted to an external device (a laser or a detector) is solved, the stray light removing effect is better, more importantly, the structure based on the gray scale etching can be realized through standard CMOS process steps, the layout is flexible, and the cost is low.

In addition, the groove is in a micron-scale, so that the process is easier to realize compared with the existing process of etching the hole/strip-shaped periodic structure with the reflecting unit in a nanometer scale, and the metal can cover the reflection of a wide waveband without considering the mode and the scattering direction.

2. The deflector can be arranged between the input waveguide and the output waveguide of the optical chip and between any two adjacent optical signal transmission waveguides of the optical chip and in any combination mode in the sensitive area of the optical chip, so that the removing effect of stray light in the optical chip is further improved.

3. The deflector can reflect the light in the light beam concentration area out of the light chip, and avoids the influence on the periphery of the area caused by the light beam concentration.

4. Based on the two points, the stray light deflector structure is used on the optical chip, so that the optical chip has the advantages of low cost, simple design, large bandwidth, insensitive mode, omnidirectional reflection characteristic and the like, and therefore, the optical chip disclosed by the invention has great advantages in large-scale production and practical application.

Drawings

Fig. 1 is a schematic diagram of a structure in which an optical chip is coupled with an external light source and an optical detector.

Fig. 2 is a schematic diagram of formation of stray light.

The reference numerals of fig. 1 and 2 are as follows:

01-laser, 02-optical fiber, 03-optical chip, 04-input waveguide, 05-optical chip loop, 06-output waveguide, and 07-optical detector.

FIG. 3 is a diagram of a structure of a one-dimensional photonic crystal.

Fig. 4 is a band gap diagram of a one-dimensional photonic crystal structure.

Fig. 5 is a schematic structural diagram of the stray light deflector.

Fig. 6 is a schematic structural diagram of embodiment 1.

Fig. 7 is a schematic structural diagram of embodiment 2.

Fig. 8 is a schematic structural diagram of embodiment 3.

FIG. 9 is a schematic structural diagram of embodiment 4.

Fig. 10 is a schematic diagram of the structure of the stray light deflector disposed on the waveguide layer.

Fig. 11 is a schematic diagram of a structure of the stray light deflector extending to each layer of the optical chip.

The reference numbers are as follows:

1-optical chip, 2-groove, 3-inclined plane, 4-metal reflecting layer, 5-input waveguide, 6-stray light deflector, 7-light source, 8-output waveguide, 9-detector, 10-optical signal transmission waveguide, 11-upper cladding, 12-waveguide layer, 13-lower cladding, 14-substrate layer and 15-sensitive region.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Stray light deflector structure

The invention provides a stray light deflector, as shown in fig. 5, which comprises a groove 2 arranged on an optical chip 1, wherein at least one of the groove walls at two sides of the groove 2 is an inclined surface 3, and a metal reflecting layer 4 capable of reflecting stray light with different wavelengths, different modes and different angles to an external space from the opening end of the groove 2 is plated on the inclined surface 3; the length, the width and the depth of the groove 2 are all in micron or submicron level; wherein the inclined surface 3 is a generally linear ramp surface (but may be a curved ramp or a rough ramp). Wherein the sloped surface is realized by designing a desired shape of the reticle and a standard etching process, such as RIE (reactive ion beam etching), although other chemical etching methods related to CMOS standard processes are equally applicable.

Based on the basic structure of the stray light deflector, the specific embodiments of the layout of several stray light deflectors in the optical chip are given firstly:

example 1

As shown in fig. 6, two grooves 2 are respectively disposed on two sides of an input waveguide 5 by using a gray scale etching process, one groove wall in each groove 2 is an inclined surface 3, and a metal reflective layer 4 for reflecting stray light with different wavelengths from an opening end of the groove 2 to an external space is plated on the inclined surface 3, so as to form a stray light deflector 6. A light source 7 (e.g., a laser or an optical fiber) is connected to a port of the input waveguide 5, and stray light is reflected out of the surface of the optical chip 1 via a stray light deflector 6. This will reduce the majority of the scattered light that can enter the detector through the various paths. If the stray light deflector is arranged at a distance far enough from the input waveguide port, the stray light absorber can be prevented from affecting the transmission of the signal light in the waveguide, and the distance is close enough to ensure that enough stray light/or most of the stray light is reflected.

Example 2

As shown in fig. 7, two grooves 2 are respectively disposed on two sides of an output waveguide 8 by using a gray scale etching process, one groove wall in each groove 2 is an inclined surface 3, and a metal reflective layer 4 for reflecting stray light with different wavelengths from an opening end of the groove to an external space is plated on the inclined surface 3, so as to form a stray light deflector 6. In this embodiment the detector 9 is ported to the output waveguide 8 and the stray light deflectors 6 are arranged on both sides of the output waveguide 8 in order to prevent stray light from entering the light detector and causing undesired crosstalk.

Example 3

As shown in fig. 8, in an optical chip, a gray scale etching process is adopted to form a groove 2 on one side or both sides of each optical signal transmission waveguide 10 in the optical chip 1, one groove wall in the groove 2 is an inclined surface 3, and a metal reflection layer 4 capable of reflecting stray light with different wavelengths from an opening end of the groove to an external space is plated on the inclined surface 3, so as to form a stray light deflector 6, wherein the metal reflection layer 4 is made of aluminum in this embodiment. The placement of the stray light deflector 6 on one or both sides of the optical signal transmission waveguide 10 in this embodiment will reduce most of the stray light that may enter the optical waveguide or detector through various paths, and may prevent crosstalk or other problems that may result from stray light re-entering the optical signal waveguide.

Example 4

As shown in fig. 9, a light chip is provided with a plurality of grooves 2 in a light chip 1 by using a gray scale etching process, the plurality of grooves 2 surround a sensitive region 15 of the light chip, each groove 2 has a groove wall that is an inclined surface, and a metal reflective layer is plated on the inclined surface, which can be used for reflecting stray light (the stray light source here is generally an optical signal transmission waveguide 10) with different wavelengths from an opening end of the groove to an external space, so as to form a stray light deflector. It should be noted that: the sensitive areas 15 described here are in particular: a micro-ring structure on the optical chip or a photodetector monitoring area.

The layout conditions of the input waveguide, the output waveguide, the optical signal transmission waveguide and the sensitive region of the stray light deflector are shown in the foregoing four embodiments, but the present invention is not limited to four conditions, and the four conditions can be combined arbitrarily to meet the product requirements.

The optical circuit consists of a plurality of planar layers. The waveguide circuit is fabricated on a substrate. Typical substrates include silicon-based wafers, quartz-based wafers, GaAs or InP-based wafers. The planar layer is formed by depositing or growing a light-transmissive material on the substrate. A lower cladding layer may be deposited or grown first as a buffer layer between the core layer and the substrate. A core layer is then deposited or grown to confine most of the optical signal, and most of the optical return functions are performed by the core layer. An upper cladding layer is deposited or grown over the core layer as a buffer layer for the optical waveguide and the external environment. Multiple layers may also be included in the optical waveguide structure, but the number and type of layers does not change the essence of the invention.

The stray light deflector 6 can be made in the waveguide layer, or in the integrated chip layer, but the principle is that the stray light deflector must not interfere with the signal waveguide. In fig. 10, the stray light deflector 6 is arranged on the waveguide layer 12, but may be extended into the lower cladding layer 13, the waveguide layer 12 and the upper cladding layer 11 as needed, or may be extended to a part of the substrate layer 14, as shown in fig. 11.

In optoelectronic chips, most of the optical circuit is a single layer. Two chip layouts are arranged in the vertical direction and correspond to two process methods.

The first approach is a simple layout of the stray light deflector in the core layer. The process flow of the etching of the groove and the metallization of the reflective material is completed on a standard CMOS process line. The grooves can be etched simultaneously with the waveguide structure, or can be etched in a distributed manner.

The second method may be gray scale etching and metallization after depositing the upper cladding layer. For example, after deposition of the waveguide layer material, the upper cladding layer protection is further deposited by etching to form a pattern. After the above steps are completed, further grooves and metal reflecting layers can be completed by photoetching and etching.

Claims

1. A stray light deflector, characterized by: the optical waveguide layer etching device comprises a groove arranged on an optical chip, wherein the groove is completed by adopting a CMOS gray scale etching process when the waveguide layer is etched, and the groove is positioned in the waveguide layer; the length, width and depth of the groove are all in micron or submicron level; the groove wall on two sides of the groove is an inclined surface, and the inclined surface is plated with a metal reflecting layer which can completely reflect stray light with different wavelengths, different modes and different angles to an external space from the opening end of the groove.

2. A stray light deflector according to claim 1, characterized in that: the inclined plane is a straight inclined plane or a curved inclined plane.

3. A stray light deflector according to claim 2, characterized in that: the metal reflecting layer is made of gold or copper or aluminum.

4. An optical chip comprising an input waveguide, an output waveguide, at least one optical signal transmission waveguide and/or at least one sensitive area; the method is characterized in that: two stray light deflectors as claimed in claims 1-3 are arranged on both sides of the input waveguide for reflecting stray light output from the input waveguide out of the groove.

5. The optical chip of claim 4, wherein: two stray light deflectors as claimed in claims 1-3 are arranged on both sides of the output waveguide for reflecting stray light output from the input waveguide out of the groove.

6. The optical chip of claim 4, wherein: the stray light deflector of claims 1 to 3 is provided on one or both sides of the optical signal transmission waveguide for reflecting stray light output from the optical signal transmission waveguide out of the groove.

7. The optical chip of claim 4, wherein: the method is characterized in that: each sensitive area is surrounded by a plurality of stray light deflectors as claimed in claims 1 to 3.

8. A method for manufacturing an optical chip is characterized by comprising the following steps:

step 1: sequentially manufacturing a lower cladding layer and a waveguide layer on the base layer in a deposition or growth mode, and forming a groove with at least one groove wall as an inclined surface on the waveguide layer by adopting a CMOS gray scale etching process; plating a metal reflecting material on the inclined surface, and removing the metal reflecting material in other areas on the optical chip body except the inclined surface, thereby forming a stray light deflector which is used for reflecting stray light with different wavelengths, different modes and different angles to an external space from the opening end of the groove;

and 2, forming the stray light deflector, and then manufacturing an upper coating layer, thereby finishing the manufacture of the optical chip.