WO2021035779A1

WO2021035779A1 - On-chip waveguide loss measurement method, and on-chip waveguide loss measurement device and manufacturing method therefor

Info

Publication number: WO2021035779A1
Application number: PCT/CN2019/104252
Authority: WO
Inventors: 汪巍; 方青; 涂芝娟; 曾友宏; 蔡艳; 余明斌
Original assignee: 上海新微技术研发中心有限公司
Priority date: 2019-08-27
Filing date: 2019-09-03
Publication date: 2021-03-04
Also published as: CN112444372A

Abstract

Provided are an on-chip waveguide loss measurement method, and an on-chip waveguide loss measurement device (1) and a manufacturing method therefor. The on-chip waveguide loss measurement device (1) comprises: an optical coupler (102) formed in top silicon (101) of a silicon (SOI) substrate (100) on an insulator; a linear waveguide (103) formed in the top silicon (101) and extending in a linear direction, a light-incident end (1031) of the linear waveguide (103) being arranged opposite a light-emergent end (1022) of the optical coupler (102) in a transverse direction; an annular resonant cavity (104) formed in the top silicon (101), the minimum distance between the annular resonant cavity (104) and the linear waveguide (103) being a first distance (r1); a polarization adjustment element (105) located at the side, close to the optical coupler (102), of the linear waveguide (103), the polarization adjustment element (105) adjusting the polarization state of light in the linear waveguide (103); a photoelectric detector (106), the photoelectric detector being formed on the top silicon (101), and detecting light output by a light output end (1032) of the linear waveguide (103) and generating a current; and a heater (107) formed at a pre-determined distance from the annular resonant cavity (104).

Description

On-chip waveguide loss measuring method, measuring device and manufacturing method thereof

Technical field

This application relates to the field of semiconductor technology, and in particular to a method for measuring waveguide loss on a silicon substrate, a measuring device and a manufacturing method thereof.

Background technique

Silicon photonics is a new generation technology based on silicon and silicon-based substrate materials (such as SiGe/Si, SOI, etc.) that uses the existing CMOS process to develop and integrate optical devices. It combines the ultra-large-scale, ultra-large-scale technology of integrated circuit technology. The characteristics of high-precision manufacturing and the advantages of ultra-high speed and ultra-low power consumption of photonic technology. Silicon photonics not only has urgent application requirements in the field of optical communication and optical interconnection at this stage, but also a potential technology for realizing in-chip optical interconnection and optical computers in the future.

Although the silicon optical chip manufacturing process is compatible with the CMOS process, the package measurement cost of the silicon optical module is difficult to effectively reduce, which also makes the cost advantage of the silicon optical chip not fully demonstrated. The transmission loss of silicon waveguides is one of the important characterization parameters of silicon optical wafers. In the prior art, the cut-back method is usually used to measure the waveguide loss.

It should be noted that the above introduction to the technical background is only for the convenience of a clear and complete description of the technical solutions of the present application, and to facilitate the understanding of those skilled in the art. It should not be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of this application.

Summary of the invention

The inventor of the present application found that when using the existing cut-back method to measure waveguide loss, light needs to be coupled into multiple waveguides of different lengths. Inconsistent fiber/coupler performance and inconsistent coupling alignment accuracy will all affect Measurement accuracy. In order to achieve relatively accurate measurement, it is necessary to design waveguide structures of different lengths, occupying a large amount of chip space; in addition, the output light needs to enter the external detector through the coupling structure to measure the output power, which further increases the measurement error and cost.

The embodiments of the application provide an on-chip waveguide loss measurement method, an on-chip waveguide loss measurement device, and a manufacturing method thereof. The on-chip waveguide loss measurement device integrates a linear waveguide and a ring resonator, and the linear waveguide is optically coupled with part of the wavelength Into the ring cavity, the light of other wavelengths in the linear waveguide is output and detected by the photodetector. The heater adjusts the temperature of the ring cavity. By measuring the optical signal output by the linear waveguide at different temperatures, it can be calculated For the waveguide loss of a linear waveguide, using the on-chip waveguide loss measurement device of the present application can effectively reduce the accuracy requirements for the alignment of the optical fiber and the chip, reduce the area of the waveguide loss measurement structure, and realize efficient and rapid waveguide loss measurement.

According to an aspect of the embodiments of the present application, there is provided an on-chip waveguide loss measurement device, including:

An optical coupler formed in the top silicon of a silicon-on-insulator (SOI) substrate;

A linear waveguide formed in the top layer of silicon and extending in a linear direction, the light incident end of the linear waveguide and the light exit end of the optical coupler are laterally opposed;

A ring resonant cavity formed in the top layer of silicon, the smallest distance between the ring resonant cavity and the linear waveguide is a first distance;

A polarization adjustment element located on the side of the linear waveguide close to the optical coupler, the polarization adjustment element adjusting the polarization state of the light in the linear waveguide;

A photodetector, which is formed on the top layer of silicon, detects the light output from the light output end of the linear waveguide and generates a current; and

The heater is formed at a predetermined distance from the ring resonant cavity.

According to another aspect of the embodiments of the present application, wherein the on-chip waveguide loss measurement device further includes:

A covering layer covers the optical coupler, the linear waveguide, the ring cavity, the polarization adjustment element, the photodetector, and the heater.

According to another aspect of the embodiments of the present application, the covering layer has an opening, and the optical coupler is located under the opening.

According to another aspect of the embodiments of the present application, the optical coupler is an end coupler or a grating coupler.

According to another aspect of the embodiments of the present application, the photodetector is a germanium (Ge) detector or a germanium tin (GeSn) detector.

According to another aspect of the embodiments of the present application, a method for measuring on-chip waveguide loss is provided. The on-chip waveguide loss measurement device described in any one of the above is used to measure the on-chip waveguide loss, and the measurement method includes:

Irradiate light to the optical coupler;

Adjusting the bias voltage of the heater, and measuring the photocurrent value output by the photodetector under different bias voltages;

According to the photocurrent value output by the photodetector, the loss of the on-chip waveguide is calculated.

According to another aspect of the embodiments of the present application, there is provided a manufacturing method of an on-chip waveguide loss measurement device, including:

An optical coupler is formed in the top silicon of a silicon-on-insulator (SOI) substrate;

A linear waveguide cavity and a ring resonant cavity are formed in the top layer of silicon, wherein the light incident end of the linear waveguide and the light exit end of the optical coupler are laterally opposed, and the ring resonant cavity is opposite to the light emitting end of the optical coupler. The minimum distance between the linear waveguides is the first distance;

Forming a polarization adjustment element on the side of the linear waveguide close to the optical coupler;

Forming a photodetector on the top layer of silicon; and

A heater is formed at a predetermined distance from the ring cavity.

According to another aspect of the embodiments of the present application, wherein the manufacturing method further includes:

A cover layer is formed, and the cover layer covers the optical coupler, the linear waveguide, the ring cavity, the polarization adjustment element, the photodetector, and the heater.

According to another aspect of the embodiments of the present application, the method further includes:

An opening is formed in the cover layer, and the optical coupler is located below the opening.

The beneficial effect of the present application is that the use of the on-chip waveguide loss measurement device of the present application to measure the waveguide loss can effectively reduce the accuracy requirements for the alignment of the optical fiber and the chip, reduce the area of the waveguide loss measurement structure, and achieve efficient and rapid waveguide loss measurement.

With reference to the following description and drawings, specific implementations of the present application are disclosed in detail, and the ways in which the principles of the present application can be adopted are indicated. It should be understood that the scope of the implementation of the present application is not limited thereby. Within the spirit and scope of the terms of the appended claims, the implementation of the present application includes many changes, modifications and equivalents.

Features described and/or shown for one embodiment can be used in one or more other embodiments in the same or similar manner, combined with features in other embodiments, or substituted for features in other embodiments .

It should be emphasized that the term "comprising/comprising" when used herein refers to the existence of a feature, a whole, a step or a component, but does not exclude the existence or addition of one or more other features, a whole, a step or a component.

Description of the drawings

The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to exemplify the embodiments of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings in the following description are only some embodiments of the application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the attached picture:

FIG. 1 is a schematic diagram of the on-chip waveguide loss measurement device in embodiment 1 of the present application in the lateral direction;

2 is a schematic diagram of the cross-section of the on-chip waveguide loss measuring device of Embodiment 1 of the present application in the longitudinal direction;

FIG. 3 is a schematic diagram of a method for calculating waveguide loss using the on-chip waveguide loss measuring device 100 of FIG. 1;

4 is a schematic diagram of the current value of the photocurrent output by the photodetector 106 changing with the temperature of the ring cavity;

FIG. 5 is a schematic diagram of the manufacturing method of the on-chip waveguide loss measurement device of this embodiment.

detailed description

With reference to the drawings, the foregoing and other features of this application will become apparent through the following description. In the specification and drawings, specific implementations of the application are specifically disclosed, which indicate some implementations in which the principles of the application can be adopted. It should be understood that the application is not limited to the described implementations. On the contrary, the present application is not limited to the described implementations. The application includes all modifications, variations and equivalents falling within the scope of the appended claims.

In the description of each embodiment of the present application, for the convenience of description, the direction parallel to the surface of the substrate is referred to as "lateral", and the direction perpendicular to the surface of the substrate is referred to as "longitudinal". Thickness refers to the dimension of the part in the "longitudinal" direction. In the "longitudinal", the direction from the buried oxide layer of the substrate to the top silicon is called the "up" direction, and the opposite of the "up" direction is the "down" direction .

Example 1

The embodiment of the present application provides an on-chip waveguide loss measurement device.

FIG. 1 is a schematic diagram of the on-chip waveguide loss measurement device of Embodiment 1 of the present application in the lateral direction, and FIG. 2 is a schematic diagram of the cross-section of the on-chip waveguide loss measurement device of Embodiment 1 of the present application in the longitudinal direction.

As shown in FIGS. 1 and 2, the on-chip waveguide loss measurement device 1 includes: an optical coupler 102, a linear waveguide 103, a ring resonator 104, a polarization adjustment element 105, a photodetector 106 and a heater 107.

As shown in FIG. 2, the optical coupler 102 is formed in the top silicon 101 of the silicon-on-insulator (SOI) substrate 100; the linear waveguide 103 and the ring cavity 104 are formed in the top silicon 101, and the light of the linear waveguide 103 The entrance end 1031 and the light exit end 1022 of the optical coupler 102 are laterally opposed, and the minimum distance between the ring resonator 104 and the linear waveguide 103 is the first distance r1 (shown in Fig. 1 and not shown in Fig. 2), At the first distance r1, the light in the linear waveguide 103 can be coupled into the ring cavity 104; the polarization adjusting element 105 is located on the side of the linear waveguide 103 close to the optical coupler 102, and the polarization adjusting element 105 adjusts the linear waveguide The polarization state of the light in 103, for example, the polarization adjustment element 105 adjusts the polarization state of the light in the linear waveguide 103 to the TE polarization state or the TM polarization state; the photodetector 106 is formed on the top silicon 101 for alignment The light output by the waveguide 103 is detected and a current is generated; the heater 107 is formed at a predetermined distance from the ring cavity 104.

In this embodiment, the on-chip waveguide loss measurement device 1 integrates a linear waveguide 103 and a ring resonator 104. The light transmitted in the linear waveguide 103 can be coupled into the ring resonator 104, and the light wave whose wavelength meets the resonance condition resonates in the ring. Resonance occurs in the cavity 104 and resides in the ring resonator 104. The light waves that do not resonate are coupled back to the linear waveguide 103 and output from the light output end 1032 of the linear waveguide 103, and the photodetector 106 The optical signal output from the linear waveguide 103 is detected. The heater 107 adjusts the temperature of the ring resonator 104, thereby adjusting the resonance frequency in the ring resonator 104. By measuring the optical signal output by the linear waveguide 103 at different temperatures, it is possible to calculate the silicon (SOI) substrate placed on the insulator The waveguide loss of the linear waveguide 103 in the top layer of silicon 101 is 100. Therefore, the use of the on-chip waveguide loss measurement device 100 of this embodiment can effectively reduce the accuracy requirements for the alignment of the optical fiber and the chip, reduce the area of the waveguide loss measurement structure, and achieve Efficient and fast waveguide loss measurement.

In this embodiment, as shown in FIG. 1, a silicon-on-insulator (SOI) substrate 100 may include: a substrate silicon layer 108, a buried oxide layer 109, and a top silicon 101. Among them, the material of the substrate silicon 108 is single crystal silicon, the material of the top silicon 101 is single crystal silicon, and the material of the buried oxide layer 109 is silicon dioxide.

In this embodiment, the optical coupler 102 may have a light entrance end 1021 and a light exit end 1022. The light incident end 1021 can receive the light incident on the optical coupler 102, and the light exit end 1022 can make the light incident on the optical coupler 102 emit light in the lateral direction.

As shown in FIG. 2, the optical coupler 102 may be a grating coupler, that is, the light incident end 1021 may be a grating structure, and the grating structure is distributed along the lateral direction, so that the grating structure can receive the light entering the optical coupler along the longitudinal direction. Light. In addition, this embodiment may not be limited to this, and the optical coupler 102 may also be an end face coupler, that is, the light incident end 1021 may also be an end face coupling structure.

In this embodiment, the light incident end 1031 of the linear waveguide 103 may be laterally opposed to the light output end 1021 of the optical coupler 102, so that the light emitted from the light output end 1021 of the optical coupler 102 in the lateral direction It can be incident on the linear waveguide 103. The linear waveguide 103 is made of top layer silicon 101.

In this embodiment, as shown in FIG. 1, the radius of the ring resonant cavity 104 may be R. The radius R and the first distance r1 can be set as required.

As shown in FIG. 2, the photodetector 106 is formed on the top silicon 101, and the light emitted from the light emitting end 1032 of the linear waveguide 103 can enter the top silicon 101 opposite to the light emitting end 1032. The top silicon 101 can introduce incident light into the photodetector 106, whereby the photodetector 106 can detect the light entering the top silicon 101 and output a current signal corresponding to the amount of incident light.

In this embodiment, the photodetector 106 may be a germanium (Ge) detector or a germanium tin (GeSn) detector. In addition, this embodiment may not be limited to this, and the photodetector 106 may also be other types of photodetectors.

In this embodiment, the heater 107 may be formed at a predetermined distance from the ring resonant cavity 104. For example, the heater 107 may be formed above the ring resonant cavity 104 or on the lateral side. Within the predetermined distance, when the heater 107 is energized and generates heat, the temperature of the ring resonant cavity 104 can change with the temperature of the heater 107.

In this embodiment, the heater 107 may be made of polysilicon or amorphous silicon, for example, and when energized, the heater 107 generates heat.

In this embodiment, as shown in FIG. 2, the on-chip waveguide loss measuring device 1 further includes: a cover layer 110. The cover layer 110 may cover the optical coupler 102, the linear waveguide 103, the ring cavity 104, the polarization adjustment element 105, the photodetector 106, and the heater 107. Thus, the covering layer 110 can protect the covered structure. The material of the cover layer 110 may be an insulating material, such as silicon dioxide.

In addition, the gap between the linear waveguide 103 and the ring cavity 104 may also be filled by the cover layer 110.

As shown in FIG. 2, the cover layer 110 may have an opening 1101, and the optical coupler 102 may be located under the opening 1101. For example, the light incident end 1021 of the optical coupler 102 as a grating structure may be located below the opening 1101, so that light may enter the light incident end 1021 through the opening 1101.

FIG. 3 is a schematic diagram of a method for calculating waveguide loss using the on-chip waveguide loss measuring device 100 of FIG. 1. As shown in FIG. 3, the method includes:

Step 301: irradiate light to the optical coupler 102;

Step 302: Adjust the bias voltage of the heater 107, and measure the current value of the photocurrent output by the photodetector 106 under different bias voltages;

Step 303: Calculate the loss of the on-chip waveguide according to the current value of the photocurrent output by the photodetector 106.

In this embodiment, in step 301, light may be irradiated from the opening 1101 to the light incident end 1021 of the optical coupler 102 through an optical fiber.

In step 202, the bias voltage of the heater 107 changes, which causes the temperature of the ring resonant cavity 104 to change, and the current value of the photocurrent output by the photodetector 106 changes periodically.

FIG. 4 is a schematic diagram of the temperature change of the current value of the photocurrent output by the photodetector 106 with strong ring resonance. In Figure 4, the horizontal axis is the temperature of the ring resonator 104 under different bias voltages of the heater 107, the vertical axis is the current value of the normalized photocurrent output by the photodetector 106, the unit of the horizontal axis and the vertical axis The unit of can be a custom unit (au). Corresponding to FIG. 4, the polarization adjustment element 105 adjusts the polarization state of the light in the linear waveguide 102 to the TE polarization state.

As shown in FIG. 4, as the bias voltage of the heater 107 increases, the temperature of the ring resonator 104 gradually increases, and the current value of the photocurrent output by the photodetector 106 periodically changes, where the current value is lower than The maximum value is 1, and the minimum value of the current value is t, where the minimum value t is related to the lowest normalized transmission coefficient T.

In step 203, the loss of the linear waveguide can be calculated according to the following equations (1) and (2):

Δω=(α+α _c )*v _g (1)

Where Δω is the width of the resonance spectrum in the ring cavity 104; α is the waveguide transmission loss, that is, the waveguide loss of the linear waveguide 103; α _c is the coupling-related loss; v _g is the group velocity; T is the lowest normalized transmission The coefficient, T, and the corresponding relationship of t in Figure 4 are known.

Δω can be calculated by the following equations (3) and (4):

Among them, FSR is the width of the free spectrum; ΔV _ω and ΔV _{FSR are} shown in Figure 4, that is, ΔV _FSR represents the temperature range corresponding to one cycle of the signal, and ΔV _ω represents the width on the horizontal axis when the signal intensity is half of the maximum value. , That is, the width at half maximum; c is the speed of light; n _g is the group refractive index; R is the radius of the ring cavity 104.

According to this embodiment, the linear waveguide 103 and the ring resonator 104 are integrated in the on-chip waveguide loss measurement device 1. By measuring the optical signals output by the linear waveguide 103 at different temperatures, the silicon on insulator (SOI) can be calculated. The waveguide loss of the linear waveguide 103 in the top silicon 101 of the substrate 100. Therefore, the use of the on-chip waveguide loss measurement device 100 of this embodiment can effectively reduce the accuracy requirements for the alignment of the optical fiber and the chip, and reduce the area of the waveguide loss measurement structure , To achieve efficient and fast waveguide loss measurement.

Example 2

Embodiment 2 provides a method for manufacturing an on-chip waveguide loss measurement device, which is used to manufacture the on-chip waveguide loss measurement device described in embodiment 1.

FIG. 5 is a schematic diagram of the manufacturing method of the on-chip waveguide loss measurement device of this embodiment. As shown in FIG. 5, in this embodiment, the manufacturing method may include:

Step 501, forming an optical coupler 102 in the top silicon 101 of the silicon-on-insulator (SOI) substrate 100;

Step 502, forming a linear waveguide cavity 103 and a ring resonant cavity 104 in the top layer of silicon 101, wherein the light incident end of the linear waveguide 103 and the light exit end of the optical coupler are laterally opposed, and the The minimum distance between the ring cavity 104 and the linear waveguide is the first distance;

Step 503: Form a polarization adjustment element 105 on the side of the linear waveguide close to the optical coupler;

Step 504, forming a photodetector 106 on the top silicon 101; and

Step 505, forming a heater 107 at a predetermined distance from the ring cavity 104.

As shown in Figure 5, the manufacturing method further includes:

Step 506, forming a cover layer 110, which covers the optical coupler 102, the linear waveguide 103, the ring resonator 104, the polarization adjustment element 105, the photodetector 106 and the heater 107.

In this embodiment, the heater 107 may be formed on the lateral side or above the ring resonant cavity 104. In the case where the heater 107 is formed above the ring resonant cavity 104,

steps

505 and 506 can be performed by the following Steps to achieve:

Step 601: After step 504, form a first covering layer covering the optical coupler 102, the linear waveguide 103, the ring cavity 104, the polarization adjustment element 105 and the photodetector 106;

Step 602: forming a heater 107 on the surface of the first covering layer; and

Step 603, forming a second covering layer, the second covering layer covering the heater 107 and the remaining first covering layer exposed from around the heater 107, wherein the first covering layer and the second covering layer together constitute the covering layer 110.

In this embodiment, as shown in FIG. 5, the manufacturing method further includes:

In step 507, an opening 1101 is formed in the cover layer 110, and the optical coupler 102 is located under the opening 1101.

The application is described above in conjunction with specific implementations, but it should be clear to those skilled in the art that these descriptions are all exemplary and do not limit the scope of protection of the application. Those skilled in the art can make various variations and modifications to the application according to the spirit and principle of the application, and these variations and modifications are also within the scope of the application.

Claims

An on-chip waveguide loss measuring device includes:

An optical coupler formed in the top silicon of a silicon-on-insulator (SOI) substrate;

A linear waveguide formed in the top layer of silicon and extending in a linear direction, the light incident end of the linear waveguide and the light exit end of the optical coupler are laterally opposed;

A ring resonant cavity formed in the top layer of silicon, the smallest distance between the ring resonant cavity and the linear waveguide is a first distance;

A polarization adjustment element located on the side of the linear waveguide close to the optical coupler, the polarization adjustment element adjusting the polarization state of the light in the linear waveguide;

A photodetector, which is formed on the top layer of silicon, detects the light output from the light output end of the linear waveguide and generates a current; and

The heater is formed at a predetermined distance from the ring resonant cavity.
The on-chip waveguide loss measuring device according to claim 1, wherein the on-chip waveguide loss measuring device further comprises:

A covering layer covers the optical coupler, the linear waveguide, the ring cavity, the polarization adjustment element, the photodetector, and the heater.
The on-chip waveguide loss measurement device according to claim 2, wherein:

The cover layer has an opening, and the optical coupler is located under the opening.
The on-chip waveguide loss measurement device according to claim 3, wherein:

The optical coupler is an end coupler or a grating coupler.
The on-chip waveguide loss measurement device according to claim 3, wherein:

The photodetector is a germanium (Ge) detector or a germanium tin (GeSn) detector.
A method for measuring on-chip waveguide loss, using the on-chip waveguide loss measuring device according to any one of claims 1-5 to measure the on-chip waveguide loss, the measurement method comprising:

Irradiate light to the optical coupler;

Adjusting the bias voltage of the heater, and measuring the photocurrent value output by the photodetector under different bias voltages;

According to the photocurrent value output by the photodetector, the loss of the on-chip waveguide is calculated.
A manufacturing method of an on-chip waveguide loss measuring device, including:

An optical coupler is formed in the top silicon of a silicon-on-insulator (SOI) substrate;

A linear waveguide cavity and a ring resonant cavity are formed in the top layer of silicon, wherein the light incident end of the linear waveguide and the light exit end of the optical coupler are laterally opposed, and the ring resonant cavity is opposite to the light emitting end of the optical coupler. The minimum distance between the linear waveguides is the first distance;

Forming a polarization adjustment element on the side of the linear waveguide close to the optical coupler;

Forming a photodetector on the top layer of silicon; and

A heater is formed at a predetermined distance from the ring cavity.
8. The method of manufacturing an on-chip waveguide loss measurement device according to claim 7, wherein the manufacturing method further comprises:

A cover layer is formed, and the cover layer covers the optical coupler, the linear waveguide, the ring cavity, the polarization adjustment element, the photodetector, and the heater.
8. The method of manufacturing an on-chip waveguide loss measurement device according to claim 8, wherein the method further comprises:

An opening is formed in the cover layer, and the optical coupler is located below the opening.