Optical Inspection Circuit Using Grating Coupler and Germanium Photodiode
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Solution Overview
Problem
Conventional optical inspection techniques using grating couplers at both input and output are limited by wavelength characteristics and require lengthy fiber alignment, making it difficult to inspect optical circuits over a wide optical wavelength range efficiently.
Innovation Solution
An optical inspection circuit that includes a semiconductor optical waveguide with a grating coupler for input and a germanium photodiode for output, connected via spot size conversion units, allowing for wider wavelength range inspection without the need for output fiber alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If grating couplers are used at both input and output for wafer level inspection, then light input and output can be achieved, but the wavelength characteristics of the grating couplers are emphasized, making it difficult to inspect device characteristics over a wide optical wavelength range
Solution Approach 1:
The invention extracts the grating coupler from the output path, keeping it only at the input side. The output side uses a simple optical waveguide connected directly to an optical fiber, eliminating the wavelength-dependent grating coupler from the output measurement path. This allows wide wavelength range inspection while accurately measuring device characteristics without grating coupler wavelength characteristics interfering with the measurements.
Solution Approach 2:
The optical waveguide serves multiple functions: it guides light from the input grating coupler through the optical circuit under inspection, and also serves as the output path directly coupled to the optical fiber. This multi-functional design eliminates the need for a separate output grating coupler, enabling wide wavelength range inspection while maintaining measurement accuracy.
2Reliability
If two optical fibers for input and output are aligned with respective two grating couplers, then complete optical path connection is achieved, but the alignment process takes longer time, reducing inspection efficiency
Solution Approach 1:
The invention removes one grating coupler from the system, eliminating the need to align an output optical fiber with an output grating coupler. Only one optical fiber needs to be aligned with the input grating coupler, significantly reducing alignment time and complexity while maintaining reliable optical path connection through the waveguide-fiber direct coupling.
3Ease of operation
If grating couplers are used at both input and output, then optical connection is established, but the wavelength characteristics are emphasized, making it difficult to evaluate device characteristics
Solution Approach 1:
The output grating coupler is removed from the system. The output optical waveguide is directly coupled to the optical fiber without requiring a grating coupler, thereby eliminating the wavelength-dependent characteristics of grating couplers from the output measurement path. This enables accurate device characteristic evaluation across wide wavelength ranges while maintaining ease of optical connection setup through the simplified waveguide-fiber interface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables faster and more comprehensive inspection of optical circuits over a wider wavelength range by utilizing a germanium photodiode for output, reducing inspection time and improving alignment efficiency.
Implementation Method 1
a grating coupler formed on the input optical waveguide via a spot size conversion unit
Implementation Method 2
a germanium photodiode for output, connected via spot size conversion units
Implementation Method 3
The spot size conversion unit includes a first optical waveguide unit that is disposed continuously to the input optical waveguide and has the same cross-sectional size as the core of the input optical waveguide
Data Source
AI summary
An optical inspection circuit includes an optical circuit to be inspected formed on a substrate, an input optical waveguide optically connected to the optical circuit, and an output optical waveguide optically connected to the optical circuit. The input optical waveguide is connected with a grating coupler for input. The grating coupler is connected with the input optical waveguide via a spot size conversion unit. The output optical waveguide is optically connected with a photodiode.