Silicon Fourier Transform Spectrometer with Spatial Heterodyne
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Solution Overview
Problem
Existing on-chip Fourier transform spectrometers face challenges in achieving high spectral resolution, miniaturization, and temperature stability, with limitations in spectral bandwidth, device size, and power consumption, particularly in the stationary wave integrated and spatial heterodyne spectrometer types.
Innovation Solution
A silicon Fourier transform spectrometer with a spatial heterodyne structure incorporating cascaded optical switches, unbalanced subwavelength grating waveguide pairs, and a germanium silicon detector on a silicon-on-insulator substrate, utilizing digital optical path selection and a spectrum reconstruction algorithm based on compressive sensing to enhance spectral resolution and temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Fourier transform spectrometer uses a mechanical motion module to achieve high measurement resolution, then spectral resolution is improved, but device size increases and portability decreases
Solution Approach 1:
The patent replaces the mechanical moving mirror system with an integrated photonic circuit that uses optical path difference introduced through waveguide design. The spectral resolution is achieved by controlling the optical path difference between reference and sample arms within the photonic integrated circuit, eliminating mechanical components entirely.
Solution Approach 2:
The patent transitions from a one-dimensional mechanical displacement approach to a multi-dimensional optical path control within the photonic circuit. By using waveguide length differences and coupling mechanisms in the integrated circuit, the system achieves optical path difference without mechanical motion, effectively adding spatial dimensionality to the resolution mechanism.
2Volume of moving object
If a SWIFT-based spectrometer uses a small chip size, then device miniaturization is achieved, but spectral bandwidth is limited due to undersampling of interference fringes
Solution Approach 1:
The patent divides the spectral measurement into multiple segments by using a detector array that captures interference patterns at different positions. Each detector element samples a specific portion of the interference fringe pattern, and the combined data from multiple segments reconstructs the full spectrum with extended bandwidth despite the small chip size.
Solution Approach 2:
The patent adds a spatial dimension to the detection by using a linear array of detector elements positioned along the waveguide. This spatial distribution of detectors allows simultaneous sampling of multiple points in the interference pattern, effectively increasing the sampling rate and enabling broader spectral bandwidth coverage.
3Measurement precision
If an SHS spectrometer uses a series of MZI arrays with different optical path differences to increase resolution, then spectral resolution is improved, but device size increases rapidly
Solution Approach 1:
The patent merges multiple MZI functions into a single integrated photonic circuit structure. By using a shared waveguide platform with variable optical path difference control, the system combines the functionality of multiple discrete MZI arrays into one compact device, achieving high resolution without proportional increase in device size.
Solution Approach 2:
The patent introduces dynamic control of the optical path difference through tunable elements within the waveguide structure. By dynamically adjusting the optical path difference using electro-optic or thermo-optic effects, the system can achieve multiple resolution settings without requiring physically separate MZI arrays for each configuration.
4Ease of operation
If a spectrometer uses thermo-optic or electro-optic effects to change optical path difference, then optical path control is achieved, but power consumption increases
Solution Approach 1:
The patent optimizes the operating parameters of the electro-optic or thermo-optic modulators to achieve the required optical path difference with minimal power consumption. By carefully selecting the modulation depth, frequency, and duty cycle, the system reduces average power consumption while maintaining the ability to dynamically control the optical path difference when needed.
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
The solution effectively increases the number of resolvable wavelength points, reduces chip size, and improves temperature stability, achieving high spectral resolution and large operating bandwidth while being compatible with CMOS processes and minimizing power consumption.
Implementation Method 1
generates interference fringes by moving a reflection mirror to change the optical path difference between two beams of light
Implementation Method 2
unbalanced subwavelength grating waveguide pairs
Implementation Method 3
germanium silicon detector
Data Source
AI summary
A silicon Fourier transform spectrometer and an optical spectrum reconstruction method are disclosed. The spectrometer includes a waveguide input coupler, cascaded optical switches, unbalanced subwavelength grating (SWG) waveguide pairs, and a germanium silicon detector, where the cascaded optical switches are connected through unbalanced SWG waveguide pairs. The state of the optical switches are adjusted to digitally configure the optical path, so as to constitute a series of unbalanced Mach-Zehnder interferometer (MZI) arrays with different optical path differences, to realize a Fourier transform spectrometer based on spatial heterodyne. The optical spectrum is reconstructed by using a compressed sensing algorithm.