Silicon Photonic Laser Chirping With Separate Phase and Gain Tuning
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Solution Overview
Problem
Existing frequency-tunable lasers used in applications like FMCW Lidar and OCT suffer from limitations such as broad spectral linewidth, limited chirp range, and nonlinear relationships between laser drive current and frequency chirp, leading to degraded chirp linearity and increased relative intensity noise.
Innovation Solution
The development of frequency-chirped silicon photonic lasers with separate gain and phase-tuning sections, decoupling optical frequency from output power, and utilizing tunable ring-resonator-based or grating-based optical filters for precise frequency tuning and narrow spectral linewidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing frequency-tunable lasers are used for FMCW Lidar and OCT applications, then frequency tuning capability is provided, but spectral linewidth becomes broad and chirp linearity degrades
Solution Approach 1:
The laser system is segmented into distinct functional modules: a fixed-frequency laser source, a separate tunable optical filter (acousto-optic or electro-optic), and a modulation section. This segmentation allows the laser source to maintain stable, narrow linewidth while the filter handles frequency tuning with linear chirp characteristics, resolving the contradiction between linewidth and chirp linearity.
Solution Approach 2:
A tunable optical filter acts as an intermediary between the fixed-frequency laser source and the output. This intermediary component enables precise frequency tuning and linear chirp generation without affecting the inherent narrow linewidth of the laser source, thereby resolving the contradiction between measurement precision and reliability.
2Speed
If laser drive current is modulated to achieve frequency chirp, then frequency tuning is achieved, but nonlinear relationship between current and frequency degrades chirp linearity
Solution Approach 1:
The patent replaces direct electrical modulation of laser current (which has nonlinear frequency-current relationship) with optical modulation using acousto-optic or electro-optic filters. This substitution provides linear relationship between control voltage and output frequency, achieving both fast tuning speed and high chirp linearity.
Solution Approach 2:
The system changes the control parameter from laser drive current to filter tuning voltage. This parameter change enables linear frequency modulation because the filter's resonant frequency has a direct, linear relationship with the applied control voltage, unlike the nonlinear current-frequency relationship of laser diodes.
3Speed
If existing lasers are used for high-speed tuning, then rapid frequency chirp is achieved, but output power uniformity deteriorates and noise increases
Solution Approach 1:
By separating the laser source (providing stable, uniform output power) from the frequency tuning function (performed by external filters), the system achieves rapid tuning rates without compromising output power uniformity. The laser operates continuously at optimal power while the filter provides fast, noise-free frequency modulation.
Solution Approach 2:
The tunable optical filter serves as an intermediary that enables rapid frequency tuning without directly affecting the laser's output power stability. This intermediary approach allows high-speed chirp while maintaining uniform output power and minimizing relative intensity noise.
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
Achieves high-performance sensing with narrow spectral linewidth and rapid tunability, improving depth resolution and reducing noise in Lidar applications, while maintaining linear chirp profiles and high output power uniformity.
Implementation Method 1
an electro-optic phase-tuner formed inside the laser cavity
Implementation Method 2
the tunable optical wavelength filter comprising a thermo-optic filter phase-tuner and an electro-optic filter phase-tuner
Implementation Method 3
utilizing tunable ring-resonator-based or grating-based optical filters for precise frequency tuning
Implementation Method 4
utilizing tunable ring-resonator-based or grating-based optical filters for precise frequency tuning
Implementation Method 5
an optical gain section comprising a diode structure formed in one of the one or more III-V waveguide sections inside the laser cavity
Data Source
AI summary
A frequency-chirped integrated silicon-photonic laser may be provided with separate gain and phase-tuning sections in the laser cavity, one or two wavelength filters forming part of the reflective structures defining the cavity, and electro-optic and optionally thermo-optic intra-cavity and filter phase tuners. The electro-optic phase tuners may be driven with synchronized voltage waveforms, at amplitudes determined, based on measurements of the laser output power and chirp, to achieve mode-hop-free frequency chirping with a target chirp amplitude. The waveforms may be predistorted to improve chirp linearity.