Silicon Photonic Tunable Laser Thermal Control for Frequency Stability
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Solution Overview
Problem
Current external cavity tunable lasers using silicon photonics face challenges in achieving precise frequency control and stability due to thermal sensitivity and thermal cross-talk, which affects their ability to meet the stringent requirements of coherent optical communication systems.
Innovation Solution
A silicon photonic tunable laser design incorporating a semiconductor gain chip and a silicon photonic filter chip with integrated ring resonators, resistance temperature sensors, and a control loop to maintain temperature stability, utilizing a Sagnac interferometer structure and thermal isolation trenches to reduce thermal cross-talk and enhance frequency accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If thermal control is implemented using integrated heaters, then frequency tuning capability is improved, but thermal cross-talk between adjacent resonators increases causing frequency instability
Solution Approach 1:
The patent divides the thermal control system into independent segments by placing individual heaters adjacent to each ring resonator. This segmentation allows independent thermal control of each resonator, minimizing thermal cross-talk and enabling precise frequency tuning without affecting adjacent resonators.
Solution Approach 2:
The patent implements local thermal control by positioning heaters directly next to specific ring resonators rather than using a single bulk heater. This local quality approach enables selective heating of individual resonators to achieve desired frequency tuning while maintaining stability of other resonators.
2Measurement precision
If temperature sensors are integrated close to ring resonators, then temperature measurement precision is improved, but optical loss increases due to sensor material absorption
Solution Approach 1:
The patent introduces an intermediary approach by placing temperature sensors in proximity to ring resonators but not in direct contact with the optical mode. This intermediate positioning allows accurate temperature measurement while minimizing optical absorption loss, as the sensors are close enough to capture thermal effects but far enough to avoid significant light absorption.
3Measurement precision
If multiple heaters are used for individual ring resonator control, then frequency tuning precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal control approach where a single controller manages multiple heaters and temperature sensors across the photonic integrated circuit. This multi-functional controller handles temperature compensation, frequency tuning, and stabilization for all resonators, reducing overall system complexity despite the presence of multiple heating elements.
Solution Approach 2:
The patent employs feedback control by continuously monitoring temperatures with integrated sensors and adjusting heater power accordingly. This closed-loop feedback mechanism automatically compensates for thermal drift and maintains precise frequency tuning, simplifying the control process despite multiple heaters by using automated temperature-based regulation.
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 design achieves precise frequency control and stability, enabling high-output power and narrow linewidth, suitable for high-order modulation formats, with frequency errors reduced to within ±0.5 GHz, meeting the stringent specifications of coherent optical communication systems.
Implementation Method 1
a resistance temperature sensor configured to measure chip temperature
Implementation Method 2
a separate heater associated with each ring resonator... adjust power to resistance heaters
Implementation Method 3
one or more connecting silicon waveguides configured to redirect light resonant with each of the at least two ring resonators back through the input-output silicon waveguide
Data Source
AI summary
A tunable solid state laser device are described comprising a semiconductor based gain chip and a silicon photonic filter chip with tuning capability. The silicon photonic filter chip can comprises an input-output silicon waveguide, at least two ring resonators formed with silicon waveguides, one or more connecting silicon waveguides interfacing with the ring resonators, a separate heater associated with each ring resonator, a temperature sensor configured to measure the chip temperature, and a controller connected to the temperature sensor and the separate heaters and programmed with a feedback loop to maintain the filter temperature to provide the tuned frequency. The one or more connecting silicon waveguides are configured to redirect light resonant with each of the at least two ring resonators back through the input-output silicon waveguide. Corresponding methods are described for the control of the laser frequency. Improved structures of the SiPho multiple filter chip involve a Zagnac interferometer.