Tuneable DBR Laser Frequency Control Without External Locker
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Solution Overview
Problem
Tuneable Distributed Bragg Reflector (DBR) lasers require external frequency lockers for precise frequency control, which add complexity and cost, and are temperature-dependent, limiting their use in low-cost and low-space applications.
Innovation Solution
A DBR laser with a phase section and a frequency tuning system using a resistance heater to adjust the Bragg frequency, where a detector monitors light intensity during dithering to maintain operation at the longitudinal mode centre, allowing frequency control without a separate locker and reducing temperature dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external frequency locker is used to control laser frequency, then frequency control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the frequency locking function from an external separate device and integrates it into the laser cavity itself through the phase section. The phase section, which already exists for mode selection, is repurposed to perform frequency locking by adjusting the optical path length to maintain alignment between the Bragg frequency and longitudinal mode frequency, thereby eliminating the need for external frequency lockers while maintaining frequency control precision
Solution Approach 2:
The phase section is designed to serve multiple functions: it acts as both a mode selector and a frequency locker. By controlling the optical path length in the phase section, the system simultaneously determines the longitudinal mode and maintains frequency alignment, making the phase section a multi-functional component that reduces overall device complexity
2Reliability
If thermal control is used to maintain operating temperature, then frequency stability is improved, but size and cost increase due to cooling requirements
Solution Approach 1:
The patent replaces the mechanical/thermal cooling system with an athermal design that uses intrinsic material properties and structural configuration to maintain frequency stability. By designing the laser cavity and DBR section with materials and geometries that compensate for thermal effects, the system achieves frequency stability without requiring active thermal management hardware
Solution Approach 2:
The patent changes the design parameters of the laser cavity and DBR section to create an athermal configuration. By carefully selecting material expansion coefficients, cavity geometries, and component arrangements, the system achieves temperature compensation where thermal expansion in one component is offset by contraction in another, maintaining overall frequency stability across temperature variations
3Device complexity
If the laser operates without a frequency locker, then device simplicity is improved, but frequency control precision deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the phase section continuously adjusts the optical path length in response to drift between the Bragg frequency and longitudinal mode frequency. This feedback loop, controlled by adjusting the phase section current or temperature, automatically corrects frequency deviations and maintains precise frequency control without requiring external frequency locking hardware
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 accurate frequency selection and extended operating temperature range without the need for a frequency locker, improving laser reliability and reducing size and cost by using mode centre control and thermal control of the DBR section.
Implementation Method 1
a resistance heater configured to apply heat to a grating of the DBR section in order to adjust a Bragg frequency of the DBR section
Implementation Method 2
thermal control is achieved by altering its temperature
Implementation Method 3
Electronic control is achieved by injecting current into the phase section, and thermal control is achieved by altering its temperature
Implementation Method 4
A detector is configured to detect laser light transmitted through the DBR section
Implementation Method 5
The frequencies of the longitudinal modes are such that the round-trip phase for light of that frequency is an integer multiple of 2 pi radians
Implementation Method 6
frequency selectivity is achieved using a length of grating, known as a distributed Bragg reflector (DBR), at one end the cavity
Data Source
AI summary
In accordance with one aspect of the present application there is provided a DBR, laser. The DBR laser comprises a phase section in a cavity of the DBR laser configured to adjust an optical path length of the cavity. The laser also comprises a DBR section comprising a frequency tuning system, the frequency tuning system comprising a resistance heater configured to apply heat to a grating of the DBR section in order to adjust a Bragg frequency of the DBR section. A detector is configured to detect laser light transmitted through the DBR section. A controller is configured: to cause the phase section to apply a dither to the optical path length of the cavity or cause the frequency tuning system to apply a dither to the Bragg frequency of the DBR section; to use the detector to monitor intensity of light transmitted from the laser cavity via the DBR section during application of the dither; to determine a deviation from longitudinal mode centre operation on the basis of the monitored intensity; to cause the phase section to adjust the optical path length of the cavity in order to reduce said deviation; to determine an output frequency of the DBR laser on the basis of a resistance of the resistance heater; and to control the output frequency of the DBR laser by controlling power to the resistance heater.