Injection-Locked Lasers for Broadband Microwave Signal Generation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing systems for generating optically synthesized microwave signals face a trade-off between broadband tunability and low phase noise, with methods like phase locking restricting tuning bandwidth and speed, and optoelectronic oscillators requiring electronic amplifiers and long fiber delays for stability.
Innovation Solution
An optically injected semiconductor laser system with optoelectronic feedback and mutual optical injection, eliminating the need for microwave amplifiers or filters, and using asymmetric mutual optical injection for long-term stability, enabling broadband tuning from 10 GHz to 110 GHz with Hz-level linewidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase locking is used to reduce phase noise, then phase noise is reduced, but tuning bandwidth and tuning speed are restricted
Solution Approach 1:
The patent replaces the mechanical/optical phase locking system with an electrical injection locking system. Instead of using optical phase-locked loops (OPPL) that rely on optical feedback and modulation, the invention uses electrical injection current from a microwave signal source to directly control the laser diode's optical output frequency. This substitution of the control mechanism allows for much faster response times and broader tuning ranges while maintaining low phase noise, as the electrical injection method has inherently faster bandwidth compared to optical phase locking approaches.
2Reliability
If optoelectronic oscillators are used to generate stable microwave signals, then signal stability is improved, but the system requires electronic amplifiers and long fiber delays
Solution Approach 1:
The patent extracts and removes the electronic amplifier and long fiber delay components from the traditional optoelectronic oscillator system. By using electrical injection locking of a laser diode, the system achieves signal stability through direct electrical control of the laser's optical frequency, eliminating the need for separate electronic amplification stages and long optical delay lines that are characteristic of conventional OEO architectures.
Solution Approach 2:
The invention merges the functions of the laser source, microwave signal generator, and frequency stabilizer into a single integrated system. The electrical injection current serves multiple purposes: it provides the optical carrier, generates the microwave signal through modulation, and stabilizes the frequency simultaneously. This consolidation eliminates the need for separate electronic amplifiers and long fiber delay components, reducing overall system complexity while maintaining stability.
3Reliability
If long fiber delays are used in optoelectronic oscillators, then Q factor is increased and linewidth is reduced, but system size and complexity increase
Solution Approach 1:
The patent replaces the long physical fiber delay line with an electrical injection locking mechanism. Instead of relying on long optical paths to achieve high Q factors and narrow linewidths, the invention uses the resonant properties of the laser diode itself, controlled by electrical injection, to achieve frequency stabilization. This substitution eliminates the need for kilometers of fiber while achieving equivalent or superior linewidth performance through the laser's inherent resonance characteristics enhanced by electrical feedback.
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
This approach achieves broadband tunability and low phase noise across a wide frequency range without the need for external amplifiers or filters, enhancing long-term stability and reducing phase noise, as demonstrated by improved phase-noise measurements and temporal stability.
Implementation Method 1
A second laser is optically coupled to the first laser and is configured to receive optical signals injected by the first laser
Implementation Method 2
A photodetector converts the optical signals from the second laser to electrical signals
Implementation Method 3
A phase modulator is coupled to the photodetector, and the electrical signals from the photodetector are operable to drive the phase modulator
Data Source
AI summary
A system and method for generating optically synthesized microwave signals with broadband tunability is disclosed. The system includes a first laser and a second laser, where the first laser and second laser are optically coupled to each other. The second laser is operable to receive optical signals injected by the first laser, and to output optical signals via one or more feedback paths. The system provides for singular or mutual optical injection. A photodetector is optically coupled to the second laser over the one or more feedback paths, and operable to convert optical signals to electrical signals. A phase modulator is coupled to the photodetector, where the electrical signals from the photodetector are operable to drive the phase modulator and close the one or more feedback paths. The respective lengths of the feedback paths may be selected such that their corresponding lengths provide a frequency spacing for optical signals therein that is significantly smaller than a frequency of microwave signals.