Integrated Optical Linewidth Reduction via External Reference Laser Feedback
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Solution Overview
Problem
Conventional linewidth reduction systems for optical signals face instability due to the laser being part of the feedback loop, resulting in weak tunability, large form factor, low wall-plug efficiency, and undesired mode hoping, which limits their effectiveness in applications like coherent optical communication and LIDAR systems.
Innovation Solution
An integrated optical linewidth reduction system that uses a phase modulator to generate a feedback control signal based on phase noise, with a true-time delay element and photo detectors to split and process optical signals, reducing linewidth through negative feedback without affecting the laser's characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional feedback technique is used to cancel phase noise, then phase noise reduction is achieved, but feedback loop instability occurs because the laser is part of the feedback loop
Solution Approach 1:
The patent extracts the laser from the feedback loop by using an external reference laser instead of feeding back to the original laser. The phase noise is measured and corrected using the reference laser as a stable基准, eliminating the instability caused by including the laser in the feedback loop while maintaining phase noise cancellation capability
Solution Approach 2:
The patent introduces an external reference laser as an intermediary element. This reference laser serves as a stable reference that mediates the phase noise measurement and correction process, allowing the system to reduce phase noise without creating feedback loop instability that would occur if the original laser were included in the loop
2Measurement precision
If conventional feedback technique is used, then phase noise is reduced, but laser characteristics such as FM response affect loop performance
Solution Approach 1:
The patent extracts the phase noise measurement process from the laser itself by using an external reference laser. This separation ensures that the feedback loop performance is independent of the laser's FM response and other characteristics, as the reference laser provides a stable基准 that is not affected by the device under test's characteristics
Solution Approach 2:
The external reference laser acts as an intermediary that decouples the feedback loop performance from the characteristics of the laser being measured. The reference laser's stable properties ensure that loop performance remains consistent regardless of variations in the original laser's FM response or other characteristics
3Measurement precision
If commercially available Sub-KHz fiber laser is used, then narrow linewidth is achieved, but form factor becomes large and wall-plug efficiency decreases
Solution Approach 1:
The patent creates a copy of the phase noise characteristics using an external reference laser instead of relying on a large, inefficient Sub-KHz fiber laser. By measuring and correcting phase noise through the reference laser, the system achieves narrow linewidth output with a more compact and efficient configuration
Solution Approach 2:
The patent replaces the mechanical/optical complexity of a Sub-KHz fiber laser system with an electronic feedback system using a phase modulator and reference laser. This substitution achieves the same narrow linewidth function with reduced form factor and improved wall-plug efficiency by using electronic control rather than relying on the inherent properties of a large fiber laser
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 system achieves reduced optical linewidth without the instability issues of conventional methods, maintaining laser tunability and efficiency, enhancing performance in applications such as coherent communication and LIDAR systems.
Implementation Method 1
a phase modulator adapted to modulate the phase of an incoming optical signal in response to a feedback control signal
Implementation Method 2
a photo detection circuit comprising first and second photo detectors. The first photo detector is adapted to generate a second electrical signal in response to the sixth optical signal
Data Source
AI summary
An integrated optical linewidth reduction system includes a phase modulator adapted to modulate the phase of an incoming optical signal in response to a feedback control signal defined by a first electrical signal. The phase modulator is further adapted to generate a first optical signal travelling through a first optical path. The first electrical signal is representative of a phase noise of the first optical signal. An optical linewidth of the first optical signal is less than an optical linewidth of the incoming optical signal.