Tunable Laser Coherence Length Control via Cavity Tuning
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Solution Overview
Problem
Existing swept-wavelength lasers face challenges in coherence length control, leading to intensity modulation and noise interference due to etalons and stray reflections, which affect measurement accuracy in applications like OCT and telecommunications testing.
Innovation Solution
The coherence length of a laser is directly modulated by adjusting parameters such as feedback mirror spacing, cavity length, or phase using tuning elements like Vernier-tuned Distributed Bragg Reflectors or external MEMS mirrors, allowing for precise control of wavelength and linewidth to reduce interference and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the coherence length of the laser is increased to improve imaging depth in OCT, then the ability to resolve deeper tissue structures is improved, but intensity modulation from etalons and noise from stray reflections increase, degrading measurement accuracy
Solution Approach 1:
The patent applies dynamics by making the coherence length adjustable rather than fixed. The laser system dynamically changes its coherence length parameter to match the specific measurement requirements, allowing optimization between imaging depth and measurement precision for different application scenarios
Solution Approach 2:
The patent implements parameter changes by modifying the laser's coherence length as a controllable parameter. Through adjusting laser operating conditions or optical path parameters, the coherence length can be varied to eliminate etalon effects and reduce stray reflection noise, thereby improving measurement accuracy
2Ease of operation
If existing methods modulate the gain to reduce coherence length, then coherence length control is achieved, but wavelength instability increases causing broader linewidth and reduced coherence length control precision
Solution Approach 1:
The patent extracts the coherence length control function from the gain modulation mechanism. Instead of using gain modulation to control coherence length, the system separates these functions and uses dedicated mechanisms (such as external cavity length adjustment) to control coherence length independently, preserving wavelength stability
Solution Approach 2:
The patent introduces an intermediary mechanism between the gain section and the coherence length control. By using an external cavity or separate optical path element to control coherence length, the system avoids direct coupling between gain modulation and coherence length, thereby maintaining wavelength stability
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 effectively reduces coherence length, eliminating intensity modulations and noise, thereby enhancing measurement accuracy and signal quality in OCT and telecommunications testing systems without requiring additional components or gain modulation.
Implementation Method 1
etalons formed from small air gaps in the optical path can lead to intensity modulation from interferences
Implementation Method 2
stray reflections from other elements in the optical system, for example lenses or beam-splitters, can introduce additional reflections that interfere with the reference signal
Data Source
AI summary
A system and method for adjusting the coherence length of a tunable laser to optimize measurements and reduce artifacts. A tuning element of the laser system modulates, adjusts, or controls parameters associate with the tunable laser, such that the output wavelength of the tunable laser is modulated or adjusted over a wavelength range within a time interval. Modulation of the parameter has the effect of increasing a linewidth of the tunable laser.