Geometric Pump Isolation in Tunable VCSELs for Noise Control
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Solution Overview
Problem
Optically pumped MEMS tunable VCSELs face challenges with noise from pump lasers, particularly in the 1060 nm wavelength band, due to factors like relative intensity noise, mode hopping, and feedback, which affect the coherence and stability of the VCSEL light.
Innovation Solution
Geometric isolation techniques are employed to reduce pump noise, including defocusing pump light and coupling it at an angle relative to the VCSEL, combined with the use of stabilized lasers like VBG or FBG, and coherence collapse methods to control noise, potentially replacing bulky Faraday isolators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Faraday isolators are used to reduce pump feedback, then pump noise is reduced, but the device becomes large, heavy, and expensive
Solution Approach 1:
The patent extracts the isolation function from traditional Faraday isolators and implements it through geometric design of the optical cavity itself. The VCSEL cavity is shaped to inherently reject feedback light through angular deviation, eliminating the need for separate heavy isolator components while maintaining noise reduction performance.
Solution Approach 2:
The patent replaces the magnetic Faraday rotation mechanism with a geometric optical path design. By carefully designing the cavity geometry and light propagation angles, the system achieves isolation through spatial separation of forward and backward propagating light, substituting magnetic field effects with geometric optical constraints.
2Object-affected harmful factors
If Faraday isolators are used to reduce pump feedback, then pump noise is reduced, but the device complexity increases
Solution Approach 1:
The patent merges the isolation function with the VCSEL cavity structure itself. The geometric isolation is integrated into the basic laser cavity design, combining the light generation and light isolation functions into a single unified structure, thereby reducing overall device complexity.
Solution Approach 2:
The VCSEL cavity is designed to automatically reject feedback light through its inherent geometric properties. The structure itself provides the isolation function without requiring external active components or complex control systems, making the device self-regulating against pump feedback.
3Use of energy by moving object
If pump light is focused tightly on the VCSEL, then pumping efficiency is improved, but feedback to the pump increases
Solution Approach 1:
The patent applies different spatial characteristics to different parts of the optical system. The pump light is focused tightly at the VCSEL active region for efficient pumping, while the cavity geometry is designed to diverge feedback light away from the pump source. This local differentiation of optical quality allows simultaneous achievement of high efficiency and low feedback.
Solution Approach 2:
The patent solves the feedback problem by transitioning from one-dimensional focusing (tight spot size) to three-dimensional angular control. The cavity geometry introduces angular divergence as an additional degree of freedom, allowing tight spatial focusing for efficiency while creating angular separation for feedback rejection.
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
These methods effectively reduce noise in the VCSEL light, improving coherence and stability, and can be applied to various wavelength bands, including 1060 nm, enhancing performance in applications like optical coherence tomography.
Implementation Method 1
Pump light absorbed in the VCSEL is then reemitted at a longer wavelength as tunable VCSEL light
Implementation Method 2
Optically pumped MEMS tunable VCSELs
Implementation Method 3
geometric isolation ideas presented here can at least reduce and possibly prevent optical feedback from the VCSEL to the pump laser. These solutions are particularly useful in miniature bulk optical packages
Implementation Method 4
VCSEL (Vertical cavity surface emitting lasers)
Implementation Method 5
pump for producing light to pump the VCSEL
Data Source
AI summary
An optically pumped tunable VCSEL swept source module has a VCSEL and a pump, which produces light to pump the VSCEL, wherein the pump is geometrically isolated from the VCSEL. In different embodiments, the pump is geometrically isolated by defocusing light from the pump in front of the VCSEL, behind the VCSEL, and/or by coupling the light from the pump at an angle with respect to the VCSEL. In the last case, angle is usually less than 88 degrees. There are further strategies for attacking pump noise problems. Pump feedback can be reduced through (1) Faraday isolation and (2) geometric isolation. Single frequency pump lasers (Distributed feedback lasers (DFB), distributed Bragg reflector lasers (DBR), Fabry-Perot (FP) lasers, discrete mode lasers, volume Bragg grating (VBG) stabilized lasers can eliminate wavelength jitter and amplitude noise that accompanies mode hopping.