Readout Mirror Assembly for Ring Laser Gyroscope Backscatter Reduction
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Solution Overview
Problem
Ring laser gyroscopes face challenges in producing high-grade, low-noise sensors due to external laser beam scatter sources, particularly from defects in the beam splitter coating and polish conditions of the backside wedge angle surface, which are difficult and costly to achieve.
Innovation Solution
A method involving a super polish of a flat surface with a high-quality beam splitter coating applied, followed by bonding to a wedge angle surface using a refractive index matching optical adhesive to minimize external cavity backscatter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a beam splitter coating is applied to a backside wedge angle surface, then the readout mirror functions properly to couple beams out of the resonant cavity, but external laser beam scatter sources are introduced due to defects in the coating and polish conditions
Solution Approach 1:
The patent introduces an optical adhesive as an intermediary layer between the wedge angle surface and the beam splitter coating. This adhesive layer has a refractive index that matches the substrate material, eliminating air gaps that cause scattering. The adhesive fills surface defects and provides a smooth interface, allowing the beam splitter coating to function properly while preventing external laser beam scatter sources.
Solution Approach 2:
The patent changes the refractive index parameter of the interface between the substrate and beam splitter coating by using an optical adhesive with matched refractive index. This parameter change eliminates the refractive index mismatch that causes scattering at interfaces, thereby reducing external laser beam scatter while maintaining the readout mirror's coupling function.
2Object-affected harmful factors
If a high grade polish condition is achieved on the backside wedge angle surface, then external backscatter is reduced, but manufacturing cost and difficulty increase significantly
Solution Approach 1:
The optical adhesive serves as a mediator that compensates for surface imperfections. Instead of requiring the substrate surface to be perfectly polished, the adhesive layer fills in defects and provides the necessary smooth interface for the beam splitter coating. This approach achieves low backscatter without the need for difficult and costly high-grade polishing of the wedge angle surface.
Solution Approach 2:
The patent replaces the need for expensive, time-consuming high-grade polishing with a more economical solution using optical adhesive. The adhesive layer is a relatively simple, cost-effective material that can be applied through standard coating processes, eliminating the need for complex and expensive surface preparation while achieving the same optical performance.
3Device complexity
If the beam splitter coating is applied directly to the wedge angle surface, then the readout mirror is simpler in structure, but defects in the coating and surface polish create scatter sources
Solution Approach 1:
The optical adhesive layer acts as an intermediary between the wedge angle surface and the beam splitter coating. This additional layer, while adding a small amount of structural complexity, eliminates the harmful scattering effects caused by direct contact between the coating and defective surface. The adhesive fills surface defects and provides a smooth interface, preventing scatter sources while maintaining overall structural simplicity.
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
Enhances the performance of ring laser gyroscopes by reducing external cavity laser light scattering, thereby improving noise performance and sensor quality.
Implementation Method 1
bonded, using an optical adhesive, to the coarse polished second upper surface portion (208) of the optical substrate component (324)... A refractive index of the optical adhesive when cured matches a refractive index of the optical part
Implementation Method 2
A first beam splitter layer (336) is on a surface of the optical part (334) that faces the second upper surface portion (330)... which couples a portion of the counter-propagating beams out from the resonant cavity
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A method of making a readout mirror for a ring laser gyroscope comprises forming an optical substrate component that includes a lower surface, a first upper surface portion substantially parallel to the lower surface, and a second upper surface portion angled with respect to the lower surface; performing a coarse polish of the second upper surface portion; forming an optical part having a first surface; performing a super polish of the first surface of the optical part; applying a first beam splitter layer to the super polished first surface of the optical part, to produce a beam splitter side of the optical part; and bonding the beam splitter side of the optical part, using an optical adhesive, to the coarse polished second upper surface portion of the substrate component, to produce a reflector member. The reflector member is configured to reduce external cavity light scattering in the ring laser gyroscope.