High Power and Versatile Optical Isolator with Reflective Faraday Rotator for 2µm fiber lasers

The project calls for a high power fiber isolator working at 2µm.  This project is technically challenging due to these aspects: Operating at average power of 100W @2µm. This power rating greatly exceeds the cutting edge at present market. Compact size of 80 mm x 50 mm x 50 mm Multiple functions, also serves as mode field adapter, being able to integrate spectral filters and tap coupler. Wide bandwidth, covering from 1900nm to 2100nm.   Our innovative reflective Faraday Rotator design provides an effective solution for the first three challenges. The reflective structure allows the laser-generated heat be dissipated directly from the surface of BIG film as the Faraday material.  Our simulation shows the resulting temperature gradient under 100W laser is no greater than 1K, essentially eliminating penalties from depolarization and thermal lensing effects caused by temperature gradient. Large beam diameter is allowed to mitigate the laser damage from the high power high energy ultra-fast laser beam. The reflective design also allows the light path be folded into the compact isolator package and leaves room for inserting additional optical components. Tap coupler is naturally created from light leaking through the rotator substrate, and no additional beam splitting element is needed. The individually constructed fiber pigtail port is able to collimate light from different type of fiber into free space Gaussian beam of same waist size; therefore the isolator becomes a mode field adapter. We also introduce Quartz rotator into the proposed isolator. Quartz rotator compensates the dispersion of the Faraday rotator, and enables broadband operation with high isolation. Our design of fiber pigtail paves the way for high coupling efficiency. Our antireflection and high reflectivity mirror coatings also ensure lower insertion loss. Raytum Photonics will design and fabricate a prototype of the proposed isolator at phase 1 work. The prototype will be evaluated by both low and high power lasers.  The PI of this proposal used to serve as the product line manager of fiber isolator products of a major photonics company and was the PI of a development project for a kW-class optical isolator.