“It’s the IR that makes isolators difficult”.
An Optical Isolator consists of a Faraday Rotator and two Polarizers, all contained in a Body.
A Faraday Rotator consists of a Magneto-Optic Material mounted in a magnetic field.
(Request separate paper on the Operation of an Optical Isolator).
The Magneto-Optic Material must have:
- low absorption at the wavelength of interest,
- ability to rotate 45º at the wavelength of interest.
This narrows down our options.
The materials for the infrared are specially formulated so as to achieve design goal performance at the wavelength of operation.
Thus, the wavelength of operation determines the choice of material and its formulation.
Even then, the optimum material for one wavelength may perform very differently at a nearby wavelength. For example, transmission at λ1 can be different at λ2, even though the two wavelengths are close together.
Because it is not feasible to have a laser for every isolator wavelength ordered, we assemble and test such isolators using the closest wavelength laser we have. With performance data at many wavelengths, accumulated over many years, we can interpolate or extrapolate to wavelengths that are close to our lasers.
In other words, we cannot always test at our customer’s wavelength, but usually we are able to predict the isolator performance (transmission) based on our accumulated data.
Still, there are some wavelengths that will have low transmission, and there is nothing we can do about this. At all times, we inform our customers of the situation at the very start. No one likes an unpleasant surprise.
Going to CLEO 2013 in San Jose? Be sure to set aside half a day and drive up to one of the world’s major astronomical observatories, the Lick Observatory in Mount Hamilton, California.
There are many places along the freeway and in San Jose where you can see the white dome on the mountain ridge.
The history is fascinating. It was built between 1880 and 1888. The Great Lick Refractor, 36-inch aperture, was the world’s largest refractor until the Yerkes 40-inch was built.
You will appreciate the engineering that went into the design. For example, not having electricity, mechanical controls were hydraulic, using water pressure from a nearby stream.
Pivoting about the center line, the eyepiece end of the telescope clearly raised or lowered as the telescope changed elevation angle. Thus, the observer sat on a platform that could be raised or lowered accordingly.
Directions to Lick Observatory
Lick Observatory is located on the summit of Mt. Hamilton in the Diablo Range east of San Jose. To get there from Interstates 101, 280, 680, take Alum Rock Avenue exit from Interstate 680 north. Turn right onto Alum Rock Avenue. Take another right on Mt. Hamilton Road (California Route 130). Allow about one hour from San Jose, and please drive carefully as the road is good, but winding*.
Open, Thursday – Sunday, noon to 5 PM
*TRIVIA: the pitch of the winding road was determined by the weight of the load that could be hauled by a team of 6 mules.
This is a not-to-be missed visit: Lick Observatory, Mount Hamilton, California