Fiber optic attenuator
Thorlabs
* Maximum Power Ratings up to 50 W
* Isolation Values from 30 to 42 dB Depending on Model
* Wavelength Ranges from 780 to 2050 nm
* Polarization Independent and Dependent Versions
* Available With or Without Connectors
Fiber isolators are used to protect laser sources from back reflections and signals that can cause instabilities and damage by allowing light to pass through in the forward direction with minimal loss, while light traveling in the opposite direction experiences maximum loss. Fiber isolators are available in both polarization-dependent and polarization-independent models for wavelengths from 780 to 1550 nm. Operating power and wavelength are the two most important factors in isolator design.
Low power (max power 1060 nm, use a Bismuth Iron Garnet (BIG) rotator, which is very compact and inexpensive. Low power isolators with a lower wavelength rely on bulk rotators, which have a much lower Verdet constant than BIG rotators, and require the use of magnets that are orders of magnitude larger and more expensive.
High power isolators, which are designed for maximum powers of 2 - 50 W (depending on model), use non-absorptive crystal polarizers as well as crystal Faraday rotators. In the reverse direction (isolation), the polarizers displace rather than absorb the return beam so that it does not couple back into the incoming fiber. These crystals require larger and more powerful magnets to achieve the desired level of isolation.
