Laser Line Tunable Filter (LLTF) 23 x 16 x 17 cm

The laser line tunable filter (LLTF) is a non-dispersive tunable bandpass filter based on volume holographic gratings. It delivers the highest signal throughput in the industry and is also unique in that it combines very high optical density (> od6) and outstanding out-of-band rejection with wide tunability. A single filter can be tuned from 400 nm to 1000 nm (VIS) or 1000 nm to 2300 nm (SWIR).
The out-of-band rejection and the optical density (OD) are two critical specifications of tunable filters. Unfortunately, these properties are often misinterpreted and their definitions tend to differ from one manufacturer to another. End users need to be careful when looking at the specifications of a filter. Also, the measurement of these properties for customers can be laborious. One needs to have sensitive instruments with a high dynamic range, a wide spectral range and a high power source. In this white paper, clear and rigorous definitions of the out-of-band rejection and the OD of widely tunable filters are presented, and the steps and instrumentation needed to accurately measure those specifications are exposed.