Temperature-compensating package for OH line filters for astronomy: II. manufacture, assembly, and performance study

Multi-channel aperiodic fiber Bragg grating (FBG) based hydroxyl (OH) line filters have attracted significant interest in ground-based near-infrared (NIR) astronomical observations. In this paper, we present the performance of what we believe to be a new self-compensating enclosure for the filters, that can be used in non-temperature-controlled environments. Our prototype encloses a 110 mm long single-mode photosensitive optical fiber with three ∼10 mm filter gratings. A fourth grating was used as a reference outside the package to measure the uncompensated wavelength shift. The prototype was tested over three thermal cycles, and showed a maximum wavelength deviation of 12 pm, a wavelength drift of only 0.37 pm/°C, over the temperature range of -17°C to 15°C. The athermalization factor, i.e., the ratio of the maximum wavelength shift of the compensated grating to the uncompensated reference filter grating was 1/22. The results demonstrate the capability of the prototype for stabilizing multi-channel long-length FBGs or chirped FBGs, particularly for astronomical applications that require sub-picometer stability.