SBIR-STTR Award

The laser sources emitting from short to long infrared wavelengths are used for environmental sensing, metrology and clinical diagnosis, LADAR applications. The second atmospheric window between 3-5 um is crucial where a large number of gases, e.g. methane, nitric oxide, carbon mono-dioxide or formaldehyde, can be detected. Due to the presence of very strong fundamental stretching modes of O-H, C-H and N-H bonds that are up to orders of magnitude stronger than the overtones in the near-IR, detection limits down to sub-ppb concentrations can be obtained. One of the necessary components for such measurements is optical isolator. However, there are no commercially available devices for this spectral range. The main objective of the current proposal is to create an optical isolator for 3-5 um that could be used in laser applications. The technical approach is to develop a vitreous material that is transparent in mid IR spectral region and can accept high concentration of ions that increase magnetooptical constant. Dependence of magnetooptical sensitivity on different dopants will be studied, a technology of fabrication of mid IR transparent magnetooptical glass will be developed and optical isolation in 3-5 um region will be demonstrated in bulk and fiber geometries.

Keywords:
Water-Free Glass, Magneto-Optical Effect, Verdet Constant, Rare-Earth Ions, Optical Isolation

The wavelength region covering short to long infrared diapasons is used for environmental sensing, metrology and clinical diagnosis, and LADAR applications. All these applications require good optical isolation to prevent laser destabilization and possible damage. The main objective of this project is creation of the suitable material for optical isolation, which includes development of a glass which shows high magnetooptical properties (large Verdet constant), low losses and high optical homogeneity, and demonstration of bulk and fiber prototypes of optical isolators in the visible, near and mid-IR spectral regions (0.4-5 um). In order to make new glass isolator material available for fiber systems, we are going to continue exploration of an efficient fabrication of optical fibers from rare earth doped germanate glasses. Our efforts will be concentrated on fabrication of a single mode magnetooptical fiber and with further design and fabrication of polarization maintaining single mode fiber.

Benefit:
Based on our studies of magneto-optical glasses doped with rare earth ions we selected several perspective candidates for an effective optical isolation in Mid-IR region. Moreover we showed the possibility of rare earth doped PTR and Ge glass fibers, which is the first step on the way of all-fiber Mid-IR optical isolators. In the framework of the Phase II we will concentrate our research on the development of the fully operated high power (up to 500 W) actively cooled optical isolator working in 3-5 um region with 30-40 dB of returning loss at all power levels. Anticipated benefits of a proposed optical isolator include reduction of weight and dimensions of the final prototype, wide transparency in mid-IR region and low loss. Potential Commercial Application are the laser systems operating in mid-IR spectral region represent a fast growing market for medical, environmental and industrial applications. Commercial applications include optical isolators for solid state and fiber lasers rare earth and transition ions doped crystals and glasses, quantum and interband cascade semiconductor lasers, etc. Mid-IR optical isolators can also be used as intracavity elements providing unidirectional lasing (for example ring-cavity single frequency lasers).