[PCG21-P01] Development of compact mid-infrared heterodyne spectroscopy by hollow optical waveguide
Keywords:Mid-infrared heterodyne spectrometer, Hollow fiber, Rectangular hollow waveguide coupler
MIR heterodyne spectrometer requires the single-mode transmission for the mixture of two beams and enough low loss rate of 0.5 dB/m for the weak source light. The hollow optical fibers was confirmed to achieved single-mode transmission with the core diameter of 1.0 mm by quantum cascade laser of 7 µm with incident F-number of ~70 and that the loss rate was less than 0.5 dB/m with the fiber core diameter of 0.7 mm by CO2 laser.
Optical grass fibers can be coupled by the fused fiber coupler which two fibers are twisted, heated, stretched, and fused to exchange the energy between cores by evanescent light. Although the hollow optical fibers cannot be used this coupler method because of no core material, we developed the Ag-coated rectangular hollow waveguide coupler which can mix MIR beams by mode couple. It can be utilized to the mixing part of the heterodyne spectrometer, which enables us to simplify the optical design of the current MIR heterodyne spectrometer and to observe with multiple local oscillators. We simulated two gauss beam was coupled with the rectangular hollow waveguide coupler by length of 15 cm.
We will evaluate the quality for heterodyne signal of source light and laser transmitted by the hollow optical fibers and will develop to the rectangular hollow waveguide coupler for beam mixture. We plan to show the plot of new compact MIR heterodyne spectrometer.