We demonstrated an all‐fiber birefringent comb filter with tunable and switchable wavelength spacing. The comb filter is based on a fiber loop mirror (FLM) with three sections of high‐birefringence (HB) fibers and polarization controllers (PCs). The transmission characteristics of the birefringent FLM are dependent of the relative phase difference of the two orthogonal polarization modes and the rotational angles of the different HB fibers. By adjusting the PCs, four different wavelength spacings can be obtained; particularly, interleaving operation—halved and quartered wavelength spacing—can be effectively realized. By using a Jones matrix method, the transmission of the birefringent comb filter is analyzed. The theoretical analysis agrees with the experimental results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1666–1670, 2014

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At Waterloo, we are developing a high power, short pulse, two-color, Yb:fiber amplifier system to generate the long wavelength (>15µm) side of the molecular fingerprint spectral region, by difference frequency mixing the two colors. This spectral region is important for trace gas detection of explosives. As an example, it has been shown that the strong spectroscopic signatures of a peroxide-based explosive triacetone triperoxide (TATP) occur between 15 and 20 µm. To date, we have achieved a tuning range from 16 to 20 µm with a maximum average power of 1.7 mW. On the short wavelength side, the two colors would need to be pulled further apart, which requires a higher power seed to beat the amplified spontaneous emission that appears at the gain peak of the amplifiers between the two seed colors. On the long wavelength side, we are limited to 20 µm by the transparency region of the nonlinear crystals. We would like to find new nonlinear materials that have transparency from 1 to 30µm. If we could generate wavelengths from 15 to 30 µm with sufficient power, we could extend the spectral region to also cover 8 to 15µm by frequency doubling the longer wavelengths. We are currently working on replacing bulk optics in the system with fiber based optical elements to select the wavelengths as well as stretch and recompress the pulses in order to make the system compact and stable. or less. For the keywords, select up to 8 key terms for a search on your manuscript's subject.