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In this letter, a torsion sensing arrangement based on a three beam path Mach–Zehnder interferometer (MZI) is presented. The MZI with three beam paths was fabricated by fusion splicing a piece of double ytterbium‐doped double‐cladding photonic crystal fiber (Yb‐d‐DPCF) between two segments of single mode fiber (SMF). Moreover, in our sensing arrangement the Yb‐d‐DPCF segment is acting both as the MZI as the gain medium. Here, a spectral MZI fringe shifting is induced by applying torsion over the Yb‐d‐DPCF. By this setup, a torsion sensitivity of 0.001 nm/° was achieved. Finally, it is shown that the sensing arrangement is compact and robust. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1857–1860, 2015

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In this work a very simple continuously tunable laser based on an erbium ring cavity and a silicon wafer is presented. This laser can be tuned with very fine steps, which is a compulsory characteristic for gas sensing applications. Moreover the laser is free of mode hopping within a spectral range sufficiently wide to match one of the ro-vibrational lines of a target molecule. Here the proposed laser reached, at ~1530 nm, a continuous tuning range of around 950 pm (>100 GHz) before mode hopping occurred, when a silicon wafer of 355 μm thickness was used. Additionally, the laser can be finely tuned with small tuning steps of  <12 pm, achieving a resolution of 84.6 pm °C−1 and by using a thermo-electric cooler (TEC) the laser showed a high wavelength stability over time. These tuning characteristics are sufficient to detect molecules such as acetylene in which the mean separation between two ro-vibrational lines is around 600 pm. Finally, it is shown that the tuning range can be modified by using wafers with different thickness.