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An enhanced Goos–Hänchen (GH) shift, which is attributed to the oscillating wave propagating in the polyimide-coated symmetrical metal cladding waveguide, is employed to optically monitor the relative humidity (RH). The interaction of polyimide with the water molecules can change the waveguide structure parameters (thickness and refractive index) and thus alter the magnitude of GH shift. In our experiment, the magnitude of GH shift is measured during the RH variation from 43% to 73% with a step of 5% and the corresponding desiccation process. The proposed optical RH sensor exhibits good linearity and high sensitivity, meanwhile provides short response time and favorable stability over a long period. In addition, since the GH shift signal is position encoded, our sensing mechanism is immune to the intensity fluctuation in the light source. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate that the bandwidth of single photons laser pulse is compressed by a factor of 58 in a periodically poled lithium niobate (PPLN) waveguide chip. A positively chirped single photons laser pulse and a negatively chirped classical laser pulse are employed to produce a narrowband single photon pulse with new frequency through sum-frequency generation. In our experiment, the frequency and bandwidth of single photons at 1550 nm are simultaneously converted. Our results mark a critical step towards the realization of coherent photonic interface between quantum communication at 1550 nm and quantum memory in the near-visible window. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate a multiwavelength fiber laser with ultradense wavelength spacing and ultrabroad bandwidth based on inhomogeneous loss mechanism with assistance of nonlinear polarization rotation. The inhomogeneous loss, implemented by incorporating a section of highly nonlinear fiber (HNLF) and a Sagnac filter in the laser cavity, can balance mode competition in erbium-doped fiber and result in ultradense multiwavelength generation. The bandwidth of the multiwavelength spectrum is greatly broadened owing to the intensity-dependent loss induced by nonlinear polarization rotation. Stable multiwavelength lasing with wavelength spacing of 0.08nm and wavelength number up to 254 is achieved at room temperature. Moreover, multiwavelength tuning is realized through modifying polarization-dependent cavity loss. [Copyright &y& Elsevier]