We demonstrate an all-fiber tunable polarization filter with high coupling efficiency based on acousto-optic coupling between two optical polarization modes of the LP(01) mode propagating in a highly birefringent single mode optical fiber. An over-coupling between the two polarization modes is realized over the wavelength range from 1530 nm to 1610 nm using traveling torsional acoustic wave. The measured 3-dB optical bandwidth of the filter was 4.8 nm at the wavelength around 1550 nm. The details of the filter transmission and the coupling characteristics are discussed.

Abstract:We propose and demonstrate phase-sensitive amplification based on cascaded second harmonic generation and difference frequency generation within a periodically poled lithium niobate waveguide. Excellent agreement between our numerical simulations and proof-of-principle experiments using a 3-cm waveguide device operating at wavelengths around 1550 nm is obtained. Our experiments confirm the validity and practicality of the approach and illustrate the broad gain bandwidths achievable. Additional simulation results show that the maximum gain/attenuation factor increases quadratically with input pump power, reaching a value of ±19.0dB at input pump powers of 33 dBm for a 3 cmlong waveguide. Increased gains/reduced powers for a fixed gain could be achieved using longer crystals.

We demonstrate an all-fiber acousto-optic tunable bandpass filter exhibiting narrow optical bandwidth and negligible polarization dependence by employing a novel ultraviolet (UV)-induced core-mode blocker written in a high numerical aperture (NA) fiber. It was demonstrated that the device had the measured 3-dB optical bandwidth of 0.65 nm, the polarization-dependent center-wavelength splitting of 0.05 nm and the extinction ratio of -22dB at the wavelength around 1550 nm. The details of the transmission characteristics and the loss mechanism of the core-mode blocking element inscribed in the high NA fiber are discussed.

We present a systematic analytic and numerical study of the detection limit of a refractive index sensor employing a directional coupler architecture within a photonic crystal fiber (PCF). The device is based on the coupling between the core mode and a copropagating mode of a satellite waveguide formed by a single hole of the PCF infiltrated by a high-index analyte. Using coupled mode theory as well as full simulations, we investigate the influence of changes in the geometrical parameters of the PCF and the analyte's refractive index on sensor performance, including sensitivity, resonance width, and detection limit. We show that regardless of the details of the sensor's implementation, the smallest detectable refractive index change is inversely proportional to the coupling length and the overlap integral of the satellite mode with the analyte, so that best performance comes at the cost of long analyte infiltration lengths. This is experimentally confirmed in our dip sensor configuration, where the lowest detection limit achievable for realistic implementation is estimated to 7 × 10 −8 refractive index units (RIU) based on realistic signal to noise ratios in a commercially available PCF.

Abstract:We report the axial strain dependence of two types of all-fiber acousto-optic tunable filters based on flexural and torsional acoustic waves. Experimental observation of the resonant wavelength shift under applied axial strain could be explained by theoretical consideration of the combination of acoustic and optical effects. We discuss the possibility of suppressing the strain effect in the filters, or conversely, the possibility of using the strain dependence for wavelength tuning or strain sensors. Lett. 11, 177-179 (1986). 13. T. Yoshino, K. Kurosawa, K. Itoh, and T. Ose, "Fiber-optic Fabry-Perot interferometer and its sensor applications," IEEE J. Quantum Electron. 18, 1624-1633 (1982). 14. J. N. Blake, S. Y. Huang, B. Y. Kim, and H. J. Shaw, "Strain effects on highly elliptical core two-mode fibers," Opt. Lett. 12, 732-734 (1987). 15. D. Östling and H. E. Engan, "Narrow-band acousto-optic tunable filtering in a two-mode fiber," Opt. Lett. 20, 1247Lett. 20, -1249Lett. 20, (1995 2009 Optical Society of America