Fares Alhassen

A highly efficient thermally controlled loss-tunable long-period fiber grating on corrugated metal substrate

We demonstrate a new approach for fabricating a compact loss-tunable long-period fiber grating (LPFG) by gluing a fiber onto a corrugated metal substrate filled with ultraviolet-cured epoxy. The strain caused by the difference in thermal expansion among the adhesive, the substrate, and the silica fiber induces a periodic microbending along the fiber when the device temperature is changed. The LPFG has an initial flat spectrum at room temperature. With 35 grating periods, a tuning range of -21 dB is achieved through core-cladding coupling for a temperature change from room temperature to 4/spl deg/C. A theoretical model is presented to explain the high tuning efficiency and the operating mechanisms of the device.

Fabrication and Mode Identification of Compact Long-Period Gratings Written by CO

We report highly compact (1.2 cm) long-period fiber gratings (LPGs) exhibiting strong grating effect (>30-dB loss) and low insertion loss (<0.25 dB) inscribed by a continuously scanned CO2 laser. The LPG resonances are also probed using traveling acoustic gratings with variable period. Our results show that these CO2 laser side-exposed LPGs predominantly couple to antisymmetrical cladding modes.

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In this letter, we investigate coherent acoustooptic coherent mode coupling from the LP01 core mode to LP1m cladding mode of a polarization-maintaining fiber (PMF) induced by two acoustic gratings. We show narrowband variable attenuation along either birefringent axis of the PMF by varying the relative phase between the two acoustic gratings. By launching two acoustic gratings at different frequencies, variable attenuation and low crosstalk along either birefringent axis within the acoustooptic coupling bandwidth are demonstrated

Laser

We demonstrate a compact, all-fiber frequency shifter by cascading a CO2-written long-period grating with a flexural acoustic-wave-induced microbending grating on a single-mode fiber. Carrier and image sideband suppressions of 30.0 and 28.1 dB, respectively, are measured. An all-fiber vibrometer based on this frequency shifter capable of nanometer resolution at frequencies up to megahertz is also demonstrated.

Acoustooptic Coherent Mode Coupling in Polarization-Maintaining Fiber and Its Application as a Variable-Polarization-Dependent Loss Element

A new method to inscribe a long-period grating (LPG) with strong grating (>25 dB loss), short grating length (1.2 cm) and low insertion loss (<1.0 dB) by using a programmable sinusoidal-dithering, linearly scanned CO2 laser beam is reported.

A Compact All-Fiber LPG-AOTF Frequency Shifter on Single-Mode Fiber and Its Application to Vibration Measurement

Transfer of orbital angular momentum from an electronically controlled acoustic vortex to an optical vortex in optical fiber is experimentally demonstrated. Potential applications include quantum key encryption and decoding and optical trapping

Ultra-Compact Long-Period Fiber Grating and Grating Pair Fabrication using a Modulation-Scanned CO 2 Laser

We demonstrate dynamic strain sensing using a fiber acousto-optic tunable filter (AOTF). The sensing mechanism is based on the shift of resonant wavelength of the AOTF filter in the presence of mechanical strain on the fiber. An input laser signal can thus be modulated by a dynamic strain. The modulation due to a low-frequency (~10 Hz) dynamic strain applied to the fiber AOTF was measured

Transfer of orbital angular momentum between acoustic and optical vortices in optical fiber

A compact all-fiber acoustooptic wavelength monitor with passive polarization-dependent loss (PDL) compensation is demonstrated. A Sagnac loop interferometer is used to compensate the intrinsic PDL, and hence, the polarization-dependent wavelength shift of the fiber acoustooptic tunable filter (AOTF). This increases the extrinsic wavelength accuracy of the device to 0.05 nm, a three-fold improvement from a previously reported uncompensated device. The relaxation in the PDL specifications for the AOTF also results in a reduction of fiber length from 38 to 14 cm.

Sensing of dynamic strain via acousto-optic coupling in single-mode fiber

We report on the acousto-optic interaction in a newly developed high-polarization-splitting fiber designed to lift the degeneracy of its cladding modes and on an all-fiber acousto-optic tunable bandpass filters based on this fiber.

A compact all-fiber PDL-compensated acoustooptic wavelength monitor

We describe the implementation of a wavelength-tunable polarization-dependent-loss element on polarization-maintaining fiber using two independently-controlled acoustic gratings. Continuous attenuation in both fast and slow axes at the same wavelength is demonstrated.