YuanYao Lin

Leakage coupling of ultrasensitive periodical silica thin-film long-period grating coated on tapered fiber

This investigation demonstrates leakage coupling between fundamental-mode and high-order mode resonance based on a periodical silica thin-film long-period grating (TFLPG) that was coated on a tapered fiber when wavelengths longer than the fundamental-mode cutoff were propagated. For the leaky guiding situation, these leakage modes still may exhibit strong mode coupling in the taper with the assistance of the TFLPG when the phase-matched condition is satisfied. An extremely high tuning efficiency of 62.9 nm/°C, which is equivalent to a measurement of sensitivity of approximately 168, 182 nm per refractive index unit, is achieved. To the best of our knowledge, this sensitivity is the highest achieved for a fiber sensor to date.

Nonlinear properties and stabilities of polaritonic crystals beyond the low-excitation-density limit

Coherent properties of a two-dimensional spatially periodic structure, polaritonic crystal (PolC) formed by trapped two-level atoms in an optical cavity array interacting with a light field, are analyzed. By considering the wave function overlapping for both photonic and atomic states, a cubic-quintic complex nonlinear Schr¨ odinger equation is derived for the dynamics of coupled atom-light states, wave function of low-branch polaritons, associated with PolC in the continuous limit. A variational approach predicts that a stable ground-state wave function of PolC exists but is accompanied by an oscillating width. For a negative scattering length, the wave function collapses in the presence of a small quintic nonlinearity appearing due to a three-body polariton interaction. By studying the nonequilibrium (dissipative) dynamics of polaritons with adiabatic approximation, we have shown that the collapse of PolC wave function can be prevented even in the presence of small decaying of a number of polariton particles. DOI: 10.1103/PhysRevA.84.013813

Widely tunable and ultrasensitive leaky-guided multimode fiber interferometer based on refractive-index-matched coupling

This investigation presents a simple, widely tunable, and ultrasensitive sensor that is based on a leaky-guided multimode fiber interferometer (MMFI) operated under refractive-index-matched coupling. By use of a material with an appropriate dispersion profile around the MMFI as a cladding yields strong index-matched coupling, which performs ultrasensitive sensing in variations of the surroundings. Index matching at a single wavelength yields a coupling wavelength dip with a narrow bandwidth and a high extinction ratio of over 25 dB. The wavelength dip can also be effectively tuned, greatly shifting with a variation in temperature (T) or refractive index (RI), when the index-matched condition is satisfied. This work demonstrates that the proposed sensor responds sensitively to T with an extremely high tuning efficiency of 50 nm/°C and an excellent sensitivity to RI of 113,500 nm per RI unit.

Transverse instability of transverse-magnetic solitons and nonlinear surface plasmons

We analyze stability of the TM polarized optical solitons and nonlinear guided waves localized at a metal-dielectric interface. We demonstrate, both analytically and numerically, that the spatial solitons can experience vectorial transverse modulational instability that leads to the generation of arrays of two-dimensional TM polarized self-trapped localized beams. In a sharp contrast, we reveal that the transverse instability is completely eliminated for nonlinear surface plasmons.

Suppression of soliton transverse instabilities in nonlocal nonlinear media

The work of Y. Lin and R.-K. Lee has been partially supported by the National Science Council of Taiwan under contracts 95-2112- M-007-058-MY3 and NSC-95-2120-M-001-006.

Simultaneous amplitude modulation and wavelength conversion in an asymmetric-duty-cycle periodically poled lithium niobate

Abstract We report the theory and experiment for an amplitude modulator and wavelength converter based on an electrode-coated asymmetric-duty-cycle periodically poled lithium niobate (PPLN). In a 56%/44% domain-duty-cycle PPLN crystal, we modulated the amplitude of the 532-nm second-harmonic output and measured a normalized half-wave voltage of 1.1 V ×d ( μm )/l eff (cm), where d is the separation of the electrodes and l eff is the effective electrode length defined by the PPLN length multiplying the deviation of the domain-duty-cycle from the 50% value. A modulation depth of 85% was obtained in the linear modulation regime. We also derived a unified theory to describe the half-wave voltage for two types of PPLN-based amplitude modulators.

Adiabatic pulse propagation in a dispersion-increasing fiber for spectral compression exceeding the fiber dispersion ratio limitation

Adiabatic soliton spectral compression in a dispersion-increasing fiber (DIF) with a linear dispersion ramp is studied both numerically and experimentally. The anticipated maximum spectral compression ratio (SCR) would be limited by the ratio of the DIF output to the input dispersion values. However, our numerical analyses indicate that SCR greater than the DIF dispersion ratio is feasible, provided the input pulse duration is shorter than a threshold value along with adequate pulse energy control. Experimentally, a SCR of 28.6 is achieved in a 1 km DIF with a dispersion ratio of 22.5.

Crescent Waves in Optical Cavities

We theoretically and experimentally generate stationary crescent surface solitons pinged to the boundary of a microstructured vertical cavity surface emission laser by triggering the intrinsic cavity mode as a background potential. Instead of a direct transition from linear to nonlinear cavity modes, we demonstrate the existence of symmetry-breaking crescent waves without any analogs in the linear limit. Our results provide an alternative and general method to control lasing characteristics as well as to study optical surface waves.

Vortex pairs in nonlocal nonlinear media

Dynamics of vortex pairs with the same and opposite circulations are studied theoretically in nonlocal nonlinear media with different intervortex separations. We demonstrate that the nonlocal nonlinear response not only leads to a dramatic suppression of the elliptical instabilities but also helps in the formation of quasi-stable rotating and breathing bound states for vortex–vortex and vortex–antivortex (vortex dipole) pairs, respectively.

Phase separation and pattern instability of laser-induced polymerization in liquid-crystal-monomer mixtures

Directly written by a ultra-short femto-second laser pulse, we report the phase separation and pattern formation induced by polymerization in a liquid-crystal-monomer mixture. By varying the scanning speed of optical fields along a line, pattern transitions of photon-induced polymer structures are illustrated in shapes of double-humped, single-humped, and broken stripes. The experimental data collected by optical microscopic images are in a good agreement with numerical simulations based on a modified set of coupled 2 + 1 dimensional diffusion equations. The demonstration in this work provides a step for controlling phase separation morphologies as well as transferring patterns in polymer-dispersed liquid crystals.