Journal of Nonlinear Optical Physics & Materials

We report the application of atomic layer deposition to manipulate the dielectric architecture of conventional and superlattice two-dimensional photonic crystal waveguides fabricated in silicon. Conformal deposition of a second dielectric layer is shown to have a dramatic influence on the photonic band structure and produces unique effects that cannot be emulated in a single dielectric slab photonic crystal material. With additional dielectric coatings, a strong decrease in photonic band frequencies and change in band slope are observed, which for the lowest photonic states produces strong degeneracies. The capability, in principle, to tune the position of bands to within 0.005% accuracy, is demonstrated. Additionally, new features are observed when differential band shifts result in band-crossing and for which like polarizations activate perturbation mechanisms that result in local and strong band curvatures. The extremely strong band bending resulting from band-band interactions could have applications, in slow light devices, and provide a way to introduce non-linear effects into tunable photonic crystal structures.

Using Lang's equation for the dynamics of injection locking of a laser diode, we show that the hysteresis property of the excess carrier density has direct influence on the mode-shift characteristics, which makes the shift of the slave laser mode to be different from the frequency detune of the external master laser signal within the locking range of the slave laser. The theoretical prediction is experimentally confirmed by the measurement of the mode-shift of an injection locked Fabry-Perot laser diode.

Nonlinear effects in optical fibers impose different limitations on the communications link, and an understanding of such effects is almost a prerequisite for actual lightwave-system designers. On the other hand, they offer a variety of possibilities for all-optical signal processing, amplification and regeneration. The nonlinear effects are enhanced dramatically, and new phenomena are observed in the so-called photonic crystal fibers. In this paper, we review the effects — both detrimental and potentially beneficial — of optical nonlinearities in conventional and in photonic crystal fibers.

In the last years, the possibility of light generation and/or amplification in silicon, based on Raman emission, has achieved great results. However, some significant limitations, inherent to the physics of silicon, have been pointed out, too. In order to overcome these limitations, a possible option is to consider low dimensional silicon. Along this line of argument, an approach based on Raman scattering in porous silicon is presented. We prove two significant advantages with respect to silicon: the broadening of spontaneous Raman emission and the tuning of the Stokes shift. Finally, we discuss the prospect of Raman amplifier in porous silicon.

A novel analyzing procedure was introduced to extract the third-harmonic susceptibility from the measured third-harmonic-generation fringe obtained by translating a wedged liquid cell along the direction perpendicular to the propagating direction of the incident fundamental beam. By Fourier transform, we can easily separate the Fourier component purely contributed by the liquid/window interface from those involving the air contribution. Comparing this spectral component with that from a reference sample with known third-harmonic susceptibility and coherence length, we can determine the third-harmonic susceptibility and coherence length of the liquid under test. Finally, Fourier analysis was used to determine the third-harmonic susceptibility and coherent length of pure water using ethanol as the reference sample and the results have shown the feasibility of the proposed procedure.

Small area metal semiconductor metal (MSM) photodiode (PD) has been one of the most favoured detector choices for high speed optoelectronics integrated circuits due to their low parasitic capacitance and simple planar device structure, which is compatible with FETs. Large MSM PDs, on the other hand, can also be useful in many network and interconnect applications such as fibre distributed data interfaces.

An MBE grown GaN metal semiconductor metal photodiode with a thin low temperature GaN (50nm) barrier enhancement layer is reported, which has low dark current. The detector using Nickel (Ni) Schottky metal fingers with 400 μm spacing on a large active area exhibit a low dark current of 1.23 mA at 10 V bias, which is about three orders of magnitude lower than that of the normal GaN Schottky photodiode.

The spectra of amplified spontaneous emission (ASE) intensity and gain have been measured for solutions of laser dye Rhodamine-640 in glycerin with light scattering TiO₂ nanoparticles. Such solutions typically manifest random lasing in backscattering geometry. In this work, the conventional transverse pump geometry is used, and the ASE gain spectra are measured using a variation of the length of the illuminated (pumped) stripe. In this geometry, with increasing concentration of nanoparticles, the "unidirectional" gain along the stripe decreases dramatically. At the same time, strong narrowing of the ASE bandwidth is observed even in the absence of net gain. The experimental results help one to understand the role of the scattering particles in the light amplification. On the one hand, the particles increase a zigzag type of the light path within the amplifying medium, which results in bandwidth narrowing and strong amplification of chaotic light beams. On the other hand, the amplification of a seed beam propagating in a selected direction is dramatically suppressed. The results are discussed using simple modeling of ASE amplification and qualitative arguments.

Para-nitroaniline(p-NA)–dimethyl formamide (DMF) adduct has been synthesized chemically. The formation of adduct is confirmed via UV, FTIR, CHN analyses and other techniques. The adduct formation takes place due to dipolar interaction and hydrogen bonding. The parent polar molecules, viz. p-NA and DMF, crystallize in symmetric forms and do not exhibit optical second harmonic generation (SHG). The adduct has been found to exhibit a considerable SHG efficiency and hence this confirms that the adduct crystallizes in a noncentrosymmetric form. These observations suggest a Λ-shaped structure of the molecule, which is further established theoretically via geometry optimization.

A novel approach to the quantitative characterization of the regularity of the opal photonic crystal lattice based on a Fourier transform analysis of the azimuth rotational symmetry of the optical transmission is proposed. The magnitudes of three harmonics in the Fourier transform related to the two-, six- and twelvefold rotational symmetry of the transmission pattern have been suggested for quantification of the lattice ordering. The specific composition of these harmonics has been observed for the transmission attenuation at different lattice planes. The diffraction at (220) and (200) families of crystal planes has been identified as the most sensitive to the crystallinity of the opal lattice. The transmission pattern obtained in the s-polarized light is recommended for comparison.

We fabricated an FePt/MgO tunneling junction (Fe 55 atomic %) on a GaAs-based light-emitting-diode structure. The out-of-plane magnetization of the FePt thin film was confirmed by a magneto-optical measurement. The electrical spin injection from FePt into GaAs at room temperature was studied using the technique of spin-polarized electroluminescence. The spin polarization of the injected electrons under the magnetic field of 1 T was at least 6.0%. The remnant polarization at 0 T, which indicates the spin injection without a magnetic field, was at least 3.3%.

Fiber couplers are widely used in telecommunications and industry as passive splitting power devices. The effective power coupling and transmission from one fiber to another is mainly determined by both the coupling length and the coupling coefficient. The coupling length can be calculated directly but the coupling coefficient depends upon the refractive index and the separation fiber axis. After the fusion processes of two SMF-28e^® couplers, the refractive index is unknown due to a change in the radius of the fiber (r_cladd < 40 μm and r_core < 1.5 μm). The coupling coefficient range is obtained from a distribution of the coupling ratio and compared with the empirical formula, which also enables one to calculate the refractive index. In this experiment, the coupling coefficient in the range of 0.6–0.9/mm is calculated as a function of the separation fiber axis and the refractive index of the core and cladding. The result shows a good correlation between experimental results and theoretical calculation.