Hamid Hatami-Hanza

Optimum dispersion profile for compression of fundamental solitons in dispersion decreasing fibers

In this paper, we have investigated the effect of dispersion profile on the performance of pulse compression in a dispersion decreasing fiber (DDF). Four closely shaped profiles, namely linear, Gaussian, exponential, and hyperbolic, have been considered. We have shown that appropriate shaping of the dispersion profile, particularly when higher order effects are accounted for, is quite effective for adiabatic compression of fundamental solitons, producing high-quality compressed pulses in the sense that the soliton pulse is compressed as a single unit and pedestals do not form. It is concluded that the linear and Gaussian dispersion profiles are nearly optimum in regards to the quality of the compressed pulse and the amount of compression achievable, in particular in the case of subpicosecond soliton pulse compression.

Logic operations in dispersion-mismatched nonlinear fibre couplers

Abstract We show by numerical simulation that a dispersion-mismatched nonlinear coupler can functions as logic OR and AND gates. It is shown that the manufacturing tolerances for these gates is large. Furthermore, the energy contrast ratio of the output signal is large, and pulse distortion is small.

A new low-loss wide-angle Y-branch configuration for optical dielectric slab waveguides

A new Y-branch configuration for dielectric slab waveguides is proposed, based on the natural refraction of optical field at the dielectric interfaces and analysed by BPM. It has been shown that the radiation loss of the structure is very small with relatively wide branching angle and fairly insensitive to the fabrication errors.<<ETX>>

A novel wide-angle low-loss dielectric slab waveguide Y-branch

A new Y-branch structure for dielectric waveguides is proposed and analysed using simple geometrical optics and beam propagation methods. It is shown both qualitatively and quantitatively that the proposed structure has larger branching angles but lower radiation loss than those associated with either conventional Y-branches or structures with antenna coupled and phase front accelerators. The optimal design parameters calculated by numerical simulations are in very good agreement with those found from the geometrical optics. The simulations also reveal that the performance is fairly insensitive to fabrication errors. >

Time-domain soliton filter based on a semidissipative dual-core fiber

We propose a time-domain dual-core fiber filter that greatly reduces soliton jitters and noise power in its application to ultrahigh-speed soliton communication systems. This filter is simply a dual-core fiber that has one core with negligible loss and the other with large loss.

Haping the switching characteristics of nonlinear directional couplers

We derive a Fourier transform relationship between the coupling coefficient and the fractional switched power of a nonlinear directional coupler. This relationship is then applied to choose the appropriate coupling coefficient to give the desired switching characteristic of the coupler. It is shown that nonlinear couplers with raised cosine or gaussian coupling functions yield a switching characteristic with very large extinction ratio. On the other hand, a suitably chosen sinusoidal coupling function renders the coupler to function as a tri-state switch.

Soliton compression and splitting in double-core nonlinear optical fibers

Abstract We consider compression of higher-order solitons in asymmetric and symmetric dual-core fibers (couplers) by means of numerical simulations of the corresponding coupled nonlinear Schrodinger equations. We demonstrate that an asymmetric coupler with different dispersion coefficients in its two cores provides almost the same degree of compression for the soliton tunneling from the core with a larger dispersion into the one with a smaller dispersion as the single-core fiber with the same jump of the dispersion coefficients. The pedestal around the compressed soliton is smaller when using the coupler; however, the necessary compression length is larger for the coupler than for the single-core fiber. An advantage of using the coupler is that it allows one to avoid a junction between two pieces of the fiber with different dispersions, which is inevitable if one uses the single-core fiber. Next, we consider compression of a higher-order soliton in a symmetric coupler. We demonstrate that, using the so-called soliton effect, one can achieve a record compression ratio (approximately 20), which is larger than that for any other known soliton compressor, with a very small share of the total energy in the pedestal. The corresponding compression length is still larger than for the single-core fiber, but the compression quality is much better. Lastly, the symmetric coupler allows, in some cases, to split the incoming pulse into two nearly identical compressed pulses outcoming from the two cores.

Optical intersecting-waveguide switches with widened angle of deflection

Reflection type optical switches with intersecting waveguides and bow-tie electrodes are proposed. The intersection angles of these switches are widened because of the implementation of the bow tie electrodes. The guided incident mode is expanded into an infinite spectrum of plane waves. Snells law is applied to calculate the reflection and refraction coefficients. It is analytically shown that the intersection angle can be almost doubled without remarkable adverse effects upon the extinction ratios and scattering loss. It is, therefore, anticipated that optical switches with bow-tie electrodes exhibit superior characteristics over those with straight ones.<<ETX>>

Extinction ratios and scattering losses of optical intersecting-waveguide switches with curved electrodes

Optical intersecting-waveguide switches with curved electrodes are analyzed. It is shown that the electrode-curvature in the form of a logarithmic spiral results in reflected field distributions in good resemblance to the incident one with reduced transverse shifts. Large extinction ratios and low scattering losses with small voltage-length product are, therefore, achievable. It is concluded that electrode curvature in the form of a logarithmic spiral is effective in realization of low insertion loss, high extinction ratios and small size optical switches. >

A multilevel soliton communication system

In conclusion, we have proposed and assessed a multilevel soliton communication system where at the multiplexing end, each soliton level is dedicated to a data channel, and demultiplexing is performed by filtering of channels each of which has experienced a different induced Raman self frequency shift after compression to the subpicosecond level at the receiver end. Preliminary calculations show that the system has the features of ultra high bit rate transmission with low error rate and is feasible with the current optical and electronic devices.