S. Medhekar

Proposal for optical switch using nonlinear refraction

We propose that using the phenomenon of refraction of two coaxially copropagating beams at the interface of two nonlinear media, a passive all-optical switch could be constructed for future integrated photonic circuits

All-optical passive transistor

We show the possibility of developing an all-optical passive transistor in a simple and novel way. This could be done by copropagating two coaxial beams through a modified optical power filter. We show NOT logic and intensity modulation of the strong beam by the weak beam obtained with the analog.

Self-tapering of elliptic Gaussian beams in an elliptic-core nonlinear fiber

We show stable modes (stationary self-trapped beams) of elliptic cross section in an elliptic-core nonlinear fiber. These stable modes can be tapered in the presence of absorption or gain. Ellipticity of the beam can be controlled by induced tapering. Another interesting feature is the possibility of conversion of an elliptic Gaussian laser beam into a circular Gaussian laser beam. A stationary self-trapped beam plus an elliptic-core nonlinear fiber form an elliptic-core linear fiber for a low-power signal beam, and hence one can induce an elliptic-core linear fiber of optically tunable parameters for a low-power signal beam.

Novel All-Optical Switch Using Nonlinear Mach-Zehnder Interferometer

Abstract Using a nonlinear Mach-Zehnder interferometer, a novel all-optical switch that can mimic NOT/XOR, AND, and NAND gates is proposed. The proposed switch is novel in the sense that it functions with mutually incoherent input beams of the same wavelength and polarization, and the NOT/XOR and NAND gates constructed using it give “pure” output (i.e., output contains only one of the all-input beams and not a mixture of the input beams). Purity of output is an important feature as it is essential for cascadability. The operating power levels of the proposed switch could be adjusted by adjusting the length of the Mach-Zehnder interferometer that makes the proposed switch easily implementable in a circuit. Moreover, a cascadable NAND gate allows for Boolean completeness.

Coupled spatial-soliton pairs in saturable nonlinear media

We present a simple and straightforward approach to investigate coupled spatial-soliton pairs of two copropagating mutually incoherent (i.e., both beams are fully spatially and temporally coherent, but are incoherent with respect to one another) light beams in saturable nonlinear media. The approach provides a deeper understanding of coupled spatial-soliton pairs and reveals many interesting features, including the entire existence curve of such solitons.

All-Optical Passive Transistor Using Counter-Propagating Beams in a Nonlinear Mach-Zehnder Interferometer

Abstract A novel all-optical passive transistor using counter propagating beams in a nonlinear Mach-Zehnder interferometer is proposed. The proposed all-optical passive transistor always gives “pure” output (i.e., output contains only one of the two input beams and not a mixture of the input beams). To the best of our knowledge, this is the first proposal of an all-optical device which (i) functions with mutually incoherent (of same wavelength and polarization) as well as mutually coherent inputs and (ii) gives a phase insensitive performance while functioning with coherent inputs. The proposed all-optical passive transistor can amplify a signal with zero amplifier noise and mimic NOT, AND, (and hence), NAND gates.

Absorption/amplification-induced self-tapering and uptapering of a laser beam in a saturable nonlinear medium: large nonlinearity

We discuss the possibility of self-taping and uptapering of a self-guided Gaussian laser beam induced by absorption and gain when the beam propagates in a medium with large saturable nonlinearity. Conditions for self-tapering/uptapering for both the cases, i.e., for absorption and gain, are discussed. The width of the tapered/uptapered beam depends on the rate of absorption and gain and on the length of the absorption and gain regions along the beam-propagation direction.

Spatial solitons of desired intensity and width and their self-tapering/uptapering in cubic quintic nonlinear medium

In this paper, we have investigated the propagation behavior of a Gaussian beam in cubic quintic nonlinear medium with and without absorption or gain. A governing differential equation for the evolution of beam width with the distance of propagation has been derived using the standard parabolic equation approach. By solving the governing equation numerically for different sets of parameters, we have shown that spatial solitons of fixed width and desired intensity and of fixed intensity and desired width are possible. Such liberty does not exist in other saturable media. We have also investigated self-tapering and self-uptapering of spatial solitons in the presence of absorption or gain and showed that the rate of self-tapering/uptapering is not only controlled by the magnitude of absorption or gain but also by the values of cubic and quintic terms. It is revealed that by self-tapering, the smallest achievable soliton width decreases/increases by increasing the magnitude of the cubic/quintic term. It is also revealed that the smallest achievable soliton width by self-tapering, is smaller for a larger initial width.

A versatile optical junction using photonic band-gap guidance and self collimation

We show that it is possible to design two photonic crystal (PC) structures such that an optical beam of desired wavelength gets guided within the line defect of the first structure (photonic band gap guidance) and the same beam gets guided in the second structure by self-collimation. Using two dimensional simulation of a design made of the combination of these two structures, we propose an optical junction that allows for crossing of two optical signals of same wavelength and same polarization with very low crosstalk. Moreover, the junction can be operated at number of frequencies in a wide range. Crossing of multiple beams with very low cross talk is also possible. The proposed junction should be important in future integrated photonic circuits.

Spatial Soliton Pairing of Two Cylindrical Beams in Saturable Nonlinear Media

In this paper, we have extended the recently introduced theory of coupled propagation of two coaxially co-propagating and mutually incoherent bright 1-D beams to coupled propagation of two 2-D (cylindrical) bright beams and investigated the propagation behavior and spatial soliton pair formation of such beams by a recently introduced simple approach. We have considered saturable form of the nonlinear medium in this paper as 2-D spatial solitons are unstable in Kerr type media. We found that many of the propagation features of two 2-D beams in saturable media are same that of 1-D beams in Kerr type media. However, many features are difierent and to the best of our knowledge, reported in this paper for the flrst time. The present version of the theory is applicable in all possible physical situations and parameters.