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The occurrence of exceptional points (EPs) is a fascinating non-Hermitian feature of open systems. A level-repulsion phenomenon between two complex states of an open system can be realized by positioning an EP and its time-reversal (T) conjugate pair in the underlying parameter space. Here, we report the fascinating nonreciprocal response of such two conjugate EPs by using a dual-mode planar waveguide system having two T-symmetric active variants concerning the transverse gain-loss profiles. We specifically reveal a comprehensive all-optical scheme to achieve correlative nonreciprocal light dynamics by using the reverse chirality of two dynamically encircled conjugate EPs in the presence of local nonlinearity. A specific nonreciprocal correlation between two designed T-symmetric waveguide variants is established in terms of their unidirectional transfer of light with a precise selection of modes. Here, the unconventional reverse chiral properties of two conjugate EPs allow the nonreciprocal transmission of two selective modes in the opposite directions of the underlying waveguide variants. An explicit dependence of the nonlinearity level on a significant enhancement of the nonreciprocity in terms of an isolation ratio is explored by investigating the effects of both local Kerr-type and saturable nonlinearities (considered separately). The physical insights and implications of harnessing the properties of conjugate EPs in nonlinear optical systems can enable the growth and development of a versatile platform for building nonreciprocal components and devices., Comment: 10 pages, 7 figures

Terahertz (THz) frequency range, lying between the optical and microwave range covers a significant portion of the electro-magnetic spectrum. Though its initial usage started in the 1960s, active research in the THz field started only in the 1990s by researchers from both optics and microwaves disciplines. The use of optical fibers for THz application has attracted considerable attention in recent years. In this article, we review the progress and current status of optical fiber-based techniques for THz generation and transmission. The first part of this review focuses on THz sources. After a review on various types of THz sources, we discuss how specialty optical fibers can be used for THz generation. The second part of this review focuses on the guided wave propagation of THz waves for their transmission. After discussing various wave guiding schemes, we consider new fiber designs for THz transmission., Comment: 15 pages

We report numerically designed highly nonlinear all glass chalcogenide microstructured optical fiber for efficient generation of light around 6 micron through degenerate four wave mixing by considering continuous wave CO laser of 5 to 10 Watts power emitting at 5.6 micron as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, narrow and broad band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 decibel is achievable for the narrow band source at 6.46 micron with a maximum power conversion efficiency of 33 percent while amplification of 22 decibel is achievable for a B-band source over the wavelength range of 5 to 6.3 micron with a conversion efficiency of 40 percent., Comment: 7 pages 7 figures

An all solid large modearea (LMA) chalcogenide based microstructured core optical fiber (MCOF) is designed and proposed for high power handling in the mid IR spectral regime, covering the entire second transparency window of the atmosphere (3 to 5 microns). The core of the proposed specialty fiber is composed of a few rings of high index rods arranged in a pattern of hexagon. Dependence of effective mode area on the pitch and radius of high index rods are studied. Ultra high effective mode area up to 75000 micron square can be achieved over this specific wavelength range while retaining its single mode characteristic. A negligible confinement loss along with a low dispersion slope (near 0.03 ps/km-nm square) and a good beam quality factor (M2 1.17) should make this LMA fiber design attractive for fabrication as a potential candidate suitable for high power, passive applications at the mid IR wavelength regime., Comment: 6 pages, 8 figures

We report design of an efficient ~ 50 cm long all-fiber compact microstructured optical fiber-based 3-4.25 um mid-IR light source with power conversion efficiency > 28% by exploiting FWM with Er3+-doped ZBLAN fiber as the pump., Comment: Three pages, 6 figures

Design of a mid-wave IR (MWIR) broad-band fiber-based light source exploiting four-wave mixing (FWM) in a meter long suitably designed highly nonlinear (NL) chalcogenide microstructured optical fiber (MOF) is reported. This superior FWM bandwidth (BW) was obtained through precise tailoring of the fibers dispersion profile so as to realize positive quartic dispersion at the pump wavelength. We consider an Erbium (Er3+) doped continuous wave (CW) ZBLAN fiber laser emitting at 2.8 micron as the pump source with an average power of 5 W. Amplification factor as high as 25 dB is achievable in the 3 to 3.9 microns spectral range with average power conversion efficiency more than 32 percent., Comment: 8 pages. arXiv admin note: text overlap with arXiv:1208.3316

We report generation of broadband low divergent supercontinuum over the entire wavelength window of 1.5 to 3.5 {\mu}m from a 2.25 meter long effective single moded photonic bandgap fiber with mode area of 1100 {\mu}m2., Comment: 3 pages

Design of a mid-wave IR broadband (3.1 - 3.8 {\mu}m) fiber-based light source exploiting FWM in a meter long suitably designed chalcogenide microstructured fiber is reported. An achievable gain more than 35 dB is demonstrated., Comment: 3 pages

We report on the design of a highly-nonlinear specialty fiber as a mid-infrared light source at 4.3 {\mu}m. A meter length of the designed solid-core chalcogenide based index-guided microstructured optical fiber (MOF) with circular air holes has been exploited to translate wavelength via four wave mixing using a thulium-doped fiber laser as the pump with a relatively low peak power of 5 W. A peak gain value of around 37 dB with full width at half maxima (FWHM) less than 3 nm is achieved., Comment: 4 pages 9 figures

We investigate the influence of the phase-front curvature of an input light beam on the transverse localization of light by choosing an evanescently coupled disordered one-dimensional semi-infinite waveguide lattice as an example. Our numerical study reveals that a finite phase front curvature of the input beam indeed plays an important role and it could degrade the quality of light localization in a disordered dielectric structure. More specifically, a faster transition from ballistic mode of beam propagation due to diffraction to a characteristic localized state is observed in case of a continuous wave (CW) beam, whose phase-front is plane as compared to one having a curved phase front., Comment: 5 pages 5 figures

The role of a prominent photonic bandgap (PBG) on the phenomenon of transverse localization of light in a semi-infinite lossless waveguide lattice consisting of evanescently coupled disordered one-dimensional optical waveguides has been investigated numerically. The interplay between the underlying photonic bandgap due to inherent periodicity of the optical system and various levels of deliberately induced transverse disorder in its refractive index periodicity has been studied. We show that the PBG indeed plays an important role and its simultaneous presence could catalyze realization of localized light even when strength of disorder is not sufficiently strong to independently cause localization of light. An important outcome of this study revealed that PBG could be gainfully exploited to tailor the spectral window for localization of light in potential applications like lasing in a disordered optical lattice., Comment: 7 pages, 5 figures