Ajanta Barh

Design and Performance Study of a Compact SOI Polarization Rotator at 1.55 μm

We numerically design a compact silicon (Si) based polarization rotator (PR) by exploiting power coupling through phase matching between the TM mode of a Si strip waveguide (WG) and TE mode of a Si-air vertical slot WG. In such structures, the coupling occurs due to horizontal structural asymmetries and extremely high modal hybridness due to high refractive index contrast of Si-on-insulator (SOI) structure. Design parameters of the coupler have been optimized to achieve a compact PR of ~135 μm length at the telecommunication wavelength of 1.55 μm. Maximum power coupling efficiency Cm, which is studied by examining the transmittance of light, is achieved as high as 80% for both polarization conversions. Fabrication tolerances and the band width of operation of the designed PR have also been studied.

An efficient broad-band mid-wave IR fiber optic light source: design and performance simulation

Design of a mid-wave IR (MWIR) broad-band fiber-based light source exploiting degenerate four-wave mixing (D-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 (Er(3+)) - doped continuous wave (CW) ZBLAN fiber laser emitting at 2.8 μm as the pump source with an average power of 5 W. Amplification factor as high as 25 dB is achievable in the 3 - 3.9 μm spectral range with average power conversion efficiency > 32%.

Design of an efficient mid-IR light source using chalcogenide holey fibers: a numerical study

We report the design of a highly nonlinear holey fiber for making a mid-infrared light source at 4.36 μm. A solid-core chalcogenide-based index-guided holey microstructured optical fiber with circular air holes has been exploited to numerically demonstrate wavelength translation via four-wave mixing. We employ a thulium-doped fiber laser as the pump with a power of 5 W. Our simulations indicate that a maximum parametric gain of 20.5 dB with a bandwidth of 16 nm is achievable in this designed fiber, resulting in a power conversion efficiency of more than 17.6%.

Specialty Fibers for Terahertz Generation and Transmission: A Review

Terahertz (THz) frequency range, lying between the optical and microwave frequency ranges 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 paper, 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.

A Tapered Chalcogenide Microstructured Optical Fiber for Mid-IR Parabolic Pulse Generation: Design and Performance Study

This paper presents a theoretical design of chalcogenide glass based tapered microstructured optical fiber (MOF) to generate high power parabolic pulses (PPs) at the mid-IR wavelength (~2 μm). We optimize fiber cross-section by the multipole method and studied pulse evolution by well-known symmetrized split-step Fourier Method. Our numerical investigation reveals the possibility of highly efficient PP generation within a very short length (~19 cm) of this MOF for a Gaussian input pulse of 60 W peak power and full width at half maximum (FWHM) of 3.5 ps. We examined quality of the generated PP by calculating the misfit parameter including the third order dispersion and fiber loss. Further, the effects of variations in input pulse power, pulse width and pulse energy on generated PP were also studied from the point of view of tolerances in fabrication of such a device.

Plastic fiber design for THz generation through wavelength translation

We report on an all-fiber terahertz (THz) radiation source by exploiting nonlinear parametric process in a theoretically designed microstructured-core double-clad plastic fiber (MC-DCPF). The required phase-matching condition is satisfied through suitable tailoring of the fiber dispersion and nonlinear properties at the pump wavelength of a high-power CO2 laser, with a CO laser of much lower power acting as a seed concomitantly. Our simulated results reveal that a THz radiation source at the frequency of ∼3  THz could be realized with a 3-dB phase-matching band width of 2.13 GHz in a 65-m-long optimized MC-DCPF. Maximum power conversion efficiency >1% is realizable even after including the material loss.

Mid-IR fiber optic light source around 6 µm through parametric wavelength translation

We report a numerically designed highly nonlinear all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6??m through degenerate four-wave mixing by considering a continuous wave CO laser of 5?10?W power emitting at 5.6??m as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, a narrow (N)- and/or broad (B)- band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20?dB is achievable for the N-band source at 6.46??m with a maximum power conversion efficiency (Cm) ~ 33%, while a amplification ~22?????2?dB is achievable for a B-band source over the wavelength range of 5?6.3??m with a Cm?>?40%.

Low-Loss Hollow Core Plastic Photonic Band-Gap Fiber for Efficient THz Transmission

We report design of a plastic photonic band-gap fiber for efficient high power THz transmission over a wide spectral range (1.65 ~ 1.95 THz) with low-loss coefficient (< 4 m-1) and low-dispersion (< 10 ps/km.nm).

Mid-IR Evanescent Field Gas Sensor Based on Silicon-on-Nitride Slot Waveguide

We propose silicon-on-nitride slot waveguide-based evanescent field absorption sensing scheme for ammonia gas in the mid-IR wavelength. Detection down to 10 ppm is feasible with estimated evanescent field fraction (EFF) ~ 43%.

Design of a compact SOI polarization rotator for mid-IR application

Design of a compact polarization rotator (PR) exploiting power coupling through phase matching between the TM mode of a strip waveguide (WG) and TE mode of a vertical slot WG is presented. Optimized cross sectional dimensions of the coupler have been achieved to use this device as a compact PR at 3 μm wavelength with device length of just 2 mm. We also investigate the device performance at the operating wavelength (λ) = 1.55 μm.