Bishnu P. Pal

Fabrication and Modeling of Fused Biconical Tapered Fiber Couplers

This article describes a model and the process technology of realizing fused fiber coupler-based branching components through the use of an experimental setup of a PC-controlled fabrication rig. To simulate the fabrication process and to interpret the experimental characteristics of such devices, a simple but realistic model based on well known super-mode-beating analysis is presented. The key results of the analysis embedded into the control software of the fabrication rig has ensured achieving repeatability in the targeted specifications of these components. Typical results of the modeling and a comparison with experimental results are also presented. The model should be very useful in defining the design parameters for realizing these fused coupler-based branching components.

Frontiers in Guided Wave Optics and Optoelectronics

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Characterization and simulation of long period gratings fabricated using electric discharge

Abstract We report the characterization and theoretical simulation of long period gratings fabricated using electric arc discharge in two different fibers namely, SMF-28 ( Δ =0.0036) and DSF ( Δ =0.009). We show that this technique can efficiently fabricate gratings with required strength of coupling on both fiber types by choosing appropriate arc current and duration of the arc. We compare the transmission spectra of the fabricated gratings to the theoretically simulated plots and find the equivalent refractive index modulation created in the grating. Unlike the case of UV-induced gratings, the resonance wavelength in these gratings depends only on the period and is independent of the arc current that is controlled to achieve different refractive index modulations. Thus this technique enables easy and independent control of the fiber parameters.

Design of dispersion-compensating Bragg fiber with an ultrahigh figure of merit

We report a novel idea for achieving highly efficient dispersion-compensating Bragg fiber by exploiting a modified quarter-wave stack condition. Our Bragg fiber yielded an average dispersion of approximately -1800 ps/(nm km) across the C band for the fundamental TE mode and an ultrahigh figure of merit of approximately 180,000 ps/(nm dB), which is at least 2 orders of magnitude higher than that of conventional dispersion-compensating fibers. The proposed methodology could be adopted for the design of a dispersion compensator across any desired wavelength range.

Dispersion-shifted dual-shape core fibers. Optimization based on spot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W responsible for splice loss, and W/sub infinity / responsible for bend loss. Dual-shape core fiber designs are given with W/sub infinity //W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 mu m at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers. >

Refractometers and tunable components based on side-polished fibers with multimode overlay waveguides: role of the superstrate

A normal mode analysis is applied to the investigation of the role of the superstrate in terms of its refractive index and thickness in estimating the performance of fiber refractometers and the tunability of fiber components based on evanescent coupling of a side-polished fiber to a multimode overlay waveguide. The model is shown to yield a complete transfer function and information about all the major characteristics of such in-line fiber devices. The results closely match the trends of the reported experiments.

Lens Coupling of Laser Diodes to Monomode Elliptic Core Fibers

Polarisation maintaining single-mode fibers have lately attracted a great deal of attention in view of their potential applications in coherent optical communications, fiber optic phase sensors etc. One of the fiber configurations used for conservation of polarisation is the elliptic core fiber [1 — 5]. Though a fair amount of literature now exists on the propagation characteristics of elliptic core fibers including their birefringence characteristics, no attempt appears to have been made to investigate the lens coupling of laser diodes to elliptic core fibers. Since the fundamental mode spot size of a fiber is typically larger than the laser mode spot size, it is well known that mode matching between the two is usually done by use of an intermediate lens. This approach formed the subject of many lensing schemes for coupling laser diodes to monomode circular core fibers, in particular, that have been reported to-date [6-14]. However, the absence of such studies in the case of elliptic core fibers motivated us to make art in-depth study of the excitation of these fibers by laser diodes through a ball lens. The results should be useful in the design of efficient laser diode to elliptic core fiber couplers, elliptic fiber connectors and for designing optimum launch optics to achieve maximum light coupling efficiency in polarisation holding fiber optic sensors as well as in coherent fiber optic communication systems.

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%.

Optimization of a dual-core dispersion slope compensating fiber for DWDM transmission in the 1480–1610 nm band through G.652 single-mode fibers

Abstract We report design optimization of a dual-core dispersion slope compensating fiber (DSCF) for broadband dense wavelength division multiplexing (DWDM) transmission separately in the S-, C-, and L-bands through a 1310 nm-optimized conventional single-mode fiber (CSF). Index profile parameters of the DSCF have been adjusted to simultaneously achieve a mode effective area, which match that of the G.652 fiber as closely as possible in order to contain potentially detrimental nonlinear propagation effects like four-wave mixing and cross-phase modulation (XPM). Theoretical figure of merit of the designed dispersion compensating fiber (DCF) is ∼900 ps/(nm-dB) @ 1550 nm, and its estimated bend loss for a single turn bend diameter of 32 mm is negligible.