Sonali Dasgupta

Single-mode tellurite glass holey fiber with extremely large mode area for infrared nonlinear applications

We report the fabrication of a large mode area tellurite holey fiber from an extruded preform, with a mode area of 3000microm(2). Robust single-mode guidance at 1.55microm was confirmed by both optical measurement and numerical simulation. The propagation loss was measured as 2.9dB/m at 1.55microm. A broad and flat supercontinuum from 0.9 to 2.5microm with 6mW output was obtained with a 9cm length of this fiber.

A silica based highly nonlinear fibre with improved threshold for stimulated brillouin scattering

8.8 dB improvement in figure of merit for SBS limited highly nonlinear fibres is reported by using a combination of Al-doping and straining of the fibre.

All-optical phase regeneration of 40Gbit/s DPSK signals in a black-box phase sensitive amplifier

We present a black-box four wave mixing based bit-rate-flexible phase sensitive amplifier and use it in the first demonstration of 40 Gbit/s DPSK phase regeneration.

Modeling Brillouin Gain Spectrum of Solid and Microstructured Optical Fibers Using a Finite Element Method

We report the first detailed implementation of a 2-D finite-element method (FEM) through a commercial FEM solver that can be universally applied to calculate the Brillouin gain characteristics of optical fibers with arbitrary refractive index profiles and material composition, including radially asymmetric and microstructured optical fibers (MOFs). Experimental results on various fabricated solid and MOFs are presented that demonstrate the widespread applicability and high accuracy of the proposed technique, which should prove to be an invaluable tool for designing novel optical fibers with tailored Brillouin response for a wide range of applications.

Use of Cross-Couplers to Decrease Size of UV Written Photonic Circuits

We demonstrate compact cross-couplers for fiber-pigtailed photonic circuitry produced by direct ultraviolet writing. A new design solution has been applied to shorten the device in length by 400% while keeping the bend loss at a level of <0.1 dB, which allows the use of cross-couplers in more complex photonic circuits with a smaller footprint and propagation loss. We demonstrate symmetrical cross-coupler operation and device performance that surpasses that of previously reported cross-couplers in terms of balanced symmetry and minimized footprint.

Silica-based highly nonlinear fibers with a high SBS threshold

Results on the suppression of stimulated Brillouin scattering in highly non linear fibers with both germanium- and aluminum-doped cores based on spooling the fiber with a linear strain gradient are compared and presented.

Design of a Bragg fiber with large mode area for mid-infrared applications

The design of an all-solid, soft glass-based, large mode area Bragg fiber for effective single mode operation with mode effective area exceeding 1100 µm(2) across the wavelength range of 2-4 μm is reported. The design adopts a new strategy to induce large differential loss between the fundamental and higher order modes for effective single-mode operation within few tens of centimetres length of an otherwise multimode fiber. In addition to having the potential for the targeted application in high power laser delivery systems; complemented by a zero dispersion wavelength at 2.04 µm and rapidly developing mid-IR optical sources, the proposed fiber should also be attractive for generation of high power, single mode and less divergent supercontinuum light over this mid-IR window.

Experimental demonstration of spectral broadening in an all-silica Bragg fiber

We present the first report on experimental observation of nonlinear spectral broadening in an all-solid photonic band gap Bragg fiber of relatively large mode area approximately 62 microm(2). The theoretically designed Bragg fiber for this specific application was fabricated by the well known MCVD technique. Nonlinear spectral broadening was observed by launching high power femtosecond pulses of 1067 nm pump wavelength. These first results indicate that fabrication of such Bragg fibers, once perfected, should potentially serve as an alternative route for realization of supercontinuum light.

Leakage channel fibers with microstuctured cladding elements: A unique LMA platform

We present a novel design of leakage channel fiber (LCF) that incorporates an air-hole lattice to define the modal filtering characteristics. The approach has the potential to offer single-mode, large mode area (LMA) fibers in a single-material platform with bend loss characteristics comparable to all-solid (LCFs) whilst at the same time providing significant fabrication benefits. We compare the performance of the proposed fiber with that of rod-type photonic crystal fibers (PCFs) and all-solid LCFs offering a similar effective mode area of ~1600μm(2) at 1.05μm. Our calculations show that the proposed fiber concept succeeds in combining the advantages of the use of small air holes and the larger design space of rod-type PCFs with the improved bend tolerance and greater higher order mode discrimination of all-solid LCFs, while alleviating their respective issues of rigidity and restricted material design space. We report the fabrication and experimental characterization of a first exemplar fiber, which we demonstrate offers a single-mode output with a fundamental mode area ~1440µm(2) at 1.06µm, and that can be bent down to a radius of 20cm with a bend loss of <3dB/turn. Finally we show that the proposed design concept can be adopted to achieve larger mode areas (> 3000µm(2)), albeit at the expense of reduced bend tolerance.

Recent advances in highly nonlinear fibres

We review recent progress in the areas of silica and compound glass based highly nonlinear fibres, highlighting and contrasting the current start-of-the-art, merits, drawbacks and future potential of both approaches.