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Yan L.,Boston University | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University
2016 Conference on Lasers and Electro-Optics, CLEO 2016 | Year: 2016

We demonstrate all-fiber STED illumination using vortex fiber modes excited via fiber gratings. The grating's high purity mode conversion (98.7%) yields a depletion beam with 20.5dB extinction ratio, and the schematic is resistant to fiber bends down to 6mm radius. © 2016 OSA.


Gregg P.,Boston University | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University
2016 Conference on Lasers and Electro-Optics, CLEO 2016 | Year: 2016

We demonstrate 13.4km propagation of OAM L=7 fiber modes with record low 0.8dB/km loss via a circulating fiber loop experiment. For well-designed fibers, we demonstrate that OAM modes can travel distances relevant for large-scale data centers. © 2016 OSA.


Slavik R.,University of Southampton | Slavik R.,Academy of Sciences of the Czech Republic | Bogris A.,National and Kapodistrian University of Athens | Bogris A.,Technological Educational Institute of Athens | And 9 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2012

The performance of future ultralong-haul communication systems exploiting phase-encoded signals is likely to be compromised by nonlinear phase noise generated during signal transmission. One potential way to mitigate against nonlinear phase noise is to use phase-sensitive amplifiers (PSAs) that have been demonstrated to help remove such phase noise as well as to provide simultaneous signal amplitude noise suppression when operated in saturation. Recently, we have shown that a PSA-based signal regenerator based on degenerate four-wave mixing could be implemented in a network-compatible manner in which only the (noisy) signal is present at the device input (black-box operation). However, this scheme was tested only with relatively highfrequency deterministic perturbations applied to the signal. Here, we address both theoretically and experimentally the important issue of how such a regenerator works with more realistic random broadband amplitude/phase noise distributions. Good regenerative performance is demonstrated and our study also illustrates an additional unique feature of PSA-based regeneratorsnamely error correction for differentially encoded signals when placed in front of a DPSK receiver. Furthermore, we present a simplified regenerator implementation providing highly stable operation and representing a significant further step toward a practical device. © 2011 IEEE.


Sygletos S.,Tyndall National Institute | Frascella P.,Tyndall National Institute | Ibrahim S.K.,Tyndall National Institute | Gruner-Nielsen L.,OFS Fitel | And 4 more authors.
Optics Express | Year: 2011

A "black-box" phase sensitive amplifier is presented achieving simultaneous suppression of deterministic phase distortion on two independent 42.66 Gbit/s DPSK modulated signal wavelengths. © 2011 Optical Society of America.


Larsen S.H.M.,Technical University of Denmark | Pedersen M.E.V.,Technical University of Denmark | Gruner-Nielsen L.,OFS Fitel | Yan M.F.,OFS Laboratories | And 3 more authors.
Optics Letters | Year: 2012

This Letter demonstrates a polarization-maintaining higher-order mode fiber module that has anomalous dispersion at 1 μm. The group velocity dispersion of the module is measured, showing a split of the two polarization axes. The excellent polarization-maintaining properties of the relevant fiber modes for the higher-order mode fiber are likewise demonstrated employing a new simple method for the measurement of the beat length of higherorder modes at a single wavelength. The higher-order fiber module is intended for group velocity dispersion compensation. © 2012 Optical Society of America.


Rishoj L.,Technical University of Denmark | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University | Rottwitt K.,Technical University of Denmark
Optics Express | Year: 2013

We experimentally investigate intermodal nonlinear interactions, such as Raman scattering and four wave mixing. The fiber used is a specially designed few moded fiber, which splits the degeneracy of the first mode group, leading to stable propagation of the two full vectorial modes, TM01 and TE 01. For the Raman experiments pumping occur in either the fundamental mode or the two full vectorial modes, whereas the signal is in the fundamental mode. In all three experiments approximately 40 dB of gain is achieved using 307W of pump peak power.When pumping in either of the full vectorial modes four wave mixing is observed. © 2013 Optical Society of America.


Gregg P.,Boston University | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University
Optics InfoBase Conference Papers | Year: 2014

We demonstrate that degenerate, higher order (|L|>1) OAM modes resist polcon-like perturbations, with coupling efficiencies at least 10dB less than that of SMF. We attribute this stability to the large angular momenta of these modes. © 2014 OSA.


Gregg P.,Boston University | Kristensen P.,OFS Fitel | Golowich S.E.,Lincoln Laboratory | Olsen J.O.,OFS Fitel | And 2 more authors.
CLEO: Science and Innovations, CLEO_SI 2013 | Year: 2013

We demonstrate modally pure propagation over a record number (12) of modes in an optical fiber. An air-core fiber enables this by supporting OAM states. We achieve mode purities >10dB over 2m for all states and >20dB after 1km for a 2 state subset. © OSA 2013.


Bozinovic N.,Boston University | Golowich S.,Lincoln Laboratory | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University
Optics Letters | Year: 2012

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1h to +1h per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states. © 2012 Optical Society of America.


Gregg P.,Boston University | Kristensen P.,OFS Fitel | Ramachandran S.,Boston University
Optica | Year: 2015

Light’s orbital angular momentum (OAM) is a conserved quantity in cylindrically symmetric media. However, it is easily destroyed by free-space turbulence or fiber bends, because anisotropic perturbations impart angular momentum. We observe the conservation of OAM even in the presence of strong bend perturbations, with fibers featuring air cores that appropriately sculpt the modal density of states. Analogous to the enhanced stability of spinning tops with increasing angular velocity, these states’ lifetimes increase with OAM magnitude. Consequently, contrary to conventional wisdom that ground states of systems are the most stable, OAM longevity in air-core fiber increases with mode order. Aided by conservation of this fundamental quantity, we demonstrate fiber propagation of 12 distinct higher order OAM modes, of which eight remain low loss and >98%pure from near-degenerate coupling after kilometer-length propagation. The first realization of long-lived higher order OAM states, thus far posited to exist only in vacuum, is a necessary condition for achieving the promise of higher dimensional classical and quantum communications over practical distances. © 2015 Optical Society of America.

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