Areas
of research:
Land-based
optical fibre networks operate in the second telecommunication
window at the wavelength of 1.3 µm. There is at
present no commercially available optical amplifier
device at this wavelength. The development of
such device is therefore of crucial importance
and great urgency.
Modern photonic
systems require a wide range of nonlinear devices.
The vast majority of these use single crystals
which are expensive and difficult to grow. Glasses
offer and attractive alternative for their ease
of manufacture and adjustable properties.
Heavy-metal
oxide glasses have good glass-forming properties
combined with high refractive indices and attractive
spectroscopic characteristics. Glass ceramics
offer routes to controlled microstructures.
589
nm Laser sources for satellite communication
Broadband
Er-doped fibre amplifiers
Heavy-metal
fluoride glasses for the 1.3 µm Pr3+-doped
optical fibre amplifier.
 
Gain in Pr3+-doped fibre amplifiers
based on cadmium halide, gallium-indium fluoride
and ZBLAN glasses: a) small-signal gain; b)
power amplifier gain.
Fluoride glasses are preferred hosts for Pr3+
due to their low phonon energies which result
in higher gain and quantum efficiency.
Achievements:
Pr3+ lifetime of 163 µs in modified
ZBLAN glass, 60% longer than in standard ZBLAN;
Pr3+ lifetime of 325 µs in cadmium
halide glass, the longest reported in any fluoride
host;
fabrication of high purity gallium-indium fluoride
and cadmium halide glasses using reactive atmosphere
processing.
Additional applications:
optical fibres transmitting in the near-UV to
near-IR range;
rare-earth doped fibre lasers in the near IR.
Collaborators:
|
ORC,
University of Southampton |
|
University
of Rennes |
|
Merck
UK |
|
BT
|

Fluoroaluminate
glasses for the 1.3 µm Nd3+-doped optical
fibre amplifier.

Gain curve in Nd3+-doped fluoroaluminate
fibres.

Grating efficiency in Ce3+-doped
fluoroaluminate glass.
Fluoroaluminate
glasses are preferred hosts for Nd3+
due to their low refractive indices and good glass
characteristics.
Achievements:
Nd3+ gain peak in fluoroaluminate fibre
at 1317 nm, the shortest wavelength ever reported;
over 90% gain in the region 1310-1320 nm;
greatly reduced signal ESA (excited state absorption);
demonstration of efficient Bragg grating in Ce3+-doped
fluoroaluminate glass.
Additional applications:
optical fibres transmitting in the near-UV to
near-IR range;
rare-earth doped upconversion fibre lasers in
the blue-violet;
applications involving fibre gratings, i.e. sensors,
WDM;
gain-flattened erbium-doped amplifiers.
Collaborators:
|
ORC, University
of Southampton |
|
Merck UK |
|
Pirelli, Milan
|

Germanium
sulphide glasses for nonlinear and active devices,
for fibre sensors, and as passive delivery fibres.
Germanium
sulphide glasses combine good glass-forming characteristics
with strong nonlinear properties, extended infrared
transmission, and high refractive indices.
Achievements:
nonlinear refractive index (n2) of 3x10-5
infrared transmission to 10 µm
Pr3+ lifetime of 210 µs
Applications:
nonlinear devices;
optical fibres with extended infrared transmission;
fibre sensors;
rare-earth doped infrared fibre lasers.
Collaborators:
|
Heriot-Watt University
|
|
NTO, Netherlands
|

589
nm Laser sources for satellite communication
Laser sources
at 589 nm are required for satellite communications.
The only two available sources are currently a
multi-laser system involving frequency mixing
and a high-power laser-pumped dye laser. We are
developing a small, light and flexible fibre laser
at 589 nm using Pr-doped fluoride glass. Figure
shows Pr emission in different glass hosts: the
chosen host glass has a stronger emission at the
required wavelength, sufficient to provide lasing
action. Other Pr-dope fluoride glasses, with larger
emission at longer wavelength, can also act as
amplfiers at the medically important 635 nm wavelength.



Broadband Er-doped
fibre amplifiers
Worldwide
demand for telecommunication bandwidth is increasing
rapidly, and can only be satisfied by a widespread
introduction of new optical technologies, such
as wavelength-division-multiplexing (WDM). WDM
requires optical amplifiers with broadband, flat
gain. Current state-of-the-art Er-doped fibre
amplifiers (EDFA) in silica glass do not provide
sufficient bandwidth. We are developing broadband
Er-doped amplifiers in modified silica and tellurite
glass hosts. The figures below show Er emission
in two of our glass compared with commercial alternatives.
Our glasses have a broader emission curve and
a larger cross-section, signalling higher, flatter
gain with a broader bandwidth.


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