Details of Grant 

EPSRC Reference:	EP/K037056/1
Title:	Wavelength tunable, pulsewidth selectable, repetition rate variable, fibre based infra red source
Principal Investigator:	Taylor, Professor RJ
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Physics
Organisation:	Imperial College London
Scheme:	Standard Research
Starts:	01 October 2013	Ends:	30 November 2014	Value (£):	111,539
EPSRC Research Topic Classifications:	Lasers & Optics Optical Devices & Subsystems
EPSRC Industrial Sector Classifications:	Aerospace, Defence and Marine
Related Grants:
Panel History:	Panel Date Panel Name Outcome 27 Feb 2013 EPSRC ICT Responsive Mode - Feb 2013 Announced
Summary on Grant Application Form
Using either passive or active mode locking techniques, short pulses are generated in conventional laser systems with a repetition rate that is primarily determined by the round trip time of the cavity. In the vast majority of cases the physical size of the cavity components results in the repetition rate being in the 10s of Megahertz regime. It is often difficult to vary and if it is variable it generally involves a reconfiguration of the cavity. Similarly, the duration of the pulses produced by the mode locking technique are predetermined by the cavity parameters and are not readily selectable over large ranges. Optical filters can be placed in the cavity to restrict the bandwidth and so affect the temporal format of the generated pulses. However, inserting such filters usually requires a reoptimisation of the cavity and pulse widths cannot be continuously selected. This places considerable restriction on the versatility and applicability of conventional laser systems. The configuration we propose employs a single pass technique. The repetition rate of the generated pulses is simply determined by the drive frequency to an in line phase modulator. In conjunction with a transmitting edge filter the signals are turned into a corresponding series of pulses. Since the input signal is also a continuously operating laser it can be easily tuned over the complete gain window of the seed laser. In order to achieve continuously selectable pulse widths from this assembly, use is made of the fact that they can be made operate in the soliton supporting region of an optical fibre. Here the nonlinear intensity dependent non linear effects can be balanced by anomalous dispersion. The generated soliton has a fixed "area". The product of intensity and duration is constant, consequently if the soliton can be amplified, and this must be undertaken adiabatically, such that no energy disperses from the soliton, its duration will decrease. The slow, exponential gain provided by Raman gain in an optical fibre is ideal for this slow adiabatic amplification. Control of the gain, simply allows control of the pulse duration and by simply changing the pump power the output pulse duration is continuously selectable over a large range. We propose to seed the system from a narrow line thulium fibre laser and amplify in a specially designed high gain Raman amplifier fibre in an all fibre configuration that will allow average powers of up to 2 watts, pulse durations selectable between 20 picoseconds and 200 femtoseconds, at repetition rates between 5 and 10 GHz . Extension up to 20 GHz should be possible in the near term. Using additional follow on in fibre non linear optical processes should permit continuous tuning from 1950 nm to 2500 nm, providing unique performance characteristics in a region of importance for medical application and molecular fingerprinting.
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