M. Alcon-Camas

Brillouin optical time-domain analysis assisted by second-order Raman amplification.

We propose and experimentally demonstrate a new method to extend the range of Brillouin optical time domain analysis (BOTDA) systems. It exploits the virtual transparency created by second-order Raman pumping in optical fibers. The idea is theoretically analyzed and experimentally demonstrated in a 50 km fiber. By working close to transparency, we also show that the measurement length of the BOTDA can be increased up to 100 km with 2 meter resolution. We envisage extensions of this technique to measurement lengths well beyond this value, as long as the issue of relative intensity noise (RIN) of the primary Raman pump can be avoided.

RIN transfer in 2nd-order distributed amplification with ultralong fiber lasers.

We investigate numerically the effect of ultralong Raman laser fiber amplifier design parameters, such as span length, pumping distribution and grating reflectivity, on the RIN transfer from the pump to the transmitted signal. Comparison is provided to the performance of traditional second-order Raman amplified schemes, showing a relative performance penalty for ultralong laser systems that gets smaller as span length increases. We show that careful choice of system parameters can be used to partially offset such penalty.

Gain bandwidth optimisation and enhancement in ultra-long Raman fibre laser based amplifiers

We show experimentally a 57nm gain bandwidth for an ultra-long Raman fiber laser based amplification technique using only a single pump wavelength. The enhanced gain bandwidth and gain flatness is investigated for single and multi-cavity designs.

Long-distance soliton transmission through ultralong fiber lasers

We present the first experimental demonstration (to our knowledge) of long-distance unperturbed fundamental optical soliton transmission in conventional single-mode optical fiber. The virtual transparency in the fiber required for soliton transmission, over 15 complete periods, was achieved by using an ultralong Raman fiber laser amplification scheme. Optical soliton pulse duration, pulse bandwidth, and peak intensity are shown to remain constant along the transmission length. Frequency-resolved optical gating spectrograms and numerical simulations confirm the observed optical soliton dynamics.

Ultra-long range distributed fibre sensing using virtually transparent propagation

Distributed fibre sensors provide unique capabilities for monitoring large infrastructures with high resolution. Practically, all these sensors are based on some kind of backscattering interaction. A pulsed activating signal is launched on one side of the sensing fibre and the backscattered signal is read as a function of the time of flight of the pulse along the fibre. A key limitation in the measurement range of all these sensors is introduced by fibre attenuation. As the pulse travels along the fibre, the losses in the fibre cause a drop of signal contrast and consequently a growth in the measurement uncertainty. In typical single-mode fibres, attenuation imposes a range limit of less than 30km, for resolutions in the order of 1–2 meters. An interesting improvement in this performance can be considered by using distributed amplification along the fibre [1]. Distributed amplification allows having a more homogeneous signal power along the sensing fibre, which also enables reducing the signal power at the input and therefore avoiding nonlinearities. However, in long structures (> 50 km), plain distributed amplification does not perfectly compensate the losses and significant power variations along the fibre are to be expected, leading to inevitable limitations in the measurements. From this perspective, it is simple to understand intuitively that the best possible solution for distributed sensors would be offered by a virtually transparent fibre, i.e. a fibre exhibiting effectively zero attenuation in the spectral region of the pulse. In addition, it can be shown that lossless transmission is the working point that allows the minimization of the amplified spontaneous emission (ASE) noise build-up.

Extended bandwidth for long haul DWDM transmission using ultra-long Raman fiber lasers

We present an ultra-long Raman fibre laser amplified system which, with only a single pump wavelength, provides comparable gain flatness and broader spectral bandwidth than a conventional gain flattened C-band EDFA. A 20×42.7Gb/s experiment shows compatibility with DWDM systems.

42.6Gb/s RZ-ASK transmission over 2500km using quasi-lossless transmission spans

We have recently shown that with the use of an advanced second order Raman pumping scheme it is possible to generate quasi-lossless conditions whereby an optical signal can propagate over long distances with very little variation in the optical power level [1]. Here, for the first time, we experimentally demonstrate optical data transmission through such quasi-lossless fibre spans, which provide an entirely different nonlinear propagation regime to conventionally EDFA/Raman amplified systems. We demonstrate 42.6Gb/s transmission over 2500km of SMF-28 with an 82km span length, and investigate the optimisation of the system in terms of launch power and nonlinear tolerance.

Application of Brillouin scattering to optical frequency combs

Optical frequency combs are a useful tool for measuring reference laser frequency whose uncertainty depends on the stability and accuracy of the reference clock. The relative uncertainty of the laser frequency measurements in the optical telecommunication band with the frequency comb technique is estimated around 10-12. In this paper, we present the development and implementation of a filtering technique on an optical frequency comb based on an Erbium optical fiber oscillator using Brillouin scattering amplification. This filtering technique allows us to isolate and transmit frequencies generated by a stabilized optical frequency comb. This method has been developed for the remote comparison of frequency combs. Finally, we present the characterization of the optical frequency comb and its application to the calibration of high wavelength resolution meters in the optical telecommunications window. Measurements with uncertainties under the resolution of the own instrument were achieved using stabilized lasers at molecular absorptions. The result is a significant improvement of the measurement capability given by the current equipment.

Enhanced supercontinuum generation using multi-fibre ultra-long Raman cavities

Supercontinuum generation in a TrueWave and SMF fibre based ultra-long Raman fibre laser cavity is investigated experimentally. By including SMF in the ultra-long Raman cavity, bandwidth and flatness can be dramatically improved.

Soliton dynamics in transmission through ultralong lasers

It has been recently demonstrated that ultra-long Raman fibre laser (URFL) cavities can be efficiently used to generate virtually lossless transmission links through a nearly ideal provision of distributed Raman gain to the signal [1]. The first experimental demonstration of long-distance “true” soliton propagation through optical fibre was recently published using such a virtually non-dissipative link [2], paving the way for multiple applications in communications and signal processing. Although both the total signal power excursion and the maximum effective local attenuation in ultra-long cavities are extremely low compared with those of conventional transmission schemes, they still show an exponential growth with span length. Furthermore, the effective attenuation profile itself can be affected by high-power transmitted signals due to pump depletion. Hence, it is of particular importance to determine the operational limits of these virtually lossless links in terms of both cavity length and nonlinear tolerance to signal characteristics.