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Carbon Nanotubes Technologies in Pulsed Fibre Lasers for Telecom and Sensing Applications

Final Report Summary - TELASENS (Carbon Nanotubes Technologies in Pulsed Fibre Lasers for Telecom and<br/>Sensing Applications)

Laser generation in Near- and Mid- IR region, 1-2 μm, is desirable for a wide range of possible applications in health-care, telecom, remote sensing, laser radar etc. This wavelength region also includes the water absorption peaks, making such lasers a unique instrument for non-invasive surgery or ophthalmology. On the other hand, there are lots of absorption lines of green-house gasses (CO and N2O) around 1.5 and 2 μm wavelength, that allows to use fibre lasers for gas detection and analysis. High power 2 μm laser sources are well suited for nonlinear frequency conversion to obtain mid-IR and THz generation. Most of current works have concentrated on mode-locking regime initiated by semiconductor saturable absorber mirrors (SESAMs), single-walled carbon nanotubes (SWCNT) and graphene based saturable absorbers. Saturable absorbers are characterized by recovery time. This should be very short for passive mode locking initiation and generating ultrashort pulses. However, shorter recovery time causes higher lasing threshold and therefor obstacles for self-starting. Application of two saturable absorbers, slow and fast, in laser cavity simultaneously helps to generate ultrashort pulses with high average power, temporal purity, and high frequency stability, while decrease the threshold and ensure self-starting mode-locking operation. Comparatively slow saturable absorber is used for mode-locking initiation as it has lower saturation threshold, whereas the light modulator with fast response time ensures efficient pulse formation and stabilization at substantially higher powers.
The M. Curie TeLaSens project joined an expertise of material and photonic scientists in order to develop new carbon nano-materials, study their optical properties and finally utilise them as nonlinear optic devices in various fibre lasers. These allowed a generation of ultra-short pulses in the Infra-Red (IR) optical range of 1000-2000 nm as shown in diagram 1.

We worked in three major directions:
1) Development of carbon nanomaterials with improved optical properties. This achieved by combination of computer modelling and experimental physical chemistry.
2) Development of novel saturable absorber devices by fabrication nano composites with carbon nanomaterials, deposition of CNT in the fibre micro-channel and on the optical mirrors.
3) We have built and achieved ultra-short pulse generation with CNT saturable absorbers in the fibre lasers with following active media: Yb, Er, Bi, Tm and Ho. This allow us to generate laser pulses in the broad spectral range between 1000 and 2000 nm.
Among the most important achievements of the project we can list following:
1. Development of the new salting-out techniques for controlling a dispersion of CNT in water and organic solvents, with a purpose to manage saturable absorber properties
2. Development of graphene based saturable absorber for Er doped fibre laser.
3. Development fiber laser with novel micro-channel mode locker device filed with CNT dispersed in organic solvents.
4. Development of the new Bi- doped fibre amplifiers and mode-locked lasers.
5. Demonstration of vector solitons with locked and precessing states of polarization regime of ultra-short pulse generation in Er doped lasers.
6. Development of high power mode-locked Tm-doped fibre lasers mode-locked by CNT.
7. Development of Q-switched and Mode-Locked pulse generation regimes in Ho- doped fibre lasers by carbon nanotubes saturable absorbers.
The overall success of proposal is directly evidenced from the publication outcome of the consortium. Also, we managed to organize 1 summer school in Finland and a workshop in Novosibirsk (Russia), which were well attended by project members.
ESR directly benefitted from comprehensive training carried out by consortium. We should stress that consortium performed 90.82 months of secondments with 40.8 months accounted on 9 ESRs from Aston University (UK), Novosibirsk State University (Russia), Fiber Optics Research Centre (Moscow, Russia) and Institute of semiconductor Physics (Kiev, Ukraine).

As a result of TeLaSens project fulfilment, we expect utilization of developed cost-effective fibre laser sources in telecom, gas sensing and medical treatment in the nearest future. This will lead to personalised healthcare, new sensors in manufacturing and transport, new type of fibre optics communication systems.

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