Multi-wavelength switchable fibre ring laser based on polarisation selective tilted fibre gratings capable of strain and temperature sensing

Using three fibre gratings with excessively tilted structures in the cavity, we have experimentally demonstrated a multiwavelength switchable erbium-doped fibre ring laser system. The three tilted gratings act as in-fibre polariser and polarisation dependent loss filters to induce the polarisation hole burning effect in the cavity for the operation of the laser at single, double, triple and quadruple wavelengths. The laser system has demonstrated good stability under room temperature conditions and also achieved a high degree of polarization (~30dB), high optical signal to noise ratio (up to 63dB) and high side mode suppression (~50dB). The system has also been investigated for temperature and strain sensing by subjecting the seeding fibre Bragg gratings (FBG) to temperature and strain variations. Since the loss band of the polarisation dependent loss filter is broader than the bandwidth of the seeding FBG, the laser output shifts in wavelength with the applied temperature and strain. The fibre ring laser has shown good responses to the temperature and strain, providing sensitivities of approximately 11.7 pm/°C and 0.85pm/µe respectively.

Polarization attractors in harmonic mode-locked fiber laser with carbon nanotubes

We study polarization dynamics of a harmonic mode-locked erbium-doped fiber laser with carbon nanotubes absorber. New types of vector solitons are shown for multi-pulse and harmonic mode-locked operation with locked, switching and precessing polarization states. © 2014 OSA.

Transition dynamics for multi-pulsing in mode-locked lasers

We consider experimentally and theoretically a refined parameter space in a mode-locked fiber laser near the transition to multi-pulsing. Increasing cavity energy drives the dynamics through a periodic instability to chaotic dynamics. © 2010 Optical Society of America.

Dispersion-modified actively mode-locked erbium fibre laser using a chirped fibre grating

The authors describe the operation of an actively modelocked Er fibre laser incorporating a chrped in fibre Bragg reflection grating as one end mirror to the cavity, acting as a lumped highly dispersive element. In one oreientation the grating shifted the cavity into normal dispersion regime and pulses of -25ps duration were produced. In the opposite oreintation, the cavity dispersion was anomalous and ~8ps pulses were produced with characterisitics typical of solitons propagating in a periodically perturbed system.

Fiber Bragg grating structures inscribed using 800nm femtosecond laser in single- and multi-core mid-IR glass fibers with their spectral, thermal and strain properties

Single- and multi-core passive and active germanate and tellurite glass fibers represent a new class of fiber host for in-fiber photonics devices and applications in mid-IR wavelength range, which are in increasing demand. Fiber Bragg grating (FBG) structures have been proven as one of the most functional in-fiber devices and have been mass-produced in silicate fibers by UV-inscription for almost countless laser and sensor applications. However, because of the strong UV absorption in germanate and tellurite fibers, FBG structures cannot be produced by UVinscription. In recent years femtosecond (fs) lasers have been developed for laser machining and microstructuring in a variety of glass fibers and planar substrates. A number of papers have been reported on fabrication of FBGs and long-period gratings in optical fibers and also on the photosensitivity mechanism using 800nm fs lasers. In this paper, we demonstrate for the first time the fabrication of FBG structures created in passive and active single- and three-core germanate and tellurite glass fibers by using 800nm fs-inscription and phase mask technique. With a fs peak power intensity in the order of 1011W/cm2, the FBG spectra with 2nd and 3rd order resonances at 1540nm and 1033nm in a single-core germanate glass fiber and 2nd order resonances between ~1694nm and ~1677nm with strengths up to 14dB in all three cores of three-core passive and active tellurite fibers were observed. Thermal and strain properties of the FBGs made in these mid-IR glass fibers were characterized, showing an average temperature responsivity of ~20pm/°C and a strain sensitivity of 1.219±0.003pm/µe.

Direct cavity assessment and mode optimisation technique for DFB fibre laser

A technique for direct real-time assessment of a distributed feedback fibre laser cavity conditions during operation is demonstrated and used to provide a cavity mode conditioning feedback mechanism to optimise output performance. Negligible wavelength drift is demonstrated over a 52 mW pump power range.

Fiber Bragg gratings inscribed using 800nm femtosecond laser and a phase mask in singleand multi-core mid-IR glass fibers

For the first time, Fiber Bragg grating (FBG) structures have been inscribed in single-core passive germanate and three-core passive and active tellurite glass fibers using 800nm femtosecond (fs) laser and phase mask technique. With fs peak power intensity in the order of 1011W/cm2, the FBG spectra with 2nd and 3rd order resonances at 1540 and 1033nm in the germanate glass fiber and 2nd order resonances at ~1694 and ~1677nm with strengths up to 14dB in all three cores in the tellurite fiber were observed. Thermal responsivities of the FBGs made in these mid-IR glass fibers were characterized, showing average temperature responsivity ~20pm/°C. Strain responsivities of the FBGs in germanate glass fiber were measured to be 1.219pm/µe.

Brillouin based distributed fibre sensor incorporating a mode-locked Brillouin fibre ring laser

A pulsed Brillouin fibre ring laser has been developed and we describe its main features. The pump and the Brillouin laser are shown to form an excellent dual frequency source for distributed sensing. A first application for fire detection is demonstrated.

Multi-wavelength erbium/Raman gain based random distributed feedback fiber laser

A multiwavelength generation in a random distributed feedback fiber laser based on hybrid Raman and erbium gain and a Lyot all-fiber spectral filter is demonstrated for the first time. The use of erbium-doped fiber allows a multi-wavelength generation to be achieved at lower pump powers in comparison with random fiber lasers based on Raman gain only. The operating bandwidth and flatness of power distribution between different lines in generation are also improved in the hybrid gain configuration.

Strong spectral filtering for a mode-locked similariton fiber laser

We propose a novel mode-locked fiber laser design that relies on attracting similariton solutions in fiber amplifiers with normal group-velocity dispersion and strong spectral filtering to compensate increased pulse duration and bandwidth. Stable high-energy, large-bandwidth pulses are obtained that can be linearly compressed, resulting in ultrashort pulses.

Drusen detection in retro-mode imaging by a scanning laser ophthalmoscope

Purpose: The Nidek F-10 is a scanning laser ophthalmoscope that is capable of a novel fundus imaging technique, so-called ‘retro-mode’ imaging. The standard method of imaging drusen in age-related macular degeneration (AMD) is by fundus photography. The aim of the study was to assess drusen quantification using retro-mode imaging. Methods: Stereoscopic fundus photographs and retro-mode images were captured in 31 eyes of 20 patients with varying stages of AMD. Two experienced masked retinal graders independently assessed images for the number and size of drusen, using purpose-designed software. Drusen were further assessed in a subset of eight patients using optical coherence tomography (OCT) imaging. Results: Drusen observed by fundus photography (mean 33.5) were significantly fewer in number than subretinal deposits seen in retro-mode (mean 81.6; p < 0.001). The predominant deposit diameter was on average 5 µm smaller in retro-mode imaging than in fundus photography (p = 0.004). Agreement between graders for both types of imaging was substantial for number of deposits (weighted ? = 0.69) and moderate for size of deposits (weighted ? = 0.42). Retro-mode deposits corresponded to drusen on OCT imaging in all eight patients. Conclusion: The subretinal deposits detected by retro-mode imaging were consistent with the appearance of drusen on OCT imaging; however, a larger longitudinal study would be required to confirm this finding. Retro-mode imaging detected significantly more deposits than conventional colour fundus photography. Retro-mode imaging provides a rapid non-invasive technique, useful in monitoring subtle changes and progression of AMD, which may be useful in monitoring the response of drusen to future therapeutic interventions.

Mode-locking in 25-km fibre laser

We demonstrate mode-locking and single-pulse generation in fibre laser with record-setting cavity length of 25 km. Substantial increase in the pulse round trip duration leads to ultra-low repetition rate of 8.097 kHz and pulse energy of 3.7 uJ.

Optical linewidth of a passively mode-locked semiconductor laser

We measured the optical linewidths of a passively mode-locked quantum dot laser and show that, in agreement with theoretical predictions, the modal linewidth exhibits a parabolic dependence with the mode optical frequency. The minimum linewidth follows a Schawlow-Townes behavior with a rebroadening at high power. In addition, the slope of the parabola is proportional to the RF linewidth of the laser and can therefore provide a direct measurement of the timing jitter. Such a measurement could be easily applied to mode-locked semiconductor lasers with a fast repetition rate where the RF linewidth cannot be directly measured.

Intra-cavity dynamics in high power mode-locked fiber lasers

A theoretical model allows for the characterization and optimization of the intra-cavity pulse evolutions in high-power fiber lasers. Multi-parameter analysis of laser performance can be made at a fraction of the computational cost.