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.

Low loss depressed cladding waveguide inscribed in YAG:Nd single crystal by femtosecond laser pulses

A depressed cladding waveguide with record low loss of 0.12 dB/cm is inscribed in YAG:Nd(0.3at.%) crystal by femtosecond laser pulses with an elliptical beam waist. The waveguide is formed by a set of parallel tracks which constitute the depressed cladding. It is a key element for compact and efficient CW waveguide laser operating at 1064 nm and pumped by a multimode laser diode. Special attention is paid to mechanical stress resulting from the inscription process. Numerical calculation of mode distribution and propagation loss with the elasto-optical effect taken into account leads to the conclusion that the depressed cladding is a dominating factor in waveguide mode formation, while the mechanical stress only slightly distorts waveguide modes.

Alternate wavelength-switching in a dual-wavelength mode-locked fibre laser

We report a stable, dual-wavelength mode-locked fiber laser at 1 GHz with a wavelength spacing of 0.7 nm. Alternate switching between single and dual wavelength output was also achieved by simple adjustment of the pump power.

Superstructure fiber gratings via single step femtosecond laser inscription

We present the development of superstructure fiber gratings (SFG) in Ge-doped, silica optical fiber using femtosecond laser inscription. We apply a simple but extremely effective single step process to inscribe low loss, sampled gratings with minor polarization dependence. The method results in a controlled modulated index change with complete suppression of mode coupling associated with the overlapping LPG structure leading to highly symmetric superstructure spectra, with the grating reflection well within the Fourier design limit. The devices are characterized and compared with numerical modeling by solving Maxwell's equations and calculating the back reflection spectrum using the bidirectional beam propagation method (BiBPM). Experimental results validate our numerical analysis, allowing for the estimation of inscription parameters such as the ac index modulation change, and the wavelength, position and relative strength of each significant resonance peak. We also present results on temperature and refractive index measurements showing potential for sensing applications.

Wideband-tuneable, nanotube mode-locked, fibre laser

Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications1–3. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses4, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths5. Semiconductor saturable absorber mirrors are widely used in fibre lasers4–6, but their operating range is typically limited to a few tens of nanometres7,8, and their fabrication can be challenging in the 1.3–1.5 mm wavelength region used for optical communications9,10. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness11–16. Here, we engineer a nanotube–polycarbonate film with a wide bandwidth (>300 nm) around 1.55 mm, and then use it to demonstrate a 2.4 ps Er31-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.

Superstructure fiber gratings via single step femtosecond laser inscription

We present the development of superstructure fiber gratings (SFG) in Ge-doped, silica optical fiber using femtosecond laser inscription. We apply a simple but extremely effective single step process to inscribe low loss, sampled gratings with minor polarization dependence. The method results in a controlled modulated index change with complete suppression of mode coupling associated with the overlapping LPG structure leading to highly symmetric superstructure spectra, with the grating reflection well within the Fourier design limit. The devices are characterized and compared with numerical modeling by solving Maxwell's equations and calculating the back reflection spectrum using the bidirectional beam propagation method (BiBPM). Experimental results validate our numerical analysis, allowing for the estimation of inscription parameters such as the ac index modulation change, and the wavelength, position and relative strength of each significant resonance peak. We also present results on temperature and refractive index measurements showing potential for sensing applications.

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.

Single polarization, dual wavelength fiber laser based on a 3-stage all fiber lyot filter

We have demonstrated a switchable dual wavelength fiber ring laser with a high degree of polarization output by using an intracavity 3-stage all fiber Lyot filter. The filter is formed by concatenating four 45° tilted fiber gratings separated by polarization maintaining fibers with a length ratio of 1:2:4 (20, 40, and 80 cm), giving a compact integrated configuration with reduced bandwidth. Switchable dual wavelength or single wavelength output at 1533.5 and 1563.3 nm has been achieved. The output lasing is considerably stable owing to the in-phase mode-selecting function of the multistage Lyot filter, and has a very high degree of polarization higher than 99.9%. © 1989-2012 IEEE.

Nonlinear mixing and mode correlations in a short Raman fiber laser

In the present paper we experimentally demonstrate a generation in a short Raman fiber laser having 10 000 different longitudinal modes only. We design the laser using 12 meters of commercially available fiber. Contrary to the recently demonstrated single longitudinal mode DFB Raman laser and short DBR Raman laser, in the laser under study the number of modes is high enough for efficient nonlinear interactions. Experimentally measured time dynamics reveals the presence of mode correlations in the radiation: the measured extreme events lasts for more than 10 round-trips.

Generation of dissipative solitons in an actively mode-locked ultralong fibre laser

A single-pulse actively mode-locked fibre laser with a cavity length exceeding 1 km has been developed and investigated for the first time. This all-fibre erbium-doped laser has a normal intracavity dispersion and generates dissipative 8-ns solitons with a fundamental repetition rate of 163.8 kHz; the energy per pulse reaches 34 nJ. The implemented mode locking, based on the use of intracavity intensity modulator, provides self-triggering and high stability of pulsed lasing. A possibility of continuous tuning of the centre lasing wavelength in the range of 1558 - 1560 nm without any tunable spectral selective elements in the cavity is demonstrated. The tuning occurs when controlling the modulation signal frequency due to the forced change in the pulse repetition time (group delay) under the conditions of intracavity chromatic dispersion. © 2013 Kvantovaya Elektronika and Turpion Ltd.

Inversed-modified soliton generation in mode-locked fibre laser at normal dispersion

We demonstrate erbium- and thulium-doped fibre ring lasers mode-locked with a single-walled carbon nanotubes (SWCNT) operating at normal intracavity dispersion and high nonlinearity. The lasers generate transform-limited picosecond inversed-modified soliton pulses. © 2014 OSA.

Higher-order femtosecond solitons generation in a hybrid mode-locked Tm-doped fibre laser

A thulium-doped all-fibre laser hybrid mode-locked by the co-action of nonlinear polarization evolution and single-walled carbon nanotubes generating 500-fs high-order solitons with the pulse energy 10.87 nJ at 1.9 μm wavelength band is demonstrated. © 2014 OSA.

300-mW average output power hybrid mode-locked thulium-doped fiber laser

We report on ring thulium-doped fiber laser hybrid mode-locked by single-walled carbon nanotubes and nonlinear polarization evolution generating 600-fs pulses at 1910-1980nm wavelength band with 72.5MHz repetition rate. Average output power reached 300mW in single-pulse operation regime, corresponding to 4.88kW peak power and 2.93nJ pulse energy.

Passive mode locking in erbium-doped fibre laser by carbon nanotubes

Passively mode locked fibre lasers have a variety of applications ranging from telecommunication to medical photonics. Carbon nanotubes (CNTs) have attracted recently a great deal of attention as a promising solution for saturable absorber elements required for laser mode locking (see e.g. [1-3] and references therein). CNTs can be used as a saturable absorber in passively mode locked fibre laser directly [1,2] or as a CNTs polymer composites [3]. An attractive feature of CNT-based solutions in fibre lasers is a possibility to maintain the compactness, robustness of all-fibre format and low cost through using all standard telecom compatible components. The two important technical challenges in such type of lasers are: (i) to achieve stable polarization properties of the generated radiation without using complex control elements, and, (ii) to avoid low frequency instabilities of the mode-locked pulse train. In this paper we report results of the experiments on mode-locked soliton fibre laser using the following standard components: 1m of highly doped erbium fibre (Liekki Er80-8/125) serves as the gain medium with nominal absorption of 80 dB/m at 1530 nm; a 976 nm laser diode providing up to 310mW power is used to pump the laser via a 980/1550 wavelength division multiplexing; an isolator is employed to ensure single direction oscillation; SMF-28 is used to create necessary amount of anomalous dispersion to form soliton pulse making the total cavity length around 7.83 m; the CNT-polyvinyl alcohol polymer saturable absorber sandwiched in the FC/PC connector is used as a mode-locker device (see [3] for details). © 2011 IEEE.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.