Highly birefringent chalcogenide optical fiber for polarization-maintaining in the 3-8.5 µm mid-IR window.

A highly birefringent polarization-maintaining chalcogenide microstructured optical fiber (MOF) covering the 3-8.5 µm wavelength range has been realized for the first time. The fiber cross-section consists of 3 rings of circular air holes with 2 larger holes adjacent to the core. Birefringence properties are calculated by using the vector finite-element method and are compared to the experimental ones. The group birefringence is 1.5x10-3 and fiber losses are equal to 0.8 dB/m at 7.55 µm.

Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber.

A low-loss suspended core As(38)Se(62) fiber with core diameter of 4.5 µm and a zero-dispersion wavelength of 3.5 µm was used for mid-infrared supercontinuum generation. The dispersion of the fiber was measured from 2.9 to 4.2 µm and was in good correspondence with the calculated dispersion. An optical parametric amplifier delivering 320 fs pulses with a peak power of 14.8 kW at a repetition rate of 21 MHz was used to pump 18 cm of suspended core fiber at different wavelengths from 3.3 to 4.7 µm. By pumping at 4.4 µm with a peak power of 5.2 kW coupled to the fiber a supercontinuum spanning from 1.7 to 7.5 µm with an average output power of 15.6 mW and an average power >5.0 µm of 4.7 mW was obtained.

Thulium pumped mid-infrared 0.9-9µm supercontinuum generation in concatenated fluoride and chalcogenide glass fibers.

We theoretically demonstrate a novel approach for generating Mid-InfraRed SuperContinuum (MIR SC) by using concatenated fluoride and chalcogenide glass fibers pumped with a standard pulsed Thulium (Tm) laser (T(FWHM)=3.5ps, P0=20kW, ν(R)=30MHz, and P(avg)=2W). The fluoride fiber SC is generated in 10m of ZBLAN spanning the 0.9-4.1µm SC at the -30dB level. The ZBLAN fiber SC is then coupled into 10cm of As2Se3 chalcogenide Microstructured Optical Fiber (MOF) designed to have a zero-dispersion wavelength (λ(ZDW)) significantly below the 4.1µm InfraRed (IR) edge of the ZBLAN fiber SC, here 3.55µm. This allows the MIR solitons in the ZBLAN fiber SC to couple into anomalous dispersion in the chalcogenide fiber and further redshift out to the fiber loss edge at around 9µm. The final 0.9-9µm SC covers over 3 octaves in the MIR with around 15mW of power converted into the 6-9µm range.

Photonic Bandgap Propagation in All-Solid Chalcogenide Microstructured Optical Fibers.

An original way to obtain fibers with special chromatic dispersion and single-mode behavior is to consider microstructured optical fibers (MOFs). These fibers present unique optical properties thanks to the high degree of freedom in the design of their geometrical structure. In this study, the first all-solid all-chalcogenide MOFs exhibiting photonic bandgap transmission have been achieved and optically characterized. The fibers are made of an As38Se62 matrix, with inclusions of Te20As30Se50 glass that shows a higher refractive index (n = 2.9). In those fibers, several transmission bands have been observed in mid infrared depending on the geometry. In addition, for the first time, propagation by photonic bandgap effect in an all-chalcogenide MOF has been observed at 3.39 µm, 9.3 µm, and 10.6 µm. The numerical simulations based on the optogeometric properties of the fibers agree well with the experimental characterizations.

Lifetime reduction due to photodarkening phenomenon in ytterbium-doped fibers and rate equation term.

In this Letter, the lifetime temporal reduction in ytterbium-doped aluminosilicate fibers due to pump-induced photodarkening (PD) has been reported. A linear correlation between lifetime reduction at equilibrium state and equilibrium losses due to the PD phenomenon was demonstrated. A squared-law dependence between lifetime reduction and dopant concentration (percent by weight) suggests a possible correction term for the rate equations system which allows improving its accuracy. Finally, a quenching effect was also observed for different pump power levels in order to find the corresponding lifetime value for different inversion levels. The quantitative analysis allows determination of the PD quenching term in the laser rate equations system to properly model a laser device that may be affected by this process.

Mitigation of photodarkening phenomenon in fiber lasers by 633 nm light exposure.

In this work, the influence of photodarkening (PD) and photobleaching (PB) on the lasing features of the ytterbium-doped aluminosilicate fiber lasers is examined. Simultaneous PD and PB with 633 nm irradiation was monitored at the lasing wavelength of 1070 nm and compared with individually caused PD and PB effects. The variation of laser threshold and slope efficiency was reported. By analyzing the laser performances it was found that the ratio of excess loss at 633 and 1070 nm is expected to be less than 20. In addition, considerable mitigation of the PD with 633 nm light irradiation is demonstrated.

Linewidth-narrowing and intensity noise reduction of the 2nd order Stokes component of a low threshold Brillouin laser made of Ge10As22Se68 chalcogenide fiber.

A compact second-order Stokes Brillouin fiber laser made of microstructured chalcogenide fiber is reported for the first time. This laser required very low pump power for Stokes conversion: 6 mW for first order lasing and only 30 mW for second order lasing with nonresonant pumping. We also show linewidth-narrowing as well as intensity noise reduction for both the 1st and 2nd order Stokes component when compared to that of the pump source.

Wavelength conversion in a highly nonlinear chalcogenide microstructured fiber.

We report on all-optical wavelength conversion of a 56 Gb/s differential quadrature phase shift keying signal and a 42.7 Gb/s on-off keying signal. Wavelength conversion is based on four-wave mixing effect in a 1 m long highly nonlinear GeAsSe chalcogenide fiber. The high nonlinearity of the fiber allows low-power penalty operation with a total average power of less than 60 mW.

Relative intensity noise and frequency noise of a compact Brillouin laser made of As38Se62 suspended-core chalcogenide fiber.

Relative intensity noise and frequency noise have been measured for the first time for a single-frequency Brillouin chalcogenide As38Se62 fiber laser. This is also the first demonstration of a compact suspended-core fiber Brillouin laser, which exhibits a low threshold power of 22 mW and a slope efficiency of 26% for nonresonant pumping.

Concentration dependence and self-similarity of photodarkening losses induced in Yb-doped fibers by comparable excitation.

We report on an extensive investigation of photodarkening in Yb-doped silica fibers. A set of similar fibers, covering a large Yb concentration range, was made so as to compare the photodarkening induced losses. Careful measurements were made to ensure equal and uniform inversion for all the tested fibers. The results show that, with the specific set-up, the stretching parameter obtained through fitting has a very limited variation. This gives more meaning to the fitting parameters. Results tend to indicate a square law dependence of the concentration of excited ions on the final saturated loss. We also demonstrate self-similarity of loss evolution when experimental curves are simply normalized to fitting parameters. This evidence of self-similarity also supports the possibility of introducing a preliminary figure of merit for Yb-doped fiber. This will allow the impact of photodarkening on laser/amplifier devices to be evaluated.

Temporal evolution and correlation between cooperative luminescence and photodarkening in ytterbium doped silica fibers.

The present work describes photodarkening from the viewpoint of cooperative luminescence. The temporal evolution of both effects was measured simultaneously by means of ytterbium doped aluminosilicate fibers for concentrations up to 1.8 wt% Yb3+. The quadratic dependence of photodarkening and cooperative luminescence versus dopant concentration was observed. The change in the photodarkening and cooperative luminescence mutual dynamics for highly and low doped fibers is ascribed to a different ion number which forms the cluster. Cooperative luminescence is proved to be a natural probe for photodarkening since it provides new pieces of information and contributes to the photodarkening mechanism description.

Efficient four-wave mixing in an ultra-highly nonlinear suspended-core chalcogenide As38Se62 fiber.

We report a chalcogenide suspended-core fiber with ultra-high nonlinearity and low attenuation loss. The glass composition is As(38)Se(62).With a core diameter as small as 1.13 µm, a record Kerr nonlinearity of 46,000 W(-1) km(-1) is demonstrated with attenuation loss of 0.9 dB/m. Four-wave mixing is experimented by using a 1m-long chalcogenide fiber for 10 GHz and 42.7 GHz signals. Four-wave mixing efficiencies of -5.6 dB at 10 GHz and -17.5 dB at 42.7 GHz are obtained. We also observed higher orders of four-wave mixing for both repetition rates.

Experimental realization of a mode-locked parabolic Raman fiber oscillator.

We report here the first demonstration of a mode-locked fiber laser delivering parabolic pulses (similaritons) at 1534 nm. The use of a Raman-based gain medium potentially allows its implementation at any wavelength. The 22nJ output similariton pulses have a true parabolic shape both in the time and spectral domains and a linear chirp. Linear recompression close to Fourier limit is demonstrated allowing us to obtain 6 ps compressed pulses with a compression factor of 75.

Casting method for producing low-loss chalcogenide microstructured optical fibers.

We report significant advances in the fabrication of low loss chalcogenide microstructured optical fiber (MOF). This new method, consisting in molding the glass in a silica cast made of capillaries and capillary guides, allows the development of various designs of fibers, such as suspended core, large core or small core MOFs. After removing the cast in a hydrofluoric acid bath, the preform is drawn and the design is controlled using a system applying differential pressure in the holes. Fiber losses, which are the lowest recorded so far for selenium based MOFs, are equal to the material losses, meaning that the process has no effect on the glass quality.

Experimental demonstration of similariton pulse compression in a comblike dispersion-decreasing fiber amplifier.

Self-similar propagation of linearly chirped hyperbolic-secant pulses in a comblike decreasing-dispersion fiber amplifier has been observed experimentally for the first time to our knowledge. The scheme takes advantage of an exact solution of the generalized nonlinear Schrödinger equation with distributed coefficients.