Demonstration of laser cooling in a novel all oxide GAYY silica glass.

We demonstrate laser induced cooling in ytterbium doped silica (SiO) glass with alumina, yttria co-doping (GAYY-Aluminum: Yttrium: Ytterbium Glass) fabricated using the modified chemical vapour deposition (MCVD) technique. A maximum temperature reduction by - 0.9 K from room temperature (296 K) at atmospheric pressure was achieved using only 6.

Extremely Efficient DFB Lasers with Flat-Top Intra-Cavity Power Distribution in Highly Erbium-Doped Fibers.

High-performance erbium-doped DFB fiber lasers are presently required for several sensing applications, whilst the current efficiency record is only a few percent. Additionally, a flat-top intra-cavity power distribution that is not provided in traditional DFB lasers is preferred. Moreover, cavity lengths of <20 cm are attractive for fabrication and packaging.

Structural and optical properties of Nd:YAB-nanoparticle-doped PDMS elastomers for random lasers.

We report the structural and optical properties of Nd:YAB (NdY Al(BO))-nanoparticle-doped PDMS elastomer films for random lasing (RL) applications. Nanoparticles with Nd ratios of x = 0.2, 0.

Theoretical investigations of power fluctuations statistics in Brillouin erbium-doped fiber lasers.

We present theoretical investigations including simulations and statistical analyses on the fluctuations of the temporal output power in a Brillouin erbium-doped fiber laser. The generation of even Stokes waves up to the 5 order is considered by solving coupled-mode equations including SBS and Kerr nonlinearities. It is demonstrated that by increasing the EDFA pump power and generating a few orders of Stokes waves in such a laser, there are strong power fluctuations and rogue events are expected.

Super-tunable, broadband up-conversion of a high-power CW laser in an engineered nonlinear crystal.

A specially-designed chirped periodically poled lithium niobate nonlinear crystal was fabricated with a phase-matching bandwidth as large as 50 nm for sum frequency generation to operate at room and higher temperatures. This device also benefits from insensitivity to laser frequency drift and fine alignment. The loosely-focused beam position of a high-power CW laser at around 1550 nm is optimized within the grating for maximum up-conversion efficiency, to realize a super-tunable source in the range of 770-778 nm by tuning a narrowband control signal over 30 nm in the communication band.

Design, fabrication and characterization of a specially apodized chirped grating for reciprocal second harmonic generation.

A specially-designed apodized chirped PPLN based on particular positioning of poled regions within the periods has been realized theoretically and experimentally to demonstrate the reciprocal response in the SHG spectra over a 30-nm bandwidth, for up-chirp and down-chirp directions. The simulation results are compared with another apodized chirped PPLN for which the placement of poled regions is deviated from optimum positions. The average power difference is less than 0.

Improved intrapulse raman scattering control via asymmetric airy pulses.

We experimentally demonstrate the possibility of tuning the frequency of a laser pulse via the use of an Airy pulse-seeded soliton self-frequency shift. The intrinsically asymmetric nature of Airy pulses, typically featured by either leading or trailing oscillatory tails (relatively to the main lobe), is revealed through the nonlinear generation of both a primary and a secondary Raman soliton self-frequency shift, a phenomenon which is driven by the soliton fission processes. The resulting frequency shift can be carefully controlled by using time-reversed Airy pulses or, alternatively, by applying an offset to the cubic phase modulation used to generate the pulses.

Tailoring and tuning of the broadband spectrum of a step-chirped grating based frequency doubler using tightly-focused Gaussian beams.

We demonstrate theoretically and experimentally, that the non-uniform spectra of second harmonic generation (SHG) from an unapodized step-chirped periodically poled nonlinear optical grating can be apodized utilizing tightly-focused Gaussian beams to suppress the ripple in its wideband response. In our example, by increasing focusing, a ripple-free response is progressively achieved over a 6-dB bandwidth of >5 nm, with a beam waist of 20 µm. With this tight focusing arrangement, a continuous tuning of 11-nm is also demonstrated by simply changing the focal point by 5.

Tunable single-to-dual channel wavelength conversion in an ultra-wideband SC-PPLN.

We experimentally demonstrate tunable dual channel broadcasting of a signal over the C-band for wavelength division multiplexed (WDM) optical networks. This is based on cascaded χ(2) nonlinear mixing processes in a specially engineered, 20-mm-long step-chirped periodically poled lithium niobate with a broad 28-nm second harmonic (SH) bandwidth in the 1.55-μm spectral range.

Agile multicasting based on cascaded χ(2) nonlinearities in a step-chirped periodically poled lithium niobate.

We experimentally demonstrate the possibility of agile multicasting for wavelength division multiplexing (WDM) networks, of a single-channel to two and seven channels over the C band, also extendable to S and L bands. This is based on cascaded χ(2) nonlinear mixing processes, namely, second-harmonic generation (SHG)-sum-frequency generation (SFG) and difference-frequency generation (DFG) in a 20-mm-long step-chirped periodically poled lithium niobate crystal, specially designed and fabricated for a 28-nm-wide SH-SF bandwidth centered at around 1.55 μm.

Tunable all-optical wavelength broadcasting in a PPLN with multiple QPM peaks.

We experimentally demonstrate tunable multiple-idler wavelength broadcasting of a signal to selective channels for wavelength division multiplexing (WDM). This is based on cascaded χ(2) nonlinear mixing process in a novel multiple-QPM 10-mm-long periodically poled LiNbO3 having an aperiodic domain in the center. The idlers' spacing is varied utilizing detuning of the pump wavelength within the SHG bandwidth.

Efficient flattop ultra-wideband wavelength converters based on double-pass cascaded sum and difference frequency generation using engineered chirped gratings.

High-efficiency ultra-broadband wavelength converters based on double-pass quasi-phase-matched cascaded sum and difference frequency generation including engineered chirped gratings in lossy lithium niobate waveguides are numerically investigated and compared to the single-pass counterparts, assuming a large twin-pump wavelength difference of 75 nm. Instead of uniform gratings, few-section chirped gratings with the same length, but with a small constant period change among sections with uniform gratings, are proposed to flatten the response and increase the mean efficiency by finding the common critical period shift and minimum number of sections for both single-pass and double-pass schemes whilst for the latter the efficiency is remarkably higher in a low-loss waveguide. It is also verified that for the same waveguide length and power, the efficiency enhancement expected due to the use of the double-pass scheme instead of the single-pass one, is finally lost if the waveguide loss increases above a certain value.

Efficient wavelength converters with flattop responses based on counterpropagating cascaded SFG and DFG in low-loss QPM LiNbO3 waveguides.

A wavelength converter based on counterpropagating quasi-phase matched cascaded sum and difference frequency generation in lossy lithium niobate waveguide is numerically evaluated and compared to a single-pass scheme assuming a large pump wavelength difference of 75 nm. A double-pass device is proposed to improve the conversion efficiency while the response flattening is accomplished by increasing the wavelength tuning of one pump. The criteria for the design of the low-loss waveguide length, and the assignment of power in the pumps to achieve the desired efficiency, ripple and bandwidth are presented.

Improved cascaded sum and difference frequency generation-based wavelength converters in low-loss quasi-phase-matched lithium niobate waveguides.

We numerically evaluate the wavelength converters based on cascaded sum and difference frequency generation in quasi-phase-matched lithium niobate waveguides with and without loss. A technique is also proposed to flatten the response by increased detuning of the pump wavelength. We present the criteria for the design of waveguide length and the assignment of pump power to achieve the desired efficiency, ripple and bandwidth, assuming a large pump wavelength difference of 75 nm.

Engineered gratings for flat broadening of second-harmonic phase-matching bandwidth in MgO-doped lithium niobate waveguides.

Novel engineered step-chirped gratings (SCG) for broadband frequency converters based on quasi-phase matched second harmonic generation in MgO-doped lithium niobate waveguides have been theoretically modeled and simulated. It is shown mathematically that engineered apodized gratings can flatten the efficiency response. Also, it is verified that the bandwidth and flatness of an apodized SCG can be improved extensively with decreasing the number of segments and increasing the apodization ratio, respectively.