Graham Town

Dual wavelength modelocked fiber laser

A dual wavelength actively modelocked erbium-doped fiber laser was constructed which generated pulses approximately 50 ps long with repetition rate 2.6 GHz at both 1544.1 nm and 1545.7 nm. The laser cavity incorporated a pair of dispersive gratings to produce temporal-spectral multiplexing of the pulses in the gain medium, which was observed to reduce cross-saturation effects.

Tunable erbium–ytterbium fiber sliding-frequency soliton laser

We characterize the soliton-train emission from an Er–Yb-doped fiber loop laser. We discuss the self-starting dynamics and pulse-repetition-rate control in this sliding-frequency soliton laser. We show that the laser truly self-starts after only one cavity round trip. In the steady state the laser emits a closely spaced train of solitons. We also show that the output pulse width may be controlled by the interplay of continuous frequency shifting, bandwidth-limited amplification, and nonlinear polarization rotation of the circulating solitons. The repetition rate is fixed by means of a weak intracavity feedback. The laser is tunable by shifting of the filter wavelength through the whole spectral band of the active fiber.

Interrelation between various branches of stable solitons in dissipative systems––conjecture for stability criterion

Abstract We show that the complex cubic-quintic Ginzburg–Landau equation has a multiplicity of soliton solutions for the same set of equation parameters. They can either be stable or unstable. We show that the branches of stable solitons can be interrelated, i.e. stable solitons of one branch can be transformed into stable solitons of another branch when the parameters of the system are changed. This connection occurs via some branches of unstable solutions. The transformation occurs at the points of bifurcation. Based on these results, we propose a conjecture for a stability criterion for solitons in dissipative systems.

Continuous-wave versus pulse regime in a passively mode-locked laser with a fast saturable absorber

The phenomenon of modulation instability of continuous-wave (cw) solutions of the cubic–quintic complex Ginzburg–Landau equation is studied. It is shown that low-amplitude cw solutions are always unstable. For higher-amplitude cw solutions, there are regions of stability and regions where the cw solutions are modulationally unstable. It is found that there is an indirect relation between the stability of the soliton solutions and the modulation instability of the higher-amplitude cw solutions. However, there is no one-to-one correspondence between the two. We show that the evolution of modulationally unstable cw’s depends on the system parameters.

Interaction of dual-frequency pulses in passively mode-locked lasers

Abstract We have found, numerically, that three stable pulses of different shapes can exist in systems described by the complex Ginzburg–Landau equation, such as passively mode-locked lasers with a fast saturable absorber. At the same cavity parameter values, however, only two of them can coexist, which two depending on the particular values of the parameters. The region of existence for each pulse is investigated numerically. The interaction between each pair of pulses is studied numerically. Using the interaction plane technique, we have found stable bound states of composite pulses.

Birefringent filter synthesis by use of a digital filter design algorithm.

We present an efficient method for designing birefringent filters comprising a number of birefringent sections with equal length and arbitrary orientation between two polarizers and for producing a specified spectral response in transmission. The method uses a digital filter design algorithm (i.e., the Remez algorithm) to determine an optimal polynomial approximation to obtain a specified finite impulse response, and a layer-peeling algorithm to calculate the filter structure parameters. The design procedure is demonstrated for a 14-section bandpass filter with sidelobes below -40 dB. The influence of errors in length and orientation of the birefringent sections on the filters spectral response is also discussed.

Design and performance of high-speed optical pulse-code generators using optical fiber Bragg gratings

The application of optical fiber Bragg grating filters to all-optical pulse-code generation was investigated. We report the design, fabrication, and testing of Bragg grating structures that convert a single picosecond input pulse into a train of output pulses, each with defined amplitude and timing. Experimental results are presented in which single 1.8 ps input pulses from a mode-locked fiber laser were efficiently converted into a 1101 optical codeword comprising a train of similar pulses, each separated by 11.1 ps.

Dual-frequency pulses in fiber lasers

Summary form only given. There is a large interest in soliton generation in fiber modelocked lasers. Several types of passively modelocked lasers have been demonstrated, which include the figure-of-eight laser and the polarization mode locked laser. However the dynamics and stability of such lasers are still far from complete understanding. In our work we study the pulse propagation in a modelocked laser with fast saturable absorption, using the quintic Ginzburg-Landau equation model.

SOLITON CODING BASED ON SHAPE INVARIANT INTERACTING SOLITON PACKETS : THE THREE-SOLITON CASE

Abstract Proposed is the transmission of optical information by soliton coding based on exact N-soliton solutions of the nonlinear Schrodinger equation whose intensity profile yields N pulses that propagate without significant changes of their relative distance and amplitude. Presented is an example of a three-soliton sequence that may be generated by phase coding three equal amplitude solitons and that stably propagates in a long distance transmission system with bandwidth limited periodic amplification.

Carbon dioxide laser-assisted poling of silicate-based optical fibers.

A novel poling method, carbon dioxide laser-assisted poling (CLAP), is demonstrated. Localized heating during CLAP is achieved through silicate absorption of the CO>(2) laser radiation. Electro-optic coefficients of 0.2 pm/V are achieved within a 55-s scan of a twin-hole fiber. It is shown that there is a range of CO>(2) laser powers for which the residual electro-optic coefficient is maximized.