Coupled-wave formalism for optical waveguiding by transverse Bragg reflection

A formalism is presented for optical waveguiding by means of Bragg reflection. The theory provides analytic expressions for field modal profiles, dispersion, and attenuation. Waveguiding in line defects of photonic bandgap crystals, a special case of the theory, is used as an example. Quantized allowed widths of the guiding channel are predicted.     

High-power and high-frequency operation of InGaAsP/InP lasers at 1.3 μm

A simultaneous operation of a semiconductor laser at high power and high speed was demonstrated in a buried crescent laser on p-InP substrate. In a cavity length of 300 μm, a maximum continuous wave (CW) power of 130 mW at room temperature was obtained in a junction-up mounting configuration. A 3dB bandwidth in excess of 12 GHz at an output power of 52 mW was observed.     

Phase transition in a system of one-dimensional bosons with strong disorder

We study one-dimensional disordered bosons at large commensurate filling. Using a real space renormalization group approach, we find a new random fixed point which controls a phase transition from a superfluid to an incompressible Mott glass. The transition can be tuned by changing the disorder distribution even with vanishing interactions. We derive the properties of the transition, which suggest that it is in the Kosterlitz-Thouless universality class.     

Low-threshold two-dimensional annular Bragg lasers

Lasing at telecommunication wavelengths from annular resonators employing radial Bragg reflectors is demonstrated at room temperature under pulsed optical pumping. Submilliwatt pump threshold levels are observed for resonators with 0.5-1.5-wavelength-wide defects of radii 7-8 microm. The quality factors of the resonator modal fields are estimated to be of the order of a few thousand. The electromagnetic field is shown to be guided by the defect. Good agreement is found between the measured and the calculated spectra.     

Nonparaxial spatial solitons and propagation-invariant pattern solutions in optical Kerr media

We investigate nonlinear propagation in the presence of the optical Kerr effect by relying on a rigorous generalization of the standard parabolic equation that includes nonparaxial and vectorial terms. We show that, in the (1 + 1)-D case, both soliton and propagation-invariant pattern solutions exist (while the standard hyperbolic-secant function is not a solution).     

Griffiths singularities in unbinding of strongly disordered polymers

Griffiths singularities occurring in the unbinding of strongly disordered heteropolymers are studied. A model with two randomly distributed binding energies, -1 and -v, is introduced and studied analytically by analyzing the Lee-Yang zeros of the partition sum. It is demonstrated that in the limit v--> infinity the model exhibits a Griffiths type singularity at a temperature T(G)=O(1) corresponding to melting of long homogeneous domains of the low binding energy. For finite v>1 the model is expected to exhibit an additional, unbinding, transition at a high temperature T(M)=O(v).     

High-quality-factor Bragg onion resonators with omnidirectional reflector cladding

We propose to approximate a spherically symmetric Bragg resonator in an onionlike geometry. We develop a transfer-matrix theory for calculation of the quality factors and analyze the effect of the onion stem on cavity Q factors. We find that it is possible to achieve significant inhibition of spontaneous emission in an onion resonator with omnidirectional cladding layers.     

Applications of a dielectric coating to semiconductor lasers

Experimental studies and theoretical analyses on the effect of dielectric coatings on semiconductor laser performance are presented. It is demonstrated that the dielectric coating technique is a powerful means of controlling the laser threshold current, external quantum efficiency, maximum output power, longitudinal mode behaviour, lasing wavelength and spectral linewidth.     

Time evolution of the pulsed HF chemical laser system. II. Irreversible thermodynamic analysis

The time rates of change of level populations and radiation densities derived from a detailed kinetic model of the F + H₂ → HF + H laser are employed as input data for a time dependent thermodynamic analysis of this system. The laser is regarded as an irreversible heat engine generating thermodynamic work in the form of laser light. The development in time of the thermodynamic functions, efficiency and irreversible entropy production is determined by computing the contributions of pumping, radiation and relaxation to the entropy and energy of the lasing molecules. Effects of specific rate processes are evaluated by considering different kinetic schemes, i.e. different combinations of kinetic processes and initial conditions. It is shown, among others, that a laser without relaxation processes (“frictionless”) has poor efficiency despite the absence of energy losses and the low irreversible entropy production. On the other hand, the efficiency is high in lasers governed by fast rotational relaxation. This is because rotational relaxation, though leading to some energy losses and irreversible entropy production, compensates for the entropy decrease of the system (while lasing under partially inverted populations) by increasing the bath entropy. The major general conclusion of the analysis is that the thermodynamic constraints related to the kinetic scheme and not the extent of irreversibility of the lasing process is the crucial factor in determining the laser efficiency.     

Statistical determination of the length dependence of high-order polarization mode dispersion

We describe a method of characterizing high-order polarization mode dispersion (PMD). Using a new expansion to approximate the Jones matrix of a polarization-dispersive medium, we study the length dependence of high-order PMD to the fourth order. A simple rule for the asymptotic behavior of PMD for short and long fibers is found. It is also shown that, in long fibers (~1000 km), at 40 Gbits/s the third- and fourth-order PMD may become comparable to the second-order PMD.