Virtual Journal of Laser

We describe a detailed model for carrier dynamics in tunneling injection quantum dot lasers. The model includes the spatial dependence of the mobile carriers and the coupling between mobile carriers and confined carriers. The Poisson and Schrodinger equations are solved together, which enables consideration of band structure modification due to an electron-hole interaction. The model is solved both in steady state and for temporal perturbations. Steady-state carrier distributions and the band structure are presented, as well as large and small signal modulation responses.

In this paper, we investigate the modal behavior and the spatial coherence properties of a gain-guided laser array emitting an optical output power of more than 50 W in quasi-continuous-wave operation at a wavelength of 1070 nm and above. The lateral near- and far-field intensity profiles and the Wigner distribution function were measured from low to high output power. The array modes were calculated by solving the waveguide equation taking into account the power-dependent temperature distribution and were also experimentally determined by a modal decomposition of the cross spectral density. The analysis revealed that, at a low power, a single array mode lases, whereas at high power, multiple single stripe modes dominate the lasing due to the thermally induced index rise under the stripes.

We demonstrate experimentally the stable continuous-wave (CW) single-mode operation of Bragg reflection waveguide (BRW) lasers from 10 to 100
$^{circ}{rm C}$. The threshold characteristics, quantum efficiency, gain, and self-heating characteristics are investigated in detail. Threefold enhancement in the optical confinement is achieved using these BRW structures for a core width two times that of their edge-emitting total internal reflection counterparts. The device shows also the high gain and characteristic temperature
$({sim}197~{rm K})$ under CW operation from 10 to 100
$^{circ}{rm C}$. The mode stability is analyzed by the calculated mode reflection spectrum, injection-current-dependent lasing spectrum, and near-field patterns.

Scalable 980-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL) arrays capable of both high output power and high modulation frequency have been fabricated and characterized. DC measurement of an array with 28 elements shows that the array operates at continuous wave (CW) powers over 200 mW at a bias current of 875 mA. AC frequency response and pulse measurements of the array give a maximum 3 dB bandwidth of 7.6 GHz and gain-switched output pulses as short as 60 ps full-width at half-maximum. Uniform current and temperature distributions verified by the radial dependence of bandwidth and wavelength show that copper plating of the array elements and flip-chip bonding provide effective thermal management for the arrays.

We propose a tunable erbium doped fiber laser based on a Fabry-Pérot (F-P) cavity tuned by an electrostatic actuator. The device is made of single crystalline silicon. The F-P cavity consists of two Bragg mirrors, one being displaced by a comb-drives actuator. The F-P cavity, grooves for optical fibers and electro-mechanical structure are fabricated by deep reactive ion etching on a 70
$mu{rm m}$ silicon on insulator wafer and are integrated in a ring fiber laser. The resulting tunable fiber laser has a tuning range of 35 nm in the C-band and a spectral width of less than 0.06 nm. The maximum applied voltage for full tuning of the laser is 37 V. The mechanical resonance frequency of the actuated mirror is 14.4 kHz allowing fast tuning of the laser. The maximum output power is 1.8 mW.

We make a systematic study to find the dependence of the threshold current density of a mid-infrared quantum-cascade laser on the waveguide ridge width. The optical and thermal parameters of the waveguide are calculated with a finite-element method, and gain is found from a self-consistent rate equation model with energy-balance. The results show the existence of an optimal ridge width that minimizes the threshold current density of the laser. The influence of the interface roughness parameters on laser performance is also discussed.

This paper analyzes a model of a transition radiation laser based on stimulated emission induced by relativistic electrons crossing the boundary between two media of different dielectric properties. Interaction between the incident radiation and the electrons in this boundary region is taken into account. Phenomenological quantum electrodynamics is applied to derive analytical expressions for stimulated emission and absorption probabilities. Analogs of Einstein's coefficients for the transition processes have also been derived and discussed. It is shown that stimulated emission is greater than absorption. The gain is then calculated.

A chemical gas-phase reaction between
${rm Cl}_{2}$ and HI was used in the generation of molecular iodine for the chemical oxygen-iodine laser (COIL) operation. A yield of
${rm I}_{2}$ in the generation reaction up to 85% was achieved in a reasonable volume of the reactor. A small-signal gain up to 0.75%/cm at a temperature of 150 K in the center of supersonic cavity was measured. A comparison with the established evaporation way of
${rm I}_{2}$ delivery confirmed that the chemical method has little or no impact on the COIL pumping kinetics. This chemical method is easily scalable and can simplify the COIL operation by providing better control of
${rm I}_{2}$ flow rate.

In this paper, precise synchronization of the femtosecond and picosecond laser regenerative amplifiers with different wavelengths and independent seed oscillators was achieved using the electronic phase-locked loop and global clock techniques. The root-mean-square relative timing jitter of the two regenerative amplifiers was measured as 0.66 ps using a modified statistical method based on the error propagation relation between the independent variables and the conventional optical cross-correlation technique. The results suggest that this method is more accurate and requires simple optical setups for low-pulse repetition rate lasers.

The dynamics of a distributed Bragg reflector laser with optical losses in the Bragg section is studied in detail. It is found that the modulation response depends not only on the detuning of the lasing wavelength from the Bragg reflectivity peak but also on the magnitude of the waveguide losses in the Bragg section. Depending on the losses, the damping of the relaxation peak can either increase or decrease when the laser is detuned on the long wavelength flank of the Bragg peak. Hence, in order to achieve maximum modulation bandwidth of the laser, the laser needs not only to have the correct detuning but also an optimized waveguide loss in the Bragg section. The physical reason for this dependence is discussed in terms of a modified rate equation model.