Theoretical analysis of pulse development in a colliding pulse mode-locked dye laser

The pulse development in colliding pulse mode-locked dye lasers is analysed theoretically. The chosen parameters belong to a c.w. argon laser pumped linear resonator arrangement with rhodamine 6G in ethylene glycol as gain medium and DODCI (3,3-diethyloxadicarbocyanine iodide) in ethylene glycol as saturable absorber. The pulse shortening and pulse broadening effects in the laser oscillator are investigated. The steady-state pulse duration is determined by equal pulse broadening and pulse shortening within a single resonator round-trip. The detuning of the absorber jet out of the middle position of the resonator is considered. Multiple transits through the resonator are simulated to study the influence of various resonator and dye parameters on the pulse development and the background signal suppression. Fast relaxations within theS ₁ andS ₀-state of DODCI are necessary for sufficient background suppression to obtain femtosecond pulse trains.     

Generation and stabilization of ultrafast optical pulse trains with monolithic mode-locked laser diodes

In this paper, we report on the generation and the stabilization of ultrafast optical pulse trains exceeding 100 GHz from monolithic mode-locked laser diodes (MLLDs) combined with some new techniques such as subharmonic synchronous mode-locking (SSML) and repetition-frequency multiplication (RFM) method. Key subjects to increase the pulse repetition frequencies of the MLLDs such as fast absorption recovery and harmonic mode-locking operation are discussed. 500 GHz optical pulse generation from a short-cavity, graded-index separated confinement heterostructure MLLD and THz-rate pulse generation by harmonic mode-locking are reported. We also demonstrate the stabilization of a 160 GHz MLLD by the SSML with subharmonic-frequency optical pulse injection and reveal that the SSML is very promising as a stabilization technique of the ultrafast MLLD beyond the limitations by the electronic device speed. A method to accurately measure the timing jitter of such ultrafast optical pulse train, all-optical down converting using a nonlinear optical device, is also presented. We also mention another choice for ultrafast optical pulse generation using the MLLD combined with a dispersive medium such as an optical fiber. We demonstrate here the generations of stable 84–256 GHz optical pulse trains by the RFM method of the MLLD stabilized by the SSML.     

Gigahertz repetition rate mode-locked Yb:KYW laser using self-assembled quantum dot saturable absorber

Fundamental mode-locking is achieved in a 1.036 GHz cavity using a semiconductor quantum dot saturable absorber mirror with a fast relaxation time component of down to 550 fs. The dispersive cavity delivers 1.7 ps wide pulses with spectra supporting sub-picosecond pulse durations and an M² of 1.3. An average output power of up to 339 mW at wavelengths around 1,032 nm is achieved and the saturable absorber’s damage threshold is identified as a limitation for further power scaling.     

Optical absorptions of a biexciton quantum dot

A investigation of the linear and nonlinear optical properties for intersubband electronic transitions associated with a biexciton in a quantum dot has been performed by using the method of few-body physics. The optical absorption coefficients and the refractive index changes have been examined based on the computed energies and wave functions. It is over two orders of magnitude higher than that obtained in an exciton quantum dot. The results show that the optical absorption saturation intensity can be controlled by the confinement potential frequency and the relaxation time.     

490 fs pulse generation from a passive C-band AlGaInAs/InP quantum well mode-locked laser

We report femtosecond pulses from a passive C-band two-section AlGaInAs/InP mode-locked laser with a monolithically integrated passive waveguide made by quantum well intermixing. Without any external pulse compression, Lorentzian pulses are generated at a repetition frequency of ~38 GHz with 490 fs pulse duration, which is, to the best of our knowledge, the shortest pulse from any directly electrically pumped quantum well semiconductor mode-locked laser. The mode-locking range is relatively large and the ultranarrow pulse width is very stable over a broad range of driving conditions.     

Optical properties of a magneto-donor in a quantum dot

The temperature-dependent magnetoresistance effect is investigated in a magnetically modulated two-dimensional (2D) electron gas (2DEG) which can be realized by depositing two parallel ferromagnets on top of a 2DEG electron gas. In the resonant tunnelling regime the transmission for the parallel and antiparallel magnetization configurations shows a quite distinct dependence on the longitudinal wave vector of the incident electrons. This leads to a very large magneto resistance ratio with a strong temperature dependence.     

Optical transitions in parabolic quantum dot

Direct optical absorption of light is theoretically investigated in a spherical quantum dot from GaAs. The confinement potential of the dot is approximated as parabolic. Three regimes of size quantization are discussed: weak, strong, and intermediate. The corresponding threshold frequencies of absorption are determined. A comparison with the case of a spherical quantum dot with rectangular infinitely high confinement potential is performed.     

Synchronization and clustering in a multimode quantum dot laser

We analyze experimentally the intensity oscillations of the longitudinal modes of quantum dot semiconductor lasers. We show that the modal intensities can oscillate chaotically with different average frequencies, but obey a highly organized antiphase dynamics leading to a constant total output power. The fluctuations are in the MHz range. We report the first experimental observation of frequency clustering associated with synchronization. We also observe the propagation of perturbations across the optical spectrum from blue to red.     

Femtosecond pulse generation in a linear passive mode-locked dye laser

The femtosecond pulse generation in a c.w. pumped linear passive mode-locked rhodamine 6G-DODCI (3,3-diethyloxadicarbo cyanine iodide) dye laser is studied experimentally. Colliding pulse mode-locking (CPM) is achieved by placing the saturable absorber jet in the centre of the linear ring resonator. The laser performance is studied as a function of the saturable absorber concentration and of the absorber jet detuning from the central position (CPM position). Without a prism pair in the resonator pulse durations down to 140 fs were obtained. Detuning the absorber jet from the CPM position resulted in a trailing pulse tail ofcirca 900 fs duration. The dependence of the laser performance on the prism pair positioning is investigated experimentally and analysed theoretically. At the prism pair balanced position, stable pulses of about 50 fs duration were generated independent of the lateral detuning of the absorber jet out of the resonator centre. The dependence of the laser wavelength on the absorber concentration is compared with theoretical predictions. In an appendix the ray-tracing inside the linear resonator is simulated by an ABCD matrix calculation for Gaussian beams.     

Suppression of Q-switching instabilities in broadened-waveguide monolithic mode-locked laser diodes

It is predicted theoretically that broadening the optical confinement layer in monolithic mode-locked semiconductor lasers may suppress Q-switching instability, by increasing the carrier transport time, and lead to emission of shorter, more stable optical pulses.     

High frequency pulse trains from a self-starting additive pulse mode-locked all-fiber laser

In this paper, a coupled-cavity Er-doped fiber laser is experimentally developed and analyzed. The proposed scheme has the advantage of an all-fiber configuration. Two similar fiber Bragg gratings are employed as reflective components of the main cavity containing the gain medium. The second cavity is generated, in one side, by the reflective flat end of a standard fiber optic pigtail of variable length and, in the other, by one of the Bragg gratings belonging to the main cavity. Depending on the ratio between the lengths of both cavities, trains of stable and short pulses were obtained with a repetition frequency larger than the frequency of the main cavity. The repetition rate of the pulse trains experimentally obtained was as high as 780 MHz (15 times the main cavity frequency) and the pulse width was ∼110 ps. Prediction of the possible repetition rates for each cavities lengths ratio and the upgrading possibilities of this laser system are analyzed.     

Optical solitons in semiconductor quantum dot waveguides

A theory of self-induced transparency for a TM-mode propagating in a planar semiconductor waveguide sandwiched between two dielectric media is developed. A transition layer between the waveguide and one of the connected media is described using a model of a two-dimensional sheet of quantum dots. Explicit analytical expressions for the optical soliton in the presence of single-excitonic and biexcitonic transitions are obtained with realistic parameters which can be reached in current experiments.     

Near-infrared subpicosecond pulse generation in a synchronously mode-locked cw dye laser

Tunable subpicosecond pulses have been obtained from a synchronously mode-locked Oxazine-1 dye laser by tandem pumping with output pulses of a mode-locked Rhodamine 6G dye laser. The effects of cavity detuning on the pulse-width and the second harmonic power (the peak intensity of the autocorrelation trace) have been investigated. The experimental results are found to be in good agreement with those predicted by a recent model analysis.     

Nearly transform-limited optical pulse from a passively mode-locked laser diode

An optical ultra-short pulse train with a duration of 2.9 ps was successfully generated from a passively mode-locked laser diode. The time-bandwidth product was 0.43, and it was very close to the transformlimited value of a Gaussian waveform. The highest peak power of 10 mW in an InP-based passively mode-locked laser has been achieved. The laser is promisng as an optical source for an ultra-high-speed bit rate transmission system, especially for the optical time division multiplexing (OTDM) system.     

Optical detection of single-electron spin resonance in a quantum dot

We demonstrate optically detected spin resonance of a single electron confined to a self-assembled quantum dot. The dot is rendered dark by resonant optical pumping of the spin with a laser. Contrast is restored by applying a radio frequency (rf) magnetic field at the spin resonance. The scheme is sensitive even to rf fields of just a few microT. In one case, the spin resonance behaves as a driven 3-level lambda system with weak damping; in another one, the dot exhibits remarkably strong (67% signal recovery) and narrow (0.34 MHz) spin resonances with fluctuating resonant positions, evidence of unusual dynamic processes.     

Optical properties of impurity-bound polaron in a parabolic quantum dot

The linear and nonlinear optical properties of an electron, which is bounded to a Coulomb impurity in a polar semiconductor quantum dot with parabolic confinement in both two and three dimensions, are studied by using the Landau-Pekar variational method and the compact density-matrix approach. With typical semiconducting GaAs-based materials, the linear, third-order nonlinear, total optical absorption coefficients and refractive indexes have been examined. We find that the all absorption spectra and refractive index changes are strongly affected by the electron-LO-phonon interaction. The results also indicate that the polaron effect increases with decreasing dimensionality of a quantum dot.     

A stability criterion for mode-locked pulses in a laser oscillator

A stability criterion for the self-pulsing laser oscillator is derived from the numerical analysis of a mathematical model previously described. A numerical solution for the pulse shape is also presented.     

Analysis and simulation of a coupled-cavity pulse compressor

An equivalent circuit model is built for a coupled-resonator pulse compressor. Based on the circuit, the general second order differential equation is derived and converted into the first order equation to save computing time. In order to analyze the transient response and optimize parameters for the pulse compressor, we have developed a simulation code. In addition, we have also designed a three-cavity pulse compressor to get the maximum energy multiplication factor. The size of the cavities and coupling apertures is determined by HFSS.