S. D. Brorson

Monolithic colliding pulse mode-locked semiconductor lasers

In this paper we investigate the temporal and spectral properties of monolithic colliding pulse mode-locked (CPM) quantum-well lasers. A large-signal model for the CPM laser is derived, which explains the mode-locking behaviour of both passively and hybridly mode-locked CPM lasers. The pulse-shaping and wavelength chirp of the CPM pulses are found to be the result of a complicated interplay between the gain and saturable absorber dynamics. The experimentally measured pulse width dependence upon variation of gain current and applied reverse bias on the saturable absorber is explained by fast gain dynamics. The experimentally observed broadening of the optical power spectrum with gain current is found mainly to be due to the self-phase modulation in the gain sections.

Time resolved four‐wave mixing technique to measure the ultrafast coherent dynamics in semiconductor optical amplifiers

A femtosecond four‐wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background‐free quasi‐degenerate four‐wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs.

Synchronization phase diagrams of monolithic colliding pulse-modelocked lasers

We present phase diagrams of colliding pulse mode locked (CPM) InGaAsP QW laser operation relevant to the ability to synchronize the repetition rate to an external clock. A three-dimensional parameter space of gain currents, absorber bias, and RF frequency is explored using an automated test set up. We find regions of modelocking, self-pulsation, and incomplete modelocking/CW lasing. We show that the modelocked region is asymmetric in RF frequency; i.e., the pulse repetition rate can be slowed down more easily than speeded up.

Chirp of monolithic colliding pulse mode-locked diode lasers

Spectrally resolved streak camera measurements of picosecond pulses emitted by hybridly colliding pulse mode-locked (CPM) laser diodes are presented in this letter. Depending on the modulation frequency both blue-chirped (upchirped) and red-chirped (downchirped) pulses can be observed. The two different regimes and the transition between them are characterized experimentally and the behavior is explained on the basis of our model for the CPM laser dynamics.

Temporal and spectral dynamics in multiquantum-well semiconductor saturable absorbers

Performing femtosecond pump-probe measurements on multiquantum-well (MQW) semiconductor saturable absorbers we find a strong spectral dependence of the absorption dynamics on a picosecond time scale. While for long wavelengths a pump pulse induced reduction of the absorption is observed, at short wavelengths the absorption increases due to the pump. We explain this behavior on the basis of a model including photo-induced field screening.

Subpicosecond heterodyne four-wave mixing experiments on InGaAsP semiconductor laser amplifiers

Abstract We give a detailed description of a recently proposed femtosecond heterodyne four-wave mixing experiment to investigate ultrafast coherent dynamics in waveguides and discuss similarities to femtosecond heterodyne pump-probe experiments. We demonstrate and discuss the potential and the limitations of the new technique on the basis of first experiments. Examples of measurements on an InGaAsP semiconductor amplifier are presented, that include transient four-wave mixing between pulses of the same and of orthogonal polarisations. Implications of our four-wave mixing results on the ultrafast dynamics in semiconductor amplifiers are discussed.

Modeling and characterization of colliding pulse mode-locked (CPM) quantum well lasers

A theoretical and experimental study of passive colliding pulse mode-locked quantum well lasers is presented. The theoretical model for the gain dynamics is based on semi-classical density matrix equations. The gain dynamics are characterized experimentally by pump-probe experiments and compared with theory. The mode-locked pulse width dependence upon dispersion, gain current and absorber bias is presented and compared with experimental results.

Microcavity Effects in Er3+-Doped Optical Fibres

As is now well known, the spontaneous emission lifetime of an excited atom can be altered if the atome is situated inside a small optical cavity (microcavity). Spontaneous emission is due to the interaction between the excited atom and the vacuum field. The transition rate (and thereby the lifetime of the atom) is given by Fermi’s Golden Rule[1].