Vertical-cavity surface-emitting lasers (VCSELs) are known to exhibit a small birefringence and dichroism whose axes are directed along the crystal axes of the quantum wells and which fix the polarization of the oscillating light. In this paper, we consider the dynamics of the polarization of light in such a laser, extended by means of a quarter-wavelength plate in an external cavity. Periodic variations are experimentally observed. A theoretical analysis and numerical results are proposed, using a recent model which includes the carriers' spin interaction. A good match is found between experimental and numerical results.

Polarization modulation dynamics of vertical-cavity surface-emitting lasers with an extended cavity

A new form of pitchfork-bifurcation-like polarization bistability in laser diodes that has major speed advantages over conventional S-shaped polarization bistability is reported. From the rate-equation analysis, it is shown that flip-flop operation with bit rates of higher than 50 Gbits/s may be achieved.

Ultrafast switching in polarization-bistable laser diodes.

A polarization‐dependent rate‐equation model on polarization‐dependent emission characteristics of internally strained 1.3‐μm InGaAsP/InP semiconductor lasers is presented. Among the rate‐equation parameters, the polarization‐dependent gain and gain‐saturation coefficients are calculated using the density‐matrix approach and the confinement factors and loss coefficients are related to the waveguide structure. Numerical simulations show that anomalous polarization‐dependent emission characteristics can occur when the internal stress is in the 108‐dyn/cm2 order of magnitude. Various types of emission characteristics from measurements and simulations are shown and the conditions for these emission characteristics are discussed. Single‐polarization emission and two‐polarization switching, including polarization bistability, are found in the low‐stress regime and two‐polarization coexisting characteristics are found in the high‐stress regime.

Polarization‐dependent gain, gain nonlinearities, and emission characteristics of internally strained InGaAsP/InP semiconductor lasers

We numerically investigate the detailed characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback. The emission of the dominant TE mode of a drive laser is rotated 90 deg and fed back to the laser with time delay. The polarization-rotated TE mode is also injected with time delay into the TM mode of a second laser. Two types of synchronization with different time-lags are found, as in the case for synchronization in semiconductor lasers with nonrotated optical feedback. However, a significant difference to the nonrotated optical feedback case is that neither of the two types of synchronization requires matching of optical carrier frequency between the two lasers.

Characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback

The switching dynamics between TE‐ and TM‐polarization states is studied in a strained ridge‐waveguide InGaAsP/InP laser that exhibits TE/TM bistability. Using current modulation with frequencies between 50 and 500 MHz, three types of emission are distinguished. With increasing modulation amplitude, the laser runs through a region of TE emission, a range of stochastic switching between TE and TM modes, and a third region of regular polarization switching. The minimum modulation amplitude for regular switching rises strongly with frequency while the respective switching times decrease from about 700 ps at 50 MHz down to 250 ps around 500 MHz, corresponding to gigahertz mode switching.

Gigahertz switching behavior of polarization‐bistable InGaAsP/InP lasers under high‐frequency current modulation

The steady-state and transient properties of polarization-bistable semiconductor lasers are investigated, both experimentally and theoretically. An analysis based on coupled rate equations for a two-mode system with unequal gain/current characteristics is presented. The simple rate-equation model explains the general features of the observed bistable-switching behaviour. The condition for the existence of polarization bistability is determined using laser parameters.

J. M. Liu

Papers

Switching mechanism in polarization-bistable semiconductor lasers