Analysis and optimization of InGaAsP electro-absorption modulators

A numerical model of bulk electro-absorption modulators has been developed based on a quasi-two-dimensional drift-diffusion approach which includes both the presence of heterostructures and the Fermi statistics for the carriers. We show that the nonlinear behavior of this type of devices is essentially related to hole pile-up and space-charge effects. The simulation results compare favourably with some laboratory measurements on a fabricated device with abrupt hetero-junctions. Two other types of structures have been simulated, one obtained with the inclusion of a thin quaternary layer and the other with a, graded hetero-junction, which eliminate the hole pile-up at the InGaAsP-InP hetero-interface. The paper demonstrates that it is possible to approach the optimum behavior using both the alternatives considered here. Finally, nonlinear effects in short modulators have been investigated     

Switch energy analysis of quantum interference directional couplers

Electronic quantum interference (QI) directional coupler switches are analyzed in terms of switching voltages, energies, and speeds and shown to be superior to present electronic switches. Comparisons with thermal and quantum limits are carried out. It is shown that the QI directional coupler (and smaller devices) is superior to present electronic devices in regard to switch energy: the latter have E_SW on the order of 60000 eV compared to the ≈4 eV derived for the QI directional coupler     

Influence of molecular tilt angle on the SHG response of pyroelectric liquid crystal polymers

Second harmonic generation in novel pyroelectric liquid crystal polymers (PLCP) made from a series binary mixtures, was studied using 1100 nm as the fundamental wavelength. The PLCPs were prepared by photo-polymerization of binary mixtures of two monomers which exhibit a smectic C^* phase, A2c (4″-(R)-(−)-2-[(10-acrylo-yloxy)decyl]oxy-3-nitrophenyl 4-{4′-[(11-acryloyloxy)-undecyloxy]phenyl}benzoate) and Alb (4″-((R)-(+)-2-octyloxy)-3″-nitrophenyl 4-(4′-(11-acryloyloxy)undecyloxy)-phenyl)-benzoate). The highest d₁₆ and d₂₃ coefficients were found to be in the range 0.65–0.8 pm/V, and differed depending on the detailed preparation of the sample. All cases of polymers formed from the chiral smectic C* phase showed an SHG-signal with no external field present, indicating that polar order became fixed. The SHG-signal was found to increase with the tilt angle of the FLC molecules.     

Active DBR filters for 2.5 Gb/s operation: linewidth, crosstalk,noise, and saturation properties

The design of four-section distributed Bragg reflector (DBR) laser filters, for application in wavelength multiplexed systems with a 2.5 Gb/s bit rate on each wavelength channel, has been analyzed. The results of the analysis indicate that optimized filters will support at least 10 channels and will have a dynamic range exceeding 10 dB. Bit error rate (BER) measurements on three-section DBR filters in a 2.4 Gb/s system experiment support this conclusion     

Fast turnoff in optical switching of low-finesse GaAs Etalonsoperating in reflection

Subnanosecond switch-off times have been found in nonlinear GaAs Fabry-Perot etalons operating in reflection. Both pump and probe beams had photon energies exceeding the bandgap energy in GaAs. A laser diode was used as pump source     

Switch energy requirements for first- and second-orderperturbations in asymmetric quantum box optical switches

We have studied the limits to the switching energy of electrically controlled optical absorption switches. Investigating a case with intraband transitions in asymmetric quantum boxes, it is shown that linear Stark shift allows switch energies of the optical switches that are comparable to the thermal noise limit at 300 K at least up to 30 GHz, provided boxes with very narrow absorption linewidth can be fabricated. This is several orders of magnitude lower energy than required by quadratic Stark shift in a similar, symmetric structure     

A transport network layer based on optical network elements

An approach to the realization of a broadband, flexible, multiwavelength transport network employing an optical network layer. The design methodology for a network demonstrator is presented, and the transmission, switching, line, and management/supervisory subsystems and components are described     

Two-channel optical filtering of 1 Gbit/s signal with DBR filter

Distributed Bragg reflector (DBR) lasers have been used as tunable, narrow-band, amplifying optical filters and as tunable oscillators in two-channel, system experiments. A bit error rate of 10/sup -9/ with -25 dBm input power has been measured at 1 Gbit/s signal rate.<>     

Tapered, resonant DBR transmission filters

Wavelength-tunable optical filters, in the form of resonant distributed Bragg reflector laser filters, have been fabricated and evaluated. The devices are specially designed as transmission filters and have a novel structure, using low coupling strength in the grating and an up-tapered active section, in order to improve the crosstalk performance and the saturation properties. Fabricated devices have 6-8-dB dynamic range and would give less than 1-dB crosstalk penalty in four-channel systems at 13-dB chip gain. System experiments with two 2-Gb/s channels are reported     

Evaluation of an automatic method to extract the grating couplingcoefficient in different types of fabricated DFB lasers

Distributed feedback (DFB) laser parameters such as grating coupling coefficient, effective indices, facet reflectances, and the phases of facet reflectances have been determined using a method based on least-square fitting of theoretical spectra to measured, subthreshold DFB laser emission spectra. The only inputs needed are geometrical parameters such as length, grating period, and internal grating phase shifts. A larger number of devices have been successfully characterized, and consistent results have been obtained in both 1.3-μm multi-quantum-well (MQW) DFB lasers with both facets as-cleaved, and in 1.55-μm MQW DFB lasers with no, one, or two facets as-cleaved