M.A. Fisher

Nonlinearities in semiconductor laser amplifiers

This review discusses the physical mechanisms of absorptive and dispersive nonlinearity in amplifiers resulting from interband and intraband electron transitions, with an assessment of the relative strengths and response times of these nonlinearities. Where appropriate, the potential applications of these nonlinearities in optical networks are also indicated.

Pulsed electrical operation of 1.5-μm vertical-cavity surface-emitting lasers

Vertical cavity surface emitting lasers operating in the 1.3- and 1.5-/spl mu/m wavelength ranges are highly attractive for telecommunications applications. However, they are far less well-developed than devices operating at shorter wavelengths. Pulsed electrically-injected lasing at 1.5 /spl mu/m, at temperatures up to 240 K, is demonstrated in a vertical-cavity surface-emitting laser with one epitaxial and one dielectric reflector. This is an encouraging result in the development of practical sources for optical fiber communications systems.<<ETX>>

Optical switching in the twin-guide Fabry-Perot laser amplifier

A recently developed theory of the twin-guide Fabry-Perot laser amplifier has been extended to include the case of optically induced switching. The effect of feedback from the facets serves to dramatically decrease the optical power required for switching as compared to that for a traveling-wave amplifier, but at the expense of accurate control of input wavelength. Switching is predicted at input powers on the order of microwatts, in good agreement with a first experimental demonstration of the effect. >

A novel twin-ridge-waveguide optical amplifier switch

A novel twin ridge-waveguide optical amplifier switch is reported. The technique of hydrogen passivation of acceptors has been applied to decrease the current spreading in the region between the ridges. The incorporation of a passive waveguide below the active waveguide leads to the result that using 1.53 mu m TE polarized light, through and cross states, each with only 1 dB insertion loss, fiber-to-fiber, can be selected in a device of 360 mu m length by varying the currents to each ridge with a total current of 140 mA. A minimum crosstalk of less than -33 dB was achieved when the cross state was selected. This is the first report of a twin ridge-waveguide amplifier switch with such a low-loss, low-polarization sensitivity, and low crosstalk.<<ETX>>

Bias dependent recovery time of all‐optical resonant nonlinearity in an InGaAsP/InGaAsP multiquantum well waveguide

The refractive nonlinearities due to bandfilling and the plasma effect in a multiquantum well buried heterostructure semiconductor waveguide under reverse bias are probed using self‐phase modulation techniques. Modeling of the self‐phase modulation has allowed the magnitude of the phase modulation and nonlinearity recovery time constant to be extracted. π radians phase shift has been obtained for a coupled pulse energy of 32 pJ. The nonlinearity recovery time constant is 18±3 ps for an applied field of 34 MV m−1, limited by thermionic emission from the quantum wells.

Nonlinear-optical absorption in InGaAs/InAlAs multiple quantum wells.

We have measured the room-temperature intensity dependence of the optical transmission of an In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As multiple-quantum-well structure from 1.5 to 1.7 microm. The absorption is calculated from the transmission by taking into account the wavelength dependence of the reflection coefficients. An intensityof 15 kW cm(-2) is required to reduce the absorption by one half for excitation at the edge of the 1H-lC transition absorption band. For intensities exceeding 10(7) W cm(-2), complete saturation of the absorption is observed. A theoretical model is described that fits the intensity dependence of the absorption right upto saturation at two wavelengths and predicts a carrier lifetime of 0.75 nsec, which has been confirmed by independent measurements.

Temperature dependent operation of 1.5 μm GaInAsP/InP VCSELs

VCSELs are an important technology with many characteristics such as high modulation bandwidth, low-threshold currents and single-mode behaviour that make them suitable for telecommunications applications. InGaAsP/InP is one material system that has been used to manufacture devices that operate in the 1.55 μm region. However, the room temperature performance of VCSELs using this material system fall below those devices using AlGaAs/GaAs operating at shorter wavelengths. Therefore, it is of interest to investigate the temperature dependence of these long wavelength devices. In this paper we describe the experimental results on an array of 64 InGaAsP/InP VCSELs and ultra-bright LEDs designed to emit at 1.5 μm. We also take a simple theoretical model and compare the results with theory.

GaInAsP/InP vertical-cavity surface-emitting laser for 1.5-μm operation

Long-wavelength vertical cavity surface emitting lasers (VCSELs) operating in the 1.3μm to 1.5μm wavelength range are ideal light sources for optical fibre communication applications. However, a number of problems have hindered progress in the development of cost-effective long wavelength VCSELs. These are (a) intrinsically high non-radiative losses, (b) difficulty in fabricating highly reflecting mirrors, lattice-matched to InP, and (c) the disparity between the predicted and observed temperature dependence of the operation of the devices. In this report we present the results of our studies concerning the pulsed operation of a bulk GaInAsP/InP VCSEL fabricated at BT laboratories. The device is tailored to emit at around 1.5 μm at room temperature. The structure has a 45 period n-doped GaInAsP/InP bottom Distributed Bragg Reflector (DBR), and a 4 period Si/Al 2 O 3 dielectric top reflector. Spectral electroluminescence (EL) from a 16 μm diameter window is measured in the pulsed injection mode. Device parameters are recorded in the temperature range between 90 K and 240K. Threshold current exhibits an approximate parabolic temperature dependence with a broad minimum of J th = 13.2 kA cm -2 , at temperatures between 170K and 195K. Temperature dependence of the threshold current is compared with the theoretical calculations which consider radiative transitions with and without k-selection. Best agreement with the experimental results is obtained when a partial k- selection model, with an energy broadening of about 4.4 meV, is used in the calculations.

Integrated lossless InGaAsP/InP 1-to-4 optical switch

The fabrication and performance of a 1-to-4 channel optical splitter/combiner are described. The design is based on the integration of a number of twin-guide amplifiers interconnected by active ridge waveguides. Lossless operation is seen fiber-to-fiber for all four ports for TE input light, with a 3-dB bandwidth of 20 nm. >

Effect of quantum well number on nonlinear refraction in semiconductor laser amplifiers biased at transparency

To be able to exploit these effects in a device, and hence to be able to evaluate its performance, we wish to understand the implications of the choice of device construction on the size of nonlinearity as well as other parameters such as background loss which will limit its performance. We therefore present in this paper the results of experiments on a series of devices with various numbers of quantum wells as well as bulk active regions.<<ETX>>