Abstract:We provide a detailed theoretical investigation of two-photon absorption photoconductivity in semiconductor microcavities. We show that a high enhancement of the non-linear response (>10000) can be obtained due to the microcavity effect. We discuss in detail the design and performance (dynamic range, speed) of such a device with the help of an example of a AlGaAs/GaAs microcavity operating at 900nm. This device is promising for low intensity fast autocorrelation and demultiplexing applications.

We report on two-photon absorption ͑TPA͒ photocurrent in semiconductor microcavities. We experimentally show a substantial increase in the TPA photocurrent generated, at resonance, in a GaAlAs/GaAs microcavity designed for TPA operation at ϳ890 nm. An enhancement factor of ϳ12 000 of the photocurrent is obtained via the microcavity effect, which could have an important impact on the use of TPA devices for high speed switching and sampling applications. Our results also show the implications of the cavity photon lifetime on autocorrelation traces measured using TPA in semiconductor microcavities. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1455694͔ Two-photon absorption ͑TPA͒ in semiconductors has recently been shown to be a serious candidate for optical autocorrelation of short pulses and for all-optical switching and sampling of high speed optical data signals in optical time division multiplexed ͑OTDM͒ systems. Experiments using TPA for these applications have been performed at many different wavelengths, using different types of semiconductor devices.1-3 However, because TPA is a very inefficient nonlinear process, it usually requires high intensity lasers or very long detectors, which could make the TPA nonlinearity unsuitable for use in practical autocorrelators and in optical switches and sampling devices for real telecommunication systems.The use of a Fabry-Pérot microcavity greatly enhances the optical intensity and thus increases the nonlinear response of the embedded material. This was recently demonstrated 4 and the optical Stark ( 3 ) effect was shown to be responsible for the high instantaneous reflectivity modulation.We show here that by using a Fabry-Pérot microcavity, it is possible to greatly enhance the TPA photocurrent. We actually demonstrate that our active length of 0.27 m is as efficient as 5.4 mm without a microcavity. A detailed theoretical study has already been undertaken, 5 so we focus here on the more technological aspects of the device. A similar effect has previously been shown in an organic material, aminopurine, 6 but the enhancement factor was only ϳ120 even though high reflectivity mirrors were used. One explanation for this lies in the fact that very short ͑100 fs͒ pulses were used which made them spectrally very broad compared with the cavity bandwidth, thus only a small fraction of the spectral range of the pulse is enhanced.The device studied for TPA absorption is a GaAlAs PIN microcavity photodetector grown on a ͑001͒ GaAs ͑tilted 3°͒ substrate. It comprises a 0.27 m Ga 0.7 Al 0.3 As active region embedded between two Ga 0.5 Al 0.5 As/AlAs Bragg mirrors. The front p doped (Cϳ10 18 cm Ϫ3 ) mirror consists of 15.5 pairs, while the back n (Siϳ10 18 cm Ϫ3 ) mirror contains 35.5 pairs designed for high reflectivity at 880 nm. The cavity resonance was measured at 890 nm and the reflectivity spectrum was in very good agreement with the simulations ͑the small discrepancies could be explained by small, a few Å, fluctuations in the layer thickness͒. The device was designed...

Two polarization-independent Michelson fiber interferometers with different optical delays were used to measure the in-band OSNR of an optical signal from 5 to 30dB within an accuracy of 0.5dB. Using an expansion of the amplitude autocorrelation function of the signal around zero delay, it was possible to perform measurements without any prior knowledge of the signal. The system is shown to be immune to the effects of modulation frequency (up to 10G), partially and fully polarized noise, chromatic dispersion and poorly biased modulators.

The re-growth free single mode lasers based on etched slots suitable for photonic integration are presented in this paper. The fabricated 650 μm long laser exhibits a threshold current and a slope efficiency of about 32 mA and 0.12 mW/mA, respectively. The stable single mode operation has been observed with a side mode suppression ratio (SMSR) over 50 dB at a current injection of 100 mA for the fabricated laser. Such a laser integrated with electroabsorption (EA) modulator is also demonstrated. The integrated device has an extinction ratio over 10 dB at 2.2V driving voltage with the lasing wavelength of around 20 nm positive detuning relative to the gain peak. The bandwidth measured is about 3 GHz for the integrated device.

Abstract-A GaAs-AlAs microcavity device has been used as a photodetector in an autocorrelator for measuring the temporal pulsewidth of 1.5-m optical pulses. Enhancement of the two-photon absorption photocurrent due to the microcavity structure results in an autocorrelation (average power times peak power) sensitivity of 9 3 10 4 (mW) 2 , which represents two orders of magnitude improvement when compared with conventional autocorrelators.