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Quantum Electronics and Laser Science Conference

fs photon-number squeezed light generation in a semiconductor waveguide via spectral filtering

M. B. Ward, Bernd Kästner, Heongkyu Ju, G.-M. Schucan, J.F. Ryan, A. M. Fox, James Stewart Aitchison, C. N. Ironside

Published May 12, 2000• 0 citations
OpenAlex

Abstract

Summary form only given. Several experiments have been performed in optical fibers to generate photon-number squeezed pulses of light. Among these, are experiments employing a spectral filter to exploit the spectral correlations created during pulse propagation along a fiber. We recently reported the generation of photon-number squeezing in an AlGaAs waveguide as a result of multi-photon absorption and we now extend this work to show an increase in the degree of squeezing obtained with appropriate spectral filtering. Unlike much of the fiber work, which used long propagation distances, the results here are produced in a 2-mm-long semiconductor waveguide. The waveguide structure is composed of AlGaAs grown on a GaAs substrate and consisted of a l /spl mu/mm planar high-index waveguiding layer with lateral confinement provided by a surface rib. The estimated effective modal area is 6 /spl mu/m/sup 2/.

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Conference on Lasers and Electro-Optics•Nov 27, 2002•1 citation
Summary form only given. Several experiments have been performed in optical fibers to generate photon-number squeezed pulses of light. Among these, are experiments employing a spectral filter to exploit the spectral correlations created during pulse propagation along a fiber. We recently reported the generation of photon-number squeezing in an AlGaAs waveguide as a result of multi-photon absorption and we now extend this work to show an increase in the degree of squeezing obtained with appropriate spectral filtering. Unlike much of the fiber work, which used long propagation distances, the results here are produced in a 2-mm-long semiconductor waveguide. The waveguide structure is composed of AlGaAs grown on a GaAs substrate and consisted of a l /spl mu/mm planar high-index waveguiding layer with lateral confinement provided by a surface rib. The estimated effective modal area is 6 /spl mu/m/sup 2/.
Summary form only given. Photon-number squeezing can occur in semiconductor waveguides due to multiphoton absorption. Previous work has been extended to demonstrate an increase in the degree of squeezing as a result of spectral filtering. In contrast to previous experiments, which were performed in long optical fibres, the results are produced in a 2 mm AlGaAs semiconductor waveguide. The results are discussed in terms of spectra correlations induced by self-phase modulation. The photon-number distribution of the output beam is then dependent on the correlations preserved by the spectral filter.
Summary form only given.We describe numerical and experimental investigations of the use of soliton spectral filtering in the spatial domain. As is well known, the nonlinear Schrodinger equation description of optical soliton propagation in single-mode fibers applies equally well to spatial solitons in nonlinear planar waveguides. Therefore, we can expect that the photon-number squeezing methods that work for temporal solitons in optical fibers apply equally well to spatial solitons. The spatial-soliton equivalent of spectral filtering is to use a spatial slit to remove the edge portions of the spatial soliton after it emerges from the planar waveguide. To optimize the experimental configuration, we have modeled the spatial-soliton propagation using a numerical quantum propagation code. Our results show that optimal squeezing is obtained at propagation distances of several soliton periods for solitons with the order N/spl sim/1.2. To experimentally demonstrate photon number squeezing by spatial filtering of spatial solitons, we have fabricated an AlGaAs planar waveguide that is 1.5 /spl mu/m thick and 1-3 cm long. For our device, the bandgap is in the vicinity of 0.8 /spl mu/m, so by using short pulses from a color-center laser tuned to 1.5- to 1.6-/spl mu/m wavelengths, we can excite reasonably large nonlinearities due to two-photon and three-photon resonances in the bandgap. This allows us to create spatial solitons. Spatial solitons created by color-center laser pulses are spatially windowed by slits at the output of the planar waveguide. The spatially filtered pulses are transmitted to a balanced mixer-detector arrangement that allows measurement of the noise of the windowed pulses relative to the shot-noise level.
Experimental demonstration of more than 50% photon-number squeezing obtained using microstructure fibers (MFs) , of which zero-dispersion wavelength locates at 820 nm, in a spectral filtering scheme with 40-fs laser pulses at /spl lambda/ = 810 nm is reported. The highest photon-number squeezing of -4.6 dB is obtained when a soliton-like Stokes Raman pulse, which broke up from the main pulse, exhibiting a self-frequency shift toward the longer wavelength, is preserved by low-pass spectral filtering from the white-light spectrum generated from the 30-cm MF.
We present experimental studies based on all three methods by which the generation of squeezed light in semiconductors has thus far been demonstrated experimentally: Fourwave mixing, multi-photon absorption and direct generation at the source. Four-wave mixing was used to generate femtosecond-pulsed quadrature squeezed light by cross-phase modulation in single-crystal hexagonal CdSe at wavelengths between 1.42 and 1.55 μm. We measured 0.4 dB squeezing (1.1 dB is inferred at the crystal) using 100 fs pulses. The wavelength and the intensity dependence, as well as variations in the local oscillator configuration were investigated. At higher intensities squeezing was shown to deteriorate owing to competing nonlinear processes. We also characterised the nonlinear optical properties of CdSe in this wavelengths range using an interferometric autocorrelator. In addition, we studied the feasibility of extending this technique to AlGaAs waveguides. The key problems are addressed and solutions are proposed. In a different experiment we used an AlGaAs waveguide to demonstrate for the first time photon-number squeezing by multi-photon absorption. By tuning the pump energy through the half bandgap energy we could effectively select two- or three-photon absorption as the dominant mechanism. Squeezing by these two mechanisms could be clearly distinguished and was found to be in good agreement with longstanding theoretical predictions. We also established the generality of the effect, by demonstrating the same mechanism in organic semiconductors, where it led to the first ever observation of squeezed light in an organic material. Finally, we present our measurements of photon-number squeezing in high-efficiency double heterojunction AlGaAs light-emitting diodes. We measured squeezing of up to 2.0 dB. In addition, we observed quantum noise correlations when several of these devices were connected in series.
Summary form only given.Spectral filtering of optical solitons has been demonstrated to squeeze their photon-number uncertainty up to a measured value of 3.8 dB. The squeezing has been explained in terms of an uneven spectral distribution of photon-number noise caused by the Kerr nonlinearity of the fiber. Some indication for correlations among different frequency components has been found in a numerical analysis. We present the first experimental evidence for such spectral correlations. The experimental setup is shown. Pulses of 130 fs centered at 1.5 /spl mu/m are launched into a 2.9-m polarization-presenting single-mode optical fiber with energies close to the fundamental soliton energy.