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Optics Communications

Photon-number squeezing by two-photon absorption in an organic polymer

Radu G. Ispasoiu, Theodore G. Goodson III

Published May 1, 2000• 11 citations
Publisher
DOI
10.1016/s0030-4018(00)00681-7

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We have demonstrated the reduction of photon-number fluctuations below the shot-noise level (photon-number squeezing) by two-photon absorption in an inorganic semiconductor material consisting of a thin film of TOPO-decorated CdSe nanocrystals embedded in a PMMA polymer host. The photon-number squeezing was measured at 800 nm, where the linear absorption of the material was negligible. The amount of photon-number squeezing from the CdSe system was ∼5% for a moderate value of nonlinear transmission. This observation was possible due to the large nonlinear absorption exhibited by the system of CdSe NCs embedded in PMMA and also due to the reduced linear scattering losses in thin films. The CdSe squeezing data are compared to results previously obtained for the first time in a nonlinear optical polymeric material. The achievement of photon-number squeezing in these novel materials gives the opportunity for future application in the improvement of the signal-to-noise ratio in optical communications.

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Two-photon excited coherence gratings in inhomogeneously broadened organic solid

Alex Karotki, Mikalai M. Kruk, Mikhail A. Drobizhev +1 more

For the first time a frequency-domain grating is observed in the visible region as a result of coherence excited by two-photon absorption of time-delayed near-IR femtosecond pulses in an inhomogeneously broadened organic solid-state system. The grating appears in chlorin (2,3-dihydroporphyrin)-doped polymer film at low temperature and is detected in two different ways. First, modulation is observed in the pure electronic fluorescence band upon 'resonant' two-photon excitation with laser carrier frequency equal to one-half of the fluorescence band maximum. Second, upon long exposure time at half of the transition frequency, a persistent spectral hole with periodic structure is observed. The two-photon absorption spectrum of the chlorin molecule in the spectral range 1130–1310nm is also presented for the first time.

Journal of Modern Optics•Mar 1, 2002•13 citations
We have demonstrated the reduction of photon-number fluctuations below the shot-noise level (photon-number squeezing) by two-photon absorption in an inorganic semiconductor material consisting of a thin film of TOPO-decorated CdSe nanocrystals embedded in a PMMA polymer host. The photon-number squeezing was measured at 800 nm, where the linear absorption of the material was negligible. The amount of photon-number squeezing from the CdSe system was ∼5% for a moderate value of nonlinear transmission. This observation was possible due to the large nonlinear absorption exhibited by the system of CdSe NCs embedded in PMMA and also due to the reduced linear scattering losses in thin films. The CdSe squeezing data are compared to results previously obtained for the first time in a nonlinear optical polymeric material. The achievement of photon-number squeezing in these novel materials gives the opportunity for future application in the improvement of the signal-to-noise ratio in optical communications.
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.
For the first time a frequency-domain grating is observed in the visible region as a result of coherence excited by two-photon absorption of time-delayed near-IR femtosecond pulses in an inhomogeneously broadened organic solid-state system. The grating appears in chlorin (2,3-dihydroporphyrin)-doped polymer film at low temperature and is detected in two different ways. First, modulation is observed in the pure electronic fluorescence band upon 'resonant' two-photon excitation with laser carrier frequency equal to one-half of the fluorescence band maximum. Second, upon long exposure time at half of the transition frequency, a persistent spectral hole with periodic structure is observed. The two-photon absorption spectrum of the chlorin molecule in the spectral range 1130–1310nm is also presented for the first time.