Abstract
The high peak intensity achieved with ultrashort pump pulses drastically increases the conversion efficiency in spontaneous parametric down-conversion. However, when ultrashort pulses are used, dispersion limits the degree of squeezing. Here, we investigate the effects of dispersion on both quadrature squeezing and photon statistics by varying the interaction length when pumping a periodically poled lithium niobate crystal with femtosecond pulses. The down-converted light in the 1550 nm telecom band attains its maximum observed squeezing level of 3.1 dB for the shortest interaction length. Our photon-statistics measurements agree with the photon-pair distribution going from thermal to Poissonian as the interaction length is increased. This is explained by considering the dispersion-induced distinguishability of the generated photon pairs.
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