**Abstract: ** We investigate generation of nonclassical photon states using nonlinear
cavities. Our goal is to develop single photon sources which are needed
e.g. in information processing, quantum computing and fundamental quantum
optical experiments. We have recently shown that antibunched photons (i.e.
nonclassical light) can be obtained from nonlinear cavities with
multi-photon absorption [Häyrynen et al., Nonlinear laser cavities as
nonclassical light sources, submitted (2012)]. The antibunching in
nonlinear cavities occurs because the energy pumping raises the
probability of states having n>0 photons but simultaneously the second
order absorption in the nonlinear element causes an additional decay for
states having n>1 photons relative to the single photon state. Therefore,
light fields which are essentially superpositions of zero photon and one
photon states are generated. These results suggest that a nonclassical
light emitter could be realized by coupling a nonlinear absorber to a
light source like a light emitting diode (LED) or by adding a nonlinear
absorbing layer into a laser cavity. The nonlinearity can be achieved e.g.
by replacing one of the cavity mirrors with a two-photon saturable
absorber mirror [Thoen et al., Two-photon absorption in semiconductor
saturable absorber mirrors, Applied Physics Letters, vol. 74, p. 3927
(1999)] or a nonlinear mirror [Schirmer et al., Nonlinear mirror based on
two-photon absorption, J. Opt. Soc. Am. B, vol. 14 p. 2865 (1997)]. This
type of a setup is technologically attractive since it potentially
provides room temperature realization of photon antibunching with
essentially standard optoelectronic materials and processing techniques.
We maximize the probability of the single photon state by optimizing the
strengths of linear losses, nonlinear absorption and photon emission.
Furthermore, we investigate the effect of exciting the photon emitter with
time dependent current pulses to provide single-photon-on-demand sources.