28 research outputs found
Polarization-selective out-coupling of whispering gallery modes
Whispering gallery mode (WGM) resonators are an important platform for linear, nonlinear and quantum optical experiments. In such experiments, independent control of in- and out-coupling rates to different modes can lead to higher conversion efficiencies and greater flexibility in the generation of non-classical states based on parametric down conversion. In this work, we introduce a scheme that enables selective out-coupling of WGMs belonging to a specific polarization family, while the orthogonally polarized modes remain largely unperturbed. Our technique utilizes material birefringence in both the resonator and the coupler such that a negative (positive) birefringence allows for polarization-selective coupling to TE (TM) WGMs. We formulate a new coupling condition suitable for describing the case where the refractive indices of the resonator and the coupler are almost the same, from which we derive a criterion for polarization-selective coupling. Finally, we experimentally demonstrate our proposed method using a lithium niobate disk resonator coupled to a lithium niobate prism, where we show a \SI{22}{dB} suppression of coupling to TM modes relative to TE modes
Nature of light correlations in ghost imaging
We investigate the nature of correlations in Gaussian light sources used for
ghost imaging. We adopt methods from quantum information theory to distinguish
genuinely quantum from classical correlations. Combining a microscopic analysis
of speckle-speckle correlations with an effective coarse-grained description of
the beams, we show that quantum correlations exist even in `classical'-like
thermal light sources, and appear relevant for the implementation of ghost
imaging in the regime of low illumination. We further demonstrate that the
total correlations in the thermal source beams effectively determine the
quality of the imaging, as quantified by the signal-to-noise ratio.Comment: 12 pages, 5 figures. To appear in Scientific Reports (NPG
Dual-pump Kerr micro-cavity optical frequency comb with varying FSR spacing
In this paper, we demonstrate a novel dual-pump approach to generate robust optical frequency comb with varying free spectral range (FSR) spacing in a CMOS-compatible high-Q micro-ring resonator (MRR). The frequency spacing of the comb can be tuned by an integer number FSR of the MRR freely in our dual-pump scheme. The dual pumps are self-oscillated in the laser cavity loop and their wavelengths can be tuned flexibly by programming the tunable filter embedded in the cavity. By tuning the pump wavelength, broadband OFC with the bandwidth of >180nm and the frequency-spacing varying from 6 to 46-fold FSRs is realized at a low pump power. This approach could find potential and practical applications in many areas, such as optical metrology, optical communication, and signal processing systems, for its excellent flexibility and robustness
Von Bezold assimilation effect reverses in stereoscopic conditions
Lightness contrast and lightness assimilation are opposite phenomena: in contrast,
grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in
assimilation, the opposite occurs. The question is: which visual process favours the occurrence
of one phenomenon over the other? Researchers provided three answers to this question. The
first asserts that both phenomena are caused by peripheral processes; the second attributes their
occurrence to central processes; and the third claims that contrast involves central processes,
whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT
system equipped with goggles for stereo vision was run. Observers were asked to evaluate the
lightness of a grey target, and two variables were systematically manipulated: (i) the apparent
distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept
constant throughout, so that the peripheral processes remained the same. The results show that
the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we
conclude that central mechanisms are involved in both lightness contrast and lightness assimilation
Experimental realization of sub-shot-noise quantum imaging
Properties of quantum states have disclosed new technologies, ranging from
quantum information to quantum metrology. Among them a recent research field is
quantum imaging, addressed to overcome limits of classical imaging by
exploiting spatial properties of quantum states of light . In particular
quantum correlations between twin beams represent a fundamental resource for
these studies. One of the most interesting proposed scheme exploits spatial
quantum correlations between parametric down conversion light beams for
realizing sub-shot-noise imaging of the weak absorbing objects, leading ideally
to a noise-free imaging. Here we present the first experimental realisation of
this scheme, showing its capability to reach a larger signal to noise ratio
(SNR) with respect to classical imaging methods. This work represents the
starting point of this quantum technology that can have relevant applications,
especially whenever there is a need of a low photon flux illumination (e.g. as
with certain biological samples)
Single photons on demand from tunable 3D photonic band-gap structures
In this article we propose to build a (semi-)deterministic photon gun by modifying the spontaneous decay in a photonic band-gap material. We show that such a device allows for deterministic and unidirectional single-photon emission with a repetition rate of the order of 100 kHz. We describe a specific realization of the 1D band-gap model by means of a 3D photonic-crystal heterostructure and the feasability of implementing such a device using Er3+ ions that produce single photons at the telecommunication wavelength of 1.55,m, important for many applications