Augmenting the Sensing Performance of Entangled Photon Pairs through Asymmetry.

We analyze theoretically and experimentally cases of asymmetric detection, stimulation, and loss within a quantum nonlinear interferometer of entangled pairs. We show that the visibility of the SU(1,1) interference directly discerns between loss on the measured mode (signal) and the conjugated mode (idler). This asymmetry also affects the phase sensitivity of the interferometer, where coherent seeding is shown to mitigate losses that are suffered by the conjugated mode; therefore increasing the maximum threshold of loss that permits sub-shot-noise phase detection.

Lifting the bandwidth limit of optical homodyne measurement with broadband parametric amplification.

Homodyne measurement is a corner-stone method of quantum optics that measures the quadratures of light-the quantum optical analog of the canonical position and momentum. Standard homodyne, however, suffers from a severe bandwidth limitation: while the bandwidth of optical states can span many THz, standard homodyne is inherently limited to the electronically accessible MHz-to-GHz range, leaving a dramatic gap between relevant optical phenomena and the measurement capability. We demonstrate a fully parallel optical homodyne measurement across an arbitrary optical bandwidth, effectively lifting this bandwidth limitation completely.

Large one-time photo-induced tuning of directional couplers in chalcogenide-on-silicon platform.

The stable one-time tuning of silicon-photonic directional couplers, over a broad range of coupling ratios, is achieved through the selective photo-removal of an upper cladding layer of chalcogenide glass. Analysis shows that the coupling coefficient per unit length between two parallel fully-etched silicon waveguides may be changed by 45%. The power coupling ratio of a 50 µm-long directional coupler between two such waveguides may be tuned arbitrarily between 0 and 1, with weak residual wavelength dependence.

Classical-to-quantum transition with broadband four-wave mixing.

A key question of quantum optics is how nonclassical biphoton correlations at low power evolve into classical coherence at high power. Direct observation of the crossover from quantum to classical behavior is desirable, but difficult due to the lack of adequate experimental techniques that cover the ultrawide dynamic range in photon flux from the single photon regime to the classical level. We investigate biphoton correlations within the spectrum of light generated by broadband four-wave mixing over a large dynamic range of ∼80  dB in photon flux across the classical-to-quantum transition using a two-photon interference effect that distinguishes between classical and quantum behavior.

Large photo-induced index variations in chalcogenide-on-silicon waveguides.

The postfabrication modification of the group delay in silicon-photonic waveguides is proposed, simulated and demonstrated experimentally. Group delay variations of 2% are achieved through photo-induced changes to an upper cladding layer of photosensitive As₁₀Se₉₀ chalcogenide glass. The illumination of the cladding layer by intense green light for a few seconds leads to mass transfer and removal of material, away from irradiated regions.