Large on-chip Brillouin net amplification in silicon-based nano-photonics

Recent developments in on-chip forward Brillouin scattering open up potential applications such as RF photonic signal processing, on-chip Brillouin amplification, and on-chip Brillouin lasers. The stimulated Brillouin scattering gain coefficients become significant with a small optical mode area, and the Brillouin net amplification has been believed to be strong with a small mode area, too. However, here, we present a theoretical study of higher net amplification with a large optical mode area than that with a small mode area and explain this counter-intuitive phenomenon by examining the contribution of various optical forces to Brillouin gain coefficients for various optical waveguide dimensions. The simulation results show that a waveguide with large optical waveguide dimensions can yield significant net amplification by high Brillouin gain coefficients and low optical losses at high pump power even if the Brillouin gain coefficients are lower than that with a small waveguide dimension. Therefore, it is necessary to optimize the optical waveguide dimensions to achieve maximum net amplification for the development of Brillouin lasers and amplifiers in silicon-based nanophotonics.11Ysciescopu

Quantum spatial superresolution by optical centroid measurements

Quantum lithography (QL) has been suggested as a means of achieving enhanced spatial resolution for optical imaging, but its realization has been held back by the low multi-photon detection rates of recording materials. Recently, an optical centroid measurement (OCM) procedure was proposed as a way to obtain spatial resolution enhancement identical to that of QL but with higher detection efficiency (M. Tsang, Phys. Rev. Lett. 102, 253601, 2009). Here we describe a variation of the OCM method with still higher detection efficiency based on the use of photon-number-resolving detection. We also report laboratory results for two-photon interference. We compare these results with those of the standard QL method based on multi-photon detection and show that the new method leads to superresolution but with higher detection efficiency.Comment: 4 pages, 2 figure

Tailorable and Broadband On-Chip Optical Power Splitter

Featured Application Silicon photonics, Quantum integrated photonic circuits, Photonic integrated circuits. Abstract An on-chip optical power splitter is a key component of photonic signal processing and quantum integrated circuits and requires compactness, wideband, low insertion loss, and variable splitting ratio. However, designing an on-chip splitter with both customizable splitting ratio and wavelength independence is a big challenge. Here, we propose a tailorable and broadband optical power splitter over 100 nm with low insertion loss less than 0.3%, as well as a compact footprint, based on 1x2 interleaved tapered waveguides. The proposed scheme can design the output power ratio of transverse electric modes, lithographically, and a selection equation of a power splitting ratio is extracted to obtain the desired power ratio. Our splitter scheme is close to an impeccable on-chip optical power splitter for classical and quantum integrated photonic circuits.11Ysciescopu

Tunability of the Nonlinear Interferometer Method for Anchoring Constructive Interference Patterns on the ITU-T Grid

Recently, a method of engineering the quantum states with a nonlinear interferometer was proposed to achieve precise state engineering for near-ideal single-mode operation and near-unity efficiency (L. Cui et al., Phys. Rev. A 102, 033718 (2020)), and the high-purity bi-photon states can be created without degrading brightness and collection efficiency. Here, we study the coarse or fine tunability of the nonlinear interference method to match constructive interference patterns into a transmission window of standard 100-GHz DWDM channels. The joint spectral intensity spectrum is measured for various conditions of the nonlinear interference effects. We show that the method has coarse- and fine-tuning ability while maintaining its high spectral purity. We expect that our results expand the usefulness of the nonlinear interference method. The photon-pair generation engineered via this method will be an excellent practical source of the quantum information process.11Ysciescopu

Observation of photon-pair generation in the normal group-velocity-dispersion regime with slight detuning from the pump wavelength

A fiber-based photon-pair source in the telecom C-band is suitable for quantum information science including quantum communications. Spontaneous four-wave mixing effects are known to create photon pairs that are slightly detuned from the pump wavelength only in the anomalous group-velocity-dispersion (GVD) regime. Here, we achieve high-quality photon-pair generation slightly detuned from the pump wavelength in the normal GVD regime through a dispersion shifted fiber, for the first time. The photon pairs in C-band exhibit strong temporal correlation with each other and excellent heralded anti-bunching property. This photon-pair generation scheme can be exploited as telecom-band quantum light sources for quantum information applications.11Ysciescopu

Discriminating Orthogonal Single-Photon Images

We can encode an image from an orthogonal basis set onto a single photon from a downconverted pair via the use of an amplitude mask. We can then discriminate the image imprinted on the photon from other images in the set using holographic-matched filtering techniques. We demonstrate this procedure experimentally for an image space of two objects, and we discuss the possibility of applying this method to a much larger image space. This process could have important implications for the manipulation of images at the quantum level

Stimulated Brillouin scattering in nanoscale silicon step-index waveguides: a general framework of selection rules and calculating SBS gain

We develop a general framework of evaluating the Stimulated Brillouin Scattering (SBS) gain coefficient in optical waveguides via the overlap integral between optical and elastic eigen-modes. This full-vectorial formulation of SBS coupling rigorously accounts for the effects of both radiation pressure and electrostriction within micro- and nano-scale waveguides. We show that both contributions play a critical role in SBS coupling as modal confinement approaches the sub-wavelength scale. Through analysis of each contribution to the optical force, we show that spatial symmetry of the optical force dictates the selection rules of the excitable elastic modes. By applying this method to a rectangular silicon waveguide, we demonstrate how the optical force distribution and elastic modal profiles jointly determine the magnitude and scaling of SBS gains in both forward and backward SBS processes. We further apply this method to the study of intra- and inter-modal SBS processes, and demonstrate that the coupling between distinct optical modes are necessary to excite elastic modes with all possible symmetries. For example, we show that strong inter-polarization coupling can be achieved between the fundamental TE- and TM-like modes of a suspended silicon waveguide.Alfred P. Sloan FoundationUnited States. Defense Advanced Research Projects Agency (MesoDynamic Architectures program

Enhancing entangled-state phase estimation by combining classical and quantum protocols

Here we describe a laboratory procedure by which we have increased the resolution of a measurement of the position of an optical component by a factor of 16. The factor of 16 arises from a four-fold quantum enhancement through the use of an N = 4 N00N state and a four-fold classical enhancement from a quadruple pass through a prism pair. The possibility of achieving supersensitivity using this method is discussed. © 2013 Optical Society of America