Controlling the spectrum of photons generated on a silicon nanophotonic chip.

Ranjeet Kumar,Shayan Mookherjea,Jun Rong Ong,Marc Savanier

doi:10.1038/ncomms6489

Ranjeet Kumar, Shayan Mookherjea + Show 2 more

Open Access

https://doi.org/10.1038/ncomms6489

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Journal: Nature Communications	Publication Date: Nov 20, 2014
Citations: 48	License type: CC BY 4.0

Affiliation: University of California, San Diego

Abstract

Directly modulated semiconductor lasers are widely used, compact light sources in optical communications. Semiconductors can also be used to generate nonclassical light; in fact, CMOS-compatible silicon chips can be used to generate pairs of single photons at room temperature. Unlike the classical laser, the photon-pair source requires control over a two-dimensional joint spectral intensity (JSI) and it is not possible to process the photons separately, as this could destroy the entanglement. Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI. By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number. Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

Highlights

Modulated semiconductor lasers are widely used, compact light sources in optical communications
One of the potential problems of spontaneous four-wave mixing (SFWM) is broad-band Raman scattering in glass optical fibres, which is partially mitigated in crystalline silicon waveguides, in which spontaneous Raman scattering (SRS) is narrow band, and the SRS-shifted light may not coincide with one of the guided modes[13]
For the type of device studied here experimentally, which consists of coupled-microring resonators, we have previously identified the range of input powers over which pair generation with a high coincidence-to-accidental ratio can be achieved, and when one of the photons can be used as a herald, projecting the other into a single-photon state, with g(2)(0)o0.2

Summary

Introduction

Modulated semiconductor lasers are widely used, compact light sources in optical communications. Directly modulated semiconductor lasers are widely used and well understood, demonstrating a similar concept in quantum optics is not simple because a number of issues have to be simultaneously addressed These include the following: showing a photon source using semiconductor technology that can be manufactured, designing internal degrees of freedom in the architecture of the source that can be externally manipulated by a user to generate different quantum spectra and developing a measurement procedure for the different photon spectra, rather than counting photons. The high SFWM nonlinearity in silicon photonic chips has been used in a number of demonstrations, including photon pairs of high quality, heralded single photons and spectral multiplexing[5,6,7,8,9,10,11] Unlike quantum dots, these photon sources can operate at room temperature and can be coupled relatively to optical fibres. In the devices studied here (see Supplementary Note 1 and Supplementary Fig. 1), the expression for Dk is more complicated, involving a discrete set of wavenumbers and terms that describe the reduction of group velocity (slow-light effects) at these wavelengths (see Supplementary Note 2)

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