We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.

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Optical-Fiber Source of Polarization-Entangled Photons in the 1550 nm Telecom Band

This tutorial describes the transmission, group delay time and quadratic dispersion properties of the four basic building blocs of optical filters built using ring resonators. These building blocs are single-ring resonators in either two-port (all-pass) or four-port (add/drop filter) configuration. The effect of waveguide and coupler loss is included throughout. Explicit expressions to compute the complex amplitude of the circulating wave in the ring, the Q factor, the finesse and the insertion loss are also given. Attention is drawn to the similarities between the ring resonator the Fabry-Pe/spl acute/rot resonator and the Gires-Tournois interferometer. Material properties and fabrication technology are not reviewed.

Transmission, group delay, and dispersion in single-ring optical resonators and add/drop filters-a tutorial overview

A compact temperature sensor based on a fiber loop mirror (FLM) combined with an alcohol-filled high-birefringence photonic crystal fiber (PCF) is proposed and experimentally demonstrated. The output of the FLM is an interference spectrum with many resonant dips, of which the wavelengths are quite sensitive to the change of the refractive index of the filled alcohol for the interference of the FLM. Simulation analysis predicts a high temperature sensitivity, and experimental results show it reaches up to 6.6 nm/°C for the 6.1-cm-long PCF used in the FLM.

High-sensitivity temperature sensor based on an alcohol-filled photonic crystal fiber loop mirror

Utilizing the high birefringence and the low-temperature coefficient of birefringence of the highly birefringent photonic crystal fiber (HiBi-PCF), a temperature-insensitive interferometer made from a HiBi-PCF fiber loop mirror (FLM) is achieved. For the wavelength spacing of 0.43 nm, a wavelength spacing variation with temperature of only 0.05 pm//spl deg/C, and a transmission peak shift of 0.3 pm//spl deg/C is demonstrated. The stability of the FLM is improved dramatically when it uses a HiBi-PCF, as compared to FLMs using conventional HiBi fibers.

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Temperature-insensitive Interferometer using a highly birefringent photonic Crystal fiber loop mirror

Sensitivity-enhanced temperature sensor with cascaded fiber optic Sagnac interferometers based on Vernier-effect

The theory and application of fiber loop reflectors, fabricated by forming a fiber loop between the output ports of a directional coupler, is described. The reflectivity of the loop is shown to depend upon the coupling characteristics of the coupler and on the degree of birefringence in the fiber loop. Measured loop reflectivities, in terms of wavelength response, coupling ratio, and loop birefringence are shown to agree very well with theory. Two applications of the fiber reflector are briefly discussed; an all fiber laser and a duplex optical communications link using a single light source. >

D.B. Mortimore

Papers

Fiber loop reflectors