Degenerate polarization entangled photon source based on a single Ti-diffusion lithium niobate waveguide in a polarization Sagnac interferometer

Combining a Ti-diffusion periodically poled lithium niobate(PPLN)waveguide with a Sagnac interferometer,two opposite directions type-II spontaneous parametric down conversions(SPDC)occur coherently and yield a high brightness,high stability polarization entanglement source.The source produces degenerate photon pairs at 1540.4 nm with a brightness of B=(1.36±0.03)×10^(6) pairs/(s·nm·m W).We perform quantum state tomography to reconstruct the density matrix of the output state and obtain a fidelity of F=0.983±0.001.The high brightness and phase stability of our waveguide source enable a wide range of quantum information experiments operating at a low pump power as well as hold the advantage in mass production which can promote the practical applications of quantum technologies.

A dual-loop Sagnac interferometer

A new type of all-fibre Sagnac interferometer composed of two loops is proposed and analysed in detail. It can be used with a very long transmission line while maintaining excellent performance characteristics due to the automatic compensation of any birefringence effects in the trunk fibre. Preliminary experiments at 1310 nm wavelength with a 70 km long trunk fibre demonstrated an interference visibility as high as 98%, indicating that this scheme has promising potential applications.

Simulation of distributed optical fiber disturbance detection system based on Sagnac/Mach-Zehnder interferometer and cross-correlation location

A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.

Two-parameter estimation in a matter-wave Sagnac interferometer

We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the Heisenberg limit(HL) simultaneously when the input state is maximally entangled. Only one of the parameters' uncertainties can approach the HL while the other is scaled by the standard quantum limit.We provide the conditions with which the measurement precision of the specific parameter can reach the HL. We also discuss and figure out the concrete expressions of the constraint conditions for saturating the quantum Cramér–Rao bound. To satisfy these constraint conditions, the evolution time has to be a series of discrete values. Additionally, we calculate the variances of the parameters through some examples under these constraint conditions. The results provided in our work show some intrinsic features of the matter-wave Sagnac interferometer for the two-parameter estimation, which can be valuable in actual experiments.

Demonstration of a 4-Sensor Folded Sangac Sensor Array with Active Phase Biasing Scheme

A 4-sensor folded Sagnac sensor array with an active phase biasing scheme is presented. The overlapping of the signal and noise pulse is avoided through a time division multiplexing scheme and the noise pulses is eliminated almost completely. The scheme can address 16 sensors when the repeat frequency of input pulse is at 68.3 kHz. The alternative phase bias technique is demonstrated, which can provide sensors with stable phase bias. The future benefit of this technique is that the 1/f noise in the circuit can be suppressed.

Generation of hyperentangled state encoded in three degrees of freedom

Hyperentanglement, the simultaneous entanglement in more than one degree of freedom(DOF), plays an important role in quantum communication and quantum information processing for it can effectively increase the channel capacity. Existing hyperentanglement sources mainly focus on the generation of the hyperentanglement in two DOFs. In this paper, we design the generation protocols for three kinds of hyperentanglement encoded in three DOFs with the practical coherent pulses sources, including the polarization-frequency-space hyperentanglement, the polarization-frequency-time-bin hyperentanglement, and the polarizationspace-time-bin hyperentanglement. These protocols exploit the spontaneous parametric down-conversion(SPDC) process and the Sagnac interferometer. The three protocols are all based on feasible experimental condition and may have potential applications in future hyperentanglement-based quantum communication and quantum information processing protocols.

High Sensitivity Temperature Sensor Based on Harmonic Vernier Effect

A high-sensitivity temperature sensor based on the harmonic Vernier effect is proposed and verified by experiments.The main component of the sensor is a Sagnac interferometer consisting of two sections of polarization maintaining fibers(PMFs)spliced with an intersection angle of 45o between their fast axes.The harmonic Vernier effect is achieved by setting the length of one of the PMFs an integral multiple(i-times)of the length of the other plus a detuning factor.Compared with the Sagnac interferometer based on the fundamental Vernier effect,the temperature sensitivity of the harmonic Vernier effect is higher,reaching i+1 times of that of the fundamental Vernier effect(i is the order of the harmonic).

Fiber-Optic Microstructure Sensors:A Review

This paper reviews a wide variety of fiber-optic microstructure(FOM)sensors,such as fiber Bragg grating(FBG)sensors,long-period fiber grating(LPFG)sensors,Fabry-Perot interferometer(FPI)sensors,Mach-Zchnder interferometer(MZI)sensors,Michelson interferometer(MI)sensors,and Sagnac interferometer(SI)sensors.Each FOM sensor has been introduced in the terms of structure types,fabrication methods,and their sensing applications.In addition,the sensing characteristics of different structures under the same type of FOM sensor are compared,and the sensing characteristics of the all FOM sensors,including advantages,disadvantages,and main sensing parameters,are summarized.We also discuss the future development of FOM sensors.

Atomic Interferometric Gravitational-Wave Space Observatory(AIGSO)

We propose a space-borne gravitational-wave detection scheme,called atom interferometric gravitationalwave space observatory(AIGSO).It is motivated by the progress in the atomic matter-wave interferometry,which solely utilizes the standing light waves to split,deflect and recombine the atomic beam.Our scheme consists of three drag-free satellites orbiting the Earth.The phase shift of AIGSO is dominated by the Sagnac effect of gravitational-waves,which is proportional to the area enclosed by the a√tom interferometer,the frequency and amplitude of gravitational-waves.The scheme has a strain sensitivity<10^(-20)/Hz^(1/2)in the 100 mHz–10 Hz frequency range,which fills in the detection gap between space-based and ground-based laser interferometric detectors.Thus,our proposed AIGSO can be a good complementary detection scheme to the space-borne laser interferometric schemes,such as LISA.Considering the current status of relevant technology readiness,we expect our AIGSO to be a promising candidate for the future space-based gravitational-wave detection plan.