Suppression of Instability on Sensing Signal of Optical Pulse Correlation Measurement in Remote Fiber Sensing

Optical fiber sensing has the potential to overcome weak points of traditional electric sensors. Many types of optical fiber sensors have been proposed according to the modulation parameter of incident light. We have proposed an optical pulse correlation sensing system that focuses on the time drift values of the propagating optical pulses to monitor the temperature- or strain-induced extension along the optical fiber in the sensing region. In this study, we consider the instability in the optical pulse correlation sensing system applied to remote monitoring over a kilometer-long distance. We introduce a method to stabilize the instability of the pulse correlation signal resulting from the time drift fluctuation along a transmission line. By using this method, we can purify the response and improve the accuracy of signals at the focused sensing regions. We also experimentally demonstrate remote temperature monitoring over a 30 km-long distance using a remote reference technique, and we estimate the resolution and the measurable span of the temperature variation as (1.1/L)∘C and (5.9×10/L)°C, respectively, where L is the length of the fiber in the sensing region

Attosecond Precision Multi-km Laser-Microwave Network

Synchronous laser-microwave networks delivering attosecond timing precision are highly desirable in many advanced applications, such as geodesy, very-long-baseline interferometry, high-precision navigation and multi-telescope arrays. In particular, rapidly expanding photon science facilities like X-ray free-electron lasers and intense laser beamlines require system-wide attosecond-level synchronization of dozens of optical and microwave signals up to kilometer distances. Once equipped with such precision, these facilities will initiate radically new science by shedding light on molecular and atomic processes happening on the attosecond timescale, such as intramolecular charge transfer, Auger processes and their impact on X-ray imaging. Here, we present for the first time a complete synchronous laser-microwave network with attosecond precision, which is achieved through new metrological devices and careful balancing of fiber nonlinearities and fundamental noise contributions. We demonstrate timing stabilization of a 4.7-km fiber network and remote optical-optical synchronization across a 3.5-km fiber link with an overall timing jitter of 580 and 680 attoseconds RMS, respectively, for over 40 hours. Ultimately we realize a complete laser-microwave network with 950-attosecond timing jitter for 18 hours. This work can enable next-generation attosecond photon-science facilities to revolutionize many research fields from structural biology to material science and chemistry to fundamental physics.Comment: 42 pages, 13 figure

Ultra-Low Noise Microwave Extraction from Fiber-Based Optical Frequency Comb

In this letter, we report on all-optical fiber approach to the generation of ultra-low noise microwave signals. We make use of two erbium fiber mode-locked lasers phase locked to a common ultra-stable laser source to generate an 11.55 GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz from the carrier.The residual frequency instability of the microwave signals derived from the two optical frequency combs is below 2.3 10^(-16) at 1s and about 4 10^(-19) at 6.5 10^(4)s (in 5 Hz bandwidth, three days continuous operation).Comment: 12 pages, 3 figure

Resources for Integrated Quantum Sensing in the Mid-infrared

Quantum states of light, with sub-classical noise statistics, are heraldedas a potential route towards enhanced absorption spectroscopy. In thisthesis we develop key infrastructure in the pursuit of quantum-enhancedabsorption spectroscopy in the 2 μm-band via the adoption of integrated silicon photonics as a deployable and scalable solution.Characterising quantum states of light in the 2 μm-band requires shot-noise limited homodyne detectors and so we start by presenting the design and characterisation of a homodyne detector that we use to make the first observation of megahertz speed vacuum shot-noise in this band. The device, designed primarily for pulsed illumination, has a 3-dB bandwidth of 13.2 MHz, total conversion efficiency of 57% at 2.07 μm, and a common-mode rejection ratio of 48 dB at 39.2 MHz.We then utilise a silicon chip to implement an all-optical noise suppressionscheme aimed at reducing the intensity noise of state-of-the-art pulsed lasers in this band via nonlinear interferometry. We find initial designs capable of noise suppression but with the addition of unwanted noise amplification from modulation instability.In the final results chapter we look to expand the applicability of quantumstates in absorption spectroscopy by analysing the effect of sample saturationon estimate precision in absorption measurements. We compare both classicaland quantum probes. A limit is derived on the maximum precision gained fromusing a nonclassical probe and a measurement strategy for saturating this bound is presented. Finally, we evaluate amplitude-squeezed light as a viable route to gaining a quantum advantage under saturation