Rayleigh Backscattering In Single-mode Fiber Research Articles

Polar Decomposition of Jones Matrix and Mueller Matrix of Coherent Rayleigh Backscattering in Single-Mode Fibers.

The Jones matrix and the Mueller matrix of the coherent Rayleigh backscattering (RB) in single-mode fibers (SMFs) have been derived recently. It has been shown that both matrices depict two polarization effects-birefringence and polarization-dependent loss (PDL)-although the SMF under investigation is purely birefringent, having no PDL. In this paper, we aim to perform a theoretical analysis of both matrices using polar decomposition. The derived sub-Jones/Mueller matrices, representing birefringence and PDL, respectively, can be used to investigate the polarization properties of the coherent RB. As an application of the theoretical results, we use the derived formulas to investigate the polarization properties of the optical signals in phase-sensitive optical time-domain reflectometry (φ-OTDR). For the first time, to our knowledge, by using the derived birefringence-Jones matrix, the common optical phase of the optical signal in φ-OTDR is obtained as the function of the forward phase and birefringence distributions. By using the derived PDL-Mueller matrix, the optical intensity of the optical signal in φ-OTDR is obtained as the function of the forward phase and birefringence distributions as well as the input state of polarization (SOP). Further theoretical predictions show that, in φ-OTDR, the common optical phase depends on only the local birefringence in the first half of the fiber section, which is occupied by the sensing pulse, irrelevant of the input SOP. However, the intensity of the φ-OTDR signal is not a local parameter, which depends on the input SOP and the birefringence distribution along the entire fiber section before the optical pulse. Moreover, the PDL measured in φ-OTDR is theoretically proven to be a local parameter, which is determined by the local birefringence and local optical phase distributions.

High-speed RF spectral analysis using a Rayleigh backscattering speckle spectrometer.

Persistent wideband radio frequency (RF) surveillance and spectral analysis is increasingly important, driven by the proliferation of wireless communication and RADAR technology. However, conventional electronic approaches are limited by the ∼1 GHz bandwidth of real-time analog-to-digital converters (ADCs). While faster ADCs exist, high data rates prohibit continuous operation, limiting these approaches to acquiring short snapshots of the RF spectrum. In this work, we introduce an optical RF spectrum analyzer designed for continuous, wideband operation. Our approach encodes the RF spectrum as sidebands on an optical carrier and relies on a speckle spectrometer to measure these sidebands. To achieve the resolution and update rate required for RF analysis, we use Rayleigh backscattering in single-mode fiber to rapidly generate wavelength-dependent speckle patterns with MHz-level spectral correlation. We also introduce a dual-resolution scheme to mitigate the trade-off between resolution, bandwidth, and measurement rate. This optimized spectrometer design enables continuous, wideband (15 GHz) RF spectral analysis with MHz-level resolution and a fast update rate of 385 kHz. The entire system is constructed using fiber-coupled off-the-shelf-components, providing a powerful new approach for wideband RF detection and monitoring.

Extreme Narrowing of the Distributed Feedback Fiber Laser Linewidth Due to the Rayleigh Backscattering in a Single-Mode Fiber: Model and Experimental Test

We present our theoretical model and experimental results on the extreme linewidth narrowing of an erbium-doped fiber distributed feedback (DFB) laser due to an additional random DFB via Rayleigh backscattering in a long single-mode fiber connected to the laser. The relative narrowing of instantaneous (<1 μs) linewidth in such a hybrid cavity configuration predicted by the theoretical model may exceed six orders of magnitude, whereas the linewidth estimated from the phase noise measurements narrows by four orders of magnitude from 15 Hz to 10–3 Hz in the hybrid configuration, with the lower limit defined by the background electrical noise. Significant narrowing was also observed for the long-term ≥10 μs) linewidth directly measured by the self-delay heterodyne technique: the values for the DFB laser and hybrid configuration amount to 6 kHz and 160 Hz, respectively.

A Novel Wavemeter With 64 Attometer Spectral Resolution Based on Rayleigh Speckle Obtained From Single-Mode Fiber

In this article, a novel method of wavelength measurement with a spectral resolution of 64 attometers (am) based on Rayleigh speckle obtained from a single-mode fiber (SMF) is proposed. A commercial standard SMF is used to provide Rayleigh backscattering signals and measured by an optical frequency-domain reflectometry (OFDR) based system. The Rayleigh backscattering in SMF is a disordered process and provides high-sensitivity wavelength-dependent speckles. In the experiments, by extracting the Rayleigh speckles from a 2-km SMF, we achieve a 64-am spectral resolution (standard deviation) with a measurement refresh rate of 3.3 kHz. Compared with some similar disordered media based wavemeter schemes, the wavelength information can be directly read out from the Rayleigh speckles without using complex algorithms, since the Rayleigh speckle is a 1-D image and shows a linear relationship with the wavelength change, which makes this scheme simple and prospective for high spectral resolution applications.

Polarization properties of Rayleigh backscattering in single-mode fibers

The state and degree of polarization (SOP, DOP) of Rayleigh backscattered light in low birefringent optical fibers was calculated using Stokes calculus. It was found that the SOP of Rayleigh backscattered light in low birefringent fiber is constant, viz. the same as the SOP of the incoming light. The DOP of Rayleigh backscattered light is one-third of the DOP of the incoming light, and not just anywhere between 0 and 100% as often mentioned in the literature. The experimental results agree with the calculations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of Rayleigh backscattering in single-mode fibers based on coherent OFDR employing a DFB laser diode

Rayleigh backscattering in a single-mode optical fiber was measured by coherent optical frequency-domain reflectometry (C-OFDR) employing a frequency-variable distributed-feedback laser diode (DFB-LD). Backscattered power from the neighborhood of the far end of a 0.5-km-long fiber was measured with a spatial resolution of 50 cm. The insertion of a delay line fiber in the reference optical path and an acoustooptic frequency shifter in the signal optical path made it possible to measure backscattering in a long optical fiber in spite of the short coherence length of the DFB-LD. >

Rayleigh backscattering measurement of single-mode fibers by low coherence optical time-domain reflectometer with 14 μm spatial resolution

An optical time-domain reflectometer (OTDR) with −136 dB minimum detectable reflectivity and 14 μm spatial resolution is developed based on low coherence interference. The high sensitivity was accomplished by using a high-power superluminescent diode module with a 1.5 mW fiber output and a new system configuration, both for effectively operating the balanced heterodyne detection. The reflectivity of −136 dB is only 6 dB above the shot noise limit. The first observation of 1.3 μm wavelength Rayleigh backscattering in single-mode fibers was successfully made by the OTDR with a 17 dB dynamic range and 14 μm spatial resolution.

Statistical properties of Rayleigh backscattering in single-mode fibers

An analytical model that takes into account the influence of the laser linewidth on Rayleigh backscattering is given. For an unmodulated source the power spectral density is found to be identical to the delayed self-homodyne spectrum of the laser. The backscattered signal was measured for different laser linewidths, and the results are compared with the theory. The effects of Rayleigh backscattering noise on fiber gyroscopes and bidirectional optical systems are discussed.