Matthew S. Wolfe

High resolution optical frequency domain reflectometry for characterization of components and assemblies

We describe a technique for polarization sensitive optical frequency domain reflectometry (OFDR) that achieves 22 micrometer two-point spatial resolution over 35 meters of optical length with -97 dB sensitivity in a single measurement taking only seconds. We demonstrate OFDRs versatility in both time- and frequency-domain metrology by analyzing a fiber Bragg grating (FBG) in both the spectral and impulse response domains. We also demonstrate how a polarization diversity receiver can be used in an OFDR system to track changes in the polarization state of light propagating through a birefringent component.

Optical vector network analyzer for single-scan measurements of loss, group delay, and polarization mode dispersion

We present a method for measuring the complete linear response, including amplitude, phase, and polarization, of a fiber-optic component or assembly that requires only a single scan of a tunable laser source. The method employs polarization-diverse swept-wavelength interferometry to measure the matrix transfer function of a device under test. We outline the theory of operation to establish how the transfer function is obtained. We demonstrate the enhanced accuracy, precision, and dynamic range of the technique through measurements of several components.

Characterization of Polarization-Maintaining Fiber Using High-Sensitivity Optical-Frequency-Domain Reflectometry

Optical-frequency-domain reflectometry is used to measure the group-index difference and the refractive-index difference (i.e., beat length) between the fast and slow modes in polarization-maintaining optical fiber. The Rayleigh scatter normally present in the fiber is measured in reflection. This measurement, in turn, enables a distributed measurement of the fibers birefringence that is rapid and completely nondestructive

Swept-wavelength interferometric interrogation of fiber Rayleigh scatter for distributed sensing applications

We review recent advancements in making high resolution distributed strain and temperature measurements using swept-wavelength interferometry to observe the spectral characteristics of Rayleigh scatter in optical fibers. Current methods available for distributed strain or temperature sensing in optical fiber include techniques based on Raman, Brillouin, and Rayleigh scattering. These techniques typically employ optical time domain reflectometry and are thus limited in spatial resolution to 0.1 to 1 m. Fiber Bragg gratings can yield higher spatial resolution but are difficult to multiplex in large numbers for applications requiring wide scale coverage. Swept-wavelength interferometry allows the Rayleigh scatter amplitude and phase to be sampled with very high spatial resolution (10s of microns). The Rayleigh scatter complex amplitude can be Fourier Transformed to obtain the Rayleigh scatter optical spectrum and shifts in the spectral pattern can related to changes in strain or temperature. This technique results in distributed strain measurements with 1 με resolution or temperature measurements with 0.1 C resolution. These measurements can be made with sub-cm spatial resolution over a 100 m measurement range or with sub-10 cm resolution over a 1 Km range. A principle advantage of this technique is that it does not require specialty fiber. Thus, measurements can be made in pre-installed single mode or multimode fibers, including those used for telecommunication networks. Applications range from fault monitoring in short range communications networks, structural health monitoring, shape sensing, pipeline and electrical transmission line monitoring, to perimeter security. Several examples are discussed in detail.

High-accuracy fiber-optic shape sensing

We describe the results of a study of the performance characteristics of a monolithic fiber-optic shape sensor array. Distributed strain measurements in a multi-core optical fiber interrogated with the optical frequency domain reflectometry technique are used to deduce the shape of the optical fiber; referencing to a coordinate system yields position information. Two sensing techniques are discussed herein: the first employing fiber Bragg gratings and the second employing the intrinsic Rayleigh backscatter of the optical fiber. We have measured shape and position under a variety of circumstances and report the accuracy and precision of these measurements. A discussion of error sources is included.

High-resolution extended distance distributed fiber-optic sensing using rayleigh backscatter

We describe the use of swept-wavelength interferometry for distributed fiber-optic sensing in single- and multimode optical fiber using intrinsic Rayleigh backscatter. The interrogation technique is based on measuring the spectral shift of the intrinsic Rayleigh backscatter signal along an unaltered standard telecommunications grade optical fiber and converting the spectral shift to strain or temperature. This technique shows great utility as a method for highly distributed sensing over great distances with existing, pre-installed optical fiber. Results from sensing lengths greater than 1 km of optical fiber with spatial resolutions better than 10 cm are reported.

Optical Frequency Domain Reflectometry for Single- and Multi-Mode Avionics Fiber-Optics Applications

In this talk, we will introduce a commercially available optical frequency domain reflectometry (OFDR) technique and its applications in avionics fiber-optics. We will provide multiple measurement examples within the avionics field not currently supported by conventional test tools or methods including high-resolution fault detection and distributed fiber sensing

Measurement of localized heating in fiber optic components with millimeter spatial resolution

We present a novel, Rayleigh backscatter based method for ultra-high resolution distributed fiber-optic temperature sensing. This technique is applied to in-situ temperature monitoring for high-power amplifier module applications where the component itself is the sensor.

Interferometric measurement of dispersion in optical components

The development of high-quality tunable lasers and very bright, incoherent sources has made high-quality interferometric measurements available to the optical telecommunications industry. These measurements have advantages at the fundamental level because they allow linear-systems concepts and analysis to be applied to optical fiber systems. In particular, phase characteristics that have been previously measured as derivatives can be acquired directly, allowing more consistent evaluation and qualification of optical components for high-bit-rate systems.

Millimeter Resolution Otpical Reflectometry Over Up to Two Kilometers of Fiber Length

In recent years, optical frequency domain reflectometry (OFDR) has emerged as an effective measurement technique for characterizing short-haul optical networks such as those used in avionics. Comparable techniques such as optical time domain reflectometry (OTDR) and optical low coherence reflectometry (OLCR) are restricted in either spatial resolution or distance range respectively compared to OFDR. Earlier papers have shown OFDR measurements over up to 500 m in length (Soler et al., 2005). In this work, the authors demonstrate OFDR measurements over two kilometers of fiber length with millimeter level spatial resolution. The data required for this measurement was acquired in less than 100 ms and results in a sensitivity of over 130 dB. This level of measurement performance enables unprecedented visibility into fiber-optic networks. In addition, OFDR can be used for distributed fiber sensing of temperature and strain. The authors demonstrate distributed temperature sensing up to 800 degC. The paper also show distributed strain measurements at a distance of 800 m with cm level spatial resolution. These link characterization and sensing capabilities of OFDR make the technique particularly well suited for test and trouble-shooting in avionics applications.