Fiber optic cables with improved performance for use in distributed sensing, for instance in distributed acoustic sensors, are disclosed. In one embodiment a fiber optic cable (210) comprises a core (208) and cladding (206) disposed within a buffer material (202) surrounded by a jacket (204) and arranged so that the core is offset from the center of the cable. By offsetting the core from the center of the jacket any bending effects on the core can be maximized compared to the core being located at the center of the cable.

Example embodiments include an optical assembly for an optical interrogation system having a single core or a multicore sensing fiber, a measurement fiber to couple light into the sensing fiber, and a reference fiber arranged with the measurement fiber as part of an optical interferometer. A beam splitter combines light from the sensing fiber and with light from the reference fiber. A polarization beam splitting prism separates the combined light into first polarized light and second polarized light that is orthogonal to the first polarized light. The optical assembly can substantially reduce the size, complexity, or cost associated with the traditional optical components in an optical interrogation system that it replaces. Other example optical assemblies are described. Embodiments describe optical interrogation systems using the example optical assemblies.

The present invention relates to a method of and a system for optically connecting an optical fiber sensor (12) to an optical shape sensing console (21). The optical shape sensing console (21) has a number of single optical channels (C1, C2, C3). The optical fiber sensor (12) has a number of single fiber cores (A1, A2, A3) angularly spaced with respect to one another around a longitudinal center axis of the fiber sensor (12) and a fiber sensor connection end (30) for connection to an optical coupler (32; 38) connected to the shape sensing console (21). The optical coupler (32; 38) has the optical channels (C1, C2, C3) arranged for optical connection with the fiber cores (A1, A2, A3). A number of single calibration data sets indicative of individual optical properties of the single fiber cores (A1, A2, A3) is assigned to the single optical channels (C1, C2, C3). The fiber sensor connection end (30) is connected to the optical coupler (32; 38) such that a first fiber core (A2) of the fiber cores (A1, A2, A3) is in optical communication with a first optical channel (C1) of the optical channels (C1, C2, C3). An optical response of the first fiber core (A2) is measured by optically interrogating the first fiber core (A2) while a first calibration data set of the calibration data sets is assigned to the first optical channel (C1). The first fiber core (A2) is identified among the fiber cores (A1, A2, A3) of the fiber sensor (12) on the basis of the measured optical response of the first fiber core (A2) and the calibration data sets of the fiber sensor (12). If the first fiber core (A2) is identified as not matching with the first calibration data set used hi measuring the optical response, then a second calibration data set of the calibration data sets, which matches with the identified first fiber core (A2), is reassigned to the first optical channel (C1), or the fiber sensor connection end (30) and/or the optical coupler (32; 38) are repositioned such that a second fiber core (A1) matching with the first calibration data set is in optical communication with the first optical channel (C1).

An optical fiber sensor includes an optical fiber. The optical fiber includes a cladding having a cladding refractive index, and a plurality of fiber cores embedded in the cladding and extending along a longitudinal axis of the optical fiber. The plurality of fiber cores include a first subset of at least one first fiber core and a second subset of at least one second fiber core. The at least one first fiber core has a first core refractive index different from the cladding refractive index and a first core radius in a direction transverse to the longitudinal axis. The at least one second fiber core has a second core refractive index different from the cladding refractive index and a second core radius transverse to the longitudinal axis. The second core refractive index and the second core radius differ from the first core refractive index and the first core radius such that a temperature sensitivity of the at least one second fiber core differs from the temperature sensitivity of the first fiber core.

An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.

A fiber includes M primary cores and N redundant cores, where M an integer is greater than two and N is an integer greater than one. Interferometric circuitry detects interferometric pattern data associated with the M primary cores and the N redundant cores when the optical fiber is placed into a sensing position. Data processing circuitry calculates a primary core fiber bend value for the M primary cores and a redundant core fiber bend value for the N redundant cores based on a predetermined geometry of the M primary cores and the N redundant cores in the fiber and detected interferometric pattern data associated with the M primary cores and the N redundant cores. The primary core fiber bend value and the redundant core fiber bend value are compared in a comparison. The detected data for the M primary cores is determined reliable or unreliable based on the comparison. A signal is generated in response to an unreliable determination.

Example embodiments include an optical interrogation system with a sensing fiber having a single core, the single core having multiple light propagating modes. Interferometric apparatus probes the single core multimode sensing fiber over a range of predetermined wavelengths and detects measurement interferometric data associated with the multiple light propagating modes of the single core for each predetermined wavelength in the range. Data processing circuitry processes the measurement interferometric data associated with the multiple light propagating modes of the single core to determine one or more shape-sensing parameters of the sensing fiber from which the shape of the fiber in three dimensions can be determined.

A multi-core optical fiber includes a central core disposed at the center of a cladding; and outer cores helically wound around the central core. The following Formula (1) is satisfied:

[00001]$\begin{array}{cc}{n}_{e1}\times \left(\frac{1}{\mathrm{fw}}-B\right)<n_{e2\mathrm{ave}}\times \left(\frac{1}{\mathrm{fw}}+A\right)<n_{e1}\times \left(\frac{1}{\mathrm{fw}}+B\right)A=\sqrt{{\left(\frac{1}{\mathrm{fw}}\right)}^2+{\left(2\pi d_{\mathrm{ave}}\right)}^2}-\frac{1}{\mathrm{fw}}B=\frac{A}{1+A.Math.\mathrm{fw}}& \left(1\right)\end{array}$

where d.sub.ave is an average of a distance d between the central core and the outer cores, f.sub.w is the number of helical turns of the outer cores per unit length, n.sub.e1 is an effective refractive index of the central core, and n.sub.e2ave is an average of effective refractive indices of the outer cores.

The present disclosure provides a sensory cable (100). The sensory cable (100) includes a central strength member (106). In addition, the sensory cable (100) includes a first layer (108). The first layer (108) surrounds the central strength member (106). The first layer (108) is made of low smoke zero halogen. Further, the sensory cable (100) includes a plurality of optical units (110). Furthermore, the sensory cable (100) includes a second layer (112). The second layer (112) is made of a plurality of glass yarns. Moreover, the sensory cable (100) includes a first jacket layer (114). The first jacket layer (114) is made of either polyethylene or polypropylene. Also, the sensory cable (100) includes a second jacket layer (116). The second jacket layer (116) is made of nylon.