Embodiments of the current disclosure include small diameter single-mode optical fibers having gratings and methods of forming thereof. In some embodiments, methods of forming a small diameter single-mode optical fibers having gratings include providing an optical fiber having a core and cladding with a combined outer diameter of 100 μm to 125 μm and a coating having a thickness of less than or equal to 20 μm, wherein the coating comprises one of: (i) a high-modulus coating layer surrounding the cladding region; or (ii) a low-modulus coating layer surrounding the cladding region and a high-modulus coating layer surrounding the low-modulus coating layer; and exposing the core, through the coating, to a pattern of ultraviolet radiation to form an optical grating within the core.

A sensing cable includes a first optical fiber, a second optical fiber that extends along the first optical fiber and that is spaced from the first optical fiber, and a transmitting material that includes an intervention portion present between the first optical fiber and the second optical fiber, the transmitting material being configured to transmit light from the first optical fiber to the second optical fiber through the intervention portion.

A tapered fiber optoacoustic emitter includes a nanosecond laser configured to emit laser pulses and an optic fiber. The optic fiber includes a tip configured to guide the laser pulses. The tip has a coating including a diffusion layer and a thermal expansion layer, wherein the diffusion layer includes epoxy and zinc oxide nanoparticles configured to diffuse the light while restricting localized heating. The thermal expansion layer includes carbon nanotubes (CNTs) and Polydimethylsiloxane (PDMS) configured to convert the laser pulses to generate ultrasound. The frequency of the ultrasound is tuned with a thickness of the diffusion layer and a CNT concentration of the expansion layer.

Distributed fiber optic sensors formed by covering the fibers with tubing are provided. The tubing including responsive materials formulated or configured to, responsive to exposure to one of a target chemical species and a target radiation particle, change a relative size and generate a localized effect on or in the optical fiber.

Embodiments of the current disclosure include small diameter single-mode optical fibers having gratings and methods of forming thereof. In some embodiments, methods of forming a small diameter single-mode optical fibers having gratings include providing an optical fiber having a core and cladding with a combined outer diameter of 100 μm to 125 μm and a coating having a thickness of less than or equal to 20 μm, wherein the coating comprises one of: (i) a high-modulus coating layer surrounding the cladding region; or (ii) a low-modulus coating layer surrounding the cladding region and a high-modulus coating layer surrounding the low-modulus coating layer; and exposing the core, through the coating, to a pattern of ultraviolet radiation to form an optical grating within the core.

A tapered fiber optoacoustic emitter includes a nanosecond laser configured to emit laser pulses and an optic fiber. The optic fiber includes a tip configured to guide the laser pulses. The tip has a coating including a diffusion layer and a thermal expansion layer, wherein the diffusion layer includes epoxy and zinc oxide nanoparticles configured to diffuse the light while restricting localized heating. The thermal expansion layer includes carbon nanotubes (CNTs) and Polydimethylsiloxane (PDMS) configured to convert the laser pulses to generate ultrasound. The frequency of the ultrasound is tuned with a thickness of the diffusion layer and a CNT concentration of the expansion layer.

A tapered fiber optoacoustic emitter includes a nanosecond laser configured to emit laser pulses and an optic fiber. The optic fiber includes a tip configured to guide the laser pulses. The tip has a coating including a diffusion layer and a thermal expansion layer, wherein the diffusion layer includes epoxy and zinc oxide nanoparticles configured to diffuse the light while restricting localized heating. The thermal expansion layer includes carbon nanotubes (CNTs) and Polydimethylsiloxane (PDMS) configured to convert the laser pulses to generate ultrasound. The frequency of the ultrasound is tuned with a thickness of the diffusion layer and a CNT concentration of the expansion layer.

Distributed fiber optic sensors formed by covering the fibers with tubing are provided. The tubing including responsive materials formulated or configured to, responsive to exposure to one of a target chemical species and a target radiation particle, change a relative size and generate a localized effect on or in the optical fiber.

An apparatus for sensing a value of a property in a borehole having hydrogen gas penetrating a subsurface formation includes an optical fiber configured to be disposed in the borehole having the hydrogen gas and comprising a core having a fiber Bragg grating that is responsive to the value of the property and a cladding disposed about the core, wherein (i) the core is doped with a first dopant that is photo-sensitive for writing the fiber Bragg grating and that has a concentration in the core of 2 Mole % or less and (ii) the cladding is doped with a second dopant that lowers an index of refraction of the cladding.

The present invention relates to a pressure sensing device (10) comprising an optical fiber (12), the optical fiber (12) comprises a central axis (L) and at least one optical fiber core (14), the at least one optical fiber core (14) having one or more reflective FBG structures, and a coating (16) surrounding the optical fiber (12), the coating (16) having mechanical properties which are radially asymmetric along the central axis (L).