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 surgical method and tool for establishing a steam bubble between a fiber tip and a surgical target. The device and process capable of maintaining the steam bubble by providing a low-power, continuous-wave laser emission. Furthermore, the method and tool capable of delivering to the surgical target through the steam bubble a therapeutic laser emission providing ablation of the surgical target.

The refractive index of a fiber core of a few mode optical fiber is n1. A cladding layer surrounding the fiber core includes: a downward-concave cladding layer surrounding the fiber core, the refractive index thereof is n2; a first upward-convex cladding layer surrounding the downward-concave cladding layer, the refractive index thereof is n3; a second upward-convex cladding layer surrounding the first upward-convex cladding layer, the refractive index thereof is n4; an outer layer surrounding the second upward-convex cladding layer, the refractive index thereof is n5. The refractive indexes of the fiber core, the downward-concave cladding layer, the first upward-convex cladding layer, the second upward-convex cladding layer, the outer layer satisfy: n.sub.1>n3>n.sub.4>n.sub.5>n.sub.2. The fiber is a non-single mode in a direct waveguide state, and equivalent single-mode transmission can be achieved when the optical fiber is bent at a specific bending radius.

An optical fiber, such as in some instances a high-power, diode-pumped, dual-clad, ytterbium-doped fiber amplifier (YDFAs), having a fundamental mode and at least one higher order mode, wherein the higher order mode or modes have mode areas that are substantially larger than a mode area of the fundamental mode.

A polymer optical fibre (POF) (30) for transmitting light of wavelength, ?i, between two separate elements of an active implantable medical device (AIMD), includes a core (31) which is cylindrical and made of a cyclic olefin polymer (COP) or copolymer (COC), having a core refractive index at the wavelength, ?i, n_core, A cladding (32) which has a cladding refractive index at the wavelength, ?i, n_clad<n_core, and which is made of a cladding copolymer including monomers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride. The cladding being itself enclosed in a coating (33) which is made of a coating polymer formed of one of the monomers of the cladding copolymer. The POF has a numerical aperture, NA, at the wavelength, ?i, of at least 0.5.

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.

Some embodiments of the disclosure relate to an optical transmission system that operates at a wavelength in the range from 950 nm to 1600 nm and that employs a single-mode optical transmitter and an optical receiver optically coupled to respective ends of a multimode fiber designed for 850 nm multimode operation. The optical transmission system also employs at least one single mode fiber situated within the optical pathway between the optical transmitter and the receiver and coupled to the multimode fiber.

Some embodiments of the disclosure relate to an optical transmission system that operates at a wavelength in the range from 950 nm to 1600 nm and that employs a single-mode optical transmitter and an optical receiver optically coupled to respective ends of a multimode fiber designed for 850 nm multimode operation. The optical transmission system also employs at least one single mode fiber situated within the optical pathway between the optical transmitter and the receiver and coupled to the multimode fiber.

Holey fibers provide optical propagation. In various embodiments, a large core holey fiber comprises a cladding region formed by large holes arranged in few layers. The number of layers or rows of holes about the large core can be used to coarse tune the leakage losses of the fundamental and higher modes of a signal, thereby allowing the non-fundamental modes to be substantially eliminated by leakage over a given length of fiber. Fine tuning of leakage losses can be performed by adjusting the hole dimension and/or spacing to yield a desired operation with a desired leakage loss of the fundamental mode. Resulting holey fibers have a large hole dimension and spacing, and thus a large core, when compared to traditional fibers and conventional fibers that propagate a single mode. Other loss mechanisms, such as bend loss and modal spacing can be utilized for selected modes of operation of holey fibers.

The refractive index of a fiber core of a few mode optical fiber is n1. A cladding layer surrounding the fiber core includes: a downward-concave cladding layer surrounding the fiber core, the refractive index thereof is n2; a first upward-convex cladding layer surrounding the downward-concave cladding layer, the refractive index thereof is n3; a second upward-convex cladding layer surrounding the first upward-convex cladding layer, the refractive index thereof is n4; an outer layer surrounding the second upward-convex cladding layer, the refractive index thereof is n5. The refractive indexes of the fiber core, the downward-concave cladding layer, the first upward-convex cladding layer, the second upward-convex cladding layer, the outer layer satisfy: n.sub.1>n3>n.sub.4>n.sub.5>n.sub.2. The fiber is a non-single mode in a direct waveguide state, and equivalent single-mode transmission can be achieved when the optical fiber is bent at a specific bending radius.