A multi core optical fiber that includes a plurality of cores disposed in a cladding. The plurality of cores include a first core and a second core. The first core has a first propagation constant .sub.1, the second core has a second propagation constant .sub.2, the cladding has a cladding propagation constant .sub.0, and (I).

An objective of the present invention is to provide a mode conversion device capable of designing any coupling efficiency and full width at half maximum, and a design method therefor.

According to the present invention, a mode conversion device includes a long period grating at a core of an optical fiber through which light is able to propagate in at least two propagation modes. The long period grating satisfies a relationship of Expression C1, where a full width at half maximum FWHM is a wavelength band in which the coupling efficiency is a half of coupling efficiency of mode conversion at a center wavelength, C is coupling efficiency, L.sub.c is a complete coupling length, L.sub.g is a grating length, ? is a grating pitch, and ?? is a propagation constant difference between the two propagation modes at the center wavelength of a mode conversion target.

[00001]$\begin{array}{cc}\left[\mathrm{Math}.C1\right]& ?\\ \begin{array}{c}?=\frac{2?}{\mathrm{??}}\\ C={\sin }^2\left(\frac{?}{2}\frac{L_g}{L_c}\right)\\ \mathrm{FWHM}.Math.L_c=b{.Math.\frac{d??}{d?}.Math.}^{-1}\\ b=-1169.3C+1705.6\end{array}& \left(C1\right)\end{array}$

A quasi-single-mode (QSM) optical fiber includes a core and a cladding surrounding the core. The core includes a centerline and an outer edge. The cladding includes an interior edge and an exterior edge. The cladding has a cladding outer diameter defined by the exterior edge of the cladding. The cladding outer diameter may be in the range of greater than 170 m to about 200 m. The QSM fiber has a cabled cutoff wavelength that is greater than about 1530 nm. The core and the cladding support a fundamental mode LP.sub.01 and a higher-order mode LP.sub.11. The fundamental mode LP.sub.01 has an effective area A.sub.eff>150 m.sup.2.

An intravascular or other 2D or 3D imaging apparatus can include a minimally-invasive distal imaging guidewire portion. A plurality of thin optical fibers can be circumferentially distributed about a cylindrical guidewire core, such as in an spiral-wound or otherwise attached optical fiber ribbon. A low refractive index coating, high numerical aperture (NA) fiber, or other technique can be used to overcome challenges of using extremely thin optical fibers. Coating and ribbonizing techniques are described. Also described are non-uniform refractive index peak amplitudes or wavelengths techniques for FBG writing, using a depressed index optical cladding, chirping, a self-aligned connector, optical fiber routing and alignment techniques for a system connector, and an adapter for connecting to standard optical fiber coupling connectors.

An optical fiber system including an optical fiber and an optical grating is provided. The optical fiber is configured to support M mode groups, where differences in effective refractive index between adjacent mode groups are substantially equal. The optical grating is optically coupled to the optical fiber, and has a period inversely proportional to the difference in effective refractive index between adjacent mode groups. The optical grating is configured to couple all adjacent mode groups in the optical fiber.

Embodiments of the present disclosure may relate to a digitized grating that may include a first unit cell that has a first period and a first length, where the first period includes a first grating element width and a first space between adjacent grating elements, and where the first length includes a number of first periods. The digitized grating may further include a second unit cell that has a second period and a second length, where the second period is different than the first period and includes a second grating element width and a second space between adjacent grating elements, and where the second length includes a number of second periods.

An intravascular or other 2D or 3D imaging apparatus can include a minimally-invasive distal imaging guidewire portion. A plurality of thin optical fibers (804) can be circumferentially distributed about a cylindrical guidewire core (1002), such as in an spiral-wound or otherwise attached optical fiber ribbon (802). A low refractive index coating, high numerical aperture (NA) fiber, or other technique can be used to overcome challenges of using extremely thin optical fibers. Coating and ribbonizing techniques are described. Also described are nonuniform refractive index peak amplitudes or wavelengths techniques for FBG writing, using a depressed index optical cladding, chirping, a self-aligned connector, optical fiber routing and alignment techniques for a system connector, and an adapter for connecting to standard optical fiber coupling connectors.

In some implementations, an optical component includes an optical medium, the optical medium having a surface, wherein the surface includes one or more hydroxyl group terminations; and a surface layer chemically bonded to the optical medium, such that the surface layer has a thickness of less than 10 nanometers and is a hydrophobic surface, the surface layer including at least one of: a hexamethyldisilazane material, a polysiloxane material, a polydimethylsiloxane material, a fluoro-polymer material, an organosilicon material, or an organofluorine material.

A wavelength division multiplexer is disclosed. The wavelength division multiplexer may include an input waveguide, in which a plurality of Bragg gratings for separating multiplexed optical signals into respective optical signals are provided, and a plurality of output waveguides connected to the input waveguide and configured to receive the optical signals separated by the plurality of Bragg gratings. The plurality of Bragg gratings may include a first Bragg grating including first protrusions each having a first width, and a second Bragg grating including second protrusions each having a second width larger than the first width. Each of the first and second protrusions may include a curved side surface, to which a corresponding one of the optical signals is incident.

A high-power fiber cladding power stripper comprises a core unit, a cladding layer, a grating structure, and a jacket. The core unit is an optical conductive material. The cladding layer is disposed outside the core unit, wherein a refractive index of the cladding layer is lower than that of the core unit. The grating structure, disposed outside the cladding layer, is for producing diffraction effects. The jacket surrounds and protects the core unit, the cladding layer, and the grating structure. Hence, in a high-power fiber laser system, the cladding power stripper can be utilized for removing residual pump energy before the laser light entering an output collimator.