An FBG element is configured to apply a phase shift to at least one of an input optical signal, a first pump light, and an idler signal between stages of a phase sensitive amplifier. The FBG element is apodized using a trapezoidal apodization function over the length of the first FBG element to enable tuning of the phase shift over a range of 2 radians.

A sensing apparatus for detecting at least one target molecule in a gaseous medium is provided, comprising an optical fiber having a core with a tilted grating, and a coating assembly. The coating assembly has a composite film layer having an outer surface in direct contact with the gaseous medium, and contains at least two compositions mixed with one another therein, which include one or more surface plasmon resonance (SPR)-active compositions and one or more reacting compositions that are reversibly reactive to the at least one target molecule. Depending on different reacting compositions, the sensing apparatus can detect various target gas molecules such as hydrogen, ammonia, methane, and formaldehyde, etc. The sensing apparatus has relatively fast response time and high resistance to deactivation. A sensing system based on the sensing apparatus, a manufacturing method of the sensing apparatus, and a detection method using the sensing system, are further provided.

Systems, apparatuses, and methods are described for modifying a beam parameter product of a laser beam. The modified beam parameter product may increase the number of tasks that may be performed using a given laser with its original beam parameter product. By increasing the beam parameter product of a laser, an initial low beam parameter product beam may be used to perform tasks requiring a higher beam parameter product. The beam may be modified to redirect portions of the beam at different angles via one or more non-imaging refracting optical components or by one or more Fiber Bragg gratings.

Optical fiber filters and uses thereof are presented. In typical implementations, there is provided a FBG taking deleterious light out of a fiber core without reflecting it into the fiber core. It also allows the unhindered transmission of useful light at a wavelength outside of the spectral band covered by the deleterious light. The filter couples the incoming deleterious light to cladding modes propagating in the opposite direction without coupling the incoming useful light to core or cladding modes propagating in the opposite direction. The filter may for example be useful as a Raman or ASE filter in a laser cavity of other optical devices.

A sensing apparatus for detecting at least one target molecule in a gaseous medium is provided, comprising an optical fiber having a core with a tilted grating, and a coating assembly. The coating assembly has a composite film layer having an outer surface in direct contact with the gaseous medium, and contains at least two compositions mixed with one another therein, which include one or more surface plasmon resonance (SPR)-active compositions and one or more reacting compositions that are reversibly reactive to the at least one target molecule. Depending on different reacting compositions, the sensing apparatus can detect various target gas molecules such as hydrogen, ammonia, methane, and formaldehyde, etc. The sensing apparatus has relatively fast response time and high resistance to deactivation. A sensing system based on the sensing apparatus, a manufacturing method of the sensing apparatus, and a detection method using the sensing system, are further provided.

An embodiment of an optical structure includes a core having first and second ends and a first side with a first grating profile having a first phase shift distributed between the first and second ends, and a cladding disposed around the core. Such an optical structure can be used in an electro-optic modulator (EOM), and can render the EOM smaller in size than currently available EOMs.

In accordance with an embodiment, a bandpass transmission filter having a center wavelength of transmission includes: a waveguide structure comprising a grating structure having changing grating pitch values configured to diffract radiation in the waveguide structure having a first wavelength lower than the center wavelength of transmission, and configured to reflect radiation in the waveguide structure having a second wavelength higher than the center wavelength of transmission; and a radiation absorbing structure configured to absorb radiation guided by the waveguide structure having a third wavelength higher than the second wavelength, wherein the radiation absorbing structure is an integrated part of the waveguide structure or comprises a layer arranged adjacent to the waveguide structure.

An in-line fiber-optic sensing element, a system, and methods for detecting strain using a fiber optic sensor are described that include using at least two chirped grating structures. In an implementation, an in-line fiber-optic sensing element that employs example techniques in accordance with the present disclosure includes an optically transmissive fiber including a core and an outer layer; a Fabry-Perot cavity defined by a portion of the optically transmissive fiber and two chirped fiber-Bragg grating structures, where the two chirped grating structures are separated and are configured to reflect light.

Optical coupling techniques between an optical fiber and another optical device, such as a planar optical waveguide, or a probed region are disclosed. An optical fiber for lateral optical coupling includes a cladding, a core disposed in the cladding, a reflecting structure inclined relative to the fiber axis, and a light-converging structure embedded in the cladding. The reflecting structure is configured to reflect light between the core and a lateral coupling path extending and providing lateral optical coupling between the core and an exterior of the fiber. The cladding-embedded light-converging structure is configured to intercept and converge light traveling along the lateral coupling path. In some implementations, the optical fiber is a fiber-optic transition coupled between a main optical fiber and another optical device or a probed region. A coupled optical system including an optical fiber coupled to another optical device is also disclosed.

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.