Provided is an optical device which can control a beam quality of outgoing light. An optical device (10) includes an entrance fiber bundle (12), an exit fiber (13), and a reduced diameter part (11). The reduced diameter part (11) has (i) an entrance end surface (11a) and (ii) an exit end surface (11b) which is narrower in area than the entrance end surface (11a). In a case where the entrance end surface (11a) is viewed from a normal direction of the entrance end surface (11a), a center (C2) of the exit end surface (11b) deviates from a center (C1) of the entrance end surface (11a).

Systems and methods are provided for stabilizing the resonance properties of a microring resonator modulator. Intrinsic optical absorption within the p-n junction of a microring modulator resonator is employed as a feedback signal for thermally stabilizing the microring resonator modulator. In some example embodiments, the input optical power provided to a bus waveguide that is optically coupled to the microring resonator modulator is sufficiently low such that the photocurrent dependence on input power is predominantly linear in nature, thereby avoiding or reducing the effect of nonlinear absorption through two-photon absorption. The example embodiments described herein may be employed to achieve a fabrication process that is free of heterogeneous device integration, for example, avoiding the integration of germanium detectors with a silicon-based integrated optical circuit or the need to sacrifice a portion of the ring resonator circumference for the integration of an extrinsic defect-mediated photodetector, thus reducing complexity and manufacturing cost.

Systems and methods are provided for stabilizing the resonance properties of a microring resonator modulator. Intrinsic optical absorption within the p-n junction of a microring modulator resonator is employed as a feedback signal for thermally stabilizing the microring resonator modulator. In some example embodiments, the input optical power provided to a bus waveguide that is optically coupled to the microring resonator modulator is sufficiently low such that the photocurrent dependence on input power is predominantly linear in nature, thereby avoiding or reducing the effect of nonlinear absorption through two-photon absorption. The example embodiments described herein may be employed to achieve a fabrication process that is free of heterogeneous device integration, for example, avoiding the integration of germanium detectors with a silicon-based integrated optical circuit or the need to sacrifice a portion of the ring resonator circumference for the integration of an extrinsic defect-mediated photodetector, thus reducing complexity and manufacturing cost.

Advantageously, at least one embodiment of the present disclosure comprises a polarization maintaining PROFA (PM-PROFA) coupler in which the polarization axes of the individual vanishing core waveguides thereof are oriented or aligned without the need to adjust the orientation of each individual VC waveguide.

A method for manufacturing an optical fiber emitting plasma light includes a coating removal step of removing a coating of an optical fiber; a photocatalyst application step of applying a photocatalyst to an end surface of a core layer of the optical fiber from which the coating has been removed through the coating removal step; and a molding step of molding the end surface of the core layer into a curved surface by applying a laser to the core layer of the optical fiber applied with the photocatalyst through the photocatalyst application step. The method for manufacturing an optical fiber including the above processes may be effectively used for therapy such as plasma disc coagulation therapy (PDCT) by converting the applied laser light into plasma light.

Provided is an optical coupler configured to cause an NA of light, which exits a taper fiber, to be smaller as compared with a conventional optical coupler. A taper fiber has a high refractive index part which is provided inside a core of the taper fiber and which has a refractive index smaller than a refractive index n.sub.core of the core. An exit end surface of each GI fiber is bonded to an entrance end surface of the taper fiber so that at least a part of the exit end surface of the each GI fiber overlaps with a section of the high refractive index part. A relative refractive index difference of the taper fiber is smaller than 0.076%.

In one example, a device includes a bus waveguide to carry a light of a carrier wavelength, a first ring waveguide with a first modulator, a first heater to adjust a resonance wavelength of the first ring waveguide, and a second ring waveguide with a second modulator. The first ring waveguide and the second ring waveguide are coupled to the bus waveguide and are to modulate the light of the carrier wavelength to impart one of at least four optical power levels to the light. In another example, a device includes, a bus waveguide, a first ring waveguide with a first modulator, and a second ring waveguide with a second modulator. The first ring waveguide and the second ring waveguide are coupled to the bus waveguide and are to modulate a light of a carrier wavelength to impart one of at least four optical power levels to the light.

An optical fiber sensor extends coaxially with a controllable heater to provide high-resolution axial measurement of thermal properties such as thermal convection of the surrounding, Heat removal by either conduction or convection may be used to deduce material height in a tank, or velocity of flow when coupled with localized heating, or other aspects of the material based on thermal conductivity.

An optical fiber sensor extends coaxially with a controllable heater to provide high-resolution axial measurement of thermal properties such as thermal convection of the surrounding, Heat removal by either conduction or convection may be used to deduce material height in a tank, or velocity of flow when coupled with localized heating, or other aspects of the material based on thermal conductivity.

A multicore fiber 1 includes: a small diameter portion 33 in which a propagation constant of light of an x.sub.1-th order LP mode of the first core 11 (here, x.sub.1 is an integer of 2 or more and x or less, x is an integer of 2 or more) and a propagation constant of light of a y1-th order LP mode of the second core 12 (here, y.sub.1 is an integer of 1 or more and y or less other than x.sub.1, y is an integer of 1 or more) coincide with each other and a large diameter portion in which a propagation constant of light of each LP mode of the first core 11 and a propagation constant of light of each LP mode of the second core 12 are configured not to coincide with each other are arranged.