Various implementations of an apparatus for sensing one or more parameters are disclosed herein. The apparatus includes a sweeping wavelength laser configured to generate a sweeping wavelength optical signal; an optical fiber including a Fiber Bragg Grating (FBG) structure configured to sense a parameter, wherein the optical fiber is configured to receive the sweeping wavelength optical signal, wherein the FBG structure is configured to produce a reflected optical signal with a particular wavelength in response to the sweeping wavelength optical signal, and wherein the particular wavelength varies as a function of the parameter; a photo detector configured to generate an electrical signal based on the reflected optical signal; a comparator configured to generate a pulse based on a comparison of the electrical signal to a threshold; and a processor configured to generate an indication of the parameter based on the pulse. The comparator may be configured as a Schmitt trigger.

The present disclosure generally pertains to systems and methods that utilize optical frequency discriminators based on fiber Bragg gratings. In some embodiments, an optical frequency discriminator has a polarization-maintaining fiber Bragg grating (PM-FBG), and an incoming polarized optical signal is reflected from the PM-FBG, which differentiates the two polarization modes in the incoming signal according its frequency relative to the two resonance peaks of the PM-FBG. The optical frequency discriminator then compares (e.g., subtracts) the reflected power in the two polarization modes to provide an output having an amplitude that varies linearly with the frequency of the incoming signal. This output may then be used to extract various information about the frequency of the incoming signal. As an example, the output may be used to recover data that has been frequency modulated onto the incoming signal or to characterize the frequency noise of the incoming signal.

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 vortex optical fiber for use in an illumination subsystem of an optical imaging system (e.g., a stimulated emission depletion (STED) microscopy system) includes an elongated optically transmissive medium having a set of regions including a core region, a trench region surrounding the core region, a ring region surrounding the trench region, and a cladding region, the set of regions having a doping profile providing a n.sub.eff for vector modes in an LP.sub.11 mode group of greater than 110.sup.4 in the visible spectral range so as to simultaneously guide stable Gaussian and orbital angular momentum (OAM) carrying modes at corresponding visible wavelengths.

A monitoring system monitors changes in an index of refraction of the grating over a time interval that includes the period of time. The monitoring system includes a light source assembly, a probing assembly, a power meter (e.g., a diffraction and/or a transmittance power meter), and a controller. The light source assembly emits a probe beam. The scanning assembly scans the probe beam over an area of the grating. The power meter measures power of a portion of the probe beam that interacts (e.g., is transmitted by or diffracted from) with the area of the grating. The controller determines changes in grating parameters (may be as a function of time) for the grating being formed based in part on measured power readings over the time interval.

A vortex optical fiber for use in an illumination subsystem of an optical imaging system (e.g., a stimulated emission depletion (STED) microscopy system) includes an elongated optically transmissive medium having a set of regions including a core region, a trench region surrounding the core region, a ring region surrounding the trench region, and a cladding region, the set of regions having a doping profile providing a n.sub.eff for vector modes in an LP.sub.11 mode group of greater than 110.sup.4 in the visible spectral range so as to simultaneously guide stable Gaussian and orbital angular momentum (OAM) carrying modes at corresponding visible wavelengths.

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 fiber Bragg grating interrogator assembly, comprising: an optical fiber including a fiber Bragg grating (FBG; 122) having a variable Bragg wavelength (.sub.B) and a dynamic range of interest (.sub.dyn,B) over which the Bragg wavelength (.sub.B) can shift during use; a light source operably connected to the optical fiber, and configured to illuminate the fiber Bragg grating to solicit a response therefrom; and an response analyzer, including: a spectrally selective device having an input port and a plurality of output ports (149-n), wherein the input port is operably connected to the optical fiber and wherein each of the output ports is associated with a respective spectral range (.sub.n), said spectrally selective device being configured to provide a spectral energy distribution of a response of the fiber Bragg grating received on the input port onto said output ports.

Application of non-uniform strain to discrete segments of a fiber grating mechanically changes the structure type of the associated device, e.g., the refractive index perturbation profile of the fiber grating is changed from uniform to phase shifted superstructured, or from chirped to superstructured. The strain may be applied with one or more deformable corrugated slides which are bonded to the fiber grating between the discrete segments. The applied strain changes the local period of fiber grating. Complex changes may be achieved via variations of corrugated slide dimensions. An LPFG may be provided with bare fiber by applying periodically longitudinal axial strain to fiber at multiple discrete segments on the fiber.

An apparatus for measuring state variables with at least one fiber-optic sensor, containing at least one optical coupler, at least one filter element and at least one photoelectric converter, where the optical coupler, the filter element and the photoelectric converter are integrated on a substrate, and the filter element contains at least one Bragg grating which is designed to supply the light portion reflected by the Bragg grating to the photoelectric converter.