30 results about "Bragg resonance" patented technology

An optical sensor for sensing information relating to an analyte liquid or gas, has a a planar substrate having a refractive index nc. The planar substrate supports a ridge waveguide having an unclad top portion having a refractive index nr. The substrate serves as cladding layer for the ridge waveguide at a location where the ridge waveguide contacts the substrate. A Bragg grating inscribed in the ridge waveguide has two modes for providing information relating to both temperature and refractive index of the surrounding analyte liquid or gas. A cladding mode has a different response to the analyte when compared to a Bragg resonance response. Both modes have a same reaction to temperature, wherein said Bragg grating is formed within the unclad region of ridge waveguide, wherein nc.<nr. Advantageously multiple parameters can be sensed using only a single Bragg grating.

A method for writing a Bragg grating in a rare-earth doped glass optical waveguide is provided. Ultrafast optical pulses are generated, preferably in the femtosecond range and having a writing wavelength in the range of 300 nm to 700 nm and an intensity sufficient to induce a change of refractive index in the rare-earth doped glass waveguide through densification. The optical pulses are diffracted using a phase mask, to generate an interference pattern having a pitch providing a fundamental Bragg resonance corresponding to the target wavelength to be reflected by the grating. The interference pattern is impinged on a region of the rare-earth doped glass waveguide, which is heated to a temperature above a threshold of about 350° C., for a predetermined heating period. Advantageously, the heating step allows the elimination of photodarkening effects which would otherwise be present in the waveguiding properties of the waveguide.

The invention belongs to the field of sensing technology, in particular to a dual-parameter measuring device for hydrogen concentration and ambient temperature based on an inclined optical fiber grating. It includes a light source, a tilted fiber grating coated with a palladium-silver alloy film, a single-mode fiber and a spectrometer. The light source is connected to a tilted fiber grating coated with a palladium-silver alloy film through a single-mode optical fiber, and the other end of the grating is connected to a spectrometer through a single-mode optical fiber. When the device is in a hydrogen environment, the palladium-silver alloy film will absorb hydrogen in the environment, causing changes in the evanescent field of the optical fiber. Its evanescent wave resonates with the surface plasmon wave generated by the free electrons on the metal surface, resulting in a resonance peak. The hydrogen concentration can be measured by using the interval between the plasma resonance peak and the Bragg resonance peak. The Bragg resonance peaks of tilted fiber gratings are sensitive to temperature. Therefore, we can use the plasmon resonance peak and Bragg resonance peak of the tilted fiber grating to realize the dual-parameter measurement of hydrogen concentration and temperature.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

The invention discloses a fiber grating Bragg resonance wavelength determination method based on period modulation. According to the invention, by imposing periodical strain on a cantilever beam, a periodically changed reflection spectrum is obtained; by carrying out Fourier transform on curves of change of an intensity value at each wavelength point of each spectrum along with the modulation time, the specific value of second harmonic generation components and fundamental components therein is solved; by use of the specific value at each wavelength point, the spectrum of narrowing down of half-height is reconstructed, so the position of a peak point of the fiber grating reflection spectrum is quite precisely acquired; and high precision demodulation of the fiber grating is achieved. Compared with the prior art, the spectrum of narrowing down of half-height is reconstructed finally, and demodulation precision is further improved.

The invention discloses a method for extracting wave height from sea echo first-order Bragg harmonic peak of a high-frequency ground wave radar. The method comprises the steps of building a response curve of the Bragg wave spectrum value based on the wave height; calibrating the first-order peak power of a long-distance unit through the wave length subjected to second-order spectrum inversion and the first-order peak powder in a near distance unit of the radar, so as to calculate the wave height distribution in the long-distance unit. The method is mainly dependent on the unsaturation feature of the Bragg wave; the wave height is extracted from the first-order Bragg resonance peak; the first-order peak under the general ocean state is obviously more than that in the second-order spectrum, so that the wave height detection distance of the high-frequency ground wave radar can be greatly improved; meanwhile, the portable radar adopting a compact receiving antenna has the space resolution for obtaining the wave height; therefore, the development, popularization and application are greatly promoted.

The invention relates to a method for realizing simultaneous sensing of temperature, strain and refractive index through a single fiber bragg grating (FBG). A localized FBG is written in a few-mode fiber by using femtosecond laser. The FBG transmitted spectrum is provided with multiple bragg resonance peaks and multiple cladding mode resonance peaks. All the bragg resonance peaks have different responses to the temperature and the strain and are not sensitive to the external refractive index. All the cladding mode resonance peaks have different responses to the external refractive index and the strain and are not sensitive to the temperature. The amount of movement of two bragg resonance peaks selected in the FBG transmitted spectrum and the normalized area ( the specific value of the area formed by enclosing of the upper and lower envelop of the cladding mode resonance peaks to the initial area) of the cladding mode resonance peaks are measured so as to realize simultaneous sensing of the temperature, the strain and the refractive index through the single FBG. The beneficial effects of the method are that the method has high sensing sensitivity, the signals are easy to demodulate, the sensing head is easy to manufacture and the mechanical strength is high with no requirement for special packaging.

The invention belongs to the laser technology field and especially relates to an all-silicon distributed feedback laser. A resonant cavity of the laser is formed through directly imprinting a Bragg grating on a nano-crystalline film. Simultaneously, the nano-crystalline film provides an optical gain so that the distributed feedback laser is formed. The nano-crystalline film is formed through carrying out heat annealing conversion on photoresist HSQ, and then high pressure hydrogen passivation processing is performed so that the nano-crystalline film possesses a high optical gain equivalent to that of a conventional laser semiconductor material. The Bragg grating is manufactured through a nanometer imprinting technology and a grating period corresponds to a second-order Bragg resonance condition of a laser wavelength. Laser light possesses high diffraction efficiency along a direction vertical to a grating surface direction and vertical emitting of the laser light can be realized. The invention provides a on-chip laser of an all-silicon material. The laser structure is compact and cost is low. A disadvantage that a silicon-based laser based on a semiconductor gain material is not compatible with a traditional silicon technology is avoided.

The present invention proposes a design method of an ultra-transmissive waveguide based on polarization resonance and Bragg resonance, and applies the ultra-transmissive waveguide to a surface plasmon waveguide system in which the basic unit consists of nano-scale metal-dielectric-metal waveguides and cyclically aligned laterally coupled resonators. Thus, the chain resonator structure has guide wave and band gap characteristics similar to that of photonic crystals. In the excitation of the single-ended waveguide mode, the waveguide mode is coupled with the lateral coupling resonance mode to modulate the transmission characteristics. In particular, the operating frequency of the waveguide structure can be controlled by the intrinsic frequency of the lateral resonator. The waveguide as a whole can achieve filtering, transmission and super transmission to form a laser state. In addition, the design method utilizes the gain and loss of the resonator to modulate the waveguide transmission characteristics. The design method gives the dispersion relation of the super transmission waveguide based on the coupling mode theory and the Bragg theory, combined with the polarization resonance and the Bragg resonance interaction.

The broadband high-efficiency muffling tube structure based on non-Bragg resonance is characterized in that the tube wall of the tubular muffling tube undulates periodically, and the undulating change of each cycle means that the inner wall of the tube is composed of adjacent concave-convex ring-shaped undulations, each change The width of the period is equivalent to the size of the average radius of the muffler tube, the frequency of the incident wave is audible, and the mode and direction of the incident wave are arbitrary; the muffler tube contains more than 5 periods. By changing the parameters of the periodic tube wall, such as the number of periods, the size of undulations, etc., the muffler volume of the muffler can be controlled. Through the selection of its pipe wall period, the anechoic frequency band can be changed according to actual engineering needs. In practical engineering applications, it can also be combined with other resistive noise reduction methods to improve the sound absorption effect. Furthermore, this structure can also be used as an acoustic filter.