Measuring vibration by using fiber Bragg grating and demodulating it by blazed grating

A method of measuring vibration by using fiber Bragg grating (FBG) and demodulating the spectrum by blazed grating is introduced. The sensor system is made of a simple supported beam with a FBG adhered to its upper surface. A blazed grating is used to demodulate the changing spectrum that is got from the sensor system, and a line charge-coupled device (CCD) is used to accept the diffraction spectrum. Through analyzing the number of the CCD's pixels, we can get the amplitude of vibration and the change of the temperature. The experimental results show that the vibration amplitude of the exciter matches the detected signal under the stable frequency. The temperature shift and vibration signal are also successfully separated.     

A strain-induced birefringent double-clad fiber Bragg grating

Fiber birefringence plays an important role in complex polarization dynamics of rare-earth-doped fiber lasers[1]. Recently some novel lasers and double-clad (DC) fiber lasers (DCFL), have attracted much interest for high power lasers. Such lasers have a second cladding area to facilitate pumping with semiconductor lasers. Different cladding structures, such as rectangular, star-shape, and circular, are all in use to provide an efficient absorption of pump energy by the fiber core. It raises…     

Encoded cell grating array in anti-counterfeit technology

The dot matrix hologram (DMH) has been widely used in anti-counterfeiting label. With the same technology and cell array configuration, we can encode to the incidence beam. These codes can be some image matrix grating with different grating gap and different grating orientation. When the multi-level phase diffractive grating is etched, the incidence beam on the cell appears as an encoding image. When the encoded grating and DMH are used in the same label synchronously, the technology of multi-encoded grating array enhances the anti-counterfeit ability.     

Multiplexed reflective-matched optical fiber grating interrogation technique

The multiplexed-reflective matched fiber grating interrogation technique was presented in this paper. The interrogation technique was based on the use of two (or more) wavelength-matched fiber Bragg gratings (FBGs) to receive the reflected signal from the sensing FBG. The two (or more) matched gratings were arranged parallelly and used as filters to convert wavelength into intensity encoded information for interrogation. Theoretical and experimental results demonstrated that the interrogation system is immune to the source fluctuation and cross-sensitivity effect between temperature and strain, and also can enlarge the dynamic range.     

Compensating large PMD by a fiber grating

In this paper, the first- and second-order polarization mode dispersion (PMD) with the amount of 132.994-ps differential group-delay (DGD) and maximum 476.129-ps/nm second-order PMD can be compensated by a two-stages PMD compensator at a 40-Gb/s optical fiber communication system. The first stage has one free degree that is used for first order and high orders PMD compensations by rotating the state of     

Fiber Bragg grating hydrophone with high sensitivity

A fiber Bragg grating(FBG)hydrophone with high sensitivity was demonstrated.This hydrophone used a rubber diaphragm and a copper hard core as the sensing element.To compensate the hydrostatic pressure, a capillary tube was fixed at the end of the hydrophone.Theoretical analysis of the acoustic pressure sensitivity was given in this letter.Experiments were carried out to test the frequency response of the hydrophone.The result shows that when the Young's modulus of the diaphragm is higher,a flatter frequency response will be obtained.     

High focusing grating reflectors with TE-polarized normal incidence

We design two types of reflectors by using subwavelength high-index contrast gratings,which exhibit similar high focusing capabilities at normal incidence with a TE-polarized plane wave.One type has bars of different heights,whereas the other has bars of different depths.Both grating reflectors are designed to be approximately 22 μm in structural length and 10 μm in focal length,at an operating wavelength of 1.55 μm.Both achieve a full-width-half-maximum of 0.9 μm at the focal plane,which is fairly close to the diffraction limit.Their reflectance reach as high as 94% and 91%.     

Fiber Bragg grating pressure sensor with enhanced sensitivity

A novel fiber Bragg grating(FBG)pressure sensor with the enhanced sensitivity has been demonstrated.A piston-like diaphragm with a hard core in the center is used to enhance the sensitivity.Both the theoretical analysis and the experimental result show that the radius of the hard core has significant effect on the pressure sensitivity.When the radius of the hard core is 1.5 ram,a pressure sensitivity of 7.23 nm/MPa has been achieved.     

Fabricating blazing grating on NGD by photochemical etching

This paper tries to introduce the reader to the method of using photochemical re-action to copy holographic optical elements(HOEs)in relief.The holographic blazing gratingso copied is groove depth adjustable phase modulability enlarged through copying and 3.3times the diffraction efficiency(DE)of the original grating.It is expected that the newmethod will lead to the mass production of the light-weight HOEs at low cost.     

‘Chirped’ grating coupler: a holographic approach

Based on a holographic approach an analysis of the chirped grating coupler is performed. Relations for the location of a focal line of a coupled out cylindrical wave for general construction parameters are obtained. Results of the analysis have been verified experimentally.     

Holographic grating formation in dry photopolymer film with shrinkage

An important issue in developing applications for photopolymers in holography is the effect of shrinkage on recording properties. In this paper, we introduce a model to describe real-time formation of a single grating in photopolymers at any geometrical angle, under the assumption that the shrinkage is in proportion to the polymerization. This model combines polymerization kinetics with the coupled-wave theory, explaining the shrinkage effect on the diffraction efficiency. The model is validated by comparing its predictions with the experimental results for a film of 99μm thickness.     

Bragg grating chemical sensor with hydrogel as sensitive element

A novel fiber Bragg grating (FBG) based chemical sensor using hydrogel, a swellable polymer, as sensitive element is demonstrated. The sensing mechanism relies on the shift of Bragg wavelength due to the stress resulted from volume change of sensitive swellable hydrogel responding to the change of external environment. A polyacrylamide hydrogel fiber grating chemical sensor is made, and the experiments on its sensitivity to the salinity are performed. The sensitivity is low due to the less stress from the shrinking or swelling of hdrogels. Reducing the cross diameter of the grating through etching with hydrofluoric acid can greatly improve the sensitivity of the sensor.     

Optimization of constant-length Rowland-circle monochromator with a varied line-spacing grating

We use a varied line-spacing (VLS) grating to improve the performances of the constant-length Rowland-circle spherical grating monochromator. The translation distance of the mirror-grating tank in a scan of certain wavelength range will get much shorter. This will make the instrument easier to realize. Based on the principle of monochromator, we study how to optimize the optical system with a VLS grating in detail. The main imaging performances of the instrument are also evaluated.     

Tow—Dimensional Micro—grating Formed by Polystyrene Spheres

We report a simple method to make two-dimensional plane gratings that can be used as splitters. In the self-assembly process, the colloidal spheres can form single layer square or triangular lattice on a fiat surface and in our experiments the triangular lattice is a more common structure. As an incident beam passes through the triangular lattice, it can be split into seven sub-beams, among which six beams have the same density and scattering angle. This grating is not sensitive to the polarization direction of the incident light.     

A new subdivision technique for grating based on CMOS microscopic imaging

We propose a new subdivision technique directly subdividing the grating stripe by using complementary metal-oxide semiconductor (CMOS) microscopic imaging system combined with image processing. The corresponding optical system, subdivision principle, and image processing methods are illuminated. The relations of systemic resolution to subdivision number, grating period, magnifying power and tilt angle are theoretically discussed and experimentally checked on the Abbe comparator. The measurement precision for displacement of the proposed subdivision system is tested in the range of 5 mm and the maximum displacement error is less than 0.4μm. The factors contributing to the systemic error are also discussed.     

Kapitza-Dirac diffraction without standing waves: diffraction without a grating?

We discuss electron diffraction from two counterpropagating light waves with two different frequencies. We show that, even though these waves do not form a standing wave, electron diffraction similar to the conventional Kapitza-Dirac effect, i.e., scattering on a standing wave, is still possible. The nonlinear response of the electron to the laser fields creates a stationary diffraction grating from which the same electron scatters.     

Optical implementation of butterfly interconnection and digital logic operation by grating

Optical butterfly interconnection and four primary optical perallel logic opera-tions are implemented by means of phase grating and liquid crystal light valve (LCLV),whichoffers a simple new scheme for implementing optical butterfly interconnections and digitalcomputations.     

Compact grating displacement measurement system with a 3 × 3 coupler

We present a compact displacement measurement system possessing the capability of nanometer-scale precision.On basis of integrating single grating with 3 × 3 coupler for phase shift in interference signal, the present scheme features advantages of simple structure, convenient alignment, and insensitivity to air turbulence. Linear comparisons between our system and HP5530 show a residual error less than 81 nm during step motions along a10 mm round-trip, and a discrepancy less than 15 nm in the case of 200 μm movement. We also demonstrate a measurement stability test in a duration of 300 s, which shows the proposed scheme potentially performs better than HP5530 in terms of long-term stability.