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An ultra-stable microwave down converted from the ultra-stable laser directly by an optical frequency comb (OFC) is built at the National Institute of Metrology China. The repetition rate (f r ) of OFC is stabilized by stabilizing the sum of the carrier envelope offset frequency (f ceo ) of OFC and the beating frequency between the ultra-stable laser (USL) and OFC. A current feedback with 30 kHz bandwidth and a piezoelectric transducer with 1 kHz bandwidth are applied for the frequency stabilization. The frequency jitter of the stabilized sum frequency is about 4 Hz. Though the counting of locked f r , the shifted frequency of the USL is about 2087 Hz/day. As the frequency jitter of the mixing frequency of f ceo and the beating frequency between this OFC and another USL is about 10Hz, the short time stability of f r is calculated to be about 5e-14. This ultra-stable microwave will be applied as the local oscillator for NIM5 Cs fountain to improve its shorter term instability.

Cadmium sulfide (CdS) nanoparticles were successfully anchored on the surface of yeast via a hydrothermal process, forming fructus rubi-like CdS@yeast hybrid microspheres. In this method, the innate functional groups inherited from the hydrophilic cell wall of microbial cells were utilized to anchor the Cd2+ ion, and then the CdS@yeast hybrid particles with fructus rubi-like morphology were obtained in the presence of thioacetamide (TAA) by a hydrothermal treatment process. The products were characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), powder X-ray diffraction (XRD) and UV-Vis diffuse reflectance spectra. The sedimentation performance of CdS@yeast microspheres in aqueous solutions was evaluated to demonstrate the unique features of CdS@yeast in comparison with bulk CdS nanoparticles. The interaction between host core yeast and guests CdS nanoparticles was investigated by Fourier transform infrared (FT-IR) spectroscopy and the possible mechanisms for the formation of CdS@yeast hybrid microspheres were proposed. The model photocatalytic test showed that the fructus rubi-like CdS@yeast microsphere could efficiently remove methylene blue (MB) dyes from aqueous solutions due to the combined functions from the bio-sorption of the yeast core and photocatalytic degradation driven by the attached CdS nanoparticles. The present approach represents a guide for the preparation of a variety of hybrid composites with similar structure for treatment of toxic organic pollutants.

A displacement self-sensing laser with a resolution of λ/8 was invented by us a few years ago. This simple laser device mainly consists of a half-intracavity He–Ne laser with a birefringence element in the cavity, outputting a beam with two orthogonally polarized components. One of its cavity mirrors can move along the optical axis of the laser to change the cavity length. When this mirror is pushed (or pulled) by an item to be measured, the polarization of the laser beam varies once every λ/8 variation of the cavity length. Though the displacement self-sensing laser has many outstanding functions, its measuring range was badly limited by inevitable misalignment resulted from sway of the cavity mirror in motion. The limited range prevents the sensor from going into actual application. This paper gives a solution to the problem, using a cat's eye retroreflector to replace the flat cavity mirror of the displacement self-sensing laser to construct an anti-misalignment cavity—cat's eye cavity (CEC). The misalignment loss in the CEC is theoretically analyzed and compared with that in a flat-concave cavity, and then the experiment to test the optical stability of CEC is carried out. Furthermore, the performance of the displacement self-sensing laser based on the CEC is also investigated. Results indicate that the misalignment tolerance of the CEC is much higher than that of the flat-concave cavity, i.e. the cavity stability is greatly improved. The measuring range of the displacement self-sensing laser can be up to 12 mm with a resolution of 79.097 nm and linearity better than 0.005%.

An 800 nm band fiber Bragg grating sensing interrogation system using tilted FBG as the core wavelength division component is presented. A charge coupled device (CCD) linear array is put on the focal plane of the lens to detect the light. TFBG is used to tap light out of the fiber core to fiber cladding. The sensing wavelength is 795 to 830 nm, with accuracy of 20 pm and scan speed 100Hz. Using FBG sensor, we achieve the temperature sensitivity of 1.8 °C and strain sensitivity of 18 μ ɛ.

We are developing a new Cs fountain frequency standard in NIM, and shooting for the frequency uncertainty of a few parts in 1016. The new fountain will run in a lab with the temperature fluctuation of 0.3K, and no active temperature control system will be added outside the flight tube. Instead, an isothermal liner will be surrounded the flight tube. It is a special type of heat pipe, made of a thin layer of vacuum tube filled with pure water. The thermal conductivity of a glass isothermal liner is about 10 times higher than that of coppers. It also works like a low pass filter reducing the temperature fluctuations of the system. The advantage of using an isothermal liner is to make the temperature of the whole interrogation region more uniform and stable. With precision standard Pt thermometers measuring the temperatures of a few locations of the flight tube, the average temperature uncertainty is less than 50 mK. The frequency shift due to the blackbody radiation can be calculated, and the relative frequency shift due to black body radiation can reach down to 7.2E-17 of this new fountain clock. Key words: Fountain clock, blackbody radiation, heat pipe.

The ultra-stable laser can be converted to microwave signal with very high fidelity combining with the optical frequency comb, and the ultra-stable microwave down converted can be used as a local oscillator for Cs fountain clocks. To produce such a microwave source, we are developing a 1542 nm laser with a potential relative stability of 10 -15 in one second. In this paper, the ultra-stable laser system with some key parameters and the Pound-Drever-Hall (PDH) locking system are introduced. Furthermore, the method and procedure of coupling the laser into the cavity resonator is described and a coupling efficiency of better than 30% is achieved. Further experiments are carried out and final results will be reported in the future.

We report the generation of a 13dB 2nd order Bragg resonance in a conventionally UV inscribed 45° tilted fiber grating, showing strong polarization dependency and its application for singe polarization output of a fiber laser. © 2010 Optical Society of America.

Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP) interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were 5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is consistent with the value of 1.22pm/µepsilon obtained for a germanate fibre FBG. The Young's modulus for germanate and tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as 24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG.

In this paper, we report a simple fibre laser torsion sensor system using an intracavity tilted fibre grating as a torsion encoded loss filter. When the grating is subjected to twist, it induces loss to the cavity, thus affecting the laser oscillation build-up time. By measuring the build-up time, both twist direction and angle on the grating can be monitored. Using a low-cost photodiode and a two-channel digital oscilloscope, we have characterised the torsion sensing capability of this fibre laser system and obtained a torsion sensitivity of ~412µs/(rad/m) in the dynamic range from -150° to +150°.

A low-cost high-resolution wavelength-division-multiplexing (WDM) interrogation system operating around 800 nm region with operational bandwidth up to 60 nm and resolution of 12.7 pm utilizing a tilted fiber Bragg grating (TFBG) and a CCD-array detector has been implemented. The system has been evaluated for interrogating fiber Bragg grating based strain, temperature sensors, giving sensitivities of 0.59 pm/muepsiv and 5.6 pm/degC, which are in good agreement with previously reported values. Furthermore, the system has been utilized to detect the refractive index change of sample liquids, demonstrating a capability of measuring index change as small as 10-5. In addition, the vectorial expression of phase match condition and fabrication of TFBG have been discussed.

A multicore fibre (MCF) sensor to measure the radial deformation of a compliant cylinder under compression is presented. The sensor is connectorised and need not be permanently bonded to the test object. A differential measurement technique using FBGs written into the MCF makes the sensor temperature insensitive. FBG measurement of axial strain of a cylinder under compression is also reported.

We report a distinctive polarisation mode coupling behaviour of tilted fibre Bragg gratings (TFBGs) with tilted angle exceeding 45°. The ex-45° TFBGs exhibit pronounced polarisation mode splitting resulted from grating structure asymmetry induced birefringence. We have studied and analysed the property of ex-45° TFBGs under transverse load applied to their equivalent fast- and slow-axis. The results show that the coupling between the orthogonally polarised modes takes place only when the load is applied to its fast-axis, giving a prominent directional loading response. This transverse load related polarisation property may be exploitable for implementation of optical fibre vector sensors capable of measuring the magnitude and orientation of the applied transverse load.

We report an accelerometer based upon a simple fibre cantilever constructed from a short length of multicore fibre(MCF) containing fibre Bragg gratings (FBGs). Two-axis measurement is demonstrated up to 3 kHz.

We report the implementation of a low-cost high-resolution WDM interrogation system operating around 800nm region with bandwidth up to 60 nm and resolution of 13 pm by utilising a tilted fibre Bragg grating as an out-coupling device and a CCD-array detector. The system has been evaluated for interrogating fibre Bragg grating based strain, temperature sensors, giving sensitivities of 0.6 pm/µe and 5.6 pm/°C which are in good agreement with previously reported values. Furthermore, the system has been utilised to detect refractive index change of sample liquids, demonstrating a capability of measuring index change as small as 10-5.

An 800nm band fiber Bragg grating sensing interrogation system using TFBG as the core wavelength division component is presented. A charge coupled device (CCD) linear array is put on the focal plane of the lens to detect the light. TFBG is used to tap light out of the fiber core to fiber cladding. The sensing wavelength is 795 to 830nm, with accuracy of 20pm and scan speed 100Hz. Using FBG sensor, we achieve the temperature sensitivity as 1.8°C and strain sensitivity as 18μe.

We report for the first time the fabrication of long-period gratings in near-single-mode GeO2glass fiber by 800nm-femtosecond-laser inscription, revealing grating resonances strongly polarisation dependent and their temperature sensitivities varying significantly from 96pm/°C to 11pm/°C.

We report an implementation of optical fibre sensors based on fibre Bragg gratings with excessively tilted (>45°) structures, showing distinctive polarisation characteristics, desirable low thermal-cross-sensitivity and enhanced responsivity to surrounding-medium-refractive-index.

A transversal-load sensor based on the local pressure-induced refractive index change in a chirped fiber Bragg grating (CFBG) is proposed. The local pressure induced refractive index change in the touch point can generate a main transmission peak and several subpeaks on the long wavelength side of the reflection band of the CFBG. The difference of the wavelength shifts for the main transmission peak and the first subpeak is used to measure transversal-load with temperature compensation capability.

For the first time, Fiber Bragg grating (FBG) structures have been inscribed in single-core passive germanate and three-core passive and active tellurite glass fibers using 800 nm femtosecond (fs) laser and phase mask technique. With fs peak power intensity in the order of 10(11)W/cm(2), the FBG spectra with 2nd and 3rd order resonances at 1540 and 1033 nm in the germanate glass fiber and 2nd order resonances at approximately 1694 and approximately 1677 nm with strengths up to 14 dB in all three cores in the tellurite fiber were observed. Thermal responsivities of the FBGs made in these mid-IR glass fibers were characterized, showing average temperature responsivity approximately 20 pm/ degrees C. Strain responsivities of the FBGs in germanate glass fiber were measured to be 1.219 pm/microepsilon.

We report a distinctive polarization mode coupling behaviour of tilted fibre Bragg gratings (TFBGs) with a tilted angle exceeding 45°. The ex-45° TFBGs exhibit pronounced polarization mode splitting resulted from the birefringence induced by the grating structure asymmetry. We have fabricated TFBGs with a tilted structure at 81° and studied their properties under transverse load applied to their equivalent fast and slow axes. The results show that the light coupling to the orthogonally polarized modes of the 81°-TFBGs changes only when the load is applied to their slow axis, giving a prominent directional loading response. For the view of real applications, we further investigated the possibility of interrogating such a TFBG-based load sensor using low-cost and compact-size single wavelength source and power detector. The experimental results clearly show that the 81°-TFBGs plus the proposed power-measurement interrogation scheme may be developed to an optical fibre vector sensor system capable of not just measuring the magnitude but also recognizing the direction of the applied transverse load. Using such an 81°-TFBG based load sensor, a load change as small as 1.6 × 10-2 g may be detected by employing a standard photodiode detector.