Chao Li

Liquid level measurement by applying the Mach–Zehnder interferometer based on up-tapers

A novel scheme for liquid level detection using an all-fiber Mach-Zehnder interferometer, based on two up-tapers, is proposed and experimentally investigated. The effective refractive indices of the axisymmetric modes LP(0n) are analyzed while it is partly immersed in liquid. The sensitivity of the sensor is greatly dependent on the fiber length between the two up-tapers, as well as the order of the cladding modes through the calculation. The experimental results show that the sensitivity of the Mach-Zehnder interferometer reaches a 22.5 nm wavelength shift per meter of level change with the middle fiber length of 14.3 cm. The proposal might be attractive since the up-tapered liquid level sensor could easily be fabricated and used for a large measuring range.

Ultrasensitive temperature fiber sensor based on Fabry-Pérot interferometer assisted with iron V-groove.

A fiber extrinsic Fabry-Pérot interferometer (EFPI) assisted with iron V-groove for temperature measurement is proposed and investigated by means of both numerical simulation and experiment for the first time to our best knowledge. The main temperature sensing component is acted by the iron V-groove whose coefficient of linear thermal expansion (CLTE) is much higher than that of the silica glass. Two fibers are stuck to the V-groove with two glued points, respectively. Maximum sensitivity of 260.7 nm/°C, which is the highest value for a fiber interferometric sensor up to now, has been achieved experimentally. It is worth noting that the temperature sensitivity of this sensor can be improved limitlessly via implementing a smaller gap size of the EFPI, longer distance between the two glued points or material with higher CLTE of the V-groove, theoretically.

Fiber-Optic Laser Sensor Based on All-Fiber Multipath Mach–Zehnder Interferometer

A novel fiber-optic sensor using fiber ring cavity laser based on multipath Mach-Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated. The m-MZI consists of a segment of four-core fiber (FCF) spliced between two single-mode fibers. The m-MZI is inserted in the fiber ring laser cavity, which acts as a bandpass filter and the sensing component simultaneously. Compared with previously reported MZI, higher phase sensitivity can be obtained in the proposed m-MZI due to the multipath interference configuration embedded in one fiber. The interference fringe of the FCF would shift with the variation of monitoring parameters and then caused the lasing wavelength changes. So it is available to measure these parameters by simply monitoring the variation of lasing wavelength. Experimental results show that the sensitivities of the sensor in strain, RI, and curvature are 2.21 pm/με, 113.27 nm/RIU, and 2.55 nm/m-1, respectively. Thus, the proposed sensor is easy to conduct and monitor, in addition, it also has the advantages of high resolution and high signal-to-noise ratio.

Frequency-reconfigurable terahertz wireless transmission using an optical frequency comb based on radio-over-fiber technology

Abstract. We propose a prototype for frequency-reconfigurable terahertz (THz) wireless transmission using an optical comb based on radio-over-fiber technology. In the proposal, an electro-absorption modulator (EAM) followed by a phase modulator and an intensity modulator are used to generate a flat optical comb with a tunable frequency spacing. Then, a different THz signal can be generated by photo-mixing of optical two-tone signals from the comb lines. In the scheme, we obtain 46 comb lines within a 1-dB power deviation with an interval of about 10 GHz, and a THz up to 440 GHz is obtained. Moreover, a much higher bandwidth can be easily reached by adjusting the driving signal of the EAM. The feasibility and tunability of the proposed scheme are confirmed by the simulations. This method shows a simple cost-efficient configuration and good performance over long-distance delivery.

High-Sensitive Microdisplacement Sensor Based on Fiber Mach–Zehnder Interferometer

A fiber-optic sensor based on Mach-Zehnder interferometer, which is composed of two cascaded fiber directional couplers, is investigated and applied for high-sensitive microdisplacement detecting. The free spectrum range of the transmission spectrum varies with the gap sizes in the sensing arm, which is used to sense displacement for the first time to the best of our knowledge. The experimental result is well agreed with the numerical simulation, and shows the maximum displacement sensitivity of 66 nm/μm which is at least forty times higher than that of the previous displacement fiber-optic sensors. Furthermore, the proposed sensor has the potential for higher sensitivity by enlarging the wavelength range of both optical source and signal detector.

Millimeter- and terahertz-waves generation with photonic frequency 32-tupling based on tunable lasers

Abstract. We propose and analyze a frequency 32-tupling scheme which is capable of generating millimeter and terahertz waves without being affected by the phase noise difference between two incoherent sources. In our work, the process of the optical sidebands’ phase noise change is theoretically analyzed and confirmed by simulations. In addition, the system performance in terms of linewidth, tunability, and stability is also investigated.

Application of phase-shifted fiber Bragg grating in single sideband transmission–based radio-over-fiber system

Abstract. We propose a prototype for single-sideband (SSB) transmission based radio-over-fiber system by employing a phase-shifted fiber Bragg grating. The grating has different transmission spectrum characteristics with different phase-shift magnitudes. Then, it is used in a millimeter-wave (mm-wave) SSB modulation scheme. In the scheme, only one PS-FBG is used to realize the following functions: first, the conversion from optical dual-sideband to optical single-sideband with carrier reduction modulation can be easily achieved and second, the optical carrier-to-sideband ratio (OCSR) can be eliminated completely. In our work, the OCSR can be reduced from 33.95 dB to the optimum 0 dB and a 60 GHz mm-wave can be detected after photodiode.

Fabrication of twin-core fiber and its application in all-fiber comb filter

Twin core fibers(TCFs) with different parameters were fabricated and its low loss splicing techniques are studied. The fiber comb filters based on a TCF coupler with an uniform free spectral range and based on a TCF M-Z interferometer with flat passband have been discussed.