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An active quasi-circulator integrated circuit relying on a differential central core is presented. Measurements on the quasi-circulator reveal that the forward transmission coefficients, S21 and S32, are both close to -4 dB in the range of 2.5 to 6 GHz. The isolation between the ports is greater than 20 dB and can reach up to 59 dB in the case of S13. The chip was fabricated on a standard 130 nm CMOS process and the core circuit area measures 0.105 mm2, making it the smallest active quasi-circulator known to date. [ABSTRACT FROM AUTHOR]

A long-period grating (LPG) sensor working in reflection mode is presented for refractive-index sensing applications. The sensor consists of an LPG, a bubble-like core mode scatterer, and a fibre end-face mirror. The light coupled by the LPG is reflected by the fibre end-face mirror and recoupled back to the core, whereas the light passing through the grating is eliminated by the core mode scatterer. The reflective LPG sensor was experimentally fabricated and demonstrated by measuring glycerol/water solutions. [ABSTRACT FROM AUTHOR]

A compact co-located MIMO structure with high port isolation is proposed for 2.4 GHz WLAN application. The antenna structure consists of a proximity-coupled square ring patch antenna, and a probe fed planar inverted F antenna co-located inside. The operating frequency of the two radiators is designed to be at the same frequency, and a high port isolation below -25 dB is achieved with an extremely narrow edge to edge inter-antenna space of 1 mm (0.008λ). The total lateral size of the co-located radiators is only 0.28λ×0.28λ, i.e. only about 25% of the size of a half-wavelength dual-port patch antenna. The MIMO structure gives high gains (>4.0 dB), low correlation (<0.2), and high diversity gain (about 10 dB). [ABSTRACT FROM AUTHOR]

A novel method of microwave frequency up/downconversion is proposed for microwave/millimetre-wave-based radio-over-fibre (RoF) systems. The uplink and downlink are both based on dual-wavelength single-longitudinal-mode fibre laser modulation and heterodyning, which provides the possibility to realise bidirectional RoF transmissions. [ABSTRACT FROM AUTHOR]

A two-PIFA antenna system for diversity/MIMO applications is designed with a narrow inter-PIFA spacing of only 3 mm (less than 0.024 wavelength). The proposed antenna system can cover the WLAN band (2.4–2.48 GHz) with an isolation of better than -20 dB and a maximum isolation of -37.1 dB at the central frequency. The mechanism is explained. The measured peak efficiency and gain, and the calculated envelope correlation coefficient are 75.02%, 3.48 dBi and 0.11, respectively. [ABSTRACT FROM AUTHOR]

A low-index-material-based nano-slot waveguide based on a quasi-Bragg-reflector buffer is presented. This quasi-Bragg-reflector buffer includes alternating low and high refractive index dielectric layers. The thicknesses of these dielectric layers are chosen optimally by using a genetic algorithm so that the leakage loss of the present optical waveguide is minimised. An SiO2-based slot-waveguide is designed as an example and the quasi-Bragg-reflector buffer is formed by using several Si/SiO2 bilayers. The theoretical leakage loss for an SiO2-based slot-waveguide with three optimised Si/SiO2 bilayers is about 0.01 dB/mm (at 1550 nm). The modal analysis with a full-vectorial finite-difference method shows that the present slot waveguide has an enhancement of the field distribution in the nano-slot region. [ABSTRACT FROM AUTHOR]

A novel ultra-long-distance (up to 76 km) fibre Bragg grating (FBG) sensor system based on a spectrum-limited Fourier domain modelocking fibre laser is proposed. Raman pumps are employed to form a Raman amplifier to compensate the transmission loss of the long fibre and ensure ultra-long-distance sensing. Strain sensing based on such an ultra-long-distance FBG sensor system is demonstrated with a signal-to-noise ratio over 22 dB and a sensitivity of 1.03 pm/µℇ in the wavelength domain or 18.3 ns/µℇ in the time domain. [ABSTRACT FROM AUTHOR]

A simple dual-wavelength single-longitudinal-mode erbium-doped fibre laser is proposed by incorporating a fibre Bragg grating pair, which is used as a Fabry-Perot filter with two ultra-narrow (∼0.12 pm) transmission bands. Stable dual-wavelength single-longitudinal-mode lasing with a wavelength spacing of ∼0.08 nm is achieved at room temperature. By beating the dual-wavelengths at a photodetector, a microwave signal at 9.616 GHz is demonstrated with a frequency stability better than 1 MHz and a spectral width less that 10 kHz. [ABSTRACT FROM AUTHOR]

A frequency doubling approach for optical generation of tunable microwave and millimetre-wave signals is proposed and verified experimentally. The experimental setup is based on an optical phase modulator and a simple uniform fibre Bragg grating. The generated signal is of high quality and can be tuned. [ABSTRACT FROM AUTHOR]

A novel layout for an ultra-compact arrayed-waveguide grating (AWG) demultiplexer is presented. The present layout has two overlapped free propagation regions, and is more compact than a conventional layout. Using αSi-on-SiO2 nanowire waveguides, an ultra-small 4×4 AWG (about 40×50 µm2) with channel spacing of 11 nm is fabricated and characterised. [ABSTRACT FROM AUTHOR]

A fibre Bragg grating feedback fibre laser with both Raman and erbium-doped fibre pumps is proposed. Dual-wavelength switching is achieved by controlling the power of the Raman pump. The characteristics of the dual-wavelength switching are studied experimentally, and the mechanism is explained physically. [ABSTRACT FROM AUTHOR]

A novel wavelength assignment method for a WDM ring is proposed. The new method can easily assign each wavelength directly and visually to specific connections on an N-node ring graph without the aid of any table or matrix or computer. A simple explicit formula for determining the assigned wavelength index for any node-pair connection is also given. The presented WLA method is more attractive in many aspects than other wavelength assignment methods that have been reported previously for a WDM ring. [ABSTRACT FROM AUTHOR]

A compact wideband printed MIMO antenna system (of four elements) with high isolation is presented. The proposed MIMO antenna system with an overall lateral size of only 0.43λ×0.43λ can offer 22.8% bandwidth (1.63–2.05 GHz) and isolation of better than 24 dB. The measured gain is larger than 2.72 dBi over the whole band, and the calculated envelope correlation coefficient is better than 0.01. The radiation patterns and MIMO channel capacity are also measured. [ABSTRACT FROM AUTHOR]

Two types of waveguide power splitters based on a bending multimode waveguide are demonstrated for an unbalanced power splitting ratio. An arbitrary splitting ratio is achieved by choosing the bending radius and the length of the multimode section appropriately. Experimental results show that the fabricated devices have wide bandwidth. [ABSTRACT FROM AUTHOR]

A flexibly tunable multi-frequency microwave source is presented based on optical heterodyning between the intensity-modulated optical carrier (incorporated four-wave mixing equalisation and stabilisation) and the frequency-shifted Stokes light generated by fibre stimulated Brillouin scattering. About 20 microwave frequencies centred at 10.77 or 21.62 GHz are experimentally observed. The central frequency and the frequency spacing of the multi-frequency microwave source can be freely tuned by changing the frequency shift of the beating optical waves and the driving frequency on the modulator. [ABSTRACT FROM AUTHOR]

A MIMO structure consisting of two extremely compact planar inverted-F antennas (PIFAs) (λ/60×λ/20×λ/60) is proposed for GSM 900 MHz and 2.4 GHz wireless local area network applications. The miniaturisation of each antenna is achieved through a spiral-shaped PIFA and a capacitive load, forming a LC resonator. Both antennas have a good impedance bandwidth of 0.88–0.945 and 2.39–2.48 GHz for 0.9 and 2.4 GHz band, respectively. The two PIFA antennas are polarised orthogonally to each other, and isolation better than -28 dB is achieved in both bands without any structure etched on the ground. The predicted results are compared with the measured data and good agreement is found. [ABSTRACT FROM AUTHOR]

A novel wavelength assignment method for a bidirectional two-fibre WDM network of star topology is proposed. It is shown that the minimal number of wavelengths required for an n-node star network is n (when n is odd) or n - 1 (when n is even). A simple and explicit recursive formula, which completes wavelength assignment quickly with a time complexity of O(n⊃2 log2(n)), is given. Simulation results show that the present method can give an optimal wavelength assignment much faster than conventional methods for a star network. [ABSTRACT FROM AUTHOR]