Jianping Yao

Continuous true-time-delay beamforming employing a multiwavelength tunable fiber laser source

A true-time-delay system for wideband continuous phased array beamforming employing a novel multiwavelength tunable fiber laser source with equally increased or decreased wavelength spacing is proposed. The wavelength tuning is realized by stretching or compressing the fiber Bragg gratings cascaded in the laser cavity. To ensure a wavelength tuning with equally increased or decreased wavelength spacing, the gratings are mounted onto a plastic plate with angles between adjacent gratings selected such that the forces applied to the gratings has an equal force increment. Time delays with equally increased or decreased time delay difference for the equally spaced wavelengths are obtained when the modulated lightwaves are reflected at different locations of a linearly chirped grating. A four-channel chirped grating based true-time-delay system using the proposed light source has been constructed and experimented. Equally increased or decreased time delays are obtained when the wavelengths are tuned.

Wideband true-time-delay unit for phased array beamforming using discrete-chirped fiber grating prism

Abstract A wideband true-time-delay (TTD) unit employing a novel fiber grating prism (FGP) for phased array beamforming is proposed in this paper. The FGP consists of a single-mode fiber delay line, a chirped grating delay line and three discrete fiber Bragg grating (FBG) delay lines. The first delay line is a length of single-mode fiber, which provides a fixed time delay for all wavelengths. The second delay line, which employs a chirped grating, is used to provide small time delays. The discrete FBG delay lines, which incorporate an array of 13 discrete FBGs, are used to provide large time delays. A 5×13 fiber-grating prism is constructed and experimented. The results show that the time delays produced by the fiber grating delay lines are independent of the microwave frequency and agree well with the calculated time delays. Based on the measured time delays, the radiation patterns of 5-element array antenna are calculated and analyzed. The beampointing direction of the antenna is independent of the microwave frequency and can be controlled by tuning the wavelength of the optical carrier. This 5×13 TTD unit can provide phased array beamforming at microwave frequencies up to 6 GHz.

Wideband true-time-delay beam former that employs a tunable chirped fiber grating prism

A fiber grating prism that consists of four tunable chirped-grating delay lines for wideband true-time-delay beam forming is proposed and demonstrated. The chirped gratings are produced by use of the grating bending technique in which a uniform grating is surface mounted on a simply supported beam. We obtained chirped gratings with different chirp rates by bending the uniform gratings with different beam deflections. Four linear chirped fiber gratings with identical spectral width but linearly increased grating length are fabricated. The spectra and time-delay responses of the tunable chirped gratings are measured. A chirped-grating prism for wideband true-time-delay beam forming by use of four chirped gratings is constructed and tested experimentally. We obtained different time delays by tuning the wavelength of the optical carrier. The proposed true-time-delay beam former with a four-element phased-array steerer is suitable for continuous beam forming at microwave frequencies up to 20 GHz.

Tunable chirping of a fiber Bragg grating without center wavelength shift using a simply supported beam

The authors propose a novel technique to pro- duce adjustable chirped gratings that allows spectral width tuning without center wavelength shift. The chirp rate can be precisely tuned by bending a uniform fiber Bragg grating (FBG) surface-mounted on one side of a simply supported beam. A maximum chirp tuning with a spectral width of 18.30 nm on a uniform FBG is obtained experimentally. Compared to the existing chirp tuning techniques, the proposed tech- nique provides larger tuning range and smaller center wave- length shift.

Continuous true-time-delay beamforming employing a tunable multiwavelength fiber ring laser source with equally increased or decreased wavelength spacing

The authors propose a true-time-delay system for wideband continuous phased array beamforming using a chirped grating-based true-time-delay beamforming network incorporating a novel multiwavelength tunable fiber ring laser with equally increased or decreased wavelength spacing. The wavelength of each lasing is determined by the fiber Bragg grating in the laser cavity and tuned by compressing or stretching the fiber Bragg grating. For simultaneously achieving N tunable lasings, N fiber Bragg gratings are used. To ensure wavelength tuning with equally increased or decreased wavelength spacing, the N fiber Bragg gratings are mounted on an organic plastic plate with angles between adjacent gratings such that the tuning forces applied to the gratings experience equal increments. Time delays with equally increased or decreased time-delay difference for the equally spaced wavelengths are obtained when the modulated light waves are reflected at different locations of a linearly chirped grating. A four-channel chirped-grating-based true-time-delay system using the proposed light source for continuous beamsteering at microwave frequencies up to 10 GHz has been constructed and demonstrated.

Wideband true-time-delay system using fiber Bragg grating prism incorporated with a wavelength tunable fiber laser source

This paper presents some experimental results of a wideband true-time-delay system.. This system consists of a wavelength tunable fiber ring laser and a photonics time-delay unit constructed using discrete fiber Bragg gratings in combination with a chirped grating to increase the microwave frequency.

Wideband tunable erbium-doped fiber ring laser using switchable parallel fiber Bragg gratings

A wideband wavelength tunable Erbium-doped fiber laser using a unidirectional traveling-wave fiber ring combined with a novel switchable fiber Bragg grating (FBG) array is presented. The switchable FBG array consists of a 1 by 3 optical switch and three parallel discrete FBGs. The central reflection wavelengths of these three discrete FBGs are 1534 nm, 1549.15 nm and 1559.4 nm, respectively. The corresponding reflectivities are 90 percent, 99 percent and 99.8 percent, respectively. The wavelength of each grating can be continuously tuned in a range of over 16 nm by stretching (7 nm) and compressing (8 nm) the FBG. Therefore a fiber ring laser with a very large wavelength tuning range has been successfully demonstrated. In our experiment, the wavelength tuning range of the Erbium-doped fiber ring laser is 38 nm, from 1527 nm to 1565 nm. Within this tuning range, the total output power is about 7-8 dBm, the 3-dB linewidth is 0.01 nm, and the side mode suppression ratio is more than 48 dB. This tunable fiber ring laser can also work in the mode-locking mode when an amplitude modulator is inserted in the cavity. By applying the driving frequency matching the round-trip frequency or its multiples to the modulator, active mode-locking is realized. The highest harmonic order achieved is 125, the repetition rate and pulse-width of the mode-locked pulses are 1.00475 GHz and 539 ps, respectively.

Wideband true-time-delay unit using discrete-chirped fiber Bragg grating prism

This paper describes a wideband true-time-delay unit constructed using discrete fiber Bragg gratings in combination with a chirped grating to increase the available maximum microwave frequency. Some preliminary experimental results are presented.

Long-period fiber grating curvature sensor based on temperature-insensitive wavelength separation measurements

Long period fiber gratings (LPFGs) have important applications in fiber sensors because of their high sensitivity to temperature, strain, and refractive index of surrounding medium, et al. In this paper, we demonstrate the bending-induced resonance mode splitting of the LPFG in three different photosensitive fibers (QPS-T)fiber, O/E Land fiber and Fiber Core fiber). For the QPS-T photosensitive fiber, when the grating is bent, the resonant dip shifts to a longer wavelength with a reduction in strength and a new dip emerges at a shorter wavelength. The wavelength separation between the new dip and the original one is linear with the deflection of the grating. The similar results are also observed in two other LPFGs. But when the grating is bent, the original dip of grating shifts to a shorter wavelength and the new dip shift to longer wavelength. The different bending properties of the LPFGs are observed in the different photosensitive fiber, which is attributed to the different fiber parameters. For the LPFG written in the QPS fiber, the bending and temperature properties of the dip corresponding to the LP09 mode is studied experimentally. Based on the property that the new dip induced by the bending of fiber has the same temperature sensitivity with the original one, a temperature-insensitive curvature sensor is proposed by measuring the wavelength separation of the two dips.

Discrete-chirped fiber Bragg grating prism for wideband true-time-delay unit

A fiber grating prism consisting of a chirped grating delay line and three delay lines with thirteen discrete fiber Bragg gratings is fabricated and experimented. The system comprises a chirped grating for short time delays and three discrete Bragg grating arrays for long time delays. The introduction of the chirped grating delay line enables the system to work for beamforming at higher microwave frequencies. The experimental results of the time delay measurements agree well with the theoretical calculations. Based on the experimental data, the radiation patterns of a 4-elements array are calculated and analyzed. This fiber grating prism can provide four-channel time-delayed signals that can be fed to an antenna array to achieve beam scanning at different radiation angle. The beampointing direction of the system is determined by the grating spacing and independent of the microwave frequency. The proposed true- time delay unit with 4 X 13 phased array steerer is suitable for beamforming at frequencies up to 6 GHz.