Haidong You

Photonic-Assisted Periodic Triangular-Shaped Pulses Generation With Tunable Repetition Rate

An optical triangular-shaped pulses generator with tunable repetition rate is proposed and analyzed. Using optical carrier suppression modulation and active polarization control, the optical intensity with its expression corresponding to the Fourier expansion of typical triangular-shaped waveform can be generated. It is also found that the pulses repetition rate is only dependent on the driving frequency of local oscillator. Thus, by changing it, continuous tunability of repetition rate is obtained. The mechanism is first analyzed by theory and then verified by simulation. Continuous tunability of the repetition rate (20–40 GBps) is obtained by using one 50/100-GHz optical interleaver. The proposal might be attractive since tuning the repetition rate requires only one frequency-tunable oscillator.

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.

Dumbbell-Shaped Mach–Zehnder Interferometer With High Sensitivity of Refractive Index

We proposed and fabricated a dumbbell-shaped Mach-Zehnder interferometer (MZI) on a single mode fiber using a revised program of the fusion splicer. To the best of our knowledge, it is the first time one has produced and applied the MZI of this configuration to detect liquids refractive indexes. The dumbbell shape has a length of 1.9 mm and a minimum waist diameter of 63 μm. The wavelengths shift with the changing of surrounding refractive indexes, and the refractive index sensitivity is as high as 251 nm per refractive index unit with the linear range of 1.333-1.391 that is tens of times higher than the MZI based on two fiber tapers.

D-band millimeter-wave generator based on a frequency 16-tupling feed-forward modulation technique

Abstract. A prototype of a 160 GHz millimeter-wave (mm-wave) generator is proposed and analyzed. In the scheme, two lasers with 100 GHz frequency interval serve as sources. Then, a frequency 16-tupling feed-forward modulation technique is employed to generate two-phase correlated sidebands with a 160 GHz interval. The desired sidebands can be selected by using optical interleavers. A 160 GHz mm-wave signal free of phase noise can be achieved.

Optical temporal differentiator using a twin-core fiber

Abstract. Twin-core fiber (TCF) can provide the required spectral response for implementing an optical temporal differentiator. It is shown that the output temporal waveform from one core of the TCF providing full energy coupling is proportional to the first derivative of the optical temporal signal launched at the input. Moreover, TCF can also be used as the first order optical temporal differentiator for multiwavelength optical signals, in which the position and the number of central wavelength can be tunable simply by changing the fiber length. Our numerical results confirmed that the TCF has a good accuracy by calculating the first time derivatives of the input optical signals with temporal features in the picosecond and subpicosecond ranges.

Bidirectional 60 GHz RoF system with two millimeter-wave signals generated by a novel generation scheme

A two millimeter-wave signal generation scheme for a bidirectional 60 GHz radio-over-fiber system is theoretically analyzed and numerically verified. Three dual-electrical Mach-Zehnder modulators (MZMs) and two optical inter-leavers (OILs) are employed, and MZM1, MZM2, and MZM3 are biased at the minimum, maximum, and minimum transmission points, respectively. The two OILs and a fiber Bragg grating are used to separate the subcarriers after transmission. In the scheme, a tunable laser serves as the optical source, and two 60 GHz millimeter-wave signals with modulating data are generated to transmit diversity, and a remote local oscillator is also generated. The analytical models for transmission through a dispersive medium are confirmed by simulations. It is found that chromatic dispersion has little impact on the bit error rate performance when a narrow-linewidth laser and a noise management technique are employed.

Multi-Wavelength Optical Single-Sideband Modulated WDM Radio-over-Fiber Systems by Employing a Twin-Core Fiber

Multi-wavelength optical single-sideband (OSSB) modulation for wavelength-division-multiplexed radio-over-fiber (WDM-RoF) systems using a twin-core fiber (TCF) is proposed and demonstrated in this study. A TCF shows a periodic transmission spectrum due to the inherent coupling between the cores. Optical double-sideband (ODSB) signals generated by a Mach-Zehnder modulator pass through the TCF to realize multi-wavelenth OSSB modulation for WDM-RoF systems. Due to the negative slope of the TCF transmission spectrum, the upper-sideband experiences higher attenuation than the lower-sideband for each wavelength channel. In addition, the optical carrier-to-sideband ratio (OCSR) also can be optimized, simultaneously, which can enhance the transmission performance of RoF links. The performance analysis of the proposal is carried out via simulations, results show that the receiver sensitivity is improved 10.35 dB with OCSR reducing from 12.48 to 6.89 dB. The RF power fluctuation also can be optimized by employing the TCF to suppress the upper-sidebnd (or lower-sideband).

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.

Design and performance analysis of high-order optical temporal differentiator with twin-core fiber

A simple and general approach for implementing all-fiber high-order optical temporal differentiator based on twin-core fiber (TCF) is presented and demonstrated. Specifically, the core 2 (or core 1) of the TCF should be cut in N sections with the same length for achieving N ’th-order optical temporal differentiator, which can be considered to consist of N cascaded first-order optical temporal differentiators based on TCF. Our simulations show that the proposed approach can provide optical operation bandwidths in the several THz regime, which is capable of accurately processing time features as short as subpicoseconds. Performance analysis results show a good accuracy calculating the high-order time differentiation of the optical signal launched at core 2 (or core 1).

Optical Signal Phase Reconstruction for WDM System by Employing Twin-Core Fiber based Differentiator

A technique based on twin-core fiber based differentiator (TCFD) for recovering phase profile of WDM signal from intensity measurements is presented. The key significance is that the phase profiles can be reconstructed for each channel.