This paper shares a conjecture that in a specific low temperature region, the fiber delay coefficient with temperature exists a transition process. In the specific low temperature region, the soft and hard state of the optical fiber coating changes with temperature, which affects the strain effect of the coating on fiber core. At normal temperature, the soft inner coating layer has no strain on fiber core, while at ultra-low temperature, the inner plastic coating becomes frozen and hard. The frozen coating exerts strain on fiber core, resulting in additional length change and the increase of fiber delay coefficient. According to the theoretical analysis and experimental data, this paper briefly introduces the sources and main influencing factors of optical fiber delay, emphatically analyzes the influence of optical fiber coating on fiber delay coefficient in a specific low temperature region, and gives the possible explanation of the action of coating on fiber delay coefficient.
This paper reviewed and summarized microwave photonics beamforming architecture which could directly apply in 5G communications in recent years. However, those research still have some limits. We investigated the connection of radio frequency (RF) links and antenna elements (AEs) at present 5G multi-antenna systems and propose a microwave photonics beamforming architecture with dynamic subarray by combing reconfigurable optical routing networks with independent optical true time delay units. Optical routing networks enable distributing signals to AEs which are any number and at any position, to accomplish the dynamic combinations of those AEs. Independent optical true-time delay units enable the array could transmit or receive the RF beams towards or from different directions simultaneously. We simulated the beam pattern of the proposed system in various communication situations to validate our concept can effectively expand the application field of microwave photonics beamforming systems and could bring the advantages of microwave photonics technology, such as large bandwidth, low loss, immunity to electromagnetic interference, and non-beam squint effect.
A real-time hybrid optoelectronic analog-to-digital converter (HOE-ADC) based on optical sampling and electronic quantization is proposed and experimentally demonstrated. In the proposed HOE-ADC, a broadband semiconductor laser is intensity modulated by electronic pulses to generate an optical sampling pulse train. The optical sampling pulse is split into multiple channels with different optical fiber delay, and the analog signal is modulated on the multichannel optical sampling pulses using a Mach–Zehnder modulator array. By broadening the optical pulses, which can be done by employing optical-fiber chromatic dispersion, the bandwidth of the sampled pulse is reduced to match the sample rate of a low-speed electronic ADC, where the broadened optical sampling pulses are quantified. The nonlinearity of optical devices is calibrated through digital signal processing. A four-channel HOE-ADC is experimentally demonstrated. A sampling rate of 12 GS / s and a system bandwidth of 10 GHz are achieved. The effective number of bit (ENOB) for a 1.5-GHz target analog signal is measured to be 5.9 bit. Further, the primary influence factors, such as delay errors, for the performance of ENOB are also discussed.
We report on a fiber-optic delay-based quasidistributed temperature sensor with high precision. The device works by detecting the delay induced by the temperature instead of the spectrum. To analyze the working principle of this sensor, the thermal dependence of the fiber-optic delay was theoretically investigated and the delay-temperature coefficient was measured to be 42.2 ps/km°C. In this sensor, quasidistributed measurement of temperature could be easily realized by dense wavelength-division multiplexing and wavelength addressing. We built and tested a prototype quasidistributed temperature sensor with eight testing points equally distributed along a 32.61-km-long fiber. The experimental results demonstrate an average error of <0.1°C. These results prove that this quasidistributed temperature sensor is feasible and that it is a viable option for simple and economic temperature measurements.
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