In this paper, two kinds of ultra-low temperature-sensitivity optical cables are proposed and demonstrated. Negative expansion coefficient material of liquid crystal polymer (LCP) is tightly integrated with conventional optical fibers through precise extrusion process. Performance investigations were conducted in detail. The temperature delay coefficients for the proposed optical cable products are within the range of 2.2~11.2 ps/km/℃ and -4.1~2.0 ps/km/℃ for the ambient temperature varied from -40 ℃ to +55 ℃. Compared with the conventional one, the attained performance improvement of an order of magnitude is quite attractive. To further verify the phase consistence in large-scale microwave photonics distribution, a microwave frequency distribution system is established. The phase difference is below 0.25° for a 10 GHz frequency signal in a normal room condition, while the absolute phase for each unit fluctuates over 1.6°. The proposed ultra-low temperature-sensitivity optical cables will promote diverse advances in large-scale distributed scientific facilities with high performance and simple system complexity.
In this paper, we develop and demonstrate a proof-of-principle OEO, which features ultra-low phase noise in a Ka frequency band. The prototype of the whole OEO is in a cylindrical form. The optical fibers are wound on the outside, while all the optoelectronic devices are in the center. The fiber transmission noise is suppressed via phase modulation for the power redistribution. The spur-level improvement and steady state operation is guaranteed by dual-loop structure with 8.7 km and 11.6 km fiber spools, respectively. The optical power loss is reduced by the dual-output electro-optical intensity modulator (DEOM) instead of another 50:50 optical coupler. The noise floor for the fiber link from laser intensity and phase noises is suppressed by the balanced photodetector (PD) with specialized working conditions. Performance is investigated in detail. The OEO operates at the frequency of 30 GHz with the spur suppression of 74.6 dBc. The phase noise of -130.7 dBc/Hz (-149.1 dBc/Hz) @1 kHz (10 kHz), respectively, are achieved. The spectral purity is much higher than the current commercial signal source and equipment. Further, the developed OEO is applied to the frequency conversion. The RF signal, to be converted with a frequency of 7 GHz, is coupled into the OEO. Each beat results with OEO are observed clearly. All these results show that OEO has broad prospects in high precision infrastructure and projects.
At present, the deficiency of large size and bad environmental adaption etc. hinders the engineering application of optoelectronic oscillator (OEO). By hybrid integration of photonic chips and electronic ones, a significantly miniaturized OEO with low phase noise is achieved and presented in this paper. Meanwhile, a frequency stabilization configuration based on hybrid optoelectronic phase locking is designed to improve the capability of environmental adaptation. Therefore, the OEO frequency can follow the external reference signal at real time and keep high stability as well. The performance for the OEO prototype with a volume of Φ100 mm×200 mm is investigated in detail. The spur suppression is over 70 dBc for the oscillation frequency of 10 GHz. And the phase noise of -145.9 dBc/Hz@10 kHz is reached.
Microwave photonic (MWP) based radio frequency (RF) channel is usually composed of three parts: microwave pre-processing part, electro-optical interconversion part and microwave post-processing part. The nonlinearity of active components causes serious harmonics at the output of MWP based RF channels. This paper mainly analyzes the harmonic distortions produced in the external-modulated optical transmission link and studies the variation of output harmonic power in the RF channel by changing the modulator bias point. According to the experiment, it is verified that the second harmonic can be effectively suppressed when the modulator is biased at high power point.
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