We present a high-precision optical phase-locking based on wideband acousto-optical frequency shifting.Increasing the modulating bandwidth stabilizes the loop at a high loop gain,thus improving phase correction capability.An optical phase-locked loop with a wide control bandwidth is constructed.The closed-loop residual phase error is only 0.26°or smaller than λ/1000.The loop exhibits excellent correction capability for high-frequency noises.The correctable frequency range reaches 35 kHz when the noise amplitude is ±λ/2,and becomes even wider for smaller noise amplitudes.
在空间相干光通信应用中,针对传统激光器线宽较宽、相位噪声大、易导致锁相环路失锁的问题,研制了单频Nd:YAG非平面环形(NPRO)激光器,其线宽小于1 k Hz,相对强度噪声(RIN)低于-150 d B/Hz,具有窄线宽、低噪声的特点。搭建了光锁相环路,在信号光功率-67 d Bm的情况下实现了两台NPRO激光器的相位锁定。在此基础上开展了信号频率为10 MHz和1.25 GHz的模拟通信实验,在信号光功率分别为-60 d Bm和-53 d Bm时可观测到较理想的眼图。在2.5 Gbps数字通信实验中,接收灵敏度达到-50 d Bm,此时误码率为3.2×10-6。系统灵敏度可接近量子极限,明显优于传统的IM/DD方式,是一种适合长距离、大容量传输的空间通信方式。
We propose a Mbius-strip-type plasmonic cavity with a silver Mbius strip sandwiched between dielectric layers.By brief theoretical and simulation analyses, we obtain that the Q factor of the cavity remains about 40 and the mode volume is ultrasmall(less than 1 μm3) which is more compact than that of the cylindric cavity. This Mbius-strip-type plasmonic cavity supporting the propagation of surface plasmon polaritons owns some unusual properties such as more effective volume and the spatial separation. More potential applications based on this cavity remain to be explored in future nanophotonics.
With propagating through a dispersive medium,the temporal–spectral profile of optical pulses should be inevitably modified.Although such dispersion effect has been well studied in classical optics,its effect on a singlephoton wave-packet has not yet been entirely revealed.In this paper,we investigate the effect of dispersion on indistinguishability between single-photon wave-packets through the Hong–Ou–Mandel(HOM)interference.By dispersively manipulating two weak coherent single-photon wave-packets which are prepared by attenuating mode-locked laser pulses before interfering with each other,we observe that the difference of the second-order dispersion between two optical paths of the HOM interferometer can be mapped to the interference curve,indicating that(i)with the same amount of dispersion effect in both paths,the HOM interference curve must be only determined by the intrinsic indistinguishability between the wave-packets,i.e.,dispersion cancellation due to the indistinguishability between Feynman paths;and(ii)unbalanced dispersion effect in two paths cannot be canceled and will broaden the interference curve thus providing a way to measure the second-order dispersion coefficient.Our results suggest a more comprehensive understanding of the single-photon wave-packet and pave ways to explore further applications of the HOM interference.
