相干探测应用对光纤时频同步技术提出了新的需求,在频率同步的基础上还要能保证相位同步,并且要求低相位噪声传输。为此,研究了一种具有相位噪声净化功能的光纤绝对一致相位同步系统。首先,通过电学锁相环净化频率信号的远端相位噪声,降低了1 GHz频率信号经过26 km长光纤传输后恶化的相位噪声,比如在100 kHz频率偏移处,相位噪声降低了17.0 dB。随后,通过控制时间脉冲的往返延迟和频率信号的往返相移,实现了本远端相位差的绝对一致。当系统经历关闭重启和更改光纤链路操作后,相位差的平均值表现出约2π全周期的1%的不一致性。所设计系统可以在实现频率信号的低相位噪声传输的同时较好地保证了相干性,在相干阵列探测等场景具有重要的应用价值。

研究半导体激光器开环单向耦合的相位混沌同步。采用希尔伯特变换提取混沌激光器光场的相位时间序列,利用互相关系数、同步误差分析半导体激光器相位同步特性。实验结果表明,当注入强度大于0.80、频率失谐为-11.0~4.0 GHz时,主、从激光器可实现同步系数大于0.95的相位混沌同步,且相位混沌同步的参数范围大于强度混沌同步。实验也依据平均相位差验证了系统的相位锁定现象。

We have recently introduced a new technique, coherent hemodynamics spectroscopy (CHS), which aims at characterizing a specific kind of tissue hemodynamics that feature a high level of covariation with a given physiological quantity. In this study, we carry out a detailed analysis of the significance of coherence and phase synchronization between oscillations of arterial blood pressure (ABP) and total hemoglobin concentration ([Hbt]), measured with near-infrared spectroscopy (NIRS) during a typical protocol for CHS, based on a cyclic thigh cuff occlusion and release. Even though CHS is based on a linear time invariant model between ABP (input) and NIRS measurands (outputs), for practical reasons in a typical CHS protocol, we induce finite “groups” of ABP oscillations, in which each group is characterized by a different frequency. For this reason, ABP (input) and NIRS measurands (output) are not stationary processes, and we have used wavelet coherence and phase synchronization index (PSI), as a metric of coherence and phase synchronization, respectively. PSI was calculated by using both the wavelet cross spectrum and the Hilbert transform. We have also used linear coherence (which requires stationary process) for comparison with wavelet coherence. Themethod of surrogate data is used to find critical values for the significance of covariation between ABP and [Hbt]. Because we have found similar critical values for wavelet coherence and PSI by using five of the most used methods of surrogate data, we propose to use the data-independent Gaussian random numbers (GRNs), for CHS. By using wavelet coherence and wavelet cross spectrum, and GRNs as surrogate data, we have found the same results for the significance of coherence and phase synchronization between ABP and [Hbt]: on a total set of 20 periods of cuff oscillations, we have found 17 coherent oscillations and 17 phase synchronous oscillations. Phase synchronization assessed with Hilbert transform yielded similar results with 14 phase synchronous oscillations. Linear coherence and wavelet coherence overall yielded similar number of significant values. We discuss possible reasons for this result. Despite the similarity of linear and wavelet coherence, we argue that wavelet coherence is preferable, especially if one wants to use baseline spontaneous oscillations, in which phase locking and coherence between signals might be only temporary.

Hemodynamic low-frequency (~0.1 Hz) spontaneous oscillations as detected in the brain by nearinfrared spectroscopy have potential applications in the study of brain activation, cerebral autoregulation, and functional connectivity. In this work, we have investigated the phase lag between oscillations of cerebral deoxy- and oxy-hemoglobin concentrations in the frequency range 0.05-0.10 Hz in a human subject during a mental workload task. We have obtained a measure of such phase lag using two different methods: (1) phase synchronization analysis as used in the theory of chaotic oscillators and (2) a novel cross-correlation phasor approach. The two methods yielded comparable initial results of a larger phase lag between low-frequency oscillations of deoxy- and oxyhemoglobin concentrations during mental workload with respect to a control, rest condition.

在波长调制法的光谱吸收型气体传感器设计中,通常采用二次谐波检测技术。然而含有气体体积分数信息的被测信号和二倍频参考信号的相位差变化严重影响了二次谐波信号测量结果。采用双光路相位保持设计来解决这一问题,设计包括移相电路和双光路两部分,移相电路由数字电路组成,调整方便,用来消除电路本身固有延时; 光路部分通过增加一路不经气室吸收的参考光路,同检测光路组成双光路,保证无论光纤长度如何变化,被测信号和参考信号相位始终相同。在波长调制的基础上引入双光路相位保持设计后,随被测信号相位0～90°变化,测量结果误差值低于±10%。这种设计提高了系统检测结果的稳定性,实现了恶劣环境中,任意距离任何位置的气体体积分数检测。