Suppression of interference noise caused by Fresnel reflection in all-fiber white-light interferometer.

We propose methods to suppress the interference noise (IN) of an all-fiber white-light interferometer (WLI), which is caused by the residual Fresnel reflective beam. The methods are proposed to ensure a wide dynamic range and enhance the accuracy of measurement. IN can cause misjudgment of the realistic optical characteristic parameters, such as the fault diagnosis and polarization coupling of the optical devices under test. In addition, IN can reduce the dynamic range of the WLI. The optical path mismatch (OPM) method and the intensity suppression (IS) method by changing the positions and intensity of the IN are presented. The two suppression methods can successfully restrain IN caused by the Fresnel reflection beams. The experimental results show that IN is successfully suppressed by the OPM method or restrained by IS method in interferograms, and the dynamic range can achieve 85 dB without IN.

Range extension of the optical delay line in white light interferometry.

We propose an effective and promising method to extend the continuous range of the optical delay line in white light interferometry. The method adopts the combination of switchable fixed delays and a continuous-scanning stage laid in one arm of the interferometer. Moreover, a fiber ring constructed by a fiber coupler is employed in the other arm to achieve self-calibration and improve the delay precision, voiding the use of a specialized measurement instrument. The range-extension method maintains the original performances of the stage just through the process of orderly copying and jointing. The setup with 16 parallel fixed delay paths is experimentally demonstrated. The insertion loss of the optical delay line will not increase as the range extension and keeps an average of 1.45 dB with a fluctuation of ±0.15 dB(3σ) over a delay range of 37.2 m without a blind zone. In addition, the delay precision as a function of the port number of the optical switch does not deteriorate and remains at a level of 10.21 µm with a standard deviation of 0.08 µm. The loss and delay precision features enable the proposed structure to be extended without limitation, which is particularly significant for practical applications.

Global Synchronization Measurement of Multivariate Neural Signals with Massively Parallel Nonlinear Interdependence Analysis.

The estimation of synchronization amongst multiple brain regions is a critical issue in understanding brain functions. There is a lack of an appropriate approach which is capable of 1) measuring the direction and strength of synchronization of activities of multiple brain regions, and 2) adapting to the quickly increasing sizes and scales of neural signals. Nonlinear Interdependence (NLI) analysis is an effective method for measuring synchronization direction and strength of bivariate neural signal. However, the method currently does not directly apply in handling multivariate signal. Its application in practice has also long been largely hampered by the ultra-high complexity of NLI algorithms. Aiming at these problems, this study 1) extends the conventional NLI to quantify the global synchronization of multivariate neural signals, and 2) develops a parallelized NLI method with general-purpose computing on the graphics processing unit (GPGPU), namely, G-NLI. The approach performs synchronization measurement in a massively parallel manner. The G-NLI has improved the runtime performance by more than 1000 times comparing to the original sequential NLI. Meanwhile, the G-NLI was employed to analyze 10-channel local field potential (LFP) recordings from a patient suffering from temporal lobe epilepsy. The results demonstrate that the proposed G-NLI method can support real-time global synchronization measurement and it could be successful in localization of epileptic focus.