Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.

How complicated must an optical component be

Abstract: We analyze how complicated a linear optical component has to be if it is to perform one of a range of functions. Specifically, we devise an approach to evaluating the number of real parameters that must be specified in the device design or fabrication, based on the singular value decomposition of the linear operator that describes the device. This approach can be used for essentially any linear device, including space-, frequency-, or time-dependent systems, in optics, or in other linear wave problems. We analyze examples including spatial mode converters and various classes of wavelength demultiplexers. We consider limits on the functions that can be performed by simple optical devices, such as thin lenses, mirrors, gratings, modulators, and fixed optical filters, and discuss the potential for greater functionalities using modern nanophotonics.

Spatially coherent white-light interferometer based on a point fluorescent source

Abstract: We developed a point-fluorescent-source-based white-light interferometer for high-resolution reflectometry, range-gating imaging, and group-velocity-dispersion measurement. The laser-pumped point fluorescent source has 9 mW of power and a spatial coherence of 0.97, which allows it to be used like a laser beam. Owing to its 40-nm FWHM spectral width, the width of its temporal autocorrelation is only 19 fs, which corresponds to that of 14-fs Gaussian pulses.

Informed spatial filtering for sound extraction using distributed microphone arrays

Abstract: Hands-free acquisition of speech is required in many human-machine interfaces and communication systems. The signals received by integrated microphones contain a desired speech signal, spatially coherent interfering signals, and background noise. In order to enhance the desired speech signal, state-of-the-art techniques apply data-dependent spatial filters which require the second order statistics (SOS) of the desired signal, the interfering signals and the background noise. As the number of sources and the reverberation time increase, the estimation accuracy of the SOS deteriorates, often resulting in insufficient noise and interference reduction. In this paper, a signal extraction framework with distributed microphone arrays is developed. An expectation maximization (EM)-based algorithm detects the number of coherent speech sources and estimates source clusters using time-frequency (TF) bin-wise position estimates. Subsequently, the second order statistics (SOS) are estimated using bin-wise speech presence probability (SPP) and a source probability for each source. Finally, a desired source is extracted using a minimum variance distortionless response (MVDR) filter, a multichannel Wiener filter (MWF) and a parametric multichannel Wiener filter (PMWF). The same framework can be employed for source separation, where a spatial filter is computed for each source considering the remaining sources as interferers. Evaluation using simulated and measured data demonstrates the effectiveness of the framework in estimating the number of sources, clustering, signal enhancement, and source separation.

Phase-locked array of antiguided lasers with monolithic spatial filter

Abstract: Phase-locked arrays with monolithically integrated diffractive spatial filters are proposed and demonstrated. Noncollinear sets of antiguides separated by a half-Talbot distance favour in-phase-mode oscillation. Diffraction-limited fundamental-mode operation is obtained to over twice threshold and in far-field patterns with as much as 75% of the energy in the main lobe.

On-sky performance during verification and commissioning of the Gemini Planet Imager's adaptive optics system

Abstract: The Gemini Planet Imager instrument's adaptive optics (AO) subsystem was designed specifically to facilitate high-contrast imaging. It features several new technologies, including computationally efficient wavefront reconstruction with the Fourier transform, modal gain optimization every 8 seconds, and the spatially filtered wavefront sensor. It also uses a Linear-Quadratic-Gaussian (LQG) controller (aka Kalman filter) for both pointing and focus. We present on-sky performance results from verification and commissioning runs from December 2013 through May 2014. The efficient reconstruction and modal gain optimization are working as designed. The LQG controllers effectively notch out vibrations. The spatial filter can remove aliases, but we typically use it oversized by about 60% due to stability problems.