Jasper R. Stroud

High-speed flow microscopy using compressed sensing with ultrafast laser pulses.

We demonstrate an imaging system employing continuous high-rate photonically-enabled compressed sensing (CHiRP-CS) to enable efficient microscopic imaging of rapidly moving objects with only a few percent of the samples traditionally required for Nyquist sampling. Ultrahigh-rate spectral shaping is achieved through chirp processing of broadband laser pulses and permits ultrafast structured illumination of the object flow. Image reconstructions of high-speed microscopic flows are demonstrated at effective rates up to 39.6 Gigapixel/sec from a 720-MHz sampling rate.

Ultrawideband compressed sensing of arbitrary multi-tone sparse radio frequencies using spectrally encoded ultrafast laser pulses

We demonstrate a photonic system for pseudorandom sampling of multi-tone sparse radio-frequency (RF) signals in an 11.95-GHz bandwidth using <1% of the measurements required for Nyquist sampling. Pseudorandom binary sequence (PRBS) patterns are modulated onto highly chirped laser pulses, encoding the patterns onto the optical spectra. The pulses are partially compressed to increase the effective sampling rate by 2.07×, modulated with the RF signal, and fully compressed yielding optical integration of the PRBS-RF inner product prior to photodetection. This yields a 266× reduction in the required electronic sampling rate. We introduce a joint-sparsity-based matching-pursuit reconstruction via bagging to achieve accurate recovery of tones at arbitrary frequencies relative to the reconstruction basis.

72 MHz A-scan optical coherence tomography using continuous high-rate photonically-enabled compressed sensing (CHiRP-CS)

Randomly spectrally patterned laser pulses acquire more information in each sample, allowing for increasing imaging speed independent of detector limitations.

High-speed all-optical Haar wavelet transform for real-time image compression

We present a high-speed single pixel flow imager based on an all-optical Haar wavelet transform of moving objects. Spectrally-encoded wavelet measurement patterns are produced by chirp processing of broad-bandwidth mode-locked laser pulses. A complete wavelet pattern set serially illuminates the object via a spectral disperser. This high-rate structured illumination transforms the scene into a set of sparse coefficients. We show that complex scenes can be compressed to less than 30% of their Nyquist rate by thresholding and storing the most significant wavelet coefficients. Moreover by employing temporal multiplexing of the patterns we are able to achieve pixel rates in excess of 360 MPixels/s.

High-speed compressed sensing measurement using spectrally-encoded ultrafast laser pulses

We present a chirp processing technique for encoding pseudorandom patterns onto the spectra of broadband optical pulses for compressed sensing (CS) measurement. We demonstrate applications to characterization of ultrawideband sparse radio frequency (RF) signals and to very high-speed continuous microscopic flow imaging. In both domains, the optical sampling technique permits accurate recovery of the signals under test from only a few percent of the measurements required for conventional Nyquist sampling, significantly relaxing the required analog-to-digital conversion bandwidth and amount of data storage.

All-optical demultiplexing of Nyquist OTDM using a Nyquist gate

We present an approach to all-optical demultiplexing of ultrafast Nyquist OTDM signals using four-wave mixing with a Nyquist gate. Our design does not suffer from the tradeoff between SNR and ISI of existing approaches.

An all-optical sample-and-hold architecture incorporating amplitude jitter suppression

We experimentally demonstrate an all-optical sample-and-hold architecture for photonically-assisted ADCs. Our scheme utilizes sub-ps sampling and dispersion to create >;100-ps hold pulses and is additionally shown to reduce laser pulse amplitude jitter by 4.2 dB.

Compressive temporal focusing microscopy (Conference Presentation)

Multiphoton microscopes are of paramount importance in capturing neural activity with cellular resolution. However, the imaging speed and field-of-view of traditional two-photon microscopes is limited by raster scanning technologies. Temporally-focused two-photon (TFTP) microscopy is a wide-field scan-free approach to increase the speed of two-photon microscopy. In conventional TFTP microscopy, wide-field depth sectioning is obtained by compressing a spatially pre-chirped pulse at the focal plane of the objective. Unfortunately, the greater imaging speed of TFTP microscopes comes at the expense of poor imaging depth in tissue due to scattering of the short-wavelength fluorescence photons en-route to the imaging camera. Here we demonstrate a compressive high-speed two-photon microscope based on wide-field temporally-focused structured illumination, which eliminates the loss of image contrast from scattering of the fluorescence signal by leveraging a single-pixel detector. Specifically, we illuminate the sample with a rapid sequence of randomly structured temporally-focused wide-field illumination pulses and integrate the net two-photon fluorescence response on a single photomultiplier tube (PMT). Notably, the longer wavelength structured illumination is significantly less susceptible to scattering and the use of integrated measurements on a single PMT provides immunity to fluorescence scattering since these measurements are solely concerned with the net fluorescence. Furthermore, our approach provides greater speed than point scanning two-photon microscopes through the use of wide-field illumination and compressive image acquisition. Experimentally we demonstrate this system operating over a 200×250-μm field-of-view and at a compression rate of 10%, which provides an order of magnitude increase in speed over a comparable point scanning architecture.

All-optical demultiplexing of Nyquist OTDM signal using a biorthogonal Nyquist gate

We present an all-optical method for demultiplexing Nyquist optical time division multiplexed (OTDM) signals using a biorthogonal Nyquist gate, which is a Nyquist gate of reduced pulse width. The biorthogonality between the Nyquist symbol and Nyquist gate creates an intersymbol interference (ISI) free spectral region in the mixed product that theoretically allows for complete elimination of ISI in the demultiplexer. Furthermore, this format transparent all-optical method produces a Nyquist signal on the output suitable for further optical processing and multiplexing. We analyze the performance of this approach through simulation in the presence of nonidealities of imperfect pulse shape, timing jitter, and dispersion. Finally, we experimentally demonstrate the performance of this approach operating on an 80-GBd Nyquist OTDM signal.

Wavelength multicasting through four-wave mixing with an optical comb source

Based on four-wave mixing (FWM) with an optical comb source (OCS), we experimentally demonstrate 26-way or 15-way wavelength multicasting of 10-Gb/s differential phase-shift keying (DPSK) data in a highly-nonlinear fiber (HNLF) or a silicon waveguide, respectively. The OCS provides multiple spectrally equidistant pump waves leading to a multitude of FWM products after mixing with the signal. We achieve error-free operation with power penalties less than 5.7 dB for the HNLF and 4.2 dB for the silicon waveguide, respectively.