Brandon W. Buckley

Digitally synthesized beat frequency multiplexing for sub-millisecond fluorescence microscopy

A confocal fluorescence microscopy scheme that maps the image to the radiofrequency spectrum by beating together two optical fields offers enhanced read-out speeds at kilohertz frame rates. It provides a new way for observing dynamic phenomena in cells.

Digital broadband linearization of optical links

We present a digital postprocessing linearization technique to efficiently suppress dynamic distortions added to a wideband signal in an analog optical link. Our technique achieves up to 35 dB suppression of intermodulation distortions over multiple octaves of signal bandwidth. In contrast to conventional linearization methods, it does not require excessive analog bandwidth for performing digital correction. This is made possible by regenerating undesired distortions from the captured output, and subtracting it from the distorted digitized signal. Moreover, we experimentally demonstrate a record spurious-free dynamic range of 120 dB·Hz(2/3) over a 6 GHz electrical signal bandwidth. While our digital broadband linearization technique advances state-of-the-art optical links, it can also be applied to other nonlinear dynamic systems.

Coherent time-stretch transformation for real-time capture of wideband signals

Time stretch transformation of wideband waveforms boosts the performance of analog-to-digital converters and digital signal processors by slowing down analog electrical signals before digitization. The transform is based on dispersive Fourier transformation implemented in the optical domain. A coherent receiver would be ideal for capturing the time-stretched optical signal. Coherent receivers offer improved sensitivity, allow for digital cancellation of dispersion-induced impairments and optical nonlinearities, and enable decoding of phase-modulated optical data formats. Because time-stretch uses a chirped broadband (>1 THz) optical carrier, a new coherent detection technique is required. In this paper, we introduce and demonstrate coherent time stretch transformation; a technique that combines dispersive Fourier transform with optically broadband coherent detection.

Coherent Time-Stretch Transform for Near-Field Spectroscopy

The coherent time-stretch transform enables high-throughput acquisition of complex optical fields in single-shot measurements. Full-field spectra are recovered via temporal interferometry on waveforms dispersed in the temporal near field. Real-time absorption spectra, including both amplitude and phase information, are acquired at 37 MHz.

All-optical time-stretch digitizer

We propose and demonstrate an all-optical time-stretch digitizer for real-time capture of ultrafast optical signals, beyond the bandwidths achievable by electronics. This approach uniquely combines four-wave mixing and photonic time-stretch technique to slow down and record high-speed optical signals. As a proof-of-concept, real-time recording of 40-Gb/s non-return-to-zero on-off-keying optical data stream is experimentally demonstrated using a stretch factor of 54 and 1.5-GHz back-end electronic bandwidth. We also report on the observation of dispersion penalty and its mitigation via single-sideband conversion enabled by an optical bandpass filter. Our technique may provide a path to real-time capture of ultrahigh-speed optical data streams.

Spectrally encoded angular light scattering

The angular light scattering profile of microscopic particles significantly depends on their morphological parameters, such as size and shape. This dependency is widely used in state-of-the-art flow cytometry methods for particle classification. We introduce a new spectrally encoded angular light scattering method, with potential application in scanning flow cytometry. We show that a one-to-one wavelength-to-angle mapping enables the measurement of the angular dependence of scattered light from microscopic particles over a wide dynamic range. Improvement in dynamic range is obtained by equalizing the angular dependence of scattering via wavelength equalization. Continuous angular spectrum is obtained without mechanical scanning enabling single-shot measurement. Using this information, particle morphology can be determined with improved accuracy. We derive and experimentally verify an analytic wavelength-to-angle mapping model, facilitating rapid data processing. As a proof of concept, we demonstrate the methods capability of distinguishing differently sized polystyrene beads. The combination of this technique with time-stretch dispersive Fourier transform offers real-time and high-throughput (high frame rate) measurements and renders the method suitable for integration in standard flow cytometers.

Ultra-wideband instantaneous frequency estimation

Determining the instantaneous frequency of a signal is required for many applications ranging from radio astronomy to defense applications. Unfortunately, the scan rate is often too long over a wideband spectrum compared to the time scale of signals of interest. We present an instantaneous frequency measurement receiver, which allows for simultaneous measurement of multiple frequencies and amplitudes across an ultra-wide instantaneous bandwidth. Powered by the photonic time stretch A/D converter, the high effective sampling throughput of the system provides high temporal resolution and improvement of frequency and amplitude estimation capability through advanced signal processing. This flexible system has adjustable instantaneous bandwidth and frequency resolution, an ultrafast sweep time, and reduced hardware complexity compared to other instantaneous frequency measurement systems.

First Demonstration of a Cross-Layer Enabled Network Node

Exploding traffic demands and increasing energy consumptions facing todays networks are driving the designs of next-generation networking technologies. Cross-layer enabled approaches will allow for the packet-level control of the optical layer, to enable dynamic resource allocation and traffic engineering at the physical layer. We demonstrate an intelligent cross-layer enabled network node that can support high-bandwidth, all-optically routed packets, using emerging photonic technologies including optical packet switched fabrics and packet-scale performance monitoring. Using a cross-layer control and management plane, the node can dynamically optimize optical switching based on higher-layer constraints such as quality-of-service and energy consumption, as well as quality-of-transmission metrics such as link integrity and bit-error rates. We demonstrate a first-generation prototype of the cross-layer node, outlining its architecture and major implemented subsystems. The packet-rate physical-layer reconfiguration of the nodes fabric is shown using an implemented performance monitor and control plane. The realized node supports 8 40-Gb/s wavelength-striped optical packets with pseudorandom data with error-free transmission (bit-error rates less than ), in conjunction with the heterogeneous transmission of video traffic using 10-Gigabit Ethernet optical network interface cards based on field-programmable gate arrays.

Cross-layer signal monitoring in an optical packet-switching test-bed via real-time burst sampling

A photonic time-stretch enhanced recording oscilloscope enabling real-time burst sampling is realized within an optical switching fabric test-bed. 10-Gb/s eye diagrams are captured with the high-speed digitizer, showcasing the potential for real-time cross-layer network optimization.

Time-stretch oscilloscope with dual-channel differential detection front end for monitoring of 100 Gb/s return-to-zero differential quadrature phase-shift keying data

Optical performance monitoring of high-capacity networks is one of the enabling technologies of future reconfigurable optical switch networks. In such networks, rapid performance evaluation of data streams becomes challenging due to the use of advanced modulation formats and high data rates. The time-stretch enhanced recording oscilloscope offers a potential solution to monitoring high-rate data in a practical time scale. Here we demonstrate an architecture with a differential detection front end for simultaneous I/Q data monitoring of a 100 gigabits/s return-to-zero differential quadrature phase-shift keying signal. This demonstration shows the potential of this technology for rapid performance monitoring of high-rate optical data streams that employ advanced modulation formats.