Impact of polarization pulling on optimal spectrometer design for stimulated Brillouin scattering microscopy.

Brillouin spectroscopy has become an important tool for mapping the mechanical properties of biological samples. Recently, stimulated Brillouin scattering () measurements have emerged in this field as a promising technology for lower noise and higher speed measurements. However, further improvements are fundamentally limited by constraints on the optical power level that can be used in biological samples, which effectively caps the gain and signal-to-noise ratio () of biological measurements.

Photonic next-generation reservoir computer based on distributed feedback in optical fiber.

Reservoir computing (RC) is a machine learning paradigm that excels at dynamical systems analysis. Photonic RCs, which perform implicit computation through optical interactions, have attracted increasing attention due to their potential for low latency predictions. However, most existing photonic RCs rely on a nonlinear physical cavity to implement system memory, limiting control over the memory structure and requiring long warm-up times to eliminate transients.

Integrated photonic encoder for low power and high-speed image processing.

Modern lens designs are capable of resolving greater than 10 gigapixels, while advances in camera frame-rate and hyperspectral imaging have made data acquisition rates of Terapixel/second a real possibility. The main bottlenecks preventing such high data-rate systems are power consumption and data storage. In this work, we show that analog photonic encoders could address this challenge, enabling high-speed image compression using orders-of-magnitude lower power than digital electronics.

Dynamic temperature-strain discrimination using a hybrid distributed fiber sensor based on Brillouin and Rayleigh scattering.

We present a distributed fiber sensor capable of discriminating between temperature and strain while performing low-noise, dynamic measurements. This was achieved by leveraging recent advances in Brillouin and Rayleigh based fiber sensors. In particular, we designed a hybrid sensor that combines a slope-assisted Brillouin optical time domain analysis system with a Rayleigh-scattering-based frequency scanning optical time domain reflectometry system.

Massively distributed fiber strain sensing using Brillouin lasing.

Brillouin based distributed fiber sensors present a unique set of characteristics amongst fiber sensing architectures. They are able to measure absolute strain and temperature over long distances, with high spatial resolution, and very large dynamic range in off-the-shelf fiber. However, Brillouin sensors traditionally provide only modest sensitivity due to the weak dependence of the Brillouin frequency on strain and the high signal to noise ratio required to identify the resonance's peak frequency to within a small fraction of its linewidth.

Enhanced bandwidth distributed acoustic sensing using a frequency multiplexed pulse train and micro-machined point reflector fiber.

In this Letter, we present an enhanced bandwidth distributed acoustic sensor (DAS) that uses a frequency multiplexed interrogation system to probe a micro-machined point reflector fiber. The fiber contains a series of discrete point reflectors with reflectance as high as -48 dB, while the frequency multiplexed interrogator allows us to increase the effective pulse repetition rate by a factor of 10. Together, this enables a phase noise as low as -101 dB (re rad/Hz) for a 2.

Frequency multiplexed coherent φ-OTDR.

We present a comprehensive analysis of a frequency multiplexed phase-measuring φ-OTDR sensor platform. The system uses a train of frequency-shifted pulses to increase the average power injected into the fiber and provide a diversity of uncorrelated Rayleigh backscattering measurements. Through a combination of simulations, numerical analysis, and experimental measurements, we show that this approach not only enables lower noise and mitigates interference fading, but also improves the sensor linearity.

Quantitative amplitude-measuring Φ-OTDR with ε/√ sensitivity using a multi-frequency pulse train.

We report an amplitude-measuring Rayleigh-based sensor that uses a series of frequency-shifted pulses to extract quantitative distributed strain measurements. By using frequency multiplexing, we are able to inject a train of 10 pulses into the fiber at once. This allows us to use a higher average input power than standard phase-sensitive optical time domain reflectometry systems, improving the sensitivity.

Suppressing non-local effects due to Doppler frequency shifts in dynamic Brillouin fiber sensors.

Brillouin fiber sensors have traditionally been limited to low-speed or static strain measurements due to the time-consuming frequency scans required. In the past decade, a number of novel high-speed measurement techniques have been proposed to enable Brillouin-based dynamic strain sensors. In this work, we present a new mechanism, which can limit the performance of high-speed dynamic Brillouin sensors.

Low-noise distributed acoustic sensing using enhanced backscattering fiber with ultra-low-loss point reflectors.

We present a low-noise distributed acoustic sensor using enhanced backscattering fiber with a series of localized reflectors. The point reflectors were inscribed in a standard telecom fiber in a fully automated system by focusing an ultra-fast laser through the fiber cladding. The inscribed reflectors provided a reflectance of -53 dB, significantly higher than the Rayleigh backscattering level of -70 dB/m, despite adding only 0.

Quantitative strain sensing in a multimode fiber using dual frequency speckle pattern tracking.

We report an amplitude-measuring multimode fiber sensor capable of making quantitative strain measurements and extracting the algebraic sign of the strain. The Rayleigh-based sensor probes the fiber with pulses of alternating optical frequency and records the backscattered speckle patterns on a high-speed camera. We show that measuring the change in the speckle pattern induced by a change in optical frequency provides a form of in situ calibration, enabling the sensor to recover the magnitude and algebraic sign of the strain.

Quantitative amplitude measuring φ-OTDR using multiple uncorrelated Rayleigh backscattering realizations.

We propose and demonstrate a technique to perform quantitative strain sensing using the amplitude of the Rayleigh backscattered light in a modified φ-OTDR system. While standard amplitude measuring φ-OTDR sensors can identify the presence of strain, they cannot perform quantitative measurements because the amplitude of the Rayleigh backscattered light exhibits a non-linear and unpredictable strain response. Here, we demonstrate a technique to computationally recover a linear strain response from a set of uncorrelated Rayleigh backscattering measurements.

Speckle-based strain sensing in multimode fiber.

The diversity of spatial modes present within a multimode fiber has been exploited for a wide variety of imaging and sensing applications. Here, we show that this diversity of modes can also be used to perform quantitative strain sensing by measuring the amplitude of the Rayleigh backscattered speckle pattern in a multimode fiber. While most Rayleigh based fiber sensors use single mode fiber, multimode fiber has the potential to provide lower noise due to the higher capture fraction of Rayleigh scattered light, higher non-linear thresholds, and the ability to avoid signal fading by measuring many spatial modes simultaneously.

Reading Level and Suitability of Congestive Heart Failure (CHF) Education in a Mobile App (CHF Info App): Descriptive Design Study.

Background: Education at the time of diagnosis or at discharge after an index illness is a vital component of improving outcomes in congestive heart failure (CHF). About 90 million Americans have limited health literacy and have a readability level at or below a 5th-grade level, which could affect their understanding of education provided at the time of diagnosis or discharge from hospital.

Objective: The aim of this paper was to assess the suitability and readability level of a mobile phone app, the CHF Info App.

Multimode fiber Φ-OTDR with holographic demodulation.

We propose and demonstrate a method to perform quantitative phase-sensitive optical time domain reflectometry (Φ-OTDR) using multimode fiber. While most Φ-OTDR sensors use single-mode fiber, multimode fiber exhibits higher thresholds for non-linear effects, a larger capture fraction of Rayleigh backscattered light, and the potential to avoid signal fading by detecting many spatial modes in parallel. Previous multimode fiber based OTDR sensors discarded most of the backscattered light and thus failed to take advantage of these noise-reducing factors.

Principal modes in multimode fibers: exploring the crossover from weak to strong mode coupling.

We present experimental and numerical studies on principal modes in a multimode fiber with mode coupling. By applying external stress to the fiber and gradually adjusting the stress, we have realized a transition from weak to strong mode coupling, which corresponds to the transition from single scattering to multiple scattering in mode space. Our experiments show that principal modes have distinct spatial and spectral characteristic in the weak and strong mode coupling regimes.

Measuring vibrational motion from a moving platform using speckle field detection.

We investigate the ability of a holographic laser vibrometer to mitigate noise introduced when operating on a moving platform or when measuring a moving target. This motion introduces a fundamental limitation on the measurement sensitivity due to the time-varying speckle pattern produced as the illumination beam scans across the target surface. In addition, since existing systems record the phase of only a single speckle grain, speckle fading imposes a limit on the coherent processing interval and thus the frequency resolution of these measurements.

Enabling time resolved microscopy with random Raman lasing.

Optical imaging of fast events and processes is essential for understanding dynamics of complex systems. A bright flash of illuminating light is required to acquire sufficient number of photons for superior image quality. Laser pulses can provide extreme brightness and are typically employed to achieve high temporal resolution; however, the high degree of coherence associated with the lasing process degrades the image quality with speckle formation.

Intracavity frequency-doubled degenerate laser.

We develop a green light source with low spatial coherence via intracavity frequency doubling of a solid-state degenerate laser. The second-harmonic emission supports many more transverse modes than the fundamental emission, and exhibits lower spatial coherence. A strong suppression of speckle formation is demonstrated for both fundamental and second-harmonic beams.

Controlling mode competition by tailoring the spatial pump distribution in a laser: a resonance-based approach.

We introduce a simplified version of the steady-state ab initio laser theory for calculating the effects of mode competition in continuous wave lasers using the passive cavity resonances. This new theory harnesses widely available numerical methods that can efficiently calculate the passive cavity resonances, with negligible additional computational overhead. Using this theory, we demonstrate that the pump profile of the laser cavity can be optimized both for highly multi-mode and single-mode emission.

The optical frequency comb fibre spectrometer.

Optical frequency comb sources provide thousands of precise and accurate optical lines in a single device enabling the broadband and high-speed detection required in many applications. A main challenge is to parallelize the detection over the widest possible band while bringing the resolution to the single comb-line level. Here we propose a solution based on the combination of a frequency comb source and a fibre spectrometer, exploiting all-fibre technology.

Spatiotemporal Control of Light Transmission through a Multimode Fiber with Strong Mode Coupling.

We experimentally generate and characterize eigenstates of the Wigner-Smith time-delay matrix, called principal modes, in a multimode fiber with strong mode coupling. The unique spectral and temporal properties of principal modes enable global control of temporal dynamics of optical pulses transmitted through the fiber, despite random mode mixing. Our analysis reveals that well-defined delay times of the eigenstates are formed by multipath interference, which can be effectively manipulated by spatial degrees of freedom of input wave fronts.