We propose pattern self-referenced single-pixel common-path holography (PSSCH), which can be realized using either the digital-micromirror-device (DMD) based off-axis scheme or the DMD-based phase-shifting approach, sharing the same experimental setup, to do wavefront reconstructions. In this method, each modulation pattern is elaborately encoded to be utilized to not only sample the target wavefront but also to dynamically introduce the reference light for single-pixel common-path holographic detection. As such, it does not need to intentionally introduce a static reference light, resulting in it making full use of the pixel resolution of the modulation patterns and suppressing dynamically varying noises. Experimental demonstrations show that the proposed method can not only obtain a larger field of view than the peripheral-referenced approach but also achieve a higher imaging resolution than the checkerboard-referenced approach. The phase-shifting-based PSSCH performs better than the off-axis-based PSSCH on imaging fidelity, while the imaging speed of the latter is several times faster. Further, we demonstrate our method to do wavefront imaging of a biological sample as well as to do phase detection of a physical lens. The experimental results suggest its effectiveness in applications.
In measuring a transmission matrix (TM) of a scattering medium, the normal way requires projecting a large number of patterns, resulting in significant measurement time. Here, we propose to do imaging through scattering media using a path-planning-based downsampling TM. The proposed method is verified by measuring TMs for imaging through scattering media when Walsh, Cake-cutting, and Russian doll Hadamard transforms (HTs) are adopted. Based on the spectral characteristics of different HTs of natural images, corresponding sampling paths are artificially planned, which guarantees the method to preferentially measure components in TM in relation to the more important spectra. This means that our method can reduce the number of patterns during measurement, thus improving the imaging speed while only sacrificing a little imaging quality. Experimental results demonstrate the effectiveness of the proposed method.
Scattering media scramble light paths, create seemingly random speckle patterns and hinder even our simple visualization of objects. Here, we demonstrate stochastic optical scattering localization imaging (SOSLI) to achieve super-resolution non-invasively through not only static, but also dynamic scattering media (up to 80% decorrelation). A camera captures multiple speckle patterns created by stochastic emitters in the object. Then our computational approach can retrieve a super-resolution image of hidden objects, surpassing the diffraction limit by factor of five, while posing no fundamental-limit in achieving higher spatial-resolution. Our demonstration paves the way to non-invasively visualize various biological samples with unprecedented levels of detail.
The long-range pipelines for coalbed methane (CBM) transport are generally laid in the field with wide coverage and under harsh operating condition. Most conventional electronic sensing technologies are not appropriate for CBM pipeline safety monitoring featuring long distance, large-capacity measuring points, and severe working condition. In view of above problems, the multi-parameter optical fiber sensing is proposed. For preventing third-party damage, a vibration sensing scheme is designed based on Φ-OTDR principle. For leakage prewaring, a ROTDR-based temperature detection scenario is realized. For pipe deformation precaution, a BOTDR-based strain sensing solution is exploited. Additionally, a cloud database is built on the server for online monitoring. The experimental results demonstrate that: the sensing range of vibration can be 12km with the 20-m spacial resolution and 8-m positioning accuracy; the temperature measurement accuracy is ±1° within the temperature range -25°~200° over the range of 10 km optical fiber; the strain measurement range is 11000 με when the measured distance is about 10 km and the spatial resolution is 1.23m. The multi-parameter detection approach by optical fiber sensing provides a new monitoring method for the safety prewaring of long-range CBM pipelines.
Phase-sensitive optical time domain reflectometry (Φ-OTDR) is a promising approach for detecting and locating vibration signals along the whole fiber link. In this paper, a novel high-speed and complete signal transmission scheme based on field programmable gate array (FPGA) and universal serial bus (USB) 2.0 is proposed and applied in the Φ-OTDR system to obtain real-time vibration location. By using the novel scheme, only the effective data is selected and transmitted to the upper system for post-processing in real time. In the experiment, the vibration signals are simulated by hand-clapping, 50 Hz square waves and 400 Hz sine waves. The experimental results demonstrate that the proposed system exhibits good frequency response for vibrations below 1 kHz over 12 km fiber length. In addition, repetition vibration tests are carried out on 4.633 km and 10.022 km, and the location error is within the range of -7 m to +11 m. Therefore, the proposed system holds considerable potential for real-time vibration location and may have a wide application range in areas such as intruder detection, premier security, oil/gas pipeline leakage detection, and railway infrastructure monitoring, etc.
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