Serial Time-encoded Amplified Microscopy Research Articles

Highly efficient single-pixel imaging system based on the STEAM structure

We propose and demonstrate a compact and highly efficient single-pixel imaging system with data compression based on the traditional serial time-encoded amplified microscopy (STEAM) structure. Our proposal solves the big data issue and low-efficiency bottleneck in the conventional STEAM systems. Also, a cascaded Mach-Zehnder interferometric (MZI) structure as the optical random pattern generator is proposed and experimentally demonstrated as the low-cost approach to achieve data compression. A 45° tilted fiber grating (TFG) is applied to increase the efficiency of the imaging system. A state-of-art experiment is performed and data compression ratios from 5% to 20% at an imaging size of 1mm*1.8mm are conducted using our proposed system for the first time to the best of our knowledge. The proposed optical imaging system mitigates the big data issue, decreases the system cost, and increases energy efficiency, and lays a solid foundation for low-cost, compact, and highly efficient ultrafast optical imaging.

A high-throughput label-free time-stretch acoustofluidic imaging cytometer for single-cell mechanotyping

Current circulating tumor cells (CTC) detection methods have to compromise between sensitivity and throughput. High-throughput imaging cytometer based on serial time-encoded amplified microscopy (STEAM) facilitates CTC detection at single-cell sensitivity from abundant cells. However, this method lacks the information to spot heterogeneity of cells with high morphological similarity. Researches on cell biophysical properties suggest cell mechanotyping can be an indicator of phenotypic heterogeneity to improve classification ability of STEAM cytometer. Here, we present a high-throughput label-free acoustofluidic imaging cytometer for single-cell mechanotyping based on STEAM and acoustofluidic technology. The generated acoustic resonance field translocates cells to different transversal exit positions under continuous flow according to their intrinsic biophysical properties. Such displacements are recorded with images simultaneously using STEAM cytometry at approximately 2000 cells/s. We experimentally verified that our method accounting for both cell images and acoustic displacements can improve mechanotyping accuracy by 12% upon image-based phenotyping method. This new acoustofluidic imaging cytometer facilitates high-accuracy and high-throughput imaging cytometry for single-cell CTC mechanotyping.

Ultrafast Imaging With Optical Encoding and Compressive Sensing

Serial time-encoded amplified microscopy (STEAM) is an emerging technology, which enables an ultrafast phenomena to be captured at GHz scan rate. The tradeoff between high imaging speed and high spatial resolution remains a problem where the maximum scan rate is limited by the sampling rate of the digitizer and the temporal dispersion in the fiber to avoid data blending. In this paper, we address these limitations using state-of-the-art optimization algorithms under compressive sensing framework and establish the data acquisition model based on our proposed experimental setup by considering the effect of individual optical components such as laser spectral profile, encoding mask patterns, dispersion of the fiber, and optical noise in the system. We introduce two methods of alternating direction method of multipliers with total variation regularization (ADMM-TV) and discrete wavelet hard thresholding (DWT-Hrd) for STEAM-based imaging systems. Our results demonstrate that a 10-GHz scan rate can be achieved compared to the conventional 1-GHz microscopy imaging system while maintaining high image reconstruction quality in terms of structural similarity index measurement (SSIM). It is shown that among the two proposed optimization algorithms, ADMM-TV outperforms DWT-Hrd by 20% in SSIM measurements. Finally, it is shown that having 70%-80% light transmission through the mask reveals the optimum results in terms of reconstruction quality.

Ultrafast time-stretch imaging at 932 nm through a new highly-dispersive fiber.

Optical glass fiber has played a key role in the development of modern optical communication and attracted the biotechnology researcher's great attention because of its properties, such as the wide bandwidth, low attenuation and superior flexibility. For ultrafast optical imaging, particularly, it has been utilized to perform MHz time-stretch imaging with diffraction-limited resolutions, which is also known as serial time-encoded amplified microscopy (STEAM). Unfortunately, time-stretch imaging with dispersive fibers has so far mostly been demonstrated at the optical communication window of 1.5 μm due to lack of efficient dispersive optical fibers operating at the shorter wavelengths, particularly at the bio-favorable window, i.e., <1.0 μm. Through fiber-optic engineering, here we demonstrate a 7.6-MHz dual-color time-stretch optical imaging at bio-favorable wavelengths of 932 nm and 466 nm. The sensitivity at such a high speed is experimentally identified in a slow data-streaming manner. To the best of our knowledge, this is the first time that all-optical time-stretch imaging at ultrahigh speed, high sensitivity and high chirping rate (>1 ns/nm) has been demonstrated at a bio-favorable wavelength window through fiber-optic engineering.

Ultrafast imaging with anti-aliasing based on optical time-division multiplexing.

Serial time-encoded amplified microscopy (STEAM) is a novel ultrafast imaging technique that is based on space-to-time-to-wavelength mapping. Nevertheless, the technique requires a high-cost electronic digitizer of several tens of gigahertz sampling rate to read out sufficient image information. To acquire a large amount of image information by using a relatively low-sampling-rate electronic digitizer, an anti-aliasing technique based on optical time-division multiplexing is proposed. A 38.88MHz line-scan imaging system is demonstrated experimentally. By using the proposed anti-aliasing technique, a 20GS/s sampling rate is achieved by employing a 10GS/s electronic digitizer. Defects and scratches on the target that were not identifiable originally can be clearly distinguished after using the proposed technique. Numerical analysis shows that the image quality can be improved by 4.16dB, compared to that not using the anti-aliasing technique and at least 2.3dB comparing to those obtained by bilinear, bicubic, and nearest-neighbor interpolation and Lanczos resampling techniques.

Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser

In this paper, a serial time-encoded amplified microscopy (STEAM) by employing a multi-wavelength laser as the light source is proposed and experimentally demonstrated. This system achieves ultrafast optical imaging with a tunable frame rate. The measuring range depends on the spectrum width of the multi-wavelength laser. Through tuning the speed of the modulating signal, the frame rate ranges from 100 to 250 MHz. In addition, the spatial resolution can be improved by increasing the group velocity dispersion and reducing the wavelength spacing. Finally, with the development of photonic integrate circuits (PIC), the multi-wavelength laser source has the potential for integration on a photonic chip and thus the size of the proposed STEAM could be reduced in the future.

Automation Highlights from the Literature

Automation Highlights from the Literature

Serial time-encoded amplified microscopy (STEAM) based on a stabilized picosecond supercontinuum source

Temporal stability of the broadband source, such as supercontinuum (SC), is the key enabling factor for realizing high performance ultrafast serial time-encoded amplified microscopy (STEAM). Owing to that the long-pulse SC (picosecond to nanosecond) generation generally results in an ultrabroadband spectrum with significant pulse-to-pulse fluctuation, only the ultrashort-pulse (femtosecond) SC sources, which offer better temporal stability, have been employed in STEAM so far. Here we report a simple approach to achieve active control of picosecond SC stability and to help extend the applicability of SC in STEAM from the femtosecond to the picosecond or even nanosecond regimes. We experimentally demonstrate stable single-shot STEAM imaging at a frame rate of 4.9 MHz using the CW-triggered picosecond SC source. Such CW-stabilized SC can greatly reduce the shot-to-shot fluctuation, and thus improves the STEAM image quality significantly.

Performance of serial time-encoded amplified microscope

Serial time-encoded amplified microscopy (STEAM) is an entirely new imaging modality that enables ultrafast continuous real-time imaging with high sensitivity. By means of optical image amplification, STEAM overcomes the fundamental tradeoff between sensitivity and speed that affects virtually all optical imaging systems. Unlike the conventional microscope systems, the performance of STEAM depends not only on the lenses, but also on the properties of other components that are unique to STEAM, namely the spatial disperser, the group velocity dispersion element, and the back-end electronic digitizer. In this paper, we present an analysis that shows how these considerations affect the spatial resolution, and how they create a trade-off between the number of pixels and the frame rate of the STEAM imager. We also quantify how STEAM's optical image amplification feature improves the imaging sensitivity. These analyses not only provide valuable insight into the operation of STEAM technology but also serve as a blue print for implementation and optimization of this new imaging technology.