Notes

Punctured spontaneous colon intramural haematoma.
Two-dimensional-material-based photodetectors are gaining prominence in optoelectronic applications, but there are certain factors to consider with bulk material usage. The demand for a highly responsive and highly efficient device with an inexpensive fabrication method is always of paramount importance. Carbon nanotubes (CNT) are well known, owing to their upheld vigorous structural and optoelectronic characteristics, but to fabricate them at a large scale involves multifarious processes. A visible range photodetector device structure developed using a simple and inexpensive drop-casting technique is reported here. The optoelectronic characteristics of the device are studied with IV measurements under the light and dark conditions by incorporating a thin CNT layer on top of tungsten-disulfide-based heterojunction photodetector to enhance the overall characteristics such as detectivity, responsivity, photocurrent, rise time, and fall time in the visible range of the light spectrum with a violet light source at 441 nm. In the DC bias voltage range of -20 to 20 V, IV measurements are carried out under dark and illumination conditions with different incident power densities. The threshold voltage is recognized at 2.0 V. Photocurrent is found to be highly dependent on the state of the incident light. For 0.3074mW/cm2 illuminated power, the highest responsivity and detectivity are determined to be 0.57 A/W and 2.89×1011 Jones. These findings encourage an alternative fabrication method at a large scale to grow CNTs for the enhancement of optoelectronic properties of present two-dimensional-material-based optoelectronic and photonics applications.We present a linearly polarized single-longitudinal-mode (SLM) ytterbium-doped fiber laser with a polarization extinction ratio (PER) of over 35 dB and a narrow linewidth of less than 4.5 kHz. The very high PER is obtained by utilizing the polarization evolution effect at the optical fiber and the high-performance polarizing beam splitter. BMS-232632 cost The SLM is achieved by using a segment of polarization-maintaining ytterbium-doped fiber as a narrowband filter. In addition, a high optical signal-to-noise ratio of 50 dB and a good slope efficiency of 60.5% are achieved. Using an ytterbium-doped fiber amplifier, a linearly polarized SLM laser system with a high power of over 2.5 W is demonstrated at 1064 nm.This feature issue of Applied Optics is dedicated to the international meeting of Information Photonics 2020 (IP'20), which was held September 11-12, 2020, in Taipei, Taiwan. IP'20 covered a broad range of topics, including advanced display techniques, optical computing, and optical storage. This feature issue, however, limits topics to unconventional imaging techniques, such as digital holography, artificial-intelligence associated imaging, compressive imaging, and single-pixel imaging.A volume holographic (VHG) grating-based multi-plane differential confocal microscopy (DCM) is proposed for axial scan-free imaging. Also, we briefly reviewed our previous works on volume holographic-based confocal imaging. We show that without degrading imaging performance, it is possible to simultaneously obtain two depth-resolved optically sectioned images with improved axial resolution using multi-plane DCM. The performance of our multi-plane DCM was evaluated by measuring the surface profile of a silicon micro-hole array with depths separation around 10 µm. The axial sensitivity of the system is around 25 nm. Our system has the advantages of multi-plane imaging with high axial sensitivity and high optical sectioning ability. Our method can be used for reflective surface profiling and multi-plane fluorescence imaging. The present methods may find important applications in surface metrology for label-free biological samples, as well as industrial applications.In this work we report on the measurement, with record accuracy, of the absolute modal effective refraction index (phase index) of single-mode optical fibers by using Bragg gratings. We also demonstrate a new method to measure the group index of the fibers from the grating's Bragg wavelength. We present as well the characterization of the thermo-optic and strain-optic coefficients as a function of the wavelength; the values we have obtained are the closest to those of pristine fiber measured with gratings technology so far. The phase index is measured with a set of gratings in the wavelength ranges from 1509 to 1563 nm, and the group index is obtained from the wavelength dependence of the phase index. Very weak gratings with reflectivity down to 10-3 have been used in order to minimize the perturbation of the pristine fiber. Results are presented at a temperature of 22°C and zero strain after preliminary calibration of the thermo-optic and strain-optic coefficients as a function of the wavelength. Accuracies better than 3×10-5 and 7×10-4 have been achieved for the phase and group indices, respectively. It is also shown that the main source of error relates to the uncertainty in pitch of the phase masks used for grating inscription. The technique is useful for testing different kinds of fibers including telecommunication, amplifying, and polarization maintaining.A high-throughput optical system possesses a large field of view (FOV) and high resolution. However, it is a major challenge to design such a telescope with these two conflicting specifications. In this paper, we propose a method to design a high-throughput telescope based on the classical off-axis three-mirror anastigmat (TMA) configuration by introducing a scanning mechanism. We derive the optimum initial design for the TMA system with no primary aberrations through characteristic ray tracing. During the design process, a real exit pupil is necessitated to accommodate the scanning mirror. By gradually increasing the system's FOV during the optimization procedure, we finally obtained a high-throughput telescope design with an F-number of 6, a FOV of 60∘×1.5∘, and a long focal length of 876 mm. In addition, a tolerance analysis is also conducted to demonstrate the instrumentation feasibility. We believe that this kind of large rectangle FOV telescope with high resolution has broad future applications in the optical remote sensing field.To achieve frequency-tunable angular selectivity at terahertz frequencies, a tunable epsilon-near-zero (ENZ) metamaterial based on a subwavelength dielectric-graphene multilayer structure is designed. The ENZ frequency of the dielectric-graphene multilayer can be dynamically tuned by the gate voltage applied to graphene. Transmittance angular spectra show that only the incident lights close to normal incidence can propagate through the structure while other incident lights cannot, which indicates that our structure can be utilized for frequency-tunable terahertz angular selection. The optimal directivity D reaches 183 and the transmittance at normal incidence reaches 0.462. This multilayer-based tunable terahertz ENZ metamaterial will possess potential application prospects in tunable highly directive antennas.Subwavelength engineering and utilizing phase-change materials with large contrast in their optical properties have become powerful design tools for integrated silicon photonics. Reversible phase-transition of phase-change materials such as Ge2Sb2Te5 (GST) provide a new degree of freedom and open up the possibility of adding new functionalities to the designed devices. We present an optical filter based on a silicon subwavelength grating (SWG) waveguide evanescently coupled to phase-change material loading segments arranged periodically around the SWG core. The effect of the GST loading segments' geometry and their distance from the SWG core on the filter's central wavelength and bandwidth are studied with three-dimensional finite-difference time-domain simulations. The employment of GST in the structure adds a switching functionality with an extinction ratio of 28.8 dB. We also examine the possibility of using the proposed structure as a reconfigurable filter by controlling the partial crystallization of the GST offering a blueshift of more than 4 nm.A graphene-embedded plasmonic rib waveguide (GEPRW) is designed for the mid-infrared electro-optic modulator. The mode characteristics and electro-optic (EO) modulation performances are simulated and optimized by using the finite element method. The results show that propagation length of 103mm and figure of merit of 106 are obtained by adjusting the bias voltage applied to the GEPRW. The EO wavelength tunings are -66.69 and -78.87nm/V for peak L and peak R in the loss spectra when w=3µm and h1=2µm. For a 100 µm long GEPRW, the modulation depths of ∼96.4,∼97.1,∼93.7, and ∼94.9%, and FWHMs of ∼30,∼74,∼34, and ∼59nm can be achieved when λ=1.55, 1.87. 1.89, and 2.23 µm. The EO modulator based on the GEPRW has a wide wavelength tuning range from 1.05 to 2.23 µm. link2 It has high modulation depth, low insertion loss, and broad bandwidth, which can be used as EO tunable devices such as optical interconnects and optical switches.The Doppler effect of motional polarization grating is studied for the first time to the best of our knowledge. link3 Based on the optical properties of polarization grating, the Doppler effect principle of polarization grating is elucidated theoretically. A method to obtain the Doppler frequency shift based on beat frequency signal that is produced by superposition of order ±1 diffraction beams of polarization grating is proposed, and a proof-of-concept experiment is conducted to measure the frequency signal of the motional polarization grating. The movement characteristics of polarization grating varying with time can be obtained after a short-time Fourier transformation of the light signal. The experimental results are in good agreement with the theoretical predication, which verifies the correctness of the theoretical analysis and achieves the measurement of linear motion velocity and acceleration of motional polarization grating with high accuracy. This study proposes a new idea for laser frequency shift and has potential significance for further development of optical heterodyne detection.Improving photothermal efficiency can reduce the melting threshold of metal nanowires. The photothermal efficiency of a polarized laser to Cu nanowires was investigated by numerical simulation and experiment. Our simulation results reveal that the photothermal efficiency of a polarized laser depends on the intensity and distribution area of surface plasmons excited by the laser. As the angle between the polarization direction of the incident laser and the long axis of the Cu nanowire increases, the laser-excited surface plasmons shift from both ends to the sidewall of the Cu nanowire. Such a distribution of surface plasmons was confirmed by the melting behavior of Cu nanowires irradiated by a 450 nm polarized laser. Increasing the laser wavelength will enhance the intensity of the surface plasmons but reduce the distribution area of the surface plasmons. As a result, a higher photothermal efficiency was achieved using a laser with a polarization direction perpendicular to the long axis of the Cu nanowire and a wavelength less than 550 nm. Due to the higher photothermal efficiency, the melting threshold of Cu nanowire irradiated by a laser with polarization perpendicular to the long axis of the Cu nanowire is 32 mW, which is around 20% lower that of Cu nanowire irradiated by a laser with polarization parallel to the long axis of the Cu nanowire.
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