Bimodal waveguide interferometer RI sensor fabricated on low-cost polymer platform

A refractive index sensor based on bimodal waveguide interferometer is demonstrated on the low-cost polymer platform for the first time. Different from conventional interferometers which make use of the interference between the light from two arms, bimodal waveguide interferometers utilize the interference between the two different internal modes in the waveguide. Since the utilized first higher mode has a wide evanescent tail which interacts with the external environment, the interferometer can reach a high sensitivity. Instead of vertical bimodal structure which is normally employed, the lateral bimodal waveguide is adopted in order to simplify the fabrication process. A unique offset between the centers of single mode waveguide and bimodal waveguide is designed to excite the two different modes with equal power which contributes to the maximum fringe visibility. The bimodal waveguide interferometer is finally fabricated on optical polymer (Ormocore) which is transparent at both infrared and visible wavelengths. It is fabricated using the UV-based soft imprint technique which is simple and reproductive. The bulk sensitivity of fabricated interferometer sensor with a 5 mm sensing length is characterized using different mass concentration sodium chloride solutions. The sensitivity is obtained as 316 pi rad/RIU and the extinction ratio can reach 18 dB

Investigation of grating-assisted trimodal interferometer biosensors based on a polymer platform

A grating-assisted trimodal interferometer biosensor is proposed and numerically analyzed. A long period grating coupler, for adjusting the power between the fundamental mode and the second higher order mode, is investigated, and is shown to act as a conventional directional coupler for adjusting the power between the two arms. The trimodal interferometer can achieve maximal fringe visibility when the powers of the two modes are adjusted to the same value by the grating coupler, which means that a better limit of detection can be expected. In addition, the second higher order mode typically has a larger evanescent tail than the first higher order mode in bimodal interferometers, resulting in a higher sensitivity of the trimodal interferometer. The influence of fabrication tolerances on the performance of the designed interferometer is also investigated. The power difference between the two modes shows inertia to the fill factor of the grating, but high sensitivity to the modulation depth. Finally, a 2050 2π/RIU (refractive index unit) sensitivity and 43 dB extinction ratio of the output power are achieved

Polymer-based microring resonator with the multimode interference coupler operating at very-near-infrared wavelengths

A microring resonator with the multimode interference coupler is fabricated on the polymer platform by using UV-based soft nanoimprint technique. A unique class of fluorinated polymer, perfluoropolyether (PFPE), is employed for the fabrication of the flexible soft mold. By optimizing the proportion between Ormocore and the thinner maT, the microring resonator is fabricated almost without residual layer. The fabricated device with a Q-factor up to 2.3 × 104 is demonstrated for very-near-infrared wavelengths, which shows high potential for sensing applications

3D Model-based Zero-Shot Pose Estimation Pipeline

Most existing learning-based pose estimation methods are typically developed for non-zero-shot scenarios, where they can only estimate the poses of objects present in the training dataset. This setting restricts their applicability to unseen objects in the training phase. In this paper, we introduce a fully zero-shot pose estimation pipeline that leverages the 3D models of objects as clues. Specifically, we design a two-step pipeline consisting of 3D model-based zero-shot instance segmentation and a zero-shot pose estimator. For the first step, there is a novel way to perform zero-shot instance segmentation based on the 3D models instead of text descriptions, which can handle complex properties of unseen objects. For the second step, we utilize a hierarchical geometric structure matching mechanism to perform zero-shot pose estimation which is 10 times faster than the current render-based method. Extensive experimental results on the seven core datasets on the BOP challenge show that the proposed method outperforms the zero-shot state-of-the-art method with higher speed and lower computation cost

Tilted fiber bragg grating sensor using chemical plating of a palladium membrane for the detection of hydrogen leakage

A tilted fiber Bragg grating (TFBG) hydrogen sensor coated with a palladium (Pd) membrane by the electroless plating method is proposed in this paper. A uniform layer of Pd metal is fabricated in aqueous solutions by the chemical coating method, which is used as the sensitive element to detect the change of the surrounding refractive index (SRI) caused by hydrogen absorption. The change in SRI causes an unsynchronized change of the cladding modes and the Bragg peak in the TFBG transmission spectrum, thereby eliminating the cross-sensitivity due to membrane expansion and is able to simultaneously monitor the presence of cracks in the pipe, as well as the hydrogen leakage. By subtracting the wavelength shift caused by fiber expansion, the change of SRI, i.e., the information from the H2 level, can be separately obtained. The drifted wavelength is measured for the H2 concentration below the hydrogen explosion limit between 1% and 4%. The chemical-based coating has the advantages of a low cost, a simple operation, and being suitable for coating on long fiber structures. The proposed sensor is able to detect the H2 signal in 5 min at a 1% H2 concentration. The proposed sensor is proved to be able to monitor the hydrogen level without the cross-sensitivity of temperature variation and expansion strains, so could be a good candidate for security applications in industr

Geo6D: Geometric Constraints Learning for 6D Pose Estimation

Numerous 6D pose estimation methods have been proposed that employ end-to-end regression to directly estimate the target pose parameters. Since the visible features of objects are implicitly influenced by their poses, the network allows inferring the pose by analyzing the differences in features in the visible region. However, due to the unpredictable and unrestricted range of pose variations, the implicitly learned visible feature-pose constraints are insufficiently covered by the training samples, making the network vulnerable to unseen object poses. To tackle these challenges, we proposed a novel geometric constraints learning approach called Geo6D for direct regression 6D pose estimation methods. It introduces a pose transformation formula expressed in relative offset representation, which is leveraged as geometric constraints to reconstruct the input and output targets of the network. These reconstructed data enable the network to estimate the pose based on explicit geometric constraints and relative offset representation mitigates the issue of the pose distribution gap. Extensive experimental results show that when equipped with Geo6D, the direct 6D methods achieve state-of-the-art performance on multiple datasets and demonstrate significant effectiveness, even with only 10% amount of data

RF Characterization of Self-Interference Cancellation Using Phase Modulation and Optical SideBand Filtering

Full-Duplex scheme transmitting and receiving signals simultaneously in the same frequency band can significantly improve the throughput and the spectrum efficiency, and is considered as a candidate technology for the fifth generation (5G) wireless communication. However, the high power transmitted signal will interfere with the in-band weak received signal, which is called as RF self-interference. It cannot be simply removed by a notch filter or a narrow bandpass filter because the same frequency band is used for both transmitter and receiver. An optical approach to implement RF self-interference cancellation is proposed. Based on the inherent out-of-phase property between the left and right sidebands of phase-modulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. The cancellation depth of the system was measured for different frequencies and bandwidths. The cancellation performance affected by the time delay deviation, the amplitude deviation and phase response is analyzed according to experimental results. It gives the direction for the improvement of system performance. Finally, the full-duplex communication by using the optical SIC approach was also investigated. Signal of interest is recovered and the constellation diagram was also shown

Evolutionary characteristics and genetic transmission patterns of predominant HIV-1 subtypes among men who have sex with men in China.

OBJECTIVES: Men who have sex with men (MSM) represent one of the major risk groups for HIV-1 infection in China, and the predominant subtypes among this population has changed over the last two decades. The objective of this study was to determine the evolutionary characteristics and transmission patterns of the dominant HIV-1 strains in the Chinese MSM population. METHODS: A total of 4980 published HIV-1 pol gene sequences from MSM in China were retrieved and comprehensive evolutionary and transmission analyses were then conducted. Bayesian coalescent-based methods and selection pressure analyses were used to reconstruct the time-scale and demographic history and to estimate other evolutionary parameters. Transmission patterns were characterized using network analyses. RESULTS: There were 2546 (51.12%) CRF01_AE, 1263 (25.36%) CRF07_BC, and 623 (12.51%) subtype B, accounting for 88.99% of the total sequences. From 2000 to 2016, the prevalence of CRF01_AE was stable, comprising nearly half of all sequences over time (58.33-45.38%, p=0.071). CRF07_BC increased slightly from 13.3% to 22.49% (p<0.001), while subtype B decreased dramatically from 41.67% to 9.04% (p<0.001). Demographic reconstruction showed that the greatest expansion of the HIV epidemic occurred between 1999 and 2005. CRF01_AE had a higher estimated evolutionary rate (2.97×10-3 substitutions/site/year) and exhibited more sites under positive selection (25/351 codons) compared to the other subtypes. Network analyses showed that CRF07_BC (68.29%, 84/123) had a higher proportion of cross-region networks than CRF01_AE (49.1%, 174/354) and subtype B (36.46%, 35/96) (p<0.001). CONCLUSIONS: The predominant subtypes of HIV-1 in Chinese MSM have different evolutionary characteristics and transmission patterns, which poses a significant challenge to HIV treatment and disease prevention

Optical Multipath RF Self-Interference Cancellation Based on Phase Modulation for Full-Duplex Communication

Optical multipath RF self-interference cancellation (SIC) based on phase modulation for full-duplex communication is proposed and demonstrated experimentally. Phase modulation is utilized to convert the RF signal into optical domain, in which the time delay tuning, amplitude tuning and phase inversion for multipath RF SIC are completed. The comprehensive theoretical model of the optical multipath RF SIC system is established, and the factors affecting SIC performance including the time delay, amplitude and phase deviations are analyzed. The experimental results verify the feasibility of the proposed scheme for full-duplex communication with the cancellation depth of 26 dB and 28 dB over 100 MHz at central frequency of 6 GHz and 10 GHz, respectively. A figure of merit of the maximum interference to signal of interest ratio is defined to characterize the SOI recovery capability of optical RF SIC system

Simulation and analysis of microring electric field sensor based on a lithium niobate-on-insulator

With the increasing sensitivity and accuracy of contemporary high-performance electronic information systems to electromagnetic energy, they are also very vulnerable to be damaged by high-energy electromagnetic fields. In this work, an all-dielectric electromagnetic field sensor is proposed based on a microring resonator structure. The sensor is designed to work at 35 GHz RF field using a lithium niobate-on-insulator (LNOI) material system. The 2.5-D variational finite difference time domain (varFDTD) and finite difference eigenmode (FDE) methods are utilized to analyze the single-mode condition, bending loss, as well as the transmission loss to achieve optimized waveguide dimensions. In order to obtain higher sensitivity, the quality factor (Q-factor) of the microring resonator is optimized to be 106 with the total ring circumference of 3766.59 μm. The lithium niobate layer is adopted in z-cut direction to utilize TM mode in the proposed all-dielectric electric field sensor, and with the help of the periodically poled lithium niobate (PPLN) technology, the electro-optic (EO) tunability of the device is enhanced to 48 pm·μm/V