On-chip mode-division multiplexing (MDM) can increase the transmission capacity of a single optical bus waveguide. It is of great significance for the MDM systems to design the multimode waveguide bends (MWBs) with compact sizes. A method of designing the MWB using the inverse design algorithm is presented in this paper. Ultra-compact MWBs with high performances are realized by changing the curvature radius of the waveguide curve, and the fabrication process only requires a single step photo-lithography and plasma etching. The three-mode bent waveguide with an effective radius of only 9.35 µm is designed and tested. The theoretical excess losses of TE 0 , TE 1 , and TE 2 mode are less than 0.04 dB in a wide spectral range of 1500 to 1600 nm, and the crosstalks between all guided modes are all less than −29 dB. For the fabricated 90°waveguide bend the measured excess losses are 0.17, 0.04, and 0.16 dB at the central wavelength of 1550 nm, respectively, and the crosstalks between all three modes are less than −21 dB in the wavelength range from 1520 to 1600 nm. The proposed design method can be also extended to more mode-channels.

Pattern unlock is a popular screen unlock scheme that protects the sensitive data and information stored in mobile devices from unauthorized access. However, it is also susceptible to various attacks, including guessing attacks, shoulder surfing attacks, smudge attacks, and side-channel attacks, which can achieve a high success rate in breaking the patterns. In this paper, we propose a new two-factor screen unlock scheme that incorporates surface electromyography (sEMG)-based biometrics with patterns for user authentication. sEMG signals are unique biometric traits suitable for person identification, which can greatly improve the security of pattern unlock. During a screen unlock session, sEMG signals are recorded when the user draws the pattern on the device screen. Time-domain features extracted from the recorded sEMG signals are then used as the input of a one-class classifier to identify the user is legitimate or not. We conducted an experiment involving 10 subjects to test the effectiveness of the proposed scheme. It is shown that the adopted time-domain sEMG features and one-class classifiers achieve good authentication performance in terms of the F 1 score and Half of Total Error Rate (HTER). The results demonstrate that the proposed scheme is a promising solution to enhance the security of pattern unlock.

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Strong light absorption by a metal-on-silicon hybrid waveguide structure can realize efficient photothermal conversion at a microscale. Based on the photothermal effect, an all-optical switch with an ultra-high tuning efficiency is experimentally demonstrated based on a suspended photonic crystal nanobeam cavity integrated with an ultra-compact metal optical heater. The measurement results exhibit a high photothermal efficiency of 15.52 nm/mW. The rising and falling times of all-optical switching are ∼6.8 and ∼1.6 μs, respectively. Moreover, the heater has only an ultra-compact footprint of only 2 μm × 0.8 μm. Since no conventional electrically driven elements are required to supply power for heating, this device is rather easy to fabricate and has a compact structure. These results show that the device can potentially provide a functionally integrated component for many kinds of efficient all-optical control applications.