Thin-film lithium niobate electro-optic modulator on a D-shaped fiber

High-performance thin-film lithium niobate electro-optic modulator based on etching slot and ultrathin silicon film

An electro-optic modulator (EOM) is an indispensable component to connect the electric and optical fields. Here, we propose a high-performance, thin-film lithium niobate-based EOM, where the modulation waveguide is formed by an etching slot on the lithium niobate film and the deposit of an ultrathin silicon film in the slot region. Therefore, a small mode size and high mode energy can be simultaneously achieved in the LN region with a high EO coefficient, which will be beneficial to increase the EO overlap and gradually decrease in the mode size. Further, we employed a waveguide structure to construct a typical Mach-Zehnder interference-type EOM. According to the requirements of high-speed traveling wave modulation, we conduct the index matching, impedance matching, and low-loss operation. From the results, the key half-wave voltage length product and 3 dB modulation bandwidth are, respectively, 1.45 V cm and 119 GHz in a modulation length of 4 mm. Moreover, a larger 3 dB bandwidth also can be achieved by shortening the modulation length. Therefore, we believe the proposed waveguide structure and EOM will provide new ways to enhance the performance of LNOI-based EOMs.

Low driving voltage lithium niobate metasurface electro-optical modulator operating in free space

A simple configuration of only λ/9 thick 2D metallic grating embedded within an electro-optic (EO) material (lithium niobate for instance) is proposed and theoretically studied to act as an EO modulator. On the one hand, this grating is used as an interdigitated comb to apply a very high and spatially periodic modification of the electrostatic field. On the other hand, the grating is designed to exhibit a Fano-like resonance in the NIR spectral range. This resonance is used to confine the electromagnetic field inside the EO material leading to an intrinsic enhancement of the EO effect. Extensive numerical simulations are performed to optimize the geometry in agreement with technological fabrication constraints. We achieved a local field factor of 24.5 leading to a local index modification Δn as large as 1 for 1 V applied voltage. This allows a modulation sensitivity of 14.35 nm/V (2000 times larger than state of the art) together with a resonance depth of 60% and a driving voltage of only 75 mV opening the way to the fabrication of ultra-thin low driving voltage EO devices.

Optical electrocardiogram monitor with a real-time analysis of an abnormal heart rhythm for home-based medical alerts

Sudden cardiac death (SCD) caused by cardiovascular disease is the greatest hidden danger to human life, accounting for about 25% of the total deaths in the world. Due to the early concealment of SCD and the heavy medical burden of long-term examination, telemedicine combined with home monitoring has become a potential medical alert method. Among all the existing human cardiac and electrophysiology monitoring methods, optics-based sensors attract the widest attention due to the advantages of low delay, real-time monitoring, and high signal-to-noise ratio. In this paper, we propose an optical sensor with the capabilities of long-term monitoring and real-time analysis. Combining an R-peak recognition algorithm, Lorenz plots (LP), and statistical analysis, we carried out the consistency analysis and result visualization of ECG sequences over 1 h. The results of 10 subjects show that the R-peak recognition accuracy of the optical ECG monitor is higher than 97.99%. The optical system can display abnormal heart rhythm in real-time through LP, and the readability is good, which makes the system suitable for self-monitoring at home. In addition, this paper provides a detailed long-term monitoring assessment method to effectively guide the practical clinical transformation of other optical wearable devices.

Evolution of Nanodomains and Formation of Self-Organized Structures during Local Switching in X-Cut LNOI

The features of nanodomain growth during local switching in X-cut lithium niobate on insulator (LNOI) were comprehensively studied using the biased tip of a scanning probe microscope. The obtained results were discussed in terms of the kinetic approach. The revealed differences in domain growth in bulk LN and LNOI were attributed to the higher bulk conductivity of LNOI. The obtained influence of humidity on the shape and growth of isolated domains was attributed to the water meniscus. Analysis of the transition between the “forward growth” and “sideways growth” stages was performed by switching to the stripe electrode. A sand-glass-shaped domain was formed due to growth in the opposite direction after the domain touched the electrode. Stable periodical domain structures down to 300 nm were created and characterized in LNOI. Highly ordered comb-like domains of various alternating lengths, including four- and eight-fold increase periods, were produced by performing biased tip scanning along the Y axis. The obtained knowledge is important for the future development of nanodomain engineering methods in monocrystalline ferroelectric thin films on insulators.