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Register a new userBreaking voltage-bandwidth limits in integrated lithium niobate modulators using micro-structured electrodes
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Electro-optic modulators with low voltage and large bandwidth are crucial for both analog and digital communications. Recently, thin-film lithium niobate modulators have enable dramatic performance improvements by reducing the required modulation voltage while maintaining high bandwidths. However, the reduced electrode gaps in such modulators leads to significantly higher microwave losses, which limit electro-optic performance at high frequencies. Here we overcome this limitation and achieve a record combination of low RF half-wave voltage of 1.3 V while maintaining electro-optic response with 1.8-dB roll-off at 50 GHz. This demonstration represents a significant improvement in voltage-bandwidth limit, one that is comparable to that achieved when switching from legacy bulk to thin-film lithium niobate modulators. Leveraging the low-loss electrode geometry, we show that sub-volt modulators with $>$ 100 GHz bandwidth can be enabled.
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Electro-optic phase modulators are critical components in modern communication, microwave photonic, and quantum photonic systems. Important for these applications is to achieve modulators with low half-wave voltage at high frequencies. Here we demonstrate an integrated phase modulator, based on a thin-film lithium niobate platform, that simultaneously features small on-chip loss (~ 1 dB) and low half-wave voltage over a large spectral range (3.5 - 4.5 V at 5 - 40 GHz). By driving the modulator with a strong 30-GHz microwave signal corresponding to around four half-wave voltages, we generate an optical frequency comb consisting of over 40 sidebands spanning 10 nm in the telecom L-band. The high electro-optic performance combined with the high RF power-handling ability (3.1 W) of our integrated phase modulator are crucial for future photonics and microwave systems.
Thin-film lithium niobate (LN) photonic integrated circuits (PICs) could enable ultrahigh performance in electro-optic and nonlinear optical devices. To date, realizations have been limited to chip-scale proof-of-concepts. Here we demonstrate monolithic LN PICs fabricated on 4- and 6-inch wafers with deep ultraviolet lithography and show smooth and uniform etching, achieving 0.27 dB/cm optical propagation loss on wafer-scale. Our results show that LN PICs are fundamentally scalable and can be highly cost-effective.
Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly > 10 dB) dominates the total insertion losses of typical LN photonic integrated circuits, where on-chip propagation losses can be as low as 0.03 - 0.1 dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetric guided mode of a LN nanowire, featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7 dB/facet with high fabrication tolerance and repeatability. Our results open door for practical integrated LN photonic circuits efficiently interfaced with optical fibers.
Acousto-optic interactions involving propagating phonons can break the time-reversal and frequency-modulation symmetry of light. However, conventional acousto-optic modulators based on bulk materials have frequency bandwidth limited to hundreds of megahertz due to their large structural sizes. Here, we experimentally demonstrate gigahertz single-sideband acousto-optic modulation on an etchless lithium niobate integrated platform by using photonic bound states in the continuum. The upper- or lower-sideband modulation of light can be obtained conveniently by choosing specific combinations of input and output channels. Under this scheme, we have realized a 3-GHz frequency shifter, which operates in the C-band with a 3-dB bandwidth of ~35 nm. The extinction ratios of the upper(lower)-sideband modulated light to the lower(upper)-sideband modulated and unmodulated light are >44 (47) and 25 (23) dB in the 3-dB operating bandwidth. The frequency-shifted light can be further processed with amplitude and frequency modulation. Therefore, the demonstrated gigahertz single-sideband acousto-optic modulation can enable many photonic applications such as optical signal processing, sensing, and ion trapping.
Modern communication networks require high performance and scalable electro-optic modulators that convert electrical signals to optical signals at high speed. Existing lithium niobate modulators have excellent performance but are bulky and prohibitively expensive to scale up. Here we demonstrate scalable and high-performance nanophotonic electro-optic modulators made of single-crystalline lithium niobate microring resonators and micro-Mach-Zehnder interferometers. We show a half-wave electro-optic modulation efficiency of 1.8V$cdot$cm and data rates up to 40 Gbps.
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