Electro-optic modulators translate high-speed electronic signals into the optical domain and are critical components in modern telecommunication networks1,2 and microwave-photonic systems3,4. They are also expected to be building blocks for emerging applications such as quantum photonics5,6 and non-reciprocal optics7,8. All of these applications require chip-scale electro-optic modulators that operate at voltages compatible with complementary metal–oxide–semiconductor (CMOS) technology, have ultra-high electro-optic bandwidths and feature very low optical losses. Integrated modulator platforms based on materials such as silicon, indium phosphide or polymers have not yet been able to meet these requirements simultaneously because of the intrinsic limitations of the materials used. On the other hand, lithium niobate electro-optic modulators, the workhorse of the optoelectronic industry for decades9, have been challenging to integrate on-chip because of difficulties in microstructuring lithium niobate. The current generation of lithium niobate modulators are bulky, expensive, limited in bandwidth and require high drive voltages, and thus are unable to reach the full potential of the material. Here we overcome these limitations and demonstrate monolithically integrated lithium niobate electro-optic modulators that feature a CMOS-compatible drive voltage, support data rates up to 210 gigabits per second and show an on-chip optical loss of less than 0.5 decibels. We achieve this by engineering the microwave and photonic circuits to achieve high electro-optical efficiencies, ultra-low optical losses and group-velocity matching simultaneously. Our scalable modulator devices could provide cost-effective, low-power and ultra-high-speed solutions for next-generation optical communication networks and microwave photonic systems. Furthermore, our approach could lead to large-scale ultra-low-loss photonic circuits that are reconfigurable on a picosecond timescale, enabling a wide range of quantum and classical applications5,10,11 including feed-forward photonic quantum computation.
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The data sets generated and/or analysed during the current study are available from the corresponding authors on reasonable request.
Reed, G. T., Mashanovich, G., Gardes, F. Y. & Thomson, D. J. Silicon optical modulators. Nat. Photon. 4, 518–526 (2010).
Miller, D. A. B. Attojoule optoelectronics for low-energy information processing and communications. J. Lightwave Technol. 35, 346–396 (2017).
Fortier, T. M. et al. Generation of ultrastable microwaves via optical frequency division. Nat. Photon. 5, 425–429 (2011).
Ghelfi, P. et al. A fully photonics-based coherent radar system. Nature 507, 341–345 (2014).
O’Brien, J. L. Optical quantum computing. Science 318, 1567–1570 (2007).
Kues, M. et al. On-chip generation of high-dimensional entangled quantum states and their coherent control. Nature 546, 622–626 (2017).
Yu, Z. & Fan, S. Complete optical isolation created by indirect interband photonic transitions. Nat. Photon. 3, 91–94 (2009).
Tzuang, L. D., Fang, K., Nussenzveig, P., Fan, S. & Lipson, M. Non-reciprocal phase shift induced by an effective magnetic flux for light. Nat. Photon. 8, 701–705 (2014).
Wooten, E. L. et al. A review of lithium niobate modulators for fiber-optic communications systems. IEEE J. Sel. Top. Quantum Electron. 6, 69–82 (2000).
Miller, D. A. B. Sorting out light. Science 347, 1423–1424 (2015).
Shen, Y. et al. Deep learning with coherent nanophotonic circuits. Nat. Photon. 11, 441–446 (2017).
Xu, Q., Schmidt, B., Pradhan, S. & Lipson, M. Micrometre-scale silicon electro-optic modulator. Nature 435, 325–327 (2005).
Sun, C. et al. Single-chip microprocessor that communicates directly using light. Nature 528, 534–538 (2015).
Ogiso, Y. et al. Over 67 GHz bandwidth and 1.5 V InP-based optical IQ modulator with n–i–p–n heterostructure. J. Lightwave Technol. 35, 1450–1455 (2017).
Aoki, M. et al. InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD. IEEE J. Quantum Electron. 29, 2088–2096 (1993).
Koeber, S. et al. Femtojoule electro-optic modulation using a silicon–organic hybrid device. Light Sci. Appl. 4, e255 (2015).
Lee, M. et al. Broadband modulation of light by using an electro-optic polymer. Science 298, 1401–1403 (2002).
Haffner, C. et al. Low-loss plasmon-assisted electro-optic modulator. Nature 556, 483–486 (2018).
Boyd, R. W. Nonlinear Optics (Academic, Cambridge, 2003).
Janner, D., Tulli, D., García-Granda, M., Belmonte, M. & Pruneri, V. Micro-structured integrated electro-optic LiNbO3 modulators. Laser Photonics Rev. 3, 301–313 (2009).
Schmidt, R. V. & Kaminow, I. P. Metal-diffused optical waveguides in LiNbO3. Appl. Phys. Lett. 25, 458–460 (1974).
Poberaj, G., Hu, H., Sohler, W. & Günter, P. Lithium niobate on insulator (LNOI) for micro-photonic devices. Laser Photonics Rev. 6, 488–503 (2012).
Liang, H., Luo, R., He, Y., Jiang, H. & Lin, Q. High-quality lithium niobate photonic crystal nanocavities. Optica 4, 1251–1258 (2017).
Wang, J. et al. High-Q lithium niobate microdisk resonators on a chip for efficient electro-optic modulation. Opt. Express 23, 23072–23078 (2015).
Wang, C., Zhang, M., Stern, B., Lipson, M. & Lončar, M. Nanophotonic lithium niobate electro-optic modulators. Opt. Express 26, 1547–1555 (2018).
Rao, A. et al. High-performance and linear thin-film lithium niobate Mach–Zehnder modulators on silicon up to 50 GHz. Opt. Lett. 41, 5700–5703 (2016).
Chen, L., Xu, Q., Wood, M. G. & Reano, R. M. Hybrid silicon and lithium niobate electro-optical ring modulator. Optica 1, 112–118 (2014).
Zhang, M., Wang, C., Cheng, R., Shams-Ansari, A. & Lončar, M. Monolithic ultra-high-Q lithium niobate microring resonator. Optica 4, 1536–1537 (2017).
Weigel, P. O. et al. Hybrid silicon photonic-lithium niobate electro-optic Mach–Zehnder modulator beyond 100 GHz. Preprint at https://arxiv.org/abs/1803.10365 (2018).
Chen, X. et al. All-electronic 100-GHz bandwidth digital-to-analog converter generating PAM signals up to 190 Gbaud. J. Lightwave Technol. 35, 411–417 (2017).
Chen, X. et al. Characterization of electro-optic bandwidth of ultra-high speed modulators. In 2017 Optical Fiber Communications Conference and Exhibition 1–3 (2017); https://doi.org/10.1364/OFC.2017.Tu2H.7
Yuan, L., Xiao, M., Lin, Q. & Fan, S. Synthetic space with arbitrary dimensions in a few rings undergoing dynamic modulation. Phys. Rev. B 97, 104105 (2018).
Winzer, P. J. & Essiambre, R. J. Advanced optical modulation formats. Proc. IEEE 94, 952–985 (2006).
Mercante, A. J. et al. 110 GHz CMOS compatible thin film LiNbO3 modulator on silicon. Opt. Express 24, 15590–15595 (2016).
Jin, S., Xu, L., Zhang, H. & Li, Y. LiNbO3 thin-film modulators using silicon nitride surface ridge waveguides. IEEE Photonics Technol. Lett. 28, 736–739 (2016).
100G/400G LN Modulator. http://www.fujitsu.com/jp/group/foc/en/products/optical-devices/100gln/
Eospace 2017 Advanced Products. http://eospace.com/pdf/EOSPACEbriefProductInfo2017.pdf
40 GHz or 40 Gb/s Lithium Niobate Modulators. https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3948
Dong, P. et al. Monolithic silicon photonic integrated circuits for compact 100+ Gb/s coherent optical receivers and transmitters. IEEE J. Sel. Top. Quantum Electron. 20, 150–157 (2014).
Thomson, D. J. et al. 50-Gb/s silicon optical modulator. IEEE Photonics Technol. Lett. 24, 234–236 (2012).
Streshinsky, M. et al. Low power 50 Gb/s silicon traveling wave Mach–Zehnder modulator near 1300 nm. Opt. Express 21, 30350–30357 (2013).
Azadeh, S. S. et al. Low V silicon photonics modulators with highly linear epitaxially grown phase shifters. Opt. Express 23, 23526–23550 (2015).
Rouvalis, E. Indium phosphide based IQ-modulators for coherent pluggable optical transceivers. In 2015 IEEE Compound Semiconductor Integrated Circuit Symposium 1–4 (2015); https://doi.org/10.1109/CSICS.2015.7314513
Letal, G. et al. Low loss InP C-band IQ modulator with 40 GHz bandwidth and 1.5 V V π. In 2015 Optical Fiber Communications Conference and Exhibition 1–3 (2015); https://doi.org/10.1364/OFC.2015.Th4E.3
Wolf, S. et al. Coherent modulation up to 100 GBd 16QAM using silicon-organic hybrid (SOH) devices. Opt. Express 26, 220–232 (2018).
Alloatti, L. et al. 100 GHz silicon–organic hybrid modulator. Light Sci. Appl. 3, e173 (2014).
Ayata, M. et al. High-speed plasmonic modulator in a single metal layer. Science 358, 630–632 (2017).
Haffner, C. et al. All-plasmonic Mach–Zehnder modulator enabling optical high-speed communication at the microscale. Nat. Photon. 9, 525–528 (2015).
We thank J. Khan for discussions on the LN platform, H. Majedi for help with the equipment, and C. Reimer, S. Bogdanović, L. Shao and B. Desiatov for feedback on the manuscript. This work is supported in part by the National Science Foundation (NSF) (ECCS1609549, ECCS-1740296 E2CDA and DMR-1231319) and by Harvard University Office of Technology Development (Physical Sciences and Engineering Accelerator Award). Device fabrication is performed at the Harvard University Center for Nanoscale Systems, a member of the National Nanotechnology Coordinated Infrastructure Network, which is supported by the NSF under ECCS award no. 1541959.
Nature thanks M. Hochberg and the other anonymous reviewer(s) for their contribution to the peer review of this work.
C.W., M.Z. and M.L. are involved in developing lithium niobate technologies at HyperLight Corporation.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
a–c, Normalized optical transmission of the 20-mm (a), 10-mm (b) and 5-mm (c) device as a function of the applied voltage, showing half-wave voltages of 1.4 V, 2.3 V and 4.4 V, respectively. The inset of a shows the measured normalized transmission (NT) on a logarithmic scale, revealing an extinction ratio of 30 dB.
a, Set-up for measuring the modulator electro-optic responses from 35 GHz to 100 GHz. b, High-speed data modulation set-up. For direct CMOS driving, the RF amplifier is bypassed. EDFA, erbium-doped fibre amplifier; FPC, fibre-polarization controller; MZM, Mach–Zehnder modulator (commercial); OSA, optical spectrum analyser; VOA, variable optical attenuator.
The measured electrical BER is 3.6 × 10−5, limited by the signal distortion from the electronic circuit.
BER versus OSNR for the three modulation schemes at 70 Gbaud.
a, b, Schematics of the cross-sections of thin-film (a) and conventional (b) LN modulators. Our thin-film modulator (a) has an oxide layer underneath the device layer, so that velocity matching can be achieved while maximum electro-optic efficiency is maintained. A conventional modulator (b) also uses a buffer oxide layer for velocity matching, but on top of LN which further compromises the electro-optic overlap. c, d, Numerically simulated microwave (c) and optical (d) field distributions (both shown in Ez components) in the cross-section of the thin-film modulator. For microwave simulations, the electric-field values are obtained when a voltage of 1 V is applied across the two electrodes. e, Group refractive indices for both optical and microwave signals as a function of the buried oxide thickness. Velocity matching can be achieved with an oxide thickness of about 4,700 nm.
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Wang, C., Zhang, M., Chen, X. et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature 562, 101–104 (2018). https://doi.org/10.1038/s41586-018-0551-y
- Microwave Photonic Systems
- Complementary Metal Oxide Semiconductor (CMOS)
- Velocity Matching
- Optical Signal-to-noise Ratio (OSNR)
- Electrical Energy Dissipation
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