High-performance Coherent Optical Modulators based on Thin-film Lithium Niobate Platform (2006.15536v1)

Abstract: The coherent transmission technology using digital signal processing and advanced modulation formats, is bringing networks closer to the theoretical capacity limit of optical fibres, the Shannon limit. The in-phase quadrature electro-optic modulator that encodes information on both the amplitude and the phase of light, is one of the underpinning devices for the coherent transmission technology. Ideally, such modulator should feature low loss, low drive voltage, large bandwidth, low chirp and compact footprint. However, these requirements have been only met on separate occasions. Here, we demonstrate integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil these requirements simultaneously. The presented devices exhibit greatly improved overall performance (half-wave voltage, bandwidth and optical loss) over traditional lithium niobate counterparts, and support modulation data rate up to 320 Gbit s-1. Our devices pave new routes for future high-speed, energy-efficient, and cost-effective communication networks.

• The paper demonstrates LNOI-based IQ modulators achieving a half-wave voltage as low as 1.9 V and bandwidths exceeding 67 GHz for high-speed digital communications.
• The paper validates advanced modulation formats, including QPSK at 110 Gbaud and 16-QAM at 80 Gbaud, with bit error rates maintained within acceptable limits.
• The paper optimizes design using thermo-optic phase shifters and balanced voltage-bandwidth trade-offs, paving the way for ultra-compact, high-data-rate optical networks.

Overview of High-Performance Coherent Optical Modulators on the LNOI Platform

This essay provides an analysis of the research paper on high-performance coherent optical modulators based on the thin-film Lithium Niobate on Insulator (LNOI) platform. The research introduces a new generation of in-phase/quadrature (IQ) modulators, leveraging the LNOI structure to advance the capabilities of digital coherent optical communication systems. These advancements are crucial for meeting the increasing demands of global internet traffic, particularly for short-reach links such as data center interconnects.

Problem Statement and Technical Context

IQ modulators are essential components in coherent transmission systems, encoding information into both the amplitude and phase of light. Traditional lithium niobate (LN) modulators have reached performance limits due to their low-index contrast and the inability to simultaneously achieve low loss, low drive voltage, large bandwidth, and compact form factors. Despite attempts to utilize alternative material platforms like silicon, indium phosphide, and polymers, achieving the ideal combination of desired characteristics in modulators remains challenging. The use of LNOI presents a promising solution to overcome these limitations.

Key Contributions and Technical Achievements

The researchers have successfully demonstrated LNOI-based IQ modulators that achieve significant improvements across several key performance metrics. The modulators offer low optical loss, reduced drive voltages, ultra-high electro-optic (EO) bandwidths, and compact footprints. Notably, these LNOI-based devices support modulation rates up to 320 Gbps, demonstrating superior performance compared to traditional LN counterparts.

Key technical contributions include:

• Achieving a remarkable half-wave voltage (Vπ) as low as 1.9 V and bandwidths greater than 67 GHz.
• Enabling high-fidelity signals through advanced modulation formats, such as QPSK at 110 Gbaud and 16-QAM at 80 Gbaud, with bit error rates well within acceptable limits.
• Optimizing device parameters to achieve a balance between the voltage-length product and bandwidth-voltage ratio, crucial figures of merit in modulator performance.
• Demonstrating stable and efficient operation using thermo-optic (TO) phase shifters for DC bias point control, offering advantages over conventional EO approaches.

Performance Validation and Practical Implications

The research presents extensive measurements validating the performance gains of the proposed modulators. Noteworthy is the ability to maintain high signal fidelity while outperforming existing technologies regarding insertion losses and bandwidth efficiency. These properties make LNOI-based modulators highly suitable for future communication networks, where minimizing power consumption and footprint is vital.

Future Directions and Theoretical Concepts

The paper suggests avenues for further development, including increasing EO bandwidths beyond 100 GHz and integrating on-chip polarization combiners. This could lead to single devices achieving data rates exceeding 1 Tbps using higher-order modulation schemes. The implications of such advances herald a shift towards more compact, efficient optical systems. Theoretically, the LNOI platform provides a fertile ground for exploring new device architectures and integration strategies that could redefine the boundaries of optoelectronic performance.

Conclusion

The demonstrated LNOI-based IQ modulators exemplify a significant evolution in the field of optical modulatory technology, promising enhancements in both operational efficiency and application scope. By marrying compact design with high-performance metrics, this research facilitates the advancement toward ultra-fast, low-power optical communications vital for future networking infrastructure. The LNOI platform stands poised to influence a range of photonic applications, underscoring the importance of material innovation in the evolution of optical communication technology.