High‐speed modulators with low driving voltage, low loss, and compact size are essential for future optical communication systems. Thin‐film lithium niobate modulators have met each of these criteria separately, but simultaneous achievement of all of them has been challenging on this platform. Low driving voltage electro‐optic modulators necessitate either a narrow gap between the electrodes or an elongated Mach–Zehnder arms, both of which adversely affect the microwave loss, hence the bandwidth. Herein, this trade‐off is alleviated by placing the optical waveguides nonsymmetrically with respect to the electrodes and by including a dielectric buffer layer beneath the electrodes. Exploiting this novel design yields a modulator with a measured roll‐off of only 2 dB from low frequencies up to 100 GHz, and with an extrapolated 3 dB bandwidth of 170 GHz. The measured voltage–length product of this subterahertz device is 3.3 V cm. Another device, optimized for a lower voltage–length product of 2.2 V cm, exhibits a 3 dB electro‐optic bandwidth of 84 GHz. The devices are also tested for eight‐level pulse‐amplitude modulation (PAM‐8) and demonstrate data rates of up to 240 Gb s−1at 80 Gbaud, validating that the modulators are a propitious candidate for next‐generation optical communication systems.
As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices.
more » « less- NSF-PAR ID:
- 10380275
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optica
- Volume:
- 9
- Issue:
- 11
- ISSN:
- 2334-2536
- Page Range / eLocation ID:
- Article No. 1268
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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