Abstract
This paper reports a hybrid silicon nitride–lithium niobate electro-optic Mach–Zehnder-interferometer modulator that demonstrates overall improvements in terms of half-wave voltage, optical insertion loss, extinction ratio, and operational bandwidth. The fabricated device exhibits a DC half-wave voltage of ∼1.3 V, a static extinction ratio of ∼27 dB, an on-chip optical loss of ∼1.53 dB, and a 3 dB electro-optic bandwidth of 29 GHz. In addition, this device operates beyond the 3 dB bandwidth, where a half-wave voltage of 3 V is extracted at 40 GHz when the device is biased at quadrature. The modulator is realized by strip-loading thin-film lithium niobate with low-pressure chemical vapor deposited silicon nitride; this enables reduced on-chip losses and allows for a lengthened 2.4 cm long interaction region that is specifically engineered for broadband performance.
Highlights
The electro-optic (EO) modulator is a vital component in the context of photonic integrated circuits (PICs) and a technological pillar of modern information technology
These materials are inherently problematic for high-power and ultra-highfrequency operation due to their high third-order nonlinear coefficients (χ)3, higher propagation loss,1–3 and a relatively low Pockels coefficient4 compared to other oxide-based ferroelectric materials (e.g., LiNbO3)
A crystal ion-sliced (CIS) thin-film of lithium niobate on insulator (TFLNOI) has been shown to reduce the optical mode size, which results in more RF-mode overlap and smaller bending radii
Summary
The electro-optic (EO) modulator is a vital component in the context of photonic integrated circuits (PICs) and a technological pillar of modern information technology. The bulk LiNbO3 based modulator, as a discrete device, has received widespread use in optical communication over the last few decades It offers very large operational bandwidths, system linearity, and negligible chirping. A crystal ion-sliced (CIS) thin-film of lithium niobate on insulator (TFLNOI) has been shown to reduce the optical mode size, which results in more RF-mode overlap and smaller bending radii.8,9 In such a layer, the optical field diameter shrinks to just ∼2% of its size in bulk material and the electrodes can be brought much closer to the waveguide, which improves field strength and lowers the Vπ. This is an incremental improvement to the current state-of-the-art in this same hybrid platform, a 1.2 cm long device possessing a Vπ of 2.5 V and a 3 dB bandwidth of 8 GHz. The previously cited state-of-the-art hybrid Si3N4–LiNbO3 MZM exhibits a high on-chip loss of 5.4 dB due to the use of plasma-enhanced chemical vapor deposition (PECVD) Si3N4 rather than LPCVD.
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