110 GHz CMOS compatible thin film LiNbO3 modulator on silicon

Abstract

In this paper we address a significant limitation of silicon as an optical material, namely, the upper bound of its potential modulation frequency. This arises due to finite carrier mobility, which fundamentally limits the frequency response of all-silicon modulators to about 60 GHz. To overcome this limitation, another material must be integrated with silicon to provide increased operational bandwidths. Accordingly, this paper proposes and demonstrates the integration of a thin LiNbO₃ device layer with silicon and a novel tuning process that matches the propagation velocities between the propagating radio-frequency (RF) and optical waves. The resulting lithium niobate on silicon (LiNOS) modulator is demonstrated to operate from DC to 110 GHz.

Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits

“…Further, the lower permeability of the silica layer helps to increase the velocity of the travelling electric wave on the electrodes, so that a lower gold electrode thickness is required in order to match the velocity of the traveling electric wave with the velocity of the optical wave. These advantages have enabled Mach‐Zehnder modulators in LNOI that achieve modulating frequencies up to 110 GHz, showing that it is a very attractive platform for ultra‐fast modulators. Special care needs to be taken for such modulators to achieve an impedance of the electrodes of 50 Ω, which reduces unwanted reflections …”

“…These advantages have enabled Mach‐Zehnder modulators in LNOI that achieve modulating frequencies up to 110 GHz, showing that it is a very attractive platform for ultra‐fast modulators. Special care needs to be taken for such modulators to achieve an impedance of the electrodes of 50 Ω, which reduces unwanted reflections …”

“…At 1.5 Vcm, LNOI modulators can be envisaged to have the same compact dimensions as the InP modulators that are now displacing traditional in‐diffused LN waveguide based modulators in coherent optical transceivers . Moreover, the fast response time of LNOI modulators (up to 110 GHz) make their modulation bandwidth more than sufficient for future 400 Gb/s channels running at over 60 Gbaud, and may prove to be a key enabler for terabit‐per‐second channels …”

“…Special care needs to be taken for such modulators to achieve an impedance of the electrodes of 50 , which reduces unwanted reflections. [76,77] Resonant structures such as ring resonators can also be used for modulating optical signals. The optical intensity modulation is achieved by electro optically shifting the resonator frequency periodically across the laser light frequency, resulting in a periodic low power transmission at the bus waveguide.…”

A Theoretical Study on Rib‐Type Photonic Wires Based on LiNbO3 Thin Film on Insulator

“…The LNOI structure has been pioneered by the groups of Osgood [4] and Günter [5] on smaller substrates. To date, many LNOI PW devices have been demonstrated, such as (CMOS-compatible) electro-optic modulator, [10][11][12][13][14][15][16][17][18][19] (electrooptically tunable) micro-ring or micro-disk resonator, [7,[19][20][21][22][23][24][25][26][27][28][29] LNOI heterogeneous photonic device, [19] grating coupler, [30,31] photonic crystal, [7,[32][33][34] transverse-electric/magnetic (TE/TM)pass polarizer, [35] quantum optics device, [36] as well as some nonlinear devices based on periodically poled LNOI (PPLNOI) PWs. in diameter) LNOI thin-film is commercially available.…”