Thin‐Film Lithium Niobate Optical Modulators with an Extrapolated Bandwidth of 170 GHz

Abstract

To reduce the size, cost, and power consumption of current optical communication systems and to meet the requirements of future networks, it is crucial to develop modulators with high speed, low driving power, low loss, low cost, and small footprint. [1,2] Currently, the majority of available commercial modulators are based on silicon (Si), [1,[3][4][5] indium phosphide (InP), [6][7][8] and bulk lithium niobate (LN). [9] Despite impressive performance of modulators on these three platforms, none are capable of complying with the required criteria for the next generation of communication systems.In recent years, modulators based on thin-film lithium niobate (TFLN) have emerged as a promising approach for ultrahigh bandwidth modulators with low driving voltages and small footprint. [10][11][12][13][14][15][16][17][18][19] The optical modes in TFLN waveguides are more compact than conventional LN counterparts, allowing the radio frequency (RF) electrode spacing to be reduced without causing detrimental optical absorption loss. Consequently, the overlap between the optical and electric fields increases, resulting in a lower driving voltage. Furthermore, using a substrate with a lower dielectric constant than bulk LN makes velocity mismatch between optical and electric fields easier, and thus improving bandwidth. [20] Another factor that can enhance the optical bandwidth is increasing the thickness of the SiO 2 insulating layer under the thin films in order to optimize the velocity mismatch. [12] Despite the above inherent advantages of the TFLN platform, a delicate design is required to reach very high-performance modulators. For example, increasing the spacing between the electrodes can minimize the RF loss, a key parameter in determining the bandwidth, but at the expense of increasing the half-wave voltage, V π . [21] Various TFLN modulators on silicon substrate have been reported to expand the 3 dB bandwidth of a single modulator up to 100 GHz and higher. [11,12,22,23] One method is to use a large gap between the electrodes, which leads to a bandwidth of more than 100 GHz, but with a V π > 13 V, [11] due to the weak overlap between the electric and optical fields inside the gap. Another approach is to utilize asymmetric arms in a Mach-Zehnder modulator (MZM) and to operate at a null point of the transfer function. This approach, however, limits the operating wavelength and is sensitive to fabrication errors. [12] The present work proposes a novel design to relieve the tradeoff between bandwidth and V π in order to achieve modulators with ultrahigh bandwidth and reasonably low voltage-length

Compact and Efficient Thin‐Film Lithium Niobate Modulators

“…Table 1 and 2 summarize the progress of different TFLN modulators with the MZI structure. [ 5,6,12,15,26–107 ] Figure summarizes the half‐wave voltage, device length, and bandwidth of etched and non‐etched TFLN modulators. Both these two kinds of modulators can realize a very high bandwidth.…”

Differential and phase-diverse electrooptic modulators

“…The optical waveguides on this maturing thin-film technology offer unrivaled properties, compared with the traditional titanium-diffused or proton-exchanged waveguides. They include high refractive-index contrast waveguides that lead to submicron cross-sections and small bending radii, as well as low-voltage and high-speed electrooptic modulators (EOMs) [7][8][9][10][11][12][13][14][15][16][17][18][19]. The FEOM presented in Fig.…”

High‐Efficiency Electro‐Optic Modulator on Thin‐Film Lithium Niobate with High‐Permittivity Cladding

“…[8][9][10] As crucial components of photonic integrated circuits, EO modulators are widely used in telecommunications, data communications, optical sensors, and quantum optics, among other DOI: 10.1002/lpor.202200927 applications. [11][12][13][14][15][16] TFLN modulators have experienced rapid development in recent years, [17][18][19][20][21][22] and numerous high-efficiency modulators have been demonstrated. [23][24][25][26][27][28][29][30] Liu et al increased the EO modulation efficiency to a voltage-length product of 1.75 V•cm using a shallowly etched lithium niobate waveguide.…”