We present a coupler from silicon photonic to vertical plasmonic metal-insulator-metal waveguides with a measured efficiency of -1.4 dB at 1550 nm, and an optical bandwidth of more than 100 nm.

An integrated photonics platform that offers high-speed modulators in addition to low-loss and versatile passive components is highly sought after for different applications ranging from AI to next-generation Tbit/s links in optical fiber communication. For this purpose, we introduce the plasmonic BTO-on-SiN platform for high-speed electro-optic modulators. This platform combines the advantages provided by low-loss silicon nitride (SiN) photonics with the highly nonlinear barium titanate (BTO) as the active material. Nanoscale plasmonics enables high-speed modulators operating at electro-optical bandwidths up to 110 GHz with active lengths as short as 5 µm. Here, we demonstrate three different modulators: a 256 GBd C-band Mach-Zehnder (MZ) modulator, a 224 GBd C-band IQ modulator – being both the first BTO IQ and the first IQ modulator on SiN for data communication – and finally, a 200 GBd O-band racetrack (RT) modulator. With this approach we show record data rates of 448 Gbit/s with the IQ modulator and 340 Gbit/s with the MZ modulator. Furthermore, we demonstrate the first plasmonic RT modulator with BTO and how it is ideally suited for low complexity communication in the O-band with low device loss of 2 dB. This work leverages the SiN platform and shows the potential of this technology to serve as a solution to combat the ever-increasing demand for fast modulators. This plasmonic BTO-on-SiN platform enables 256 GBd high-speed data transmission. It can further operate beyond 200 GBd for IQ and O-band racetrack modulators within highly compact device footprints.

The Pockels effect is essential for controlling optical signals at the highest speeds, particularly for electro-optic modulators in photonic integrated circuits. Lithium niobate (LN) and barium titanate (BTO) are two excellent Pockels materials to this end. Here we measure the Pockels coefficients and permittivity in LN and BTO over a continuous frequency range from 100 MHz to 330 GHz. These properties are constant across this frequency range in LN, but have a strong frequency dependence in BTO. Still, our measurements show that BTO has remarkable electro-optic properties compared with LN. Furthermore, we show how BTO devices can be designed with a flat electro-optic frequency response despite the Pockels coefficient dispersion. Finally, we expound our method for broadband characterization of these vital electro-optic properties, utilizing specialized integrated electro-optic phase shifters. Altogether, this work empowers the design of high-speed BTO devices and the development of new electro-optic materials.

Barium titanate’s (BTO) exceptionally large Pockels coefficients and permittivity are shown to have a strong frequency dependence from 100 MHz to 330 GHz [1]. These data and the integrated characterization method are crucial for developing high-speed photonic integrated circuits.

Efficient fiber-to-chip coupling is demonstrated for SiN photonics with simple and fabrication-tolerant amorphous silicon overlay gratings. This elegant approach offers coupling loss of only 0.43 dB and 1.11 dB with and without back-reflector, respectively.

We demonstrate the first O-band BaTiO 3 -plasmonic modulator on SiN. Featuring symbol rates of up to 200 GBd, 2 dB on-chip loss, and 70 GHz bandwidth, this approach proves suitable for low-loss, high-speed, and low-complexity communication.

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

Electro-optic modulators are key elements in high-speed optical telecommunication links and preferably rely on materials with a linear electro-optic effect. Choosing adequate waveguide geometries is a key challenge in the design of electro-optic modulators. While all-dielectric geometries promise high-speed modulation with low propagation loss, their modulation efficiency suffers from low confinement and weak electrical fields, resulting in lengthy devices. Plasmonic geometries, on the other hand, allow for most compact devices featuring highest electro-optical bandwidths, but at the cost of higher losses. Alternatively, hybrid photonic–plasmonic solutions open a sweet spot for high-speed modulators with moderate loss. In this review, we discuss the three waveguide types by analyzing and comparing their performance and their sensitivity to variations in geometry with respect to a choice of the electro-optical Pockels-effect material.

A plasmonic Mach-Zehnder modulator based on thin-film barium titanate is introduced demonstrating line rates up to 200 Gbit/s. The structure enables low insertion loss and high optical power stability without a DC bias during operation.

The Pockels coefficients in thin-film barium titanate (BTO) and lithium niobate (LN) have been measured for modulating frequencies up to 300 GHz. BTO’s effective nonlinearity is ~10 times larger than LN’s with a small frequency dependence.

Achieving electrically driven light sources on a silicon substrate is one of the great challenges in integrated optics. For low-power applications, one possible candidate could be Light Emitting Tunnel Junctions (LETJs) [1] . Unlike many semiconductor light sources that rely on direct-bandgap materials, the emission characteristics of LETJs are not strongly dependent on the material choice, but are determined by the electrical and optical environment of the tunnelling interface. While most electrons tunnel elastically from one electrode to the other, some can couple to and excite electromagnetic modes in a broad range of frequencies, spanning the microwave to the visible [1] – [3] .

Resonant modulators encode electrical data onto wavelength-multiplexed optical carriers. Today, silicon microring modulators are perceived as promising to implement such links; however, they provide limited bandwidth and need thermal stabilization systems. Here we present plasmonic micro-racetrack modulators as a potential successor of silicon microrings: they are equally compact and compatible with complementary-metal–oxide–semiconductor-level driving voltages, but offer electro-optical bandwidths of 176 GHz, a 28 times improved stability against operating temperature changes and no self-heating effects. The temperature-resistant organic electro-optic material enables operation at 85 °C device temperature. We show intensity-modulated transmission of up to 408 Gbps at 12.3 femtojoules per bit with a single resonant modulator. Plasmonic micro-racetrack modulators offer a solution to encode high data rates (for example, the 1.6 Tbps envisioned by next-generation communications links) at a small footprint, with low power consumption and marginal, if no, temperature control.

A high-speed and compact plasmonic organic racetrack modulator is shown to be orders of magnitude more robust against operating condition changes compared to resonant modulators based on the plasma dispersion effect while maintaining thermal tunability. Stable operation at 80°C is shown with no degradation. © 2022 Optica

We demonstrate a 216 GBd plasmonic ferroelectric modulator monolithically integrated with a foundry-produced silicon nitride platform. The combination of low-loss waveguiding, nanoscale plasmonics, and strong Pockels coefficients in barium titanate offers a platform for next-generation optical interconnect systems.

The electro-optical frequency response of thin-film barium titanate (BTO) has been characterized in hybrid plasmonic-photonic phase shifters across the spectral range from 20 to 270 GHz. A flat frequency response was found.

OOK line rates of 220 Gbit/s and 408 Gbit/s 8PAM and transmission over 100 m are demonstrated with a resonant plasmonic racetrack modulator. The device requires low 0.6 Vp driver voltages, offers a bandwidth >110 GHz and on-chip losses of 1.0 dB.

Plasmonics has emerged as a promising technological solution for realizing high-performance nanoscale communication photonic devices. This paper reports our recent advances on high-performance plasmonic modulators and photodetectors.

We present a plasmonic platform featuring efficient, broadband metallic fiber-to-chip couplers that directly interface plasmonic slot waveguides, such as compact and high-speed electro-optic modulators. The metallic gratings exhibit an experimental fiber-to-slot coupling efficiency of -2.7 dB with -1.4 dB in simulations with the same coupling principle. Further, they offer a huge spectral window with a 3 dB passband of 350 nm. The technology relies on a vertically arranged layer stack, metal-insulator-metal waveguides, and fiber-to-slot couplers and is formed in only one lithography step with a minimum feature size of 250 nm. As an application example, we fabricate new modulator devices with an electro-optic organic material in the slot waveguide and reach 50 and 100 Gbit/s data modulation in the O- and C-bands within the same device. The devices' broad spectral bandwidth and their relaxed fabrication may render them suitable for experiments and applications in the scope of sensing, nonlinear optics, or telecommunications.

Metallic grating couplers can be extremely broadband and efficient. In this work, we investigate an all-plasmonic fiber-to-chip coupler with a coupling efficiency of -2.7 dB and an optical 3-dB passband of 300 nm.

A ferroelectric, metal-oxide-semiconductor (MOS) based, hybrid-plasmonic modulator is shown to feature bandwidths of >150 GHz and is tested with 32 Gbit/s NRZ. The device is relying on BaTiO3-on-SOI and potentially offers CMOS compatibility.