Chip-scale integration of electronics and photonics is recognized as important to the future of information technology, as is the exploitation of the best properties of electronics, photonics, and plasmonics to achieve this objective. However, significant challenges exist including matching the sizes of electronic and photonic circuits; achieving low-loss transition between electronics, photonics, and plasmonics; and developing and integrating new materials. This review focuses on a hybrid material approach illustrating the importance of both chemical and engineering concepts. Silicon–organic hybrid (SOH) and plasmonic–organic hybrid (POH) technologies have permitted dramatic improvements in electro-optic (EO) performance relevant to both digital and analog signal processing. For example, the voltage–length product of devices has been reduced to less than 40 Vμm, facilitating device footprints of <20 μm2 operating with digital voltage levels to frequencies above 170 GHz. Energy efficiency has been improved to around a femtojoule/bit. This improvement has been realized through exploitation of field enhancements permitted by new device architectures and through theory-guided improvements in organic electro-optic (OEO) materials. Multiscale theory efforts have permitted quantitative simulation of the dependence of OEO activity on chromophore structure and associated intermolecular interactions. This has led to new classes of OEO materials, including materials of reduced dimensionality and neat (pure) chromophore materials that can be electrically poled. Theoretical simulations have helped elucidate the observed dependence of device performance on nanoscopic waveguide dimensions, reflecting the importance of material interfaces. The demonstration and explanation of the dependence of in-device electro-optic activity, voltage–length product, and optical insertion loss on device architecture (e.g., slot width) suggest new paradigms for further dramatic improvement of performance.

Efficient electro-optic (EO) modulators crucially rely on advanced materials that exhibit strong electro-optic activity and that can be integrated into high-speed and efficient phase shifter structures. In this paper, we demonstrate ultra-high in-device EO figures of merit of up to n 3 r33 = 2300 pm/V achieved in a silicon-organic hybrid (SOH) Mach-Zehnder Modulator (MZM) using the EO chromophore JRD1. This is the highest materialrelated in-device EO figure of merit hitherto achieved in a high-speed modulator at any operating wavelength. The π-voltage of the 1.5 mm-long device amounts to 210 mV, leading to a voltage-length product of UπL = 320 Vµm -the lowest value reported for MZM that are based on low-loss dielectric waveguides. The viability of the devices is demonstrated by generating high-quality on-off-keying (OOK) signals at 40 Gbit/s with Q factors in excess of 8 at a drive voltage as low as 140 mVpp. We expect that efficient high-speed EO modulators will not only have major impact in the field of optical communications, but will also open new avenues towards ultra-fast photonicelectronic signal processing.

Electro-optic modulators for high-speed on-off keying (OOK) are key components of short- and medium-reach interconnects in data-center networks. Small footprint, cost-efficient large-scale production, small drive voltages and ultra-low power consumption are of paramount importance for such devices. Here we demonstrate that the concept of silicon-organic hybrid (SOH) integration perfectly meets these challenges. The approach combines the unique processing advantages of large-scale silicon photonics with unrivalled electro-optic (EO) coefficients obtained by molecular engineering of organic materials. Our proof-of-concept experiments demonstrate generation and transmission of OOK signals at line rates of up to 100 Gbit/s using a 1.1 mm-long SOH Mach-Zehnder modulator (MZM) featuring a π-voltage of only 0.9 V. The experiment represents the first demonstration of 100 Gbit/s OOK on the silicon photonic platform, featuring the lowest drive voltage and energy consumption ever demonstrated for a semiconductor-based device at this data rate. We support our results by a theoretical analysis showing that the nonlinear transfer characteristic of the MZM can help to overcome bandwidth limitations of the modulator and the electric driver circuitry. We expect that high-speed, power-efficient SOH modulators may have transformative impact on short-reach networks, enabling compact transceivers with unprecedented efficiency, thus building the base of future interfaces with Tbit/s data rates.

Three-dimensional (3D) nano-printing of freeform optical waveguides, also referred to as photonic wire bonding, allows for efficient coupling between photonic chips and can greatly simplify optical system assembly. As a key advantage, the shape and the trajectory of photonic wire bonds can be adapted to the mode-field profiles and the positions of the chips, thereby offering an attractive alternative to conventional optical assembly techniques that rely on technically complex and costly high-precision alignment. However, while the fundamental advantages of the photonic wire bonding concept have been shown in proof-of-concept experiments, it has so far been unclear whether the technique can also be leveraged for practically relevant use cases with stringent reproducibility and reliability requirements. In this paper, we demonstrate optical communication engines that rely on photonic wire bonding for connecting arrays of silicon photonic modulators to InP lasers and single-mode fibres. In a first experiment, we show an eight-channel transmitter offering an aggregate line rate of 448 Gbit/s by low-complexity intensity modulation. A second experiment is dedicated to a four-channel coherent transmitter, operating at a net data rate of 732.7 Gbit/sa record for coherent silicon photonic transmitters with co-packaged lasers. Using dedicated test chips, we further demonstrate automated mass production of photonic wire bonds with insertion losses of (0.7 ± 0.15) dB, and we show their resilience in environmental-stability tests and at high optical power. These results might form the basis for simplified assembly of advanced photonic multi-chip systems that combine the distinct advantages of different integration platforms.

Structuring optical materials on a nanometer scale can lead to artificial effective media, or metamaterials, with strongly altered optical behavior. Metamaterials can provide a wide range of linear optical properties such as negative refractive index 1,2 , hyperbolic dispersion 3 , or magnetic behavior at optical frequencies 4 . Nonlinear optical properties, however, have only been demonstrated for patterned metallic films 5-10 which suffer from high optical losses 11 . Here we show that second-order nonlinear metamaterials can also be obtained from non-metallic centrosymmetric constituents with inherently low optical absorption.In our proof-of-principle experiments, we have iterated atomic-layer deposition (ALD) of three different constituents, A = Al 2 O 3 , B = TiO 2 and C = HfO 2 . The centrosymmetry of the resulting ABC stack is broken since the ABC and the inverted CBA sequences are not equivalent -a necessary condition for non-zero second-order nonlinearity. To the best of our knowledge, this is the first realization of a bulk nonlinear optical metamaterial.The basic idea of metamaterials is simple, yet powerful: Using ordinary constituents shaped on a sufficiently small spatial scale, effective material properties that go qualitatively beyond those of the ingredients become possible 12,13 . Early examples are stacks of isotropic layers leading to nanolaminates with an effective anisotropic electromagnetic response 14 . Metamaterials may also lead to properties that are typically not present in nature, such as hyperbolic dispersion observed in layered metal-dielectric structures 3 or negative refractive indices which can be exploited to create superlenses 2 .However, while these examples refer to linear optical properties only, nonlinear phenomena are of fundamental technological importance as well. For example, optical nonlinearities are utilized for generating frequencies otherwise hardly accessible 7 , for modulating light at hundreds of GHz 15 , or for creating optical gates 16 . Nonlinear optics additionally enables fundamental components for quantum applications, such as sources of entangled photons by spontaneous down-conversion 17 .Second-order nonlinear optical crystals, such as potassium dihydrogen phosphate (KDP), lithium niobate (LiNbO 3 ) or superlattices grown by molecular-beam epitaxy (MBE) 18 are readily available, but these materials are difficult to incorporate in most photonic platforms. Nonlinear optical metamaterials are therefore interesting not only for answering general physical questions, but also because they may offer a method of incorporating second-order nonlinear materials on photonic platforms.Current research on nonlinear optical metamaterials has shown interesting results already such as high-harmonic generation 9 or giant surface nonlinearities 5 . However, most results available so far report on enhancements of pre-existing nonlinearities which originate at metal-dielectric interfaces 5,[8][9][10]19 . Furthermore, nonlinear metamaterials available so far consist of met...

We report on compact and efficient silicon-organic hybrid (SOH) Mach-Zehnder modulators (MZM) with low phase shifter insertion loss of 0.7 dB. The 280 µm-long phase shifters feature a π-voltage-length product of 0.41 Vmm and a loss-efficiency product as small as aUπL = 1.0 VdB. The device performance is demonstrated in a data transmission experiment, where we generate on-off-keying (OOK) and four-level pulse-amplitude modulation (PAM4) signals at symbol rates of 100 GBd, resulting in line rates of up to 200 Gbit/s. Bit error ratios are below the threshold for hard-decision forward error correction (HD-FEC) with 7 % coding overhead, leading to net data rates of 187 Gbit/s. This is the highest PAM4 data rate ever achieved for a sub-1 mm silicon photonic MZM.

We demonstrate the generation of higher-order modulation formats using silicon-based inphase/quadrature (IQ) modulators at symbol rates of up to 100 GBd. Our devices exploit the advantages of silicon-organic hybrid (SOH) integration, which combines silicon-on-insulator waveguides with highly efficient organic electro-optic (EO) cladding materials to enable small drive voltages and sub-millimeter device lengths. In our experiments, we use an SOH IQ modulator with a π-voltage of 1.6 V to generate 100 GBd 16QAM signals. This is the first time that the 100 GBd mark is reached with an IQ modulator realized on a semiconductor substrate, leading to a single-polarization line rate of 400 Gbit/s. The peak-to-peak drive voltages amount to 1.5 V, corresponding to an electrical energy dissipation in the modulator of only 25 fJ/bit.

High-speed interconnects in data-center and campus-area networks crucially rely on efficient and technically simple transmission techniques that use intensity modulation and direct detection (IM/DD) to bridge distances of up to a few kilometers. This requires electrooptic modulators that combine low operation voltages with large modulation bandwidth and that can be operated at high symbol rates using integrated drive circuits. Here we explore the potential of silicon-organic hybrid (SOH) Mach-Zehnder modulators (MZM) for generating high-speed IM/DD signals at line rates of up to 120 Gbit/s. Using a SiGe BiCMOS signalconditioning chip, we demonstrate that intensity-modulated duobinary (IDB) signaling allows to efficiently use the electrical bandwidth, thereby enabling line rates of up to 100 Gbit/s at bit error ratios (BER) of 8.5 × 10 −5 . This is the highest data rate achieved so far using a silicon-based MZM in combination with a dedicated signal-conditioning integrated circuit (IC). We further show four-level pulse-amplitude modulation (PAM4) at lines rates of up to 120 Gbit/s (BER = 3.2 × 10 −3 ) using a high-speed arbitrary-waveform generator and a 0.5 mm long MZM. This is the highest data rate hitherto achieved with a sub-millimeter MZM on the silicon photonic platform.