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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., Nature Photonics, 17 (4), ISSN:1749-4885, ISSN:1749-4893

Plasmonic modulators have been assessed for operation up to 200 GBaud in a turbulent 53 km free-space-optical link. They are shown to withstand space radiation and large temperature ranges making them ideal for space applications., Optical Fiber Communication Conference (OFC) 2023, ISBN:978-1-957171-18-0

A method for reducing the training time of a deep learning based digital backpropagation (DL-DBP) is presented. The method is based on dividing a link into smaller sections. A smaller section is then compensated by the DL-DBP algorithm and the same trained model is then reapplied to the subsequent sections. We show in a 32 GBd 16QAM 2400 km 5-channel wavelength division multiplexing transmission link experiment that the proposed stacked DL-DBPs provides a 0.41 dB gain with respect to linear compensation scheme. This needs to be compared with a 0.56 dB gain achieved by a non-stacked DL-DBPs compensated scheme for the price of a 203% increase in total training time. Furthermore, it is shown that by only training the last section of the stacked DL-DBP, one can increase the compensation performance to 0.48 dB., IEEE Photonics Technology Letters, 34 (7), ISSN:1041-1135, ISSN:1941-0174

As bit rates of optical interconnects increase, a large amount of complicated signal conditioning is needed to compensate for the insufficient bandwidth of current modulators. In this paper, we evaluate the reduced equalization requirements of high-bandwidth plasmonic modulators in short-reach transmission experiments. It is shown that transmission of 100 Gbit/s non-return-to-zero (NRZ) and 112 Gbit/s pulse-amplitude modulation-4 over 1 km and 2 km distance is possible without any receiver equalization. At higher bit-rates, such as 120 Gbit/s NRZ, data transmission is demonstrated over 500 m with reduced receiver equalization requirements. Transmission up to 200 Gbit/s over 1 km is also shown with more complex receiver equalization. The reduced complexity of the receiver digital signal processing is attributed to a flat frequency response of at least 108 GHz of the plasmonic modulators. All single wavelength transmissions have been performed at 1540 nm in standard single mode fiber.

A new plasmonic Mach-Zehnder modulator is demonstrated at a bit rate of 120 Gb/s NRZ-OOK with low peak-to-peak driving voltages of 178 mVpp below the HD-FEC limit. Such record low driving voltage requirements potentially translate into an electrical drive power consumption of 862 aJ/bit. The low drive voltages have been made possible by a new differential Mach-Zehnder modulator electrode design. The differential electrode design is optimized for the balanced driving circuitry and reduces the effectively required driving voltage by a factor of four (Vπ/4). The potential of the transmitter scheme is further demonstrated by a transmission experiment over 500 m of single mode fiber at the C-band with a BER performance below the KP4 FEC limit.

A 1 Tbit/s 53km single channel free-space optical (FSO) link is demonstrated. High bandwidth, high order modulation formats and advanced adaptive optics are utilized. We show that the absence of a nonlinear-Shannon limit in combination with adaptive optics enables record data-transmission with low link failures.

A transparent Optical-subTHz-Optical link providing record-high single line rates of 240 Gbit/s and 192 Gbit/s on a single optical carrier over distances from 5 to 115 m is demonstrated. Besides a direct mapping of the optical to a 230 GHz subTHz-carrier frequency by means of a uni-traveling carrier (UTC) photodiode, we demonstrate direct conversion of data from the subTHz domain back to the optical domain by a plasmonic modulator. It is shown that the subTHz-to-optical upconversion can even be performed at good quality without any electrical amplifiers. Finally, at the receiver, the local oscillator is employed to directly map the optical signal back to the electrical baseband within a coherent receiver., Journal of Lightwave Technology, 40 (6), ISSN:0733-8724, ISSN:1558-2213

To address the challenge of increasing data rates, next-generation optical communication networks will require the co-integration of electronics and photonics. Heterogeneous integration of these technologies has shown promise, but will eventually become bandwidth-limited. Faster monolithic approaches will therefore be needed, but monolithic approaches using complementary metal–oxide–semiconductor (CMOS) electronics and silicon photonics are typically limited by their underlying electronic or photonic technologies. Here, we report a monolithically integrated electro-optical transmitter that can achieve symbol rates beyond 100 GBd. Our approach combines advanced bipolar CMOS with silicon plasmonics, and addresses key challenges in monolithic integration through co-design of the electronic and plasmonic layers, including thermal design, packaging and a nonlinear organic electro-optic material. To illustrate the potential of our technology, we develop two modulator concepts—an ultra-compact plasmonic modulator and a silicon-plasmonic modulator with photonic routing—both directly processed onto the bipolar CMOS electronics. The monolithic integration of electronic and plasmonic technologies can be used to create electro-optic transmitters capable of symbol rates beyond 100 GBd.

We summarize our experimental exploration of the capabilities of an ultrabroad-bandwidth plasmonic Mach-Zehnder modulator (MZM), in an intensity modulation and direct detection (IM/DD) system for short-reach optical transmission up to 10 km. We study modulation, transmission, and reception of ultrahigh-symbol-rate (up to 304 GBd) multi-level optical signals with two different signaling schemes: pulse amplitude modulation (PAM), with up to 8 amplitude levels and partial-response-encoded binary (polybinary) modulation with memory length up to 4. By mapping the performance to a concatenated soft-decision (SD) and hard-decision (HD) forward error correction (FEC) coding scheme, a net bitrate of 363.4 Gbit/s is possible with PAM-8 signaling and 279.0 Gbit/s with tetrabinary (polybinary) signaling after 10 km standard single-mode fiber transmission. Considering an HD-only coding scheme, a net bitrate of 318.0 Gbit/s is possible with PAM-6 and 277.1 Gbit/s with tetrabinary., Journal of Lightwave Technology, 40 (10), ISSN:0733-8724, ISSN:1558-2213

The first transparent Optical-subTHz-Optical link providing record-high line-rates of 240 and 190 Gbit/s over distances from 5 to 115 m was recently demonstrated. The link has been based on a direct data-conversion from optical to subTHz using a > 500 GHz plasmonic Mach-Zehnder modulator. We discuss the potential of plasmonic devices in subTHz wireless links to efficiently bridge optical fiber networks, Proceedings of SPIE, 12027, ISSN:0277-786X, Metro and Data Center Optical Networks and Short-Reach Links V

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., 2021 European Conference on Optical Communication (ECOC), ISBN:978-1-6654-3868-1, ISBN:978-1-6654-1150-9

Integrated ferroelectric plasmonic modulators featuring large bandwidths, broad optical operation range, resilience to high temperature and ultracompact footprint are introduced. Measurements show a modulation bandwidth of 70 GHz and a temperature stability up to 250{\deg}C. Mach-Zehnder interferometer modulators with 10-$\mu$m-long phase shifters were operated at 116 Gbit/s PAM-4 and 72 Gbit/s NRZ. Wide and open eye diagrams with extinction ratios beyond 15 dB were found. The fast and robust devices are apt to an employment in industrial environments.

A computationally efficient deep learning based digital backpropagation (DL-DBP) algorithm providing a 1.9 dB SNR over a conventional linear compensation (chromatic dispersion compensation algorithm) and a 1 dB gain over a conventional back-propagation algorithm of the same complexity is presented. The algorithm has been tested in a 1200km transmission experiment. Also, if the algorithm is tested against a conventional digital backpropagation algorithm with the gain, then the new algorithm requires a factor 6 lower complexity. We discuss its training procedure and its principle. We discuss its training procedure and its principle. ISSN:0277-786X

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., Nano Letters, 21 (11), ISSN:1530-6984, ISSN:1530-6992

New high-speed photonic technologies and co-integration with electronics are required to keep up with the demand of future optical communication systems. In this paper, plasmonics is presented as one of the most promising next-generation photonic technologies that already fulfils these requirements in proof-of-concept demonstrations. Plasmonics features not only modulators and detectors of highest speed, but also compactness, cost- and energy-efficiency, and compatibility with CMOS electronics. Recently, co-integration with electronics was demonstrated with record performances of 222 GBd in a hybrid InP electronic-plasmonic transmitter assembly and of 120 GBd with a monolithic BiCMOS electronic-plasmonic transmitter., Japanese Journal of Applied Physics, 60, ISSN:0021-4922, ISSN:1347-4065

A new deep learning training method for digital back propagation (DBP) is introduced. It is invariant to polarization state rotation and phase noise. Applying the method one gains more than 1 dB over standard DBP.

Plasmonic modulators allow for high-speed data modulation beyond 200GBd at the micrometer-scale and low driving voltages below 700mV. The compact footprint enables dense integration and makes plasmonic modulators a promising solution for next-generation optical interconnects. (C) 2020 The Author(s)

ACS Photonics, 5 (8), ISSN:2330-4022

Nature, 556, ISSN:0028-0836, ISSN:1476-4687

The electro-optical Pockels effect is an essential nonlinear effect used in many applications. The ultrafast modulation of the refractive index is, for example, crucial to optical modulators in photonic circuits. Silicon has emerged as a platform for integrating such compact circuits, but a strong Pockels effect is not available on silicon platforms. Here, we demonstrate a large electro-optical response in silicon photonic devices using barium titanate. We verify the Pockels effect to be the physical origin of the response, with r42 = 923 pm V−1, by confirming key signatures of the Pockels effect in ferroelectrics: the electro-optic response exhibits a crystalline anisotropy, remains strong at high frequencies, and shows hysteresis on changing the electric field. We prove that the Pockels effect remains strong even in nanoscale devices, and show as a practical example data modulation up to 50 Gbit s−1. We foresee that our work will enable novel device concepts with an application area largely extending beyond communication technologies. Electro-optic modulators based on epitaxial barium titanate (BTO) integrated on silicon exhibit speeds up to 50 Gbit s–1 while the Pockels coefficient of the BTO film is found to be approaching the bulk value.

A monolithic BiCMOS-plasmonic transmitter offering 120 GBd NRZ-OOK is demonstrated. The chip comprises an electronic-photonic layer stack. The SiGe BiCMOS electrical layers offer PRBS generation and 4:1 power multiplexing, while the plasmonic layer offers electro-optical modulation at highest speed., 45th European Conference on Optical Communication (ECOC 2019), ISBN:978-1-83953-185-9

Coherent optical communications provides the largest data transmission capacity with the highest spectral efficiency and therefore has a remarkable potential to satisfy today’s ever-growing bandwidth demands. It relies on so-called in-phase/quadrature (IQ) electro-optic modulators that encode information on both the amplitude and the phase of light. Ideally, such IQ modulators should offer energy-efficient operation and a most compact footprint, which would allow high-density integration and high spatial parallelism. Here, we present compact IQ modulators with an active section occupying a footprint of 4 × 25 µm × 3 µm, fabricated on the silicon platform and operated with sub-1-V driving electronics. The devices exhibit low electrical energy consumptions of only 0.07 fJ bit−1 at 50 Gbit s−1, 0.3 fJ bit−1 at 200 Gbit s−1, and 2 fJ bit−1 at 400 Gbit s−1. Such IQ modulators may pave the way for application of IQ modulators in long-haul and short-haul communications alike., Nature Communications, 10, ISSN:2041-1723

The monolithic integration of power-efficient optoelectronic devices with CMOS circuits is critical for future on-chip optical communication. In such platforms, ultra-high-speed photodetectors operating at datacom wavelengths are essential to convert optical signals in the electrical domain. Here, we demonstrate ultra-compact high-speed III-V/Si photodetectors integrated on silicon photonics and exclusively fabricated with processes and materials compatible with CMOS foundries. The sub-femtofarad capacitance, high responsivity photodetectors demonstrate a bandwidth around 65 GHz and data reception at 100 GBd OOK. Their thickness and efficiency enable an integration in the back-end-of-line without using an amplifier, further reducing the power consumption of the link.

We demonstrate an on-chip coherent mode scrambling demultiplexer for polarization multiplexed few mode signals. The device has been fabricated in the standard silicon-on-insulator platform. The mode demultiplexer consists of an array of 2D grating couplers for dual polarization few mode fiber-to-chip coupling and optical hybrids realized by 4×4 MMIs. The array of perfect vertical 2D grating couplers allows us an efficient fiber-to-chip coupling with experimental peak coupling efficiencies of -5.2 dB and -9.0 dB at 1570 nm for LP01 and LP11 modes, respectively, while simulated coupling efficiencies at 1550 nm are -3.6 dB and -3.3 dB for LP01 and LP11, respectively. We successfully performed a back-to-back three LP modes division multiplexing transmission experiment with single polarization 32 Gbaud QPSK signals using the fabricated mode demultiplexer relying on offline MIMO DSP techniques.

In this paper, we demonstrate ultra-fast millimeter wave beam steering with settling times below 50 ps. A phased array antenna with two elements is employed to realize beam steering. The phased array feeder is implemented with a recently introduced time delay line that provides, at the same time, an ultra-fast tunability, broadband operation, and continuous tuning. Our implementation is used to perform symbol-by-symbol steering. In our demonstration, the beam direction is switched between two sequentially transmitted symbols toward two receivers placed 30° apart. We show the successful symbol-by-symbol steering for data streams as fast as 10 GBd. The suggested scheme shows that the ultra-fast beam steering is becoming practical and might ultimately enable novel high bit-rate multiple access schemes.

100 Gb/s NRZ-OOK transmission over 14 km standard single mode fiber in the C-band is demonstrated with a simple intensity modulation and direct detection scheme. The transmission concept utilizes single sideband modulation and comprises a single differential digital-to-analog converter with adjustable phase offset, a new dual electrode plasmonic Mach-Zehnder modulator, a laser at 1537.5 nm, standard single mode fibers, a photodiode, an analog-to-digital converter, and linear offline digital signal processing. The presented SSB concept requires no DSP and complex signaling at the transmitter. The demonstrated SSB transmitter increased the possible transmission distance by a factor of 4.6 compared to a DSB transmitter. We also investigated the equalization requirements. A T/2-spaced feedforward equalizer requires 27 taps to achieve transmission over 10 km with a BER below the HD-FEC limit. In comparison to a DSB transmitter, the SSB transmitter reduced the receiver DSP complexity by a factor of 13.7.

We demonstrate a novel, ultra-compact, waveguide-integrated, and plasmonically enhanced graphene photodetector featuring a responsivity of 0.5 A/W and a bandwidth exceeding 110 GHz. We show for the first time 100 GBd data reception with a graphene-based device.

Two-dimensional (2D) materials integrated with planar photonic elements enable a new class of electro-optical components and hold much promise for a novel 2D material integrated circuit technology. Here, we present a few-layer MoTe2 waveguide photodetector that is operable across the entire O-band of the near-infrared optical telecommunication spectral range. The device is realized in a two-terminal in-plane electrode configuration without applying external gating. It features a competitive photoresponsivity of 23 mA/W as well as a low dark current, both of which lead to a highly sensitive photodetection with a large dynamic range. Moreover, the design of the photodetector exhibits a fast photoresponse with a bandwidth approaching 1 GHz, outperforming prior TMDC-based photodetectors. Optical data experiments proved the operation of our device at data rates of 1 Gbit/s, revealing the applicability of integrating 2D materials for practical optical data communication applications. ISSN:2330-4022

We present an integrated ferroelectric BaTiO 3 /Si plasmonic modulator and test its performance at 116 Gbit/s. The modulator has been tested to withstand temperatures up to 250°C.

Multi-scale (correlated quantum and statistical mechanics) modeling methods have been advanced and employed to guide the improvement of organic electro-optic (OEO) materials, including by analyzing electric field poling induced electro-optic activity in nanoscopic plasmonic-organic hybrid (POH) waveguide devices. The analysis of in-device electro-optic activity emphasizes the importance of considering both the details of intermolecular interactions within organic electro-optic materials and interactions at interfaces between OEO materials and device architectures. Dramatic improvement in electro-optic device performance--including voltage-length performance, bandwidth, energy efficiency, and lower optical losses have been realized. These improvements are critical to applications in telecommunications, computing, sensor technology, and metrology. Multi-scale modeling methods illustrate the complexity of improving the electro-optic activity of organic materials, including the necessity of considering the trade-off between improving poling-induced acentric order through chromophore modification and the reduction of chromophore number density associated with such modification. Computational simulations also emphasize the importance of developing chromophore modifications that serve multiple purposes including matrix hardening for enhanced thermal and photochemical stability, control of matrix dimensionality, influence on material viscoelasticity, improvement of chromophore molecular hyperpolarizability, control of material dielectric permittivity and index of refraction properties, and control of material conductance. Consideration of new device architectures is critical to the implementation of chipscale integration of electronics and photonics and achieving the high bandwidths for applications such as next generation (e.g., 5G) telecommunications.

Radically novel approaches will be needed to support the 1,000 times increase in data rates expected from next-generation wireless communications (5G). Integrated microwave photonics (IMWP) techniques have been identified as an enabling technology for 5G, as they have the potential to improve the performance of electronics by leveraging the broadband characteristics and flexibility of operation of photonic integrated circuits. Important applications of IMWP are optical signal generation and distribution of mm-waves towards antenna terminals, frequency-reconfigurable filtering, optical control of antenna arrays, and more. The rapidly growing field of plasmonics has shown a breakthrough in performance for optical modulators with ultra-fast operation $\mathbf{(> 170 GHz)}$ and ultra-compact footprint $\mathbf{(10s\ \mu m^{2})}$ . This paper reports recent achievements on the use of integrated plasmonic devices for millimeter-wave signal conversion and pro-cessina for next-generation wireless systems.

We demonstrate driver-less 100 GBd operation of a plasmonic intensity modulator. Drive voltages below 1V lead to low power consumption of 2.84 fJ/bit for 100 Gbit/s with a direct detected BER below the HD-FEC limit.

We report on a waveguide-integrated plasmon-enhanced graphene photodetector demonstrating simultaneously a responsivity of 0.5 A/W and a bandwidth beyond 67 GHz. The device capabilities are shown in a 100 Gbit/s PAM-4 data reception experiment.

OSA Technical Digest, Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), ISBN:978-1-943580-43-9

We show cascaded 100-Gb/s sub-channel add/drop from a 1-Tb/s MB-OFDM or Nyquist-WDM super-channel having ultra-low inter-sub-channel guard-bands within a recirculating loop via a hierarchical ROADM using high-resolution filters, showcasing up to 1000-km transmission reach and five ROADM node passages for the add/drop sub-channel when hybrid Raman-EDFA is used.

A timing recovery algorithm is introduced that operates with less than two samples per symbol and provides an enormous complexity reduction. The complexity reduction is due to a synergy with the already existing Fourier transforms in a coherent receiver, an avoidance of terms that are dominated by noise, and a complete elimination of multiplications. A simulation and an experiment with a single carrier modulation format show that the inherent timing jitter is, despite of the significant complexity reduction, comparable with the state of the art, and in particular outperforms the Godard algorithm for low roll-off factors. In addition, it is one of the few algorithms that operates with less than two samples per symbol in the frequency domain, and thus enables the lowest complexity in a receiver.

We demonstrate a plasmonic Mach-Zehnder (MZ) modulator with a flat frequency response exceeding 170 GHz. The modulator comprises two phase modulators exploiting the Pockels effect of an organic electro-optic material in plasmonic slot waveguides. We further show modulation at 100 GBd NRZ and 60 GBd PAM-4. The electrical drive signals were generated using a 100 GSa/s digital to analog converter (DAC). The high-speed and small-scale devices are relevant for next-generation optical interconnects.

Asia Communications and Photonics Conference, ACP, ISBN:978-1-943580-34-7

Demonstration of a real-time receiver working with 28 GBd at 32 GSa/s. The signal processing is done on a single FPGA. The resource-saving non-integer oversampling of 8/7 is enabled by a timing synchronization in the frequency domain.

A blind frequency and phase search algorithm for joint frequency and phase recovery is introduced. The algorithm achieves low complexity due to processing in polar coordinates, which reduces the amount of multiplications. We show an implementation for real-time processing at 32 GBd on FPGA hardware. The hardware design allows for dynamic multi-format operation, where the format can be switched flexibly after each clock cycle (250 MHz, 128 Symbols) between 4QAM, 8QAM, and 16QAM. The performance of the algorithm is evaluated with respect to laser phase noise, carrier frequency offset, and carrier frequency offset drift. The effect of working with limited hardware resources is investigated. An FPGA implementation shows the feasibility of our carrier recovery algorithm with a negligible penalty when compared to a floating point simulation., Optics Express, 24 (22), ISSN:1094-4087

In the version of this Letter originally published online, the ORCID number, 0000-0002-8900-3237, of the author A. Josten was missing; and in Fig. 2b, in the y axis label, ‘×105’should have been ‘×103’. These errors have now been corrected in all versions.

Constellation modulation (CM) is introduced as a new degree of freedom to increase the spectral efficiency and to further approach the Shannon limit. Constellation modulation is the art of encoding information not only in the symbols within a constellation but also by encoding information by selecting a constellation from a set of constellations that are switched from time to time. The set of constellations is not limited to sets of partitions from a given constellation but can e.g., be obtained from an existing constellation by applying geometrical transformations such as rotations, translations, scaling, or even more abstract transformations. The architecture of the transmitter and the receiver allows for constellation modulation to be used on top of existing modulations with little penalties on the bit-error ratio (BER) or on the required signal-to-noise ratio (SNR). The spectral bandwidth used by this modulation scheme is identical to the original modulation. Simulations demonstrate a particular advantage of the scheme for low SNR situations. So, for instance, it is demonstrated by simulation that a spectral efficiency increases by up to 33% and 20% can be obtained at a BER of 10-3 and 2×10-2 for a regular BPSK modulation format, respectively. Applying constellation modulation, we derive a most power efficient 4D-CM-BPSK modulation format that provides a spectral efficiency of 0.7 bit/s/Hz for an SNR of 0.2 dB at a BER of 2 × 10-2.

Flexible optical networking is identified today as the solution that offers smooth system upgradability towards Tb/s capacities and optimized use of network resources. However, in order to fully exploit the potentials of flexible spectrum allocation and networking, the development of a flexible switching node is required capable to adaptively add, drop and switch tributaries with variable bandwidth characteristics from/to ultra-high capacity wavelength channels at the lowest switching granularity. This paper presents the main concept and technology solutions envisioned by the EU funded project FOX-C, which targets the design, development and evaluation of the first functional system prototype of flexible add-drop and switching cross-connects. The key developments enable ultra-fine switching granularity at the optical subcarrier level, providing end-to-end routing of any tributary channel with flexible bandwidth down to 10Gb/s (or even lower) carried over wavelength superchannels, each with an aggregated capacity beyond 1Tb/s. © 2014 IEEE.

Complementing plasmonic slot waveguides with highly nonlinear organic materials has rendered a new generation of ultracompact active nanophotonic components that are redefining the state of the art. In this paper, we review the fundamentals of this so-called plasmonic–organic–hybrid (POH) platform. Starting from simple phase shifters to the most compact $IQ$ modulators, we introduce key devices of high-speed data communications. For instance, all-plasmonic Mach–Zehnder modulators (MZMs) are reviewed and long-term prospects are discussed. This kind of modulator already features unique properties such as a small footprint ( $ 20 $\mu$ m $^{2}$ ), a large electro–optic bandwidth ( $>$ 110 GHz), a small energy consumption ( $\sim$ 25 fJ/b), a large extinction ratio ( $>$ 25 dB) in combination with a record small voltage-length product of 40 V $\mu$ m. Finally, as an example for seamless integration we introduce novel plasmonic $IQ$ modulators. With such modulators we show the generation of advanced modulation formats (QPSK, 16-QAM) on footprints as small as 10 $\mu{\hbox {m}}\times {\hbox {75}}\ \mu{\hbox {m}}$ . This demonstration ultimately shows how plasmonics can be used to control both phase and amplitude of an optical carrier on the microscale with reasonably low losses.

We demonstrate a 222 GBd on-off-keying transmitter in a short-reach intra-datacenter scenario with direct detection after 120 m of standard single mode fiber. The system operates at net-data rates of >200 Gb/s OOK for transmission distances of a few meters, and >177 Gb/s over 120 m, limited by chromatic dispersion in the standard single mode fiber. The high symbol rate transmitter is enabled by a high-bandwidth plasmonic-organic hybrid Mach–Zehnder modulator on the silicon photonic platform that is ribbon-bonded to an InP DHBT 2:1 digital multiplexing selector. Requiring no driving RF amplifiers, the selector directly drives the modulator with a differential output voltage of 622 mV pp measured across a 50 Ω resistor. The transmitter assembly occupies a footprint of less than 1.5 mm × 2.1 mm., Journal of Lightwave Technology, 38 (9), ISSN:0733-8724, ISSN:1558-2213