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# Eye diagram after 2 km. (a) PAM-2 at 30 Gb/s, (b) PAM-2 at 50 Gb/s, (c) PAM-4 at 60 Gb/s, (d) PAM-4 at 80 Gb/s, (e) PAM-4 at 100 Gb/s, and (f) PAM-4 at 112 Gb/s.

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We present a silicon photonic traveling-wave Mach–Zehnder modulator operating near 1550 nm with a 3-dB bandwidth of 35 GHz. A detailed analysis of traveling-wave electrode impedance, microwave loss, and phase velocity is presented. Small- and large-signal characterization of the device validates the design methodology. We further investigate the pe...

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... length by 5 GHz [12]. Fig. 8(d) demonstrates the extracted characteristic impedance of the TW-MZM from S-parameters under different bias voltages. The measured characteristic impedance has excel- lent agreement with the calculated results presented in Fig. 3(b), with less than 4% variations from the calculated values. The predicted impedance dispersion at higher frequencies is clearly observed in the measured results; however, over the 50 GHz frequency range, the impedance only varies by 2 . Moreover the EE 6.4 dB and the EO 3 dB bandwidths shown are very close, indicating that the performance of the modulator is not limited by velocity mismatch [12]; this validates the design methodology outlined in Section 2. The observed EE S 21 value of 21 GHz is lower than the calculated value of 25 GHz. This can be due to the neglected radiation losses and higher actual surface resistances. Next, we examine the large signal performance of the modulator using an Agilent wide band oscilloscope. At the input of the modulator a tunable laser with maximum output power of 14 dBm is used. The modulator is operated at the quadrature point using the tunable laser. At this wavelength, the modulated signal power is À 3.8 dBm and a 3 V DC bias voltage is applied using a RF probe to reverse bias the PN junctions. A 10 31 À 1 pseudorandom bit sequence (PRBS) signal generated by a SHF pulse pattern generator is amplified using a wide band microwave amplifier and attenuated by passive RF attenuators to obtain a 4.6 V pp driving signal This signal is then applied to the modulator using a high-frequency RF probe. Fig. 9 shows eye diagrams for 30, 40, 50, and 55 Gb/s with extinction ratios of 11.58, 7.59, 5.35, and 4.30 and SNR of 10.31, 6.55, 4.32, and 3.18, respectively. Eye diagrams, shown in Fig. 9, provide a visual qualitative presentation of the performance of the device. In order to quantitatively evaluate the performance of the modulator, bit error rate (BER) test of the system is performed. To do this, the input laser power to the modulator is set to 14.5 dBm. The output of the modulator is fed to an AC coupled Picometrix PD þ TIA receiver which is then connected to a SHF bit error tester. An error-free ð BER G 10 À 12 Þ operation up to 45 Gb/s is obtained with received power of À 3.5 dBm, limited by the bandwidth of the PD þ TIA receiver. The small optical insertion loss, together with the high optical extinction ratio of the transmission spectra and the high E-O bandwidth make this modulator an ideal transmitter for multilevel modulation formats. In this section we compare the performance of the modulator with PAM-2 and PAM-4 modulation formats over different lengths of fiber to reach a 100G Ethernet transport rate. At the input of the modulator, the same tunable laser with 14 dBm output power is used. The RF driving signal is generated using an AC coupled 8-bit Digital to Analog Converter (DAC) operating at 70 GSa/s. Use of a DAC allows us to apply digital signal processing (DSP) at the transmitter side. Four processes are applied to the waveform. First the symbol stream is up- sampled from one sample per symbol to 70 = R B , where ð R B Þ is the desired symbol rate. Next a root raised cosine pulse shaping filter is applied. Thirdly, to equalize the spacing between modulated optical power levels, the nonlinearity of the power transfer function of the TW-MZM is com- pensated by applying an arcsin function to the waveform. Finally the frequency response of DAC, RF amplifier and TW-MZM cascade is pre-compensated by applying an inverse response function. An amplifier is used to amplify the DAC output to 2.2 V pp which is then applied to the modulator using RF probes. The modulated signal is propagated through 1, 2, and 5 km of Corning SMF 28e þ fiber. The PD þ TIA is used for opto-electrical (O-E) conversion before an Agilent real time oscilloscope serving as an 8-bit Analog to Digital converter (ADC) sampling at 80 GSa/s. At the receiver side, the digital signal processing is performed offline. First the signal is resampled from ADC rate of 80 GSa/s to twice the symbol rate R B . Next a matched filter defined at 2 samples per symbol is applied to the signal. The stream of samples is then fil- tered by a linear FIR filter. To recover the transmitter's clock and to apply symbol decision at the correct sampling instant, a digital clock recovery algorithm is implemented [7]. The output symbols are then used for error counting and to calculate the signal to noise ratio (SNR) and quality factor of the system. The DSP applied at the transmitter and receiver sides is discussed in detail in [7]. Fig. 10 illustrates the block diagram of the transmission system explained above. We present the system performance qualitatively using eye diagrams and quantitatively by measuring BER and SNR. BER measurement is done by error counting. For PAM-N formats, SNR is defined as the ratio of the average signal power over average noise power. Fig. 11 shows eye diagrams for PAM-2 and PAM-4 formats at different baud rate after propagating through 2 km of fiber. In currently deployed metro and long haul fiber optic transmission systems, Forward Error Correction (FEC) is used to significantly lower the BER. Based on OT4U standard [2], a client payload of 100 Gb/s is transmitted at line rate of 112 Gb/s, which includes 6.7% (FEC) over head. A BER measurement below the pre-BER threshold of 4 : 4 Â 10 À 3 results in an output BER G 10 À 15 , viewed as error free transmission in the context of optical transmission. In this paper we assume FEC encoding and decoding at the transmitter and receiver side. All eye diagrams are obtained after receiver DSP. A successful 100 Gb/s PAM-4 post-FEC error-free transmission through 2 km of fiber is achieved in all cases. After 5 km, for the same bit rate of fiber the pre-FEC BER is measured at 4 Â 10 À 3 which is slightly lower than FEC threshold of 4 : 4 Â 10 À 3 . For PAM-2, a maximum of 64 Gb/s transmission was achieved at pre- FEC BER of 1 : 31 Â 10 À 4 which was limited by DAC's bandwidth. Fig. 12 illustrates SNR and BER at various bit rates. We observe that, as the bit rate increases, the SNR and BER performance of the system degrades. The DAC has a 3 dB bandwidth of 15 GHz; however, using Nyquist sampling theory, the DAC can generate frequencies up to 35 GHz when sampling at 70 GSa/s. At higher bit rates the signal has higher frequency content. After digital compensation of the frequency response of the DAC, a signal of larger spectral content will have reduced V pp swing out of the DAC, worsening the RF signal quality. At the receiver side, the same large bandwidth signal will integrate more inband noise power, further deteriorating the SNR. The cumulative effect of transmitter and receiver signal worsening as the symbol rate increases is observed in Fig. 12. The low insertion loss of the device allowed the full operation of the modulator without the need for optical amplifiers, which further differentiates this work from other modulators presented in the literature [5], [7], [12]. In this paper, we present the design and characterization of a low voltage silicon photonic traveling wave modulator. A thorough analysis of the implemented traveling wave electrode is presented. It is shown that using a CPS geometry, it is possible to minimize the mismatch between the microwave phase velocity and optical group velocity by careful design. As a result, the main bandwidth limiting factor is determined to be the microwave loss. A 3 dB electro-optic bandwidth of 35 GHz under 3 V DC bias is demonstrated. We further investigate the performance of the device in a short reach transmission system. By applying digital signal processing on transmitter and the receiver side we obtain a successful 112 Gb/s transmission of 4 level pulse amplitude modulation over 5 km of SMF below pre-FEC hard decision threshold of 4 : 4 Â 10 À 3 . We present an alternative solution to 4 Â 25 Gb/s WDM transmission systems. We demonstrate that higher modulation formats such as PAM-4, together with digital signal processing can be used to achieve 100 Gb/s transmission on a single wavelength. The authors gratefully acknowledge CMC Microsystems for enabling fabrication and providing access to simulation and CAD ...

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## Citations

... Because the calculations of OCU are all passive, its power consumption mainly comes from the data loading and photodetection process. Schemes of photonics modulator with small driving voltage [57,58,59] have been proposed recently to provide low power consumption, and integrated photodetectors [60,61] are also investigated with negligible energy consumed. Therefore, the total power of an OCU with equivalent kernel size of H can be calculated as Eq. ...

The ever-growing deep learning technologies are making revolutionary changes for modern life. However, conventional computing architectures are designed to process sequential and digital programs, being extremely burdened with performing massive parallel and adaptive deep learning applications. Photonic integrated circuits provide an efficient approach to mitigate bandwidth limitations and power-wall brought by its electronic counterparts, showing great potential in ultrafast and energy-free high-performance computing. Here, we propose an optical computing architecture enabled by on-chip diffraction to implement convolutional acceleration, termed optical convolution unit (OCU). We demonstrate that any real-valued convolution kernels can be exploited by OCU with a prominent computational throughput boosting via the concept of structral re-parameterization. With OCU as the fundamental unit, we build an optical convolutional neural network (oCNN) to implement two popular deep learning tasks: classification and regression. For classification, Fashion-MNIST and CIFAR-4 datasets are tested with accuracy of 91.63% and 86.25%, respectively. For regression, we build an optical denoising convolutional neural network (oDnCNN) to handle Gaussian noise in gray scale images with noise level {\sigma} = 10, 15, 20, resulting clean images with average PSNR of 31.70dB, 29.39dB and 27.72dB, respectively. The proposed OCU presents remarkable performance of low energy consumption and high information density due to its fully passive nature and compact footprint, providing a highly parallel while lightweight solution for future computing architecture to handle high dimensional tensors in deep learning.

... Thus, PAM4 has been standardized for short reach interconnects up to 10 km because of its simplicity and lower power requirements compared to the other modulation formats [1]. PAM modulation can be achieved through using directly modulated lasers (DMLs) [2], externally modulated lasers (EMLs) [3], or external optical modulators [4][5][6][7][8][9]. The main material systems used in fabricating these modulators are lithium niobite (LiNbO3), indium phosphide (InP), gallium arsenide (GaAs), and silicon (Si), out of which silicon is the only material system that is fully compatible with the complementary metal oxide semiconductor (CMOS) processing. ...

... Thus, silicon photonics modulators are anticipated to dominate the market because of the low fabrication costs and scalable production [10,11]. Si-photonic modulators have a very slow roll-off frequency response, allowing the operation at high symbol rates [4,5,7,9,12]. Moreover, the advancement on the electronics side is pushing the limits of what can be achieved with Si-photonics. ...

... It has a 4 mm phase-shifter at a fill factor of 85%, and it is terminated on-chip with a 50 Ω highly doped Si resistor. The TW electrodes are designed such that a good velocity matching between the optical signal and the RF signal is established at a characteristic impedance of 50 Ω [7]. The measured DC Vπ is 5 V at 0 V reverse bias, corresponding to an inverse phase-shifting efficiency (VπL) of 2 V.cm. ...

In this work, IBM, CMC, AMF, and McGill University work together to verify a simplified packaging scheme for Si-photonic devices based on incorporating IBM’s polymer photonic interface into AMF’s Si-photonic fabrication process flow. The proposed procedure is used in packaging an O-band Si-photonic traveling wave Mach-Zehnder modulator (TW-MZM) yielding a fiber-to-fiber insertion loss of 16.5 dB and 16 GHz 3-dB bandwidth. Employing the packaged module without RF or optical amplification, we demonstrate the transmission of 28 Gbaud PAM4 (net 53 Gbps) over 2 km of SSMF using a linear feed-forward equalizer below the 2.4×10
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KP4-FEC BER threshold with 750 mVpp, and under the 3.8×10
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HD-FEC threshold at 500 mVpp. Besides, we transmit 36 Gbaud (net 67 Gbps) under HD-FEC at 830 mVpp. Operating with an RF driver; we transmit 70 Gbaud PAM4 below HD-FEC, which corresponds to a net rate of 131 Gbps. The achieved transmission performance highlights the potential of the proposed packaging scheme.

... Therefore, it affects the performance in terms of FOM 2 according to Eq. (7). Initially, the maximal doping concentration possible was considered [28], lowering the doping levels results in higher heat conductivity and lower electrical conductivity which both provide better results. In addition, when attenuation is taken into account as well, lower doping level produce less attenuation. ...

Thermo-optic phase shifter (TOPS) based on doped silicon (Si) heaters is commonly used to compensate for device structure imbalance of high-speed Mach-Zehnder modulator (MZM) due to fabrication errors. However, this functionality required more electrical power for setting the MZM to be active around the linear transfer function at π/2 phase shift. To solve this issue, we proposed an optimal design of doped Si heaters using the standard commercial 220 nm Si layer in rib waveguide structure which can improve the electrical energy efficiency and reduce optical losses. Numerical simulations and optimizations were carried out on the key parameters, heater locations, doping concentration, etching depth, and laser wavelength drift. Results show that the optimal design has a low power consumption of 19.1 mW for obtaining a phase shift of π with a good time constant of 2.47 µs and low optical losses of 2.37 dB/cm at the 1550 nm operated wavelength. Thus, an excellent figure of merit (FOM) of 47.2 mWµs is obtained for the optimal design. Also, the proposed device has good stability to the laser wavelength drift effect in the C-band range. This TOPS can be very useful for improving the transmitter system performances based on high-speed MZM technology.

... It consists of two child MZMs placed in each arm of a parent MZI. The design of the child MZMs is based on the single drive series push-pull traveling wave MZM described in [22]. The modulators are realized with lateral pn-junction phase shifters using the iSiPP50G silicon photonics platform of IMEC [23]. ...

An integrated photonics based scheme for radio-frequency self-interference cancellation is proposed and demonstrated. It is achieved using a dual-parallel Mach-Zehnder modulator that eliminates the interference signal in the optical domain. The output of the modulator is a carrier suppressed double-sideband waveform that contains only the signal of interest. Finally, the signal of interest is recovered by combining the modulator output with a local optical carrier and detecting it at a high-speed photodetector. We present a detailed theoretical analysis and derive the optimal condition for self-interference cancellation for small modulation indices. The modulators were designed and fabricated on IMEC’s Silicon-on-Insulator iSiPP50G platform. Using this technique, we experimentally obtain a cancellation depth of 30 dB and a signal to interference ratio of 25 dB for frequencies up to 20 GHz, limited only by the equipment used. This is the first demonstration of self-interference cancellation on a silicon photonics platform and a further expansion of the functionalities offered by integrated microwave photonics.

... For the 1.5 mm lumped MZM studied in this work, the corresponding f τ of 22.9 GHz should be investigated for the 25 Gbaud PAM4 signals in question. As a judge of its potential impact, Fig. 5 plots the magnitude squared of the frequency response resulting from (9). Notably, the roll-off is virtually identical over this range of frequencies to that of a fourth-order Bessel filter with the same 3 dB bandwidth. ...

The use of electrical precompensation for high-speed operation of lumped MZMs is demonstrated for 50 Gb/s PAM4 modulation through experiment and simulation. An accurate equivalent circuit model is fitted to S11 measurements and then used to analyse design trade-offs in terms of system performance, energy consumption and drive voltage requirements. If precompensation is not used, careful selection of source resistance with respect to electrode and packaging inductance is shown to be crucial for high-speed modulation. Increasing the electrode inductance is shown to be beneficial as it introduces inductive peaking, which allows optimum performance with a higher source impedance. Furthermore, combining precompensation with a slight inductive peaking and optimised source resistance is demonstrated to reduce drive voltage requirements and further reduce the energy dissipated in the equivalent circuit.

... The IQM is composed of two parallelly connected child TW-MZMs. Each of the child MZMs requires a single RF signal; as it is a single segment MZM with the PN junctions designed for series pushpull (SPP) driving configuration [11]. The traveling-wave electrodes of each MZM are terminated with an on-chip 50 Ω termination (OCT) for maximum power transfer and ease of testing. ...

... The reverse DC bias is applied through a high-inductance line so that the RF and DC are separated. The complete design procedure of the employed TW-MZM coplanar strip electrodes is presented in [11]. The foundry process flow uses a 2 μm thick aluminum layer for metallization. ...

... The foundry process flow uses a 2 μm thick aluminum layer for metallization. As in [11], the width and separation between MZM electrodes are set to 36 μm and 60 μm, respectively. These values ensure that each of the electrodes has a 50 Ω characteristic impedance, besides ensuring a good velocity matching between the optical and RF signal. ...

There is a continuous need to scale optical communication networks' capacity to cope with the exponential growth of data traffic. Silicon photonics (SiP) retains significant potential as a platform for optical transceivers due to its CMOS compatibility, despite its limited electro-optic bandwidth and high driving voltage requirements. Here we present the design and characterization of two single-segment C-band SiP in-phase quadrature modulators (IQM) that differ in the phase shifter length, and we analyze the design tradeoffs based on their transmission performance. The large-signal transmission experiments indicate that the long IQM supports higher data transmission rates, which has 36 GHz 6-dB bandwidth and 10.5 V DC Vπ under 1 V reverse bias. With all-electronic equalization and on a single polarization, we transmit net 413 Gbps (95 Gbaud 32QAM) over 80 km of standard single-mode fiber (SSMF) under the 14.8% overhead concatenated forward error correction (C-FEC) BER threshold of 1.25×10<sup>-2</sup>. Using dual-polarization (DP) emulation and lookup table-based non-linear pre-distortion (NLPD), we demonstrate the transmission of 95 Gbaud DP-32QAM and 115 Gbaud DP-16QAM over 80 km of SSMF below the C-FEC BER threshold, corresponding to net rates of 827 Gbps and 800 Gbps, respectively. Moreover, we transmit 105 Gbaud DP-64QAM over 80 km below the 25% overhead soft-decision (SD) FEC BER threshold of 5×10<sup>-2</sup>; featuring the first demonstration of net 1 Tbps transmission using an all-silicon IQM. Employing only electronic equalization and single-segment IQM preserves the conventional architecture of coherent networks and transceivers, and highlights the potential of SiP as a platform for next-generation 800G applications.

... Néanmoins, l'ajout de tels convertisseurs dans les émetteurs-récepteurs hauts-débits peut représenter un coût énergétique et économique important [81]. Plusieurs de ces démonstrations reposent sur la structure communément appelée series-push-pull MZM ou SPP-MZM [91,92,94]. Cette dénomination désigne un agencement particulier des régions dopées d'un MZM, où deux régions dopées de chaque bras sont réunies en une seule (par exemple les deux régions P sont mises en commun, Fig. 3.5 [92]). ...

... Plusieurs de ces démonstrations reposent sur la structure communément appelée series-push-pull MZM ou SPP-MZM [91,92,94]. Cette dénomination désigne un agencement particulier des régions dopées d'un MZM, où deux régions dopées de chaque bras sont réunies en une seule (par exemple les deux régions P sont mises en commun, Fig. 3.5 [92]). Les deux diodes sont ainsi connectées l'une à l'autre en série. ...

... Un avantage de cette structure est de n'avoir qu'un seul accès RF, aux bornes duquel aucune tension DC n'est requise [91]. D'autre part, cette configuration permet de réduire l'atténuation de l'onde électrique [92,100]. En revanche l'opération forcée en push-pull du modulateur limite sa flexibilité pour d'autres applications. ...

La photonique silicium est une technologie de choix pour l’intégration de circuits photoniques complexes sur des puces de quelques mm² pouvant être fabriquées massivement et à faible coût. L’un des enjeux principaux de cette plateforme est la réalisation d’émetteurs-récepteurs optiques miniatures pour assurer les télécommunications haut-débits entre les différents serveurs des centres de données ou datacenters. De nombreuses autres applications ont émergé récemment : la spectroscopie, la radio-sur-fibre ou encore le LIDAR. Pour l’essentiel de ces nouvelles applications, un outil se révèle particulièrement utile : les peignes de fréquences optiques. Peu après l’invention du laser, ces structures spectrales consistants en un ensemble de raies laser régulièrement espacées en fréquence et mutuellement cohérentes ont suscité un fort intérêt, permettant d’améliorer considérablement la précision et la simplicité des mesures de fréquences optiques. Plusieurs stratégies ont été développées pour leur génération, l’une d’elle exploite la modulation électro-optique. L’objectif de ma thèse a été d’étudier numériquement et expérimentalement l’aptitude et les performances de modulateurs silicium à la fois dans le cadre des communications numériques hauts-débits à courte portée et de la génération de peignes de fréquence par voie électro-optique. Les modulateurs silicium reposent sur l’effet de dispersion de plasma de porteurs libres, qui implique une réponse non-linéaire de la variation d’indice de réfraction à l’application d’une tension, ainsi qu’une variation de l’absorption optique du matériau. D’autre part, plusieurs effets électroniques et opto-électroniques impactent la rapidité des modulateurs. Une première partie de mes travaux a donc été consacrée à la modélisation numérique d’un modulateur de phase en silicium tenant compte de ces effets statiques et dynamiques. Ce modèle réaliste est basé sur des mesures expérimentales de modulateurs réels et a été employé dans la suite des travaux pour simuler ou analyser les performances de structures modulantes. Une seconde partie a consisté dans l’étude d’un modulateur Mach-Zehnder pour la génération du format PAM-4. Un aspect important de ce type d’application est de pouvoir générer un signal à quatre niveaux sans recourir à des composants électroniques coûteux énergétiquement. D’autre part, il est préférable d’assurer ces transmissions fibrées dans une région spectrale où la dispersion optique est minimale. J’ai ainsi réalisé une démonstration expérimentale d’une génération de signal PAM-4 à 20 Gb/s sans utiliser de convertisseur numérique/analogique et en bande O où la dispersion est proche de 0 ps/nm/km. Enfin, une troisième partie est dédiée à la génération de peignes de fréquences optiques par des modulateurs en silicium. Les exigences quant aux propriétés des peignes dépendent des applications, mais on peut noter deux caractéristiques généralement désirées : un grand nombre de raie, et une puissance également distribuée parmi les raies (c’est-à-dire un peigne plat). À travers une étude numérique, j’ai pu montrer que deux structures différentes basées sur des modulateurs silicium permettent de générer 9 raies égalisées (<2 dB de fluctuations) dont l’espacement peut être accordé de 0 à 7 GHz. En segmentant les modulateurs sur une structure, la simulation révèle que la plage d’accordabilité peut être étendue à 39 GHz. En plaçant un modulateur de phase dans un résonateur en anneau, j’ai également estimé numériquement que le nombre de raies obtenue dans une fenêtre de 50 dB peut être étendu d’environ 30 à plus de 110. J’ai pu concevoir ce composant qui est en cours de fabrication. Enfin, j’ai réalisé une expérience de spectroscopie à deux peignes à partir de peignes issus de modulateurs silicium, ouvrant la voie aux nouvelles applications de ces dispositifs.

... Transmission rates up to several hundred Gbps have been reported by resorting to advanced modulation IQ schemes. [105][106][107][108] Regarding the dynamic control of free carriers in silicon, various configurations have been explored over the years. These configurations include capacitor-like structures for carrier accumulation and appropriately biased p-n/p-i-n junctions for carrier depletion/injection. ...

... Ultimately, a 28-GHz EO bandwidth is achieved with the demonstration of a 60 Gbps transmission rate (OOK) and a 3.6 dB dynamic ER; similar metrics have been reported in the literature for other reverse-biased junction configurations. 106,112,117 Alternatively, forward-biased p-i-n junctions [ Fig. 8(d)] provide lower voltage-length products but require (passive) equalizing RF circuits, which mostly lower the equivalent electrical capacitance to allow for comparably high-speed operation at the expense of modulation efficiency: In Ref. 110, a V π L = 0.62 V cm (60-µm-long device) is reported with a 17-GHz EO BW and a 2.1-dB dynamic ER at a 25-Gbps transmission rate (OOK). ...

... 108,122,123 MZMs on the other hand, exhibit more flexibility in IQ modulation schemes, which can be realized using nested interferometers in each parent branch or by appropriately driven cascaded phase shifters. 15 Although such schemes require more complex electrical circuits, single-or double-polarization 4-PAM, 106 QPSK, 105 and 16-QAM 107,124 modulations have been successfully demonstrated, with the reported symbol rates typically reaching 50 GBd, resulting in data rates up to 240 Gbps for single-polarization 107 or 320 Gbps for dual-polarization 16-QAM. 124 Other alternatives have also been considered in Si modulators, such as slow-wave structures which increase the phaseshifting efficiency due to the reduced group velocity of the guided light; works on Bragg gratings and photonic-crystal structures report notable metrics. ...

Electro-optic modulators are an indispensable part of photonic communication systems, largely dictating the achievable transmission rate. Recent advances in materials and fabrication/processing techniques have brought new elements and a renewed dynamic to research on optical modulation. Motivated by the new opportunities, this Perspective reviews the state of the art in integrated electro-optic modulators, covering a broad range of contemporary materials and integrated platforms. To provide a better overview of the status of current modula-tors, an assessment of the different material platforms is conducted on the basis of common performance metrics: extinction ratio, insertion loss, electro-optic bandwidth, driving voltage, and footprint. The main physical phenomena exploited for electro-optic modulation are first introduced, aiming to provide a self-contained reference to researchers in physics and engineering. Additionally, we take care to highlight topics that can be overlooked and require attention, such as the accurate calculation of carrier density distribution and energy consumption, the correct modeling of thin and two-dimensional materials, and the nature of contact electrodes. Finally, a future outlook for the different electro-optic materials is provided, anticipating the research and performance trends in the years to come.

... GHz was presented in [6]. In [7], a TW series push-pull Siphotonic multi-electrode MZM was experimentally demonstrated. ...

This paper investigates the seamless mapping of wireless mmWave phase-levels to the optical phase-levels in a seamless digital mmWave-to-photonic converter. We report a non-linear mapping of phase-levels from the wireless to the optical domain which results in digital symbol degeneracy. Our work provides various optimum design guidelines to make such seamless converters practically feasible in digital communication links. The latency and the design complexity of such a seamless converter are expected to be appreciably lower than those of a conventional converter, thereby making it more suitable for 6G communication systems. Although the wireless operating frequency considered in this paper belongs to the mmWave band, all the contributions presented are equally applicable and relevant in the THz wireless band as well.

... GHz was presented in [6]. In [7], a TW series push-pull Siphotonic multi-electrode MZM was experimentally demonstrated. ...

This paper investigates the seamless mapping of wireless mmWave phase-levels to the optical phase-levels in a seamless digital mmWave-to-photonic converter. We report a non-linear mapping of phase-levels from the wireless to the optical domain which results in digital symbol degeneracy. Our work provides various optimum design guidelines to make such seamless converters practically feasible in digital communication links. The latency and the design complexity of such a seamless converter are expected to be appreciably lower than those of a conventional converter, thereby making it more suitable for 6G communication systems. Although the wireless operating frequency considered in this paper belongs to the mmWave band, all the contributions presented are equally applicable and relevant in the THz wireless band as well.