Graphene is an ideal material for optoelectronic applications. Its photonic properties give several advantages and complementarities over Si photonics. For example, graphene enables both electro-absorption and electro-refraction modulation with an electro-optical index change exceeding 10 −3 . It can be used for optical add-drop multiplexing with voltage control, eliminating the current dissipation used for the thermal detuning of microresonators, and for thermoelectric-based ultrafast optical detectors that generate a voltage without transimpedance amplifiers. Here, we present our vision for graphene-based integrated photonics. We review graphene-based transceivers and compare them with existing technologies. Strategies for improving power consumption, manufacturability and wafer-scale integration are addressed. We outline a roadmap of the technological requirements to meet the demands of the datacom and telecom markets. We show that graphene based integrated photonics could enable ultrahigh spatial bandwidth density , low power consumption for board connectivity and connectivity between data centres, access networks and metropolitan, core, regional and long-haul optical communications.Photonics is poised to play an increasingly important role in ICT ( Fig. 1a), since the fixed high capacity links are largely based on photonic technologies. Photonic devices need to support ultra-large bandwidth operation, for example, 200 Tb s−1 in a single fibre[9] and >10 Tb s −1 cm −2 in integrated Si photonics chips [10]. To achieve this, the key components of Si photonics, photodetectors and modulators, need very high performances in terms of speed (≥25 Gb s −1 ), footprint (<1 mm 2 ), insertion loss (<4 dB), manufacturability (>10 6 pieces per year) and power consumption (<1 pJ bit −1 ). To date, these requirements have not been fulfilled in one system [11]. Furthermore, in terms of production volumes, photonics is not yet comparable to microelectronics [12], even if the increase in demand for optical networks would, by 2021, lead to an average global Internet Protocol (IP) traffic of 3.3 ZB (zettabytes), corresponding to an average usage data rate of ~800 Tb s −1 (refs[13,14]). In the context of the IoT[7], other applications, including infrared (IR) sensors, biosensors, environmental sensors, metrology, quantum communications and machine vision, will require even larger production volumes [13,15].The telecom network can be divided into three segments: access, aggregation and core (Fig. 1a). The access network is the interface between subscribers and the immediate service provider. The aggregation network aggregates all the input data streams from tributary access networks, converging towards the higher-level core network. The aggregation network includes local and metropolitan networks, which then converge to regional networks. A local area network (LAN) interconnects computers within a limited area, such as a residence, school, laboratory, university or office building. A metropolitan area network (MAN) interconnects us...

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We present a micrometer scale, on-chip integrated, plasmonic enhanced graphene photodetector (GPD) for telecom wavelengths operating at zero dark current. The GPD is designed and optimized to directly generate a photovoltage and has an external responsivity∼12.2V/W with a 3dB bandwidth∼42GHz. We utilize Au split-gates with a∼100nm gap to electrostatically create a p-n-junction and simultaneously guide a surface plasmon polariton gap-mode. This increases light-graphene interaction and optical absorption and results in an increased electronic temperature and steeper temperature gradient across the GPD channel. This paves the way to compact, on-chip integrated, power-efficient graphene based photodetectors for receivers in tele and datacom modules.The ever-growing demand for global data traffic[1] is driving the development of next generation communication standards [2,3]. The increasing numbers of connected devices[4], the need for new functionalities, and the development of high-performance computing [5,6] require optical communication systems performing at higher speeds, with improved energy-efficiency, whilst maintaining scalability and cost-effective manufacturing. Si photonics[7-9] offers the prospect of dense (nanoscale) integration[10] relying on mature, low-cost (based on complementary metal-oxide-semiconductor (CMOS) fabrication processes) manufacturing [8,9], making it one of the key technologies for short-reach (<10km) optical interconnects[11] beyond currently employed lithium niobate[12] and indium phosphate[13]. A variety of functionalities have been developed and demonstrated in Si photonics for local optical interconnects[11]. Electro-optic modulators based on carrier-depletion (phase-modulation) in Si[14, 15] or the Franz-Keldysh effect[16] (amplitude-modulation) in strained Si-Ge[17, 18] encode information into optical signals at telecom wavelengths (λ =1.3-1.6µm). On the receiver side, Ge[19] or bonded III-V[20, 21] photodetectors (PD) are needed for optical-to-electrical signal conversion, since the telecom photon energies are not sufficient for direct (band-to-band) photodetection in Si[22].On-chip integrated Ge PDs [23][24][25][26][27] are standard components in Si photonics foundries [8,9,22]. Their external responsivities (in A/W), R I = I ph /P in , where I ph is the photocurrent and P in is the incident optical power, can exceed 1A/W [8,23] and their bandwidth can reach 60GHz [25][26][27]. Following the development of high temperature (> 600 • C) [19] heterogeneous integration of Ge-on-Si using epitaxial growth and cyclic thermal annealing [19,28,29], the concentration of defects and threading dislocations in Ge epilayers and at Si/Ge interfaces can be reduced [19], resulting in low (<10nA[9, 27]) dark current in waveguide integrated Ge p-i-n photodiodes [24,27]. However, Ge-on-Si integration is a complex process [19,22,29], as the lattice mismatch between Si and Ge [19], ion implantation [23,25], thermal budget (i.e. thermal energy transfer to the wafer) management [22], and the non-plan...

The power spectral density of an orthogonal frequency-division multiplexing (OFDM) signal after a saturated high-power amplifier (HPA) is analytically derived. The distortion of the HPA-processed OFDM signal is defined, and its power spectrum is computed. The spectra of the signal and of the distortion are used to get an accurate estimate of the bit-error rate of an OFDM transmission system and to derive compensation at the receiver, which leads to performance improvement

In this paper we report on an electro-refractive modulator based on single or double-layer graphene on top of silicon waveguides. The graphene layers are biased to the transparency condition in order to achieve phase modulation with negligible amplitude modulation. By means of a detailed study of both the electrical and optical properties of graphene and silicon, as well as through optimization of the geometrical parameters, we show that the proposed devices may theoretically outperform existing modulators both in terms of V(π)L and of insertion losses. The overall figures of merit of the proposed devices are as low as 8.5 and 2dB∙V for the single and double layer cases, respectively.

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We investigate the efficiency of transmission through photonic crystal Y junctions and show the importance of matching mode symmetries. Furthermore, we show that by adding tuning holes to the input waveguide it is possible to achieve almost perfect impedance matching, leading ideally to unitary transmission through the junction. The model system is based on a triangular photonic lattice of holes in dielectrics to reflect experimental reality.

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