The optoelectronic properties of graphene attracted a lot of interest in recent years. Several demonstrations of integrated graphene based modulators, switches, detectors and non-linear devices have been reported. We present here a comprehensive study investigating the different design trade-offs involved in realizing in particular graphene based modulators and switches. We compare 4 representative hybrid graphenewaveguide configurations, focusing on optimizing their dimensions, the gate-oxide thickness, the polarization, the operating wavelength and contact definition. We study both static and dynamic behavior, defining a relevant figure of merit. We find that a 20 m device based on silicon waveguides should allow for 25 GBit/s modulation rate and an extinction ratio of 5 dB. A 200 m long SiN-device on the other hand should allow for 23dB extinction ratio and switching speeds down to 0.4 ns.

In this letter, we demonstrate a compact optical switch realized by integrating a graphene layer with a silicon photonic crystal cavity fabricated using deep UV immersion lithography and a novel transfer printing approach. A 17-dB extinction ratio and 0.75-nm shift in the cavity resonance are measured for a swing voltage of only 1.2 V. The graphene layer is limited to 1 × 5 µm in size. The experimental results are linked to a theoretical model and used to predict possible improvements to the design.

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100-Gb/s single-channel optical data communication transceivers can provide a compact and cost-effective solution for the exponentially growing data-center traffic. One of the enabling technologies is electro-absorption-modulated single-mode lasers which are very compact, efficient, and fast. In this letter, such a transmitter integrated on a silicon photonics platform is demonstrated. While low loss and high contrast waveguides are provided by Si photonics, the gain and efficient electroabsorption are provided by the InP-based multi-quantum-well structure. A lumped electro-absorption modulator integrated with a distributed feedback laser is designed and fabricated in this platform. The epitaxial stack is identical for the laser and the modulator, which eases the fabrication process considerably. In this way, we successfully demonstrate 100-Gb/s single-channel electrical duobinary optical data transport over˜100 m of fiber with a bit error rate of 1.6e-3.

We present an InP-on-Si DFB laser integrated with electro-absorption modulators on each side, using a single epitaxial structure for laser and modulators. Two electrically isolated tapers couple the light to the Si waveguide, while simultaneously acting as modulators.

Externally modulated lasers have proven to be key components for optical communication because of their compactness, low-power consumption, and speed. In this paper, we present unique heterogeneously integrated InP-on-Si electro-absorptionmodulated DFB lasers, which were used to implement two optical modulation schemes. The first scheme uses a double-sided externally modulated DFB laser. Two taper sections on each side of the single DFB laser are fabricated with an identical epitaxial structure as the laser and perform two roles: coupling the light to the underlying Si waveguide and acting as modulators. These taper sections are electrically isolated from the DFB laser cavity. Each section can independently be driven with a 56-Gb/s nonreturn-to-zero (NRZ) on-off-keying signal resulting in 112-Gb/s aggregate data transmission from the device over 2-km non-zero dispersion-shifted single-mode fiber. The second scheme is an original method to generate an optical pulse amplitude modulation (PAM) signal using a similar device structure. By simultaneously directly modulating the DFB laser and one of the tapers (operating as an electro-absorption modulator) with two independent NRZ signals, we demonstrate the generation of a PAM-4 signal. In this way, the PAM-4 signal generation can be shifted from the electrical to the optical domain in a rather simple and power efficient way. We demonstrate the transmission of 25-Gbaud PAM-4 over 2-km non-zero dispersion-shifted single-mode fiber.

We demonstrate a new printing method for transferring micron-size graphene films to desired sites on a target substrate. After patterning the graphene layer, a photoresist mask is used to realize a suspended graphene-resist stack. This stack is then transferred toward the desired site on the target substrate using a patterned polydimethylsiloxane (PDMS) stamp in a transfer printing tool. The Raman spectra of the transferred graphene films confirm that no defects are introduced in the process. Si 3 N 4 waveguides with graphene transferred on top exhibit the expected absorption of 0.054 dB/μm. The sheet resistance and contact resistance of graphene transferred on pre-patterned palladium contacts are 398 /sq and 2990 .μm, respectively, comparable to measurements on the original source wafer. These results prove our method enables simple and cost-effective integration of graphene on a semiconductor target wafer, which may expand the application range of graphene for photonics and electronics. In recent years, an enormous amount of effort has been devoted to the development of high quality graphene growth, mainly on metal substrates 1-3 but also on dielectric substrates. [4][5][6][7] Integrated photonic devices on the other hand are often fabricated by patterning silicon, III-V semiconductors or silicon nitride layers, not compatible with direct graphene growth. Therefore there is a need for transferring graphene or other 2D materials from its original growth substrate to another substrate. [8][9][10][11] Thus far, in most cases large size CVD-grown graphene films or individual flakes of exfoliated material are thereby transferred. [12][13][14][15][16][17][18][19] Such an approach might have considerable drawbacks however. It leads to an inefficient use of the graphene film, especially on large scale photonic integrated circuits, requiring only graphene in a small area of the entire circuit. In some cases, e.g. on preprocessed substrates with large topography, it might even be impossible to transfer full films of 2D-materials. Therefore it is essential to develop a method to transfer small patches of graphene to dedicated locations on a target wafer. Though many such techniques have been proposed, 20-22 a scalable approach allowing transfer of graphene patches at a given set of locations on a target wafer substrate has not yet been demonstrated. To date, the methods employed for the transfer of micron-size graphene layers rely on manual processes derived from the conventional wet transfer, 20-22 using home-built tools, and are strongly dependent on the handling skills of the operator. In most cases they are difficult to upscale to full wafer processing.In this paper, we present a new method that allows transfer of micron-size graphene toward any desired site on a target substrate, relying on a commercially available tool used also in the solar, display and electronics industry 23-25 and more recently also for the transfer of III-V semiconductors on silicon waveguide circuits. 26 We demonstrate the transfer of pattern...

Synthetic aperture radar is a remote sensing technology finding applications in a wide range of fields, especially related to Earth observation. It enables a fine imaging that is crucial in critical activities, like environmental monitoring for natural resource management or disasters prevention. In this picture, the scan-on-receive paradigm allows for enhanced imaging capabilities thanks to wide swath observations at finer azimuthal resolution achieved by beamforming of multiple simultaneous antenna beams. Recently, solutions based on microwave photonics techniques demonstrated the possibility of an efficient implementation of beamforming, overcoming some limitations posed by purely electronic solutions, offering unprecedented flexibility and precision to RF systems. Moreover, photonics-assisted RF beamformers can nowadays be realized as integrated circuits, with reduced size and power consumption with respect to digital beamforming approaches. This paper presents the design analysis and the challenges of the development of a hybrid photonicintegrated circuit as the core element of an X-band scanon-receive spaceborne synthetic aperture radar. The proposed photonic-integrated circuit synthetizes three simultaneous scanning beams on the received signal, and performs the frequency down-conversion, guaranteeing a compact 15 cm 2 -form factor, less than 6 W power consumption, and 55 dB of dynamic range. The whole photonics-assisted system is designed for space compliance and meets the target application requirements, representing a step forward toward a deeper penetration of photonics in microwave applications for challenging scenarios, like the observation of the Earth from space.