We demonstrate a high-contrast electro-optic modulation of a photonic crystal nanocavity integrated with an electrically gated monolayer graphene. A high quality (Q) factor air-slot nanocavity design is employed for high overlap between the optical field and graphene sheet. Tuning of graphene's Fermi level up to 0.8 eV enables efficient control of its complex dielectric constant, which allows modulation of the cavity reflection in excess of 10 dB for a swing voltage of only 1.5 V. We also observe a controllable resonance wavelength shift close to 2 nm around a wavelength of 1570 nm and a Q factor modulation in excess of three. These observations allow cavity-enhanced measurements of the graphene complex dielectric constant under different chemical potentials, in agreement with a theoretical model of the graphene dielectric constant under gating. This graphene-based nanocavity modulation demonstrates the feasibility of high-contrast, low-power frequency-selective electro-optic nanocavity modulators in graphene-integrated silicon photonic chips.Graphene has intriguing optical properties and enables a range of promising optoelectronic devices [1][2][3][4][5][6][7][8][9]. To enhance the inherently weak light-matter interaction in this single atomic layer material, grahene has been coupled to optical waveguides and cavities [6,[10][11][12][13]. In the limit of wavelength-scale confinement, we recently demonstrated a dramatic enhancement of the light-matter interaction for graphene coupled to a planar photonic crystal (PPC) nanocavity, which reduced the cavity reflection by more than 20 dB [14]. Here, we employ this system to demonstrate a high contrast electro-optical modulation of the cavity reflection, in excess of 10 dB. The modulation is achieved by electrical gating of the graphene monolayer using an electrolyte, which, while slow, shows the fundamental capability arXiv:1211.0458v1 [physics.optics]

Nanoscale and power-efficient electro-optic (EO) modulators are essential components for optical interconnects that are beginning to replace electrical wiring for intra-and inter-chip communications [1][2][3][4]. Silicon-based EO modulators show sufficient figures of merits regarding device footprint, speed, power consumption and modulation depth [5][6][7][8][9][10][11]. However, the weak electrooptic effect of silicon still sets a technical bottleneck for these devices, motivating the development of modulators based on new materials. Graphene, a two-dimensional carbon allotrope, has emerged as an alternative active material for optoelectronic applications owing to its exceptional optical and electronic properties [12][13][14]. Here, we demonstrate a high-speed graphene electro-optic modulator based on a graphene-boron nitride (BN) heterostructure integrated with a silicon photonic crystal nanocavity. Strongly enhanced light-matter interaction of graphene in a submicron cavity enables efficient electrical tuning of the cavity reflection. We observe a modulation depth of 3.2 dB and a cut-off frequency of 1.2 GHz.

We demonstrate the controlled enhancement of photoresponsivity in a graphene photodetector by coupling to slow light modes in a long photonic crystal linear defect cavity. Near the Brillouin zone (BZ) boundary, spectral coupling of multiple cavity modes results in broad-band photocurrent enhancement from 1530 nm to 1540 nm.Away from the BZ boundary, individual cavity resonances enhance the photocurrent eight-fold in narrow resonant peaks. Optimization of the photocurrent via critical coupling of the incident field with the graphene-cavity system is discussed. The enhanced photocurrent demonstrates the feasibility of a wavelength-scale graphene photodetector for efficient photodetection with high spectral selectivity and broadband response. a) These authors contribute equally to this work 1 arXiv:1311.2080v1 [cond-mat.mes-hall] 8 Nov 2013The unique properties of graphene have generated strong interest in developing optoelectronics devices based on the material 1,2 . Examples include graphene-based high speed electro-optical modulators 3,4 , photodetectors 5,6 , saturable absorbers 7,8 , and nonlinear media for four-wave mixing 9-11 . Intrinsic graphene exhibits absorption of 2.3% 12 in the infrared to visible spectra range. While this absorption coefficient is remarkably high for a single atomic layer, for practical applications, a larger absorption coefficient is needed. To increase the light-matter interactions in graphene, approaches to date have included the integration of graphene with optical micro-cavities 13-17 , plasmonic nanostructures 18-22 and silicon photonic waveguides 3,4,23,24 .In this paper, we demonstrate a graphene photodetector integrated in a linear defect cavity defined in a planar photonic crystal (PPC). A single graphene layer strongly couples to the cavity evanescent field, increasing the light-matter interaction in graphene 25 for photocurrent generation. Coupled mode theory predicts maximal absorption into the graphene absorber when the intrinsic cavity loss rate, κ c , equals the loss rate into the graphene sheet, κ cg 25 .Upon optimization of the cavity design, we obtain nearly critical coupling with κ cg /κ c ≈ 1.3 and observe an eight-fold enhancement of photocurrent in the graphene photo-detector. The observed reflectivity and photocurrent spectra in the graphene detector agree well with the coupled graphene-cavity model. Spatial mapping of the photocurrent allows us to compare the response of the graphene detector with and without optical enhancement via the PPC cavity.The PPC cavity-integrated graphene photodetector is illustrated in Fig. 1(a). An airsuspended PPC cavity was fabricated on a silicon-on-insulator wafer with a 260 nm thick silicon (Si) membrane, using a combination of electron beam lithography (EBL) and dry/wet etching steps. The PPC has a lattice spacing of a = 450 nm and hole radius of 0.29a. A linear defect in the center of the PPC lattice forms a long cavity ( Fig. 1(b)), producing bounded cavity modes. A layer of 20 nm hafnium oxide (HfO 2 ), deposited by atomic...

Push–pull polymeric electro-optic Mach–Zehnder (MZ) modulators with Vπ of 1.2 and 1.8 V at 1310 and 1550 nm, respectively, with an interaction length of 2 cm are demonstrated. These devices were made from second-order nonlinear optic guest–host polymers that consisted of a phenyltetraene bridged high μβ chromophore guest and an amorphous polycarbonate host. Poling was done in N2 atmosphere to avoid chromophore bleaching by oxidation. A MZ-like two-arm microstrip line was used as the driving electrode in these devices. The optical response dropped 3 dB electrical from 2 to 20 GHz. These 3 cm long devices have 5 dB total chip loss at both wavelengths and good thermal stability.