Chirp management in silicon-graphene electro absorption modulators

Abstract

Abstract:We study the frequency chirp properties of graphene-on-silicon electro-absorption modulators (EAMs). By experimentally measuring the chirp of a 100 µm long single layer graphene EAM, we show that the optoelectronic properties of graphene induce a large positive linear chirp on the optical signal generated by the modulator, giving rise to a maximum shift of the instantaneous frequency up to 1.8 GHz. We exploit this peculiar feature for chromatic-dispersion compensation in fiber optic transmission thanks to the pulse temporal lensing effect. In particular, we show dispersion compensation in a 10Gb/s transmission experiment on standard single mode fiber with temporal focusing distance (0-dB optical-signal-to-noise ratio penalty) of 60 km, and also demonstrate 100 km transmission with a bit error rate largely lower than the conventional Reed-Solomon forward error correction threshold of 10 −3 .

Optical Pre-Emphasis by Cascaded Graphene Electro Absorption Modulators

“…However, as reported in Fig. 6, and similarly to what happens to the single graphene EAM [9], the time lens effect, given by the combination of the signal chirp and the fiber dispersion, compresses the optical bits giving a net eye opening and a correspondent sensitivity improvement. The improvement has its maximum at 40 km, where the sensitivity is 27 dB (a slight eye opening can be also appreciated comparing the eye diagrams at 10 and 40 km reported in the right part of Fig.6).…”

“…As recently reported in [9], the 100 μm graphene EAM has a 5 GHz 3-dB electrooptic bandwidth, a modulation efficiency of 1dB/V, a maximum attainable extinction ratio of 4.5 dB. In addition, itshows an opposite optical transmissivity and refractive index change dependence with respect to the applied voltage.…”

“…The comparison is made using a 100 μm long single EAM, like the one reported in [9], and the 100 μm plus the 50 μm long modulator driven like reported in Fig. 3, i.e., with the same sequence with opposite sign, after attenuation and proper delay.…”

“…The fabricated device is made by cascading two single layer Graphene (SLG) on Si waveguide EAMs similar to the one recently reported in [7], [9]. As shown in Fig.…”

“…Graphene electro absorption modulators (EAMs), in particular, have been reported working at 10 Gb/s [7], and very recently, at 20 Gb/s [8], using a single layer configuration, being mainly bandwidth limited by the graphene-metal electrical contact resistance value. Additionally, graphene EAMs show significant positive linear chirp associated to the Fermi level electrical gating responsible for the absorption changes [9]. The presence of chirp with the right sign on the modulated signals makes possible chromatic dispersion compensation while transmitting on standard single mode fibers (SMFs).…”