Abstract
We demonstrate vertical-incidence electroabsorption modulators for free-space optical interconnects. The devices operate via the quantum-confined Stark effect in Ge/SiGe quantum wells grown on silicon substrates by reduced pressure chemical vapor deposition. The strong electroabsorption contrast enables use of a moderate-Q asymmetric Fabry-Perot resonant cavity, formed using a film transfer process, which allows for operation over a wide optical bandwidth without thermal tuning. Extinction ratios of 3.4 dB and 2.5 dB are obtained for 3 V and 1.5 V drive swings, respectively, with insertion loss less than 4.5 dB. For 60 ?m diameter devices, large signal modulation is demonstrated at 2 Gbps, and a 3 dB modulation bandwidth of 3.5 GHz is observed. These devices show promise for high-speed, low-energy operation given further miniaturization.
Highlights
The substantial communication bandwidth required for short-distance interconnects in nextgeneration high-performance computing systems and large-scale data centers may soon exceed the capabilities of conventional electrical links, due to pin density constraints, power consumption, and signal integrity issues at high bit rates
In addition to promising work on waveguide modulators based on the FranzKeldysh effect in bulk SiGe [3, 4], there has been additional interest in utilizing the stronger electroabsorption contrast afforded by the quantum-confined Stark effect (QCSE) in Ge quantum well (QW) structures
The asymmetric Fabry-Perot modulator, whose basic structure is shown in Fig. 2(a), consists of two mirrors surrounding a QW region, in which the absorption can be altered by application of an electric field
Summary
The substantial communication bandwidth required for short-distance interconnects in nextgeneration high-performance computing systems and large-scale data centers may soon exceed the capabilities of conventional electrical links, due to pin density constraints, power consumption, and signal integrity issues at high bit rates. Progress in the growth [5, 6] and modeling [7,8,9] of Ge QWs on Si substrates has enabled the fabrication of QCSE modulators using this CMOS-compatible material system [10,11,12,13,14] Many of these recently demonstrated modulators are waveguide-integrated devices. Asymmetric Fabry-Perot modulators exhibit low insertion loss, polarization independence, and larger alignment tolerance compared to waveguide devices They are suitable for dense 2-D array integration, which could enable spatially multiplexed free-space optical links with thousands of channels. We obtain open eye diagrams at 2 Gbps and a 3 dB modulation bandwidth of 3.5 GHz on 60 μm diameter modulators, suggesting that smaller devices will be capable of low-power, high-speed operation at tens of gigahertz
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