Silicon photonics has traditionally focused on near infrared wavelengths, with tremendous progress seen over the past decade. However, more recently, research has extended into mid infrared wavelengths of 2 μm and beyond. Optical modulators are a key component for silicon photonics interconnects at both the conventional communication wavelengths of 1.3 μm and 1.55 μm, and the emerging mid-infrared wavelengths. The mid-infrared wavelength range is particularly interesting for a number of applications, including sensing, healthcare and communications. The absorption band of conventional germanium photodetectors only extends to approximately 1.55 μm, so alternative methods of photodetection are required for the mid-infrared wavelengths. One possible CMOS compatible solution is a silicon defect detector. Here, we present our recent results in these areas. Modulation at the wavelength of 2 μm has been theoretically investigated, and photodetection above 25 Gb/s has been practically demonstrated.
We report on the developments of Ge/SiGe quantum well (QW) waveguide modulators operating at 1.3 μm. First we studied QW structures grown on a 13-μm SiGe buffer on bulk silicon. Light was directly coupled and propagated in the active region. Using a 3-μm wide and 50-μm long modulator, an extinction ratio larger than 4 dB was obtained for a drive voltage lower than 5 V in a 15 nm wavelength range. Then simulations were performed to evaluate the performances of an integrated modulator on silicon on insulator (SOI) platform. An eigenmode expension method was used to model the vertical optical coupling between SOI waveguide and Ge/SiGe devices. It is shown that a reduction of the thickness of the buffer leads to a significant improvement in the performances (extinction ratio, insertion loss) and footprint of the waveguide-integrated devices.
We report on the electro-refractive effect in Ge/SiGe multiple quantum wells grown by low energy plasma enhanced chemical vapor deposition (LEPECVD). The electro-refractive effect was experimentally characterized by the shift of Fabry-Perot fringes in the transmission spectra of a 64 μm long slab waveguide. A refractive index variation up to 1.3 × 10-3 was measured with an applied electric field of 88 kV/cm at 1475 nm, 50 meV below the excitonic resonance, with a VπLπ figure of merit of 0.46 V×cm. The device performances are promising for the realization of Mach Zehnder modulators in the Ge-Si material platform.
We report different experimental results showing the large potential of Ge/SiGe quantum well structures as a promising
solution forlow power consumption and large bandwidth optical modulators in silicon photonics technology. First, high
speed operation of such a Ge/SiGe multiple quantum well (MQW) electro-absorption modulator is reported, with 23
GHz bandwidth demonstrated from a 3 μm wide and 90 μm long Ge/SiGe MQW waveguide. Then the flexibility to shift
the absorption band edge from 1.42 to 1.3 μm is illustrated by strain engineering of the Ge wells. Finally electrorefraction by Quantum Confined Stark Effect (QCSE) is demonstrated, opening the route towards phase modulators
based on Ge/SiGe MQWs.
High speed Ge multiple quantum well (MQWs) electro-absorption (EA) modulator is reported. Device development
procedures from the epitaxial growth of high quality Ge MQWs by LEPECVD technique, fabrication, and
characterization of optoelectronic device are described.
Room temperature direct gap electroluminescence (EL) from a Ge/Si0.15Ge0.85 MQW waveguide was experimentally
studied. The dependence of the EL intensity on the injection current and temperature was measured. The direct gap EL
from Ge/SiGe MQWs was shown to be transverse-electric (TE) polarized, confirming that the EL originates from
recombination with a HH state.