Abstract
Experimental demonstrations of silicon-on-insulator waveguide-based free-carrier effect modulators operating at 3.8μm are presented. PIN diodes are used to inject carriers into the waveguides, and are configured to (a) use free-carrier electroabsorption to create a variable optical attenuator with 34dB modulation depth and (b) use free-carrier electrorefraction with the PIN diodes acting as phase shifters in a Mach-Zehnder interferometer, achieving a VπLπ of 0.052 V·mm and a DC modulation depth of 22dB. Modulation is demonstrated at data rates up to 125Mbit/s.
Highlights
There has been rapid progress in the development of a library of silicon-on-insulator (SOI) waveguide-based building blocks for photonic integrated circuits (PICs) that can operate in the mid-infrared, since the mid-IR portion of the electromagnetic spectrum is of great interest for a variety of practical applications [1]
Because of the wide use of SOI for near-infrared (NIR) silicon photonics, SOI should still be considered to be the first choice when building PICs that are required to operate at wavelengths at which it is transparent
The first modulator operates as a variable optical attenuator (VOA) in which carriers injected into the waveguide core absorb the propagating light
Summary
Design and simulation: Two types of free-carrier modulators were designed, both exploiting free-carrier injection into waveguides using a PIN diode. The second modulator was an asymmetric Mach–Zehnder interferometer (MZI) with PIN diodes placed in each arm, in which carriers are injected into the waveguide in one of the MZI arms in order to change the refractive index of the Si in the waveguide core, creating a phase shift in the waveguide arm.
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