Large optoelectronic chromatic dispersion in PN-type silicon photodiodes and photovoltaic cells

Optoelectronic chromatic dispersion (OED) is a significant source of effective chromatic dispersion in photodiodes. We present an experimental and theoretical study of OED in PN-type Si photodiodes and photovoltaic cells and report on a very large effective chromatic dispersion in these devices. As measured with the modulation phase-shift technique at a frequency of 4 kHz for these slow devices, the OED spectral sensitivity for a commercial Si photodiode is approx. 0.02 deg/nm in the 720–850 nm wavelength band and increases to 0.25 deg/nm at λ = 1µm. For a Si photovoltaic cell, the OED is approx. 0.09 deg/nm in this spectral region. These values translate into an effective chromatic dispersion parameter of approx. 10¹² ps/(nm × km) for these sub-millimeter device lengths, which is over eight orders of magnitude larger than high-dispersion materials such as chalcogenide glass. The enormous dispersion in these sub-millimeter sized silicon-based devices can be utilized for on-chip optoelectronic sensors such as wavelength monitoring and spectroscopy. The substantial OED of photovoltaic cells can be utilized for the characterization and optimization and new applications for optical sensing with these self-powered devices.