Optical phase and amplitude modulator and photonic integration for long wave infrared free space optical telecommunications.

Overview & Synopsis

Free-Space Optical (FSO) communications has become a field of growing interest over the past years in which optoelectronic devices operating in the Long ave Infrared (LWIR) wavelength range could be serious competitors to traditional telecom wavelengths for atmospheric links as they are less impacted by atmospheric perturbations. However, the deployment of LWIR FSO communications is limited by the availability of basic passive and active building blocks such as high-speed modulators and beam combiners among others. In this work, we present an external integrated modulator based on inter-subband Stark effect operating at λ= 9 µm. This effect is of particular interest for modulation due to its intrinsically fast response, high wavelength tunability under applied bias and low RF power consumption. We embedded asymmetrical coupled quantum wells within a deep ridge InGaAs on InP core waveguide in order to increase the optical interaction and reduce the geometrical capacitance. The result is a versatile modulator able to perform either amplitude or phase modulation by an appropriate choice of applied DC bias and RF modulation. In addition, we designed and fabricated passive waveguide beam combiners based on Multi Mode Interferometer (MMI) and quantum cascade detectors (QCD). We present their performance and in particular 2x2 3dB MMIs splitter as well as 2x4 90 degree Hybrid MMIs which are critical building blocks for integrated transceivers based on complex modulation format and are planned to be integrated with a QCD.