We present a novel InGaAs/InAlAs/InP quantum cascade detector (QCD) operating in the long wave infrared (LWIR) range, crucial for the exploitation of new free-space optical telecommunication channels at wavelengths between 8-12 µm. The comparison of differently sized detector ridges, processed on substrates with a 15-period as well as a single-period design, allows a characterization of the spectral photocurrent and a comparison of their performance in terms of sensitivity, spectral responsivity, detector noise etc. The goal is to distinguish design guidelines for the best candidate to establish a monolithic-integrated heterodyne detection system, able to secure high-speed and low-noise free-space data transmission.
Silicon photonics technology has demonstrated, over the years, Photonic Integrated Circuits (PICs) relying on Si or Si3N4 materials that feature advanced functionalities for a wide area of applications. However, the fabrication of such PICs is usually compatible only with Front-End-of-Line (FEOL) processes that render very difficult post processing of the involved chips towards providing efficient interfaces with optical sources. This is a major problem for the next generation photonic circuits that are expected to co-integrate III-V laser sources on the Si substrate in a monolithic way, as the coupling interface between the active and the passive part of the PIC should be developed after the epitaxy and the fabrication of the lasers. In this work, we report on the development of a novel Silicon Rich Nitride (SRN) material with low stress and high refractive index (n<3.16), close to that of InP and InGaAsP which are commonly utilized for the laser sources. The SRN has been characterized with spectroscopic ellipsometry and Fourier-Transform Infrared Spectroscopy for estimation of complex refractive index and hydrogen content in the film. Based on this material, a trilayer stack has been developed for the formation of waveguides compatible with the Back-End-of-Line (BEOL) processes, while propagation losses have been extracted through cut-back measurements. These experimental results were then inserted as input parameters in 2D- and 3D-FDTD simulations for the design of efficient interfaces between III-V lasers and Si3N4 waveguides providing coupling efficiencies that can reach 83.81% and back-reflections of 0.032%.
Free space optical (FSO) communications are a potential application envisioned for Quantum Cascade Lasers technology. In this paper, we sketch out the main market scenarii for FSO communications, where data channels should reach up to Tbit/s over distances that range from 0.1 to 36000 km. We analyze where QCLs can be relevant, and what standards they must meet to be relevant at the industrial level. The following topics are discussed: competing technologies, atmospheric transmission physics, signal processing and multiplexing. We try and translate the constraints of the system-level into challenges for device-level research and development.
Noise in quantum cascade detectors is studied experimentally and theoretically. Measurements were performed in dark
conditions on a quantum cascade detector operating at 14.5 μm, in the very long wave infrared range. To investigate the
signal-to-noise contributions of each intersubband transition involved in the transport, a model of noise has been
developed. It is based on a noise equivalent electrical circuit of the quantum cascade detector. Non-radiative diagonal
transitions (fundamental state to levels of the cascade structure) are identified as dominant contributions to the dark
current and noise in the measured device. Based on these theoretical considerations, new optimized structures for the
very long wave-infrared range are designed and exhibit a noise reduction down to a factor three at optimum responsivity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.