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INsPIRE Report Summary

Project ID: 639107
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - INsPIRE (Chip-scale INtegrated Photonics for the mid-Infra REd)

Reporting period: 2015-04-01 to 2016-09-30

Summary of the context and overall objectives of the project

Mid-infrared (mid-IR) spectroscopy is a nearly universal way to identify chemical and biological substances, as most of the molecules have their vibrational and rotational resonances in the mid-IR wavelength range. Commercially available mid-IR systems are based on bulky and expensive equipment, while lots of efforts are now devoted to the reduction of their size down to chip-scale dimensions. The demonstration of mid-IR photonic circuits on silicon chips will benefit from reliable and high-volume fabrication to offer high performance, low cost, compact, low weight and power consumption photonic circuits, which is particularly interesting for mid-IR spectroscopic sensing systems that need to be portable and low cost. In this context, the INsPIRE project will address a new route towards key advances in the development of chip-scale integrated circuits on silicon for the mid-IR wavelength range. The original idea is to use nonlinear optical properties in Ge/SiGe quantum well (QW) active devices combined with Ge-rich-SiGe waveguides. The objectives of the project are far beyond the state of the art, by targeting the monolithic integration of passive and active devices for operation in the 3 to 15 µm wavelength range. As a main cornerstone we will demonstrate an optical photonic circuit based on Ge/SiGe QWs relying on a mid-IR light emitter combined with a mid-IR spectrometer and a detector array. The integration will be performed using Ge-rich-SiGe waveguides allowing the extension of the wavelength range up to 15 µm. Such demonstration, which will constitute a breakthrough for establishing chip-scale circuits for the mid-IR photonics, requires a deep knowledge and understanding of Ge/SiGe optical properties. In particular, second- and third-order nonlinear optical properties of Ge/SiGe QW structures will be investigated in a wide spectral range from 3 to 15 µm.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first objective of the project was to characterize the loss of Ge-rich SiGe alloys in the mid-IR, as only few data have been reported in the literature regarding the loss of these materials in this wavelength range. As a main achievement we demonstrated low-loss Ge-rich SiGe (with 80% of germanium) waveguides on graded SiGe substrates operating in the mid-infrared wavelength range. Propagation losses as low as (1.5 ± 0.5) dB/cm and (2 ± 0.5) dB/cm were measured at λ = 4.6 µm for the quasi-TE and quasi–TM polarizations, respectively. As a second objective, we explored SiGe waveguides as active building blocks to develop integrated nonlinear optical devices with broadband operation in the mid-IR. A tight mode confinement as well as a flat anomalous dispersion is required to optimize the performances of active devices based on nonlinear optical effects. A new graded SiGe waveguide design has been proposed for this purpose. It was theoretically demonstrated that the vertical Ge gradient concentration in the waveguide core renders unique properties to the guiding optical mode, providing optimum mid-IR tight mode confinement over a broad wavelength range. In addition these new waveguides provide efficient tailoring of the chromatic dispersion curves in the mid-IR, achieving broadband flat anomalous dispersion for the quasi-TM optical mode with γmax = 14 ps/nm/km over ~ 1.4 octave spanning (λ ~ 3 - 8 µm). This result confirm the potential of graded SiGe waveguides with high top Ge concentration as an alternative platform to current mid-IR nonlinear approaches requiring broadband waveguide dispersion engineering strategies.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Mid-IR spectroscopy is a nearly universal way to identify chemical and biological substances. In the so-called “fingerprint” region, most molecules have their vibrational and rotational resonances. Mid-IR spectroscopy thus provides powerful informations for performing non-intrusive diagnostics of composite systems. The mid-IR region also contains two important windows (3-5µm and 8-13 µm) in which the atmosphere is relatively transparent. These wavelength ranges can be exploited to detect small traces of environmental and toxic vapours in a variety of applications including defense, security and industrial solutions. In this context the INsPIRE project will make key advances beyond the state of the art for operation from 3 to 15 µm wavelength. Specifically the integration of the mid-IR systems on silicon chips will benefit from high-volume and low-cost fabrication in microelectronic. High performance, low cost, small size, low weight and low power consumption systems are thus expected. In the first period of the project a new and unique mid-IR set-up was created to characterize photonic integrated circuits (PIC) in this wavelength range. The results that have been obtained in the first period already confirm the strong potential of the Ge-rich-SiGe platform for high performance mid-IR photonic integrated circuits.
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