Quantum cascade laser on silicon

Abstract

The mid-infrared spectral region, 2-20 μm, is of great interest for sensing and detection applications, in part because the vibrational transition energies of numerous molecules fall in that region. Silicon photonics is a promising technology to address many of these applications on a single integrated, low-cost platform. Near-infrared light sources, heterogeneously integrated on silicon, have existed for more than a decade, and there have been numerous incorporations of mid-infrared optical devices on silicon platforms. However, no lasers fully integrated onto silicon have previously been demonstrated for wavelengths longer than 2.0 μm. Here we report, to the best of our knowledge, the first quantum cascade lasers on silicon emitting 4.8 μm light, integrated with silicon-on-nitride-on-insulator (SONOI) waveguides, and operating in pulsed mode at room temperature. The broadband and versatile nature of both quantum cascade lasers and the SONOI platform suggests that this development can be expanded to build photonic integrated circuits throughout the near-and mid-infrared on the same chip.

Mid-infrared integrated photonics on silicon: a perspective

“…Cascade lasers operating in the continuous wave (CW) mode at room temperature cover almost the entire mid-IR spectrum (3-20 μm) and are now available as commercial offthe-shelf (COTS) components. Heterogeneous integration of QCLs with Si photonics was first demonstrated by Spott et al [72] and emits at around 4.8-μm wavelength. The substrate was a silicon-on-nitride-on-insulator wafer fabricated by bonding an SOI wafer to a nitride-on-insulator (SONOI) wafer.…”

Heterogeneously Integrated Distributed Feedback Quantum Cascade Lasers on Silicon

“…The integrated laser structure, SONOI waveguide platform, and fabrication process are described in [17]. Figure 1a shows a three-dimensional (3D) illustration of the SONOI waveguide with an etched surface grating underlying the III-V layers and Figure 1b illustrates the DFB QCL, which consists of a hybrid Si/III-V active region coupled by III-V tapers to passive silicon waveguides on both sides.…”

“…Figure 2 shows active region cross-sections for the four designs labeled A-D. Designs A-C contain fully etched narrow III-V ridges as in [17], with mesa widths of 4 µm, 6 µm and 8 µm, respectively. Design D alternatively has a 6-µm-wide upper cladding combined with a 24-µm-wide active region.…”

“…As a first step toward this objective, we recently reported the first successful demonstration of QCLs on silicon [17]. These Fabry-Pérot lasers emitted at 4.8 µ m when operated in pulsed mode at room temperature, with peak output powers up to 31 mW when tapers were used to transfer light from the hybrid Si/III-V active gain region into passive silicon waveguides.…”

“…Both the QCLs from [17] and the devices discussed here were integrated on the silicon-on-nitride-on-insulator (SONOI) waveguide platform, which consists of silicon waveguides above a thin Si3N4 cladding, a thick SiO2 cladding, and a silicon substrate. This SONOI waveguide can support wavelengths from 1.2 µ m to 6.7 µ m. Additionally, by etching off the top silicon waveguide layer, nitride-on-insulator waveguides can be constructed for propagation at 350 nm to 3.5 µ m. Thus, by employing both of these options in different regions, a single silicon photonic chip can be constructed that supports all wavelengths from 350 nm to 6.7 µ m.…”