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.

Heterogeneous integration enables the construction of silicon (Si) photonic systems, which are fully integrated with a range of passive and active elements including lasers and detectors. Numerous advancements in recent years have shown that heterogeneous Si platforms can be extended beyond near-infrared telecommunication wavelengths to the mid-infrared (MIR) (2-20 μm) regime. These wavelengths hold potential for an extensive range of sensing applications and the necessary components for fully integrated heterogeneous MIR Si photonic technologies have now been demonstrated. However, due to the broad wavelength range and the diverse assortment of MIR technologies, the optimal platform for each specific application is unclear. Here, we overview Si photonic waveguide platforms and lasers at the MIR, including quantum cascade lasers on Si. We also discuss progress toward building an integrated multispectral source, which can be constructed by wavelength beam combining the outputs from multiple lasers with arrayed waveguide gratings and duplexing adiabatic couplers.

Here we demonstrate an 8x4 multi-wavelength selective ring resonator based crossbar switch matrix implemented in a 220-nm silicon photonics foundry for interconnecting electronic packet switches in scalable data centers. This switch design can dynamically assign up to two wavelength channels for any port-port connection, providing almost full connectivity with significant reduction in latency, cost and complexity. The switch unit cell insertion loss was measured at 0.8 dB, with an out-of-band rejection of 32 dB at 400 GHz channel separation. All the ring resonator heaters were thermally tuned, with heaters controlled by a custom 64-channel DAC driver. Detailed measurements on the whole switch showed standard deviation of 2 dB in losses across different paths, standard deviation of 0.33 nm in resonant wavelength and standard deviation of 0.01 nm/mW in ring heater tuning efficiency. Data transmission experiments at 40 Gbps showed negligible penalty due to crosstalk paths through the switch.

Mid-infrared (MIR) silicon photonic systems show great promise for miniaturizing a variety of sensing and detection technologies. Rapid progress has been made in recent years, and numerous passive and active MIR devices have now been constructed on various silicon-based platforms. We previously reported the heterogeneous integration on silicon of Fabry–Perot and distributed feedback quantum cascade lasers (QCLs) operating at 4.8 μm. Interband cascade lasers (ICLs) will be preferred for many on-chip sensing technologies because they operate in the 3–6 μm range with threshold drive powers 1–2 orders of magnitude lower than QCLs. In this work, we demonstrate the integration of ICLs on a silicon substrate. These lasers emit 3.6 μm light into silicon-on-insulator waveguides in pulsed mode at temperatures up to 50°C. This represents an important step toward MIR photonic integrated circuits on silicon that operate with much lower drive power and therefore an even smaller footprint.

Here we experimentally demonstrate room temperature, continuous-wave (CW), 2.0 μm wavelength lasers heterogeneously integrated on silicon. Molecular wafer bonding of InP to Si is employed. These hybrid silicon lasers operate CW up to 35°C and emit up to 4.2 mW of single-facet CW power at room temperature. III–V tapers transfer light from a hybrid III–V/silicon optical mode into a Si waveguide mode. These lasers enable the realization of a number of sensing and detection applications in compact silicon photonic systems.

Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Pérot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for mid-infrared (MIR) silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon has been reported to date. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-on-insulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning.