Low-loss silicon platform for broadband mid-infrared photonics

Abstract

Broadband mid-infrared (mid-IR) spectroscopy applications could greatly benefit from todays well-developed, highly scalable silicon photonics technology; however, this platform lacks broadband transparency due to its reliance on absorptive silicon dioxide cladding. Alternative cladding materials have been studied, but the challenge lies in decreasing losses while avoiding complex fabrication techniques. Here, in contrast to traditional assumptions, we show that silicon photonics can achieve low-loss propagation in the mid-IR from 3 6 µm wavelength, thus providing a highly scalable, well-developed technology in this spectral range. We engineer the waveguide cross section and optical mode interaction with the absorptive cladding oxide to reduce loss at mid-IR wavelengths. We fabricate a microring resonator and measure an intrinsic quality (Q) factor of 10 6 at wavelengths from 3.5 to 3.8 µm. This is the highest Q demonstrated on an integrated mid-IR platform to date. With this high-Q silicon microresonator, we also demonstrate a low optical parametric oscillation threshold of 5.2 mW, illustrating the utility of this platform for nonlinear chip-scale applications in the mid-IR. arXiv:1703.03517v1 [physics.optics]

Mid-infrared integrated photonics on silicon: a perspective

“…Despite the onset of optical absorption in SiO 2 , it is worth noting that low loss propagation can still be maintained in multi-mode or large-core ridge SOI waveguides at wavelengths above 3.5 μm, where strong modal confinement in the Si core leads to negligible absorption contribution from the cladding [8]. This is evident from Figure 2, which plots the simulated absorption losses in SOI waveguides with and without oxide top cladding and of two different core dimensions [9]. Modeling results show that SOI waveguides with a large Si core and no oxide top cladding can effectively mitigate such parasitic optical losses.…”

“…Silicon-on-insulator [5,8,[40][41][42][43] 4.3 0.2 (3.8 μm) [9] Silicon-on-insulator (multi-mode) [9] 6.7 Silicon-on-porous silicon [5] 6.7 3.9 (3.39 μm) [ [38] 4.3 20 (10.6 μm) [38] a…”

“…The simulated TM mode confinement factors in the gas phase and in the oxide pedestal are 10% (averaged over 3-3.8 μm) and 1.8% (at 3.8 μm), respectively, and the latter indicates a negligible loss ceiling of 0.1 dB/cm due to oxide absorption. We therefore assume an SOI waveguide loss of 0.2 dB/cm based on literature values [9] and a spiral length L = 21.7 cm according to Eq. (10).…”

Midinfrared Electro-optic Modulation in Few-Layer Black Phosphorus

“…It is highly desirable to realize mid-IR systems that are fully integrated, compact and portable for widespread applications. While mid-IR laser sources have become commercially available 33 and integrated photonic circuits have been developed on the ubiquitous silicon-on-insulator platform 31,34 , mid-IR photodetection still relies on narrowband compound semiconductors such as InAsSb and HgCdTe, which are difficult to be integrated with silicon. As an alternative, BP mid-IR photodetectors have already been demonstrated with promising performance 25,26 .…”

Quantum cascade lasers grown on silicon

“…MIR Si photonics could thus lead to integrated, compact, cost-effective, smart spectroscopy instruments 21,23 . Several groups have already demonstrated MIR platforms at different wavelengths using various Si-based technologies [24][25][26][27][28][29] . Frequency combs have been shown spanning near-to mid-infrared wavelengths on silicon [30][31][32] .…”