Abstract-Passively mode-locked interband cascade optical frequency combs

Mahmood Bagheri, Clifford Frez, Lukasz A. Sterczewski, Ivan Gruidin, Mathieu Fradet, Igor Vurgaftman, Chadwick L. Canedy, William W. Bewley, Charles D. Merritt, Chul Soo Kim, Mijin Kim,  Jerry R. Meyer

https://www.nature.com/articles/s41598-018-21504-9

Since their inception, optical frequency combs have transformed a broad range of technical and scientific disciplines, spanning time keeping to navigation. Recently, dual comb spectroscopy has emerged as an attractive alternative to traditional Fourier transform spectroscopy, since it offers higher measurement sensitivity in a fraction of the time. Midwave infrared (mid-IR) frequency combs are especially promising as an effective means for probing the strong fundamental absorption lines of numerous chemical and biological agents. Mid-IR combs have been realized via frequency down-conversion of a near-IR comb, by optical pumping of a micro-resonator, and beyond 7 μm by four-wave mixing in a quantum cascade laser. In this work, we demonstrate an electrically-driven frequency comb source that spans more than 1 THz of bandwidth centered near 3.6 μm. This is achieved by passively mode-locking an interband cascade laser (ICL) with gain and saturable absorber sections monolithically integrated on the same chip. The new source will significantly enhance the capabilities of mid-IR multi-heterodyne frequency comb spectroscopy systems.

Abstract-Atomic-scale photonic hybrids for mid-infrared and terahertz nanophotonics

• Joshua D. Caldwell,
• Igor Vurgaftman,
• Joseph G. Tischler,
• Orest J. Glembocki,
• Jeffrey C. Owrutsky
• & Thomas L. Reinecke
• 
  • a,b, Illustration of XHs using van der Waals (a) and covalently (b) bonded materials. Phonon polariton layers are highlighted by the ions of a polar crystal attached by 'springs' (bonds).

http://www.nature.com/nnano/journal/v11/n1/fig_tab/nnano.2015.305_F5.html

The field of nanophotonics focuses on the ability to confine light to nanoscale dimensions, typically much smaller than the wavelength of light. The goal is to develop light-based technologies that are impossible with traditional optics. Subdiffractional confinement can be achieved using either surface plasmon polaritons (SPPs) or surface phonon polaritons (SPhPs). SPPs can provide a gate-tunable, broad-bandwidth response, but suffer from high optical losses; whereas SPhPs offer a relatively low-loss, crystal-dependent optical response, but only over a narrow spectral range, with limited opportunities for active tunability. Here, motivated by the recent results from monolayer graphene and multilayer hexagonal boron nitride heterostructures, we discuss the potential of electromagnetic hybrids — materials incorporating mixtures of SPPs and SPhPs — for overcoming the limitations of the individual polaritons. Furthermore, we also propose a new type of atomic-scale hybrid the crystalline hybrid — where mixtures of two or more atomic-scale (~3 nm or less) polar dielectric materials lead to the creation of a new material resulting from hybridized optic phonon behaviour of the constituents, potentially allowing direct control over the dielectric function. These atomic-scale hybrids expand the toolkit of materials for mid-infrared to terahertz nanophotonics and could enable the creation of novel actively tunable, yet low-loss optics at the nanoscale.