Mid-infrared, long-wave infrared, and terahertz photonics: introduction.

This feature issue presents recent progress in long-wavelength photonics, focusing on wavelengths that span the mid-infrared (3-50 µm), the long-wavelength infrared (30-60 µm), and the terahertz (60-300 µm) portions of the electromagnetic spectrum. The papers in this feature issue report recent progress in the generation, manipulation, detection, and use of light across this long-wave region of the "photonics spectrum," including novel sources and cutting edge advances in detectors, long-wavelength non-linear processes, optical metamaterials and metasurfaces, and molecular spectroscopy. The range of topics covered in this feature issue provide an excellent insight into the expanding interest in long-wavelength photonics, which could open new possibilities for basic research and applications in industries that span health, environmental, and security.

Demonstration of a cw room temperature mid-IR microlaser.

We report a demonstration of the first continuous-wave (cw) mid-IR microlaser operating at room temperature (RT). Our whispering-gallery-mode microlaser-operating at 2.71 µm-is based on a heavily erbium-doped high-Q ZBLAN microsphere optically pumped by a 980 nm diode laser; with a threshold pump power of <150 µW.

Thermo-optomechanical oscillations in high-Q ZBLAN microspheres.

We report stable thermo-optomechanical oscillations in high-Q-spherical ZBLAN microcavities. The oscillations are manifested as a complex combination of fast and slow oscillation periods. This behavior appears to be a consequence of the interplay between the negative thermo-optic effect, thermal expansion, and the Kerr effect. We have characterized the oscillatory behavior and measured the corresponding frequencies as a function of input power, wavelength detuning, and loaded optical quality factor. Our analysis shows that, as a gas sensor in the mid-IR spectral region, this thermo-optomechanical oscillator is two orders of magnitude more sensitive than previously demonstrated hybrid microtoroidal oscillators operating in the near-IR spectral region.

High-Q microresonators for mid-IR light sources and molecular sensors.

We propose and demonstrate a simple and reliable method for fabricating high-quality whispering-gallery mode (WGM) optical microresonators in "mid-IR relevant" low-loss ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) glasses. Intrinsic quality factors of 10(7) have been demonstrated, providing great promise for WGM-based mid-IR (MIR) devices. Absorption-limited Q-factors of over 3×10(8) are anticipated over the 2.0 to 3.2 µm MIR wavelength range in ZBLAN microcavities in the foreseeable future.

Detailed analysis of evolution of the state of polarization in all-fiber polarization transformers.

We present a detailed analysis of key attributes and performance characteristics of controllably-spun birefringent-fiber-based all-fiber waveplates or "all fiber polarization transformers" (AFPTs), first proposed and demonstrated by Huang [11]; these AFPTs consist essentially of a long carefully-designed "spin-twisted" high-birefringence fiber, fabricated by slowly varying the spin rate of a birefringent fiber preform (either from very fast to very slow or vice versa) while the fiber is being drawn. The evolution of the eigenstate from a linear polarization state to a circular polarization state, induced by slow variation of the intrinsic structure from linear anisotropy at the unspun end to circular anisotropy at the fast-spun end, enables the AFPT to behave like an all-fiber quarter-wave plate independent of the wavelength of operation. Power coupling between local eigenstates causes unique evolution of the polarization state along the fiber, and has been studied to gain insight into - as well as to understand detailed characteristics of -- the polarization transformation behavior. This has been graphically illustrated via plots of the relative power in these local eigenstates as a function of distance along the length of the fiber and plots of the extinction ratio of the output state of polarization (SOP) as a function of distance and the normalized spin rate. Deeper understanding of such polarization transformers has been further elucidated by quantitative calculations related to two crucial requirements for fabricating practical AFPT devices. Our calculations have also indicated that the polarization mode dispersion behaviour of the AFPT is much smaller than that of the original birefringent fiber. Finally, a specific AFPT was experimentally investigated at two widely-separated wavelengths (1310 nm and 1550 nm) of interest in telecommunications systems applications, further demonstrating and elucidating the broadband character of such AFPTs.

Near-IR tunable laser with an integrated LiTaO3 electro-optic deflector.

We report the successful demonstration of a near-IR tunable laser (1525.4-1558.2 nm) that uses an integrated LiTaO3 deflector in combination with a reflection grating as an electronically tunable filter. The electro-optic deflector is a unique integrated optical device and consists of a horn-shaped array of electro-optic prisms in series. The almost 33 nm of tuning covers a wavelength region of high interest to the communications industry (1527-1550 nm).