Thursday, July 19, 2018
OT- LUNA Upcoming Webinar: Optical Backscatter Reflectometry: The Key to Accelerating Design Verification and Troubleshooting of Next Generation Optical Network Components
High-resolution optical backscatter reflectometry (OBR) has become a valuable tool in the design, test and diagnostics of fiber components, photonic integrated circuits (PICs) and short fiber networks. In much the same way that standard OTDRs identify and locate issues and sources of loss in long-range fiber optic systems, high-resolution OBRs can locate and identify issues and defects with sub-millimeter resolution and since they don't suffer from the "deadzones" associated with OTDR, they are ideal for components and short-run optical networks like those found in modern, high-speed communications networks and data links. This webinar will review how OBR technology works, how it differs from alternative reflectometry techniques, and describe real-world application examples. These application examples include characterizing the optical performance and quality of silicon photonic components such as waveguides and troubleshooting short fiber networks like those found in data centers and on aircraft. These application examples will illustrate how high-resolution OBR delivers an extreme level of detail and sensitivity in identifying sources of loss (bends, breaks, bad splices, defects, interfaces, etc.), as well as making very precise latency measurements. The webinar will include live software demos to illustrate the operation of OBR instruments with real-world optical components and systems.
Clotilde Prophète, Romain Pierrat, Hervé Sik, Emmanuel Kling, Rémi Carminati, and Julien de Rosny
In this paper we propose and discuss coherent terahertz sources based on charge density wave (plasmon) amplification in two-dimensional graphene. The coupling of the plasmons to interband electron-hole transitions in population inverted graphene layers can lead to plasmon amplification through stimulated emission. Plasmon gain values in graphene can be very large due to the small group velocity of the plasmons and the strong confinement of the plasmon field in the vicinity of the graphene layer. We present a transmission line model for plasmon propagation in graphene that includes plasmon dissipation and plasmon interband gain due to stimulated emission. Using this model, we discuss design for terahertz plasmon oscillators and derive the threshold condition for oscillation taking into account internal losses and also losses due to external coupling. The threshold condition is shown to depend on the ratio of the external impedance and the characteristic impedance of the plasmon transmission line. The large gain values available at terahertz frequencies in graphene can lead to integrated oscillators that have dimensions in the 1-10 mum range.
Abstract-Contactless Transient THz Temperature Imaging by Thermo-transmittance Technique on Semi-transparent Materials
M. Bensalem, A. Sommier, J. C. Mindeguia, J. C. Batsale, Luis-David Patino-Lope, C. Pradere,
THz waves have shown to be effective for several applications, such as security, non-destructive testing, and water content monitoring for porous materials and food products. This study aims to highlight the use of THz radiation to measure temperature variations of thin insulating materials opaque in the visible or IR range (PVC, PTFE, PMMA, and wood) by using a spectral thermo-transmittance technique. THz wave optical transmittance in materials show high sensitivity to temperature variations. The goal of this paper is to demonstrate the transient temperature gradient dependence of THz transmitted signals inside materials to develop a new contactless method for measuring temperature of thin materials semi-transparent to THz radiation. The principle is based on synchronous detection, using an infrared camera coupled with a THz to infrared thermal converter (TTC) with modulated millimeter-scale waves (2.7 mm). The results show a correlation between the transient temperature and the optical transmittance coefficient. Several types of samples semi-transparent to THz radiation are tested, and the corresponding thermo-transmittance coefficients as reported for PVC, PTFE, PMMA, and wood are respectively 0.805, 0.395, 0.640, and 1.177 K m.
Abstract-Dynamic Photo-induced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures
Yuncheng Zhao, Yaxin Zhang, Qiwu Shi, Shixiong Liang, Wanxia Huang, Wei Kou, Ziqiang Yang,
Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, realizing a large phase shift using a one-layer structure in transmission mode has been difficult. In this paper, utilizing a composite unit cell by coupling the traditional metallic wire dipolar resonance and the split-ring capacitive inductance resonance results in an enhanced resonance coupling mode. Combined with a vanadium dioxide (VO2) nanostructure and applying the photo-induced phase transition, the resonant intensity of the mode can be dynamically controlled, which leads to an ultralarge phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138 degrees near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575 GHz-630 GHz) bandwidth, the phase shift exceeds 130 degrees. This attractive phase shift modulation may provide prospective applications in THz imaging, communications, etc.
Wednesday, July 18, 2018
Shuai Lin, Sinhara Silva, Jiangfeng Zhou, Diyar Talbayev
The magneto‐optical properties of conduction electrons in InSb in Voigt geometry at oblique incidence angles are explored. In parallel magnetic field, the oblique incidence reflectance exhibits high nonreciprocity, while the transmittance remains reciprocal. This phenomenology, combined with the unique magnetoplasmonic properties of InSb (high electron mobility, low effective mass, and temperature‐tunable bulk plasma frequency), allows the design of a simple and high‐performance THz optical isolator that works directly with linearly polarized light. It is demonstrated that the isolation power of the device exceeds 35 dB with the insertion loss of only −6.2 dB. The simplicity of the isolator design is unmatched among the proposed THz isolator concepts to date.