Micro-displacement sensors based on plastic photonic bandgap Bragg fibers

We demonstrate an amplitude-based micro-displacement sensor that uses a plastic photonic bandgap Bragg fiber with one end coated with a silver layer. The reflection intensity of the Bragg fiber is characterized in response to different displacements (or bending curvatures). We note that the Bragg reflector of the fiber acts as an efficient mode stripper for the wavelengths near the edge of the fiber bandgap, which makes the sensor extremely sensitive to bending or displacements at these wavelengths. Besides, by comparison of the Bragg fiber sensor to a sensor based on a regular multimode fiber with similar outer diameter and length, we find that the Bragg fiber sensor is more sensitive to bending due to presence of mode stripper in the form of the multilayer reflector. Experimental results show that the minimum detection limit of the Bragg fiber sensor can be smaller than 5 um for displacement sensing

Live streaming of uncompressed HD and 4K videos using terahertz wireless links

RÉSUMÉ: Taming the Terahertz waves (100 GHz-10 THz) is considered the next frontier in wireless communications. While components for the ultra-high bandwidth Terahertz wireless communications were in rapid development over the past several years, however, their commercial availability is still lacking. Nevertheless, as we demonstrate in this paper, due to recent advances in the microwave and infrared photonics hardware, it is now possible to assemble a high-performance hybrid THz communication system for real-life applications. As an example, in this paper, we present the design and performance evaluation of the photonics-based Terahertz wireless communication system for the transmission of uncompressed 4K video feed that is built using all commercially available system components. In particular, two independent tunable lasers operating in the infrared C-band are used as a source for generating the Terahertz carrier wave using frequency difference generation in a photomixer. One of the IR laser beams carries the data which is intensity modulated using the LiNbO 3 electro-optic modulator. A zero bias Schottky diode is used as the detector and demodulator of the data stream followed by the high-gain and low-noise pre-amplifier. The Terahertz carrier frequency is fixed at 138 GHz and the system is characterized by measuring the bit error rate for the pseudo random bit sequences at 5.5 Gbps. By optimizing the link geometry and decision parameters, an error-free (BER <; 10 -10 ) transmission at a link distance of 1 m is achieved. Finally, we detail the integration of a professional 4K camera into the THz communication link and demonstrate live streaming of the uncompressed HD and 4K video followed by the analysis of link quality

A fundamental relation between phase and group velocity, and application to the failure of perfectly matched layers in backward-wave structures

http://link.aps.org/doi/10.1103/PhysRevE.79.065601We demonstrate that the ratio of group to phase velocity has a simple relationship to the orientation of the electromagnetic field. In nondispersive materials, opposite group and phase velocity corresponds to fields that are mostly oriented in the propagation direction. More generally, this relationship (including the case of dispersive and negative-index materials) offers a perspective on the phenomena of backward waves and left-handed media. As an application of this relationship, we demonstrate and explain an irrecoverable failure of perfectly matched layer absorbing boundaries in computer simulations for constant cross-section waveguides with backward-wave modes and suggest an alternative in the form of adiabatic isotropic absorbers

Fabrication and Characterization of an 8 × 8 Terahertz Photoconductive Antenna Array for Spatially Resolved Time Domain Spectroscopy and Imaging Applications

ABSTRACT: Terahertz (THz) technology is promising in several applications such as imaging, spectroscopy and communications. Among several methods in the generation and detection of THz waves, a THz timedomain system that is developed using photoconductive antennas (PCA) as emitter and detector presents several advantages such as simple alignment, low cost, high performance etc. In this work, we report the design, fabrication and characterization of a 2-D PCA array that is capable of detecting both the amplitude and phase of the THz pulse. The PCA array is fabricated using LT-GaAs and has 8 channels with 64 pixels (8 × 8). A novel approach using a spatial light modulator (SLM) to steer and focus the infrared probe beam towards pixels of the PCA array is presented. Each channel records the photocurrent generated by the THz signal (amplitude and phase) separately and frequencies up to 1.4 THz can be detected. Furthermore, the parameters such as directional time delay of the THz pulse, crosstalk between the channels etc., were characterized. Finally, we show that the proposed 2D PCA array design is flexible and can be used for accelerated THz spectral image acquisition

Quantitative super-resolution solid immersion microscopy via refractive index profile reconstruction

Solid Immersion (SI) microscopy is a modern imaging modality that overcomes the Abbe diffraction limit and offers novel applications in various branches of visible, infrared, terahertz, and millimeter-wave optics. Despite the widespread use, SI microscopy usually results in qualitative imaging. Indeed, it presents only the raw distributions (in the image plane) of the backscattered field intensity, while unlocking the information about the physical properties of an imaged object, such as its complex refractive index (RI) distribution, requires resolving the inverse problem and remains a daunting task. In this paper, a method for resolving the SI microscopy inverse problem is developed, capable of reconstructing the RI distribution at the object imaging plane with subwavelength spatial resolution, while performing only intensity measurements. The sample RI is retrieved via minimization of the error function that characterizes discrepancy between the experimental data and the predictions of analytical model. This model incorporates all the key features of the electromagnetic-wave interaction with the SI lens and an imaged object, including contributions of the evanescent and ordinary-reflected waves, as well as effects of light polarization and wide beam aperture. The model is verified numerically, using the finite-element frequency-domain method, and experimentally, using the in-house reflection-mode continuous-wave terahertz SI microscope. Spatial distributions of the terahertz RIs of different low-absorbing optical materials and highly absorbing biological objects were studied and compared to a priori known data to demonstrate the potential of the novel SI microscopy modality. Given the linear nature of the Maxwell’s equations, the developed method can be applied for subwavelength-resolution SI microscopy at other spectral ranges

Soft capacitor fibers using conductive polymers for electronic textiles

A novel, highly flexible, conductive polymer-based fiber with high electric capacitance is reported. In its crossection the fiber features a periodic sequence of hundreds of conductive and isolating plastic layers positioned around metallic electrodes. The fiber is fabricated using fiber drawing method, where a multi-material macroscopic preform is drawn into a sub-millimeter capacitor fiber in a single fabrication step. Several kilometres of fibers can be obtained from a single preform with fiber diameters ranging between 500um -1000um. A typical measured capacitance of our fibers is 60-100 nF/m and it is independent of the fiber diameter. For comparison, a coaxial cable of the comparable dimensions would have only ~0.06nF/m capacitance. Analysis of the fiber frequency response shows that in its simplest interrogation mode the capacitor fiber has a transverse resistance of 5 kOhm/L, which is inversely proportional to the fiber length L and is independent of the fiber diameter. Softness of the fiber materials, absence of liquid electrolyte in the fiber structure, ease of scalability to large production volumes, and high capacitance of our fibers make them interesting for various smart textile applications ranging from distributed sensing to energy storage