Near-field Mapping System Research Articles

High Spatial Resolution Photodetectors Based on Nanoscale Three-Dimensional Structures

A high spatial resolution photodetector is designed and realized using a newly developed two-sided nanoscale three-dimensional fabrication technique. Two types of nanophotodetectors with slab and channel structures are fabricated and characterized. By comparison, nanophotodetectors with channel structures show a 10 times lower dark current, higher detection resolution, and signal-to-noise ratio than nanophotodetectors with slab structures. The smallest nanophotodetector fabricated is as small as 100 nm wide. A responsivity of 0.19 A/W at 1310-nm wavelength and 3-V bias for a channelized nanophotodetector is registered, with a photocurrent of 135 nA over a dark current of 1.25 nA. In addition, using a modified near-field scanning optical microscopy-based photocurrent mapping system, we demonstrated a high spatial resolution photodetection of 400 nm using a nanophotodetector with channel structure fabricated.

Applications of the Near-Field Techniques in EMC Investigations

A completely automatic near-field mapping system has been developed within the Research Institute for Electronic Embedded Systems (IRSEEM) in order to determine the electromagnetic field created by electronic systems and components. This test bench uses a 3-D positioning system of the probe to make accurate measurements. This paper presents some applications of the near-field techniques in EMC investigations. In the first part, near-field measurements are used to locate precisely the electromagnetic sources of a limiter device. In the second part, we present an equivalent model of the radiated emission of an integrated circuit. In the last part, the near-field test bench is used to characterize faults in a cable.

Near-Field Mapping System Using Fiber-Based Electro-Optic Probe for Specific Absorption Rate Measurement

We have developed a near-field mapping system with a fiber-based electro-optic (EO) probe for microwave antenna characterization. In this probe, an EO crystal is mounted on the tip of an optical fiber through a collimating lens. Since the lens allows the crystal thickness to be lengthened by reducing the loss of an optical beam coupling back to the optical fiber, sensitivity is improved. Because the tip of the EO probe consists of a 1-mm-cubic EO crystal and contains no metallic components, there is very little disturbance of the mapped electric field. Fixing the optical fiber in a thin glass tube provides stable sensitivity during long-term mapping over a large area. The fabricated EO probe has a dynamic range larger than 45 dB, flat sensitivity from 1.95 to 20 GHz, and directivity with cross-axis sensitivity isolation greater than 30 dB, A comparison of the measured and calculated near fields of a dipole antenna showed negligible static or inductive coupling between the EO probe and the dipole antenna. Using a tissue-equivalent phantom to assess the specific absorption rate (SAR), we demonstrated the potential of the EO probe for mapping the electric field with information of amplitude and phase. The EO probe can detect an electric field of less than 0.6 V/m, which corresponds to a SAR of 0.5 mW/kg. This value satisfies the minimum detection limit defined in the regulations for determining SAR. This result shows the potential of the near-field mapping system with the fiber-based EO probe in practical applications.

Characterization of Surface Wave Propagation in UC-PBG Patch Antenna by Using an Electrooptic Near-Field Mapping System

An electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing stationary and transient near-field patterns of conventional and uniplanar compact photonic band gap (UC-PBG) patch antennas. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was experimentally verified by comparing stationary and transient near-field measurement of the conventional and UC-PBG patch antennas.

Investigation of Surface-Wave Reduction in UC-PBG Patch Antenna by Using a Transient Electrooptic Near-Field Mapping Technique

A transient electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing transient near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) patch antennas fabricated on a low-cost FR4 substrate. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was investigated experimentally by comparing transient near-field patterns of the conventional and UC-PBG patch antennas

Characterization of uniplanar compact photonic-bandgap finite-width conductor-backed coplanar waveguide by using an electrooptic near-field mapping technique

An electrooptic near-field mapping system based on a gain-switched distributed-feedback pulsed laser and a CdTe electrooptic crystal was used for characterizing transient and stationary near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of transient and stationary near-field patterns of FW-CBCPWs visually shows that parasitic parallel-plate modes in the FW-CBCPW are effectively suppressed by the UC-PBG pattern on side-ground plates.

CHARACTERIZATION OF THE OPEN-ENDED COAXIAL PROBE USED FOR NEAR-FIELD MEASUREMENTS IN EMC APPLICATIONS

A completely automatically near-field mapping system is developed within IRSEEM (Research Institute for Electronic Embedded Systems) in order to determine electromagnetic field radiated by electronic systems. This test bench uses a 3D positioning system of the probe to make accurate measurements. The main element of this measurement tool is the probe. This paper presents a characterization of the open-ended coaxial probe which is used to measure the normal component of the electric field.

Investigation of microstriplike mode suppression in UC-PBG FW-CBCPW by using an electro-optic near-field characterization

Near-field patterns of uniplanar compact photonic bandgap (UC-PBG) and non-UCPBG finite-width conductor-backed coplanar waveguides (FW-CBCPWs) are characterized using an electro-optic near-field mapping system. This system is very effective in visually showing the role of the UC-PBG structure in the suppression of microstriplike (MSL) modes in the FW-CBCPWs. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 119–122, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21098

Characterization of picosecond electric-pulse propagation on CPW components by transient near-field mapping

For the first time, the picosecond electric-pulse propagation characteristics of a few coplanar waveguide (CPW) components, including transmission lines, capacitive open and short terminations and a right-angle bend, have been successfully measured by mapping the time-dependent tangential near-electric-field distributions. The measurement was performed using a two-dimensional photoconductive (PC) near-field mapping system incorporating a recently developed novel PC electric-field probe, which could measure the separate picosecond orthogonal electric-field components with minimal loading effects. The resulting field-images mapped over the structural capacitive open termination and the short termination, showed previously unknown, and quite remarkable, transient picosecond electric-pulse reflection phenomena, which cannot be measured using conventional test instruments. In addition, the images showed that reflection-phenomenon itself required about 1 ps of propagation delay, and that the pulse-reflection from the capacitive open-termination required additional time delay matched to the length of the open-gap between the two slots of the CPW.