Masato Kishi

Fiber-edge electrooptic/magnetooptic probe for spectral-domain analysis of electromagnetic field

We propose a new class of an electromagnetic-held probing scheme for microwave planar circuit diagnosis. The measurement principle is based on the electrooptic/magnetooptic effects of crystals glued at optical fiber facets. We have combined the concept of those fiber-edge probes with a fiber-optic RF spectrum analyzing system containing a continuous-wave semiconductor laser source, a fast photodetector, and an RF spectrum analyzer to realize a highly sensitive measurement equipment of local impedance. Electromagnetic-field intensity on a microstrip transmission line has been measured in the frequency domain, where voltage and current amplitudes have been independently investigated with sensitivities of 16 mV/Hz-1/2 and 0.33 mA/Hz-1/2, respectively. In addition, it has been shown that the former value can be improved to be 0.7 mV/Hz-1/2 or smaller by the resonant cavity enhancement effect.

Stimulated brillouin scattering and its dependences on strain and temperature in a high-delta optical fiber with F-doped depressed inner cladding

Stimulated Brillouin scattering (SBS) in a high-delta fiber with F-doped depressed inner cladding is studied through considering the interaction of acoustic and optical modes in the fiber. It is found that the number of acoustic modes in the fiber is reduced and the frequency spacing between neighboring modes is enlarged because of the F doping. The dependences of SBS on strain and temperature are measured and compared for each acoustic mode to investigate the feasibility of discriminative sensing of strain and temperature by use of the fiber.

High-repetition-rate distributed Brillouin sensor based on optical correlation-domain analysis with differential frequency modulation

A kind of high-repetition-rate distributed Brillouin sensor is proposed and experimentally demonstrated based on optical correlation-domain analysis with differential frequency modulation, where the optical frequencies of the pump and the probe waves are modulated at slightly different RFs so that the temporal position of the measurement is continuously and repeatedly swept along a fiber under test. A distribution map of Brillouin frequency variation along a 100 m optical fiber is acquired at a repetition rate of 20 Hz with an accuracy of ±2.5 MHz and a spatial resolution of about 80 cm.

Observation of stimulated Brillouin scattering in polymer optical fiber with pump–probe technique

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter was experimentally observed for the first time, to the best of our knowledge, at 1.55 μm wavelength with the pump-probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1 m) and scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature sensing systems.

5,000 points/s high-speed random accessibility for dynamic strain measurement at arbitrary multiple points along a fiber by Brillouin optical correlation domain analysis

We demonstrate dynamic strain measurement at arbitrary multiple points along a fiber simultaneously using random accessibility of a Brillouin optical correlation domain analysis system with a 5,000 points/s sampling rate. A voltage-controlled oscillator is introduced for faster sweeping of the probe wave frequency to obtain the Brillouin gain spectrum. A higher-speed lock-in amplifier is also used for data detection. Several patterns of dynamic strain applied at five points selected arbitrarily along the fiber are measured simultaneously at a 5,000 points/s sampling rate with random accessibility. This is the highest speed of random accessibility reported so far in Brillouin-based distributed fiber sensors.

1-cm spatial resolution with large dynamic range in strain distributed sensing by Brillouin optical correlation domain reflectometry based on intensity modulation

We experimentally demonstrate distributed strain measurement with a high spatial resolution and a large dynamic range by proposing a system for Brillouin optical correlation domain reflectometry with an intensity modulation scheme. With the optimized intensity modulation, the optical power spectrum of the light source is properly modified so that the accumulated background noise in the Brillouin gain spectrum is significantly reduced. It is confirmed that the proposed system enables us to extend the maximum measurable strain up to ~7000 με, which is sufficient for practical applications of a distributed sensing, with 1-cm spatial resolution. This resolution is the best result ever reported in reflectometries based on spontaneous Brillouing scattering by using a conventional single mode fiber.

Magnetic near-field measurements over LSI package pins by fiber-edge magnetooptic probe

To establish a method for investigating hidden radiation sources and their mechanisms in a printed circuit board, we performed preliminary measurements of one-dimensional magnetic near-field distribution over pins of a large-scale integrated circuit (LSI) package by means of an optical method: the fiber-edge magnetooptic (FEMO) probing technique. The FEMO probe consists of fiber optics and a magnetooptic crystal glued at a fiber edge. Its planar spatial resolution is approximately 100 /spl mu/m. It was found that a magnetic field generated from each LSI pin could be distinguished and some radiation was generated from ground and power supply lines. We compared the measured results with corresponding radiated electric field strength that was separately measured. The frequency of interest was the tenth harmonic of the output signal. We observed a strong correlation between those two experimental results, which suggests the effectiveness of our proposed method for near-field investigation. One of the beneficial features of the FEMO probe is its small probe head, due to which one can perform detailed near-field evaluations in a microscopic region. Furthermore, we tried to specify a major electromagnetic interference source by additional measurements of near-field distributions and frequency dependence of magnetooptic signals. It was suggested that the short-through current flowing in the power-supply system of the input/output circuits caused high-level radiated emission.

10 GHz-Class Magneto-Optic Field Sensing with Bi-Substituted Rare-Earth Ion Garnet Rotation Magnetization Employed

We have experimentally investigated RF sensitivity and frequency response of the rotation magnetization (RM) based Faraday effect in a Bi-substituted rare-earth iron garnet plate, with the aim of exploring the possible implementation of an optical instrument for wideband magnetic field probing. We have pointed out and confirmed experimentally the effectiveness of applying an in-plane static magnetic field for the sensitivity enhancement of RM signal detection; the signal-to-noise ratio was improved by 40 dB or more. The RM frequency response is flat within a fluctuation of 2.5 dB from 10 MHz up to 3 GHz and its 3 dB bandwidth is as broad as 14 GHz. We have also proposed fiber-edge magneto-optic probe head structures which may provide the frequency response and sensitivity mentioned above.

Implementation of Magneto-Optic Probe with > 10 GHz Bandwidth

Magneto-optic probes with bandwidths of > 10 GHz were implemented for the first time. Rotation magnetization in a Bi-substituted rare-earth iron garnet crystal is utilized as a fast magnetization phenomenon for magnetic field sensing through the sensitive fiber-optic Faraday effect detection system with the magneto-optic crystal attached onto its fiber facet. Its minimum detectable current is around 140 µA rms. A method to further extend the bandwidth by introduction of elastic strain was discussed while successful demonstration of two-dimensional magnetic field mapping was performed over a GHz-band microstrip line circuit.

Three-dimensional magneto-optic near-field mapping over 10-50 /spl mu/m-scale line and space circuit patterns

We report on the first fine x-z mapping experiment of magnetic near-field distribution over fine circuit patterns. Required three-dimensional (3D) spatial resolution was brought about by utilizing the fiber-edged magneto-optic (FEMO) probe structure. The 3D mapping technique of electromagnetic fields provides more information about finer variations in the vertical (z) direction in cases of finer circuits. The electro-optic/magneto-optic (EO/MO) probing techniques are promising toward this purpose since one can take its attractive natures such as wide-bandwidth, high-sensitivity, low invasiveness, and relatively high-spatial-resolution.