Tadayuki Funaba

Optical multimode frequency-domain reflectometer

A multimode laser can instantaneously generate a carrier frequency of significantly wide band. The proposed systems, composed of a free-running multimode laser diode, an optical spectrometer, and a computing system for fast Fourier transformation, can easily provide the potential for ultrahigh resolution of the order of 10 microm without scanning frequencies as in frequency-domain reflectometers of either the continuously or the stepwise-swept variety.

Self-fractional Hankel functions and their properties

A new formula for generating the self-fractional Hankel functions (SFHF) is proposed. Some properties of the SFHF are investigated. It is shown that any integrable function can be represented as a linear combination of M SFHFs with angle π/M.

Multimode-laser reflectometer with a multichannel wavelength detector and its application

A multimode-laser reflectometer that detects an interference spectrum by use of a multichannel wavelength detector was developed and its characteristics evaluated experimentally. A spatial resolution of 24 mum and a maximum detectable length of 510 mum were achieved. Thickness mapping of a coverglass was attempted as an application and was compared with an interference fringe between the surface and the back. Good results that reflected the tendency of an interference fringe were obtained.

Optical Spectral Domain Reflectometer With Multimode Coherency Using Multichannel Wavelength Detector

were made by a reflecting mirror that was attached on a tilting table. Three orthogonal functions calculated by PCM are shown in Fig. 1. Three non-negative filter functions calculated by a neural network algorithm is shown in Fig. 2. Spectral distribution of color of any OPD values can be retrieved by a linear combination of three functions in Figs. 1 and 2. In Fig. 3, the learning data were plotted on a three-dimensional subspace spanned by three orthogonal basis vectors in Fig. 1. If a spectral intensity of unknown OPD is projected on the subspace, OPD is determined as a parameter value of the nearest point on the curve from the projected point. Colored fringes obtained by a surface of a bearing bawl was analyzed and results are shown in Fig. 4. A resultant averaged radius of curvature that is 1.989 mm coincided with that obtained by a digital micrometer, 1.984 mm. FP2 1400

High-resolution optical time domain reflectmetry based on a broadband continuous wave multimode laser diode

A broadband light source can be obtained by operating a multimode laser diode with a bias current below threshold. We propose an optical time domain reflectometer for high-resolution with a broadband cw multimode laser. The emission spectrum of the multimode laser diode that affects an interference signal is investigated. With this method, the spatial resolution is measured as 11.5 μm, corresponding to that of 38.3-fs pulses, and a minimum detectable reflectivity < -90 dB is achieved.