In this paper, the authors propose a new mode analyzer. This mode analyzer is composed of an obliquely polished optical fiber and a high index prism placed in contact with the oblique section. Modes which have the different equivalent refractive indices are separated due to the different angles of refraction. A mode analyzer using a focusing fiber was made, and modes were successfully separated. The refractive index n(0) at the center axis, the coefficient g of the parabolic term in the refractive index distribution, and the refractive index in the cladding were evaluated from the measurement of angles of refraction. The obtained value of refractive index n(0) at the center axis almost agreed with the value obtained by the interference method. As the application of this mode analyzer, the measurement of group-delay differences of modes and amplitude distribution of modes in a long fiber, and the measurement of the constants of fiber are considered.

A new method of the information reduction of the three-dimensional image is proposed and experimentally verified. This method, the optically sectionned holography, is based on the principle of the coincidence of the time of arrival of the object and the reference beam in the holography. The resolution in depth is analyzed by taking into account the phantom imaging of the optical sectioned holography. The result gives the information content of the obtained hologram. The resulted information content is in the same order to that of the monocular three-dimensional image. So, this system can reduce the fairly amount of the information, comparing to the Burckhard's sampled holography. The system for the optically sectioned hologram by using the mode-locked, and the second harmonic generating c. w. N_d: Y AG laser is experimentally realized, and the optically sectioned holograms are obtained. From these holograms, the three-dimensional image of the original object is restored. A c. w. dye-laser is also used to obtain the optically sectioned hologram. The resulted resolution in depth is about 5 mm, which corresponds to the pulse width of the N_d: Y AG laser.

We have developed LITHAN (LIsten-THink-ANswer) speech understanding system which automatically recognizes continuously uttered speech utilizing higher linguistic information such as syntactic, semantic and pragmatic information. This system predicts possible words utilizing linguistic information at the unrecognized portion of the input utterance, and identifies each predicted word by the use of the optimum matching algorithm between a recognized phoneme string and the representative one in the word dictionary. We propose an effective tree search method of parsing when the results of phoneme recognition and word identification are not error free. LITHAN uses many types of a priori information; the statistic of each phoneme; the similarity matrix between phonemes; the word dictionary; the spoken grammar with the additional information as regards the spoken grammar; the semantic and pragmatic information. We have applied this efficient, flexible system to restricted utterances with vocabulary of about 100 words which concerned with operational commands and queries of the status of a computer network. According to the results tested on a sample 200 sentences spoken by 10 male speakers at a normal speed, 64% of the sentences and 93% of the output words were correctly recognized.

Atmospheric refractivity gradient in the vicinity of the equator were analyzed, based on the radiosonde data in Indonesia and Singapore. Further study was made for estimation on the variation of refractivity gradient in the South-East Asian area, by means of combining with the results in and around Japan.