An algorithm is proposed to obtain minimum tree representation of a chordal graph on an algorithm obtained in Ref.(5), and we prove that any tree obtained by this algorithm is optimal for two kinds of optimization problems, that is 1) to obtain a clique tree with the minimum sum of weights on edges and 2) to obtain a clique tree with the minimum sum of weights of subtrees corresponding to vertices.

Centering effect in single mode multi-fiber connectors in investigated precisely by measuring connector loss with various clearances. By comparing the measured loss with the theoretical estimate, the range of clearance over which the centering effect holds is determined.

This paper presents the derivation of the detection performance of a receiver with square-law postdetection integrator for a Rayleigh correlated fluctuating target in a correlated Gaussian clutter plus white noise environment. The analytic expressions describing the detectability as function of signal-to-noise power ratio (SNR), clutter-to-noise power ratio (CNR), number of pulses integrated and the correlation matrices of both clutter plus noise and signal fluctuation are obtained. The numerical results for a first order Markov exponentially correlation model of clutter under fully correlated and partially correlated as well as independent fluctuating target assumptions are given in a set of plots.

A short birefringent launching fiber is proposed to reduce the fluctuation of backscattering from single-mode fibers. The fluctuation is due to polarization-sensitive measurements. It is analyzed that the polarization direction of linearly polarized inputted light is required to make an angle of 27.4 with respect to the principal axes of the birefringent launching fiber. It is also clarified that degree of coherence should vanish at the group delay of τ and 2 τ where τ is the group delay difference of the orthogonal polarization modes in the birefringent launching fiber. Experiments reveal that the birefringent launching fiber of only 3-m length makes it possible to reduce the backscattered power fluctuation to less than 0.05 dB. Required properties of laser diodes are discussed by considering the coherency of the laser diodes with multi-longitudinal modes.

This paper proposes an intrasystem interference cancellation technique for spread spectrum multiple access (SSMA) systems to improve the simultaneous operation performance. Theoretical analysis of its performance and experimental results are described. Although thermal noise and interference from other communication systems can not be recovered at the receiver, it is possible to reproduce interchannel interference signals within an SSMA system, because the spreading codes are known to the receiver. The reproduced interference signals are subtracted from the received signal to cancel the interference signals. An interference signal recovery circuit comprises a conventional SSMA demodulator and a re-spread modulator. The interchannel interference power is reduced by a factor of (n-1)/G as compared with a conventional SSMA demodulator where, G is the process gain and n is the number of simultaneously operating channels. Factors degrading interference cancellation performance are carrier phase error, SS code phase error, delay time error, amplitude variation and waveform degradation due to bandwidth limitation. Theoretical considerations and experimental results on the quantitative effect of these factors are presented.

An optical fiber-coupled type laser has been optimized by taking account of field disturbance on a coupling aperture mirror, and this has been examined by using conventional CO₂ laser. Solving the eigen equations for a quasi-hemispherical resonator with a coupling aperture to find the field distribution on the plane mirror with an aperture, its effective transmittance is analytically evaluated as a function of normalized aperture ξ by the mirror size and is well approximated by the power series expansion up to the fourth order for various mirror Fresnel numbers N and the g parameter of resonator. Using this obtained and typical laser parameters for the experimental set to be used, the coupling aperture is optimized to yield the maximum power. As a result, the optimum aperture becomes a minimum at a specific g₂ parameter of the concave mirror, i.e. g₂0.73, implying that the optimum configuration corresponds to be slightly off from a pure hemispherical setting. These theoretical estimates of the output power vs aperture have been compared with the experimental results obtained for a CO₂ laser, being in qualitative agreements with each other in overall characteristics. By this optimization the maximum output power 6.0 W was extracted from the aperture of 2.4 mm.