Abstract: In an optical transmission system, a lens converges an optical signal outputted from a light emission element. The optical signal having passed .through the lens enters a multi-mode fiber (MMF). A vertex of the lens and an input plane of the MMF are at a distance. The distance is set to a value which is not equal to the distance from the vertex to a focal point of the lens. As a result, a lowcost optical transmission system can be provided in which the influence of mode dispersion is reduced.

Abstract: A digital electrical signal Vin for transmission is supplied to a transistor Q12, a current compensation circuit 11, and a signal current source 13 to be band-compensated for generating a signal current I0. A predetermined current Id for a constant-current source 14 is subtracted from the signal current I0, and the result is an injection current Iin that drives an LED 15. The current Id is adjusted so that the injection current Iin becomes 0 at the low level. Thus, a signal-to-noise (S/N) ratio in waveform of light outputted from the LED 15 can be improved. Accordingly, the S/N ratio of the transmitted signal can be improved with band compensation.

Abstract: In an optical transmission system Sa, a lens 112 converges an optical signal OSin outputted from a light emission element 111. The optical signal OSin having passed through the lens 112 enters a multi-mode fiber (MMF) 12. A vertex Z0 of the lens 112 and an input plane Fin of the MMF 12 are at a distance Z1. The distance Z1 is set to a value which is not equal to the distance from the vertex Z0 to the focal point Zfp of the lens 112. As a result, a low-cost optical transmission system can be provided in which the influence of mode dispersion is reduced.

Abstract: A digital electrical signal Vin for transmission is supplied to a transistor Q12, a current compensation circuit 11, and a signal current source 13 to be band-compensated for generating a signal current I0. A predetermined current Id for a constant-current source 14 is subtracted from the signal current I0, and the result is an injection current Iin that drives an LED 15. The current Id is adjusted so that the injection current Iin becomes 0 at the low level. Thus, a signal-to-noise (S/N) ratio in waveform of light outputted from the LED 15 can be improved. Accordingly, the S/N ratio of the transmitted signal can be improved with band compensation.

Abstract: Ceramic materials within particular ranges of the ternary system Pb(Sn.sub.1/3 Sb.sub.2/3) O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3 in solid solution form exhibit high planar coupling coefficient along with high dielectric constant, and are useful in electromechanical transducers. The ceramic materials are those within the area A, B, C, D, E and F of FIG. 2.

Abstract: A process for preparing strengthened ferroelectric ceramics, which comprises sintering ceramic materials and then heat treating the sintered ceramics at a temperature from about 100.degree. to about 400.degree.C lower than the final sintering temperature of ceramics, for about 1 to about 60 hrs., and then cooling at a rate from about 300.degree. to about 10.degree.C per hour. Strengthened ferroelectric ceramics are obtained among the following ferroelectric ceramic compositions:I. pb([B.sub.1 ].sub.A Ta.sub.1.sub.-A)O.sub.3 --PbTiO.sub.3 --PbZrO.sub.3, where [B.sub.1 ] is Mg, Zn, Cd, Sn, Mn, Fe, Co, and Ni when A=1/3 and [B.sub.1 ] is Li and Cu when A=1/4,Ii. pb([B.sub.2 ].sub.B Ta.sub.1.sub.-B)O.sub.3 --Pb([B.sub.3 ].sub.C Ta.sub.1.sub.-C)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3, where [B.sub.2 ] and [B.sub.3 ], [B.sub.2 ].noteq.[B.sub.3 ], are Mg, Zn, Cd, Sn, Mn, Fe, Co and Ni when B and C=1/3, and [B.sub.2 ] and [B.sub.3 ], [B.sub.2 .noteq.[B.sub.3 ], are Li and Cu when B and C=1/4,Iii. pb([B.sub.1 ].sub.A Ta.

Abstract: A process for preparing strengthened ferroelectric ceramics, which comprises heat treatment of sintered ceramics after sintering of ceramic materials at a temperature range from about 100.degree. to about 400.degree.C. lower than the final sintering temperature of ceramics, holding it for about 1 to about 60 hrs, and then cooling it at a cooling rate from about 300.degree. to about 10.degree.C. per hour. Strengthened ferroelectric ceramics are obtained among the following ferroelectric ceramic compositions:I. pb([B.sub.1 ].sub.A Nb.sub.1-A )O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3, where [B.sub.1 ] is Mg, Zn, Cd, Sn, Mn, Fe, Co and Ni when A=1/3 and [B.sub.1 ] is Li and Cu when A=1/4,Ii. pb([B.sub.2 ].sub.B Nb.sub.1-B )O.sub.3 -Pb([B.sub.3 ].sub.C Nb.sub.1-C )O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3, where [B.sub.2 ] and [B.sub.3 ], [B.sub.2 ].noteq.[B.sub.3 ], are Mg, Zn, Cd, Sn, Mn, Fe, Co and Ni when B and C=1/3, and [B.sub.2 ] and [B.sub.3 ], [B.sub.2 ].noteq.[B.sub.3 ], are Li and Cu when B and C=1.4,Iii. pb([B.sub.