PURPOSE:To obtain the different diameter type optical transmitter which has superior optical transmission efficiency, the spot light source, spot light source array, parallel light source, and parallel light source array which have superior light utilization effi ciency, the liquid crystal display device which makes an excellent display and has a wide visual angle, the measuring instrument which has superior light utilization efficiency, and the optical transmission connector which is superior in the efficiency of a connection with the different diameter optical transmitter. CONSTITUTION:This invention offers an optical transmitter composed of a rotationally symmetrical photoconductor 1 with graded indexes, varies in external diameter having a gradient, and has different diameters at both ends. The spot light source, spot light source array, parallel light source, or parallel light source array with combining lenses with the optical transmitter and light source at need. The liquid crystal display device using the parallel light source array as a light source, a measuring instrument having the spot light source, etc., as a light source, and an optical transmission connector composed of the optical transmitter.
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