PURPOSE:To reduce the coupling loss of optical signals, by changing the waveguide spot size of a wave guiding type light controlling element which outputs optical signals prepared by adding various kinds of control to the output light of a luminous element to an optical fiber between its luminous element side end face and optical fiber side end face. CONSTITUTION:The waveguide 105 spot size at the end face 107 at the side to be coupled wit a luminous element 101 having a smaller spot size is made smaller and the spot size at the end face 108 at the side to be coupled with an optical fiber 110 having a larger spot size is made larger so that the spot size can be made coincident with the spot size of the optical fiber 110. Then the module of a light controlling element, in which the luminous element 101, wave guiding type optical element 109, and optical fiber 110 are united in one body is constituted, by directly terminal-couplling between the luminous element 101 and waveguiding type light controlling element 109 and between the wave guiding type light controlling element 109 and optical fiber 110, respectively. Therefore, the module of a light controlling element which is low in loss and light in weight can be obtained and this module can be used for high-speed optical communication system.
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