Patent ID: 7274837

Claim:
An optical transmitter in which a microstripline is formed by a signal wiring pattern and a GND conductor pattern on a circuit board, and a signal lead of a light emitting element module is mounted in a signal lead mounting hole of said circuit board connected with said signal wiring pattern so as to be connected with said signal wiring pattern, wherein a pattern adapted to add capacitance between a stem of said light emitting element module and said signal wiring pattern is provided on said signal wiring pattern on said circuit board, wherein the pattern adapted to add capacitance has a size corresponding to ±50% of a capacitance C≈L/Zo 2 , where Zo is signal line impedance, and L is the signal lead inductance; wherein said GND conductor pattern is formed on a surface of a light emitting element module side of said circuit board and said signal wiring pattern is formed on another surface of said circuit board, wherein said pattern adapted to add capacitance is formed with a substantially rectangular shape around said signal lead on said surface of the light emitting element module side of said circuit board, and wherein said signal wiring pattern and said pattern adapted to add capacitance are electrically connected through another hole of said circuit board different from said signal lead mounting hole.