Abstract

A new type of transmitter optical subassembly (TOSA) especially suitable for fiber optic communication. The TOSA has a light source such as a laser diode, preferably of the surface-emitting type, with an inherent mode-field diameter matched without a lens to that of the optical fiber, resulting in enhanced light coupling, more relaxed tolerances, and less sensitivity to laser misalignment. The TOSA can be in a receptacle form, with an annulus having a light conductor matched to the light source and the fiber, or can be in "pigtail" form with a permanently attached buffered optical fiber. Only one active alignment is required, and can be eliminated, if the laser diode is aligned passively using lands on the annulus or the end of the fiber cladding, and matching lands on a mounting substrate, with molten solder alignment used to draw the two into alignment. To reduce reflections back into the laser the laser sides of the annulus and the light conductor can be machined at an angle with respect to the optic axis, or the diode can be placed at an angle relative to the fiber. This design not only reduces back reflections into the laser diode, but the reflected light can be used to monitor and control the laser diode output.