A Compact Single-Frequency Laser Package With 1 MHz linewidth and ±10 MHz Frequency Stability

A compact single-frequency laser package is reported. In this device, a distributed feedback laser is coupled to a graded-index rod external cavity. hen light fed back into the laser cavity is at the proper phase, linewidth narrowing is obtained. The package consists of a laser source, the graded-index rod optics, a piezo-electric crystal, a milli-Kelvin temperature control element, and a microwave bias board, all in a 1 in thermally insulated enclosure. Miniaturization is made possible by a novel collinear optical assembly. A linewidth of 1.3 and a short-term frequency stability of +10 nliz have been measured. Direct frequency modulation with the injection current is possible with this short external coupled cavity arrangement. At 565 kb/s, a frequency modulation index of 1 was achieved for a 1010 pattern with negligible linewidth broadening. Error-free transmission was measured in a frequency-shift-keying heterodyne detection experiment for fixed word patterns at this data rate. The compact size and the FM properties of the unit are attractive for use either as a transmitter or as a local oscillator in coherent optical communication systems.