Abstract

We are characterizing polyimide-embedded ridge-waveguide ring lasers with Y-guide out- couplers to better understand their behavior and to determine their suitability for integrated-optics uses. These lasers, fabricated by reactive ion beam etching with a single-quantum-well active region, have a cw threshold current of <60 mA (300-μm ring diameter × 8-μm waveguide). The wide waveguide in these devices leads to lasing in whispering gallery modes with the highest gain modes being those which minimize their loss because of out-coupling at the Y-guide. This behavior limits the output power with increasing current. The Y-guide also acts as a wavelength selection mechanism for the whispering gallery modes. As the current is increased, the wavelength of the lasing mode increases slightly; this in turn affects the mode propagation around the ring at the Y-guide out-coupler. With increasing current, eventually the mode loss at the Y- guide becomes large enough to allow lasing on a new family of higher gain whispering gallery modes. This mode change is evidenced by a jump in wavelength. This Y-guide mode selection mechanism aids in attaining single-frequency operation providing a side-mode rejection ratio as high as 23 dB with an over-a-limited current range corresponding to a particular mode family.

© 1991 Optical Society of America