THE EFFECTS OF EXTREMELY-SHORT EXTERNAL CAVITY OPTICAL
Telecommunications is a growing and intensely competitive global multi-trillion dollar industry that specializes in the transmission of information all over the world. The data for every television show, website, and telephone conversation travels through one of the industry s many information networks. One of the most common methods of transmission is using fiber optic networks, in which a laser is modulated to send light signals into an optical fiber. The importance of vertical-cavity surface-emitting lasers (VCSELs) to the telecommunications industry is growing rapidly. VCSELs are more cost-efficient to mass-produce and they have better fiber coupling efficiencies as compared to the edge-emitting semiconducting lasers that are the current industry standard. VCSELs were developed with the hope that they would not be subject to some of the main failings of edge-emitting lasers, such as sensitivity to optical feedback. This occurs when some of the emitted light from a laser is accidentally reflected off other optical components in a system, like the end of an optical fiber, back into the laser. The space between the aperture of the laser and the reflective surface is defined as an external cavity. Extremely-short external-cavity (ESEC) optical feedback is feedback that occurs from a surface within a few microns of the VCSEL aperture. In an unmodulated VCSEL, ESEC feedback has been shown to produce periodic variation in the VCSEL's threshold current, output power , polarization switching current and polarization switching current hysteresis width , with respect to variation in the external cavity length. The experimental setup for this experiment mimics the operational setup of a modulated fiber coupled VCSEL as it would be used for data transmission. This presentation will examine those same laser characteristics under the effects of ESEC optical feedback on VCSELs modulated up to 10 GHz.