(A) study on fabrication and analysis of long cavity laser diode using TIR

Abstract

Serpentine shaped laser diodes(SSLD) with 14 dry etched total internal reflection(TIR) mirrors and 2 cleaved facets are fabricated for OEIC and PIC application.SSLDs are fabricated using two step $Cl_2$ and $CCl_2F_2$ mixed gas reactive ion beam etching(RIBE). The etching result of RIBE using $Cl_2,\ CCl_2F_2$, and $Ar_2$ gases exhibit excellent anisotropic etching charateristics, which minimize ion bombardment induced damage to etched sidewall surfaces. It is found that the self-aligned TIR mirrors have a high reflectivity of 0.85. In the spectra od SSLD, several disticnt characteristics have been observed. The Faby-Perot laser shows simultaneous oscillations of many longitudinal modes whose intensity profile follows more or less the spontaneous emission profile. SSLDs, on the other hand, show either one dominant longitudinal mode or a limited number of dominant longitudinal modes which are far apart at high current injection level. In order to understand TIR mirror effect on the wavelength, Y-branch with TIR mirror, laser diode, and photodetector is fabricated. Some refelction to backward direction at the TIR mirror is observed using Y-branch. This result imply that TIR mirrors of SSLD make the cavity structure like coupled cavity structure with a number of small cavities. Also, roof-top-reflector(RTR)-shaped lasers are designed and fabricated. Differency of spectra between RTR-shaped laser with and without trench in the center of the cavity is another example of strong mode selectivity and gain perturbation of TIR mirror. A simple calculation based on transfer matrix method is excuted to clarify the spectrum behavior of SSLD and various shaped lasers with TIR mirrors. The results show that small backward reflection at the dry eched TIR mirror significantly effect on spectra characteristics of laser.