(Invited) Growth and Processing Techniques for Fabricating Ultra Broadband High-Power Low-Cross-Talk Semiconductor Optical Amplifiers

Recent development of fibers with very low losses over the entire spectral range between 1200 and 1700 nm has laid a foundation for future ultra-broadband (UBB) optical communications. To fully utilize this potential it is expected that next generation photonic components will be able to cover such broad windows for interconnect, switching and networking applications. Currently the major obstacle on the path towards UBB optical communications is lack of a gain material that operates over the entire 500 nm spectrum, rather than just the narrow 40-nm portion covered by the EDFA. To achieve such a broad gain spectrum one needs to combine materials with different effective bandgaps within one waveguide. This can be done either longitudinally (when bandgap is graded along the waveguide) or vertically (when the bandgap is graded in the direction of growth). We have explored both methods and achieved very promising results. Using selective area growth (SAG) technique1 we can grow multiple quantum well (MQW) materials with variable effective bandgaps on the same substrate. This is achieved by grading both MQW composition and sizes. Fig. 1 shows the SAG mask, a fabricated and bonded device, and it electroluminescence (EL) spectra with and without AR coating. An alternative method of getting broad gain is to stack different gain regions vertically and connecting them via tunnel junctions. Such a cascaded UBB SOA is shown in Fig. 2and it incorporates multiple different gain regions ranging from 1200 to 1700nm.