Simultaneous measurements of the optical phase & amplitude modulation of injection-locked VCSELs modulated at GHz rates

Using a coherent optical demodulation technique, we have independently measured the AM and PM resulting from current modulation at GHz rates of an I.L. VCSEL at 1.55 μm. The variation of the depth of AM and PM are measured as function of RF modulation frequency and power. Two regimes of modulation for the I.L. VCSEL are explored: 1) At low frequencies <; 10 MHz where thermal modulation dominates and mainly PM is generated; 2) At high frequencies >; 100 MHz where carrier concentration modulation dominates and both AM and PM are significant. This data is vital for the use of VCSELs as modulators in communications systems.