Measurement of the spectral amplitude and phase of a free-running 40 GHz quantum-dash modelocked laser diode

Quantum-dash modelocked laser diodes (QD-MLLD) are capable of producing short optical pulses at extremely high repetition rates. As such they are ideally suited to many telecommunications applications. In this paper we present a linear self-referenced measurement of the spectral amplitude and phase of a free-running quantum-dash modelocked laser diode. The technique is suitable for measuring optical signals with repetition rates up to 100 GHz. In contrast to many other linear techniques it requires no external electronic clock synchronized to the signal under test. Using this method we show that compensating for the intra-cavity dispersion of the diode results in 500 fs pulses at a repetition rate of 39.8 GHz.