Passively Mode-Locked 4.6 and 10.5 GHz Quantum Dot Laser Diodes Around 1.55 μm With Large Operating Regime

Abstract

Passive mode-locking in two-section InAs/InP quantum dot laser diodes operating at wavelengths around 1.55 µm is reported. For a 4.6-GHz laser, a large operating regime of stable mode-locking, with RF-peak heights of over 40 dB, is found for injection currents of 750 mA up to 1.0 A and for values of the absorber bias voltage of 0 V down to −3 V. Optical output spectra are broad, with a bandwidth of 6-7 nm. However, power exchange between different spectral components of the laser output leads to a relatively large phase jitter, resulting in a total timing jitter of around 35 ps. In a 4-mm-long, 10.5-GHz laser, it is shown that the operating regime of stable mode-locking is limited by the appearance of quantum dot excited state lasing, since higher injection current densities are necessary for these shorter lasers. The output pulses are stretched in time and heavily up-chirped with a value of 16-20 ps/nm. This mode of operation can be compared to Fourier domain mode-locking. The lasers have been realized using a fabrication technology that is compatible with further photonic integration. This makes such lasers promising candidates for, e.g., a coherent multiwavelength source in a complex photonic chip.

Dual-wavelength passive and hybrid mode-locking of 3, 45 and 10 GHz InAs/InP(100) quantum dot lasers

“…The coupling is attributed to spectral energy exchange between optical modes. The observations are consistent with the results presented in [9]. We verify the pulsed operation of both mode groups further in the next section by investigation of time traces.…”

“…The negative chirp was verified when the chirp was (almost) compensated for by using length sections of single mode fibers with normal dispersion. The results presented in this paper complement and extend the previously reported results on the 4.6GHz laser [9,23]. Comparing the chirp results of the different devices gives some insight into the dynamics when the operating current density and roundtrip losses are considered.…”

“…Such devices generate elongated pulses with a relatively wide, i.e. 8nm, optical bandwidth [8,9]. Our observations have demonstrated operating regimes that have outputs which look similar to FM locking [10] and our devices show different ML properties in comparison with InGaAs/GaAs QD-based lasers.…”

“…In case of the 3GHz laser, we can apply a 6GHz real-time oscilloscope. This allows for a study of the purely passively mode-locked state similar to the way presented in [9]. This will also allow us a comparison with (more accurate) results from hybrid modelocking in the next section 5.2.…”

“…To evaluate the value of chirp in devices under test, a similar approach as reported in [9] is adopted. A schematic of the measurement setup is shown in Fig.…”