Modulation dynamic response of optical-injection-locked wavelength-tunable semiconductor laser diodes

The effect of optical injection locking (OIL) on modulation dynamics of tunable laser diodes (TLDs) is investigated. The stable locking boundary map of OIL TLD which depends on the lasing wavelength was calculated and the TLD response in different injection states was investigated. Dramatic change in the emission spectra and the relaxation oscillation frequency (ROF) and huge improvement of these characteristics under OIL is demonstrated. Effect of the OIL parameters (frequency detuning and power ratio) on the TLD dynamics was studied for different tuning wavelengths. We show that forward optical injection and positive frequency detuning and blue-wavelength tuning are preferable regimes for enhanced modulation performance of OIL TLDs. Large increase of the ROF (>20GHz) and the modulation bandwidth (>25GHz) of the OIL TLD are demonstrated. The novel feature of the modulation response of the OIL TLD compared with usual single-mode lasers emitting at a fixed wavelength is the frequency dispersion of the differential gain in TLDs which increases with wavelength tuning. It is shown that the differential gain increase with wavelength tuning and the optical injection effect on the cavity resonance frequency shift contribute to a substantial enhancement of the modulation response of the OIL TLD.