External-cavity quantum-dot laser tunable through 1.55 μ m

The optical performance of external-cavity lasers based on InAs ∕ InGaAsP quantum dot laser diodes is investigated. The broad electroluminescence reveals a gain spectrum with full width at half maximum of at least 175 nm . By fabricating as-cleaved ridge lasers of different length and width, tuning ranges as high as 110 nm have been achieved at wavelengths encompassing 1.55 μ m . The tuning ranges and efficiencies obtained are limited by internal losses and competition between the external-cavity lasing modes and the laser diode natural lasing modes. The laser diode length is found to affect both the wavelength tuning range and the threshold current density, which is consistent with a quantum-dot type density of states.