Voltage tuning of gain spectra in quantum cascade lasers

The voltage tuning of gain spectra in three types of Quantum Cascade laser designs is investigated. The gain spectra of the luminescence device are tunable over the whole voltage operation range for all designs. The lasers are as tunable as the electroluminescence below threshold, while a reduced tunability is observed in all lasers above threshold. This is attributed to the decrease of resistance across the laser active region as the photon density increases. A resumed tunability high above threshold occurs in all lasers based on the anti-crossed designs. Lasers based on the anti-crossed diagonal transition are tunable above threshold, with a tuning range of about 40 cm^-1 (∼4% of the laser emission wavenumber) at room temperature, i.e. a tuning rate of 800 cm^-1 per volt per period of active region and injector.