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It is shown that optical synthesis of terahertz and millimeter-wave frequencies can be achieved using two-mode and mode-locked discrete mode diode lasers. These edge-emitting devices incorporate a spatially varying refractive index profile which is designed according to the spectral output desired of the laser. We first demonstrate a device which supports two primary modes simultaneously with high spectral purity. In this case sinusoidal modulation of the optical intensity at terahertz frequencies can be obtained. Cross saturation of the material gain in quantum well lasers prevents simultaneous lasing of two modes with spacings in the millimeter-wave region. We show finally that by mode-locking of devices that are designed to support a minimal set of four primary modes, we obtain a sinusoidal modulation of the optical intensity in this frequency region.

The wavelength switching dynamics of two-colour semiconductor lasers with optical injection and feedback are presented. These devices incorporate slotted regions etched into the laser ridge waveguide for tailoring the output spectrum. Experimental measurements are presented demonstrating that optical injection in one or both modes of these devices can induce wavelength bistability. Measured switching dynamics with modulated optical injection are shown to be in excellent agreement with numerical simulations based on a simple rate equation model. We also demonstrate experimentally that time-delayed optical feedback can induce wavelength bistability for short external cavity lengths. Numerical simulations indicate that this two-colour optical feedback system can provide fast optical memory functionality based on injected optical pulses without the need for an external holding beam.

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