Photonic switching in AlGaAs large optical cavity laser structures

Abstract

In a large optical cavity (LOC) diode laser structure, a relatively thick (2 μm) and lightly doped waveguide layer is grown adjacent to the laser's active layer. Such a structure is attractive for use as an optical waveguide device or a dual mode laser/detector.1 In this experiment an AlGaAs liquid phase epitaxy grown LOC structure was used as a photonic switch, employing the Franz-Keldysh effect. The electric field-induced shift in the absorption edge was measured by recording the transmission spectrum of 1.5-mm long waveguides for different reverse bias voltages. Based on this, a diode laser operating at a wave length of 890 nm was selected to be used as a probe. Its transmission through the waveguide was reduced by a factor of 20 as the reverse bias voltage was increased from 0 to 8 V. The photocurrent, measured simultaneously, increased by a similar factor. All optical switching was investigated by combining a λ = 810-nm switching beam with the probe beam in the single-mode input optical fiber. With the diode reverse biased to a normally off condition, 100 gW of power at 810 nm switched the waveguide to an on state, increasing its transmission by a factor of 3.