A high-order external distributed feedback polymer laser with low working threshold

Abstract

In this paper, we report a high-order distributed feedback (DFB) polymer laser with low working threshold. Using the high-order grating increases the lithographic tolerances, providing coherent light sources that are more amenable to mass-manufacturing techniques, such as laser direct writing lithography and roll-to-roll processing. To enable high-order DFB lasing, an unconventional working configuration is designed in which the grating is situated on top of the uniform conjugated polymer film. In addition, a novel Forster energy transfer blend of two conjugated polymers is used as the gain medium. Upon pumping, the device emits lasing around 603.6 nm with a bandwidth of 0.5 nm. The threshold is around 20.5 μJ cm−2 (~2.56 kW cm−2), about to enter the regime of inexpensive LED pumping. A further increase in pump energy results in simultaneous oscillations at the 29th and 30th Bragg orders. Operating principles of the high-order DFB polymer laser, including spectral performance and threshold dependence on pump length, are investigated. This approach represents a step towards low-cost, even ‘disposable’ polymer lasers.