Broad-band self-injection organic laser amplifier based on a DBR microcavity

Abstract

We report a thin-film laser amplifier based on a microcavity scheme using distributed Bragg reflectors (DBR). The amplifier is fabricated on the front surface of a glass substrate, whereas, an aluminum (Al) layer is deposited on the back surface, which supplies optical feedback for broadband injection into the amplifier. The Bragg gratings acting as the reflectors for the microcavities are fabricated by interference lithography and the active layer of super-yellow light-emitting PPV copolymer (SY-PPV) is spin-coated onto the top surface, forming a periodical array of DBR microcavities filling with SY-PPV. The broadband reflection by the Al layer is coupled again into the microcavity through the photoresist Bragg gratings and is coupled out of the microcavities after multiple rounds of regenerative amplification. A power amplification factor larger than 22 has been achieved for such a microcavity laser amplifier, so that an average power of about 16 μW (16 nJ in pulse energy) has been measured at the output of the amplifier for a pump fluence of 35 μJ cm⁻². Considering that the optical feedback scheme using the high-reflection Al film for the amplifier is also a part of the DBR oscillators, we define such an amplifier as a self-injection-locked laser amplifier device. Thus, the amplification process also has a pump threshold, which is apparently much lower than that of the oscillator, since the injection supplies additional optical feedback. This work proposes a new design both for organic thin-film laser devices and for microcavity laser amplifiers, which is important for integrated photonic and optoelectronic systems.