Effect of gain localization in circular-grating distributed feedback lasers

Abstract

We explore the influence of gain localization on the lasing performance of circular-grating distributed feedback ͑CDFB͒ lasers. The effect is studied in an optically pumped CDFB laser resonator based on a waveguide of the conjugated polymer poly͓2-methoxy-5-͑2Јethylhexyloxy͒-1,4-phenylene vinylene͔. Variations in lasing threshold and slope efficiency are determined as a function of the radius of the optical excitation. The experimental lasing results are compared with predictions from a theoretical analysis based on an adaptation of the transfer matrix method. We find that a strong localization of the gain near the center of the CDFB laser can lead to both a substantial reduction in threshold and increase in output efficiency. As the excitation radius changes from a 90 to a 15 m radius, the threshold energy decreases from 5.3 to 0.29 nJ, and the surface-emitted output efficiency increases by an order of magnitude. A simple model is developed that confirms that the significant reduction in threshold can be explained by an enhanced overlap of the population inversion with the resonant mode.

Surface-Emitting Circular Bragg Lasers – A Promising Next-Generation On-Chip Light Source for Optical Communications

“…In practical situations, the pumping profile is usually nonuniform, distributed either in a Gaussian shape in optical pumping (Olson et al, 1998;Scheuer et al, 2005a) or in an annular shape in electrical pumping (Wu et al, 1994). The effects of nonuniform pumping have been investigated theoretically (Kasunic et al, 1995;Greene & Hall, 2001) and experimentally (Turnbull et al, 2005) for circular DFB lasers. In this subsection we will study and compare the nonuniform effects on the three types of surface-emitting circular Bragg lasers.…”

“…With a more rigorous theoretical framework, Shams-Zadeh-Amiri et al analyzed their above-threshold properties and radiation fields (Shams-Zadeh-Amiri et al, 2000. More recently, organic polymers are also used as the gain medium for these lasers due to their low fabrication cost (Jebali et al, 2004;Turnbull et al, 2005;Chen et al, 2007). The circular gratings in the above-referenced work are designed radially periodic.…”

Surface-emitting circular DFB, disk-, and ring-Bragg resonator lasers with chirped gratings III: gain saturation effects and above-threshold analysis

“…A comparison of this expression with the first term on the left-hand side of Eq. (4) indicates that all the power terms are in units of the saturation power 2 sat sat 4 . P E D β ≡…”

“…Wu et al were the first to experimentally realize such lasers in semiconductors [2]. More recently, organic polymers are also used as the gain medium for these lasers due to their low fabrication cost [3][4][5].…”

“…In previous parts of this paper series [7,8], we have solved the modes and compared the modal properties, by both analytical and numerical approaches, of the three types of lasers at threshold. Gain saturation effects in above-threshold operation were previously studied in both linear and circular DFB and DBR lasers [4,[9][10][11][12]. This paper presents an abovethreshold analysis for the three types of radially chirped circular grating lasers to investigate their energy conversion efficiency, intensity-dependent modal selectivity, and optimal design.…”