A transfer-matrix technique is used to calculate the lasing thresholds of second-order circular-grating polymer lasers operating at 630 nm. By use of poly[2-methoxy-5-(2Ј-ethyl-hexyloxy)-p-phenylenevinylene] as an example polymer material, it is also shown how known optical properties of polymeric materials may be incorporated into the analysis of both the transverse waveguiding and the distributed feedback in circular-grating distributed-feedback polymer lasers.

We explore the influence of grating characteristics on the lasing performance of polymer circular-grating distributed-feedback lasers. A range of circular-grating sizes and profiles were fabricated on a single silica substrate, which was coated with a thin film of the conjugated polymer poly͓2-methoxy-5-͑2'ethylhexyloxy͒-1,4-phenylene vinylene͔. Variations in lasing threshold and surface-emitted slope efficiency were determined as a function of grating outer diameter and duty cycle. The experimental lasing results are compared with predictions from a theoretical analysis based on an adaptation of the transfer matrix method. We find that an outer diameter of at least 200 m is required to minimize the threshold and optimize the surface-emitted slope efficiency. A groove-to-period duty cycle of ϳ25% gives the lowest lasing thresholds by optimizing the in-plane feedback. We also find that the structure of the polymer-air surface varies substantially with substrate duty cycle, which has implications for optimum device design.

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.

No abstract

No abstract