Gupta Greeshma, Kuo Ying-Hao, Tazawa Hidehisa, Steier William H, Stapleton Andrew, O'Brien John D
Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089-0483, USA.
Appl Opt. 2009 Oct 1;48(28):5324-36. doi: 10.1364/AO.48.005324.
We describe postfabrication trimming of coupling in both laterally and vertically coupled polymer microring resonators (MRRs), using photobleaching. For both cases, a tapered directional-coupler-based simple analytical model is developed to simulate the change in coupling due to a bleaching-induced decrease in refractive index. A tightly focused laser beam spot (a few kilowatts per square centimeter) is used to precisely bleach the coupling region alone. Coupling control is achieved for (1) high-Q passive rings by bleaching the vertically coupled chromophore-doped bus waveguide, and for (2) laterally coupled electro-optic ring modulators, by bleaching both the ring and the waveguide in the coupling region. The power coupling ratio (PCR) of an undercoupled high-Q MRR filter is reduced by 0.54 percentage points for the TE mode, causing the MRR finesse to increase from a value of 72 to 108. For a ring modulator, the PCR was increased by 3.5 percentage points for the TM mode, causing a 6 dB increase in extinction ratio, to achieve a final value of nearly 25 dB. Phase/group-delay characterization confirmed that the ring was trimmed toward critical coupling.
我们描述了利用光漂白对横向和垂直耦合的聚合物微环谐振器（MRR）中的耦合进行制造后微调的方法。对于这两种情况，都建立了基于锥形定向耦合器的简单分析模型，以模拟由于漂白导致折射率降低而引起的耦合变化。使用紧密聚焦的激光束光斑（每平方厘米几千瓦）精确地单独漂白耦合区域。通过漂白垂直耦合的发色团掺杂总线波导，实现了对（1）高Q值无源环的耦合控制；通过漂白耦合区域中的环和波导，实现了对（2）横向耦合电光环调制器的耦合控制。对于欠耦合的高Q值MRR滤波器，TE模式的功率耦合比（PCR）降低了0.54个百分点，使得MRR的精细度从72增加到108。对于环形调制器，TM模式的PCR增加了3.5个百分点，消光比增加了6dB，最终达到近25dB的值。相位/群延迟特性表征证实，该环已调整至临界耦合状态。
