有机光子晶体耦合腔波导中的高效慢光与高归一化延迟带宽比

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本文是一篇发表在《应用光学》(Applied Optics)第59卷第3/2期(2020年1月20日)的研究论文，标题为"有机光子晶体耦合腔波导中的高正常化延迟-带宽产品慢光"。作者是洪武、沈康汉、冯丽和张志宏，他们来自江苏省新能源工程技术实验室和南京邮电大学科学学院。研究主要关注的是在有机基底上构建的光子晶体耦合腔波导，这种新型结构能够实现高效、低群速度色散的慢光传播。正常化的延迟-带宽产品是一个重要的性能指标，它衡量了系统的带宽扩展与信号延迟之间的平衡。在这个研究中，通过优化结构参数，研究人员成功将正常化的延迟-带宽产品提升到了一个显著的值，即0.809，这意味着在保持信号质量的同时，信号可以以极低的速度传递，这对于光通信和光存储等领域具有潜在应用价值。此外，该优化后的耦合腔波导还展现出良好的可调性，这意味着设计者可以根据实际需求灵活调整系统的性能参数，这在实现定制化光子设备和集成光子系统中显得尤为重要。群速度色散被控制在10^4(ps^2/km)的低水平，进一步减小了信号失真的可能性，确保了信息传输的高速度和准确性。这项工作对理解和控制光的传播特性，特别是在有机材料平台上的光子学调控具有重要意义，为未来的光电子学和量子信息处理技术提供了新的设计思路和实验依据。整体而言，这篇论文不仅展示了理论上的突破，也为实验层面的实际应用提供了理论支持。

642 Vol. 59, No. 3 / 20 January 2020 / Applied Optics

Research Article

Slow light with high normalized delay–bandwidth

product in organic photonic crystal coupled-cavity

waveguide

Hong Wu,

* Shengkang Han,

Feng Li,

AND Zhihong Yang

1,2

New Energy Technology Engineering Laboratory of Jiangsu Province & School of Science, Nanjing University of Posts and Telecommunications

(NJUPT), Nanjing 210023, China

e-mail: yangzhihong@njupt.edu.cn

*Corresponding author: wuhong@njupt.edu.cn

Received 28 October 2019; revised 19 December 2019; accepted 19 December 2019; posted 20 December 2019 (Doc. ID 381562);

published 14 January 2020

In this theoretical study, a photonic crystal coupled-cavity waveguide created on polymer substrate was demon-

strated to provide high-performance slow light with low group-velocity dispersion and large normalized

delay–bandwidth product. Combined with structural-parameter optimization, the normalized delay–bandwidth

product was enhancedto a large value of 0.809, and the group-velocity dispersion was on the order of 10

(ps

/km).

Furthermore, the optimized coupled-cavity waveguide had tunability capabilities by changing the external pump

laser power. Importantly, while adjusting the slow light, the normalized delay–bandwidth product values remained

America

https://doi.org/10.1364/AO.381562

1. INTRODUCTION

Recently,slow light with an extraordinary low group velocity has

become a hot topic thanks to its promising properties in time-

domain optical signal processing and spatial compression of

optical energy, which are beneﬁcial for all-optical communica-

tions and nonlinear optical effects. Among all the technologies

to realize slow light, photonic crystal waveguides (PCWs) have

attracted much attention since they support room-temperature

operation, and the corresponding devices are compatible

with on-chip integration. Many theoretical and experimental

investigations show that PCWs lead to impressive results, par-

ticularly in line-defect waveguides [1–15] and coupled-cavity

waveguides (CCWs) [16–21].

There are several important and not always independent

parameters to evaluate the slow light effect. The group index

= c/v

, with v

being the group velocity, is the slow-down

factor of light propagating in PCWs compared with that in

vacuum. Considering the pulsed operation, n

should remain

at a constant value in a certain bandwidth, i.e., group velocity

dispersion (GVD) should be as small as possible, avoiding the

problem of pulse broadening and distortion. Meanwhile, a wide

useful bandwidth for a ﬁxed n

with small GVD is very neces-

sary for realistic systems. However, there is a tradeoff between n

and bandwidth in that increasing the former results in decrease

of the latter. To combine these two parameters, many researchers

focus on improving normalized delay–bandwidth product

(NDBP), which is deﬁned as the product of n

and normalized

bandwidth.

In view of these parameters, the PC CCWs used so far have

some advantages and disadvantages. One advantage is that a

high group index of up to 3000 can be obtained by placing

multiple cavities on a row [22]. However, the typically narrow

bandwidth and small NDBP value will limit the application of

slow light in buffering devices. To solve this problem, various

structures optimized by changing the radius or position of

certain defects have been reported [17–23]. So far, slow light

with NDBP around 0.6 and GVD less than 10

(ps

/km)

can be obtained in CCW systems [20]. However, as reported

in Ref. [20], to adjust n

and the working bandwidth, the

structural parameters must be changed. Therefore, it is still a

challenge to adjust the slow light performance while keeping the

structure unchanged.

In fact, for many practical applications, it is desirable that the

slow light properties be adjusted after the device is fabricated.

For example, optical buffers need to store and release optical

data under an external command. Recently, a novel way to

realize the dynamic modulation of PC devices by the optical

nonlinearity of inﬁltrated polymers has been proposed. The

basic idea is to modify the refractive index of polymers using a

pump laser and electrical ﬁeld according to the nonlinear Kerr

effect. Many theoretical and experimental works indicate that

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