Coupling length variation and multi-wavelength
demultiplexing in photonic crystal waveguides
Ziming Wang (王梓名)
1
, Kang Su (苏 康)
1
, Bo Feng (冯 波)
1
, Tianhua Zhang (张天华)
2
,
Weiqing Huang (黄维清)
1
, Weicheng Cai (蔡伟成)
1
, Wei Xiao (肖 威)
1
,
Hongfei Liu (刘鸿飞)
1
, and Jianjun Liu (刘建军)
1,
*
1
Key Laboratory for Micro-/Nano- Optoelectronic Devices of Ministry of Education, School of Physics and Electronics,
Hunan University, Changsha 410082, China
2
SK Hynix Memory Solutions, 3103 North First Street, San Jose, CA 95134, USA
*Corresponding author: jianjun.liu@hnu.edu.cn
Received June 18, 2017; accepted September 22, 2017; posted online November 7, 2017
In this Letter, the effects of material/structure parameters of photonic crystal (PhC) parallel waveguides on
the coupling length are investigated. The results show that, increasing the effective relative permittivity of
the PhC leads to a downward shift of the photonic bandgap and a variation of the coupling length. A compact
PhC 1.31/1.55 μm wavelength division multiplexer (WDM)/demultiplexer with simple structure is proposed,
where the output power ratios are more than 24 dB. This WDM can multiplex/demultiplex other light waves
efficiently.
OCIS codes: 130.5296, 060.4510, 060.4230, 250.5300.
doi: 10.3788/COL201816.011301.
In the past decades, due to the photonic bandgap (PBG)
and the ability to control electromagnetic wave propaga-
tion, photonic crystals (PhCs) made from micro-/
nanoscale periodic dielectric materials have been inten-
sively studied and employed to develop novel photonic
devices for photonic integrated circuits (PICs)
[1–5]
. PhC
waveguides, formed by introducing a linear defect into
a perfect PhC structure, is one of the essential ingredients
in PICs. 2D PhC waveguides were proposed
[6]
and demon-
strated experimentally
[7,8]
. Based on this structure, many
components such as Mach–Zehnder devices
[9]
, filters
[10,11]
,
modulators
[12]
, detectors
[13]
, sensors
[14]
, and directional cou-
plers
[15]
can be created. A primary PhC directional coupler
is formed by introducing two parallel linear defects into
PhCs close to each other. Using the PhC coupler, devices
like optical switches
[16,17]
, optical diodes
[18]
, and wavelength
division multiplexer (WDM)/demultiplexers
[19]
can be
built.
Up to now, many kinds of PhC WDMs/demultiplexers
have been proposed
[20–29]
. Many of them are designed for
1.31/1.55 μm channels
[20–27]
. For the design of PhC 1.31/
1.55 μm WDMs, three factors shou ld be considered. First,
this device should be compact and the coupling length
should be short enough to fit the PICs. Second, the trans-
mission and the output power ratios (OPRs) (or cross talk,
extinction ratios) should be improved as high as possible
to make the device efficient and reliable. Last, the struc-
ture should be simple to make the fabrication easy. The
previously proposed PhC 1.31/1.55 μm WDMs are be
listed in Table
1. As shown in Table 1, there are some im-
provements from the previous work, such as only being
used to demultiplex as in Ref. [
21], difficult to fabricate
the structure of the resonator as in Ref. [
23] and 1D-2D
hybrid PhC waveguides as in Ref. [
26], easy to result in
the power leakage with self-imaging waveguides as in
Ref. [
25], and the coupling length is long as in Ref. [27].
In general, the previously proposed PhC WDMs are lim-
ited to operating only 1.31 and 1.55 μm wavelengths and
cannot be applied to multiplex/demultiplex other telecom
wavelengths. In addition, the effects of material/structure
parameters of PhC waveguides on the coupling length for
both the 1.31/1.55 μm wavelengths were not investigated.
The deduced optimal parameters from these parameter-
effect relations will be helpful in the fabrication of the
PhC waveguides and the PhC WDMs.
Therefore, in this Letter, the material/structure param-
eter dependence on the coupling length is investigated and
Table 1. Some Previous PhC 1.31/1.55 μm WDMs
Refs.
OPRs
(dB)
L
c
(μm) Func. Str.
[
21]162–3 Demux Loop
[
23] 15 5 Mux/Demux Resonator/
Loop
[
25] 17 10 Mux/Demux Periodic
dielectric self-
imaging
waveguides
[
26] 25.8/22.9 14 Mux/Demux 1D-2D hybrid
PhC
waveguides
[
27] NA 19 Mux/Demux Multimode
interference
waveguides
COL 16 (1), 011301(2018) CHINESE OPTICS LETTERS January 10, 2018
1671-7694/2018/011301(5) 011301-1 © 2018 Chinese Optics Letters