Photonic integrated technology for multi-wavelength laser emission
CHEN XiangFei
2
LIU Wen
1
AN JunMing
0
LIU Yu
0
XU Kun
3
WANG Xin
0
LIU JianGuo
0
JI YueFeng
3
ZHU NingHua
)
0
0
Institute of Semiconductors, Chinese Academy of Sciences
,
Beijing 100083, China
1
State Key Laboratory of Optical Communication Technologies and Networks, Wuhan Research Institute of Posts & Telecommunications
, Wuhan 430074,
China
2
National Laboratory of Microstructures, Nanjing University
, Nanjing 210093,
China
3
Institute of Optical Communication and Optoelectronics, Beijing University of Posts and Telecommunications
,
Beijing 100876, China
We summarized the design, fabrication challenges and important technologies for multi-wavelength laser transmitting photonic integration. Technologies discussed include multi-wavelength laser arrays, monolithic integration and modularizing coupling and packaging. Fabrication technique requirements have significantly declined with the rise of reconstruction-equivalent-chirp and second nanoimprint mask technologies. The monolithic integration problem between active and passive waveguides can be overcome with Butt-joint and InP array waveguide grating technologies. The dynamic characteristics of multi-factors will be simultaneously measured with multi-port analyzing modules. The performance of photonic integration chips is significantly improved with the autoecious factors compensation packaging technique.
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Photonic integrated circuits (PICs) are important for
realizing large-capacity and low-energy consumption future
optical networks. In PICs, parallel photonic integrated chips
with multi-wavelength laser emission will become
important for high-speed data transmission, and with
largescale photonic integration, will undertake similar tasks to
integrated circuits. Thus, PIC has received much recent
research attention. Since 2004, the United States, Europe and
Japan have launched large-scale research projects involving
photonic integration, including the IRIS and LASOR
projects in the United States, the EuroPIC, PLATON and
HELIOS projects in Europe and the PiFAS project in
Ireland. The world pioneer in PIC technology is the Infinera
Corporation from the United States. They have developed
PIC-based wavelength division multiplexing (WDM)
transmission equipment, which is now commercially
available. The Infinera PIC chip is realized through the
integration of more than 50 discrete functions in a single
monolithic chip.
The structure of a PIC with multi-wavelength laser
transmitter is shown in Figure 1. The chip is constructed of
a multi-wavelength laser array, modulator array, light
detector array for monitoring optical power, semiconductor
optical amplifier (SOA) array for power balancing and
WDM combiner (usually an array waveguide grating
(AWG)). Although the technology for discrete components
is largely mature in commercial applications, it still remains
a significant challenge to integrate these different functional
optoelectronic devices into a single chip. There are many
scientific and technical challenges, including the
preparation compatibility issues for different functional micro-nano
structures, the multi-wavelength laser emission that meets
the requirement of ITU-T specifications, the laser mode
stability, and laser mode crosstalk problems caused by the
The Author(s) 2011. This article is published with open access at Springerlink.com
Figure 1 Integrated chip for multi-wavelength laser transmitter.
interaction of microwaves and light waves inside the chip.
Light detector array, SOA array and WDM combination
in PICs is well advanced and will not be further discussed
here. However, there is a big difference between
multiwavelength laser arrays and single-channel lasers, and many
important issues need to solve. For example, to achieve
accurate 100 GHz wavelength spacing, a grating period
spacing of 0.12 nm is necessary. Traditional holographic
exposure to fabricate gratings cannot meet these demanding
requirements to achieve the precise control of the lasing
wavelength. Point-by-point writing techniques using
highprecision electron beam (E-beam) lithography can achieve a
precision of 0.1 nm. However, this technology has a long
writing time, high cost, low yield and poor reproducibility.
E-beam lithography is a useful laboratory tool but
unsuitable for large-scale commercial applications [1]. The Infinera
Corporation uses selective area growth (SAG) method to
control the structural parameters of the active layer of each
laser, including thickness and material components. Fine
wavelength alignment in the multi-wavelength laser array
can be realized through micro-heating resistors to adjust the
temperature of individual lasers [2]. However, this method
is costly and unable to meet the requirements of low-cost
and large-scale production.
To solve these important technology issues for chips with
multi-wavelength laser emission, innovative design is
necessary. Based on the epitaxial growth of different band
structures, low-cost large-scale PIC product (...truncated)