Low-power photonic components for optical interconnects
Author(s):
Po Dong;
Shirong Liao;
Hong Liang;
Ning-Ning Feng;
Wei Qian;
Roshanak Shafiiha;
Dazeng Feng;
Guoliang Li;
Xuezhe Zheng;
John E. Cunningham;
Ashok V. Krishnamoorthy;
Mehdi Asghari
Show Abstract
Silicon-based optical interconnects are expected to provide high bandwidth and low power consumption solutions for
chip-level communication applications, due to their electronics integration capability, proven manufacturing record and
attractive price volume curve. In order to compete with electrical interconnects, the energy requirement is projected to be
sub-pJ per bit for an optical link in chip to chip communication. Such low energies pose significant challenges for the
optical components used in these applications. In this paper, we review several low power photonic components
developed at Kotura for DARPA's Ultraperformance Nanophotonic Intrachip Communications (UNIC) project. These
components include high speed silicon microring modulators, wavelength (de)multiplexers using silicon cascaded
microrings, low power electro-optic silicon switches, low loss silicon routing waveguides, and low capacitance
germanium photodetectors. Our microring modulators demonstrate an energy consumption of ~ 10 fJ per bit with a drive
voltage of 1 V. Silicon routing waveguides have a propagation loss of < 0.3 dB/cm, enabling a propagation length of a
few tens of centimeters. The germanium photodetectors can have a low device capacitance of a few fF, a high
responsivity up to 1.1 A/W and a high speed of >30 GHz. These components are potentially sufficient to construct a full
optical link with an energy consumption of less than 1 pJ per bit.
Grating-coupler-based optical proximity coupling for scalable computing systems
Author(s):
Jin Yao;
Xuezhe Zheng;
Guoliang Li;
Ivan Shubin;
Ying Luo;
Hiren Thacker;
Attila Mekis;
Thierry Pinguet;
Subal Sahni;
Kannan Raj;
John E. Cunningham;
Ashok V. Krishnamoorthy
Show Abstract
Silicon photonics is envisioned as a promising solution to address the interconnect bottleneck
in large-scale multi-processor computing systems, owing to advantageous attributes such as wide
bandwidth, high density, and low latency. To leverage these advantages, optical proximity coupler is
one of the critical enablers. Chip-to-chip, layer-to-layer optical proximity couplers with low loss,
large bandwidth, small footprint and integration compatibility are highly desirable. In this paper, we
demonstrate chip-to-chip optical proximity coupling using grating couplers. We report the
experimental results using grating couplers fabricated in a photonically-enabled commercial 130nm
SOI CMOS process.
Evaluation of graded index glass waveguides for board-level WDM optical chip-to-chip communications
Author(s):
J. Schrage;
O. Stuebbe;
L. Brusberg;
Y. Soenmez;
H. Schroeder;
R. Schuhmann
Show Abstract
A Proof-of-Concept for a multi-channel WDM board-level optical communications link is under development. This
paper is focusing on theoretical and experimental evaluation of thin-glass based nearly single mode graded index optical
waveguides with regard to low loss in the 1310nm regime. Results from waveguide characterization will be reported.
Waveguide modes are determined theoretically from the measured refractive index profiles. Towards improvement of
the robustness of the coupling efficiency against misalignments, investigations on the use of tapered waveguide
structures will be presented too.
PCB with fully integrated optical interconnects
Author(s):
Gregor Langer;
Valentin Satzinger;
Volker Schmidt;
Gerhard Schmid;
Walter R. Leeb
Show Abstract
The increasing demand for miniaturization and design flexibility of polymer optical waveguides integrated into electrical
printed circuit boards (PCB) calls for new coupling and integration concepts.
We report on a method that allows the coupling of optical waveguides to electro-optical components as well as the
integration of an entire optical link into the PCB. The electro-optical devices such as lasers and photodiodes are
assembled on the PCB and then embedded in an optically transparent material. A focused femtosecond laser beam
stimulates a polymerization reaction based on a two-photon absorption effect in the optical material and locally increases
the refractive index of the material. In this way waveguide cores can be realized and the embedded components can be
connected optically. This approach does not only allow a precise alignment of the waveguide end faces to the
components but also offers a truly 3-dimensional routing capability of the waveguides.
Using this technology we were able to realize butt-coupling and mirror-coupling interface solutions in several
demonstrators. We were also manufacturing demonstrator boards with fully integrated driver and preamplifier chips,
which show very low power consumption of down to 10 mW for about 2.5 Gbit/s. Furthermore, demonstrators with
interconnects at two different optical layers were realized.
Optical loss characterization of polymer waveguides on halogen and halogen-free FR-4 substrates
Author(s):
Brandon W. Swatowski;
Christopher T. Middlebrook;
Karl Walczak;
Michael C. Roggemann
Show Abstract
In order to characterize and optimize the overall link budget for an optical communication channel, the absorption loss
of the waveguides must be well known, stable, and minimized. Research and characterization has been performed to
ascertain the impact of the use of halogen vs. halogen free FR-4 circuit boards. Halogen is utilized within glass resin
epoxy circuit boards as a flame retardant. An analysis of rectangular multi-mode polymer waveguide structures, with a
fixed core dimension of 50 μm × 50 μm, was done to characterize the effects of the halogen FR-4 on the absorption
loss. Thermal cycling times were varied in order to determine the relationship between heating of the polymer
material, halogen diffusion into the optical cladding and core layer, and optical losses.
20 Gbps optical link with high-efficiency 1060 nm VCSEL
Author(s):
Jean Benoit Héroux;
Keishi Takaki;
Masao Tokunari;
Shigeru Nakagawa
Show Abstract
Measurement results of a high speed, low power single channel optical link operating at 1060 nm are presented. The link
is composed of low power VCSEL devices fabricated and provided by Furukawa Electric Co. Ltd. and a low cost OM2
fiber. Clear eye openings are observed at 20 Gbps with a 2 mA DC bias. A modulation voltage of 150 mVp-p results in a
-4.1 dBm OMA at the fiber output in a back-to-back configuration, with 0.19 unit amplitude eye opening and 32 ps total
jitter extrapolated to a 10-12 bit error ratio. The insertion of a 100 m-long OM2 fiber causes a small signal degradation
due to low attenuation and dispersion. For an ideal index profile optimized for dual wavelength operation (850 and
1300 nm), the minimum modal dispersion of the fiber is in the vicinity of the current operation wavelength.
Hybrid-integrated silicon photonic bridge chips for ultralow-energy inter-chip communications
Author(s):
Hiren D. Thacker;
Ivan Shubin;
Ying Luo;
Joannes Costa;
Jon Lexau;
Xuezhe Zheng;
Guoliang Li;
Jin Yao;
Dinesh Patil;
Frankie Liu;
Ron Ho;
Thierry Pinguet;
Po Dong;
Dazeng Feng;
Mehdi Asghari;
Kannan Raj;
James G. Mitchell;
Ashok V. Krishnamoorthy;
John E. Cunningham
Show Abstract
We present a hybrid integration technology platform for the compact integration of best-in-breed VLSI and photonic
circuits. This hybridization solution requires fabrication of ultralow parasitic chip-to-chip interconnects on the candidate
chips and assembly of these by a highly accurate flip-chip bonding process. The former is achieved by microsolder bump
interconnects that can be fabricated by wafer-scale processes, and are shown to have average resistance <1 ohm/bump
and capacitance <25fF/bump. This suite of technologies was successfully used to hybrid integrate high speed VLSI chips
built on the 90nm bulk CMOS technology node with silicon photonic modulators and detectors built on a 130nm
CMOS-photonic platform and an SOI-photonic platform; these particular hybrids yielded Tx and Rx components with
energies as low as 320fJ/bit and 690fJ/bit, respectively. We also report on challenges and ongoing efforts to fabricate
microsolder bump interconnects on next-generation 40nm VLSI CMOS chips.
Thin glass based packaging and photonic single-mode waveguide integration by ion-exchange technology on board and module level
Author(s):
Lars Brusberg;
Günter Lang;
Henning Schröder
Show Abstract
The proposed novel packaging approach merges micro-system packaging and glass integrated optics. It provides 3D
optical single-mode intra system links to bridge the gap between novel photonic integrated circuits and the glass fibers
for inter system interconnects. We introduce our hybrid 3D photonic packaging approach based on thin glass substrates
with planar integrated optical single-mode waveguides for fiber-to-chip and chip-to-chip links. Optical mirrors and
lenses provide optical mode matching for photonic IC assemblies and optical fiber interconnects. Thin glass is
commercially available in panel and wafer formats and characterizes excellent optical and high-frequency properties as
reviewed in the paper. That makes it perfect for micro-system packaging. The adopted planar waveguide process based
on ion-exchange technology is capable for high-volume manufacturing. This ion-exchange process and the optical
propagation are described in detail for thin glass substrates. An extensive characterization of all basic circuit elements
like straight and curved waveguides, couplers and crosses proves the low attenuation of the optical circuit elements.
A concept for the assembly and alignment of arrayed microelectronic and micro-optical systems for optical multi-gigabit communication
Author(s):
Fernando Merchán;
Karl-Heinz Brenner
Show Abstract
In the first part of this contribution we present a concept for the fabrication, assembly and alignment of a multichannel
micro optical-coupler and arrayed microelectronic devices placed on a PCB. This concept is based on a micro opticalcoupler
that integrates several optical sub-systems in a monolithic substrate in order to simplify adjustment processes.
The optical-coupler is fabricated by plastic replication of a metal master with the negative shape of the coupler. For the
fabrication on the PCB, only one alignment step is necessary. By placing markers on the PCB it is possible to position
the coupler over the VCSEL or photodiode array. The placement and connections between the electronic devices on the
PCB are taken into account in the design of the coupler. The mechanical assemblies for populating PCBs with electronic
devices have an accuracy of a few micrometers. Using these techniques an optimal position of the coupler relative to the
VCSEL or photodiode array can be found. In the second part we examine with the help of simulations the effect of
misalignment and tilt of the optical surfaces and possible differences between the optical fibers like decentering. Bitrates
of 120 Gbps in a 12-channel system can be reached using this coupler with commercial electronic devices. Applications
for this system are active optical cables and ultra wide-band board to board communication systems. A FPGA-board for
the test of this concept is in the design phase and will be reported.
Packaging technology enabling flexible optical interconnections
Author(s):
Erwin Bosman;
Geert Van Steenberge;
Jeroen Missinne;
Bram Van Hoe;
Sandeep Kalathimekkad;
Peter Van Daele
Show Abstract
This paper reports on the latest trends and results on the integration of optical and opto-electronic devices and
interconnections inside flexible carrier materials. Electrical circuits on flexible substrates are a very fast growing
segment in electronics, but opto-electronics and optics should be able to follow these upcoming trends. This paper
presents the back-thinning and packaging of single opto-electronic devices resulting in highly flexible and reliable
packages. Optical waveguides and optical out-of-plane coupling structures are integrated inside the same layer stack,
resulting in complete VCSEL-to-PD links with low total optical losses and high resistance to heat cycling and moisture
exposure.
Transfer and characterization of silicon nanomembrane-based photonic devices on flexible polyimide substrate
Author(s):
Xiaochuan Xu;
Harish Subbaraman;
Daniel Pham;
Amir Hosseini;
Xiaohui Lin;
Ray T. Chen
Show Abstract
In this paper, we report the transfer and characterization of in-plane silicon nanomembrane based photonic devices on a
Kapton polyimide flexible substrate. Compared with electronic devices and surface normal optical devices, in-plane
photonic devices have stringent requirements on transfer precision because any shift in the position or breakage can
affect the performance of devices. Therefore, a supporting layer consisting of a photoresist is exploited to protect the
device during the transfer process. A modified stamp-assisted transfer technique is employed in order to transfer
nanomembrane devices onto the flexible film and the transfer of large aspect ratio (up to 4000) waveguides and 1x6
multimode interference (MMI) couplers on a flexible Kapton substrate is demonstrated. A two-step cleaving method is
developed in order to prepare the facets of the transferred waveguides and in-plane light coupling into a 60μm wide,
8mm long flexible waveguide from a lensed fiber is demonstrated. This demonstration opens limitless possibilities for a
whole new area of high performance flexible photonic components using silicon nanomembrane technology.
Autonomous and dynamic reconfigurable waveguide for optical interconnection with large shift-tolerance
Author(s):
Atsushi Okamoto;
Kazutaka Hira;
Alexander A. Grabar;
Hisatoshi Funakoshi;
Yuta Wakayama;
Akihisa Tomita
Show Abstract
In order to realize a dynamic reconfiguration technique that automatically switches configurations and functions of an
optical device, we need a technique to control freely the connections of light inside and between devices without needing
submicron-level alignments. In this study, we investigate the behavior of dynamic index gratings with nanoscale
reversible self-organization in Sn2P2S6 crystals that we have newly developed so as to realize an autonomous and
dynamic reconfigurable optical waveguide by externally controlling its motions with light and examine its basic
properties. Experimental results showed autonomous and dynamic reconfigurations of the optical waveguide formed in a
Sb doped Sn2P2S6 crystal with a 4 mm thickness for variations of an incident light position. We have successfully
reconfigured the waveguide by a self-organization based on a photorefractive effect without cutting time series signals
flowing through the waveguide, for variations of an incident light position long as approximately 2000 μm. Furthermore,
we have recognized tolerance up to around 0.2 degrees for incidence angles in the experiment. This technique allows us
to connect light freely without needing spatial adjustments in a nanostructured optical waveguide seen in photonic crystal
fibers. Moreover, it is a technique that can be applied to dynamic connections between optical fibers and integrated
waveguides accompanied with time variations of spatial modes. We also verified a possibility of removable and
replaceable optical connection by utilizing large shift-tolerance of the autonomous and dynamic reconfigurable
waveguide.
Inter-channel crosstalk analysis for W-shaped and graded-index core polymer optical waveguides with ray tracing method
Author(s):
Hsiang-Han Hsu;
Keishiro Shitanda;
Takaaki Ishigure
Show Abstract
For high-density and high-speed optical interconnections using parallel polymer optical waveguides (PPOW), we
theoretically and experimentally demonstrate that W-shaped refractive index profiles in the cores are capable of
decreasing the inter-channel crosstalk compared to step-index (SI) and even to graded index (GI) waveguides. In this
paper, first we analyze the optical characteristics of polymer waveguides with different index profiles by means of the
ray tracing model with scattering effect previously we developed. The calculation results confirm the index valley
surrounding each core works properly for preventing the power coupling from the cladding modes to the propagation
modes. Next, we show the fabrication process (preform method) for such a waveguide, where the cladding material is
composed of a copolymer of methyl methacrylate (MMA) and benzyl methacrylate (BzMA). Compared to a GI-core
PPOW we previously fabricated with the same core material, the 1-m long PPOW with W-shaped refractive index
profile exhibits not only a low propagation loss (0.027 dB/cm), but an even lower inter-channel crosstalk value (-32 dB).
300 Gb/s bidirectional fiber-coupled optical transceiver module based on 24 TX + 24 RX "holey" CMOS IC
Author(s):
Fuad E. Doany;
Clint L. Schow;
Alexander V. Rylyakov;
Benjamin G. Lee;
Christopher Jahnes;
Young Kwark;
Christian Baks;
Daniel M. Kuchta;
Frank Libsch;
Jeffrey A. Kash
Show Abstract
A novel, compact 48-channel optical transceiver module has been designed and fabricated based on a "holey" Optochip
- a single-chip CMOS transceiver IC with 24 receiver and 24 laser driver circuits each with a corresponding throughsubstrate
optical via (hole). The holes enable 24-channel 850-nm VCSEL and photodiode arrays to be directly flip-chip
soldered to the CMOS IC to maximize high-speed performance and facilitate direct fiber-coupling to a standard 4 x 12
MMF array. The Optochips were packaged into complete modules by flip-chip soldering to high-density, high-speed
organic carriers. All 48-channels showed good performance up to 12.5 Gb/s/ch providing a 300 Gb/s bidirectional
aggregate data rate.
Group velocity independent coupling into slow light photonic crystal waveguide on silicon nanophotonic integrated circuits
Author(s):
Che-Yun Lin;
Xiaolong Wang;
Swapnajit Chakravarty;
Wei-Cheng Lai;
Beom Suk Lee;
Ray T. Chen
Show Abstract
Slow light in photonic crystal waveguide can significantly enhance the light-matter interaction, which is a promising
approach toward building ultra-compact photonic devices. However, optical coupling from strip waveguide to slow light
photonic crystal waveguide is challenging due to the group velocity mismatch between these waveguides. This issue can
be addressed by designing a photonic crystal taper that allows the defect guided mode in photonic crystal waveguide to
slow down gradually when it enters the photonic crystal waveguide from strip waveguide, thereby minimizing the group
velocity mismatch. By using the photonic crystal taper design, experimental results show coupling efficiency can be
enhanced by more than 20dB in normal group velocity region with 5dB less fluctuation as compared to the control
group, which does not have photonic crystal taper. Enhancement right before photonic bandgap cutoff can be up to
28dB. Measurement results show excellent agreement with two-dimensional (2D) finite-difference time domain (FDTD)
simulation.
High-density active optical cable: from a new concept to a prototype
Author(s):
Denis Wohlfeld;
Frank Lemke;
Holger Froening;
Sven Schenk;
Ulrich Bruening
Show Abstract
Evolution in high performance computing (HPC) leads to increasing demands on bandwidth, connectivity and flexibility.
Active optical cables (AOC) are of special interest, combining the benefits of electrical connectors and optical
transmission. Optimization and development of AOC solutions requires enhancements concerning different technology
barriers. Area and volume occupied by connectors is of special interest within HPC networks. This led to the
development of a 12x AOC for the mini-HT connector creating the densest AOC available. In order to integrate
electrical optical conversion into a module not higher than 3 mm, a new concept of coupling fibers to VCSELs or
photodiodes had to be developed. This unique concept is based on a direct replication process of an integrated fiber
coupler consisting of a 90° light deflecting and focusing mirror, a fiber guiding structure, and a fiber funnel. The
integrated fiber coupler is directly replicated on top of active components, reducing the distance between active
components and fibers to a minimum, thus providing a highly efficient light coupling. As AOC prototype, multi-chipmodules
(MCM) including the complete electrical to optical conversion for send and receive connected by two 12x fiber
ribbons have been developed. The paper presents the integrated fiber coupling technique and also design and
measurement data of the prototype.
Novel organic-inorganic hybrid materials for optical interconnects
Author(s):
Tetsuo Sato
Show Abstract
Optical materials in the optical printed circuit board are required to overcome soldering process. In detail, the material
should not have absorption and shape changes after several tens of seconds heating at around 250°C. For such
application field, we have developed a novel organic-inorganic hybrid material having a high thermal stability and low
absorption at telecom wavelength.
The material is designed to UV and/or Thermal curable resin, and soluble to popular organic solvents. We fabricated a
rigid optical waveguides on a SiO2/Si wafers by UV lithography. The size of waveguide was 40 μm in width, 30 μm in
height, and 7 cm in length. Optical attenuation of the waveguide measured by the cut back method was 0.1 dB/cm at 850
nm, 0.29 dB/cm at 1310 nm, and 0.45 dB/cm at 1550 nm. These values are good low attenuation for the Near-IR optical
communication. The 5% weight loss temperature of the UV cured material was 402°C. The waveguide showed almost no
attenuation increase even after 1min heating at 300°C.
In addition, the material is having a high refractive index of n=1.60 at 633 nm and a low curing shrinkage of 4.7%. We
have demonstrated to fabricate a bulk body sample by UV curing, and obtained high uniformity cured materials with 5
mm-thick and 1 cm-diameter.
From these properties, the developed organic-inorganic material is expected to be beneficial for the optical
interconnection such as micro lenses and optical packages.
Densely aligned graded-index multiple-core polymer optical waveguide: fabrication and inter-channel crosstalk property
Author(s):
Takaaki Ishigure;
Kenshiro Matsuo;
Yosuke Nitta;
Yusuke Sugimori;
Shin Morikawa
Show Abstract
We present two methods for fabricating densely-aligned graded-index (GI) multiple-core polymer optical waveguides
utilizing soft-lithography and dispensers. For on-board optical interconnects with polymer waveguides, much higher data
rate and channel density have been required in the past few years. However, because of the high scattering loss of
polymer waveguides, their inter-channel crosstalk is of great concern, when narrower pitch is required. Meanwhile, we
have demonstrated low propagation loss and low inter-channel crosstalk of polymer optical waveguides with GI cores
due to the optical confinement effect of the GI-core. Hence, the channel density could be increased for GI multiple-core
waveguides. In this paper, we successfully fabricate a polymer waveguide with GI cores directly on a substrate utilizing
the soft-lithography method or a dispenser. We experimentally confirm that near parabolic refractive index profiles are
formed in the parallel cores with 50 μm x 30 μm size at 125-μm pitch in a length of 20 cm. We also use a copolymer for
forming the GI profile, and then, confirm the high-temperature stability of the parabolic index profile compared to the
one formed with a doped polymer. Finally, we discuss the crosstalk properties of the fabricated waveguides.
Experimental studies of the Franz-Keldysh effect in CVD grown GeSi epi on SOI
Author(s):
Ying Luo;
John Simons;
Joannes Costa;
Ivan Shubin;
Winnie Chen;
Bill Frans;
Mac Robinson;
Roshanak Shafiiha;
Shirong Liao;
Ning-Ning Feng;
Xuezhe Zheng;
Guoliang Li;
Jin Yao;
Hiren Thacker;
Mehdi Asghari;
Keith Goossen;
Kannan Raj;
Ashok V. Krishnamoorthy;
John E. Cunningham
Show Abstract
Electroabsorption from GeSi on silicon-on-insulator (SOI) is expected to have promising
potential for optical modulation due to its low power consumption, small footprint, and more
importantly, wide spectral bandwidth for wavelength division multiplexing (WDM) applications.
Germanium, as a bulk crystal, has a sharp absorption edge with a strong coefficient at the direct
band gap close to the C-band wavelength. Unfortunately, when integrated onto Silicon, or when
alloyed with dilute Si for blueshifting to the C-band operation, this strong Franz-Keldysh (FK)
effect in bulk Ge is expected to degrade. Here, we report experimental results for GeSi epi when
grown under a variety of conditions such as different Si alloy content, under selective versus non
selective growth modes for both Silicon and SOI substrates. We compare the measured FK effect
to the bulk Ge material.
Reduced pressure CVD growth of GeSi heteroepitaxy with various Si content was studied
by different characterization tools: X-ray diffraction (XRD), atomic force microscopy (AFM),
secondary ion mass spectrometry (SIMS), Hall measurement and optical transmission/absorption
to analyze performance for 1550 nm operation. State-of-the-art GeSi epi with low defect density
and low root-mean-square (RMS) roughness were fabricated into pin diodes and tested in a
surface-normal geometry. They exhibit low dark current density of 5 mA/cm2 at 1V reverse bias
with breakdown voltages of 45 Volts. Strong electroabsorption was observed in our GeSi alloy
with 0.6% Si content having maximum absorption contrast of Δα/α ~5 at 1580 nm at 75 kV/cm.
A novel boundary-confined method for microlens arrays fabrication
Author(s):
Hsin-Ta Hsieh;
Vinna Lin;
Guo-Dung John Su
Show Abstract
We present a technique to improve microlens arrays (MLAs) uniformity after the thermal reflow process. Traditional
photo resist thermal reflow processes cause micro lenses merge together easily due to an inexact reflow time and
temperature distribution. This results in poor uniformity and low lens height. A new MLAs fabrication method, called
the boundary-confined method, was proposed and demonstrated. By two tones of photoresist (PR), positive and negative,
only one photo mask and two photolithography steps are needed in the process. After lithography processes, the positive
PR is a slightly little smaller than the circular pattern on a photo mask and negative PR is slightly larger than it. Two
tones of PR increase tolerance to mask alignment. Fill-factor is high because of high resolution on a thin boundary. All
of flowing PR is stopped by the boundary; uniformity is improved without tight thermal dose constrains. Meanwhile,
microlenses with a large height are achievable due to "no cling" effect. The method has advantages, not only for large
area MLAs but also for a microlens that require precision diameter or positioning. Besides, we replicate MLAs with the
optical polymer to verify some optical specifications. Both the fabrication and replication are straightforward and
reliable. Our results show that the microlens is approximately a hemispherical profile. The gap between microlenses with
48 μm diameter in hexagonal arrangement is 2 μm and the height of microlens is 22 μm.
Self-organization of optical Z-connections in three-dimensional optical circuits simulated by the finite difference time domain method
Author(s):
Tetsuzo Yoshimura;
Kazuyuki Wakabayashi
Show Abstract
To reduce efforts for optical assembly with micron/submicron accuracy, we developed the reflective self-organized
lightwave network (R-SOLNET). In R-SOLNET, optical devices with wavelength filters on their core facets are placed
in a photo-polymer. Write beams from some of the devices and reflected write beams from the wavelength filters of the
other devices overlap. In the overlap regions, the refractive index of the photo-polymer increases, pulling the write
beams to the wavelength filter locations (the "pulling water" effect). By self-focusing, self-aligned optical waveguides
are formed between the optical devices. In the present work, we simulated self-organization of optical Z-connections
utilizing R-SOLNET in three-dimensional optical circuits by the finite difference time domain method. A 2-μm-thick
core with a 45° mirror is on a 0.5-μm-thick under clad layer to form an optical waveguide film. Two optical waveguide
films are stacked with a 10-μm gap filled with a photo-polymer, whose refractive index varies from 1.5 to 1.7 with write
beam exposure. From the simulation, it is found that the "pulling water" effect is induced even when ~1-μm
displacement exists between the two optical waveguide films and the coupling efficiency increases from 30% to 60%.
Modeling and design of a tunable refractive lens based on liquid crystals
Author(s):
Liwei Li;
Lei Shi;
Doug Bryant;
Tony Van Heugten;
Dwight Duston;
Philip J. Bos
Show Abstract
We show the modeling, design and fabrication for a tunable refractive lens based on liquid crystals. The lens has about
80 rings of transparent ITO conductor with an inter-ring resistor network. The width of each electrode is calculated to
have maximum phase step within each electrode region about 1/8 λ. The gap between any 2 adjacent electrodes is 3 μm.
The active diameter is about 4.7 mm, and our lens has a substrate gap of 10 μm, filled with a LC material of a large
birefringence of Δn = 0.27. Through a via in a SiO2 layer deposited on the ITO pattern, we run metal lines to every 10th ring electrode for establishing the voltage profile, which is calculated by our simulation, taking into account the details
of the electrode structure, the properties of the LC material used, and the desired focal length. To characterize the optical
performance: we use a Mach-Zehnder interferometer to obtain the actual phase profile across the lens aperture, which
fits the calculation very well in parabolic shape. An eye chart image through the lens is also taken, which shows very
good resolution and contrast.
Micro-optics packaging and integration for high-power diode laser beam combining
Author(s):
Y. G. Soskind
Show Abstract
High power diode laser beam combining using micro-optics components is emerging as a cost-effective technique for
producing high power laser output from small-sized laser packages. Packaging of micro-optics lenses and lens arrays
that are matched to lithographically fabricated diode laser waveguides provides a practical approach for combining
multiple field distributions into a single high output power beam. Beam combining is often associated with additional
output beam shaping that is tailored to a specific photonics application which the laser is intended for, such as surface
treatment or micro-fabrication, photomedicine, laser pumping, or remote spectroscopy.
It is shown that packaging imperfections and components' misalignments during the packaging phase influence the
output laser beam spatial characteristics and produce specific beam distortions. Micro-optics design optimized for
packaging and integration reduces the beam distortions caused by packaging imperfections, such as post-bonding
shifts and lens-induced aberrations. Another role of optical design optimization and tolerance analysis is in providing a
deterministic approach for distinguishing specific misalignment effects based on the observed distortions of the beam
distributions. This, in turn, is used to develop appropriate compensation techniques that can be applied to improve the
quality of the combined beam output during the fabrication process.
Photonic switching for reliable nanoscale three-dimensional integrated network-on-chips
Author(s):
Ivan B. Djordjevic
Show Abstract
As the multi-core architecture is becoming a prevailing high-performance chip design approach, power efficiency,
limited bandwidth and low reliability have been recognized as major communication bottlenecks for on-chip networks
(NOCs). To simultaneously tackle the above problems, we propose a three-dimensional integrated (3DI) photonic NOC
architecture. This architecture is composed of the following layers: (i) the multi-core processor layer that host multiple
heterogeneous processing cores together with corresponding local memories and network interfaces, (ii) multiple 3D
memory layers that provide the bulk of on-chip memory, and (iii) photonic NOC layer. The photonic NOC layer is
based on the optical cross-point switches (OXSs) implemented using active vertical coupler (AVC) structures. The use of
this photonic NOC layer will provide ample bandwidth at reduced latencies along with low power consumption. The
nanoscale photonic NOCs are sensitive to process variation and reliability issues. To deal with these problems, we
proposed the use of LDPC codes with decoding based on simple majority-logic.
Pure silicon - high performance: advanced optical receivers in standard silicon BiCMOS technologies
Author(s):
K. Schneider-Hornstein;
R. Swoboda;
B. Goll;
H. Zimmermann
Show Abstract
We present the state of the art of integrated silicon photodetectors and circuits by concentrating on the progress in the
last decade. Especially three highlights will be presented in more detail.
In this paper a vertical pin-photodiode in a 0.6μm BiCMOS technology, consisting of an n-buried cathode, an n- epi
layer, and a p+ anode will be discussed. The measured responsivities for different wavelengths are 0.33A/W @ 850nm
and 0.46A/W @ 660nm, respectively. Really outstanding is the reached speed of the photodiodes. The -3dB cut-off
frequencies of these 50x50μm2 diodes are up to 2.1GHz @850nm light and up to 3GHz @660nm light, depending on the
reverse bias voltage.
This high performance photodiode allows the competition of pure silicon optoelectronic integrated circuits (OEICs) even
with GaAs OEICs. A silicon OEIC reaches at 2.5Gb/s1 a higher sensitivity than a GaAs OEIC2. It also consumes less
power and a remarkably smaller chip area.
Massive parallel integration of optical receivers enables an extremely high total data rate. A new OEIC consisting of 45
parallel channels with a data rate of 3Gb/s @850nm each allows an overall data rate of 135Gb/s.
High-speed CMOS optical communication using silicon light emitters
Author(s):
Marius E. Goosen;
Petrus J. Venter;
Monuko du Plessis;
Ilse J. Nell;
Alfons W. Bogalecki;
Pieter Rademeyer
Show Abstract
The idea of moving CMOS into the mainstream optical domain remains an attractive one. In this paper we discuss our
recent advances towards a complete silicon optical communication solution. We prove that transmission of baseband
data at multiples of megabits per second rates are possible using improved silicon light sources in a completely native
standard CMOS process with no post processing. The CMOS die is aligned to a fiber end and the light sources are
directly modulated. An optical signal is generated and transmitted to a silicon Avalanche Photodiode (APD) module,
received and recovered. Signal detectability is proven through eye diagram measurements.
The results show an improvement of more than tenfold over our previous results, also demonstrating the fastest optical
communication from standard CMOS light sources. This paper presents an all silicon optical data link capable of 2 Mb/s
at a bit error rate of 10-10, or alternatively 1 Mb/s at a bit error rate of 10-14. As the devices are not operating at their
intrinsic switching speed limit, we believe that even higher transmission rates are possible with complete integration of
all components in CMOS.
The effect on Strehl ratio from thickness variations in liquid crystal diffractive lenses
Author(s):
Lu Lu;
Lei Shi;
Dwight Duston;
Tony Van Heugten;
Philip J. Bos
Show Abstract
We analyzed a design of a liquid crystal-based diffractive lens for the effect of thickness variations from the design
values. This diffractive lens contains 20 resets, with a focal length around 1 meter; optical phase difference (OPD) is 1
wavelength; liquid crystal cell gap of is 3 μm and a lens radius of around 4.5 mm. Our mathematical analysis is
performed by using numerical calculations that take into account the details of the electrode structure and the physical
properties of the liquid crystal material.
Polymeric waveguide array with 45 degree slopes fabricated by bottom side tilted exposure
Author(s):
Xiaohui Lin;
Xinyuan Dou;
Alan X. Wang;
Ray T. Chen
Show Abstract
This paper demonstrated a practical fabrication process of polymeric waveguide array (12 channels) with
50μm(W)×50μm(H)×23mm(L) dimension and mirror embedded 45° degree slopes for vertical coupling purpose. The
entire process contained three main parts: a SU8 pre-mold with 45° slope, a PDMS mold and the final waveguide array
device. The key step of fabricating the pre-mold included a bottom side tilted exposure of SU8 photo resist. By placing
the sample upside down, tilting by 58.7° and immersing into DI water, the ultraviolet (UV) beam that shined vertically
was directed to go through from the bottom of the glass substrate into top side SU8 resist with 45° angle to form the
surface. This method was able to guarantee no-gap contact between the mask pattern and the photo resist when exposing.
By comparing the process complexity and achieved structure of the top and bottom side exposure, the later was proved to
be a promising method for making high quality tilted structure without any tailing effect. The reversed PDMS mold was
then fabricated on the SU8 pre-mold. The PDMS mold was used to imprint the cladding layer of the waveguide array.
After metal deposition, core filling and top cladding layer coating, the final polymeric waveguide array device was
achieved. For performance evaluation, 850nm laser beam from VCSEL was modulated to 10Gbps signals and vertically
coupled into the waveguide array. The eye diagrams revealed high Q factor when transmitting signals along these
waveguide array.