Ring waveguide resonating structures with high quality factors are the key components servicing silicon photonic links. We demonstrate highly efficient spectral tunability of the microphotonic ring structures manufactured in commercial 130 nm SOI CMOS technology. Our rings are fitted with dedicated heaters and integrated with silicon micro-machined features. Optimized layout and structure of the devices result in their maximized thermal impedance and increased efficiency of the thermal tuning.

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.

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.

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.

In next generation optical printed circuit board, functional optical circuits will be required. We present recent progress of photonics polymers and waveguide-type device fabrication for high performance optical integrated circuit modules.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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%.

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 10^th 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.

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.

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.

We propose a new dynamic D-latch for low-power high-speed SerDes in chip-to-chip optical interconnect. The overall SerDes circuit uses 3.6 times less number of transistors, with smaller SerDes occupying 50% less area, compared to the previous works. The SerDes operates up to 10 Gbps data rate, and the power consumption is 49.3 mW at 1.8 V, which is 30 % less power.

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.

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.

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.

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.