Hermetic packaging of the high-speed optoelectronics devices is important not only for robustness but also to protect the device from adverse operational environments and ensure reliable communications. We have developed a complete hermetic packaging assembly process for a photonic Mini-DIL module of 10.0Gbps type. We have developed and simulated the step by step fluxless reflow soldering process (pick and place) of the whole mini-module package and finally, the hermetic sealing by Finite Element Analysis (FEA) simulation. A commercially available, general purpose, finite element program - ABAQUS has been used along with Altair HyperWorks as pre and post processor for this numerical simulation. The actual 3-D model has been simplified to the 2-D model for the hermetic sealing, radiation heat transfer prediction to reduce computational complicacy. During the sealing process at a high temperature, there is a possibility of considerable heat transfer from the module top sealing cap to the high temperature susceptible LD (Laser Diode). In the event of a critical temperature the LD may suffer malfunction and eventual destruction. Radiation along with the conduction heat transfer mechanism has been modeled for this sealing to predict the temperature variation as a result of heat transfer from wledspots to the LD. Various issues with cavity radiations such as, effect of radiation view factor, surface blocking and surface emissivity have been considered and results discussed. The convection mechanism has been neglected considering the hermeticity of the sealing.
The design and fabrication of a polymer optical waveguide based true time delay (TTD) device is described. Optimization of the fabrication process decreased the waveguide propagation loss from more than 1.55 dB/cm to 0.38 dB/cm at a wavelength of 1.55um. Waveguide bend loss structures were fabricated and measurement results were compared to simulations. A bend radius of 3 mm provides low insertion loss and small device size. 2x2 thermo-optic TIR switches were fabricated with insertion losses of 2.8 dB. A 4-bit TTD device for use with a 4x4 sub-array of a 10GHz phased array antenna was calculated to have an insertion loss of 23.88 dB.
Design trade-offs and integration challenges of High Dynamic Range Integrated (HDRI) receivers for next generation long haul and dynamic metro networks are presented. Extended receiver dynamic range is achieved by integrating Variable Optical Attenuator (VOA) and optical receiver functionalities in a single hermetic package. The HDRI receiver provides a cost-effective alternative to a discretely packaged VOA and receiver combination, resulting in a substantial reduction in size, fiber management and total insertion loss. Different VOA integration schemes are considered. Important optical design aspects of different VOA schemes are discussed in detail including field distributions at the optical blocker and at the VOA output plane, the VOA attenuation characteristics as a function of the beam blocker position, as well as the optical return loss. Simulation results for a single mode fiber output field and its Gaussian beam approximations are compared. The optical return loss analysis is performed in 3D space to exclude from coupling spatial domains exceeding the back-reflection specification value. A novel single lens in-line micro-optics integration approach is presented, providing a compact and cost-effective coupling scheme with minimal insertion loss and packaging complexity.
A silica micro-lens pair has been proposed which can be integrated
with planar optical waveguide circuits. The lens pair enables an
optical signal to travel in free space between two opposing planar
waveguides with minimal optical loss. Each lens in the lens pair
consists of a slab GRIN lens with a convexly shaped front face. This paper briefly reviews the micro-lens design process and reports progress in fabricating the device. The characterisation of the GRIN
layer and masking experiments used to evaluate the deep oxide etch
are presented. A selectivity of 250:1 was achieved for the deep oxide etch using a NiCr mask.
Two polymer technology platforms incorporating both polymer-based materials and UV-assisted and hot embossing fabrication processes have been developed for planar optical waveguiding applications. Firstly, a novel hybrid organic-inorganic (sol-gel) materials system with epoxy functionality has been developed for use in short-range optical interconnect applications. The sol-gel material can be easily formulated and deposited by spin or dip coating to form layers of up to 25μm in thickness. The resulting film can be selectively cross-linked using photo-lithography, as part of a UV-Thermal curing process. The basic refractive index of as-deposited layers can be adjusted between 1.48 and 1.515 by modifying the concentration of DPDMS present. The near-field image of transmitted radiation (633nm) demonstrated waveguiding and efficient light confinement within the UV-thermally produced core regions. Preliminary Telcordia reliability testing indicates that the hybrid material waveguides have good thermo-mechanical stability and meet the requirements for central office (CO) operation. This represents a significant improvement in thermal stability over previous inorganic-organic hybrid waveguide materials systems containing acrylate or methacrylate groups that are easily cured by thermal processes. Secondly, an imprint embossing process has been developed for fabrication of all polymer waveguiding components enabling simultaneous embossing of both waveguide and optical fibre alignment grooves. Optimised pairings of polymer materials for the substrate of the device, into which the waveguide grooves are imprinted, and the core, which provides the refractive index step necessary for guiding light through the device, have been identified and evaluated. Insertion loss measurements were performed at 850 and 1330nm using the cleave-back method and were found to be 0.4dB cm-1 and 0.7 dB cm-1 respectively. The measured waveguide loss from the optimised devices at 850nm after thermal reliability testing was 1.0dB/cm. These measurements indicate that polymer optical waveguides manufactured using this embossing process will satisfy several envisaged optical interconnect datacom applications.
Bandwidth demand is still growing and it is becoming more difficult for copper based interconnect technologies to meet system requirements. Considerable progress is being made in the development of optical interconnect technology. Recent publications have shown improved integration of turning mirrors and connectors for board level applications. This paper presents recent work on a siloxane-based waveguide material that is optimized for 850nm board level optical interconnect applications. The material under development is a negative acting photoimageable material that can be processed with conventional Printed Wire Board (PWB) or CMOS processing techniques and chemistries. Meter long waveguides have been fabricated on both silicon and FR4 substrates with optical loss performance of 0.027dB/cm and 0.067dB/cm respectively. Data illustrating the effect of bend radii and splitter performance is reported. Lastly, the ability of the siloxane material to withstand PWB fabrication and assembly processes such as lamination, metallization and reliability is demonstrated.
Prototypes of optical interconnect (OI) modules for backplane applications are presented. The transceivers attached to the linecards E/O convert the signals that are passed to and from the backplane by optical jumpers terminated with MTP-type connectors. The connectors plug into adaptors attached to the backplane and the microlens arrays mounted in the adaptors couple the light between the fibers and waveguides. Planar polymer channel waveguides with 30-50 μm cross-sections route the optical signals across the board with propagation losses as low as 0.05 dB/cm @ 850 nm. The 45º-tapered integrated micromirrors reflect the light in and out of the waveguide plane with the loss of 0.8 dB per mirror. The connector displacement measurements indicate that the adaptor lateral assembly accuracy can be at least ±10 μm for the excess loss not exceeding 1 dB. Insertion losses of the test modules with integrated waveguides, 45º mirrors, and pluggable optical jumper connectors are about 5 dB. Eye diagrams at 10.7 Gb/s have typical width and height of 70 ps and 400 mV, respectively, and jitter of about 20 ps.
Passive optical components for optical interconnection using hybrid optical printed-circuit boards (PCBs) where electrical and optical layers are integrated into one board has been studied. We present detailed fabrication processes and optical characteristics of optical PCBs and connectors for optical coupling between vertical and horizontal directions. Two kinds of optical PCBs, polymer-waveguide-embedded and silica-fiber-embedded PCBs, were prepared. For the polymer-waveguide-embedded PCB, the polymer waveguide was formed lithographically on a FR-4 board and its core has 100 μm width and 60 μm thickness. The waveguide-defined board was covered with another FR4 plate and then laminated at 185°C under the pressure of 35 kg/cm2. After lamination the transmission loss of the waveguide was -0.53 dB/cm. For the fiber-embedded PCB, fibers with 100 μm core diameter were inserted in grooves formed on a FR-4 board and they followed a similar lamination processes. The propagation loss of the fiber-embedded board at 850 nm was negligible in board scale. We also prepared 2 types of connectors for optical coupling between the surface mounted transmitter or receiver modules and the optical PCBs; 45°-ended fiber block and 90°-bent fiber connector. The insertion losses of the 2 kinds of connectors were, respectively, -0.15 dB and -0.25 dB. The best combination between the optical PCBs and connectors in view of optical characteristics and packaging is fiber-embedded board and 90°-bent fiber connector. They show successfully optical link of 2.5 Gbps with a very low coupling losses of -4.4 dB and a low optical crosstalk of -53 dB.
We present a novel array waveguide evanescent coupler (AWEC) for card-to-backplane or other appropriate optical interconnect applications. Three approaches to realize the AWEC ribbons were experimentally demonstrated. These results show that the new coupler facilitates easy coupling between card and backplane waveguides. It eliminates the problems of 90° out of plane turn using 45° etched waveguide mirror and local waveguide termination. The implementation of the coupler ribbon and coupler hardware at low cost will be significant for high-speed optical data bus in advanced computing systems.
A high performance polymer waveguide array with 45° micromirrors was fabricated by soft molding to achieve fully embedded board-level optoelectronic interconnects. One-step-transferring of a 3-D polymer structure is demonstrated. Low-loss and thermally stable UV curable polymers based on fluorinated acrylate are chosen as waveguide core and cladding materials. A 45° total interior reflection (TIR) micromirror was formed by two methods: blade cutting and mechanical polishing. And the surface roughnesses are further improved by using a focused ion beam (FIB) technique. The high-quality 45° micromirror was obtained to provide surface-normal light coupling between waveguide and the optoelectronic devices. The measured propagation loss of the multimode waveguide was 0.156dB/cm at 850nm wavelength. The excess loss of the mirror was less than 1.5dB.
We present the main applications for contact-less (radiation-) temperature measurement with thermopile sensors and show how the large number of different requirements associated with them can be matched using a low-cost sensor module construction set in a TO39 housing. The main components are: A choice from different MEMS-thermopile sensors or sensor arrays, one of two programmable ASIC’s, IR optical components to be integrated, such as filters, IR lenses, a Winston cone reflector and different caps. Of the latter, a significant innovation is the isothermal cap, which integrates the mechanical functionality of a cap with optical functions such as the reduction of ghost images and most importantly the thermal functionality of a massive heat sink. This way a complete pyrometer can be build into a TO39 housing.
We have developed VCSEL based fiber optics transceivers for PCS fiber systems. The PCS fiber has a core diameter of 200μm. The relatively large diameter enables the usage of low cost optical connectors for the fiber link and provides wide alignment tolerances. The measured lateral and longitudinal 3dB coupling tolerances are ±100μm and 500μm, respectively. The VCSEL is integrated with an electronics driver chip and some passive electronics components on a leadframe structure before plastic encapsulation. The hybrid integration on the leadframe enables batch processing to increase throughput and lower manufacturing cost. No full-hermetic sealing is required for the VCSEL chosen. The variation of optical output power is less than 0.2dB from -40°C to 105°C. Eye diagrams show wide open eyes at a data rate of 500Mbit/s at wide temperature range up to 105°C. The technology can go up to data rates in the Gbit/s range, but this is currently not required for the target applications. The module is reliable over 1000 temperature cycles from -40°C to 125°C. For the receiver side we developed high speed MSM photodetectors. The large area MSM photodetectors relax the coupling alignment tolerance to the core of the optical fiber for 80μm and 4000μm in lateral axis and longitudinal axis, respectively. The MSM photodetector is capable of data rates of 3.2Gb/s. At this high speed the sensitivity is better than -18dBm for the MSM photodetector co-packaged with a suitable transimpedance amplifier (TIA).
A low-cost coarse-wavelength-division multiplexer (CWDM) transmitter that combines four channels (wavelengths) in the infrared spectrum (~1310 nm) in a small form-factor un-cooled package is demonstrated. The package utilizes precision molded optics to multiplex beams from four grating-outcoupled surface-emitting (GSE) lasers into a single beam suitable for coupling into multimode fiber. This paper summarizes the optical and opto-mechanical design, fabrication and assembly of prototypes, and optical, thermal and electrical measurement results of the prototypes. This unique design enables multiplexing of wavelengths without the use of filters, waveguides, couplers and fiber splicing. Commercial fabrication and alignment technology is used to manufacture the package, resulting in a more robust, reliable and low-cost transmitter. The transmitter package is enabled by the unique characteristics of the long-wavelength GSE laser.
The optical waveguide entry facet of high-speed, 40 GHz waveguide photodetectors is usually obtained by manual cleaving, which has limited accuracy (± 10 μm) and reduces fabrication yields. In our new fabrication process, the waveguide facet is obtained with Chemically Assisted Ion Beam Etching (CAIBE). Length is therefore precisely controlled by photolithography. The antireflection coating is also deposited collectively on the whole wafer, which further reduces costs. The bandwidth of the photodiodes is 50 GHz, and their optical responsivity is 0.6 A/W at 1.55 μm wavelength. Other techniques, such as Inductively Coupled Plasma Etching (ICP), were also investigated for reducing leakage current.