The design of a biwavelength transceiver (TRx) module for parallel simultaneous bidirectional optical interconnects is described. The TRx module has been implemented using two different wavelengths, 850 and 1060 nm, to send and receive signals simultaneously through a common optical interface while optimizing cost and performance. Filtering mirrors are formed in the optical fibers which are embedded on a V-grooved silicon substrate for reflecting and filtering optical signals from/to vertical-cavity surface-emitting laser (VCSEL)/photodiode (PD). The VCSEL and PD are flip-chip bonded on individual silicon optical benches, which are attached on the silicon substrate for optical signal coupling from the VCSEL to fiber and from fiber to the PD. A high-speed and low-loss ceramic printed circuit board, which has a compact size of 0.033 cc, has been designed to carry transmitter and receiver chips for easy packaging of the TRx module. Applied for quad small form-factor pluggable applications at 40-Gbps operation, the four-channel biwavelength TRx module showed clear eye diagrams with a bit error rate (BER) of 10 −12 at input powers of −5 and −5.8 dBm for 1060 and 850 nm operation modes, respectively.
An analytical model based on interconnect parameters is presented for the analysis of thermal effects on crosstalk and performance of multi-channel optoelectronic modules. The model is accurate for computing crosstalk of interconnects used in chip packaging. In addition, model is used to determine the thermal critical frequency, fcrit, above which signals becomes severely deteriorated and can be applied in the design and packaging of optoelectronic transmitter modules for reliable data transmission.
In this paper, a crosstalk expression and equivalent circuit model have been proposed based on RLC line model and interconnect parameters for wire-bonded and flip-chip bonded multichannel optoelectronic modules. The analytical expression and model are accurate for computing crosstalk of interconnects used in chip packaging. In addition, full-wave simulation and experimental results from total crosstalk measurement are discussed.
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.
This paper proposes a low-loss and thermally stable waveguide component for optical printed-circuit board (OPCB)
applications. The proposed waveguide component is formed using silica fiber as a waveguide medium and seamlessly
linking the 90°-bent parts to the planar optical layer. The component was designed through considerations of optical loss,
mechanical failure, thermal stability, module packaging, and applicability in PCB system in determination of fiber-core-diameter,
bending radius, waveguide-mounting epoxy material, and packaging structure. In the experiment, we used a
multimode fiber with 100μm-core-diameter, a MT-ferrule component to hold the 90°-bent fiber and to package the
surface modules, and a 353ND thermo-curable epoxy resin to mount the ferrule parts on planar fiber layer. The
optimized bending radius was selected near 3mm to avoid mechanical failure. The measured average value of the
insertion loss for the whole waveguide component was as low as -0.145dB. In the thermal test similar to the PCB
lamination process, the loss characteristics were not significantly degraded. In the packaging of optical transmitter (Tx)
and receiver (Rx) modules, we used a ceramic lid on which optical devices and IC chips were integrated and guide holes
were formed. The optical Tx/Rx modules assembled on the waveguide plate showed a successful data transmission up to
8Gbps. The results demonstrate that our proposed waveguide component can be applied for a simple fabrication of
OPCBs.
KEYWORDS: Clocks, Digital electronics, Eye, Analog electronics, Transistors, Field programmable gate arrays, Field effect transistors, Optical design, Switching, Multiplexing
An analog-type high-speed serializer/deserializer (SerDes) has been designed for optical links especially between CPU
and memory. The circuit uses a system clock and its phases to multiplex data to the serial link which avoids the need for
a PLL-based high frequency clock generation used in serializing parallel data as in conventional SerDes design. The
multiplexed link combined with the de-serializing clock is used as a reference signal for de-serialization. The SerDes is
being designed in a 0.13 μm Si-CMOS technology. The fabricated serializer has a core chip size of 360 x750 μm2. Power
dissipation for the SerDes is 71.4 mW operating up to 6.5 Gbps.
A platform for video data link between FPGA microprocessors based on an optical printed-circuit board (OPCB)
was implemented. Optimized compact size of 9.5 x 10.5 x 1.0 mm3 Tx/Rx modules were prepared and applied for the
optical link of the platform. A low insertion loss of 0.42 dB and stable optical fiber-layer integrated with connectors was
embedded in FR4 board for the implementation of the OPCB. The platform shows that embedding the optical fiber-layer
with connectors can improve the degree of freedom for packaging as well as optical and physical characteristics. Real
time video image from a charge-coupled-device (CCD) camera was successfully transmitted to a monitor through optical
link between FPGA microprocessors of the platform. The captured image was successfully saved in a static random
access memory (SRAM) and clearly shown on the monitor. This study shows that chip-to-chip optical interconnection
technology based on fiber-layer embedded OPCB can be applied for the CPU-to-CPU/memory optical interconnections.
Optical interface multichip modules promise to alleviate the bottlenecks of electrical interconnection. Two kinds of optical transmitter multichip module were fabricated for optical printed circuit board (OPCB) based interconnections for performance analysis. Each of the modules consist of 1 x 4 bottom-emitting VCSELs flip-chip bonded on a CMOS driver array IC for optical interconnection; among them one is an 850nm short-wavelength and the other is a 1310nm long-wavelength VCSEL. The short- and long-wavelength VCSELs have -3dB bandwidth of about 3.6 GHz and 2.6 GHz, respectively. Four-channel driver array which has been fabricated in a 0.18μm Si-CMOS technology requires 1.8V of power supply, is used for the both multichip transmitter modules. Short- and long-wavelength multichip modules are bumped with Au/Sn solder and gold stud bump wire respectively using the flip-chip bonding technology. The multichip modules have a dimension of 1.1mm x 1.2mm x 0.5mm for the four channels. The multichip module employing flip-chip bonding technology reduces unwanted crosstalk due to bond wires. The two modules showed BER less than 10-12 and clear eye openings at 2.5 Gbps. We measured the frequency response and crosstalk of long-wavelength multichip module and will compare them with the short-wavelength multichip module to evaluate which module is preferable for the optical interconnection applications on optical PCBs.
Two kinds of optical transmitter (Tx) modules using an 1310 nm long-wavelength and an 850 nm short-wavelength 4-channel VCSELs have been fabricated and characterized for comparison. 4-channel VCSEL driver has been fabricated by a CMOS 0.18 μm process and used in common for the fabrication of both modules. Both of the modules showed less than 1 x 10-12 of bit error rates (BERs) and clear eye openings at the speed of 2.5 Gbps and 3. 5 Gbps. 3dB bandwidths of the two different Tx modules of 850 nm and 1310 nm VCSELs are 3.76 GHz for 850 nm VCSEL and 3.80 GHz for 1310 nm VCSEL. The optical crosstalks of the both transmitter modules are less than -50 dB in common. Crosstalk evaluation of the two optical interconnection systems using these two Tx modules shows that the application of the 1310 nm wavelength VCSEL as well as 850 nm wavelength VCSEL for the optical interconnections is expected to be possible.
A stable and high-efficiency optical transmitter module was fabricated for optical printed circuit board (OPCB) based
interconnections. A bottom-emitting VCSEL was directly bonded on a 90°-bent fiber connection block. Since this
transmitter module does not have free space between the VCSEL and the connection block, it reduces the optical losses
due to the scattering and beam divergence at the interface between the VCSEL and the connection block. A ray trace
simulation for the optical loss supports the conclusion that closer contact of VCSEL to the connection block can provide
higher coupling efficiency by eliminating the optical losses induced by the Fresnel reflection and the beam divergence.
The index matching fluid treatment between the VCSEL and the connection block improves the coupling efficiency
especially in the longitudinal direction. This trend was experimentally identified. Effective heat discharge through the
contacted connector in this module improves significantly the power characteristics of the VCSEL. The L-I-V curves
demonstrate that the fabricated VCSEL module shows higher optical powers than the bare VCSEL improving from +0.3
dB to +3.3 dB. Successful eye diagram at the speed of 5 Gb/s/ch with 850 nm was obtained. The bit error rate was 10-9 at
the speed of 5 Gb/s/ch, and it became lower than 10-12 at the speed below 3 Gb/s/ch.
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.
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