In this study, a low-cost (with bare chips) and high (optical, electrical, and thermal) performance optoelectronic system with
a data rate of 10Gbps is designed and analyzed. This system consists of a rigid printed circuit board (PCB) made of FR4
material with an optical polymer waveguide, a vertical cavity surface emitted laser (VCSEL), a driver chip, a 16:1 serializer,
a photo-diode detector, a Trans-Impedance Amplifier (TIA), a 1:16 deserializer, and heat spreaders. The bare VCSEL, driver
chip, and serializer chip are stacked with wire bonds and then solder jointed on one end of the optical polymer waveguide on
the PCB via Cu posts. Similarly, the bare photo-diode detector, TIA chip, and deserializer chip are stacked with wire bonds
and then solder jointed on the other end of the waveguide on the PCB via Cu posts. Because the devices in the 3D stacking
system are made with different materials, the stresses due to the thermal expansion mismatch among various parts of the
system are determined.
There is an increasing demand for tunable lasers in telecommunications networks for test equipment, optical components
and other applications. In DWDM systems, multiple data streams propagate concurrently on a single mode fiber.
DWDM networks are based on a DFB lasers operating at a wavelength defined by ITU wavelength grid. Statistical
variations associated with the manufacture of DFB laser results in yield losses. Continuously tunable external lasers are
developed to overcome the limitations of DFB lasers. Various laser tuning mechanisms are being explored to provide
external cavity tunable lasers to provide a stable single mode output.
The packaged tunable laser source (TLS) for DWDM network also need to include several optical elements for isolation
and data modulation like collimator, focusing lens, fiber pigtail, a modulator and output fiber segment. In this
publication, we propose a novel semi integrated miniature high frequency tunable laser design based on Silicon Optical
Bench (SiOB) concept. One of the mirrors is a movable MEMS structure changing the optical path length. We propose
micro optical design between laser diode and the MEMS mirror for efficient optical coupling and side mode suppression.
We also present the compatibility between the optical coupling and MEMS actuation range. We present the coupling
efficiency results over the tuning range. We also propose a method of monitoring the output power of the tunable laser
using waveguide coupler structures which are integrated in the silicon wafer and method of packaging in a miniature
package compatible to the industry standard form factor.
Silicon Optical Bench (SiOB) is a popular solution for passive assembly of optical module. In order to realize an optical
transmitter or receiver module, it is necessary to integrate high frequency optoelectronic components such as signal
photodiodes (PD) or laser diodes (LD) onto the SiOB. In this way, the module's electrical and optical performances can
be further improved, and a higher degree of miniaturization can be achieved. The challenge for this integration is not
only on the assembly accuracy for the LD and PD, it required the design of low loss electrical interconnect at high
frequency. However, the standard silicon substrate used in the SiOB has a high electrical loss especially at high
frequency. This imposed a limitation on the electrical interconnection length between the optoelectronic components and
their I/O interfaces. It is proposed here to design the electrical interconnection using a layer of SiO<sub>2</sub> sandwiched between
two layers of metal layer. Simulations have demonstrated that by varying the thickness of the SiO<sub>2</sub> layer, an optimum
electrical performance can be achieved.
An optical sub-assembly of MUX/DEMUX where optical devices are hybrid-integrated on a silicon optical bench (SiOB)
using a low cost passive alignment method was reported. A tight tolerance of positional and tilting angular accuracy is
required for optical devices attachment in order to maximize the coupling efficiency. The critical positioning transverse
to the optical axis merely depends on the symmetry, and accuracy of the position and shape of trenches. Any inaccuracy
primarily affects the non-critical positioning, i.e., z-axis & θz, in the direction along the optical axis; misalignment
accumulated and causes undesired insertion loss. All the piece parts, i.e., mirror, thin-film filters (TFFs), ball lens, SiOB
etc., have a defined tolerance in their dimensions and surfaces which increases the challenge in achieving high placement
accuracy along the optical axis. The effects from these inherent inaccuracies of the position and shape of trenches and
piece parts could be minimized by improve the bottom flatness, and proper procedure selection. Misalignment at each
axis, e.g. x-, y-, z-, θx, θy & θz was characterized and its effect to the coupling efficiency was discussed.
In this paper, the optical design of 4-channel WDM Transmission Optical Subassemblies (TOSA)/Receiver Optical
Subassemblies (ROSA) is reported. The TOSA and ROSA are being developed for uncooled modules for CWDM
applications and are compatible with the SFP/SFF form factor TOSA and ROSA. The physical dimension of OSA
together with the electronic circuitries is limited to 10×6×5 mm<sup>3</sup>. The designs of TOSA and ROSA are employed using
four thin film filters (TFFs) to select the specific channel wavelength, four 500 μm ball lenses, one 2.5 mm ball lens and
a high reflection mirror using folded optical configuration. The optical elements are to be assembled on a SiOB, except
the 2.5 mm ball lens. The simulation results are used to estimate the required optical components assembly accuracy.
Based on the simulation results, the tolerance requirement for tilting the mirror and first thin film filter is approximately
± 0.2° for the longest optical path namely Channel 4.
A compact wavelength division multiplexing (WDM) module is designed using discrete micro optics
components assembled on silicon optical bench for multiple-channel transceivers. This design is optimized
for a 4-channel multiplexer (MUX) plus a 4-channel demultiplexer (DEMUX). In this design, the micro
optics components for the MUX and DEMUX are integrated, and the MUX and DEMUX share the same
space. This helps to minimize the number of components required and hence reduce the cost and size.
Therefore, the module is compact enough to be put in small standard packages (SFF/SFP).