Passive Alignment Method Research Articles

Passive mold alignment for the fabrication of polymer through-holes using punching and double-sided hot embossing

Aligning two mold inserts is one of the most important steps in the punching of through-holes for polymer microfluidic devices. Significant misalignment of the mold inserts could reduce device functionality or allow for interference between mold inserts. Active and iterative methods require repetitive experiments, characterization, and mold adjustments making the process tedious. Passive set-up alignment using a temporary kinematic coupling can be an alternative to the active and iterative methods. To do this, the three v-grooves on the primary mold insert mate with the three spheres set in dimples on the complementary mold insert. Once the mold inserts are aligned and secured, the spheres are removed, and face-to-face contact between the mold inserts can be achieved for the molding operation. This aligns the primary and complementary mold inserts without any repeated measurements or adjustments. To validate the proposed design, primary and complementary mold inserts were fabricated with alignment joints and features to conduct a punching process. Prior to assembling the mold inserts to the thermal press for punching, they were pre-assembled to inspect the innate misalignment due to the machining of the mold inserts. Along the X-Axis, the X-magnitude (∆Xi) of the mean misalignment ranged from 2 to 7 µm and the Y-magnitude (∆Yi,) of the mean misalignment were from 7 to 13 µm. The X- and Y-magnitude (∆Xj and ∆Yj) of mean misalignment along the Y-Axis ranged from 1 to 4 µm, and 5–12 µm, respectively. The mold inserts were aligned and subsequently mounted to the thermal press. Punching was conducted on a polymer substrate Misalignment was the displacement of the center-point of a die hole impression from the center point of a through-hole. The X- and Y-magnitudes of the mean misalignment (∆Xk and ∆Yk) along the X-Axis ranged from 12 to 82 µm and 32–72 µm, respectively. The X- and Y-magnitudes of the misalignment (∆Xl and ∆Yl) along Y-Axis were 11–71 µm and 32–70 µm, respectively. The results of experiments showed that the proposed passive alignment method is applicable to the punching of through-holes for polymer microfluidic devices.

Passive Alignment Method for the Bonding of Flat Surfaces Using a Squeeze Flow

A method to passively align bonded components without direct mechanical contact has been developed. This method uses the pressure field generated by the squeeze flow between the parts during the bonding process to increase the parallelism of planar components. A computational fluid dynamic (CFD) model has been developed to study the squeeze flow phenomenon and to determine generated efforts. Based on these calculations, an assembly stage standing on a flexure pinned linkage has been developed. This assembly stage had two purposes. The first was to show the possibility of passive mechanical alignment using a squeeze flow. The second was to measure efforts to confirm the CFD model. These measurements have led to a refined CFD model taking into account the non-Newtonian behavior of the fluid at high shear rates. This technique was initially developed for the assembly of a fiber-optic-to-silicon-chip-interface. Other potential applications could be wafer bonding, bonding of multiple wafer stacks, or 3D integrated circuits.

Pluggable photonic circuit platform for single-mode waveguide connections using novel passive alignment method

We describe a novel photonic circuit platform and a method for its passive alignment that will allow pluggable and large-scale multi-chip integration for highly functional single-mode waveguides based on planar lightwave circuit (PLC) chips. We achieve our proposed passive alignment method by employing precise mechanical interdigitation between optical fiber based spacers and dry etched rectangular grooves in silica-based PLCs. The method was applied to a PLC–PLC connection device in which two daughter PLC chips were mounted on a mother PLC chip. The assembled device successfully yielded a low connection loss of less than 0.4 dB for all 16 ports with an extremely simple assembly process. We also determined the alignment accuracy of our method by measuring and calculating the connection losses of an assembled Vernier pitch device. The estimated results show that our passive alignment method efficiently provides high alignment accuracy with submicron accuracy.

Fully passive-alignment pluggable compact parallel optical interconnection modules based on a direct-butt-coupling structure for fiber-optic applications

A low-cost packaging method utilizing a fully passive optical alignment and surface-mounting method is demonstrated for pluggable compact and slim multichannel optical interconnection modules using a VCSEL/PIN-PD chip array. The modules are based on a nonplanar bent right-angle electrical signal path on a silicon platform and direct-butt-optical coupling without a bulky and expensive microlens array. The measured optical direct-butt-coupling efficiencies of each channel without any bulky optics are as high as 33% and 95% for the transmitter and receiver, respectively. Excellent lateral optical alignment tolerance of larger than 60 μm for both the transmitter and receiver module significantly reduces the manufacturing and material costs as well as the packaging time. The clear eye diagrams, extinction ratios higher than 8 dB at 10.3 Gbps for the transmitter module, and receiver sensitivity of better than −13.1 dBm at 10.3 Gbps and a bit error rate of 10−12 for all channels are demonstrated. Considering that the optical output power of the transmitter is greater than 0 dBm, the module has a sufficient power margin of about 13 dB for 10.3 Gbps operations for all channels.

Development of Optical MUX/DEMUX on Silicon Optical Bench—Assembly Accuracies

An optical subassembly of MUX/DEMUX where optical devices are hybrid-integrated on a silicon optical bench (SiOB) using a passive alignment method is 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 noncritical positioning, i.e., <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -axis and thetas <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> , 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 optimizing the adhesive volume, improve the bottom flatness, proper procedure selection. Misalignment at each axis, e.g., <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -, thetas <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , thetas <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> , and thetas <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> was characterized and its effect to the coupling efficiency was discussed.

Design and Fabrication of 1.25-Gb/s Full-Triplex Transceiver Module With PLC on a Lossy Si Substrate for G/E-PONs

1.25 Gb/s optoelectronic full-triplex transceiver module with planar-lightwave-circuits was designed and fabricated for the fiber-to-the-home services according to G/E-PONs standards. A low electrical crosstalk of the critical characteristics for the reliable operation of the 1.25 Gb/s full-triplex transceiver module is intensively investigated because the electrical crosstalk on a resistive silicon substrate is more serious than that on a dielectric substrate. It is observed that the performances of the transmitter and receiver satisfy the transmitter and receiver specifications defined in the standards. From this proposed module layout, a design convenience as well as a great reduction of the silicon substrate size by about 50% was completely achieved. Consequently, the 1.25 Gb/s full-triplex transceiver module was fabricated with electrical and mechanical packaging technologies such of a low crosstalk design and a passive alignment method.

High-reliability flexible optical printed circuit board for opto-electric interconnections

A rigid flexible optical electrical printed circuit board (RFOE-PCB) with both electrical layers and an optical layer was fabricated using a conventional PCB manufacture process. The RFOE-PCB is applicable to fold-type mobile devices such as mobile phones and laptop computers. The RFOE-PCB was designed to be embedded with a flexible 45-deg-ended optical waveguide, which was made using a polymeric material. The precise lamination between an electrical layer and an optical layer was achieved by a passive alignment method. We carried out the repetitive folding test and an environment test for physical and optical reliability suitable for mobile devices. Data transmission of 2.5 Gb/s was demonstrated with a clear eye diagram using the fabricated RFOE-PCB.

Simultaneous optical/electrical interconnection of polymer planar-lightwave-circuit chip based on polymer MOEMS and replication technology

For simultaneous optical/electrical interconnection of a polymeric planar-lightwave-circuit (PLC) chip, a polymer micro-opto-electro-mechanical system (MOEMS)-based passive alignment method was designed and realized in thermosetting polymer using a UV imprinting technique. To reduce the steps for fabricating alignment structures, waveguide cores and micro-pedestals were formed at the same time with only one step of imprinting. By inserting the electrode-patterned micro-pedestals on the polymer PLC chip into the alignment pits of the silicon optical bench, optical/electrical interconnections were accomplished simultaneously and automatically. An assembled polymeric optical device shows a coupling loss of about 1.7 dB per coupling face and a good electrical interconnection at a wavelength of 1.5 μm.

Integration of a polymeric planar-lightwave-circuit chip based on a polymer microsystem and a UV imprinting technique

Despite the numerous advantages of polymeric optical waveguide devices, the issue of a simple and faster optical interconnection between the waveguide and the fiber has been critical for the cost-effective manufacturing of optical modules of the multichannel high-density polymer planar-lightwave-circuit (PLC)-type. A polymer microsystem-based passive alignment method was therefore designed and realized in thermosetting polymers by using a UV imprinting technique. The main design issue is the cost-effective fabrication of the polymer PLC chip and the plastic optical platform. The removal of supplementary thermal oxide on a silicon mold improves the surface profiles of imprinted polymer microstructures. This process provides good optical coupling properties and an attractive solution for cost-effective integration of various polymer microsystems and polymer MEMS/MOEMS.

Passive Alignment Method of Polymer PLC Devices by Using a Hot Embossing Technique

A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices.

Submicron Bonding Technology with Passive Alignment for Optical Modules.

In the field of optical module assemblies, there is a demand for the passive alignment method, which is considered to contribute both to the cost reduction and the throughput enhancement. Although the optical modules require submicron level bonding accuracy, the conventional bonders can offer no better than ±5μm level accuracy.In this paper, upgrading technologies for passive alignment bonder are reported, i.e. enhanced recognition accuracy of fiducial marks which are placedon the electrode surfaces of LD chips and silicon substrate respectively, anti-vibration structures, and anti-thermal expansion solutions. On the third issue, particularly, a new calibration method has been developed to compensate the thermal expansion that causes 1μm positional shifting at 1°C temperature change in the atmosphere or of the machine. Verification of test results on mounting accuracy is also reported.

A passive alignment method utilizing reference posts and its application in multi-level LIGA processing

Many MEMS applications require multi-level microstructures in which two or more levels have to be aligned to each other in the processing. A passive alignment method based on a mechanical registration concept utilizing reference posts has been described in our early work [1]. An alignment accuracy of 1 μm for a two layers optical lithography has been achieved. In this paper the experimental results on improvement of the alignment accuracy and expanding this alignment method to multi-level X-ray or combined optical/X-ray lithography are presented.

Direct coupling of VCSELs to plastic optical fibers using guide holes patterned in a thick photoresist

In this letter, we report a simple passive alignment method to couple plastic optical fibers (POFs) to vertical-cavity surface-emitting lasers (VCSELs) for use in parallel optical interconnects. Polymer guide holes were fabricated directly on the top of VCSELs by means of standard photolithography using SU-8 epoxy-based thick photoresist. Perfluorinated graded-index POFs were inserted and fixed in the guide holes to provide butt-coupled packaging modules. For a VCSEL of 15-/spl mu/m diameter and a POF of 124-/spl mu/m core diameter, coupling efficiencies were obtained between about 80% and 50%, depending on drive current. The standard deviation of the efficiency at a drive current of 10 mA was 5.9% for a 1 /spl times/ 5 array.

High power and high sensitivity planar lightwave circuit module incorporating a novel passive alignment method

A high-power, high-sensitivity planar lightwave circuit (PLC) module, comprising a laser diode (LD) and a photodiode (PD) surface mounted on a PLC platform, has been realized by a novel passive alignment technique. We used a spot-size transformed LD and a corner-illuminated PD to form a highly efficient optical coupling between the devices and a PLC waveguide. We used the unique marker alignment method to ensure accurate positioning of them. The positioning precision achieved in the lateral direction was within 1 /spl mu/m for the LD's and within 10 /spl mu/m for the PD's. The rotational precision was within 0.4/spl deg/ for both chips. We realized high power operation (>8 mW) with a high receiver sensitivity (0.3 A/W). In this paper, we describe a high power, high sensitivity PLC incorporating a novel passive optical alignment technique for LD's and PD's.