Passive Alignment Technique Research Articles

Optical Free-Form Couplers for High-density Integrated Photonics (OFFCHIP): A Universal Optical Interface

Coupling of light between different photonic devices, for example on-chip waveguides, fibers, and free-space optical elements, is an essential function enabling integrated optical systems. Efficient optical coupling demands matching the optical mode profiles and effective indices between two devices, and often changing propagation direction of the light. To date, such coupling is pre-dominantly accomplished via direct butt coupling of two devices, or meticulously optimized diffraction gratings. In this article, we present a new coupling scheme based on microfabricated free-form optical reflectors. The free-form reflector simultaneously achieves the functions of light beam re-directing and shaping (for mode matching), and can be versatilely adapted for coupling between photonic chips, fibers, and free-space surface-incident devices. We show that this technology uniquely fulfills all key performance requirements for optical interfaces with exceptionally low coupling loss (0.2–0.3 dB per coupler), large bandwidth (over half an octave), high density (large 2-D coupler arrays), polarization diversity, and superior alignment tolerance commensurate with passive alignment techniques. Preliminary experimental validation demonstrates waveguide-to-fiber coupling with a low insertion loss (IL) of 0.9 dB. We foresee that the technology will become a promising solution to the chip-level photonic interconnection and packaging challenges plaguing integrated photonics.

Development of method for active alignment of multiple time delay and integration detectors in the optically butted focal plane assembly of high-resolution spaceborne imaging systems

Time delay and integration (TDI) detectors are preferred image sensors for high-resolution spaceborne imaging systems for cartographic applications as they provide higher sensitivity by integrating charges over multiple TDI stages in push broom mode. Large swath requirements are met using multiple TDI detectors in optical butting configuration in the focal plane assembly (FPA) to form a single image line on the ground. These detectors need to be aligned with subpixel accuracy to avoid motion smear and errors in the image mosaicking process. Alignment of the multiple TDI detectors in the FPA is a challenging task and is accomplished using custom methods and setups. Passive alignment techniques rely on very high-resolution microscopes for achieving desired accuracies. Active method requires TDI detectors to be operated in staring mode, which is architecturally and functionally not supported by TDI detectors. We developed a scheme for operating the TDI detectors in staring mode without any smear effects to aid in the active alignment process. Based on this, we propose an active alignment approach. The proposed approach is highly advantageous as it can be used throughout the imaging system development phase to demonstrate stability of the alignment and also helps in cross validation with the passive alignment. The developed method was test validated on qualification model FPA, and alignment accuracy of the order of 0.4 μm in tilt and 1.2 μm in line shift has been demonstrated, against the requirements of ±1.5 μm. This method has been extensively used in Cartosat-2S series imaging systems and will be very useful for upcoming high-resolution missions of the Indian Space Research Organisation.

Silicon Photonic Hybrid Ring-Filter External Cavity Wavelength Tunable Lasers

Si-photonic hybrid ring external cavity wavelength tunable lasers by passive alignment techniques with more than 100-mW fiber-coupled power and linewidth narrower than 15 kHz along the whole C-band are demonstrated. These attractive performances are achieved due to very low loss Si-wire waveguides, of which loss is lower than 0.5 dB/cm. Obtained results show excellent features of Si-photonics toward commercial products.

Electrooptic sensor module fabrication for near-field intrabody communication

In this paper, we describe how to obtain a low cost electrooptic (EO) sensor module for the mass production of near-field intrabody communication devices. In our previous study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes. In this study, we fabricated EO modulators as a miniaturized chip sensor without a base portion, and clarified the feasibility of assembling optical components by only a passive alignment technique with a compact housing.

An Effective Integration Solution for 100 Gb/s DP-QPSK Coherent Receiver With a Small Skew

We propose and develop a simple hybrid integration solution for a 100 Gb/s dual polarization quadrature phase shift keying coherent receiver. The cost-effective, precise, and passive alignment technique can be used to couple four output waveguides of planar lightwave circuits (PLCs) based 90 ° optical hybrid (OH) with a 1 × 4 photodiode (PD) array directly, adopting an infrared charge-coupled device camera to monitor the light spots, a beam of infrared light to illuminate the light spots and the active areas of PD array, and an epoxy glue to adhere the PLC-based 90 ° OH to the heat sink. Based on this proposed coupling scheme, the responsivity variation for the coherent receiver is less than ±0.18 dB for all PD channels in an environment temperature range of -5°C-80 °C and the skew of this coherent receiver is only 1.96 ps.

Low Cost, Precision, Passive-Alignment Technique for 100 Gb/s DP-QPSK Receiver

We propose and develop a passive alignment technique of 4 output waveguides of PLC-based 90° OH and a 1×4 PD array. This alignment technique only uses an infrared CCD camera and an infrared light.

Electro-Optical Sensor Fabricated Using a Bulk Cleavage Technique and Its Characteristics for Near-Field Intra-Body Communication

This paper describes how to obtain a low cost electro-optical (EO) sensor module for the mass production of near-field intra-body communication devices. In this study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes, and clarified the feasibility of assembling optical components using only a passive alignment technique with a compact housing.

Simple and high-accuracy integration for parallel optical subassembly with 120-Gbits/s data transmission

Abstract. We integrate transmitting and receiving parallel optical sub-assemblies POSAs that are suitable for high-speed and parallel opticalmodules between optical components by using a simple and high-accuracy alignment technique. Characteristics of the proposed POSAsinclude a low coupling loss of 0.75 dB, a wide bandwidth for 10 Gbits/stransmission per channel, and low optical and electrical crosstalk of lessthan 30 dB. As a result, a data transmission rate of 10 Gbits/s 12channels is well demonstrated with clean eye diagrams. © 2010 Society ofPhoto-Optical Instrumentation Engineers. DOI: 10.1117/1.3486205 Subject terms: parallel optical subassembly; microlens; silicon optical bench;passive alignment technique . Paper 100082R received Jan. 30, 2010; revised manuscript received Jul. 16,2010; accepted for publication Jul. 23, 2010; published online Sep. 2, 2010. 1 Introduction With the increasing construction of servers in office build-ings and data centers, the networks of these centers must beable to provide high-capacity data transmissions.Also, highdata transmissions are required for various multimedia ser-vices such as real-time data communications. Thus, thedriving force for these requirements has stimulated the re-cent development of parallel optical interconnections.

Low-cost high-efficiency optical coupling using through-silicon-hole in parallel optical transceiver module

We present a cost-efficient parallel optical transceiver module based on a 1×4 VCSEL array, a 1×4 PD array, and a 12-wide multimode fiber ribbon for very-short-reach application. A passive alignment technique using through-silicon-hole (TSH) has been developed to realize high-efficient butt-coupling between optoelectronic arrays and multimode fibers. In this paper, the detail optical coupling structure, misalignment tolerance, micro-assembly process, and measurement results are mainly discussed. Finally, lensed multimode fibers formed by chemical etching are proposed, which exhibit a great potential for further improvement of coupling performance.

Polymer-Waveguide-Based Board-Level Optical Interconnect Technology for Datacom Applications

On the basis of a realized 12times10 Gb/s card-to-card optical link demonstrator, the capabilities of a polymer-waveguide-based board-level optical interconnect technology are presented. The conception and realization of the modular building blocks required for this board-level optical interconnect technology are described in detail. In particular, we report on the fabrication and characterization of board-integrated optical low-loss polymer waveguides that are compatible with printed circuit board (PCB) manufacturing processes. We also explain our fully passive alignment technique, superseding time-consuming active positioning of components and connectors. To realize optical transceiver modules comprising vertical cavity surface emitting laser (VCSEL) arrays with laser drivers and photodetector arrays with transimpedance amplifiers (TIAs), a mass-production concept based on wafer-level processing has been elaborated and successfully implemented.

A novel method for nanoprecision alignment in wafer bonding applications

Wafer bonding has been identified as a promising technique to enable fabrication of many advanced semiconductor devices such as three-dimensional integrated circuits (3D IC) and micro/nano systems. However, with the device dimensions already in the nanometre range, the lack of approaches to achieve high precision bonding alignment has restricted many applications. With this increasing demand for wafer bonding applications, a novel mechanical passive alignment technique is described in this work aiming at nanoprecision alignment based on kinematic and elastic averaging effects. A number of cantilever-supported pyramid and V-pit microstructures have been incorporated into the outer circumference area of the to-be-bonded Si chips, respectively. The engagement between the convex pyramids and concave V-pits and the compliance of the support cantilever flexures result in micromechanical passive alignment which is followed by direct bonding between the Si chips. The subsequent infrared (IR) and scanning electron microscopy (SEM) inspections repeatedly confirmed the achievement of alignment accuracy of better than 200 nm at the bonding interface with good bonding quality. The impact and potential applications of the developed alignment technique are also discussed.

Buried Sol-gel/SiON Waveguide Structure for Passive Alignment to Single-Mode Fiber on Si Substrate

Buried sol-gel/SiON waveguide structure is proposed for efficient optical coupling to single-mode fiber (SMF) using passive alignment technique on silicon substrate. Difficulties of photolithographic patterning on highly nonplanar surfaces were resolved by fabricating the waveguide devices at a distance from the proximity of deep grooves and by using the sol-gel material for producing negative images of the cores in the buried waveguide structure. A good optical coupling between the waveguide and SMF is obtained by bringing the SMF in close contact to the waveguide facet after saw-cutting the SiON cladding away. The loss due to fiber displacement is about 0.6 dB per facet

Low-cost 10-gb/s optical receiver module using a novel plastic package and a passive alignment technique

A new low-cost 10-Gb/s optical receiver module constructed using a novel plastic package is proposed. Passive alignment using a glass V-groove substrate and an edge-illuminated refracting-facet photodiode (RFPD) was employed to reduce cost. Instead of a conventional GaAs IC, a Si-bipolar preamplifier IC was mounted on the package to reduce power consumption. High-speed signal lines with a bandwidth of more than 10 GHz were realized using a three-dimensional electromagnetic-field analysis. For the fabricated module, a 3-dB detection bandwidth of 7.7 GHz and a sensitivity of less than -14 dBm at 10 Gb/s were achieved. To confirm the reliability of the fabricated module, a damp-heat test without bias voltage and a temperature-cycling test were performed. The results show that the optical receiver module, if covered with silicone resin, has the ability to withstand humidity and thermal stress.

Fabrication of optical splitter and passive alignment technique with a femtosecond laser

A novel packaging process using a femtosecond laser has been developed for passive alignment of planar lightwave circuit devices. With only one step of micromachining, optical splitter and U-grooves for fiber aligning are simultaneously defined on fused silica glass. The fiber aligned optical splitter has a low insertion loss, less than 4 dB, including an intrinsic splitting loss of 3 dB and excess loss due to the passive alignment of a single-mode fiber. Finally, the output field pattern is presented, demonstrating the splitting ratio of the optical splitter is approximately 1 : 1.

Precision passive mechanical alignment of wafers

A passive mechanical wafer alignment technique, capable of micron and better alignment accuracy, was developed, fabricated and tested. This technique is based on the principle of elastic averaging: It uses mating pyramid (convex) and groove (concave) elements, which have been previously patterned on the wafers, to passively align wafers to each other as they are stacked. The concave and convex elements were micro machined on 4-in (100) silicon wafers using wet anisotropic (KOH) etching and deep reactive ion etching. Submicron repeatability and accuracy on the order of one micron were shown through testing. Repeatability and accuracy were also measured as a function of the number of engaged elements. Submicrometer repeatability was achieved with as little as eight mating elements. Potential applications of this technique are precision alignment for bonding of multiwafer MEMS devices and three-dimensional (3-D) interconnect integrated circuits (ICs), as well as one-step alignment for simultaneous bonding of multiple wafer stacks. Future work will focus on minimizing the size of the elements.

Flat and high responsivity CWDM photoreceiver using silica-based AWG with multimode output waveguides

A multiwavelength photoreceiver with high responsivity and a flat passband was fabricated by using a passive alignment technique. A responsivity of ∼0.8 A/W, flatness <1 dB, and 1.25 Gbit/s×eight-channel simultaneous operation were achieved from the S to the L band.

Passively aligned LD/PD array submodules by using micro-capillaries

A passive alignment technique using micro-capillaries has been developed for multichannel optical interconnection modules. The technique is applicable when coupling a four-channel LD array to a hemispherically lensed fiber array, or a four-channel PD array to a slant-polished fiber array. Alignment time was reduced to less than 1/20 that of conventional active alignment by simply positioning the fiber array through capillaries in V grooves in the Si-platform, while obtaining high coupling efficiency of -3.4/spl plusmn/0.5 dB for LD submodules and -0.4/spl plusmn/0.1 dB for PD submodules.

Flip-chip packaging using micromachined conductive polymer bumps and alignment pedestals for MOEMS

Using flip-chip bonding techniques with micromachined conductive polymer bumps and passive alignment techniques with electroplated side alignment pedestal bumps, a prototype microoptoelectromechanical systems (MOEMS) structure for optical input/output (I/O) couplers has been designed, fabricated and characterized. A top MOEMS substrate has through holes, contact metal pads, and side alignment pedestals with electroplated NiFe to align GaAs metal-semiconductor-metals (MSMs). Conductive polymer bumps have been formed on contact metal pads of GaAs MSMs using thick photoresist bump-holes as molding patterns. A diced GaAs photodetectors die with micromachined conductive polymer bumps was aligned to the side alignment pedestals and flip-chip bonded onto the substrate. This conductive polymer flip-chip bonding technique allowed a very low contact resistance (/spl sim/10 m/spl Omega/), a lower bonding temperature (/spl sim/170/spl deg/C), and simple processing steps. The GaAs MSM photodetectors flip-chip mounted on the top of OE-MCM substrate showed a low dark current of about 10 nA and a high responsivity of 0.33 A/W.

A simple passive-alignment packaging technique for laser diode modules

A simple passive-alignment packaging technique has been developed for the fabrication of a laser diode connection to a singlemode fiber pigtail. The fabrication begins with a multimode fiber soldered in a U-groove with 5 μm tolerance. Then the laser chip with a junction-up diebond is passively aligned to a multimode fiber and converted into a singlemode fiber. The tolerance as measured for the multimode fiber at 10% loss of maximum coupling from the laser diode is 11 μm. Because the tolerance of the multimode fiber from the laser chip is larger (11 μm) than that of the fiber in the U-groove (5 μm), this passive alignment is easily obtained. In contrast to other passive-alignment techniques, the advantages of this technique are that it is less sensitive to transverse misalignment and requires no complicated alignment marks. From laser to multimode fiber a coupling efficiency of greater than 80% and a bandwidth of greater than 1 GHz have been achieved. In this package, the overall coupling efficiency from laser to singlemode fiber is 16%. The resulting laser module with compact size and fewer components should make it highly suitable for use in low-cost telecommunication applications.

Hybrid integrated four-channel SS-SOA array moduleusing planar lightwave circuit platform

The authors have succeeded in the hybrid integration of a four-channel 1.55 µm spot-size converted optical amplifier (SS-SOA) array on a planar lightwave circuit (PLC) platform using a passive alignment technique. They have achieved module gains of 8.1 to 9.6 dB, and extinction ratios of 52.5 to 55.8 dB among four channels at an SOA injection current of 40 mA. They have also achieved a switching speed of better than 1 ns.