Over the last few years, Motorola has been applying a different kind of semiconductor laser technology to a family of datalink and discrete products. The laser technology is commonly referred to as Vertical Cavity Surface Emitting Lasers (VCSELs). This technology is now emerging from advanced development and research laboratories into the market place, and there is a number of introductory texts, inaddition to journal articles that describe the technology . Motorola, has chosen the VCSEL technology to be the back-bone of it's optical program and has developed products such as the OPTOBUSTM datalink [1,2,3], which interconnects arrays of VCSELs inside a small, compact module via parallel fiber ribbon to receiver modules. As an extension to this technology, Motorola has designed new and novel ways to package the VCSELs. This paper will detail, inaddition to the packaging used in OPTOBUSTM, two approaches to discrete VCSEL packaging that are commercially competitive; the flip-chip and the angled angle TO-can. The essence of both these package designs is what is usually termed as 'auto-power control' (APC). This allows a feedback mechanism to feedback a signal to the laser, to control or change its output power level with respect to system conditions. Usually, this is accomplished by back facet monitor photodetectors in conventional edge emitting laser systems. As the VCSEL does not have facets, alternative solutions have to developed; the flip-chip and angled TO-can are shown to be good candidate.
As optics and optical subsystems assume a larger role in consumer electronics, cost, size and reliability issues are generating requirements for a higher level of integration in optical devices. The trend is continuously for smaller and cheaper devices without sacrificing performance. It is also critical to improve the interface of optics with electronics. Diode lasers, LEDs and photodetectors are packaged as individual modules; they are rarely integrated directly with electronic chips. The practical integration of optics with electronics will require optical elements manufactured in a manner similar to integrated circuits. Optical elements, as well as lasers and detectors will be fabricated lithographically and configured using the packaging tecimologies developed for ICs and multi-chip modules. Such a system was recently developed for a particularly low cost, high volume application. This application is a "floptical" drive which features a conventional magnetic floppy disk with an optical tracking servo to permit a much higher track pitch on the media. The media features a microscopic stitch pattern, laser branded into the lower surface ofthe floppy disk. By tracking the magnetic head relative to these stitches, pitch density can be increased dramatically. The disk can store over 100 megabytes of data. The key to drive operation is the precise registration ofthe magnetic head to the track on the media, which is accomplished by a multi-beam optical tracking head. Because the same magnetic head technology is used, the drive is reverse compatible with conventional floppies. This broad compatibility makes the drive very attractive to portable computer users, who are typically limited to only one disk drive bay. For desktop personal computers, the standard drive bay is 25.4mm high. The standard floptical drive features an optical tracking head which is large, with macroscopic lenses, diffractive elements, lasers and detectors which are assembled into a molded metal chassis. To extend floptical technology to laptop computers required reducing the drive height to fit in a 12.7 mm slot. This necessitated a significant reduction in the size and mass ofthe optics head. The device would be required to have the structural integrity to carry the electrical leads for servo interfacing while maintaining precise alignment to the magnetic head. To achieve the required size reductions in the optical head required a fundamental change from conventional optical systems to integrated micro-optical systems (IMOS). In IMOS, the optical elements are lithographically generated with integrated alignment and bonding features. The source and detector elements are assembled into the system at the chip level, using flip-chip techniques to mechanically and electrically connect them. The assembled IMOS chip is then attached to a flexible printed circuit, or in some cases a second integrated circuit chip. The core components of IMOS are the optical elements and the chip-to-chip packaging technology. None ofthe techniques or elements described in this paper are new, but the integration and packaging ofthese elements into a complete and manufacturable device is representative of a new paradigm in optical system design. In this paper, we will describe the application of IMOS technology to reduce the size, weight and cost of a floptical tracking head. In section 2, we will describe the system requirements. The optical design approach will be related in section 3, followed by the assembly challenges encountered, in section 4. Section 5 willreview the performance of the phase one prototype, identifying key issues which were resolved in the phase two device. The conclusions, acknowledgments and directions for future applications ofIMOS are related in section 6.
The hybrid integration of microlenses and arrays of microlenses in micro-optical systems is simplified using contactless embossing of microlenses (CEM) in combination with LIGA microfabrication. CEM is anew fabrication technique for the production of precise refractive microlens arrays. A high precision matrix of holes made by LIGA technique is used as a compression molding tool to form the microlenses. The tool is pressed onto a thermoplastic sample which is heated close to the glass transformation temperature of the material. The material bulges into the openings of the molding tool due to the applied pressure and forms lens-like spherical structures. The name refers to the fact that the surface of the microlens does not get in contact with the compression molding tool during the shaping process and optical quality of the surface is maintained. Microlenses and arrays of microlenses with lens diameters from 30 micrometers up to 700 micrometers and numerical aperture values of up to 0.25 have been fabricated in different materials. Cost-effectiveness in the production process, excellent optical performance and the feature of easy replication are the main advantages of this technique. The most promising feature of this method is the possibility to obtain self- aligned assemblies then can be further integrated into a micro-optical bench setup. The CEM fabrication method in combination with LIGA microfabrication considerably enhances the hybrid integration in micro-optical devices which results in a more cost-effective production of compact micro-opto-electro-mechanical systems.
The integration of small electronic packaging and miniature optics has led to a growth in opto-electronic applications. Cost and size reduction achieved by using smaller packaged systems allows for the possibility of building systems previously not possible because of cost or size constraints. Examples include low cost laser range finders for automotive adaptive cruise control and back up aid, and miniature focused laser assemblies for pollution monitoring, testing, telecommunications, and defense applications. A system is described here, which contains a near IR laser diode, a microlens, and a hybrid driving circuit, packaged within a 0.5 inch TO-8 can. The circuit enables the transmitter to produce optical pulses with pulsewidths less than 10 ns and peak pulse powers greater than 40 watts. A variable pulse repetition rate from 0.22 kHz is controlled externally. A cylindrical microlens is used to collimate the fast axis of the optical beam form the laser diode. The use of a small focal length microlens enables near collimation of the laser beam fast axis to a waist diameter of 0.004 inches. However, and cost effective for high volume production, automation of the critical alignment processes is necessary. An automation station for actively aligning a microlens in 1 to 3 minutes has been developed and is described. The system uses high precision motion controllers, machine vision, and computer automation for performing both rough alignment and fine alignment of the microlens to the laser diode.
The incorporation of non-imaging optical concentrations in uncooled mid-IR LEDs is described. Novel micromachining methods are used to produce optical concentrators in the growth substrate of epitaxial InSb/InAlSb heterostructures. Resultant large area LED arrays, displaying both positive and negative luminescence, are shown to have optical gains of 3.5 over conventional mesas made form the same material. The LED technology shown also relies on the micromachined substrate being transparent to 3-5 micrometers radiation and to act as a low resistance common contact. The use of degenerate doping in InSb is described, resulting in a shift in the room-temperature transmission to the 3-5micrometers atmospheric window and providing high electrical conductivities.
Due to advances in spatial light modulator technology and high-speed imagers, optical correlators are becoming viable for a variety of high-speed image processing applications. However, conventional approaches to assembling correlators produce systems which are costly to manufacture, and which are too large for some uses. We are investigating approaches to the construction of compact, highly integrated correlators that combine ferroelectric liquid-crystal-on- VLSI spatial light modulators, a CMOS imager, and diffractive optical elements.
This paper reviews the assembly and packaging of miniature liquid-crystal-on-silicon (LCOS) displays. Reflective-mode LCOS displays require thin cell gaps with strict tolerances - a difficult optoelectronics assembly problem. Important assembly and packaging considerations include the substrate thermal properties, substrate flatness and packaging chronology. Two approaches are described: spatial light modulator assembly using self-pulling solder reflow and wafer scale display assembly using photo-definable resins. Simulation and experimental results are summarized.
Optical connectors utilize microlens elements for coupling light into and out of fibers. Typically, these lenses are based on sapphire ball lenses or Gradient Index lens elements.However, lenses that are on the same scale as the single-mode fiber itself have not been previously realized. This paper introduces an optical lens element that fits into the single-mode optical ferrule, without any modifications to the connector package. This approach offers substantial performance and cost benefits over other methods.Both theoretical and experimental results are presented.
We have developed a modeling tool that integrates optical, cost, thermal, mechanical, and solder models under a common user interface. The models are connected together to allow trade-off studies between parameters existing within different models. We have applied the integrated models to a family of optical interconnect modules. In this paper we will show how the integrated models can help the users design, as well as understand tradeoffs, in optical modules.
A new concept is proposed for lenses fibers fabricated according to a collective and low cost process is based on the cleaving and splicing of optical fiber ribbons and is suitable for the coupling of laser diode arrays and fiber ribbons.
Today's assembly of fiber-optic connectors is characterized by a high manual assembly share. Because of the dimensions of the fiber and the ferrule in the range of 125 micrometers , high precision in the assembly process is required,especially concerning the insertion process of the fiber into the glue- filled ferrule. Still, at present there is no implementation of a process monitoring in the connector assembly to guarantee high and reproducible quality. We will present an assembly cell for an automated insertion process with integrated process monitoring and finally discuss the theoretical aspects behind the process monitoring.
A new pre-molded organic package with optical fiber guide pipe has been developed to meet the demand of significant package cost reduction in subscriber systems. The new pre- molded package is composed of a new organic materia which has high anti-moisture reliability. The new pre-molded package has not degraded after reliability test including thermal shock, temperature cycling and PCT of 0 to 100C/500 cycle, -40 to 84 C/500 cycle and 121C/2atm, respectively. The new developed pre-molded package with the guide pipe can be used in the subscriber systems with low- cost effect and high reliability.
We report on an advanced polymer technology that enable the low-cost monolithic integration of micro-optical elements with planar waveguiding circuitry. We have developed high- performance organic polymeric materials in which both micro- optical and waveguiding structures can be formed with controlled geometries. These materials are formed form highly-crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, toughness, contrast, loss, and stability against yellowing. Waveguides with microns to tens of microns dimensions as well as micro- optical structures that are up to several hundred microns in thickness are printed photolithographically, withthe liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct-writing. Precise control of the photochemical reaction dynamics results in high resolution in the complete thickness range. A variety of rigid and flexible substrates can be utilized, including glass, quartz, silicon, glass-filled epoxy printed circuit board substrate, and flexible polyimide film. We discuss the production of various novel micro-optical elements that we routinely integrate with waveguiding circuits. These elements include fiber grippers for waveguide pigtailing, prisms for coupling of light from VCSELs into waveguides and from guides into photodetector chips, and pedestals for passive alignment of fiber ribbons or waveguide-array strips to waveguides.
A new single-mode optical waveguide on a ceramic substrate has been developed to obtain opto-electronic multichip modules for use of high operating frequencies. Propagation loss of the single-mode optical waveguide formed on ceramic substrate is 0.14dB/cm for 1.3 micrometers wavelength.It is fabricated utilizing a siloxane polymer. The film of siloxane polymer can cut-off surface roughness of ceramic substrate. So the optical waveguide on ceramic substrate utilizing the siloxane polymer has fine optical characteristics.
This paper describes work in the area of hybridization of optoelectronic devices and passive optical waveguide elements. The potential coupling efficiency of a laser diode to silica waveguides and fibers was improved by waveguide engineering. These diodes displayed far field angels of 16.5 degrees in the transverse direction. Strategies for passively aligning the didoes to planar silica waveguides on silicon substrates are also presented.
Silicon micromachining technology has opened up many new possibilities in implementing optical and optoelectronic systems in micro scale. It offers unparalleled capabilities in extending the functionality of optical devices and the miniaturization of optical systems. Movable structures, microactuators, micropositioners and micro-optical elements can be monolithically integrated on the same substrate-using batch processing technologies. In this paper, we report the recent progresses in developing of MEMS actuators and micropositioners based on silicon surface micromachining technology. In particular, free-space fiber optic switches and micro-XYZ stages will be discussed. A 2 X 2 free- space fiber optic switch consist of an out-of-plane micromirror driven by integrated scratch device actuators (SDA), and a build-in balancing spring. A fall time and a rise time of 15 ms and 6 ms have been achieved, respectively. In addition, a self-assembled micro-XYZ stage, hybrid-integrated with a 300 micrometers micro-ball lens has been demonstrated for active alignment in the free-space Si micro-optical bench. We have achieved up to 100 micrometers in all three independent axes for the micro ball lens with integrated SDAs that have a step resolution of 27 nm. This novel device can be used for dynamic tracking and alignment between fiber/fiber and fiber/laser free-space optical interconnects, with increased efficiency and vibration stability.
This paper describes methods for attaching a vertical cavity surface emitting laser (VCSEL) on to a surface micromachined die. Techniques investigated include silver paste, soldering, wire bonding, and gold pads with integrated resistive heaters. Each technique is evaluated based on reliability, positioning tolerances, and secondary effects. Applications include single chip laser beam scanning.
We discuss the characteristics of a novel microelectromechanical cylindrical focusing mirror having a focal length which is controlled by active and intrinsic stresses in the thin films composing it. The unactuated mechanical state of the mirror is determined by intrinsic stress levels in a SiN structural layer and a piezoelectric PZT actuator layer which are part of a doubly clamped cantilever beam. The stresses are controlled by the sputter- deposition parameters and annealing conditions. The stresses concentrate curvature in the thin central mirror portion of the beam and can give the mirror a minimum focal length of as little as 100 micrometers . The focal length is increased during actuation of the PZT layer by inducing a differential tensile stress which reduces the curvature. Theoretical results are presented which predict the maximum focal length range and operating speed for a given device design. They indicate that operating frequencies of greater than 100 kHz can be achieved for a device with a focal length range of 100 micrometers to infinity. Experimental results will verify the operating principal of the proposed device.
Diffractive optical encoders have quickly established themselves in the marketplace because of their small seize, high accuracy and relaxed alignment tolerances, but current products are still composed of carefully packages, discrete optical and electro-optical components. MicroE and Digital Optics Corporation have been working together on the next generation of these encoders, which replaces all discrete and refractive elements with DOE's and more completely integrates the requisite optical and electro-optical components. In this paper we describe a monolithic source/optics/detector encoder module we have designed and prototyped for a satellite application under a NASA Phase I SBIR contract.
Two different types of color sensor have been developed, which are adaptable to a wide variety of industrial applications. One kind of sensor was developed by depositing dielectric interference filters directly on photoelectric cells, applying a low temperature coating procedure. This way it was possible to accommodate spectral characteristics to the specific spectral sensitivity of the photoelectric cells, minimizing losses by absorption and scattered light in the desired spectral region. The geometric shape of these coated cells is suitable especially for color measurements using fibers. The second kind of color sensors, consisting of miniaturized photoelectric cell arrays and three different micro-patterned interference filter arrays, arranged on a glass substrate, make it possible to distinguish and measure colors with a local resolution. The honey-comb-arrangement of filter- and receiver cells and a flexible setup also permits a fast adaptation to different applications. In this paper design and development of both miniaturized interference filers are described. The different manufacturing procedures are depicted, advantages and questions arising with the employment of interference filters are discussed and the entire assembly of both sensors is presented.
A new method of assembling MEMS is being developed that uses solder surface tension force to manipulate and assemble MEMS 3D structures. Modeling is critical to design solder joints for precision assembly. An accurate model has been developed based on the principle of surface energy minimization. Using surface evolver software, this model considers 3D MEMS configurations with different pad dimensions, geometries, and volumes of the solder joint. The software calculates solder shapes with local minimum surface energies and identifies the final shape with the global minimum energy. A two-plate popped-up MEMS structure was modeled and experimentally measured. The experiment confirmed the model could predict the final, equilibrium angle to within +/- 2 degrees. This accuracy level is actually limited by the experimental error bar of +/- 2 degrees, which was caused by the volume variation of the solder spheres used. The model's accuracy is expected to be much better. Nevertheless, the present model, with the verified accuracy, can help MEMS researchers design innovative 3D MEMS assembled using solder.