Selected Topics in Photonics/Optoelectronics Research at the University of Cincinnati

The purpose of this article is to provide an overview of the research activities in photonics and optoelectronics being carried out at the Univer- sity of Cincinnati (UC). The article presents brief summaries of several topics covering research in optical sensors, near-field optical microscopy, optical displays, optical memory, visible and infrared light emitters. The summaries are certainly not comprehensive, nor does this article capture the totality of photonics-related research at UC. It is only intended to provide a window on our activities through which we encourage the readers to learn more by contacting us. Faculty with interest in photonics and optoelectronics at UC span a variety of disciplines including Electrical En- gineering, Materials Science, Physics, Medicine, etc. Compiled by Prof. A. J. Steckl University of Cincinnati Cincinnati, OH 45221 ([email protected]) Optically Interrogated MEMS Pressure Sensors for Propulsion Applications

Prof J. T. Boyd and Prof H. E. Jackson with the cavity covered by a thin silicon We designed pressure sensors to re- [email protected], [email protected] diaphragm which has been electrostati- spond over the pressure range 0 – 30 psi, cally bonded to the patterned glass wafer. to operate at a wavelength of 850 nm, Pressure sensors utilizing The position of the diaphragm deflects in and chose the radius of the circular dia- microelectromechanical systems (MEMS) response to pressure. A hole from the bot- phragm to be 300 µm as a size compati- technology for fabrication of the sensing tom of the plate to the cavity can be in- ble with testing and fabrication. For this element and interrogation by fiber optics cluded depending on whether an absolute maximum pressure and diaphragm ra- are being investigated.1 Optically interro- or relative pressure sensor is needed. Light dius, the diaphragm thickness of about gated MEMS devices are more rugged is introduced into the cavity from an opti- 25 µm will provide the desired response. than electrically interrogated MEMS de- cal fiber through the glass and propagates We thus fabricated diaphragms having vices so with sturdy packaging these opti- perpendicular to the diaphragm-cavity thickness close to this value. The cal devices are thus suitable for many pro- interface. The silicon diaphragm-cavity in- glass-diaphragm structure and an optical pulsion applications involving harsh terface reflects most of the light and the fiber are mounted in a sturdy Lexan environments.2 The configuration of the cavity-glass interface acts as the second package which has been designed and individual MEMS/optical fiber pressure reflector, thus forming a Fabry-Perot constructed to be able to maintain their sensor is shown in the insert of Fig. 1. It interferometer. Pressure causes the thin Si proximity to each other in the presence consists of a glass plate with a shallow cy- diaphragm to move and thus changes the of harsh external environments. The lindrical cavity etched into one surface separation between reflectors. This change packaged sensors were then placed onto results in a differ- a mounting assembly suitable for static ent amount of light and dynamic testing. reflected; thus Detailed static calibration runs of the measurement of sensor unit were carried out over a pres- this change of re- sure range of 0.5 psi to 30 psi. A LED flected light is re- source was utilized and reflected light lated to pressure. monitored by photodetectors. A linear The key design pa- variation of signal output as a function rameters of dia- of pressure was observed and a sensor phragm thickness, sensitivity of 1.77 mV/psi is measured, a initial cavity value within a factor of 2 of what is esti- depth, and cavity mated based on the design and the input diameter can be LED power utilized. Similar data was ac- varied to provide cumulated over several cycles to ensure linear response no drift occurred in the readings. Scatter over various pres- in the data was less than 0.25%. sure ranges. Our The dynamic response of the pressure design software al- sensor was characterized with shock lows us to select tube testing. The shock tube facility at the pressure range Wright State University, a facility de- and frequency re- signed for dynamic calibration of pres- sponse appropriate sure transducers for turbomachinery ap- M Figure 1. The transfer function of the pressure sensor as a function of fre- for several applica- plications, was used. The shock tube quency. tions. generated a total pressure rise at the

1 J. Zhou, S. Dasgupta, H. Kobayashi, J. M. Wolff, H. E. Jackson and J. T. Boyd, submitted for publication. 2 G. N. De Brabander, G. Beheim, and J. T. Boyd, Applied Optics, Vol. 37, p. 3264, May 1998.

February, 2000 M LEOS NEWSLETTER 3 sensor of about 10 psi. Typical time with a frequency resolution increment measurement capability for high speed traces of the response of the detector 1.22 kHz. Multiple time traces were in- propulsion applications, such as for gas due to the shock wave sampled at a 5 dividually analyzed, and then averaged turbines. Others participating in this re- MHz rate show sharp response to the in the frequency domain. The transfer search include Adjunct Research Assis- shock wave pressure rise. The sensor function as a function of frequency is tant Professor S. Dasgupta, J. M. Wolf, shows some overshoot before reaching a shown in the attached figure. An impor- Assistant Professor at Wright State Uni- constant output. The pressure step mag- tant result of these dynamic calibration versity and graduate student J. Zhou. nitude is about 10 psi as expected from tests is the usable frequency of the fabri- This work has been supported in part by the theoretical calculation. cated sensor. The flat response of the a joint AFRL/DAGSI (Dayton Area Grad- A frequency response analysis is per- sensor extends up to 30 kHz. Therefore, uate Studies Institute) grant, AFOSR, formed by taking 4096 points of data it has an adequate unsteady pressure and NASA. Near Field Imaging of Vertical Cavity Surface Emitting Lasers

Prof H. E. Jackson and Prof J. T. Boyd lobed shape with a null at the center. The in oxidized VCSELs also results in more fundamental width (2.5 µm) is much less distinct and complex multimode emission, Understanding integrated optic struc- than the 6 µm width which indicates the demanding a novel method to identify the tures, including vertical cavity surface presence of index guiding at this injection VCSEL modal structures. We have ob- emitting laser (VCSEL) structures, requires current. An analysis of these data allow tained spatially and spectrally resolved im- a spatial resolution which exceeds the dif- the calculation of a lateral index gradient ages of both subthreshold emission and fraction limit. Utilizing near field scanning across the aperture due to local carrier or lasing emission from a selectively oxidized optical microscopy (NSOM) and spectros- temperature variations. VCSEL operating at a wavelength of 850 copy, we have studied in detail the spatial Very recently we have used the same nm. Below threshold, highly local high electric field intensities associated with op- technique to study selectively oxidized gain regions, emitting local intensity max- tical channel waveguides3 , directional VCSELs. Selective oxidation is an efficient ima within the active area, were observed; couplers, y-junctions, and, most recently, and convenient current confinement these same areas were found to serve as vertical cavity surface emitting lasers4. scheme which, because of superior electri- lasing centers just above threshold. Above VCSELs offer numerous promising appli- cal confinement within the active area, is threshold, the near field spatial modal dis- cations that take advantage of such excel- leading to lower threshold currents. The tributions of low-order transverse modes lent VCSEL properties as low threshold, existence of an oxidized layer also pro- were identified by spectrally analyzing the integrability into two dimensional laser ar- vides optical confinement in the laser cav- emission; these were found to be complex rays, and high coupling efficiency of their ity and thus optical modes are more and different from those measured in the light into single mode fibers. We have tightly confined in the active area than for far field. Several graduate students (J. used spectrally resolved near field imaging an implanted VCSEL; this results in low Kim, D. Naghski, and S. M. Lindsay) have to study small aperture proton implanted diffraction loss enabling high efficiency. been participating in this research, which VCSELs. The spectroscopy is accomplished The higher optical confinement behavior is partially sponsored by ARO. by coupling the light collected by the ~100 nm near field tip which is scanned about 10 nm above the surface of the sample into a spectrometer. Consider a small aperture (~6 µm) proton implanted vertical cavity surface emitting laser fabricated by MOCVD with the 1λ active region containing four 8 nm thick Al0.3Ga0.7As/A10.6Ga0.4As quantum wells. We have studied the spontaneous emission, the above threshold emission (lasing), and the mode structure of such a microcavity structure. The spatial distribu- tion of below threshold and above threshold emissions sharply narrows as one goes above threshold, a phenomena resulting from gain guiding. If one now makes a near field spectroscopic measurement, we find that the spatial extent of the fundamental mode is distinctively different from the higher order modes. The lasing spectrum showing three lines as well as the individual intensity images for the fundamental mode and the two first-order modes over a 7µmx7µm area are dis- played in Fig. 2. The fundamental mode has a Gaussian profile at the aperture cen- µ ter with a 2.5 m full width at half maxi- M Figure 2. VCSEL lasing spectrum showing three lines as well as the individual intensity images for the mum; the first-order modes have a double fundamental mode and the two first-order modes over a 7µm x 7µm area.

3 C.D. Poweleit, D.H. Naghski, S.M. Lindsay, J.T. Boyd, and H.E. Jackson, Appl. Phys. Lett, Vol. 69, p. 3471, 1996. 4 J. Kim, D. E. Pride, J. T. Boyd, and H. E. Jackson, Appl. Phys. Lett, Vol. 72, p. 3112, 1998.

4 LEOS NEWSLETTER M February, 2000 3-D IC Vision Display using MEMS Technology

Prof S. T. Kowel ([email protected] ) The goal of IC Vision is to produce a real-time, full-color, autostereoscopic display. Depth perception and motion paral- lax are provided by integrating flat-panel displays with directing optics. A directing array directs modulated light to a set of virtual viewing zones in space, displaying a series of stereoscopic image pairs which can be easily fused by the viewer. No headgear is required to view these images generated with incoherent light. Two approaches have been investigated - diffractive gratings and reflective MEMS micromirrors. Prototype displays were based on the diffractive partial pixels approach, in which gratings direct different views into appropriate viewing zones.5 However, the major challenge is how to make a larger screen display while main- taining color and high resolution. Since the partial pixels were spatially multiplexed for eight stereo pairs (16 views) and three prime colors, a large number of pixels is required to maintain resolution. As an example, a color VGA (640×480) M Figure 3. Scanning micromirror array for 3-D ICvision display display with 16 views will need 640×480×16×3 ≈ 14.7 million partial pix- quentially on a spatial light modulator design and fabrication of static els, far beyond current capabilities. focussed on the micromirror array. micromirrors; (c) design and fabrica- An alternative time-multiplexed ap- The scanning micromirrors are de- tion of dynamic micromirrors; (d) proach based on reflective micromirror signed for two goals: (1) light redirec- auto-stereoscopic image processing for arrays is being investigated. As shown tion - directing the light to the appro- real imagery. Graduate student J. Yan in Fig. 3, for every pixel of a 3-D im- priate viewing slits; (2) image quality - is also participating in this research, age, one scanning micromirror pro- mirror dimensions less than the resolv- which is partially sponsored through duces the 16 views sequentially. Thus ing limit of human eye. Current re- an NSF grant at the University of Ala- we eliminate the factor of partial-pixel search activities and plans include the bama, Huntsville. number, and the factor of prime colors following: (a) optical system design for by reflection. The views are written se- scanning micromirror approach; (b)

Optical Memory Storage and Display Devices in the Blue Region Using Organic Materials

Prof. S. J. Clarson and Prof. A. J. Steckl few years with storage densities of the materials are also excellent candidates ([email protected]) order of 1012 bits/cm3. Currently com- for electroluminescent devices as they pact discs offer about 650 MB of storage can be designed to have large area light Over the past two decades organic space with writing and reading, both in emitting displays, which can be operated materials have shown an increasingly the red region of the spectrum. With a at low drive voltages. Thin films of poly- important potential for application in layer that can be easily processed and mers can be very easily obtained by ei- the fields of lasers and electro-optics. Ex- deposited on the CD as an active layer ther spin-coating them or by dip-coat- ploiting the high flexibility of synthetic that can be written on in the blue region ing. Generation of light in these systems routes of organic systems as opposed to the memory space that the device can is by recombination of holes and elec- conventional mineral compounds, a offer would triple. The driving forces be- trons injected from the electrodes. wide variety of organic materials can be hind developing two-photon based We currently have a research pro- addressed. memory systems are the low cost and gram to fabricate devices that can be There are a great number of widely ease of fabrication and high data storage used as image storage devices operating diversified applications of two-photon densities among others. The use of in the blue region. This work has also technology consisting of optical memory two-photon materials for data storage in led to the fabrication of low drive volt- devices to lithography and imaging. the red region using a high two-photon age organic LED’s emitting in the blue. There has been a tremendous need for absorption cross-section chromophore Efficient organic LED’s are currently be- large memory storage devices in the last has recently been demonstrated. Organic ing considered as low cost alternatives

5 G. P. Nordin, M. W. Jones, J. H. Kulick, R. G. Lindquist and S. T. Kowel, Optical Engineering, Vol. 35, p. 3404, 1996.

February, 2000 M LEOS NEWSLETTER 5 for applications such as backlights in liquid-crystal displays, automotive dome lights and other illumination purposes. The commercially available polymer poly(vinyl-carbazole) (PVK) was used in the fabrication of these devices. The active layer in the storage device consisted of the polymer doped with a high two- photon cross section chromophore (N,N- Diphenyl-7-{2-(4-pyridinyl)-ethenyl}-9, 9-di-n-decyl-9H-fluorene-2-amine) (AF-50). The data was written onto the sample using a He-Cd laser and read using an Ar+ laser. The organic LED we have fabricated utilizes three principal organic layers. The device uses the same polymer as the hole transport layer and the addition of an exciton confinement layer and the use of polyaniline doped to be an effective electron transport layer have helped in the fabrication of the low drive-voltage device. The device emits in the blue and can be operated with less than 1 volt. Several graduate students (R. Sivaraman, B. K. Lee) are participating in M Figure 4. Photoluminescence spectra of the chromophore and the polymer doped with the chromophore this research, which is partially sponsored showing the blue shift on irradiation with the He-Cd laser at 325 nm. by WPAFB and DAGSI.

Smart Optical Storage Read Head Devices Implemented with Photonic CMOS Technology

Prof F. R. Beyette Jr. generation of high-density optical storage 5×5 detector array that was fabricated devices must provide page-oriented access. entirely in a standard CMOS device pro- As the incorporation of CD technol- In a page-oriented environment, the data cess. Designed to detect the very low ogy into electronic computing systems read rate is multiplied by the page size. power levels expected from optical stor- has demonstrated, optical storage device Even with a modest page size (100×100 age devices, individual photoreceivers in can play a significant role in the archival bits) the search time on a petabyte storage the 5×5 array have produced a digital storage of digital information. Over the device can be reduced to less than 1 hour. logic swing (0 volt to 5 volt on the out- next decade, storage requirements are To date, predictions of enhanced perfor- put pin) for changes in optical power of expected to reach the terabyte level for mance have been based on the ability of less than 1 nWatt. To illustrate the abil- personal users and the petabyte level for next generation optical storage media to ity of this detector array to interface large database and knowledge base ap- produce page-oriented optical output. with existing electronic processing cir- plications. While considerable effort is While the ability to output data in a cuits, the detector array has been con- being devoted toward the development page-oriented format has been a necessary nected to a digital logic circuit that in- of optical storage media to meet this de- condition for the demonstration of large cludes a buffer circuit and a 25 element mand, relatively little work has been capacity high data rate optical storage me- array of digital line drivers. The line done to develop the optical read head dia, the development of practical optical drivers were used to drive a 5×5 LED ar- technology that will be necessary to in- storage systems will depend on the dem- ray arranged to mimic the input pattern terface these ultra high density storage onstration of optical read head technolo- detected by the photoreceiver array. Fig. devices with existing electronic comput- gies that are capable of processing data in 5 shows the input and output patterns ing hardware. a page-oriented fashion. generated during the evaluation of the One difficulty faced in the design of ul- In order to demonstrate the viability photoreceiver array. tra high capacity optical storage systems is of page-oriented optical storage devices, The second path of our investigation the von Neumann bottleneck that exists we are pursuing research along two involves the development of smart pixel between the memory system and a com- paths. First, we have been working to based processing circuitry suitable for puters microprocessor. To illustrate the develop a photoreceiver array6 technol- manipulating page-oriented data.7 While impact of this problem, consider the time ogy that can be easily integrated into the the ability to generate and detect required to search through every bit in a read head of future optical storage sys- page-oriented data are clearly necessary petabyte storage space. Assuming a 50 tems. Based on a Photonic VLSI device components of an efficient high capacity Mbyte/sec read rate (consistent with a 400 technology that combines the unifor- storage system, they are not sufficient to MHz clock) this search operation would mity and reliability of CMOS circuitry overcome the von Neumann bottleneck take ~230 days. To overcome this prob- with the two dimensional accessibility of associated with getting data from the lem, it has been suggested that the next optics, we have recently demonstrated a storage device into the CPU of an elec- 6 J. Tang, B. Seshadri, S. Konanki and F. R. Beyette Jr., Proc. SPIE Annual Meeting, Advanced Optical Memories and Interfaces to Computer Systems II, Denver CO, July 1999. 7 F. R. Beyette, Jr., P. A. Mitkas, M. Schaffer, E. Hayers, R. Pu. R. Jurrat, and C. W. Wilmsen, SPIE Proc. Vol. 3110, p. 838, The 10th Meeting on Optical Engineering in Israel, Sept. 1997.

6 LEOS NEWSLETTER M February, 2000 data passed into the computer. By pre-processing the page-ori- CPU is discarded. ented data, it is possible to discard un- Thus, the low band- wanted data prior to conversion between width, word-ori- page-oriented and word-oriented data. In ented connection addition to the circuitry required for between storage de- searching and data reformatting, the pro- vice and CPU is pre- posed database filter chip includes dominately used to word-oriented data buffers that hold valid carry useless data data that is waiting for transfer into the that is subsequently host computer. The capacity of these buff- M × Figure 5 (a) Input pattern used to evaluate the 5 5 photoreceiver array. discarded by the ers (along with full buffer indicators) in- (b) Image captured from a 5×5 LED array driven by the 5×5 photoreceiver array. CPU. To overcome sures that storage device read operations this potentially sig- and electronic host data transfers will pro- tronic computing system. Unfortunately, nificant problem we are currently work- ceed independently with out the loss of current microprocessor designs are I/0 ing to design and demonstrate smart valid data during the search process. By pin limited to word-oriented bus archi- read head devices that pre-process the reading data in a page-oriented fashion, tectures. Further, the electronic nature data prior to transfer between the stor- pre-processing the data in the read head of microprocessors available in the fore- age device and the CPU. The smart read and then passing only valid data through seeable future, suggests that word-ori- head device currently being developed the von Neumann bottleneck, it will be ented bus architectures are likely to integrate the photoreceiver technology possible to significantly reduce the search dominate over the next decade. described above with CMOS based logic time in a petabyte memory device. Several To appreciate the underlying problem circuits to produce a compact smart graduate students (J. Tang, and B. with a word-oriented bus architecture, pixel device suitable for incorporation Seshadri) are participating in this research, consider the execution of a search oper- directly into the read head of a page-ori- which is partially sponsored by NSF. ation in a large database management ented optical storage device. system. Current search techniques fre- One example of this technology is a quently require passing the entire data- smart read head device that is specifically base into the CPU where the search op- designed to execute search operations in a eration is executed. Since the results of relational database system. The chip is de- many database search operations in- signed to accept page-oriented data from cludes less than 10% of the total volume an optical storage device and produce of data searched, better than 90% of the word-oriented data as output to the host

High Density Optical Memory Based on Erbium-Doped GaN by Focus Ion Beam Implantation

Prof A. J. Steckl and Prof F. J. Beyette cal diffraction limit. Data bits would con- A demonstration of the GaN:Er optical sist of pattern of implanted locations as memory concept based on upconversion The advent of digital technologies, such “1”s and unimplanted locations as “0”s. In emission of Er ions is shown in Fig. 7. An as database systems, full text electronic principle, this could result in an area bit array of Er-doped GaN bits was written publishing, and multimedia, has fueled the density of 1010 to 1012 ever-increasing demand for archival data bits/cm2.Toread the stored storage. Current planar optical storage de- information we take advan- vices such as CD-ROM, WORM, CDR, tage of the upconversion CDRW, MO, DVD are insufficient to cope process in Er ions. with the explosive growth of storage capac- Upconversion involves the ity requirements which are expected to ex- absorption of two photons ceed the terabyte level. Nor are their cur- of same or different energies rent access speeds on the order of 10 producing the emission of a Mbits/s adequate to deal with the terabyte third photon of energy level of data processing time. We have re- higher than that of either of cently initiated an investigation of optical the incident photons. This memory systems based on rare-earth dop- process permits utilizing ants such as Erbium. (Er) which could pro- high power IR lasers to ex- vide simultaneous increases in density and cite visible emission. access time through 3D storage approaches. Upconversion emission has In these storage systems, information is been obtained8 from Er im- stored by implanting a closely spaced pat- planted GaN by FIB. As tern of Er ions into the optically transpar- shown in Fig.6, a pair of vis- ent wide band-gap semiconductor GaN. ible (green) emission peaks This write process is carried out using fo- at 523 and 546 nm are ex- cused ion beam implantation (FIB) which cited by either one or two is capable of spatial resolutions nearly 2 IR lasers with wavelengths M Figure 6. Upconversion processes and Er energy levels for FIB im- orders of magnitude smaller than the opti- of 840 nm and 1 µm. planted GaN optical memory device.

8 L.C. Chao, B. K. Lee, C. J. Chi, J. Cheng, I. Chyr, and A. J. Stecki, Appl. Phys. Lett., Vol. 75, p. 1833, Sept. 1999.

February, 2000 M LEOS NEWSLETTER 7 by FIB implantation using an Er-Ni liquid number of species used, alloy ion source developed9 for this pur- a2n increase of storage pose. Fig. 7 shows the optical upconver- states is possible. In this sion signal from a 2×2 segment of the im- work, we have demon- planted bit array when interrogated by strated a simple method the 1 µm laser. The spatial scanning pro- of utilization of file of each implanted bit (~3×6 µm) is RE-based optical storage currently limited by the laser beam diam- implemented by FIB eter. This approach can be extended to a Er-GaN. It is therefore 3D memory by growing multilayer GaN very attractive to con- films, with bits written into each layer by struct 3D optical mem- FIB Er implantation. This can greatly in- ory devices based on RE crease the obvious increase of storage doped wide band-gap density (to ~1011 bits/cm3) due to more semiconductor. Several effective use of three-dimensional space. graduate students (R. Our research results have also showed Chi, B. Lee, J. Tang) that upconversion intensity changed with and post-doctoral fellow implanted Er dose. At least 22 gray scale Dr. L. C. Chao are par- levels for each written bit can be created. ticipating in this re- With this scheme, 3D storage density can search, which is par- M × be further boosted. Furthermore, more tially sponsored by NSF. Figure 7. Visible upconversion signal obtained by IR excitation 2 2 bit pattern produced by FIB implanted ER-GaN. than one RE species can be implanted into GaN films. For each additional n

Rare Earth Doping of GaN for Light Emission Applications

Prof A. J. Steckl bandgap semiconductor (WBGS) GaN in Fig. 8, emission of the three primary 3+ The rare earth (RE) elements in the with the goal of making semiconduc- colors has been accomplished using Er 10 3+ 3+ lanthanide series have been exploited for tor-based electroluminescent devices doping for green light, Eu or Pr dop- 3+ their optical emission properties primarily (ELDs). The advantages of WBGS over ing for red light, and Tm doping for by being incorporated in glasses and ce- smaller gap semiconductors and glasses blue light. These very sharp emission ramics, such as Er-doped glass fiber used include greater chemical stability, carrier lines are due to 4ƒ inner shell radiative in telecommunications. We have been generation (to excite the rare earths), and transitions of RE ions caused by impact studying RE-incorporation in the wide physical stability over-a wide tempera- excitation from energetic carriers injected ture range. The III-N semiconducting into the GaN. The GaN:RE ELD structure compounds are of which we are utilizing is shown in the in- particular interest be- sert to Fig. 8. It uses an indium-tin oxide cause of their direct (ITO) layer patterned to form both recti- bandgap and generally fying (small) and relatively ohmic (large) high level of optical contacts to the GaN. ITO has the advan- activity. The large tage of being both optically transparent GaN bandgap also and highly conducting. The primary color makes transparent to GaN:RE ELDs match very well the speci- infrared and visible fications chosen for the US standards for RE emission. We have color television displays. In addition to grown RE-doped GaN the primary colors, mixed colors of vari- films grown by molec- ous hues have been achieved by the ap- ular beam epitaxy propriate combination of RE multiple (MBE) in a Riber doping. For example, the combination of MBE-32 system on Er and Tm has yielded a blue-green color primarily on (111) Si (“aqua”). and sapphire sub- Visible emission from RE-doped GaN strates. Solid sources has also been accomplished by RE fo- are employed to sup- cused ion beam (FIB) implantation. FIB ply the Ga and RE technology is a maskless and resistless fluxes, while an “direct-write” process, which can be ap- rf-plasma source is plied with great versatility11 to the fabri- used to generate cation of photonic devices. FIB micro- atomic nitrogen. Typi- and nano-fabrication (with ion beam di- cal GaN growth rates ameters ranging from less than 100 nm M Figure 8. Visible electroluminescence spectra from four rare-earth- are 0.8-1.0 µm/hr at to a few µm) can be utilized to reduce doped GaN devices: Tm for blue emission, Er for Green emission, Eu and growth temperatures the complexity required of conventional Pr for red emission. The insert shows the cross-section schematic of ° GaN:RE ELDs. of ~750 C. As shown photonic fabrication technology (in

9 L. C. Chao and A. J. Steckl, J. Vac. Sci. Technol. B Vol. 17, pp. 1051-1053, May 1999. 10 For a review and additional references see A. J. Steckl and J. M. Zavada, MRS Bulletin, Vol. 24, p.33, Sept. 1999. 11 A. J. Steckl, Proc. Advanced Workshop on Frontiers in Electronics, IEEE Cat.# 97TH8292, 47 (Jan. 1997).

8 LEOS NEWSLETTER M February, 2000 particular lithography, etching and im- Pr ion sources suitable for FIB implanta- nonlinear optical properties of GaN:RE plantation), which has to satisfy various tion have been developed by combining in-situ and FIB-doped are being investi- requirements for different components the rare earth elements with other met- gated. Several post-doctoral fellows (R. fabricated on the same substrate. FIB als to form alloys with lower melting Birkhahn, L.C. Chao) and graduate stu- can be used to effect local changes in to- points and vapor pressures. The emitted dents (M. Garter, J. Heikenfeld, I. Chyr, pology (through micromachining), in spectrum from FIB RE-doped GaN is es- D. S. Lee) are participating in this re- electrical and optical properties (through sentially identical to that obtained with search, which is partially sponsored by dopant ion implantation and/or mixing). in-situ doped GaN, thus establishing the ARO/BMDO, and NSA. For example, we have used Ga+ FIB to feasibility of FIB direct write with REs achieve the micromachining of for GaN ELD fabrication. Finally, waveguides and gratings in GaN. Er and frequency upconversion and other

First CPMT/LEOS Workshop on Fiber-Optics, Optoelectronics, Photonics Assembly, Packaging and Manufacturing Yields Prosperous Results

The inaugural IEEE sponsored work- Chip Mueller, W.L. Gore, shop on Fiber-Optics, Optoelectronics, “VCSEL Technology - Photonics Assembly, Packaging and Enabling Parallel Optics Manufacturing was held Sept. 15-17, Solutions” 1999 in scenic Vail, Colorado. The work- Fumihiro Ashiya, NTT, shop was organized jointly by CPMT and “Multi-fiber Optical Con- the LEOS to provide an open forum in- nector Interface and Align- formation exchange environment that ment Technologies for complements current ongoing commit- PLCs and Optical Trans- tee activities germane to optoelectronics ceiver Modules” Gilbert packaging and manufacturing (namely Lecarpentier, Karl Suss, ECTC and the LEOS Annual Meeting). “Alignment and Bonding Both NIST and NSF provided grant sup- Solutions for Optical port for this first time event. Packaging” The workshop attracted 170 atten- dees from around the globe, including David Ramsey, Lucent Technol- participation from Australia, Europe, ogies, “Hermetic Packaging Far-East, Middle East, and North Amer- Overview” From Left to Right: Michael Lebby, Mario ica. The workshop covered topics rang- John Osenbach, Lucent Tech- Dagenais, Werner Hunziker, Mino Dautartas, Dariusz Sieniawski, Mark Beranek, Robert Payer. ing from Package Design, Package Com- nologies, “Non-Hermetic ponents, High Speed Packaging, Array Optoelectronic Packaging: Packaging, Alignment Techniques/Tools, Opportunities and Con- Bonding and Sealing, Hermetic and straints” Non-Hermetic Packaging, and WDM Michael Chow, Lucent Technol- Component Assembly and Packaging. ogies, “Packaging Platform 10 invited speakers and approximately for Isolated Analog and 15 contributed presentations were given Digital Laser Modules” throughout the three day event. Session panelists added insight to the workshop Jean-Noel Dody, EGIDE, topics during lively question and answer “Standardization in Mate- discussions following the various presenta- rial and Design Shape on tions. Due to heightened interest devel- Ceramic 14 pin Butterfly oped during the daily sessions, a special Packages" John Rowlette and Werner Hunziker running spe- evening session was added to enable all Robert McLeod, E-TEK Dy- presentations to be heard and discussed. cial evening session on alignment tech- namics, “WDM Component niques/tools. And during “off-hours”, a special case Packaging Design Method- study problem challenged workshop at- ology” tendees to design the OPTO VEHICLE of Kyocera; Joe Ford, Lucent Technologies; David Wardle, JDS Uniphase, “Manufac- the future. Many innovative designs were Dariusz Sieniawski, Nortel. turing Issues for Component WDMs” presented during the workshop’s Case As the fiber-optics industry moves Study judging segment. into the next millenium and market de- Workshop Session Panelists mand for optoelectronic components Workshop Invited continues to soar, the issues of manufac- Al Benzoni, Ortel; Michael Meis, 3M; turing and testing automation, packag- Presentations James Guenter, Honeywell; Randall ing standardization, higher speed pack- Badri Gomatam, Vitesse Semiconductor, Heyler, Newport; Mark Beranek, Boeing; aging, higher density packaging, and “Advances in High Volume Optoelec- Bob Comizzoli, Lucent Technologies; packaging integration are becoming tronic Component Manufacturing” Hongtao Han, Digital Optics; Mark Voitek, more significant. The workshop setting

February, 2000 M LEOS NEWSLETTER 9