Erbium-doped planar optical amplifiers can find numerous applications in photonic integrated circuits operating at 1.5 μm. The challenge is to fabricate these devices with high gain, operating at low pump power, and having small overall size. In this paper a review is given of our recent work in the area of Er-doped waveguide materials and amplifiers based on three materials classes: oxide films (A12O3, Y2O3, SiO2), polymers, and silicon.

The factors limiting the efficiency of Er3+ luminescence at 1.54 μm (0.8 eV) in erbiumdoped barium titanate films were studied. To investigate the effect of film stoichiometry on luminescence efficiency films were annealed in oxygen and in vacuum. For films annealed in oxygen at temperatures of 700–900°C a nominal increase in the luminescence efficiency was observed. Vacuum annealing resulted in strong quenching of the emission intensity. Transient photoluminesence measurements showed that the emission lifetime also decreased for the reduced films. This effect was reversible; upon oxygen annealing both the emission intensity and lifetime were restored to their original values. These results indicate that the Er3+ luminescence efficiency strongly depends on film stoichiometry.

The waveguiding and 1.54 μm Er3+ photoluminescent properties of Er doped silicon-rich silicon oxide (SRSO) are investigated. Erbium-doped SRSO films, which consist of nanocrystalline Si clusters embedded inside Si0 2 matrix, were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium. The excess Si content of the SRSO films ranged from 0 to 10 at. %, and Er content ranged from 0.01 to 0.3 at. %. After deposition, films were rapid thermal annealed at temperatures between 750 and 1150°C for durations ranging from 2 to 20 min. to precipitate silicon nanoclusters. All films show strong room temperature 1.54 μm Er3+ photoluminescence. The luminescence lifetimes that can be > 6 msec. The refractive indices of the SRSO films range from 1.48 to 2.47, increasing with increasing excess Si content. Thus, waveguides can be formed easily by depositing erbium doped SRSO films on 1 μm thick SiO2 films. Furthermore, carrier-induced de-excitation mechanisms of excited erbium atoms in SRSO are nearly completely suppressed in such SRSO films, indicating that population inversion of Er3+ ions by carrier-mediated excitation is possible.

The effect of controlling the interaction between the erbium atoms and the carriers of the host matrix is investigated using erbium doped Si/SiO2 superlattices. Based on the previous finding that controlling the location of the erbium atoms by doping only the SiO2 layers improves both the Er3+ photoluminescence intensities and the temperature quenching of the Er3+ luminescence, we identify controlling the interaction between erbium atoms and the carriers in the Si layer to be the key point. We demonstrate that by further isolating the erbium atoms from the Si layers by depositing thin buffer layers of pure SiO2 improves the Er3+ photoluminescence by several orders of magnitude while still allowing efficient excitation by carriers to dominate. Finally, we demonstrate that efficient waveguides can be fabricated using such erbium doped Si/SiO2 superlattices.

Through optimal thermal annealing of the active region of a 1.3 μm GaInNAs/GaAs single-quantum-well laser diode, we obtained a characteristic temperature (T0) of 215 K under pulsed operation from 20°C to 80°C. This is the highest yet reported value for a 1.3-μm semiconductor laser. Even under continuous-wave operation, the T0 was as high as 147 K. The lasing-wavelength change with temperature was as small as 0.39 nm/°C, indicating the excellent stability for a GalnNAs laser diode with T0 of over 200 K. These results demonstrate that GaInNAs is a promising material for fabricating long-wavelength laser diodes used for opticalfiber communications.

Silica-based planar lightwave circuits (PLC) provide various important devices for both optical wavelength division multiplexing (WDM) networks and optical access networks. This paper is an overview of recent progress in PLC technology including optical power splitters, arrayed-waveguide gratings, thermo-optic switches, and hybrid integrated PLCs.

Polycrystalline Si (poly-Si) waveguides offer design flexibility and multilayered structures in Si-integrated photonic devices. However, as-deposited poly-Si surfaces are rough compared with single-crystalline Si, and a rough surface causes significant waveguide scattering loss at the surface. In this study, surface smoothing of poly-Si waveguides with a gas-cluster ion beam (GCIB) was demonstrated as a new smoothing technique. As the GCIB process is a directional ion-beam process, in principle it can be applied not only to plane surfaces but also to three-dimensional or non-flat structures, such as waveguide ridges.

The initial average roughness of as-deposited poly-Si films (625°C, 1 μm thick) ranged from 15 nm to 22 nm, and the grain sizes were distributed from 0.2 to 0.4μm. This rough surface was dramatically smoothed to a roughness of 1.5 nm by Ar cluster ion irradiation. From the relation between the sputtered depth and the surface roughness, the sputtered depth must be greater than the height difference of the roughness (peak-to-valley) to obtain smooth surfaces. Optical transmission losses at λ =1.54 μm were measured using cutback measurement from samples before and after the smoothing by GCIB. After surface smoothing with GCIB, the optical loss decreased from 85 dB/cm to 54 dB/cm.

Modal loss coefficients for a planar leaky wave-guide are obtained by two new methods. One is a numerical calculation combining optical thin film theory with optical wave-guide theory; another is an analytical derivation based on analogy to Beer's law. Considering the influence of the modal loss, a modified mode equation for the planar leaky wave-guide is obtained, which greatly increases the accuracy of the refractive index and thickness of the thin film in a planar leaky wave-guide coupler (prism I film I substrate).

A novel bandp ass filter consisting of graded refractive index profiles and a three-cavity stack was designed. It exhibits good optical characteristics, i.e., high transmittance (>99%) at the designated wavelength of 1550±25 nm and high reflectance (>99%) in wavelength regions of 1400±50 nm and 1780±100 nm. This designed 33-layer TiO2-SiO2 film with graded refractive index profiles was prepared by helicon plasma sputtering. The measured transmittance spectrum exhibited good agreement with the designed spectrum. The microstructure of this multilay er film was investigated using electron microscopy.

Porous silicon was used to fabricate refractive index lattices. Patterned n-doping and/ or substrate etching were used to introduce lateral periodicity. By anodizing p-type substrate with an n-doped area, we realized large refractive index contrast two-dimensional lattices with underlying cladding layer. The anodization process showed an effect specific to the small dimensional patterning and this effect has significant influence on the formed refractive index structure.

Thin films of sol-gel SiO2 and TiO2 were used to fabricate two types of onedimensional photonic crystals: an omnidirectional reflector and microcavity resonator. The reflector consisted of six SiO2/TiO2 bilayers, designed with a stopband in the near infrared. Reflectance measurements over an incident angle range of 0–80° showed an omnidirectional band of 70 nm, which agrees with theoretical predictions for this materials system. The microcavity resonator consisted of a TiO2 Fabry-Perot cavity sandwiched between two SiO2/TiO2 mirrors of three bilayers each. We have fabricated a microcavity with resonance at λcavity = 1500nm and achieved a quality factor of Q=35. We measured a modulation in the cavity resonance frequency with a change of defect layer thickness and incident angle of light. This work demonstrates the feasibility of fabricating photonic crystals via the sol-gel method.

Optical communications are becoming technologically important on progressively shorter length scales. As computer chip speeds increase longer metal wire interconnects become problematic and may limit device performance. Wide bandwidth optical interconnects may be used to address this problem. Silicon oxide and silicon nitride were explored as prospective optical and processing materials in the making of optical interconnects. Etching of slopes, which would be an important process for making optical interconnects, was studied. Slopes with angles ranging from 5 to 50 degrees were fabricated using a silicon oxide / silicon nitride stack.

Many organic-based optical components are based on refractive index modulation or contrast as the origin of their activity. These range from passive components such as waveguides, to active components that include electro-optic switches, photorefractive information processing elements, and holographic storage media. Common to the materials used in these applications is the need for charge and/or molecular migration in their preparation or utilization. This paper focuses on some of these migration effects, with special attention paid to a new class of photopolymers being designed for high density digital holographic data storage applications.

We present data on the fabrication process of optical waveguides from four different polymers, which have been patterned either by standard lithographical masking and reactive ion beam etching (RIE) or by direct lithographical exposure of photosensitive material. Three of the resists were directly photosensitive, they could be exposed and developed. Thereafter they can be cured and remain stable. Waveguide losses of 3.5 dB/cm had to be accepted for the photosensitive materials, while the non-sensitive polymers formed very good guides (0.8 dB/cm), but were more difficult to process. We demonstrate the coupling of the strip waveguides to optical fibers on one side and to very thin metal-semiconductor-metal (MSM) photodetectors at the other side. A beam propagation method computer code has been used to evaluate the best coupling efficiencies between the guides and the detectors, which are ultrafast (3.5 ps FWHM) due to their very thin silicon slab design (Si thickness 400 nm, sandwiched between two Schottky contacts).

Organic light emitting diodes (OLEDs) which consists of 8-hydroxyquinoline aluminum (Alq3) and diamine derivative (TPD) were directly fabricated on a polymer waveguide device. Polymer waveguide device consists of deuterated methacrylate polymer core and UV cured epoxy resin cladding. One of the edges of the polymer waveguide was cut in 45 degree, which was served as a mirror, in order to introduce the output light from OLED to the waveguide. Indium-tin oxide (ITO) or semi-transparent aluminum metal was deposited onto the polymer waveguide, which served as anode. The OLED was directly fabricated by evaporation technique at the edge of a waveguide, whose edge served as a mirror.

Emission and transmission characteristics of the light from red-light-emitting OLED are also discussed as a light source for the polymer based waveguide with low transmission loss.

We have demonstrated a 3 to 13 times increase in the effective electro-optic (EO) coefficient of electrode poled nonlinear optical polymers using a conductive polymer cladding, compared to using passive polymer claddings. We have also demonstrated the lowest poling voltage to date, 300 V, for a 2 μm thick NLO polymer film. Since the cladding material is more conductive than the core material, the majority of the applied poling voltage is dropped across the core, realizing a higher EO coefficient than for conventional devices using passive polymer claddings and has the potential for in-situ poling. These results show promise for shorter, lower operating voltage devices.

Gemfire is developing a novel wall-mounted display technology called Polymer Switch Matrix (PSM). Featuring significant advantages in performance, manufacturability and scalability, it represents a fundamental change in the way flat panel displays are designed and manufactured. The perceived market opportunity, operating principle, system architecture and feasibility demonstration of this radically new laser based technology are described.

In this work. we report on characterization methods and the optical properties of a polyimide (Ultradel 9020D). The prism coupling technique was used to couple light into polyimide thin films. The scattered light from the surface was imaged to determine the optical loss at different wavelengths. The coupling angle was used to find the refractive index of the films. The stability of the polymer in terms of refractive index and absorption losses was studied by heat treatment under nitrogen at elevated temperatures. No significant change was observed in the properties of the film at annealing temperatures below 200°C. The bulk and surface losses were separated and it was found that the waveguide losses were dominated by bulk losses. Temperature stability of the polymer was evaluated by annealing the polymer at 125°C for up to 30 hours. No significant changes were seen in the optical losses for these times.

Presently commercial optical fiber links experience an explosive growth. On the other hand, the integration of optical functions on a single substrate (“Integrated Optical Device”) is still mostly limited to the R & D-laboratories. Only Mach-Zehnder modulators, made from ferroelectric crystals, have found commercial applications so far. The development phase of the integrated optical devices, based on bulk crystalline LiNbO3, is now covering a time span of nearly 30 years. In comparison, the development of the thin film growth of optical oxide ferroelectrics or of tailored optical polymers is just a few years old and we are still at the beginning of the learning curve.

In the process of developing thin film electro-optical waveguides we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO3 thin films. These films are grown by on-axis pulsed laser deposition (PLD) on MgO(100), MgAl2O4(100), SrTiO3(100) and MgO buffered A12O3(1102) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C). X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). BaTiO3 films on MgO(100) substrates show planar waveguide losses of 3 dB/cm and ridge waveguide losses of 5 dB/cm at a wavelength of 633 nm.