Polymer Channel Waveguide Research Articles

Filtering characteristics of hybrid integrated polymer and compound semiconductor waveguides

This paper reports a study on a compact filter fabricated using hybrid integration of compound semiconductors and polymers. A GaAs epilayer is glued onto a polymer channel waveguide forming a highly asymmetrical directional coupler. This approach results in a narrow band filter due to very different dispersion characteristics of the compound semiconductor and the polymer materials. Furthermore, fiber coupling loss has been significantly reduced, since the input and output coupling is done through the polymer waveguide. Filtering characteristics can be engineered by changing the thickness and the length of the semiconductor epilayer. This can be done precisely using etch stop layers and noncritical lithography. The spectral response of such a filter can also be tuned electronically either using the electro-optic properties of the compound semiconductor or the thermo-optic properties of the polymer.

Optoelectronic integration of polymer waveguide array and metal-semiconductor-metal photodetector through micromirror couplers

We report the design and formation of a high-performance polymer waveguide array with 45/spl deg/ micromirror couplers for achieving fully embedded board-level optoelectronic interconnects. We have used Si CMOS process compatible polymer as the fabrication material, which is relatively easy to process and has low propagation loss at 850-nm wavelength, 45/spl deg/ total interior reflection (TIR) micromirror couplers fabricated within the channel waveguides provide surface-normal light coupling between the waveguide and the optoelectronic devices, thus forming a fully embedded three-dimensional optoelectronic interconnect. We have demonstrated a hybrid optoelectronic integrated system of GaAs MSM photodetector array and polymer channel waveguide array with 45/spl deg/ micromirror couplers, showing an aggregate 3-dB bandwidth of 32 GHz.

Polarization dependent loss in polymeric rib channel waveguide

Large polarization dependent loss (PDL) as high as 15 dB was observed in the rib-type channel waveguide fabricated using a birefringent polymer. The PDL mechanism was explained by the mode-mode coupling between the TM mode of a rib and the TE mode of a slab waveguides. This TM-TE mode conversion is due to nonuniform off-diagonal component of the dielectric susceptibility tensor which is generated by a thermal stress during the curing process.

Ultra-low-loss polymeric waveguide circuits for optical true-time delays in wideband phased-array antennas

The optical true-time-delay line is a key building block for modern broadband phased-array antennas, which have become one of the most critical technologies for both military and civilian wireless communications. We present our research results in developing an optical polymer-based waveguide true-time-delay module for multilink phased- array antennas by incorporating wavelength-division multiplexing (WDM) technology. The demonstrated optical polymeric waveguide circuits can provide a large number of optical true-time delays with a dynamic range of 50 ns and a time resolution of 0.1 ps. Various fabrication techniques are investigated for producing ultralong low-loss (0.02 dB/cm) polymeric channel waveguides with tilted waveguide grating output couplers. Fast photodiode arrays are fabricated and rf signals with frequencies of 10 to 50 GHz are generated through the optical heterodyne technique. A detailed study of waveguide amplification to achieve loss-less polymeric waveguide is conducted. The optical amplification of 3.8 dB/cm is achieved at a wavelength of 1064 nm in a Nd3+-doped polymeric waveguide. WDM techniques are also employed for potential multilink applications. The presented methodologies enable hybrid integration with a reduced cost in optoelectronic packaging and an increased reliability and decreased payload for the next generation of phased-array antennas.

Scanning photothermal beam deflection- and scanning photothermal displacement-imaging of polymer channel waveguides: a comparison

In this paper we compare two non-destructive imaging techniques based on thermal and absorptive properties of polymeric channel waveguides: scanning photothermal beam deflection- and scanning photothermal displacement-imaging. The lateral resolution of both methods is identical. There are differences in the sensitivity at a given heat source, the interpretation of the data and the data acquisition time for both methods. The photothermal deflection method is more suitable for laterally structured polymer films.

High-performance metal-clad multimode interference devices for low-index-contrast material systems

Metal cladding is proposed for enhancing performance of multimode interference (MMI) devices for low-index-contrast material systems and numerically investigated by the beam propagation method (BPM). Metal-cladding eliminates spurious phase errors due to the Goos-Hahnchen shift and thus yields improved imaging. The application of this concept is demonstrated by the simulation of a 1/spl times/8 MMI-based wavelength router using a typical low-index-contrast polymer channel waveguide and the results show that the crosstalk is significantly improved.

End-face scattering loss in integrated-optical waveguides

An experimental technique to determine the end-face scattering loss in electro-optic polymer channel waveguides is presented. The technique combines the cut-back and the optimum end-fire coupling methods. A loss resulting from the scattering was a prominent source of waveguide coupling loss and was strongly dependent on the end-face roughness of the guiding and cladding layers induced by cleaving. With the use of our investigation methods, other losses could also be examined with ease and high reliability.

Mode selective polymer channel waveguide defined by the photoinduced change in birefringence

A transverse electric (TE) mode selective polymer waveguide was fabricated by a photobleaching process using a urethane–urea copolymer. The output power of the TE modes through the waveguide was higher than that of the transverse magnetic (TM) modes, when the TE and TM modes were excited equally, the TE mode to TM mode extinction ratio being 27 dB. Mode selectivity was explained by the following relation of the refractive index: the refractive index for the TE modes in the core region was higher than that in the cladding region, while the refractive index for the TM modes in the core was lower than that in the cladding. This relation was attained by the photoinduced change in birefringence of the polymer layer.

Quasi-phase-matched second-harmonic generation in diazo-dye-substituted polymer channel waveguides

First-order quasi-phase-matched (QPM) second-harmonic generation (SHG) is demonstrated in a poled diazo-dye-substituted polymer channel waveguide. The channel waveguide with a nonlinear grating was fabricated by the serial grafting technique using conventional photolithography and reactive ion etching. The dependence of the conversion efficiency on both the waveguide parameter and the grating structure was derived theoretically. A normalized internal conversion efficiency of 1.1% W/sup -1/ cm/sup -2/ at 1.586 /spl mu/m was obtained in the fabricated waveguide with a phase-matched interaction length of 3.4 mm. The experimentally obtained conversion efficiency is compared with the theoretical value, taking into account the effect of mode-mismatching and propagation loss.

Spectral broadening measurements in poly(phenylene vinylene) polymer channel waveguides

In a polyconjugated main chain polymer strip waveguide the nonlinear, nonresonant refractive index n2 was measured by monitoring the signal spectrum broadening due to self-phase modulation. The two photon absorption coefficient α2 was obtained by calibrating the inverse transmission measurement. The nonlinear coefficients were determined to be n2=0.85×10−14 cm−2/W andα2=0.08 cm/GW at a wavelength λ=885.6 nm. The used polymer was poly[1,4-phenylene1,2-di(phenoxyphenyl)vinylene]. The result is in good agreement with interferometer measurements. The material is suitable for all-optical switching.

Modal dispersion phase matching over 7 mm length in overdamped polymeric channel waveguides

Phase-matched second harmonic generation over 7 mm is demonstrated using the modal dispersion of a composite 4-dimethylamino-4′-nitrostilbene/polyetherimde channel waveguide. For a 1-mm-long sample a record figure of merit for polymers of η=P2ω/(PωL2)=14%/W cm2 was measured at 1550 nm. This is comparable to the value reported for LiNbO3 at that wavelength. The efficiency in longer samples is limited by fundamental and harmonic waveguide losses.

Comparison of quasi-phase-matching geometries for second-harmonic generation in poled polymer channel waveguides at 1.5 μm

We have investigated three different quasi-phase-matching approaches to second-harmonic generation (SHG) in DANS (4-dimethylamino-4′-nitrostilbene) poled polymer channel waveguides at 1.5 μm. Periodic photobleaching and periodically poled electrodes deposited directly on the film produced unacceptably high propagation losses. However, periodic electrodes on the substrate gave low losses and useful SHG.

Second harmonic generation in polymeric channel waveguides using modal dispersion

The authors report phase-matched second harmonic generation using the modal dispersion of a polymeric channel waveguide. An internal figure of merit of 1%/W cm2 was obtained for TM00ω to TM202ω conversion. Phase matching was maintained for 2 mm using multilayer spincoating technology.

Photostability of Nonlinear Optical Copolymer Under Irradiation with Infrared Light

Abstract Nonlinear optical copolymer with 4-dimethylamino-4′-nitrostilbene as a side chain group was investigated for the photostability by irradiation of infrared light. The light at 1.313 μm, which is very low absorptive for the material, was coupled into the polymeric channel waveguide formed by photobleaching technique. Transmission loss of the infrared light through the channel waveguide has been negeligibly changed even after for a long irradiation. Also, the refractive index change in slab waveguide is undetectable. The nonlinear optical polymer used in this study turns out to be quite reliable in terms of photostability.

Modeling photobleached optical polymer waveguides

One of the most efficient ways to prepare nonlinear optical polymer channel waveguides is by photobleaching. To control the index profile precisely and to design and improve the performance of active electro-optical devices, modeling of the photobleaching process is important. We report our phenomenological bleaching model, which uses a stretched exponential time dependency technique that predicts the index profile for polymer channel waveguides and present design rules for active optical switches and modulators. One way to verify the bleaching model is to calculate the effective index and compare this with our measured effective index obtained with prism-coupling techniques. The bleaching model shows good agreement with experiments.

Stable highly transparent nonlinear optical polymer for laser frequency doubling

Channel waveguides of a polymer with nonlinear optical properties and transparency down to 400 nm were fabricated to be used for laser frequency doubling. The polymer was corona poled to induce orientation of the nonlinear chromophores, resulting in a stable poled polymer. End-fire coupling was used to couple the fundamental beam into the polymer channel waveguide. Green light was observed in the form of Cerenkov radiation using a Q-switched Nd-YAG laser lasing at 1064 nm as the fundamental beam. The total efficiency of the second harmonic conversion was 1.4 × 10 −3 %/W.

Laser ablation of nonlinear-optical polymers to define low-loss optical channel waveguides

Laser photoablation of polymeric channel waveguides with embedded contact masks is described. The ablation technique is capable of forming low-optical-loss waveguides with an end-face quality suitable for pigtailed devices at rapid rates. The optical-mode profiles and the optical-loss measurements are reported, and scanning electron microscopy characterization and laser ablation rate measurements are described. The end-face quality processed by laser ablation is sufficiently good for end-fire coupling and thus can permit the elimination of polishing steps.

Second harmonic generation by counter propagating beams in 4-dimethylamino-4′-nitrostilbene side-chain polymer channel waveguides

We demonstrate surface emitted second harmonic generation due to mixing of counter propagating waves in in-plane poled, low loss, channel waveguides of 4-dimethylamino- 4′-nitrostilbene (DANS) side-chain polymers. Single film DANS side-chain polymer waveguides yield high conversion efficiency devices.

Optical intensity modulation in a vertically stacked coupler incorporating electro-optic polymer

A vertically stacked directional coupler incorporating electro-optic poled polymer was fabricated by spin coating, photolithography, and reactive ion etching processes, based on the fabrication technique used for polymeric single-mode channel waveguides. Vertically coupled operation at 1.3 μm have been achieved between two stacked channels which were kept 3.5–5 μm apart by a narrow cladding layer. The intensity modulation has been clearly demonstrated in the coupler with electrodes when a voltage is applied at 10 kHz between them.

Cerenkov type phase-matched second harmonic generation in polymeric channel waveguides

Fabrication of polymer channel waveguides by etching on glass is reported. Results on second harmonic generation (SHG) in the Cerenkov mode from stable poled polymeric channel waveguides are presented. The waveguide conversion efficiency for doubling of Nd:YAG laser beam was estimated to be 0.1%/W with a total efficiency of 4.9×10 −7%/W.