Polarization dependent loss in polymeric rib channel waveguide

Large-core, tapered Al 2 O 3 :Nd3+ channel waveguides have been fabricated and optical amplification at a wavelength of 880 nm has been characterized. Amplification in optical backplanes has been demonstrated by inserting such Al 2 O 3 :Nd3+ channel waveguides in between two polymer waveguides. A maximum 0.21-dB internal net gain has been demonstrated in an Al 2 O 3 :Nd3+ waveguide coupled in between two polymer channel waveguides. The gain can be improved by increasing the pump power and adjusting the waveguide geometry and dopant concentration for the chosen pump power. Use of such rare-earth-ion-doped waveguide amplifiers can provide a solution for compensating the losses occurring in optical interconnects.

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.

We present the core thickness dependence of the propagation loss and the polarization dependence loss (PDL) of hollow waveguides of various air core thicknesses. The addition of phase-control layers to GaAs/AlAs multilayer mirrors enables us to reduce the PDL by one order of magnitude. The propagation loss and the PDL of a 5 µm air core hollow waveguide are 2.8 dB/cm and 1.7 dB/cm, respectively, which are currently limited by the reflectivity (0.998) of the GaAs/AlAs multilayer mirrors.

Channel waveguides at 1540 nm in X- and Z-cut LiNbO3 are formed by one-step multienergy MeV O2+ implantation. Single perpendicular mode in both planar and channel waveguides is demonstrated. In the ne channel waveguide, double transverse modes are observed because of the large index difference and broad width of the channel. A single transverse mode is obtained in the no channel waveguide. The thickness of the waveguide is less than 2 mum, and the compactness of the waveguide is attributed to the large index difference between the guiding region and the low-index barrier. The mode patterns and the waveguide loss are measured and analyzed. The loss of 0.9 and 0.7 dB/cm are obtained from the no and ne channel waveguides, respectively.

We present an array of electro-optic Bragg gratings for on-chip optical waveguide interconnect applications. These electro-optical gratings can serve as switchable couplers to couple high-speed optical signals from a vertical cavity surface emitting lasers (VCSEL) to on-chip polymeric waveguides and from waveguides to photodetectors. The unique switching feature provides a promising solution to facilitate dynamically reconfigurable on-chip optical interconnects architecture for intra-chip, chip-to-chip and board-to-board data communications. We demonstrate on-chip switched optical waveguide interconnect using electro-optic grating and polymeric channel waveguides on a silicon substrate.

Fluorinated polyimide (FPI) is an attractive material for fabricating low-loss optical waveguides at 1.55 micrometers , because of its superior optical and thermal properties. Although FPI planar lightwave circuits (PLCs) are usually fabricated on silicon substrate, such PLCs exhibit relatively high polarization dependence and high transmission loss compared with those of silica PLCs. Use of an FPI substrate overcomes these problems that mainly originate from the difference in thermal expansion coefficient between FPI and silicon. It improves the optical property of FPI waveguides, e.g., the transmission loss and polarization dependent loss for straight waveguides reduce to less than 0.3 dB/cm and 0.1 dB, respectively, in the 1.55-micrometers band. The use of FPI substrates will enable the fabrication of high-optical-quality FPI PLCs such as 1x8 splitters.

Using an analytical description of the profile of the indexes of refraction of birefringent Ti:LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> channel waveguides, a very fast method was developed to compute the optical mode field distributions. Using these results, field overlap integrals were evaluated to calculate the pump threshold power of integrated optical parametric oscillators with Ti:LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> channel waveguides. A variation of the guide parameters enabled the determination of optimized profiles yielding minimum oscillation threshold. The pump threshold power of doubly and singly resonant structures was evaluated as a function of the resonator parameters, waveguide losses, mirror reflectivities, and device length. In the doubly resonant configuration, threshold powers lower than 10 mW can be expected.

Optical gains at 637 nm wavelength using light‐emitting diodes (LEDs) instead of traditional semiconductor lasers as pumping sources are demonstrated in the organic molecule 2,6‐bis[4‐(diphenylamino)phenyl]‐9,10‐anthracenedione (AQ(PhDPA)2)‐doped polymethylmethacrylate (PMMA) and SU‐8 polymer waveguides. Under excitation of four blue‐violet LEDs with different central wavelengths, fluorescence in the red band is observed owing to the transition of AQ(PhDPA)2from the excited states to the ground state based on the thermally activated delayed fluorescence (TADF) mechanism. Channel waveguides with a cross‐section of 6 µm × 5 µm are fabricated. The relative gains of 5.0 and 4.0 dB cm−1are obtained in rectangular waveguides with active core layers as AQ(PhDPA)2doped PMMA and SU‐8, respectively. Optical gains have also been achieved in waveguides based on evanescent‐wave coupling. By using the vertical top pumping mode of a 450 nm LED, a gain of 2.6 dB cm−1is obtained in a passive SU‐8 waveguide with AQ(PhDPA)2doped PMMA as the upper cladding. In contrast, the replacement of SU‐8 with AQ(PhDPA)2doped SU‐8 as the active material, triples the optical gain, which reaches to 7.8 dB cm−1owing to the presence of stimulated excitation in both channel waveguide and upper cladding.

We reported on, to our knowledge the first time, the channel waveguide formation in KTiOPO4 crystal by the implantation of protons with a special designed photoresist mask. The 2-D refractive index profile was constructed according to the measured dark-mode spectroscopy (for longitudinally planar configuration) as well as the shape of the channel waveguide cross section. Based on this index distribution, the modal profile was calculated through a numerical simulation, which showed reasonable agreement with the near-field light intensity distribution of the guided mode that was obtained by an end-coupling method. After annealing at 200deg C for 30 min in air, propagation loss of the channel waveguides was determined to be as low as ~2.9 dB/cm at wavelength of 632.8 nm.

The buried channel waveguides on optical glass is fabricated by a high electric field technique. The 900V voltage was applied on the glass to accelerate the field-driven ion exchange process by expeditiously replacing host sodium ions in the glass with silver ions. As a result, the lowest optical loss was achieved on waveguides fabricated at 350°C. The optical loss for channel waveguides was measured using the interference technique with a 0.6328&#956;m He-Ne laser. And the loss of 0.30 dB/cm was obtained for channel waveguides of 20&#956;m in depth, relatively low for waveguides of such depth at red wavelength. A nearly Gauss refractive index profile was observed from every channel waveguide fabricated.

The adhesive bonding technique is widely used for joining similar or dissimilar materials in various engineering areas. Mismatches in the thermal expansion coefficients of adhesive and adherend materials in the vicinity of bi-material interfaces result in incompatible thermal strains and discontinuous thermal stress distributions along the bi-material interfaces. During the adhesive curing process, thermal residual stresses are induced due to the chemical and physical changes in adhesive material. The expansion of the adhesive with changes in moisture and temperature levels is the reason for hygroscopic residual stresses. Non-uniform temperature or material composition distributions also result in non-uniform thermal strain and stress distributions. Loading with a relatively high frequency cyclic component may result in a temperature rise due to internal heat generation and consideration of viscoelastic time-temperature effects may become necessary in the stress analysis even at moderately low temperatures. The crack nucleation, initiation and propagation around bi-material notches, and the fatigue crack growth in adhesively bonded integrated structures are important design considerations under cycling thermal loads. Therefore, the thermal strain and stress states of the adhesive joints should be analysed in order to predict the joint strength accurately and to improve joint service life. This article reviews from simple to more complicated mathematical models to analyse the thermal stress and deformation states of various adhesive joints under both steady state and transient thermal conditions.

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single-m,ode fibers. The taper smoothly converts a highly elliptical waveguide mode into a bigger and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5-2 mm in length is made in the low index upper cladding to reduce its thickness from several micrometers to zero, followed by the coating of a second upper cladding with index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows bigger a light propagates, whereas the confinement by the lower cladding and lateral confinement are hardly affected. The waveguide mode grows in the vertical direction away from the lossy ground electrode and substrate; therefore no compromise between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and tapered photoresist etching mask, are develop for making this vertical taper. Mode expansion and a 1.8 dB reduction in coupling los, which is not sensitive to waveguide width and polarization, is obtained in our preliminary experiment.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Various techniques have been used for the fabrication of polymeric channel waveguide for active and passive devices: poling, photobleaching, photolocking, reactive ion etching, etc. Among them, photobleaching offers simple processibility and controllability. Some authors[1,2] have reported on the fabrication of channel waveguides by this tehnique. However, it takes long time, typically on the order of tens to hundreds hours, to bleach out a nonlinear optical polymer (NLO) thin film with the thickness of a few µm using mask aligner.

The moisture diffusion phenomenon and moisture stress in a specific LED module was studied in this paper. Firstly, the finite element model of the LED module was built. The moisture diffusion distribution at operation condition with 25 °C ∼ 85 °C, was analyzed. Secondly, the temperature distribution and moisture distribution of the LED module during reflow soldering process were simulated at the initial moisture condition of 85%RH. The thermal stress, moisture stress were analyzed, respectively. The simulation shows that maximum thermal stress in the LED module was 30.1 MPa and the maximum moisture stress was 7.8MPa. Furthermore, integrated vapor pressure, moisture stress and thermal stress modeling of LED module during reflow were established. The resulting maximum integrated stress was up to 178 MPa. Thirdly, a curing process at the condition of 125°C which was assumed to dry out the moisture in the LED package before reflow process was modeled and the corresponding moisture diffusion distribution was obtained.

We derive exact mathematical expressions for both the amplitude and phase evolution of optical waves due to linear and nonlinear interactions in a waveguide device and propose a section-wise-exact coupled-mode theory analysis for quasi-phase-matched second-harmonic generation in the waveguide. Section-wise-exact coupled-mode theory is readily applicable to nonuniform quasi-phase-matched gratings and can be useful as a quantitative method in their analysis and design. Using the method, several numerical results are presented for second-harmonic generation in periodically poled LiNbO/sub 3/ channel waveguides. In addition, we introduce a split-step method which takes propagation losses into account and which can include linear and two-photon absorption and waveguide losses.