Optical communication systems have evolved from simple point-to-point transmission systems in the late 1970's to today's multi-channel DWDM systems integrated with optical switching. These advanced DWDM systems have very stringent optical performance, system reliability, and cost requirements. As a result, deployment of these systems has been limited to date. This situation has started to change recently and a lot of industry interest is now focused on deploying advanced optical systems in high performance telecommunication environments. Integrating optical functions in a single opto-electronic integrated circuit (OEIC) has the potential to accelerate this deployment by reducing manufactured costs, reducing physical card size, and increasing reliability. This paper will describe a specific instance of a DWDM transport and optical switching system, and its functional decomposition into individual cards. The requirements that are then imposed on the optical components placed on these cards are described. We will show the function of advanced switching and optical monitoring. Initial validation of a system card was made using off-the-shelf discrete optical components and then replaced with an OEIC implementation. Results of the integration experience will be presented.
High-Speed silicon modulators, based on carrier dependent absorption effects, have recently been reported in the literature. For improved performance, these modulators rely on a MOS configuration to control carrier accumulation, rather than on carrier injection from the contacts, to induce an index perturbation for controlling the phase of a propagating signal. Accurate simulation of the carrier distribution is required for the analysis of such a device. This entails the self-consistent solution of the coupled electro-thermal transport equations. An appropriate absorption model is also required in order to couple the carrier distribution to the propagating optical field, via a complex index perturbation. Finally, in order to determine performance, the full optical problem must be solved throughout the device domain.
The present work integrates the Box Integral Method of solving the active device transport equations with the Vector Beam Propagation Method (BPM) typically used to analyze passive waveguide structures. A modified Drude Model and Kramers-Kronig relations are used to determine the carrier density dependent absorption and refractive index perturbations. This complex index perturbation is determined as a function of the applied voltage, and used by a simulator based on the BPM to determine the optical performance of an example silicon modulator. Both steady-state and frequency responses are considered. This comprises a general methodology for analyzing realistic semiconductor photonic devices in which the optical propagation is affected by the electro-thermal transport within the device.
We demonstrate high packing density true-time-delay lines using 3D integrated polymer waveguides. Although several relatively new delay-line approaches based on the use of optical fibers offer excellent performance, they require complicated, bulky, and costly packaging. The demonstrated 3D integrated polymer waveguide delay lines will overcome these shortcomings. Packaging is greatly simplified, and the layered integration of the waveguides offers greater compactness.
A novel approach for laser beam deflection using the thermal optic prism array in a polymeric planar waveguide is developed. This approach is based on the different thermo- optic properties between polymer and silica, the two optical materials employed for the guided wave beam deflector. A waveguide structure with the core layer composed of inversely positioned polymer and silica triangles forming a polymer/silica prism array has been fabricated. Through electrical heating, a temperature change results in an index difference between the two optical materials and creates an optical prism structure in the polymer/silica planar waveguide. A beam deflection of 5.4 degree was observed under a temperature change of 60 degrees C in the fabricated prism array. The sensitivity of the device is 0.09 degrees/degrees C. A maximal number of resolvable spots of 8 was achieved at a low driving power from the thermo-optic prism array structure. The accuracy of beam deflection approaches 16 micro-radian. The device fabricated has a thickness of 5 microns, a prism aperture width of 600 microns, and a device length of 7 mm. Optimal design to maximize the deflection angle and the number of resolvable spots has been evaluated.
CMOS compatible optical polyimide based thermo-optic switches have the potential use as low-power switches. These switches would have many advantages over other switches based on inorganic crystals. For one, they can be integrated into module-to-module systems using currently available VLSI fabrication techniques. Polyimide based, 1 by 2 thermo-optic switches are fabricated onto silicon wafers and tested. We report the properties and characteristics of digital thermo- optic switches designed to operate at 1.3 micrometers . Also, the switching characteristics at different heating electrode voltages are tested and compared.
A beam deflector device has been demonstrated that used thin-film electro-optical polymeric waveguide. Prism cascade was fabricated within a planar waveguide. We report the detail of the design and fabrication of new polymer material beam deflector to operate at 1.3 micrometers .
We present an innovative approach for fabricating a polarization modulator, which outputs light alternating in time between left- and right-hand circular. The aim is to replace bulky and expensive photoelastic, liquid-crystal, or inorganic-crystal polarization modulators for certain applications. We use a single-mode polymer waveguide, where a controllable amount of birefringence via the electro-optic effect adjusts the output polarization. It has a very small mass, low power consumption, and very compact size. Other desirable attributes are its use of no moving parts, low voltages, and a single high-speed voltage source. The wavelength of operation is adjustable from 700 to 1600 nm. Furthermore, it can operate at arbitrary frequencies up to the GHz range as compared to the KhZ operating frequencies of photoelastic and liquid-crystal modulators. We show how to overcome the problem of different TE an TM mode amplitudes in polymer waveguides and how to ease the fabrication and packaging tolerances. We present some performance data on a polymer waveguide that outputs circularly polarized light.
Polymer thermooptic waveguide taps have a potential application as light routers for guided wave optical interconnects involving cascaded fanouts. The taps can guide light form an optical bus bar and direct it into other devices in a switching/modulation network. Thermooptic waveguide taps are designed and fabricated on silicon wafers using standard VLSI fabrication techniques. Coupling of light into an adjacent waveguide tap is observed to increase by 12.3 percent from 38.7 percent to 51.0 percent with the application of 34 mW of power.
We report a surface-micromachined electrostatic deflector as a controlling element for a novel micro-opto-electro- mechanical (MOEM) bandpass tunable filter for a wavelength- division-multiplexed optical-fiber sensor system. Such a tunable MOEM filter involves multiplexed volume holograms, a surface micromachined electrostatic deflector, and an array of Si photodetectors. The micromachined electrostatic deflector, providing fast and repeatable adjustments, greatly enhances the dynamic tuning range of the filter. To micromachine the electrostatic deflector, we use thick photoresist as a sacrificial layer that is patterned using conventional microlithography, followed by electroplating. Ten deflectors with different lengths have been fabricated, and the electrostatic actuation of each device has been demonstrated. DuPont photopolymer film is employed for forming multiplexed volume holograms, which in conjunction with a photodetector array will allow the filter to operate at many wavelength windows. The incorporation of the multiplexed volume hologram with the electrostatic deflector will allow us to tune dynamically the filter.
We report the demonstration of a compact laser-beam deflector based on electro-optic prisms formed within a thin-film polymer waveguide. We fabricate planar waveguides using a polymer that can be readily poled and cured through the simultaneous application of a poling voltage and heat. The index of refraction of each prism in the cascade, but not of the surrounding polymer, is modulated by the electro- optic effect through the application of a drive voltage. A laser beam, to be deflected, is coupled into and out of the planar waveguide by cylindrical lenses. The application of a drive voltage creates a sequence of prisms in the planar waveguide, which change the path of propagation of beam through the planar waveguide with a variable angle of refraction depending upon the voltage. The deflection efficiency is observed to be nearly 100 percent and the laser beam maintains its Gaussian intensity profile after propagating through the device.
A beam deflector has been designed and fabricated that uses a nonlinear-optical polymer. The device is composed of a cascade of polymeric electro-optic prisms formed within a planar waveguide of the same polymer system. A laser beam, to be deflected, is coupled into and out of the planar waveguide by cylindrical lenses. The light path of the laser beam within the planar waveguide is adjusted to pass through the successive prisms of the cascade, where the Gaussian transverse-mode profile is centered (initially) within each of the prisms. The index of refraction of each prism in the cascade, but not of the surrounding polymer, is modified by the electro-optic effect when a drive voltage is then applied. The application of a drive voltage thus causes the planar waveguide to function as a sequence of prisms that change the path of propagation of the beam through the planar waveguide. The collimated beam formed by the output cylindrical lens deflects. The extent of deflection is proportional to the amount of refractive-index change induced in the prism cascade. A uniform electrode structure can drive the electro- optic prism cascade, which should enable the device to operate at high speeds when traveling-wave driven.
We use high temperature liquid-contact poling as a method to pole efficiently cladded nonlinear optical polymer films. Poling voltage as high as 400 volts is applied to planar waveguides which have a nonlinear optical film of 1.2 im thick. The lack of a quick method to characterize the poled cladded nonlinear optical films inspires us to devise a new electrooptic measurement method. This method can determine r33 and r13 separately because it uses light of single polarization state to probe the nonlinear optical film. The interference between the modulated light and the unmodulated light in the reflected beam is used to extract electro-optic coefficients. Theoretical analysis of the relationship between the reflected light intensity and the electro-optically modulated signal is consistent with the experimental results. Formulae to calculate electro-optic
coefficients are deduced. This method uses an even simpler experimental setup than that of the widely used ellipsometric
method.
An analysis is made of the effect of tiled-poling-induced birefringence on the polarization conversion in single mode waveguides. A polarization-independent electro-optic modulator with continuous-electrode structure for high speed modulation is designed by using formulae deduced from coupled mode theory. This device uses a Mach-Zehnder structure where both arms are constructed using tilted poling. The same device can be operated in two different modes. One is common-mode which has the advantage of polarization preserving, while the other is differential- mode which features a low driving voltage. An estimation of the influence of misalignment of the poling electrodes on the extinction ratio shows a large fabrication tolerance.
In this paper, a unidirectional electrooptic modulator based on an asymmetrical highly multi-mode wavedguide coupler is proposed. The energy distribution of all the guided modes within a highly multi-mode waveguide is studied and a new conclusion is obtained. Furthermore, the whole coupling process among all the guided modes between two nonidentical highly multi-mode waveguides is analyzed and the total coupling efficiency is calculated. To achieve high switching performance in a guided-wave coupler, a larger guide is made to have a dumping effect, which can be implemented by using an absorbing material or a grating. Based on the dumping effect, the dumping process is theoretically modeled and the dumping efficiency is simulated. Not only can a high dumping efficiency of 100 percent be achieved, but a high electrooptic modulation depth more than 90 percent can also be implemented.
LD-3 polymer directional couplers have the potential use as low-voltage modulators and switches. They can be integrated into module-to-module systems using currently available VLSI fabrication techniques. Modes of channel waveguides are calculated and coupling lengths are determined using BPM_CAD. We report the fabrication of LD-3 polymer directional couplers designed to operate at 1.3 micrometers .
Directional couplers with four sections poled in four perpendicular directions are proposed for the first time as a new electro-optic switch configuration in which complete conversion of both TE and TM light from one waveguide to the other can be achieved simultaneously by a low driving voltage adjustment. The perpendicularly poled sections of the switch make the device completely polarization- independent, and the inversely poled sections offer an extremely relaxed fabrication tolerance for the device. This configuration of each section poled in a different direction also makes it possible to drive the electro-optic coupler with a uniform electrode, which ensures high-speed operation of the device. Both the switching characteristics and the fabrication tolerance are simulated.
Domain-inverted electro-optic films have many applications in photonic devices such as high-speed electro-optic switches and quasi-phase-matched second-harmonic generators. For example, inverted domains allow a uniform electrode structure to be used in a reversed-(Delta) (beta) directional coupler. Since corona poling is not applicable to create inversely poled structures in a crosslinkable polymer, direct-contact poling and liquid-contact poling are investigated. In unidirectional poling, liquid-contact poling allows poling electric fields higher than 250 V/micrometer to be applied, which is comparable to electricfield strengths in corona poling but much higher than those in direct-contact poling. For domain-inversion, the results also show that liquid-contact poling allows much higher poling electric fields to be applied than in direct- contact poling.
Second-harmonic generation from chiral surfaces has different responses to fundamental beams that are left- and right-hand circularly polarized. This form of nonlinear optical activity can occur within the electric-dipole approximation. However, second-order nonlinearities involving magnetic-dipole transitions, which can be strong in chiral media, also contibute to the circular-difference response. We describe a new measurement technique that is based on continuous variation of the state of polarization of the incoming fundamental field, which allows us to assess the relative importance of the electric- and magnetic-dipole contributions to the circular-difference response. We will report the results of our measurements on second- harmonic generation from surfaces consisting of thin films of chiral polymers.
We report on a novel class of optically nonlinear polymeric materials realized by processing onto a substrate a combination of molecules and polymers comprising hyperpolarizable and thus optically nonlinear molecular groups, liquid crystal moieties, and chiral moieties. Since processing of this combination of materials leads to a spontaneously noncentrosymmetric bulk orientation of the hyperpolarizable moieties in its thermodynamically most stable state, the material exhibits second-order nonlinear-optical properties that can be used for second-order nonlinear-optical effects such as frequency doubling of optical radiation, the linear electro- optic of Pockels effects, magneto-optic effect, nonlinear dichroism, etc. We will present and discuss the experimental results concerning the nonlinear-optical properties obtained via frequency doubling of light in these materials.
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