Analysis And Simulation Of Integrated Waveguide Electro-optic Switch Based On Poled Polymer

Optical switches and arrays are key components in optical communicationnetworks especially the dense wavelength division multiplexing (DWDM) systems.Compared to other-type optical switches, electro-optic (EO) switches utilizing EOeffect take the advantages of fast switching speed, large transmission capacity, et al,and the researches on such switches including both experiment and theory have beenincreasing dramatically. This paper focuses on novel structure design and noveltheoretical analysis method, and the detailed contents of this paper are given as below.Firstly, as the basic design theory, the mode effective refractive index and modeloss coefficient of five-layer medium-absorption slab waveguide and seven-layermetal-clad slab waveguide are analyzed by using the perturbation theory and thedifferentiation method. The characteristic equation and mode absorption coefficient ofmetal-clad rib waveguide are derived, and the mode distribution of rib waveguide andthe directional coupling between two rib waveguides are analyzed. In the following,the change of refractive index ellipse of poled polymer is discussed. The EOmodulation coefficient and effective index change are obtained. When the electrode isinfinitely thin or finitely thick, the point-matching method and extendedpoint-matching method are adopted for analyzing the electric distribution. Themicrowave characteristic parameters and impedance match are addressed.Secondly, as one main work in this paper, a multifunctional polymer asymmetricMach-Zehnder interferometer (AMZI) electro-optic switch/filter comprising twoserial-cascaded phase-generating couplers (PGCs) and a pair of microstrip electrodesis proposed. Theory, structure and formulation on the multifunctionalspectrum-periodic polymer AMZI EO switch/filter based on two serial-cascadedPGCs are proposed. The output powers, phase compensation condition and ERcompensation condition are derived, and the switching condition and characteristicformulation are obtained. For realizing the above two compensation conditions, design and optimization on the AMZI switch/filter with uniform free spectrum range(FSR) of20nm within1400~1600nm are performed. The filtering and switchingcharacteristics as well as their temperature dependency are discussed, and acomparison is carried out to show the superiority of this device.The device has two input ports (A1and B1) and two output ports (A2and B2),port A2contains10channels numbered from#7to#2, and port B2contains9channels numbered from#7to#1. The ON state indicates that the switching powerat the central wavelength of each channel reaches the maximum, and the OFF stateindicates that the switching power at the central wavelength of each channel reachesthe minimum. The ON-and OFF-states voltages are0and8.06V, respectively. As anoptical filter (ON-state), the wavelength space of each channel is within19.2~21.0nm(standard value20.0nm) with the maximum period variation less than1nm. Theinsertion loss for channels#7to#2of port A2is within2.69~19.30dB, and that forchannels#7to#1of port B2is within2.09~20.20dB. As an EO switch, the ER ofeach channel between ON-state and OFF-state for port A2is more than15.70dB, andthat for port B2is more than12.60dB.Thirdly, by using two-section cosine-transitive coplanar waveguide grounded(CPWG) electrodes, a polymer directional coupler (DC) EO switch is optimallydesigned with both relaxed fabrication tolerance under cross-state and high switchingspeed over100GHz. By using the extended point-matching method, its waveguideand electrode parameters are optimized. Based on the given transfer matrix, a novelFourier analysis technique is proposed, and formulations regarding the time-andfrequency-domain responses are derived. The static characteristic under direct-currentvoltages, the modulating characteristic under positive cosine-wave signals, and theswitching characteristic under positive square-wave signals are described. Acomparison between our technique and the BeamPROP software and a comparisonbetween the performance of this switch and that of our previously reported switchwith two-section separated reversed electrodes are both carried out.Under1550nm, the bar-and cross-state voltages are0and2.67V, respectively,for the switch with a total length of8.38mm. The insertion loss and crosstalk are lessthan3.89and–30dB, respectively. The3dB modulating bandwidth and cutoffswitching frequency are about110.0GHz and131.6GHz, respectively, and the10~90%rise time and fall time are both about3.80ps. Owning to this configuration, its cutoff switching frequency is enhanced to9times of that of our previouslyreported EO switch with two-section separated reversed electrodes, which expands theultra-high speed and large capacity applications for such switches. The proposedFourier analysis method can also be adopted to evaluate the responses under theoperation of any other form driving signals with Fourier transformation.Specially speaking, the novelties of this thesis are concluded as follows.(1) By adding additional phase to the impulse-response of the traditional AMZI,its spectrum is periodized, and phase compensation condition is derived. The noveluniversal spectrum-periodized theory for designing a spectrum-periodic AMZI filter isproposed by using two PGCs.(2) A multifunctional polymer AMZI EO switch/filter comprising twoserial-cascaded PGCs and a pair of microstrip electrodes is realized. Under ON-statewhen no voltage is applied, the device can be treated as a filter with periodic spectrum,whereas under OFF-state, the light power at the central wavelength of each channel isturned off, then the switch acts as a wavelength-selective electro-optic switch.(3) Since the switch with two separated electrode sections cannot be configuredas traveling-wave style but only be driven in lumped parameter way, the cutoffswitching frequency depending on the product between the capacity of the electrodeand the equivalent resisters of the cable and voltage source is usually small. Apolymer DC EO switch with traveling-wave driving configuration is proposed.Through optimization on waveguide parameters in EO region and transition region,this switch reveals a high cutoff switching frequency over100GHz in theory.(4) Although we have proposed the micro-element propagation analysis methodon the time-domain response of EO switches, it can only be used to evaluate theresponse parameters under the operation of strict step-style square-wave signal. As anobvious improvement to this method, a novel Fourier analysis technique and relatedformulas are especially presented for analyzing the modulating and high-speedswitching performances under positive cosine-wave and square-wave signals. Thismethod can also be utilized to analyze the response characteristics under the operationof any other style signals by use of Fourier transformation.