Optical modulator electrode

Interest has developed in electrochromic light transmission modulators, which are called smart windows , for control of temperature and lighting in buildings and automobiles. A cross section of an electrochromic light transmission modulator is shown in Fig. 11.31 (Rauh and Cogan, 1988). The two electrochromic elements of the structure are designated ECl and EC2, and are sandwiched between two thin film, optically transparent, electrodes of ITO and separated by an electrolyte. The ECl layer should colour when a negative potential is applied and the EC2 layer should either colour under positive potentials or remain in a transparent state. This is indicated by the chemical reactions ... 

Electro-optical modulators are other examples whose efficiency is enhanced in the presence of ion-radicals. These devices are based on the sandwich-type electrode structures containing organic layers as the electron/hole-injecting layers at the interface between the electrode and the emitter layer. The presence of ion-radicals lowers the barrier height for the electron or hole injection. Anion-radicals (e.g., anion-radicals from 4,7-diphenyl-l,10-phenanthroline—Kido and Matsumoto 1998 from tetra (arylethynyl) cyclooctatetraenes—Lu et al. 2000 from bis (1-octylamino) perylene-3,4 9,10-bis (dicarboximide)s— Ahrens et al. 2006) or cation-radicals (e.g., cation-radicals from a-sexithienyl—Kurata et al. 1998 l,l-diphenyl-2-[phenyl-4-A/,A- /i(4 -methylphenyl)] ethylene— Umeda et al. 1990, 2000), all of them are electron or hole carriers. 

Figure 3.19 Intensity-modulated photocurrent spectroscopy, showing (a) the layout of a typical spectrometer, and (b) the response obtained AOM, acousto-optic modulator RE, reference electrode WE, working electrode CE, counter electrode FRA, frequency response analyzer...

As already noted, resistive loss in metal electrode structures and in transition from millimeter wave waveguides to the electrode structure is the greatest problem in achieving 100 GHz and higher electro-optic modulation. Fetterman and co-workers [301] have shown by pulse techniques that the 3-dB bandwidth of polymeric electro-optic materials is typically in the order of 360 GHz for 1 cm of material. Stripline electrode structures have been used to achieve operation to somewhat above 100 GHz. Fetterman and co-workers [282] have recently described a novel finline transition between a millimeter waveguide and such elec-... 

Measurement of device bandwidths in the order of 100 GHz typically requires heterodyne detection and a stripline electrode configuration such as that illustrated in Fig. 31. The response of polymeric electro-optic modulators is typically flat to 100 GHz. Fall off above that frequency (Fig. 32) can be traced to resistive losses in millimeter wave transmission structures and in the metal electrodes. 

Fig. 10.5 High frequency optical modulators and switches (a) construction of a rib wave guide with microwave strip line upper electrode, and plan views of (b) Mach-Zehnder, (c) birefringent, and (d) bi-directional coupler modulators. Reproduced with permission of Wiley-VCH from Dalton et al. (1995).

Skeie, H. and Johnson, R.V. 1991. Linearization of electro-optic modulators by a cascade coupling of phase modulating electrodes. In Integrated Optical Circuits, SPIE Vol. 1583, pp. 153-164, SPIE. 

Very recently. Block et al. [133] reported on optical modulators with ring diameters smaller than 50 pm in a silicon nitride based waveguide system on silicon oxide with a top cladding of an electro-optic polymer, namely AJTB141 chromophore 28% wt into an amorphous polycarbonate polymer. Using Cu electrodes they attained a high frequency modulator with modulation up to 10 GHz with low drive voltage (2.7 Vpp). 

Ion-storage electrodes with higher charge capacities and small optical modulation were obtained with mixed oxides. An overview of the photopic transmittance of 24 different counter-electrode films in the intercalated (Tins) and deintercalated states (Text) and their maximal possible charge was reported by Opara Krasovec et al. (2002) and is shown in Figure 35-5. The photopic transmittance Tvi of the films was determined from the UV/VIS spectra of the films in toth states by... 

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