Realization of Polymeric Electro-Optic Modulators with Less Than One Volt Drive Voltage Requirement
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sophisticated integration [11,12]. Very low crosstalk is observed for densely packaged modulators [13]. Robust modulator circuits can be fabricated [14] particularly when attention is given to the details of materials processing (spin casting, poling, and lattice hardening) [15]. In short, the ease of processing of polymeric materials into sophisticated 3-D circuits has been proven to be a significant advantage for the use of such materials. Although a number of chromophores have been synthesized with large molecular hyperpolarizabilties, β, and dipole moments, µ [16-18]. Long anticipated large macroscopic electro-optic coefficients have only recently been realized for poled polymer materials [11,19]. Fortunately, the advent of modified CLD-type chromophores (structure shown in figure 1 below) has permitted realization of devices with digital level 90 85 80
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drive Figure 1. Variation of the electro-optic coefficient (pm/V) with CLD-1chromophore loading (wt/wt %) in poly(methylmethacrylate) is shown. Electro-optic coefficients were measured at 1.06 µm; the maximum observed electro-optic coefficient at 1.3 µm lies in the range 55-60 pm/V. Observation of a maximum in such plots is typical for chromophores with dipole moments greater than 7 Debye. Key to realization of these large optical nonlinearities is the isophorone group sterically protecting the polyene bridge structure and the bulky TBDMSO groups at the donor end. Even larger electrooptic coefficients (>100 pm/V at 1.06 µm) is obtained for a somewhat longer polyene bridge sterically protected by fused isophorone groups (referred to as the GLD series). drive voltage requirements. Typical results for CLD-1 covalently incorporated into 3-D crosslinked polyurethane materials is shown in table I. Even lower drive voltages have
Table I. Performance Characteristics of CLD-PU Modulators Vπ = 2.5 V @ 1300 nm ; 3.7 V @ 1550 nm Frequency to ~ 60 GHz; Temperature Maximum ~90°C Insertion Loss 5 - 6 dB; Extinction ratio 25-30 dB
recently been observed by researcher at TACAN Corporation employing CLD-1 in PMMA or amorphous poly(carbonate), APC, and a push-pull Mach Zehnder modulator configuration [20,21]. They observed an average drive voltage of 0.8 volts for six 3-cm interaction length modulators tested and an average drive voltage of 1.08 volts for six 2cm interaction length modulators. A poling voltage of 500 volts was used to prepare the 3-cm modulators and a poling voltage of 750 volts was used in the preparation of the 2cm modulators. The preceding results, achieved for the CLD-1 chromophore incorporated in various polymer lattices, suggest that the putative high electro-optic activity of organic materials can indeed be realized. It is important for us to understand the process by which these improved electro-optic materials were produced and to understand what can be expected in the future. To do this, we must understand the
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