Design considerations for monolithic beam formers based on electro-optic polymer phase modulators and strain-induced optical waveguides

In recent broadband photonic network system, high speed optical data transmission is required. Electrooptic (EO) polymers are attractive because of their large nonlinearity, fast response time and ease of device fabrication. Therefore the EO polymers are expected for the application of ultra-high speed EO switch and/or wide bandwidth EO modulator, both of which will be used in future photonic network. In this report, recent progress of EO polymers and their application to waveguide type devices are described.

A new host-guest electro optic (EO) polymer, in which a chromophore can be reacted with the polymer main chain during poling to give the corresponding side-chain EO polymer, has been prepared for improving EO effect and its thermal stability. Polyisoimide (PII) synthesized from 2, 2-bis (4-aminophenyl) hexafluoropropane and oxydiphthalic anhydride and Disperse Red 1 (DR1) were used as a host and a guest, respectively. A model compound reaction and Infrared spectra of the host-guest film after annealing at various temperatures show that the reaction between the isoimide groups in PII and the hydroxyl groups in DR1 occurs around 140 °C. The glass transition temperatures of the resulting EO polyamic aicd ester-imide copolymer with 0, 10, 20 and 30 wt. % of chromophore concentration were 275, 219, 160, and 124 °C, respectively. The EO coefficient obtained at a wavelength of 1.55 νm was 5.3 and 10.5 pm/V from the EO polymer film with 20 and 30 wt. % DR1. The EO signals exhibited only a slight decay at high temperature due to the chemical reaction between the host and guest during poling.

Multimode interference waveguide switch of electro-optic polymer with tapered access waveguides

Electro-optical modulator based on lithium niobate notched-ring plasmonic metasurface coated with electro-optical polymer

We present the design of a 2×2 photonic switch operating at 1.55-μm wavelength using electro-optic (EO) polymer waveguides. A Mach-Zehnder interferometer (MZI) is used to implement the proposed switch in which two identical 2×2 multimode interference (MMI) couplers are connected by two identical parallel single mode waveguides (two MZI arms). These two single-mode waveguides with electrodes allow modulating the phase difference between the two MZI arms based on the EO effect. In the proposed switch, the EO polymer, IPC-E/polysulfone, is used for the core layer of optical waveguides. UV15 and NOA61 are employed for the lower and upper cladding layers, respectively. The singlemode waveguide structure and 2×2 MMI coupler have been designed and analyzed for the EO switch. Device performance has been simulated using the beam propagation method. It is found that the switch performance is most sensitive to the MMI width and less sensitive to the MMI length. Optimized structure has been obtained for the 2×2 polymeric EO switch, which has a crosstalk level better than -25 dB and insertion loss lower than -1.8 dB. This performance makes the switch a potential candidate for practical use in photonic systems.

Short-range optical fiber communication is the key in intra and inter data center network, which is recently required significant improvement in signal processing speed because of the increasing data traffic of video streaming service and many other applications. The electro-optic (EO) polymer modulator is the promising device to be used in such fiber network application because of the advanced modulation performance with low driving voltage and high frequency response. However, previous EO polymer modulators have demonstrated the modulation at the wavelength of 1.55 μm (C-band) because of the optical loss limitation at shorter wavelengths of such as 1.31 μηι (O-band). In this study, we fabricated silicon-organic hybrid modulator for O-band operation by replacing the pervious EO polymer. The modulator consists of the Mach-Zehnder interferometer Si waveguide with a hybrid slot and polymer phase shifter. The measured half-wavelength voltage product (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π·</inf> L) was 0.56 V·cm. We demonstrate 40 Gbps on-off-keying modulation, and show that the fabricated modulator is promising the higher bit rate signaling for O-band optical fiber communication application.

As a consequence of the urgent demand for an electro-optic (EO) polymer modulator with an elevated temperature stability, we have prepared a selection of EO polymers having glass transition temperatures of up to 194°C. The measured half-wave voltage characteristics of the fabricated Mach-Zehnder interference modulators revealed an excellent thermal resistance at 105°C for approximately 2,000 hours. By utilizing traveling-wave electrodes on the modulator, the high-frequency response at 10-40 GHz was evaluated under ascending temperatures. The advantage of such high-temperature stability EO polymer modulators was clearly demonstrated by the continuous frequency response up to 130°C.

Low voltage electro-optic polymer light modulator using attenuated total internal reflection

An electrooptic (EO) polymer was used to fabricate phase modulators and Mach-Zehnder modulators on Si wafers. This glassy polymer is from a class of nonlinear, optical materials that have large EO coefficients, low dielectric constants, and small dispersion from dc to optical frequencies. The modulators were fabricated on Si wafers using conventional IC manufacturing equipment. Three polymer layers were deposited: a hard acrylate cladding layer, followed by an EO polymer from Akzo Research, by1 then another cladding layer. The waveguides were photobleached using an IC mask aligner, and microstrip electrodes were formed by gold plating. The active polymer layer was poled2 through the cladding, and waveguide end faces were prepared by cleaving. The Mach-Zehnder modulator was designed so that each arm could be modulated independently with a separate 50-Ω microstrip electrode; the modulator response was measured up to 20 GHz. Data from each type of modulator are presented. These devices illustrate that polymers offer certain advantages over standard inorganic EO materials, such as LiNbO3 and GaAs, in that multilayer integrated optical circuits can be fabricated on top of electronic substrates using processes and equipment that are largely in place for manufacturing integrated circuits.

We present a complete model and design approach for high speed electro-optic (EO) polymer modulators. A general numerical model for arbitrary travelling-wave EO modulators is built, and the dispersion characteristic of each polymer layer in the device stack is carefully considered and integrated into the model. A velocity compensation layer is added to allow more room for increasing the waveguide core index to optimize half-wave voltage of the device. Microstrip mode analysis is also included to estimate the influence of different polymer stack to the E filed distribution inside the waveguide core. The device has been successfully designed and achieves more than 45 GHz EO bandwidth with a half-wave voltage of 3.2 V. A 100 Gbps EO modulator is under development.

In this paper we review on polymer micro-resonators incorporating both passive and electro-optic polymers. We have presented recent data on micro-resonator strain sensors. The fabrication, analysis, and measurement of the optical strain sensors have been presented. Tunable laser mirrors based on coupled electro-optic micro-resonators instead of Bragg gratings has been proposed.

The full potential of second order nonlinear polymers can be utilized in electro-optic polymer modulators with a DC biased operation scheme to greatly reduce the V<SUB>(pi</SUB> ). This technique makes use of the total achievable electro-optic coefficient, which can be more than three times as high as the residual value after the fast partial relaxation following corona or contact poling. As the result of the DC bias and with high (mu) (beta) chromophores, a low V<SUB>(pi</SUB> ) of 1.5 V was achieved with 2 cm long birefringent waveguide modulators at the wavelength of 1.3 micrometer. Results of 200 degrees Celsius stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the stability required for high temperature hermetic sealing because the polymer does not need to be poled before device packaging.

We review recent research using amorphous electrooptic (EO) polymers for generation and detection of broadband terahertz radiation (0.3 THz -30 THz). The advantages of amorphous EO polymers over other materials for broadband THz generation (via optical rectification) and detection (via EO sampling) include a lack of phonon absorption (good transparency) in the THz regime, high EO coefficient and good phase-matching properties, and, of course, easy fabrication (low cost). Our ~12-THz, spectral gap-free THz system based on a polymer emitter-sensor pair is an excellent demonstration of the advantages of the use of EO polymers. This system has been employed as a wideband spectrometer to study dielectric materials in the THz regime.

We have synthesized a novel electrooptic (EO) polymer based on a high /spl mu//spl beta/ chromophore incorporating tricyanobutadiene acceptors. A crosslinked polyurethane network was also adopted to enhance its thermal stability. In order to find the optimum poling condition for the polymer, the influence of the electric poling profile on optical characteristics such as the EO effect, thermal stability, and damage was investigated. Then a high-speed intensity modulator using the EO polymer was designed and fabricated. The measured half-wave voltage V/sub /spl pi// was 4.5 V at the wavelength of 1.31 /spl mu/m. Accordingly, the achieved EO coefficient r/sub 33/ was as high as 25 pm/V, and the thermal stability of the poled polymer was as high as 95/spl deg/C. Finally, the modulator was successfully operated up to 40 GHz.

We report the enhanced conductivity of sol-gel silica under-cladding for efficient poling of electro-optic (EO) polymer in a hybrid EO polymer/TiO2 vertical slot waveguide modulator. The electrical volume conductivity of sol-gel silica cladding increases approximately 30 times when the calcining time of the cladding layer is critically reduced to 45 minutes, which increases the in-device EO coefficient of the 600-nm-thick EO polymer film in modulators and reduces the lower halfwave voltage (Vπ) of the modulators. The lowest driving voltage (Vπ) of the TiO2 slot waveguide modulator is 2.0 V for an electrode length (Le) of 10 mm and wavelength of 1550 nm (VπLe = 2.0 V·cm) for the low-index guest-host EO polymer SEO125. The optical propagation loss is reduced to 7 dB/cm.