Electro-optic Polymer Modulators Research Articles

High Δn strip-loaded electro-optic polymer waveguide modulator with low insertion loss

We demonstrate a novel electro-optic polymer modulator design which shows a record low optical insertion loss of 5.7 dB at 1550 nm. The modulator consists of a high numerical aperture passive waveguide which is converted to a strip-loaded electro-optic polymer waveguide through refractive index tapers. The device is fabricated using all wet-etch techniques which results in low excess loss from roughness created during fabrication and, employs new low loss passive sol-gel materials. The fabricated device also shows a low half-wave voltage of 2.8 V.

Ultra-High-Speed Deeply Etched Electrooptic Polymer Modulator With Profiled Cross Section

In this paper, we present a novel ultra-high-speed polymer based electrooptic modulator that features a profiled, deeply etched cross section. We show that by profiling the side walls of the modulator and varying the thickness of the dielectric stack that broadband operation can be achieved whilst maintaining a very low drive voltage in a compact device. Initially a quasi-TEM analysis is undertaken in order to determine the modulators response to topographical variation followed by a full-wave analysis on the optimized device. The full-wave analysis is employed in order to determine any frequency dispersion effects with respect to the modulators characteristic impedance Zc, microwave effective index Nm, microwave and dielectric losses alphac and alphad , and the half-wave voltage-length product V pi L.

Ultra-High-Speed Deeply Etched Electrooptic Polymer Modulator

In this paper, we present a novel ultra-high-speed polymer-based electrooptic modulator that incorporates high permittivity material cladding on the side walls of the device. We show that by packing the side walls of the modulator with this material and varying the width of the dielectric stack and electrodes that broadband operation can be achieved while maintaining a very low drive voltage in a compact device. Initially, a quasi-TEM analysis is undertaken in order to determine the modulators response to topographical variation followed by a full-wave analysis on the optimized device. The full-wave analysis is employed in order to determine any frequency dispersion effects with respect to the modulators characteristic impedance Zc, microwave effective index Nm, microwave and dielectric losses αc and αd and the half-wave voltage-length product VπL.

Broadband electro-optic polymer modulators with high electro-optic activity and low poling induced optical loss

A screening method is reported for electro-optic (EO) polymers with an emphasis on broadband device suitability. The method is based on comparing the signal from second harmonic generation (SHG) and the leak through current (LTC) during poling. Plots of the SHG and LTC are used to define high EO activity-low current poling windows that are critical for low driving voltage, broadband devices with relatively low optical loss. The screening procedure was used to select an EO polymer core that resulted in a 40Gbits∕s broadband modulator with a driving voltage of 1.3V and an insertion loss of <8dB.

Electrooptic Polymer Modulator With Single-Mode to Multimode Waveguide Transitions

Grayscale lithography has been used to create refractive index (RI) tapers in an electrooptic (EO) polymer modulator. These RI tapers are used to convert a passive single-mode photobleached polymer waveguide to the fundamental mode of an unbleached, active multimode polymer waveguide. The benefits of this modulator design include a coupling loss reduction of 2.6 dB per interface and an increased confinement factor of 0.83. Using this design, an EO polymer modulator was fabricated with a half-wave voltage of 1.9 V, modulation extinction ratio of 15 dB, and a fiber to lens insertion loss of 11.6 dB.

An electro-optic polymer modulator based on the free-space coupling technique

An electro-optic (EO) polymer modulator employing a symmetrical metal-cladding waveguide structure is presented. Based on the free-space coupling technique, the energy of incident light on the metal-cladding is coupled directly from free space into the waveguide without using a prism, grating and other coupling components. An externally applied voltage modulates the reflected light intensity by changing the energy coupling efficiency of the incident light into the waveguide through the refractive index of the EO polymer. The fabricated modulator achieves an 8.2% modulation depth with 10 Vp−p driving voltage at 1 MHz. The device also provides the benefits of simple fabrication and compact size owing to the use of the free-space coupling technique.

HYBRID SOL-GEL ELECTRO-OPTIC POLYMER MODULATORS: BEATING THE DRIVE VOLTAGE/LOSS TRADEOFF

There has been great progress in the development of electro-optic (EO) polymers with exceptionally high r33 coefficients, with values ranging from 100–400 pm/V now being reported for single layer electro-optic polymer films. While this enables the fabrication of EO modulators with sub-volt operation, it is also necessary to make devices with acceptably low insertion loss (< 6 dB) in order to compete with existing technology. We have developed a solution to the voltage/insertion loss tradeoff in EO polymer modulators by adopting a hybrid geometry that provides for low optical coupling loss, electro-optic polymer limited propagation loss, highly efficient poling, and low cost fabrication. This combination of properties has allowed us to achieve r 33 = 170 pm/V in an EO phase modulator. In addition to this proven approach to optimizing the figure of merit, there are several other approaches that can have high impact. The development of low loss EO polymer and cladding materials and waveguides can greatly reduce the insertion loss of EO polymer modulators, through chemical substitution techniques such as selective halogenation, as well as through improved processing to reduce roughness, stress and poling induced losses. Halogenation can be used to reduce the number of C – H bonds, which have well-known stretch and bend vibrational modes whose overtones extend into the optical communications bands at 1550 nm and 1310 nm. While roughness and stress effects are well-understood from work on passive waveguides, the poling process can produce inhomogeneities that lead to increased scattering loss; molecular design can be used to reduce poling induced loss. Another approach is to adopt non-waveguide device formats that are more tolerant of material losses, such as Fabry-Perot etalons. While etalons may not be viable for very high speed applications (i.e., GHz regime), they present entirely new application areas for electro-optic polymers.

Conductivity-dependency-free in-plane poling for Mach-Zehnder modulator with highly conductive electro-optic polymer

This letter presents the in-plane poling in electro-optic (EO) polymer modulators with conductivity dependency of core and claddings eliminated. A Mach-Zehnder (MZ) modulator with a highly conductive EO polymer, AJLS102/APC, is realized and poled by the in-plane coplanar waveguide poling electrode. Vπ of 7.7V in a single-arm poled MZ (3.8V for push-pull operation) is achieved and the evaluated r33 is 65pm∕V. Combined with the r33’s of the previously measured single layers and MZ modulators using two other EO polymers, this experiment proves that the r33 proportional to the single layer r33 can be achieved in an in-plane MZ device regardless of the material conductivities.

Fabrication and characteristics of thermal crosslinking polyurethane integrated double-channel electro-optic modulator

The fabrication and characteristics of a new type of polymeric electro-optic modulator with double channels in attenuated total reflection (ATR) configuration, made of a thermally crosslinkable polyurethane, has been demonstrated in this paper. The fabrication procedure of proposed double-channel ATR modulator is extremely simple, it can be implemented by replacing a single electrode with two discrete electrodes in a single channel ATR modulator. Independent operation of both channels is demonstrated at a modulation speed of 500 MHz. The total measured insertion loss of the modulator is below 1.5 dB. There are no measurable cross talks due to the large horizontal separation of two channels and the small vertical separation of the electrode pair. A long-term thermal stability of the fabrication modulator at an elevated temperature, 100 °C, is obtained due to crosslinking polyurethane as the waveguide layer of the devices.

Polymeric electrooptic light modulator based on grating-coupled surface plasmon resonance

In summary, in this work, we demonstrated the application of the grating-coupled SPR for the fabrication of an EO light modulator. SPR-based EO modulators reported to date have mostly used the Kretchmann configuration. To the best of authors’ knowledge, this work reports the first fabrication and demonstration of a grating-coupled EO modulator. By switching on and off of the applied voltage of 5 V, the subsequent variation of SPR was observed clearly. It should be mentioned that currently our study was limited to show the feasibility of our concept. For practical applications, further optimization of SPR signal will be required, which is a subject of our ongoing research.

Optimizing Design for the Traveling Wave Electrodes in Low-Drive High-Speed Electro-Optic Polymer Modulators

Electro-optic (EO) polymer modulators are very promising in the realization of cost-effective and high-performance optical transmissions. In this article, general strategies and specific designs of the traveling wave electrodes in EO polymer modulators were presented to reduce the modulator drive power while maintaining a broadband response. The optimum device parameters and corresponding conditions were estimated using finite element method based on electrode design. In calculating the results, the comprehensive characteristics of polymer modulator with 1.21 V half-wave voltage and 91 GHz bandwidth was demonstrated with electro-optic interaction length is 20 mm, electro-optic coefficient is 55 pm/V, and operation wavelength is 1.319 μm. These results agree with the 0.8 V half-wave voltage and 30 mm electro-optic interaction length reported in Science. In the five designs presented, a hybrid electrode structure combining CPW and microstrip lines were advanced. The characteristics of this structure are like that of microstrip lines with a single-arm electrode on one arm of the waveguide, but it solves the problem of microstrip to coaxial line transition and corona polarization.

Side-chain electro-optic polymer modulator with wide thermal stability ranging from −46°Cto95°C for fiber-optic gyroscope applications

Electro-optic (EO) polymer modulators with a wide range of thermal stability from −46°Cto95°C for fiber-optic gyroscope applications are reported. The synthesized EO side-chain polymer used has a glass transient temperature (Tg) of 200°C and a large EO coefficient of 25.2pm∕V in a real device measurement. Mach–Zehnder (MZ) intensity and optical phase modulators are implemented based on this high-Tg side-chain EO polymer, exhibiting ∼3.75V half-wave voltage with 1.5cm interaction length and 2.3cm total length at 1.55μm wavelength. The optical fiber-to-lens insertion loss is ∼7.5dB in the MZ interferometers and ∼6dB in the straight waveguides. We examine the long-term thermal stability of these devices and demonstrate their ability to meet the strict requirements of various EO device applications, particularly fiber-optic gyroscopes.

A Low-loss Electro-optic Waveguide Polymer Modulator and its Optimization Design

Generally, the core is made up of EO materials in electro-optic waveguide polymer modulators and thus lightwave carrier is modulated in the core. In this case, the loss from chromophores is often large because the most of light power are confined to cores. In order to reduce the optical loss, we presented an approach that the lightwave was modulated only in claddings; that is to say, the EO polymer is only used in claddings and the core material is low-loss passive. Results indicate the propagation loss of this kind of modulator is about 1/3 of the former. Although the modal overlap integral between the microwave and the lightwave weakened under this condition, it could be improved by optimizing the dimension of waveguide. Due to the lower propagation loss, the interaction length of the modulator may be lengthened. Thus, the half-wave voltage can be decreased further. Also, some considerations on optimization design of this modulator are discussed. Especially, the effect of conductor loss and velocity mismatching should be taken into account in order to achieve the theoretical optimal half-wave voltage and the device bandwidth.

Radiation resistance of electro-optic polymer-based modulators

Mach–Zehnder interferometric electro-optic polymer modulators composed of highly nonlinear phenyltetraene bridge-type chromophores within an amorphous polycarbonate host matrix were investigated for their resistance to gamma rays and 25.6 MeV protons. No device failures were observed and the majority of irradiated modulators exhibited decreases in half-wave voltage and optical insertion losses compared to nonirradiated control samples undergoing aging processes. Irradiated device responses were attributed to scission, cross-linking, and free volume processes. The data suggests that strongly poled devices are less likely to de-pole under the influence of ionizing radiation.

A wide-band polymeric electro-optic modulator array based on unidirectional coupling between multi-mode waveguide array and a vertical configured dumping planar waveguide

A polymeric wide-band electro-optic (EO) modulator array based on unidirectional mode-coupling between the guiding multi-mode waveguide array and a vertical configured planar dumping waveguide was developed. A low insertion loss of <1.7 dB was obtained due to asymmetrically designed guiding waveguide and the dumping waveguide. A modulation depth of 91% was achieved with the device length of 3.5 cm at a low driving voltage of 3.2 V. The employment of the dumping planar waveguide not only provides an efficient way to achieve the unidirectional coupling mechanism, but also effectively confines the light coupled from the guiding waveguides within the planar dumping waveguide. The combination of unidirectional coupling and light confinement effects ensures low cross talk of <22 dB between adjacent guiding waveguides. Since the proposed modulator is based on the unidirectional coupling mechanism, it is intrinsically wide-band. A wide-band operation from 1308 to 1324 nm was experimentally obtained. The unidirectional mode-coupling-based wide-band modulation principle can be readily applied to other wavelengths, such as 1330 and 1550 nm ranges.

Thermal relaxation trimming for enhancement of extinction ratio in electro-optic polymer Mach-Zehnder modulators

We propose and demonstrate a trimming method to enhance extinction ratio in an electro-optic (EO) polymer modulator with a Mach-Zehnder interferometer structure. In order to adjust the power splitting ratio at Y-branches, which is a main factor determining the extinction ratio, our method is exploited by using a change of the refractive index of the poled EO polymer due to thermal relaxation. The trimming is controlled by heating the Y-branch area via a heater. By using the thermal relaxation trimming, the extinction ratio in the adjusted EO modulator is enhanced by more than 7dB without excess loss.

Linearity of ring resonator-based electro-optic polymer modulator

The linearity of a ring resonator-based electro-optic polymer modulator is experimentally studied. The modulator shows a suppression of third-order distortion near a half transmission bias point. From the experimental transfer function and typical link parameters, the inter-modulation-free dynamic range is predicted to be 123 dBHz 4/5 .

Analysis of e-o polymer mode converter with bottom transverse poling electrodes

The operation of integrated-optics electrooptic (EO) polymer modulators relies on the Pockel effect that is generated by applying an electric field to the optical waveguides. Birefringent behavior occurs because of the dipole realignment of the poled polymer film. In this paper, the static-field analysis of the electric field distribution for the mode converters with bottom transverse electrodes incorporating a buffer layer was done by using an efficient discrete Fourier transform domain technique. According to the numerical analysis results, the electric-field distribution in the guiding layer is the function of electrode geometric configuration. Two parameters, the electrode width and spacing, were considered for the optimum arrangements of the coplanar electrodes deposited on the polymer waveguide modulator. Also studied was the influence of the asymmetric electrode width of the coplanar electrodes on the sample surface.

Polarization-insensitive transition between sol-gel waveguide and electrooptic polymer and intensity modulation for all-optical networks

An intensity modulation using a hybrid electrooptic (EO) polymer/sol-gel straight channel waveguide, useful in the 1550-nm wavelength regime is demonstrated without using Mach-Zehnder interferometric waveguide. The sol-gel waveguide is selectively buried so that a vertical transition into and out of an EO polymer coated on the sol-gel waveguide is arranged. The throughput ratio for transverse electric (TE) and transverse magnetic (TM) modes of the light coupled out of the hybrid waveguide is improved up to 0.9 dB with the help of reduced birefringence of the EO polymer after corona poling. We show that the fabrication process of such hybrid-type waveguides enables production of a phase modulator operating at 1550-nm wavelength. The fabricated straight channel waveguide modulator exhibits stable- and high-intensity modulation efficiency (82%) using a simple cross-polarization setup after the polarization dependence is reduced. We demonstrate an all wet-etching process to fabricate polymeric EO modulators.

Thermal bias operation in electro-optic polymer modulators

An electro-optic polymer Mach–Zender modulator based on thermal biasing is proposed and demonstrated. The bias point of the modulator is controlled through the thermo-optic effect. Biasing is achieved by thermally changing the optical path length of one arm of the Mach–Zender interferometer. Tuning of bias points is realized by applying an electrical power of only 14 mW. It is verified that this approach is stable and substantially dc-drift free.