Electric field poled organic electro-optic materials: state of the art and future prospects.

The ability to determine absolute distance to an object is one of the most basic measurements of remote sensing. High-precision ranging has important applications in both large-scale manufacturing and in future tight formation-flying satellite missions, where rapid and precise measurements of absolute distance are critical for maintaining the relative pointing and position of the individual satellites. Using two coherent broadband fibre-laser frequency comb sources, we demonstrate a coherent laser ranging system that combines the advantages of time-of-flight and interferometric approaches to provide absolute distance measurements, simultaneously from multiple reflectors, and at low power. The pulse time-of-flight yields a precision of 3 µm with an ambiguity range of 1.5 m in 200 µs. Through the optical carrier phase, the precision is improved to better than 5 nm at 60 ms, and through the radio-frequency phase the ambiguity range is extended to 30 km, potentially providing 2 parts in 1013 ranging at long distances. Using two coherent broadband fibre-laser frequency comb sources, a coherent laser ranging system for absolute distance measurements is demonstrated. Its combination of precision, speed and long range may prove particularly useful for space-based sciences.

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Rapid and precise absolute distance measurements at long range

Micro- and nanopatterning techniques for organic electronic and optoelectronic systems.

Electro–optic (EO) modulators are typically made from inorganic materials such as LiNbO3, but replacing them with organic EO materials, that is, ones with optical properties that change in response to an electric field, could be a promising alternative because they offer large bandwidth, ease of processing and relatively low cost. Here we incorporate a doped, crosslinked organic EO polymer into hybrid polymer/sol–gel waveguide modulator devices with exceptional performance. The half-wave voltages of the resulting Mach–Zehnder (MZ) and phase modulators at 1550 nm are 1 V and 2.5 V, respectively. The unique properties of the sol–gel cladding materials used in the hybrid structure result in a 100% device poling efficiency, leading to respective in-device EO coefficients of 138 pm V–1 and 170 pm V–1 in the MZ and phase modulators. These results are the first to show in-device EO coefficients that are five to six times larger than those of the benchmark inorganic material.

Hybrid polymer/sol–gel waveguide modulators with exceptionally large electro–optic coefficients

Chromophores with optimized second-order optical nonlinearity to optical loss ratios are synthesized, poled with an electrical field, and coupled into hardened polymer matrixes. Acentric order, which is necessary for electro-optic activity, is optimized by the consideration of chromophore−chromophore electrostatic interactions as well as chromophore−poling field interactions and thermal collisions which randomize chromophore orientations with respect to the applied field direction. Reactive ion etching and/or multicolor photolithography are used to fabricate buried channel waveguide structures out of the resulting polymeric electro-optic materials and to integrate polymeric waveguides with silica optical fibers. Tapered transitions are developed to minimize coupling (insertion) loss. Both vertical and horizontal integration of polymeric electro-optic modulator circuitry with semiconductor very large scale integration circuitry is demonstrated. Modulation to 113 GHz is demonstrated. Polymeric modulators ar...

http://depts.washington.edu/eooptic/publications/files/IndEngChemRescgi.pdf

Polymeric Electro-optic Modulators: From Chromophore Design to Integration with Semiconductor Very Large Scale Integration Electronics and Silica Fiber Optics

The Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor permits absolute distance measurement with subnanometer accuracy, an improvement of 4 orders of magnitude over current techniques. The system uses fast phase modulators to resolve the integer cycle ambiguity of standard interferometers. The concept is described and demonstrated over target distances up to 1 m. The design can be extended to kilometer-scale separations.

MSTAR: a submicrometer absolute metrology system.

A high-performance electro-optic (EO) polymer modulator on a flexible substrate was fabricated using a polymer substrate layer lift-off method. The SU-8 polymer has widely different adhesion properties on Si and gold substrates that makes selective lift-off possible. The flexible EO polymer modulators on a 100-μm polymer substrate layer have a Vπ of 2.6 V and extinction ratio better than 20 dB at 1550 nm. The bending loss of the flexible waveguide was unchanged at bending radii as small as 1.5 mm, and no effect on Vπ was observed for a 5 mm bending radius.

Flexible low-voltage electro-optic polymer modulators

We have demonstrated a hybrid Mach–Zehnder optical modulator consisting of a large-core, low-loss fluorinated passive polymer waveguide and an electro-optic (EO) polymer waveguide. The combination exhibits low fiber coupling loss to the passive waveguide and reduced transmission loss because the EO polymer waveguide is used only in the active region. The two waveguides are connected by vertical tapers that permit low-loss adiabatic coupling between the two modes. The half-wave voltage and the insertion loss of the fabricated modulator are 3.6 V and 6 dB, respectively, at a wavelength of 1.55 µm. The estimated coupling loss with the standard single-mode fiber is ∼0.5 dB.

Integration of electro-optic polymer modulators with low-loss fluorinated polymer waveguides.

A tunable wavelength filter was proposed and demonstrated by using the ultraviolet nanoimprint technique. It consists of a Bragg grating in polymer waveguides and a heating electrode. The creation of the grating was substantially simplified with the introduction of a smart imprint stamp containing a waveguide pattern integrated with the grating pattern. The center wavelength of the filter was successfully tuned by taking advantage of the thermooptic effect in polymers, which was induced by supplying electrical power to the electrode. For the fabricated device, a transmission dip of ∼15dB and a 3dB bandwidth of 0.8nm were obtained at the Bragg wavelength of ∼1560nm. The achieved thermooptic tuning rate was ∼0.28nm∕mW, while the center wavelength was shifted from 1560nm to 1558nm with the electrical power consumption of 7mW.

Tunable polymeric Bragg grating filter using nanoimprint technique

A polymeric microring resonator has been proposed and fabricated using the nanoimprint technique based on a stamp incorporating a smoothing buffer layer. It played a pivotal role in improving the sidewall roughness of the waveguide pattern engraved on the stamp and thus reducing its scattering loss. Eventually, the quality factor of the resonator could be enhanced. It also helped narrow down the gap between the ring and the bus effectively to strengthen the coupling between them. For the fabricated device, the quality factor of /spl sim/103 800 and the extinction ratio of /spl sim/11 dB were achieved at 1550 nm, while the estimated scattering loss was reduced from 38 to 0.0005 dB/mm with the help of the smoothing layer.

Seh-Won Ahn

Papers

MSTAR: a submicrometer absolute metrology system.

Flexible low-voltage electro-optic polymer modulators

Integration of electro-optic polymer modulators with low-loss fluorinated polymer waveguides.

Tunable polymeric Bragg grating filter using nanoimprint technique

Polymeric microring resonator using nanoimprint technique based on a stamp incorporating a smoothing buffer Layer