Vadim Chuyanov

Three-dimensional integrated optics using polymers

Some of the key components are demonstrated to make three-dimensional (3-D) optical integrated circuits possible using polymers. Fabrication techniques of shadow reactive ion etching, shadow photolithography, and gray-level photolithography to produce complex 3-D integrated optic structures are demonstrated. Vertical waveguide bends exhibit excess losses of <0.3 dB, and vertical power splitters possess predictable output splitting ratios between multiple core levels with excess losses of <0.5 dB. Vertical polarization splitters exhibit power extinction ratios of 15 dB between the output core layers. A 1/spl times/4 vertical-horizontal power splitter is also demonstrated. Additionally, these techniques are used to integrate different polymer materials into the same optical circuit while easily solving the mode mismatch problem. To show the technique, a polymer electrooptic modulator is vertically integrated with a low-loss waveguide.

Polymer electro-optic devices for integrated optics

Abstract Recent advances in polymer electro-optic polymers and in fabrication techniques have made possible advances in polymer optical guided wave devices which bring them much closer to system ready. The processing of a new thermal set FTC polymer and its incorporation into a high-frequency, low-Vπ optical amplitude modulator are reviewed. The design and fabrication of 100 GHz modulators and their integration with rectangular metal waveguides using an anti-podal finline transition with a flexible Mylar substrate is discussed. High-speed polymer modulators with balanced outputs and the in situ trimming of the output coupler is described. More complex guided wave devices using polymers are demonstrated by the photonic rf phase shifter. Techniques for integrating both passive and active polymers into the same optical circuit without the need for mode matching is presented and demonstrated. To reduce the Vπ of a polymer amplitude modulator to 1 V or under, a technique of constant-bias voltage is demonstrated. Finally, a technique to directly laser write electro-optic polymer devices is reviewed.

Electro-optic polymer modulators for 1.55 μm wavelength using phenyltetraene bridged chromophore in polycarbonate

Electro-optic polymer modulators operating at 1550 nm are demonstrated based on a nonlinear optical polymer of a phenyltetraene bridged chromophore in polycarbonate. It has a large electro-optic coefficient (r33=55 pm/V at 1550 nm), good thermal stability (90 °C), and low loss (1.7 dB/cm). A thin protective layer was used in the fabrication of ridge waveguides on the nonlinear polymer. We measured Vπ of 2.4 and 3.7 V at 1300 and 1550 nm, respectively. The chip loss of the modulator at both wavelengths was 5 dB, not including fiber coupling losses.

Vertically integrated waveguide polarization splitters using polymers

Design considerations, fabrication procedures, and experimental results are presented for vertically integrated waveguide polarization splitters. These devices separate the TE and TM polarizations onto different vertical levels of a three-dimensionally integrated optic circuit. This provides increased integration density for polarization diverse structures. The vertical polarization splitters utilize birefringent polymer materials to create an adiabatic structure. Experimental results yielded extinction ratios as high as 22 and 12 dB for TE and TM polarizations, respectively.

Optical intensity modulator based on a novel electrooptic polymer incorporating high /spl mu//spl beta/ chromophore

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.

Monolithic integration of waveguide polymer electrooptic modulators on VLSI circuitry

We demonstrated some of the critical technology that is needed for the monolithic integration of polymer electrooptic modulators and VLSI circuitry by fabricating and testing a phase slab modulator on nonplanar VLSI circuits. We demonstrated the survival of GaAs MESFETs to the high-voltage poling and polymer modulator fabrication procedures. We also implemented an electrical interconnect scheme between the electronics and photonics layers.

Vertically tapered polymer waveguide mode size transformer for improved fiber coupling

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling be- tween channel waveguides and single mode fibers. The taper smoothly converts a highly elliptical waveguide mode into a large and more circu- lar mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5 to 2 mm in length is made in the upper cladding to reduce its thickness from a few micrometers to zero. The taper is sub- sequently covered by an upper cladding. The new upper cladding has an index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows larger as light propagates toward the end of the device, whereas the confinement by the lower cladding and the lateral confinement are not significantly affected. The waveguide mode grows upward away from the lossy ground electrode and substrate commonly found in many poly- mer devices; therefore, no trade-off between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and etching with a tapered photoresist mask, are developed to make the vertical taper. Mode expansion and a 1.8 dB reduction in coupling loss per tapered end are demonstrated experimen- tally. The performance of the mode size transformer is found to be in- sensitive to both waveguide width and polarization.

DC biased electro-optic polymer waveguide modulators with low half-wave voltage and high thermal stability

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 half-wave voltage. This technique makes use of the total achievable electro-optic coefficient, which can be more than three times the value that is used by the conventional devices of poled electro-optic polymer. As the result of the DC bias and with high-μβ chromophores, a low half-wave voltage of 1.5 V was achieved with 2-cm-long birefringent waveguide modulators at the wavelength of 1.3 μm. Results of a 200°C stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the short-term high-temperature stability requirement because the polymer does not need to be poled prior to high-temperature steps.

EO polymer-based integrated-optical acoustic spectrum analyzer

An acoustic spectrum analyzer based on electrooptic (EO) polymer integrated optics is presented. The device is used in a scanning heterodyne geometry by zero biasing a Michelson interferometer. It is capable of detecting vibrations from DC to GHz range. The novelty of the work is applying EO polymers to high frequency acoustic sensing applications. EO polymers have been extensively used for communication devices. However, their use in high frequency sensing applications remains unexplored. The sensor presented is designed to analyze thin film structure by utilizing high frequency capabilities of EO polymers. The advantage of this approach over existing methods is in its potential to detect vibrations over 100 GHz with low drive voltages (V/sub /spl pi// less than 1 V), using a device that is completely electrically controlled with no mechanical moving parts. Low frequency tests indicate good agreement between experimental results and theoretical predictions. Acoustic vibrations excited by pulsed Nd-YAG laser are detected to frequencies up to 200 MHz using the device presented.

Integrated polymer waveguide mode size transformer with a vertical taper for improved fiber coupling

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single-m,ode fibers. The taper smoothly converts a highly elliptical waveguide mode into a bigger and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5-2 mm in length is made in the low index upper cladding to reduce its thickness from several micrometers to zero, followed by the coating of a second upper cladding with index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows bigger a light propagates, whereas the confinement by the lower cladding and lateral confinement are hardly affected. The waveguide mode grows in the vertical direction away from the lossy ground electrode and substrate; therefore no compromise between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and tapered photoresist etching mask, are develop for making this vertical taper. Mode expansion and a 1.8 dB reduction in coupling los, which is not sensitive to waveguide width and polarization, is obtained in our preliminary experiment.