Min-Cheol Oh

Poling-induced waveguide polarizers in electrooptic polymers

In order to demonstrate polymeric waveguide polarizers, photobleached polymer waveguides supporting both TE and TM modes are integrated with poling induced polymer waveguides that support either TE or TM modes. Fabrication parameters like UV exposures and poling voltages are controlled to reduce excess losses due to the mode profile mismatch between the connected waveguides. A TM-pass polarizer is realized by poling the polymer in the vertical direction. For TE-pass polarizer the polymer is poled horizontally by using four poling electrodes which enhance the uniformity of the poling field direction. The measured excess loss is less than 0.5 dB, and polarization extinction ratios for TM-pass and TE-pass polarizers are 20.7 dB and 17.1 dB, respectively.

Wavelength insensitive passive polarization converter fabricated by poled polymer waveguides

A passive TE to TM polarization mode converter is fabricated by using poled polymer waveguides. The optic axis of the poling induced waveguide is slowly rotated 90° by using a slowly varying structure of poling electrodes. Thus the polarization conversion is achieved as the guided mode propagates through the waveguide. TE to TM mode conversion is observed with a polarization extinction ratio higher than 30 dB, and the excess loss is less than 1 dB. The polarization conversion is relatively insensitive to wavelength since the device contains no periodic structures. These devices are easier to fabricate than others containing periodic structures.

Simulation of polarization converter formed by poling-induced polymer waveguides

A polarization converter using electrooptic (EO) polymer waveguides is proposed and it is simulated by a full vectorial beam propagation method (VBPM) for anisotropic medium. First, an efficient structure of poling electrodes is proposed for the fabrication of TE-mode poling-induced waveguides in EO polymer. For given electrode structures of both TE-mode and TM-mode waveguides, poling-induced dielectric tensors are calculated by the finite-element method to provide refractive index distribution, data for VBPM simulation. It is shown numerically that the poled TE and TM mode waveguides work efficiently as the corresponding polarization filters. Then, new poling electrodes are suggested to fabricate a waveguide device formed by connecting the TE and TM mode waveguides adiabatically with a slowly varying structure. This waveguide device has the optic axis slowly rotating as one moves along the propagation direction, so that it will act as polarization converter. VBPM simulation shows that the polarization of the guided mode rotates following the optic axis distribution. Polarization conversion is demonstrated successfully with high conversion efficiency and low excess loss. >

POSTPHOTOBLEACHING METHOD FOR THE CONTROL OF COUPLING CONSTANT IN AN ELECTRO-OPTIC POLYMER DIRECTIONAL COUPLER SWITCH

A method to control the coupling constant of a directional coupler switch made of electro‐optic polymer after completing the device fabrication is demonstrated. The method utilizes the selective postphotobleaching of the gap region to lower its effective refractive index while monitoring optical output power from each arm. The output power changes gradually and the crossover states are successively observed as the postphotobleaching proceeds. It is shown that the method can be utilized to tune the initial output to the crossover state to have a good switching extinction.

Integrated optical high-voltage sensor using a Z-cut LiNbO/sub 3/ cutoff modulator

An integrated optical AC high-voltage sensor based on a Z-cut LiNbO/sub 3/ cutoff modulator is fabricated by the proton diffusion method. It is a passive sensor that does not require any electrical bias or any voltage divider. Its sensing voltage range is extended by using the following method. First, its inherent linear range is extended, both by utilizing a novel electrode structure with dummy electrodes and by shortening the electrode length. The dummy electrodes reduce the magnitude of the Z-component electric field applied to the cutoff modulator. Second, a sensor configuration is designed to adjust its operating bias point optically by annealing and thus to utilize the whole extended linear range. The sensing voltage range of the cutoff modulator sensor exceeds AC 1000 V peak to peak. >

Polymeric polarization-independent modulator incorporating twisted optic-axis waveguide polarization converters

A polarization-independent intensity modulator made of electrooptic polymer waveguides is proposed and its theoretical performance is discussed. The device includes twisted optic-axis waveguide polarization converters and phase modulators in the arms of Mach-Zehnder interferometer. For arbitrary input polarization states the extinction ratio of better than 30 dB is possible, and its half-wave voltage is 1.5 times that of the conventional Mach-Zehnder modulator.

TE-TM polarization converters based on electro-optic poled polymer

Passive and active polarization converters have been designed and fabricated using electro- optic poled polymers. The devices utilize the controllability of the poling induced optic axis by using specially designed poling electrodes. In the passive TE-TM polarization mode converter, the optic axis of the poling induced waveguide is slowly rotated by using a slowly varying structure of poling electrodes. The polarization conversion is achieved as the guided mode propagates through the waveguide. Complete TE to TM mode conversion is observed and the polarization extinction ratio of the output light is higher than 30 dB. Because the device does not contain any periodic structure, it is wavelength insensitive and easy to fabricate. An active TE-TM mode converter utilizes a 45 degree off poling configuration, which can be obtained by arranging upper and lower stripe poling electrodes with proper lateral displacement. The poling electrodes themselvees can be used as driving electrode. The mode conversion properties and electro-optic effects are demonstrated by using a vector beam propagation method.

Y-cut LiNbO/sub 3/ directional coupler with a self-aligned electrode

A 2/spl times/2 Y-cut LiNbO/sub 3/ directional coupler switch using a self-aligned uniform /spl Delta//spl beta/ electrode is fabricated by the proton diffusion method. Our design method makes it possible to form the electrode without the delicate alignment of the electrode pattern mask and optical waveguide. The switching voltage is also reduced due to the enhanced electro-optic efficiency by using the self-aligned electrode. To achieve the initial cross state of the uniform /spl Delta//spl beta/ switch that is essential for low crosstalk, we control the proton diffusion time successively after the proton exchange. The measured crosstalk level of the directional coupler switch is -23 dB/spl sim/-29 dB and its voltage-length product is as small as 9.6 Vmm. >

Explicit vector beam propagation method for uniaxial poled polymer waveguide devices

For the design and the analysis of integrated optic devices, the beam propagation method (BPM) has been widely used. A vectorial BPM (VBPM) was also developed to simulate the polarization effects and to analyze waveguide structures having large index discontinuities. Recently, the VBPM was extended to treat anisotropic medium by taking the tensorial character of the dielectric constant /spl epsiv/ into account. However, this method using implicit numerical analysis is very complex and needs long computing time. To handle three-dimensional uniaxial waveguide devices that consist especially of a poled electro-optic (EO) polymer waveguide, we developed a new VBPM based on an explicit finite difference (EFD) algorithm. This method is straightforward and easy to program. A novel polarization converter that may be implemented by appropriate poling of the EO polymer waveguide is also proposed and analyzed.