Chirped Bragg gratings can be utilized in various application regions due to their characteristic spectral and
group delay responses. Chirped Bragg gratings based on the planar waveguide technology can present several
advantages over chirped fiber Bragg gratings. We have proposed and demonstrated that the chirp characteristics
of waveguide Bragg grating (WBG) devices can be tailored by adopting specifically tapered core profiles. On the
ground of our analytical and experimental results, we established the dependence of the modal effective index
on the core width. Using the relationship, we designed and fabricated polymeric WBG devices with precisely
controlled linear chirp parameters. Then, one of the fabricated WBG device was packaged and applied to tunable
dispersion compensation (TDC) for 40-Gbps optical signal transmission. It was ascertained that the optical signal
quality was significantly improved by tuning the operation condition of the packaged TDC module.
Replication technologies have been recommended as an alternative means of high volume manufacturing of the polymer
optical components with low-cost. We demonstrated replication technology as a means of implementing polymer-based
MOEMS. To achieve this, a polymer optical bench with embedded electric circuits was designed to integrate the
functional planar-lightwave-circuit (PLC)-type optical waveguide devices; the designed packaging structures were
realized using a novel fabrication process that incorporated the UV imprint technique. In addition, the detail fabrication
steps of the UV imprint process were investigated. The optical bench has v-grooves for the fiber ribbon and the
alignment pits for opoelectronic interconnection. The plastic mold for imprinting the designed optical bench was made of
UV-transparent perfluorinated polymer material. The designed optical bench was configured on the electric-circuitpatterned
silicon substrate. Flip-chip bonded polymer optical waveguide device showed not only a good electric contact
but also a coupling loss of 0.9 dB at a wavelength of 1.5 ?m. It was concluded that replication technology has versatile
application capabilities in manufacturing next generation optical interconnect systems.
To improve the reproducibility of passive alignment, large core single mode waveguides are demonstrated, which can be connected to thermally expanded core fibers so as to increase alignment tolerance. It is shown that polymer waveguide with a core dimension of 25 μm x 25 μm and an index contrast less than 0.001 can satisfy single mode condition. As a novel functional device incorporating the large core waveguide, variable optical attenuators (VOA) are designed and fabricated. For the fabrication of the thick core structure, a soft molding process is developed. Due to the small index contrast of the waveguide, efficient attenuation is expected for the smaller electrical power consumption, which is confirmed by 3-dimensional beam propagation method. From the fabricated VOA device, more than 20 dB of attenuation is obtained by applying 20 mW.
Despite many advantages toward nonlinear optical (NLO) waveguide devices, NLO polymers have not been adopted successfully into practical wavelength converters due to their high absorption losses. Empirical and theoretical understandings about NLO susceptibilities imply the fundamental trade-off between optical absorption and nonlinearity. Our theoretical analysis elucidates the effect of absorption losses on second-harmonic generation, difference-frequency generation, and cascaded wavelength conversion. We compare analytically maximum conversion efficiencies for those NLO processes with several NLO polymers and suggest that the cascaded wavelength conversion is a plausible application of NLO polymers. Furthermore, we found a convincing approach for the development of NLO polymers with the optimum combination of high optical nonlinearity and low material absorption, which leads us to realize efficient polymeric wavelength converters.
The PbSe nanocrystals were synthesized without impurity from lead oleate and Se(TOP) by heating in phenyl ether. The particle size increases the synthesis temperature. The PbSe QD / PPA nanocomposite was made with the synthesized PbSe nanocrystals and the amine-containing PPA polymer by using the ligand exchange method. The PbSe nanocrystals were well dispersed in the PbSe QD / PPA nanocomposite. The PbSe QD / PPA nanocomposite film has the broad PL peak around 1300 nm with FWHM of ~ 170 nm. The time constant in the PbSe QD / PPA nanocomposite film is as slow as ~ 150 ns. We investigated the structures of the developed PbSe QD / PPA nanocomposite film as well as their optical properties, and then suggested their photonic applications.
A 16-arrayed polymeric optical modulator is fabricated using an electro-optic (EO) polymer with a large EO coefficient and good thermal stability. The 16-arrayed modulator has lumped type electrodes with a response time of less than one nanosecond. The 16-arrayed modulator has good uniform modulation characteristics between the individual modulators. The deviation of half-wave voltages is 0.2 V and that of insertion losses about 1 dB. Crosstalks range from -28 to -36dB and extinction ratios are more than 21 dB.
Recently, we developed a wavelength converter, a 16-arrayed electro-optic (EO) Mach-Zehnder (MZ) modulator, polarization adjustable and athermal arrayed waveguide gratings (AWGs), and a wavelength channel selector by using all polymers. We designed and fabricated periodically poled nonlinear optical (NLO) polymer waveguides for the wavelength converter. Difference-frequency generation (DFG) process with a quasi-phase-matching (QPM) scheme was used. An all polymer-based wavelength channel selector composed of 16-channel EO polymer modulator array between two polymer AWGs is proposed and fabricated using chip-to-chip bonding of the three optical polymeric waveguide devices. For this, the 16-arrayed polymeric optical modulator and AWGs are respectively fabricated using EO and low-loss optical polymers. For these two-typed devices, we have synthesized new side chain NLO polymers and used low-loss optical polymers, designed and developed by ZenPhotonics, Inc. The developed these photonic devices were discussed in details from materials to packaging.
A polymeric 1 X 8 arrayed waveguide grating wavelength multiplexer with 1.6 nm (200 GHz) channel spacing has been designed and realized for operating around a 1550 nm wavelength. Two kinds of fluorinated polymers, perfluorocyclobutane and fluorinated poly(ether ketone) polymers were used for the low loss waveguides. As a core layer, fluorinated poly(ether ketone) polymer, which has a low propagation loss, a good processibility and high thermal stability up to 460 degree(s)C was newly synthesized. The propagation loss of a buried rib waveguide is less than 0.5 dB/cm at the 1550 nm wavelength. The refractive index difference between the core and the clad layers is 0.0273 ((Delta) equals 1.8%). The bending radius of curved waveguides is 7.5 mm. The device size is 39 mm long and 13 mm wide. Fiber-to-fiber insertion losses of the multiplexer are between 7 dB and 8 dB, and a 3-dB bandwidth is 0.6 nm. The crosstalk of all 8 channels is less than -24 dB. And the polarization (TE-TM mode) related wavelength shift is approximately 3.4 nm.
Bi-stable microactuators are necessary to implement optical switch and microrelay with low power and high reliability. In this work, we analyzed the buckling and vibration characteristics of a planar microactuators with shallow arch- shaped leaf springs. To investigate elastic stability of the proposed microactuator, we derived static buckling modes. A concentrated force of 0.35 muN at the center of beam was required for the snap-through motion for the beam length of 1600 micrometer, thickness of 3 micrometer, beam width of 6.5 micrometer and initial rise of 15 micrometer considering only the first buckling mode. We also analyzed vibration characteristics of arch-shaped leaf spring. The resonant frequencies of the first modes across over the second mode and keeps constant resonant frequencies over the cross point. On the contrary, the resonant frequencies of second modes become almost constant regardless of initial rise. The planar microactuator with shallow arch-shaped leaf springs at both sides were fabricated using silicon micromachining technology. The vertical structure of the planar microactuator features simplicity and consists of p-doped polysilicon as a structural layer and LTO (Low Temperature Oxide) as a sacrificial layer. The polysilicon was annealed for the relaxation of residual stress and HF GPE (gas-phase etching) process was finally employed in order to release the microactuators. These bi- stable planar microactuators with shallow arch-shaped leaf springs showed a high stiffness against external disturbance, and would be very useful for the stable operation of micro optical switch and microrelay.
An electro-optic polymer guest-host system has been constructed and demonstrated. The polymer host is a polyimide (PIQ2200) and the guest chromophores are dimethyl (or diethyl) amino alkyl sulfone stilbenes. The alkylated-NLO moieties as guest chromophores have been modified, yielding new alkylated-NLO moieties. The higher content of alkylated-NLO moieties, compared to unmodified NLO moieties, was doped into a polyimide host system due to the improved solubility of new alkylated-NLO moieties. To the 40 wt%, the new alkylated- NLO moiety has been completely dissolved in the preliminary experiment, leading to the increase of refractive index by 0.0016. These polyimide-based guest-host systems exhibited a significant improvement in the thermal stability at high temperatures exceeding 250 degree(s)C. The electro-optic coefficient reported in the present study is 13 pm/V for the 40 wt% DASS-6- doped polymer system poled at the 135 V/micrometers . However, further increase up to 25 pm/V may easily be achieved by increasing the amount of guest moieties and/or the intensity of the poling field. This work presents new materials for photonic switching devices with low operating voltage.