Young-Ouk Noh

Continuously tunable compact lasers based on thermo-optic polymer waveguides with Bragg gratings

Based on the thermo-optic tuning of a polymer waveguide Bragg reflector, we demonstrated a cost-effective tunable wavelength laser for WDM optical communications. The excellent thermo-optic effect of the polymer waveguide enabled direct tuning of the Bragg reflection wavelength by controlling the electrical power on a micro-heater. Wavelength tuning for 32 channels with 0.8 nm wavelength spacing was demonstrated as well as a continuous tuning with wavelength steps of 0.1 nm. To be qualified as a tunable laser for WDM-PON applications, wavelength stability within 0.15 nm was confirmed for an operating temperature range from -10 to 70 degrees C.

Thermooptic 2/spl times/2 asymmetric digital optical switches with zero-voltage operation state

Thermooptic 2/spl times/2 switches with zero-voltage operation state are demonstrated. The devices made of ultraviolet curable fluorinated polymer are composed of four asymmetric digital optical switches and designed for bar-state operation with initial zero-voltage state. This zero-voltage operation is essential for protection switching in optical networks. The crosstalks of initial bar and cross states are more than 40 dB. The insertion loss and the polarization-dependent loss of the device are less than 1.8 and 0.1 dB for both states, respectively. The power consumption is about 350 mW. The wavelength and temperature dependences of the insertion loss are less than 0.3 dB.

Flexible polymer waveguide tunable lasers

A flexible polymeric Bragg reflector is fabricated for the purpose of demonstrating widely tunable lasers with a compact simple structure. The external feedback of the Bragg reflected light into a superluminescent laser diode produces the lasing of a certain resonance wavelength. The highly elastic polymer device enables the direct tuning of the Bragg wavelength by controlling the imposed strain and provides a much wider tuning range than silica fiber Bragg gratings or thermo-optic tuned polymer devices. Both compressive and tensile strains are applied within the range from -36000 microepsilon to 35000 microepsilon, so as to accomplish the continuous tuning of the Bragg reflection wavelength over a range of up to 100 nm. The external feedback laser with the tunable Bragg reflector exhibits a repetitive wavelength tuning range of 80 nm with a side mode suppression ratio of 35 dB.

2.5-Gb/s hybridly-integrated tunable external cavity laser using a superluminescent diode and a polymer Bragg reflector

We presented a hybridly-integrated tunable external cavity laser with 0.8 nm mode spacing 16 channels operating in the direct modulation of 2.5-Gbps for a low-cost source of a WDM-PON system. The tunable laser was fabricated by using a superluminescent diode (SLD) and a polymer Bragg reflector. The maximum output power and the power slope efficiency of the tunable laser were 10.3 mW and 0.132 mW/mA, respectively, at the SLD current of 100 mA and the temperature of 25 degrees C. The directly-modulated tunable laser successfully provided 2.5-Gbps transmissions through 20-km standard single mode fiber. The power penalty of the tunable laser was less than 0.8 dB for 16 channels after a 20-km transmission. The power penalty variation was less than 1.4 dB during the blue-shifted wavelength tuning.

Tunable External Cavity Laser by Hybrid Integration of a Superluminescent Diode and a Polymer Bragg Reflector

We report a tunable external cavity laser (T-ECL) using a superluminescent diode (SLD) and a polymer Bragg reflector with 0.8-nm mode spacing 25 channels operating in the direct modulation of 2.5 Gb/s for a low-cost source of a wavelength division multiplexed passive optical network (WDM-PON) system. The maximum output power is 12.2 mW and the slope efficiency of the T-ECL is about 0.12-0.17 mW/mA in the tuning range of 20 nm at the SLD current of 50 mA and at the temperature of 25°C. The T-ECL successfully operated in the direct modulation for 2.5-Gb/s transmission through 20-km standard single-mode fiber. The power penalty of the T-ECL is less than 0.8 dB for 25 channels after the 20-km transmission. The power penalty variation is less than 1.5 dB in the wavelength-tuning range of 20 nm. The performance of the T-ECL satisfies the requirements of the WDM-PON system.

Fabrication of 10-Channel Polymer Thermo-Optic Digital Optical Switch Array

We present a 10-channel polymer thermo-optic digital optical switch (DOS) array with very low optical crosstalk. The 10-channel DOS array has a crosstalk-improved structure in which radiation-type attenuators are integrated in a series with a conventional 1 times 2 DOS. It is fabricated using a quartz substrate on which grid patterns for dispersion of stray light are formed to reduce the optical crosstalk. The measured crosstalk values are as low as -45 dB at a low electrical power of 50 mW. Insertion losses of less than 1.35 dB are achieved for all channels.

Variable optical attenuator based on large-core single-mode polymer waveguide

To improve the reproducibility of passive alignment, large-core single-mode waveguides are demonstrated, which can be connected to thermally expanded core fibers with increased alignment tolerance. It is shown that polymer waveguides with a core dimension of 25 /spl times/25 /spl mu/m/sup 2/ 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 (VOAs) 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 small electrical power consumption, which is confirmed by three-dimensional beam propagation method. From the fabricated VOA, more than 20 dB of attenuation is obtained by applying 20 mW.

Polarization-Splitting Waveguide Devices Incorporating Perfluorinated Birefringent Polymers

Low-loss perfluorinated polymers with a controllable optical birefringence were synthesized for the purpose of fabricating polarization-splitting waveguide devices, which have become an essential part of polarization-multiplexed coherent optical communications. The birefringent polymer was embedded on one branch of the asymmetric Y-branch waveguide to produce polarization-dependent mode evolution due to the effective birefringence. The device with a branch angle of 1/300 rad and birefringence of 0.007 showed a crosstalk of -25 dB and an insertion loss of 1.5 dB from fiber to fiber. The polarization splitters based on adiabatic mode evolution exhibited negligible wavelength dependence and large tolerance in waveguide dimension.

Tunable external cavity laser employing uncooled superluminescent diode.

We have fabricated a tunable external cavity laser (T-ECL) based on a superluminescent diode and a polymeric waveguide Bragg reflector, providing a cost-effective solution for wavelength division multiplexing-passive optical network (WDM-PON) systems. The wavelength of the T-ECL is tuned through 100 GHz-spacing 16 channels by the thermo-optic tuning of the refractive index of the polymer waveguide at a low input power of 70 mW. The maximum output power and the slope efficiency of the uncooled diode at 20 (75) degrees C are 8.83 (3.80) mW and 0.107 (0.061) W/A, respectively. The T-ECL operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

Polymer Waveguide Birefringence Modulators

Birefringence modulators for controlling the phase retardation between transverse electric (TE) and transverse magnetic (TM) polarizations are demonstrated based on polymeric waveguides. Highly birefringent polymer material is incorporated to increase the polarization dependence of the thermo-optic (TO) effect. The TO coefficient for each polarization is measured using a Mach-Zehnder device, and the polarization dependence of the TO effect is found to be 1.0 × 10-5/°C. By applying 70 mW of heating power with an integrated heater, π-phase difference is achievable between the TE and TM polarizations. For 45° input polarization, the output polarization is successfully modulated to cover the entire Poincare sphere.