Hiroki Miura

Low driving voltage Mach-Zehnder interference modulator constructed from an electro-optic polymer on ultra-thin silicon with a broadband operation

An electro-optic (EO) polymer waveguide using an ultra-thin silicon hybrid has been designed and fabricated. The silicon core has the thickness of 50 nm and a width of 5 μm. The waveguide was completed after covering the cladding with the high temperature stable EO polymer. We have demonstrated a low half-wavelength voltage of 0.9 V at the wavelength of 1.55 μm by using a Mach-Zehnder interference modulator with TM mode operation. The measured modulation corresponded to an effective in-device EO coefficient of 165 pm/V. By utilizing the traveling-wave electrode on the modulator the high-frequency response was tested up to 40 GHz. The 3 dB modulation bandwidth was measured to be 23 GHz. In addition, the high frequency sideband spectral measurement revealed that a linear response of the modulation index against the RF power was confirmed up to 40 GHz signal.

High thermal stability 40 GHz electro-optic polymer modulators

As a consequence of the urgent demand for an electro-optic (EO) polymer modulator with an elevated temperature stability, we have prepared a selection of EO polymers having glass transition temperatures of up to 194°C. The measured half-wave voltage characteristics of the fabricated Mach-Zehnder interference modulators revealed an excellent thermal resistance at 105°C for approximately 2,000 hours. By utilizing traveling-wave electrodes on the modulator, the high-frequency response at 10-40 GHz was evaluated under ascending temperatures. The advantage of such high-temperature stability EO polymer modulators was clearly demonstrated by the continuous frequency response up to 130°C.

An electro-optic polymer-cladded TiO2 waveguide modulator

Organic electro-optic (EO) materials and their hybrid systems have received considerable attention for high-performance modulators. In this work, we demonstrate the design and fabrication of an EO modulator with a low half-wave voltage (Vπ) and a RF modulation response up to at least 10 GHz. The polymer used in this work has a glass transition temperature of 172 °C, which makes it stable even under high temperature RF sputtering. As a result, an EO polymer-cladded titanium dioxide (TiO2) waveguide structure can be utilized to enlarge the confinement factor, and thus, enable a low Vπ. The response of the modulator from 4 to 10 GHz has been measured, which shows a flat frequency response up to 10 GHz and a potential for the application in several tens GHz.

Response of the far scrape-off layer plasma to strong gas puffing in the high poloidal beta configuration of the QUEST spherical tokamak

The response of the far scrape-off layer (far-SOL) to strong gas puffing (SGP), and its role as the boundary condition for core plasma, are investigated using a two-point Langmuir probe measurement in the high poloidal beta configuration in the QUEST spherical tokamak. The temperature and heat flux behave in an opposite way in the far-SOL and end-plate region after SGP, although SGP increases the density globally. The apparent density decay time in the far-SOL area is much longer than that in the core. Significant co-current flow is driven solely by the electron cyclotron wave in the far-SOL flow. Sheared flow is also observed in the perpendicular velocity profile during the recovered current flat-top phase, and such flow profiles are flattened by SGP. These flow profiles are attributed not only to drift-driven flow but also to transport-driven flow, the sink effect on the end-plate, and the balance of the neutral particle source.

96 Gbit/s PAM-4 Generation using an Electro-Optic Polymer Modulator with High Thermal Stability

The thermal stability of electro-optic polymer modulators is improved using a common ridge and hybrid silicon-to-polymer waveguide-structure. It reveals excellent thermal resistance at 105°C for ∼2, 000 hours and generates 56Gbit/s OOK and 96Gbit/s PAM-4 successfully.

Temperature stable electro-optic polymer modulators using high Tg polymer matrix (Conference Presentation)

In this work, we synthesized temperature stable electro-optic (EO) polymers by post-functionalization technique. The EO polymer consists of high molecular hyperpolarizability chromophores and PMMA-based polymer with a high glass transition temperature. We attached chromophores to the high Tg polymers with controlling the loading concentrations. We found that the use of adamantly methacrylate enhanced the thermal resistance of the EO activity at elevated temperatures. We characterized synthesized EO polymers by using the size exclusion chromatography, UV-vis spectroscopy, and Tg analyzers. The thermal and temporal stability of the EO polymers were tested in the Mach-Zehnder interferometer waveguide modulators. The fabrication was based on our previous technique, resulting the measured Vp of around 2-4 V. The r33 of the waveguide corresponds to 60-80 pm/V at the wavelength of 1550 nm. We found the excellent thermal stability of the EO polymer modulator, showing little degradation of the EO activity under high temperature test at 105C for longer than 2000 hours. The results are attributed to the high Tg property of the synthesized EO polymers.

Enhanced thermal stability of electro-optic polymer modulator

We synthesized the EO polymer having a glass transition temperature (Tg) higher than 190°C. The fabricated waveguide modulator was tested for the thermal and temporal stability at 105 °C for longer than 2000 hours. The EO activity of the measured polymer modulator is attributed to the high molecular hyperpolarizability of the used chromophores, and thermal stability to the high Tg of the EO polymer.

Hybrid ultra thin silicon and electro-optic polymer waveguide modulator

Compact and, low driving voltage optical modulator is the key device for high-speed on-chip optical interconnects. We have fabricated a hybrid silicon and electro-optic (EO) polymer modulator and demonstrated its EO properties. We used thin silicon core and planar electrodes to enable the modulator a low driving voltage.

Temperature stable electro-optic polymer modulator using ultra-thin silicon waveguide

We demonstrate the broadband electro-optical (EO) polymer modulator in the hybrid silicon Mach-Zehnder interferometer. The waveguide consists of the 50 nm-thick silicon core with the EO polymer cladding. The fabrication of the hybrid waveguide can be totally carried out by using the conventional photolithography technique. The recorded half-wave voltage (Vπ) of the modulator was 0.9 V at 1550 nm. The traveling-wave electrode was applied to the modulator to test the frequency response up to 40 GHz. The modulator showed the excellent temperature stability at 85° for longer than 2000 hours.

Broadband hybrid electro-optic polymer device to silicon Mach-Zehnder modulator (Conference Presentation)

We demonstrate the hybrid silicon and electro-optic (EO) polymer modulator for low-driving voltage and high bandwidth applications. The designed hybrid waveguide was fabricated by the conventional photolithography technique, so that this widespread compatibility enabled the construction of the unique polymer photonic devices. The waveguide consists of the silicon core with a 50 nm-thick and 2 m-wide core and the EO polymer cladding. The optical mode calculation indicates that the large extension of the optical field into the EO polymer provides the EO coefficient of about 80 pm/V in the waveguide. Therefore, the half-wave voltage of the hybrid waveguide was recorded only 1.1 V at 1550 nm in the Mach-Zehnder modulator. The measured insertion loss was about 15 dB, which included the materials absorption loss of the EO polymer. The traveling-wave-electrodes were applied to the hybrid waveguide in order to evaluate the frequency response of the modulator up to 40 GHz by measuring the S21 parameter. The -3 dB bandwidth of 20 GHz and a 6 dB reduction in response at 40 GHz were measured. This bandwidth is mainly limited by the conductor loss of the electrode, which can be improved further by the fabrication. The hybrid waveguide showed the excellent temperature stability at 85C for longer than 2000 hours.