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.
In this work, we have demonstrated a phase modulator and a ring resonator modulator by using a thin TiO<sub>2</sub> and electrooptic (EO) polymer derived hybrid waveguide structure. This TiO<sub>2</sub> layer enables the modulators to be constituted without a top cladding, and also can enhance in-device EO coefficient from 70 to 120 pm/V. We utilized the high refractive index TiO<sub>2</sub> to confine a large fraction of light in the relatively low refractive index EO polymer layer. As a result, the phase modulator has a VπL of 3.3 V·cm, corresponding to 1.65 V·cm in a push-pull Mach-Zehnder interferometer structure. For the ring modulator, the resonance was observed to shift by 0.02 nm/V, and a modulation depth of 3dB was observed at the frequency response function at 20 kHz using 2 V<sub>p-p</sub> clock signal.
Copper-doped planar glass waveguides were prepared by the thermal ion-exchanged of commercial soda-lime glass
wafers in molten mixture of CuSO<sub>4</sub> with sodium sulfates at temperature of about 600°C. The effective indices were
measured by means of prism-coupled technique, and the guided modes were not monotonic increasing with the ionexchange
times. The properties of photoluminescence (PL) spectra of the waveguides were studied. The broad emission
bands centered at around 520 nm (at the excitation wavelength of 310 nm, at the room temperature) were measured on
the samples, which were also strongly influenced by the ion-exchange times and the intensity of the PL emission is not
monotonic increasing with the ion-exchange times as well.