Ultra-compact non-volatile Mach-Zehnder switch enabled by a high-mobility transparent conducting oxide.

Compact and broadband non-volatile silicon devices are mainly absorption based. Hence, access to low-loss non-volatile phase shifters is still a challenge. Here, this problem is addressed by using a high-mobility transparent conducting oxide such as cadmium oxide as a floating gate in a flash-like structure. This structure is integrated in a Mach-Zehnder interferometer switch. Results show an active length of only 30 µm to achieve a $ \pi $π phase shift. Furthermore, an extinction ratio of 20 dB and insertion loss as low as 1 dB may be attained. The device shows an optical broadband response and can be controlled with low-power pulses in the nanosecond range. These results open a new, to the best of our knowledge, way for enabling compact silicon-based phase shifters with non-volatile performance.

Enhancing Pockels effect in strained silicon waveguides.

The magnitude and origin of the electro-optic measurements in strained silicon devices has been lately the object of a great controversy. Furthermore, recent works underline the importance of the masking effect of free carriers in strained waveguides and the low interaction between the mode and the highly strained areas. In the present work, the use of a p-i-n junction and an asymmetric cladding is proposed to eliminate the unwanted carrier influence and improve the electro-optical modulation response. The proposed configuration enhances the effective refractive index due to the strain-induced Pockels effect in more than two orders of magnitude with respect to the usual configuration.

Non-volatile epsilon-near-zero readout memory.

The lack of memory effect of silicon makes it unfeasible to store electronic data in photonics. Here we propose a non-volatile readout photonic memory, which is electronically written/erased and optically read. The memory utilizes indium tin oxide as a floating gate and exploits its epsilon-near-zero regime and electro-optic activity. Extinction ratios greater than 10 dB in a bandwidth of 100 nm for a 5 µm long memory are obtained. Furthermore, power consumption in the order of microwatts with retention times of about a decade have been predicted. The proposed structure opens a pathway for developing highly integrated electro-optic devices such as memory banks.

Experimental demonstration of a tunable transverse electric pass polarizer based on hybrid VO2/silicon technology.

A tunable transverse electric (TE) pass polarizer is demonstrated based on hybrid vanadium dioxide/silicon (VO2/Si) technology. The 20-µm-long TE pass polarizer exploits the phase transition of the active VO2 material to control the rejection of the unwanted transverse magnetic (TM) polarization. The device features insertion losses below 1 dB at static conditions and insertion losses of 5.5 dB and an attenuation of TM polarization of 19 dB in the active state for a wavelength range between 1540 nm and 1570 nm. To the best of our knowledge, this is the first time that tunable polarizers compatible with Si photonics are demonstrated.

Optical switching in hybrid VO2/Si waveguides thermally triggered by lateral microheaters.

The performance of optical devices relying in vanadium dioxide (VO2) technology compatible with the silicon platform depends on the polarization of light and VO2 properties. In this work, optical switching in hybrid VO2/Si waveguides thermally triggered by lateral microheaters is achieved with insertion losses below 1 dB and extinction ratios above 20 dB in a broad bandwidth larger than 30 nm. The optical switching response has been optimized for TE and TM polarizations by using a homogeneous and a granular VO2 layer, respectively, with a small impact on the electrical power consumption. The stability and reversibility between switching states showing the possibility of bistable performance is also demonstrated.

On the influence of interface charging dynamics and stressing conditions in strained silicon devices.

The performance of strained silicon devices based on the deposition of a top silicon nitride layer with high stress have been thoroughly analyzed by means of simulations and experimental results. Results clearly indicate that the electro-optic static response is basically governed by carrier effects. A first evidence is the appearance of a variable optical absorption with the applied voltage that should not occur in case of having a purely electro-optic Pockels effect. However, hysteresis and saturation effects are also observed. We demonstrate that such effects are mainly due to the carrier trapping dynamics at the interface between the silicon and the silicon nitride and their influence on the silicon nitride charge. This theory is further confirmed by analyzing identical devices but with the silicon nitride cladding layer optimized to have intrinsic stresses of opposite sign and magnitude. The latter is achieved by a post annealing process which produces a defect healing and consequently a reduction of the silicon nitride charge. Raman measurements are also carried out to confirm the obtained results.