Enhanced efficiency thermo-optic phase-shifter by using multi-mode-interference device

We demonstrate a method for power reduction in thermo-optic based Mach-Zehnder interferometer (MZI) by using the multimode region of a 2x2 Multi-Mode-Interferometer (MMI) as the modulation region. The light is circulated through the same multimode region twice and therefore utilizes the already present change in temperature leading to additional phase change, and an increase in efficiency. Power saving of 29.6% compared to a conventional thermo-optic phase shifter using single mode waveguides has been experimentally demonstrated. The reported devices show minimal insertion loss penalty compared to generic devices and do not add any additional fabrication complexity. Such an approach could also be applied to higher speed devices, for example those employing free carrier effects.

A Current Reconstruction Strategy Following the Operation Area in a 1-Shunt Inverter System

To reduce the cost of the inverter system in home appliances, a method using a shunt resistor at the DC-link can be substituted for a method using two current sensors at the inverter output. However, the minimum time of the active vector is required to sample the accurate current using a 1-shunt resistor. Therefore, many studies have been conducted investigating current reconstruction methods in the unmeasurable region of the current. The conventional methods using voltage injection have some problems such as high THD (Total Harmonic Distortion) and acoustic noise, because the PWM pattern is shifted. In addition, the current reconstruction is inaccurate in a low modulation region. In this paper, the cause of the noise in conventional methods is analyzed and a simple current reconstruction method based on an average current estimation and a current reference is utilized for reducing acoustic noise. In an immeasurable area, especially a low modulation region, an intermittent PWM shift method is proposed to enhance the accuracy of the reconstructed current. Therefore, a control strategy that combines all of the mentioned methods is implemented for the entire operating range. The effectiveness of the proposed methods is verified through the experimental results and the results of sound measurement in an anechoic chamber are included to compare with the acoustic noise.