Hisato Sakuma

SOA-Booster Integrated Mach–Zehnder Modulator: Investigation of SOA Position

Integration of a booster semiconductor optical amplifier (SOA) is an efficient way of overcoming losses in InP based Mach-Zehnder modulators. We analyze the impact of locating the SOA before and after the MZM, respectively, in terms of output power and signal integrity at 10 Gb/s, both experimentally and theoretically. For a device with 10 dB MZM loss it is found that, for a fixed power consumption, locating the SOA after the MZM provides 7-9 dB higher output power. This advantage is reduced for lower MZM losses but remains significant. With the SOA after the MZM, the gain is restricted by dynamic saturation effects (waveform distortion), which is not the case if the SOA is at the input of the MZM. The waveform distortion is accompanied by a spectral red-shift, which degrades the transmission performance. Simulations show that for MZM losses below ~4 dB, locating the SOA before the MZM can provide a higher power with no waveform distortion and negative chirp, at the cost of a higher SOA gain. For higher MZM losses it is unfeasible to locate the SOA before the MZM, due to a prohibitively large power consumption.

Virtual integration technology of distributed energy storages

Widely spread renewable energies (REs) will destabilize electricity supply-demand balancing because of their uncontrollability and unpredictability. Therefore effective balancing technology is required. We focus on distributed energy storages (ESs) and propose a novel balancing technology using distributed ESs, “Virtual Integration (VI) of distributed ESs”. VI enables us to control multiple ESs as a concentrated single ES: VI can make ESs respond quicker, control electric-charge/discharge of ESs precisely, and achieve reliable property of ESs. The feature of VI is that by regarding the difference in dynamic status of each ES as a functional characteristic of ES, a virtually integrated ES is built to create new functions by arranging functional characteristics appropriately. In other words, VI technology properly assigns real-time charging/discharging power to each ES on the basis of each characteristic. For an example of reliable control of ESs, we numerically demonstrated VI suppresses capacity degradation of lithium Ion batteries by 20%.

Liquid-gas heat exchanger for low pressure refrigerant application

Liquid-gas heat exchanger has been developed for subcooling-superheating process of vapor compression refrigeration cycle. Refrigeration cycle utilizes low pressure refrigerant, which facilitates in easy piping installation and spill-proof operation. Experimental and numerical studies have been performed in order to quantify and understand thermal-hydraulic behavior of subcooling-superheating (liquid-gas) heat exchanger. As a result of low pressure refrigerant application, low volumetric flow rate in liquid domain can result in dominant natural convection and thus, poor heat exchanging performance. Also, high volumetric flow rate of low pressure gas refrigerant can increase gas side pressure drop. Both phenomenon were observed in conventional shell and tube heat exchanger application and resulted in system COP (Coefficient of Performance) degradation. This paper deals with development of efficient heat exchanger providing high heat transfer, designed for specific application, composed of multiple-fin and microchannel tubes type heat exchanger installed in shell structure. CFD (Computational Fluid Dynamics) methods are used for design optimization; leading toward improved system performance along with size reduction in comparison to shell and tube heat exchanger.