Takeshi Kuboki

Bandwidth enhancement for high speed amplifier utilizing mutually coupled on-chip inductors

This paper discusses bandwidth enhancement technique for high speed amplifier. Inductive peaking is a common practice for bandwidth enhancement, however the area occupied by on-chip inductors is a heavy disadvantage. We utilize mutually coupled inductors for effective inductive peaking. A Laser-Diode (LD) driver for optical communication system is designed in a 0.18//m CMOS. Measurement results show that the mutually coupled inductor can achieve 16Gbps operation and 26% area reduction compared to conventional shunt peaking.

Low-Power Design of CML Driver for On-Chip Transmission-Lines Using Impedance-Unmatched Driver

This paper proposes a design technique to reduce the power dissipation of CML driver for on-chip transmission-lines. CML drivers can operate at higher frequency than conventional static CMOS logic drivers. On the other hand, the power dissipation is larger than that of CMOS static logic drivers. The proposed method reduces the power dissipation by using an impedance-unmatched driver instead of the conventional impedance-matched driver. Measurement results show that the proposed method reduces the power dissipation by 32% compared with a conventional design at 12.5 Gbps.

A 16Gbps laser-diode driver with interwoven peaking inductors in 0.18-µm CMOS

A laser-diode (LD) driver with interwoven mutually-coupled peaking inductors for high-speed optical networks is presented. Six and four inductors are interwoven into two sets of inductors for area-effective implementation as well as performance enhancement. The proposed circuit is fabricated in CMOS 0.18-µm process. The circuit area is 0.34mm2 and the maximum operating speed is 16Gbps. Compared to a conventional LD driver in 0.18-µm CMOS, the proposed circuit achieves 1.6 times faster operation, 26% smaller area with 60% reduction in power consumption under the condition for the same amount of data transmission and the LD driving current.

A 10Gbps/channel On-Chip Signaling Circuit with an Impedance-Unmatched CML Driver in 90nm CMOS Technology

An on-chip signaling system consists of a CML driver, a differential transmission-line and a CML receiver is fabricated. We developed an impedance-unmatched driver for power reduction. The impedance-unmatched driver reduces the tail current of the CML buffer by tuning the load resistance. The designed circuit achieves 3mm, 10Gbps/channel on-chip signal transmission and the impedance-unmatched driver saves the energy per bit by 21% compared with a conventional impedance-matched driver.

Wavelength stabilization within 0.05 GHz with photo-mixing technique and laser current controlling

The lasers for the WDM system with the flexible grid need to have highly accurate wavelength tuning and stability. Instead of using optical filters, we propose the microwave photonics approach with photo-mixing technique and the laser current controlling. Experimental results show that the optical frequency is stabilized with the accuracy of 0.05GHz.

Proposal of THz phase control system utilizing chromatic dispersion at optical device and its feasibility demonstration

We propose a novel THz wave phase control system consisting of an optical device whose chromatic dispersion changes the phase difference between two lightwaves for photomixing. Our devised Mach-Zehnder modulation technique reveals the feasibility of full-range THz wave phase control with the semiconductor phase modulator.

Proposal of cost-efficient and low-complexity platform for software defined visible light communication

With the increasing popularity of LED lighting and a growing demand for bandwidth in wireless communication, the visible light communication (VLC) is one of the promising scheme for addressing the bottleneck in the emerging broadband access networks. For research in the field of VLC focused on solutions of contradiction between massive available bandwidth and limited modulation bandwidth of LED, the purpose of this paper is to design an VLC experiment platform with characteristics of high flexibility and rapid productization. As a result, this platform not only expand the concept of software defined communication, but has the advantage of simple structure and low cost.

Optical-to-wireless media conversion by utilizing cross gain modulation at semiconductor optical amplifier

We devise an optical-to-wireless media conversion method by XGM at the SOA aiming for a future use at a THz-wave access. We investigate the XGM characteristics and the performance of our proposed media conversion method. We configure the media-converted data transmission system and demonstrate an error free transmission.

Linearizer for wavelength sweep at tunable DBR-LD and linearity evaluation of sweep

We constructed the linear wavelength sweeping system with 2-μm-band distributed Bragg reflector laser for the second-harmonic-detection wavelength modulation spectroscopy. Using our devised linearity evaluation method with a germanium etalon filter, we experimentally confirmed that the nonlinearity of the laser can be efficiently compensated.

Fast wavelength stabilization of tunable laser after starting laser oscillation

For fast wavelength switching within the full available wavelength range of the tunable laser array, we investigated a wavelength stabilizing method after switching on the injection current to the lasers active layer. Experimental results demonstrated that our feedback controller dramatically reduced wavelength switching time from 800 μs to 2.0 μs.