Koji Akimoto

Super-dense WDM transmission of spectrum-sliced incoherent light for wide-area access network

This paper presents a detailed study on superdense wavelength-division multiplexing (WDM) transmission of spectrum-sliced incoherent light used for a wide-area access network. The transmission performance possible with this approach is evaluated numerically with regard to the following items: the transmission limit due to the chromatic dispersion, optimized signal-to-noise ratio design for the optical spectral width taking into account the adjacent-channel crosstalk, and the nonlinear effect generated by four-wave mixing at around the zero-dispersion wavelength. Superdense WDM transmission is also performed experimentally using 25-GHz channel-spaced, 15-GHz wide, up-to 156-Mb/s signals through up to 120 km of dispersion-shifted fiber.

Optical reflective filter with comb-drive nickel micromirror for optical fiber communication

A novel nickel micromirror with an electrostatic comb-drive actuator has been developed. It is fabricated by nickel surface micromachining, which features a thick photoresist molding process and nickel electroplating. It has a precise controllability and a wide tuning range. As an example of an application to optical communications, an optical reflective filter, which is an etalon constructed of a flat-end optical fiber facet and the micromirror, is demonstrated.

Spectrum-sliced, 25-GHz spaced, 155 Mbps/spl times/32 channel WDM access

We estimated the BER performance of spectrum-sliced WDM access influenced by adjacent crosstalk numerically and experimentally. The BER performance was improved as the spectral width was widened, while it was degraded by the crosstalk as the spectral width approached the channel spacing. We derived the optimum spectral width as 14 GHz at a channel spacing of 25 GHz and a bit rate of 155 Mbps, and the BER was estimated to be less than 10/sup -15/ between 12 to 16 GHz. The transmission performance was also measured by experiments using 15-GHz wide, 25-GHz channel-spaced, 155-Mbps /spl times/ 32-channel transmissions through 50-km of DSF, and showed good agreement with the calculated results.

Microelectromechanical systems (MEMS) and their photonic application

THe fabrication of tunable optical devices by using Si free- space micro-optics and Ni micromirrors has demonstrated the applicability of MEMS technologies to photonic devices. Compact, multi-functional, assembly-free, micro-optical systems have been developed by using MEMS technologies to integrate optical devices and micromechanics onto the same wafer. A high aspect-ratio Si plate which works as a beam splitter has been fabricated using Si micromachining. A tunable laser diode with an external Si mirror has been fabricated and shown to have wavelength tunability. A Ni micromirror with comb-drive actuator has been developed and applied it to both a tunable optical filter and a tunable laser diode. Due to the precise motion of the micromirror, accurate optical tunability has been obtained.

Micromechanically controlled GT interferometer for optical-pulse narrowing

Abstract A micromechanically controlled Gires–Tournois interferometer (micro-GTI) is proposed for a tunable dispersive medium for use in optical-pulse compression. Its dispersive properties, which are controlled by comb-drive micromirror actuation, were theoretically and experimentally evaluated to verify its capability to generate ultra-short optical pulses. Pulse compression performed using this micro-GTI generated nearly transform-limited pulses with a duration of 0.43 ps.

Widely tunable mode-locked laser diodes using optical disk filter

We present a scheme for generating high-repetition-rate mode-locked optical pulses within a wide wavelength-tuning range. This scheme utilizes an external-cavity laser configuration with a disk-shaped bandpass filter (disk filter), which is set in the external cavity. The disk filter can tune its transmission wavelength by rotating parallel to the external mirror. This simple wavelength-tuning scheme allows a short external cavity, which is necessary for generating high-repetition-rate optical pulses. This paper describes a preliminary experimental demonstration exhibiting 100%-modulated mode-locked pulses at 8 GHz in the 1535-1587-nm range.