Tetsuro Komukai

Upconversion pumped thulium-doped fluoride fiber amplifier and laser operating at 1.47 /spl mu/m

A 1.064-/spl mu/m band upconversion pumped Tm/sup 3+/-doped fluoride fiber amplifier and a laser both operating at 1.47 /spl mu/m are investigated in detail. The two devices are based on the /sup 3/F/sub 4//spl rarr//sup 3/H/sub 4/ transition in a trivalent thulium ion, which is a self-terminating system. When pumped at 1.064 /spl mu/m, the amplifier has a gain of over 10 dB from 1.44 to 1.51 /spl mu/m and a low-noise characteristic. Also, the fiber laser generates a high-output power of over 100 mW with a slope efficiency of 59% at around 1.47 /spl mu/m. These levels of performance will be important for optical communication systems. >

Dispersion tuning of a linearly chirped fiber Bragg grating without a center wavelength shift by applying a strain gradient

We propose a new method for controlling the chirp of a linearly chirped fiber Bragg grating (FBG) without a center wavelength shift by using beam bending. The beam consists of a plastic sleeve enclosing a 10-cm-long chirped FBG and a metal rod. The grating pitch could be varied to give positive or negative chirp as well as zero chirp (i.e. uniform pitch) as applying displacement to one end of the beam without rotation. The dispersion at the two extremes of mechanical displacement were -791 ps/nm and +932 ps/nm. The center wavelength shift of the FBG was as small as 0.09 nm over the dispersion tuning range.

Multicarrier Light Source With Flattened Spectrum Using Phase Modulators and Dispersion Medium

This paper describes a phase-locked multicarrier light source that employs a continuous wave (CW) light source, two phase modulators, and a dispersion medium. A sinusoidal phase modulation (PM) with a modulation index of ¿/4 and a group velocity dispersion of ±1/(4¿fm 2), where fm is the modulation frequency, are applied to a CW light followed by a large sinusoidal PM. This configuration provides a multicarrier light with a flattened optical power spectrum for any modulation index of the second PM. By adopting a chirped fiber Bragg grating (FBG) as a dispersion medium instead of a long normal dispersion fiber, we can increase the stability of the optical output spectrum and reduce the size of the multicarrier light generator. We have built a prototype with this configuration that generates a 61-carrier light with a 25 GHz interval and a power deviation of less than 8 dB.

An efficient 0.04-nm apodized fiber Bragg grating and its application to narrow-band spectral filtering

A narrow-band apodized fiber Bragg grating was fabricated with a phase mask method that incorporated a fluorescence monitoring technique. The grating length was 100 mm and the 3-dB reduced bandwidth was as small as 0.04 nm. The 20-dB reduced bandwidth was 0.1 nm at a center wavelength of 1554 mm. A single longitudinal oscillation mode of a 10-GHz pulse train from a mode-locked fiber laser was successfully extracted using the grating.

Adaptive dispersion slope equalizer using a nonlinearly chirped fiber Bragg grating pair with a novel dispersion detection technique

We realized the first adaptive-dispersion equalizer that equalizes dispersion over a wide wavelength range (6 nm) in the zero-dispersion wavelength region of a dispersion-shifted fiber (DSF). The equalizer is based on a pair of nonlinearly chirped fiber Bragg gratings, which are designed to equalize exactly the dispersion profile of a DSF. The dispersion changes were tracked using a technique that employs opposite dispersion fibers to identify the sign of the dispersion change. Unlike previous approaches, no additional sources or changes in the source wavelength are required. We demonstrate the adaptive equalization of the dispersion changes in an 83-km DSF, induced by temperature changes between -10/spl deg/C and 60/spl deg/C.

Highly efficient tunable fiber Bragg grating filters using multilayer piezoelectric transducers

Abstract We realized a wavelength tunable optical filter based on a fiber Bragg grating using multilayer piezoelectric transducers (MLP). The Bragg wavelength of the filter can be easily tuned in proportion to an applied low DC voltage. The tuning range efficiency was as high as 0.2 nm/V. We realized a 10 nm Bragg wavelength shift by applying as low as 50 V to the MLP. The MLP was also used in a higher order dispersion equalizer which consists of a pair of nonlinearly chirped gratings. A zero dispersion wavelength shift of 7 nm was successfully realized for the equalizer.

The design of dispersion equalizers using chirped fiber Bragg gratings

Dispersion equalizers designed to compensate for the arbitrary dispersion characteristics of optical fibers can be synthesized by cascading chirped fiber Bragg gratings and optical circulators. We have derived a synthesis rule for the equalizers and applied it to the fabrication of a third-order dispersion equalizer operating at the zero dispersion wavelength.

Experimental demonstration of multi-degree colorless, directionless, contentionless ROADM for 127-Gbit/s PDM-QPSK transmission system

We experimentally demonstrate the feasibility of a multi-degree colorless, directionless, and contentionless (C/D/C-less) ROADM node composed of high port count wavelength-selective switches and transponder aggregators using silica-based planar lightwave circuit technology. The experimental results show that the introduction of a C/D/C-less function to a multi-degree ROADM node induces no significant penalty in a 127-Gbit/s PDM-QPSK signal transmission.

40-Gb/s RZ transmission over transoceanic distance in a dispersion managed standard fiber using a new inline synchronous modulation method

We propose a modified soliton control method for a strongly dispersion managed line, which employs a highly nonlinear fiber in addition to conventional inline synchronous modulation. This method enables us to transmit a 10-Gb/s return-to-zero signal over 20000 km using a dispersion managed line composed of a standard (nondispersion shifted) fiber and dispersion compensation. Optimizing the length of the highly nonlinear fiber greatly increases the power margin of the transmitted optical power.

Group delay ripple reduction and reflectivity increase in a chirped fiber Bragg grating by multiple-overwriting of a phase mask with an electron-beam

The phase errors in electron-beam-written step-chirped masks can be reduced by using a method based on the continuous movement approach and overwriting a pattern at the same place on the substrate several times. The group delay ripple of chirped fiber Bragg gratings fabricated by a four-times-overwritten phase mask is comparable with that of gratings obtained using a holographically written chirped phase mask.