T. Imai

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.

A Wavelength Tunable Q-Switched Erbium-Doped Fiber Laser with Fiber Bragg Grating Mirrors

Q-switched operation of an erbium-doped fiber laser with fiber grating mirrors is demonstrated for the first time. The resonator was formed by splicing two fiber gratings to erbium-doped fiber ends. One of the fiber gratings was periodically stretched by a piezoelectric transducer for the Q-switching operation. An output pulse with a pulse width of 2.46 µ s and a peak power of 2.1 mW was obtained for a 1.48 µ m pump power of 26 mW. The oscillation wavelength was 1.552 µ m and the repetition rate was 1 kHz. The laser oscillation wavelength was tuned from 1.552 µ m to 1.556 µ m by applying lateral stress to one of the fiber grating mirrors.

A Novel Technique for Measuring Group Velocity Dispersion of an Installed Ultralong Fiber by Using Erbium-Doped Fiber Amplifiers

A new technique is presented for measuring the group velocity dispersion (GVD) of optical fibers. It makes it possible to measure the GVD of an already installed ultralong dispersion-shifted fiber. The method is based on phase rotation measurement, but it includes erbium amplifiers and an optical circulator or a 100% reflector. This allows round-trip propagation of the modulated signal and the GVD was successfully measured at one terminal. The maximum measurable length is as long as 125 km.

High speed optical path routing by using four-wave mixing and a wavelength router with fiber gratings and optical circulators

A novel all-optical-path-routing technique is described, which employs four-wave mixing in a dispersion-shifted fiber and a wavelength router with fiber gratings and optical circulators. The signal wavelength is converted to a specified channel by four-wave mixing, and is finally selected with the wavelength router. It offers good potential for enabling the number of output ports of a wavelength router to be extended as it provides a very sharp spectral edge and a low insertion loss.

40 Gbit/s soliton transmission field experiment over 1,020 km and its extension to 1,360 km using in-line synchronous modulation

We report the details of a 40-Gbit/s soliton transmission field experiment over 1,020 km, which used a dispersion-compensation technique. The transmission distance was extended to 1,360 km by installing in-line synchronous modulation.

Optical Cable Amplifier

An erbium-doped fiber amplifier installed inside an optical fiber cable is reported. This optical cable amplifier is mechanically flexible as the result of using a flexible stainless steel tube and wire mesh as the amplifier cavity and outer cover, respectively. The amplifier is pumped with a 0.98μm laser diode to reduce both the electric driving power and the wavelength dependence of optical gain. Backward pumping is used to obtain a high optical output power. A gain of 27.5dB and a maximum optical output power of + 10dBm have been successfully realized. The wavelength dependence of the optical gain was 2.1dB between 1540nm and 1560nm. A two-channel optical cable amplifier with two EDFAs in the cable is also described. The noise figure of the amplifiers was approximately 6dB and the output power dependence on ambient temperature change was less than ±0.2dB between 20°C and 60°C.