Seiko Mitachi

Crosstalk reduction in a 10-GHz spacing arrayed-waveguide grating by phase-error compensation

The crosstalk in arrayed-waveguide grating multiplexers with a channel spacing of 10 GHz is reduced by compensating for the phase errors after fabrication. We used the thermooptic effect realized with a thin-film heater and the photoelastic effect obtained with amorphous silicon film, respectively, for dynamic and static phase-error compensation. These two methods were applied to confirm the principle and to realize a stable, stand-alone device, respectively. We have achieved a crosstalk of less than -35 dB for the TE polarization mode in a 16/spl times/16, 10 GHz-spacing arrayed-waveguide grating by using these two phase-error compensation techniques. Static phase-error compensation results in a stable multiplexer which features a low crosstalk of less than -30 dB for one of the two polarization modes of all the channels without any external control equipment.

Reduction of impurities in fluoride glass fibers

In order to realize a low-loss fluoride Optical fiber, impurity reduction is indispensable. The methods of recrystallization, extraction, chemical vapor-phase deposition, distillation, and sublimation were tried to purify the starting materials for a fluoride fiber. These purification methods were evaluated by measuring transmission loss of the fibers prepared by using the purified materials. It was found that recrystallization was useful for reducing impurities in ZrF 4 to the level of below 1 ppm. The extraction technique could be also applicable to purification of BaF 2 and GdF 3 . It was concluded that the sublimation was the most probable purification in order to prepare fluoride materials with less than 0.1-ppm impurities. As a result, a low-loss fiber with 8.5 dB/km at 2.12 μm was obtained by using the starting materials purified by sublimation.

Reduction of Impurities in Fluoride Glass Optical Fiber

A sublimation purification technique was developed for fluoride fiber materials, ZrF4, BaF2, GdF3, and AlF3. Using these purified materials and a build-in casting method, the low-transmission-loss of 8.5 dB/km at 2.12 µm was o btained, which is the lowest loss in an infrared ray transmitting fluoride glass fiber. The impurity level of the fiber was estimated as below 0.5 ppm by loss-factor analysis.

Relationship between Scattering Loss and Oxygen Content in Fluoride Optical Fibers

To clarify the cause of scattering loss in fluoride optical fibers, oxygen content in fibers having various loss values is analyzed by activation analysis using a cyclotron. It is found that fibers with higher loss contain a higher oxygen content. It is concluded that oxygen tends to cause scattering loss in fluoride optical fibers.

Fabrication of fluoride glass single-mode fibers

Single-mode optical fibers are obtained using ZrF 4 -based fluoride glasses. The fibers are drawn from a preform and jacketing tube. The preform with cladding/core ratio of 5.1 is made by using a built-in casting method. The cutoff wavelength of the fiber is experimentally determined to be 2.7 μm by bending loss measurement. Minimum transmission loss of the obtained fiber is 160 dB/km at a wavelength of 3.28 μm. The V -value at this wavelength is estimated to be 2.03 from the core diameter and the refractive index difference.

Polarization crosstalk dependence on length in silica-based waveguides measured by using optical low coherence interference

We describe a powerful method for precisely measuring polarization crosstalk dependence on length for birefringent waveguides which uses optical low coherence interference between excited and orthogonally coupled light waves. This method is applied to 10-m long silica-based waveguides with the total polarization crosstalks of 8.9/spl times/10/sup -3/ and 7.5/spl times/10/sup -3/. The spatial resolution is 10 cm and the measurement error for a waveguide part longer than 1 m is /spl les/10%. A comparison of measured and theoretical crosstalk curves for the waveguides enables us to confirm that the bends in the waveguides are the main origin of the crosstalk. The polarization crosstalk per bent section is /spl sim/4/spl times/10/sup -5/.

A fluoride glass optical fiber operating in the mid-infrared wavelength range

An optical fiber operating in the mid-infrared wavelength range is fabricated using ZrF4-based fluoride glass. Material purification, the fiber fabrication process, and transmission properties are presented. The starting materials, ZrF4, BaF2, GdF3, AlF3, and SbF3are carefully purified by sublimation techniques. The built-in casting technique, specially developed for fluoride glass fiber, is used for preparing cladded type fiber with a smooth core-cladding interface. Spectral loss is measured in the 0.7- to 5.5-μm wavelength region, and a minimum loss of 12 dB/km is attained at 2.55 μm. Based on the refractive-index spectrum measured in the0.4-5-mum range, material dispersion characteristics are also investigated. It is indicated that material dispersion falls to zero at 1.52 μm and exhibits a gentle wavelength dependence in the present glass system.

Tunable narrow-band light source using two optical circulators

We report a tunable narrow-band light source with a spectral width of 0.26/spl plusmn/0.04 nm, a 0-dBm output power, and a reduced background spectrum in the 1.5-/spl mu/m band, which we have developed for optical low coherence reflectometry. The Rayleigh backscatter signal fluctuations were reduced to within /spl plusmn/0.4 dB by using this source. The source will also be used in a system for measuring optical waveguide circuits. This is because the coherence length is about 1 cm and, by using a fiber-optic depolarizer, the degree of polarization is less than 0.016.

Dispersion measurement on fluoride glasses and fibers

An overview is given of dispersion measurements on fluoride glasses and fibers, and the dispersion compensating capability of fluoride fibers is discussed. The temperature dependence of refractive-index dispersion and material dispersion of fluoride glasses is measured. These measurements indicate that fluoride glasses can compensate for temperature-dependent changes of refractive indices and material dispersion in silica glasses and fibers. >

Fabrication of Low OH and Low Loss Fluoride Optical Fiber

Low OH and low loss fluoride optical fiber of 6.3 dB/km at 2.13 µm is obtained by dry processing technique. This is the lowest loss fluoride fiber yet reported. The OH peak at 3 µm is reduced to less than one-hundredth that of conventional fiber preparation.