Michito Matsumoto

Characteristics of thermally expanded core fiber

Thermally expanded core (TEC) fiber is expected to reduce fiber-to-fiber and fiber-to-laser diode connection loss. This paper describes the characteristics of TEC fiber theoretically and experimentally. We reveal theoretically that when fabricating TEC fiber the mode field diameter (MFD) is enlarged more effectively by increasing the heating temperature rather than the heating time. In the 1300-1600/spl deg/C temperature range with heating times between 0 and 60 min, it is necessary to control the temperature accurately so that no deviation from the target temperature is more than /spl plusmn/30/spl deg/C. This is in order to ensure that any connection loss caused by MFD mismatch is less than 0.1 dB. We show experimentally that the propagation loss of TEC fiber is dependent on the heating region and wavelength by using a micro burner with a propane/oxygen flame. Based on the relationship between the loss characteristics and the expanded MFD, we suggest a method for nondestructively measuring the MFD in TEC fibers.

Connection loss reduction by thermally-diffused expanded core fiber

Connection loss reduction in ten fiber connectors prepared by the thermally diffused expanded core (TEC) method has been confirmed. The mode field diameters (MFDs) of conventional single mode (SM) fibers were expanded from 9.8 to 13 mu m by thermal treatment considering the influence of loss increase due to fiber axis misalignment. An average connection loss of 0.15 dB for 4-SM-fiber connectors was realized, which was improved by 0.22 dB compared with previous value of 0.37 dB without thermal treatment. The TEC method promises to reduce the coupling loss, which is caused by lateral offset of multifiber connectors, fiber/LD modules, and fiber/waveguide device modules.<<ETX>>

Loss characteristics of thermally diffused expanded core fiber

The authors have clarified experimentally the dependence of loss characteristics on wavelength for thermally diffused expanded core (TEC) fiber applied to connectors. Based on the relationship between the loss characteristics and the expanded mode field diameter (MFD), they suggest a method for measuring the MFD in TEC fibers nondestructively.<<ETX>>

Monitoring method for axis alignment of single-mode optical fiber and splice-loss estimation.

A new method for core-axis alignment and precise splice-loss estimation for single-mode optical fibers is presented. By using a differential interference contrast microscope, we can achieve core-axis alignment with an offset below 0.3 microm, which results in a butt-joint loss increase of 0.04 dB compared with that obtained by alignment using a conventional optical monitoring method. Furthermore, splice-loss estimation with a precision of 0.05 dB is attained for a low-loss region without using an index-matching liquid.

Design and development of an automatic cutting tool for optical fibers

A new type of automatic cutting tool for obtaining good fiber end-surface has been proposed. In principle, a bare fiber is scored by rotating a broadaxe-shaped blade, while the fiber is supported by two magnetic clamps. The fiber is then fractured by applying bending and tensile stresses. The tool is 10 cm wide, 7.5 cm high, 9 cm long, weighs about 500 g, and is battery-driven. Optimum cutting conditions have been investigated, revealing that the blade pressure should be 10 g, bending stress should be 15 kg/mm2, and tensile stress should be 6 kg/mm2. Under these conditions, an average endface inclination of 0.42 ° is easily obtained. Stable cutting is confirmed during 1000 cutting trials, with a failure rate of 0.3 percent.

Design and characteristics of reinforcement method for fusion spliced optical fiber

In developing a reinforcement method, optimum material and structure must be selected to prevent optical-fiber failure. This paper discusses a splice reinforcement element to compensate for shrinkage of the plastic coating due to aging and thermal cycling. In prior designs, shrinkage causes buckling and increases the failure probability of the reinforced section. Also, torsion propagation, introduced during fabrication of the splice, shows an adverse effect. These concepts have not been considered up to now and the new reinforcement method, using a heat shrinkable tube, shows good performance. The loss increase at a spliced portion without nylon coating, where a heat shrinkable tube is used, is below 0.02 dB at -70°C. It has also been verified that proof testing with approximately 15-kg/mm2proof stress is necessary for long-term durability of a spliced portion with a reinforcement element.