Fiber physical contact (FPC) is proposed and demonstrated as a new method designed to enable fibers to be connected easily with a small structure while maintaining high optical performance. FPC is performed by mating two bare optical fibers in a micro sleeve and fixing them to a holder while they are buckled. Buckling is a phenomenon whereby a long column is bent by compression along its length. PC connection is realized by the buckling force of the fibers themselves and does not require any springs. Optical fiber buckling is studied both theoretically and experimentally. The buckling force, which is determined by an initial span between the optical fiber holding points, remains constant when the span is changed and is useful as the PC force. The buckling amplitude which is determined by the span reduction must be so small that it does not cause excess radiation loss. A suitable span is about 7 mm. This generates a 0.7 N. The allowed span reduction is 0.1 mm. This results in a buckling amplitude of 0.64 mm which prevents radiation losses of above 0.1 dB for 1.31 µm light. Based on a study of fiber buckling, we demonstrate the optical performance for FPC connection with a 0.126 mm diameter micro sleeve in which optical fibers are mated and with polished fiber end faces. The insertion loss is under 0.3 dB and the average return loss is 50 dB for 1.31 µm light. These values are stable in the 20 to 70 temperature range. We confirm that FPC connection realizes high optical performance with a small simple structure.

A novel flexible ferrule only 0.8 mm in diameter is proposed and demonstrated as a key element in optical fiber connectors. Miniature aggregated multiple fiber connectors with a fiber pitch of 2-5 mm are possible with this Flexible Fine ferrule" (FF-ferrule). This paper presents the fundamental concept of the FF-ferrule. Then, ferrule bending characteristics, a distinctive mechanical feature of this ferrule, are discussed in detail both theoretically and experimentally. The method of designing the FF-ferrule is also described based on the theoretical results. A prototype FF-ferrule was made by precision transfer molding. Connection loss was as small as 0.6 dB, because the ferrule bending can compensate for axial misalignments up to 0.5 mm. In addition, 20% of the measured connections showed a connection loss of less than 0.3 dB. The high pressure contact from the small cross-section of the ferrule makes physical contact" between the endfaces of the fiber.

The statistical properties of insertion losses and return losses for optical connectors are investigated theoretically using the probability theory and the Monte Carlo simulation. Our investigation is focused on an orientation method for reducing insertion loss by which a fiber-core center is adjusted in a region of within a certain angle to the positioning key direction. It is demonstrated that the method can significantly improve insertion losses, and that an adjusting operation angle of 90 degrees is sufficient to realize an insertion loss of less than 0.5 dB with 99% cumulative probability. Good agreement was obtained between the theoretical distribution and the experimental results for single-mode fiber connection. Consequently, it is indicated that the statistical distributions of insertion losses and return losses of optical connectors in the field can be predicted theoretically from the values measured in the factory by connection to a master connector.

This paper describes the optical characteristics and static fatigue reliability of a zirconia alignment sleeve, which is a component part of an optical connector with zirconia ferrules. This combination of sleeve and ferrules hardly generates any wear debris during connector insertion and removal cycles. This has reduced the cleaning frequency of the ferrule endface during cycles and greatly improved the return loss stability of the optical connectors. The zirconia alignment sleeve enables stable return loss characteristics to be achieved over a wide temperature range as it has the same thermal expansion coefficient as the zirconia ferrule. Furthermore, the gauge retention force for the zirconia alignment sleeve is defined with a view to its practical use. This force must be between 2.0 and 3.9 N to allow stable optical connections to be made under various mechanical and environmental conditions. We also clarify the conditions for a proof test by which to prevent the occurrence of static fatigue fractures in the sleeve, and we confirm the validity of the test. The static fatigue parameters for zirconia ceramics and derived from the static fatigue theory for brittle materials and fracture testing. We use these static fatigue parameters to predict the lifetime of a zirconia sleeve under working stress. An appropriate stress level for the proof test which eliminates weak sleeves, is about 3 times greater than working stress. The strength of the sleeve as demonstrated in the proof test is confirmed by accelerative stress aging. The performance of this sleeve is superior to that of a conventional copper alloy sleeve and the proof test confirms its reliability; under 0.1 FIT for 20 years of use.

Failure probability of a split ceramic alignment sleeve in an optical fiber connector has been predicted based on slow crack growth theory. Applying the theory to split zirconia ceramic alignment sleeves, a failure probability of 104 for 20 years is predicted and the value is expected to decrease to almost zero when an appropriate proof test is introduced.