Polarization-maintaining photonic crystal fiber couplers (PM-PCFCs) were fabricated using a CO2 laser irradiation technique. We could control the states of air holes in the tapered region of couplers by adjusting the laser power density in the fusion and the elongation processes. It was demonstrated that the air hole remaining PM-PCFC exhibited polarization-splitting characteristics and that the air hole collapsed PM-PCFC had polarization insensitive coupling characteristics.

A new optical fan-out adapter is proposed and fabricated by applying the jacket removing system with a CO2 laser. The fan-out adapter has both the multi-fiber connection function and the fiber separating function for single-fiber connections. In order to remove the jacket of a fiber ribbon to connectorize and fabricate the fan-out adapter, the optimum conditions of the laser power P and the scan speed V are clarified for the jacket removing. Based on the optimum conditions, the fan-out adapter was fabricated successfully. Individual fibers could be taken out from the MT connector of the fan-out adapter. The connection losses of the fabricated fan-out adapter were comparable with the values of commercially available MT connectors and SC connectors. The length of the fabricated fan-out adapter was 27 mm, including 2 MT connectors. This result clarifies that the size of the connection with a fan-out can be reduced dramatically by the proposed fan-out adapter.

For the construction of photonic crystal fiber (PCF) systems using their unique properties, a PCF coupler (PCFC) is one of the key components of the systems. The characteristics of the PCFC depend on the state of air holes in the tapered region of the PCFC because the state of air holes in the tapered region affects light propagation in the PCFC taper. In this paper, coupling characteristics of PCFCs were theoretically investigated. In PCFCs with air hole remaining tapers, we found that a smaller elongation ratio i.e. a stronger elongation is required to obtain optical coupling as an air hole pitch or a ratio of air hole diameter to pitch is larger. In PCFCs with air hole collapsed tapers, it was clarified that a dependence of extinction ratio on air hole collapsed elongation ratio is higher for smaller elongation ratio. It was also clarified that an air hole remaining PCFC has slow wavelength characteristics in extinction ratio compared to an air hole collapsed PCFC. Air hole remaining PCFCs and air hole collapsed PCFCs were fabricated using a CO2 laser irradiation technique. We could successfully control whether air holes in the PCFC taper were remaining or collapsed by adjusting the irradiated laser power in the elongation process of the PCFC fabrication. It was experimentally clarified that the air hole remaining PCFC has slow wavelength characteristics in extinction ratio compared to the air hole collapsed PCFC. The tendencies of the measured wavelength characteristics of PCFCs agree with those of numerical results.

Long-period fiber gratings (LPGs) using a high-silica core fiber are presented. A high-silica core fiber has a residual stress in the core, and the grating structure is formed by stress releasing of the core using a focused CO2 laser beam. The dependence of the transmission spectrum on temperature and tensile strength is measured, and low dependence compared with conventional LPGs is observed. These unique characteristics are caused by the difference of temperature and tensile strength changes of the effective indices for the fundamental propagation mode and the cladding mode in the high-silica core fiber.

The Michelson-interferometer (MI) optical resonator has been applied, together with physical interests, to a low pressure and slow-flow type CO2 laser for specifying the system to a probe laser source. The fundamental characteristics online-selection, oscillation power and transverse mode are also investigated in comparison to the CO2 laser obtained for various resonators such as an open-ended reflective-multiple interferometer (RMI), an open-sided MI, a Fox-Smith interferometer and soon. Consequently, it is confirmedthat the MI type laser proposed can be one of the promising scheme, without losing oscillation power much and transverse mode quality as a probe laser towards lineshape (or laser) parameter analysis. Translating one of the MI mirror by a slight distance on the order of a micron meter along the gain axis, we can not only switch either a single rotational-vibrational line or combination of multiple lines, but also obtain different combination of lines by translating a large amount of the translation distance of the order of 100 µm. Moreover, elimination of one of the side-mirrors in the MI resonator enables us to switch the oscillation lines at the expense of some output power.

Improvement of fatigue behavior of a fusion spliced portion on a carbon-coated fiber is achieved by recoating carbon using a thermal-CVD process with a CO2 laser as a local heat source. The fatigue parameters, so-called n-values, of 121 and 94 are obtained on the non-spliced portion and the spliced portion, respectively. Assuming a life time prediction model, these high values have been proved to have an advantage in a long-term reliability and to be sufficient in a practical submarine cable use.