A passive branched optical network unified for broadcasting and communication utilizing a set of Fabry-Perot etalons with different cavity lengths is proposed and its basic operation including thermal stability of broadcasting channel is demonstrated. It is confirmed that a high transmission frequency in common for a pair of fiber Fabry-Perot etalons is always found however environmental temperature changes.

An effective spatial resolution enhancement method for distributed strain measurement by BOTDR is proposed. An optical fiber is glued to a structure by a length less than the spatial resolution defined by the pulse width, and the Brillouin spectrum of the light scattered from the glued optical fiber is investigated theoretically. The apparent strain xp observed in the fiber is found to be proportional to the accurate strain a. The ratio r=xp/a coincides with the ratio of the glued length to the spatial resolution. Spatial resolution as small as 0.2 m is demonstrated experimentally for small strains of less than 10-3.

The feasibility of a 1600 mechanical optical switch is demonstrated. The maximum insertion loss is 0.2 dB and the loss variation throughout 500 switching cycles is less than 0.1 dB for both multimode and single-mode fibers at wavelengths of 0.85, 1.3, and 1.53 µm. The maximum switching time is 3.4 seconds.

Theoretical and experimental studies on power flow in a bent step index fiber are made. Theoretical study is made on a slab model under the condition that mode conversion occurs at joints between straight parts and bent parts of a fiber. It is assumed that the propagation angle deviation by mode conversion depends both on the propagation angle and the curvature radius of the bent part. The power flow equation in a partially bent fiber is derived and solved generally by series expansion. Theoretical mode power distributions at different propagation lengths are compared with the experimental results and they are in good agreement with each other. The mode power distribution expressed by the first term of the series, which is considered to be the theoretical steady state mode power distribution, is observed experimentally.

When a linearly polarized light is launched into a birefringent material, the output light is generally elliptically polarized. The ratio of the major and minor axes of the polarization ellipse varies depending on the angle between the polarization direction of the input light and the birefringent axis of the medium. The maximum ratio is determined only by the retardation due to the birefringence. Utilizing this phenomena, birefringence of a medium whose principal axis direction is unclear is measured with high precision by measuring the maximum extinction ratio for various input light polarization directions. Ambiguity in retardation associated with angular function solution is removed by measurement at two adjacent wavelengths. The measurement principle of the new method is confirmed by applying it to a quarter wave plate made of quartz. Birefringence of a 3 m long ribbon fiber as small as 10-7 is successfully measured.

Some optical components have polarization dependent loss (PDL), which degrades the performance of optical measurement systems. Various PDL suppression methods have been proposd, most of them have rather complicated structures. In this paper we propose a new simple method for PDL suppression, in which a single birefringent element is concatenated to a PDL device with their birefringent axes offset by π/4. The effectiveness of the proposed method is verified by experiments, that is, polarization dependent loss variation amplitude V of a device relative to its average loss is reduced from 90% to 2% by using a 2 m long PANDA fiber for an LED light source whose central wavelength λ0 and spectral width Δλ are 847 nm and 55 nm, respectively. Furthermore, for an SLD light source with λ0=1539 nm and Δλ=71 nm, V as much as 80% is reduced to 2% by using the same PANDA fiber.

A heterodyne interferometer utilizing a light source with short coherence length has led to a significant improvement in distance resolution of an optical reflectometer. The resolution less than 1 cm along a fiber is easily achieved by a Fabry-Perot type diode as a short coherence length source.

A new type of fiber Fabry-Perot interferometer buried in a fiber connector housing was proposed. The transmission spectra revealed double peaks due to birefringence in the fiber and the peak separation showed a temperature dependence as large as -7. 7 MHz/deg, which was 2 orders of magnitude larger than that estimated from the thermal characteristics of its component materials.

In an optical time domain reflectometer type strain measurement system, we theoretically derive the shape of the Brillouin gain spectrum produced in an optical fiber under a parabolic strain distribution which is formed in a uniformly loaded beam. Based on the derived result, we investigate the effects of the parabolic strain distribution parameters and the measurement conditions such as the launched pulse width and the measurement position on the beam on the deformation of the Brillouin backscattered-light power spectrum shape. In addition, we investigate the strain measurement error resulting from the deformation of the power spectrum shape by analyzing the peak-power frequency at which the power spectrum is maximized.

We propose a set of Fabry-Perot etalons integrated in a planar lightwave circuit (PLC-FPE) designed for a unified system for broadcasting and communication. A PLC-FPE containing four etalons having different cavity lengths is fabricated and their loss and frequency characteristics are investigated. The total loss and the maximum finesse were found to be 8 dB and 34, respectively.