Katsuyuki Imoto

Guided-wave multi/demultiplexers with high stopband rejection

A new guided-wave multi/demultiplexer with high stopband rejection is made using high-silica embedded channel waveguides. This consists of three directional couplers of the same structure, that is, the second and third directional couplers are connected with two output waveguides from the first directional coupler, which suppresses undesired optical signals. This optical device is fabricated using low temperature CVD, lithography, and a reactive ion etching process. It is possible to apply a high-reliability fail-safe module, two-way repeater transmission module using wavelength division multiplexing; it also has other uses.

Optical fiber drawing method with gas flow controlling system

A method for reducing the diameter variation of optical fibers during fiber drawing is described. The method is based on the control of gas flow and drawing speed. Rapid fluctuations in diameter are suppressed by adjusting the gas flow rate, and slower ones are controlled by changing the drawing speed. The efficiency of this method has been tested by applying stepwise disturbance of +or-63% in preform feeding speed. Fluctuations of fiber diameter are controlled within +or-1 mu m despite the forced disturbance. By applying this method to high-speed drawing (30 m/min), a high-tensile-strength fiber, with diameter fluctuations within +or-1 mu m and transmission losses near the 0.85- mu m wavelength region of approximately 3 dB/km, is achieved. >

Plastic optical fiber star coupler

A new plastic optical fiber star coupler and the means of fabricating it have been developed. This coupler has been realized by twisting and pulling the waist region of a biconical tapered fiber bundle made by pretapered fibers while heating. Controlling the biconical tapered shape has been achieved by jetting gas on the fiber surface while heating the fiber bundle. By using this fabrication method, the desired diameter mixing portion can be formed without breakage from melting. Low-cost optical star couplers with large port number, low excess loss, and small power deviation can be obtained.

New biconically tapered fiber star coupler fabricated by indirect heating method

A new biconically tapered fiber star coupler is developed. The fiber bundle is inserted in a quartz protection tube and the tube is heated with an oxyhydrogen burner while the fibers are twisted and pulled. The tube ends are then sealed with adhesive agent. Excess loss for the new coupler is approximately \log_{10}m for input/output fiber port number m . Furthermore, the coupling ratio is almost independent of wavelength and polarization of incident light. The new fabrication method offers high reproducibility and stability.

Novel manufacturing process of waveguide using selective photobleaching of polysilane films by UV light irradiation

We have tried to develop the technology for selective bleaching of core patterns of waveguides on polysilane films by UV light irradiation without wet development and RIE process. Furthermore, we have examined heat treatment of films in order to make transmission loss low instead of introducing fluorine groups in the polymer structure which conventional polymeric material are applied. As a waveguide device, evaluation of low loss straight-line waveguides and multilayered laminating type waveguides at 850nm for MM, and splitter of 8 branches (1×8) at 1550nm for SM was carried out. This new technology is expected to establish the low-cost manufacturing process of optical waveguides which are important components of passive optical devices for PON (passive optical network) system and optical interconnects.

Transmission characteristics of VAD fibers using a multiple burner with single source gas nozzle

Abstract A vapor phase axial deposition (VAD) method using a multiple burner with single source gas nozzle is presented. Fibers fabricated by this technique feature very low loss and wide bandwidth characteristics, although the refractive index profile slightly deviates from the ideal, on the outer side of the core part. This technique is expected to provide a simple method of fabricating low loss and wide bandwidth fibers.

High-silica guided-wave optical devices

A high-silica embedded channel waveguide with low loss and high precision structure has been fabricated using low-temperature glass formation, lithography, reactive ion etching, and a flame hydrolysis glass deposition processes. Fusion splicing of the waveguide and single-mode fiber has also been achieved by CO/sub 2/ laser beam irradiation. Furthermore, this waveguide structure can be applied to many devices such as multi/demultiplexers, star couplers, and hybrid integration of optical active components.<<ETX>>

Compensation for fabrication-induced center wavelength shift in a coupled waveguide type multi/demultiplexer

A new coupled waveguide type multi/demultiplexer is proposed together with a fabrication method which can compensate for the shift Deltalambda(0) in wavelength caused by fabrication errors. This waveguide formed on a low refractive index layer is embedded by a cladding layer with index n(c). In this structure, Deltalambda(0) can be compensated for by optimizing n(c) (which is calculated by measuring the deviations from the design values for core width, core height, and waveguide separation) before cladding the waveguide. A cladding material with an optimum n(c) is coated on the entire waveguide including the cores.

Bottom shape control of optical fiber soot preform by modified VAD method

Control of the bottom shape of an optical fiber soot preform fabricated by a modified vapor-phase axial deposition (VAD) method is proposed as a way to realize indirect control of the refractive index profile exponent during soot deposition. The technique is based on the close correlation between the profile and the bottom shape. Diameter and refractive index profile fluctuations of the preform with and without control are analyzed. In the case of no control, the fluctuations are larger, and unstable growth of the preform is observed. By controlling the bottom shape, axial fluctuations in the refractive index profile of a transparent preform are reduced to half the magnitude for preforms with no control, and axial diameter fluctuations of the soot and transparent preform are reduced to below +or-0.5%. As a result, fibers with a bandwidth of about 1 GHz km at a wavelength of 0.85 mu m can be stably fabricated. >

Properties of polarization noise caused by external disturbances in single-mode fiber transmission systems

The properties of polarization noise caused by external disturbances in intensity modulation/direct detection transmission systems that have polarization-dependent optical devices are analyzed. It is experimentally shown that the noise consists of additive noise and multiplicative noise. The multiplicative noise directly disturbs signals, even if the external disturbance is of a low frequency. The signal to polarization noise ratio easily reaches the ratio at which flickers obstruct the picture in an analog TV transmission system. The polarization noise caused by external disturbances is also discussed. It is shown that disturbances to the fiber can make the maximum noise n/sup 2/ times greater than the noise caused by a single disturbance, where n is the number of disturbances. >