Hitachi Cable has applied Fine Semiconductor processing techniques & Optical Fiber manufacturing techniques to PLC (Planar Light wave Circuits), and by using these techniques has successfully started full scale mass production of a WDM: Wavelength Division Multiplexer. We took notice of and started researching & developing PLC which will be able to bring down the cost on optical devices such as optical amplifiers, switches & splitters etc. at a fairly early stage. We achieved excellent results when in 1992 we made it possible to develop a 1 x N splitter & coupler PLC device. We subsequently supplied these parts as they became important in the use of River & Road Surveillance Systems with Video Monitoring & in PHS Optical Networks.

In the meantime, in response to the fact that recently, information volume on the long haul optical network system, that provides the basic support for the Multi Media's highly integrated Information Network has suddenly increased, we have made it possible to simultaneously transmit multiple close proximity optical signal wave lengths through one optical fiber. It also looks likely that they will soon start using this WDM system in America. In the long run by using this system it will be possible to simultaneously transmit images, voice & data etc., namely large quantities of different kinds of information through one circuit, taking full advantage of optical fiber. But, to enable this to happen many close proximity optical signal wavelengths have to be sent to a single optical fiber by 'Multiplexing', moreover when these multiple optical signals have been sent through this Multiplexer, they along with the wave lengths need to go through 'Demultiplexing' equipment. All in all, it is necessary to use a wavelength Division Multi/Demultiplexer. Up to now devices such as Dielectric Multi-layered Thin Film Filters have been used but there are many problems related to their efficiency, reliability & size etc., so we have been eagerly awaiting the appearance of this Wavelength Division Multi/Demultiplexer.

Answering to these needs we have developed a manufacturing method by combining Fine Semiconductor Processing Technique and Optical Fiber construction technique. According to this method we have developed and are now mass producing Silica based Planar Light Wave Circuits for Dense Wavelength Division Multiplexing (an 8 Channel Guided Wave Optical Multi/Demultiplexer). This Guided Wavelength Division Multi/Demultiplexer can Multi/Demultiplex 8 optical signals of a 1.5 µm bandwidth( with channel spacing intervals of 2 nm (nanometer:1 nm = 10mm). Following are some of its other special features:

1.	Low loss and Flat Passband.
2.	Low occurrence of Crosstalk.
3.	There is low Polarization Dependence Loss.
4.	Temperature stability.
5.	The Wave Guide & the Optical Fiber are Fusion Spliced, therefore reliability is extremely high.
6.	Possible to make compact: ( 13cm(L) x 5cm(W) x 3cm(H) )

Furthermore we have taken another step forward and as well as developing even narrower wave length spacing (@ 1nm) we are also devoting ourselves to developing a 16 - 32 wave Channel Dense Wavelength Division Multiplexing Guided Wave Optical Multi/Demultiplexer, which will be due for production in the not to distant future. We know that it is important to invest in the market at an early stage by being the first to produce ultra modern goods to suit the market needs and because of this, in this progressive information society, we are certainly strengthening our position to be ranked amongst the world's leading companies in key technological areas such as the PLC and the WDM sphere.