1. Field of the Invention
The present invention relates to a technology for an optical wavelength multiplexing system, an optical wavelength multiplexing method, and a computer product.
2. Description of the Related Art
High volume data such as images and moving images is transmitted more frequently than ever before with the spread of the Internet. To transmit such high volume data at high speed, a network line using x Digital Subscriber Line (xDSL) technology enabling high-speed network communication is generally and frequently used. Recently, however, an optical network which is a higher speed network such as Fiber To The Home (FTTH) using an optical fiber cable is also used.
As a technology of effectively using the optical fiber cable, wavelength division multiplexing (WDM) draws attention. The WDM is a technology for transmitting a plurality of signals having different wavelengths over one optical fiber cable. Specifically, this technology increases transmission capacity of the optical fiber cable by simultaneously using the optical signals having different wavelengths.
In an optical wavelength multiplexing system including an Optical Add and Drop Multiplexer (OADM) that adds an optical signal having an arbitrary wavelength and drops and receives the optical signal using the WDM, individual frequencies are assigned to a plurality of ports respectively. An optical wavelength converter that converts (outputs) an input optical signal into an optical signal having an assigned frequency is connected to each of the ports.
Specifically, optical wavelength converters that output assigned frequencies need to be correctly connected to the ports respectively. However, because the number of optical wavelengths to be multiplexed in the OADM increases in recent years, the OADM is caused to have many ports. As a result, there occur many cases of causing an incorrect connection. The incorrect connection indicates that an optical wavelength converter outputs a wavelength different from the wavelength assigned to the connected port and available for optical wavelength division multiplexing. Hence, various technologies for detecting such an incorrect connection are disclosed.
Japanese Patent Application Laid-Open No. 2004-32088 discloses a technology of detecting the incorrect connection by using a wavelength-dependent arrayed waveguide grating (AWG) in multiplexing optical wavelengths. Specifically, the AWG having the wavelength dependency has a characteristic that, even when an optical signal having a wavelength different from the wavelength assigned to each port is input, a passing of the optical signal through the AWG is prevented. By using this characteristic, the incorrect connection is detected based on a comparison of an optical power level at each port of the AWG to which the wavelength is assigned with an optical power level after multiplexing and branching optical signals having different wavelengths input through the ports. Specifically, when there is any port which is incorrectly connected, an error is presented between optical power levels before and after the multiplexing of the optical signals. Therefore, by detecting the error, the incorrect connection in each port is detected.
However, the conventional technology has a problem that the arrayed waveguide grating (AWG) is very expensive, thereby causing the cost for constructing the optical wavelength multiplexing system to increase.