The MT9812B is a nine channel mainframe providing high accuracy and reliable applications for the evaluation of various optical devices and systems including WDM. It can incorporate up to nine units of DFB-LD light sources and high-accuracy optical sensors which support optical frequencies conformable to ITU-T recommendations. Moreover, by adopting the format of a plug in unit, it can meet a wide range of requirements. Setting of each unit and checking of the setting conditions can be carried out on the front panel. In addition, GPIB and RS-232C are provided as standards, making it easy to configure the measuring system.