The definition and realization of optical splitter multiplexer

OADM device is one of the key node devices in all-optical network. WDM signals contain channels of multiple wavelengths, which are multiplexed in a single fiber, and each wavelength channel carries an independent traffic stream.

Assuming that only one wavelength of light is transmitted in a fiber; this is expensive relative to the cost of the fiber. Transmitting multiple wavelengths of light in a single fiber, without interfering with each other, saves money and increases bandwidth. Current WDM technology transmits optical signals of multiple wavelengths in a single fiber. Optical signals of each wavelength represent a channel, and multiple channels transmit data simultaneously in a fiber, that is, the multiplexing of a fiber.

In the optical domain, OADM performs the function of traditional electrical SDH subdivision multiplexing in the time domain. Moreover, it has transparency and can process signals of any format and rate, which is superior to the electrical ADM (subdivision multiplexer) used in SDH network.

• On the road means that a new wavelength channel is added to the optical signal that goes into the optical splitter and is multiplexed into the optical fiber along with other channels.

• Down means that one wavelength channel is removed from the optical signal entering into the optical split-multiplexer, and the other independent channels pass directly through the split-multiplexer. Note: the down channel is directly transferred to the equipment for business processing.

OADM technology and product development trends

At present, reconfigurable OADM has become the development direction. Besides the use of optical switches to dynamically select upper and lower wavelengths, the use of tunable filters is also a hot spot.

• Italy reported a tunable splitter filter made of SiO2/Si acoustic waveguide for 4-way WDM systems with wavelength interval of 3.2nm and crosstalk between the splitter channels of less than one 18dB;

• Japan reported that OADM, which is composed of semiconductor waveguides coupled vertically and opposite directions, has a tunable range of 11nm and a loss change of less than 1dB;

• The tunable OADM reported in Canada is made of FBG. In the 1.55LM window, there are 8 tunable filters with wavelength interval of 0.8nm. Thermal tuning is used to make the grating period of FBG linearly change and the wave band is relaxed

• Chinese scholars have also studied OADM based on acousto-optic tunable filter. The extinction ratio of the device reaches 32dB and the insertion loss is 3dB.