Dense wavelength division multiplexing (DWDM) is an advancing fiber-optic transmission technology which combines multiple optical channels at different light wavelengths and then transmits them over the same optical fiber. Theoretically, the DWDM technology can multiplex hundreds and even thousands of separate wavelengths into a single optical fiber. To achieve this goal, the DWDM multiplexer is one of the most important parts needing to be improved. This article will discuss several commonly used technologies in the wavelength-selective mechanism of the DWDM multiplexer.
Key Optical Parameters of the DWDM Multiplexer
To better understand those technologies, we need to have a basic knowledge of the DWDM multiplexer’s main optical parameters which are center frequency, insertion loss, pass-band and cross talk.
Center frequency is usually defined as either the arithmetic mean or the geometric mean of the lower cutoff frequency and the upper cutoff frequency of a band-pass system or a band-stop system. Insertion loss is the input-to-output power loss caused by the insertion of a device in a transmission line or optical fiber. A pass-band is the portion of the frequency spectrum that is transmitted (with minimum relative loss or maximum relative gain) by some filtering device. Wider and flatter pass-band makes the system more tolerable to wavelength drift of the laser transmitter. The energy leakage from adjacent and nonadjacent channels in the DWDM system is defined as cross talk.
Technologies Used in the Wavelength-selective Mechanism of the DWDM Multiplexer
Interference filter, bulk grating, array waveguide grating (AWG), and Mach-Zehnder (MZ) interferometer are the four common-used technologies in the DWDM multiplexer.
Consisting of multiple thin layers of dielectric material having different refractive indices, the interference filter reflects one or more spectral bands or lines and transmits others. The dielectric thin-film filter is one of the most popular technologies use to make the DWDM multiplexer.
Being a classical optics technology that has been in existence for over 100 years, bulk grating is now one of the newest technological forerunners in the field of DWDM.
As the AWG is capable of multiplexing a large number of wavelengths into a single optical fiber, it is commonly used as optical (de)multiplexers in wavelength division multiplexed (WDM) systems, which considerably increases the transmission capacity of optical networks.
As a basic interference device, the MZ interferometer is consist of two couplers connected by two waveguides of different length. It is widely used in various fibre-optic communications applications.
A high-performance DWDM multiplexer should have small polarization-dependent loss (PDL), low polarization mode dispersion (PMD), and the same performance under hostile environment temperature. A series of DWDM MUX/DEMUX modules are provided by Fiberstore, which is with as more as 96 channels (50GHz, 100GHz, or 200GHz spaced) in simplex or duplex configurations. All the DWDM modules are available with three types of packaging: ABS Pigtailed Box, Rack Chassis and LGX Cassette.