As an unprecedented opportunity to dramatically increase the bandwidth capacity, WDM(Wavelength Division Multiplexing) technology is an ideal solution to get more bandwidth and lower cost in nowadays telecommunications networks. WDM Filters can separate or combine optical signals carried on different wavelengths in a cost-effective manner.
Splitters versus Filters
One issue with WDM-PON(Passive Optical Network) is that there is no industry-accepted definition. WDM-PON is an architecture based on optical filters rather than Fiber Optic Filter. Following are two reasons:
One is the insertion loss. Choosing filters imply arrayed waveguide gratings (AWGs). No other filter technology is seriously considered for WDM-PON if filters are used.
With an AWG, the insertion loss is independent of the number of wavelengths supported. This differs from using a splitter-based architecture where every 1×2 device introduces a 3dB loss. Using a 1×64 splitter, the insertion loss is 14 or 15dB whereas for a 40-channel AWG the loss can be as low as 4dB. Thus using filters rather than splitters, the insertion loss is much lower for a comparable number of client ONUs.
There is also a cost benefit associated with a low insertion loss. To limit the cost of next-generation PON, the transceiver design must be constrained to a 25dB power budget associated with existing PON transceivers.
To live with transceivers with a 25dB power budget, the insertion loss of the passive distribution network must be minimized, explaining why filters are favored.
The other main benefit of using filters is security. With a filter-based PON, wavelength point-to-point connections result. This is an issue with PON where traffic is shared.
Arrayed Waveguide Grating (AWG)
AWG, including Athermal AWG (AAWG) and Thermal AWG (TAWG), is commonly used as optical MUX/DeMUX in WDM systems. AAWG have equivalent performance to standard TAWG but require no electrical power, software or temperature.
Fiber Bragg Grating (FBG)
FBGs are versatile wavelength filters for multiplexing and demultiplexing WDM signals. They also can compensate for chromatic dispersion that can degrade the quality of the WDM signal in an optical fiber.
Thin Film Filter (TFF)
Thin film filters were adopted very early on and have been widely deployed since because they have the unique attributes that meet the stringent requirements of optical communication systems. The main advantage of thin film filters is its ability to achieve high accuracy in the processing in small device sizes when compared it to competing technologies.
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