FWDM – Filter-based Wavelength Division Multiplexer

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Definition

Filter-based Wavelength Division Multiplexer (Filter WDM, or FWDM) is based on the mature membrane filter technology, with a wide channel bandwidth, low insertion loss, high channel isolation degrees and high environmental stability and reliability. The Filter-Based WDM is extensively used in EDFA, Raman amplifiers, WDM networks and fiber optics instrumentation. The device combines or separates light at different wavelengths in a wide wavelength range. They offer very low insertion loss, low polarization dependence, high isolation and excellent environmental stability.

These passive optical thin film filters systems are arranged to process specific wavelengths in and out of the transport stream. As these are optical devices they can be used for both multiplexing and demultiplexing or both. The process of filtering the wavelengths can be performed with prisms, but more common technologies used are thin film filters, dichroic filters or interference filters which are used to selectively reflect a single wavelength of light, but pass all others transparently. Each filter is tuned for a specific wavelength which is why it’s important to connect the correct wavelength to the corresponding I/O port.

Benefits

WDM-PON is an architecture based on optical filters rather than fiber optic splitters. Choosing filters implies 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 minimised, explaining why filters are favoured. 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.

Filter-Based WDM Product Family

Filter-Based WDM product family covers following wavelength windows commonly used in optical fiber systems: 1310/1550nm (for WDM or DWDM optical communications), 1480/1550nm (for high-power DWDM optical amplifier and EDFA), 1510/1550nm (for DWDM multi-channel optical networks) and 980/1550nm (for high performance DWDM optical amplifier and edfa amplifier) and 1310/1490/1550nm (for PON, FTTX and test instrument).

1310/1490/1550 FTTX FWDM is based on filter based platform for optical device. 1490/1310/1550nm FTTH FWDM can realize the multiplexing and de-multiplexing of two communication signal 1490/1310 and 1550nm. It can expand the capacity of a single fiber to achieve bidirectional communication, so that widely used in optical network upgrade and expansion, or introduce new comprehensive business.

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