CWDM Three Port Device | Definitions | Corning

The performance of all couplers varies with wavelength. Couplers are usually specified over a wavelength window, or in some cases, multiple windows. The center wavelength is the nominal wavelength of operation of the coupler, while the bandpass is the range of wavelengths over which the specifications are guaranteed. In many cases, couplers will perform adequately over a range outside their bandpass, but adherence to specifications is not guaranteed in this region.

Coupling ratio or splitting ratio is defined as the ratio of the optical power from one output port of the coupler to the sum of the total power from all output ports. The coupling ratio is measured at the specified center wavelength and is normally expressed as a percentage.

Excess loss is the ratio of the optical power launched at the input port of the coupler to the total optical power measured from all output ports, expressed in dB. Typical excess loss is the expected value of the excess loss measured at the specified center wavelength.

Insertion loss is the ratio of the optical power launched at the input port of the coupler to the optical power from any single output port, expressed in dB. The insertion loss includes the coupler spitting loss and excess loss and is the most useful parameter for system design. The maximum and minimum insertion loss is the upper and lower limit, respectively, of the insertion loss of the coupler and applies over the entire wavelength range specified in the bandpass. The typical insertion loss is the expected value of the insertion loss measured at the specified center wavelength. Multimode couplers are measured with an equilibrium mode fill.

Uniformity is a measure of how evenly power is distributed between the output ports of the coupler. Uniformity applies to couplers with a nominally equal coupling ratio and is defined as the difference between the highest and lowest insertion loss between all of the coupler output ports, expressed in dB. Uniformity is a typical value across the entire bandpass.

Directivity is the ratio of the optical power launched into an input port to the optical power returning to any other input port. Directivity has been referred to as near-end isolation or near-end crosstalk. Return loss is the ratio of optical power launched into an input port to the optical power returning to the same input port. Both directivity and return loss are expressed as positive dB and are measured with all output ports optically terminated. Reflectance is the negative of return loss. In many instances, reflectance and return loss are used synonymously. Minimum directivity and return loss are the lower limits which apply over the entire wavelength range specified in the bandpass.

Wavelength isolation is a measure of how well different wavelengths are separated at the output of a wavelength division demultiplexer. It is defined as the ratio of the optical power at the two output ports of the demultiplexer at a given wavelength, expressed in dB. The minimum wavelength isolation is the lower limit to the wavelength isolation measured over the entire wavelength range of the specified bandpass. Wavelength isolation has also been referred to as far-end crosstalk. 

All the optical parameter definitions for CWDM will be similar to DWDM except the channel spacing for CWDM is 20 nm

The center wavelength of CWDM is not on DWDM ITU-T grid. For 8-channel CWDM, they are 1YY0(or 1YY1) nm, YY = 47, 49, 51, 53, 55, 57, 59, 61

Defined as IYY ±B/2, this is a spectral width value centered on the ITU-T specific wavelength IYY. YY is used to denote the channel number associated with the pass channel of a filter.

The adjacent channels of channel YY are channel YY-2 and channel YY+2.

The non-adjacent channels of channel YY are channel YY-4 and below and channel YY+4 and above

This is the loss measured from the 0 dB level to the pass channel spectrum minimum point in the minimum passband region for channel YY over temperature and all polarization states.

The is the loss measured from the 0 dB level to the pass channel spectrum peak in the minimum passband region for channel YY over temperature and all polarization states.

This is the difference between ILmax and ILmin for a given pass channel in any one state of temperature and polarization.

This is the difference between the minimum point on the pass channel spectrum within the minimum passband of channel YY over temperature and the maximim point within the adjacent channels minimum passband over temperature and all polarization states.

This is the difference between the minimum point on the pass channel spectrum within the minimum passband of channel YY over temperature and the maximum point within minimum passband across all non-adjacent channels over temperature and all polarization states.

This is the loss measured from the 0 dB level to the express channel spectrum minimum point in the minimum passband region for adjacent express channels over temperature and all polarization states. 

This is the loss measured from the 0 dB level to the express channel spectrum minimum point in the minimum passband region across all non-adjacent express channels over temperature and all polarization states.

This is the difference between the minimum point on the express channel spectrum within the minimum passband of adjacent channels over temperature and the maximum point within the minimum passband of pass channel YY over temperature and all polarization states.

The return loss is the back reflectance along the same optical path from any port with the other ports optically terminated. The return loss spec applies to the minimum passband of channel YY and the minimum passband of all its adjacent and non-adjacent channels over temperature.

The directivity is the leakage of signal into undesirable optical path due to scattering, which is the insertion loss between pass port and express port with the common port optically terminated for 3-port device. It applies to the minimum passband of channel YY and the minimum passband of all its adjacent and non-adjacent channels over temperature.

PDL is the maximum difference in attenuation of signals over all states of polarization. It applies to the minimum passband of channel YY and the minimum passband of all its adjacent and non-adjacent channels over temperature.

PMD is the dispersion of an optical signal due to the different polarizations of light traveling at different speeds through optical component. It applies to the minimum passband of channel YY and the minimum passband of all its adjacent and non-adjacent channels over temperature.

The temperature range over which the filter is expected to maintain measured values within all defined specifications.

The filter will meet all specifications while the total power at any port remains within the range 0 mW to maximum power.

IL, PDL, and isolation data need to be collected over the minimum passband width of the pass channel and/or its adjacent and non-adjacent channels. The spec applies to whole temperature range of operation and all polarization states. If the PDL variation over the minimum passband of pass channel is very small, single point test at passband CWL will be sufficient. Also the express channel PDL and pass channel PDL over the minimum passband width of its adjacent and non-adjacent channels are very small and can be neglected.

Directivity and pass-port RL data need to be collected over the minimum passband width of the pass channel; however, the common port and express port RL data needs to be collected over the minimum passband width of the pass channel and its adjacent and non-adjacent channels.

The separation of ITU-T frequency grid positions and it has an absolute value of 100 GHz for 100 GHz, 200 GHz for 200 GHz DWDM.

Defined as IXX ±B/2, this is a spectral width value centered on the ITU-T specific wavelength IXX. XX is used to denote the ITU-T channel number associated with the pass channel of a filter, for example, XX = 33 for ITU-T channel 33.

The adjacent channels of channel XX are channel XX-1 and channel XX+1 for 100 GHz channel spacing, channel XX-2 and channel XX+2 for 200 GHZ channel spacing.

The non-adjacnt channels of channel XX are channel XX-2 and below and channel XX+2 and above for 100 GHz channel spacing, channel XX-4 and below and channel XX+4 and above for 200 GHz channel spacing.

This is the loss measured from the 0 dB level to the pass channel spectrum minimum point in the minimum passband region for channel XX over temperature and all polarization states.

This is the loss measured from the 0 dB level to the pass channel spectrum peak in the minimum passband region for channel XX over temperature and all polarization states.

This is the difference between ILmax and ILmin for a given pass channel in any one state of temperature and polarization

This is the difference between the minimum point on the pass channel spectrum within the minimum passband of chanel XX over temperature and the maximum point within the adjacent channels minimum passband over temperature and all polarization states.

This is the difference between the minimum point on the pass channel spectrum within the minimum passband of channel XX over temperature and the maximum point within minimum passband across all non-adjacent channels over temperature and all polarization states.

This is the loss measured from the 0 dB level to the express channel spectrum minimum point in the minimum passband region for adjacent express channels over temperature and all polarization states.

This is the loss measured from the 0 dB level to the express channel spectrum minimum point in the minimum passband region across all non-adjacent express channels over temperature and all polarization states.

This is the difference between the minimum point on the express channel spectrum within the minimum passband of adjacent channels over temperature and the maximum point within the minimum passband of pass channel XX over temperature and all polarization states.

The return loss is the back reflectance along the same optical path from any port with the other ports optically terminated. The return loss spec applies to the minimum passband of channel XX and the minimum passband of all its adjacent and non-adjacent channels over temperature.

The directivity is the leakage of signal into undesirable optical path due to scattering, which is the insertion loss between pass-port and express port with the common port optically terminated for 3-port device. It applies to the minimum passband of channel XX and the minimum passband of all its adjacent and non-adjacent channels over temperature.

PDL is the maximum difference in attenuation of signals over all states of polarization. It applies to the minimum passband of channel XX and the minimum passband of all its adjacent and non-adjacent channels over temperature.

PMD is the dispersion of an optical signal due to the different polarizations of light traveling at different speeds through optical component. it applies to the minimum passband of channel XX and the minimum passband of all its adjacent and non-adjacent channels over temperature.

The temperature range over which the filter is expected to maintain measured values within all defined specifications.

The filter will meet all specifications while the total power at any port remains within the range 0 mW to maximum power.

IL, PDL, and isolation data need to be collected over the minimum passband width of the pass channel and/or its adjacent and non-adjacent channels. The spec applies to whole temperature range of operation and all polarization states. If the PDL variation over the minimum passband of pass channel is very small, single point test at passband CWL will be sufficient. Also the express channel PDL and pass channel PDL over the minimum passband width of its adjacent and non-adjacent channels are very small and can be neglected.

Directivity and pass-port RL data need to be collected over the minimum passband width of the pass channel; however, the common port and express port RL data needs to be collected over the minimum passband width of the pass channel and its adjacent and non-adjacent channels.