Passive Optical Components
Passive optical components for light waveguides are characterized by a number of technical parameters. The parameters give the optical attenuation between 2 or more ports of the component. Important parameters of a passive POF component are:
- Insertion Loss: The insertion loss indicates the optical loss between 2 ports of the optical component. It is measured in dB.
- Excess Loss: The excess loss of a passive optical component describes the fraction of coupled light that does not exit to other ports. It is measured in dB. The excess loss is thus a measure of the component internal light loss and describes technologically related losses as material attenuation, end face quality or not perfect cross-section matching between coupled waveguide. A hypothetically perfect technology could reduce the excess loss of a passive optical component to 0dB.
- Splitting Loss: The splitting loss describes the inevitable insertion loss between ports caused by dividing the light into multiple parts. Thus, a symmetrical 1×2 splitter has an inevitable power loss of 3dB.Only an active amplifier in the component compensate it.
- Crosstalk:The crosstalk counts the mostly unwanted, but in some applications non-interfering over-coupling of optical power from one port of the passive optical component on its neighbor ports. But if the component is used in optical transmission systems with only one POF wire or sensor systems with POF simplex cables, the crosstalk of strong transmitted signals interferes with the signal at high-sensitivity receivers and perturbates this signal significantly. In a data transmission system crosstalk limits receiver sensitivity and maximum transmission distance, respectively. In fiber optic sensor systems sensor sensitivity is reduced.
DieMount passive optical components are made of bare fiber POF; as a consequence excess loss figures are very low.
A special feature of DieMount passive optical components arises from the special and patented polishing technology for so-called POF splitter blanks. These blanks are the basic part of every 1×2 POF splitter. Coating the blanks with optically active layers results in a light barrier between the splitter branches that reduces crosstalk and generates high crosstalk attenuation.
1×2 splitter with high crosstalk attenuation require a greater fabrication effort and are more expensive compared with standard splitters. The following sketches shall facilitate the decision which splitter type is required for the system application at hand.
An important note to crosstalk determination in POF data transmission systems or sensors is the influence of the connected POF cable to the crosstalk. At the connection point between POF splitter and POF cables crosstalk can be generated by an insufficiently prepared end surface of the cable, poor concentricity of the plug connection or by reflection from the opposite cable endface.
The division ratio of a splitter is the ratio of optical powers in the ports related to the optical power in all other ports. E.g., a symmetrical splitter is characterized by a splitting ratio 50:50. Non symmetrical splitter are made of non symmetrically polished splitter blanks in a splitting ratio of up to 25:75. Splitter with stronger asymmetry require alternative mechanical designs. Splitter blanks for splitter with a splitting ratio of 90:10 would be mechanically instable.
The table above shows the endfaces of the common port for some splitter types with differnet splitting ratios. 1×7 and 1×19 POF splitter are feasible. But they need a common taper waveguide between input and output ports.
Passive optical POF components of increased complexity are developed for special applications like POF PON data transmission systems, e.g. on the basis of G.hn, or fiber optic sensors comprising more than one different wavelength light sources. Devices like 2×2, 2×3 or 2×4 are feasible. The principle of design bases on the processes as given above.
DieMount Splitter and passive optical components can be assembled with many commonly used today connectors. Some examples show the following photos. However, not every splitter is integrable into any type of connector; if the structure of the splitter spatially does not fit into the required connector ferrule, an alternative must be sought. Another type of connector may be a solution, but also POF pigtails with prefabricated connectors that are fixed to the splitter. The pigtail and the additional coupling point, respectively, however, increases the excess loss of the component.