The requirements for testing fiber optic networks will vary according to the specific type of network and the overall testing requirements of the network designer. Regardless of the type, two basic or general-purpose optical test equipment will be used; an optical time domain reflector or OTDR, and a pair of optical test equipment called a power meter and a light source. These tests are usually in units of "dB". The term dB is the expression of attenuation or power loss when the fiber is transmitted from the terminal to a point along the fiber path. After connecting the optical fiber to the active device, all tests are in dBm. Active devices will transmit actual or real optical power at a specific wavelength, and use 1mW as a reference.
PON power meters are essential for field technicians to install or maintain any type of PON network. The PON power meter can simultaneously test the upstream and downstream wavelengths of 1490nm, 1550nm and 1310nm through optical fiber, as well as estimate the signals of voice, data and video streams.
The term PON stands for "passive optical network". PON is a fiber optic telecommunication network that provides broadband to transmit data to customer premises via fiber optic cables. Its architecture realizes the point-to-point or point-to-multipoint node arrangement in the communication network. Point-to-multipoint networks use a single optical fiber to provide services to multiple endpoints through the use of passive or passive optical splitters. Splitters are used to distribute fiber bandwidth among multiple access points. Passive optical networks are often referred to as the "last mile" between the Internet Service Provider (ISP) and its customers.
Point-to-point or P-T-P optical network
A P-T-P network is a network with two terminal points and no content in between. As with all fiber optic networks, when constructing a fiber optic network, the fiber must be terminated for any testing. Therefore, terminate one end of the network and perform an OTDR test on each fiber to ensure that there is no problem with the termination and the excess fiber length. The test result will be stored for future needs and expressed in "dB". If the network needs fusion splicing, after the fiber fusion splicing, use the OTDR again to ensure that the splicing and the increased fiber length meet the requirements again. The test using OTDR continues and is completed after the end of each fiber is terminated. At this point, another set of tests is needed, usually called end-to-end testing. The test requires the use of a light source and a power meter, and all test results will be stored again. The optical power meter will be set to "dB" and refer to the light source commonly referred to as "zeroing". Then move these units to opposite ends, and the field technician will send and receive the wavelength specified by the designer. Again, this is a measure of the designer's overall link loss budget. The P-T-P network refers to its terminals as "A" and "B" and will transmit and receive at least two unique wavelengths through each fiber. This usually requires ensuring that any wavelength used by the transmitter can be used between the two specified wavelengths. The network designer will define these wavelengths and provide labels for these ends. The technician performing the test will reference these tags in any report returned to the designer.
Point-to-multipoint PON type network
Now, when building a point-to-multipoint network (such as a passive optical network or PON), many tests and test equipment remain the same, but some special functions are required. The OTDR test during the construction period remains unchanged, and the test is performed every time the fiber is terminated or spliced. Again, this will continue to the far end of the fiber after the fiber is terminated. After terminating all the fibers, they will be tested again with a power meter and light source. The activation phase of the PON network requires special equipment. This is the similarity between P-T-P and P-T-Multipoint.
The PON network activation stage first connects the power meter to an active device called an optical line terminal or OLT and sets it to an appropriate wavelength, and sets the unit to "dBm", which becomes the reference power.
Note: There are several generations of PON network OLTs that use different wavelengths, so the optical power meter must be able to set these wavelengths. GPON is 1490nm, XGPON is 1577nm, NGPON has multiple wavelengths from 1596nm to 1602nm.
When the link is connected to the far end, the technician will repeat the test and make sure there is no problem. This kind of test continues to the far end, in the PON network there is an active device called an optical network terminal or ONT or sometimes called an optical network unit or ONU. In any case, the device receives the light from the OLT transmitter and communicates with the OLT through its own transmitter. The ONT cannot communicate with the OLT without first receiving the OLT's transmitter wavelength. At this time, it is absolutely necessary to use a special optical power meter to measure the power of the OLT, and allow the power to pass through and provide the signal to the ONT/ONU so that it can send back the signal.
The PON meter has two test ports; one is named DROP and the other is named ONT or ONU. The technician will connect the branch that is connected to the OLT through the optical fiber to the port named DROP, and then connect the optical fiber pigtail of the ONT/ONU connector to the ONT/ONU port. The PON meter is now connected in series between the OLT and the ONT/ONU, and allows the OLT to communicate with the ONT/ONU. The technician will observe the input OLT power level and the output ONT/ONU power level again. If everything is normal, the slave station is connected to the ONT/ONU, and the service activation task can continue.
