Describe the process of testing a fiber optic cable for continuity using a visual fault locator (VFL) and an optical power meter (OPM).

Testing a fiber optic cable for continuity using a Visual Fault Locator (VFL) and an Optical Power Meter (OPM) involves two separate procedures that, when combined, provide a good indication of whether the fiber is intact and transmitting light. To test with a VFL, first, connect the VFL to one end of the fiber optic cable. Ensure the connectors are clean before connecting. Activate the VFL. At the opposite end of the cable, visually check for the red or green light emitted by the VFL. If the light is visible, this indicates that the fiber is continuous and not broken. However, a VFL can only indicate the presence of a break or severe bend but doesn't provide information about the cable's performance or signal loss. To test with an OPM, you will also need a light source. Connect the light source to one end of the fiber optic cable. Set the light source to the appropriate wavelength for the fiber type (e.g., 1310 nm or 1550 nm for single-mode fiber). At the opposite end of the cable, connect the OPM. Set the OPM to the same wavelength as the light source. Read the power level displayed on the OPM. This reading indicates the amount of optical power that is being transmitted through the cable. A reading close to the expected value (based on the light source power and the cable's attenuation characteristics) indicates that the fiber is continuous and that the signal loss is within acceptable limits. No reading or a very low reading indicates a break or excessive loss in the cable. For example, if the light source is transmitting at -5 dBm and the OPM reads -8 dBm, the cable has a loss of 3 dB. If the expected loss for the cable length is around 3 dB, the cable is likely in good condition. If the OPM reads -30 dBm, then there is likely a break or severe attenuation in the cable. Combining the VFL test with the OPM test provides a more comprehensive assessment of the fiber optic cable's condition. The VFL confirms physical continuity, while the OPM quantifies the signal loss and verifies that the cable is capable of transmitting light with sufficient power.