This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. This article has been rated as C-class on Wikipedia's content assessment scale. Vital articles Wikipedia:WikiProject Vital articles Template:Vital article vital articles Optical isolator has been listed as a level-5 vital article in Technology. Vital articles : Level 5 / Technology C‑class Time-resolved return loss measurements (see above) are extensively used for monitoring fiber-optic links.This article is of interest to the following WikiProjects: In optical fiber communications, back-reflected light may increase the bit error rate.High- gain optical amplifiers, for example fiber amplifiers (but not optical parametric amplifiers), are also sensitive because any back-reflected light will again be amplified, and might destroy parts of the amplifier or components connected to its input.A too low return loss of attached devices may destabilize the laser operation, i.e., cause excessive laser noise and/or emission on multiple optical frequencies. Many lasers, in particular single-frequency lasers, are sensitive to back-reflected light.In various situations, it can be important that the return loss of some optical arrangement is sufficiently high. There, one measures the time-resolved return loss, which can reveal various information of interest, for example propagation losses of fibers and isolated losses and reflections e.g. This is exploited in the context of optical time-domain reflectometry, which is widely used for monitoring the status of fiber-optic links. The actual return loss may be specified for a situation where all light from the output is reflected back to the isolator.Ī fiber itself can have some finite return loss due to Rayleigh backscattering. Similarly, a Faraday isolator would ideally not reflect any light, but some finite return loss results from imperfections. With angle-cleaved splices, even substantially higher values are possible. Good splices should have a return loss of at least 45 dB. Also low-quality splices can lead to increased return loss. However, some finite return loss (often many tens of decibels) may be caused, for example, when the fiber of the coupler has different guiding properties ( refractive index, effective mode area, etc.) than the fibers spliced to the input and output of the fiber coupler. For example, a fiber coupler (which is a unidirectional coupler) should split the power of incident light between two or more outputs, but should not reflect any light back to the source (assuming that no light is reflected from its outputs). The term return loss is most often used in cases where ideally there would be no reflected light at all. Note that only directly returning light is counted – and no light which is reflected into a different direction, e.g. For example, if the return loss is 30 dB, the returning light has only 1/1000 of the power of the incident light. Usually, the return loss is specified in decibels. The return loss (or reflection loss) of some optical device (or a combination of devices) specifies how much lower the optical power of the returning (reflected) light is compared with the light sent into the device.
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