There several types of passive optic components that are used in a modern day optical transmission system to help perform a number of functions. These components are divided into four categories- branching devices such as couplers and splitters; connecting devices such as connectors and splices; performance-improving devices such as attenuators, polarizers, dispersion compensators, and isolators and; filtering devices such as fiber Bragg gratings, add/drop filters, and wavelength-division multiplexers (WDMs)/demultiplexers.
In a fiber optic system isolators have been playing a very important role. And on the other hand where all the passive components that reciprocal, isolators are opposite, they normally are nonreciprocal. They let the passage come through of the optical beam in the forward direction with negative losses and at the same time blocking the transmission in the backward direction with 40- to 70-dB losses.
Types of fiber optic isolators:
- Polarization effect: a p-dependent isolator should be used if the extinction ratio is important for one. And it can be used with anything, either polarization-maintaining fiber or a regular single-mode fiber. But if the system lacks the polarization dependence, the obvious choice has to be the p-independent isolator.
- Single-stage or dual-stage: there are two isolator modules in a single package of a dual stage fiber optic isolator allowing >55 dB of isolation. And in most of the applications, a single stage fiber optic provides the required amount of isolation. Dual-stage isolators only add to the cost of the process and bring in losses. A lot of manufacturers out there offer more than two in a single category. If you have a system that would require a lesser grade, it should be taken into consideration for saving yourself from the losses.
- Wavelength: if you want to go for something that is lesser expensive and highly available then the obvious choice to go for would be standard telecommunications wavelengths of 1310 and 1550 nm. The more commonly available fiber-optic isolators for the visible and near-infrared portions of the spectrum are the ones that are bulky and far more expensive in comparison to the standard telecommunications type.
- Reliability: until and unless your vendor is ready to provide you with a test report on reliability, make sure you always perform a few quality tests after getting the isolators. The easiest and the most important test that you can conduct is the temperature cycling test. You can use a freezer and a laboratory oven or a hot plate to let go the isolators through a few temperature cycles, in case the environmental chamber is not available. Once you are done with the temperature cycling test, also go for a quick check of measuring the important parameters at room temperature.
- Termination: maybe it is necessary to use a frequent connection, but chances are it’s not, in these cases always use a fusion splice in place of connectors because the differences in performance in insertion loss and return loss are significant.
- Price: you can do two important things and significantly save a lot of costs. Firstly, you should always stick to standard products. And secondly, if you want to combine two or three functions into one component, go ahead with hybrid components
Each and every optical system has its own set of requirements and buying a fiber optic isolator can be a very confusing task. So follow these thumb rules to buy yourself one and make your task a cake walk.