2. Types of fiber-optic sensors

Fiber-optic sensors can be classified by many parameters, one of which is the classification based on the coding of measured information:


Another classification of fiber-optic sensors is by the work principle:


You can also classify sensors by localization of the measured parameter:

Fiber-Optic Temperature Sensors with Chalcogenide Glass and Crystalline Sensing Element DOI: http://dx.doi.org/10.5772/intechopen.89207


All of the mentioned fiber-optic sensors have certain advantages and disadvantages associated with their design, operation principle, etc. All of this affects on their price and application possibilities.

For example, phase sensors using laser radiation sources are quite common but mostly in lab installations and not in industry. This is due to the needs of accurate adjustment of devices and presence of additional phase-adjustment schemes, which greatly complicate their design. In addition, such sensors do not allow measurements of absolute values. To eliminate these disadvantages, several frequencies of optic radiation are used, which makes this method an intermediate type of measurements between phase and spectral [12], which are presented below.

Sensors with spectral coding are mostly promising in terms of their implementation into the industry due to their resistance to various parasitic parameters: drift of radiation power source, uncontrolled power loss in fibers, losses due to fiber coupling using connectors, etc. In addition, this type of sensors allows measurements of absolute values and does not require recalibration after switching off the instrument. For now, this measurement method was considered very difficult and expensive. It needed the presence of a spectrometer and optic image processing equipment. But the situation is changing, and due to the cheapening of the methods of optic spectrum processing, development of microprocessor technology and the technology of receiving an optic image, and cheapening of optoelectronic components, the price of the fiber-optic measurement channel comes close to electronic analogues [13].

Amplitude sensors have their area of application due to their low cost and can be used where there is no need for high measurement accuracy (e.g., as counters of rotation, microphones, temperature distribution sensors, etc.). However, in highprecision measuring systems, they are not widely used due to their relatively low accuracy and probability of parameter drift.

Tunnel sensors are highly sensitive devices, but they also have parameter drift, so they can only find limited use, for example, in high-precision positioning devices, microphones, hydrophones, etc.

Polarizing sensors, in essence, are analogues to interference sensors. Their commercialization is mainly hampered by the need to use expensive fiber while maintaining polarization.
