In contrast, optical sensors based on the electro-optic effect have been widely studied [15,16]. The electro-optic effect refers to the alterations in the optical properties of a medium caused by an imposed E-field, which varies slowly compared with the optical frequency. Optical sensors can be classified into several types according to selleck catalog their specific optical properties.(1) Based on the Change of Absorption LossIn the electro-absorption effect, the absorption coefficient of an optical medium is altered by the E-field such that the optical intensity could be modulated by the E-field [17]. An E-field sensor based on the electro-absorption modulator was developed by Heinzelmann et al. with a minimum detectable field of 0.1 V/m and a bandwidth of 6 GHz [18].
This sensor is an active type and is unsuitable Inhibitors,Modulators,Libraries for intense E-field measurement.In the electro-chromatic effect, a certain absorption band is generated by an E-field, resulting in a color change of the optical medium [19]. Based on this effect, a fiber E-field sensor was developed by F. Valdivielso et al., in which a single mode fiber was tapered and surrounded by an electro-chromic polymer solution [20]. The response time of this sensor is ~100 s, which is suitable only for extremely low-frequency field measurement.(2) Based on the Change of Refractive IndexThe Kerr effect, also known as the quadratic electro-optic effect, refers to changes in the medium refractive index that are proportional to the square of the electric field strength [3]. The Kerr effect exists in any medium with a symmetrical structure.
The electro-optic coefficient is small (10?16 to 10?14 m/V2), and therefore, sensors based on the Kerr effect have a low Inhibitors,Modulators,Libraries sensitivity and are typically used in the study of E-field distributions in transformer oil [21,22].The Pockels effect, also known as the linear electro-optic effect, refers to changes in the medium refractive Inhibitors,Modulators,Libraries index that are proportional to the electric field strength [3]. A sensor based on the Pockels effect has several advantages: it is a passive device that does not need bias voltage and Inhibitors,Modulators,Libraries is based on a dielectric material, thus creating little interference to the original field. The modulation of the optical signal produces a wide frequency bandwidth and a fast response. The transmission of optical signals using a fiber can generate electromagnetic immunity and electrical isolation.
Optical sensors based on the Pockels effect have been widely studied, and this technical area could be further classified according to whether the sensors are based on bulk optics or integrated optics.A bulk optic sensor is a common path interferometer based on the birefringence AV-951 of Veliparib cost electro-optic materials and is also known as a Pockels Cell [3]. Since the 1970s, several electric corporations have applied the Pockels Cell to voltage measurement [23,24]. Additionally, the Pockels Cell is also used to detect E-fields [25].