Electric field sensor

An electric field sensor comprising:

• a light source;
• an electro-optical crystal on which light in a predetermined polarization state based on light emitted by the light source is incident and which receives an electric field generated by an object;
• a first separator that separates light emitted from the electro-optical crystal into a P wave and an S wave;
• a first wavelength plate that is disposed at a pre-stage of the electro-optical crystal and changes a phase of light at a pre-stage of the first separator;
• a second wavelength plate that is disposed at a post-stage of the electro-optical crystal and changes a phase of light at a post-stage of the first separator;
• a first light receiver that receives the P wave light and converts the received light into a first electrical signal;
• a second light receiver that receives the S wave light and converts the received light into a second electrical signal;
• a differential amplifier that generates a differential signal between the first electrical signal converted by the first light receiver and the second electrical signal converted by the second light receiver;
• and
• a controller that adjusts a wavelength of the light source such that an output value of a direct-current component of the differential amplifier is within a predetermined value range in a state in which light is emitted from the light source and the electric field is applied to the electro-optical crystal.

An electric field sensor comprising:

• a light source;
• an electro-optical crystal on which light in a predetermined polarization state based on light emitted by the light source is incident and which receives an electric field generated by an object;
• a separator that separates light emitted from the electro-optical crystal into a P wave and an S wave;
• a first wavelength plate that changes a phase of light at a pre-stage of the first separator;
• a first light receiver that receives the P wave light and converts the received light into a first electrical signal;
• a second light receiver that receives the S wave light and converts the received light into a second electrical signal;
• a differential amplifier that generates a differential signal between the first electrical signal converted by the first light receiver and the second electrical signal converted by the second light receiver;
• a controller that adjusts a wavelength of the light source such that an output value of a direct-current component of the differential amplifier is within a predetermined value range in a state in which light is emitted from the light source and the electric field is applied to the electro-optical crystal;
• a transparent electrode;
• a mirror;
• a first optical attenuator provided between the first separator and the first light receiver;
• and
• a second optical attenuator provided between the first separator and the second light receiver,
• wherein, in the electro-optical crystal, the transparent electrode is disposed on one surface thereof to face each other, and the mirror is disposed on another surface thereof,
• wherein light in the predetermined polarization state based on light emitted by the light source is incident from the transparent electrode, the light incident from the transparent electrode is reflected by the mirror, the reflected light is emitted from the transparent electrode, and the light emitted from the transparent electrode is incident on the separator, and
• wherein the controller adjusts an attenuation rate of each of the first optical attenuator and the second optical attenuator such that an output of the differential amplifier is within a predetermined range in a state in which the light source emits light and the electric field is not generated by the object.