Electric field sensor having sensor head with unbalanced electric field shield to shield branched optical waveguides against an applied electric field

An electric field sensor comprising:

• a sensor head having a structure such that an intensity of a transmitted light beam is varied in response to an electric field intensity applied thereto,
• an incident/outgoing optical fiber connected to said sensor head,
• a circulator coupled to an incident/outgoing end of said incident/outgoing optical fiber,
• a light source for irradiating a light beam to said incident/outgoing optical fiber through said circulator, and
• an optical detector for detecting said transmitted light beam emitted from said circulator,
• wherein said sensor head comprises:
• a substrate,
• an incident/outgoing optical waveguide formed on said substrate and connected to said incident/outgoing optical fiber,
• first and second branched optical waveguides formed on said substrate to be branched from said incident/outgoing optical waveguide and having refractive indexes which are variable in response to said electric field intensity applied thereto, and
• a reflection mirror formed on said substrate for reflecting light beams from said branched optical waveguides back into said first and second branched optical waveguides as reflected light beams, said reflected light beams coming back to said incident/outgoing optical fiber through said incident/outgoing optical waveguide.