Chirality Of Periodically Poled Lithium Niobate By Electro-optic Effect And Its Application In Optical Isolation

An optical isolator, or optical diode, is an optical component whichallows the transmission of light in only one direction. It plays an importantrole in fiber communication, optical information processing system, opticalfiber sensors and precision optical measurement system. It is typically used toprevent unwanted feedback into an optical oscillator, such as a laser cavity.Optical signal isolation requires time-reversal symmetry breaking. In bulkoptics, this is achieved by using materials that exhibit the magneto-opticeffect via the Faraday effect. The polarization plane of linearly polarized lightrotates when passing through some materials under the influence of magneticfield. The rotation doubles after a round trip through the materials, and opticalpropagation is nonreciprocal in Faraday effect.There is increased demand for non-magnetic optical isolation with thedevelopment of science and technology. Various alternative mechanisms havebeen proposed, such as the use of left-handed periodic structures, layer photonic crystals and nonlinear optical processes. In these systems, however,optical isolation is available only in specific power ranges. In addition,research has been aimed at achieving optical isolation in reciprocal structuresthat have no inversion symmetry, e.g., chiral structures. In these cases,however, apparent isolation occurs only for a restricted photon state in thebackward pass and not for an arbitrary backward incident state.Based on the electro-optic effect of the lithium niobate, which is a kindof periodic domain inversion ferroelectric material, we proposed the chiralityand chirality control of periodically poled lithium niobate (PPLN) withdifferent domain structures. PPLN shows optical activity similar to naturaloptical activity by electro-optic effect; meanwhile, chirality of PPLN can bechanged by altering the direction of the external electric field. Underquasi-phase-matching condition, each domain serves as a half-wave plate. Byadding an additional half domain to the normal PPLN, the azimuth angle ofthe reflected light that incidents on the PPLN can be changed. The opticalpropagation path of the reflected light is therefore changed and opticalrotation is thus accumulated. The polarization plane of the reflected light thattransmits out of the PPLN can be perpendicular to that of the incident lightunder proper electric field. And optical isolation happens in this way. We alsofound that light rotates in the reverse sense in the forward and backward path in PPLN with odd number of domains, and PPLN of this kind shows opticalactivity similar to Faraday effect. Optical isolation can be realized based onthis kind of optical activity in PPLN with odd and a half domain byelectro-optic effect.