Dispersion Measurement of Electro-Optic Coefficient γ22 of Lithium Niobate Based on Photoelastic Modulation

Abstract

A novel method for determining the electro-optic (EO) coefficient γ 22 of lithium niobate and its dispersion using photoelastic modulation is presented. A spectroscopic polarimetry was constructed with the photoelastic modulator (PEM), and a monochromator was selected to automatically scan the wavelength of a light source. Phase retardation induced by an EO sample was loaded into the modulation signals to demodulate the EO coefficients. The PEM and data processing were controlled in the same field programmable gate array (FPGA), and the DC and harmonic terms were extracted simultaneously by employing digital phase-locked technology. An experimental system was built to analyze the principle of this scheme in detail. After the modulation phase retardation amplitude of the PEM was precisely calibrated, the EO coefficient γ 22 of a Y-cut lithium niobate crystal plate was measured in the spectral range from 0.42 to 0.8 µm. The experimental results demonstrated that the measurement sensitivity of the system was 1.1 × 10 − 14 m / V for a sampling time of 198.9 ms. Plotting the measured results against the light wavelength, the dispersion of the EO coefficients was obtained similar to the Cauchy dispersion formula γ 22 = 5.31 × 10 − 12 + 4.071 × 10 − 13 λ 2 + 7.184 × 10 − 14 λ 4 in the visible light range. This method is suitable for studying dispersion of the EO coefficients of crystals as well as of thin films and two-dimensional materials.

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“…A promising method that has been proposed recently, for determining electro-optic coefficients, uses a photoelastic modulator, operating as a dynamic retarder to compensate for the retardation introduced by the sample. The results so far reported for this method only include the linear electro-optic effect [ 18 , 19 ].…”

The research of birefringence of infrared optical crystal ZnS and Si

“…As shown in Fig. 1, the design of the optical path system is based on laser polarization technology [15][16][17][18] , and it is established as a single optical path crystal stress birefringence testing system with reference to the polarization state modulation and demodulation structure [19] . First, the Mueller matrix for a polarizer oriented at -45° with respect to the transmission axis is as:…”

Research on Compressed Sensing Spectrometry Based on Electro-Optical Transmittance Coding

“…In Figure 1, two transverse refractive index axes of the LiNbO 3 electro-optic crystal are formed at 45 • around the X axis under the action of an electric field, and the value of the crystal's refractive index changes according to the applied electric intensity. When the incident light passes through the electro-optical coding modulator between the polarizers, the optical transmittance can be described as [15] T (λ,V) = I (λ,V) /I 0(λ) ∝ sin 2 (δ (λ,V) /2), (1) where, λ is the wavelength of the incident light; V is the voltage of the external electric field applied to the electro-optical transmittance coding modulator; I 0(λ) and I (λ,V) are the light intensity before and after passing through the modulator, respectively; δ (λ,V) is the phase retardation of two polarization components in the LiNbO 3 electro-optic crystal, and it changes with the change of the refractive index, which can be expressed as [16] δ…”