Developments and applications of a dual-channel phase measurement system are being proposed and experimentally studied by utilizing an optical homodyne technique. In this measurement system, the phase modulation was adopted by using a near-stable Zn-indiffused lithium niobate phase modulator. The proposed method was successfully applied on the simultaneous measurements of the phase-retardation difference between a transmitted light and a reflected light after passing through a nonpolarization beam splitter. The measured stability of the phase-retardation difference was approximately 0.0013 rad.
In this paper, we develop an optical measurement system with capabilities of phase unwrapping, real-time and long-term monitoring for measuring a phase drift caused by photorefractive effects in lithium niobate phase modulators. To extract the phase-drift variations, the measurement setup uses a homodyne interferometer with a phase modulation and a Fast Fourier Transform (FFT) demodulation scheme. The phase-drift characteristics of a traditional Ti-indiffused and a Zn-indiffused phase modulator have been investigated under different applied voltages and throughput powers. These experiments were conducted as a proof-of-concept to demonstrate that the apparatus worked successfully to measure the phase drift of a device in the presence of photorefractive effects. The results indicate that the Zn-indiffused phase modulators have better photorefractive stability than the Ti-indiffused phase modulators.
INTRODUCTIONMach-Zehnder optical modulators are important components in optical-communication and sensor systems, which have been demonstrated and investigated on different materials [1][2][3]. For highspeed and low-voltage operation, Ti indiffusion (TI) LiNbO 3 waveguide modulators are among the most favored candidates due to their low propagation loss and large electrooptic (EO) coefficient; commercially available Mach-Zehnder modulators used for optical communication at the 1.55-m wavelength have achieved switching rates of 40 GHz. Although the TI waveguide devices have remarkable properties for applications in optical integrated circuits, the annealing proton exchanged (APE) and Zn indiffusion (ZI) waveguides are still studied extensively due to less susceptible to photorefractive damage, particularly compared to those at wavelengths below 0.8 m [4,5].Recently, Er-doped waveguide amplifiers on LiNbO 3 with a 1.48-m or 0.98-m pumping wavelength have been demonstrated in order to realize waveguide lasers at around 1.55-m wavelength [6]. The active properties of the Er:LiNbO 3 can be further combined with the excellent electro-optic and acusto-optic properties of LiNbO 3 in order to make a more compact device, such as a mode-locked laser, Q-switch laser, or integrated transmitter [7,8]. Reports on model calculations and experiments with Er:LiNbO 3 waveguide amplifiers have shown that a higher efficiency can be obtained at the 0.98-m pumping wavelength than at 1.48 m [6]. The results also show that the ZI waveguide with higher optical resistance than the TI one is more suitable for fabricating a waveguide amplifier at the 0.98-m pumping wavelength. Similar to the reported transmitter [8], in principle, an improved transmitter with higher pumping efficiency and lower operating voltage can be realized by using the ZI waveguide pumped with a TM-polarized wave of 0.98 m. Therefore, investigations of the ZI Mach-Zehnder modulator employing the r 33 coefficient are essential at the 1.55-m wavelength. In the past, detailed fabrications and basic characterizations of ZI waveguides at 0.6328 m have been reported [9], where the ZI waveguides support both ordinary and extraordinary polarizations or single extraordinary polarization, depending upon the diffusion parameters. Our previous reports show that the ZI Mach-Zehnder modulator operating at 1.32 m has the same great EO effect as that of the TI one [10]. Moreover, the Zn indiffusion needs no additional out-diffusion suppression because of a higher diffusion coefficient of the Zn atom than that of the Ti atom, which provides more flexibility for the fabrication of optical waveguides. In this paper, the ZI Mach-Zehnder modulators operating at the 1.55-m wavelength are fabricated on z-and y-cut LiNbO 3 substrates for the first time. With some specified diffusion parameters, the z-and y-cut waveguides can support only extraordinary polarization; then the r 33 coefficient is employed for electro-optic modulation. The switching voltages are measured and the values of voltage-...
Abstract:In this paper, an optical angle sensor with a birefringent transducer for measuring angular displacement based on a heterodyne interferometry is proposed. The achievable repeatability and linearity provide sufficient evidence for the practical use. As a result, a resolution of 5.8ˆ10´6 with a dynamic range of 5˝has been achieved by utilizing a KTP (potassium titanyl phosphate) plate immersed in a high refractive index oil with refractive index of 1.7.
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