In situ measurement of group refractive index using tandem low-coherence interferometer

The group refractive index of BK-7 glass material is accurately measured using a tandem low-coherence interferometer, which is composed of a Mychelson interferometer and a Fizeau interferometer, within a combined standard uncertainty of 8.4 ppm. The experimental results are compared with the value calculated from the conventional data base on the phase refractive index, within a difference of about 4.7 ppm. This new method is applicable to in situ measurement due to the principle of its common optical path.     

Multiple-surface testing by a wavelength-scanning interferometer for refractive index inhomogeneity measurement

Wavelength-scanning interferometers can separate the multiple interference signals generated by several reflecting surfaces in the frequency space. Optical thickness variations of a three-layer object and its top surface shape were measured simultaneously by a wavelength-scanning Fizeau interferometer. An efficient sampling window for the phase detection has been derived that can compensate for the frequency detuning of the interference signal and suppress the cross talk from noise components in other frequencies. From the experimental results, the refractive index variation of a glass plate was calculated with an accuracy of ∼1 ppm, which is equivalent to several tens of nanometers in optical thickness variations. The text was submitted by the authors in English.     

Simulation of simultaneous measurement for red blood cell thickness and refractive index

Red blood cell (RBC) parameters are of great importance for diagnostic purposes. Using the simulation method, the variations of both the thickness and the refractive index of a RBC were investigated in a dual-medium quantitative measurement (DMQ), which is realized via phase-shifting digital holography with two types of cell media. Results show that both the calculated thickness and the calculated refractive index agree well with the original ones with an average relative deviation of 2.13% and of 0.12% in valid regions, respectively. The simulation for RBC will provide some guidance for experimental parameter setting and data processing in DMQ.     

Simultaneous measurement of refractive index and thickness with a convergent beam

A new approach to the simultaneous measurement of refractive index and thickness based on the focus shifts of a convergent beam intercepted by a test plate is proposed. By using ray optics, a defined focus shift can be derived as a function of the refractive index and thickness as well as the angular position of the test plate with respect to the optical axis. From a pair of focus shifts obtained at two different angular positions, it is shown that the desired measurands can be simultaneously determined without prior knowledge of either parameter. A simulation result for the proposed concept based on graphically solving the equations of their respective focus shifts is presented.     

Real-time measurement of glucose concentration and average refractive index using a laser interferometer

This study presents a non-destructive, highly precise optical metrology system for measuring the average refractive index of a liquid solution such that its glucose concentration can be derived. The metrology system is employed to measure the average refractive indices of samples with known glucose concentrations ranging from 0 to 200 g/l. By applying a regressional analysis technique to the experimental results, an analytical expression is derived to describe the relationship between the refractive index and the glucose concentration. An excellent agreement is observed between the experimentally determined values of the glucose concentration and the analytically derived results. For an assumed laser interferometer resolution of 1 nm, the measurement resolution of the proposed metrology system is found to be at least F=0.05 g/l, which is significantly better than that of F=2 g/l obtained using the polarimetric glucose sensor presented by Lo and Yu [A polarimetric glucose sensor using a liquid-crystal polarization modulator driven by a sinusoidal signal. Opt Commun, 2006; 259: 40–8].     

Photonic crystal fiber tip interferometer for refractive index sensing

In this paper we present an interferometer based on photonic crystal fiber (PCF) tip ended with a solid silica-sphere for refractive index sensing. The sensor is fabricated by splicing one end of the holey PCF to a single mode fiber (SMF) and applying arc at the other end to form a solid sphere. The sensor has been experimentally tested for refractive index and temperature sensing by monitoring its wavelength shift. Measurement results show that the sensor has the resolution of the order of 8.7×10(-4) over the refractive index range of 1.33-1.40, and temperature sensitivity of the order of 10 pm/°C in the range of 20-100 °C.     

Dual-confocal fiber-optic method for absolute measurement of refractive index and thickness of optically transparent media

We present a novel noncontact optical method for absolute measurement of refractive index and thickness of optically transparent media. The method is based on a simple dual-confocal fiber-optic sensor design. It includes two independent confocal channels consisting of two identical apertureless fiber-optic-type confocal microscopes constructed by use of a single 2x2 fiber coupler. A geometrical-ray model is used to obtain the analytical dependence between the sample's refractive index and its thickness. The measurement method provides high accuracy in spatially locating the specific imaging points that correspond to the backreflected intensity peaks of the confocal responses. Thus, a simultaneous measurement of the sample refractive index and thickness is achieved.     

迈克耳孙干涉仪测量介质板折射率的问题研究

使用迈克耳孙干涉仪测量较厚介质板的折射率时,发现迈克耳孙干涉仪中放入待测介质板后,反射镜M1的调节方向异常.针对这一实验现象,从理论上进行分析,解释了实验中出现的异常现象,并推导出反射镜M1在两次观测中移动的距离与介质板折射率的关系式.实验结果进一步证明理论与公式的正确性.     

Long period grating cascaded to photonic crystal fiber modal interferometer for simultaneous measurement of temperature and refractive index

We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82 nm/RIU (refractive index unit) and 47.4 pm/°C by the LPG, and 171.96 nm/RIU and 10.4 pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.     

Determining the refractive index of liquids using a modified Michelson interferometer

An accurate method for measuring the refractive index of liquids is proposed, modeled, and experimentally verified. The experimental setup is a modified Michelson interferometer employing a novel liquid chamber that allows the optical pathlength to be continuously varied without moving a mirror. This experiment allows determining the refractive index of a given liquid to high precision, with an accuracy limited only by the normal random variables encountered in interferometric measurements and ultimately the accuracy to which the wavelength of the laser light is known.     

Modified Michelson interferometer for probing refractive index of birefringent crystal CSBN50

Based on the modified Michelson interferometer and phase analysis method, a high-accuracy method for probing the refractive index (RI) of transparent medium is proposed. The validated test was performed on a birefringent crystal CSBN50 with the estimated accuracy being up to 10⁻⁴. The ordinary and extraordinary refractive indices of CSBN50 at 632.8 nm are determined as n₀=2.32853±0.00016 and n_e=2.27664±0.00016, respectively.     

利用迈克尔孙干涉仪测定液体折射率

介绍一种用迈克尔孙干涉仪测定液体折射率的简单可行的方法。     

迈克耳孙干涉仪测折射率时的异常现象研究

针对迈克耳孙干涉仪以激光为光源测量玻璃板折射率所产生的异常现象,本文从几何光学理论出发进行了讨论,简明直观地给出了干涉条纹吞吐转折点与零光程点、光程、虚光源相对位置之间的关系,并与实验数据进行了对比.     

用迈克耳孙干涉仪测量厚透明材料折射率

使用迈克耳孙干涉仪测量了厚透明材料的折射率.在光路中一半视场平行放入待测材料,对应的条纹出现压缩,根据条纹隐入和涨出计算待测材料的折射率,并进行了相关实验和误差分析.应用Zemax软件对实验进行了模拟,验证了其可行性.     

Continuous-wave measurement of the fiber nonlinear refractive index

We propose a technique for measuring the nonlinear refractive index of fiber based on transmission-coefficient measurements in a fiber Sagnac interferometer. In contrast with traditional methods, the proposed method uses a single optical source operating in cw mode and direct intensity measurement, enabling one to avoid the errors caused by fiber dispersion and uncertainty of spectral peak difference measurements that occur with pulse-based methods. The nonlinear refractive index in 20-mol. % GeO(2) fiber was measured to be (3.1 +/- 0.2) x 10(-16) cm(2) W(-1) at 1064 nm.     

Precise measurement of group refractive indices and temperature dependence of refractive index for Nd-doped yttrium orthovanadate by intracavity spontaneous mode locking

We report on a novel method based on intracavity spontaneous mode locking to precisely measure the group refractive indices and temperature dependence of refractive index of Nd:YVO(4) crystal at the wavelength of 1064 nm. All the experimental results are found to agree very well with the most recent measured values. We also confirm that the developed method is applicable to measuring the group refractive indices and the temperature dependence of the refractive indices of other vanadate crystals, as well as nonlinear crystals.     

薄透明体厚度及折射率的测量

介绍了测量薄透明体厚度及折射率的一种方法.     

Measuring the refractive index of crude oil using a capillary tube interferometer

A method for measuring the refractive index of low-transparent crude oils using a capillary tube interferometer is described. The method is based on analyzing the resulting transverse interference fringe patterns in terms of their positions with respect to the lens/capillary tube interferometer. The refractive indices of seven blended crude oils of low transparency were measured with accuracy of up to six decimal digits and were related to the API gravity of the oils. The ray tracing inside the capillary tube is explained and the transverse bell-shaped interference fringes are interpreted.     

Z-scan measurement of the nonlinear refractive index of graphene

Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n(2)?10(-7) cm(2) W(-1), almost 9 orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.