A near-infrared zero-order achromatic retarder

Phase retarders normally show strong wavelength dependence. Achromatic retarders which exhibit nearly identical characteristics over a wide wavelength spectrum is used in polychromatic light. The present investigation deals with a technique to design and study the characteristics of an achromatic combination of birefringent plates in 800–2000 nm range. The retarder has been designed using calcite, crystalline quartz and ADP. The thicknesses of the plates are 19.38 μm, 446.14 μm and 12.57 μm respectively. The new arrangement of three birefringent plates proposed has the promise of producing a zero-order quarter wave achromatic combination with fairly good accuracy.     

用于全场光学相干层析成像的无色散相移器研究

提出了基于旋转λ/2波片无色散相移器的理论模型,和实施该相移器功能的全场光学相干层析成像(Optical coherence tomography,OCT)系统,为实现快速、高分辨光学相干层析成像提供了一种有效方法。该相移器能在宽光谱范围内无色散地获得八倍于λ/2波片旋转角的相移量,避免了利用单色光相移算法提取信号时存在的系统误差。针对修正Carré算法和三步相移算法所要求的不同相移量,在240 nm波长范围内,对相移器的性能进行了数值分析。结果表明,在给定光谱范围内,相移量越大,相移误差的绝对值也越大,幅值比变化范围也越大。用于实施无色散相移器功能的全场光学相干层析成像系统结构,与现有结构相比,具有一些有益的特点。     

Terahertz achromatic quarter-wave plate

Phase retarders usually present a strong frequency dependence. We discuss the design and characterization of a terahertz achromatic quarter-wave plate. This wave plate is made from six birefringent quartz plates precisely designed and stacked together. Phase retardation has been measured over the whole terahertz range by terahertz polarimetry. This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.     

Tuneable Sagnac comb filter including two wave retarders

In this paper we study theoretically and experimentally a wavelength-tuneable Sagnac birefringence filter. The device is a Sagnac interferometer including a symmetric fibre coupler and a length of high-birefringence fibre in the loop. A wave retarder is inserted at each end of the birefringent fibre for absolute wavelength tuning. We show theoretically that wavelength tuning through wave plate orientation ensuring constant amplitude of the filtering function is possible only if a minimum of two wave retarders are included in the setup. The position of the transmission peaks then varies linearly with the angle of one of the retarders and can be adjusted over one entire channel spacing. This happens only when a quarter-wave retarder and a half-wave retarder are used, if the former is oriented at 45° with respect to the fibre birefringence axes, while the orientation of the latter serves as the adjustment parameter. The theoretical predictions are confirmed by the experimental results.     

Compensated Polarization Scrambler for Raman Depolarization and Intensity Measurements on Microsamples

It has long been recognized ^1,2,3,4,5 in measuring relative intensities and depolarization ratios of Raman lines that prism and grating spectrometers have different transmittances for light polarized parallel (T_∥) and perpendicular (T_⊥) to the slit. Several methods have been used to give equal instrument response to parallel and perpendicular polarization. Stitt and Yost³ used a Nicol prism parallel to the high-transmittance direction of the spectrometer, combined with a rotatable mica half-wave plate to transmit either vector to the Nicol prism. This method has the advantage of having a higher spectrometer transmittance, but the mica plate gives exact half-wave retardation at only a single wavelength. A mica quarter-wave plate ^4,5 averages the transmittances of the spectrometer for the two polarization directions, but is also wavelength dependent. Virtually achromatic circular polarizers have been designed and constructed ^6,7, but these devices are too bulky and expensive for the clear apertures needed for fast spectrometers.     

红外波段复合消色差1/4波片的优化设计

 在三元复合式消色差波片设计的基础上,对拓宽消色差范围的重要因素——单波片延迟量和复合角度进行了进一步分析和测试,提出了优化设计方案;利用石英晶体设计了适用于红外光通信波段的复合消色差波片。理论和实验均表明：通过调整单波片延迟量或改变复合角度可使该波片在中心波长为1 400 nm的900 nm~1 800 nm波长范围内最大延迟偏差≤5%,而在光通信波段（1 200 nm~1 600 nm）该复合波片的最大延迟偏差只有3.2%。     

Optimal design of achromatic quarter-wave plate using twisted nematic liquid crystal cells

A novel configuration of achromatic quarter-wave plate using two twisted nematic liquid crystal (TNLC) cells is presented. The 4 × 4 Mueller matrix is used to describe the optical properties of the liquid crystal cells. The universal tabu (Utabu) search method is used for optimizing the structural parameters. Simulation results indicate that the designed structure is capable of turning a linearly polarized light into perfectly circularly polarized light and vice versa in wavelength range 1200–1650 nm. The manufacturing tolerances of cell gap, twisted angle, etc. are good.PACS: 42.79.K     

全场光学相干层析成像系统的研制

研制了一套采用旋转1/2波片无色散移相器进行移相操作的全场光学相干层析成像系统.该移相器能在宽光谱范围内无色散地获得8倍于1/2波片旋转角的移相量,能快速、方便地为各种移相算法提供所需的移相量.移相量实测结果表明：系统获得了8倍旋转角的移相量,提出的移相器结构正确.采用Hariharan移相算法对反射镜样品进行的成像实验表明系统具有较高的移相精度.最后进行的实物样品成像实验,检验了系统的有效性. 关键词： 全场光学相干层析成像 无色散移相器 旋转1/2波片     

Achromatic snapshot imaging polarimeter using modified Savart polariscopes and hybrid (refractive–diffractive) lenses

This paper presents the layout of achromatic snapshot imaging polarimeter (SIP) using modified Savart plates (MSPs) and working under nature light. The hybrid (refractive–diffractive) lenses are used to achieve the achromatic point-spread function (PSF), and the design probe the four Stokes vectors of the object by using polarization analyzing optics comprising two MSPs, a half wave plate, and an analyzer. In comparison with the monochromatic or quasi-monochromatic SIP using MSPs reported previously, the most remarkable property of the proposed layouts is to have the capability of directly detecting the object with natural illumination. Also, the configuration is more easily manipulated and robust than achromatic conventional Savart polariscopes reported previously in probing the object with axial movement. The feasibility is verified by numerical simulation for natural light.     

A spatially coherent achromatic fourier transformer

A specific configuration is proposed wherein two zone plates combined with an achromatic objective permits to cancel the chromatic scale factor as broad-band illumination is used in the Fraunhofer diffraction process. The set-up acts as a wavelength-independent Fourier transformer yielding an achromatic diffraction pattern of any complex pupil. Experimental results are also presented and demonstrate the ability of the system to work over the visible spectrum.     

消色差相位延迟器的光谱特性测试研究

本文应用归一化偏振调制原理建立的测试系统 ,对常规菲涅耳菱体、改进型菲涅耳菱体、斜入射型以及直角棱镜组合型的消色差相位延迟器的光谱特性进行了测试研究 ,得到了各延迟器的消色差特性曲线 ,并对测试结果进行了分析。结果表明改进型菲涅耳菱体以及直角棱镜组合型消色差相位延迟器 ,是目前较理想的实用型消色差相位延迟器。     

消色差谱相位延迟器的光谱特性测试研究

本文应用归一化偏振调制原理建立的测试系统，对常规菲涅耳菱体，改进型菲涅菱体，斜入射型以及直角棱镜组合型的消色差相位延迟的光谱特性进行了测试研究，得到了各延迟器的消色差特性曲线，并对测试结果进行了分析。结果表明改进型菲涅耳菱体以及直色棱镜组合型型消色差相位延迟器，是目前较理想的实用型消色相位延迟器。     

Achromatic Schmidt corrector plates

Two types of achromatic Schmidt corrector plate are described; both give an on-axis Strehl number S 0.8 over an extended wavelength region. It is found that this specification can only be achieved by combining a positive and a negative plate and by restricting the speed ratio D/N³ of the system. The theory is illustrated by numerical examples.     

Retardation calculation for achromatic and apochromatic quarter and half wave plates of gypsum based birefringent crystal

This paper presents retardation calculations for achromatic and apochromatic half and quarter wave retarders of gypsum based birefringent crystal. The calculations indicate that an achromatic wave plates can be obtained by combining gypsum crystal with KDP, ADP, MgF₂, sapphire and calcite birefringent crystals. The residual variation percentages of retardations as a function of wavelength for gypsum/KDP, gypsum/ADP, gypsum/MgF₂, gypsum/sapphire and gypsum/calcite were found to be ± 1.7%, ± 3%, ± 12.2%, ± 12.0% and ± 7.2%, respectively. To reduce the spectral variation of retardations, a third layer (apochromatic) of birefringet material is added to the aforementioned achromatic wave plates. The proposed apochromatic wave plates are gypsum/KDP/quartz, gypsum/ADP/quartz, MgF₂/ADP/gypsum, MgF₂/KDP/gypsum and gypsum/sapphire/MgF₂. The addition of a third layer has reduced spectral residual variation percentages of retardations of the aforementioned apochromatic designs to ± 0.27, ± 0.33, ± 0.3, ± 0.17 and ± 0.45, respectively.     

Design of broadband achromatic metasurface device based on phase-change material Ge2Sb2Te5

Based on the phase-change material Ge₂Sb₂Te₅ (GST), achromatic metasurface optical device in the longer-infrared wavelength is designed. With the combination of the linear phase gradient GST nanopillar and the adjustment of the crystalline fraction m value of GST, the polarization insensitive achromic metalenses and beam deflector metasurface within the longer-infrared wavelength 9.5 μm to 13 μm are realized. The design results show that the achromatic metalenses can be focused on the same focal plane within the working waveband. The simulation calculation results show that the full-width at half-maximum (FWHM) of the focusing spot reaches the diffraction limit at each wavelength. In addition, the same method is also used to design a broadband achromatic beam deflector metasurface with the same deflection angle of 19°. The method proposed in this article not only provides new ideas for the design of achromatic metasurfaces, but also provides new possibilities for the integration of optical imaging, optical coding and other related optical systems.     

二元光学透镜在资源卫星中的应用

使用一种基于二元光学透镜的分光成像及消色差原理的新方法来设计资源卫星的中继光学系统。通过分析二元光学透镜的分光成像原理、消色差原理、衍射效率与阶数和工作波长及设计波长的比之间的关系,又考虑到单独设计制造二元光学透镜的难度,采用折衍混合成像光学系统来拟定资源卫星中继光学系统的设计方案,给出用ZEMAX软件设计的具体结果。设计实例及分析结果表明,包含二元光学透镜的折衍混合成像系统可以很好的实现光谱波段分离,用于资源卫星的光学系统具有一定的适用性。     

A three-spectrum method for accurate calibration of bi-plate zero-order retarder

A new spectroscopic method is proposed for the characterization of optical zero-order retarders. It is demonstrated that the retardance as well as the variation of the effective fast axis of a bi-plate zero-order quarter retarder （633 nm） can be obtained with high accuracy in a broadband wavelength range by taking spectra at only three independent angular orientations of the retarder. The calibration results excellently agree with theoretical models, indicating the new method could be used as a simple and reliable way for efficient self-spectral-calibration of optical zero-order retarders.     

Switchable and tuneable multi-wavelength Er-doped fibre ring laser using Sagnac filters

We demonstrate experimentally a simple configuration to perform wavelength-tuning and multi-wavelength operation in a fibre ring laser that is composed of an Erbium-doped fibre and includes a fibre-optic Sagnac interferometer as a spectral filter. We consider three different Sagnac filters including a 3 dB coupler, two wave retarders (WRs) and respectively 7 cm, 1 and 7 m of high birefringence fibre. The transmission spectrum of each filter is sinusoidal with a 70, 6, and 0.85 nm period, and its maxima can be shifted over one period by adjusting the angle of the retarders in the loop. By adjusting the WRs included in the filter and in the laser ring, tuneable single wavelength and several two- or three-wavelength lasing regimes were observed. In particular, fine adjustments of the WRs allow observing two- and three- wavelength operation with wavelength separations well below the homogeneous bandwidth of the gain medium. The stability of these modes of operation however strongly depends on environmental conditions at room temperature.     

An instrument for measuring low optical rotation angle

This paper develops a linear heterodyne interferometer based on phase-locked extraction for measuring low optical rotation angle. The validity of the proposed design is demonstrated by measuring a half-wave plate. The average relative error in the measured rotation angle of the half-wave plate is determined as just 0.74%. When applied to the measurement of glucose solutions with concentrations ranging from 0 to 1.2 g/dl, the average relative error in the measured rotation angle of glucose solutions is determined to be 1.46%. The correlation coefficient between the measured rotation angle and the glucose concentration is determined to be 0.999991, while the standard deviation is just 0.00051°. The current system is capable of measuring glucose concentration as low as 0.01 g/dl with an error of 6.67% in the rotation angle measurement. Overall, the experimental results demonstrate the ability of the proposed system to obtain highly accurate measurement of the optical rotation angle.     

可变波片构造等效线性可转波片的研究

利用四元数理论分析了可变延迟波片,并依此由可变延迟波片组合构造了等效可转线性半波片和四分之一波片.提出由可变延迟波片按可转波片控制算法设计偏振控制器,以避免可变延迟波片偏振控制器所需的复位重置过程.仿真结果显示,按此构想得到的四波片控制器,能把任意偏振态转换为固定线偏振输出,其光强波动小于1%,相移范围不超过2π,控制过程不需要附加复位操作,其相移变化平缓.