Translator Disclaimer
Open Access Paper
17 September 2019 Simplified Stokes polarimeter based on division-of-amplitude
Author Affiliations +
Proceedings Volume 11144, Photonics and Education in Measurement Science 2019; 111441B (2019)
Event: Joint TC1 - TC2 International Symposium on Photonics and Education in Measurement Science 2019, 2019, Jena, Germany
A polarization state detector (PSD) measures the state of polarization of the detected light. The state of polarization is fully described by the Stokes vector containing four Stokes parameters. A division-of-amplitude photopolarimeter (DOAP) measures the four Stokes parameters by simultaneously acquiring four intensities using photodetectors. A key component of the DOAP is the first beam splitter, which splits up the incoming beam into two beams. The effect of the beam splitter on the state of polarization of the reflected (r) and transmitted (t) beam is determined by six parameters: R, T, ψr, ψt, Δr, and Δt. R and T are the reflectance and transmittance, and (ψr, Δr) and (ψt, Δt) are the ellipsometric parameters of the beam splitter in reflection and transmission, respectively. To measure the Stokes vector with high accuracy, the six optical parameters must be chosen appropriately. In previous work, the optimal parameters of the beam splitter have been determined as R = T = 1/2, cos2r = 1/3, ψt = π/2 - ψr, and Δrt modulo π=π/2 by calculating the maximum of the absolute value of determinant of the instrument matrix. Using additional quarter-wave plates eliminates the constraint on the retardance and hence simplifies the manufacturing process of the beam splitter, especially when broadband application is intended. To compensate a suboptimal value of Δrt, the azimuthal angles of the principal axes of the retarders must be adjusted, for which we provide analytic formulas. Hence, a DOAP with retarders is also optimal in the sense that the same values for the determinant and condition number of the instrument matrix are obtained. When using two additional retarders, it is necessary to install both on the same light path in order to obtain an optimal DOAP. We will show that is also possible to get an optimal DOAP with only one additional quarter-wave plate instead of two, if one of the Wollaston prisms is rotated.



The interaction of light and matter often results into a change of the state of polarization (SOP). This effect is used in many applications in industry, surface characterization, material science and thin film measurement.16 Depending on the application, polarized or unpolarized light might be emitted. The measurement of the SOP is always a key component in applications using polarization-sensitive sensors. Polarization state detectors (PSD) measure the complete SOP, in contrast to incomplete polarimeters. The Stokes vector is a common notation to describe the complete SOP.

A PSD called division-of-amplitude photopolarimeter (DOAP) using only four intensity measurements to determine the Stokes vector has been proposed in the previous work.7 It has no moving parts and the four intensity measurements are conducted simultaneously. Therefore, the DOAP is well suited for measuring the SOP at high sampling rates. The measurement error of the calculated Stokes vector can be assessed by the instrument matrix of the DOAP. Two quality measures are usually used to determine the measurement error of a PSD: the determinant and the condition number of the instrument matrix. We will show that both quality measures of the instrument matrix are simultaneously optimal.

The first beam splitter, which splits up the incoming light into two light beams, has a significant influence on the measurement error. Beam splitters consisting of optically isotropic media can be characterized by six optical parameters, if the plane of incidence remains unchanged while the light propagates through the beam splitter. The optical parameters of the DOAP must fulfill some constraints in order to achieve a low measurement error. These make the production of the beam splitter difficult, especially for broadband application, and in the end lead to higher production costs of the PSD.

In this article we will show how to simplify the production of the beam splitter by mounting additional quarter-wave plates while maintaining the optimality of the DOAP. This leads to a relaxation of the constraint on the retardance of the beam splitter. Quarter-wave plates with anti-reflection coatings (T > 99.7%) are manufactured in bulk and are therefore cheaper than specially designed optical components*. Although the retardance is fixed to the quarter of a wave, rotating the quarter-wave plates has the same effect on the absolute value of the determinant as a variable retardance. Furthermore, we present a DOAP suited for broadband application and verify our calculations by using the physical optics software VirtualLab Fusion from LightTrans.



The measurement of the SOP can be performed in various ways e.g. by division-of-amplitude,8 division-of-wavefront,9 the four-detector photopolarimeter,10 rotating compensators,11 or liquid-crystals.12 The focus of this article is restricted to the DOAP. A scheme of the DOAP is shown in Figure 1. The DOAP splits up the the incoming light beam into four linearly polarizes light beams with lower amplitude which are detected e.g. by four photodetectors. The first beam splitter BSi splits up the incoming light beam into the reflected (r) and transmitted (t) beam. The DOAP has also two polarizing beam splitters, BSr and BSt, which split up the incoming light wave into two orthogonal linearly polarized waves. BSr and BSt could be e.g. Rochon prisms, Wollaston prisms, Nomarski prisms, Glan-Thompson prisms, or polarizing beam splitters like cubes or plates. The azimuthal angles of the polarizing beam splitters BSr and BSt are γr = γt = 45°.8, 13 We will use the Stokes-Mueller formalism14, 15 and the Nebraska ellipsometry conventions16 to deal with the change of polarization of a light beam passing through polarizing optical elements. It is assumed that the diameter of the detectors is grater than the diameter of the incoming light beam. Otherwise, the relationship between the amplitude and intensity of a light beam at reflection and refraction17, 18 must be taken into account, when calculating the measured intensities with the Stokes-Mueller formalism.

Figure 1.

Scheme of the DOAP.


The Stokes-Mueller formalism is used to calculate the instrument matrix depending on the parameters of the DOAP e.g. the optical parameters of BSi. In this article, we analyse the influence of sensor noise on the calculation of the SOP by assessing the absolute and relative measurement error. A more accurate noise model consisting of an additive white Gaussian noise and Poisson noise has also been examined in previous work. 19 By maximizing the absolute value of the determinant of the instrument matrix, optimal values for the reflectance (R), transmittance (T), diattenuations (Ψr and Ψt), and retardances (Δr and Δt) of BSi can be obtained:8 R = T = 1/2, cos2r = 1/3, ψt = π/2 − ψr, and (Δr − Δt) modulo π = π/2. It has also been noted that optimizing the condition number instead of the determinant results to similar optical parameters.8 Different optical parameters for the diattenuations have been calculated in previous work by optimizing the condition number:20 R = T = 1/2, Ψr = π/8, Ψt = π/2 − Ψr, and (Δr − Δt) modulo π = π/2. The definition of the condition number has been taken from. 13 In contrast to previous work, we will show that maximizing the absolute value of the determinant is equivalent to minimizing the condition number, while using the same definition of the condition number. 13

Several beam splitters BSi have been proposed for the DOAP based on uncoated prisms,20 coated prisms,21, 22 and interference filters.23 Interference filters can lead to very good values for determinant of the instrument matrix but only for a limited spectral range. Furthermore, they are also quite expensive.

Recently, we proposed a DOAP with rotating quarter-wave plates.24, 25 Designs of a DOAP with half-wave or quarter-wave plates, one on the reflected and one on the transmitted path, have also been proposed independently in previous work. 26 In that publication, calculations revealed that quarter-wave plates are better suited than half wave plates. Although a DOAP with one wave plate on each path can improve the instrument matrix when (Δr − Δt) modulo ππ/2, it does not always lead to an optimal DOAP for all values of Δr − Δt, as we have shown previously.25 In contrast, by using two quarter-wave plates on the same path, an optimal DOAP can be obtained for any value of Δr − Δt.25 In this article, we provide analytic formulas for determining the rotational angles of the retarders depending on the value of Δr − Δt. Furthermore, we will present another optimal DOAP with only one quarter-wave plate on the reflected path. To get an optimal DOAP, the rotational angle γr of BSr has to be adjusted depending on Δr − Δt.



The state of polarization of a plane wave is fully described by the Stokes vector S:15


I, I90°, I45°, and I−45° are the measured intensities of a light wave after passing linear polarizers with azimuthal angles 0°, 90°, 45°, and −45°, respectively. IR and IL are the measured intensities after it passes left and right circular polarizers. Although it is possible to measure the Stokes vector S by six intensities according to Equation (1), only four intensity measurements I = (I1, I2, I3, I4)T are necessary which are measured by the photodetectors D1, …, D4. The instrument matrix A defines a linear map between S and I


The sensor model in Equation (2) is a simplification of the real-world scenario. For instance, the quantization of the photodetector signals and the quantum efficiency of the photodetectors have been omitted. The Stokes vector S of the incoming light beam can be calculated from the measured intensities I by inverting Equation (2).

The change of the SOP of a light beam passing through an optical system consisting of n optical components can be described by subsequent linear maps


where M1, M2, …, Mn are the Mueller matrices of the optical components. The change of the SOP of a light beam, which is reflected at BSi and then impinges on BSr before it is detected by D1, can be described by the Mueller matrix


where Mp(α) is the Mueller matrix of a polarizer rotated at the azimuthal angle α and MSr, Δr, R) is the Mueller matrix of an ellipsometric surface described by the ellipsometric parameters Ψr, Δr, and the reflectance R. Let I1 be the intensity measured by the polarization-insensitive photo-detector D1 for the previously described light path and let q := (1,0,0,0)T. I1 is then calculated by:


By using the corresponding formulas for I2, I3 and I4, we get the following instrument matrix of the DOAP:


The determinant of A is given by:8


Maximizing |det A| leads to the following optimal optical parameters of BSi:8


The resulting instrument matrix will be denoted as ADOAP and the following holds:


To measure how close alternative designs of the DOAP reach the optimal value, the normalized determinant is defined as follows:22


Furthermore, we define the condition number of a non-singular instrument matrix A as follows:12


where σmax and σmin are the maximum and minimum singular values of A, respectively. Although we did not find a closed form for Equation (11) in order to calculate the minimum, numerical simulations reveal that the optimal condition number has the following value which is consistent with previous work:12, 13, 27


Analogous to Equation (10), we define the normalized condition number as:


From Equation (9) and Equation (12) we get:


In previous work it has been stated that the optimal values for BSi minimizing the condition number are:20


We denote the resulting instrument matrix as 00055_PSISDG11144_111441B_page_5_4.jpg. To calculate the optimal values in Equation (15), an alternative definition of the condition number has been used:


where 00055_PSISDG11144_111441B_page_5_6.jpg and 00055_PSISDG11144_111441B_page_5_7.jpg are the maximum and minimum eigenvalues of the symmetric matrix AT A, respectively. However, both definitions of the condition number lead to the same values


which means that ADOAP is better than 00055_PSISDG11144_111441B_page_5_10.jpg independent which definition is used. Furthermore, it has been stated that the two conditions are not fulfilled simultaneously.13 As we have shown in Equation (14), this is not true. It can be summarized that the optimal values for BSi from Equation (8) simultaneously maximize condnorm(A), leading to a minimum relative error,13 and minimize |detA|norm, leading to a minimum absolute error.8 Furthermore, the optimization of |detA|norm and condnorm(A) does not lead to similar8 but equal results. It should be noted that the optimal parameters found by maximizing |detA|norm or condnorm(A) are only equal if |detA|norm = 1. If there is no parameter set satisfying |detA|norm = 1, it is possible that the optimum of |detA|norm and condnorm(A) correspond to different parameters.



A design of the DOAP with two rotated quarter-wave plates is shown in Figure 2 where βr and 00055_PSISDG11144_111441B_page_5_11.jpg are the azimuthal angles of the quarter-wave plates. Let MQ(α) be the Mueller matrix of a quarter-wave plate with the fast axis at the azimuthal angle α. As mentioned previously, a quarter-wave plate with high transmission has nearly a theoretical optimal Mueller matrix:


Let 00055_PSISDG11144_111441B_page_5_13.jpg be the instrument matrix of the aforementioned DOAP with two retarders, where R, T, Ψr, and ψt are optimal (according to Equation (8)) but Δr and Δt are not:


For any value of Δr and Δt, we can achieve 00055_PSISDG11144_111441B_page_6_2.jpg by using the following formula for βr and 00055_PSISDG11144_111441B_page_6_3.jpg:


Figure 3 show the azimuthal angles βr and 00055_PSISDG11144_111441B_page_6_7.jpg resulting from Equation (21) and (22) depending on the values of Δr and Δt.

Figure 2.

DOAP with two quarter-wave plates mounted at the reflected path


Figure 3.

Azimuthal angles βr and 00055_PSISDG11144_111441B_page_7_2.jpg of the quarter-wave plates leading to an optimal DOAP.


There is another possibility not mentioned in previous work to get an optimal DOAP with only one quarter-wave plate: The quarte-wave plate is mounted at the reflected path at the fixed azimuthal angle βr = 45°. To get an optimal DOAP, the azimuthal angle of BSr has to be adjusted, while the azimuthal angle of BSt remains unchanged γt = 45°. Adjusting γr using the following formula also gives |detA|norm = condnorm(A) = 1:


It should be mentioned that adjusting the azimuthal angles according to Equation (21), (22), and (23) not only improves |detA|norm for optimal values of R, T, Ψr, and Ψt but for any values. The factorization of det A in Equation (7) means that the optimization of R, T, Ψr, and Ψt is independent from the optimization of Δr and Δt. The latter can be achieved by improving the beam splitter or by using the proposed designs with quarter-wave plates. Finally, BSi should be a non-absorbing beam splitter with R + T = 1 to get a low measurement error. In this case, only the reflectance for the p– and s–polarization, Rp and Rs, has to be optimal:


The other conditions 00055_PSISDG11144_111441B_page_7_4.jpg, and 00055_PSISDG11144_111441B_page_7_5.jpg follow directly from Equation (24).



A DOAP with a prism made of a low-refractive-index coating on a high-refractive-index substrate (MgF2 on ZnS (Cleartran)) has been proposed in previous work.21 The refractive index of the coating is nF = 1.38 and the refractive index of the substrate is nS = 2.3 at λ = 632.8 nm. For further examination we will just use the prism substrate without the coating, as a coating enhances the variation of the optical parameters in a broad wavelength range. It has turned out that high-refractive-index materials are well suited to get optimal values for Rp and Rs according to Equation (24). The optimal angle of incidence of the incoming light impinging the surface of the prism is θ = 82°. From θ we get the following angles describing the geometry of the prism: α = 25.2°, β = 90°, and γ = 64.8°. It is assumed that the prism has an anti-reflection coating on the exit surface of the transmitted beam to avoid an intensity loss. Anti-reflection coatings do not change the state of polarization at normal incidence. A suitable coating for monochromatic measurement (λ = 632.8 nm) would be e.g. a glass with a refractive index of nF = 1.53 and a thickness of d = 67.2 nm. For broadband application a broadband anti-reflection coating would be necessary. Furthermore, it is assumed that the Mueller-matrix of the quarter-wave plate is constant for all wavelengths (according to Equation (19)). A Fresnel rhomb with anti-reflection coatings on the entrance and exit surface are a good approximation for this assumption. The Fresnel rhomb can be mounted at the reflected path rotated at βr = 0° to fulfill Δr − Δt = π/2. Figure 4 shows the values of the normalized determinant and condition number obtained with the proposed setup for λ ∈ [400nm, 1000nm]. The values have been calculated with Mathematica and Matlab using the plane-wave approximation and assuming the mentioned ideal optical components with ideal (broadband) anti-reflection coatings. In order to verify the calculations, the physical optics software VirtualLab Fusion from LightTrans has been used to simulate measurements with the DOAP including a model of the proposed beam splitter with the aforementioned single-layer anti-reflection coating. A right-handed circularly polarized, monochromatic (λ = 632.8 nm) Gaussian beam with a waist radius of 100 μm has been propagated through the DOAP by using the “2nd generation field tracing” feature of VirtualLab Fusion.

Figure 4.

Normalized determinant and condition number obtained with a high-refractive-index prism.


The following intensity vectors have been obtained with the simulation in VirtualLab Fusion and Matlab:


where IV and IM are the calculated intensities with VirtualLab Fusion and Matlab, respectively. Although there are small deviations, the values are comparable and the calculations plausible.



In this article we proposed a simplification of previous designs of a DOAP for measuring the SOP of a light beam. A critical component of the DOAP is the first beam splitter, which splits up the incoming beam into two beams. To get a low measurement error, the reflectance, transmittance, diattenuation and retardance of the beam splitter need to be optimal. Using additional quarter-wave plates relaxes the constraint on the retardance. This provides an additional degree of freedom when designing the beam splitter. For example, reflection and refraction at dielectrics usually results into a retardance of 0° or 180° but for a DOAP without retarders a retardance of 90° is required. We presented a DOAP consisting of two quarter-wave plates mounted at the reflected path and provided analytic formulas to calculate the azimuthal angles. It can been shown that this design is better than mounting one quarter-wave plate at each path, because the negative effect resulting from beam splitters with suboptimal retardances can always be compensated. A similar design with only one quarter-wave plate has also been provided. Furthermore, simulations revealed that if the normalized determinant is equal to one, the same holds for the normalized condition number, and vice versa. As a consequence, the absolute and relative measurement errors are minimized simultaneously at an optimal DOAP. Additionally, we presented the optical setup of a DOAP consisting of a special beam-splitter prism, which is suitable for broadband application resulting into a normalized determinant greater than 0.99 from λ ∈ [400nm − 1000nm]. For the best of our knowledge, previous designs of the DOAP achieve a normalized determinant greater than 0.99 only for a narrow wavelength range. Other proposed designs used for broadband application do not reach such a high value for the normalized determinant. We assumed that a perfect achromatic quarter-wave retarder with appropriate (broadband) anti-reflection coatings is available. To simulate the measurement of a monochromatic Gaussian beam with the DOAP consisting of the proposed beam splitter prism, the physical optics simulation software VirtualLab Fusion has been used. The results are comparable to the calculations performed in Mathematica and Matlab using the plane-wave approximation. Further simulations are planned to simulate the calibration and measurement of the DOAP for the whole spectral range and to simulate a realistic model of the achromatic retarder with appropriate broadband anti-reflection coatings.



Meriaudeau, F., Ferraton, M., Stolz, C., Morel, O., and Bigue, L., “Polarization imaging for industrial inspection,” in SPIE Proceedings, (2008). Google Scholar


Wolff, L. B., “Polarization-based material classification from specular reflection,” IEEE Transactions on Pattern Analysis and Machine Intelligence, 12 (11), 1059 –1071 (1990). Google Scholar


Morel, O., Ferraton, M., Stolz, C., and Gorria, P., “Active lighting applied to shape from polarization,” in IEEE International Conference on Image Processing, 2006, 2181 –2184 (2006). Google Scholar


Canillas, A., Polo, M. C., Andújar, J. L., Sancho, J., Bosch, S., Robertson, J., and Milne, W. I., “Spectroscopic ellipsometric study of tetrahedral amorphous carbon films: optical properties and modelling,” Diamond and Related Materials, 10 (3-7), 1132 –1136 (2001). Google Scholar


Cui, Y. and Azzam, R. M., “Applications of the normal-incidence rotating-sample ellipsometer to high- and low-spatial-frequency gratings,” Applied optics, 35 (13), 2235 –2238 (1996). Google Scholar


Han, C.-Y., Lee, Z.-Y., and Chao, Y.-F., “Determining thickness of films on a curved substrate by use of ellipsometric measurements,” Applied Optics, 48 (17), 3139 (2009). Google Scholar


Azzam, R. M. A., “Division-of-amplitude Photopolarimeter (DOAP) for the Simultaneous Measurement of All Four Stokes Parameters of Light,” Optica Acta: International Journal of Optics, 29 (5), 685 –689 (1982). Google Scholar


Azzam, R. M. A. and De, A., “Optimal beam splitters for the division-of-amplitude photopolarimeter,” Journal of the Optical Society of America A, 20 (5), 955 (2003). Google Scholar


Collett, E., “Determination of the ellipsometric characteristics of optical surfaces using nanosecond laser pulses,” Surface Science, 96 (1-3), 156 –167 (1980). Google Scholar


Azzam, R. M. A., Masetti, E., Elminyawi, I. M., and Grosz, F. G., “Construction, calibration, and testing of a four-detector photopolarimeter,” Review of Scientific Instruments, 59 (1), 84 –88 (1988). Google Scholar


Sabatke, D. S., Descour, M. R., Dereniak, E. L., Sweatt, W. C., Kemme, S. A., and Phipps, G. S., “Optimization of retardance for a complete stokes polarimeter,” Optics Letters, 25 (11), 802 (2000). Google Scholar


Peinado, A., Lizana, A., Vidal, J., Iemmi, C., and Campos, J., “Optimization and performance criteria of a stokes polarimeter based on two variable retarders,” Optics express, 18 (10), 9815 –9830 (2010). Google Scholar


Brudzewski, K., “Static stokes ellipsometer: General analysis and optimization,” Journal of Modern Optics, 38 (5), 889 –896 (1991). Google Scholar


Azzam, R. M. A.-G. and Bashara, N. M., Ellipsometry and polarized light, 4North-Holland personal library, Elsevier, Amsterdam (1999). Google Scholar


Fujiwara, H., Spectroscopic ellipsometry: Principles and applications, John Wiley & Sons, Chichester and England and Hoboken and NJ (2007). Google Scholar


Hauge, P. S., Muller, R. H., and Smith, C. G., “Conventions and formulas for using the Mueller-Stokes calculus in ellipsometry,” Surface Science, 96 (1-3), 81 –107 (1980). Google Scholar


Hecht, E., Optics, 4Addison-Wesley, Reading and Mass (2002). Google Scholar


Beyerer, J., Puente Leon, F., and Frese, C., Automatische Sichtprüfung: Grundlagen, Methoden und Praxis der Bildgewinnung und Bildauswertung, 2.Springer Vieweg, Berlin and Heidelberg (2016). Google Scholar


Mu, T., Chen, Z., Zhang, C., and Liang, R., “Optimal configurations of full-stokes polarimeter with immunity to both poisson and gaussian noise,” Journal of Optics, 18 (5), 055702 (2016). Google Scholar


Compain, E., Poirier, S., and Drevillon, B., “General and self-consistent method for the calibration of polarization modulators, polarimeters, and mueller-matrix ellipsometers,” Appi. Opt., 38 3490 –3502 (1999). Google Scholar


Azzam, R., “Beam-splitters for the division-of-amplitude photopolarimeter,” Optica Acta: International Journal of Optics, 32 (11), 1407 –1412 (1985). Google Scholar


Azzam, R. M. A. and Sudradjat, F. F., “Single-layer-coated beam splitters for the division-of-amplitude photopolarimeter,” Applied Optics, 44 (2), 190 (2005). Google Scholar


Yuan, W., Shen, W., Zhang, Y., and Liu, X., “Dielectric multilayer beam splitter with differential phase shift on transmission and reflection for division-of-amplitude photopolarimeter,” Optics Express, 22 (9), 11011 (2014). Google Scholar


Negara, C., “Fast polarization state detection by division-of-amplitude in a simple configuration setup,” in Proceedings of the 2015 Joint Workshop of Fraunhofer IOSB and Institute for Anthropomatics, Vision and Fusion Laboratory, 75 –89 (2016). Google Scholar


Negara, C., “Different designs for a polarization state detector based on division-of-amplitude,” in Proceedings of the 2016 Joint Workshop of Fraunhofer IOSB and Institute for Anthropomatics, Vision and Fusion Laboratory, 85 –107 (2017). Google Scholar


Zeng, L., Cai, Y., Tan, C., and Huang, Z., “Optimization of stokes optical polarization measurement system,” Laser Technology, 41 (1), 74 (2017). Google Scholar


Tyo, J. S., “Noise equalization in stokes parameter images obtained by use of variable-retardance polarimeters,” Optics Letters, 25 (16), 1198 (2000). Google Scholar


[1] For example: Thorlabs zero-wave plate with article number WPQSM05-633

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Christian Negara, Zheng Li, Thomas Längle, and Jürgen Beyerer "Simplified Stokes polarimeter based on division-of-amplitude", Proc. SPIE 11144, Photonics and Education in Measurement Science 2019, 111441B (17 September 2019);

Back to Top