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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 25 — Dec. 7, 2009
  • pp: 23044–23057
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Optimum input states of polarization for Mueller matrix measurement in a system having finite polarization-dependent loss or gain

H. Dong, Y. D. Gong, Varghese Paulose, P. Shum, and Malini Olivo  »View Author Affiliations


Optics Express, Vol. 17, Issue 25, pp. 23044-23057 (2009)
http://dx.doi.org/10.1364/OE.17.023044


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Abstract

We present the theoretical and simulation results of the relationship between three input states of polarization (SOP) and the Mueller matrix measurement error in an optical system having birefringence and finite polarization-dependent loss or gain (PDL/G). By using the condition number as the criterion, it can be theoretically demonstrated that the three input SOPs should be equally-spaced on the Poincaré sphere and centered on the reversed PDL/G vector to achieve better measurement accuracy in a single test. Further, an upper bound of the mean of the Mueller matrix measurement error is derived when the measurement errors of output Stokes parameters independently and identically follow the ideal Gaussian distribution. This upper bound also shows that the statistically best Mueller matrix measurement accuracy can be obtained when the three input SOPs have the same relationship mentioned above. Simulation results confirm the validity of the theoretical findings.

© 2009 OSA

1. Introduction

For an optical system having birefringence and small polarization-dependent loss or gain (PDL/G), we have demonstrated that, by theoretical analysis and simulations, the Mueller matrix measurement error (M3E) seriously depends on the choice of the three input states of polarization (SOP) [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. When we use the preconditions that 1) the measurement errors of output SOPs are far larger than those of input SOPs and 2) SOP measurement errors independently and identically follow the Gaussian distribution N(0,σ2), it can be demonstrated that the minimum M3E is statistically achieved when the three input SOPs are coplanar with an angle of 120° between any two of them in Stokes space [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. Three standard input SOPs (1,1,0,0)T, (1,0.5,0.866,0)T and (1,0.5,0.866,0)Thas been suggested as they obviously have a larger probability to result in a smaller M3E than other input SOPs [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

].

However, the above conclusion is valid only when the PDL/G is less than 0.35dB. Some optical systems may have a large PDL/G value from several dB to tens of dB, for example, a long-distance optical fiber communication system [2

2. N. Gisin and B. Huttner, “Combined effects of polarization mode dispersion and polarization dependent loss in optical fibers,” Opt. Commun. 142(1-3), 119–125 ( 1997). [CrossRef]

]. In such a system, PDL/G has adverse effect on both analog and digital optical signals [3

3. K. Kikushima, K. Suto, H. Yoshinaga, and E. Yoneda, “Polarization dependent distortion in AM-SCM video transmission systems,” IEEE J. Lightwave Technol. 12(4), 650–657 ( 1994). [CrossRef]

, 4

4. E. Lichtmann, “Performance degradation due to polarization dependent gain and loss in lightwave systems with optical amplifiers,” IEEE Photon. Technol. Lett. 5, 1969–1970 ( 1993).

]. Combined effect of PDL/G and polarization mode dispersion (PMD) gives rise to anomalous pulse broadening and deteriorates the bit error rate [2

2. N. Gisin and B. Huttner, “Combined effects of polarization mode dispersion and polarization dependent loss in optical fibers,” Opt. Commun. 142(1-3), 119–125 ( 1997). [CrossRef]

, 5

5. B. Huttner and N. Gisin, “Anomalous pulse spreading in birefringent optical fibers with polarization-dependent losses,” Opt. Lett. 22(8), 504–506 ( 1997). [CrossRef] [PubMed]

]. To monitor the PDL/G and PMD values in such a system, its Mueller matrix is required to be accurately measured [6

6. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Generalized Mueller matrix method for polarization mode dispersion measurement in a system with polarization-dependent loss or gain,” Opt. Express 14(12), 5067–5072 ( 2006), http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-12-5067. [CrossRef] [PubMed]

, 7

7. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain,” Opt. Commun. 274(1), 116–123 ( 2007). [CrossRef]

].

When the PDL/G has a finite value, such as 5 or 10 dB, the optimum input SOPs will definitely rely on the PDL/G of the system under test, including both the modulus and the direction of PDL/G vector. In this paper, we will present the detailed theoretical and simulation results of this problem. Firstly, in Section 2, the condition number (CN) of the matrix Fout(Fouthas been defined in Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

].) is used to evaluate M3E. By calculating the minimum of this CN, the relationship among the three optimum input SOPs, which can lead to a smaller M3E in a single test, is clearly presented. Secondly, in Sections 3 and 4, the statistical relationship between M3E and the three input SOPs is investigated under the same two preconditions mentioned above. Finally, some simulation results are used to verify the theoretical findings.

2. Optimization using CN as the criterion

In this section, the measurement errors of both input and output SOPs will be considered. From Eq. (10) of Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

], we have
ΔM˜=Fout1(ΔFinΔFoutM˜ΔFoutΔM˜)
(1)
All variables in Eq. (1) have been defined in Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. When Fout1ΔFout<1, M3E, which is depicted by the matrix norm ΔM˜, is bounded by
ΔM˜M˜Cond(Fout)1Cond(Fout)ΔFoutFout(ΔFinFin+ΔFoutFout)
(2)
where, Cond(Fout)=FoutFout1 is the CN. It is obvious that this upper bound seriously depends on the value of CN. The smaller CN is, the more possibleΔM˜/M˜ is to be smaller in a single test, regardless of the actual noise realizations of ΔFin/Fin and ΔFout/Fout. Actually, the CN has been widely used to evaluate the measurement uncertainty of a measurement system [8

8. A. Ambirajan and D. C. Look, “Optimum angles for a polarimeter: part I,” Opt. Eng. 34(6), 1651–1655 ( 1995). [CrossRef]

].

When the Frobenius matrix norm is adopted, the detailed expression of the CN is calculated as
Cond(Fout)=(1+ρouts2)sout02+(1+ρoutt2)tout02+(1+ρoutu2)uout02+sout02tout02uout02(Bout12+Bout22)|M˜|×{sout02tout02[(1+ρouts2)(1+ρoutt2)(1+ρoutsρouttcosαout)2]+sout02uout02[(1+ρouts2)(1+ρoutu2)(1+ρoutsρoutucosβout)2]+tout02uout02[(1+ρoutt2)(1+ρoutu2)(1+ρouttρoutucosγout)2]}(Bout12+Bout22)4[sout02tout02aout2+sout02uout02bout2+tout02uout02cout2]Bout12+|M˜|[(1+ρouts2)(1+ρoutt2)(1+ρoutu2)(1+ρoutu2)(1+ρoutsρouttcosαout)2(1+ρoutt2)(1+ρoutsρoutucosβout)2(1+ρouts2)(1+ρouttρoutucosγout)2+2(1+ρoutsρouttcosαout)(1+ρoutsρoutucosβout)(1+ρouttρoutucosγout)]sout0tout0uout0|Bout12Bout22|
(3)
where
{Bout12=ρouts2ρoutt2ρoutu2(1cos2αoutcos2βoutcos2γout+2cosαoutcosβoutcosγout)Bout22=(aout+bout+cout)(aout+bout+cout)(aoutbout+cout)(aout+boutcout)/4aout=ρouts2+ρoutt22ρoutsρouttcosαoutbout=ρouts2+ρoutu22ρoutsρoutucosβoutcout=ρoutt2+ρoutu22ρouttρoutucosγout
(4)
It can be easily noticed that the CN is completely determined by three 4-dimensional (4D) output Stokes vectors, including their powers(sout0,tout0,uout0), their degrees of polarization (DOP) (ρouts,ρoutt,ρoutu) and the three angles (αout,βout,γout)between any two of them in Stokes space. From Eqs. (3) and (4), it can be observed that the value of the CN will remain unchanged when any two 4D output Stokes vectors are interchanged. Therefore, the CN in Eq. (3) is a symmetric function of three 4D output Stokes vectors. According to the Purkiss Principle [9

9. W. C. Waterhouse, “Do symmetric problems have symmetric solutions?” Am. Math. Mon. 90(6), 378–387 ( 1983). [CrossRef]

], the CN must have a local maximum or minimum when
{sout0=tout0=uout0ρouts=ρoutt=ρoutuαout=βout=γout
(5)
In fact, it is easy to verify that this is a local minimum. In this paper, we do not demonstrate whether this local minimum is the global minimum or not; we are only interested in the relationship among the three 4D input Stokes vectors when this local minimum is achieved.

Due to Sout=M˜Sin, considering the input lights are partially polarized, we can obtain the generalized form of Eq. (7) in Re [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. Then, an equation group, relating the input and output powers, can be derived as
{sout0=Tusin0(1+ρinsDcosθs)tout0=Tutin0(1+ρintDcosθt)uout0=Tuuin0(1+ρinuDcosθu)
(6)
where Dis the value of PDL/G ; θs, θt and θu are the angles between the PDL/G vector and input SOPs Sin, Tin and Uin in Stokes space, respectively [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. Another equation group, relating the input and output DOPs, has already been obtained as [10

10. H. Dong, J. Q. Zhou, M. Yan, P. Shum, L. Ma, Y. D. Gong, and C. Q. Wu, “Quasi-monochromatic fiber depolarizer and its application to polarization-dependent loss measurement,” Opt. Lett. 31(7), 876–878 ( 2006). [CrossRef] [PubMed]

]
{ρouts=1(1D2)(1ρins2)/(1+ρinsDcosθs)2ρoutt=1(1D2)(1ρint2)/(1+ρintDcosθt)2ρoutu=1(1D2)(1ρinu2)/(1+ρinuDcosθu)2
(7)
From SoutTout=|M˜|SinTin [7

7. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain,” Opt. Commun. 274(1), 116–123 ( 2007). [CrossRef]

], and also considering the input lights are partially polarized, we can also obtain the generalized form of Eq. (8) in Re [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. Then, the third equation group can be written as
{ρoutsρouttcosαout=1(1D2)(1ρinsρintcosαin)(1+ρinsDcosθs)(1+ρintDcosθt)ρoutsρoutucosβout=1(1D2)(1ρinsρinucosβin)(1+ρinsDcosθs)(1+ρinuDcosθu)ρouttρoutucosγout=1(1D2)(1ρintρinucosγin)(1+ρintDcosθt)(1+ρinuDcosθu)
(8)
From Eqs. (6), (7) and (8), when the above-mentioned local minimum is achieved, it can be seen that 1) if sin0=tin0=uin0 and ρins=ρint=ρinuare satisfied, we haveθs=θt=θu and αin=βin=γin ; 2) when the input powers or DOPs of three inputs are different, the relative relationship among the three input SOPs and between the three inputs and the PDL/G vector will become complicated.

Fortunately, most of the light sources used in modern polarization measurement systems, such as the tunable laser source in a polarization-mode dispersion measurement system [11

11. H. Dong, P. Shum, Y. D. Gong, M. Yan, J. Q. Zhou, and C. Q. Wu, “Virtual generalized Mueller matrix method for measurement of complex polarization-mode dispersion vector in optical fibers,” IEEE Photon. Technol. Lett. 19(1), 27–29 ( 2007). [CrossRef]

] and the photoconductive switch emitter in a terahertz time-domain spectroscopy system [12

12. E. Castro-Camus, J. Lloyd-Hughes, M. D. Fraser, H. H. Tan, C. Jagadish, and M. B. Johnston, “Detecting the full polarization state of terahertz transients,” Proc. SPIE 6120, 61200Q ( 2005). [CrossRef]

], are completely polarized. Moreover, the input power can remain unchanged by using some well-designed polarization state generation approaches [7

7. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain,” Opt. Commun. 274(1), 116–123 ( 2007). [CrossRef]

, 13

13. H. Dong, Y. D. Gong, V. Paulose, and M. H. Hong, “Polarization state and Mueller matrix measurements in terahertz-time domain spectroscopy,” Opt. Commun. 282(18), 3671–3675 ( 2009). [CrossRef]

]. Therefore, in the rest of this paper, we consider that sin0=tin0=uin0 and ρins=ρint=ρinu=1 are always satisfied for both theoretical analysis and simulations. Further, since all input and output Stokes vectors can be normalized by the input power, sin0=tin0=uin0=1 can be adopted without any influence to the results.

Under the above conditions, Eqs. (3) and (4) can be simplified as
Cond(Fout)=2(Ds2+Dt2+Du2)+Ds2Dt2Du2(Bout12+Bout22)/(1D2)2×{Ds2Dt2[4(1+cosαout)2]+Ds2Du2[4(1+cosβout)2]+Dt2Du2[4(1+cosγout)2]}(Bout12+Bout22)8[Ds2Dt2(1cosαout)+Ds2Du2(1cosβout)+Dt2Du2(1cosγout)]Bout12+2(1D2)2[4+(1+cosαout)(1+cosβout)(1+cosγout)(1+cosαout)2(1+cosβout)2(1+cosγout)2]DsDtDu|Bout12Bout22|
(9)
and
{Bout12=1cos2αoutcos2βoutcos2γout+2cosαoutcosβoutcosγoutBout22=4(1cosβout)(1cosγout)(1+cosαoutcosβoutcosγout)2
(10)
where Ds=1+Dcosθs, Dt=1+Dcosθtand Du=1+Dcosθu. According to the Purkiss Principle [9

9. W. C. Waterhouse, “Do symmetric problems have symmetric solutions?” Am. Math. Mon. 90(6), 378–387 ( 1983). [CrossRef]

], the CN in Eq. (9) has a local maximum or minimum when θs=θt=θu=θ and αin=βin=γin=α. Consequently, θ and α are actually related, no matter they are optimized or not, by
cosθ=±1+2cosα3
(11)
By substituting Eq. (11) into Eq. (9) and doing numerical calculations with different values of PDL/G, we can find that 1) this is a local minimum and it is achieved when the minus sign is chosen in Eq. (11); 2) this local minimum is indeed the global minimum. Under this condition, the relationships between the optimum angles αopt, θopt and the PDL/G (in dB) are calculated and plotted in Fig. 1
Fig. 1 The relationships between the optimum angles of inputs and the values of PDL/G when the CN takes the global minimum.
.

It is evident that αoptis close to 120° when PDL/G is small. This is consistent with the conclusion we have obtained in Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. When PDL/G increases, the optimum angle αopt decreases. For a given PDL/G vector, the three optimum input Stokes vectors should be equally-spaced on the Poincaré sphere and centered on the reversed PDL/G vector as shown in Fig. 2
Fig. 2 The relative relationship of three input Stokes vectors and the PDL/G vector on the Poincaré sphere to achieve the minimum of the CN.
.

Figure 3
Fig. 3 The relationship between the minimum of the CN and the values of PDL/G.
shows that, for different values of PDL/G, the minimum of the CN is also different. It is obvious that M3E will dramatically increase when the value of PDL/G is up to tens of dB. Therefore, when the system under test has such a big PDL/G, its Mueller matrix cannot be accurately measured by using only three inputs in a single test.

In this section, we use the CN as the criterion to find out the appropriate input SOPs. The results show that the minimum CN is achieved when the three input SOPs are equally-spaced on the Poincaré sphere and centered on the reversed PDL/G vector. The larger the PDL/G, the closer the three input SOPs is to the reversed PDL/G vector.

From Eq. (2), M3E depends on not only the CN, but also on the noise realization. When many tests can be performed, the mean of M3E should be investigated. To carry out such an investigation, we must know the statistical properties of the Stokes parameter measurement errors in advance. In this paper, we assume that all Stokes parameter measurement errors independently and identically follow the Gaussian distribution N(0,σ2), which has been used in Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. This means that we assume that an ideal polarimeter, which has such statistical properties, is used in the measurement system.

3. Statistical properties of Δ|M˜|

In the following, we still consider that the measurement errors of the input SOPs can be neglected as we have done in Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

]. Under the conditions Δsoutj,Δtoutj,Δuoutj(j=1,2,3,4)N(0,σ2), we know that Δ|M˜|=0. Hence, the variance of Δ|M˜| is needed to evaluate the measurement uncertainty. It can be derived as
Var(Δ|M˜|)=2Tu2σ2KΔ|M|
(12)
where

KΔ|M|=(Ds+Dt)2+(Ds+Du)2+(Dt+Du)2(1D2)(3cosαincosβincosγin)(3cosαincosβincosγin)2
(13)

Obviously, KΔ|M| is also a symmetric function of the three input SOPs. Based on the Purkiss Principle and numerical calculations, its global minimum is also achieved when θs=θt=θu=θ, αin=βin=γin=α. When KΔ|M| takes the global minimum, the relationships between the optimum angles and the PDL/G is shown in Fig. 5
Fig. 5 The relationships between the optimum angles and the PDL/G. Solid lines are based on the minimum of KΔ|M| and dash lines are based on the minimum of the CN.
using solid lines. As a comparison, the optimum angles, corresponding to the CN, are also plotted in Fig. 5 using dashed lines. It is clear that they are different corresponding to the same value of PDL/G.

4. Upper bound of ΔM˜

When D has a finite value, from Eq. (14) of Ref [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

], we have
ΔM˜=M˜Fin1ΔFoutM˜
(14)
Due to the existence of the complex Mueller matrix M˜, it is difficult to calculate ΔM˜ starting from Eq. (14). To overcome the mathematical difficulty, we can start from the following equation
FinM˜1=Fout
(15)
Based on the relations that M˜1=M˜T/|M˜| [1

1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

] and (M˜+ΔM˜)T=M˜T+ΔM˜T, it can be derived that
ΔM˜T=Fin1ΔF˜out
(16)
where
F˜out=(isout0   sout1   sout2   sout3itout0     tout1   tout2   tout3iuout0   uout1   uout2uout3Aout0|M˜|Aout1|M˜|   Aout2|M˜|   Aout3|M˜|)
(17)
ΔF˜out=ΔF˜out1ΔF˜out2
(18)
In Eq.(18),ΔF˜out1=(iΔsout0Δsout1   Δsout2Δsout3iΔtout0Δtout1   Δtout2Δtout3iΔuout0     Δuout1Δuout2Δuout3ΔAout0|M˜|ΔAout1|M˜|   ΔAout2|M˜|   ΔAout3|M˜|)andΔF˜out2=Δ|M˜||M˜|(0     0     0     00     0     0     00     0     0     0Aout0Aout1   Aout2   Aout3).

Based on the definition of the Frobenius matrix norm, it is easy to know that ΔM˜=ΔM˜T. Then, by substituting Eq. (18) into Eq. (16), we have
ΔM˜=ΔM˜T=Fin1ΔF˜out1Fin1ΔF˜out2=Tr(ΔF˜out1HFΔF˜out1+ΔF˜out2HFΔF˜out2ΔF˜out1HFΔF˜out2ΔF˜out2HFΔF˜out1)
(19)
whereF=(Fin1)HFin1.

Unfortunately, we cannot directly calculate ΔM˜ because of the difficulties in mathematics. As an alternative, we can calculate an upper bound as
ΔM˜ΔM˜2=Tr(ΔF˜out1HFΔF˜out1)+Tr(ΔF˜out2HFΔF˜out2)Tr(ΔF˜out1HFΔF˜out2)Tr(ΔF˜out2HFΔF˜out1)
(20)
The four terms in Eq. (20) are calculated as
Tr(ΔF˜out1HFΔF˜out1)=2σ2{2j=13fjj+f44{4[Ds3Dt3(1cosαin)+Ds3Du3(1cosβin)+Dt3Du3(1cosγin)]/(1D2)3[Ds4Dt4(1cosαin)2+Ds4Du4(1cosβin)2+Dt4Du4(1cosγin)2]/(1D2)4}}
(21)
Tr(ΔF˜out2HFΔF˜out2)=f44Ds2Dt2Du2(Bout12+Bout22)(1D2)3Var(Δ|M˜|)|M˜|
(22)
Tr(ΔF˜out1HFΔF˜out2)=Tr(ΔF˜out2HFΔF˜out1)=0
(23)
In Eqs. (21) and (22), fjj are the diagonal elements of the matrix F, which are
{f11={[4(1+cosγin)2](Bin12+Bin22)8(1cosγin)Bin12}/(Bin12Bin22)2f22={[4(1+cosβin)2](Bin12+Bin22)8(1cosβin)Bin12}/(Bin12Bin22)2f33={[4(1+cosαin)2](Bin12+Bin22)8(1cosαin)Bin12}/(Bin12Bin22)2f44=2[4+(1+cosαin)(1+cosβin)(1+cosγin)(1+cosαin)2(1+cosβin)2(1+cosγin)2]/(Bin12Bin22)2
(24)
where
{Bin12=1cos2αincos2βincos2γin+2cosαincosβincosγinBin22=4(1cosβin)(1cosγin)(1+cosαincosβincosγin)2
(25)
Finally, we have
ΔM˜ΔM˜2=KΔMσ
(26)
where
KΔM=22j=13fjj+f44{4[Ds3Dt3(1cosαin)+Ds3Du3(1cosβin)+Dt3Du3(1cosγin)](1D2)3[Ds4Dt4(1cosαin)2+Ds4Du4(1cosβin)2+Dt4Du4(1cosγin)2Ds2Dt2Du2(Bout12+Bout22)KΔ|M|](1D2)4}
(27)
Apparently, this upper bound is completely determined by αin,βin,γin and θs,θt,θu. And it is easy to know that KΔM is also a symmetric function of (αin,βin,γin) and (θs,θt,θu). Also from the Purkiss Principle and numerical calculation, KΔM takes its global minimum when αin=βin=γin=α,θs=θt=θu=θ. From Eq. (27), the relationship between the optimum angles and the value of PDL/G, when KΔM takes the global minimum, can be shown in Fig. 6
Fig. 6 The relationships between the optimum angles and the PDL/G. Solid lines are based on the minimum of KΔM and dash lines are based on the minimum of the CN andKΔ|M|.
using solid lines. As a comparison, the optimum angles, corresponding to the CN andKΔ|M|, are also plotted in Fig. 6 using dashed lines. It is clear that, although the value of PDL/G is the same, different criteria lead to different optimum angles.

For different values of PDL/G, the minimum of KΔM is also different. As shown in Fig. 7
Fig. 7 The relationship between the minimum of KΔM and the values of PDL/G.
, M3E will dramatically increase when the value of PDL/G is up to tens of dB. Therefore, when the system under test has such a big PDL/G, the mean of the Mueller matrix also cannot be accurately measured.

When the value of PDL/G is 5 dB, the relationship between KΔM and the angle α is shown in Fig. 8
Fig. 8 The relationship between KΔMand the angle αwhen the value of the PDL/G is 5 dB. The inset shows the “zoom in” view of the same data.
. The curve in Fig. 8 gives us a partial information of the function of KΔM.

5. Simulation results

6. Conclusion

We presented the relationship between three input SOPs and M3E in a system having birefringence and a finite PDL/G. Firstly, by using the CN as the criterion, it has been demonstrated that the three optimum input SOPs should be equally-spaced and centred on the reversed PDL/G vector for achieving a smaller M3E in a single test. Secondly, the statistical relationship, which is expressed as an upper bound of the mean of M3E, has been derived when SOP measurement errors follow the same Gaussian distribution. This upper bound also tells us that the minimum M3E will be statistically achieved when the three input SOPs are equally-spaced and centred on the reversed PDL/G vector. Finally, the simulation results confirm the validity of the proposed conclusion.

This conclusion can be used in real measurements. If the PDL/G vector of the system under test can be known before the measurement, the three input SOPs, with the relative relationship shown in Section 2, should be adopted in a single test. If the PDL/G vector is unknown, the polarimeter has the statistical properties we have used in this paper and the measurement can be repeated for many times [14

14. M. Reimer and D. Yevick, “Least-squares analysis of the Mueller matrix,” Opt. Lett. 31(16), 2399–2401 ( 2006). [CrossRef] [PubMed]

], the measurement can be performed using the following steps:

  • 1) The PDL/G vector can be measured in the first test using three “not-too-bad” input SOPs, for example, the three inputs we suggested in Ref [1

    1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

    ];
  • 2) The second test is carried out using three input SOPs optimized using the relative relationship shown in Section 4 and the PDL/G vector measured in the first test. Then a more accurate PDL/G vector can be obtained;
  • 3) The third test is carried out based on the knowledge of the more accurate PDL/G to result in a further more accurate PDL/G vector;
  • 4) The measurement is repeated in this iterative way. Then the final averaged measurement result will be statistically the best.

Moreover, if the measurement errors of input SOPs cannot be neglected, the three statistically optimum input SOPs will depend on not only the PDL/G vector, but also on the birefringence. A detailed analysis will be presented in another paper.

On the other hand, if the polarimeter used in the measurements does not have the statistical properties we adopted in this paper, the statistical relationship between M3E and the three input SOPs will not be as same as the one we obtained in this paper. It will be polarimeter-dependent. Further analysis will be presented in other papers.

Acknowledgements

This work is supported by Singapore A-star, Singapore Bioimaging Consortium, SBIC Grant Ref: SBIC RP C-014/2007.

References and Links

1.

H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 ( 2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017. [CrossRef] [PubMed]

2.

N. Gisin and B. Huttner, “Combined effects of polarization mode dispersion and polarization dependent loss in optical fibers,” Opt. Commun. 142(1-3), 119–125 ( 1997). [CrossRef]

3.

K. Kikushima, K. Suto, H. Yoshinaga, and E. Yoneda, “Polarization dependent distortion in AM-SCM video transmission systems,” IEEE J. Lightwave Technol. 12(4), 650–657 ( 1994). [CrossRef]

4.

E. Lichtmann, “Performance degradation due to polarization dependent gain and loss in lightwave systems with optical amplifiers,” IEEE Photon. Technol. Lett. 5, 1969–1970 ( 1993).

5.

B. Huttner and N. Gisin, “Anomalous pulse spreading in birefringent optical fibers with polarization-dependent losses,” Opt. Lett. 22(8), 504–506 ( 1997). [CrossRef] [PubMed]

6.

H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Generalized Mueller matrix method for polarization mode dispersion measurement in a system with polarization-dependent loss or gain,” Opt. Express 14(12), 5067–5072 ( 2006), http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-12-5067. [CrossRef] [PubMed]

7.

H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain,” Opt. Commun. 274(1), 116–123 ( 2007). [CrossRef]

8.

A. Ambirajan and D. C. Look, “Optimum angles for a polarimeter: part I,” Opt. Eng. 34(6), 1651–1655 ( 1995). [CrossRef]

9.

W. C. Waterhouse, “Do symmetric problems have symmetric solutions?” Am. Math. Mon. 90(6), 378–387 ( 1983). [CrossRef]

10.

H. Dong, J. Q. Zhou, M. Yan, P. Shum, L. Ma, Y. D. Gong, and C. Q. Wu, “Quasi-monochromatic fiber depolarizer and its application to polarization-dependent loss measurement,” Opt. Lett. 31(7), 876–878 ( 2006). [CrossRef] [PubMed]

11.

H. Dong, P. Shum, Y. D. Gong, M. Yan, J. Q. Zhou, and C. Q. Wu, “Virtual generalized Mueller matrix method for measurement of complex polarization-mode dispersion vector in optical fibers,” IEEE Photon. Technol. Lett. 19(1), 27–29 ( 2007). [CrossRef]

12.

E. Castro-Camus, J. Lloyd-Hughes, M. D. Fraser, H. H. Tan, C. Jagadish, and M. B. Johnston, “Detecting the full polarization state of terahertz transients,” Proc. SPIE 6120, 61200Q ( 2005). [CrossRef]

13.

H. Dong, Y. D. Gong, V. Paulose, and M. H. Hong, “Polarization state and Mueller matrix measurements in terahertz-time domain spectroscopy,” Opt. Commun. 282(18), 3671–3675 ( 2009). [CrossRef]

14.

M. Reimer and D. Yevick, “Least-squares analysis of the Mueller matrix,” Opt. Lett. 31(16), 2399–2401 ( 2006). [CrossRef] [PubMed]

OCIS Codes
(060.2300) Fiber optics and optical communications : Fiber measurements
(060.2310) Fiber optics and optical communications : Fiber optics
(260.3090) Physical optics : Infrared, far
(260.5430) Physical optics : Polarization

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: August 31, 2009
Revised Manuscript: November 9, 2009
Manuscript Accepted: November 9, 2009
Published: December 2, 2009

Citation
H. Dong, Y. D. Gong, Varghese Paulose, P. Shum, and Malini Olivo, "Optimum input states of polarization for Mueller matrix measurement in a system having finite polarization-dependent loss or gain," Opt. Express 17, 23044-23057 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-25-23044


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References

  1. H. Dong, Y. D. Gong, V. Paulose, P. Shum, and M. Olivo, “Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain,” Opt. Express 17(15), 13017–13030 (2009), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-15-13017 . [CrossRef] [PubMed]
  2. N. Gisin and B. Huttner, “Combined effects of polarization mode dispersion and polarization dependent loss in optical fibers,” Opt. Commun. 142(1-3), 119–125 (1997). [CrossRef]
  3. K. Kikushima, K. Suto, H. Yoshinaga, and E. Yoneda, “Polarization dependent distortion in AM-SCM video transmission systems,” IEEE J. Lightwave Technol. 12(4), 650–657 (1994). [CrossRef]
  4. E. Lichtmann, “Performance degradation due to polarization dependent gain and loss in lightwave systems with optical amplifiers,” IEEE Photon. Technol. Lett. 5, 1969–1970 (1993).
  5. B. Huttner and N. Gisin, “Anomalous pulse spreading in birefringent optical fibers with polarization-dependent losses,” Opt. Lett. 22(8), 504–506 (1997). [CrossRef] [PubMed]
  6. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Generalized Mueller matrix method for polarization mode dispersion measurement in a system with polarization-dependent loss or gain,” Opt. Express 14(12), 5067–5072 (2006), http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-12-5067 . [CrossRef] [PubMed]
  7. H. Dong, P. Shum, M. Yan, J. Q. Zhou, G. X. Ning, Y. D. Gong, and C. Q. Wu, “Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain,” Opt. Commun. 274(1), 116–123 (2007). [CrossRef]
  8. A. Ambirajan and D. C. Look, “Optimum angles for a polarimeter: part I,” Opt. Eng. 34(6), 1651–1655 (1995). [CrossRef]
  9. W. C. Waterhouse, “Do symmetric problems have symmetric solutions?” Am. Math. Mon. 90(6), 378–387 (1983). [CrossRef]
  10. H. Dong, J. Q. Zhou, M. Yan, P. Shum, L. Ma, Y. D. Gong, and C. Q. Wu, “Quasi-monochromatic fiber depolarizer and its application to polarization-dependent loss measurement,” Opt. Lett. 31(7), 876–878 (2006). [CrossRef] [PubMed]
  11. H. Dong, P. Shum, Y. D. Gong, M. Yan, J. Q. Zhou, and C. Q. Wu, “Virtual generalized Mueller matrix method for measurement of complex polarization-mode dispersion vector in optical fibers,” IEEE Photon. Technol. Lett. 19(1), 27–29 (2007). [CrossRef]
  12. E. Castro-Camus, J. Lloyd-Hughes, M. D. Fraser, H. H. Tan, C. Jagadish, and M. B. Johnston, “Detecting the full polarization state of terahertz transients,” Proc. SPIE 6120, 61200Q (2005). [CrossRef]
  13. H. Dong, Y. D. Gong, V. Paulose, and M. H. Hong, “Polarization state and Mueller matrix measurements in terahertz-time domain spectroscopy,” Opt. Commun. 282(18), 3671–3675 (2009). [CrossRef]
  14. M. Reimer and D. Yevick, “Least-squares analysis of the Mueller matrix,” Opt. Lett. 31(16), 2399–2401 (2006). [CrossRef] [PubMed]

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