OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 2 — Jan. 27, 2014
  • pp: 1971–1980
« Show journal navigation

Electronic polarization-division demultiplexing based on digital signal processing in intensity-modulation direct-detection optical communication systems

Kazuro Kikuchi  »View Author Affiliations


Optics Express, Vol. 22, Issue 2, pp. 1971-1980 (2014)
http://dx.doi.org/10.1364/OE.22.001971


View Full Text Article

Acrobat PDF (853 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We propose a novel configuration of optical receivers for intensity-modulation direct-detection (IM·DD) systems, which can cope with dual-polarization (DP) optical signals electrically. Using a Stokes analyzer and a newly-developed digital signal-processing (DSP) algorithm, we can achieve polarization tracking and demultiplexing in the digital domain after direct detection. Simulation results show that the power penalty stemming from digital polarization manipulations is negligibly small.

© 2014 Optical Society of America

1. Introduction

The dual-polarization (DP) transmission scheme has been introduced into practical optical communication systems for the first time by using recently-developed digital coherent receivers [1

1. E. Yamazaki, S. Yamanaka, Y. Kisaka, T. Nakagawa, K. Murata, E. Yoshida, T. Sakano, M. Tomizawa, Y. Miyamoto, S. Matsuoka, J. Matsui, A. Shibayama, J. Abe, Y. Nakamura, H. Noguchi, K. Fukuchi, H. Onaka, K. Fukumitsu, K. Komaki, O. Takeuchi, Y. Sakamoto, H. Nakashima, T. Mizuochi, K. Kubo, Y. Miyata, H. Nishimoto, S. Hirano, and K. Onohara, “Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP, ” Opt. Express 19, 13139–13184 (2011). [CrossRef]

]. Controlling the state of polarization (SOP) of the DP signal in the digital domain, such receivers can demultiplex two polarization tributaries in an adaptive manner [2

2. K. Kikuchi, “Performance analyses of polarization demultiplexing based on constant-modulus algorithm in digital coherent optical receivers,” Opt. Express 19, 9868–9880 (2011). [CrossRef] [PubMed]

]. The efficient SOP control based on digital signal processing (DSP) is owing to the phase information of the DP signal, which is obtained from coherent detection employing phase and polarization diversities [3

3. K. Kikuchi, “Digital coherent optical communication systems: Fundamentals and future prospects,” IEICE Electron. Express 8, 1642–1662 (2011). [CrossRef]

].

On the other hand, it has been believed that in conventional intensity-modulation direct-detection (IM·DD) systems, we cannot manipulate the signal SOP even by using DSP, because the phase information of the DP signal is entirely lost after direct detection; therefore, in order to demultiplex the DP signal, we need to rely on bulky and slow optical polarization controllers, which prohibit practical implementation of DP-IM·DD systems.

Contrary to such a common belief, this paper proposes a novel configuration of direct-detection receivers, which enables polarization-division demultiplexing the DP-IM signal in the digital domain without using optical polarization controllers. Implementing the Stokes analyzer and low-complexity DSP in the receivers, we can achieve tracking of SOP fluctuations and polarization-division demultiplexing of the DP-IM signal in the digital domain. Simulation results show that the power penalty stemming from digital polarization manipulations is negligibly small even under very fast SOP fluctuations. This technique may be useful for 100-Gbit/s short-reach optical transmission systems based on the IM·DD scheme, because the 50-GS/s sampling rate of analog-to-digital converters (ADCs) is currently available [1

1. E. Yamazaki, S. Yamanaka, Y. Kisaka, T. Nakagawa, K. Murata, E. Yoshida, T. Sakano, M. Tomizawa, Y. Miyamoto, S. Matsuoka, J. Matsui, A. Shibayama, J. Abe, Y. Nakamura, H. Noguchi, K. Fukuchi, H. Onaka, K. Fukumitsu, K. Komaki, O. Takeuchi, Y. Sakamoto, H. Nakashima, T. Mizuochi, K. Kubo, Y. Miyata, H. Nishimoto, S. Hirano, and K. Onohara, “Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP, ” Opt. Express 19, 13139–13184 (2011). [CrossRef]

] and the bit rate can easily be doubled with our proposed method.

The organization of the paper is as follows: Section 2 discusses the SOP of the DP-IM signal. Section 3 deals with the configuration of the proposed direct-detection receiver composed of the Stokes analyzer. In Sec.4, we discuss the polarization-tracking and polarization-demultiplexing algorithm used in the DSP circuit. Simulation results on the bit-error rate (BER) performance of the proposed receiver is described in Sec.5, and the effectiveness of the proposed algorithm is validated. Finally, Sec.6 concludes this paper.

2. SOP of the DP signal

Figure 1 shows the configuration of the DP-IM transmitter. We assume that two independent laser diodes, LD 1 and LD 2, are intensity-modulated with the same clock using either the direct-modulation method or the external modulation method. The two signals are polarization-multiplexed with a half-wave plate (λ/2) and a polarization beam combiner (PBC). The tributary 1 has the linear x polarization at the transmitter, whereas the tributary 2 does the linear y polarization. The intensity of the lasers is modulated in a binary manner. In a low logic level, the intensity of each tributary is zero. In the following analysis, we assume that the intensity of each tributary in a high logic level is two so that the average intensity is normalized to unity when both logic levels occur at the same probability of 1/2.

Fig. 1 Configuration of the DP-IM transmitter. Intensities of two independent laser diodes (LDs) are modulated either by direct modulation or by external modulation with the same clock. The two signals are polarization-multiplexed by a half-wave plate (λ/2) and a polarization beam combiner (PBC).

The total intensity of the DP-IM signal is classified into three cases shown in Table 1. In the case (I), logic levels of both of the polarization tributaries are low and the total signal intensity is zero. In the case (II), one tributary is in the high level, and the other in the low level; therefore, the total intensity is two. In the case (III), both of the tributaries are in the high level, and the total intensity is four.

Table 1. Classification of the state of the DP-IM signal based on the total peak intensity.

table-icon
View This Table

Corresponding to these cases, the SOP of the DP-IM signal is classified as follows: In the case (I), we have no signal. The SOP in the case (II) at the transmitter is determined either from the linear x polarization ((II)(a)) or from the linear y polarization ((II)(b)). On the other hand, in the case (III), the DP signal never has a fixed SOP, because phases of the two tributaries are not correlated. Noting that intensities of x-polarization and y-polarization components of the DP signal are the same, we find that S1 of the Stokes vector of the DP signal is zero, whereas S2 and S3 are fluctuating at the speed of the laser linewidth under the condition that S22+S32=4. Thus, we have the relation of the three Stokes vectors shown in Fig. 2: Normalized Stokes vectors S/S0 in cases (II)(a) and (II)(b) are pointed to opposite directions, and the normalized Stokes vector in the case (III) is orthogonal to these vectors in spite of its fluctuations. This orthogonal relation among the three normalized Stokes vectors is unchanged at the receiver although these vectors walk around on the Poincaré sphere due to fluctuations of fiber birefringence.

Fig. 2 Relation among normalized Stokes vectors in cases (II)(a), (II)(b), and (III). Normalized Stokes vectors in cases (II)(a) and (II)(b) are pointed to opposite directions, whereas the normalized Stokes vector in the case (III) is orthogonal to these vectors. The vector v(n) denotes the reference Stokes vector discussed in Sec. 4.

3. Receiver configuration

Figure 3 shows the schematic diagram of our proposed receiver. The incoming DP-IM signal is equally split into four branches after optical pre-amplification and optical filtering if necessary. In the first branch, we measure the signal intensity It. Inserting a polarizer (0° Pol), whose transmission axis is the x axis, we measure the intensity of the x-polarization component Ix in the second branch. Using a polarizer (45° Pol), whose transmission-axis is rotated by 45° with respect to the positive x axis, we detect the intensity of the 45° linearly-polarized component I45° in the third branch. With a quarter-wave plate (λ/4), whose fast axis is aligned to the x axis, and a 45°-rotated polarizer (45° Pol), we measure IR, which is the intensity of the right-circularly-polarized component, in the fourth branch. This configuration is known as the Stokes analyzer, which determines Stokes parameters from It, Ix, I45°, and IR [4

4. C. Brosseau, Fundamentals of Polarized Light (John Wiley & Sons, Inc. 1998).

] as
S0=It,
(1)
S1=2IxS0,
(2)
S2=2I45°S0,
(3)
S3=2IRS0.
(4)

Fig. 3 Receiver configuration for polarization-division demultiplexing the DP-IM signal. The part surrounded by broken lines represents the Stokes analyzer. Four outputs from photodiodes (PDs) are sent to the DSP circuit.

The four outputs of photodiodes (PDs) in Fig. 3 are converted to digital data using four-channel ADCs. The clock (CLK) extracted from the first branch of the Stokes analyzer controls sampling instances of the ADCs. The sampling rate is one sample/bit. The sampled data are sent to the DSP circuit.

4. DSP circuit

In the DSP circuit shown by Fig. 4, after calculations of Stokes parameters using Eqs. (1)(4), polarization tracking and demultiplexing are done by the algorithm given in the following.

Fig. 4 DSP circuit for polarization-division demultiplexing the DP-IM signal. The intensity discriminator determines the case (I) shown in Table 1. Cases (II)(a), (II)(b), and (III) in Table 1 are separated through discrimination of the Stokes-vector amplitude along the reference Stokes-vector direction.

First, in the intensity discriminator, we separate the case (I) from cases (II) and (III) (see Table 1) by intensity discrimination of the measured S0(n) with the threshold Sth, where n denotes the number of samples. When S0(n) ≤ Sth, both of the tributaries are decided to be in the low level.

Next, in the Stokes-vector amplitude discriminator and the reference Stokes-vector updater, we process the cases (II) and (III). Let the reference Stokes vector v(n) be a noise-free unit vector expressing the SOP of the tributary 1 at the receiver (See Fig. 2). Note that the SOP for the tributary 2 is given as −v(n) in such a case. Provided that v(n) is known, we can calculate the inner product between the received normalized Stokes vector S(n)/S0(n) and the reference Stokes vector v(n) as
u(n)=[S(n)S0(n)]v(n),
(5)
which means the normalized Stokes-vector amplitude along the direction of the reference Stokes vector. Then, Fig. 2 shows that we can separate the three cases (II)(a), (II)(b), and (III), discriminating the distribution of u(n) into three regions. Let discrimination thresholds for u(n) be uth(> 0) and −uth. When u(n) ≥ uth, we decide that the measured sample belongs to the tributary 1. In such a case, the tributary 1 is in the high level, whereas the tributary 2 is in the low level. The reference Stokes vector is then updated as
v(n+1)=v(n)+μ[S(n)S0(n)v(n)]v(n)+μ[S(n)S0(n)v(n)],
(6)
where μ is the step-size parameter. Equation (6) shows that the reference vector v(n) is modified by using the error signal ε = S(n)/S0(n) − v(n) and tracks the SOP of the tributary 1 even when it fluctuates on the Poincaré sphere due to the random change in fiber birefringence. A smaller value of μ improves the signal-to-noise ratio of v(n) but reduces the SOP tracking speed; therefore, we need to choose an optimum value of μ, depending on the SOP fluctuation speed.

On the other hand, when u(n) ≤ −uth, we decide that the measured sample belongs to the tributary 2. In such a case, the tributary 1 is in the low level, whereas the tributary 2 is in the high level. Reversing the sign of the normalized Stokes vector in Eq. (6), we have the update formula for v(n) given as
v(n+1)=v(n)+μ[S(n)S0(n)v(n)]v(n)+μ[S(n)S0(n)v(n)],
(7)
where the error signal ε = −S(n)/S0(n) − v(n) controls the reference Stokes vector.

When |u(n)| < uth, both of the tributaries are in the high level. We do not update the reference Stokes vector, because the SOP is not fixed in such a case. It should be noted that in cases (I) and (III), we do not update the reference Stokes vector and keep that defined in the nearest preceding case of (II); however, since the fluctuation speed of the reference Stokes vector is much slower than the bit rate, such thinned-out operation of the update process never degrades the BER performance as shown in 5.3.

Although we have assumed that v(n) is known, the update process using Eqs. (6) and (7) can start from an arbitrary reference vector in the blind mode. However, depending on the initial choice of the reference Stokes vector, the tributaries 1 and 2 may be exchanged. After a sufficient number of iteration with the proper choice of μ, the initial tracking process is converged and we can find an accurate estimate for v(n) even under very fast SOP fluctuations. Thus, we can discriminate the four cases (I), (II)(a), (II)(b), and (III). Finally, we complete the demodulation process, aligning bit sequences of the tributaries.

5. Simulation results

5.1. Simulation model

In computer simulations, we generate IM signals having binary random bit patterns for the two polarization tributaries. The number of bits for each tributary is N = 220. The Jones vector of the DP signal at the transmitter is written as
Ein(n)=[Ein,x(n)Ein,y(n)].
(8)
Complex amplitudes of electric fields Ein, x(n) and Ein, y(n) are given as
Ein,x(n)=sx(n)exp[iϕx(n)]+nx(n),
(9)
Ein,y(n)=sy(n)exp[iϕy(n)]+ny(n).
(10)
In these equations, sx(n) and sy(n) are signal amplitudes, which are either 2 (High level) or 0 (Low level) so that the average intensity of each polarization is unity. Parameters nx(n) and ny(n) are complex-valued Gaussian noises. The variance of the real part of nx, y(n) and that of the imaginary part of nx, y(n) are represented as σs2. Then, the carrier-to-noise ratio (CNR) of each polarization is expressed as
CNR/pol=12σs2.
(11)
The value of CNR/pol is controlled by the amount of Gaussian noise, while the average signal intensity is kept at a unity for each tributary. We do not take the CNR reduction by branching of the signal into account. This is valid for the optically pre-amplified signal [5

5. T. Okoshi and K. Kikuchi, Coherent Optical Communication Systems (KTK/Kluwer, 1988), Chap. 6.

].

Parameters ϕx(n) and ϕy(n) are phase noises of the lasers LD 1 and LD 2, respectively. We express them as
ϕx(n+1)=ϕx(n)+Δϕx(n),
(12)
ϕy(n+1)=ϕy(n)+Δϕy(n),
(13)
Parameters Δϕx(n) and Δϕy(n) are real-valued Gaussian noises and their variance σp2 is given [6

6. K. Kikuchi, “Characterization of semiconductor-laser phase noise and estimation of bit-error rate performance with low-speed offline digital coherent receivers,” Opt. Express 20, 5291–5302 (2012). [CrossRef] [PubMed]

] as
σp2=2πδfT,
(14)
where δf is the 3-dB spectral width of the lasers and T the bit duration.

After suffering from the random change in fiber birefringence, the Jones vector of the DP signal at the receiver is given as
Eout(n)=J(n)Ein(n),
(15)
where J(n) is the Jones matrix of the fiber for transmission. From Eout (n), Stokes parameters of the received signal is obtained [4

4. C. Brosseau, Fundamentals of Polarized Light (John Wiley & Sons, Inc. 1998).

] as
S0(n)=|Eout,x(n)|2+|Eout,y(n)|2,
(16)
S1(n)=|Eout,x(n)|2|Eout,y(n)|2,
(17)
S2(n)=2|Eout,x(n)||Eout,y(n)|cos[δ(n)],
(18)
S3(n)=2|Eout,x(n)||Eout,y(n)|sin[δ(n)],
(19)
where δ(n) = arg[Eout, y(n)/Eout, x(n)]. Equations (16)(19) are equivalent to Eqs. (1)(4).

When we scramble the SOP of the signal to emulate random fluctuations of fiber birefringence, the Jones matrix is expressed as
J(n)=[exp[iϕr(n)2]cos[θr(n)2]sin[θr(n)2]sin[θr(n)2]exp[iϕr(n)2]cos[θr(n)2]].
(20)
The polar angle and the azimuthal angle of the SOP randomly fluctuate on the Poincaré sphere in a bit-by-bit manner through ϕr(n) and θr(n). Parameters ϕr(n) and θr(n) including fluctuations obey the following equations:
ϕr(n+1)=ϕr(n)+Δϕr(n),
(21)
θr(n+1)=θr(n)+Δθr(n),
(22)
where Δϕr (n) and Δθr (n) are real-valued Gaussian noises having the variance given as
σ02=AT.
(23)
The parameter A with the dimension of s−1 is a constant under a specific condition of the fiber for transmission.

5.2. Determination of discrimination thresholds

In 5.2, we determine the optimum threshold Sth for discriminating S0(n) and uth for discriminating u(n) through computer simulations. Ignoring the laser phase noise, we assume that δf = 0 in Eq. (14). The fluctuation of the received SOP is also neglected throughout 5.2; then, we assume that J = 1 in Eq. (15).

Figure 5 shows the simulation result of the probability-density function of the intensity S0(n) when CNR/pol=10, 12, and 14 dB. The cases (I) and (II) are clearly separated, and we can decide that both logic levels of the tributaries are low, when the measured intensity S0 is smaller than the threshold Sth = 0.6 shown by the sold line. On the other hand, the discrimination ability between (II) and (III) is so poor that the intensity discrimination shown by the broken line cannot be applied to separate (II) and (III).

Fig. 5 Probability-density function of the intensity of the DP-IM signal. The cases (I) and (II) are discriminated by the solid line; on the other hand, the intensity discrimination shown by the broken line cannot be applied to separate (II) and (III).

We can understand the noise distribution shown in Fig. 5 as follows [5

5. T. Okoshi and K. Kikuchi, Coherent Optical Communication Systems (KTK/Kluwer, 1988), Chap. 6.

]: When we consider that the Gaussian noise originates from amplified spontaneous emission (ASE) of optical pre-amplifiers, the noise distribution in the case (I) is determined from the spontaneous-spontaneous beat-noise process. On the other hand, since the signal-spontaneous beat noise is predominant in the case (II), the probability distribution in the case (II) is broader than that in the case (I). In the case (III), two stochastically independent signal-spontaneous beat noises for orthogonal polarizations are added together; therefore, the variance of the noise in the case (III) is twice as large as that in the case (II).

Figure 6 shows the simulation result on the probability-density function of the inner product u(n) given by Eq. (5), when CNR/pol=10, 12, and 14 dB. Three peaks clearly appear in this function and we can optimally discriminate (II)(a), (II)(b), and (III) when uth = 0.55 as shown by solid lines.

Fig. 6 Probability-density function of u(n), which represents the normalized Stokes-vector amplitude along the reference-vector direction. The three cases (II)(a), (II)(b), and (III) are discriminated by solid lines.

5.3. BER performance

In BER calculations, we scramble the SOP of the signal, assuming that the parameter A in Eq. (23) is 105 [s−1]. The variance σf (N)2 of ϕr (n) and θr (n) at the N-th bit is written as
σf(N)2=σ02N=ANT.
(24)
Therefore, if we assume the 25-Gbit/s/pol system (T = 40 [ps]), the standard deviation is 2 rad in a 40-μs time span for N = 220 bits. This value is much larger than SOP fluctuations observed in real systems [7

7. P. M. Krummrich and K. Kotten, “Extremly fast (microsecond timescale) polarization changes in high speed long haul WDM transmission systems,” in 2004 OSA Technical Digest of Optical Fiber Communication Conference (Optical Society of America, 2004), FI3.

]. The step-size parameter μ is set at 1/27 to track the SOP fluctuation most accurately. We also include the effect of the laser linewidth δf, assuming that δf ·T = 1×10−3, which means δf = 25 MHz at the bit rate of 25 Gbit/s/pol.

Figure 7 shows the typical convergence property of the error magnitude ||ε|| controlling the reference Stokes vector, where we use the moving average with the span of 21 samples. Within 1,000-sample periods, the SOP tracking process is stabilized; then bit errors are counted after the convergence of the error magnitude.

Fig. 7 Convergence property of the error magnitude updating the reference Stokes vector. Since the SOP tracking process is stabilized within 1,000-sample periods, bit errors are counted after the convergence of the error magnitude.

Figure 8 shows BERs calculated as a function of CNR/pol. The red curve is the BER of each polarization tributary of the DP-IM signal demodulated with our proposed method. The black curve represents the BER performance of the single-polarization (SP) IM signal for comparison. In the DP-IM scheme, we find that both of the polarization tributaries have almost the same BER characteristics and the power penalty from the SP-IM scheme is negligible. Thus, the digital polarization-manipulation process does not generate any harmful effect even under very fast SOP fluctuations.

Fig. 8 BERs as a function of CNR/pol for the DP-IM signal which is demodulated with our proposed method. The BER curve of the single-polarization signal is also shown for comparison.

Fig. 9 BERs as a function of CNR/pol for the DP-IM signal with and without chromatic dispersion. BERs of the single-polarization signal are also shown for comparison.

6. Conclusions

We have proposed a novel configuration of IM·DD receivers, which enables polarization-division demultiplexing in the digital domain after direct detection. Simulation results show that the power penalty stemming from digital polarization-division demultiplexing is negligibly small even under very fast SOP fluctuations. The proposed method is useful for 100-Gbit/s short-reach optical transmission systems based on the IM·DD scheme, because the bit rate can easily be doubled.

Acknowledgments

This work was supported in part by Grant-in-Aid for Scientific Research (A) ( 25249038), the Ministry of Education, Culture, Sports, Science and Technology in Japan.

References and links

1.

E. Yamazaki, S. Yamanaka, Y. Kisaka, T. Nakagawa, K. Murata, E. Yoshida, T. Sakano, M. Tomizawa, Y. Miyamoto, S. Matsuoka, J. Matsui, A. Shibayama, J. Abe, Y. Nakamura, H. Noguchi, K. Fukuchi, H. Onaka, K. Fukumitsu, K. Komaki, O. Takeuchi, Y. Sakamoto, H. Nakashima, T. Mizuochi, K. Kubo, Y. Miyata, H. Nishimoto, S. Hirano, and K. Onohara, “Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP, ” Opt. Express 19, 13139–13184 (2011). [CrossRef]

2.

K. Kikuchi, “Performance analyses of polarization demultiplexing based on constant-modulus algorithm in digital coherent optical receivers,” Opt. Express 19, 9868–9880 (2011). [CrossRef] [PubMed]

3.

K. Kikuchi, “Digital coherent optical communication systems: Fundamentals and future prospects,” IEICE Electron. Express 8, 1642–1662 (2011). [CrossRef]

4.

C. Brosseau, Fundamentals of Polarized Light (John Wiley & Sons, Inc. 1998).

5.

T. Okoshi and K. Kikuchi, Coherent Optical Communication Systems (KTK/Kluwer, 1988), Chap. 6.

6.

K. Kikuchi, “Characterization of semiconductor-laser phase noise and estimation of bit-error rate performance with low-speed offline digital coherent receivers,” Opt. Express 20, 5291–5302 (2012). [CrossRef] [PubMed]

7.

P. M. Krummrich and K. Kotten, “Extremly fast (microsecond timescale) polarization changes in high speed long haul WDM transmission systems,” in 2004 OSA Technical Digest of Optical Fiber Communication Conference (Optical Society of America, 2004), FI3.

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4080) Fiber optics and optical communications : Modulation

ToC Category:
Optical Communications

History
Original Manuscript: November 29, 2013
Revised Manuscript: January 11, 2014
Manuscript Accepted: January 13, 2014
Published: January 23, 2014

Citation
Kazuro Kikuchi, "Electronic polarization-division demultiplexing based on digital signal processing in intensity-modulation direct-detection optical communication systems," Opt. Express 22, 1971-1980 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-2-1971


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. E. Yamazaki, S. Yamanaka, Y. Kisaka, T. Nakagawa, K. Murata, E. Yoshida, T. Sakano, M. Tomizawa, Y. Miyamoto, S. Matsuoka, J. Matsui, A. Shibayama, J. Abe, Y. Nakamura, H. Noguchi, K. Fukuchi, H. Onaka, K. Fukumitsu, K. Komaki, O. Takeuchi, Y. Sakamoto, H. Nakashima, T. Mizuochi, K. Kubo, Y. Miyata, H. Nishimoto, S. Hirano, K. Onohara, “Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP, ” Opt. Express 19, 13139–13184 (2011). [CrossRef]
  2. K. Kikuchi, “Performance analyses of polarization demultiplexing based on constant-modulus algorithm in digital coherent optical receivers,” Opt. Express 19, 9868–9880 (2011). [CrossRef] [PubMed]
  3. K. Kikuchi, “Digital coherent optical communication systems: Fundamentals and future prospects,” IEICE Electron. Express 8, 1642–1662 (2011). [CrossRef]
  4. C. Brosseau, Fundamentals of Polarized Light (John Wiley & Sons, Inc. 1998).
  5. T. Okoshi, K. Kikuchi, Coherent Optical Communication Systems (KTK/Kluwer, 1988), Chap. 6.
  6. K. Kikuchi, “Characterization of semiconductor-laser phase noise and estimation of bit-error rate performance with low-speed offline digital coherent receivers,” Opt. Express 20, 5291–5302 (2012). [CrossRef] [PubMed]
  7. P. M. Krummrich, K. Kotten, “Extremly fast (microsecond timescale) polarization changes in high speed long haul WDM transmission systems,” in 2004 OSA Technical Digest of Optical Fiber Communication Conference (Optical Society of America, 2004), FI3.

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited