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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 26 — Dec. 10, 2012
  • pp: B232–B237
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Experimental Investigation of 126-Gb/s 6PolSK-QPSK signals

Johannes Karl Fischer, Saleem Alreesh, Robert Elschner, Felix Frey, Christian Meuer, Lutz Molle, Carsten Schmidt-Langhorst, Takahito Tanimura, and Colja Schubert  »View Author Affiliations


Optics Express, Vol. 20, Issue 26, pp. B232-B237 (2012)
http://dx.doi.org/10.1364/OE.20.00B232


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Abstract

We experimentally generate 28-GBd 6-ary polarization-shift keying quadrature phase-shift keying (6PolSK-QPSK) signals by utilizing a high-speed 4-channel digital-to-analog converter and an integrated dual-polarization I/Q modulator. In WDM transmission experiments over up to 4800 km standard single-mode fiber, we compare the performance of 126-Gb/s 6PolSK-QPSK and 112-Gb/s polarization-division multiplexing (PDM) QPSK signals. Furthermore, we discuss the implications of applying an inner Reed-Solomon RS(511,455) forward error correction code in order to correct burst errors due to the anti-Gray mapping of 6PolSK-QPSK.

© 2012 OSA

1. Introduction

Recently, optimized four-dimensional (4D) modulation formats have received a lot of attention since they promise a better sensitivity than conventional quadrature amplitude modulation (QAM) formats. In particular, polarization-switched (PS) quadrature phase-shift keying (QPSK) was experimentally realized [1

1. M. Sjödin, P. Johannisson, H. Wymeersch, P. A. Andrekson, and M. Karlsson, “Comparison of polarization-switched QPSK and polarization-multiplexed QPSK at 30 Gbit/s,” Opt. Express 19(8), 7839–7846 (2011). [CrossRef] [PubMed]

] after it had been theoretically described [2

2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

]. In theory, PS-QPSK offers 0.97 dB better sensitivity at a bit-error ratio (BER) of 10−3 when compared to polarization-division multiplexed (PDM) QPSK at the same bit rate. PS-QPSK enabled experimental demonstration of record sensitivities at bit rates of 84 Gb/s and 112 Gb/s [3

3. J. K. Fischer, L. Molle, M. Nölle, D.-D. Groß, C. Schmidt-Langhorst, and C. Schubert, “Experimental investigation of 84-Gb/s and 112-Gb/s polarization-switched quadrature phase-shift keying signals,” Opt. Express 19(26), B667–B672 (2011). [CrossRef] [PubMed]

]. In ultra-long haul wavelength-division multiplexing (WDM) transmission experiments, it was observed that PS-QPSK increases the maximum reach compared to PDM-QPSK by more than 30% at a bit rate of 42.9 Gb/s [4

4. D. S. Millar, D. Lavery, S. Makovejs, C. Behrens, B. C. Thomsen, P. Bayvel, and S. J. Savory, “Generation and long-haul transmission of polarization-switched QPSK at 42.9 Gb/s,” Opt. Express 19(10), 9296–9302 (2011). [CrossRef] [PubMed]

] and by about 10% at a bit rate of 112 Gb/s [5

5. M. Nölle, J. K. Fischer, L. Molle, C. Schmidt-Langhorst, D. Peckham, and C. Schubert, “Comparison of 8 × 112 Gb/s PS-QPSK and PDM-QPSK signals over transoceanic distances,” Opt. Express 19(24), 24370–24375 (2011). [CrossRef] [PubMed]

]. However, spectral efficiency has to be sacrificed when using PS-QPSK, since only 3 bit/symbol are encoded compared to 4 bit/symbol for PDM-QPSK. This means that a PS-QPSK signal requires 4/3 times the bandwidth as a PDM-QPSK signal in order to transmit the same bit rate. Considering bandwidth-constrained components (e.g. modulators, analog-to-digital converters), this additional bandwidth demand of PS-QPSK may lead to an increased implementation penalty compared to PDM-QPSK.

In a recent publication, PS-QPSK was described as a parity check code for PDM-QPSK and its suitability for practical applications was questioned [6

6. B. Krongold, T. Pfau, N. Kaneda, and S. C. J. Lee, “Comparison between PS-QPSK and PDM-QPSK with equal rate and bandwidth,” IEEE Photon. Technol. Lett. 24(3), 203–205 (2012). [CrossRef]

]. The authors argue that when comparing PS-QPSK and PDM-QPSK at the same symbol rate, one could use additional coding for PDM-QPSK in order to achieve a comparable or even better sensitivity than PS-QPSK at the same net bit rate. Such an approach was also discussed in [7

7. H. Bülow, “Ideal POL-QAM modulation for coherent detection schemes,” in Proc. Signal Processing in Photonic Communications (2011), paper SPTuB1.

], where it was concluded that additional coding may result in significantly increased processing complexity. However, PS-QPSK does not require additional processing complexity to achieve its sensitivity. In fact, its generation is very simple and at the receiver more or less the same signal processing can be used as for PDM-QPSK [8

8. J. Renaudier, P. Serena, A. Bononi, M. Salsi, O. Bertran-Pardo, H. Mardoyan, P. Tran, E. Dutisseuil, G. Charlet, and S. Bigo, “Generation and detection of 28 Gbaud polarization switched-QPSK in WDM long-haul systems,” J. Lightwave Technol. 30(9), 1312–1318 (2012). [CrossRef]

]. Thus, PS-QPSK is not a replacement for PDM-QPSK but may find application in software-defined optics as a complement to PDM-QPSK. Furthermore, it may enable certain 100G upgrade scenarios of legacy submarine links, where 100G PDM-QPSK is not feasible.

An attractive alternative 4D modulation format was proposed by Bülow [9

9. H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.

]. It transmits a QPSK symbol in one of six different states of polarization (SOP). We therefore use the name 6-ary polarization-shift keying (6PolSK) QPSK in the remainder of this paper following the naming used in [10

10. H. Bülow and E. Masalkina, Coded modulation in optical communications,” in Proc. Opt. Fiber Commun. Conf. (2011), paper OThO1.

]. This modulation format has a spectral efficiency of 4.5 bit/symbol. Furthermore, it was shown to offer 0.5 dB better power efficiency than PDM-QPSK at the same bit rate [2

2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

]. The additional spectral efficiency can be exploited to add an inner forward error correction (FEC) code, thereby improving the sensitivity compared to PDM-QPSK significantly [9

9. H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.

], [10

10. H. Bülow and E. Masalkina, Coded modulation in optical communications,” in Proc. Opt. Fiber Commun. Conf. (2011), paper OThO1.

]. Just recently, 6PolSK-QPSK was also realized experimentally [11

11. J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, C. Meuer, L. Molle, C. Schmidt-Langhorst, T. Tanimura, and C. Schubert, “Experimental investigation of 126-Gb/s 6PolSK-QPSK signals,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.1.C.4.

], [12

12. F. Buchali and H. Bülow, “Experimental transmission with POLQAM and PS-QPSK modulation format using a 28-Gbaud 4-D transmitter,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.3.A.1.

].

This contribution is an extension of our recent work [11

11. J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, C. Meuer, L. Molle, C. Schmidt-Langhorst, T. Tanimura, and C. Schubert, “Experimental investigation of 126-Gb/s 6PolSK-QPSK signals,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.1.C.4.

]. We experimentally generate 28-GBd (126-Gb/s) 6PolSK-QPSK signals with and without an additional inner Reed-Solomon (RS) forward error correction (FEC) code. This is achieved by using a high-speed digital-to-analog converter (DAC) to produce the electric drive signals for an integrated dual-polarization (DP) in-phase and quadrature (I/Q) modulator. We compare the performance of 28-GBd 6PolSK-QPSK and PDM-QPSK signals in WDM transmission experiments over a dispersion uncompensated ITU-T G.652 standard single-mode fiber (SSMF) link. Furthermore, the potential benefit of the inner RS code is investigated.

2. Experimental setup

The experimental setup is shown in Fig. 1
Fig. 1 Experimental setup for the generation of 20 × 112-Gb/s PDM-QPSK and 20 × 126-Gb/s 6PolSK-QPSK signals. (a) Optical envelope before ILV (top) and electrical drive signal (bottom) for 126-Gb/s 6PolSK-QPSK, (b) optical envelope before ILV (top) and electrical drive signal (bottom) for 112-Gb/s PDM-QPSK and (c) spectrum of the 20 × 126 Gb/s 6PolSK-QPSK WDM signal.
. At the transmitter, an external cavity laser (ECL) with a linewidth of ~100 kHz is used as a light source for the channel under test. For the remaining WDM channels, distributed feedback lasers (DFB) with linewidths <10 MHz are used. In total, 20 WDM channels are considered, including the probe channel. The WDM channels are located on the 50-GHz ITU-T channel grid starting at 192.95 THz. The center frequency of the probe channel is 193.4 THz. Even and odd channels are separately modulated by two integrated DP I/Q-modulators.

The drive signals for the modulators are generated by a 4-channel DAC with a sample rate of 56 GS/s and a resolution of 8 bits. The DAC features on-chip memory for storage of up to 262144 samples per channel. The DAC evaluation board provides a 3-dB bandwidth of about 8 GHz. This makes digital pre-emphasis of the drive signals necessary, which is applied offline before the samples are loaded onto the DAC chip. The transmitted data is a de Bruijn binary sequence of length 214. Gray mapping is applied for PDM-QPSK, while the mapping rule proposed in [2

2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

] is applied for 6PolSK-QPSK, which maps nine bits into two symbols. We use the 6PolSK-QPSK constellation points { ± √2, ± √2, 0, 0} with arbitrary sign and permutation as described in [2

2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

]. This allows generation of 6PolSK-QPSK by using 3-level electrical drive signals. An eye diagram of the resulting 3-level output signal of the DAC is shown in Fig. 1(a). The resulting 6PolSK-QPSK signal has six states of polarization ( ± S1, ± S2, ± S3 in Stokes space) as shown in Fig. 2(a)
Fig. 2 (a) Back-to-back time-resolved SOP (~105 symbols) and (b) corresponding constellation diagram of 126-Gb/s 6PolSK-QPSK at maximum OSNR (~5 × 106 symbols).
. After modulation, even and odd channels are combined by a 50-GHz interleaver (ILV). The optical envelope of a single-channel 28-GBd 6PolSK-QPSK signal after the interleaver is shown in Fig. 1(a). For comparison, the corresponding optical envelope and binary electrical drive signal for PDM-QPSK are reported in Fig. 1(b).

After the interleaver, the combined WDM signal can be launched into a recirculating fiber loop incorporating three 80-km spans of SSMF. The fiber loss is compensated by erbium-doped fiber amplifiers (EDFA). In order to avoid unrealistic accumulation of polarization-dependent impairments, a loop-synchronous polarization scrambler is inserted into the loop.

Once per loop roundtrip, the WDM spectrum is flattened by a programmable gain equalizing filter. The 20 × 126 Gb/s 6PolSK-QPSK spectra after the interleaver at the transmitter and after 2400 km (10 loop round trips) are reported in Fig. 1(c).

At the receiver, the optical signal-to-noise ratio (OSNR) can be degraded by noise loading using a variable optical attenuator (VOA) followed by an EDFA. The delivered OSNR at the receiver is measured in front of the 0.4-nm channel selection filter with a resolution bandwidth of 0.1 nm. The local oscillator (LO) ECL has a linewidth of ~100 kHz. LO and signal are superimposed in a polarization-diversity optical 90° hybrid. The outputs of the hybrid are connected to four balanced photo-detectors. The resulting signals are digitized by four analog-to-digital converters (ADC) with a sample rate of 50 GS/s and a bandwidth of 20 GHz. The digital samples are then processed offline in a computer.

In the digital signal processing, the signal is up-sampled to two samples per symbol. After frontend corrections and frequency-domain compensation of the chromatic dispersion, the signal is fed to a data-aided frequency-domain equalizer (DA-FDE). The channel transfer matrix as well as the frequency offset between LO and signal are estimated based on pilot symbol sequences. We use constant-amplitude zero-autocorrelation sequences containing 16 symbols [13

13. F. Pittalà, F. N. Hauske, Y. Ye, N. G. Gonzalez, and I. T. Monroy, Data-aided frequency-domain 2 × 2 MIMO equalizer for 112 Gbit/s PDM-QPSK coherent transmission systems,” in Proc. Opt. Fiber Commun. Conf. (2012), paper OM2H.4.

]. The frame synchronization is based on an autocorrelation metric [14

14. K. Shi and E. Serpedin, “Coarse frame and carrier synchronization of OFDM systems: a new metric and comparison,” IEEE Trans. Wirel. Comm. 3(4), 1271–1284 (2004). [CrossRef]

]. The total overhead for the header symbols is 1.17%, resulting in a negligible required OSNR penalty of less than 0.1 dB. After equalization, a Viterbi-Viterbi carrier phase estimation with 32 taps is used for PDM-QPSK. For 6PolSK-QPSK the algorithm is slightly modified, such that for symbols having SOP = ± S1, only the polarization tributary with larger absolute value is taken into account for phase estimation. The constellation diagram of the recovered signal is shown in Fig. 2(b). From the constellation, it becomes clear that 6PolSK-QPSK can be viewed as a combination of PDM-QPSK (constellation points with high density) and polarization-switched (PS) QPSK (points with low density). Due to the applied bit mapping, the decision based on Euclidean distance in 4D-space is performed for two consecutive 6PolSK-QPSK symbols at once. After demapping, bit errors are counted and the resulting bit error ratio (BER) is converted to a Q-factor.

3. Results and discussion

Figure 3
Fig. 3 Measured back-to-back Q-factor for 112-Gb/s PDM-QPSK (squares), 126-Gb/s 6PolSK-QPSK (circles) and 112-Gb/s 6PolSK-QPSK with inner RS (511,455) (triangles). The solid lines show the theoretical Q-factor for an AWGN channel [2].
shows the measured back-to-back Q-factor as symbols. For reference, the solid lines show the theoretical limit for an additive white Gaussian noise (AWGN) channel [2

2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

] and the hard-decision (HD) FEC threshold at BER = 3.8 × 10−3. Please note that both modulation formats are compared at the same symbol rate of 28 GBd resulting in a bit rate of 112 Gb/s for PDM-QPSK and 126 Gb/s for 6PolSK-QPSK. Therefore, 6PolSK-QPSK requires a slightly larger OSNR at the HD-FEC threshold than PDM-QPSK, although it has a better power efficiency.

The measured required OSNR for a Q-factor above the FEC threshold is approximately 14.1 dB for PDM-QPSK and 16.1 dB for 6PolSK-QPSK. This corresponds to implementation penalties of 2.1 dB and 3.4 dB, respectively. Although pre-emphasis is applied, the 8-GHz bandwidth of the DAC evaluation board clearly results in some degradation of the 28-GBdsignals. Furthermore, the increased number of levels in the drive signals for 6PolSK-QPSK results in an additional 1.3 dB implementation penalty compared to PDM-QPSK. By using DACs with higher bandwidth and better resolution it is expected that the implementation penalty of 6PolSK-QPSK can be reduced to be comparable to implementation penalties encountered in contemporary PDM-QPSK systems. Another way to reduce the implementation penalty could be an alternative transmitter setup as proposed in [9

9. H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.

], which removes penalties associated with the DAC.

In order to estimate the reach for WDM transmission, the fiber launch power per channel was varied between −4 dBm and + 1 dBm. The Q-factor after transmission over the fiber loop is shown in Fig. 4(a)
Fig. 4 Q-factor versus (a) transmitted distance for −2 dBm launch power per channel and (b) launch power per channel after 2400 km.
for the optimum launch power of −2 dBm per channel. The maximum reach with a Q-factor above the FEC threshold for the probe channel was 3360 km for 6PolSK-QPSK and 4320 km for PDM-QPSK.

The dependence of the Q-factor on launch power is shown in Fig. 4(b) after ten loop round trips (2400 km). Both formats show approximately 1-dB Q-factor penalty when increasing the power per channel from −2 dBm to 0 dBm, indicating a similar tolerance to nonlinear impairments. The reported results are obtained for uncoded signals. However, as pointed out in [7

7. H. Bülow, “Ideal POL-QAM modulation for coherent detection schemes,” in Proc. Signal Processing in Photonic Communications (2011), paper SPTuB1.

], [9

9. H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.

] and [10

10. H. Bülow and E. Masalkina, Coded modulation in optical communications,” in Proc. Opt. Fiber Commun. Conf. (2011), paper OThO1.

], the increased spectral efficiency of 6PolSK-QPSK by 12.5% compared with PDM-QPSK allows application of an additional inner FEC, correcting for the burst errors due to the anti-Gray bit mapping.

In order to investigate the possible benefit of such an approach, a serial concatenation of two levels of coding was considered as shown in Fig. 5
Fig. 5 The block diagram of 6PolSK-QPSK encoder with two levels of coding [9].
. The Reed-Solomon RS(511,455) code with 12.5% overhead was implemented as an inner FEC code. It uses one bit per super symbol (two 6PolSK-QPSK symbols) as parity symbols. The code has the capability to correct up to 28 symbol errors per FEC frame.

The measured BER in a back-to-back configuration for the case of coded modulation is shown in Fig. 3 (blue triangles). Application of the inner RS(511,455) code leads to approximately 1.5 dB coding gain at the HD-FEC threshold. However, due to higher implementation penalty for 6PolSK-QPSK in our particular implementation no improvement was observed compared to PDM-QPSK at the same bit rate.

As it can be seen from Fig. 4(a), the application of an inner FEC increases the reach of 6PolSK-QPSK to 4320 km. Overall, the performance improvement due to the RS(511,455) code is significant but not sufficient to offset the increased implementation penalty of 6PolSK-QPSK. However, the availability of DACs with sufficient bandwidth and resolution for low implementation penalties is just a question of time. Furthermore, advanced coded modulation schemes could yield more coding gain. For example, the application of a soft-decision FEC in combination with iterative demapping might be a more promising approach [7

7. H. Bülow, “Ideal POL-QAM modulation for coherent detection schemes,” in Proc. Signal Processing in Photonic Communications (2011), paper SPTuB1.

].

5. Conclusion

We have described the experimental generation of 126-Gb/s 6PolSK-QPSK signals. In WDM transmission experiments over an SSMF link, a maximum reach of 3360 km was measured compared to 4320 km for PDM-QPSK. Over uncompensated SSMF, the tolerance of the 126-Gb/s 6PolSK-QPSK signals to nonlinear impairments is comparable to that of 112-Gb/s PDM-QPSK signals. Application of an inner RS (511,455) code to the 6PolSK-QPSK results in 1.5dB coding gain compared with uncoded 6PolSK-QPSK at the HD-FEC limit. This extends the maximum reach by approximately 29% from 3360 km to 4320 km.

Acknowledgments

Saleem Alreesh gratefully acknowledges funding by the German Research Foundation (DFG) under grant GR 3774/2-1.

References and links

1.

M. Sjödin, P. Johannisson, H. Wymeersch, P. A. Andrekson, and M. Karlsson, “Comparison of polarization-switched QPSK and polarization-multiplexed QPSK at 30 Gbit/s,” Opt. Express 19(8), 7839–7846 (2011). [CrossRef] [PubMed]

2.

E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol. 27(22), 5115–5126 (2009). [CrossRef]

3.

J. K. Fischer, L. Molle, M. Nölle, D.-D. Groß, C. Schmidt-Langhorst, and C. Schubert, “Experimental investigation of 84-Gb/s and 112-Gb/s polarization-switched quadrature phase-shift keying signals,” Opt. Express 19(26), B667–B672 (2011). [CrossRef] [PubMed]

4.

D. S. Millar, D. Lavery, S. Makovejs, C. Behrens, B. C. Thomsen, P. Bayvel, and S. J. Savory, “Generation and long-haul transmission of polarization-switched QPSK at 42.9 Gb/s,” Opt. Express 19(10), 9296–9302 (2011). [CrossRef] [PubMed]

5.

M. Nölle, J. K. Fischer, L. Molle, C. Schmidt-Langhorst, D. Peckham, and C. Schubert, “Comparison of 8 × 112 Gb/s PS-QPSK and PDM-QPSK signals over transoceanic distances,” Opt. Express 19(24), 24370–24375 (2011). [CrossRef] [PubMed]

6.

B. Krongold, T. Pfau, N. Kaneda, and S. C. J. Lee, “Comparison between PS-QPSK and PDM-QPSK with equal rate and bandwidth,” IEEE Photon. Technol. Lett. 24(3), 203–205 (2012). [CrossRef]

7.

H. Bülow, “Ideal POL-QAM modulation for coherent detection schemes,” in Proc. Signal Processing in Photonic Communications (2011), paper SPTuB1.

8.

J. Renaudier, P. Serena, A. Bononi, M. Salsi, O. Bertran-Pardo, H. Mardoyan, P. Tran, E. Dutisseuil, G. Charlet, and S. Bigo, “Generation and detection of 28 Gbaud polarization switched-QPSK in WDM long-haul systems,” J. Lightwave Technol. 30(9), 1312–1318 (2012). [CrossRef]

9.

H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.

10.

H. Bülow and E. Masalkina, Coded modulation in optical communications,” in Proc. Opt. Fiber Commun. Conf. (2011), paper OThO1.

11.

J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, C. Meuer, L. Molle, C. Schmidt-Langhorst, T. Tanimura, and C. Schubert, “Experimental investigation of 126-Gb/s 6PolSK-QPSK signals,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.1.C.4.

12.

F. Buchali and H. Bülow, “Experimental transmission with POLQAM and PS-QPSK modulation format using a 28-Gbaud 4-D transmitter,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.3.A.1.

13.

F. Pittalà, F. N. Hauske, Y. Ye, N. G. Gonzalez, and I. T. Monroy, Data-aided frequency-domain 2 × 2 MIMO equalizer for 112 Gbit/s PDM-QPSK coherent transmission systems,” in Proc. Opt. Fiber Commun. Conf. (2012), paper OM2H.4.

14.

K. Shi and E. Serpedin, “Coarse frame and carrier synchronization of OFDM systems: a new metric and comparison,” IEEE Trans. Wirel. Comm. 3(4), 1271–1284 (2004). [CrossRef]

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
(060.4080) Fiber optics and optical communications : Modulation

ToC Category:
Transmission Systems and Network Elements

History
Original Manuscript: October 2, 2012
Revised Manuscript: November 7, 2012
Manuscript Accepted: November 7, 2012
Published: November 29, 2012

Virtual Issues
European Conference on Optical Communication 2012 (2012) Optics Express

Citation
Johannes Karl Fischer, Saleem Alreesh, Robert Elschner, Felix Frey, Christian Meuer, Lutz Molle, Carsten Schmidt-Langhorst, Takahito Tanimura, and Colja Schubert, "Experimental Investigation of 126-Gb/s 6PolSK-QPSK signals," Opt. Express 20, B232-B237 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-26-B232


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References

  1. M. Sjödin, P. Johannisson, H. Wymeersch, P. A. Andrekson, and M. Karlsson, “Comparison of polarization-switched QPSK and polarization-multiplexed QPSK at 30 Gbit/s,” Opt. Express19(8), 7839–7846 (2011). [CrossRef] [PubMed]
  2. E. Agrell and M. Karlsson, “Power-efficient modulation formats in coherent transmission systems,” J. Lightwave Technol.27(22), 5115–5126 (2009). [CrossRef]
  3. J. K. Fischer, L. Molle, M. Nölle, D.-D. Groß, C. Schmidt-Langhorst, and C. Schubert, “Experimental investigation of 84-Gb/s and 112-Gb/s polarization-switched quadrature phase-shift keying signals,” Opt. Express19(26), B667–B672 (2011). [CrossRef] [PubMed]
  4. D. S. Millar, D. Lavery, S. Makovejs, C. Behrens, B. C. Thomsen, P. Bayvel, and S. J. Savory, “Generation and long-haul transmission of polarization-switched QPSK at 42.9 Gb/s,” Opt. Express19(10), 9296–9302 (2011). [CrossRef] [PubMed]
  5. M. Nölle, J. K. Fischer, L. Molle, C. Schmidt-Langhorst, D. Peckham, and C. Schubert, “Comparison of 8 × 112 Gb/s PS-QPSK and PDM-QPSK signals over transoceanic distances,” Opt. Express19(24), 24370–24375 (2011). [CrossRef] [PubMed]
  6. B. Krongold, T. Pfau, N. Kaneda, and S. C. J. Lee, “Comparison between PS-QPSK and PDM-QPSK with equal rate and bandwidth,” IEEE Photon. Technol. Lett.24(3), 203–205 (2012). [CrossRef]
  7. H. Bülow, “Ideal POL-QAM modulation for coherent detection schemes,” in Proc. Signal Processing in Photonic Communications (2011), paper SPTuB1.
  8. J. Renaudier, P. Serena, A. Bononi, M. Salsi, O. Bertran-Pardo, H. Mardoyan, P. Tran, E. Dutisseuil, G. Charlet, and S. Bigo, “Generation and detection of 28 Gbaud polarization switched-QPSK in WDM long-haul systems,” J. Lightwave Technol.30(9), 1312–1318 (2012). [CrossRef]
  9. H. Bülow, “Polarization QAM modulation (POL-QAM) for coherent detection schemes,” in Proc. Opt. Fiber Commun. Conf. (2009), paper OWG2.
  10. H. Bülow and E. Masalkina, Coded modulation in optical communications,” in Proc. Opt. Fiber Commun. Conf. (2011), paper OThO1.
  11. J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, C. Meuer, L. Molle, C. Schmidt-Langhorst, T. Tanimura, and C. Schubert, “Experimental investigation of 126-Gb/s 6PolSK-QPSK signals,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.1.C.4.
  12. F. Buchali and H. Bülow, “Experimental transmission with POLQAM and PS-QPSK modulation format using a 28-Gbaud 4-D transmitter,” Proc. Eur. Conf. Opt. Commun. (2012), paper We.3.A.1.
  13. F. Pittalà, F. N. Hauske, Y. Ye, N. G. Gonzalez, and I. T. Monroy, Data-aided frequency-domain 2 × 2 MIMO equalizer for 112 Gbit/s PDM-QPSK coherent transmission systems,” in Proc. Opt. Fiber Commun. Conf. (2012), paper OM2H.4.
  14. K. Shi and E. Serpedin, “Coarse frame and carrier synchronization of OFDM systems: a new metric and comparison,” IEEE Trans. Wirel. Comm.3(4), 1271–1284 (2004). [CrossRef]

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