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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 8 — Apr. 22, 2013
  • pp: 10383–10392
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Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission

Y. Jung, Q. Kang, V. A. J. M. Sleiffer, B. Inan, M. Kuschnerov, V. Veljanovski, B. Corbett, R. Winfield, Z. Li, P. S. Teh, A. Dhar, J. Sahu, F. Poletti, S. -U. Alam, and D. J. Richardson  »View Author Affiliations


Optics Express, Vol. 21, Issue 8, pp. 10383-10392 (2013)
http://dx.doi.org/10.1364/OE.21.010383


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Abstract

We successfully fabricate three-mode erbium doped fiber with a confined Er3+ doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative thickness of the ring-doped layer in the active fiber and pump launch conditions. A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.

© 2013 OSA

1. Introduction

2. Modal gain performance in a ring-doped TM-EDF

2. System performance of a ring-doped TM-EDFA

To evaluate the performance of the ring-doped TM-EDFA in a transmission system, 17 external cavity lasers at distinct wavelengths across the C-band were multiplexed and modulated with 256-Gb/s DP-16QAM using an IQ-modulator and polarization-multiplexing stage. The data stream was split up into three equally powered signals and fed to the mode multiplexer (MUX) as described in [2

2. R.-J. Essiambre, G. Kramer, P. J. Winzer, G. J. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol. 28(4), 662–701 (2010). [CrossRef]

]. A 6m long ring-doped TM-EDF was used as the gain medium in conjunction with offset pump launch to reduce the mode dependent gain.

2.1 Gain spectra and BER performance of the TM-EDFA

To evaluate the bit error rate (BER) performance, the three output ports of the DEMUX were plugged into 50GHz tunable optical filters and commercial coherent receivers. The samples obtained from the digital sampling scopes were recorded and processed offline using data-aided digital signal processing. Figure 4(a)
Fig. 4 BER performance of the TM-EDFA as a function of (a) input signal power per mode and (b) launched pump power. The constellations are the recovered 256-Gb/s DP-16QAM at an input signal power of −5dBm per mode.
shows the BER measurement results for the TM-EDFA as a function of the input signal power per mode at a fixed pump power of 22dBm. It is clearly seen that the BER performance is highly dependent on the input signal power and that too low an input signal power leads to a rapid degradation in the BER, due to the increased level of ASE (reduced optical signal to noise ratio (OSNR)). We also tested the BER performance of the amplifier for various pump powers at a fixed input signal power of −5dBm per mode. As depicted in Fig. 4(b), the experimental BER curve shows that an optimum pump power exists that gives the best BER performance for a given input signal power. Generally, the higher the population inversion, the lower the amplifier noise figure. Thus, at low pump powers (<22dBm), the BER was improved with an increase in pump power due to the increased population inversion towards the input end of the amplifier preventing absorption of the input signal and resulting in OSNR improvement. However as the pump power was increased even further (>22dBm), the population inversion at the output end of the amplifier (which was also the pumping end) became significantly higher than that required for the amplification of the incoming signal. The excess population inversion contributed to the generation of ASE within the TM-EDFA resulting in a drop in OSNR and the degradation in BER.

Figure 5(a)
Fig. 5 (a) The measured BER performances at 1550.2 nm for various input signal power into the TM-EDFA and (b) measured BER at the edge channels of C-band (1527.994nm and 1564.217nm) at the input signal power of −5dBm. The constellations are the recovered 112Gb/s DP-QPSK for an input signal power of −5dBm per mode with an OSNR of 15dB/0.1nm.
shows the averaged BER curves of all spatial modes (LP01, LP11a and LP11b) for a 112Gb/s DP-QPSK signal at the center wavelength of the C-band (1550.2nm). As described in Fig. 4(a), the overall BER performance is strongly dependent on the input signal power into the TM-EDFA and which effects the output OSNR. The induced power penalty from the TM-EDFA was 0.1, 0.2, 0.5 and 1.5dB, respectively, for the −2, −5, −8 and −11dBm input signal power per mode cases compared to the back-to-back condition (only MUX/DEMUX without amplifier). The observed power penalty is small but it could be further reduced by applying a gain flattening filter after the amplifier and reducing remnant Fresnel reflections from the fiber end facets. We further tested the BER performance of our MM-amplifier at the edge channels of the C-band (1527.994nm and 1564.217nm). As shown in Fig. 5(b), the edge channel also shows a good power penalty of less than 0.2dB at the input signal power of −5dBm per mode.

3. Gain dynamics within a TM EDFA

To investigate the gain dynamics within our ring-doped TM-EDFA, three channels at different wavelengths (two LP01 and one LP11) were multiplexed using free space optics as shown in Fig. 6(a)
Fig. 6 (a) Experimental setup for investigating transient effects in a TM-EDFA. (b) Normalized input and output signal channels in the event of modulation of Ch1. BS: beam splitter, AOM: acousto-optic modulators, SMF: single mode fiber, TMF: three mode fiber, Ch1: channel 1, NBF: narrow bandwidth filter.
. An acousto-optic modulator (AOM) was placed in one of the LP01 lines, which we refer to as Ch1, and was used to generate a square wave with 50% duty cycle in order to allow us to simulate the impact of adding/dropping one (or multiple) spatial channels. Ch2 (LP01) and Ch3 (LP11) were used as “surviving channels” in order to investigate the mode dependent gain saturation and associated transient effects. The three mode fiber output from the multiplexer was spliced to a 6m-long length of ring-doped TM-EDFA and an offset pump launch scheme was adopted in order to minimize the gain differential between the LP01 and LP11 modes. For ease of demultiplexing the individual spatial channels at the output of the TM-EDFA, the wavelengths of Ch1, Ch2, and Ch3 were chosen to be 1548nm, 1553nm, and 1558nm respectively. A tunable narrow bandpass filter (NBF, Δλ = 2nm) was then used at the output of the amplifier to separate the individual spatial channels. The temporal response of each channel was recorded using 1.2GHz InGaAs photodiodes (DET01CFC, Thorlabs) and a digital oscilloscope (TDS5032B, Tektronix). Unless otherwise stated the input power for each channel was kept constant at −6dBm (which we take to be representative of the power of a single “data stream”) and the pump power was fixed at 23dBm.

3.1. Transient response of a TM-EDFA

Figure 6(b) shows the normalized input and output signal channels as one of the channels is modulated. The add/drop input channel Ch1 has a power of 1.78dBm (equivalent in average power terms to 6 data streams each of −6dBm power) and was modulated using the AOM with a 50% duty cycle at a frequency of 10 Hz. The input of the surviving channels was kept constant (Ch2 = −6dBm, Ch3 = −6dBm equivalent to the power of 1 data stream of −6dBm power). The temporal measurements of the output signal channels are shown in Fig. 6(b). All channels experience significant signal power excursions (defined as the ratio between the maximum and minimum channel power in the absence and presence respectively of the Ch1 signal) as a result of cross gain saturation in the TM-EDFA. During a “channel-add” event (presence of Ch1), the surviving channels experience a drop in output power due to the increased competition for gain from the available population inversion resulting from the presence of Ch1. Conversely, during a “channel-drop” event, the surviving channels experience a sudden increase in inversion due to the disappearance of Ch1 and the original output power levels are restored. It is to be noted that the transient responses of the two different spatial modes (LP01 in Ch2 and LP11 in Ch3) are very similar.

To check the pump power dependence, we changed the pump power from 22.6dBm to 26.2dBm with a constant signal input power of Ch1 (1.78dBm). From Fig. 8(a)
Fig. 8 The effect of pump power on gain dynamics as a function of (a) power excursion and (b) transient setting time. (c, d) Power excursion as a function of the modulation frequency.
, we can define the transient settling time (rise or fall time) as the time taken for the power excursion to go from 10% to 90% of the maximum steady state power excursion. In Fig. 8(b), we plot the measured transient settling time for both spatial modes. Both exhibit almost identical behavior with a settling time decreasing from 5.3ms to 1.1ms when increasing the pump power from 22.6dBm to 26.2dBm. Generally, the transient settling time is dependent on the level of saturation of the amplifier and in particular becomes shorter for higher pump or signal powers. Consequently the transient response becomes faster as the pump power increases.

To examine the dependence of the power excursion on modulation frequency the modulation frequency of the AOM was gradually increased from 10Hz to 10kHz with a constant amplifier input signal power (Ch1 = 1.78dBm, Ch2 = −6dBm, Ch3 = −6dBm) and pump power (25.7dBm). As shown in Fig. 8(a), the total power excursion decreases as the modulation frequency is increased. At frequencies higher than 5kHz the surviving channels cannot follow the fast modulation and only a steady-state gain compression appears due to the slow response of the population inversion, which has an excited state lifetime of ~10ms. As shown in Fig. 8(d), the total power excursion for the LP01 and LP11 modes at 10Hz was 3.8dB and 3.2dB respectively, which decreased to less than 0.2dB at modulation frequencies higher than 5kHz.

4. Conclusion

Acknowledgment

This work was supported by the European Communities 7th Framework Programme under grant agreement 258033 (MODE-GAP).

References and links

1.

A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]

2.

R.-J. Essiambre, G. Kramer, P. J. Winzer, G. J. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol. 28(4), 662–701 (2010). [CrossRef]

3.

P. J. Winzer and G. J. Foschini, “MIMO capacities and outage probabilities in spatially multiplexed optical transport systems,” Opt. Express 19(17), 16680–16696 (2011). [CrossRef] [PubMed]

4.

R. Ryf, S. Randel, A. H. Gnauck, C. Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96km of few-mode fiber using coherent 6x6 MIMO processing,” J. Lightwave Technol. 30(4), 521–531 (2012). [CrossRef]

5.

S. Randel, R. Ryf, A. Sierra, P. J. Winzer, A. H. Gnauck, C. A. Bolle, R. J. Essiambre, D. W. Peckham, A. McCurdy, and R. Lingle Jr., “6×56-Gb/s mode-division multiplexed transmission over 33-km few-mode fiber enabled by 6×6 MIMO equalization,” Opt. Express 19(17), 16697–16707 (2011). [CrossRef] [PubMed]

6.

N. Bai, E. Ip, Y. K. Huang, E. Mateo, F. Yaman, M. J. Li, S. Bickham, S. Ten, J. Liñares, C. Montero, V. Moreno, X. Prieto, V. Tse, K. Man Chung, A. P. T. Lau, H. Y. Tam, C. Lu, Y. Luo, G. D. Peng, G. Li, and T. Wang, “Mode-division multiplexed transmission with inline few-mode fiber amplifier,” Opt. Express 20(3), 2668–2680 (2012). [CrossRef] [PubMed]

7.

C. Koebele, M. Salsi, D. Sperti, P. Tran, P. Brindel, H. Mardoyan, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, F. Cerou, and G. Charlet, “Two mode transmission at 2×100 Gb/s, over 40 km-long prototype few-mode fiber, using LCOS-based programmable mode multiplexer and demultiplexer,” Opt. Express 19(17), 16593–16600 (2011). [CrossRef] [PubMed]

8.

Y. Jung, S. Alam, Z. Li, A. Dhar, D. Giles, I. P. Giles, J. K. Sahu, F. Poletti, L. Grüner-Nielsen, and D. J. Richardson, “First demonstration and detailed characterization of a multimode amplifier for space division multiplexed transmission systems,” Opt. Express 19(26), B952–B957 (2011). [CrossRef] [PubMed]

9.

Y. Jung, S. Alam, Z. Li, A. Dhar, D. Giles, I. Giles, J. Sahu, L. Grüner-Nielsen, F. Poletti, and D. Richardson, “First demonstration of multimode amplifier for spatial division multiplexed transmission systems,” in 37th European Conference and Exposition on Optical Communications, OSA Technical Digest (CD) (Optical Society of America, 2011), paper Th.13.K.4.

10.

Q. Kang, E. L. Lim, Y. Jung, J. K. Sahu, F. Poletti, C. Baskiotis, S. U. Alam, and D. J. Richardson, “Accurate modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping and a simple LP01 pump configuration,” Opt. Express 20(19), 20835–20843 (2012). [CrossRef] [PubMed]

11.

V. A. J. M. Sleiffer, Y. Jung, V. Veljanovski, R. G. H. van Uden, M. Kuschnerov, Q. Kang, L. Grüner Nielsen, Y. Sun, D. J. Richardson, S. Alam, F. Poletti, J. K. Sahu, A. Dhar, H. Chen, B. Inan, A. M. J. Koonen, B. Corbett, R. Winfield, A. D. Ellis, and H. de Waardt, “73.6Tb/s (96x3x256-Gb/s) mode-division-multiplexed DP- 16QAM transmission with inline MM-EDFA,” in 38th European Conference and Exposition on Optical Communications, OSA Technical Digest (CD) (Optical Society of America, 2012), paper Th.3.C.

12.

V. A. J. M. Sleiffer, Y. Jung, V. Veljanovski, R. G. H. van Uden, M. Kuschnerov, H. Chen, B. Inan, L. G. Nielsen, Y. Sun, D. J. Richardson, S. U. Alam, F. Poletti, J. K. Sahu, A. Dhar, A. M. J. Koonen, B. Corbett, R. Winfield, A. D. Ellis, and H. de Waardt, “73.7 Tb/s (96 x 3 x 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA,” Opt. Express 20(26), B428–B438 (2012). [CrossRef] [PubMed]

13.

C. R. Giles, E. Desurvire, and J. R. Simpson, “Transient gain and cross talk in erbium-doped fiber amplifiers,” Opt. Lett. 14(16), 880–882 (1989). [CrossRef] [PubMed]

14.

Y. Sun, J. L. Zyskind, A. K. Srivastava, and L. Zhang, “Analytical formula for the transient response of erbium-doped fiber amplifiers,” Appl. Opt. 38(9), 1682–1685 (1999). [CrossRef] [PubMed]

15.

A. K. Srivastava, Y. Sun, J. L. Zyskind, and J. W. Sulhoff, “EDFA transient response to channel loss in WDM transmission system,” IEEE Photon. Technol. Lett. 9(3), 386–388 (1997). [CrossRef]

16.

P. C. Becker, N. A. Olsson, and J. R. Simpson, Erbium-Doped Fiber Amplifiers: Fundamentals and Technology (Academic Press, 1999), Chap. 2.

17.

J. E. Townsend, S. B. Poole, and D. N. Payne, “Solution-doping technique for fabrication of rare-earth-doped optical fibres,” Electron. Lett. 23(7), 329–331 (1987). [CrossRef]

18.

K. Lyytikainen, S. Huntington, A. Carter, P. McNamara, S. Fleming, J. Abramczyk, I. Kaplin, and G. Schötz, “Dopant diffusion during optical fibre drawing,” Opt. Express 12(6), 972–977 (2004). [CrossRef] [PubMed]

19.

F. Z. Tang, P. McNamara, G. W. Barton, and S. P. Ringer, “Multiple solution-doping in optical fibre fabrication II- Rare earth and aluminium co-doping,” J. Non-Cryst. Solids 354(15-16), 1582–1590 (2008). [CrossRef]

20.

N. Shukunami and S. Inagaki, “Doped optical fiber having core and clad structure for increasing the amplification band of an optical amplifier using the optical fiber,” US Patent 5,778,129 (1998).

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: January 29, 2013
Revised Manuscript: April 5, 2013
Manuscript Accepted: April 11, 2013
Published: April 19, 2013

Citation
Y. Jung, Q. Kang, V. A. J. M. Sleiffer, B. Inan, M. Kuschnerov, V. Veljanovski, B. Corbett, R. Winfield, Z. Li, P. S. Teh, A. Dhar, J. Sahu, F. Poletti, S. -U. Alam, and D. J. Richardson, "Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission," Opt. Express 21, 10383-10392 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-8-10383


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References

  1. A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol.28(4), 423–433 (2010). [CrossRef]
  2. R.-J. Essiambre, G. Kramer, P. J. Winzer, G. J. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol.28(4), 662–701 (2010). [CrossRef]
  3. P. J. Winzer and G. J. Foschini, “MIMO capacities and outage probabilities in spatially multiplexed optical transport systems,” Opt. Express19(17), 16680–16696 (2011). [CrossRef] [PubMed]
  4. R. Ryf, S. Randel, A. H. Gnauck, C. Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96km of few-mode fiber using coherent 6x6 MIMO processing,” J. Lightwave Technol.30(4), 521–531 (2012). [CrossRef]
  5. S. Randel, R. Ryf, A. Sierra, P. J. Winzer, A. H. Gnauck, C. A. Bolle, R. J. Essiambre, D. W. Peckham, A. McCurdy, and R. Lingle., “6×56-Gb/s mode-division multiplexed transmission over 33-km few-mode fiber enabled by 6×6 MIMO equalization,” Opt. Express19(17), 16697–16707 (2011). [CrossRef] [PubMed]
  6. N. Bai, E. Ip, Y. K. Huang, E. Mateo, F. Yaman, M. J. Li, S. Bickham, S. Ten, J. Liñares, C. Montero, V. Moreno, X. Prieto, V. Tse, K. Man Chung, A. P. T. Lau, H. Y. Tam, C. Lu, Y. Luo, G. D. Peng, G. Li, and T. Wang, “Mode-division multiplexed transmission with inline few-mode fiber amplifier,” Opt. Express20(3), 2668–2680 (2012). [CrossRef] [PubMed]
  7. C. Koebele, M. Salsi, D. Sperti, P. Tran, P. Brindel, H. Mardoyan, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, F. Cerou, and G. Charlet, “Two mode transmission at 2×100 Gb/s, over 40 km-long prototype few-mode fiber, using LCOS-based programmable mode multiplexer and demultiplexer,” Opt. Express19(17), 16593–16600 (2011). [CrossRef] [PubMed]
  8. Y. Jung, S. Alam, Z. Li, A. Dhar, D. Giles, I. P. Giles, J. K. Sahu, F. Poletti, L. Grüner-Nielsen, and D. J. Richardson, “First demonstration and detailed characterization of a multimode amplifier for space division multiplexed transmission systems,” Opt. Express19(26), B952–B957 (2011). [CrossRef] [PubMed]
  9. Y. Jung, S. Alam, Z. Li, A. Dhar, D. Giles, I. Giles, J. Sahu, L. Grüner-Nielsen, F. Poletti, and D. Richardson, “First demonstration of multimode amplifier for spatial division multiplexed transmission systems,” in 37th European Conference and Exposition on Optical Communications, OSA Technical Digest (CD) (Optical Society of America, 2011), paper Th.13.K.4.
  10. Q. Kang, E. L. Lim, Y. Jung, J. K. Sahu, F. Poletti, C. Baskiotis, S. U. Alam, and D. J. Richardson, “Accurate modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping and a simple LP01 pump configuration,” Opt. Express20(19), 20835–20843 (2012). [CrossRef] [PubMed]
  11. V. A. J. M. Sleiffer, Y. Jung, V. Veljanovski, R. G. H. van Uden, M. Kuschnerov, Q. Kang, L. Grüner Nielsen, Y. Sun, D. J. Richardson, S. Alam, F. Poletti, J. K. Sahu, A. Dhar, H. Chen, B. Inan, A. M. J. Koonen, B. Corbett, R. Winfield, A. D. Ellis, and H. de Waardt, “73.6Tb/s (96x3x256-Gb/s) mode-division-multiplexed DP- 16QAM transmission with inline MM-EDFA,” in 38th European Conference and Exposition on Optical Communications, OSA Technical Digest (CD) (Optical Society of America, 2012), paper Th.3.C.
  12. V. A. J. M. Sleiffer, Y. Jung, V. Veljanovski, R. G. H. van Uden, M. Kuschnerov, H. Chen, B. Inan, L. G. Nielsen, Y. Sun, D. J. Richardson, S. U. Alam, F. Poletti, J. K. Sahu, A. Dhar, A. M. J. Koonen, B. Corbett, R. Winfield, A. D. Ellis, and H. de Waardt, “73.7 Tb/s (96 x 3 x 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA,” Opt. Express20(26), B428–B438 (2012). [CrossRef] [PubMed]
  13. C. R. Giles, E. Desurvire, and J. R. Simpson, “Transient gain and cross talk in erbium-doped fiber amplifiers,” Opt. Lett.14(16), 880–882 (1989). [CrossRef] [PubMed]
  14. Y. Sun, J. L. Zyskind, A. K. Srivastava, and L. Zhang, “Analytical formula for the transient response of erbium-doped fiber amplifiers,” Appl. Opt.38(9), 1682–1685 (1999). [CrossRef] [PubMed]
  15. A. K. Srivastava, Y. Sun, J. L. Zyskind, and J. W. Sulhoff, “EDFA transient response to channel loss in WDM transmission system,” IEEE Photon. Technol. Lett.9(3), 386–388 (1997). [CrossRef]
  16. P. C. Becker, N. A. Olsson, and J. R. Simpson, Erbium-Doped Fiber Amplifiers: Fundamentals and Technology (Academic Press, 1999), Chap. 2.
  17. J. E. Townsend, S. B. Poole, and D. N. Payne, “Solution-doping technique for fabrication of rare-earth-doped optical fibres,” Electron. Lett.23(7), 329–331 (1987). [CrossRef]
  18. K. Lyytikainen, S. Huntington, A. Carter, P. McNamara, S. Fleming, J. Abramczyk, I. Kaplin, and G. Schötz, “Dopant diffusion during optical fibre drawing,” Opt. Express12(6), 972–977 (2004). [CrossRef] [PubMed]
  19. F. Z. Tang, P. McNamara, G. W. Barton, and S. P. Ringer, “Multiple solution-doping in optical fibre fabrication II- Rare earth and aluminium co-doping,” J. Non-Cryst. Solids354(15-16), 1582–1590 (2008). [CrossRef]
  20. N. Shukunami and S. Inagaki, “Doped optical fiber having core and clad structure for increasing the amplification band of an optical amplifier using the optical fiber,” US Patent 5,778,129 (1998).

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