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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 16 — Jul. 30, 2012
  • pp: 17386–17392
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47-km 1.25-Gbps transmission using a self-seeded transmitter with a modulation averaging reflector

Tin Komljenovic, Dubravko Babić, and Zvonimir Sipus  »View Author Affiliations


Optics Express, Vol. 20, Issue 16, pp. 17386-17392 (2012)
http://dx.doi.org/10.1364/OE.20.017386


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Abstract

We demonstrate an extended-cavity (1-km round trip) transmitter employing a reflective-semiconductor optical amplifier (RSOA) self-seeded by spectrally-sliced passive modulation-averaging reflector. We show that using modulation averaging reflectors in self-seeded transmitters improves link margin, allows a wider range of bias conditions for the RSOA by removing the modulation in the seeding light and consequently allows operation with higher extinction ratios. We furthermore demonstrate 47 km transmission at 1.25 Gbps with a 16-channel fully passive remote node. This type of transmitter is suitable for application in colorless WDM-PON systems.

© 2012 OSA

1. Introduction

2. Modulation averaging reflector

Figure 1
Fig. 1 Schematic view of the demonstrated WDM transmitter employing a modulation-averaging reflector with n mirrors. The last layer is terminated with unit reflectivity (rHR = 1), while all other mirrors are semi-transparent (r < 1).
shows a proposed self-seeded spectrally-sliced optical transmitter which includes a modulation-averaging reflector (AR). The time delay between the mirrors is τ/2 so that the round-trip between reflections at two adjacent mirrors is τ, which defines the AR design line rate Bτ = 1/τ. All the mirrors distributed along the fiber are semi-transparent with power reflection coefficient r except the last one which has reflectivity close to unity.

3. System design considerations

The active optical element was a CIP Technologies SOA-R-C-7S-FCA RSOA. According to the specification, the polarization dependent gain (PDG) ratio of this RSOA is around 20 dB. The device is modulated and biased through a 50-Ω input impedance SMA port and has a direct modulation bandwidth of 1.2 GHz. We used seven-bit pseudorandom binary sequence (PRBS7) for all experiments. In PRBS7, the bit sequence repeats after 127 bits and the maximum run length (MRL) is 7 bits. This short test sequence was used to mimic 8b10b encoding used in Gigabit Ethernet (MRL = 5 bits). The averaging is expected to improve with the increasing ratio of the expected delay in the reflector ED (expressed in bits) to the MRL of the bit stream since in most AR designs, the increase in the number of mirrors in the AR proportionally increases the ED [6

6. T. Komljenovic, D. Babić, and Z. Sipus, “Modulation-Averaging Reflectors for Extended-Cavity Optical Sources,” J. Lightwave Technol 29(15), 2249–2258 (2011). [CrossRef]

]. In the opposite limit, when MRL >> ED, the AR converges to a HR. The expected delay of the AR used in these experiments is ~20 bits, hence MRL < ED. The AWG is a 16 channel flat-top filter with Δλ = 1.2 nm (σλ = 0.37 nm) and channel separation of 200 GHz. The distance from AWG to ONU (RSOA) is L1 = 500 m. In our experiment with smaller optical bandwidth, we used a DWDM filter with Δλ = 0.6 nm (σλ = 0.17 nm; 100 GHz spacing). Based on these optical bandwidths, the coherence time τcoh of the incoming light beam is significantly shorter than the round trip time τ: τcoh << τ as is required by the design [6

6. T. Komljenovic, D. Babić, and Z. Sipus, “Modulation-Averaging Reflectors for Extended-Cavity Optical Sources,” J. Lightwave Technol 29(15), 2249–2258 (2011). [CrossRef]

]. The cavity length (L1) of this light-source is significantly larger than both the coherence length and the bit length, conditions satisfied in a laser cavity. Consequently, this is an incoherent (thermal) light source. All measurements were performed at room temperature.

4. Transmitter performance

Figure 3 illustrates the difference in seeding performance of the HR and AR systems. For the HR case, the performance improves when the RSOA drive in the logical zero is increased: either by increasing DC bias current or decreasing the modulation depth (ΔV). This is because there always has to be sufficient self-seeding power returning to the RSOA to maintain a working link; hence providing sufficient power in the logical zero at all times becomes imperative. The system with the AR behaves differently: The logical zero can be very low (even below pn-junction threshold), and only the average power must be above some limit for the system to be steadily seeded. The increase in performance due to increase in ΔV at same DC bias can be explained by highly nonlinear relation between optical power and applied current around self-seeding threshold (see Fig. 2(a)). In this way, as the modulation voltage (ΔV) is increased, the average optical power is also increased. Therefore, using AR indeed allows for a wider range of bias conditions for the RSOA relative to the HR case and provides for a potential increase in the optical modulation amplitude of the transmitter.

The output beam from the optical source in all of these experiments was linearly polarized due to high polarization dependent gain of the RSOA. We observed neither RSOA seeding instability [9

9. M. Presi and E. Ciaramella, “Stable self-seeding of R-SOAs for WDM-PONs,” Conf. on Opt. Fiber Comm. and Expo., Pisa, (2011).

] nor a need to control the polarization [5

5. E. Wong, K. L. Lee, and T. B. Anderson, “Directly modulated self-seeding reflective semiconductor optical amplifiers as colorless transmitters in wavelength division multiplexed passive optical networks,” J. Lightwave Technol. 25(1), 67–74 (2007). [CrossRef]

]. Experiments with a depolarizer placed in front of the array reflector in location 1 in Fig. 1 provided similar results as when no depolarizer was present. For these reasons we omitted the depolarizer in the experiments reported. A method to provide unpolarized light at the output of the optical source as well as undepolarized seeding light would be to insert a depolarizer inside the extended cavity at location 2 in Fig. 1.

5. Transmission experiments

We performed transmission measurements over a range of standard G.652 fiber lengths of up to 47 km (L1 + L2) for two optical bandwidths (Δλ = 0.6 nm and Δλ = 1.2 nm). The measurement system is shown in Fig. 1 and the measurement results in Fig. 5
Fig. 5 Transmission performance over various fiber lengths of standard G.652 fiber with a fully passive remote node for two optical bandwidths (Ibias = 35 mA, VRF = 2 Vpp).
. A fully passive remote node was used with C = 50%. The data shown in Fig. 5 exhibit dispersion penalty approximately consistent with the optical bandwidth and fiber length. Read from the far left limit of the data, dispersion penalties were 0.3 dB and 1 dB for Δλ = 0.6 nm and Δλ = 1.2 nm, respectively. In the high power limit, we observe an error floor that depends on both the optical bandwidth and the fiber length. In spite of the error floor, even after 47 km of transmission it is still possible to obtain BER < 10−4 in both configurations, which is sufficient for data extraction using RS(255,239) FEC code [10

10. ITU-T Recommendation G.975: Forward Error Correction for Submarine Systems (10/2000).

].

6. Conclusion

Acknowledgments

The authors gratefully acknowledge Pavle Sedić, Marcus Nebeling, and Bernd Hesse for their technical advice and help with the equipment. This work would not have been possible without the generous support from Business Innovation Center of Croatia (BICRO) and Fiber Network Engineering, Inc. of Foster City, CA, USA.

References and links

1.

C.-H. Lee, W. V. Sorin, and B. Y. Kim, “Fiber to the home using a PON infrastructure,” J. Lightwave Technol. 24(12), 4568–4583 (2006). [CrossRef]

2.

C. F. Lam, Passive Optical Networks: Principles and Practice (Academic Press, 2007).

3.

B. Kim and B.-W. Kim, “WDM-PON development and deployment as a present optical access solution,” Conf. on Opt. Fiber Comm., San Diego (2009).

4.

P. Chanclou, A. Cui, F. Geilhardt, H. Nakamura, and D. Nesset, “Network operator requirements for the next generation of optical access networks,” IEEE Netw. 26(2), 8–14 (2012). [CrossRef]

5.

E. Wong, K. L. Lee, and T. B. Anderson, “Directly modulated self-seeding reflective semiconductor optical amplifiers as colorless transmitters in wavelength division multiplexed passive optical networks,” J. Lightwave Technol. 25(1), 67–74 (2007). [CrossRef]

6.

T. Komljenovic, D. Babić, and Z. Sipus, “Modulation-Averaging Reflectors for Extended-Cavity Optical Sources,” J. Lightwave Technol 29(15), 2249–2258 (2011). [CrossRef]

7.

J. W. Goodman, Statistical Optics (Wiley Classics Library, 2000).

8.

A. J. Keating and D. D. Sampson, “Reduction of excess intensity noise in spectrum-sliced incoherent light for WDM applications,” J. Lightwave Technol. 15(1), 53–61 (1997). [CrossRef]

9.

M. Presi and E. Ciaramella, “Stable self-seeding of R-SOAs for WDM-PONs,” Conf. on Opt. Fiber Comm. and Expo., Pisa, (2011).

10.

ITU-T Recommendation G.975: Forward Error Correction for Submarine Systems (10/2000).

11.

A. D. McCoy, P. Horak, B. C. Thomsen, M. Ibsen, and D. J. Richardson, “Noise suppression of incoherent light using a gain-saturated SOA: implications for spectrum-sliced WDM systems,” J. Lightwave Technol. 23(8), 2399–2409 (2005). [CrossRef]

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2340) Fiber optics and optical communications : Fiber optics components

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: May 30, 2012
Revised Manuscript: July 8, 2012
Manuscript Accepted: July 11, 2012
Published: July 16, 2012

Citation
Tin Komljenovic, Dubravko Babić, and Zvonimir Sipus, "47-km 1.25-Gbps transmission using a self-seeded transmitter with a modulation averaging reflector," Opt. Express 20, 17386-17392 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-16-17386


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References

  1. C.-H. Lee, W. V. Sorin, and B. Y. Kim, “Fiber to the home using a PON infrastructure,” J. Lightwave Technol. 24(12), 4568–4583 (2006). [CrossRef]
  2. C. F. Lam, Passive Optical Networks: Principles and Practice (Academic Press, 2007).
  3. B. Kim and B.-W. Kim, “WDM-PON development and deployment as a present optical access solution,” Conf. on Opt. Fiber Comm., San Diego (2009).
  4. P. Chanclou, A. Cui, F. Geilhardt, H. Nakamura, and D. Nesset, “Network operator requirements for the next generation of optical access networks,” IEEE Netw. 26(2), 8–14 (2012). [CrossRef]
  5. E. Wong, K. L. Lee, and T. B. Anderson, “Directly modulated self-seeding reflective semiconductor optical amplifiers as colorless transmitters in wavelength division multiplexed passive optical networks,” J. Lightwave Technol. 25(1), 67–74 (2007). [CrossRef]
  6. T. Komljenovic, D. Babi?, and Z. Sipus, “Modulation-Averaging Reflectors for Extended-Cavity Optical Sources,” J. Lightwave Technol 29(15), 2249–2258 (2011). [CrossRef]
  7. J. W. Goodman, Statistical Optics (Wiley Classics Library, 2000).
  8. A. J. Keating and D. D. Sampson, “Reduction of excess intensity noise in spectrum-sliced incoherent light for WDM applications,” J. Lightwave Technol. 15(1), 53–61 (1997). [CrossRef]
  9. M. Presi and E. Ciaramella, “Stable self-seeding of R-SOAs for WDM-PONs,” Conf. on Opt. Fiber Comm. and Expo., Pisa, (2011).
  10. ITU-T Recommendation G.975: Forward Error Correction for Submarine Systems (10/2000).
  11. A. D. McCoy, P. Horak, B. C. Thomsen, M. Ibsen, and D. J. Richardson, “Noise suppression of incoherent light using a gain-saturated SOA: implications for spectrum-sliced WDM systems,” J. Lightwave Technol. 23(8), 2399–2409 (2005). [CrossRef]

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