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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 8 — Apr. 16, 2007
  • pp: 4863–4868
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A self-restorable architecture for bidirectional wavelength-division-multiplexed passive optical network with colorless ONUs

Kwanil Lee, Sang Bae Lee, Ju Han Lee, Young-Geun Han, Sil-Gu Mun, Sang-Mook Lee, and Chang-Hee Lee  »View Author Affiliations


Optics Express, Vol. 15, Issue 8, pp. 4863-4868 (2007)
http://dx.doi.org/10.1364/OE.15.004863


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Abstract

We propose and experimentally demonstrate a novel protection scheme for wavelength-division-multiplexed passive optical network (WDM-PON) employing colorless optical transceivers. The proposed network employs 2 × N arrayed waveguide gratings (AWGs) to utilize its routing characteristics. The colorless operation is achieved by using wavelength-locked Fabry-Perot laser diodes (FP-LDs) injected with spectrum-sliced amplified spontaneous emission (ASE) light. The experimental results show that the restoration can be achieved within 8 ms against the feeder fiber fault and the power penalty introduced by the restoration process is negligible.

© 2007 Optical Society of America

1. Introduction

In this paper, we propose a new self-restorable architecture for bidirectional WDM-PON. It utilizes two different wavelength assignments and a pair of 2 × N AWGs, each port of AWGs is coupled to a working and a backup feeder fiber, respectively. Thus, in the case of a working fiber failure, the interrupted signal traffic is recovered via a backup fiber. In this case, the assigned wavelengths are one channel shifted to the longer wavelength side due to the routing property of the AWGs. This scheme works for WDM-PONs employing colorless transceivers. It can be cost-effectively implemented using a minimum amount of redundant network resources. The feasibility of the proposed scheme is experimentally verified using the WDM-PON based on low-cost FP-LDs wavelength-locked to the spectrum-sliced light from a broadband erbium fiber ASE light.

2. Proposed self-restorable network architecture

Figure 1 shows the proposed scheme in a bidirectional WDM-PON employing ASE-injected FP-LDs, which uses two different wavelength bands for upstream and downstream transmission. It consists of OLT located in a central office (CO), a RN connected to the OLT by a working feeder fiber or a backup fiber, and a plurality of subscriber units (N ONUs) connected to the RN through distribution fibers. The OLT comprises two broadband light sources (BLS), a fiber fault monitor, two 1 × 2 optical switch units, a 2 × N AWG (AWG1), and N transceivers (TRx). The wavelength bands of two different BLSs (A- and B-band) are separated by an integer multiple of the free spectral range (FSR) of the AWG. The operating principle of the colorless bidirectional WDM-PON with FP-LDs wavelength-locked to an injected spectrum-sliced ASE light is fully described in Ref. [12

12. H. D. Kim, S. -G Kang, and C. -H. Lee, “A low cost WDM source with an ASE injected Fabry-Perot semiconductor laser,” IEEE Photon. Technol. Lett. 12, 1067–1069 (2000). [CrossRef]

]. The RN consists of 2 × N AWG (AWG2). Moreover, the first port of AWG2 is coupled to a working fiber, while the second port of AWG2 is coupled to a backup fiber. For the restoration of the network against the feeder fiber failure, it uses the routing property of AWGs and a backup fiber. For this scheme, colorless operation of the optical transceivers both at the OLT and the ONUs is essential, since the assigned wavelengths are changed in the process of restoration.

Under normal operation, since the signal traffic is carried via the working fiber, the wavelengths {λ1b ~ λNb} and {λ1a ~ λNa} are assigned for the downstream and the upstream signals, respectively, as shown in Fig. 1(b). However, in the case of feeder fiber failure, the fault monitor detects the working feeder fiber failure by monitoring the optical power of upstream signals from ONUs and then triggers 1 × 2 optical switches to change their connecting states to the other ports of AWGs. As a result, the upstream traffic can be communicated via the wavelengths {λ2a ~ λ(N+1)a}, while the downstream signals are assigned to the wavelengths {λ2b ~ λ(N+1)b}. In this way, the proposed network architecture offers a self restoration function.

Fig. 1. Self-restorable bidirectional WDM-PON scheme.

3. Experiment and results

In order to verify the proposed scheme, we performed an experimental demonstration using the setup shown in Fig. 2. We composed 8-channel WDM-PON with 16 FP-LDs wavelength-locked by spectrum-sliced ASE injection. Here, the FP-LDs are directly modulated at 155 Mb/s with a 231-1 pseudo-random bit sequence (PRBS) data due to limited availability of fast laser drivers in the laboratory. It may be noted that the proposed scheme works for WDM-PONs with colorless optical transceivers regardless of the transmission speed. The AWG1 at the CO and the AWG2 at the RN have a 100-GHz channel spacing and a free spectral range (FSR) of 31 nm. We used C- and L-bands for the upstream and downstream transmission, respectively. Thus C/L band WDM filters were used to separate upstream and downstream signals. To experimentally simulate the feeder fiber break, we inserted a typical fiber optic switch (OS3 in Fig. 2) between the working fiber and the first port of AWG2. The downstream and upstream signals are transmitted through the working fiber in the normal state. When a fault occurs in the working fiber (OS3 is in the ‘OFF’ state), the controller detects the loss of the upstream signal and triggers the 1 × 2 optical switches (OS1 and OS2) to the ‘restoration’ state to redirect the signals to the backup fiber.

Fig. 2. Experimental setup (P1: Measurement point, OS: Optical switch, C/L: WDM filter, PPG: Pulse pattern generator, TIA: Trans impedance amplifier, BLS: Broadband light source).

The optical spectra of the downstream and upstream signals were monitored at the position P1 by use of a tap coupler and an optical spectrum analyzer (OSA). Figure 3 shows the measured optical spectra of the downstream and upstream signals. The solid and dash lines represent signals in the normal and restoration state, respectively. Note that all wavelengths for the downstream and upstream signals in the restoration state are 100 GHz shifted to the longer wavelength due to the routing property of AWGs. The power difference of the upstream signals between in the normal and restoration states is due to insertion losses of OS3, 90/10 tap coupler, and optical connectors. Also, the different power and spectral shape of each channel in Fig. 3 is attributed to the fact that power of ASE-injected FP-LDs is very sensitive to the front facet reflectivity of each FP-LD and the detuning condition between the lasing wavelength of FP-LD mode and injected ASE wavelength. When the FP-LD mode completely overlaps with the injected sliced ASE, the FP-LD has a single peak spectrum and the higher optical power. On the other hand, under a large detuning condition, it has a double peak spectrum and the lower optical power. But this power variation associated with each channel does not cause any difficulty in network planning due to sufficient power margin. In other words, the transmission performance of the network is maintained regardless of the detuning.

Fig. 3. Measured optical spectra in the normal (solid line) and restoration (dash line) state.

We also measured the restoration switching time. Figure 4 shows the measured restoration characteristics of the proposed WDM-PON. The upper trace represents the output of the monitor signal, while the middle and lower traces represent the optical power of the upstream and downstream signals at the OLT and ONU ends, respectively. The restoration time was measured to be about 8 ms. Double peaks in the upstream and downstream signals in Fig. 4 can be attributed to the following two factors: the difference in switching time between OS1 and OS2 and a small amount of transient overshoot in the switching operation.

Fig. 4. Measured restoration switching time.

Finally, we measured the bit-error-rate (BER) performance in the normal and restoration states with channel 6, and the measurement results are shown in Fig. 5. As a reference, the BER performances for the back-to-back transmission are also shown. In each case, the BER performance was observed to be slightly different. The difference can be attributed to the fact that the relative intensity noise (RIN) of ASE-injected FP-LD depends on the detuning condition between the lasing wavelength of FP-LD mode and injected ASE wavelength. The ASE-injected FP-LD with single peak spectrum has a better performance than the FP-LD with double peak spectrum. This explains why the upstream signal in the normal state, which corresponds to the asymmetric double peak spectrum around 1552nm in Fig. 3, has a worse BER performance [solid circle in Fig. 5] than in the restoration state [open circle]. However, considering the different detuning after the restoration process, we found that the restoration process did not cause any power penalty.

Fig. 5. Measured BER curves of downstream and upstream signals in the normal and restoration state (+ x: back-to-back transmission, solid: normal state, open: restoration state).

4. Conclusion

We have proposed a novel, self-restorable bidirectional WDM-PON architecture based on the periodic spectral transmission property and routing characteristics of 2 × N AWG and experimentally demonstrated its feasibility using a WDM PON system incorporating low-cost FP-LDs wavelength-locked to an injected spectrum-sliced ASE light. The experiment showed that the restoration switching could be done within 8 ms with negligible power penalty. We believe that this proposed self-restorable WDM-PON should prove to be useful for future access network applications due to its simple architecture.

References and links

1.

S. -J. Park, C. -H. Lee, K. -T. Jeong, H. -J. Park, J. -G. Ahn, and K. -H. Song, “Fiber-to-the-home services based on wavelength-division-multiplexing passive optical network,” J. Lightwave Technol. 22, 2582–2591 (2004). [CrossRef]

2.

C. K. Chan, F. Tong, L. K. Chen, K. P. Ho, and D. Lam, “Fiber-fault identification for branched access networks using a wavelength-sweeping monitoring source,” IEEE Photon. Technol. Lett. 5, 614–616 (1999). [CrossRef]

3.

J. -H. Park, J. -S Baik, and C. -H. Lee, “Fault-localization in WDM-PONs,” in Proc. Optical Fiber Communication Conference (Optical Society of America, 2006), paper JThB79.

4.

U. Hilbk, M. Burmeister, B. Hoen, T. Herems, J. Saniter, and F. -J. Westphal, “Selective OTDR measurements at the central office of individual fiber links in a PON,” in Proc. Optical Fiber Communication Conference (Optical Society of America, 1997), paper TuK3. [CrossRef]

5.

K. Lee, S. B. Kang, D. S. Lim, H. K. Lee, and W. V. Sorin, “Fiber link loss monitoring scheme in bidirectional WDM transmission using ASE-injected FP-LD,” IEEE Photon. Technol. Lett. 18, 523–525 (2006). [CrossRef]

6.

T. J. Chan, C. K. Chan, L. K. Chen, and F. Tong, “A self-protected architecture for wavelength-division-multiplexed passive optical networks,” IEEE Photon. Technol. Lett. 15, 1660–1662 (2003). [CrossRef]

7.

X. Sun, C. K. Chan, and L. K. Chen, “A survivable WDM-PON architecture with centralized alternate-path protection switching for traffic restoration,” IEEE Photon. Technol. Lett. 18, 631–633 (2006). [CrossRef]

8.

S. Park, D. K. Jung, D. J. Shin, H. S. Shin, S. Hwang, Y. J. Oh, and C. S. Shim, “Bidirectional wavelength-division-multiplexing self-healing passive optical network,” in Proc. Optical Fiber Communication Conference (Optical Society of America, Anaheim, CA., 2005), paper JWA57.

9.

E. S. Son, K. H. Han, J. H. Han, J. H. Lee, and Y. C. Chung, “Survivable network architectures for WDM-PON,” in Proc. Optical Fiber Communication Conference (Optical Society of America, Anaheim, CA., 2005), paper OFI4.

10.

Z. Wang, X. Sun, C. Lin, C. -K. Chan, and L. K. Chen, “A novel centrally controlled protection scheme for traffic restoration in WDM passive optical networks,” IEEE Photon. Technol. Lett. 17, 717–719 (2005). [CrossRef]

11.

H. Nakamura, H. Suzuki, J. Kani, and K. Iwatsuki, “Reliable wide-area wavelength-division-multiplexing passive optical network accommodating GbE and 10-Gb Ethernet services,” IEEE. J. Lightwave. Technol. 24, 2045–2051(2006). [CrossRef]

12.

H. D. Kim, S. -G Kang, and C. -H. Lee, “A low cost WDM source with an ASE injected Fabry-Perot semiconductor laser,” IEEE Photon. Technol. Lett. 12, 1067–1069 (2000). [CrossRef]

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4250) Fiber optics and optical communications : Networks

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: February 9, 2007
Revised Manuscript: April 3, 2007
Manuscript Accepted: April 4, 2007
Published: April 6, 2007

Citation
Kwanil Lee, Sang Bae Lee, Ju Han Lee, Young-Geun Han, Sil-Gu Mun, Sang-Mook Lee, and Chang-Hee Lee, "A self-restorable architecture for bidirectional wavelength-division-multiplexed passive optical network with colorless ONUs," Opt. Express 15, 4863-4868 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-8-4863


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References

  1. S. -J. Park, C. -H. Lee, K. -T. Jeong, H. -J. Park, J. -G. Ahn, and K. -H. Song, "Fiber-to-the-home services based on wavelength-division-multiplexing passive optical network," J. Lightwave Technol. 22, 2582- 2591 (2004). [CrossRef]
  2. C. K. Chan, F. Tong, L. K. Chen, K. P. Ho, and D. Lam, "Fiber-fault identification for branched access networks using a wavelength-sweeping monitoring source," IEEE Photon. Technol. Lett. 5, 614-616 (1999). [CrossRef]
  3. J. -H. Park, J. -S, Baik, C. -H. Lee, "Fault-localization in WDM-PONs," in Proc. Optical Fiber Communication Conference (Optical Society of America, 2006), paper JThB79.
  4. U. Hilbk, M. Burmeister, B. Hoen, T. Herems, J. Saniter, and F. -J. Westphal, "Selective OTDR measurements at the central office of individual fiber links in a PON," in Proc. Optical Fiber Communication Conference (Optical Society of America, 1997), paper TuK3. [CrossRef]
  5. K. Lee, S. B. Kang, D. S. Lim, H. K. Lee, and W. V. Sorin, "Fiber link loss monitoring scheme in bidirectional WDM transmission using ASE-injected FP-LD," IEEE Photon. Technol. Lett. 18, 523-525 (2006). [CrossRef]
  6. T. J. Chan, C. K. Chan, L. K. Chen, and F. Tong, "A self-protected architecture for wavelength-division-multiplexed passive optical networks," IEEE Photon. Technol. Lett. 15, 1660-1662 (2003). [CrossRef]
  7. X. Sun, C. K. Chan, and L. K. Chen, "A survivable WDM-PON architecture with centralized alternate-path protection switching for traffic restoration," IEEE Photon. Technol. Lett. 18, 631-633 (2006). [CrossRef]
  8. S. Park, D. K. Jung, D. J. Shin, H. S. Shin, S. Hwang, Y. J. Oh, and C. S. Shim, "Bidirectional wavelength-division-multiplexing self-healing passive optical network," in Proc. Optical Fiber Communication Conference (Optical Society of America, Anaheim, CA., 2005), paper JWA57.
  9. E. S. Son, K. H. Han, J. H. Han, J. H. Lee, and Y. C. Chung, " Survivable network architectures for WDM-PON," in Proc. Optical Fiber Communication Conference (Optical Society of America, Anaheim, CA., 2005), paper OFI4.
  10. Z. Wang, X. Sun, C. Lin, C. -K. Chan, and L. K. Chen, "A novel centrally controlled protection scheme for traffic restoration in WDM passive optical networks," IEEE Photon. Technol. Lett. 17,717-719 (2005). [CrossRef]
  11. H. Nakamura, H. Suzuki, J. Kani, and K. Iwatsuki, "Reliable wide-area wavelength-division-multiplexing passive optical network accommodating GbE and 10-Gb Ethernet services," IEEE.J. Lightwave. Technol. 24, 2045-2051(2006). [CrossRef]
  12. H. D. Kim, S. -G Kang, and C. -H. Lee, "A low cost WDM source with an ASE injected Fabry-Perot semiconductor laser," IEEE Photon. Technol. Lett. 12,1067-1069 (2000). [CrossRef]

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