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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 27 — Dec. 19, 2011
  • pp: 26928–26935
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Fiber optical CATV transport systems based on PM and light injection-locked DFB LD as a duplex transceiver

Heng-Sheng Su, Chung-Yi Li, Wen-Yi Lin, Hai-Han Lu, Ching-Hung Chang, Po-Yi Wu, Ying-Pyng Lin, and Chia-Yi Chen  »View Author Affiliations


Optics Express, Vol. 19, Issue 27, pp. 26928-26935 (2011)
http://dx.doi.org/10.1364/OE.19.026928


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Abstract

A bidirectional fiber optical CATV transport system employing phase modulation (PM) scheme and frequency up-conversion technique to deal with downstream CATV signals, and using light injection-locked distributed feedback laser diode (DFB LD) as a duplex transceiver at the receiving site is proposed and experimentally demonstrated. With optimum injection wavelength and power level, a DFB LD is efficiently employed for both the transmitter and receiver operations. Such DFB LD is used to replace the functions of delay interferometer (DI) and CATV receiver, and also to be as the upstream light source. To the best of our knowledge, it is the first time to successfully utilize a DFB LD to detect the phase-modulated CATV signals. Impressive experimental results prove that our proposed systems not only can employ the PM scheme and the frequency up-conversion technique to optimize the overall performances of systems, but also can use an injection-locked DFB LD to detect the downstream phase-modulated CATV signals as well as to transmit the upstream CATV ones simultaneously.

© 2011 OSA

1. Introduction

2. Experimental setup

To verify the implementation of frequency up-conversion, two microwave signal generators are used to simulate two up-converted CATV channels. The experimental configuration of the simulated up-conversion CATV transport system is shown in Fig. 2
Fig. 2 The experimental configuration of the simulated up-conversion CATV transport systems.
. Two microwave carriers (f1 = 9.994 GHz, f2 = 10 GHz) are provided for two-tone signal measurement. Over a 40-km SMF link, the optical signal is injected into another DFB LD to obtain the microwave signals, and then frequency down-converted into the CATV frequency band (CH77 and CH78). Subsequently, the signal is purified by passing through a RF BPF (50-550 MHz), and finally the third-order intermodulation distortion to carrier ratio (IMD3/C) parameter is analyzed by a spectrum analyzer.

3. Experimental results and discussions

Electrical spectrum of the received two carriers (CH77 and CH78, down-converted from f1 and f2) is shown in Fig. 3
Fig. 3 Electrical spectrum of the received two carriers (CH77 and CH78, down-converted from f1 and f2).
. It is obvious that the residue IMD3/C level of −69 dBc is obtained. In PM scheme, noise and distortion will be reduced dramatically resulting in a large improvement of IMD3/C value. There are many advantages to PM and one of them is a great reduction in noise and distortion which will affect the signals amplitude. If the changes in amplitude can be reduced, then systems will have good transmission performances. For PM scheme, the amplitude limitation removes the effect of noise and distortion but does not disturb the original modulating information. In addition, it has been experimentally shown that a DFB LD injection-locked to a phase-modulated optical signal can convert the PM signal into the IM one. It should be noted that no RF signal is obtained as the DFB LD is not injection-locked to the phase-modulated signal. However, as the DFB LD is locked to the phase-modulated signal, two carriers at frequencies of 9.994 and 10 GHz are detected. The outer boundary of the locking range for laser under light injection is given by [11

11. S. Mohrdiek, H. Burkhard, and H. Walter, “Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection,” IEEE/OSA, J. Lightwave Technol. 12(3), 418–424 (1994). [CrossRef]

]
d<±kc2πSiS(1+α2)
(1)
where the frequency detuning d = finjffree (finj is the frequency of master laser, ffree is the frequency of free running slave laser), kc is the coupling coefficient, Si/S is the injection ratio, and αis the linewidth enhancement factor. An optimum injection locking can be achieved if the frequency of the master laser (DFB LD1) is lower than that of the slave laser (DFB LD3), i.e., negative detuning [11

11. S. Mohrdiek, H. Burkhard, and H. Walter, “Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection,” IEEE/OSA, J. Lightwave Technol. 12(3), 418–424 (1994). [CrossRef]

-12

12. G. Yabre, “Effect of relatively strong light injection on the chirp-to-power ratio and the 3 dB bandwidth of directly modulated semiconductor lasers,” IEEE/OSA, J. Lightwave Technol. 14(10), 2367–2373 (1996). [CrossRef]

]. Within the injection locking range, the frequency of the slave laser is locked nearly to the frequency of the master laser. However, outside the locking range, severe oscillation occurs. When DFB LD3 is injection-locked, its optical spectrum shifts a slightly longer wavelength (0.12 nm), matching to that of λ1. The injection locking behavior happens when an injection source laser is slightly detuned to wavelength slightly longer than that of the injection-locked laser. The optimal injection locking condition is found when the detuning between λ1 and the λ3 is + 0.12 nm (1549.53nm - 1549.41nm = 0.12nm) where the best CSO and CTB performances are found.

Figure 4 (a), (b) and (c)
Fig. 4 The measured downstream (a) CNR, (b) CSO, and (c) CTB values of system II; as DFB LD3 under 3, 0, and −3 dBm injection power levels, respectively.
illustrate the measured downstream CNR, CSO and CTB values of system II; as the DFB LD3 under 3, 0, and −3 dBm injection power levels, respectively. Employing an injection-locked semiconductor laser to detect phase-modulated optical signal was firstly proposed by Lidoyne and Gallion in [7

7. O. Lidoyne and P. Gallion, “Analysis of receiver using injection-locked semiconductor laser for direct demodulation of PSK optical signals,” Electron. Lett. 27(11), 995–997 (1991). [CrossRef]

], but this is the first time to employ this technique in a multi-carrier transport system. From these three figures, it is clear that the measured CNR, CSO and CTB values will be affected by the DFB LD3 injection power level. When the injection power is −3 dBm, the CNR, CSO and CTB values are limited at around 49, 66, and 65 dB, respectively. Nevertheless, when the injection power is increased up to 3 dBm, the CNR, CSO and CTB values are increased by 2.5, 5, and 5 dB, respectively. These results prove that the DFB LD3 is successfully employed to replace a DI and a CATV receiver, as well as its detection efficiency is in proportion to the injection power level.

Figure 5(a), (b) and (c)
Fig. 5 The measured downstream (a) CNR, (b) CSO, and (c) CTB values for BTB, system I, and system II (DFB LD3 with 3 dBm injection).
show the measured downstream CNR, CSO and CTB values for back-to-back (BTB), system I (40km IM), and system II (40km PM, DFB LD3 under 3 dBm injection power level), respectively. For CNR performance (Fig. 5(a)), there exists a power penalty of about 1.5 dB between the BTB case (≥53 dB) and systems I and II (≥51.5 dB). It also indicates that the CNR values of systems I and II are almost identical. The CNR value can be improved by higher EDFA input power. Higher EDFA input power increases EDFAs’ CNRsig-sp (due to signal-spontaneous beat noise) and CNRsp-sp (due to spontaneous-spontaneous beat noise) values, in which leading to an improvement of CNR value. Similarly, good performances of CSO/CTB are achieved for systems I (≥73/72 dB) and II (≥71/70 dB), due to the use of up-converted technique to reduce the CSO/CTB distortions and the constant power operation characteristic of PM scheme [5

5. P. Y. Wu, H. H. Lu, C. L. Ying, C. Y. Li, and H. S. Su, “An up-converted phase modulated fiber optical CATV transport system,” IEEE/OSA, J. Lightwave Technol. 29(16), 2422–2427 (2011). [CrossRef]

]. There exists a power penalty of about 3 dB between the BTB case (≥76/75 dB) and system I. This CSO/CTB degradations can be attributed to the fiber dispersion-induced distortion. And further, there exists a power penalty of about 2 dB between the system I and system II. The dynamic nonlinearity of the laser is very large at the resonance frequency when light injection is employed. As RF band around the resonance frequency is being used for the CATV transmission, this large dynamic laser nonlinearity degrades the transmission performance of systems. Nevertheless, the CSO/CTB performances of system II still satisfy the requirements of fiber optical CATV systems at the optical node (≥60/60 dB). Furthermore, to achieve acceptable quality of service (QoS) for clients, the received optical power level at the clients’ premises needs to be kept at −3 ~ + 3 dBm. Since the CATV signal is broadcast to all subscribers after received by the CATV receiver. To meet the CNR/CSO/CTB demands at the subscriber (43/53/53 dB), the maximum subscriber numbers for each CATV receiver are 200. Light injection-locked DFB LD as a duplex transceiver is worth employing owing to sophisticated and expensive DI as well as CATV receiver are not required at the receiving site. Furthermore, in order to know how much CSO and CTB performances improvements are based on each of the schemes, systems II with up-converted technique alone has been employed to measure the CSO and CTB values (>66/65 dB). Also, system II with PM scheme alone has been used to measure the CSO and CTB values (>67/66 dB). It means that when system II employs the up-converted technique or the PM scheme alone to compensate the CSO and CTB distortions, the compensation results are limited. The large improvements in CSO and CTB performances (>71/70 dB) are the results of employing up-converted and PM schemes simultaneously.

4. Conclusions

A novel and bidirectional fiber optical CATV transport system is proposed and experimentally demonstrated. By employing a frequency up-conversion technique and a PM scheme to optimized the downstream transmission performances, some unwanted noise and distortion are reduced dramatically. And further, by using an injection-locked DFB LD to detect the downstream phase modulated CATV signals and to transmit the upstream CATV ones simultaneously, sophisticated and expensive DI as well as CATV receiver are not required at the receiveing site. Our proposed systems present brilliant performances and cost-effective characteristic in transmitting CATV signals over fiber links.

References and links

1.

S. J. Tzeng, H. H. Lu, C. Y. Li, K. H. Chang, and C. H. Lee, “CSO/CTB performance improvement by using Fabry-Perot etalon at the receiving site,” Prog. Electromagn Res Lett. 6(14), 107–113 (2009). [CrossRef]

2.

H. H. Lu, A. S. Patra, S. J. Tzeng, H. C. Peng, and W. I. Lin, “Improvement of fiber optical CATV transport systems performance based on lower-frequency side mode injection-locked technique,” IEEE Photon. Technol. Lett. 20(5), 351–353 (2008). [CrossRef]

3.

D. Piehler, X. Zou, C. Y. Kuo, A. Nilsson, J. Kleefeld, G. Garcia, J. D. Ralston, and A. Mathur, “55dB CNR over 50km of fiber in an 80-channel externally-modulated AM-CATV system without optical amplification,” Electron. Lett. 33(3), 226–227 (1997). [CrossRef]

4.

H. Kim, S. B. Jun, and Y. C. Chung, “Raman crosstalk suppression in CATV overlay passive optical network,” IEEE Photon. Technol. Lett. 19 (9), 695–697 (2007). [CrossRef]

5.

P. Y. Wu, H. H. Lu, C. L. Ying, C. Y. Li, and H. S. Su, “An up-converted phase modulated fiber optical CATV transport system,” IEEE/OSA, J. Lightwave Technol. 29(16), 2422–2427 (2011). [CrossRef]

6.

X. Xue, X. Zheng, H. Zhang, and B. Zhou, “Optical beamforming networks employing phase modulation and direct detection,” Opt. Commun. 284(12), 2695–2699 (2011). [CrossRef]

7.

O. Lidoyne and P. Gallion, “Analysis of receiver using injection-locked semiconductor laser for direct demodulation of PSK optical signals,” Electron. Lett. 27(11), 995–997 (1991). [CrossRef]

8.

N. Hoghooghi, I. Ozdur, S. Bhooplapur, and P. J. Delfyett, “Direct modulation and channel filtering of phase-modulated signals using an injection-locked VCSEL,” IEEE Photon. Technol. Lett. 22(20), 1509–1511 (2010). [CrossRef]

9.

Q. Gu, W. Hofmann, M. C. Amann, and L. Chrostowski, “Optically injection-locked VCSEL as a duplex transmitter/receiver,” IEEE Photon. Technol. Lett. 20(7), 463–465 (2008). [CrossRef]

10.

S. Wieczorek, W. W. Chow, L. Chrostowski, and C. J. Chang-Hasnain, “Improved semiconductor-laser dynamics from induced population pulsation,” IEEE J. Sel. Top. Quantum Electron. 42(6), 552–562 (2006). [CrossRef]

11.

S. Mohrdiek, H. Burkhard, and H. Walter, “Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection,” IEEE/OSA, J. Lightwave Technol. 12(3), 418–424 (1994). [CrossRef]

12.

G. Yabre, “Effect of relatively strong light injection on the chirp-to-power ratio and the 3 dB bandwidth of directly modulated semiconductor lasers,” IEEE/OSA, J. Lightwave Technol. 14(10), 2367–2373 (1996). [CrossRef]

13.

H. H. Lu, H. C. Peng, W. S. Tsai, C. C. Lin, S. J. Tzeng, and Y. Z. Lin, “Bidirectional hybrid CATV/radio-over-fiber WDM transport system,” Opt. Lett. 35(3), 279–281 (2010). [CrossRef] [PubMed]

14.

M. R. Phillips and D. M. Ott, “Crosstalk due to optical fiber nonlinearities in WDM CATV lightwave systems,” IEEE/OSA, J. Lightwave Technol. 17(10), 1782–1792 (1999). [CrossRef]

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
(060.2380) Fiber optics and optical communications : Fiber optics sources and detectors

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: November 2, 2011
Revised Manuscript: December 1, 2011
Manuscript Accepted: December 12, 2011
Published: December 16, 2011

Citation
Heng-Sheng Su, Chung-Yi Li, Wen-Yi Lin, Hai-Han Lu, Ching-Hung Chang, Po-Yi Wu, Ying-Pyng Lin, and Chia-Yi Chen, "Fiber optical CATV transport systems based on PM and light injection-locked DFB LD as a duplex transceiver," Opt. Express 19, 26928-26935 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-27-26928


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References

  1. S. J. Tzeng, H. H. Lu, C. Y. Li, K. H. Chang, and C. H. Lee, “CSO/CTB performance improvement by using Fabry-Perot etalon at the receiving site,” Prog. Electromagn Res Lett.6(14), 107–113 (2009). [CrossRef]
  2. H. H. Lu, A. S. Patra, S. J. Tzeng, H. C. Peng, and W. I. Lin, “Improvement of fiber optical CATV transport systems performance based on lower-frequency side mode injection-locked technique,” IEEE Photon. Technol. Lett.20(5), 351–353 (2008). [CrossRef]
  3. D. Piehler, X. Zou, C. Y. Kuo, A. Nilsson, J. Kleefeld, G. Garcia, J. D. Ralston, and A. Mathur, “55dB CNR over 50km of fiber in an 80-channel externally-modulated AM-CATV system without optical amplification,” Electron. Lett.33(3), 226–227 (1997). [CrossRef]
  4. H. Kim, S. B. Jun, and Y. C. Chung, “Raman crosstalk suppression in CATV overlay passive optical network,” IEEE Photon. Technol. Lett.19 (9), 695–697 (2007). [CrossRef]
  5. P. Y. Wu, H. H. Lu, C. L. Ying, C. Y. Li, and H. S. Su, “An up-converted phase modulated fiber optical CATV transport system,” IEEE/OSA, J. Lightwave Technol.29(16), 2422–2427 (2011). [CrossRef]
  6. X. Xue, X. Zheng, H. Zhang, and B. Zhou, “Optical beamforming networks employing phase modulation and direct detection,” Opt. Commun.284(12), 2695–2699 (2011). [CrossRef]
  7. O. Lidoyne and P. Gallion, “Analysis of receiver using injection-locked semiconductor laser for direct demodulation of PSK optical signals,” Electron. Lett.27(11), 995–997 (1991). [CrossRef]
  8. N. Hoghooghi, I. Ozdur, S. Bhooplapur, and P. J. Delfyett, “Direct modulation and channel filtering of phase-modulated signals using an injection-locked VCSEL,” IEEE Photon. Technol. Lett.22(20), 1509–1511 (2010). [CrossRef]
  9. Q. Gu, W. Hofmann, M. C. Amann, and L. Chrostowski, “Optically injection-locked VCSEL as a duplex transmitter/receiver,” IEEE Photon. Technol. Lett.20(7), 463–465 (2008). [CrossRef]
  10. S. Wieczorek, W. W. Chow, L. Chrostowski, and C. J. Chang-Hasnain, “Improved semiconductor-laser dynamics from induced population pulsation,” IEEE J. Sel. Top. Quantum Electron.42(6), 552–562 (2006). [CrossRef]
  11. S. Mohrdiek, H. Burkhard, and H. Walter, “Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection,” IEEE/OSA, J. Lightwave Technol.12(3), 418–424 (1994). [CrossRef]
  12. G. Yabre, “Effect of relatively strong light injection on the chirp-to-power ratio and the 3 dB bandwidth of directly modulated semiconductor lasers,” IEEE/OSA, J. Lightwave Technol.14(10), 2367–2373 (1996). [CrossRef]
  13. H. H. Lu, H. C. Peng, W. S. Tsai, C. C. Lin, S. J. Tzeng, and Y. Z. Lin, “Bidirectional hybrid CATV/radio-over-fiber WDM transport system,” Opt. Lett.35(3), 279–281 (2010). [CrossRef] [PubMed]
  14. M. R. Phillips and D. M. Ott, “Crosstalk due to optical fiber nonlinearities in WDM CATV lightwave systems,” IEEE/OSA, J. Lightwave Technol.17(10), 1782–1792 (1999). [CrossRef]

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