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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 20 — Sep. 27, 2010
  • pp: 21162–21168
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18 wavelengths 83.9Gs/s optical sampling clock for photonic A/D converters

Guiling Wu, Siqi Li, Xinwan Li, and Jianping Chen  »View Author Affiliations


Optics Express, Vol. 18, Issue 20, pp. 21162-21168 (2010)
http://dx.doi.org/10.1364/OE.18.021162


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Abstract

In this paper, a simple approach to generate the time-wavelength interleaved sampling clock for photonic A/D converters is proposed using commercially available mode-locked femtosecond fiber laser and optical wavelength/time division multiplexing (WDM/OTDM) techniques with low cost passive optical components. A time and wavelength mapping module is configured using specially designed wavelength division multiplexer and mechanical tunable fiber stretchers. OTDM modules with low optical insertion loss and flexibly configurable multiple factor are implemented with the fused-biconical optical fiber couplers. Experiment is carried out using 18 WDM channels and 128 times OTDM to demonstrate the generation of 83.9Gs/s time-wavelength interleaved sampling clock.

© 2010 OSA

1. Introduction

In order to overcome the limitation of electronic analog-to-digital converters (EADCs) in ultra high speed applications, such as high performance communications, advanced radar and electronic instrumentation, etc., photonic ADCs (PADCs) have been proposed as a promising alternative with the unique features of ultra stable and high-speed sampling, broad bandwidth, and nearly lossless signal remoting [1

1. G. C. Valley, “Photonic analog-to-digital converters,” Opt. Express 15(5), 1955–1982 (2007). [CrossRef] [PubMed]

,2

2. F. X. Kartner, R. Amataya, G. Barbastathis, H. Byun, F. Gan, C. W. Holzwarth, J. L. Hoyt, E. P. Ippen, O. O. Olubuyide, J. S. Orcutt, M. Park, M. Perrott, M. A. Popovic, P. T. Rakich, R. J. Ram, H. I. Smith, M. Geis, M. Grein, T. Lyszczarz, S. Spector, and J. U. Yoon, “Silicon electronic photonic integrated circuits for high speed analog to digital conversion,” 3rd OEEE International Conference on Group IV Photonics 2006, pp. 203–205.

]. In many schemes studied so far, the wavelength-division multiplexing(WDM) based photonic ADC, which employs time-wavelength interleaved optical sampling and electronic quantization, is one of the most practically feasible methods [2

2. F. X. Kartner, R. Amataya, G. Barbastathis, H. Byun, F. Gan, C. W. Holzwarth, J. L. Hoyt, E. P. Ippen, O. O. Olubuyide, J. S. Orcutt, M. Park, M. Perrott, M. A. Popovic, P. T. Rakich, R. J. Ram, H. I. Smith, M. Geis, M. Grein, T. Lyszczarz, S. Spector, and J. U. Yoon, “Silicon electronic photonic integrated circuits for high speed analog to digital conversion,” 3rd OEEE International Conference on Group IV Photonics 2006, pp. 203–205.

,3

3. T. R. Clark, J. U. Kang, and R. D. Esman, “Performance of a time- and wavelength-interleaved photonic sampler for analog-digital conversion,” IEEE Photon. Technol. Lett. 11(9), 1168–1170 (1999). [CrossRef]

]. Its crucial issue is the generation of time-wavelength interleaved sampling clock [3

3. T. R. Clark, J. U. Kang, and R. D. Esman, “Performance of a time- and wavelength-interleaved photonic sampler for analog-digital conversion,” IEEE Photon. Technol. Lett. 11(9), 1168–1170 (1999). [CrossRef]

,4

4. M. P. Fok, K. L. Lee, and C. Shu, “4×2.5GHz repetitive photonic sampler for high-speed analog-to-digital signal conversion,” IEEE Photon. Technol. Lett. 16(3), 876–878 (2004). [CrossRef]

]. Multiple lasers with different wavelength, multiple wavelength laser, and spectral slicing of single broad bandwidth laser are three typical ways to generate such clock [5

5. A. Yariv and R. G. M. P. Koumans, “Time interleaved optical sampling for ultra-high speed A/D conversion,” Electron. Lett. 34(21), 2012–2013 (1998). [CrossRef]

7

7. M. Mielke, G. Alphonse, and P. J. Delfyett, “60×3.6Gb/s optical WDM transmitter using a multiwavlength modelocked semiconductor laser,” in Proc. IEEE/LEOS Annual Meeting, 2001, vol. 2, pp. 713–714.

]. Spectral slicing approach is relatively cost-effective and mature. Unfortunately, broadband lasers with high repetition rate are not commercially available yet. There are two methods to solve the problem. One is to use super continuum generation to broaden the spectral width of mode-locked picosecond fiber laser with gigahertz repetition rate [8

8. T. R. Clark, P. J. Matthews, and M. Currie, “Real-time photonic analog-digital converter based on discrete wavelength-time mapping,” in IEEE International Topical Meeting on Microwave Photonics, 1999.

]. The other is to increase the repetition rate of broadband femtosecond fiber laser by optical time division multiplexing (OTDM). In this paper, we present a simple approach to generate high-repetition-rate time-wavelength interleaved sampling clock with channels more than ten using commercially available broadband femtosecond fiber laser and low cost optical passive devices. The relative key techniques such as low loss and braodband WDMs, large multiple factor OTDM and the low cost precise delay control are studied. An 18 channels 83.9Gs/s time-wavelength interleaved sampling clock is generated. The number of channels is important for achieving WDM based PADCs with high sampling rate since the sampling rate of the single channel is limited by the sampling rate of EADCs used in back end, whose ENOB(effective number of bits) of EADCs decreases with its bandwidth. The state-of-art resolution of commercially available EADCs is about 8 around 4 Gs/s, e.g. EV10AQ190 from e2v (8.7 @ 5 Gs/s). In order to reach 80Gs/s PADC system with ENOB of 8, about 20 channels are needed.

2. System architecture

The architecture of photonic ADC based on WDM is shown in Fig. 1
Fig. 1 The architecture of photonic ADC based on WDM
. The multiple wavelength interleaved pulse generator (MWPG) is used to generate time-wavelength interleaved optical sampling pulse train. The optical sampling pulse train inputs to an electro-optic modulator (EOM) to sample the RF signal, and then is demultiplexed to multiple wavelength channels. On each wavelength channel, the sampling optical signal is detected by a photo detector (PD) and quantized by EADCs. The quantized data on each channel are combined to form the digitized result of the RF analog signal in digital processing unit.

Figure 2
Fig. 2 Experimental setup of the time-wavelength interleaved sampling clock generator (FRM: Faraday Rotation Mirror, VOA: Variable Optical Attenuator, TFS: Tunable Fiber Stretchers)
shows the proposed architecture of MWPG. Pulses from a broadband mode-locked femtosecond fiber laser (MLFLL) at the repetition rate of f are input to a time and wavelength mapping module (TWMM), which spectrally slices each input pulse into N pulses of different wavelengths and maps the sliced pulses to different time positions with appropriate fiber delay lines (FDLs) to form a pulse train as shown in Fig. 2. The output pulse train from TWMM is then sent to an OTDM module with multiple factor of M to generate the time-wavelength interleaved sampling clock with the interval 1/(f×N×M).

The OTDM module in Fig. 2 consists of b and d stages of 2 × 2 and 3 × 3 cascaded optical fiber couplers, respectively. Hence appropriate M ( = 2b + 3d) can be obtained flexibly by selecting b and d. The fused-biconical 2 × 2 fiber couplers are placed before the 3 × 3 ones. In such arrangement, the optical power loss, ILOTDM, of the OTDM module consists only of the excess loss of each coupler and the insertion loss of the last coupler. If the excess loss of each coupler is the same, we have:
ILOTDM=i=1bELi2×2+i=1dELi3×3+ILl×l
(1)
where ELi2×2 and ELi3×3 are the excess loss of the 2 × 2 and 3 × 3 couplers, respectively; ILl×l is the insertion loss of the last coupler (l = 2 for 2 × 2 coupler and l = 3 otherwise). In addition to provide flexibility in determining M, the use of 3 × 3 couplers can also minimize the coupler stages [9

9. X. Li, L. Peng, S. Wang, Y.-C. Kim, and J. Chen, “A novel kind of programmable 3(n) feed-forward optical fiber true delay line based on SOA,” Opt. Express 15(25), 16760–16766 (2007). [CrossRef] [PubMed]

].

3. Experimental results and discussion

Figure 4
Fig. 4 OTDM pulse output for one WDM channel. (a) 4.66Gs/s pulse train measured using digital sampling oscilloscope. (b) pulse width observed by a digital sampling oscilloscope (left) and its autocorrelator curve (right).
shows the OTDM pulse output for one WDM channel observed using a 50GHz photodetector (PD) and a 60GHz digital sampling oscilloscope (Tektronix, TDS8200). The sampling rate is about 4.66Gs/s, corresponding to a pulse interval of 1/(36.44 × 128) = 214.39ps. The full width at half maximum of pulses is broadened from 4.18ps (measured using autocorrelator FR-103XL) to about 14ps [see Fig. 4(b)] due to the limited bandwidth of the PD and the oscilloscope used, which make us unable to record 18 wavelengths 83.9Gs/s sampling clock using the 60GHz oscilloscope directly.

In order to observe the 18 wavelengths 83.9Gs/s sampling clock, we measure the optical pulse train of even number channels and odd number channels referring to a common pulse, respectively, then display them together using the WaveStar software from Tektronix, Inc. Figure 5(a)
Fig. 5 (a) The optical pulse trains of 9 channels with even number (left) and 9 channels with odd number (right). (b) Corresponding spectrum.
shows the pulse trains of 9 even channels and 9 odd channels, respectively. Figure 5(b) shows the corresponding spectrum in the two cases. Figure 6
Fig. 6 The composed 18 channels 83.9 Gs/s pulse train (a) and the spectrum of time-wavelength interleaved sampling clock (b).
shows the spectrum of time-wavelength interleaved sampling clock of 18 wavelengths and the composed 18 channels 83.9Gs/s pulse train.

4. Conclusion

The generation of time-wavelength interleaved sampling clock is one of the key issues for WDM based photonic ADC. We presented a simple approach to generate high repetition rate time-wavelength interleaved sampling clock with channels larger than ten by combining a commercially available broadband low-repetition-rate femtosecond fiber laser and optical wavelength/time division multiplexing techniques. A time and wavelength mapping module is configured using a specially designed 200GHz-channel-spacing WDM and manually tunable mechanical fiber stretchers. An OTDM module with low insertion loss and flexible multiplexing factor is proposed with the low cost fused single-mode fiber couplers. Generation of 18-wavelength 83.9Gs/s time and wavelength interleaved optical sampling clock is demonstrated using an 18-channel WDM and a 128 times OTDM.

Acknowledgments

This work was supported in part by “973” program (ID2011CB301700), the National Science Foundation of China (NSFC) (60877012), and the STCSM Project (10DJ1400402, 09JC1408100).

References and links

1.

G. C. Valley, “Photonic analog-to-digital converters,” Opt. Express 15(5), 1955–1982 (2007). [CrossRef] [PubMed]

2.

F. X. Kartner, R. Amataya, G. Barbastathis, H. Byun, F. Gan, C. W. Holzwarth, J. L. Hoyt, E. P. Ippen, O. O. Olubuyide, J. S. Orcutt, M. Park, M. Perrott, M. A. Popovic, P. T. Rakich, R. J. Ram, H. I. Smith, M. Geis, M. Grein, T. Lyszczarz, S. Spector, and J. U. Yoon, “Silicon electronic photonic integrated circuits for high speed analog to digital conversion,” 3rd OEEE International Conference on Group IV Photonics 2006, pp. 203–205.

3.

T. R. Clark, J. U. Kang, and R. D. Esman, “Performance of a time- and wavelength-interleaved photonic sampler for analog-digital conversion,” IEEE Photon. Technol. Lett. 11(9), 1168–1170 (1999). [CrossRef]

4.

M. P. Fok, K. L. Lee, and C. Shu, “4×2.5GHz repetitive photonic sampler for high-speed analog-to-digital signal conversion,” IEEE Photon. Technol. Lett. 16(3), 876–878 (2004). [CrossRef]

5.

A. Yariv and R. G. M. P. Koumans, “Time interleaved optical sampling for ultra-high speed A/D conversion,” Electron. Lett. 34(21), 2012–2013 (1998). [CrossRef]

6.

K. L. Lee, C. Shu, and H. F. Liu, “10 Gsample/s photonic analog-to-digital converter constructed using 10-wavelength jitter-suppressed sampling pulses from a self-seeded laser diode,” CLEO 2001, pp. 67–68.

7.

M. Mielke, G. Alphonse, and P. J. Delfyett, “60×3.6Gb/s optical WDM transmitter using a multiwavlength modelocked semiconductor laser,” in Proc. IEEE/LEOS Annual Meeting, 2001, vol. 2, pp. 713–714.

8.

T. R. Clark, P. J. Matthews, and M. Currie, “Real-time photonic analog-digital converter based on discrete wavelength-time mapping,” in IEEE International Topical Meeting on Microwave Photonics, 1999.

9.

X. Li, L. Peng, S. Wang, Y.-C. Kim, and J. Chen, “A novel kind of programmable 3(n) feed-forward optical fiber true delay line based on SOA,” Opt. Express 15(25), 16760–16766 (2007). [CrossRef] [PubMed]

10.

M. Li, G. Wu, P. Guo, X. Li, and J. Chen, “Analysis and compensation of dispersion-induced bit loss in a photonic A/D converter using time-wavelength interweaved sampling clock,” Opt. Express 17(20), 17764–17771 (2009). [CrossRef] [PubMed]

11.

X. Wang, S. Chen, Z. Du, X. Wang, C. Shi, and J. Chen, “Experimental study of some key issues on fiber-optic interferometric sensors detecting weak magnetic field,” IEEE Sens. J. 8(7), 1173–1179 (2008). [CrossRef]

12.

P. J. Delfyett, C. DePriest, and T. Yilmaz, “Signal processing at the speed of lightwaves,” IEEE Circuits Devices Mag. 18(5), 28–35 (2002). [CrossRef]

13.

P. W. Juodawlkist, J. J. Hargreaves, R. D. Younger, R. C. Williamson, G. E. Belts, and C. Twichell, “Optical Sampling for High-Speed, High-Resolution Analog-to-Digital Converters,” International Topical Meeting on Microwave Photonics, 2003, pp. 75–80.

OCIS Codes
(230.0250) Optical devices : Optoelectronics
(250.4745) Optoelectronics : Optical processing devices
(060.5625) Fiber optics and optical communications : Radio frequency photonics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: June 14, 2010
Revised Manuscript: August 18, 2010
Manuscript Accepted: September 1, 2010
Published: September 22, 2010

Citation
Guiling Wu, Siqi Li, Xinwan Li, and Jianping Chen, "18 wavelengths 83.9Gs/s optical sampling clock for photonic A/D converters," Opt. Express 18, 21162-21168 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-20-21162


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References

  1. G. C. Valley, “Photonic analog-to-digital converters,” Opt. Express 15(5), 1955–1982 (2007). [CrossRef] [PubMed]
  2. F. X. Kartner, R. Amataya, G. Barbastathis, H. Byun, F. Gan, C. W. Holzwarth, J. L. Hoyt, E. P. Ippen, O. O. Olubuyide, J. S. Orcutt, M. Park, M. Perrott, M. A. Popovic, P. T. Rakich, R. J. Ram, H. I. Smith, M. Geis, M. Grein, T. Lyszczarz, S. Spector, and J. U. Yoon, “Silicon electronic photonic integrated circuits for high speed analog to digital conversion,” 3rd OEEE International Conference on Group IV Photonics 2006, pp. 203–205.
  3. T. R. Clark, J. U. Kang, and R. D. Esman, “Performance of a time- and wavelength-interleaved photonic sampler for analog-digital conversion,” IEEE Photon. Technol. Lett. 11(9), 1168–1170 (1999). [CrossRef]
  4. M. P. Fok, K. L. Lee, and C. Shu, “4×2.5GHz repetitive photonic sampler for high-speed analog-to-digital signal conversion,” IEEE Photon. Technol. Lett. 16(3), 876–878 (2004). [CrossRef]
  5. A. Yariv and R. G. M. P. Koumans, “Time interleaved optical sampling for ultra-high speed A/D conversion,” Electron. Lett. 34(21), 2012–2013 (1998). [CrossRef]
  6. K. L. Lee, C. Shu, and H. F. Liu, “10 Gsample/s photonic analog-to-digital converter constructed using 10-wavelength jitter-suppressed sampling pulses from a self-seeded laser diode,” CLEO 2001, pp. 67–68.
  7. M. Mielke, G. Alphonse, and P. J. Delfyett, “60×3.6Gb/s optical WDM transmitter using a multiwavlength modelocked semiconductor laser,” in Proc. IEEE/LEOS Annual Meeting, 2001, vol. 2, pp. 713–714.
  8. T. R. Clark, P. J. Matthews, and M. Currie, “Real-time photonic analog-digital converter based on discrete wavelength-time mapping,” in IEEE International Topical Meeting on Microwave Photonics, 1999.
  9. X. Li, L. Peng, S. Wang, Y.-C. Kim, and J. Chen, “A novel kind of programmable 3(n) feed-forward optical fiber true delay line based on SOA,” Opt. Express 15(25), 16760–16766 (2007). [CrossRef] [PubMed]
  10. M. Li, G. Wu, P. Guo, X. Li, and J. Chen, “Analysis and compensation of dispersion-induced bit loss in a photonic A/D converter using time-wavelength interweaved sampling clock,” Opt. Express 17(20), 17764–17771 (2009). [CrossRef] [PubMed]
  11. X. Wang, S. Chen, Z. Du, X. Wang, C. Shi, and J. Chen, “Experimental study of some key issues on fiber-optic interferometric sensors detecting weak magnetic field,” IEEE Sens. J. 8(7), 1173–1179 (2008). [CrossRef]
  12. P. J. Delfyett, C. DePriest, and T. Yilmaz, “Signal processing at the speed of lightwaves,” IEEE Circuits Devices Mag. 18(5), 28–35 (2002). [CrossRef]
  13. P. W. Juodawlkist, J. J. Hargreaves, R. D. Younger, R. C. Williamson, G. E. Belts, and C. Twichell, “Optical Sampling for High-Speed, High-Resolution Analog-to-Digital Converters,” International Topical Meeting on Microwave Photonics, 2003, pp. 75–80.

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