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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 18 — Aug. 30, 2010
  • pp: 18697–18702
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All-optical fiber-based ultrafast amplitude jitter magnifier

Christophe Finot and Julien Fatome  »View Author Affiliations


Optics Express, Vol. 18, Issue 18, pp. 18697-18702 (2010)
http://dx.doi.org/10.1364/OE.18.018697


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Abstract

In this work, we describe an all-fibered set-up that allows the optical magnification of the amplitude jitter of low-fluctuation pulse trains, enabling an easy measurement of the statistical properties by usual photodiodes and electronic equipments.

© 2010 OSA

1. Introduction

We report here an easy-to-implement technique that is suitable to any repetition rate and that is fully compatible with widely spread photodiodes, oscilloscopes and communication signal analyzer softwares. Our solution relies on a nonlinear fiber-based device that enables the optical magnification of the fluctuations in such a way that they become easily and reliably detectable by usual electronics. At first, we shall describe the experimental set-up and the principle of the optical amplitude jitter magnifier. We then present a set of experimental results assessing the performance of the proposed device at telecommunication wavelengths. A magnification by a factor ten is achieved and more remarkably, the probability distribution of the fluctuations is conserved and monitored.

2. Experimental set-up

The configuration we investigate is sketched in Fig. 1
Fig. 1 Experimental set-up
. The experimental set-up relies exclusively on commercially available components commonly used for optical telecommunications. A low jitter fiber laser source is actively mode-locked by a 10-GHz RF signal and delivers Fourier-transform-limited picosecond pulses (2.4 ps). An intensity optical modulator driven by an arbitrary waveform generator artificially degrades the high quality pulse train. The resulting signal under test (SUT) is thus affected by a controlled level of amplitude jitter and is sent into an erbium-doped fiber amplifier (EDFA) with a moderate output average power of 14mW.

The amplified pulse train then propagates into a highly nonlinear fiber (HNLF). This fiber is 920 meter long and presents a low anomalous dispersion coefficient (D = 0.7 ps/km/nm) combined with a high value of nonlinearity (10 /W/km). The linear losses and dispersion slope are both reduced (0.5 dB/km and 0.01 ps2.km/nm, respectively). The nonlinearity of the fiber leads to a spectral expansion of the pulses due to self-phase modulation. At the output of the fiber, an optical bandpass filter (OBPF) made of a fiber Bragg grating associated with an optical circulator (OC) is used to carve into the expanded spectrum. The OBPF is fixed at the same central wavelength as the incoming signal, has a Gaussian spectral intensity profile and a full spectral width at half maximum of 200 GHz The resulting signal is detected by means of a fast photodetector combined with a high speed sampling oscilloscope (50 GHz bandwidth).

3. Principle of operation and design guidelines

On the contrary, the application we target here dictates the use of a TF presenting a very pronounced slope as illustrated in Fig. 2(a)
Fig. 2 (a) TF of the device and associated parameters. Inset: optical spectrum at the local minimum of the TF before the OBPF (black line) compared with the OBPF (green line). (b) Pulse train with 1% initial relative amplitude jitter: SUT (b1) is compared to the pulse train obtained after optical magnification (b2). (c) Comparison of the TF based on the peak-powers of the incoming and outcoming pulses (red curve) with the TF relying on pulse energy (blue curve) or average pulse energy when the train exhibits 5% relative fluctuations (dotted black line). (d) Probability distribution of the output parameter (peak-power: red ; pulse energy: blue) compared to the distribution of the initial peak-powers magnified by a factor 10 (dotted black line). The initial distribution of the peak powers is plotted in solid black-line.
, typical of very pronounced A-regime. Whereas the achievement of B-regime requires a very precise balance between the linear and non-linear properties of the fiber under use [6

6. J. Fatome and C. Finot, “Scaling guidelines of a soliton-based power limiter for 2R-optical regeneration applications,” J. Lightw. Technol. DOI: (2010). [CrossRef]

], we have found from systematic numerical simulations based on the standard nonlinear Schrödinger equation that it was rather easy to work in the expected A-regime. The main condition to be fulfilled deals with the length of the fiber, which has to be much shorter than the typical dispersive length [6

6. J. Fatome and C. Finot, “Scaling guidelines of a soliton-based power limiter for 2R-optical regeneration applications,” J. Lightw. Technol. DOI: (2010). [CrossRef]

,10

10. L. A. Provost, C. Finot, P. Petropoulos, K. Mukasa, and D. J. Richardson, “Design scaling rules for 2R-optical self-phase modulation-based regenerators,” Opt. Express 15(8), 5100–5113 (2007). [CrossRef] [PubMed]

]. This leads to a large tolerance on the experimental choice of the fiber parameters. Let us note however, the following general trend, shorter the fiber is, higher the working power of the device should be, which qualitatively maintains a constant nonlinear phase shift. Concerning the OBPF properties, we have checked that it was not a crucial parameter and that similar features can be observed as long as the spectral width of the OBPF is equal to or shorter than the initial pulse spectrum.

Regarding the shape of the TF, for the range of powers under consideration, the TF should be ideally monotonous and should be approximated over a wide part by its tangent. More precisely, if PC is the abscissa at the origin of the tangent to the curve for a working power PE0, it can be easily shown that the fluctuations of the pulse train are amplified if the simple condition 0 < PC < 2 PE0 is fulfilled. A magnification factor of the device can be defined as the ratio of the relative fluctuations of the outcoming signal over the relative fluctuations of the SUT, i.e. (σS/PS0) / (σE/PE0) with σE, σS being the standard deviations of the input and output pulse streams respectively.

In order to more concretely illustrate the operating principle, let us consider a working power located in the middle of second rising segment of the TF (Fig. 2(a)). The tangent to the TF accurately describes the TF over a wide range. It is interesting to notice that for such a configuration the power PC physically corresponds to the power where the output optical spectrum splits into two lobes, leading to little energy remaining in the central filtered part (inset Fig. 2(a)). Remark that such a property has been beneficial in the past in the framework of optical analog to digital conversion [11

11. S. Oda and A. Maruta, “Two-bit all-optical analog-to-digital conversion by filtering broadened and split spectrum induced by soliton effect or self-phase modulation in fiber,” IEEE J. Sel. Top. Quantum Electron. 12(2), 307–314 (2006). [CrossRef]

]. Numerical simulations reported in Fig. 2(b) clearly illustrate how the initial pulse train with very low power fluctuations (Fig. 2(b1)) is converted into a train with much more noticeable fluctuations (Fig. 2(b2)).

Ideally, the proper analysis of the peak-power of the pulses requires to resolve the ultrashort pulses, which needs onerous devices. But from numerical simulations presented in Fig. 2(c), we can make out that this difficulty can be overcome by considering the energy of the output pulses instead of their peak power: as the nonlinear scheme does not induce significant fluctuations of the output temporal duration, nearly identical transfer functions will be recorded. We have also checked that considering the average energy of a pulse train with a reduced level of fluctuations does not induce any artificial distortions of the TF.

Finally, we compare in Fig. 2(d) the statistical distributions of the initial pulse train to the outcoming optical magnified one: superposition of the probability distributions based on output peak-power (red curve), on output energy (blue curve) and on the initial peak-power distribution magnified by a factor 10 (black dotted curve) demonstrates the ability of the device to stretch the fluctuations and to maintain the general shape.

4. Experimental results

Transfer function and magnification factor

Figure 3(a)
Fig. 3 (a) Experimental transfer function of the device (black circles) compared to the numerical simulations (blue line). Subplots (a1) and (a2) illustrate the statistical distribution of the peak powers of the input and output pulse trains respectively (subplot (a1) is partly impaired by the electronic noise contribution). (b) Evolution of the magnification factor according to the working average power (an initial jitter of 4 percent is superimposed on the modelocked train). Experimental results (black circles) are compared with the results of numerical simulations (blue line) (c) Relative output jitter versus input jitter (rms values).
reports the experimental TF (solid black circles). Quantitative agreement with the numerical simulations is remarkably achieved. Systematic measurements of the output amplitude jitter according to the input pulse energy (Fig. 3(b)) are also presented. In more details, between 0 and 0.5 pJ, due to the proportional nature of the section of the TF (in other words, PC = 0 so that the required condition of jitter amplification is not fulfilled), the measurement gives a value close to one. Between 0.5 and 0.8 pJ, a small decrease of the fluctuations can be noticed, which can be explained by the previously mentioned optical limiting properties of the device [6

6. J. Fatome and C. Finot, “Scaling guidelines of a soliton-based power limiter for 2R-optical regeneration applications,” J. Lightw. Technol. DOI: (2010). [CrossRef]

]. By increasing initial average power (0.8-1.2 pJ), a significant increase of the jitter is detected. However, given the negative slope of the curve (corresponding to PE0 < PC < 2 PE0), the resulting histogram will suffer from an inversion so that this range of powers is not the best suited for an accurate monitoring of the statistical properties. It is indeed more convenient to work with higher powers, typically between 1.3 and 1.5 pJ where the TF is monotonously increasing. Therefore, by positioning adequately the working power PE0 compared to the corresponding threshold PC, the condition 0 < PC < PE0 ensures both magnification of the amplitude jitter and the conservation of the distribution. Subplots 3(a1) and 3(a2) illustrate the benefits of the device: whereas the analysis of the SUT is severely compromised by electronic noise, after optical magnification by a factor slightly above 10, the fluctuations become clearly distinct and can be straightforwardly recorded.

Experimental magnification factors have also been compared to results based on the numerical integration of the standard nonlinear Schrödinger equation: from the simulated TF, the resulting jitter enhancement can be predicted using the simple following formula: 1/(1 - PC /PE0) (blue solid line). The excellent agreement that is once again observed confirms that dispersion, Kerr nonlinearity and spectral filtering fully explain the recorded trends.

Complementary experimental results

Complementary measurements are reported in Fig. 3(c). By varying the calibrated level of initial fluctuation that is superimposed over the initial signal, we have checked that the jitter magnification does not depend of the initial level of jitter as long as it remains below 5 percent, which is fully consistent with the purpose of the device. Another very important feature that we have experimentally checked is the ability of the set-up not to distort the statistical distribution of the fluctuations. We have indeed tested various kinds of statistical fluctuations that we have accurately controlled thanks to the electrical arbitrary waveform generator. Preliminary results based on a white Gaussian noise (Figs. 3(a1) and 3 (a2)) have been confirmed with more complex fluctuations such as modulation of the pulse train by low-frequency low-amplitude sinusoidal (Fig. 4(a)
Fig. 4 Signal recorded before (subplots 1) and after (subplots 2) the optical jitter magnifier. SUT may be impaired by the electrical noise contribution of the oscilloscope (leading to a relative amplitude jitter estimated to 1%). Eye-diagrams and associated histograms of a pulse train modulated by a low frequency sinusoidal wave or by a low frequency periodic triangular wave are plotted on subplots a and subplots b, respectively. Results dealing with a 40-GHz pulse train made of four time-interleaved 10 GHz pulse trains are given on subplots (c).
) or triangular (Fig. 4(b)) waves. The resulting histograms exhibit the expected two peak structure or constant distribution respectively. In other words, after calibration, the linear nature of the TF enables not only a convenient measurement of the initial rms amplitude jitter but also preserves the shape of the statistical distribution of the fluctuations. As a consequence, and contrary to techniques detailed in refs [2

2. J. Fatome, J. Garnier, S. Pitois, M. Petit, G. Millot, M. Gay, B. Clouet, L. Bramerie, and J. C. Simon, “All-optical measurements of background, amplitude, and timing jitters for high speed pulse trains or PRBS sequences using autocorrelation function,” Opt. Fiber Technol. 14(1), 84–91 (2008). [CrossRef]

,4

4. D. Von der Linde, “Characterization of the noise in continuously operating mode-locked lasers,” Appl. Phys. B 39(4), 201–217 (1986). [CrossRef]

,5

5. M. C. Gross, M. Hanna, K. M. Patel, and S. E. Ralph, “Spectral method for the simultaneous determination of uncorrelated and correlated amplitude and timing jitter,” Appl. Phys. Lett. 80(20), 3694–3696 (2002). [CrossRef]

], no assumption such as a Gaussian distribution is required.

As a final proof of the very high sensitivity of the device, we present an experiment where four trains at 10 GHz are time-interleaved in order to obtain a 40 GHz pulse train. Time interleaving is achieved through a widely spread optical bit rate multiplier made of optical delay lines and couplers and where a careful balance of the powers of the four channels has to be found. Visual level equalization made with the direct detection on the oscilloscope leads to the record presented on Fig. 4(c1) where no difference in the level of the interleaved channels can be distinguished. After evolution in the optical magnifier (Fig. 4(c2)), differences in the level of the 10 GHz trains is readily apparent, which may facilitate further fine level adjustment.

5. Conclusion

To conclude, we have demonstrated a practical and flexible fiber-based device that provides an all-optical magnification of the amplitude jitter by one order of magnitude. The quasi-instantaneous nonlinear Kerr response of silica facilitates the measurement of the jitter level of stable ultrafast pulse trains and also provides an easy way to get access to the associated statistical distribution of pulse trains exhibiting low fluctuations. Potential applications are not restricted to optical telecommunications: the proposed optical amplitude jitter magnifier may become essential for the design and performance analysis of all the applications based on a highly stable pulse sources.

Our set-up relies on an anomalous highly nonlinear fiber combined with central bandpass spectral filtering. However, other fiber based schemes could also provide alternative such as normally dispersive fibers with spectral offset filtering [10

10. L. A. Provost, C. Finot, P. Petropoulos, K. Mukasa, and D. J. Richardson, “Design scaling rules for 2R-optical self-phase modulation-based regenerators,” Opt. Express 15(8), 5100–5113 (2007). [CrossRef] [PubMed]

,12

12. P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in European Conference on Optical Communication, ECOC'98, 1998), 475–476.

]. Nevertheless let us point out that the involved physical process should be dependant on the peak-power of the pulse. Consequently, schemes such as nonlinear optical loop mirrors [13

13. S. Boscolo, S. K. Turitsyn, and K. J. Blow, “Nonlinear loop mirror-based all-optical signal processing in fiber-optic communications,” Opt. Fiber Technol. 14(4), 299–316 (2008). [CrossRef]

] where the instantaneous power is taken into account are not suitable [14

14. M. Rochette, L. B. Fu, V. G. Ta'eed, D. J. Moss, and B. J. Eggleton, “2R optical regeneration: an all-optical solution for BER improvement,” IEEE J. Sel. Top. Quantum Electron. 12(4), 736–744 (2006). [CrossRef]

]. We may also anticipate that the proposed technique will soon benefit from the recent progresses in highly nonlinear waveguides [3

3. T. D. Vo, M. D. Pelusi, J. Schröder, F. Luan, S. J. Madden, D.-Y. Choi, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Simultaneous multi-impairment monitoring of 640 Gb/s signals using photonic chip based RF spectrum analyzer,” Opt. Express 18(4), 3938–3945 (2010). [CrossRef] [PubMed]

,15

15. R. Salem, M. A. Foster, A. C. Turner, D. F. Geraghty, M. Lipson, and A. L. Gaeta, “Signal regeneration using low-power four-wave mixing on silicon chip,” Nat. Photonics 2(1), 35–38 (2008). [CrossRef]

] and photonic integration that will ultimately offer compact and low cost approaches.

Acknowledgements

This work was supported by the Agence Nationale de la Recherche (ANR SOFICARS and ILIADE projects: ANR-07-RIB-013-03 and ANR-07-BLANC-183657).

References and links

1.

Z. Pan, C. Yu, and A. E. Willner, “Optical performance monitoring for the next generation optical communication networks,” Opt. Fiber Technol. 16(1), 20–45 (2010). [CrossRef]

2.

J. Fatome, J. Garnier, S. Pitois, M. Petit, G. Millot, M. Gay, B. Clouet, L. Bramerie, and J. C. Simon, “All-optical measurements of background, amplitude, and timing jitters for high speed pulse trains or PRBS sequences using autocorrelation function,” Opt. Fiber Technol. 14(1), 84–91 (2008). [CrossRef]

3.

T. D. Vo, M. D. Pelusi, J. Schröder, F. Luan, S. J. Madden, D.-Y. Choi, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Simultaneous multi-impairment monitoring of 640 Gb/s signals using photonic chip based RF spectrum analyzer,” Opt. Express 18(4), 3938–3945 (2010). [CrossRef] [PubMed]

4.

D. Von der Linde, “Characterization of the noise in continuously operating mode-locked lasers,” Appl. Phys. B 39(4), 201–217 (1986). [CrossRef]

5.

M. C. Gross, M. Hanna, K. M. Patel, and S. E. Ralph, “Spectral method for the simultaneous determination of uncorrelated and correlated amplitude and timing jitter,” Appl. Phys. Lett. 80(20), 3694–3696 (2002). [CrossRef]

6.

J. Fatome and C. Finot, “Scaling guidelines of a soliton-based power limiter for 2R-optical regeneration applications,” J. Lightw. Technol. DOI: (2010). [CrossRef]

7.

M. Asobe, A. Hirano, Y. Miyamoto, K. Sato, K. Hagimoto, and Y. Yamabayashi, “Noise reduction of 20 Gbit/s pulse train using spectrally filtered optical solitons,” Electron. Lett. 34(11), 1135–1136 (1998). [CrossRef]

8.

T. Ohara, H. Takara, S. Kawanishi, T. Yamada, and M. M. Fejer, “160 Gb/s all-optical limiter based on spectrally filtered optical solitons,” IEEE Photon. Technol. Lett. 16(10), 2311–2313 (2004). [CrossRef]

9.

M. Gay, M. Costa e Silva, T. N. Nguyen, L. Bramerie, T. Chartier, M. Joindot, J. C. Simon, J. Fatome, C. Finot, and J. L. Oudar, “170 Gbit/s bit error rate assessment of regeneration using a saturable absorber and a nonlinear fiber based power limiter,” IEEE Photon. Technol. Lett. 22(3), 158–160 (2010). [CrossRef]

10.

L. A. Provost, C. Finot, P. Petropoulos, K. Mukasa, and D. J. Richardson, “Design scaling rules for 2R-optical self-phase modulation-based regenerators,” Opt. Express 15(8), 5100–5113 (2007). [CrossRef] [PubMed]

11.

S. Oda and A. Maruta, “Two-bit all-optical analog-to-digital conversion by filtering broadened and split spectrum induced by soliton effect or self-phase modulation in fiber,” IEEE J. Sel. Top. Quantum Electron. 12(2), 307–314 (2006). [CrossRef]

12.

P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in European Conference on Optical Communication, ECOC'98, 1998), 475–476.

13.

S. Boscolo, S. K. Turitsyn, and K. J. Blow, “Nonlinear loop mirror-based all-optical signal processing in fiber-optic communications,” Opt. Fiber Technol. 14(4), 299–316 (2008). [CrossRef]

14.

M. Rochette, L. B. Fu, V. G. Ta'eed, D. J. Moss, and B. J. Eggleton, “2R optical regeneration: an all-optical solution for BER improvement,” IEEE J. Sel. Top. Quantum Electron. 12(4), 736–744 (2006). [CrossRef]

15.

R. Salem, M. A. Foster, A. C. Turner, D. F. Geraghty, M. Lipson, and A. L. Gaeta, “Signal regeneration using low-power four-wave mixing on silicon chip,” Nat. Photonics 2(1), 35–38 (2008). [CrossRef]

OCIS Codes
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(060.5530) Fiber optics and optical communications : Pulse propagation and temporal solitons

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: April 29, 2010
Revised Manuscript: July 22, 2010
Manuscript Accepted: July 29, 2010
Published: August 18, 2010

Citation
Christophe Finot and Julien Fatome, "All-optical fiber-based ultrafast amplitude jitter magnifier," Opt. Express 18, 18697-18702 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-18-18697


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References

  1. Z. Pan, C. Yu, and A. E. Willner, “Optical performance monitoring for the next generation optical communication networks,” Opt. Fiber Technol. 16(1), 20–45 (2010). [CrossRef]
  2. J. Fatome, J. Garnier, S. Pitois, M. Petit, G. Millot, M. Gay, B. Clouet, L. Bramerie, and J. C. Simon, “All-optical measurements of background, amplitude, and timing jitters for high speed pulse trains or PRBS sequences using autocorrelation function,” Opt. Fiber Technol. 14(1), 84–91 (2008). [CrossRef]
  3. T. D. Vo, M. D. Pelusi, J. Schröder, F. Luan, S. J. Madden, D.-Y. Choi, D. A. P. Bulla, B. Luther-Davies, and B. J. Eggleton, “Simultaneous multi-impairment monitoring of 640 Gb/s signals using photonic chip based RF spectrum analyzer,” Opt. Express 18(4), 3938–3945 (2010). [CrossRef] [PubMed]
  4. D. Von der Linde, “Characterization of the noise in continuously operating mode-locked lasers,” Appl. Phys. B 39(4), 201–217 (1986). [CrossRef]
  5. M. C. Gross, M. Hanna, K. M. Patel, and S. E. Ralph, “Spectral method for the simultaneous determination of uncorrelated and correlated amplitude and timing jitter,” Appl. Phys. Lett. 80(20), 3694–3696 (2002). [CrossRef]
  6. J. Fatome and C. Finot, “Scaling guidelines of a soliton-based power limiter for 2R-optical regeneration applications,” J. Lightw. Technol. DOI: (2010). [CrossRef]
  7. M. Asobe, A. Hirano, Y. Miyamoto, K. Sato, K. Hagimoto, and Y. Yamabayashi, “Noise reduction of 20 Gbit/s pulse train using spectrally filtered optical solitons,” Electron. Lett. 34(11), 1135–1136 (1998). [CrossRef]
  8. T. Ohara, H. Takara, S. Kawanishi, T. Yamada, and M. M. Fejer, “160 Gb/s all-optical limiter based on spectrally filtered optical solitons,” IEEE Photon. Technol. Lett. 16(10), 2311–2313 (2004). [CrossRef]
  9. M. Gay, M. Costa e Silva, T. N. Nguyen, L. Bramerie, T. Chartier, M. Joindot, J. C. Simon, J. Fatome, C. Finot, and J. L. Oudar, “170 Gbit/s bit error rate assessment of regeneration using a saturable absorber and a nonlinear fiber based power limiter,” IEEE Photon. Technol. Lett. 22(3), 158–160 (2010). [CrossRef]
  10. L. A. Provost, C. Finot, P. Petropoulos, K. Mukasa, and D. J. Richardson, “Design scaling rules for 2R-optical self-phase modulation-based regenerators,” Opt. Express 15(8), 5100–5113 (2007). [CrossRef] [PubMed]
  11. S. Oda and A. Maruta, “Two-bit all-optical analog-to-digital conversion by filtering broadened and split spectrum induced by soliton effect or self-phase modulation in fiber,” IEEE J. Sel. Top. Quantum Electron. 12(2), 307–314 (2006). [CrossRef]
  12. P. V. Mamyshev, “All-optical data regeneration based on self-phase modulation effect,” in European Conference on Optical Communication, ECOC'98, 1998), 475–476.
  13. S. Boscolo, S. K. Turitsyn, and K. J. Blow, “Nonlinear loop mirror-based all-optical signal processing in fiber-optic communications,” Opt. Fiber Technol. 14(4), 299–316 (2008). [CrossRef]
  14. M. Rochette, L. B. Fu, V. G. Ta'eed, D. J. Moss, and B. J. Eggleton, “2R optical regeneration: an all-optical solution for BER improvement,” IEEE J. Sel. Top. Quantum Electron. 12(4), 736–744 (2006). [CrossRef]
  15. R. Salem, M. A. Foster, A. C. Turner, D. F. Geraghty, M. Lipson, and A. L. Gaeta, “Signal regeneration using low-power four-wave mixing on silicon chip,” Nat. Photonics 2(1), 35–38 (2008). [CrossRef]

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