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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 2 — Jan. 16, 2012
  • pp: 1230–1236
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Generation of multi-wavelength picosecond pulses with tunable pulsewidth and channel spacing using a Raman amplification-based adiabatic soliton compressor

Quang Nguyen-The, Hung Nguyen Tan, Motoharu Matsuura, and Naoto Kishi  »View Author Affiliations


Optics Express, Vol. 20, Issue 2, pp. 1230-1236 (2012)
http://dx.doi.org/10.1364/OE.20.001230


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Abstract

We experimentally demonstrate pulsewidth-tunable picosecond multi-wavelength pulse generation at 10 Gb/s by the use of a Raman amplification-based adiabatic soliton compressor (RA-ASC). Multi-wavelength seed pulse trains are generated by a commercially available electroabsorption modulator and then compressed by using the RA-ASC. The pulsewidths of the compressed pulses can be simultaneously controlled from 16.0 ps to 2.0 ps by adjusting Raman pump power. Operating wavelength range of our scheme are also investigated, showing the possibility for wide channel spacing operations.

© 2011 OSA

1. Introduction

Multi-wavelength optical short pulse generation has attracted a lot of interest due to its important applications in all-optical signal processing, fiber-optical sensing and ultrahigh capacity transmission systems based on optical time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) systems. Moreover, a multi-wavelength pulse source providing pulsewidth tunability and wavelength reconfigurability would be highly desirable for various applications in future photonic networks.

In this paper, we experimentally demonstrate a short pulsewidth-tunable multi-wavelength pulse generation using Raman amplification-based adiabatic soliton compressor (RA-ASC). A single distributed Raman amplifier (DRA) is used to compress simultaneously two 10 GHz pulse trains to picosecond pulsewidth range. By changing the gain of the DRA, the pulsewidth of both compressed pulse trains can be simultaneously controlled from 16.0 ps to 2.0 ps. Both compressed pulses exhibit almost same pulsewidth. Operating wavelength range of our scheme is also investigated, showing the possibility for wide channel spacing operations.

2. Principle and experimental setup

The scheme for multi-wavelength pulse generation using RA-ASC is shown in Fig. 1. The RA-ASC operates on the basis of adiabatic soliton compression in distributed Raman amplifier. The adiabatic soliton compression is based on the relation the dispersion length (LD=T02/β2) and the nonlinear length (LNL = 1/(γP)) when a fundamental soliton pulse is propagated in anomalous dispersion fiber (β2 < 0) [15

15. P Govind. Agrawal, Nonlinear Fiber Optics (Academic Press, New York, 1995).

]:
T02β2=1γP
(1)
where P, T0, β2, and γ are the soliton peak power, pulsewidth of the soliton pulse, the group velocity dispersion coefficient and the Kerr coefficient of the fiber, respectively. From the relation (1), adiabatic soliton compression can be achieved via propagation along a dispersion profiled fiber such as a DDF, SDPF, or CDPF: the pulsewidth of the soliton pulse T0 is reduced as the group velocity dispersion coefficient β2 is made to properly decrease along the fiber. However, it is difficult to design and manufacture that dispersion profiled fiber. On the other hand, the pulsewidth of the soliton pulse T0 is inversely proportional to the soliton peak power P in Eq. (1). In our scheme, we use the RA-ASC, which employs a dispersion-shifted fiber (DSF) and a wavelength tunable Raman fiber laser (TRFL) to obtain the adiabatic soliton compression. In the RA-ASC, the pulsewidth of the pulse could be compressed as its peak power increases with the increase of the Raman pump power since the soliton condition is maintained during the amplification. By changing the Raman pump power, it is also possible to perform the pulsewidth-tunable multi-wavelength pulse generation.

Fig. 1 Experimental setup for generation of multi-wavelength picosecond pulses with tunable pulsewidth and channnel spacing by using a Raman amplification-based adiabatic soliton compressor. ECL: external-cavity laser-diode, EAM: electroabsorption modulation, EDFA: erbium-doped fiber amplifier, TDCM: tunable dispersion-compensating module, AWG: array waveguide grating, VOA: variable optical attenuator, WDM-PC: WDM power controller, TFRL: tunable fiber Raman laser, DSF: dispersion-shifted fiber, OBPF: optical bandpass filter.

In the experimental setup, to generate two seed pulse trains of 10 GHz repetition rate for the pulse compression, two continuous waves (CWs) at wavelengths: λ1 =1546.1 nm (channel 1) and λ2 =1549.3 nm ∼ 1557.3 nm (channel 2) from external-cavity lasers (ECLs) were simultaneously modulated by an electroabsorption modulator (EAM), driven by a 10 GHz synthesizer. An erbium-doped fiber amplifier (EDFA) was used after EAM to compensate for the EAM insertion loss. To compensate the frequency chirp induced by the EAM for multi-wavelength pulse trains, conventional technique using a dispersion-compensating fiber (DCF) [11

11. M. Matsuura, B. P. Samarakoon, and N. Kishi, “Wavelength-shift-free adjustment of the pulsewidth in return-to-zero on-off keyed signals by means of pulse compression in distributed Raman amplification,” IEEE Photon. Technol. Lett. 21, 572–574 (2009). [CrossRef]

] is no longer suitable due to its large dispersion slope. Here, we utilized a tunable dispersion-compensating module (TDCM) for simultaneous chirp compensation for two pulse trains. It is important to ensure fundamental soliton powers of the two seed pulse trains for adiabatic soliton compression. Here, a WDM power controller (WDM-PC) was constructed with following an EDFA for power adjustment before the RA-ASC. This WDM-PC consisted of an arrayed waveguide grating (AWG), variable optical attenuators (VOAs) and a coupler. Wavelength setting in the AWG was done in accordance with the wavelength of two input channels. Before injected into the RA-ASC, the pulsewidths of the two pulse trains at a bit-rate of 10 Gb/s were around 18 ps full width at half maximum (FWHM). The RA-ASC operates on the basis of adiabatic soliton compression in distributed Raman amplifier. In the RA-ASC, a 17 km dispersion-shifted fiber (DSF) was employed for adiabatic soliton compression technique. The second- and third-order dispersions of the DSF are 3.8 ps/nm/km and 0.059 ps/nm2/km, respectively. The Raman pump signal generated by a tunable fiber Raman laser (TFRL) was injected into the counter-propagating direction by using a WDM coupler. The wavelength of TFRL can be tuned in the range between 1425 nm and 1495 nm. To achieve high quality compression performance, Raman pump wavelength was optimized for the two seed pulse trains. The pulsewidths of the two seed pulse trains are compressed as its peak power increases with the increase of the Raman pump power since the soliton condition is maintained in the DSF during the amplification. At the output of RA-ASC, the compressed two pulses are filtered by two 3-nm optical bandpass filters (OBPFs) for pulse measurements. The output spectrum and waveform were measured by a spectrum analyzer and an autocorrelator, respectively.

3. Experimental results and discussion

To investigate the performance of the RA-ASC, we evaluate the compressed pulses in terms of pulsewidth and peak-to-pedestal ratio, which are the important parameters to characterize the pulse’s quality. The former parameter gives strong influence to the transmission performance in the photonic networks. The latter parameter is defined by the ratio of the peak to the second peak of the autocorrelation trace of the pulse. In a high-speed optical system, a less pedestal is beneficial for avoiding intersymbol interference (ISI) and improving the signal quality. Moreover, at the same average optical power, a pulse with a larger pedestal would have smaller peak power, which is crucial for the high-power pulse applications. In our scheme, the output pulsewidth and peak-to-pedestal ratio of the compressed pulses were measured independently by using two 3.0-nm OBPFs after the RA-ASC. Figure 2 shows (a) the optical spectra after the RA-ASC, and the autocorrelation traces at (b) channel 1 and (c) channel 2 of the output pulses as a function of Raman pump power (Pr) with channel spacing (Δλ = λ2λ1) of 3.2 nm. Both the optical spectra and autocorrelation traces of the compressed pulses were well fitted to sech2 functions. It can be seen that over the adiabatic soliton compression with the increase in the Raman pump power, output spectra of the two pulses were broadened at the same time, and their pulsewidths were compressed. The input pulsewidths (18.02 ps, 18.08 ps) at (channel 1, channel 2) were considerably compressed to (5.58 ps, 5.84 ps), (3.03 ps, 2.92 ps) and (2.63 ps, 2.65 ps) as the Raman pump power was set at 0.75 W, 0.90 W and 0.95 W, respectively.

Fig. 2 (a) Optical spectra after RA-ASC, and autocorrelation traces at (a) channel 1 and (b) channel 2 of the output pulses measured in various case of Raman pump power (Pr) with 3.2 nm channel spacing.

Figure 3(a), (b) show the output pulsewidth and peak-to-pedestal ratio of the compressed pulses at both channels for different Raman pump powers, respectively. It is found that the compressed pulses at both channels have similar characteristics. In Fig. 3(a), the output pulsewidth can be tuned from 16 ps to 2 ps by adjusting the Raman pump power from 0.4 W to 0.95 W. Small difference in pulsewidth was observed between two channels. The peak-to-pedestal ratio of the output pulse decreases slightly as the Raman pump power becomes larger in both channels as seen in Fig. 3(b). The pedestals associated with the compressed pulses were observed due to the slight deviation from adiabatic conditions in the experiment. However, throughout the tuning range, the peak-to-pedestal ratio was above 11.5 dB.

Fig. 3 Raman pump power dependency of (a) the pulsewidth, (b) the peak-to-pedestal ratio of the compressed pulses with 3.2 nm channel spacing.

To investigate the operating channel spacing of the RA-ASC, we fixed λ1 at 1546.1 nm and tuned λ2 from 1549.3 nm to 1557.3 nm corresponding for channel spacing from 3.2 nm to 11.2 nm. It should be noted that the pulse waveforms were distorted due to the deviations from the adiabatic condition when the Raman pump power was over an optimum Raman pump power (Pr,opt). Figure 4(a) shows the optical spectra of the output compressed pulses when the Raman pump power was set to Pr,opt at each case of channel spacing. Figure 4(b), (c) show corresponding autocorrelation traces of the output compressed pulses at channel 1, channel 2, respectively. In Fig. 4(b), (c), the solid line shows the measured waveform whereas the dashed line shows the sech2 fitting waveform. In all cases of Raman pump power and channel spacing setting, the output compressed pulses could be fitted with sech2 waveform both in spectrum and waveform. The time-bandwidth product of the compressed pulses at all Raman pump power and channel spacing were found to be less than 0.41. These results show good-quality output pulses were obtained for both channels at the same time by our scheme.

Fig. 4 (a) Optical spectra after RA-ASC and autocorrelation traces at (b) channel 1, (c) channel 2 of the output pulses measured in various case channel spacing. Raman pump power was set to Pr,opt in each case.

As only the case of channel spacing of 3.2 nm shown in Fig. 3, Raman pump power dependency of the pulsewidth and peak-to-pedestal ratio of the compressed pulse were investigated in various cases of channel spacing. Figure 5(a) shows the output pulsewidth of channel 1 as function of Raman pump power in various cases of channel spacing from 3.2 nm to 11.2 nm. Our measurements show small pulsewidth differences between channel 1 and 2 in all cases. These results show that both channels have similar characteristics. As seen in Fig. 5(a), pulsewidth of channel 1 was compressed to picosecond range between 16 ps and 2 ps by increasing the Raman pump power. Moreover, larger channel spacing required larger Raman pump power to obtain output pulsewidth. For example, in order to obtain pulsewidth of around 2.5 ps, while Raman pump power of 0.95 W was needed with 3.2 nm channel spacing, it was 1.15 W in the case of 11.2 channel spacing. Figure 5(b) shows the optimum Raman pump power Pr,opt and peak-to-pedestal ratio of the output pulse at both channels as the function of channel spacing. Pr,opt increased and the peak-to-pedestal ratio decreased slightly as the channel spacing increase from 3.2 nm to 11.2 nm. The peak-to-pedestal ratio was above 7.7 dB for both channels in all setting of Raman pump power and channel spacing.

Fig. 5 (a) Raman pump power dependency of the pulsewidth of the compressed pulse (at channel 1) and (b) channel spacing dependency of the optimum Raman pump power (Pr,opt) and peak-to-pedestal ratio of the output pulse.

4. Conclusion

We have successfully demonstrated a short pulsewidth-tunable multi-wavelength pulse generation by means of adiabatic soliton compression in a single distributed Raman amplifier. Both pulse trains were compressed with flexibly pulsewidth-tunable range from 16 ps to 2 ps by controlling the Raman pump power. High quality compressed pulses were achieved in all operating Raman pump powers in wide channel spacing operations.

References and links

1.

Z. Chen, H. Sun, S. Ma, and N. K. Dutta, “Dual-wavelength mode-locked erbium-doped fiber ring laser using highly nonlinear fiber,” IEEE Photon. Technol. Lett. 20, 2066–2068 (2008). [CrossRef]

2.

W. Zhang, J. Sun, J. Wang, and L. Liu, “Multiwavelength mode-locked fiber-ring laser based on reflective semiconductor optical amplifier,” IEEE Photon. Technol. Lett. 19, 1418–1420 (2007). [CrossRef]

3.

Z. Yusoff, P. Petropoulos, K. Furusawa, T. M. Monro, and D. J. Richardson, “A 36-channel×10-GHz spectrally sliced pulse source based on super-continuum generation in normally dispersive highly nonlinear holey fiber,” IEEE Photon. Technol. Lett. 15, 1689–1691 (2003). [CrossRef]

4.

Y. Dong, Z. Li, C. Yu, Y. J. Wen, Y. Wang, C. Lu, W. Hu, and T. H. Cheng, “Generation of multi-channel short-pulse sources using nonlinear optical loop mirror based on photonic crystal fiber,” in Proc. Optical Fiber Communication and the National Fiber Optic Engineers Conference (OFC/NFOEC) (2007), JWA9.

5.

M. Matsuura, N. Kishi, and T. Miki, “Widely pulsewidth-tunable multi-wavelength synchronized pulse generation utilizing a single SOA-based delayed interferometric switch,” IEEE Photon. Technol. Lett. 17, 902–904 (2005). [CrossRef]

6.

S. V. Chernikov, D. J. Richardson, E. M. Dianov, and D. N. Payne, “Picosecond soliton pulse compression based on dispersion decreasing fiber,” Electron. Lett. 28, 1842–1844 (1992). [CrossRef]

7.

S. V. Chernikov, J. R. Taylor, and R. Kashyap, “Comblike dispersion-profiled fiber for soliton pulse train generation,” Opt. Lett. 19, 539–541 (1994). [CrossRef] [PubMed]

8.

S. V. Chernikov, J. R. Taylor, and R. Kashyap, “Experimental demonstration of step-like dispersion profiling in optical fibre for soliton pulse generation and compression,” Electron. Lett. 30, 433–435 (1994). [CrossRef]

9.

K. Iwatsuki, K. Suzuki, and S. Nishi, “Adiabatic soliton compression of gain-switched DFB-LD pulse by distributed fiber Raman amplification,” IEEE Photon. Technol. Lett. 3, 1074–1076 (1991). [CrossRef]

10.

T. Kogure, J. H. Lee, and D. J. Richardson, “Wavelength and duration-tunable 10-GHz 1.3-ps pulse source using dispersion decreasing fiber-based distributed Raman amplification,” IEEE Photon. Technol. Lett. 16, 1167–1169 (2004). [CrossRef]

11.

M. Matsuura, B. P. Samarakoon, and N. Kishi, “Wavelength-shift-free adjustment of the pulsewidth in return-to-zero on-off keyed signals by means of pulse compression in distributed Raman amplification,” IEEE Photon. Technol. Lett. 21, 572–574 (2009). [CrossRef]

12.

Q. Nguyen-The, H. Nguyen Tan, M. Matsuura, and N. Kishi, “Multi-wavelength pulse generation using a Raman amplification-based adiabatic soliton compressor,” in Proc. 37th European Conference and Exhibition on Optical Communication (ECOC) (2011), We.10.P1.10.

13.

Q. Nguyen-The, M. Matsuura, H. Nguyen Tan, and N. Kishi, “All-optical NRZ-to-RZ data format conversion with picosecond duration-tunable and pedestal suppressed operations,” IEICE Transaction on Electronics , E94-C, 1160–1166 (2011). [CrossRef]

14.

H. Nguyen Tan, Q. Nguyen-The, M. Matsuura, and N. Kishi, “Raman amplification-based multiwavelength synchronous pulse compressor and its application to all-channel OTDM demultiplexing in a single parametric-gate,” in Proc. 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), We.P-6.

15.

P Govind. Agrawal, Nonlinear Fiber Optics (Academic Press, New York, 1995).

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(190.5650) Nonlinear optics : Raman effect
(320.5520) Ultrafast optics : Pulse compression
(250.4745) Optoelectronics : Optical processing devices

ToC Category:
Fibers, Fiber Devices, and Amplifiers

History
Original Manuscript: September 30, 2011
Revised Manuscript: November 19, 2011
Manuscript Accepted: November 23, 2011
Published: January 5, 2012

Virtual Issues
European Conference on Optical Communication 2011 (2011) Optics Express

Citation
Quang Nguyen-The, Hung Nguyen Tan, Motoharu Matsuura, and Naoto Kishi, "Generation of multi-wavelength picosecond pulses with tunable pulsewidth and channel spacing using a Raman amplification-based adiabatic soliton compressor," Opt. Express 20, 1230-1236 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-2-1230


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References

  1. Z. Chen, H. Sun, S. Ma, and N. K. Dutta, “Dual-wavelength mode-locked erbium-doped fiber ring laser using highly nonlinear fiber,” IEEE Photon. Technol. Lett.20, 2066–2068 (2008). [CrossRef]
  2. W. Zhang, J. Sun, J. Wang, and L. Liu, “Multiwavelength mode-locked fiber-ring laser based on reflective semiconductor optical amplifier,” IEEE Photon. Technol. Lett.19, 1418–1420 (2007). [CrossRef]
  3. Z. Yusoff, P. Petropoulos, K. Furusawa, T. M. Monro, and D. J. Richardson, “A 36-channel×10-GHz spectrally sliced pulse source based on super-continuum generation in normally dispersive highly nonlinear holey fiber,” IEEE Photon. Technol. Lett.15, 1689–1691 (2003). [CrossRef]
  4. Y. Dong, Z. Li, C. Yu, Y. J. Wen, Y. Wang, C. Lu, W. Hu, and T. H. Cheng, “Generation of multi-channel short-pulse sources using nonlinear optical loop mirror based on photonic crystal fiber,” in Proc. Optical Fiber Communication and the National Fiber Optic Engineers Conference (OFC/NFOEC) (2007), JWA9.
  5. M. Matsuura, N. Kishi, and T. Miki, “Widely pulsewidth-tunable multi-wavelength synchronized pulse generation utilizing a single SOA-based delayed interferometric switch,” IEEE Photon. Technol. Lett.17, 902–904 (2005). [CrossRef]
  6. S. V. Chernikov, D. J. Richardson, E. M. Dianov, and D. N. Payne, “Picosecond soliton pulse compression based on dispersion decreasing fiber,” Electron. Lett.28, 1842–1844 (1992). [CrossRef]
  7. S. V. Chernikov, J. R. Taylor, and R. Kashyap, “Comblike dispersion-profiled fiber for soliton pulse train generation,” Opt. Lett.19, 539–541 (1994). [CrossRef] [PubMed]
  8. S. V. Chernikov, J. R. Taylor, and R. Kashyap, “Experimental demonstration of step-like dispersion profiling in optical fibre for soliton pulse generation and compression,” Electron. Lett.30, 433–435 (1994). [CrossRef]
  9. K. Iwatsuki, K. Suzuki, and S. Nishi, “Adiabatic soliton compression of gain-switched DFB-LD pulse by distributed fiber Raman amplification,” IEEE Photon. Technol. Lett.3, 1074–1076 (1991). [CrossRef]
  10. T. Kogure, J. H. Lee, and D. J. Richardson, “Wavelength and duration-tunable 10-GHz 1.3-ps pulse source using dispersion decreasing fiber-based distributed Raman amplification,” IEEE Photon. Technol. Lett.16, 1167–1169 (2004). [CrossRef]
  11. M. Matsuura, B. P. Samarakoon, and N. Kishi, “Wavelength-shift-free adjustment of the pulsewidth in return-to-zero on-off keyed signals by means of pulse compression in distributed Raman amplification,” IEEE Photon. Technol. Lett.21, 572–574 (2009). [CrossRef]
  12. Q. Nguyen-The, H. Nguyen Tan, M. Matsuura, and N. Kishi, “Multi-wavelength pulse generation using a Raman amplification-based adiabatic soliton compressor,” in Proc. 37th European Conference and Exhibition on Optical Communication (ECOC) (2011), We.10.P1.10.
  13. Q. Nguyen-The, M. Matsuura, H. Nguyen Tan, and N. Kishi, “All-optical NRZ-to-RZ data format conversion with picosecond duration-tunable and pedestal suppressed operations,” IEICE Transaction on Electronics, E94-C, 1160–1166 (2011). [CrossRef]
  14. H. Nguyen Tan, Q. Nguyen-The, M. Matsuura, and N. Kishi, “Raman amplification-based multiwavelength synchronous pulse compressor and its application to all-channel OTDM demultiplexing in a single parametric-gate,” in Proc. 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), We.P-6.
  15. P Govind. Agrawal, Nonlinear Fiber Optics (Academic Press, New York, 1995).

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