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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 16 — Aug. 6, 2007
  • pp: 9963–9969
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Slow-to-fast light using absorption to gain switching in quantum-well semiconductor optical amplifier

Piotr Konrad Kondratko and Shun-Lien Chuang  »View Author Affiliations


Optics Express, Vol. 15, Issue 16, pp. 9963-9969 (2007)
http://dx.doi.org/10.1364/OE.15.009963


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Abstract

Room temperature quantum-well semiconductor optical amplifier with large input power is utilized in both the absorption and gain regime as an optical group delay and advance (slow and fast light), respectively. Material resonance created by coherent population oscillation and four wave mixing is tuned by electrical injection current, which in turn controls the speed of light. The four-wave mixing and population oscillation model explains the slow-to-fast light switching. Experimentally, the scheme achieves 200 degrees phase shift at 1 GHz, which corresponds to 0.56 delay-bandwidth product. The device presents a feasible building block of a multi-bit optical buffer system.

© 2007 Optical Society of America

1. Introduction

For a long time, controlling the propagation speed of light has been considered a challenging problem. Recently, several experiments have demonstrated that the group velocity of light can be reduced to as small as 17 meters per second [1

1. L. V. Hau, S. E. Harris, Z. Dutton, and C. H. Behroozi, “Light speed reduction to 17 metres per second in an ultracold atomic gas,” Nature 397, 594–598 (1999). [CrossRef]

]. Today, slow light research has caught a lot of attention for both its intriguing physics and potential applications. These include all-optical buffers, variable true-time delay lines [2

2. C. J. Chang-Hasnain, P.-C. Ku, J. Kim, and S. L. Chuang, “Variable optical buffer using slow light in semiconductor nanostructures,” Proc. IEEE 91, 1884–1897 (2003). [CrossRef]

], and nonlinear optics [3

3. S. E. Harris and L. V. Hau, “Nonlinear optics at low light levels,” Phys. Rev. Lett. 82, 4611–4614 (1999). [CrossRef]

], which may become essential components for all-optical signal processing and optical communication systems in the near future. From an application point of view, the so called delay-bandwidth product is more important than the absolute delay time. The delay-bandwidth product indicates how many bits can be delayed through the slow-light medium. In order to modify the group velocity of light in an optical medium, a large waveguide dispersion or material dispersion needs to be induced. Recent experiments have demonstrated that a large signal delay of more than 10 bits can be achieved from waveguide dispersion using photonic crystals [4

4. F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nat. Photonics 1, 65–71 (2006). [CrossRef]

]. However, delay tuning ability and relatively slow switching time are typically disadvantages of using waveguide dispersion. We have been studying slow light and fast light using the material dispersion approach by coherent population oscillation (CPO) and four wave mixing (FWM) in quantum well (QW) and quantum dot (QD) semiconductor optical amplifiers (SOA) [5

5. S.-W. Chang, P. K. Kondratko, H. Su, and S. L. Chuang, “Slow light based on coherent population oscillation in quantum dots at room temperature,” IEEE J. Quantum Electron. 43, 196–205 (2007). [CrossRef]

, 6

6. H. Su and S. L. Chuang, “Room temperature fast light in a quantum-dot semiconductor amplifier,” Appl. Phys. Lett. 88, 061,102 (2006). [CrossRef]

, 7

7. H. Su and S. L. Chuang, “Room temperature slow light in quantum-dot devices,” Opt. Lett. 31, 271–273 (2006). [CrossRef] [PubMed]

]. Our studies coincide to pioneering work using material resonances of CPO and FWMeffects in crystals [8

8. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Observation of ultraslow light propagation in a ruby crystal at room temperature,” Phys. Rev. Lett. 90, 1139,031–1139,034 (2003). [CrossRef]

, 9

9. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Superluminal and slow light propagation in a room temperature solid,” Science 301, 200–202 (2003). [CrossRef] [PubMed]

, 10

10. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Ultra-slow and superluminal light propagation in solids at room temperature,” J. Cond. Matt. Phys. 16, 1321–1342 (2004). [CrossRef]

]. Semiconductors have several advantages such as compactness, large bandwidth, and easy and quick response of delay tuning by direct current injection or optical pumping. We recently studied that a single microwave modulated optical beam in a SOA gives a relatively large signal delay due to strong signal to conjugate coupling effect (FWM) [11

11. H. Su, P. Kondratko, and S. L. Chuang, “Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers,” Opt. Express 14, 4800–4807 (2006). [CrossRef] [PubMed]

]. This is in contrast to the two beam experiment (a pump and a probe in counter-propagating directions) in which only the coherent population effect due to the pump beam dominates while FWM is negligible due to phase-matching consideration [7

7. H. Su and S. L. Chuang, “Room temperature slow light in quantum-dot devices,” Opt. Lett. 31, 271–273 (2006). [CrossRef] [PubMed]

, 12

12. P. K. Kondratko, H. Su, and S. L. Chuang, “Room temperature variable slow light using semiconductor quantum dots,” CLEO/QELS/Phast CThW5 (2006).

]. In this paper, we investigate both slow light and fast light in a QW-SOA using a single co-propagating modulated beam (the pump is the carrier and the probe is the sidebands created by modulation). Similar studies have been demonstrated previously in a single quantum-dot devices [13

13. M. van der Poel, J. Mørk, and J. M. Hvam, “Controllable delay of ultrashort pulses in a quantum dot optical amplifier,” Opt. Express 13, 8032–8037 (2005). [CrossRef] [PubMed]

] and in a monolithically integrated device consisting of two SOA-EA pairs (which show a device with net gain) [14

14. F. Öhman, K. Yvind, and J. Mørk, “Voltage-controlled slow light in an integrated semiconductor structure with net gain,” Opt. Express 14, 9955–9962 (2006). [CrossRef] [PubMed]

]. Other studies show very large bandwidths and consider limitations of CPO/FWM in active semiconductors [15

15. F. Öhman, K. Yvind, and J. Mørk, “Slow light at high frequencies in an amplifying semiconductor waveguide,” vol. CMN1 (CLEO/QELS/Phast, Long Beach Convention Center, California, 2006).

, 16

16. J. Mørk, R. Kjær, M. van der Poel, and K. Yvind, “Slow light in a semiconductor waveguide at gigahertz frequencies,” Opt. Express 13, 8136–8145 (2005). [CrossRef] [PubMed]

].

In this work, we experimentally present more than half-cycle optical advance-delay at GHz bandwidth. This observation of large delay-bandwidth product is attributed to a large variation in saturation power with current controlled QW-SOA. The scheme presents a discrete optical delay block, which could be utilized in a cascaded setup (with coupled optical attenuators and optical filters) as an active optical delay capable of multi-bit delays. The experimental results and theoretical models with mean filed approximations are coherently compared for analysis.

Fig. 1. The experimental setup of slow-to-fast light scheme by means of CPO and FWM in QW-SOA. The variable injection current of the SOA from absorption to gain region produces large delay tunability. ISO: optical isolator, SOA: semiconductor optical amplifier, VOA: variable optical attenuator. The power input to the variable SOA (because of the pre-amplifier) is on the order of or greater than saturation power of the current varied SOA.

2. Device and experimental investigation

The device considered in this work, shown in Fig. 1, is made up of a current driven variable QW-SOA, whose optical input (pump [5 dBm at 1310 nm] and probe sidebands) is pre-amplified using a booster SOA. The electrically varied QW-SOA is about 2.5 mm in length with about 25 dB small-signal gain at 500 mA. An isolator, in the path of the optical modulated signal guarantees that the spontaneous emission from the variable QW-SOA does not affect the booster pre-amplifier. The amplified optical signal is large in power (larger or on the order of the saturation power Psat of the variable QW-SOA), therefore, the modulated carrier response can be measured under very strong absorption. The pump-probe interaction via FWMand CPO within the QW-SOA active medium is responsible for electrically (current injection) tuned large optical delay or advance.

The experimental analysis is performed at fixed frequency (1 GHz), where the optical transfer function, the magnitude of small signal gain and its RF phase, is measured. The analysis is equivalent to an optical network thru S- parameter analysis with the current bias control into the QW-SOA. Figure 1 is a representation of a discrete device capable of a large delay-bandwidth product at GHz frequencies. Hence, this scheme can be used in a cascaded setup, coupled with isolators and signal filters, to produce multi-bit, large variable optical delays at GHz bandwidths.

3. Model analysis

Fig. 2. Theoretical model of RF phase spectra for QW-SOA switching from absorption to gain. The zero modal gain (when the medium is purely intrinsic) is the switching point from slow-to-fast light. The large response under negative modal gain is attributed to large Pin/Psat, or very small saturation power of the QW-SOA under absorption.
Fig. 3. Fixed frequency (1 GHz) RF phase variation versus linearly varying modal gain (bottom axis) and linear Pin/Psat (top axis). The figure inset shows modal gain behavior, and illustrates the absorption to gain (slow-to-fast light) switching of the QW-SOA.

4. Experimental results

Fig. 4. (top) Probe RF gain at 1 GHz vs. current. (bottom) RF phase (left axis) and time delay (right axis) vs QW-SOA bias current for a 1 GHz modulated optical pump.

Fig. 5. Time domain 1 GHz waveforms at different current bias into the QW-SOA. In time domain, the scheme achieves nearly half a cycle (171° or 0.475 ns variable delay). The absorption to gain switching of the SOA is responsible for very large delay-bandwidth tuning.

In correlation to the RF network analysis, a high speed optical oscilloscope is utilized to obtain both, time waveforms and observable tunable delay of this scheme. The oscilloscope traces for a 1 GHz modulation (1 ns period), shown in Fig. 5, are plotted at various currents into the QW-SOA. The time waveform data, by using methods of cross-correlation, can be used to extract the time delay, and also the RF phase. The extracted time delays (and RF phase) from the time domain measurement are shown (as square scatter) for comparison to the RF analysis in Fig. 4. A good match between the two observations is evident. Moreover, this time analysis clearly shows the relative slow-to-fast light scheme because in the extraction a comparison of all subsequent current traces is made to 25 mA data. Since the 25 mA waveform is the smallest current (absorptive SOA) at which the oscilloscope detector can resolve the waveforms, a smaller total relative delay of 0.475 ns is observed.

5. Conclusion

Acknowledgments

References and links

1.

L. V. Hau, S. E. Harris, Z. Dutton, and C. H. Behroozi, “Light speed reduction to 17 metres per second in an ultracold atomic gas,” Nature 397, 594–598 (1999). [CrossRef]

2.

C. J. Chang-Hasnain, P.-C. Ku, J. Kim, and S. L. Chuang, “Variable optical buffer using slow light in semiconductor nanostructures,” Proc. IEEE 91, 1884–1897 (2003). [CrossRef]

3.

S. E. Harris and L. V. Hau, “Nonlinear optics at low light levels,” Phys. Rev. Lett. 82, 4611–4614 (1999). [CrossRef]

4.

F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nat. Photonics 1, 65–71 (2006). [CrossRef]

5.

S.-W. Chang, P. K. Kondratko, H. Su, and S. L. Chuang, “Slow light based on coherent population oscillation in quantum dots at room temperature,” IEEE J. Quantum Electron. 43, 196–205 (2007). [CrossRef]

6.

H. Su and S. L. Chuang, “Room temperature fast light in a quantum-dot semiconductor amplifier,” Appl. Phys. Lett. 88, 061,102 (2006). [CrossRef]

7.

H. Su and S. L. Chuang, “Room temperature slow light in quantum-dot devices,” Opt. Lett. 31, 271–273 (2006). [CrossRef] [PubMed]

8.

M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Observation of ultraslow light propagation in a ruby crystal at room temperature,” Phys. Rev. Lett. 90, 1139,031–1139,034 (2003). [CrossRef]

9.

M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Superluminal and slow light propagation in a room temperature solid,” Science 301, 200–202 (2003). [CrossRef] [PubMed]

10.

M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Ultra-slow and superluminal light propagation in solids at room temperature,” J. Cond. Matt. Phys. 16, 1321–1342 (2004). [CrossRef]

11.

H. Su, P. Kondratko, and S. L. Chuang, “Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers,” Opt. Express 14, 4800–4807 (2006). [CrossRef] [PubMed]

12.

P. K. Kondratko, H. Su, and S. L. Chuang, “Room temperature variable slow light using semiconductor quantum dots,” CLEO/QELS/Phast CThW5 (2006).

13.

M. van der Poel, J. Mørk, and J. M. Hvam, “Controllable delay of ultrashort pulses in a quantum dot optical amplifier,” Opt. Express 13, 8032–8037 (2005). [CrossRef] [PubMed]

14.

F. Öhman, K. Yvind, and J. Mørk, “Voltage-controlled slow light in an integrated semiconductor structure with net gain,” Opt. Express 14, 9955–9962 (2006). [CrossRef] [PubMed]

15.

F. Öhman, K. Yvind, and J. Mørk, “Slow light at high frequencies in an amplifying semiconductor waveguide,” vol. CMN1 (CLEO/QELS/Phast, Long Beach Convention Center, California, 2006).

16.

J. Mørk, R. Kjær, M. van der Poel, and K. Yvind, “Slow light in a semiconductor waveguide at gigahertz frequencies,” Opt. Express 13, 8136–8145 (2005). [CrossRef] [PubMed]

17.

G. P. Agrawal, “Population pulsations and nondegenerate four-wave mixing in semiconductor lasers and amplifiers,” J. Opt. Soc. Am. B 5, 147–159 (1988). [CrossRef]

18.

T. Mukai and T. Saitoh, “Detuning characteristics and conversion efficiency of nearly degenerate four-wave-mixing in a 1.5 µm traveling-wave semiconductor-laser amplifier,” IEEE J. Quantum Electron. 26, 865–875 (1990). [CrossRef]

19.

G. Eisenstein, N. Tessler, U. Koren, J. M. Wiesenfeld, G. Raybon, and C. A. Burrus, “Length Dependence of the Saturation Characteristics in 1.5-µm Multiple Quantum Well Optical Amplifiers,” IEEE Photon. Technol. Lett. 2, 790–791 (1990). [CrossRef]

20.

T. W. Berg, J. Mørk, and J. M. Hvam, “Gain dynamics and saturation in semiconductor quantum dot amplifiers,” New J. Phys. 6, 178–201 (2004). [CrossRef]

OCIS Codes
(140.4480) Lasers and laser optics : Optical amplifiers
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(230.1150) Optical devices : All-optical devices

ToC Category:
Slow Light

History
Original Manuscript: May 25, 2007
Revised Manuscript: July 6, 2007
Manuscript Accepted: July 16, 2007
Published: July 24, 2007

Citation
Piotr K. Kondratko and Shun-Lien Chuang, "Slow-to-fast light using absorption to gain switching in quantum-well semiconductor optical amplifier," Opt. Express 15, 9963-9969 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-16-9963


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References

  1. L. V. Hau, S. E. Harris, Z. Dutton, and C. H. Behroozi, "Light speed reduction to 17 metres per second in an ultracold atomic gas," Nature 397, 594-598 (1999). [CrossRef]
  2. C. J. Chang-Hasnain, P.-C. Ku, J. Kim, and S. L. Chuang, "Variable optical buffer using slow light in semiconductor nanostructures," Proc. IEEE 91, 1884-1897 (2003). [CrossRef]
  3. S. E. Harris and L. V. Hau, "Nonlinear optics at low light levels," Phys. Rev. Lett. 82, 4611-4614 (1999). [CrossRef]
  4. F. Xia, L. Sekaric, and Y. Vlasov, "Ultracompact optical buffers on a silicon chip," Nat. Photonics 1, 65-71 (2006). [CrossRef]
  5. S.-W. Chang, P. K. Kondratko, H. Su, and S. L. Chuang, "Slow light based on coherent population oscillation in quantum dots at room temperature," IEEE J. Quantum Electron. 43, 196-205 (2007). [CrossRef]
  6. H. Su and S. L. Chuang, "Room temperature fast light in a quantum-dot semiconductor amplifier," Appl. Phys. Lett. 88, 061,102 (2006). [CrossRef]
  7. H. Su and S. L. Chuang, "Room temperature slow light in quantum-dot devices," Opt. Lett. 31, 271-273 (2006). [CrossRef] [PubMed]
  8. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, "Observation of ultraslow light propagation in a ruby crystal at room temperature," Phys. Rev. Lett. 90, 1139,031-1139,034 (2003). [CrossRef]
  9. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, "Superluminal and slow light propagation in a room temperature solid," Science 301, 200-202 (2003). [CrossRef] [PubMed]
  10. M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, "Ultra-slow and superluminal light propagation in solids at room temperature," J. Cond. Matt. Phys. 16, 1321-1342 (2004). [CrossRef]
  11. H. Su, P. Kondratko, and S. L. Chuang, "Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers," Opt. Express 14, 4800-4807 (2006). [CrossRef] [PubMed]
  12. P. K. Kondratko, H. Su, and S. L. Chuang, "Room temperature variable slow light using semiconductor quantum dots," CLEO/QELS/Phast CThW5 (2006).
  13. M. van der Poel, J. Mørk, and J. M. Hvam, "Controllable delay of ultrashort pulses in a quantum dot optical amplifier," Opt. Express 13, 8032-8037 (2005). [CrossRef] [PubMed]
  14. F. Ohman, K. Yvind, and J. Mørk, "Voltage-controlled slow light in an integrated semiconductor structure with net gain," Opt. Express 14, 9955-9962 (2006). [CrossRef] [PubMed]
  15. F. Ohman, K. Yvind, and J. Mørk, "Slow light at high frequencies in an amplifying semiconductor waveguide," vol. CMN1 (CLEO/QELS/Phast, Long Beach Convention Center, California, 2006).
  16. J. Mørk, R. Kjær, M. van der Poel, and K. Yvind, "Slow light in a semiconductor waveguide at gigahertz frequencies," Opt. Express 13, 8136-8145 (2005). [CrossRef] [PubMed]
  17. G. P. Agrawal, "Population pulsations and nondegenerate four-wave mixing in semiconductor lasers and amplifiers," J. Opt. Soc. Am. B 5, 147-159 (1988). [CrossRef]
  18. T. Mukai and T. Saitoh, "Detuning characteristics and conversion efficiency of nearly degenerate four-wavemixing in a 1.5 μm traveling-wave semiconductor-laser amplifier," IEEE J. Quantum Electron. 26, 865-875 (1990). [CrossRef]
  19. G. Eisenstein, N. Tessler, U. Koren, J. M. Wiesenfeld, G. Raybon, and C. A. Burrus, "Length Dependence of the Saturation Characteristics in 1.5- μm Multiple Quantum Well Optical Amplifiers," IEEE Photon. Technol. Lett. 2, 790-791 (1990). [CrossRef]
  20. T. W. Berg, J. Mørk, and J. M. Hvam, "Gain dynamics and saturation in semiconductor quantum dot amplifiers," New J. Phys. 6, 178-201 (2004). [CrossRef]

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