OSA's Digital Library

Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 14, Iss. 26 — Dec. 25, 2006
  • pp: 13083–13088
« Show journal navigation

Generation of two-mode bright squeezed light using a noise-suppressed amplified diode laser

Yun Zhang, Kazuhiro Hayasaka, and Katsuyuki Kasai  »View Author Affiliations


Optics Express, Vol. 14, Issue 26, pp. 13083-13088 (2006)
http://dx.doi.org/10.1364/OE.14.013083


View Full Text Article

Acrobat PDF (350 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We present the generation of nonclassical state using an amplified diode laser as a light source. The intensity noise of an amplified diode laser was significantly suppressed and reached the shot noise limit at 15 MHz using both a filter cavity and resonant optical feedback. Frequency doubling efficiency of 66% and up to 120 mW output power of green has been achieved in cw second-harmonic generation from 1080 nm to 540 nm. Bright two-mode amplitude-squeezed state was generated from a type-II nondegenerate optical parametric amplifier pumped by generated green light. The measured noise reduction is 2.1±0.2 dB below the shot-noise level.

© 2006 Optical Society of America

1. Introduction

Among many methods of generation of squeezed state, the optical parametric oscillator (OPO) and amplifier (OPA) appear to be relatively simple and efficient method. Type-II continuous–wave nondegenerate optical parametric oscillators (cw-NOPOs) have been utilized to generate quantum-correlated twin beams and two-mode squeezed vacuum when they are operating above and below their threshold, respectively [1

1. K. C. Peng, Q. Pan, H. Wang, Y. Zhang, H. Su, and C. D. Xie, “Generation of two-mode quadrature-phase squeezing and intensity-difference squeezing from a cw-NOPO,” Appl. Phys. B 66, 755–758(1998). [CrossRef]

]. In most of these experiments, type-II KTP crystals were usually used with Nd:YAG lasers as pump source since stable diode-pumped Nd:YAG lasers are commercially available [2

2. J. Mertz, T. Debuisschert, A. Heidmann, C. Fabre, and E. Giacobino, “Improvements in the observed intensity correlation of optical parametric oscillator twin beams,” Opt. Lett. 16, 1234–1236 (1991). [CrossRef] [PubMed]

, 3

3. A. S. Villar, L. S. Cruz, K. N. Cassemiro, M. Martinelli, and P. Nussenzveig, “Generation of bright two-color continuous variable entanglement” Phys. Rev. Lett. 95, 243603 (2005). [CrossRef] [PubMed]

]. Unfortunately, these experimental setups have a severe problem of non-zero walk-off, which leads to a limited nonlinear interaction length and polarization crosstalk. In addition, it is impossible to operate under frequency degenerate condition without walk-off compensation when one uses the KTP crystal with the Nd:YAG laser at 1064 nm. The fundamental wavelength of 1080 nm can solve this problem since it can realize type II noncritical phase matching (NCPM) in an a-cut KTP crystal. Kimble’s group and group of Shanxi University conducted lots of interesting experiments using an a-cut KTP crystal pumped by their homemade Nd:YAP laser at 1080 nm, such as the landmark experiment of realization of EPR paradox [4

4. Z. Y. Ou, S. F. Pereira, H. J. Kimble, and K. C. Peng, “Realization of the Einstein-Podolsky-Rosen paradox for continuous variables” Phys. Rev. Lett. 68, 3663–3666(1992). [CrossRef] [PubMed]

], quantum dense coding [5

5. X. Y. Li, Q. Pan, J. T. Jiang, J. Zhang, C. D. Xie, and K. C. Peng, “Quantum dense coding by exploiting a bright Einstein-Podolsky-Rosen beam,” Phys. Rev. Lett. 88, 047904 (2002). [CrossRef] [PubMed]

] and entanglement swapping [6

6. X. J. Jia, X. L. Su, Q. Pan, J. R. Gao, C. D. Xie, and K. C. Peng, “Experimental demonstration of unconditional entanglement swapping for continuous variables,” Phys. Rev. Lett. 93, 250503 (2005). [CrossRef] [PubMed]

]. In their successful experiments, not only the experimental setup is simplified but also intracavity losses are reduced and the efficiency of downconversion is improved by exploiting the type-II NCPM condition in an a-cut KTP crystal.

In this paper, we report the first experiment on generation of a two-mode bright squeezed state by NOPA using the above-mentioned noise-suppressed amplified diode laser. To our best knowledge, the setup is the first cw NOPA pumped by a frequency-doubled diode laser. The measured noise reduction is 2.1±0.2 dB below the shot noise level.

2. Experimental setup

The experimental setup is shown schematically in Fig. 1. A grating-stabilized single-mode extended-cavity diode laser (ECDL) severs as the primary light source. The wavelength of diode laser is selected at 1080 nm in our experiment. The master laser provides 50 mW of power after the grating, and more than 30 mW is available for injection into the tapered amplifier chip. The output power from the amplifier chip is about 450 mW. To reduce the excess noise of the diode laser, we sent the beam through a filter cavity and used the resonant optical feedback. A small fraction of the transmitted light was picked off by the polarizing beamsplitter (PBS) with a half wave plate, which can also control the optical feedback level, and sent into ECDL as a resonant optical feedback. When the cavity is locked, we measured more than 200 mW transmitted light power for an incident power of 380mW, representing a transmission efficiency of 53%. Most of the noise suppressed laser power is introduced into the frequency doubler to generate second harmonic at 540 nm as pump beam for the NOPA. About 5 mW of power is injected to the NOPA as a seed wave. The polarization of seed wave is 45° relative to the b axis of the KTP crystal, and it is decomposed to signal and idler seed waves with identical intensity and the orthogonal polarizations along the b and c axes, respectively, which correspond to the vertical and horizontal polarization. The generated bright two-mode squeezed state is detected by a homodyne detector.

Fig. 1. Experimental setup. SHG, second harmonic generator; NOPA, nondegenerate optical parametric amplifier; λ/2, half wave plate; BS, beamsplitter; P, polarizing beamsplitter.

3. Results and discussion

Fig. 2. Amplitude noise of our noise suppressed diode laser as a function of frequency. Trace a is the electronic noise of detector, trace b is the shot-noise limit, trace c and trace d are the noise power spectrum of the suppressed laser field and unsuppressed laser field respectively. resolution bandwidth, 300 kHz; video bandwidth, 3 kHz.

η=(4Tin)2ENLPω(Tin+LSHG+ηENLPω)4,
(1)

where η=P 2ω/Pω is the SHG efficiency and LSHG=0.4% is a total round-trip loss of SHG cavity determined by the measured finesse of 250. The single-pass conversion efficiency ENL of the crystal, which is set to the value ENL=1.1×10-3 W -1, is the only adjustable parameter. The experimental results are in reasonable agreement with the expected curves. The maximum green output power of 120 mW is obtained when the input fundamental power is 180 mW. The directly measured doubling efficiency is 66%.

Fig. 3. The output green power and conversion efficiency versus input fundamental power. Solid curves, theoretical calculation; Dots and triangles, experimental values.

The NOPA has a semimonolithic configuration consisting of a concave mirror of 20-mm radius of curvature was coated with a Tout=2% transmission for 1080 nm and high reflection for 540 nm. It serves as an output coupler for our NOPA. A facet of KTP inside the cavity was coated for antireflection at both 1080 and 540 nm. The other facet was coated for antireflection at 540 nm and high reflection at 1080 nm. It acts as the input mirror of the pump field at 540 nm. The measured finesse of the resonator is 300, the free spectral range is 6 GHz, and the cavity bandwidth is γc=20 MHz. We calculated a total round-trip loss of LNOPA=0.3% by the measured finesse. The escape efficiency of ξ=Tout/(Tout+LNOPA)=0.87 is obtained. Due to the large transmission of input coupler at 540 nm, the pump field only passes the cavity twice without resonating. The crystal nonlinear efficiency of ENL=1.1×10-3 W -1 was estimated from the SHG process. From this we deduce an expected threshold pump power for parametric oscillation, Pth=(Tout+LNOPA)2/4ENL=120 mW.

The principal difficulty of the NOPA resides in frequency-degenerate operation. There are several ways to solve this problem, such as seed injection [10

10. Y. Zhang, H. Wang, X. Y. Li, J. T. Jing, C. D. Xie, and K. C. Peng, “Experimental generation of bright two-mode quadrature squeezed light from a narrow band nondegenerate optical parametric amplifier,” Phys. Rev. A , 62, 023813 (2000). [CrossRef]

], inserting a half-wave plate in cavity [11

11. J. Laurat, L. Longchambon, C. Fabre, and T. Coudreau, “Experimental investigation of amplitude and phase quantum correlations in a type II optical parametric oscillator above threshold: from nondegenerate to degenerate operation,” Opt. Lett. 30, 1177–1179 (2005). [CrossRef] [PubMed]

], and active adding phase-locking between the signal and idler [12

12. S. Feng and O. Pfister, “Quantum Interference of Ultrastable Twin Optical Beams,” Phys. Rev. Lett. 92, 203601 (2004). [CrossRef] [PubMed]

]. For this purpose, the seed wave is injected in our work. The NOPA cavity must be simultaneously resonant at the signal and idler of seed beam frequency. By fine tuning of the crystal temperature the birefringence between the signal and idler waves in KTP is compensated and the simultaneous resonance is obtained. Once the double resonance is completed, phase-sensitive parametric amplification/deamplification was realized. Operating below threshold and scanning the pump phase with the PZT one observes maximum amplification factors up to 20. Stable operation of the squeezer can be achieved by locking the cavity on the frequency of the seed wave via a dither-locking technique.

Fig. 4. Noise power of i + and i - generated at the homodyne detector. Measured frequency, 16 MHz; resolution bandwidth, 300 kHz; video bandwidth, 3 kHz. For details see text.

Figure 4 shows the measured variances at ƒ=16 MHz when the pump power was about 100 mW. Trace (b) and (c) refer to the amplitude noise and the shot noise limit, respectively, when the pump phase is fixed on deamplification operating. A measurement of V det(i +) and V det(i -) is also given in traces (f) and (e) when the phase is scanned. The amplitude squeezing up to 2.1±0.2 dB is measured under the total detection efficiency of η=86% (detector quantum efficiency 90% and propagation efficiency 96%). Trace (d) gives the measured shot noise limit without pump and trace (a) gives the electronic noise of our detector. We note that the noise powers for the available light power is close to that the electronic noise floor, so the electronic noise floor should be subtracted. The inferred value after taking into account the electronics floor is 2.5±0.2 dB. In a simplified mode the measured amplitude spectrum is expressed by [14

14. K. Schneider, R. Bruckmeier, H. Hansen, S. Schiller, and J. Mlynek, “Bright squeezed-light generation by a continuous-wave semimonolithic parametric amplifier,” Opt. Lett. 21, 1396–1398 (1996). [CrossRef] [PubMed]

]

Vsq,det=1ηξ4PpumpPth(1+PpumpPth)2+(2fγc)2.
(2)

Using the parameters of our experiment indicated in the preceding paragraphs, a theoretical squeezing of 2.5 dB is predicted. The experiment results are very well in agreement with this prediction.

Although the squeezing of just 2.1dB is observed, it is the first experiment on generation squeezed state using LD as a light source directly. The frequency at which the noise of LD was suppressed to shot noise level can be further decreased by exploiting a high-finesse cavity. Therefore, a large magnitude of squeezing may be generated at low frequency. Furthermore, we can separate the two-mode squeezing state into signal and idler beams. The quantum correlation between amplitude and phase quadratures of intense signal and idler beams can be directly used as the quantum entanglement source for quantum information and communications experiments.

4. Conclusion

In conclusion, two-mode bright amplitude squeezing of 2.1±0.2 dB at an output power of about 1 mW is obtained from the type-II NCPM NOPA pumped by the 540 nm green light. The pump light, as great as 120 mW, is obtained by frequency doubling of a noise-suppressed diode laser operating at 1080 nm. We have demonstrated good agreement between our experimental results and the theoretical predictions.

Acknowledgments

We are grateful to T. Hirano for helpful discussions.

References and links

1.

K. C. Peng, Q. Pan, H. Wang, Y. Zhang, H. Su, and C. D. Xie, “Generation of two-mode quadrature-phase squeezing and intensity-difference squeezing from a cw-NOPO,” Appl. Phys. B 66, 755–758(1998). [CrossRef]

2.

J. Mertz, T. Debuisschert, A. Heidmann, C. Fabre, and E. Giacobino, “Improvements in the observed intensity correlation of optical parametric oscillator twin beams,” Opt. Lett. 16, 1234–1236 (1991). [CrossRef] [PubMed]

3.

A. S. Villar, L. S. Cruz, K. N. Cassemiro, M. Martinelli, and P. Nussenzveig, “Generation of bright two-color continuous variable entanglement” Phys. Rev. Lett. 95, 243603 (2005). [CrossRef] [PubMed]

4.

Z. Y. Ou, S. F. Pereira, H. J. Kimble, and K. C. Peng, “Realization of the Einstein-Podolsky-Rosen paradox for continuous variables” Phys. Rev. Lett. 68, 3663–3666(1992). [CrossRef] [PubMed]

5.

X. Y. Li, Q. Pan, J. T. Jiang, J. Zhang, C. D. Xie, and K. C. Peng, “Quantum dense coding by exploiting a bright Einstein-Podolsky-Rosen beam,” Phys. Rev. Lett. 88, 047904 (2002). [CrossRef] [PubMed]

6.

X. J. Jia, X. L. Su, Q. Pan, J. R. Gao, C. D. Xie, and K. C. Peng, “Experimental demonstration of unconditional entanglement swapping for continuous variables,” Phys. Rev. Lett. 93, 250503 (2005). [CrossRef] [PubMed]

7.

K. Hayasaka, Y. Zhang, and K. Kasai, “Generation of twin beams from an optical parametric oscillator pumped by a frequency-doubled diode laser,” Opt. Lett. 29, 1665–1667 (2004). [CrossRef] [PubMed]

8.

Y. Zhang, K. Hayasaka, and K. Kasai, “Efficient noise suppression of amplified diode laser,” to be published in Appl. Phys. B (online first http://dx.doi.org/10.1007/s00340-006-2436-2).

9.

K. Hayasaka, Y. Zhang, and K. Kasai, “Generation of 22.8 mW single-frequency green light by frequency doubling of a 50-mW diode laser,” Opt. Express 12, 3567 (2004). [CrossRef] [PubMed]

10.

Y. Zhang, H. Wang, X. Y. Li, J. T. Jing, C. D. Xie, and K. C. Peng, “Experimental generation of bright two-mode quadrature squeezed light from a narrow band nondegenerate optical parametric amplifier,” Phys. Rev. A , 62, 023813 (2000). [CrossRef]

11.

J. Laurat, L. Longchambon, C. Fabre, and T. Coudreau, “Experimental investigation of amplitude and phase quantum correlations in a type II optical parametric oscillator above threshold: from nondegenerate to degenerate operation,” Opt. Lett. 30, 1177–1179 (2005). [CrossRef] [PubMed]

12.

S. Feng and O. Pfister, “Quantum Interference of Ultrastable Twin Optical Beams,” Phys. Rev. Lett. 92, 203601 (2004). [CrossRef] [PubMed]

13.

Y. Zhang, K. Kasai, and M. Watanabe, “Classical and quantum properties of optical parametric amplifier/deamplifier,” Phys. Lett. A 297, 29 (2002). [CrossRef]

14.

K. Schneider, R. Bruckmeier, H. Hansen, S. Schiller, and J. Mlynek, “Bright squeezed-light generation by a continuous-wave semimonolithic parametric amplifier,” Opt. Lett. 21, 1396–1398 (1996). [CrossRef] [PubMed]

OCIS Codes
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(270.0270) Quantum optics : Quantum optics
(270.6570) Quantum optics : Squeezed states

ToC Category:
Quantum Optics

History
Original Manuscript: September 27, 2006
Revised Manuscript: November 30, 2006
Manuscript Accepted: December 10, 2006
Published: December 22, 2006

Citation
Yun Zhang, Kazuhiro Hayasaka, and Katsuyuki Kasai, "Generation of two-mode bright squeezed light using a noise-suppressed amplified diode laser," Opt. Express 14, 13083-13088 (2006)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-26-13083


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. K. C. Peng, Q. Pan, H. Wang, Y. Zhang, H. Su and C. D. Xie, "Generation of two-mode quadrature-phase squeezing and intensity-difference squeezing from a cw-NOPO," Appl. Phys. B 66, 755-758(1998). [CrossRef]
  2. J. Mertz, T. Debuisschert, A. Heidmann, C. Fabre, and E. Giacobino, "Improvements in the observed intensity correlation of optical parametric oscillator twin beams," Opt. Lett. 16, 1234-1236 (1991). [CrossRef] [PubMed]
  3. A. S. Villar, L. S. Cruz, K. N. Cassemiro, M. Martinelli, and P. Nussenzveig, "Generation of bright two-color continuous variable entanglement" Phys. Rev. Lett. 95, 243603 (2005). [CrossRef] [PubMed]
  4. Z. Y. Ou, S. F. Pereira, H. J. Kimble, and K. C. Peng, "Realization of the Einstein-Podolsky-Rosen paradox for continuous variables" Phys. Rev. Lett. 68, 3663-3666(1992). [CrossRef] [PubMed]
  5. X. Y. Li, Q. Pan, J. T. Jiang, J. Zhang, C. D. Xie, and K. C. Peng, "Quantum dense coding by exploiting a bright Einstein-Podolsky-Rosen beam," Phys. Rev. Lett. 88, 047904 (2002). [CrossRef] [PubMed]
  6. X. J. Jia, X. L. Su, Q. Pan, J. R. Gao, C. D. Xie, and K. C. Peng, "Experimental demonstration of unconditional entanglement swapping for continuous variables," Phys. Rev. Lett. 93, 250503 (2005). [CrossRef] [PubMed]
  7. K. Hayasaka, Y. Zhang, and K. Kasai, "Generation of twin beams from an optical parametric oscillator pumped by a frequency-doubled diode laser," Opt. Lett. 29, 1665-1667 (2004). [CrossRef] [PubMed]
  8. Y. Zhang, K. Hayasaka, and K. Kasai, "Efficient noise suppression of amplified diode laser," to be published in Appl. Phys. B (online first http://dx.doi.org/10.1007/s00340-006-2436-2).
  9. K. Hayasaka, Y. Zhang, and K. Kasai, "Generation of 22.8 mW single-frequency green light by frequency doubling of a 50-mW diode laser," Opt. Express 12, 3567 (2004). [CrossRef] [PubMed]
  10. Y. Zhang, H. Wang, X. Y. Li, J. T. Jing, C. D. Xie, and K. C. Peng, "Experimental generation of bright two -mode quadrature squeezed light from a narrow band nondegenerate optical parametric amplifier," Phys. Rev. A,  62, 023813 (2000). [CrossRef]
  11. J. Laurat, L. Longchambon, C. Fabre, and T. Coudreau, "Experimental investigation of amplitude and phase quantum correlations in a type II optical parametric oscillator above threshold: from nondegenerate to degenerate operation," Opt. Lett. 30, 1177-1179 (2005). [CrossRef] [PubMed]
  12. S. Feng and O. Pfister, "Quantum interference of Ultrastable Twin Optical Beams," Phys. Rev. Lett. 92, 203601 (2004). [CrossRef] [PubMed]
  13. Y. Zhang, K. Kasai, M. Watanabe, "Classical and quantum properties of optical parametric amplifier/deamplifier," Phys. Lett. A 297, 29 (2002). [CrossRef]
  14. K. Schneider, R. Bruckmeier, H. Hansen, S. Schiller, and J. Mlynek, "Bright squeezed-light generation by a continuous-wave semimonolithic parametric amplifier," Opt. Lett. 21, 1396-1398 (1996). [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1. Fig. 2. Fig. 3.
 
Fig. 4.
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited