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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 24 — Nov. 23, 2009
  • pp: 22073–22080
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Blue light generated by intra-cavity frequency doubling of an edge-emitting diode laser with a periodically poled LiNbO3 crystal

Kang Li, Aiyun Yao, N. J. Copner, C. B. E. Gawith, Ian G Knight, Hans-Ulrich Pfeiffer, and Bob Musk  »View Author Affiliations


Optics Express, Vol. 17, Issue 24, pp. 22073-22080 (2009)
http://dx.doi.org/10.1364/OE.17.022073


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Abstract

We demonstrate for the first time to our knowledge intra-cavity frequency doubling (ICFD) of an edge-emitter diode laser using a 10 mm-long 5.0 μm periodically poled LiNbO3 (PPLN) crystal. An optical output power of 33 mW second harmonic blue light at 490.5 nm is generated at 1.0 A injection current, equivalent to an overall wall-plug efficiency of 1.8%. The measured M2 values of blue beam are 1.7 and 2.4 along the fast and slow axis.

© 2009 OSA

1. Introduction

During the past few years high power laser sources in the blue-green frequency range have been attracting increasing interest in various application fields such as displays, optical recording and storage, bio-medical instrumentation, digital imaging and reprographics, space based satellite laser and underwater strategic communication etc [1

1. W. P. Risk, T. R. Gosnell, and A. V. Nurmikko, Compact Blue-Green Lasers (Cambridge University Press, 2003).

]. In particular, high-brightness, high-efficiency, low-cost red-green-blue laser sources constitute a large and potentially high margin market opportunity in laser projection display systems that allow scalable screen size, high contrast, and high brightness.

Diode pumped solid state laser (DPSS) [2

2. G. D. Miller, R. G. Batchko, W. M. Tulloch, D. R. Weise, M. M. Fejer, and R. L. Byer, “42%-efficient single-pass cw second-harmonic generation in periodically poled lithium niobate,” Opt. Lett. 22(24), 1834–1836 ( 1997). [CrossRef] [PubMed]

] and optically-pumped semiconductor laser (OPSL) [3

3. J. L. A. Chilla, H. Zhou, E. Weiss, A. L. Caprara, Q. Shou, S. V. Govorkov, M. K. Reed, and L. Spinelli, “Blue & Green Optically-Pumped. Semiconductor Lasers for Display,” Proc. SPIE 5740, 41–47 ( 2005).

] usually provide a platform as light sources to produce blue and green light by second-harmonic generation (SHG). The DPSS systems can be designed in a compact package with high-quality beam, high power output and low loss. However, they still suffer from low wall-plug efficiency owing to heat management problems. Optically pumped semiconductor disk lasers, which are also known as vertical external cavity surface emitting lasers (VECSEL) [4

4. M. Kuznetsov, F. Hakimi, R. Sprague, and A. Mooradian, “Design and characteristics of high-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM00 beams,” IEEE Photon. Technol. Lett. 9, 1063–1065 ( 1997). [CrossRef]

] combine the benefits of semiconductor lasers with the advantages of DPSS and external cavity flexible application. Recently Coherent Inc. offered the first commercial solid-state laser with CW output up to 2 W at 460 nm and 8 W at 532 nm based on frequency doubling of an optically pumped VECSEL. However, the challenges for laser projection still focus on the scalable greater powers and extremely low cost requirement of the consumer electronics markets.

2. ICFD model

In order to derive a model for CW frequency doubling efficiency in the laser cavity based on applicable laser rate equations, the diode laser ICFD can be described as in Fig. 1
Fig. 1 Simplified diode laser ICFD layout
.

For an ICFD laser, the harmonic conversion is always considered as a nonlinear loss of the fundamental wave (FW) photons. Therefore the basic laser rate equations which describe the interaction of the photons and electrons in the single-mode diode laser ICFD can be expressed as [12

12. P. W. Milonni, and J. H. Eberly, Lasers (Wiley InterScience, 1988).

,13

13. T. Baer, “Large-amplitude fluctuations due to longitudinal mode coupling in diode-pumped intra-cavity doubled Nd:YAG lasers,” J. Opt. Soc. Am. B 3(9), 1175–1180 ( 1986). [CrossRef]

]
dndt=Ieβqnnτ
(1)
dqdt=βqnσqKq2
(2)
where n is the total population inversion between the two laser levels; Ie is the pump injection current divided by the electronic charge; τ is the carrier lifetime (fluorescence mainly); q is the total number of photons in the cavity at the laser frequency; K is the nonlinear coupling coefficient and Kq2 represents the nonlinear loss due to harmonic conversion.

By using the Eq. (6-11), the second harmonic power for our system is described by:
P2ω=2hν4β2τ2[(K+σβτ)K(K+σβτ)2K4βτ(σβIeτ)]2
(12)
where K is the nonlinear coefficient; and can be calculated from Eq. (8-11) using:

K=χc2hνL2
(13)

3. Experimental setup and results

Figure 2
Fig. 2 Optical set-up of ICFD based on an edge emitting diode laser using a PPLN bulk crystal
shows the scheme of ICFD based on an edge emitting diode laser using a PPLN bulk crystal. The cavity consists of a single edge emitter as gain medium, microlens in fast and slow axes L1, focus lens L2 and L3, infrared filter P1, half-wave plate P2, PPLN and output coupling mirror. The single edge emitter is 3.6 mm long and 0.4 mm wide. The beam size from the single emitter is 0.5 μm in fast axis and 3 μm in slow axis with lateral far field divergence of 5-9 degrees and vertical far field of 18.5-23.5 degrees. Ultra-low coating reflectivity on the front facet is less than 0.1% in a wavelength range around 976 nm. This high performance facet AR coating must inhibit the original diode laser cavity, allowing the extended longer laser cavity to dominate. In addition, this AR coating must not perturb the laser to cause detrimental spectral and intensity effects through the coupled cavity mechanism.

The microlens L1 is a commercially available product for single emitters with standard AR coating at 790-990 nm from LIMO Lissotschenko Mikrooptik GmbH. The output light is collimated in the fast and slow axes to produce a near symmetrical focus by only the microlens element, which is composed of a monolithic glass block with two opposite crossed cylindrical surfaces and passive alignment edges. The beam waist on the focus is imaged through a 5 mm focal length lens L2 such that it gives a near symmetrical 30 μm beam radius focused to the midpoint of a 10 mm-long 0.5 mm-thick 5.0 μm period PPLN crystal supplied by Covesion. The PPLN temperature is stabilized using an oven in order to achieve phase matching at the laser wavelength. A thin film narrow bandwidth IR filter is inserted in the cavity before the PPLN to restrict the spectral laser bandwidth to <0.1 nm so that optimal frequency conversion can be obtained. A half-wave plate is inserted in the beam path for accurate control of the pump polarization. The beam waists are positioned at the input focal plane of the focusing lens L3 while the output focal plane is positioned at the end mirror. P2, L2, L3, and PPLN have the AR coating both at 488 nm and 976 nm. Retro-reflection of the IR light is achieved at end mirror coated for high reflectivity in the near-infrared range and transparency for blue light. P1 AR coated at 976 nm has a reflectivity >95% for unpolarized light at wavelengths of 488 nm. In order to extract the counter propagation SHG beam, a tilt from filter P1 in the cavity will provide a near collinear but translated beam output. This level of translation would ensure no interference between the beams and allows this beam to be losslessly coupled out. The position of the beam waist is very important. If the position is shifted, it will cause a defocusing loss in the cavity, especially when coupling the light back into the laser emitter.

We aligned all the components to the optimum position. A maximum of 33 mW blue laser output is obtained and the SHG power characteristics are shown in Fig. 3
Fig. 3 SHG conversion for different cavity (coupling) losses.
. Here the solid lines are theoretical curves based on Eq. (12) for SHG conversion with different cavity (coupling) losses. The asterisks are the experimental data, which indicate a real cavity loss of around 70% in the experiments. Table 1

Table 1. Parameters in laser diode ICFD model

table-icon
View This Table
shows the parameters used for the laser diode ICFD model. Clearly, the coupling and reflection loss of the laser light into the laser chip is a key driver of the performance. The coupling efficiency quoted depends on a number of key parameters but the main one is the optical specification and alignment of the key micro-lens in the system. In addition, losses may be incurred by unwanted reflections and insertion loss.

The spectrum of the blue laser emission at an injection current of 1.0 A is shown in Fig. 4
Fig. 4 Spectrum of a generated blue light at an injection current of 1.0 A with an output power of 33 mW.
, which is measured using an Ocean Optics USB2000 miniature fiber optic spectrometer. A narrow peak at an emission wavelength of 490.5 nm was observed. The bandwidth of 0.65 nm is dominated by the resolution limit of the spectrometer.

Figure 5
Fig. 5 Caustic of the blue beam for both axes at an optical output power of 33 mW. The hyperbolic fit corresponds to a beam quality of M 2=1.7 in the fast axis (blue squares) and M 2=2.4 in the slow axis (black dots).
shows the caustic for both axes at an injection current of 1.0 A. The output blue beam was focused by a 100 mm focal length lens and the beam profiles were recorded using Thorlabs BP109 Beam Profiler. The M 2 values of the output blue beam at an injection current of 1.0 A were measured to be 1.7 and 2.4 along the fast and slow axis, respectively. The asymmetrical blue beam profiles are due to the asymmetrical IR beam profiles along the fast and slow axis at the beam waist. The M 2 value of the infrared beam of the diode laser was measured to be approximately 1.9 along the slow axis and the beam along the fast axis was found to be nearly diffraction limited.

In the experiments the crystal is temperature stabilized using an oven in order to achieve phase matching at the laser wavelength. Figure 6
Fig. 6 PPLN crystal temperature dependence of blue light outputs.
shows the dependence of blue light output on crystal temperature. The optimal phase-matching temperature at a blue output power of 33 mW is around 187 °C. This shows that the acceptance bandwidth of the PPLN crystal used in our work is less than around one degree.

4. Summary and Conclusion

We have demonstrated for the first time to our knowledge that stable ICFD is possible using telecom high power diode lasers with PPLN and that our model correlates with the experimental data. A blue output optical power of 33 mW was achieved at an injection current of 1.0 A with an optimal phase-matching PPLN temperature of 187 °C. The M 2 values of the output blue beam were measured to be 1.7 and 2.4 along the fast and slow axis, respectively. To increase the efficiency further, careful design of the lens used for the fast and slow axis beam shaping and use of lower-temperature MgO-doped PPLN can be considered.

Acknowledgments

The authors wish to acknowledge Dermot Quinn and Graham Moss from Digital Projection Ltd, Rob Zaple and Phil Henderson from Gooch & Housego Ltd for the helpful discussion. This project was supported by the Technology Strategy Board (TSB) with the DBERR Project No: TP/6/EPH/6/S/K2515A

References and links

1.

W. P. Risk, T. R. Gosnell, and A. V. Nurmikko, Compact Blue-Green Lasers (Cambridge University Press, 2003).

2.

G. D. Miller, R. G. Batchko, W. M. Tulloch, D. R. Weise, M. M. Fejer, and R. L. Byer, “42%-efficient single-pass cw second-harmonic generation in periodically poled lithium niobate,” Opt. Lett. 22(24), 1834–1836 ( 1997). [CrossRef] [PubMed]

3.

J. L. A. Chilla, H. Zhou, E. Weiss, A. L. Caprara, Q. Shou, S. V. Govorkov, M. K. Reed, and L. Spinelli, “Blue & Green Optically-Pumped. Semiconductor Lasers for Display,” Proc. SPIE 5740, 41–47 ( 2005).

4.

M. Kuznetsov, F. Hakimi, R. Sprague, and A. Mooradian, “Design and characteristics of high-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM00 beams,” IEEE Photon. Technol. Lett. 9, 1063–1065 ( 1997). [CrossRef]

5.

A. V. Shchegrov, D. Lee, J. P. Watson, A. Umbrasas, E. M. Strzelecka, M. K. Liebman, C. A. Amsden, A. Lewis, V. V. Doan, B. D. Moran, J. G. McInerney, and A. Mooradian, “488 nm coherent emission by intracavity frequency doubling of extended cavity surface-emitting diode lasers,” Proc. SPIE 4994, 197–205 ( 2003).

6.

A. V. Shchegrov, A. Umbrasas, J. P. Watson, D. Lee, C. A. Amsden, W. Ha, G. P. Carey, V. V. Doan, B. Moran, A. Lewis, and A. Mooradian, “532-nm laser sources based on intracavity frequency doubling of extended-cavity surface emitting diode lasers,” Proc. SPIE 5332, 151–156 ( 2004).

7.

J. P. Watson, A. V. Shchegrov, A. Umbrasas, D. Lee, C. A. Amsden, W. Ha, G. P. Carey, V. V. Doan, A. Lewis, and A. Mooradian, “Laser sources at 460 nm based on intracavity doubling of extended cavity surface emitting lasers,” Proc. SPIE 5364, 116–121 ( 2004).

8.

M. Jansen, B. D. Cantos, G. P. Carey, R. Dato, G. Giaretta, S. Hallstein, W. R. Hitchens, D. Lee, A. Mooradian, R. F. Nabiev, G. Niven, A. V. Shchegrov, A. Umbrasas, and J. P. Watson, “Visible laser and laser array sources for projection displays,” Proc. SPIE, 6135, 61350T.1–61350T.6 (2006).

9.

A. Mooradian, G. Carey, R. Carico, R. Dato, J. Dudley, G. Giaretta, S. Hallstein, J. Hofler, F. Hu, M. Jansen, C. Kocort, J. Krueger, S. Lim, N. McKinnon, G. Niven, Y. Okuno, A. Tandon, and A. Umbrasas, “Surface-emitting-diode lasers and laser arrays for displays,” J. SID 15, 805–809 ( 2007).

10.

Y. Hirano, S. Yamamoto, Y. Akino, A. Nakamura, T. Yagi, H. Sugiura, and T. Yanagisawa, “High Performance Micro Green Laser for Laser TV,” in Advanced Solid-State Photonics, OSA Technical Digest Series (CD) (Optical Society of America, 2009), paper WE1. http://www.opticsinfobase.org/abstract.cfm?URI=ASSP-2009-WE1

11.

Y. Hirano, S. Yamamoto, Y. Koyata, M. Imaki, M. Okano, T. Hamaguchi, A. Nakamura, T. Yagi, and T. Yanagisawa, “Highly Efficient Planar-Waveguide Green Laser,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2008), paper CPDA3. http://www.opticsinfobase.org/abstract.cfm?URI=CLEO-2008-CPDA3

12.

P. W. Milonni, and J. H. Eberly, Lasers (Wiley InterScience, 1988).

13.

T. Baer, “Large-amplitude fluctuations due to longitudinal mode coupling in diode-pumped intra-cavity doubled Nd:YAG lasers,” J. Opt. Soc. Am. B 3(9), 1175–1180 ( 1986). [CrossRef]

14.

D. Fluck, “Theory on phase-matched second-harmonic generation in biaxial planar waveguides,” IEEE J. Quantum Electron. 35(1), 53–59 ( 1999). [CrossRef]

15.

G. D. Boyd and D. A. Kleinman, “Parametric interaction of focused Gaussian beams,” J. Appl. Phys. 39(8), 3597–3639 ( 1968). [CrossRef]

OCIS Codes
(140.2020) Lasers and laser optics : Diode lasers
(140.3410) Lasers and laser optics : Laser resonators
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4360) Nonlinear optics : Nonlinear optics, devices

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 9, 2009
Revised Manuscript: October 8, 2009
Manuscript Accepted: October 8, 2009
Published: November 18, 2009

Citation
Kang Li, Aiyun Yao, N. J. Copner, C. B. E. Gawith, Ian G Knight, Hans-Ulrich Pfeiffer, and Bob Musk, "Blue light generated by intra-cavity frequency doubling of an edge-emitting diode laser with a periodically poled LiNbO3 crystal," Opt. Express 17, 22073-22080 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-24-22073


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References

  1. W. P. Risk, T. R. Gosnell, and A. V. Nurmikko, Compact Blue-Green Lasers (Cambridge University Press, 2003).
  2. G. D. Miller, R. G. Batchko, W. M. Tulloch, D. R. Weise, M. M. Fejer, and R. L. Byer, “42%-efficient single-pass cw second-harmonic generation in periodically poled lithium niobate,” Opt. Lett. 22(24), 1834–1836 (1997). [CrossRef] [PubMed]
  3. J. L. A. Chilla, H. Zhou, E. Weiss, A. L. Caprara, Q. Shou, S. V. Govorkov, M. K. Reed, and L. Spinelli, “Blue & Green Optically-Pumped. Semiconductor Lasers for Display,” Proc. SPIE 5740, 41–47 (2005).
  4. M. Kuznetsov, F. Hakimi, R. Sprague, and A. Mooradian, “Design and characteristics of high-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM00 beams,” IEEE Photon. Technol. Lett. 9, 1063–1065 (1997). [CrossRef]
  5. A. V. Shchegrov, D. Lee, J. P. Watson, A. Umbrasas, E. M. Strzelecka, M. K. Liebman, C. A. Amsden, A. Lewis, V. V. Doan, B. D. Moran, J. G. McInerney, and A. Mooradian, “488 nm coherent emission by intracavity frequency doubling of extended cavity surface-emitting diode lasers,” Proc. SPIE 4994, 197–205 (2003).
  6. A. V. Shchegrov, A. Umbrasas, J. P. Watson, D. Lee, C. A. Amsden, W. Ha, G. P. Carey, V. V. Doan, B. Moran, A. Lewis, and A. Mooradian, “532-nm laser sources based on intracavity frequency doubling of extended-cavity surface emitting diode lasers,” Proc. SPIE 5332, 151–156 (2004).
  7. J. P. Watson, A. V. Shchegrov, A. Umbrasas, D. Lee, C. A. Amsden, W. Ha, G. P. Carey, V. V. Doan, A. Lewis, and A. Mooradian, “Laser sources at 460 nm based on intracavity doubling of extended cavity surface emitting lasers,” Proc. SPIE 5364, 116–121 (2004).
  8. M. Jansen, B. D. Cantos, G. P. Carey, R. Dato, G. Giaretta, S. Hallstein, W. R. Hitchens, D. Lee, A. Mooradian, R. F. Nabiev, G. Niven, A. V. Shchegrov, A. Umbrasas, and J. P. Watson, “Visible laser and laser array sources for projection displays,” Proc. SPIE, 6135, 61350T.1–61350T.6 (2006).
  9. A. Mooradian, G. Carey, R. Carico, R. Dato, J. Dudley, G. Giaretta, S. Hallstein, J. Hofler, F. Hu, M. Jansen, C. Kocort, J. Krueger, S. Lim, N. McKinnon, G. Niven, Y. Okuno, A. Tandon, and A. Umbrasas, “Surface-emitting-diode lasers and laser arrays for displays,” J. SID 15, 805–809 (2007).
  10. Y. Hirano, S. Yamamoto, Y. Akino, A. Nakamura, T. Yagi, H. Sugiura, and T. Yanagisawa, “High Performance Micro Green Laser for Laser TV,” in Advanced Solid-State Photonics, OSA Technical Digest Series (CD) (Optical Society of America, 2009), paper WE1. http://www.opticsinfobase.org/abstract.cfm?URI=ASSP-2009-WE1
  11. Y. Hirano, S. Yamamoto, Y. Koyata, M. Imaki, M. Okano, T. Hamaguchi, A. Nakamura, T. Yagi, and T. Yanagisawa, “Highly Efficient Planar-Waveguide Green Laser,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2008), paper CPDA3. http://www.opticsinfobase.org/abstract.cfm?URI=CLEO-2008-CPDA3
  12. P. W. Milonni, and J. H. Eberly, Lasers (Wiley InterScience, 1988).
  13. T. Baer, “Large-amplitude fluctuations due to longitudinal mode coupling in diode-pumped intra-cavity doubled Nd:YAG lasers,” J. Opt. Soc. Am. B 3(9), 1175–1180 (1986). [CrossRef]
  14. D. Fluck, “Theory on phase-matched second-harmonic generation in biaxial planar waveguides,” IEEE J. Quantum Electron. 35(1), 53–59 (1999). [CrossRef]
  15. G. D. Boyd and D. A. Kleinman, “Parametric interaction of focused Gaussian beams,” J. Appl. Phys. 39(8), 3597–3639 (1968). [CrossRef]

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