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6672 OPTICS LETTERS / Vol. 39, No. 23 / December 1, 2014 Efficient yellow-green light generation at 561 nm by frequency-doubling of a QD-FBG laser diode in a PPLN waveguide Ksenia A. Fedorova,1,* Grigorii S. Sokolovskii,2,3 Maksim Khomylev,4 Daniil A. Livshits,4 and Edik U. Rafailov1 1 School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham B4 7ET, UK 2 Ioffe Physico-Technical Institute, 26 Polytechnicheskaya Str., St. Petersburg 194021, Russia 3 Saint-Petersburg State Polytechnical University, St. Petersburg 195251, Russia 4 Innolume GmbH, 11 Konrad-Adenauer-Allee, Dortmund 44263, Germany *Corresponding author: [email protected] Received September 1, 2014; revised October 20, 2014; accepted October 24, 2014; posted October 24, 2014 (Doc. ID 222071); published November 24, 2014 A compact high-power yellow–green continuous wave (CW) laser source based on second-harmonic generation (SHG) in a 5% MgO doped periodically poled congruent lithium niobate (PPLN) waveguide crystal pumped by a quantum-dot fiber Bragg grating (QD-FBG) laser diode is demonstrated. A frequency-doubled power of 90.11 mW at the wavelength of 560.68 nm with a conversion efficiency of 52.4% is reported. To the best of our knowledge, this represents the highest output power and conversion efficiency achieved to date in this spectral region from a diode-pumped PPLN waveguide crystal, which could prove extremely valuable for the deployment of such a source in a wide range of biomedical applications. © 2014 Optical Society of America OCIS codes: (140.3515) Lasers, frequency doubled; (230.4320) Nonlinear optical devices; (230.7370) Waveguides; (140.5960) Semiconductor lasers; (250.5590) Quantum-well, -wire and -dot devices. http://dx.doi.org/10.1364/OL.39.006672 Compact continuous wave (CW) lasers in the visible spectral region at around 560 nm are attractive for a variety of cutting-edge applications in many diverse fields. In particular, such lasers have already found valuable applications in cosmetic dermatology for photodynamic rejuvenation therapy [1] and cancer phototherapy [2,3] for a selective treatment of cancer cells without toxic repercussions on normal cells by driving a controlled photorelease of drugs with the 561 nm irradiation. The yellow–green lasers of this wavelength also play an important role in ophthalmology [4] and are ideal for treatments around the macula because of the high absorption in hemoglobin and a negligible absorption by melanin in the retinal pigment epithelium and macular xanthophyll. Furthermore, the lasers near 561 nm have found an application in flow cytometry [5,6], Laser Doppler velocimetry [7], and confocal microscopy [8], and are used to excite phycoerythrin and its tandem, as well as red fluorescent proteins such as mCherry, mStrawberry, DsRed, and dTomato. Recently, such lasers have also attracted attention for their application in interferometry [9] and spectroscopy [10]. Since the yellow region of the optical spectrum, where a range of important fluorescent proteins are optimally excited, remains inaccessible to conventional diode lasers, frequency-doubling and sum-frequency generation in second-order nonlinear crystals using infrared laser sources are traditionally used. Several systems generating yellow–green light at ∼561 nm wavelength were recently reported. In particular, CW laser sources at 561 nm using frequency doubling of an Nd:YAG laser in an LBO crystal have been demonstrated with output power of 1.2 W [11], 2.3 W [4], and 60 W [12], and optical-to-optical conversion efficiency of 13.3%, 10.6%, and 6.1%, respectively. Second harmonic generation (SHG) at 561 nm using an Nd:YAG laser and a KTA crystal with 0146-9592/14/236672-03$15.00/0 output power of 55 mW [13] and 2.6 W [14], and corresponding conversion efficiency of 23% and 8.7%, has also been reported. Output power of 0.5 W [7] and 8.1 W [15], and optical-to optical efficiency of 17.9% and 5.5%, respectively, from frequency doubled Nd:YAG/KTP lasers at 561 nm has been recently obtained. Up to 570 mW of output power at 561 nm with an optical-to-optical conversion efficiency of 3.3% has also been achieved from an Nd:KGdWO4 2 self-Raman laser by intracavity sum-frequency mixing of fundamental and first-Stokes wavelengths in an LBO crystal [16]. Recently, Yang et al. demonstrated a laser source at 561 nm with output power of 10 mW and conversion efficiency of 2% by frequency doubling of an Nd:YAG monoplane laser in a PPLN [10]. An attractive way to develop a compact, efficient, and low-cost yellow laser source is SHG in a periodically poled nonlinear crystal containing a waveguide [17] which because of the high pump light intensities over a long interaction length allows highly efficient frequency conversion even at low and moderate pump power levels. In this respect, a PPLN waveguide crystal, which offers high nonlinearity along with strong confinement of light, is one of the best candidates for highly efficient nonlinear wavelength conversion. Recent progress in the fabrication of good quality waveguides in PPLN crystals in combination with the availability of low-cost, highly efficient semiconductor diode lasers allows compact CW laser sources in the visible spectral region to be realized [18]. Today, the emphasis in laser technology has moved to novel quantum-dot (QD) lasers which offer the flexibility in choice of semiconductor material compounds allowed for a wide spectral range to be covered. Laser sources based on InAs/GaAs QD structures, offering the coverage of a broad wavelength range between 1 and 1.3 μm [19,20], are especially useful in this regard. © 2014 Optical Society of America December 1, 2014 / Vol. 39, No. 23 / OPTICS LETTERS 6673 In recent years, several laser sources generating visible light in periodically poled lithium niobate waveguide crystals have been demonstrated. In particular, blue light generation with output power up to 189 mW [21] and conversion efficiency up to 52% [22] by SHG in a PPLN waveguide has been obtained. Frequency doubling in an MgO: PPLN waveguide was also used to demonstrate the generation of green light at 530 nm [23] and 556 nm [24] with output power of 107 and 11.8 mW and conversion efficiency of 51% and 52.5%, respectively. Generation of yellow light at 575 [25] and 578 nm [26] in a PPLN waveguide with output powers of 40 and 10 mW, and conversion efficiencies of 7% and 29.6%, respectively, has been reported. The output power of 494 mW with overall conversion efficiency of 41% at 589 nm by sum–frequency generation in a Zn:PPLN ridge waveguide pumped by two Nd:YAG lasers at 1064 and 1319 nm was also recently obtained [27]. However, to date, only 32 mW of yellow–green emission at 560 nm with conversion efficiency of 32% generated by SHG from a broad area laser diode and PPLN waveguide has been demonstrated [28]. Here, we report on a compact frequency-doubling scheme generating over 90 mW of CW yellow–green light at 561 nm with a conversion efficiency in excess of 52% in the periodically poled lithium niobate waveguide pumped by a quantum-dot fiber Bragg grating (QD-FBG) laser. The experimental setup consisted of a QD-FBG pump laser (Innolume GmbH) operating at ∼1122 nm and a PPLN waveguide crystal (as illustrated in Fig. 1). The QD-FBG pump laser consisted of a 6 mm long gain chip with a ridge waveguide normal to the facets. An active region of the chip was similar to that described in [20] and contained InAs QD layers, incorporated into Al0.35 Ga0.65 As cladding layers and grown by molecular beam epitaxy (MBE). The front facet of the gain chip was anti-reflective (AR) coated guaranteeing the back reflection below 0.03%, and the back facet had high reflective coating. The gain chip was embedded in a 14-pin butterfly package with the laser output coupled into a single-mode polarization maintaining fiber PM-980. The external cavity was closed with the fiber Bragg grating (FBG) of 10% peak reflection at 1122 nm, which was located in 100 cm from the chip. The QD-FBG laser was mounted on a copper heatsink, and its temperature was controlled by a thermo-electric cooler. The temperature of the laser was set at 25°C with a wavelength of 1121.4 nm. The maximum output power of the QD- FBG laser diode used in our experiments was 350 mW (limited mainly by the thermal rollover). The output of the laser was collimated with a 30× (NA ∼ 0.50) ARcoated aspheric lens and then coupled into the PPLN waveguide using a 40× (NA ∼ 0.55) AR-coated aspheric lens with ∼50% laser-to-waveguide coupling efficiency. A half-wave plate was used to adjust the polarization for optimal SHG in the PPLN crystal. The frequencydoubled output was then collimated by a 30× (NA∼ 0.50) AR-coated aspheric lens onto a power meter after a suitable filter at the fundamental wavelength. The frequency-doubling crystal waveguide used in this work was a 5% MgO-doped Y-cut congruent lithium niobate (HC Photonics Corp) which was periodically poled for SHG at ∼1122 nm. The crystal facets were optically polished at ∼5.4° and had an AR-coating for 1122 nm (R < 0.5%) and 561 nm (R < 1%) on both input/output facets. The PPLN crystal was 10 mm in length and contained a channel waveguide with a cross-sectional area of ∼4 × 5 μm2 which was covered by an additional lithium niobate layer on top of the waveguide to support a more symmetric mode profile. For quasi-phase-matching, the temperature of the crystal was stabilized at 25°C. The measured second harmonic output power and conversion efficiency as functions of the launched pump power are shown in Fig. 2. The output power is quadratically increased as pump power increases, as expected. The maximum frequency-doubled power of 90.11 mW at the wavelength of 560.7 nm from 172 mW of pump power was obtained. This corresponded to an opticalto-optical conversion efficiency of 52.4% and a wall-plug efficiency of 4.3%. To the best of our knowledge, the demonstrated output power and conversion efficiency are the highest at this wavelength reported until now from a frequency-doubled diode laser in a PPLN waveguide crystal. The obtained maximum SHG output power was only limited by the available pump power from the QD-FBG laser. No degradation of the nonlinear waveguide crystal was observed in our experiments (although, no long-term stability tests were performed). The experimental results Fig. 1. Simplified schematic of the experimental setup (including quantum-dot fiber bragg grating (QD-FBG) laser, aspheric lenses, half-wave plate (λ∕2), 5% MgO doped periodically poled congruent lithium niobate waveguide crystal (PPLN), and filter at 1122 nm. Fig. 2. Dependences of the frequency-doubled output power and conversion efficiency on the launched pump power. The curves are the numerical tanh2 -fit of the experimental data according to the depleted pump approximation with normalized conversion efficiency of 500%/W. 6674 OPTICS LETTERS / Vol. 39, No. 23 / December 1, 2014 Fig. 3. Optical spectrum of the second harmonic generated output at 560.7 nm. Inset: the optical spectrum of the pump QD-FBG laser (1121.4 nm). were numerically fitted according to the depleted pump approximation with normalized conversion efficiency of 500%/W (Fig. 2). The optical spectrum of the yellow–green laser emission at 560.7 nm was measured with an Ocean Optics spectrometer (Fig. 3) and exhibited a spectral width of around 0.5 nm (limited only by the instrumental resolution of the spectrometer used). The inset of Fig. 3 depicts the measured optical spectrum of the pump QD-FBG laser at 1121.4 nm with a spectral width of ∼0.3 nm, which was dominated by the resolution limit of the optical spectrum analyzer (OSA Advantest Q8384) used to monitor the laser spectrum. No degradation of the beam quality of the yellow–green light was observed in the whole range of output powers. To summarize, a highly efficient frequency-doubling of a CW QD-FBG laser was demonstrated using a 5% MgOdoped PPLN waveguide crystal. Yellow–green CW light at 561 nm with more than 90 mW of output power was generated with conversion efficiency in excess of 52%. To the best of our knowledge, this is the highest output power and conversion efficiency at the wavelength around 560 nm reported until now from a frequencydoubled diode laser in a PPLN waveguide crystal. Compactness, simplicity, high power, and relatively low cost make this yellow–green laser well suited as a source for many emerging biomedical applications. The work on further improvement of SHG output power and conversion efficiency is currently underway. This work was partly supported by the EU FP7 programme through the FAST-DOT project (contract no. 224338) and RFBR grant no. 14-02-01160. The authors wish to acknowledge HC Photonics Corp. for the fabrication of the PPLN waveguide crystal. References 1. V. Van Kets, A. Karsten, and L. M. Davids, Laser Med. Sci. 28, 589 (2013). 2. V. Voliani, G. Signore, O. Vittorio, P. Faraci, S. Luin, J. PerezPrieto, and F. Beltram, J. Mater. Chem. B 1, 4225 (2013). 3. V. Voliani, F. Ricci, G. Signore, R. Nifosi, S. Luin, and F. Beltram, Small 7, 3271 (2011). 4. J. Gao, X. Dai, L. Zhang, H. Sun, and X. Wu, J. Opt. Soc. Am. B 30, 95 (2013). 5. V. Kapoor, V. Karpov, C. Linton, F. V. Subach, V. V. Verkhusha, and W. G. Telford, Cytometry Part A 73A, 570 (2008). 6. W. G. Telford, T. Hawley, F. Subach, V. Verkhusha, and R. G. Hawley, Methods 57, 318 (2012). 7. T. Georges, C. Chauzat, and A. Poivre, Proc. SPIE 7578, 75780T (2010). 8. E. Simbuerger, T. Pflanz, and A. Masters, in Physics’ Best (Wiley-VCH Verlag GmbH & Co. KGaA, 2008), pp. 10–13. 9. E. C. Merritt, A. G. Lynn, M. A. Gilmore, and S. C. Hsu, Rev. Sci. Instrum. 83, 033506 (2012). 10. T. Yang, F. Meng, Y. Zhao, Y. Peng, Y. Li, J. Cao, C. Gao, Z. Fang, and E. Zang, Appl. Phys. B 106, 613 (2012). 11. Y. Yao, Q. Zheng, D. P. Qu, K. Zhou, Y. Liu, and L. Zhao, Laser Phys. Lett. 7, 112 (2010). 12. Z. Wang, Q. Peng, Y. Bo, S. Xie, C. Li, Y. Xu, F. Yang, J. Xu, J. Zhang, D. Cui, and Z. Xu, Opt. Commun. 285, 328 (2012). 13. E. Raikkonen, O. Kimmelma, M. Kaivola, and S. C. Buchter, Opt. Commun. 281, 4088 (2008). 14. J. Gao, W. Xiaodong, W. Bing, and D. Xianjin, in Proceedings of the Russian-Chinese Symposium on Laser Physics and Laser Technologies and Academic Symposium on Optoelectronics Technology (IEEE, 2010), pp. 20–22. 15. H. B. Shen, Q. P. Wang, Y. X. Zhang, Z. J. Liu, F. Bai, L. Gao, W. X. Lan, Z. G. Wu, W. T. Wang, Y. G. Zhang, and C. Wang, Laser Phys. 23, 035402 (2013). 16. J. Xia, Y. F. Lu, X. H. Zhang, W. B. Cheng, Z. Xiong, J. Lu, L. J. Xu, G. C. Sun, Z. M. Zhao, and Y. Tan, Laser Phys. Lett. 8, 21 (2011). 17. K. A. Fedorova, G. S. Sokolovskii, P. R. Battle, D. A. Livshits, and E. U. Rafailov, Laser Phys. Lett. 9, 790 (2012). 18. A. Jechow, R. Menzel, K. Paschke, and G. Erbert, Laser Photonics Rev. 4, 633 (2010). 19. E. U. Rafailov, M. A. Cataluna, and W. Sibbett, Nature Photon. 1, 395 (2007). 20. K. A. Fedorova, M. A. Cataluna, I. Krestnikov, D. Livshits, and E. U. Rafailov, Opt. Express 18, 19438 (2010). 21. M. Iwai, T. Yoshino, S. Yamaguchi, M. Imaeda, N. Pavel, I. Shoji, and T. Taira, Appl. Phys. Lett. 83, 3659 (2003). 22. A. Jechow, M. Schedel, S. Stry, J. Sacher, and R. Menzel, Opt. Lett. 32, 3035 (2007). 23. H. K. Nguyen, M. H. Hu, N. Nishiyama, N. J. Visovsky, Y. Li, K. Song, X. Liu, J. Gollier, L. C. Hughes, Jr., R. Bhat, and C.-E. Zah, IEEE Photon. Technol. Lett. 18, 682 (2006). 24. H. Jiang, G. Li, and X. Xu, Opt. Express 17, 16073 (2009). 25. S. Sinha, C. Langrock, M. J. F. Digonnet, M. M. Fejer, and R. L. Byer, Opt. Lett. 31, 347 (2006). 26. W.-K. Lee, C. Y. Park, D.-H. Yu, S. E. Park, S.-B. Lee, and T. Y. Kwon, Opt. Express 19, 17453 (2011). 27. T. Nishikawa, A. Ozawa, Y. Nishida, M. Asobe, F.-L. Hong, and T. W. Hansch, Opt. Express 17, 17792 (2009). 28. T. Hara, H. Oguri, M. Yatsuki, Y. Yamane, and M. Mure, in Proceedings of the Conference on Lasers and ElectroOptics/Quantum Electronics and Laser Science (Optical Society of America, 2005), paper JTuC26.