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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 15 — Jul. 19, 2010
  • pp: 16193–16205
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High power red and near-IR generation using four wave mixing in all integrated fibre laser systems

Laure Lavoute, Jonathan C. Knight, Pascal Dupriez, and William J. Wadsworth  »View Author Affiliations


Optics Express, Vol. 18, Issue 15, pp. 16193-16205 (2010)
http://dx.doi.org/10.1364/OE.18.016193


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Abstract

We demonstrate high power generation of visible red and near IR light by four wave mixing in photonic crystal fibres (PCFs) pumped at 1064 nm with picosecond pulses (30 – 80 ps). 30% conversion efficiency is demonstrated in a single pass using fibre lengths less than 1 m, with signal wavelengths from 650 nm to 820 nm selectable by choice of PCF. An all fibre integrated system delivers 2.16 W at 740 nm with a pulse repetition frequency of 20 MHz. We discuss the overall parameter space for this type of wavelength conversion in PCF with different fibre designs suitable for delivering a particular wavelength at low or high power.

© 2010 OSA

1. Introduction

Lasers are the light source of choice for many applications because they can be focused to small spots or can propagate for long distances as collimated beams. The well-defined wavelength of many lasers is also often a great advantage. However there are very few wavelengths at which lasers are commonly available at low cost, so any application requiring a specific wavelength which is not covered by well-developed commercial lasers is made considerably more difficult or more expensive. It would be of great assistance to be able to provide laser sources with narrow bandwidth (few nm) providing continuous (selectable or tuneable) coverage over the visible and near-IR by nonlinear wavelength conversion of existing well-developed lasers.

Optical parametric oscillators and amplifiers (OPOs and OPAs) based on parametric down-conversion in χ (2) nonlinear crystals can, of course, provide such a wavelength conversion [1

1. M. H. Dunn and M. Ebrahimzadeh, “Parametric generation of tunable light from continuous-wave to femtosecond pulses,” Science 286(5444), 1513–1517 (1999). [CrossRef] [PubMed]

]. However in practice bulk OPO and OPA systems are generally not a low-cost or simple solution. On the other hand, selecting a single wavelength from a continuum [2

2. J. K. Ranka, R. S. Windeler, and A. J. Stentz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,” Opt. Lett. 25(1), 25–27 (2000), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-25-1-25. [CrossRef]

4

4. J. M. Stone and J. C. Knight, “Visibly “white” light generation in uniform photonic crystal fiber using a microchip laser,” Opt. Express 16(4), 2670–2675 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2670. [CrossRef] [PubMed]

] clearly gives broad spectral coverage and wavelength selectability or tunability, but also gives a relatively modest output power at any single wavelength – of the order of a few mW/nm in a watt-level commercial supercontinuum source.

Parametric conversion through χ (3) (four-wave mixing, FWM) in optical fibres has been extensively studied (mainly fibre based OPO) as a mechanism for broadband or tuneable wavelength conversion [5

5. J. E. Sharping, “Microstructure fiber based optical parametric oscillators,” J. Lightwave Technol. 26(14), 2184–2191 (2008), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-26-14-2184. [CrossRef]

]. Tuneable output lying in the telecom band [6

6. G. K. L. Wong, S. G. Murdoch, R. Leonhardt, J. D. Harvey, and V. Marie, “High-conversion-efficiency widely-tunable all-fiber optical parametric oscillator,” Opt. Express 15(6), 2947–2952 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-6-2947. [CrossRef] [PubMed]

,7

7. Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Raman-assisted continuous-wave tunable all-fiber optical parametric oscillator,” J. Opt. Soc. Am. B 26(7), 1351–1356 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=josab-26-7-1351. [CrossRef]

] (using dispersion shifted fibre) or/and in the visible range [8

8. R. Jiang, R. E. Saperstein, N. Alic, M. Nezhad, C. J. McKinstrie, J. E. Ford, Y. Fainman, and S. Radic, “Continuous-Wave Band Translation Between the Near-Infrared and Visible Spectral Ranges,” J. Lightwave Technol. 25(1), 58–66 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=JLT-25-1-58. [CrossRef]

,9

9. Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Widely tunable photonic crystal fiber Fabry-Perot optical parametric oscillator,” Opt. Lett. 33(12), 1351–1353 (2008), http://www.opticsinfobase.org/abstract.cfm?URI=ol-33-12-1351. [CrossRef] [PubMed]

] (using PCFs) have then been demonstrated. The FWM process will occur provided the different waves (signal, pump(s) and idler) are phase-matched along their propagation inside the fibre and will therefore depend on the propagation constant(s) β of the guided mode(s). Conventional step-index fibres cannot provide the phase matching condition required to get visible output from near IR pump, however photonic crystal fibres (PCFs) are able to achieve such a conversion. By changing the pitch Λ and the hole diameter d, a wide range of appropriate β curves are achievable. We have previously shown >30% conversion of sub-nanosecond pulses from 1064 nm to 740 nm in a single pass of a 3 m long PCF [3

3. W. Wadsworth, N. Joly, J. Knight, T. Birks, F. Biancalana, and P. Russell, “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres,” Opt. Express 12(2), 299–309 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-2-299. [CrossRef] [PubMed]

]. This is an extremely simple system, only requiring the addition of a section of fibre at the output of a fixed wavelength laser.

In 2008, Sloanes et al. demonstrated single pass conversion of the picosecond radiation emitted from a bulk Nd:YVO4 laser (pump wavelength, λp = 1064 nm, pulse duration, τ = 27 ps) in a PCF [10

10. T. Sloanes, K. McEwan, B. Lowans, and L. Michaille, “Optimisation of high average power optical parametric generation using a photonic crystal fiber,” Opt. Express 16(24), 19724–19733 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-24-19724. [CrossRef] [PubMed]

]. However with a pump peak power of less than 1 kW they were unable to exceed 2% conversion efficiency, demonstrating that higher peak power is necessary in such a case. In work simultaneous with ours [15

15. L. Lavoute, W. J. Wadsworth, and J. C. Knight, “Efficient four wave mixing from a picosecond fibre laser in photonic crystal fibre,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–4, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_4.

] Nodop et al. [16

16. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high power generation of pulsed red light via four-wave-mixing in a large-mode-area, endlessly single-mode photonic-crystal fiber,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–5, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_5.

,17

17. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber,” Opt. Lett. 34(22), 3499–3501 (2009), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-34-22-3499. [CrossRef] [PubMed]

] have demonstrated the efficient (35%) generation of red light (673 nm) using bulk lasers amplified in low nonlinearity, large mode area, PCF amplifiers (τ1 = 200 ps, τ2 = 50 ps) delivering pulses with 10s kW peak power (P1 = 40 kW, P2 = 30 kW, resp.) with a bandwidth of 4 pm for the 200 ps source. Neither system addressed the possibility of using spectrally broad and simple pump lasers for FWM.

In this paper we investigate the potential applicability of wavelength conversion of high power picosecond Yb3+ fibre lasers to the visible using FWM in PCF. These lasers are relatively low cost and have already found many applications in visible microscopy and spectroscopy through supercontinuum generation in PCF [12

12. P. Blandin, S. Lévêque-Fort, S. Lécart, J. C. Cossec, M. C. Potier, Z. Lenkei, F. Druon, and P. Georges, “Time-gated total internal reflection fluorescence microscopy with a supercontinuum excitation source,” Appl. Opt. 48(3), 553–559 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=ao-48-3-553. [CrossRef] [PubMed]

14

14. S. Schlachter, A. Elder, J. H. Frank, A. Grudinin, and C. F. Kaminski, “Spectrally Resolved Confocal Fluorescence Microscopy with a Supercontinuum Laser,” Microscopy and Analysis 22, 11–13 (2008), http://www.microscopy-analysis.com/magazine-article/spectrally-resolved-confocal-fluorescence-microscopy-supercontinuum-laser?c=.

]. Using suitably designed 1064 nm fibre lasers and FWM in PCF we demonstrate efficient conversion to individual wavelengths in the red and near-IR (650 – 750 nm) with output powers of up to 100 mW/nm at 1 MHz pulse repetition rate. To adapt this laboratory experiment to a commercial product with high stability, an all fibre system is crucial. Using an example PCF spliced into an integrated system, we show an all fibre device as efficient as the free space one, delivering 2.16 W at 740 nm at 20 MHz pulse repetition rate. We also investigate theoretically the range of PCFs possible to achieve the broadest wavelength coverage in high or low pulse energy operation.

2. Theoretical analysis of FWM process in PCFs pumped at 1064 nm

2.1 Investigation of signal wavelength evolution in PCFs pumped at 1064 nm

The aim of this general study was to identify the shortest signal wavelength achievable through the FWM process in PCFs pumped at the standard wavelength of 1064 nm. It is important to remember that generating short wavelengths increases the frequency shift Ω = ωp – ωi = ωs – ωp (ω is the angular frequencies and p, s and i subscripts refer respectively to the pump, signal and idler pulses). In practice this reduces the parametric gain of the nonlinear process [18

18. G. P. Agrawal, Nonlear Fiber Optics, 3rd ed., (Academic Press, 2001).

20

20. J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express 14(20), 9491–9501 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-20-9491. [CrossRef] [PubMed]

]. Thus high peak pump power (in the range of several kW to hundreds of kW) is necessary to obtain high conversion efficiency from IR radiation to visible light.

For a specific PCF and for a range of pump wavelength λp lying around the first zero dispersion wavelength λZD of the fibre, the evolutions of parametric wavelengths λs and λi as a function of λp is usually summarised in a so-called phasematching diagram. As an example, the phasematching diagram has been computed for a PCF with Λ = 3 μm and d/Λ = 0.3, referred to as PCF-A in the following sections (Fig. 1
Fig. 1 Phasematching diagram computed for the specific fibre PCF-A (Λ = 3 μm and d/Λ = 0.3) when the pump wavelength is varied from 950 to 1200 nm and for a pump peak power of 10 kW and 50 kW.
). The computation and all the following theoretical studies presented in the paper were performed using the finite element method, FEM (Comsol software). In all our calculations, the nonlinear refractive index was taken equal to 3 × 10−20 m2 W−1 and the mode effective area Aeff was approximated as π Λ2 (which is generally an overestimate meaning that the calculated powers will be an overestimate of the real powers required).

The pump peak power Ppeak was taken, for these computations, as 50 kW and 10 kW. The first value is the one chosen for all the other calculations presented in this paper as it corresponds to a central value in between 10 and 80 kW, the range of powers used in our experiments (see section 3). The 10 kW value matches the power used in the experiment carried out with PCF-A (see section 3). According to Fig. 1, the PCF-A should generate a signal at 724 nm (or 713 nm) and an idler close to 2004 nm (or 2094 nm) when pumped at 1064 nm with Ppeak close to 10 kW (or 50 kW).

Figure 2
Fig. 2 Evolution of - signal wavelengths (colour plot and black contours) in nm, - walk off length (white lines) between the pump and the idler in m, for τ = 30 ps, when λp = 1064 nm, Ppeak = 50kW and for a wide range of PCFs with pitch [2.5-7] μm and d/Λ [0.2-0.4]. The specific area where λZD = λp = 1064 nm is shown with the thick green line.
shows the evolution of the signal wavelengths λs (colour plot and black contours) for such PCFs when Ppeak = 50 kW on which are superimposed white lines showing the evolution of the walk-off length (see section 2.2) for the different PCFs. The thick green line represents the specific area where λZD = λp = 1064 nm.

From Fig. 2 one can see that the shortest signal wavelengths are achieved for pitches close to 2.5 – 3 μm. This includes the area where the computation is not strictly valid, however even if the FWM wavelength may not be accurate, the general behaviour is unlikely to change. For a pitch of 2 µm, when d/Λ becomes close to 0.32 the computed parametric wavelengths increase rapidly from 640 nm (for d/Λ = 0.324) to 730 nm (for d/Λ = 0.325). This implies that the generation of short signal wavelengths around 650 nm from such small pitch structures would be very sensitive to the geometrical parameters variations (e.g. for d/Λ = 0.324 ± 0.001, λs = 685 ± 45 nm when Λ = 2.5 μm). Structural variations in a small-core PCF has previously been shown to lower the parametric gain over long lengths of fibre [19

19. M. Karlsson, “Four-wave mixing in fibers with randomly varying zero-dispersion wavelength,” J. Opt. Soc. Am. B 15(8), 2269–2275 (1998), http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-15-8-2269. [CrossRef]

,20

20. J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express 14(20), 9491–9501 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-20-9491. [CrossRef] [PubMed]

]. As a consequence, short pieces of fibre (a few tens of centimetres) must be used and combined with a high pump peak power to ensure a good conversion efficiency.

Looking at the right hand side of Fig. 2, when the pitch is much larger, around 6 – 7 μm, one should note that short signal wavelengths can still be generated, although not quite as short as for small pitch. The sensitivity to the geometrical parameters is drastically reduced for this range of structures. For all d/Λ in between 0.2 and 0.4, λs lies in the range from 650 to 680 nm. The efficiency of the nonlinear process should be limited less by the fluctuations along the fibre length and the generated radiation should be much more stable.

2.2 Temporal walk off

The FWM process remains highly efficient as long as there is temporal overlap between the three pulses at pump, signal and idler wavelengths. Because these waves propagate with different group velocities vg, the conversion efficiency increases more slowly after the walk off length (Lw.o). FWM starts from noise which is exponentially amplified for L smaller than Lw.o., and linearly amplified for longer fibre lengths. For two waves a and b propagating with vga and vgb respectively and with pulse durations τ, Lw.oabis given by:

Lw.oab=τ1vga1vgb

As well as affecting the signal conversion efficiency, a fibre longer than the walk-off length also allows other unphasematched processes to grow. The spontaneous Raman effect grows linearly with the length, and will cause broadening of the pump and signal (which we consider in section 3.1). As the FWM usually occurs for λp slightly below λZD, Raman broadening of the pump to longer wavelengths often puts power beyond the zero dispersion wavelength where supercontinuum is observed for long fibres. This effect was very pronounced in the work of Sloanes et al. [10

10. T. Sloanes, K. McEwan, B. Lowans, and L. Michaille, “Optimisation of high average power optical parametric generation using a photonic crystal fiber,” Opt. Express 16(24), 19724–19733 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-24-19724. [CrossRef] [PubMed]

].

Lw.oip, usually shorter than Lw.ospand Lw.oisand is referred to in what follows by Lw.o, was computed for a pulse duration of 30 ps (white lines in Fig. 2). It is clear from Fig. 2 that most of the PCFs under study would exhibit Lw.o < 3 meters for such a pulse duration instead of a few tens (or hundreds) of meters when τ = 600 ps (e.g. from a microchip laser [3

3. W. Wadsworth, N. Joly, J. Knight, T. Birks, F. Biancalana, and P. Russell, “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres,” Opt. Express 12(2), 299–309 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-2-299. [CrossRef] [PubMed]

]). As expected, Lw.o tends to decrease with decreasing λs.

Moreover, Fig. 2 shows that, for short signal wavelengths in particular, the structural parameters can be adapted to reduce potential walk off problems. For example, around λs = 660, Lw.o can be increased from 35 cm (point D) to about 1 m (point F) by reducing the pitch of the structure and selecting the hole diameter appropriately. However, from the discussion presented in section 2.1, point F would clearly correspond to a structure where the FWM wavelength is very sensitive to small structural changes. A PCF with parameters lying around point E, with a pitch close to 3 μm and a d/Λ close to 0.27 might provide a good compromise. It would be less sensitive to the geometrical fluctuations and would exhibit a relatively long Lw.o close to 60 cm. Such a structure, which has a relatively small core diameter, might not withstand extremely high pump powers but could provide high nonlinearity, and would be particularly suited to convert low power IR radiation to red light. Conversely for PCFs close to the point D, the nonlinear gain would be significantly lower than in the small pitch case, and Lw.o is short. However the mode area is large (at least, for a nonlinear fibre), Aeff ≈100 μm2, when Λ = 6 μm, so the peak power may be increased without fibre damage. As a consequence these Large Mode Area (LMA) PCFs are particularly suitable for high power / high energy applications.

Finally, from Fig. 2 we note that a 620 nm signal wavelength would correspond to a walk-off length shorter than 20 cm. With such a short walk off length and also a fibre which is very sensitive to structural variations and a large frequency shift Ω, a very high peak power may be required for FWM. Combined with the difficulty of coupling a high power into a small core, the generation of this shortest signal wavelength through FWM appears to be particularly challenging. A practical minimum wavelength may then be ~650 nm for pumping at 1064 nm. Pumping at shorter wavelengths in the Yb3+ gain band is considered in section 5.

3. Experimental results

3.1 Standard mode area PCF

In our first experiment to characterize the efficiency of the FWM process in the short pulse regime (ps), a standard endlessly singlemode PCF, the PCF-A (Λ = 3 μm, d / Λ = 0.3, Fig. 1) was used. The nonlinear process in this fibre was already studied successfully in the ns regime (fibre D in [3

3. W. Wadsworth, N. Joly, J. Knight, T. Birks, F. Biancalana, and P. Russell, “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres,” Opt. Express 12(2), 299–309 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-2-299. [CrossRef] [PubMed]

], [22

22. C. Xiong, Z. Chen, and W. J. Wadsworth, “Dual-wavelength-pumped supercontinuum generation in an all-Fiber device,” J. Lightwave Technol. 27(11), 1638–1643 (2009), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-27-11-1638. [CrossRef]

]). In such a fibre the nonlinear coefficient is relatively high and the nonlinear process can be expected to be quite stable against structural variations (Fig. 2). This fibre has a similar mode field diameter to conventional singlemode fibre designed for 1064 nm and may be spliced to Corning HI-1060 fibre with low loss (<0.4 dB).

The fibre was pumped at 1064 nm using a fibre laser (FemtoPower 1060-PP, Fianium Ltd [23]) with a pulse duration of 30 ps, a pulse repetition rate of 4 MHz, an average power close to 3 W and a bandwidth less than 0.5 nm. The combination of a polarizing beamsplitter (PBS) and a half-wave plate (λ/2) was used to control the power launched into the fibre (Fig. 3
Fig. 3 Schematic of the experimental set up.
). The coupling efficiency was measured to be close to 50%, giving a peak power of 12.5 kW in the fibre. A signal at λs-A ~742 nm was generated, in good agreement with theoretical results from Fig. 1 when Ppeak = 10 kW.

Even though the signal power Ps should theoretically increase with the fibre length [14

14. S. Schlachter, A. Elder, J. H. Frank, A. Grudinin, and C. F. Kaminski, “Spectrally Resolved Confocal Fluorescence Microscopy with a Supercontinuum Laser,” Microscopy and Analysis 22, 11–13 (2008), http://www.microscopy-analysis.com/magazine-article/spectrally-resolved-confocal-fluorescence-microscopy-supercontinuum-laser?c=.

], in practice, the achievable power will be limited by the walk off and the Raman effect as discussed in section 2.2. If the FWM appears first but the length is still long enough to provide Raman conversion, the signal power will increase but there will be a spectral broadening of the signal pulse spectrum. As a consequence, to ensure high spectral power density for the signal, the fibre length must be a trade off between a high FWM gain and a minimal Raman generation from the pump and the signal band.

For the PCF-A under test, Lw.o was calculated to be between 1 and 2 metres (Fig. 2). Taking the walk off length into account, a 2 m long piece of fibre was selected and progressively cut back. The influence of the Raman effect was investigated for each fibre length using two interference filters at the fibre output (Fig. 3). Filter 1 (filter 2) exhibits a 10 nm (40 nm) bandwidth centred at 740 nm (750 nm). The power transmitted by the filter 1 will therefore correspond only to the initial FWM band, whereas the power transmitted by the filter 2 will include any power converted from the initial FWM band to the first Raman Stokes wavelength at ~767 nm. The input pump power Pin was varied to measure the evolution of the total output power Pout, and the signal powers P1 and P2 after the filter 1 and the filter 2 respectively (P1 and P2 are corrected for filter transmission stated by the manufacturer).

Figure 4a
Fig. 4 (a) Evolution of P1 (open symbols, FWM signal only) and P2 (filled symbols, FWM and associated Raman) versus Pout, for a 2 m long fibre (rectangles) and a 1 m long fibre (circles). (b) Signal band spectrum for different pump powers, Pin, (fibre length 2 m).
shows the evolution of P1 and P2 when Pout was varied, for a 2 m long piece of fibre and a 1 m long piece of fibre. For the longer fibre, the signal wavelength appeared at a threshold total power output of less than 400 mW (Pin ~930 mW with 43% input coupling efficiency). Once Pout ≥ 550 mW (Ppeak ~4.6 kW, energy: E ~238 nJ), the power in the narrower spectral width (P1) progressively stopped increasing to remain constant at a maximum value of 180 mW while the power in the larger spectral band (P2) kept on increasing up to 260 mW. This phenomenon clearly highlights the spectral broadening due to the Raman effect which is confirmed by looking at the evolution of the signal band spectra measured at the fibre output (Fig. 4b) when the input power Pin is increased.

Conversely for the 1 m long piece of fibre there was a higher threshold of Pout = 700 mW, but no evidence of saturation of P1 due to the Raman effect for Pout as high as 1.04 W (Ppeak ~8.7 kW, E ~260 nJ), which corresponds to an input power of 2200 mW (circles on Fig. 4a). The signal power P1 reached a maximum of 298 mW (Ppeak ~2.5 kW, E ~75 nJ), corresponding to an internal conversion efficiency, η, from pump at 1064 nm to signal at 742 nm of 28% (very close to the 27% efficiency obtained when Pout = 550 mW for the 2 m long piece of fibre). The spectrum measured at the output of the 1 m long fibre (Fig. 5
Fig. 5 Spectrum measured at the output of the 1 m long piece of PCF-A at a signal power of 298 mW.
) shows a well defined signal band without any Raman broadening. The signal band full width at half maximum (FWHM) was measured to be 3.25 nm corresponding to a power density close to 90 mW/nm for the emitted red light. Our intention in this first study was to optimize the fibre length to obtain a maximum efficiency in a small bandwidth of <10 nm. It is obvious that the signal power should be further scalable if this restriction can be relaxed.

With these results we can see that a conversion efficiency close to 30% can be achieved with a narrow spectral bandwidth for different pulse peak power using appropriate fibre lengths. Finally, one would note that the average power of the source may obviously be scaled by increasing the pulse repetition frequency above the current 4 MHz.

A slightly different PCF from the same set of fibres but drawn to get longer λs, was pumped in the same conditions as PCF-A. We obtained similar results in terms of efficiency and spectral bandwidth at signal wavelength of 814 nm.

We chose PCF-A to demonstrate an all-spliced integrated high power 740 nm laser source. In the experiments described so far the fibre laser has an optical isolator and free-space output, and is coupled into the FWM fibre using bulk optics. In moving to a practical all-spliced system the fibre length before the FWM fibre is slightly increased, leading to larger nonlinear spectral broadening of the pump pulses. For a given peak power, P, the nonlinear phase accumulated through self-phase modulation after propagating a length l is simply γPl (γ being the nonlinear parameter of the fibre). A transform limited pulse is broadened to approximately twice its initial bandwidth for a phase shift of 0.63π [18

18. G. P. Agrawal, Nonlear Fiber Optics, 3rd ed., (Academic Press, 2001).

]. Therefore one can achieve the narrow spectral bandwidth of ~1 nm required for FWM, whilst maintaining high peak power in a longer fibre by reducing the initial pulse bandwidth (increasing the pulse duration). Moreover, to get the simplest system, the pulse picker was removed. The RR was therefore increased to 20 MHz which is the lowest value achievable without a pulse picker. We constructed a fibre laser at 1064 nm and 80 ps pulse duration. 2.16 W of average signal power (Ppeak ~1.35 kW, E ~110 nJ) was extracted at 742 nm (η ~34%) with Pin close to 6.36 W (Ppeak ~4 kW, E ~320 nJ). The FWM fibre length (several meters) was not optimised for narrow signal bandwidth in this case, and there was significant Raman broadening of the signal. From the data obtained with the 30 ps laser (Fig. 4a) a length of 2 m is probably appropriate for this peak power level (equivalent to ~500 mW for the 30 ps – 4 MHz laser).

3.2 Large Mode Area PCF

The theoretical predictions being well confirmed with this first experiment, a set of PCFs with parameters lying in the right hand side of Fig. 2 (“stable” LMA PCFs) were drawn to generate shorter signal wavelengths when pumped at 1064 nm. They were designed with a pitch close to 6 μm and a d/Λ around 0.3 (i.e. λZD ~1090 nm). The loss was measured to be 7 dB/km and 4 dB/km at 650 nm and 1064 nm respectively, using a cut-back method over 250 m of fibre. The results obtained using two of these fibres, named PCF-B and PCF-C, are reported here. Their pitch and d/Λ were measured using SEM (Scanning Electron Microscope) images and their parametric wavelengths λs and λi were computed using these parameters (Table 1

Table 1. Characteristics of PCF-B and PCF-C: Λ and d/Λ, measured from SEM pictures; theoretical (Theo.) and experimental (Exp.) signal wavelengths, idler wavelength (calculated from the experimental signal wavelength) and the powers Psignal and Ptotal, power density and conversion efficiency measured when the PCFs are pumped at 1064 nm.

table-icon
View This Table
).

Fibre lengths were optimized for narrow signal linewidth and high efficiency of the FWM process with the maximum pump power available. According to Fig. 2, PCF-B and -C should experience walk off lengths of a few tens of centimetres. Following the same process as for PCF-A, we found that for these new PCFs a 50 cm long piece of fibre was a good compromise between walk-off, Raman degradation and FWM gain at high pump peak power. The PCFs under test were pumped under the same conditions as PCF-A except that the repetition rate was reduced from 4 MHz to 1 MHz to ensure higher pump peak power (constant average power). The input pulse FWHM was measured to be close to 1.7 nm.

Spectra measured at the output of 50 cm long pieces of PCF-B and PCF-C, when the output power was close to 2.5 W (Ppeak ~83 kW, E ~2.5 μJ), are shown in Fig. 6
Fig. 6 Optical spectra measured at the output of PCF-B (black line) and PCF-C (red line) (Pin ~2.5 W).
. There is no evidence of spectral broadening due to the Raman effect on the signal peaks for the PCFs under test. The signal FWHM was measured to be close to 7 nm on both spectra.

A prism was used to characterize the power of the signal Psignal emitted at the fibre output. P’signal, the signal power after the prism, P’total, the total power after the prism and Ptotal the total power at the output of the PCFs were measured leading to Psignal = P’signal × Ptotal / P’total. The signal wavelength, the powers Psignal and Ptotal measured at the output of PCF-B and PCF-C, the power density of the signal peak and the conversion efficiency for each fibre are summed up in Table 1.

The efficiency of the process and the power density of the signal peak obtained with the LMA-PCF-B are quite similar to those obtained using the standard PCF-A but a much shorter wavelength of 665 nm was reached. A higher peak power is required, partly because of the large frequency shift, but also because this fibre has approximately twice the mode field diameter, and hence four times the effective area. The nonlinear process in the LMA-PCF-C gave rise to the shortest signal wavelength (650 nm) generated by FWM in a PCF pumped at 1064 nm. Nevertheless, one can note that the nonlinear process is slightly less efficient than previously. This is thought to be due to the fact that the frequency shift Ω is very large in this case, making phase matching harder to maintain over a long length, and reducing the walk-off length. Increasing the pump peak power, or reducing the pump bandwidth should improve the nonlinear gain. The 50 cm length we used is longer than the walk-off length (close to 35 cm for the PCF-C) which is expected to limit the conversion efficiency.

Finally, it is important to note, as a proof of the influence of the pump spectral bandwidth on the conversion efficiency, that using another laser with Ppeak, τ and RR similar to those of the above mentioned laser but exhibiting slightly larger bandwidth of 2.5 nm, no red light could be efficiently generated with PCF-B and PCF-C.

4. Discussion

The measured signals generated in PCF-B and PCF-C are computed to correspond to idler wavelengths as high as 2620 nm and 2770 nm respectively. We have not measured the attenuation at the idler wavelength experimentally. Instead, the attenuation measured for these two fibres over the range 500 – 1750 nm combined with the ‘wet’ and ‘dry’ silica attenuation data given in Ref. [24

24. O. Humbach, H. Fabian, U. Grzesik, U. Haken, and W. Heitmann, “Analysis of OH absorption bands in synthetic silica,” J. Non-Cryst. Solids 203, 19–26 (1996). [CrossRef]

] were used to estimate the attenuation at the idler wavelengths. The total absorption was estimated to be close to 3.6 dB/m and 26.3 dB/m at 2620 nm and 2770 nm respectively. These loss values are high, especially for PCF-C (13 dB for the 50 cm used) and they might be an extra factor reducing the efficiency of the FWM.

However, FWM in the PCF-B was characterized at lower power with a microchip laser (λp ~1064 nm, τ = 600 ps, Ppeak = 10 kW) and 30% of conversion from the pump to the 665 nm signal were measured in a 6.6 m long fibre which corresponds to idler loss of about 24 dB (higher than the loss evaluated for 50 cm of PCF-C). Moreover, Nodop et al. have recently demonstrated the emission, through the degenerate FWM process, of 450 mW at λi = 2539 nm in a 1.4 m long LMA-PCF (Λ = 6.6 μm, d/Λ = 0.46) pumped with a hybrid microchip-fibre laser (λp ~1064 nm, τ = 200 ps, Ppeak = 40 kW) [17

17. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber,” Opt. Lett. 34(22), 3499–3501 (2009), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-34-22-3499. [CrossRef] [PubMed]

]. 35% conversion efficiency was obtained for the signal at 673 nm. We conclude that the conversion from IR to red light remains efficient even when the idler wavelength (λi > 2.5 μm) experiences significant attenuation. We may consider this in two stages, defining the idler loss length, Li. Firstly the idler wave needs to exist as a guided wave in order for the calculated phasematching to be meaningful. In that case we at least need to be able to define a fibre mode, so the loss must be low on the order of the Rayleigh length – in this case 40 µm (so Li > 40 µm or αi < 25000 dB/m). Secondly we may make a comparison with a singly resonant χ(2) OPO. In that case growth of the output signal is seen over many round trips of the cavity even though the idler is completely lost on each round trip. In fibre we identify the OPO cavity round trip with the loss length for the idler, Li, in the fibre. It then follows that once a small amount of signal is generated together with its idler wave, then we would still expect the signal to propagate and continue to grow over many times Li.

Measurable idler output even at high loss wavelengths is also relatively simple to understand. If the fibre is short enough that the signal power is still growing in the final section of the fibre, a small gain factor can lead to a significant gain in power as one approaches the final high output power. Each signal photon must be accompanied by an idler photon, so the number of output idler photons should be approximately the same as the gain in signal photons in the end section of fibre of length Li. In Ref. [17

17. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber,” Opt. Lett. 34(22), 3499–3501 (2009), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-34-22-3499. [CrossRef] [PubMed]

], conversion efficiencies of 35% for the signal and 6% for the idler are achieved. The idler conversion is not a great deal lower than the ideal situation (one signal photon for one idler photon) that would give 9%.

Extending this argument to predict the longest loss-limited idler wavelength, the attenuation spectra given in Fig. 1 of Ref. [24

24. O. Humbach, H. Fabian, U. Grzesik, U. Haken, and W. Heitmann, “Analysis of OH absorption bands in synthetic silica,” J. Non-Cryst. Solids 203, 19–26 (1996). [CrossRef]

]. for ‘wet’ (F100) and ‘dry’ (F300) bulk synthetic silica, reveal a plateau from 3 μm to 3.45 μm where the attenuation is of the order of 50 dB/m. This is not a great deal higher than the loss at 2770 nm for which we have already observed the corresponding signal. As a consequence, generation of visible light through FWM in silica fibre may be expected to be efficient until this upper limit of 3.45 μm (λs ~630 nm when λp = 1064 nm), particularly if a short piece of fibre can be used (very high peak pump power). We see from Fig. 2 and section 2 that it may be difficult to achieve the correct structure to reach this wavelength from the current pump wavelength, but the process should at least not be severely limited by idler absorption.

5. Theoretical study of signal wavelength tuneable range when the pump wavelength is tuned from 1020 to 1080 nm

The output wavelength from an Yb3+ doped fibre laser can potentially be tuned (or selected) over the range 1020 to 1080 nm. The evolution of the signal wavelength when the pump wavelength is tuned over such a range is presented here.

Figure 7
Fig. 7 Lower part of the parametric diagram of the PCF-A and tuning range of the signal wavelength achievable when the pump is tuned from 1020 to 1080 nm and for Ppeak = 10 kW and 50 kW.
represents a zoom on the lower part of the parametric diagram (signal evolution) computed for PCF-A (Λ = 3 μm, d/Λ = 0.3) when the pump power is 10 kW (to be in agreement with the experimental power previously used in section 3.1) and 50 kW (to fit with the general calculations). It appears that tuning the pump wavelength over the 60 nm range from 1020 to 1080 nm would tune the signal wavelength by 181 nm from 610 to 791 nm when Ppeak ~10 kW. The corresponding idler tunability range would be 1400 nm, from 3110 to 1700 nm, and the longest wavelength should not significantly limit the efficiency of the nonlinear process, as previously discussed. Note that increasing the pump power from 10 to 50 kW theoretically decreases the range of signal (608 – 767 nm) and idler (3170 - 1830 nm) wavelengths achievable by tuning the pump wavelength from 1020 to 1080 nm.

Extending the results presented in Fig. 7 to the wide range of PCFs studied in section 2 we found that the widest tunability range Δλs-MAX would lie around the line where λZD = 1050 nm (central wavelength of the pump tunability range). Such a behaviour was expected. Actually, while the pump is tuned from 1020 nm to 1080 nm, the dispersion, firstly normal, is getting progressively anomalous and according to the general shape of the phase matching diagram, passing through λZD would give the highest λs shift. When Ppeak = 50kW, Δλs-MAX, which theoretically occurs for Λ = 2.5 μm and d/Λ = 0.35, is computed to be close to 250 nm. In such a case, the signal wavelength would be tuned from λs < 615 nm (λi > 3461 nm) to λs ~855 nm (λi ~1467 nm).

Once again, the smaller the pitch, the higher the signal wavelength variation around a single λs. As a consequence, PCF-B and PCF-C would exhibit a tunability range lower than PCF-A and close to 60-70 nm tunability around 660 nm.

6. Conclusion

We have demonstrated high power, narrow band, visible and near infrared light generation by efficient four wave mixing in photonic crystal fibres. Efficiencies close to 30% were achieved for a range of signal wavelengths between 650 nm and 820 nm with bandwidths equal to 3 to 7 nm. In an all-fibre integrated system a power of 2.16 W at 740 nm was achieved at a repetition rate of 20 MHz. We also present a detailed analysis of the full range of endlessly single mode PCFs available for pumping close to 1064 nm with a discussion of the important design considerations for selecting the correct fibre design and fibre length for a particular pump laser. We show that idler absorption is not a limiting factor for idler wavelengths up to 2.9 µm, and is only expected to become important beyond 3.45 µm.

Acknowledgements

The authors thank D. M. Bird1 for helpful discussions. This work was supported in part by the EU Framework 7 under Grant HEALTH-F5-2008-201076, “nEUROPt” and by the UK Technology Strategy Board project No: TP11 /LLD/6/I/AF052H, “WhiteLase”. W. J. Wadsworth acknowledges funding through a Royal Society University Research Fellowship.

References and links

1.

M. H. Dunn and M. Ebrahimzadeh, “Parametric generation of tunable light from continuous-wave to femtosecond pulses,” Science 286(5444), 1513–1517 (1999). [CrossRef] [PubMed]

2.

J. K. Ranka, R. S. Windeler, and A. J. Stentz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,” Opt. Lett. 25(1), 25–27 (2000), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-25-1-25. [CrossRef]

3.

W. Wadsworth, N. Joly, J. Knight, T. Birks, F. Biancalana, and P. Russell, “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres,” Opt. Express 12(2), 299–309 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-2-299. [CrossRef] [PubMed]

4.

J. M. Stone and J. C. Knight, “Visibly “white” light generation in uniform photonic crystal fiber using a microchip laser,” Opt. Express 16(4), 2670–2675 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2670. [CrossRef] [PubMed]

5.

J. E. Sharping, “Microstructure fiber based optical parametric oscillators,” J. Lightwave Technol. 26(14), 2184–2191 (2008), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-26-14-2184. [CrossRef]

6.

G. K. L. Wong, S. G. Murdoch, R. Leonhardt, J. D. Harvey, and V. Marie, “High-conversion-efficiency widely-tunable all-fiber optical parametric oscillator,” Opt. Express 15(6), 2947–2952 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-6-2947. [CrossRef] [PubMed]

7.

Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Raman-assisted continuous-wave tunable all-fiber optical parametric oscillator,” J. Opt. Soc. Am. B 26(7), 1351–1356 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=josab-26-7-1351. [CrossRef]

8.

R. Jiang, R. E. Saperstein, N. Alic, M. Nezhad, C. J. McKinstrie, J. E. Ford, Y. Fainman, and S. Radic, “Continuous-Wave Band Translation Between the Near-Infrared and Visible Spectral Ranges,” J. Lightwave Technol. 25(1), 58–66 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=JLT-25-1-58. [CrossRef]

9.

Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Widely tunable photonic crystal fiber Fabry-Perot optical parametric oscillator,” Opt. Lett. 33(12), 1351–1353 (2008), http://www.opticsinfobase.org/abstract.cfm?URI=ol-33-12-1351. [CrossRef] [PubMed]

10.

T. Sloanes, K. McEwan, B. Lowans, and L. Michaille, “Optimisation of high average power optical parametric generation using a photonic crystal fiber,” Opt. Express 16(24), 19724–19733 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-24-19724. [CrossRef] [PubMed]

11.

Europoan project Neuropt, www.neuropt.eu.

12.

P. Blandin, S. Lévêque-Fort, S. Lécart, J. C. Cossec, M. C. Potier, Z. Lenkei, F. Druon, and P. Georges, “Time-gated total internal reflection fluorescence microscopy with a supercontinuum excitation source,” Appl. Opt. 48(3), 553–559 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=ao-48-3-553. [CrossRef] [PubMed]

13.

J. M. Langridge, T. Laurila, R. S. Watt, R. L. Jones, C. F. Kaminski, and J. Hult, “Cavity enhanced absorption spectroscopy of multiple trace gas species using a supercontinuum radiation source,” Opt. Express 16(14), 10178–10188 (2008), http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-14-10178. [CrossRef] [PubMed]

14.

S. Schlachter, A. Elder, J. H. Frank, A. Grudinin, and C. F. Kaminski, “Spectrally Resolved Confocal Fluorescence Microscopy with a Supercontinuum Laser,” Microscopy and Analysis 22, 11–13 (2008), http://www.microscopy-analysis.com/magazine-article/spectrally-resolved-confocal-fluorescence-microscopy-supercontinuum-laser?c=.

15.

L. Lavoute, W. J. Wadsworth, and J. C. Knight, “Efficient four wave mixing from a picosecond fibre laser in photonic crystal fibre,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–4, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_4.

16.

D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high power generation of pulsed red light via four-wave-mixing in a large-mode-area, endlessly single-mode photonic-crystal fiber,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–5, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_5.

17.

D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber,” Opt. Lett. 34(22), 3499–3501 (2009), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-34-22-3499. [CrossRef] [PubMed]

18.

G. P. Agrawal, Nonlear Fiber Optics, 3rd ed., (Academic Press, 2001).

19.

M. Karlsson, “Four-wave mixing in fibers with randomly varying zero-dispersion wavelength,” J. Opt. Soc. Am. B 15(8), 2269–2275 (1998), http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-15-8-2269. [CrossRef]

20.

J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express 14(20), 9491–9501 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-20-9491. [CrossRef] [PubMed]

21.

T. A. Birks, J. C. Knight, and P. St. J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22(13), 961–963 (1997), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-22-13-961. [CrossRef] [PubMed]

22.

C. Xiong, Z. Chen, and W. J. Wadsworth, “Dual-wavelength-pumped supercontinuum generation in an all-Fiber device,” J. Lightwave Technol. 27(11), 1638–1643 (2009), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-27-11-1638. [CrossRef]

23.

Fianium, http://www.fianium.com.

24.

O. Humbach, H. Fabian, U. Grzesik, U. Haken, and W. Heitmann, “Analysis of OH absorption bands in synthetic silica,” J. Non-Cryst. Solids 203, 19–26 (1996). [CrossRef]

OCIS Codes
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(140.7300) Lasers and laser optics : Visible lasers
(190.4370) Nonlinear optics : Nonlinear optics, fibers
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: February 25, 2010
Revised Manuscript: May 31, 2010
Manuscript Accepted: July 2, 2010
Published: July 16, 2010

Citation
Laure Lavoute, Jonathan C. Knight, Pascal Dupriez, and William J. Wadsworth, "High power red and near-IR generation using four wave mixing in all integrated fibre laser systems," Opt. Express 18, 16193-16205 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-15-16193


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References

  1. M. H. Dunn and M. Ebrahimzadeh, “Parametric generation of tunable light from continuous-wave to femtosecond pulses,” Science 286(5444), 1513–1517 (1999). [CrossRef] [PubMed]
  2. J. K. Ranka, R. S. Windeler, and A. J. Stentz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,” Opt. Lett. 25(1), 25–27 (2000), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-25-1-25 . [CrossRef]
  3. W. Wadsworth, N. Joly, J. Knight, T. Birks, F. Biancalana, and P. Russell, “Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres,” Opt. Express 12(2), 299–309 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-2-299 . [CrossRef] [PubMed]
  4. J. M. Stone and J. C. Knight, “Visibly “white” light generation in uniform photonic crystal fiber using a microchip laser,” Opt. Express 16(4), 2670–2675 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2670 . [CrossRef] [PubMed]
  5. J. E. Sharping, “Microstructure fiber based optical parametric oscillators,” J. Lightwave Technol. 26(14), 2184–2191 (2008), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-26-14-2184 . [CrossRef]
  6. G. K. L. Wong, S. G. Murdoch, R. Leonhardt, J. D. Harvey, and V. Marie, “High-conversion-efficiency widely-tunable all-fiber optical parametric oscillator,” Opt. Express 15(6), 2947–2952 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-6-2947 . [CrossRef] [PubMed]
  7. Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Raman-assisted continuous-wave tunable all-fiber optical parametric oscillator,” J. Opt. Soc. Am. B 26(7), 1351–1356 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=josab-26-7-1351 . [CrossRef]
  8. R. Jiang, R. E. Saperstein, N. Alic, M. Nezhad, C. J. McKinstrie, J. E. Ford, Y. Fainman, and S. Radic, “Continuous-Wave Band Translation Between the Near-Infrared and Visible Spectral Ranges,” J. Lightwave Technol. 25(1), 58–66 (2007), http://www.opticsinfobase.org/abstract.cfm?URI=JLT-25-1-58 . [CrossRef]
  9. Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Widely tunable photonic crystal fiber Fabry-Perot optical parametric oscillator,” Opt. Lett. 33(12), 1351–1353 (2008), http://www.opticsinfobase.org/abstract.cfm?URI=ol-33-12-1351 . [CrossRef] [PubMed]
  10. T. Sloanes, K. McEwan, B. Lowans, and L. Michaille, “Optimisation of high average power optical parametric generation using a photonic crystal fiber,” Opt. Express 16(24), 19724–19733 (2008), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-24-19724 . [CrossRef] [PubMed]
  11. Europoan project Neuropt, www.neuropt.eu .
  12. P. Blandin, S. Lévêque-Fort, S. Lécart, J. C. Cossec, M. C. Potier, Z. Lenkei, F. Druon, and P. Georges, “Time-gated total internal reflection fluorescence microscopy with a supercontinuum excitation source,” Appl. Opt. 48(3), 553–559 (2009), http://www.opticsinfobase.org/abstract.cfm?URI=ao-48-3-553 . [CrossRef] [PubMed]
  13. J. M. Langridge, T. Laurila, R. S. Watt, R. L. Jones, C. F. Kaminski, and J. Hult, “Cavity enhanced absorption spectroscopy of multiple trace gas species using a supercontinuum radiation source,” Opt. Express 16(14), 10178–10188 (2008), http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-14-10178 . [CrossRef] [PubMed]
  14. S. Schlachter, A. Elder, J. H. Frank, A. Grudinin, and C. F. Kaminski, “Spectrally Resolved Confocal Fluorescence Microscopy with a Supercontinuum Laser,” Microscopy and Analysis 22, 11–13 (2008), http://www.microscopy-analysis.com/magazine-article/spectrally-resolved-confocal-fluorescence-microscopy-supercontinuum-laser?c= .
  15. L. Lavoute, W. J. Wadsworth, and J. C. Knight, “Efficient four wave mixing from a picosecond fibre laser in photonic crystal fibre,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–4, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_4 .
  16. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high power generation of pulsed red light via four-wave-mixing in a large-mode-area, endlessly single-mode photonic-crystal fiber,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ5–5, http://www.opticsinfobase.org/abstract.cfm?URI=CLEO_E-2009-CJ5_5 .
  17. D. Nodop, C. Jauregui, D. Schimpf, J. Limpert, and A. Tünnermann, “Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber,” Opt. Lett. 34(22), 3499–3501 (2009), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-34-22-3499 . [CrossRef] [PubMed]
  18. G. P. Agrawal, Nonlear Fiber Optics, 3rd ed., (Academic Press, 2001).
  19. M. Karlsson, “Four-wave mixing in fibers with randomly varying zero-dispersion wavelength,” J. Opt. Soc. Am. B 15(8), 2269–2275 (1998), http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-15-8-2269 . [CrossRef]
  20. J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express 14(20), 9491–9501 (2006), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-20-9491 . [CrossRef] [PubMed]
  21. T. A. Birks, J. C. Knight, and P. St. J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett. 22(13), 961–963 (1997), http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-22-13-961 . [CrossRef] [PubMed]
  22. C. Xiong, Z. Chen, and W. J. Wadsworth, “Dual-wavelength-pumped supercontinuum generation in an all-Fiber device,” J. Lightwave Technol. 27(11), 1638–1643 (2009), http://www.opticsinfobase.org/JLT/abstract.cfm?URI=JLT-27-11-1638 . [CrossRef]
  23. Fianium, http://www.fianium.com .
  24. O. Humbach, H. Fabian, U. Grzesik, U. Haken, and W. Heitmann, “Analysis of OH absorption bands in synthetic silica,” J. Non-Cryst. Solids 203, 19–26 (1996). [CrossRef]

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