Article
Efficiency pedestal in quasiphasematching devices with random dutycycle errors
E L Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.
Optics Letters (Impact Factor: 3.29). 03/2011; 36(6):8646. DOI: 10.1364/OL.36.000864 Source: PubMed
ABSTRACT
It is shown that random dutycycle errors in quasiphasematching (QPM) nonlinear optical devices enhance the efficiency of processes far from the QPM peak. An analytical theory is shown to agree well with numerical solutions of secondharmonic generation (SHG) in disordered QPM gratings. The measured efficiency of 1550 nm band SHG in a periodically poled lithium niobate (PPLN) waveguide away from the QPM peak agrees with observations of domain disorder in a PPLN wafer by Zygo interferometry. If suppression of parasitic nonlinear interactions is important in a specific application of QPM devices, control of random dutycycle errors is critical.

 "Here we fit with a quadratic function of the form α P 2 p + β P p + DC where α/β are free parameters and DC is the dark count of the detector. This is the expected behaviour of this system, the noise being a result of two processes: (i) the pump inducing photons at the input frequency via weakly phasematched downconversion due to nonperfect poling [56] "
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ABSTRACT: We report on an experiment demonstrating storage of singlephotonlevel light pulses at telecommunication wavelength by frequency upconverting them to the visible range to be resonant with a solidstate optical memory based on a $\mathrm{Pr}^{3+}$:$\mathrm{Y}_2\mathrm{Si}\mathrm{O}_5$ crystal. We convert the telecom photons at $1570\,\mathrm{nm}$ to $606\,\mathrm{nm}$ using a periodicallypoled potassium titanyl phosphate nonlinear waveguide. The maximum device efficiency is inferred to be $\eta_{\mathrm{dev}}^{\mathrm{max}} = 22 \pm 1\,\%$ with a signal to noise ratio exceeding 1 for singlephotonlevel pulses with durations of up to 560$\,$ns. The converted light is then stored in the crystal using the atomic frequency comb scheme with storage and retrieval efficiencies exceeding $\eta_{\mathrm{AFC}} = 20\,\%$ for predetermined storage times of up to $5\,\mu\mathrm{s}$. The retrieved light is time delayed from the noisy conversion process allowing us to measure a signal to noise ratio exceeding 100 with telecom singlephotonlevel inputs. These results represent the first demonstration of singlephotonlevel optical storage interfaced with frequency upconversion. 
 "(b) Fourier spectrum of the nonlinear distribution shown in (a). in unpoled regions. While the SH output profile in space becomes strongly dependent on the wavelength (in the absence of effective selffocusing via cascading [37] [38] [39] [40]), the randomized quasiphase matching (rQPM) process is quite broadband [41] [42] [43] [44]. "
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ABSTRACT: Export Date: 18 September 2012, Source: Scopus, Art. No.: 606892, doi: 10.1155/2012/606892, Language of Original Document: English, Correspondence Address: Assanto, G.; Nonlinear Optics and OptoElectronics Laboratory (NooEL), University Roma Tre, Via della Vasca Navale 84, 00146 Rome, Italy; email: assanto@uniroma3.it, References: De Salvo, R., Hagan, D.J., SheikBahae, M., Stegeman, G., Van Stryland, E.W., Vanherzeele, H., Selffocusing and selfdefocusing by cascaded secondorder effects in KTP (1992) Optics Letters, 17, pp. 2830;International Journal of Optics 01/2012; 2012(1). DOI:10.1155/2012/606892  [Show abstract] [Hide abstract]
ABSTRACT: We theoretically study the parametric wave interaction in nonlinear optical media with randomized distribution of the quadratic nonlinearity $\chi ^{(2)}$ . In particular, we discuss the properties of second and cascaded third harmonic generation. We derive analytical formulas describing emission properties of such harmonics in the presence of $\chi ^{(2)}$ disorder and show that the latter process is governed by the characteristics of the constituent processes, i.e. second harmonic generation and sum frequency mixing. We demonstrate the role of randomness on various second and third harmonic generation regimes such as Raman–Nath and Čerenkov nonlinear diffraction. We show that the randomnessinduced incoherence in the wave interaction leads to deterioration of conversion efficiency and angular spreading of harmonic generated in the processes relying on transverse phase matching such as Raman–Nath interaction. On the other hand, the Čerenkov frequency generation is basically insensitive to the domain randomness.Applied Physics B 12/2012; 109(4). DOI:10.1007/s0034001251244 · 1.86 Impact Factor
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