Normalized Conversion Efficiency Research Articles

High-efficiency frequency converters with periodically-poled Rb-doped KTiOPO4

Periodic structuring of ferroelectric domains in 2mol% Rb-doped KTP is demonstrated using a room-temperature electric-field poling. Drastically reduced ionic conductivity in this material, or 2-orders of magnitude lower than in flux-grown KTP, makes it a good candidate for fabrication of quasi-phase-matched frequency converters. A coercive field of 3.4kV/mm has been measured at room temperature. The dispersion of the index of refraction and effective nonlinearity in quasi-phase-matched structures in Rb-doped KTP did not show significant difference from KTP. A normalized conversion efficiency of 2.5%W−1cm−1 for the frequency-doubling of 908.4nm has been obtained. A singly-resonant mid-infrared optical parametric oscillator with periodically-poled Rb-doped KTP generating 1.53μm signal and 3.49μm idler had threshold of 51MW/cm2 which is comparable to the best-quality periodically-poled KTP structures in the same optical cavity.

Enhanced second-harmonic generation in AlGaAs/Al_xO_y tightly confining waveguides and resonant cavities

We demonstrate second-harmonic generation (SHG) from sub-micrometer-sized AlGaAs/AlxOy artificially birefringent waveguides. The normalized conversion efficiency is the highest ever reported. We further enhanced the SHG using a waveguide-embedded cavity formed by dichroic mirrors. Resonant enhancements as high as approximately 10x were observed. Such devices could be potentially used as highly efficient, ultracompact frequency converters in integrated photonic circuits.

Quasi-phase-matched adhered ridge waveguide in LiNbO3

Uniform periodically poled domains were demonstrated in an insulator-sandwiched structure with z-cut lithium niobate wafers for an adhered ridge waveguide. Efficient quasi-phase-matched second harmonic generation was achieved in a mechanically defined ridge waveguide. Strong confinement in the waveguide produced second-harmonic-generation normalized conversion efficiency of 370%∕Wcm2 in the 1.5μm wavelength region.

Simultaneously phase-matched second- and third-harmonic generation from 155 μm radiation in annealed proton-exchanged periodically poled lithium niobate waveguides

Third-harmonic generation (THG) in the cw regime from C-band radiation was achieved in annealed proton-exchanged periodically poled lithium niobate (PPLN) waveguides. By suitable design of fabrication parameters and operating conditions, quasi-phase-matching (QPM) is obtained simultaneously for the second-harmonic generation process (omega-->2omega, first-order QPM) and for the sum-frequency-generation process (omega+2omega-->3omega, third-order QPM), which provides the third harmonic of the pump field. The high overlap between the field profiles of the interacting modes--TM00 at omega and TM10 at 2omega and 3omega--results in what is believed to be the highest ever reported normalized conversion efficiency for THG from telecommunication wavelengths, equal to 0.72%W(-2) cm(-4).

High-Beam-Quality Continuous Wave 3 W Green-Light Generation in Bulk Periodically Poled MgO:LiNbO3

Continuous-wave 3 W green-light generation at 542 nm is reported in bulk periodically poled MgO:LiNbO3 using single-pass frequency doubling of a Yb-doped fiber laser operating at 1084 nm. The Yb-doped fiber laser had an output power of 9 W, single polarization, beam quality factor M2∼1.05, and a spectrum bandwidth of 0.07 nm. MgO:LiNbO3 samples of 1.0 mm thickness, 25 mm interaction length, and 7.38 µm domain period were fabricated by using a high-voltage multi pulse poling method. A maximum green power of 3 W with a 34% infrared-to-green conversion efficiency and a 6%/W normalized conversion efficiency was obtained. In addition, the generated green light possessed beam quality factor (M2) of less than 1.1 and an output stability of 1.5%.

Effect of varying effective index and random deviations of domain boundary on sum-frequency-generation in quasi-phase-matching waveguides

The effect of varying effective index and random deviations of domain boundary on sum frequency generation (SFG) in quasi-phase-matching waveguides are analyzed and analytical expressions of the conversion efficiency are provided for the first time to our knowledge. By simplifying the coupled equations of SFG in waveguide, we provide analytical expressions of the conversion efficiency for the first time. Four models for variations of effective index and random errors of domains are investigated. The results demonstrate that, when effective index varying regularly along the waveguide, the normalized conversion efficiency η ^ of SFG is reduced and the curves of η ^ are no longer sinc 2 function but ripple profiles, which is different from the situation in bulk crystals; with the same magnitude, random period error is of much more significance than random duty cycle error, which is similar with the case in bulk crystals.

Influence of stochastic deviations of domain boundary and varying effective index on difference frequency mixing in quasi-phase-matching waveguides

Influence of stochastic deviations of domain boundary and varying effective index on the conversion efficiency of difference frequency mixing (DFM) in quasi-phase-matching waveguides are analyzed. By simplifying the coupled equations of DFM in waveguide according to the actual situation, we provide analytical expressions of the conversion efficiency for the first time. Four models for random errors of domains and variations of effective index are investigated. The results demonstrate that, when the effective index varies regularly along the waveguide, the normalized conversion efficiency ηˆ of DFM is dramatically reduced and the curves of ηˆ on phase mismatch are no longer sinc2 function but ripple profiles, which is different from the situation in bulk crystals. With the same magnitude, random period error cast much larger effect on ηˆ than random duty cycle error, which is similar with the case in bulk crystals.

Continuous-wave ultraviolet generation at 354nm in a periodically poled MgO:LiNbO3 by frequency tripling of a diode end-pumped Nd:GdVO4 microlaser

Continuous-wave UV radiation at 354nm, the third harmonic of a Nd:GdVO4 laser operating at 1063nm, is reported from single-pass cascaded, first-order periodically poled MgO:LiNbO3 (PPMgLN) crystals. A high-voltage multipulse poling method was used in order to realize PPMgLN with uniform domain period (Λ) of micron-order width and 50% duty cycle along the entire crystal length. Initially, second-harmonic generation of the 1063nm Nd:GdVO4 laser at 2.1%∕W conversion efficiency, producing 1.15W at 531nm, is obtained from a 10-mm-long PPMgLN with Λ=6.95μm. Sum frequency mixing of this 531nm light with the residual 1063nm fundamental radiation in a 3.6-mm-long PPMgLN with Λ=1.78μm produces 47mW of UV with 3.9%∕W∕cm normalized conversion efficiency.

Optimizing non-resonant frequency conversion in periodically poled media

Non-resonant frequency conversion into the blue, green, orange, and red spectral regions is reported. Fundamental light sources were continuous-wave non-planar monolithic single-mode ring Nd : YAG lasers as well as a standing-wave multi-mode Nd : YAG laser. Periodically poled KTiOPO4 was employed as the nonlinear medium, but the considerations could also be applied to other periodically poled materials. A multi-pass scheme resulted in a normalized conversion efficiency as high as 27.2 % W-1 for frequency doubling in the small-signal regime at 1064 nm.

Room-temperature, continuous-wave 1-W green power by single-pass frequency doubling in a bulk periodically poled MgO:LiNbO3 crystal.

Continuous-wave high-power green light generation at room temperature is reported in a single-pass frequency-doubling configuration with bulk periodically poled MgO:LiNbO3 crystal placed outside a diode end-pumped Nd:GdVO4 laser. The MgO:LiNbO3 samples of 6.95-microm domain period, uniform periodicity, and 50% duty cycle along the entire crystal length are fabricated by use of a high-voltage multipulse poling method. A maximum power of 1.18 W at 531 nm with 16.8% conversion efficiency is obtained from a 2-mm-thick, 25-mm-long MgO:LiNbO3 crystal; the corresponding internal green power and conversion efficiency are 1.38 W and 19.6%, respectively, whereas the normalized conversion efficiency is 3.3%/W.

Second-harmonic generation in periodically poled GaN

We report the experimental demonstration of second-harmonic generation in periodically poled GaN by first-order quasiphase matching. The periodically poled structure was grown by plasma-assisted molecular-beam epitaxy. We observed about 9 μW of second-harmonic power from a fundamental input laser wavelength of 1658.6 nm with a normalized conversion efficiency of 12.76% W−1 cm−2. The ability to perform nonlinear wavelength conversion by periodic poling and the fact that GaN has a very wide window of transparency, pave the way for GaN to be used for nonlinear optical devices in telecommunications as well as a nonlinear light source for biochemical detection in the far infrared and deep ultraviolet.

Efficient 340-nm light generation by a ridge-type waveguide in a first-order periodically poled MgO:LiNbO3.

Quasi-phase-matched (QPM) UV second-harmonic generation (SHG) in a periodically poled MgO:LiNbO3 waveguide is presented. A ridge-type waveguide with high nonlinearity and strong resistance to photorefractive damage was achieved by use of an ultraprecision machining technique. By use of this waveguide in 1.4-microm periodically poled MgO:LiNbO3, a first-order QPM SHG device for 340-nm UV radiation was demonstrated. In a single-pass configuration, continuous-wave 22.4-mW UV light was generated for a fundamental power of 81 mW, corresponding to a normalized conversion efficiency of 340%/W.

Generation of 360-nm ultraviolet light in first-order periodically poled bulk MgO:LiNbO3.

Ultraviolet second-harmonic generation in first-order periodically poled MgO:LiNbO3 is presented. Using a high-voltage multipulse application method, we fabricated a first-order nonlinear grating with a period of 1.8 microm and depth of approximately 150 microm over 10-mm interaction length in a 1-mm-thick MgO:LiNbO3 substrate. In a single-pass configuration, continuous-wave 30-mW UV light at 362.5 nm was generated for a fundamental power of 522 mW, corresponding to a normalized conversion efficiency of 11%/W.

Efficiency improvement by high-index cladding in LiNbO3 waveguide quasi-phase-matched wavelength converter for optical communication

Quasi-phase-matched difference frequency generation devices for the 1.5-μm band using a LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> waveguide with a high-index cladding layer of As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were designed and fabricated. By the cladding, the guided mode profiles were modified, and their overlap was increased. A high normalized conversion efficiency of 790%/W was obtained for 30-mm interaction length.

Observation of all-optical wavelength conversion based on cascaded effect in periodically poled lithium niobate waveguide

We experimentally demonstrate multi-channel wavelength conversion through the cascaded second-order nonlinear processes in periodically poled lithium niobate waveguide in the optical communication wavelength band of 1.5 μm . The normalized conversion efficiency as high as 90% W −1 cm −2 is obtained. Wavelength conversion over a broad wavelength range of 66 nm has been confirmed.

Highly efficient second-harmonic generation in buried waveguides formed by annealed and reverse proton exchange in periodically poled lithium niobate

Efficient three-wave mixing devices have numerous applications, including wavelength conversion, dispersion compensation, and all-optical switching. Second-harmonic generation (SHG) is a useful diagnostic for near-degenerate operation of these devices. With buried waveguides formed in periodically poled lithium niobate by annealed and reverse proton exchange, we demonstrate what is believed to be the highest normalized conversion efficiency (150%/W cm(2)) for SHG in the 1550-nm communications band reported to date.

Parametric fluorescence in oxidized aluminum gallium arsenide waveguides

Parametric fluorescence in low-loss oxidized aluminum gallium arsenide heterostructure waveguides is quantitatively analyzed. A parametric fluorescence efficiency as high as 6×10−7 W/W has been measured in a 3.2-mm-long waveguide. This corresponds to a normalized conversion efficiency, scaled with the waveguide length, of about 1000% cm−2 W−1, eight times higher than with LiNbO3 waveguides. This opens the perspective of a microoptical parametric oscillation threshold below 100 mW.

Efficient second-harmonic generation in birefringently phase-matched GaAs/Al_2O_3 waveguides

We report efficient second-harmonic generation of femtosecond pulses in birefringently phase-matched GaAs/Al(2)O(3) waveguides pumped at 2.01mum. By use of pump pulses of ~200-fs duration and type I interaction, practical second-harmonic average powers of up to ~650muW were obtained, with an average input power of ~50muW. Waveguides of four different widths and two different lengths were investigated, and a normalized conversion efficiency of greater than 1000%W(-1)cm(-2) was obtained for a 1-mm waveguide. Measurements of pump and second-harmonic spectra provided clear evidence of phase matching and depletion of the pump spectrum. The measured bandwidth of the second harmonic was ~1.3nm. From the measurements of transmitted pump power at the phase-matching wavelength, pump depletions of more than 80% were recorded.

M-waveguide structures for direct phase matching in AlGaAs

In this paper the potential of M-waveguide structures for direct phase matching in AlGaAs is investigated by numerical simulations. Principal waveguiding characteristics are discussed. The impact of the optical layer thicknesses is analyzed with respect to phase matching and conversion efficiency for second harmonic generation (SHG). An optimization of the M-waveguide parameters yields a normalized conversion efficiency of 153 or 214 %/W respectively.

Variations of optical M-waveguides for direct phase matching in AlGaAs

Two variations of an optical indexwise M-shaped waveguide structure in AlGaAs are presented as results of numerical simulations. The principal differences of the waveguiding aspects are discussed. The impact of the optical layer thicknesses is investigated with respect to phase matching and conversion efficiency for second-harmonic generation (SHG). Despite large differences in the interacting mode distributions, both waveguide configurations yield comparable nonlinear normalized conversion efficiencies. The technologically simple waveguide designs represent an attractive alternative for phase matched SHG.