We assessed the impact of text messaging as the preferred method of communicating positive Chlamydia trachomatis test results in an urban sexual health clinic. Following the introduction of a text messaging service to communicate positive C trachomatis test results to patients, the time between test and treatment in 293 consecutive patients was compared with 303 historic controls. No significant difference was found in either median time to treatment for all patients (3 days in 2005; 4 days in 2007) or median time to treatment (both 7 days) for those not treated immediately. There was no significant difference in time to treatment between those using a landline or mobile phone. Mobile phone use was significantly higher in 2007. Overall, we treated more cases within 4 weeks in 2007 (98.6% cf 96%). The lack of difference in time to treatment showed the use of this technology is as effective as more traditional means of communication. The increase in cases of C trachomatis treated within 4 weeks may reflect the significant increase in mobile phone use and improved ability to contact people rather than simply the introduction of text messaging.

Nonlinear frequency conversion in waveguides has been investigated since the first days of integrated optics, but practical applications were hampered by a lack of suitable pump lasers and the often inconvenient phase-matching characteristics of the available waveguides. Recent developments in high power (>100 mW) single-mode diode lasers and quasi-phase-matching techniques have led to renewed interest in waveguide frequency conversion. Periodic modulation of the optical properties of a nonlinear medium, quasi-phase-matching, is an attractive technique as it decouples phase-matching from birefringence and thus allows any interaction within the transparency range of the medium using any component of the nonlinear susceptibility tensor. The most efficient form of quasi-phase-matching involves periodic reversal of the sign of the nonlinear susceptibility (χ(2)) of the medium, with a period equal to an odd multiple of the coherence length of the interaction. In ferroelectrics, such a periodic sign reversal in χ(2) can be accomplished by periodic reversals in the orientation of the spontaneous polarization. Periodic incorporation of dopants has been found to induce domain reversal in several ferroelectrics, e.g. Ti or Li in LiNbO3, H in LiTaO3, and Rb and Ba in KTP, leading to rapid progress in device demonstrations in these material systems. [1–5] Several milliwatts of blue light generated by quasi-phase-matched (QPM) frequency doubling have been demonstrated in LiNbO3[3],[6], Ktp [4], and LiTaO3 waveguides [5], as has QPM difference frequency generation of 2.1 μm radiation in LiNbO3 waveguides. [7]

We discuss second harmonic generation of green and blue light in periodically-poled LiNbO3 and LiTaO3 waveguides, and difference frequency generation of infrared radiation in periodically-poled LiNbO3 waveguides.

We report quasi-phase-matched difference-frequency generation of 2.1 μm radiation at room temperature using the d33 nonlinear coefficient in a periodically poled lithium niobate channel waveguide. A tunable Ti:Al2O3 laser (λ≊0.8 μm) and a Nd:YAG laser (λ=1.32 μm) were the pump and signal sources, respectively. With 160 mW of 0.81 μm and 1 mW of 1.32 μm radiation coupled into the waveguide, 1.8 μW of 2.1 μm radiation was generated, tunable over a 6 nm bandwidth. We also show that the annealed proton exchange process can change the shape of ferroelectric domains in lithium niobate.

Blue light was generated at room temperature by quasiphase-matched second harmonic generation in planar and channel lithium tantalate (LiTaO3) annealed proton exchange wave-guides using the d33 nonlinear coefficient. Alternating ferro-electric domains for third order quasiphase matching were created by poling the substrates with a periodic electric field.

Proton exchanged waveguides are often used in quasiphase-matched nonlinear devices in LiNbO 3 . Conversion efficiencies are often significantly smaller than the theoretical values, indicating the need for accurate measurements of the nonlinear susceptibility of proton exchanged LiNbO 3 . Reflected second harmonic generation (SHG) from interfaces can be used to measure the nonlinear susceptibility of a film on a nonlinear substrate; however, the air–film and film–substrate interfaces both contribute to the total reflected SH signal. Generation of harmonic wavelengths above the film absorbtion edge will discriminate against the film–substrate interface reflection, so that the reflected harmonic will only be sensitive to the nonlinear properties of the film. We report measurements of the d 33 nonlinear coefficient of proton exchanged LiNbO 3 using reflected SHG of 266-nm radiation and find that upon proton exchange d 33 is reduced to ≈1% of the bulk LiNbO 3 value. This result disagrees with previous reports of ≈50% reduction for doubling 1.06-µm radiation. 1 , 2 A discussion of the discrepancy among these measurements along with additional measurements of d 33 as a function of annealing are presented.

The demand for sources of coherent blue light with milliwatt output powers has stimulated much research activity in guided-wave devices for second-harmonic generation (SHG). To address the inability of otherwise-suitable materials to phase-match birefringently, quasi-phase-matching (QPM) has been used for SHG of visible radiation in LiNbO 3 , 1,2 polymer, 3 and KTP 4 waveguides. This paper reports blue light generated by quasi-phase-matched SHG in a periodically poled LiTaO 3 waveguide.

Nonlinear frequency conversion is an attractive technique for extending the spectral range of solid-state coherent sources. Waveguide interactions are useful to increase the efficiency of devices based on low-power pump lasers, e.g. second harmonic generation (SHG) of the output of AlGaAs laser diodes to produce blue light. While the large nonlinear susceptibility and well-developed waveguide technologies available in LiNbO 3 are attractive for device design, LiNbO 3 does not have adequate birefringence for phasematching SHG of blue light. Compensating for phase-velocity mismatch by reversing the sign of the nonlinear susceptibility with a period equal to the coherence length, quasi-phase-matching (QPM), allows phase-matching of any interaction within the transparency range of the crystal using the large d 33 nonlinear coefficient. QPM has been investigated in LiNbO 3 waveguides, where the sign changes were due to periodic reversal of the orientation of the ferroelectric domains accomplished by a patterned doping process. 1-3 We have succeeded in generating green and blue light by QPM SHG of the output of infrared lasers in such waveguides.

Inhomogeneities in waveguide dimensions are a serious problem for guided-wave frequency conversion devices. We discuss waveguide designs that make the phase matching ‘‘noncritical’’ with respect to small changes in dimensions. Application of noncritical phase matching results in larger fabrication tolerances, facilitating the practical realization of nonlinear devices with long interaction lengths. We experimentally demonstrate the existence of a noncritical thickness in a lithium niobate waveguide, and analyze the dimensional tolerances for second-harmonic generation in a polymer waveguide.

Phase-matching nonlinear interactions by periodic variations in the nonlinear susceptibility, quasi-phase-matching, offers advantages in accessible tuning range and in choice of nonlinear coefficients over the conventional birefringent technique. Periodically reversed ferroelectric domains can be used to create monolithic structures with the necessary high-spatial-frequency variations in the nonlinear susceptibility. We present two techniques for the fabrication of periodically-poled lithium niobate crystals, and results for bulk and guided-wave second harmonic generation of blue and green light.

Blue light at 410 nm was generated by continuous-wave frequency-doubling in a periodically poled lithium niobate channel waveguide at room temperature. Quasi-phasematching allowed generation of the blue light using the d/sub 33/ nonlinear coefficient.<>

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text G. A. Magel, E. J. Lim, M. M. Fejer, and R. L. Byer, "Second harmonic generation in periodically-poled LiNbO3," Optics News 15(12), 20-21 (1989) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Periodically-poled, planar waveguides in lithium niobate were used to generate 532 nm and 424 nm radiation at room temperature by continuous-wave frequency-doubling with conversion efficiencies of 2.4 − 5% per W-cm2. Quasiphasematching allowed generation of the second harmonic using the d33 nonlinear coefficient.