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Fig. 8. Images of graded-depth fused-silica waveguides illuminated with fiber coupled white light. The white light mode images match the control mode shape at both the front and back face (data obtained from Ref. [247]). — Figure 8 Images of graded-depth fused-silica waveguides illuminated with fiber coupled white light. The white light mode images match the control mode shape at both the front and back face (data obtained from Ref. [247]).

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$Fig. 1. (a) Refractive index profile for a BiB;O, (BIBO) waveguide formed by 2.8 MeV He ion implantation at the dose of 2 x 10!° ions/cm. For comparison, the nuclear energy loss as a function of the penetration depth (vacancy distribution) in the crystal is also represented [153]; (b) ordinary refractive index profile of a Nd:Y VO, waveguide produced by 3.0 MeV Si* ion implantation at the dose of 1 x 10!> ions/cm? before (solid line) and after (dashed line) annealing treatment at 240 °C for 60 min. (MeV) [ 4-20]. Althoug h the related topics have been stud- ied for more than 30 years, there is no a unique explanation for all materials, because of the diversity of configuration and pro perties, althoug h there are some typical responses where we do understand the processes. However, there is one sim in 1976 explana of light ion at least for ple model, which was firstly raised by Townsend as a prediction [2 1], that seems to be a reasonable most crystals. When implantation ions at energies of several MeV are performed, a majority of the lattice damage occurs at the end of the ion trac k inside the substrates, which results in a decrease of physical density by means of volume expansion and hence a reduced refractive index of an optical barrier. Such a barrier confines the light in a narrow layer with relatively high refractive index between itself and the crystal surface, forming an optical waveguide [14]. If the barrier is not ade- quate high or wide, the so-called tunneling effect may take place, accompanying leakage of light energy [22,23]. Fig. la shows a typical barrier-type refractive index profile, which is for a BiB;0¢ waveguide formed by 2.8 MeV He™ ion implantation at the dose of 2 x 10'° ions/em*. Moreover, one should note that for the waveguides in some crystals, some indices of refraction might first experience a positive change in the main region of the ion range, forming an enhanced index well, which restricts the guided light in a non-tunneling way [24-26]. Fig. 1b shows the ordinary refractive index profile of a Nd:YVO,4 waveguide, which is produced by 3.0 MeV Si* ion implantation at the dose of 1 x 10'° ions/em*. Such a model seems to be also appli- cable to the formation of waveguides in some non-crystal-$

Fig. 1. (a) Refractive index profile for a BiB;O, (BIBO) waveguide formed by 2.8 MeV He ion implantation at the dose of 2 x 10!° ions/cm. For comparison, the nuclear energy loss as a function of the penetration depth (vacancy distribution) in the crystal is also represented [153]; (b) ordinary refractive index profile of a Nd:Y VO, waveguide produced by 3.0 MeV Si* ion implantation at the dose of 1 x 10!> ions/cm? before (solid line) and after (dashed line) annealing treatment at 240 °C for 60 min. (MeV) [ 4-20]. Althoug h the related topics have been stud- ied for more than 30 years, there is no a unique explanation for all materials, because of the diversity of configuration and pro perties, althoug h there are some typical responses where we do understand the processes. However, there is one sim in 1976 explana of light ion at least for ple model, which was firstly raised by Townsend as a prediction [2 1], that seems to be a reasonable most crystals. When implantation ions at energies of several MeV are performed, a majority of the lattice damage occurs at the end of the ion trac k inside the substrates, which results in a decrease of physical density by means of volume expansion and hence a reduced refractive index of an optical barrier. Such a barrier confines the light in a narrow layer with relatively high refractive index between itself and the crystal surface, forming an optical waveguide [14]. If the barrier is not ade- quate high or wide, the so-called tunneling effect may take place, accompanying leakage of light energy [22,23]. Fig. la shows a typical barrier-type refractive index profile, which is for a BiB;0¢ waveguide formed by 2.8 MeV He™ ion implantation at the dose of 2 x 10'° ions/em*. Moreover, one should note that for the waveguides in some crystals, some indices of refraction might first experience a positive change in the main region of the ion range, forming an enhanced index well, which restricts the guided light in a non-tunneling way [24-26]. Fig. 1b shows the ordinary refractive index profile of a Nd:YVO,4 waveguide, which is produced by 3.0 MeV Si* ion implantation at the dose of 1 x 10'° ions/em*. Such a model seems to be also appli- cable to the formation of waveguides in some non-crystal-

Fig. 2. Schematic for single-energy implantation into KNbO; crystal of trapezoidal channel waveguides by direct use of a photoresist mask with wedged edges (data obtained from Ref. [39)).

Fig. 3. Aligned and random spectra of 2.8 MeV P* ion-implanted LiNbO; at dose of 1x 10! jons/em? before and after annealing at 200 °C for 30 min. One can see that after moderate annealing the lattice of implanted region could recover, compatible to the original case [97].

Fig. 4. Schematic of the fabrication processing by producing surrounding areas with decreased refractive index in KTiOPO, by ion irradiation (data obtained from Ref. [128]). The SHG was reported in He*-implanted KTP wave- guides with conversion efficiency of 25% for incident pulses of 1 pJ and length of 20 ns [124]. The most advantageous of frequency doubling of such waveguide was, when small sig-

Fig. 5. Response time ¢ versus the intensity of light inside the BaTiO; waveguide (filled diamond) and inside the bulk crystal (filled square). The straight lines are numerical adjustments of the experimental data according to power laws J5, (data obtained from Ref. [181)).

Fig. 6. Erasure times of two-wave mixing of (a) Cu-KNSBN with 2.8- MeV He? implantation at dose of 1 x 10!° ions/em? and (b) Cu-K NSBN without ion implantation [184].

$Fig. 7. Near-field intensity distribution of quasi-TM modes measured at the output facet of the Nd: YVO, channel waveguides formed by 3.0 MeV O* ion implantation at dose of 1 x 10!° ions/em?: (a) TMoo, (b) TMio of 4 m-wide, (c) TM29 of 5 um-wide, (d) TM); of 6 pum-wide channels after annealing at 260 °C for 30 min, and (e) TMoo of 4 um-wide waveguide after annealing at 260 °C for 150 min + 360 °C for 120 min [208]. We reported on the first planar waveguide in Nd: YVO, crystals by 3.0 MeV Si’ ion implantation at the dose of 1 x 10'° ions/cm? [203]. The induced large positive change of ng (An, ~ 0.1) was found to be responsible for the wave- guide formation. The profile of m. in the waveguide was a typical barrier-confined one. The possible reason for the large increase of n, after the implantation may be a combi- nation of irradiation effects and high birefringence of the substrate crystal (nm, — my =0.22). Usually the former induces refractive index decrease by nuclear energy deposi- tion, and the latter causes higher index to decrease while The Nd, Er, or Tm doped NaY(WO,). waveguides were successfully fabricated by MeV He’ ions at the doses of ~10!° ions/em* [211,212]. When heavier ions, e.g. P* or Ni’, were used, the doses for waveguide formation in NaY(WO,)> could be reduced, namely to be ~10!° ions/ cm? [212]. It was found that for all the NaY(WOg,)> wave- guides, barrier-type refractive index profiles were recon- structed according to the measured effective refractive indices of the modes. Compared with He* ion implanta-$

Fig. 7. Near-field intensity distribution of quasi-TM modes measured at the output facet of the Nd: YVO, channel waveguides formed by 3.0 MeV O* ion implantation at dose of 1 x 10!° ions/em?: (a) TMoo, (b) TMio of 4 m-wide, (c) TM29 of 5 um-wide, (d) TM); of 6 pum-wide channels after annealing at 260 °C for 30 min, and (e) TMoo of 4 um-wide waveguide after annealing at 260 °C for 150 min + 360 °C for 120 min [208]. We reported on the first planar waveguide in Nd: YVO, crystals by 3.0 MeV Si’ ion implantation at the dose of 1 x 10'° ions/cm? [203]. The induced large positive change of ng (An, ~ 0.1) was found to be responsible for the wave- guide formation. The profile of m. in the waveguide was a typical barrier-confined one. The possible reason for the large increase of n, after the implantation may be a combi- nation of irradiation effects and high birefringence of the substrate crystal (nm, — my =0.22). Usually the former induces refractive index decrease by nuclear energy deposi- tion, and the latter causes higher index to decrease while The Nd, Er, or Tm doped NaY(WO,). waveguides were successfully fabricated by MeV He’ ions at the doses of ~10!° ions/em* [211,212]. When heavier ions, e.g. P* or Ni’, were used, the doses for waveguide formation in NaY(WO,)> could be reduced, namely to be ~10!° ions/ cm? [212]. It was found that for all the NaY(WOg,)> wave- guides, barrier-type refractive index profiles were recon- structed according to the measured effective refractive indices of the modes. Compared with He* ion implanta-

Summary of SHG in ion-implanted waveguides Table 1

Summary of two-wave mixing in ion-implanted planar waveguides Table 2

Fig. 9. Recorded spectrum of the laser emission at 1064 nm in a proton- implanted Nd:YAG planar waveguide when pumped at 822nm. The narrow peak is centered at 1064.4nm. The inset image shows a photograph of a waveguide laser output (data obtained from Ref. [199)).

Fig. 11. Interaction scheme of pump (green light from an Ar* ion laser, dashed lines) and probe beam (red light from a He-Ne laser, solid lines) inside the SBN waveguide. When the pump beam is off or when it has low intensity (linear propagation) the intensity of the red beam is measured by a photodiode. When the pump beam is switched on (non-linear propa- gation), the green beam is self-focused and self-bent to the left, trapping the red beam that moves away from the photodiode (data obtained from Ref. [170]). Acknowledgements Fig. 10. Intensity profiles at the exit face of the SBN waveguide measured for different externally applied electric fields E. For comparison, the solid curve shows the input beam profile (shifted for better viewing; data obtained from Ref. [171)).

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