High performance mode adapters based on segmented SPE:LiNbO_3 waveguides

Abstract

We propose a new mode adapter which allows more efficient launching of the optical power selectively in the fundamental mode of a multimode waveguide. Theoretical and experimental results confirm that such a mode adapter increases the performances in terms of coupling efficiency, coupling tolerances and transmitted power with respect to previously proposed solutions. Proof of principle of device operation is obtained with a simple Coupled Mode Theory model. Experimental results are obtained at a wavelength of 840 nm in Lithium Niobate Soft Proton Exchanged waveguides and agree very well with theoretical predictions.

Analysis of High-Index Contrast Lithium Niobate Waveguides Fabricated by High Vacuum Proton Exchange

“…As it is well known the corresponding waveguides exhibit very low propagation losses (<0.5 dB/cm) and the nonlinear coefficients are not or only slightly affected by the exchange process [9]. In paragraph IV, a particular attention will be paid to investigate the quality of channel waveguides fabricated at ρ LB =2.5%.…”

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“…In order to separate TM and TE polarizations, a polarizer was introduced between the sample and the screen placed just a few centimeters away. When only TE polarization is passing, it can be observed characteristic semicircles corresponding to the light radiating into the substrate, the been measured by using the Fabry-Pérot cavity technique [31]. For each channel waveguide, the single mode propagation was tested by investigating the near-field pattern at the output of the waveguide.…”

“…These are ma modified area of the cry The strain induced in polarization coupling w modes (EH modes) wh substrate. been measured by using the Fabry-Pérot cavity technique [31]. For each channel waveguide, the single mode propagation was tested by investigating the near-field pattern at the output of the waveguide.…”

“…Its excellent electro-optical and nonlinear optical properties are exploited in various applications such as: laser frequency doublers, wideband tunable light sources, light amplification, quasi-phase-matched frequency convertors, surface acoustic waves, optical switches and modulators, multiplexors and for many other all-optical signals processing. Most of the integrated optics devices designed for these applications are based on waveguides fabricated either by Ti-indiffusion [1,2] or by one of the proton exchange techniques namely Annealed Proton Exchange (APE) [3][4][5], Reverse Proton Exchange (RPE) [6] or Soft Proton Exchange (SPE) [7][8][9][10]. All these techniques allow fabricating low loss waveguides with preserved electro-optical and nonlinear properties, but in return lead to low refractive index increase typically in the range of ∆n e =0.01 for Tiindiffusion [11], ∆n e =0.02 for APE and RPE [6] and ∆n e =0.03 for SPE [7].…”