Abstract
Ion exchange in glass has a long history as a simple and effective technology to produce gradient-index structures and has been largely exploited in industry and in research laboratories. In particular, ion-exchanged waveguide technology has served as an excellent platform for theoretical and experimental studies on integrated optical circuits, with successful applications in optical communications, optical processing and optical sensing. It should not be forgotten that the ion-exchange process can be exploited in crystalline materials, too, and several crucial devices, such as optical modulators and frequency doublers, have been fabricated by ion exchange in lithium niobate. Here, however, we are concerned only with glass material, and a brief review is presented of the main aspects of optical waveguides and passive and active integrated optical elements, as directional couplers, waveguide gratings, integrated optical amplifiers and lasers, all fabricated by ion exchange in glass. Then, some promising research activities on ion-exchanged glass integrated photonic devices, and in particular quantum devices (quantum circuits), are analyzed. An emerging type of passive and/or reconfigurable devices for quantum cryptography or even for specific quantum processing tasks are presently gaining an increasing interest in integrated photonics; accordingly, we propose their implementation by using ion-exchanged glass waveguides, also foreseeing their integration with ion-exchanged glass lasers.
Highlights
Ion exchange in glass has been exploited since the early Middle Ages to color glasses: marvelous stained glass windows, obtained by ion exchange from a silver paste, are still visible in many European cathedrals
In order to make clear the above considerations, and after describing, for the sake of completeness, the fundamental aspects of quantum integrated optical elements in Section 4.1, we present, in Section 4.2, an integrated generator of quantum light states |L based on the use of integrated optical lasers and directional couplers and mainly intended for quantum cryptography
In this work we have presented a review on active and quantum integrated photonic elements fabricated by ion exchange in glass, which have a remarkable impact in different fields such as classical and quantum optical communications, optical processing and optical sensing
Summary
Ion exchange in glass has been exploited since the early Middle Ages to color (stain) glasses: marvelous stained glass windows, obtained by ion exchange from a silver paste, are still visible in many European cathedrals. The process (sometimes called ion stuffing or just chemical strengthening) became a standard in the industry in the 1960s, when, for instance, Corning developed Chemcor® glass, a chemically strengthened glass that was intended to be used in phone booths, prison windows, eyeglasses and automobile windshields In parallel to these events, there were interesting advances in the optical field, too: in the 1910s it was observed that the ion-exchange process was inducing a change in the refractive index of the glass, and in the 1960s integrated optics moved its first steps, with waveguiding structures that required materials having slightly different refractive indices [3]. Despite the suggestion, several years ago, by the group of one of the present authors [49], a platform based on ion-exchanged glass (IExG) circuits has not been considered so far as an effective integration technology for quantum photonics.
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