Femtosecond-laser micromachining (also known as inscription or writing) has been developed as one of the most efficient techniques for direct three-dimensional microfabrication of transparent optical materials. In integrated photonics, by using direct writing of femtosecond/ultrafast laser pulses, optical waveguides can be produced in a wide variety of optical materials. With diverse parameters, the formed waveguides may possess different configurations. This paper focuses on crystalline dielectric materials, and is a review of the state-of-the-art in the fabrication, characterization and applications of femtosecond-laser micromachined waveguiding structures in optical crystals and ceramics. A brief outlook is presented by focusing on a few potential spotlights.

Optical waveguides in crystalline dielectric materials produced by femtosecond-laser micromachining

Development of ion-implanted optical waveguides in optical materials: A review

Energetic ion beams with diverse energies, species and beam dimensions have been extensively utilized to modify the properties of materials to achieve versatile applications in many aspects of industry, agriculture and scientific research. In optics, the ion-beam technology has been applied to fabricate various micro- and submicrometric guiding structures on a wide range of optical crystals through the efficient modulation of the refractive indices or structuring of the surface, realizing various applications in many branches of photonics. The ion-beam fabricated optical waveguides and other photonic structures have shown good guiding performance as well as properties related to the materials, suggesting promising potential for many aspects of photonics. This paper gives the state-of-the-art review of fabrication, characterization and application on the ion-beam-processed micro- and submicrometric photonic structures by highlighting the most recent research progress. A brief prospect is presented by focusing on a few potential spotlights.

Micro- and submicrometric waveguiding structures in optical crystals produced by ion beams for photonic applications

A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimen...

Photonic guiding structures in lithium niobate crystals produced by energetic ion beams

Abstract. Ion implantation has demonstrated to be an efficient and reliable technique for the fabrication of optical waveguides in a diversity of transparent materials. Photo-thermal-refractive glass (PTR) is considered to be durable and stable holographic recording medium. Optical planar waveguide structures in the PTR glasses were formed, for the first time to our knowledge, by the C3+-ion implantation with single-energy (6.0 MeV) and double-energy (5.5+6.0  MeV), respectively. The process of the carbon ion implantation was simulated by the stopping and range of ions in matter code. The morphologies of the waveguides were recorded by a microscope operating in transmission mode. The guided beam distributions of the waveguides were measured by the end-face coupling technique. Comparing with the single-energy implantation, the double-energy implantation improves the light confinement for the dark-mode spectrum. The guiding properties suggest that the carbon-implanted PTR glass waveguides have potential for the manufacture of photonic devices.

Optical planar waveguides in photo-thermal-refractive glasses fabricated by single- or double-energy carbon ion implantation

Multienergy Cu+ ions with total dose of
∼1014 ions/cm2 were implanted into
LiNbO3 crystals to form a nearly homogenous damage profile
from the sample surface to the end of the ions’ track. The
extraordinary refractive-index enhancement was found in the damage
region by observation of the dark mode. The extraordinary index
showed an increasing trend until the ion dose reached a critical
value. The largest index enhancement was ∼0.0132. By use of
low-dose ion implantation, we determined that the decreased spontaneous
polarization caused the extraordinary index increase.

Extraordinary Refractive-Index Increase in Lithium Niobate Caused by Low-Dose Ion Implantation

The planar waveguide has been fabricated in a Nd:YVO4 crystal by 3.0 MeV Si+ ion implantation at a dose of 1×1015 ions/cm2 at room temperature. The waveguide was characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 240 °C for 60 min in air. The refractive index profile is reconstructed using reflectivity calculation method. It is found that relatively large positive change of ordinary refractive index happens in the guiding region, which is quite different from most of the observed ion-implanted waveguides. The TRIM’98 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding for the waveguide formation.

Optical waveguides formed in Nd:YVO4 by MeV Si+ implantation

The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 22MeV O+ ion implantation at doses ranging from 5×1012 to 5×1014ions∕cm2 at room temperature The waveguides were characterized by the prism-coupling method Monomode, nonleaky planar waveguides at λ=633nm in β-BBO single crystals were fabricated at doses from 5×1012 to 2×1013ions∕cm2, and two mode and three mode waveguides were fabricated at doses from 4×1013 to 5×1014ions∕cm2, respectively The refractive index profiles of the waveguides are reconstructed using reflectivity calculation method The propagation loss of the measured ion implanted waveguide was about 16dB∕cm It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such changes increased with the doses, which were different from most of the observed ion-implanted waveguides

Planar optical waveguides in β-BaB2O4 produced by oxygen ion implantation at low doses

The planar waveguides in z-cut stoichiometric LiNbO3 crystal have been fabricated by 3.0 MeV oxygen ion implantation with the dose of 6×1014ions∕cm2 at room temperature. The modes of the waveguides were measured by the prism-coupling method with the wavelength 633 and 1539 nm, respectively. The refractive index profiles of the waveguides were reconstructed using reflectivity calculation method. The Rutherford backscattering/channeling technique was used to investigate the damage produced by the ion implantation, the minimum yield of the spectra was 4.52%. The propagation loss of waveguide was 0.61 dB/cm obtained by fiber probe technique. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such change increased after the annealing treatment at 260 °C for 60 min.

Ding-Yu Shen

Papers

Extraordinary Refractive-Index Increase in Lithium Niobate Caused by Low-Dose Ion Implantation

Optical waveguides formed in Nd:YVO4 by MeV Si+ implantation

Planar optical waveguides in β-BaB2O4 produced by oxygen ion implantation at low doses

Optical properties of stoichiometric LiNbO3 waveguides formed by low-dose oxygen ion implantation

Ion-implanted waveguides in Nd3+-doped silicate glass and Er3+/Yb3+ co-doped phosphate glass