Abstract
Depressed cladding optical waveguides have been fabricated in a zinc sulfide (ZnS) crystal by femtosecond laser inscription. The structures support single- or multi-mode guidance at the mid-infrared wavelength of ~4 μm. The two-dimensional refractive index profiles of the single-mode waveguides have been reconstructed, and the modal profiles of TE and TM modes were calculated numerically, that show very good agreement with the measured near-field modal profiles. The minimum propagation losses of the multimode cladding waveguides at 4 μm were ~1.1 dB/cm for the TE polarization and ~1.3 dB/cm for the TM polarization.
Highlights
Since the emergence of type-II quantum well lasers and InP-based quantum cascade lasers [1,2,3,4,5], light in the mid-infrared (MIR) spectral band has been very attractive owing to the various intriguing applications in a number of aspects, such as optical sensing, thermal imaging, biomedicine, free-space communications, etc [6]
We report, to our best knowledge for the first time, on the fabrication of depressed optical cladding waveguides in zinc sulfide (ZnS) crystal by the fs laser inscription
The angle θm was measured by the modified end-face coupling arrangement in which a large YAG ceramic cuboid, used to
Summary
Since the emergence of type-II quantum well lasers (based on GaSb and dilute-nitride semiconductors) and InP-based quantum cascade lasers [1,2,3,4,5], light in the mid-infrared (MIR) spectral band has been very attractive owing to the various intriguing applications in a number of aspects, such as optical sensing, thermal imaging, biomedicine, free-space communications, etc [6]. As one of the most efficient techniques for three-dimensional (3-D) volume microstructuring of transparent dielectrics, the femtosecond (fs) laser inscription has been widely applied to fabricate optical waveguides in numerous optical materials, including optical crystals [11,12,13,14], ceramics [15,16,17,18], glasses [19,20,21], and polymers [22]. The ZnS crystal is one of the most promising materials with a wide range of applications It is an excellent optical material for using in MIR waveguide devices due to its high refractive index (~2.2523 at the wavelength of 4 μm) and huge transparency window covering from visible to infrared wavelengths (0.37~14 μm) [34]. The guiding properties of the ZnS waveguides are investigated at the MIR wavelength of 4 μm
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