Writing waveguides inside monolithic crystalline silicon with nanosecond laser pulses

Abstract

Direct three-dimensional (3D) laser writing of waveguides is highly advanced in a wide range of bandgap materials, but has no equivalent in silicon so far. We show that nanosecond laser single-pass irradiation is capable of producing channel micro-modifications deep into crystalline silicon. With an appropriate shot overlap, a relative change of the refractive index exceeding 10^-3 is obtained without apparent nonuniformity at the micrometer scale. Despite the remaining challenge of propagation losses, we show that the created structures form, to the best of our knowledge, the first laser-written waveguides in the bulk of monolithic silicon samples. This paves the way toward the capability of producing 3D architectures for the rapidly growing field of silicon photonics.

Femtosecond laser written waveguides deep inside silicon

“…Using a technique based on the one we have demonstrated in Ref. [22], the possible creation of waveguides using nanosecond pulses have recently been reported [23]. However, no experimental evidence of actual guidance of light was provided, only that the scattered light followed a linear pattern.…”

Necklaces of PT-symmetric dimers

“…For example, let us consider the case of laser inscribed waveguides in silicon, c:Si, for telecommunication wavelength, λ = 1550 nm. Current techniques allow for control of refractive index properties, ∆n = n core − n bulk ∈ [1, 6] × 10 −3 , as well as losses, [0.1, 3]dB/cm, with waveguide length of about a centimetre [22,23]. We use the commercial finite element software COMSOL to simulate a necklace of two identical passive PT -symmetric dimers realized by four waveguides, radius r = 2.230 µm, in the configuration shown in Fig.…”

Laser-written depressed-cladding waveguides deep inside bulk silicon

“…The in-chip technology is an emerging field, where there is a significant interest to build a photonics toolbox for nearinfrared applications, including fabrication of spatial light control elements [17,[19][20][21]. Notably, the wafer surface is unaltered after laser writing, thus the fabrication of in-chip devices leaves room for further on-chip or in-chip devices, with significant potential for multilayered functionality and novel 3D architectures [17,20].…”

“…In addition, they are highly desirable for integrating microfluidic technologies with photonic devices [8,13,23]. However, in spite of their importance for integrated optics [19] and biophotonics applications, in-chip waveguides remain limited to devices that require ultrafast lasers [20,21], or are created with nanosecond pulses where beam propagation suffers from scattering losses as the beam propagates in the laser-modified area [19]. In fact, to the best of our knowledge, there is only one other manuscript reporting performance of an in-chip waveguide by measuring its loss coefficient [21].…”

“…In this paper, we demonstrate low-loss, depressed-index cladding in-chip waveguides fabricated with nanosecond pulses and characterize the waveguide behavior at the wavelength of 1.3 μm. In general, laser-written waveguides based on a refractive-index depression require a more complex 3D topology [17], compared to those based on an optical index increase [19,20]. However, the depressed-index type waveguides have an architectural advantage because the beam propagates in the unmodified core, which has well-known optical and material properties.…”