Alexander Mikhailovich Streltsov

Fabrication and analysis of a directional coupler written in glass by nanojoule femtosecond laser pulses

A directional coupler written in a glass sample by the focused 400-nm output from a 25-fs oscillator is reported. The coupler is single mode; the splitting ratio is 1.9 dB at 633 nm. A refractive-index profile of the waveguide with a magnitude of Dn = 4.5 x 10(-3) was retrieved from a near-field mode pattern.

Rare earth-doped glass microbarcodes

The development of ultraminiaturized identification tags has applications in fields ranging from advanced biotechnology to security. This paper describes micrometer-sized glass barcodes containing a pattern of different fluorescent materials that are easily identified by using a UV lamp and an optical microscope. A model DNA hybridization assay using these “microbarcodes” is described. Rare earth-doped glasses were chosen because of their narrow emission bands, high quantum efficiencies, noninterference with common fluorescent labels, and inertness to most organic and aqueous solvents. These properties and the large number (>1 million) of possible combinations of these microbarcodes make them attractive for use in multiplexed bioassays and general encoding.

Origin of the refractive-index increase in laser-written waveguides in glasses

We present firm evidence that the mechanism for the refractive-index increase in fused silica caused by irradiation with ultrafast intense laser pulses is the densification of glass. This conclusion is based on the correlation observed between the refractive-index values in waveguides in silica produced by focused femtosecond laser pulses and the shift of the central frequency of ω4 (TO) band (Si–O stretching mode) in micro-Raman spectra. These data were compared with the relation of the Raman shift to density and to refractive index changes in glasses modified by high pressure or irradiation. We conclude that the measured refractive-index increase in silica waveguides can be explained by densification of glass and exclude other hypothesis such as fictive-temperature effect, color center formation, etc.

Extraordinary laser-induced swelling of oxide glasses

We describe a novel process of laser-assisted fabrication of surface structures on doped oxide glasses with heights reaching 10 - 13% of the glass thickness. This effect manifests itself as a swelling of the irradiated portion of the glass, which occurs in a wide range of glass compositions. The extent of such swelling depends on the glass base composition. Doping with Fe, Ti, Co, Ce, and other transition metals allows for adjusting the absorption of the glass and maximizing the feature size. In the case of bumps grown on borosilicate glasses, we observe reversible glass swelling and the bump height can increase or decrease depending on whether the consecutive laser pulse has higher or lower energy compared with the previous one. The hypothetical mechanism includes laser heating of glass, glass melting, and directional flow. We review several potential applications of such glass swelling.

Laser texturing of doped borosilicate glasses

We describe a novel process of laser-assisted fabrication of surface structures on doped oxide glasses with heights reaching 10 - 13% of the glass thickness. This effect manifests itself as a swelling of the irradiated portion of the glass, and occurs in a wide range of glass compositions. The extent of such swelling depends on the glass base composition. Doping with Fe, Ti, Co, Ce, and other transition metals allows for adjusting the absorption of the glass and maximizing the feature size. In the case of bumps grown on borosilicate glasses, we observe reversible glass swelling and the bump height can increase or decrease depending on whether the consecutive laser pulse has higher or lower energy compared with the previous one. To understand the hypothetical mechanism, which includes laser heating of glass, glass melting, and directional flow, we explored density, refractive index, fictive temperature, and phase separation dynamics.

Laser-written high-contrast waveguides in glass

Laser writing of waveguides in bulk glasses opens the opportunity for creating three-dimensional photonic devices. In order to become practical, the numerical aperture (NA) of these waveguides should be significantly higher than currently achievable of 0.1 - 0.15. One reason is that with higher NAs one can decrease the bending radii of the embedded photonic devices without significant loss penalty and make them compact. Thus, femtosecond-laser-written waveguides in glasses do not allow bending radii smaller than 15 - 20 mm. In order to overcome this limitation, we propose to fabricate waveguides in phase-separable and leachable glass where the index contrast is determined by the difference between the refractive indices of the unprocessed glass and of the leached porous glass. We show that we can achieve the NA = 0.25 prior to optimization. Surface and sub-surface treatment with a nanosecond ultraviolet (UV) laser produces a similar effect with even higher NA = 0.35. Applications may include a range of tightly packed embedded and three-dimensional photonic devices in bulk glass like directional couplers, splitters, interferometers, etc.

Laser processing of glass for consumer electronics: opportunities and challenges

Laser processing has demonstrated great capabilities for processing the flat panel display glass, strengthened glass, and flexible glass for consumer electronics. In this paper, a variety of laser processing techniques and their applications are discussed. The techniques include glass cutting, drilling, and surface modification. To assess each technique, a matrix of criteria, such as speed, surface quality, strength, and process stability is proposed. Based on the matrix, future needs for laser processing of glass are outlined.

Laser-formed bumps on glass for precision alignment of planar optical components

This paper describes hybrid assembly of a wavelength selective switch using laser-formed glass bumps. Recently, a process was developed for forming raised bumps on IR-absorbing glass substrates using a focused laser beam. Glass bumps with heights exceeding 90 μm have been formed with an accuracy of ~100 nm using multiple laser shots. Proper selection of materials permits the bump height to be raised or lowered via subsequent laser shots by adjusting laser power. Processes are described for precision alignment of planar AWG components to a pedestal-mounted planar SOA array by forming three glass laser bumps beneath the AWG components. While the iterative process of bump formation and component position assessment was performed manually, this work demonstrates that the process is predictable and well-suited for automation.

Refractive-index increase in laser-written waveguides in glasses

We present estimates of the refractive-index change in waveguides in silica produced by focused femtosecond laser pulses. The estimates are based on the shift of the central frequency of ω4 (TO) band (Si-O stretching mode) in micro-Raman spectra. These data were compared with the relation of this parameter to density and to refractive index changes in seen in glasses modified by high pressure or irradiation. We conclude that the measured refractive-index increase in the waveguides can be explained by densification of glass.