A liquid-assisted, laser machining process is described for high-aspect ratio micro-holes (<200-um diameter), which are produced in a variety of glass substrates with precise geometry control. Such features are difficult or impossible to fabricate using alternative approaches.
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.
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.
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 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.
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.
Fabrication and characterization of tracks in calcium fluoride and crystalline quartz are described. These tracks were created using ultrashort near-infrared (NIR) laser pulses in a manner similar to that of writing waveguides in glasses. Unlike the tracks in glasses the laser-written tracks in crystals have the depression of the refractive index. The magnitude of the depression is about 0.01 or more that may enable creation of high-contrast structures in crystals. Depending on the writing conditions the tracks' diameter may vary from around 1 micrometer to 10 micrometers.
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