Acousto-optic modulation of a wavelength-scale waveguide
We demonstrate a collinear acousto-optic modulator in a suspended film of lithium niobate employing a high-confinement, wavelength-scale waveguide. By strongly confining the optical and mechanical waves, this modulator improves by orders of magnitude a figure-of-merit that accounts for both acousto-optic and electro-mechanical efficiency. Our device demonstration marks a significant technological advance in acousto-optics that promises a novel class of compact and low-power frequency shifters, tunable filters, non-magnetic isolators, and beam deflectors.
Acousto-optic interactions involving propagating phonons can break the time-reversal and frequency-modulation symmetry of light. However, conventional acousto-optic modulators based on bulk materials have frequency bandwidth limited to hundreds of megahertz due to their large structural sizes. Here, we experimentally demonstrate gigahertz single-sideband acousto-optic modulation on an etchless lithium niobate integrated platform by using photonic bound states in the continuum. The upper- or lower-sideband modulation of light can be obtained conveniently by choosing specific combinations of input and output channels. Under this scheme, we have realized a 3-GHz frequency shifter, which operates in the C-band with a 3-dB bandwidth of ~35 nm. The extinction ratios of the upper(lower)-sideband modulated light to the lower(upper)-sideband modulated and unmodulated light are >44 (47) and 25 (23) dB in the 3-dB operating bandwidth. The frequency-shifted light can be further processed with amplitude and frequency modulation. Therefore, the demonstrated gigahertz single-sideband acousto-optic modulation can enable many photonic applications such as optical signal processing, sensing, and ion trapping.
Cutting applications for carbon dioxide lasers with acousto-optic modulators
A new carbon dioxide laser range integrates an acousto-optic modulator (AOM) that has a rise/fall time of less than 1 μs, making it suitable for cutting applications.
In recent years, South Korean companies have been dominant in the display industry, particularly in the organic light-emitting diode (OLED) market. Additional investments have also recently started with Chinese companies, and this trend is expected to continue for three to four years. With the expansion of the display industry, ultrashort-pulse (USP) laser markets have grown as a result of applications such as OLEDs, which require higher laser power and more-precise processing quality. This industry is prepared to pay for better laser-based solutions, which has fueled the demand for shorter-pulsed carbon dioxide (CO2) lasers for film cutting applications. One of the key features required in the market is to minimize the heat effect on the material during the cutting process.
In order to address this demand, Luxinar (Kingston upon Hull, England) has launched the SR AOM CO2 laser range, which integrates an acousto-optic modulator (AOM) and has a rise/fall time of <1 μs. The SR AOM lasers minimize unnecessary heat energy while processing when compared with traditional CO2 laser sources, which typically produce longer pulse rise/fall times of approximately 60 μs.
In addition to the display industry, the electronic manufacturing services (EMS), automotive, and flexible packaging industries demand a reduced heat-affected zone (HAZ) for laser processing, with microcontrolled processes becoming more common. The above lasers could be a possible solution for many of these applications.
The most important feature of the SR AOM series is its exceptionally fast optical rise/fall time capability of <1 μs. Without the AOM function, a typical optical rise and fall time of a CO2 laser is approximately 60 μs. While this is acceptable for many laser processing applications, it can lead to the creation of HAZ on thin polymer-based materials. This is unacceptable for many of the materials used in the electronics industry.
Figure 1 shows the typical 2 μs demand pulse shape that has approximately 350 ns pulse rising time. This short rise/fall time would help to minimize HAZ.
The clear benefit of the short rise/fall time is in cutting thin film. A wide range of thin films are used in many different industries, including display, automotive, EMS, lighting, and flexible packaging. An AOM-integrated CO2 laser can bring a higher-quality cutting edge with less HAZ compared to a standard pulsed CO2 laser.
Figure 2 shows the results of cutting polarization film (3-layer, 0.23 mm thick) using a standard CO2 laser and a CO2 laser with AOM. The AOM-integrated CO2 laser creates approximately 30% less HAZ and a significantly better edge quality.
