To support the miniaturization of optical devices and components, a scientific team led by researchers at ITMO University has devised a quick, affordable method to make visible-light nanophotonic chips. The light source for the chip can be grown directly on a waveguide in a Petri dish using solution chemistry methods — a much less expensive approach than nanolithography. Today’s optical chips operate in the infrared (IR) range. “But to make the devices even more compact, we need to work in the visible range, as the size of a chip depends on the wavelength of its emission,” researcher Sergey Makarov said. The modern photonics industry is constantly working on making its devices more compact, be it computing systems or sensors and lidars. For this purpose, it is necessary to make lasers, transistors, and other elements smaller. A team of scientists led by ITMO researchers proposed a quick and affordable method to create optical chips right in a Petri dish. Courtesy of P. Trofimov et al. The standard silicon waveguides used in IR optics do not work in the visible range, researcher Ivan Sinev said. “They transmit the signal no further than several micrometers,” he said. “For an optical chip, we need to transmit along tens of micrometers with a high localization, so that the waveguide would have a very small diameter and the light would go sufficiently far through it.” The scientists first tried replacing silicon waveguides with silver ones, but the transmission distance was insufficient. They ended up using gallium phosphide (GaP) for the waveguides, choosing this material because it has low losses in the visible band. They embedded the GaP nanowires directly into compact perovskite-based light sources. The perovskite microcrystals supported stable room temperature lasing and broadband chemical tuning of the emission wavelength in the range of 530 to 680 nm, while the GaP nanowaveguides supported the efficient outcoupling of light, its subwavelength confinement, and long-range guiding over distances more than 20 μm. To demonstrate their approach, the researchers performed sequential transfer and conversion of light using an intermediate perovskite nanoparticle in a chain of GaP nanowaveguides. The size of the new chip’s elements is about three times smaller than chips that work in the IR spectral range. Although creating a source that would emit in the green or red part of the spectrum is relatively easy, the team said, creating waveguides for these wavelengths can be challenge. “The chip’s important property is its ability to tune the emission color from green to red by using a very simple procedure — an anionic exchange between perovskite and hydrogen halides vapor,” researcher Anatoly Pushkarev said. “Importantly, you can change the emission color after the chip’s production, and this process is reversible. This could be useful for the devices that have to transmit many optical signals at different wavelengths. For example, you can create several lasers for such a device, connect them to a single waveguide, and use it for transmitting several signals of different colors at once.” (l) to (r): ITMO researchers Pavel Trofimov, Anatoly Pushkarev, Ivan Sinev, and Sergey Makarov. Courtesy of P. Trofimov et al. The scientists equipped the chip with an optical nanoantenna made of perovskite. The nanoantenna receives the signal traveling along the waveguide and allows two chips to be united in a single system. “We added a nanoantenna at the other end of our waveguide, so now we have a light source, a waveguide, and a nanoantenna that emits light when pumped by the microlaser’s emission,” researcher Pavel Trofimov said. “We added another waveguide to it: As a result, the emission from a single laser went into two waveguides,” Trofimov said. “At the same time, the nanoantenna did not just connect these elements into a single system, but also converted part of the green light into the red spectrum.” The research was published in ACS Nano (www.doi.org/10.1021/acsnano.0c01104).