Deuterium makes the production of optical chips much easier
A research team from Singapore has developed a novel silicon nitride waveguide that can generate light over a particularly large spectral range on a chip. The hydrogen isotope deuterium was crucial to the success.
Isotope displaces hydrogen
By using it, the researchers were able to produce the chip component on an 8-inch wafer at low temperatures. This could make the technology suitable for large-scale production using established semiconductor processes. The in Optics Express Published research comes from researchers at the Singapore University of Technology and Design (SUTD) and the A*STAR Institute of Microelectronics. Their goal was to make so-called supercontinuum light sources more compact and energy efficient. Such light sources are used, among other things, for high-resolution medical imaging, precise measurement methods and optical frequency combs.
To date, supercontinuum sources have often been based on specially developed glass fibers. These systems require a comparatively large amount of space and power and are difficult to combine with other components on a chip. Although silicon nitride is considered a particularly suitable material for integrated photonics, conventional manufacturing processes have a crucial disadvantage: hydrogen in the material absorbs light in the range of important telecommunications wavelengths. To remove it, temperatures of up to 1200 degrees Celsius are required.
This is unsuitable for many semiconductor processes and can also cause tension in the material. The researchers therefore replaced hydrogen with deuterium. This shifts the disturbing absorption maximum to a range of around 2.1 micrometers. A complex high-temperature treatment is no longer necessary. Instead, an 800-nanometer-thick film could be deposited onto a full 8-inch wafer at less than 400 degrees Celsius.
Wider spectrum
According to the researchers, the finished waveguide has a light loss of just 0.54 decibels per centimeter. In a test with 500 femtosecond short infrared pulses at 1555 nanometers, the spectrum was expanded to a range of 587 to 1883 nanometers. This meant that the light generated reached from the visible red range deep into the infrared. The stability of the light source was also examined. At moderate pulse energies, the measured spectral coherence was above 0.81.
However, at higher energies the noise increased. As a next step, the researchers want to optimize the length and design of the waveguides and integrate the light sources together with modulators and detectors on a chip. The aim is, among other things, applications in medicine, measurement technology and optical communication.
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