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Waveguide Array Transports Light Without Distortion

posted by Fnord666 on Friday May 15 2020, @09:12AM   
from the Enhance-34-to-46 dept.

Arthur T Knackerbracket has found the following story:

One of the challenges of optical microscopy is to continually increase the imaging power, or resolution. In the past three hundred odd years, scientists have been building ever-better microscopes. The limit, for a long time, was determined by only two factors: the contrast of the object being viewed, and the resolving power of the optics in the microscope. The last 50 years, in particular, have led to an explosion in techniques to improve both the contrast of object and the quality of the optics.

One such technology is called a superlens. The superlens makes use of some of the peculiarities of waves to be able to resolve details that would otherwise be hidden from view. Now, researchers from Nanjing University in China have published results on a waveguide array that provides many of the benefits of a superlens. Along with that, the waveguide array does not have the technological difficulties that are usually associated with superlens fabrication.

[...] A superlens is designed to capture these detail-holding evanescent waves. To enable that, the lens must be constructed from a metamaterial that has a negative refractive index (normal materials have a positive refractive index). However, metamaterials are not easy to make, and don't perform well. Most of the light that hits a superlens is reflected from it, while internally, the substances that are used to create the metamaterial absorb a lot of light. Hence, the lens captures fine details, but the image contrast is poor.

This is where the work of Song and coworkers comes into play. Their lens consists of an array of waveguides that are placed very close to each other. Each waveguide captures light from just in front of the waveguide opening. The light is transported to the other end of the waveguide array, where it is used to (in principle) recreate an image.

[...] The demonstrated structure has other uses. Integrated optical circuits for computing and communications are, compared to electronic systems, large. The spacing is dictated by the need to control the coupling between neighboring waveguides. This research shows how to have high density waveguides without unwanted coupling. In the end, that could find applications more widespread than high resolution imaging.

More information: Wange Song et al. Subwavelength self-imaging in cascaded waveguide arrays, Advanced Photonics (2020). DOI: 10.1117/1.AP.2.3.036001, www.spiedigitallibrary.org/jou … 1.AP.2.3.036001.full

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Original Submission

• Star Blazers (Score: 0) by Anonymous Coward on Friday May 15 2020, @03:02PM

  by Anonymous Coward on Friday May 15 2020, @03:02PM (#994637)

  Now we just need to raise the Yamato!

• These phys.org blurbs can be very frustrating (Score: 0) by Anonymous Coward on Friday May 15 2020, @04:13PM

  by Anonymous Coward on Friday May 15 2020, @04:13PM (#994678)

  I'm a research physicist and often times these Phys.org summaries are confusing as hell. They bend over backwards to relate it to a general audience, but they use descriptions and metaphors that are wrong, or at least very confusing. Typically I have to go to the paper they are talking about to look at the general overview they give in the Introductory section to figure out what the paper is really dealing with.

  For instance, here there is a paragraph or two explaining how super lenses are super because they capture evanescent waves (not a necessary and sufficient condition!), but no where in the research paper does it even talk about evanescent waves! If you go to the Wikipedia page on super lenses, it has it all over the place, but as far as I can tell, this paper isn't looking at the evanescent wave spectrum, but is dealing with transporting conventional signals through waveguides without them getting mixed up.

  Here is the paper conclusion:

  We experimentally demonstrated optical self-imaging beyond the resolution limit in a 1-D silicon waveguide array. By connecting straight and curved waveguides, perfect self-imaging of an initial input state without crosstalk is realized in a high-density configuration. This design is implemented by tuning the coupling in the curved waveguides to be negative, mimicking the negative index material. Note that the subwavelength imaging can also be realized by plasmonics and metamaterials designs, such as plasmonic lenses and hyperlenses. Compared with these designs, our scheme has advantages in lower loss, easier fabrication requirements, and a naturally satisfied impedance matching condition. In principle, this coupled waveguide array system can be extended to a two-dimensional lattice to achieve a real imaging lens, though there would be more challenges in nanofabrications. Nevertheless, our approach provides a practical solution for efficient subwavelength self-imaging in on-chip optical signal routings, which is important in high-density photonic integrations.

  I suspect that evanescent waves are involved with the plasmonic designs that are mentioned and that they are not relevant here, but who knows?