TOKYO, October 18, 2016—Canon Inc. announced today the successful development of the world’s first* indium phosphide (InP) immersion grating.† Strengthening its lineup of immersion gratings, which includes gratings made from germanium (Ge) and cadmium zinc telluride (CdZnTe), Canon is contributing to even greater progress in cosmological observation by expanding the range of observable infrared frequencies.
In order to retrieve information contained within light emitted from space, astronomical telescopes and man-made satellites are equipped with spectroscopes—devices that incrementally divide light by its different frequencies—that play a vital role in cosmological observation. Compared with typical reflective elements, immersion gratings enable spectrometers that are smaller in size and realize higher levels of performance. With the addition of an InP immersion grating to Canon’s lineup, spectrometers could be reduced to approximately 1/27th the volume of those equipped with typical reflective elements that cover the same frequencies. Overcoming restrictions on size and weight, which, until now, made it difficult to launch man-made satellites equipped with high-performance spectrometers, is expected to further expand the possibilities of cosmological observation. What’s more, the application of this grating to next-generation large ground-based telescopes, which face the problem of ever-increasing sizes, could lead to reductions in size without sacrificing performance.
With the addition of an InP immersion grating, Canon’s immersion grating lineup now covers light from near infrared to far infrared, enabling observation of almost the entire spectrum of infrared frequencies used in the field of astronomy (from 1 to 20 μm‡). Infrared light can be captured from much farther distances than visible light, making detection of matter in space possible on a molecular, and even atomic, level. As such, the new InP immersion grating could facilitate research into not only the origin of life and planets, but also the origin of the universe itself, contributing to even greater developments in space science.
While the benefits of fabricating immersion diffractive gratings were realized long ago, because the transmissive semiconductor materials suited to the infrared frequencies used in the field of astronomy (from 1 to 20 μm) are particularly brittle, achieving a surface of virtually perfect regularity with grooves measuring only a few nanometers§proved difficult. Canon applied its own ultra-precision processing technology, cultivated through the manufacture of precision components, using only machining processes to successfully develop immersion gratings even with such brittle semiconductor materials. The resulting InP immersion grating realizes an arrangement of 990 steps at 47 μm intervals.
Diffractive elements for use with high-dispersion infrared spectra ordinarily have an absolute diffraction efficiency¶of 50–60%. Canon’s InP immersion grating, however, achieves an absolute diffraction efficiency of approximately 75%. With its high-efficiency performance, enabling superior light capture even amid low light intensity, it will enable small telescopes to achieve high precision measurement, and large telescopes to measure infrared light from much farther distances in space.
Canon will host a presentation on its indium phosphide immersion grating at the International Conference on Space Optics 2016, to be held from October 18 to 21, 2016, in Barritz, France.
| * | Among immersion gratings made from indium phosphate. According to a Canon survey. |
| † | Indium phosphide immersion grating refers to a spectrographic optical element capable of covering the indium phosphide transmissive frequency range of the infrared spectrum between approximately 1.5 and 8 μm. Compared with conventional reflective diffractive gratings, immersion gratings make possible higher dispersion relative to the refractive index (approx. 3.2 for InP). |
| ‡ | 1 μm (micrometer) is one-millionth of a meter (or one-thousandth of a millimeter). |
| § | 1 nm (nanometer) is one-billionth of a meter (or one-thousandth of a micrometer). |
| ¶ | Absolute diffraction efficiency is the ratio of the diffracted light intensity to the incident light intensity, specifically, at the precise point of the strongest diffracted light intensity. In the case of Canon’s InP immersion grating, the theoretical absolute diffraction efficiency limit is said to be 85%. |
Setting sights on medical and communication applications
Going forward, Canon intends to develop an immersion grating from materials suitable for frequencies close to visible light (0.8–1.2 μm), and with the successful development of its InP immersion grating, the Company is one step closer to achieving that goal. By developing a lineup of immersion gratings using a variety of different materials, users can choose the optimal grating based on the frequency range it will be used with to make possible a wide range of applications in the field of infrared spectroscopy. Canon anticipates applications in the fields of medicine, communication and, of course, astronomy.