Higher-order optical filters use microring resonators

10 October 2003 Annapolis Junction, MD Lightwave -- Little Optics has introduced very high order multi-cavity filters based on its proprietary compact microring resonator technology. The filters have up to 11 cavities, giving them what the company terms "unprecedented performance" for 50-GHz, 25-GHz, or narrower band applications. They are designed to be particularly useful where high out-of-band rejection is required or where large 3- to 25-dB shape factors are needed.

10 October 2003 Annapolis Junction, MD Lightwave -- Little Optics has introduced very high order multi-cavity filters based on its proprietary compact microring resonator technology. The filters have up to 11 cavities, giving them what the company terms "unprecedented performance" for 50-GHz, 25-GHz, or narrower band applications. They are designed to be particularly useful where high out-of-band rejection is required or where large 3- to 25-dB shape factors are needed. For example, rejection ratios that exceed 100 dB, and shape factors that exceed 75% are possible. Filters with various free-spectral ranges can be produced.

High-order microring resonators mark a breakthrough in WDM filter technology, the company believes. Little Optics says almost arbitrarily high orders can be produced with microring resonators, as all cavities reside in a single dielectric layer. In comparison, thin-film-filter technology typically requires 200 to 400 dielectric layers to be sequentially deposited to create a fourth-order cavity for 25-GHz applications. Microring resonators also have the advantage of four spatially separated ports, which gives them advantages in optical circuit architectures.

The microring filters can be thermally tuned to produce tunable filters with 0.5-GHz positioning accuracy. Microring resonators are used in a variety product applications including:


  • Amplitude filters for WDM
  • All pass filters for phase filtering
  • Tunable filters
  • Hyperfine filters (bandwidths of 12.5 GHz, 6.25 GHz, or less)
  • Sensors for biological, chemical and gas detection
  • Optical spectrometers.


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