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Optical Frequency Comb Generator Based on Nonlinear Effect in On-Chip Microring Resonator
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Digital Broadcasting, Telecommunication and Optoelectronics

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Opportunity

Optical frequency comb (a laser source whose spectrum is a series of discrete, equally spaced frequency lines) offers a direct link from radio frequency standards to optical frequencies. However, the 3 common ways of generating optical frequency combs, namely, femtosecond mode locked lasers, electro-optic modulator (EOM) and one basing on nonlinear Kerr effect of micro-cavities, suffer lack of flexibility, in that the frequency spacing and the shape of the generated comb cannot be changed easily.
This invention depicts an optical frequency comb generator basing on a CMOS-compatible on-chip microring resonator. It shows great potential in many different applications, such as ultrafast accurate optical clocks, coherent optical communications, molecular spectroscopy, and signal processing in different domains. The CMOS-compatible characteristics of the microring resonator will also make the optical frequency comb generator compact and power-efficient, raising the possibility of mass production. 

Technology

The invention uses a CMOS-compatible on-chip microring resonator. It provides a convenient and cost-effective solution for the broadband optical frequency comb generation with large and tunable frequency spacing.  It is basing on the nonlinear Kerr effect in the microring resonator basically, but two fiber loop cavities are utilized and connected via the microring device. In this configuration, the two fiber-loop cavities are absolutely symmetrical, and each of them comprises an optical amplifier to provide the sustained energy in the cavity, a polarization controller to adjust the polarization state into the microring resonator, an isolator to ensure lightwave propagating in the same direction, and an optical bandpass filter to select all the oscillating modes together with the same microring resonator. The microring resonator is made from high-index doped silica glass with a Q value of more than one million, which acts not only the fine filter but also the nonlinear element in both the fiber-loop cavities. Four wave mixing (FWM) effect occurs under the low-power pump situation in this structure to generate the broadband optical frequency combs, which is tapped and observed through an optical coupler in one of the fiber-loop cavity. 

Advantages

  • The current invention utilizes two fiber-loop cavities and one microring cavity, which extends both frequency spacing and bandwidth of the generated optical frequency comb.
  • Strict wavelength matching and thermal stabilization are not necessary, and the power from each of the optical amplifier can also be reduced.
  • The frequency spacing of the generated comb can be changed discretely from tens to hundreds GHz according to the parameters of microring and optical bandpass filters.
  • The shape of the generated optical frequency comb can also be adjusted when optical bandpass filters with different passbands are used.

Applications 

  • Ultrafast accurate optical clocks, astronomy
  • Molecular and biological spectroscopy
  • Coherent optical communications, microwave photonics, signal processing 
IP Status
Patent granted
Technology Readiness Level (TRL)
3
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Optical Frequency Comb Generator Based on Nonlinear Effect in On-Chip Microring Resonator

 

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