March 01, 2019

Adiabatic mode converters for silicon photonics: Power and polarization broadband manipulators

  • Dong P.
  • Melikyan A.

Broadband, low-loss, and fabrication-tolerant photonic passives are of paramount importance in any photonic integrated circuit (PIC). Among others, the adiabatic couplers can have those merits premised on their one-to-one mode transformation characteristics. These devices are usually designed comprising linear waveguide tapers and have typical lengths of 1 mm, in order to minimize inter-modal coupling along the device. The large footprints and, therefore, the fabrication sensitivity can eventually become a barrier toward their widespread applications. Here, we discuss an intuitive generic method for designing compact broadband adiabatic mode converters. The method can be used to design broad types of adiabatic devices for power and polarization manipulations on silicon PICs. Exemplary devices such as polarization beam splitters and polarization rotator splitters, 3 dB power splitters/combiners for quasi-TE and for quasi-TM polarizations, and power tapper for quasi-TE polarization are discussed. The devices provide insertion losses of <1 dB and extinction ratios in the range of 10-20 dB across the 85 nm measurement window. As an important application of the adiabatic devices, we also report on a broadband optical 90° hybrid with an operating bandwidth of 85 nm.

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