The design, fabrication, and characterization of an amplifying transverse magnetic ͑TM͒-mode optical waveguide isolator operating at a wavelength of 1300 nm are presented. The magneto-optical Kerr effect induces nonreciprocal modal absorption in a semiconductor optical amplifier with a laterally magnetized ferromagnetic metal contact. Current injection in the active structure compensates for the loss in the forward propagation direction. Monolithic integration of this optical isolator configuration with active InP-based photonic devices is straightforward. An optical isolator allows to avoid one of the main noise sources in an optical communication system by blocking optical feedback in the laser source. Current commercial isolators are bulk components requiring collimating lenses and expensive alignment techniques when applied in a laser diode package. Development of an integrated laser-isolator system is highly desirable as it would reduce cost and size and enhance mechanical and thermal stability. The cost reduction of a laser diode package would be the largest with directly modulated lasers, operating at 1300 nm. Traditional research focuses on applying ferrimagnetic garnets to induce nonreciprocity. 1 The interest in this class of materials comes from their unique combination of low optical loss at telecom wavelengths and a considerably strong magneto-optical ͑MO͒ effect, the source of the nonreciprocity. Stand-alone devices with good isolation performance have been reported. The integration with III-V host material however remains an issue. The best reported result demonstrated isolation not higher than 5 dB in a device several millimeters in length. 2A different research approach is based on the requirement that for monolithic integration, the isolator structure should be very similar to that of the laser it is to be integrated with. If, in a standard semiconductor optical amplifier ͑SOA͒, an adequately magnetized ferromagnetic metal is placed very close to the guiding region, the MO Kerr effect induces a nonreciprocal complex shift of the complex effective index of the guided mode. In other words, the modal absorption is different in both propagation directions. The remaining loss in the forward direction can be compensated for by current injection in the active material. The result is a component which-being transparent or amplifying in one direction, while providing loss in the opposite direction-is isolating and can be monolithically integrated with InP-based active photonic devices. A configuration for transverse magnetic ͑TM͒-polarized light was theoretically proposed in 1999 ͑Ref. 3͒ and demonstrated in 2004. 4 Recently, a variant for transverse electric-mode operation has been demonstrated. 5 In spite of the high levels of nonreciprocal absorption that have been reported, all results so far suffer from a large level of insertion loss with consequently an impractically large injection current. In this letter, we present the design, fabrication, and characterization of a TM-mode device demonstratin...

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