Transverse magnetic mode nonreciprocal propagation in an amplifying AlGaInAs∕InP optical waveguide isolator

Abstract

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...

Enhancement of the transverse non-reciprocal magneto-optical effect

“…The ellipticity is close to circular for the waveguiding mode. That is the reason why the experimentally observed transverse nMO effect in waveguides is substantial [9][10][11][12] . The data were calculated by solving Maxwell's equations and utilizing known optical and magneto-optical constants of transition metals 19,20 and semiconductors 21 .…”

“…The second example is light propagation in an optical waveguide covered by a ferromagnetic metal. In the case of a magnetic field applied perpendicularly to the light propagation direction in a waveguide plane, the absorption of the waveguide mode is significantly different for two opposite directions of the magnetic field [8][9][10][11][12] . The third example is a waveguide covered by a transparent MO material, in this case the propagation speed of waveguide mode changes when the applied magnetic field is reversed 13,14 .…”

Spectral dependence of the magnetic modulation of surface plasmon polaritons in noble/ferromagnetic/noble metal films

“…This modification occurs in both the real and imaginary part of k sp : k (1), the SPP modification under an applied magnetic field is nonreciprocal [k sp (B 0 ) = −k sp (B 0 )], thus making this kind of system very interesting for the design of integrated optical isolators, [22][23][24][25][26] another fundamental piece for the development of nanophotonic circuits. Another advantage of the magnetic field driven systems is related to its potential switching speed, as it has been recently demonstrated that materials magnetization switching is an ultrafast phenomenon that can achieve the terahertz regime.…”

Optimized Magneto-optical Isolator Designs Inspired by Seedlayer-Free Terbium Iron Garnets with Opposite Chirality

“…Garnets, with their unique magneto-optical (MO) properties have been the material of choice for building passive non-reciprocal devices [7][8][9][10] . In general, non-garnet non-reciprocal devices are active devices that require external power sources, which increase the complexity and cost of the device [11][12][13][14] . MO effects in garnets are the result of non-zero off-diagonal components in the dielectric matrix (ε) which break time-reversal symmetry.…”