Dr. Vadym Zayets

Transverse Magneto-Optical effect

Spin-polarized electrons excited utilizing transverse MO effect

 The transverse MO effect can be used to excite the spin-polarized electrons in a material. Spin excitation in waveguide utilizing transverse MO effect does not suffer the problem of TE-TM mode phase mismatch and can be used for reliable creation of spin accumulation by waveguiding light.

Conventional method of optical excitement of spin-polarized electrons

Fig.1 Conventional method to excite spin-polarized electrons by circularly-polarized light. The  circularly polarized light is absorbed in GaAs and excites the spin-polarized electrons

 

Since the electrons of one spin direction interact with only light either of left or right circular polarization, when circularly-polarized light is absorbed in a material exciting electrons, the photo-excited electrons are spin-polarized. The spin polarization is either along or opposite to the light propagation direction.

This method is widely used to create a spin  accumulation in material.

I have used this method in experiment to test recording speed of the spin-photon memory.

 

 

 

 

 

 

 

 

 

Conventional method to excite spin in an optical waveguide

Fig.2 Conventional method to excite spin-polarized electrons by circularly-polarized light in a waveguide. The circularly- polarized light is propagate in transparent AlGaAs waveguide and it is absorbed in GaAs exciting the spin-polarized electrons

Similar method of spin excitation may be used utilizing waveguiding light. However, since propagation constants of waveguide TE and TM modes are different, generally the circular-polarized light can not propagate in the waveguide. However, in specially designed waveguides, it is possible to achieve zero TE-TM mode mismatch and the circulary polarized light can propagate in such waveguides. The technology to achieve zero TE-TM mode phase mismatch was well developed for CdMnTe waveguides.

Another method to utilize circulary polarized in waveguide is phase control between TE-TM mode. Even if the waveguide has non-zero TE-TM mode phase mismatch, by controlling the phase between TE and TM mode at waveguide input, the circular polarization of light can be achieved at waveguide output. This method is called "TE-TM mode phase locked method". This method I have used for testing the high-speed recording of the spin-photon memory integrated with a waveguide.

I would like to emphasize that using the circular polarized light with waveguides is always a difficult task. In the next chapter I will show that it is possible to use conventional linear polarized TM mode in waveguide to excite the spin polarized electrons.

Spin-polarized electrons excited utilizing transverse MO effect

Fig.3 Linearly-polarized TM mode excites spin-polarized electrons when absorbed in GaAs due to transverse MO effect.

Spin excitation in waveguide utilizing transverse MO effect does not suffer from the problem of TE-TM mode phase mismatch and can be used for reliable creation of spin accumulation by waveguiding light in future spintronics and spin-photonics devices.

For example, let us consider the propagation of linearly-polarized TM mode in a transparent AlGaAs waveguide. A part of waveguide is covered by GaAs, which absorbs the light. Since in GaAs optical field has an evanescent component along x-axis, the polarization of light inside GaAs is transverse-elliptical. Therefore, light will excites spin-polarized electrons in GaAs. The spin direction will be perpendicular to the light propagation direction. In example of Fig.3, the spin direction is either along or opposite the direction of y-axis.