Nonreciprocal polarization converter consisting of asymmetric waveguide with ferrimagnetic Ce:YIG

Transcription

1 8th International Conference on Numerical Simulation of Optoelectronic Devices Nonreciprocal polarization converter consisting of asymmetric waveguide with ferrimagnetic Ce:YIG Research Center for Advanced Science and Technology, Univ. of Tokyo T. Amemiya, T. Tanemura, and Y. Nakano

2 Introduction Commercially available optical isolators Faraday rotation of the magneto-optical materials (garnets). Conventional bulk isolators are not suitable for monolithic integration with other waveguide-based optical devices.

3 Waveguide-based unilateral devices Waveguide-based unilateral devices enhancement of stability in photonic integrated circuits reduction of cost and size of laser diode package laser diode unilateral device

4 Waveguide isolators studied in recent years Type Material Performance Fabrication Size QPM faraday rotation Nonreciprocal phase shift (NRPS) Nonreciprocal loss (NRL) Ce:YIG/ GaAs/AlGaAs Ce:YIG/ GaInAsP/InP Fe/ GaInAsP/InP < 10 db/mm < 1 mm 30 db/mm 2-4 mm 15 db/mm < 0.5 mm QPM NRPS NRL APL 88, (2006) Appl. Opt. 39, 6158 (2000) APL 88, (2006) JLT 24, 38 (2006)

5 Concept of nonreciprocal polarization converter I. I. By By inserting a NRPC NRPC at at the the output output port port of of a laser, laser, we we can can suppress the the coherent interference between the the lasing lasing light light and and back-reflected light. light. II. II. We We can can also also make make a waveguide isolator isolator by by combining the the NRPC NRPC with with a waveguide polarizer or or mode mode splitter. splitter.

6 Structure of our NRPC Our device has several advantages over other waveguide-based unilateral devices reported so far. Material Performance Fabricatio Over 90 % nonreciprocal n Ce:YIG/ polarization conversion GaInAsP/InP (without electric power) Size < 0.3 mm

7 Basic principle of our NRPC β 1 TE-polarized light β 2 The The values values of of β 1 and 1 andβ 2 are 2 are different between forward and and backward propagations because of of the the magneto-optic transverse Kerr Kerr effect effect induced by by the the ferrimagnetic Ce:YIG.

8 Parameters for Symbol Parameter Value ε 1 Refractive index of InP 3.16 ε 2 Refractive index of GaInAsP 3.4 ε 3 Refractive index of Ce:YIG 2.2 Θ Magneto-optical effect for Ce:YIG (deg/cm) θ Angle of the asymmetric waveguide 53 h Height of the device 1.1 (μm) w Width of the device (μm)

9 Simulation process <x-y plane> With the aid of FDM (full-vector wave equations) (1)Propagation constant for each mode (2)Electric field distribution Optimize the device structure <z-axis> With the aid of vectorially corrected (VC) method Power intensity along light propagation W. P. Huang, JQE 29, 2639 (1993) M. Fontaine, JOSA B 15, 964 (1998)

10 Full-vector wave equations (x-y plane) ε r 0 0 μν Dielectric tensor of each layer ε = 0 εr jα 0 jα ε r Non-magnetic layer 1 1 E + E + ( k ε β ) E + ( ε E ) + ( ε E ) = 0 1st 2nd x x y x 0 r x x x r x x y r y εr εr 1 1 E + E + ( k ε β ) E + ( ε E ) + ( ε E ) = x y y y 0 r y y x r x y y r y εr εr Magnetic layer 1 1 Ψ E + E + ( k ε β ) E + ( ε E ) + ( ε E ) + αωμ ( ) = 0 1st 2nd x x y x 0 r x x x r x x y r y 0 x εr εr εr 1 1 Ψ E + E β E +Λ+ ( ε E ) + ( ε E ) + αωμ ( ) = x y y y y y x r x y y r y 0 y εr εr εr 2 αωε εβ 2 εr β Ψ= [ ( x Ey x yex) x( εrex) y( εrey) Ey] εβ α α α r 0 r k0 k0 k α αβk ε β Λ= ( ) + [ ( ) + ( ) + ] εβ α εβ α r r x Ey x yex x εrex y εrey Ey + k0 r + k0 α

11 FDM solution (x-y plane) Using the discrete form of the differential operators, we obtained finite-difference equations for electric field component E x and E y. Ex1,Ey1 Mesh: Mesh width: 50 (nm) Ex81,Ey81 Ex1 Ex2 1st Full-vector equation Ex 6400 = Ey1 Ey 2nd 2 Full-vector equation Ey Ex80, Ey80 Exr,Eyr Ex6400,Ey6400 W. P. Huang, JQE 29, 2639 (1993)

12 Refractive index for orthogonal two modes M Mode1 (Electric field) M Effective refractive index = β / k 0 Mode2 (Electric field)

13 Electric field distributions in our device Mode1 Mode1, E x Mode1, E y x=15 Mode2 Mode2, E x Mode2, E y 10 x x=-5

14 Simulation process <x-y plane> With the aid of FDM method (full-vector wave equations) (1)Propagation constant for each mode (2)Electric field distribution Optimize the device structure <z-axis> With the aid of vectorially corrected (VC) method Power intensity along light propagation W. P. Huang, JQE 29, 2639 (1993) M. Fontaine, JOSA B 15, 964 (1998)

15 Optimizing the device structure (I) Half Beat length π L = β β 1 2 TE-polarized light TE TM Rotation parameter The The necessary conditions for for efficient nonreciprocal conversion Backward half-beat length length is is twice twice as as large large as asforward one. one. Angle Angle φ should should be be almost almost R = A A ε E dxdy r r 2 y ε E dxdy 2 x R=1 φ=45 K. Saitoh et al., JLT 19, 405 (2001)

16 Optimizing the device structure (II) To To achieve achieve an an effective effective nonreciprocareciprocal conversion, conversion, non- (I)The (I)The half-beat half-beat length length for for backward backward light light must must be be twice twice as as large large as as that that for for forward. forward. (II)The (II)The rotation rotation parameter parameter R should should be be near near We optimized structure of the device. w = 1.0 μm, h = 1.1 μm

17 Simulation process <x-y plane> With the aid of FDM method (full-vector wave equations) (1)Propagation constant for each mode (2)Electric field distribution Optimize the device structure <z-axis> With the aid of vectorially corrected (VC) method Power intensity along light propagation W. P. Huang, JQE 29, 2639 (1993) M. Fontaine, JOSA B 15, 964 (1998)

18 Power intensity along light propagation TE mode TM mode uz () = ( β1 β2 ) 1 exp iz 1 R+ exp R M. Fontaine, JOSA B 14, 1444 (1997) M. Fontaine, JOSA B 15, 964 (1998) ( iz β1 β2 ) Device Device length: length: 0.27mm 0.27mm Nonreciprocal Nonreciprocal polarization polarization conversion: conversion: 92% 92% Forward Forward light: light: TE TE TE TE Backward Backward light: light: TE TM TE TM

19 Summary We proposed a nonreciprocal TE-TM polarization converter for avoiding the problems caused by undesired reflections of light in photonic integrated circuits. Material Performance Size Ce:YIG/ GaInAsP/InP 93 % nonreciprocal polarization conversion Forward: TE TE Backward: TE TM 0.27 mm