河北师范大学：《电动力学》课程教学资源（PPT课件讲稿）第七章 光波导技术（7.5.2）Splitters and couplers

Splitters and Couplers

Splitters and Couplers

What needed? to combine signals and/or to split them multiple ways up to 1000x 1000 for WDM LANs three important characteristics Return Loss: the amount of power that is reflected and thus lost Insertion LoSs: the amount of signal lost in the total transit through the device Excess Loss additional loss of a device over and above the loss required by theory

What needed? • to combine signals and/or to split them multiple ways. • up to 1000x1000 for WDM LANs • three important characteristics – Return Loss:the amount of power that is reflected and thus lost. – Insertion Loss:the amount of signal lost in the total transit through the device. – Excess Loss:additional loss of a device over and above the loss required by theory

Resonant Coupling Cladding Glass Port 1 Port 2 Gap-5 microns Port 4 Port 3 Sngle mode cores Coupling Length power will oscillate from one fibre core to the other

Resonant Coupling power will oscillate from one fibre core to the other

Single-Mode Propagation Cladd Core Cladding Part of wawe extends to cadang Field Amplitude EJe sp Fibre Fibre Fibre Cladding Core Cladding

Single-Mode Propagation

Theory Equations △β R dr/dz-joR=-jKS dS/dz+ joS =-jKR AH=R exp(-joz) A、=Sexp(z tuning coefficient:8=(β、-P1 Coupling coefficient: K

Theory • Equations： dR/dz- jdR = -jKS; dS/dz+ jdS = -jKR • Am =R exp(-jdz); • An= S exp(jdz) • Detuning coefficient：d=(bn-bm )/2 • Coupling coefficient: K

Solution R=cos(√K2+2-)+~ sin(√K2+82z) K2+δ iK sin(√K2+62z) K2+6

Solution sin( ) cos( ) sin( ) 2 2 2 2 2 2 2 2 2 2 K z K j K S K z K j R K z d d d d d d + + = - + + = + +

Mode coupling between two fibres δ=0,R2(z)=cos2(Kz) 2D S(z=sin(Kz) ° coupling length 2D o=/2K Coupling coefficient 4ka Ka=K -a(d-2D) 12 21 β(1+aD(kx+a2) k2=n2k2-B2;a2=B2-n2k

Mode coupling between two fibres d=0，R2 (z)=cos2 (Kz) S 2 (z)=sin2 (Kz) • coupling length ： L0 =p/2K • Coupling coefficient ： 2 0 2 2 2 2 2 2 0 2 1 2 1 ( 2 ) 2 2 1 2 2 1 1 2 2 1 ; (1 )( ) 4 k n k n k e D k k K K x d D x x = - = - + + = = - - b  b b     2D 2D d n2 n1 n2 n1 n2

Important points The coupling length"is formally defined (at a particular wavelength) as the length at which 100%of the power entering at a particular input port is transferred to the other fibre The amount of coupling and hence the coupling length is strongly dependent on the separation between the two single-mode cores. The further apart they are the greater the coupling length

Important points • The “coupling length” is formally defined (at a particular wavelength) as the length at which 100% of the power entering at a particular input port is transferred to the other fibre. • The amount of coupling and hence the coupling length is strongly dependent on the separation between the two single-mode cores. The further apart they are the greater the coupling length

Important points The coupling lengths are strongly wavelength dependent! Different wavelengths yield different coupling lengths

Important points • The coupling lengths are strongly wavelength dependent! Different wavelengths yield different coupling lengths

Mode coupling of two mixed signal(of different wavelength)

Mode coupling of two mixed signal(of different wavelength)