半导体激光器半高宽(FWHM)计算
一、问题描述
Estimate the spot size (FWHM) in the lateral and transverse directions for
a 1.3-um semiconductor laser whose active region is 0.2-um thick and
1-um wide. Assume u2=3.5and u1=3.2.
二、问题分析
单模半导体激光器的线宽通常定义为输出信号光谱的半高宽(FWHM):full
width at half maximum,功率函数峰值 3dB 处相距的频率宽度即为 FWHM。
2
2
1.首先考虑 TE 模,即只考虑 y 方向,由书本第二章式 2.5.10:
d
dy
求其通解可以得到式 2.5.14:
0
[
]
2
2
2
0
b
e
偶模:
(y)
奇模:
(y)
cos( y)
eA
B exp[
e
sin( y)
eA
B exp[
e
(| y | d/ 2)]
(| y | d/ 2)]
for | y | d/ 2
for | y | d/ 2
for | y | d/ 2
for | y | d/ 2
其中,
k
k
0
2
2 1/2
(
)
e
2 1/2
(
)
1
2
2
0
e
1 为包层折射率, 2 为有源区折射率, e 为有效折射率, 1 < e < 2 。
和 /d
dy 在| y | d/ 2
处连续,并且有边界条件:
cos( d/ 2)
A
B
e
e
cos( d/ 2)
A
B
e
e
TE
偶模:
TE
= tan( d/ 2)
=- cot( d/ 2)
奇模:
2.考虑 TM 模,即只考虑 x 方向,由书本上式 2.5.34:
(x)
e
2
(x)]
2
0
2
[
e
2
2
x
=
i
0
0
/ 2
=3.5
,
=1.3um
可得到 TM 模的解:
2
2
x
2
e
[
0
2
(x)
2
]
0
类似的,求出方程的通解:
(x)
eA
B exp[
e
cos( x)
(| x | d/ 2)]
for | x |
for | x |
w
w
/ 2
/ 2
由题目可知如下参数:d=0.2um,w=0.1um, 1
=3.2
,
2
计算 e :ue=sqrt(u1^2+GamaT*(u2^2-u1^2));
三、MATLAB 仿真结果
TE 模:fwhmvalue =
0.2930
Transverse Modes FWHM
3
2.5
2
1.5
1
0.5
2
)
y
i
h
p
(
0
-1
-0.8
-0.6
-0.4
-0.2
0.2
Thickness d (um)
0
0.4
0.6
0.8
1
TM 模:fwhmvalue =
1.0220
2
)
x
i
h
p
(
3
2.5
2
1.5
1
0.5
0
-3
Lateral Modes FWHM
-2
-1
0
Width d (um)
1
2
3
四、总结
本次实验的主要内容为求解半导体激光器的 FWHM。通过非微扰特征方程,求特征方程的
通解,结合边界条件求解。考虑横模 TE 和纵模 TM 两种情况,分别进行求解。
附:
1.TE-mode
%%TEmodeFWHM
clearall
clc
d=0.2; %um
w=1; %um
u1=3.2;
u2=3.5;
lamada=1.3;
k0=2*pi/lamada;
D=k0*sqrt((u2^2-u1^2))*d;
GamaT=D^2/(2+D^2);
ue=sqrt(u1^2+GamaT*(u2^2-u1^2));
lamda=1.3; %um
k0=2*pi/lamda;
k=k0*sqrt(u2*u2-ue*ue);
gamma=k0*sqrt(ue*ue-u1*u1);
Ae=1.6;
Be=Ae*0.882;
y=-1:0.0005:1;
phi_y=zeros(1,length(y));
fori=1:length(y)
if (abs(y(i))<=d/2)
phi_y(i)=(Ae*cos(k*y(i))).^2;
else
phi_y(i)=(Be*exp(-gamma*(abs(y(i)
)-d/2))).^2;
end
end
figure
plot(y,phi_y)
xlabel('Thickness d (um)');
ylabel('(pih_y)^2')
title('Transverse Modes FWHM')
holdon
gridon
phi_mid=max(phi_y)/2;
y_mid=zeros(1,2);
fori=1:(length(y)-1)/2
if (abs(phi_y(i)-phi_mid)<0.01)
y_mid(1)=y(i);
end
end
fori=(length(y)+1)/2:length(y)
if (abs(phi_y(i)-phi_mid)<0.01)
y_mid(2)=y(i);
end
end
plot(y_mid(1),phi_mid,'gp',y_mid
(2),phi_mid,'rp')
fwhmvalue=abs(y_mid(2)-y_mid(1))
% um
2.TM-mode
%%TMmode FWHM
clearall
clc
d=0.2; %um
clc
clf
w=1; %um
u1=3.2;
u2=3.5;
lamada=1.3;
k0=2*pi/lamada;
D=k0*sqrt((u2^2-u1^2))*d;
GamaT=D^2/(2+D^2);
ue=sqrt(u1^2+GamaT*(u2^2-u1^2));
lamda=1.3; %um
k0=2*pi/lamda;
k=1.4745;
gamma=k0*sqrt(ue*ue-u1*u1)
Ae=1.6;
Be=Ae*0.745;
x=-3:0.0005:3;
phi_x=zeros(1,length(x));
fori=1:length(x)
if (abs(x(i))<=w/2)
phi_x(i)=(Ae*cos(k*x(i))).^2;
else
phi_x(i)=(Be*exp(-gamma*(abs(x(i)
)-w/2))).^2;
end
end
figure
plot(x,phi_x)
xlabel('Width d (um)');
ylabel('(pih_x)^2')
title('Lateral Modes FWHM')
holdon
gridon
phi_mid=max(phi_x)/2;
x_mid=zeros(1,2);
fori=1:(length(x)-1)/2
if (abs(phi_x(i)-phi_mid)<0.01)
x_mid(1)=x(i);
end
end
fori=(length(x)+1)/2:length(x)
if (abs(phi_x(i)-phi_mid)<0.01)
x_mid(2)=x(i);
end
end
plot(x_mid(1),phi_mid,'gp',x_mid
(2),phi_mid,'rp')
fwhmvalue=abs(x_mid(2)-x_mid(1))
% um