diff --git a/mode-matching/mode-matching.py b/mode-matching/mode-matching.py
new file mode 100644
index 0000000..188af11
--- /dev/null
+++ b/mode-matching/mode-matching.py
@@ -0,0 +1,11 @@
+from numpy import pi
+
+L = 140.#mm
+R = 900.#mm
+lambd = 1542.#nm
+
+g = 1-L/R
+print('g = %f'%g)
+
+w0 = ((L*lambd/pi)*(g/(1-g))**0.5)**0.5
+print('w0 = %f um'%w0)