adding dbs check

kat_test/physics/dbs.kat

+# Testing dbs with squeezed light.
+# Squeezer and Filter cavity
+# ---------------
+sq sq1 0 10 0 nSq
+s lsq 0 nSq nFC1
+bs mFC1 0.99 0.01 0 0 nFC1 nFC2 nFC3 nFC4
+s lFCcav1 16 nFC3 nFC2_1
+s lFCcav2 16 nFC2_2 nFC4
+bs mFC2 1 0 0 0 nFC2_1 nFC2_2 nFC2_3 nFC2_4
+attr mFC1 Rc -15.9
+attr mFC2 Rc 15.9
+s lFC 0 nFC2 n2
+# -----------------
+# Directional beam splitter
+# ---------------------------
+# n1 - connected to IFO (just a mirror)
+# n2 - connected to the FC
+# n3 - output port
+# n4 - Unused
+dbs dbs1 n1 n2 n3 n4
+# isol* FI 100000 n3 n1 n2
+#s lunused 0 n4 nUnused
+#m mUnused 0 1 0 nUnused dump
+# ----------------------------
+# IFO
+# --------------
+s lIFO 0 n1 nIFO1
+m mIFO 1 0 0 nIFO1 nIFO2
+attr mIFO Rc 15.9
+# ----------------
+# Instructions
+# --------------
+noxaxis
+fsig noise 1
+# Gaussian beams
+# ---------------------------
+maxtem 0
+cav cavFC mFC1 nFC3 mFC1 nFC4
+# ----------------------------
+# ...or plane waves
+# --------------------------
+# maxtem off
+# --------------------------
+# Detectors
+# ----------------------
+# out of n1
+qd qd1a 0 0 n1    # amplitude   
+qd qd1p 0 90 n1   # phase
+# Into n1 
+qd qd1_a 0 0 n1*  # amplitude 
+qd qd1_p 0 90 n1* # phase
+qd qd2a 0 0 n2
+qd qd2p 0 90 n2
+qd qd2_a 0 0 n2*
+qd qd2_p 0 90 n2*
+qd qd3a 0 0 n3
+qd qd3p 0 90 n3
+qd qd3_a 0 0 n3*
+qd qd3_p 0 90 n3*
+qd qd4a 0 0 n4
+qd qd4p 0 90 n4
+qd qd4_a 0 0 n4*
+qd qd4_p 0 90 n4*
+
+gnuterm no

kat_test/physics/reference/dbs.out

+ 0.00000000000000  10.0000000000015  0.100000000000017  10.0000000000015  0.100000000000017  1.00000000000000  1.00000000000000  10.0000000000015  0.100000000000017  10.0000000000015  0.100000000000017  1.00000000000000  1.00000000000000  1.00000000000000  1.00000000000000  1.00000000000000  1.00000000000000