optical channel bugfix

models/optical_channel.py

@@ -127,7 +127,7 @@ class OpticalChannel(defs.Channel):
 
         # Symbol Decisions
         idx = np.arange(self.filter_samples/2, t.shape[0] - (self.filter_samples/2),
-                        self.symbol_period/self.sample_period, dtype='int16')
+                        self.symbol_period/self.sample_period, dtype='int64')
         t_descision = self.sample_period * idx
 
         if self.show_graphs: