diff --git a/src/single-core-data-gen/generate_signal.py b/src/single-core-data-gen/generate_signal.py
index de23574..957a008 100644
--- a/src/single-core-data-gen/generate_signal.py
+++ b/src/single-core-data-gen/generate_signal.py
@@ -244,8 +244,8 @@ def initialize_fiber_and_data(config, input_data_override=None):
         D=config["fiber"]["d"],
         S=config["fiber"]["s"],
     )
-    if config["fiber"]["birefsteps"] > 0:
-        config["fiber"]["birefseed"] = config["fiber"].get(
+    if config["fiber"].get("birefsteps", 0) > 0:
+        seed = config["fiber"].get(
             "birefseed", (int(time.time() * 1000)) % 2**32
         )
         py_fiber.birefarray = pypho.birefringence_segment.create_pmd_fibre(
@@ -253,7 +253,7 @@ def initialize_fiber_and_data(config, input_data_override=None):
             py_fiber.l / config["fiber"]["birefsteps"],
             # maxDeltaD=config["fiber"]["d"]/5,
             maxDeltaBeta = config["fiber"].get("max_delta_beta", 0),
-            seed=config["fiber"]["birefseed"],
+            seed=seed,
         )
     c_params = pypho.cfiber.ParamsWrapper.from_fiber(
         py_fiber, max_step=1e3 if py_fiber.gamma == 0 else 200
@@ -296,7 +296,7 @@ def save_data(data, config):
         f"alpha = {config['fiber']['alpha']}",
         f"D = {config['fiber']['d']}",
         f"S = {config['fiber']['s']}",
-        f"birefsteps = {config['fiber']['birefsteps']}",
+        f"birefsteps = {config['fiber'].get('birefsteps',0)}",
         f"max_delta_beta = {config['fiber'].get('max_delta_beta', 0)}",
         f"birefseed = {hex(birefseed)}" if birefseed else "; birefseed = not set",
         "",
@@ -336,7 +336,7 @@ def save_data(data, config):
         config["fiber"]["d"],
         config["fiber"]["s"],
         f"{config['signal']['modulation'].upper()}{config['signal']['mod_order']}",
-        config["fiber"]["birefsteps"],
+        config['fiber'].get('birefsteps',0),
         config["fiber"].get("max_delta_beta", 0),
     )
 
@@ -366,7 +366,7 @@ def length_loop(config, lengths, incremental=False, bireflength=None, save=True)
         else:
             print(f"\nGenerating data for fiber length {length}m")
         config["fiber"]["length"] = length
-        if bireflength is not None:
+        if bireflength is not None and bireflength > 0:
             config["fiber"]["birefsteps"] = length // bireflength
             birefsteps_running += config["fiber"]["birefsteps"]
         # set the input data to the output data of the previous run
@@ -520,9 +520,15 @@ if __name__ == "__main__":
     add_pypho.show_log()
     config = get_config()
 
-    # lengths = np.arange(50000, 150000+6000, 10000)
-    lengths = [10000]
-    length_loop(config, lengths, incremental=False, bireflength=1000, save=True)
+    ranges = (10000,)
+    # scales = tuple(range(1, 10))
+    scales = (1,)
+    lengths = [range_ * scale for range_ in ranges for scale in scales]
+    # lengths.append(10*max(ranges))
+    lengths = [*lengths, *lengths]
+    lengths = sorted(lengths)
+
+    length_loop(config, lengths, incremental=False, bireflength=None, save=True)
     # birefringence is constant over coupling length -> several 100m -> bireflength=1000 (m)
 
     # single_run_with_plot(config, save=False)