diff --git a/tidy3d/components/__init__.py b/tidy3d/components/__init__.py
index f9a55006de..27e2aa11a9 100644
--- a/tidy3d/components/__init__.py
+++ b/tidy3d/components/__init__.py
@@ -28,7 +28,7 @@
 
 # monitor
 from .monitor import AbstractFieldMonitor, FreqMonitor, TimeMonitor, FieldMonitor, FieldTimeMonitor
-from .monitor import AbstractFluxMonitor, FluxMonitor, FluxTimeMonitor, ModeMonitor
+from .monitor import Monitor, AbstractFluxMonitor, FluxMonitor, FluxTimeMonitor, ModeMonitor
 
 # simulation
 from .simulation import Simulation
diff --git a/tidy3d/components/grid.py b/tidy3d/components/grid.py
index 86955930a5..c7629f62c0 100644
--- a/tidy3d/components/grid.py
+++ b/tidy3d/components/grid.py
@@ -35,6 +35,11 @@ class Coords(Tidy3dBaseModel):
     y: Coords1D
     z: Coords1D
 
+    @property
+    def to_list(self):
+        """Return a list of the three Coord1D objects."""
+        return list(self.dict().values())
+
 
 class FieldGrid(Tidy3dBaseModel):
     """Holds the grid data for a single field.
diff --git a/tidy3d/components/simulation.py b/tidy3d/components/simulation.py
index 569ac4b629..00228cc342 100644
--- a/tidy3d/components/simulation.py
+++ b/tidy3d/components/simulation.py
@@ -562,7 +562,7 @@ def pml_thicknesses(self) -> List[Tuple[float, float]]:
         """
         num_layers = self.num_pml_layers
         pml_thicknesses = []
-        for num_layer, boundaries in zip(num_layers, self.grid.boundaries.dict().values()):
+        for num_layer, boundaries in zip(num_layers, self.grid.boundaries.to_list):
             thick_l = boundaries[num_layer[0]] - boundaries[0]
             thick_r = boundaries[-1] - boundaries[-1 - num_layer[1]]
             pml_thicknesses.append((thick_l, thick_r))
@@ -768,8 +768,8 @@ def frequency_range(self) -> FreqBound:
             at 5 standard deviations.
         """
         source_ranges = [source.source_time.frequency_range for source in self.sources]
-        freq_min = min(freq_range[0] for freq_range in source_ranges)
-        freq_max = max(freq_range[1] for freq_range in source_ranges)
+        freq_min = min([freq_range[0] for freq_range in source_ranges], default=0.0)
+        freq_max = max([freq_range[1] for freq_range in source_ranges], default=0.0)
         return (freq_min, freq_max)
 
     """ Discretization """
@@ -783,7 +783,7 @@ def dt(self) -> float:
         float
             Time step (seconds).
         """
-        dl_mins = [np.min(sizes) for sizes in self.grid.sizes.dict().values()]
+        dl_mins = [np.min(sizes) for sizes in self.grid.sizes.to_list]
         dl_sum_inv_sq = sum([1 / dl ** 2 for dl in dl_mins])
         dl_avg = 1 / np.sqrt(dl_sum_inv_sq)
         return self.courant * dl_avg / C_0
@@ -904,7 +904,7 @@ def discretize_inds(self, box: Box) -> List[Tuple[int, int]]:
             ind_min = 0 if len(inds_leq_pt_min) == 0 else inds_leq_pt_min[-1]
 
             # store indexes
-            inds_list.append((ind_min, ind_max + 1))
+            inds_list.append((ind_min, ind_max))
 
         return inds_list
 
@@ -927,7 +927,8 @@ def discretize(self, box: Box) -> Grid:
         for axis_label, axis_inds in zip("xyz", disc_inds):
             # copy orginal bound coords into subgrid coords
             bound_coords = self.grid.boundaries.dict()[axis_label]
-            sub_cell_boundary_dict[axis_label] = bound_coords[axis_inds[0] : axis_inds[1]]
+            # axis_inds[1] + 1 because we are selecting cell boundaries not cells
+            sub_cell_boundary_dict[axis_label] = bound_coords[axis_inds[0] : axis_inds[1] + 1]
 
         # construct sub grid
         sub_boundaries = Coords(**sub_cell_boundary_dict)
diff --git a/tidy3d/convert.py b/tidy3d/convert.py
index ffbeaacc47..97b64d6673 100644
--- a/tidy3d/convert.py
+++ b/tidy3d/convert.py
@@ -227,10 +227,7 @@ def old_json_sources(sim: Simulation) -> List[Dict]:
         src = {}
 
         if isinstance(source, VolumeSource):
-            """TODO: Is polarization the right word if we're talking about J and M?
-            Check Lumerical notation."""
-            component = "E" if source.polarization[0] == "J" else "H"
-            component += source.polarization[1]
+            component = source.polarization
             if all(s == 0 for s in source.size):
                 src = {
                     "name": name,