From 55210a1e2b9ae9e9e432b03f3ba51eac3dd06004 Mon Sep 17 00:00:00 2001
From: bsnyder <b.snyder@psiquantum.com>
Date: Sun, 25 Sep 2022 21:32:04 +0200
Subject: [PATCH] Added parabolic width_type to taper_cross_section

---
 gdsfactory/components/__init__.py            |  2 ++
 gdsfactory/components/taper_cross_section.py |  7 ++++++-
 gdsfactory/cross_section.py                  |  2 +-
 gdsfactory/path.py                           | 15 ++++++++++++++-
 gdsfactory/types.py                          |  2 +-
 5 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/gdsfactory/components/__init__.py b/gdsfactory/components/__init__.py
index 4cad19ad14..216801bbf3 100644
--- a/gdsfactory/components/__init__.py
+++ b/gdsfactory/components/__init__.py
@@ -220,6 +220,7 @@
 )
 from gdsfactory.components.taper_cross_section import (
     taper_cross_section_linear,
+    taper_cross_section_parabolic,
     taper_cross_section_sine,
 )
 from gdsfactory.components.taper_from_csv import (
@@ -270,6 +271,7 @@
     crossing45=crossing45,
     taper_cross_section_linear=taper_cross_section_linear,
     taper_cross_section_sine=taper_cross_section_sine,
+    taper_cross_section_parabolic=taper_cross_section_parabolic,
     taper=taper,
     taper2=taper2,
     taper_0p5_to_3_l36=taper_0p5_to_3_l36,
diff --git a/gdsfactory/components/taper_cross_section.py b/gdsfactory/components/taper_cross_section.py
index 55b721fa03..e969da462c 100644
--- a/gdsfactory/components/taper_cross_section.py
+++ b/gdsfactory/components/taper_cross_section.py
@@ -12,6 +12,7 @@ def taper_cross_section(
     length: float = 10,
     npoints: int = 100,
     linear: bool = False,
+    width_type: str = "sine",
     **kwargs
 ) -> Component:
     r"""Returns taper transition between cross_section1 and cross_section2.
@@ -22,6 +23,7 @@ def taper_cross_section(
         length: transition length.
         npoints: number of points.
         linear: shape of the transition, sine when False.
+        width_type: shape of the transition ONLY IF linear is False
         kwargs: cross_section settings for section2.
 
 
@@ -42,7 +44,7 @@ def taper_cross_section(
     transition = gf.path.transition(
         cross_section1=gf.get_cross_section(cross_section1),
         cross_section2=gf.get_cross_section(cross_section2, **kwargs),
-        width_type="linear" if linear else "sine",
+        width_type="linear" if linear else width_type,
     )
     taper_path = gf.path.straight(length=length, npoints=npoints)
 
@@ -54,6 +56,9 @@ def taper_cross_section(
 
 taper_cross_section_linear = gf.partial(taper_cross_section, linear=True, npoints=2)
 taper_cross_section_sine = gf.partial(taper_cross_section, linear=False, npoints=101)
+taper_cross_section_parabolic = gf.partial(
+    taper_cross_section, linear=False, width_type="parabolic", npoints=101
+)
 
 
 if __name__ == "__main__":
diff --git a/gdsfactory/cross_section.py b/gdsfactory/cross_section.py
index e15db3f215..e2d7ff6baf 100644
--- a/gdsfactory/cross_section.py
+++ b/gdsfactory/cross_section.py
@@ -19,7 +19,7 @@
 LAYER = TECH.layer
 Layer = Tuple[int, int]
 Layers = Tuple[Layer, ...]
-WidthTypes = Literal["sine", "linear"]
+WidthTypes = Literal["sine", "linear", "parabolic"]
 
 LayerSpec = Union[Layer, int, str, None]
 LayerSpecs = Union[List[LayerSpec], Tuple[LayerSpec, ...]]
diff --git a/gdsfactory/path.py b/gdsfactory/path.py
index 7911ade99c..cb19834a15 100644
--- a/gdsfactory/path.py
+++ b/gdsfactory/path.py
@@ -137,6 +137,15 @@ def sine(t):
     return sine
 
 
+def _parabolic_transition(y1, y2):
+    dy = y2 - y1
+
+    def parabolic(t):
+        return y1 + np.sqrt(t) * dy
+
+    return parabolic
+
+
 def _linear_transition(y1, y2):
     dy = y2 - y1
 
@@ -225,8 +234,12 @@ def transition(
                 width_fun = _linear_transition(width1, width2)
             elif width_type == "sine":
                 width_fun = _sinusoidal_transition(width1, width2)
+            elif width_type == "parabolic":
+                width_fun = _parabolic_transition(width1, width2)
             else:
-                raise ValueError(f"width_type={width_type!r} must be {'sine','linear'}")
+                raise ValueError(
+                    f"width_type={width_type!r} must be {'sine','linear','parabolic'}"
+                )
 
             if section1.layer != section2.layer:
                 hidden = True
diff --git a/gdsfactory/types.py b/gdsfactory/types.py
index 9aca6f5bd4..c22a30c804 100644
--- a/gdsfactory/types.py
+++ b/gdsfactory/types.py
@@ -58,7 +58,7 @@
 ]
 Axis = Literal["x", "y"]
 NSEW = Literal["N", "S", "E", "W"]
-WidthTypes = Literal["sine", "linear"]
+WidthTypes = Literal["sine", "linear", "parabolic"]
 
 
 class Label(LabelPhidl):