Directional coupler and grating coupler added

README.md

@@ -1,4 +1,4 @@
-# <span style="color: #6decff;">mxPIC Quick-Reference Style Guide</span>
+# <span style="color: #5573fa;">mxPIC Quick-Reference Style Guide</span>
 
 Welcome to the collaboration of the repository of **mxPIC** program. This repository is aimed for a self-designed PDK that based on ***nazca***, ***gdstk*** and other libraries for the functional build up of photonic integrated circuits (PIC).
 
@@ -11,7 +11,35 @@ This is the fast-track guide to contributing to **mxPIC**. Adherence to these ru
 - pandas 0.12.0
 - 
 
-## <span style="color: #ff57c7;">1. Annotation & Documentation</span>
+## <span style="color: #ff57c7;">1. File & architecture</span>
+The repository have an archtecture like this.
+
+```
+mxpic_forge/
+├── primitives/
+│   ├── edge_couplers/
+│   │   └── EC_dual_layer_px3.py
+│   ├── multimode_interferomters/
+│   ├── directional_couplers/
+│   ├── grating_couplers/
+│   └── microring_modulators/
+├── composite/
+│   └── mach_zender_modulators/
+├── electronics/
+│   ├── resistors/
+│   ├── inductors/
+│   ├── vias/
+│   └── pads/
+├── others/
+├── structures/
+├── routing/
+├── foundries/
+└── docs/
+    └── source/
+        └── conf.py
+```
+
+## <span style="color: #ff57c7;">2. Annotation & Documentation</span>
 We strictly use **Type Hints** (PEP 484) and **NumPy-Style Docstrings**.
 
 * <span style="color: #d2a8ff;">**Rule:**</span> Every function MUST have its parameter types and return type explicitly declared.
@@ -42,7 +70,7 @@ We strictly use **Type Hints** (PEP 484) and **NumPy-Style Docstrings**.
 ```
 
 ---
-## <span style="color: #ff57c7;">2. Class mangement of devices</span>
+## <span style="color: #ff57c7;">3. Class mangement of devices</span>
 The devices are divided into four major types, which is <span style="color: #d2a8ff;">**primitives, composite, electronics, and others**</span>. All photonic and electronic devices are built within the for types.   
 In the definitial of classes, compulsary keys are required, including **name** , **show_pins** , all defaults are None.  
 All classes are cored at the **cell** class of **nazca**, which is generated through an internal method named "generate_gds" 
@@ -62,7 +90,7 @@ class GratingCoupler():
         return C 
 ```
 ---
-## <span style="color: #ff57c7;">3. Port information formatting</span>
+## <span style="color: #ff57c7;">4. Port information formatting</span>
 The basic routing algorthium is based the information between nodes, which is the **pin** attribute inside each file. The formatting of **pin** name will be important.  
 
 **<span style="color: #bf0000;">Note</span>**: The pin name should only be related to different functionalities instead of material, layer or shaped. Say, the pin name of a *silicon directional coupler* is the same as a *silicon nitride directional coupler*.
@@ -77,3 +105,11 @@ The basic routing algorthium is based the information between nodes, which is th
 | Transistors (MOS)| ele_   | gt/su/dr    | 1~x   | ele_gt1   | MOSFET
 
 
+## <span style="color: #ff57c7;">5. Layer and cross-sections</span>
+Inside **nazca**, an important feature is the concept of **cross-sections (xs)**. Typically, **xs** is a conbination of different layers which is required by the foundry DRC. Below is a example in Silterra tapeout.
+``` python
+nazca.add_xsection("strip")
+nazca.add_layer_to_xsection("WG_HM",growx=2,growy=2)
+nazca.add_layer_to_xsection("WG_STRIP",growx=2,growy=2)
+```
+