在ipkiss中，通常以i3.Circuit来设计线路（见教程2），以i3.Pcell的框架也可以来设计线路：
以SplitterTree为例：

线路仿真结果：

所有代码如下：

from si_fab import all as pdk
import ipkiss3.all as i3

class SplitterTree(i3.PCell):
    class Layout(i3.LayoutView):
        def _generate_instances(self, insts):
            insts += i3.place_and_route(
                insts={
                    "splitter1": pdk.MMI1x2Optimized1550(),
                    "splitter2": pdk.MMI1x2Optimized1550(),
                    "splitter3": pdk.MMI1x2Optimized1550(),
                },
                specs=[
                    i3.Place('splitter1', (0, 0)),
                    i3.Place('splitter2', (100, -30)),
                    i3.Place('splitter3', (100, 30)),
                ]
            )
            insts = i3.place_and_route(
                insts=insts,
                specs=[
                    i3.ConnectBend("splitter1:out1", "splitter2:in1", bend_radius=10),
                    i3.ConnectBend("splitter1:out2", "splitter3:in1", bend_radius=10),
                ]
            )
            return insts

        def _generate_ports(self, ports):
            ports += i3.expose_ports(
                instances=self.instances,
                port_name_map={
                    "splitter1:in1": "in1",
                    "splitter2:out1": "out1",
                    "splitter2:out2": "out2",
                    "splitter3:out1": "out3",
                    "splitter3:out2": "out4",
                }
            )
            return ports

    class Netlist(i3.NetlistFromLayout):
        pass

    class CircuitModel(i3.CircuitModelView):
        def _generate_model(self):
            return i3.HierarchicalModel.from_netlistview(self.netlist_view)


if __name__ == '__main__':
    SplitterTree().Layout().visualize(annotate=True)
    import numpy as np
    from matplotlib import pyplot as plt

    wavelengths = np.linspace(1.5, 1.6, 2001)
    cm = SplitterTree().CircuitModel()
    S = cm.get_smatrix(wavelengths=wavelengths)
    plt.plot(wavelengths, i3.signal_power_dB(S["out1", "in1"]), label="in1 -> out1")
    plt.plot(wavelengths, i3.signal_power_dB(S["out2", "in1"]), label="in1 -> out2")
    plt.plot(wavelengths, i3.signal_power_dB(S["out3", "in1"]), label="in1 -> out3")
    plt.plot(wavelengths, i3.signal_power_dB(S["out4", "in1"]), label="in1 -> out4")
    plt.plot(wavelengths, i3.signal_power_dB(S["in1", "in1"]), label="in1 -> in1")
    plt.legend()
    plt.xlabel("Wavelengths [um]")
    plt.ylabel("Transmission")
    plt.show()

以pcell的方式定义线路需要分别定义：Layout、Netlist 以及CircuitModel

Layout给出线路的版图：

    class Layout(i3.LayoutView):
        def _generate_instances(self, insts):
            insts += i3.place_and_route(
                insts={
                    "splitter1": pdk.MMI1x2Optimized1550(),
                    "splitter2": pdk.MMI1x2Optimized1550(),
                    "splitter3": pdk.MMI1x2Optimized1550(),
                },
                specs=[
                    i3.Place('splitter1', (0, 0)),
                    i3.Place('splitter2', (100, -30)),
                    i3.Place('splitter3', (100, 30)),
                ]
            )
            insts = i3.place_and_route(
                insts=insts,
                specs=[
                    i3.ConnectBend("splitter1:out1", "splitter2:in1", bend_radius=10),
                    i3.ConnectBend("splitter1:out2", "splitter3:in1", bend_radius=10),
                ]
            )
            return insts

        def _generate_ports(self, ports):
            ports += i3.expose_ports(
                instances=self.instances,
                port_name_map={
                    "splitter1:in1": "in1",
                    "splitter2:out1": "out1",
                    "splitter2:out2": "out2",
                    "splitter3:out1": "out3",
                    "splitter3:out2": "out4",
                }
            )
            return ports

Netlist 给出线路中的逻辑连接关系：
layout中定义了ports，Netlist可以直接从Layout继承

class Netlist(i3.NetlistFromLayout):
        pass

CircuitModel 给出线路中的逻辑连接关系：
线路中的每个器件都有了CircuitModel，所有整个线路的CircuitModel可以通过HierarchicalModel来定义

class CircuitModel(i3.CircuitModelView):
        def _generate_model(self):
            return i3.HierarchicalModel.from_netlistview(self.netlist_view)

线路仿真：

	import numpy as np
    from matplotlib import pyplot as plt
    wavelengths = np.linspace(1.5, 1.6, 2001)
    cm = SplitterTree().CircuitModel()
    S = cm.get_smatrix(wavelengths=wavelengths)
    plt.plot(wavelengths, i3.signal_power_dB(S["out1", "in1"]), label="in1 -> out1")
    plt.plot(wavelengths, i3.signal_power_dB(S["out2", "in1"]), label="in1 -> out2")
    plt.plot(wavelengths, i3.signal_power_dB(S["out3", "in1"]), label="in1 -> out3")
    plt.plot(wavelengths, i3.signal_power_dB(S["out4", "in1"]), label="in1 -> out4")
    plt.plot(wavelengths, i3.signal_power_dB(S["in1", "in1"]), label="in1 -> in1")
    plt.legend()
    plt.xlabel("Wavelengths [um]")
    plt.ylabel("Transmission")
    plt.show()

线路仿真结果：