步骤5： MMI级联

本案例利用步骤2(步骤2： 利用基础模块搭建基本链路)中的多模干涉仪结构实现多层级联结构，并实现版图绘制。

导入步骤2(步骤2： 利用基础模块搭建基本链路)创建的多模干涉仪结构:

from step.step2.mmi1x2 import MMI1x2

定义级联MMI类，方便后面直接调用:

@dataclass(eq=False)
class MMITree(fp.PCell):
    def build(self):
        insts, elems, ports = super().build()
        TECH = get_technology()

        x_spacing = 50
        end_y_spacing = 50
        order = 2
        mmi = MMI1x2()
        num_per_col = []
        v_spacing = []

        for i in range(order):
            num_per_col.append(2**i)
            v_spacing.append(end_y_spacing*(2**(order - i - 1)))

        for i in range(order):
            for j in range(num_per_col[i]):
                x = i * x_spacing
                y = (-(num_per_col[i] - 1) * v_spacing[i]/2) + j * v_spacing[i]
                mmi = mmi["op_0"].repositioned(at=(x,y)).owner
                insts += mmi, f"{i},{j}"

        mmi_tree = cast(Mapping[str, fp.ICellRef], insts)
        for i in range(order):
            for j in range(num_per_col[i]):
                if i < order-1:
                    link1 = fp.LinkBetween(start=mmi_tree[f"{i},{j}"]["op_1"],
                                           end=mmi_tree[f"{i+1},{2*j}"]["op_0"],
                                           bend_factory=TECH.WG.FWG.C.WIRE.BEND_CIRCULAR)
                    insts += link1
                    link2 = fp.LinkBetween(start=mmi_tree[f"{i},{j}"]["op_2"],
                                           end=mmi_tree[f"{i+1},{2*j+1}"]["op_0"],
                                           bend_factory=TECH.WG.FWG.C.WIRE.BEND_CIRCULAR)
                    insts += link2

        ports += mmi_tree["0,0"]["op_0"].with_name("op_0")
        for i in range(num_per_col[-1]):
            ports += mmi_tree[f"{order - 1},{i}"]["op_1"].with_name(f"op_{2*i+1}")
            ports += mmi_tree[f"{order - 1},{i}"]["op_2"].with_name(f"op_{2*i+2}")

        # fmt: on
        return insts, elems, ports

需要说明的是:

order = 2

这个参数表示的是级联的层级，本案例中我们取的是4。

调用类，并通过布尔运算实现版图设计:

library += MMITree()
device = MMITree()
cor = device.polygon_set(layer=TECH.LAYER.FWG_COR)
cld = device.polygon_set(layer=TECH.LAYER.FWG_CLD)
tre = fp.el.PolygonSet.boolean_sub(cld, cor, layer=TECH.LAYER.FWG_TRE)
library += fp.Device(content=[tre.translated(300, 0)], ports=[])
fp.export_gds(library, file=gds_file)
fp.plot(library)

MMI级联结构图例展示

../_images/MMI_tree.png

其中左侧为包含所有图层信息的版图，局部放大如下

../_images/MMI_initial.png

右侧为经过布尔运算的得到的，局部图为

../_images/MMI_boolean.png