Attributes · laylight tour

Attributes

Attributes are values that a cell computes from its parameters and makes available to others:

cell Mmi {
    param {
        wg_len  size = 10um
        mmi_len size = 30um
    }
    attribute {
        total_length wg_len * 2 + mmi_len
        description  "a simplified MMI"
    }
    ...
}

An attribute is read-only. Inside the cell it is used by its name, like a parameter. From outside it is read through a named instance, after a dot — and so are the instance's parameters:

place Mmi at (0, 0) as a
place Mmi at (a.total_length, 0) as b    # b starts where a ends

Attributes can use parameters, global constants and other attributes. They are also written to the GDSII output, together with the parameter values, so that tools can read them back.

Exercise

Give Mmi an attribute total_length, the length of both waveguides and the body together. Then use it in Chain to put the three splitters end to end, the first one at the origin.

import "tech.lyl" # A simplified MMI: input waveguide, multimode body, output waveguide. cell Mmi { param { wg_len size = 10um mmi_len size = 30um } layer si { shape rect with wg_len, 500nm as input shape rect with mmi_len, 4um as body clone input as output place input.left_center at self.origin place body.left_center at input.right_center place output.left_center at body.right_center } } cell Chain { place { Mmi at (0, 0) as a Mmi with mmi_len = 20um at (60um, 0) as b Mmi with mmi_len = 10um at (110um, 0) as c } }