siph_ybranch :
An optical Y-shaped branch.

The siph_ybranch primitive represents an optical Y-shaped branch, which can serve either as a power splitter or as a power combiner. In other words, the primitive can split the incident wave entering the port in into two waves leaving the ports thru_1 and thru_2, or combine the incident waves entering the ports thru_1 and thru_2 into a wave leaving the port in. The waves experience the delays as they propagate through the Y-branch, which is equal to the optical path length between the port in and port thru_1 or thru_2 (specified by the parameter oplength) divided by the speed of light in free space (c0=2.99792458e8 meters/sec).

                 +-------- thru_1
                /
    in --------+
                \
                 +-------- thru_2

The parameter gain_thru specifies the transmission gain between the port in and port thru_1 or thru_2 (default: 0.7071). The siph_ybranch primitive is a reciprocal element that can receive incident waves from any port and propagate waves with the symmetrical transfer characteristics.

The parameter oplength specifies the optical path length between the port in and port thru_1 or thru_2 in meters, which is equal to the waveguide’s propagation delay multiplied by the speed of light in free space (c0). For instance, a quarter-wavelength Y-branch for a 1550nm laser would have an optical path length of 1550nm/4=387.5nm. Note that this primitive does not model the dependency of the gain gain_thru on the light’s wavelength or waveguide’s length.

The parameter Zrel specifies the Y-branch’s characteristic impedance relative to a reference impedance (Z0) of your choice. Note that the use of this relative impedance allows one to determine the amount of reflections at impedance discontinuities without having to know the absolute values of the characteristic impedances. While the choice of the reference impedance (Z0) can be arbitrary, it must be consistent across all the silicon-photonic components used in a system. In other words, all the equivalent circuit elements describing the impedance relationships at the optical ports must use the impedance values relative to the same Z0.

Input/Output Terminals

Name	I/O	Type	Description
in	input	xreal	input port
thru_1	input	xreal	thru port #1
thru_2	input	xreal	thru port #2

Parameters

Name	Type	Default	Unit	Description
Zrel	real	1.0	None	relative characteristic impedance
oplength	real	15.5e-6	meters	optical path length
gain_thru	real	0.7071	None	transmission gain (in-to-thru)