siph_ringfilter :
An optical ring resonator filter.

The siph_ringfilter primitive represents an optical ring resonator filter, which splits the incident wave entering the port in into two waves leaving the ports thru and drop, where the transmission gain to the port thru and coupling gain to the port drop vary with the incident wave’s wavelength depending on the presence of resonance in a coupled closed-loop path. A typical silicon microring resonator filter is made of a waveguide that connects between the ports in and thru, a waveguide that connects between the ports add and drop, and a ring waveguide that forms a closed loop between these two waveguides and is coupled to them via a pair of directional couplers. The siph_ringfilter primitive models the optical ring resonator filter as a reciprocal element that can receive incident waves from any port and propagate waves with the symmetrical transfer characteristics.


                 in  --------------------- thru
                              ---
                             /   \
                            |     |
                             \   /
                              ---
               drop  --------------------- add

The parameter oplength_cpl specifies the optical path length of the directional couplers in meters, which is equal to the shortest delay between the ports in and thru or between the ports add and drop multiplied by the speed of light in free space (c0=2.99792458e8 meters/sec). The parameters gain_thru1 and gain_cpl1 specify the transmission and coupling gains of the directional coupler coupling between the in-to-thru waveguide and the ring, and the parameters gain_thru2 and gain_cpl2 specify the transmission and coupling gains of the directional coupler coupling between the add-to-drop waveguide and the ring, respectively. For both directional couplers, the wave being coupled to an opposite-side waveguide experiences a -pi/2 phase shift. Note that this primitive does not model the dependencies of the gains gain_thru and gain_cpl on the light’s wavelength or waveguide’s length.

The parameter oplength_ring specifies the optical path length of the ring, including the optical path lengths of the directional couplers. Therefore, the resonance occurs when the value of the oplength_ring is equal to an integer-multiple of the wavelength of the incident wave. The parameter gain_ring specifies the additional gain through a round trip of the ring waveguide excluding the transmission gains of the two directional couplers. It is assumed that the two directional couplers are located at the symmetrical positions on the ring.

The parameter dispersion specifies the total group delay dispersion (GDD) of the ring waveguide at the center wavelength specified by the parameter wavelength. The GDD is defined as the change in the group delay (tg) with respect to the angular frequency (w), which can be measured directly or derived from the dispersion coefficient (D) (in second/meter^2) as:


         dtg       (wavelength)^2               (wavelength)^2         (oplength)
  GDD = ----- = - ---------------- * D * l = - ---------------- * D * ------------.
         dw            2*PI                         2*PI                   ng

Note that such dispersion in the group delay can cause shifts in the periodic patterns of the ring resonator filter’s frequency response.

The parameter Zrel specifies the waveguides’ 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	input	xreal	thru port
add	input	xreal	add port
drop	input	xreal	drop port

Parameters

Name	Type	Default	Unit	Description
Zrel	real	1.0	None	relative characteristic impedance
oplength_cpl	real	38.75u	meters	optical path length of coupler
oplength_ring	real	155u	meters	optical path length of ring
gain_thru1	real	0.99	None	transmission gain of coupler #1
gain_cpl1	real	0.14	None	coupling gain of coupler #1
gain_thru2	real	0.99	None	transmission gain of coupler #2
gain_cpl2	real	0.14	None	coupling gain of coupler #2
gain_ring	real	1.0	None	additional gain of ring
dispersion	real	0.0	second^2	group delay dispersion
wavelength	real	1550n	meters	center wavelength

siph_ringfilter :An optical ring resonator filter.

siph_ringfilter :
An optical ring resonator filter.