Power splitter/combiner with parameter tolerance and design process therefor

Abstract

A splitter/combiner that is highly tolerant to parameter deviations as a result of fabrication errors, for example, which might otherwise create undesirable frequency dependency and polarization dependency. It is specifically applicable to integration into the transmission and/or reflection light paths of systems. In this power splitter/combiner system, each splitter/combiner is comprised of two or more directional couplers serially connected to two or more phase shifts in an alternating order (i.e., directional coupler, phase shift, directional coupler, phase shift, directional coupler). The invention addresses the problem of parameter deviations in splitter/combiners by connecting multiple directional couplers and multiple phase shifts and selecting specific coupling and phase values for the directional couplers and phase shifts to minimize the impact of parameter changes on the output signal. The invention also addresses the problem of differential deviations in parameters by providing tunable phase shifts employing controlled effects, such as electro-optic or thermo-optic refractive index changes.

What is claimed is:  
     
         1 . A splitter/combiner system comprising: 
 a serial connection of at least two couplers and at least two phase shifts in which coupling coefficients of the couplers and propagation constants of the phase shifts are selected to minimize changes in an output signal in response to changes in the coupling coefficients and the propagation constants.    
     
     
         2 . A splitter/combiner system of  claim 1 , wherein the coupling coefficients of the couplers and the propagation constants of the phase shifts are selected to minimize changes in a spectral flatness of the output signal in response to changes in the coupling coefficients and the propagation constants.  
     
     
         3 . A splitter/combiner system of  claim 1 , wherein the coupling coefficients of the couplers and the propagation constants of the phase shifts are selected to minimize changes in a ripple of the output signal in response to changes in the coupling coefficients and the propagation constants.  
     
     
         4 . A splitter/combiner system of  claim 1 , wherein the serial connection of at least two couplers and at least two phase shifts is fabricated in a planar waveguide system.  
     
     
         5 . A splitter/combiner system of  claim 4 , wherein a contrast between an index of refraction of waveguides of the planar waveguide system relative to a cladding of the waveguides is greater than 1%.  
     
     
         6 . A splitter/combiner system of  claim 1 , wherein the propagation constant of the phase shift is tunable.  
     
     
         7 . A splitter/combiner system of  claim 1 , wherein the propagation constant of the phase shift is thermo-optically tunable.  
     
     
         8 . A splitter/combiner system of  claim 1 , wherein a modification to the propagation constants of the phase shifts is determined in a post fabrication calibration step, which is thereafter used to control waveguide heaters.  
     
     
         9 . A splitter/combiner system of  claim 1 , wherein the output signal is split between two output waveguides.  
     
     
         10 . A splitter/combiner system of  claim 9  further comprising three phase shifts that are serially connected with the two couplers in an alternating fashion.  
     
     
         11 . A splitter/combiner system of  claim 1  further comprising an external system that is reflective in a frequency range of interest.  
     
     
         12 . A splitter/combiner system of  claim 11  including two phase shifts that are serially connected with the two couplers in an alternating fashion.  
     
     
         13 . A splitter/combiner system of  claim 11 , where in an input signal is received at a first waveguide of a first one of the combiners and the output signal is provided at a second waveguide of the first combiner.  
     
     
         14 . A splitter/combiner system of  claim 1  further comprising a second serial connection of at least two couplers and at least two phase shifts, which is coupled to the external system.  
     
     
         15 . A splitter/combiner system of  claim 14 , wherein the output signal is provided at the second serial connection.  
     
     
         16 . A splitter/combiner system of  claim 15 , wherein the output signal is provided substantially on one waveguide from the second serial connection.  
     
     
         17 . A splitter/combiner system of  claim 1  further comprising an external system that is reflective and transmissive in a frequency range of interest.  
     
     
         18 . A splitter/combiner system of  claim 17 , wherein the input signal is received at a first waveguide of a first one of the combiners and the output signal is provided at a second waveguide of the first combiner.  
     
     
         19 . A splitter/combiner system of  claim 17 , wherein the external system comprises a resonator system.  
     
     
         20 . A splitter/combiner system of  claim 17  further comprising a second serial connection of at least two couplers and at least two phase shifts, which is connected to the external system.  
     
     
         21 . A splitter/combiner system of  claim 17 , wherein the external system comprises two resonator sub-elements with the input signal being split between the sub-elements by the serial connection.  
     
     
         22 . A design process for a splitter/combiner system comprising: 
 providing a serial connection of at least two couplers and at least two phase shifts to couple an input waveguide to an external system; and    proscribing coupling coefficients of the couplers and propagation constants of the phase shifts to minimize changes in an output signal in response to changes in the coupling coefficients and the propagation constants.    
     
     
         23 . A design process as claimed in  claim 22 , wherein the step of proscribing the coupling coefficients of the couplers and the propagation constants of the phase shifts comprises minimizing changes in a spectral flatness of the output signal in response to changes in the coupling coefficients and the propagation constants.  
     
     
         24 . A design process as claimed in  claim 22 , wherein the step of proscribing the coupling coefficients of the couplers and the propagation constants of the phase shifts comprises minimizing changes in a ripple of the output signal in response to changes in the coupling coefficients and the propagation constants.  
     
     
         25 . A design process as claimed in  claim 22  further comprising designing the serial connection of at least two couplers and at least two phase shifts for a planar waveguide system.  
     
     
         26 . A splitter/combiner system of  claim 22 , wherein a contrast between indices of refraction for waveguides of the planar waveguide system relative to a cladding of the waveguides is greater than 1%.  
     
     
         27 . A design process as claimed in  claim 22  further comprising configuring the serial connection to split the output signal between two output waveguides.  
     
     
         28 . A design process as claimed in  claim 22  further comprising providing three phase shifts that are serially connected with the two couplers in an alternating fashion.  
     
     
         29 . A design process as claimed in  claim 22 , wherein the external system is reflective in a frequency range of interest.  
     
     
         30 . A design process as claimed in  claim 29  further comprising providing an input signal at a first waveguide of a first one of the combiners and the output signal is provided at a second waveguide of the first combiner.  
     
     
         31 . A design process as claimed in  claim 22  further comprising providing a second serial connection of at least two couplers and at least two phase shifts, which is connected to the external system.  
     
     
         32 . A design process as claimed in  claim 31  further comprising providing the output signal from the second serial connection.  
     
     
         33 . A design process as claimed in  claim 32  further comprising providing the output signal substantially on one waveguide from the second serial connection.  
     
     
         34 . A design process as claimed in  claim 22 , wherein the external system is reflective and transmissive in a frequency range of interest.  
     
     
         35 . A design process as claimed in  claim 34  further comprising receiving the input signal at a first waveguide of a first one of the combiners and the output signal is provided at a second waveguide of the first combiner.  
     
     
         36 . A design process as claimed in  claim 34 , wherein the external system comprises a resonator system.  
     
     
         37 . A design process as claimed in  claim 34  further comprising providing a second serial connection of at least two couplers and at least two phase shifts, which is connected to the external system.  
     
     
         38 . A design process as claimed in  claim 34 , wherein the external system comprises two resonator sub-elements with the input signal being split between the sub-elements by the serial connection.