Optical waveguide

Abstract

A first branched optical waveguide and a second branched optical waveguide, to constitute a Mach-Zehnder type optical waveguide, are formed at the surface of a substrate. A first ground electrode, a signal electrode and a second ground electrode are provided on a buffer layer formed on the substrate. The second ground electrode is partially cut away and divided, to form a ditch therein, so that the modulating electrode composed of the signal electrode, the first and the second ground electrodes are substantially symmetrized on the center line between the first and the second optical waveguides. Then, the ratio (d 2 /d 1 ) of the distance d 2 between the signal electrode and the second branched optical waveguide to the distance d 1 between the signal electrode and the first electrode is set within 3.5-7.5.

1 . An optical waveguide element comprising a substrate made of a material with electro-optical effect, a Mach-Zehnder type optical waveguide formed at the main surface of the substrate, and a modulating electrode to control an optical wave through the Mach-Zehnder type optical waveguide, 
 the Mach-Zehnder type optical waveguide including a first branched optical waveguide and a second branched optical waveguide,    the modulating electrode including a signal electrode to modulate an optical wave through the first branched optical waveguide of the Mach-Zehnder type optical waveguide and a ground electrode serving as an opposed electrode for the signal electrode,    the ground electrode being composed of a first ground electrode and a second ground electrode which are opposed each other with sandwiching the signal electrode,    the first branched optical waveguide being disposed under the signal electrode or in between the first ground electrode and the signal electrode,    the second branched optical electrode being disposed under the second ground electrode,    the second ground electrode being partially cut away along the long direction and divided, to substantially symmetrize the modulating electrode composed of the signal electrode, the first and the second ground electrodes on the center line between the first and the second branced optical waveguides,    the ratio (d 2 /d 1 ) of the distance d 2  between the signal electrode and the second branched optical waveguide to the distance d 1  between the signal electrode and the first branched optical waveguide being set within 3.5-7.5.    
     
     
         2 . An optical waveguide element comprising a substrate made of a material with electro-optical effect, a Mach-Zehnder type optical waveguide formed at the main surface of the substrate, and a modulating electrode to control an optical wave through the Mach-Zehnder type optical waveguide, 
 the Mach-Zehnder type optical waveguide including a first branched optical waveguide and a second branched optical waveguide,    the modulating electrode including a signal electrode to modulate an optical wave through the first branched optical waveguide of the Mach-Zehnder type optical waveguide and a ground electrode serving as an opposed electrode for the signal electrode,    the ground electrode being composed of a first ground electrode and a second ground electrode which are opposed each other with sandwiching the signal electrode,    the first branched optical waveguide being disposed under the signal electrode or in between the first ground electrode and the signal electrode,    the second branched optical electrode being disposed under the second ground electrode,    the second ground electrode being partially cut away along the long direction and divided, to substantially symmetrize the modulating electrode composed of the signal electrode, the first and the second ground electrodes on the center line between the first and the second branched optical waveguides,    the ratio (Ws/Wg) of the width Ws of the signal electrode to the width Wg of the divided part of the second ground electrode located near the signal electrode being set within 0.5-4.    
     
     
         3 . An optical waveguide element as defined in  claim 2 , wherein the ratio (d 2 /d 1 ) of the distance d 2  between the signal electrode and the second branched optical waveguide to the distance d 1  between the signal electrode and the first branched optical waveguide being set within 3.5-7.5.  
     
     
         4 . An optical waveguide element comprising a substrate made of a material with electro-optical effect, a Mach-Zehnder type optical waveguide formed at the main surface of the substrate, and a modulating electrode to control an optical wave through the Mach-Zehnder type optical waveguide, 
 the Mach-Zehnder type optical waveguide including a first branched optical waveguide and a second branched optical waveguide,    the modulating electrode including a signal electrode to modulate an optical wave through the first branched optical waveguide of the Mach-Zehnder type optical waveguide and a ground electrode serving as an opposed electrode for the signal electrode,    the ground electrode being composed of a first ground electrode and a second ground electrode which are opposed each other with sandwiching the signal electrode,    the first branched optical waveguide being disposed under the signal electrode or in between the first ground electrode and the signal electrode,    the second branched optical electrode being disposed under the second ground electrode,    the second ground electrode being partially cut away along the long direction and divided into three parts, the divided first part being disposed on the almost center line between the first and the second branched optical waveguides, the divided second part and the divided third part being almost the same as the signal electrode and the first ground electrode in figuration and dimension, respectively, to substantially symmetrize the modulating electrode composed of the signal electrode, the first and the second ground electrodes on the center line between the first and the second branched optical waveguides,    the width W 1  of the divided first part being set 0.5-20 times as large as the width Ws of the signal electrode.    
     
     
         5 . An optical waveguide element as defined in  claim 4 , wherein the ratio (d 2 /d 1 ) of the distance d 2  between the signal electrode and the second branched optical waveguide to the distance d 1  between the signal electrode and the first branched optical waveguide being set within 10-27.  
     
     
         6 . An optical waveguide element as defined in any one of claims  1 - 5 , wherein a thin film is formed of a conductive material at a ditch formed at the divided second ground electrode.  
     
     
         7 . An optical waveguide element comprising a substrate made of a material with electro-optical effect, a Mach-Zehnder type optical waveguide formed at the main surface of the substrate, and a modulating electrode to control an optical wave through the Mach-Zehnder type optical waveguide, 
 the Mach-Zehnder type optical waveguide including a first branched optical waveguide and a second branched optical waveguide,    the modulating electrode including a signal electrode to modulate an optical wave through the first branched optical waveguide of the Mach-Zehnder type optical waveguide and a ground electrode serving as an opposed electrode for the signal electrode,    the ground electrode being composed of a first ground electrode and a second ground electrode which are opposed each other with sandwiching the signal electrode,    the first branched optical waveguide being disposed under the signal electrode or in between the first ground electrode and the signal electrode,    the second branched optical electrode being disposed under the second ground electrode,    the second ground electrode being partially cut away along the long direction and divided, to balance and substantially symmetrize the stresses for the first and the second branched optical waveguides from the modulating electrode composed of the signal electrode, the first and the second ground electrodes on the center line between the first and the second branched optical waveguides.    
     
     
         8 . An optical waveguide element as defined in any one of claims  1 - 7 , wherein the chirp characteristic is controlled.