Semiconductor modulator with a .pi. shift
First Claim
1. A semiconductor Mach-Zehnder modulator having first and second Y-junction waveguide couplers, each coupler having a single waveguide optically coupled with first and second branch waveguides of the coupler, wherein the Y-junction waveguide couplers are optically coupled in Mach-Zehnder configuration to define first and second interferometric arms optically in parallel that extend from where light launched into the single waveguide of the first Y-junction waveguide coupler is divided into two components to where these two components interfere in the second Y-junction waveguide coupler, wherein the first and second interferometric arms are provided with electrode means by which an electric field is applicable to modulate their differential effective optical path length which, in the absence of any applied electric field, has a non-zero value providing, for a wavelength of light launched into the single waveguide of the first Y-junction waveguide coupler and transmitted to where said two components interfere in the second Y-junction waveguide coupler, a phase difference between said two components where they so interfere of π
- , or an integral odd multiple thereof.
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Abstract
A MQW semiconductor Mach Zehnder phase modulator is formed by two Y-junctions (12, 32), each having a single waveguide (14) optically coupled with two branch waveguides (18, 20). The branch waveguides of the two Y-juntions are optically coupled in Mach-Zehnder configuration that, under zero bias conditions, has one interferometric arm longer than the other to provide a π phase shift. The additional length is preferably accommodated in the branches of the Y-junctions. The phase shift, in combination with voltage dependent absorption properties and non-linear phase variations of the MQW guided regions in the Mach-Zehnder modulator results in a negative chirp and high extinction ratio for an equal, push-pull device configuration.
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Citations
12 Claims
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1. A semiconductor Mach-Zehnder modulator having first and second Y-junction waveguide couplers, each coupler having a single waveguide optically coupled with first and second branch waveguides of the coupler, wherein the Y-junction waveguide couplers are optically coupled in Mach-Zehnder configuration to define first and second interferometric arms optically in parallel that extend from where light launched into the single waveguide of the first Y-junction waveguide coupler is divided into two components to where these two components interfere in the second Y-junction waveguide coupler, wherein the first and second interferometric arms are provided with electrode means by which an electric field is applicable to modulate their differential effective optical path length which, in the absence of any applied electric field, has a non-zero value providing, for a wavelength of light launched into the single waveguide of the first Y-junction waveguide coupler and transmitted to where said two components interfere in the second Y-junction waveguide coupler, a phase difference between said two components where they so interfere of π
- , or an integral odd multiple thereof.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of modulating an optical signal of known free space wavelength, which method comprises transmitting the signal through a semiconductor Mach-Zehnder modulator having first and second Y-junction waveguide couplers, each coupler having a single waveguide optically coupled with first and second branch waveguides of the coupler, which Y-junction waveguide couplers are optically coupled in Mach-Zehnder configuration to define first and second interferometric arms optically in parallel that extend from where light launched into the single waveguide of the first Y-junction waveguide coupler is divided into two components to where these two components interfere in the second Y-junction waVeguide coupler, which first and second interferometric arms are provided with electrode means by which an electric field is applicable to modulate their differential effective optical path length which, in the absence of any applied electric field, has a non-zero value providing, for light of said free space wavelength launched into the single waveguide of the first Y-junction waveguide coupler, a phase difference between said two components where they interfere of π
- , or an integral odd multiple thereof, and which method additionally comprises applying modulating voltages to said electrode means.
- View Dependent Claims (10, 11, 12)
Specification