Electro-optic modulator having identical forward and backward electro-optic response

Patent metadata

Field	Value
Publication number	US-9810964-B2
Application number	US-201314394206-A
Country	US
Kind code	B2
Filing date	Mar 6, 2013
Priority date	Apr 16, 2012
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

An electro-optic modulator includes a waveguide of a nonlinear optical material and an electrode line for generating an electrical field in a modulating region of the waveguide when a voltage is applied to the electrode line, thereby modulating light passing through the waveguide. Therein, the forward electro-optic response of the modulating region is the same as the backward electro-optic response; and the electro-optic response has a band-pass or a low-pass characteristic. A distance measuring device includes a light source emitting light, and such an electro-optic modulator arranged such that the emitted light passes through the electro-optic modulator in a first direction before being emitted from the distance measuring device, and after being reflected from a target passes through the electro-optic modulator in a second direction which is opposite to the first direction.

First claim

The invention claimed is:

1. An electro-optic modulator, comprising:
a straight waveguide of a nonlinear optical material; and,
an electrode line arranged to generate an electrical field in a modulating region of the waveguide when a voltage is applied to the electrode line so as to modulate a phase of light passing through the waveguide,
wherein the electrode line comprises a first branch and a second branch, wherein each branch:
extends from a beginning to an end of a first line section parallel to the waveguide in a first direction for a first distance,
extends from the beginning to an end of a second line section parallel to the waveguide for a second distance in a second direction, said second direction being opposite to said first direction and said second distance being equal to said first distance,
wherein the first and second line sections of the branch affect a modulation subregion of the waveguide; and wherein
the electro-optic modulator comprises a signal generator configured to apply a voltage to a terminal of the electrode line, and thereby generates a microwave signal in the branches of the electrode line, wherein a frequency of the microwave signal is at or near a center frequency, the center frequency corresponding, in each branch, to a center wavelength of the microwave signal, wherein in each branch the center wavelength of the microwave signal or an integer multiple of the center wavelength, is equal to twice the first distance,
wherein the waveguide and the electrode line are configured to provide a forward electro-optic response in the modulating region and a backward electro-optic response in the modulating region, said forward and backward electro-optic responses being equal to one another, and
the waveguide and the electrode line are configured such that the forward and backward electro-optic responses have a band-pass or a low-pass characteristic.

2. The electro-optic modulator of claim 1 , wherein the waveguide and the electrode line are constructed such that a center of gravity of the modulation, which is a point along the waveguide at which the total modulation of light in one section is equal to the total modulation of light in a second section, is independent of modulation frequency.

3. The electro-optic modulator of claim 1 , wherein:
the modulating region comprises a first subregion and a second subregion and,
the electrode line is adapted to provide a first effective modulation on light passing in one direction through the first subregion and a second effective modulation on light passing in the opposite direction through the second subregion, wherein the first effective modulation is equal to the second effective modulation.

4. The electro-optic modulator of claim 1 , wherein
a microwave signal propagation time from the beginning of the first line section to the end of the second line section of the first branch is equal to a microwave signal propagation time from the beginning of the first line section to the end of the second line section of the second branch.

5. The electro-optic modulator of claim 4 , wherein
each branch, from the end of the second line section:
runs in a third line section parallel to the waveguide for a third distance in the first direction,
and wherein the microwave signal propagation time from the beginning of the first line section to the end of the third line section of the first branch is equal to the microwave signal propagation time from the beginning of the first line section to the end of the third line section of the second first branch.

6. The electro-optic modulator of claim 1 , said electrode line comprises:
a first branch, a second branch, and a midpoint between the first and second branches, wherein
the electrode line is adapted, when connected to an electric microwave signal source, to generate an electrical field distribution in the waveguide that is symmetrical with respect to the midpoint.

7. The electro-optic modulator of claim 4 , wherein the electrode line comprises a midpoint between the first branch and the second branch, and wherein the electrode line is adapted, when connected to an electric microwave signal source, to generate an electrical field distribution in the waveguide that is symmetrical with respect to the midpoint.

8. The electro-optic modulator of claim 6 , wherein the shape of the electrode line comprising the first and the second branch is mirror-symmetric with respect to a plane that passes through the midpoint and normal to the waveguide.

9. The electro-optic modulator of claim 6 , wherein the shape of the electrode line comprising the first and the second branch has a rotational symmetry around an axis that passes through the midpoint and normal to the plane in which the electrode line lies.

10. The electro-optic modulator of claim 1 , wherein a bottom face of a substrate, opposed to a substrate surface at which the waveguide and electrode line are arranged, is roughened to a degree of at least Ra=0.3 micrometers or inclined relative to the substrate surface at which the waveguide and electrode line are arranged.

11. An electro-optic distance measuring device comprising the electro-optic modulator of claim 1 .

12. The distance measuring device of claim 11 , further comprising a light source emitting light, wherein the electro-optic modulator is arranged in the distance measuring device such that light emitted by the light source passes through the modulating region of the waveguide in a first direction before being emitted from the distance measuring device, and such emitted light after being reflected from a target outside the distance measuring device passes through the modulating region of the waveguide in a second direction, which is opposite to the first direction.

13. An electro-optic modulator, comprising:
a straight waveguide of a nonlinear optical material; and
an electrode line arranged to generate an electrical field in a modulating region of the waveguide when a voltage is applied to the electrode line so as to modulate a phase of light passing through the waveguide,
wherein: the electrode line comprises a first branch and a second branch, each branch:
extending from a beginning to an end of a first line section parallel to the waveguide in a first direction for a first distance, and
extending from the beginning to an end of a second line section parallel to the waveguide for a second distance in a second direction, said second direction being opposite to said first direction and said second distance being equal to said first distance,

wherein the first and second line sections of the branch affect a modulation subregion of the waveguide; and wherein
a microwave signal propagation time from the beginning of the first line section to the end of the second line section of the first branch is equal to a microwave signal propagation time from the beginning of the first line section to the end of the second line section of the second branch,
the electrode line comprises a midpoint between the first branch and the second branch, and
the electrode line is adapted, when connected to an electric microwave signal source, to generate an electrical field distribution in the waveguide that is symmetrical with respect to the midpoint,
wherein the waveguide and the electrode line are configured to provide a forward electro-optic response in the modulating region and a backward electro-optic response in the modulating region, said forward and backward electro-optic responses being equal to one another, and
the waveguide and the electrode line are configured such that the forward and backward electro-optic responses have a band-

Assignees

• Leica Geosystems Ag

Inventors

• Porte Henri
• Mottet Alexandre
• Luthi Thomas
• Bockem Burkhard

Classifications

• G02F1/0356

  controlled by a high-frequency electromagnetic wave component in an electric waveguide structure · CPC title

• G01B11/14

  for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00) · CPC title

• G02F1/365

  in an optical waveguide structure (G02F1/377, {G02F1/395} take precedence) · CPC title

• G01S7/4812

  transmitted and received beams following a coaxial path · CPC title

• G01S17/36

  with phase comparison between the received signal and the contemporaneously transmitted signal · CPC title