Electro-optic electric field sensor and method of fabrication
A novel method for producing a novel electro-optic electric-field sensor is disclosed. The resulting end product from this production method is a unique electro-optic electric-field sensor that includes thin film optical waveguides made from an electro-optic material on a low dielectric constant substrate. An optical circuit fabricated utilizing this production method may be a Mach-Zehnder interferometer or a micro-ring modulator. The low dielectric constant substrate allows the electric field to have high strength in the electro-optic thin film section, which in turn enables high sensitivity. In addition, for the Mach-Zehnder modulator sensor structure, phase matching is achieved between the RF or THz signal and the optical signal, resulting in an ultra-high-speed sensor for detection of Terahertz (THz) e-fields. An alternative design with a micro-ring electric-field sensor structure is also disclosed for high-spatial resolution electric-field sensing applications. The micro-ring configuration enables high sensitivity and spatial resolution.
1. A method for producing an electro-optic electric field sensor, the method compromising the steps of:
placing and bonding an electro-optic material layer on top of a low dielectric constant substrate;
forming a thin film of the electro-optic material layer on top of the low dielectric constant substrate;
depositing and patterning metallic electrode layers on the remaining electro-optic material and the low dielectric constant substrate to accommodate poling that alternates ferroelectric domains of the electro-optic electric field sensor whenever necessary for a Mach-Zehnder-type sensor structure;
poling to reverse a direction of spontaneous polarization of the remaining electro-optic material in selected regions, whenever reversing the direction of spontaneous polarization in the selected regions is desired;
etching the metallic electrode layers to achieve a resulting structure with no metallic parts;
utilizing lithography and etching to define a ridge waveguide structure;
encapsulating the ridge waveguide structure in a top cladding layer; and
aligning and attaching fiber optic cables to the ridge waveguide structure to constitute the electro-optic electric field sensor.
2. The method of claim 1 , further comprising a step of performing an ion implantation on top of the low dielectric constant substrate prior to the step of placing and bonding an electro-optic material layer on top of the low dielectric constant substrate.
3. The method of claim 1 , wherein the electro-optic material layer is made of lithium niobate or lithium tantalite, and the low dielectric constant substrate is made of glass, crystalline, or amorphous quartz.
4. The method of claim 1 , wherein the electro-optic electric field sensor is a Mach-Zehnder modulator with a first arm poled opposite to a second arm.
5. The method of claim 1 , wherein the electro-optic electric field sensor is a Mach-Zehnder modulator with a first arm poled opposite to a second arm, and wherein the first arm is longer than the second arm to control the bias point of the sensor by changing a laser wavelength.
6. The method of claim 1 , wherein the electro-optic electric field sensor is a Mach-Zehnder modulator with a first arm poled opposite to a second arm, and wherein the metallic electrode layers are deposited to function as an antenna that enhances an input signal reception sensitivity of the electro-optic electric field sensor.
7. The method of claim 1 , wherein the electro-optic electric field sensor is a micro-ring resonator coupled to a bus waveguide to form a high-sensitivity compact sensor.
8. The method of claim 1 , wherein the electro-optic electric field sensor includes two coupled micro-ring resonators in which one ring is coupled to a bus waveguide to form a high-sensitivity high frequency sensor.
9. The method of claim 1 , wherein the electro-optic electric field sensor is part of an electro-optic system comprising a laser, a detector, and a feedback loop to control a wavelength of a laser to achieve correct bias point for the sensor at a maximum sensitivity.
10. The method of claim 1 , wherein the electro-optic electric field sensor is part of a time-domain THz spectroscopy system in which a THz signal is generated by a femtosecond laser and detected by the electro-optic electric field sensor.
11. The method of claim 1 , wherein the electro-optic electric field sensor is part of a frequency domain THZ spectroscopy system in which a THZ signal is generated with two CW laser sources and detected by the electro-optic electric field sensor.