RU2794061C1 - Thin-film converter for electro-optical crystal - Google Patents

Abstract

FIELD: measuring technology; electric field transducers.

SUBSTANCE: converter is based on a typical waveguide structure of a Mach-Zehnder interferometer based on ridge waveguides of thin films of an electro-optical crystal on a silicon and silicon dioxide substrate and has a remote antenna and electrodes for supplying an external electric field to the optical circuit. An optical radiation source and a photodetector are monolithically integrated into the device substrate.

EFFECT: integration of optoelectronic components, coupled with the use of thin-film ridge waveguides, makes it possible to miniaturize the device and, as a result, expand the frequency range in which the device is capable of performing measurements.

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Description

The invention relates to measuring technology, namely to electric field transducers.

An electro-optical transducer can be used to measure the electric field strength. Thus, the converter can be industrially applicable and have the following applications:

- control and measurement tests for electromagnetic compatibility;

- control and measurement of radio networks;

- measurement of electric fields for metrological purposes.

Integrated optical circuit - a photonic device made of an optically transparent crystal and performing the functions of processing optical signals. Any optical integrated circuit contains at least one waveguide. A waveguide is an inhomogeneous structure consisting of a core, a material with a high refractive index, and a cladding, a material with a lower refractive index. The shell is located around the core of the waveguide, the difference between the refractive indices of the shell and the core of the waveguide leads to the effect of total internal reflection. Thus, the light propagating along the waveguide, reflected from the interface between the cladding and the core, does not go beyond the waveguide.

The Mach-Zehnder interferometer (MZI) is a typical waveguide structure widely used in integrated optics. The IMC consists of two rectilinear waveguides (input and output); two Y-couplings - waveguides diverging into 2 waveguides; arms - two parallel rectilinear waveguides connecting two Y-couplings to each other. The first Y-coupling, which plays the role of a splitter, is connected to the output of the input waveguide, shoulders are connected to the outputs of the first coupling - two rectilinear parallel waveguides connecting the output of the first coupling with the inputs of the second coupling, which plays the role of a connector, the output of the second coupling is connected to the output waveguide.

The use of optical integrated circuits based on thin films of electro-optical crystals in the development of electro-optical sensors and converters will make it possible to reduce the size of devices and, accordingly, increase the frequency range in which measurements can be performed.

Known electro-optical sensor of the electric field, based on the Fabry-Perot interferometer (US 5041779A, Int. Cl. G01R 31/00, publ. 20.08.1991). The disadvantage of this sensor is the use of bulk optical elements (such as lenses, mirrors, etc.) and also the use of a bulk sample of an electro-optical crystal as a sensitive element, which makes it impossible to implement such a design in an integrated design and also limits the possibilities for its miniaturization.

Known electro-optical sensor of the electric field, based on the Pockels cell (CA 2239722C, Int. Cl. G01R 31/00, publ. 19.06.1997). The disadvantage of this technical solution is that the modulator based on the Pockels cell has half the dynamic range compared to the modulator in the configuration of the Mach-Zehnder interferometer.

Known electro-optical sensor of the electric field, based on an optical fiber using a nonlinear electro-optical Kerr effect (US 005936395A, Int. Cl. G01R 31/00, publ. 10.08.1999). The disadvantage of this technical solution lies in the complexity of detection due to the use of a nonlinear electro-optical effect. Detection in the case of a quadratic electro-optical effect, in comparison with the case of a linear electro-optical effect, is complicated by the fact that in order to extract information about the magnitude of the electric field acting on the sensor, a more complex mathematical operation will be required, in view of the nonlinear characteristic of the phase change, which can adversely affect the speed characteristics sensor.

Known electro-optical sensor based on the MMC with a domain-inverted structure in one of the shoulders (US 5267336A, Int. Cl. G02B 6/10, publ. 30.11.1993). The disadvantage of this electro-optical sensor is the use of methods for the formation of waveguide structures (the method of titanium diffusion into a bulk lithium niobate crystal or the method of proton exchange in a bulk lithium niobate crystal), which does not imply the possibility of miniaturization of waveguide structures.

The prototype of the device is an electro-optical electric field sensor based on two phase-shifting optical waveguides (US 005488677A, Int. Cl. G02F 1/035, publ. 30.01.1996). The prototype consists of an optical waveguide circuit of the MMC, made on a substrate, a housing containing the MMC, electrodes located in the shoulder region of the MMC and connected to an antenna fixed on the housing. The disadvantage of the prototype is the need to connect an external source of laser radiation and a receiver of laser radiation.

The proposed converter, as well as the prototype, has an optical waveguide circuit MMC formed on a substrate of silicon and silicon dioxide, has an antenna placed outside the optical circuit and electrodes located parallel to the arms of the MMC connected to the antenna.

The essential features of the proposed converter as a technical solution include:

1) the presence of waveguide structures formed from comb waveguides;

2) use as a basis for the formation of ridge waveguides, thin films of an electro-optical crystal on a substrate of silicon and silicon dioxide;

3) the presence of a laser and a photodetector integrally integrated into the substrate.

The transducer is based on a ridge waveguide MMC on a silicon and silicon dioxide substrate. The use of a substrate made of silicon and silicon dioxide makes it possible to integrate the optoelectronic part of the sensor system into the substrate, which makes it possible to locate the entire sensor system on a single chip.

The technical result of the invention is the miniaturization of the device, the increase in the operating frequency band and the monolithic integration of optoelectronic components into a semiconductor substrate.

The technical result of miniaturization is achieved through the use of thin films of an electro-optical crystal as a basis for waveguide structures.

The technical result of the increase in the frequency band is achieved due to the fact that the use of thin films as a basis for the formation of comb waveguides makes it possible to reduce the length of the MMC, which allows the use of shorter electrodes capable of transmitting higher frequency signals to supply an electric field.

This technical result is confirmed mathematically. The bandwidth of the electrodes at the level of -3 dB is determined by the expression:

where c is the speed of light in vacuum, n ₁ is the refractive index of a thin film of an electro-optical crystal from which waveguide structures are formed, ε _r is the relative permittivity of a thin film of an electro-optical crystal, L is the length of the electrodes. It is clear from expression (1) that since the bandwidth is inversely proportional to the length of the electrodes, the reduction in the length of the electrodes, which is possible due to the miniaturization of the optical waveguide circuit, will lead to an increase in the bandwidth of the electrodes.

The technical result of the integration of optoelectronic components into the substrate is achieved through the use of a substrate of silicon and silicon dioxide.

The principle of operation of the transducer is electro-optical modulation of the laser radiation intensity by an external electric field. The level of radiation intensity at the output of waveguide structures varies depending on the strength of the external electric field.

Figure 1 shows a diagram of the device: 1 - remote antenna, 2 - electrodes located parallel to the shoulders of the IMC; 3 - monolithically integrated into the silicon substrate source of laser radiation; 4 - IMC input waveguide made of a thin film of an electro-optical crystal; 5 - Y-coupling of the IMC, which plays the role of an optical power splitter, made of a thin film of an electro-optical crystal; 6 - shoulders of the IMC; 7 - Y-coupling IMC, which plays the role of an optical power connector; 8 - output waveguide IMC; 9 - photodetector monolithically integrated into the substrate.

The above-described waveguide structure of the MMC, formed from ridge waveguides, is located on a substrate of silicon and silicon dioxide. A laser radiation source monolithically integrated into the substrate is docked to the input waveguide of the MMC, and a photodetector monolithically integrated into the substrate is attached to the output of the MMC. Parallel to the arms of the MMC, electrodes connected to external antennas are installed.

The external electric field is transmitted from the antenna (1) to the electrodes (2) installed parallel to the arms of the MMC (6), due to which a linear electro-optical effect occurs in the arm of the MMC (6). The laser emitter (3) directs its radiation into the MMC through the input waveguide (4), the radiation propagates through the Y-coupling (5), which plays the role of a splitter, passes through the arms of the MMC (6), the separated radiation fluxes meet in the second Y-coupling (7 ), which plays the role of a connector, go to the output waveguide of the MMC (8) and fall on the photodetector (9) monolithically integrated into the substrate. The presence of an electro-optical effect in the arm of the MMC (6) causes a change in the intensity of the laser radiation. The receiver fixes the magnitude of the radiation intensity at the output of the interferometer. The level of optical radiation intensity measured by a photodetector allows us to conclude that there is an electric field in the external environment and determine the magnitude of the field strength.

Since the proposed converter contains an optical thin-film integrated waveguide circuit on a substrate of silicon and silicon dioxide, any electro-optical crystal that can be made in the form of a thin film and has a refractive index greater than that of dioxide can serve as a material for manufacturing a waveguide optical circuit. silicon. Thus, electro-optical crystals that meet the above criteria are: lithium niobate, lithium tantalate, and potassium dihydrogen phosphate.

Figure 2 shows a top view of the optical waveguide scheme of the IMC: 10 - layer of silicon dioxide.

Similarly, figure 3 shows a front view of the optical waveguide circuit: 11 - silicon base of the substrate.

Figure 4 shows the dependence of the transmission coefficient of the IMC, made of an electro-optical crystal, intensity on the magnitude of the applied voltage.

Figure 5 shows a cross section of an example implementation of a comb waveguide from a thin film of an electro-optical crystal on a substrate of silicon and silicon dioxide: 12 - a comb waveguide from a thin film of an electro-optical crystal.

Claims (4)

1. An electro-optical converter, including a Mach-Zehnder interferometer, having an antenna placed outside the optical circuit, characterized in that the optical waveguide circuit is made in the form of comb waveguides based on a thin film of an electro-optical crystal deposited on a substrate of silicon and silicon dioxide, in which monolithic integrated laser source and photodetector. 2. An electro-optical converter according to claim 1, characterized in that the electro-optical crystal is lithium niobate. 3. An electro-optical converter according to claim 1, characterized in that the electro-optical crystal is lithium tantalate. 4. An electro-optical converter according to claim 1, characterized in that the electro-optical crystal is potassium dihydrogen phosphate.

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