RU204196U1 - Hermetically sealed multifunctional integrated optical circuit - Google Patents

Abstract

The utility model relates to the field of sealed packaging of multifunctional integrated-optical circuits, which are intended for use in fiber-optic interferometric sensors as a polarizer, splitter and modulator of an optical signal. waveguides made of diffused titanium, forming two input and two output ports, is placed inside the all-metal enclosure of sealing and fixed to the bottom of the enclosure using a conductive adhesive, and optical DLP fibers, optically connected to channel waveguides of the integrated-optical circuit, are placed in through-flow tubes made of kovar, which are fixed inside the outlet tubes of the enclosure enclosure by means of glass solder, forming fiber sealed leads, the enclosure also has sealed leads of electrical contacts for controlling multifunctional integral optical circuit and closed by a lid fixed by seam-roller welding, at least one getter is also placed inside the housing, and the internal volume of the sealing housing is filled with dry nitrogen. The device improves the quality of the housing sealing, prevents structural changes in the lithium niobate crystal and reduces the pyroelectric effect, which leads to an increase in the stability of the operation of an integrated optical circuit based on a lithium niobate crystal in a sealed package, as well as to a decrease in the value of introduced polarization transformations in optical BRL fibers. 3 ill.

Description

The utility model relates to the field of sealed packaging of multifunctional integrated-optical circuits (hereinafter referred to as MIOS), which are intended for use in fiber-optic interferometric sensors as a polarizer, splitter and modulator of an optical signal.

The principle of operation of these devices is based on the optical properties of semiconductor crystals such as lithium niobate crystal. The optical properties of semiconductor crystals change depending on the applied electrical voltage, the presence of water vapor in the environment, changes in the ambient temperature and the gas composition of the environment. To maintain the stable operation of integrated optical circuits, it is necessary to maintain environmental conditions throughout the entire service life.

It is known (RS Moyer, R. Grencavich, FF Judd, R. C. Kershner, WJ Minford, RW Smith, Design and qualification of hermetically packaged lithium niobate optical modulator // IEEE Transactions on Components, Packaging, and Manufacturing Technology: 1998, Part B, vol. 21, No. 2, pp. 130-135,) a device of a hermetically packed optical modulator based on a lithium niobate crystal.

A modulator on a lithium niobate crystal is placed inside a kovar case (NK-29 alloy) and is fixed to the bottom of the case by means of an epoxy-based adhesive. The sealed conduit of optical fibers is carried out by means of a ceramic throughput tube, inside which optical fibers (hereinafter referred to as fiber) pre-metallized with nickel and gold by electrodeposition are fixed. Ceramic tubes are fixed to optical fibers using metal fusible solder. After that, the ceramic tube is fixed in the outlet tube of the housing using the same metal fusible solder. Glass capillaries are put on the end of the optical fibers, which are polished at the desired angle and are joined to the lithium niobate crystal by means of a UV-curable optically transparent adhesive. The body is closed with a lid by the method of seam-roller welding. The body is fired in a vacuum environment to reduce the number of hydrogen molecules. After firing, the body is filled with a gas mixture of dry nitrogen and helium through a hole in the lid, which, after filling the body with a gas mixture, is sealed with metal solder.

Nitrogen is used to reduce the activity of the internal environment of the sealed modulator housing. Also, the presence of nitrogen reduces the number of penetrating hydrogen molecules, the presence of which leads to the formation of water vapor.

The disadvantages of this solution are the inconsistency of the thermal expansion coefficients (hereinafter - CTE) of quartz, from which the fiber is produced, and the metal solder used to fix the fiber in the ceramic sleeve. Also, due to the inconsistency of the CTE between the lithium niobate crystal and the case, mechanical stress may occur in the area of the fiber-lithium niobate crystal joining. These mechanical stresses can compromise the sealing of the enclosure in the event of temperature fluctuations.

It is known (US patent 8070368) a device of a hermetically packed integrated optical circuit with an oxidizing gas inside the housing.

An integrated-optical circuit made on a lithium niobate crystal, fixed on a stainless steel substrate using conductive silicone, is placed inside a kovar case and fixed with the same silicone on the bottom of the case. The fibers are sealed off by means of hermetically sealed tubes on the fibers, which are soldered with lead-tin solder in the outlet tubes of the housing. On the end of the optical fibers, sleeves are put on, which are polished at the desired angle and adhered to the lithium niobate crystal by means of a UV-curable optically transparent adhesive. The body is closed with a lid fixed by seam-roller welding. The body is fired for 12 hours at a temperature of 100 ° C in a vacuum environment. After firing, the body is filled with a dry gas mixture of oxygen (40%) and helium (60%). Helium additionally serves as a tracer gas when conducting leak tests of the internal environment of the housing.

The disadvantages of the known solution are the low service life of adhesives based on epoxy resin, as well as the release of oxygen by the epoxy resin in a housing with a lithium niobate crystal, which reacts with hydrogen and forms water molecules. Another problem is the CTE mismatch between the quartz from which the fiber is made and the metals used as solder to provide a solder joint between the sleeve and the body. Due to this inconsistency, with a large temperature gradient, mechanical stresses on the fiber arise, which introduce errors into the sensor signal.

It is known (A. Mottet, S. Jilard, J. Hauden, N. Grossard, H. Porte, J. Tchahame, D. Veyrie, O. Gilard, Packaging improvement of LiNbO3 modulators and space evaluation results // ISCO 2018, 111803K, 2019) a hermetically sealed modulator device based on lithium niobate, selected as a prototype for the proposed utility model.

In this solution, the body is made of kovar. The waveguides of the integrated optical circuit were obtained by the titanium diffusion method. And on the side edge of the case there are sealed leads of electrical contacts designed to control the integrated-optical circuit. The lithium niobate crystal is attached to the bottom of the case with conductive silicone. The junction of the fiber with the body is cleaned to the quartz part and metal is applied to it. On the metallized part of the fiber, a passage made of kovar coated with gold is put on. There is a glass sleeve at the end of the fiber, which allows for easy coupling of the fiber to the integrated optical circuit. After joining the fiber with the integrated-optical circuit, the Kovar-on-fiber passage tube is inductively sealed with an output tube located at the end of the housing, forming a fiber sealed lead. Before fitting the cover, the body is fired to remove organic elements and water vapor contained in the used adhesives. The housing cover is fixed by seam-roller welding in a nitrogen-helium environment. Helium is used as a tracer gas to facilitate leak testing.

The disadvantages of this solution are insufficient information about the process of sealing the fiber terminals. The metal used for sputtering the stripped portion of the fiber is not known; in this connection, its CTE is not known and how much it differs from the CTE of quartz, from which the fiber is made. There is no known solder material that was used to secure the Kovar fiber pass tube with the Kovar outlet tube to the end of the housing, if any. The disadvantage is also the discrepancy between the CTE of lithium niobate and kovar, from which the body is made.

The technical problem to be solved is to improve the design of the device to achieve a technical result.

The achieved technical result is an increase in the stability of the integrated optical circuit based on a lithium niobate crystal in a sealed case by improving the quality of sealing, preventing structural changes in the lithium niobate crystal and reducing the pyroelectric effect.

The task is solved in the following way.

A multifunctional integrated optical circuit (MIOS), made on a lithium niobate crystal substrate with diffused titanium channel waveguides, forming two input and two output ports, is placed inside an all-metal encapsulation body (hereinafter referred to as the body) and fixed to the bottom of the body using a conductive adhesive ; Optical birefringent (DLP) fibers are optically connected to the channel waveguides of the integrated optical circuit, fixed with glass solder in Kovar flow tubes, which are fixed inside the output tubes of the housing with the help of low-melting metal solder, forming fiber sealed leads, while the formation of sealed leads is carried out for two optical DLP fibers.

A getter is placed inside the case, and on the side edge of the case there are sealed leads of electrical contacts, and the case is closed with a lid fixed by seam-roller welding; The inner volume of the sealing housing is filled with dry nitrogen, and, with the MIOS placed in the housing on a lithium niobate substrate, a reduction annealing has been carried out beforehand.

The essence of the claimed utility model is explained as follows. The device is based on a lithium niobate crystal, which is a multifunctional integrated optical circuit with two input ports and two output ports. Optical DLP fibers are optically connected to each port. The use of optical DLP fibers in the claimed utility model is due to the need to maintain the polarization of the optical signal modulated by the multifunctional integrated-optical circuit in interferometric fiber-optic sensors.

The crystal itself is fixed to the bottom of the case with conductive epoxy glue. The glue creates a short circuit, which promotes the accelerated relaxation of charges that arise on the faces of the lithium niobate crystal due to the pyroelectric effect. The pyroeffect describes the phenomenon in which a change in the temperature of a lithium niobate crystal leads to the formation of free charges on its surface, during the migration of which the optical properties of the semiconductor crystal change. Also in the body there is a getter that adsorbs hydrogen and water molecules. The body is made from a solid piece of metal alloy.

Before installing the integrated-optical circuit on the bottom of the case, it undergoes preliminary reduction annealing. This annealing restores lithium and niobium molecules, as a result of which oxygen vacancies are created, which leads to an increase in the electronic and ionic conductivity and reduces the influence of the pyroelectric effect on the optical signal. In addition, due to the use of preliminary annealing, the structural change in the lithium niobate crystal is reduced, which leads to an increase in the stability of the multifunctional integrated-optical circuit. The use of conductive epoxy glue, a getter, and filling the internal medium of the case with dry nitrogen also contributes to a decrease in the influence of the pyroelectric effect on the optical properties of a lithium niobate crystal. Nitrogen creates a dry environment, preventing the formation of OH compounds, and does not chemically interact with the lithium niobate crystal.

DLP optical fibers are fixed in the pass-through tubes with glass solder. The use of glass solder minimizes the mechanical deformation of the optical bridged laser fibers, which prevents the occurrence of polarization transformations. Kovar flow tubes are sealed with low-melting metal solder in the outlet tubes of the housing. The formation of sealed leads is carried out for two optical DLP fibers.

Due to the use of Kovar and glass solder in the housing design, the CTE is matched between the housing components, which leads to a decrease in the likelihood of mechanical deformations of the sealed housing, leading to a deterioration in the quality of sealing, as well as a decrease in the value of introduced polarization transformations in optical DLP fibers. Due to the use of preliminary annealing, the structural change of the lithium niobate crystal is reduced, and due to the use of conductive epoxy glue, getter and filling the internal medium of the case with dry nitrogen, the pyroelectric effect on the optical properties of the lithium niobate crystal is reduced, which leads to an increase in the stability of the operation of the multifunctional integrated optical circuit.

The essence of the proposed solution is illustrated in Fig. 1, fig. 2, fig. 3, where in FIG. 1 is a top view of the device without a cover; in fig. 2 - fiber sealed lead; in fig. 3 is a general view of the device closed with a lid.

FIG. 1, fig. 2 and FIG. 3 the following designations are adopted:

1 - all-metal body (hereinafter - sealing body),

2 - MIOS,

3 - sealed leads of electrical contacts,

4 - optical DLP fibers in a protective sheath,

5 - section of optical DLP fibers stripped to the quartz part,

6 - glass substrate with V-shaped grooves,

7 - fiber sealed lead formed for two optical birefringent fibers,

8 - recess at the bottom of the sealing body;

9 - getter,

10 - passage tube,

11 - glass solder,

12 - hole for pouring adhesive based on epoxy resin,

13 - adhesive based on epoxy resin,

14 - outlet tube,

15 - metal solder,

16 - cover.

A hermetically packed multifunctional integrated optical circuit (Fig. 1) contains an all-metal case 1, at the bottom of which MIOS is fixed on a substrate made of lithium niobate 2, sealed leads of electrical contacts 3, intended for modulating an optical signal, optical DLP fibers 4 with a stripped section 5 for docking with MIOS using glass substrates with V-shaped grooves 6, fiber sealed leads 7 and recesses on the bottom of the housing 8 for placing glass substrates with V-shaped grooves and getters 9.

FIG. 2 optical DLP fibers 4 are placed in the passage tube 10 and in the stripped section 5 are sealed into the tube using glass solder 11, the passage tube has a hole 12 through which it is filled with epoxy adhesive 13, and in the outlet tube 14 the passage tube is fixed with metal solder 15.

FIG. 3 - all-metal case 1, with MIOS 2 fixed inside, sealed leads of electrical contacts 3 and with fiber sealed leads 7, case 1 is filled with dry nitrogen and closed with a lid 16.

The operation of the device is as follows: an optical signal propagates along one of the optical fibers 4 and enters the MIOS 2 waveguides from one side. When the optical signal passes through the MIOS 2 waveguides, its phase is modulated using electrical contacts 3, after which the radiation comes out from the other side of MIOS 2 and enters the optical fibers 4 from the side opposite to the input.

As a specific example of the implementation of the device, it is proposed to use a multifunctional integrated-optical circuit on a substrate made of a lithium niobate crystal with waveguides obtained by diffusion of titanium, with two input and two output ports. Before installation in the MIOS housing, preliminary reduction annealing takes place in a mixture of dry gases of hydrogen and nitrogen. The device case is proposed to be made of stainless steel, for example, grade 30X13. MIOS has a bevel on the side of the input and output ports to reduce back reflections from the ends. At the bottom of the MIOS case, it is fixed with epoxy conductive glue, for example, ZIPSIL 520 EPK-01. On the side of the lithium niobate crystal ends, there are a pair of optical birefringence fibers. The end of the optical DLP fibers is stripped to a quartz base. A glass solder preform in the form of an oval is placed on each pair of stripped fibers with DLP, which, using the induction soldering method, fixes the fiber in the passage tubes. The ends of each pair of optical DLP fibers are glued with UV-curable glue into the V-grooves of the glass substrate, which are also beveled and optically connected to the MIOS ports using UV-curable glue. The distance between the grooves coincides with the distance between the MIOS ports. To simplify the joining of fibers in the V-shaped grooves with MIOS, recesses are made on the bottom of the housing. The flow tubes are sealed by induction and a low-melting metal solder, for example, tin-lead, in the outlet tubes of the housing, thereby forming fiber sealed leads. In the recesses on the bottom of the case, there is a getter that adsorbs hydrogen and water molecules, for example, based on titanium. One of the possible options for the location of the getter can also be the inner side face of the body or the inner side of the body cover. At the stage of securing the lid, for example, by seam welding, the MIOS housing is placed in a dry nitrogen environment, thereby keeping the dry nitrogen environment inside the housing.

Thus, what has been considered shows that the claimed utility model is feasible and ensures the achievement of a technical result, which consists in improving the quality of the enclosure sealing, preventing structural changes in the lithium niobate crystal and reducing the pyroelectric effect, which increases the stability of the operation of an integrated optical circuit based on a lithium niobate crystal in a sealed the case. In addition, the use of glass solder minimizes the mechanical deformation of the optical birefringence fibers, which prevents the occurrence of polarization conversions.

Claims (1)

A hermetically packed multifunctional integrated-optical circuit made on a substrate made of a lithium niobate crystal with channel waveguides made of diffused titanium, placed inside an all-metal enclosure enclosure and fixed to the bottom of the enclosure using a conductive adhesive, and optical fibers optically connected to the channel waveguides of the integrated-optical circuit , are placed in the passage tubes, which are fixed by means of metal solder and soldering inside the outlet tubes of the sealing housing located at its end, forming fiber sealed leads, on one of the outer side faces of the housing there are sealed leads of electrical contacts, the internal volume of the sealing housing is filled with a mixture of gases and closed with a lid by means of seam-roller welding, characterized in that a reduction annealing was carried out with a multifunctional integrated-optical circuit placed in the sealing housing on a lithium niobate crystal substrate, and the channel The waveguides of the multifunctional integrated-optical circuit form two input and two output ports, and each sealed lead is formed for two optical birefringent fibers fixed in the passage tube using glass solder, the inner volume of the enclosure is filled with dry nitrogen, and on one of the inner edges of the casing is fixed at least one getter.

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