CN1333276C - Liquid filling shock isolation encapsulation technology for optical fibre grating - Google Patents

Abstract

The present invention relates to a liquid filling shock isolation packing technology for an optical fiber grating, which is a practical packing technology which can ensure the stable work wavelength of the optical fiber grating and compensate temperature; the present invention can be widely applied to light communication aspects. The technology adopts material with the certain requirement of physical characteristics as a packing outer shell (such as duralumin material); both ends of the packing outer shell and the optical fiber grating are sealed by adopting an oil seal technology; liquid (such as silicone) with a certain pressure is filled in the packing outer shell; an optical fiber grating temperature compensation loading stage (such as a loading stage made of ceramic with negative temperature coefficients or duplex metal material) is connected with and fixed to the outer shell through a gasket. Both ends of the optical fiber grating is fixed on the platform and are exposed in the liquid. The shock isolating packing outer shell is provided with a liquid filling port for filling liquid, the shock isolating packing outer shell is also provided with an interface connected with a pressure meter for connecting with the pressure meter for observing the liquid pressure in a cavity in real time. The device can realize shock isolation and automatically keep the purpose of stable work wavelength of the optical fiber grating.

Description

Liquid-filled shock-isolation packaging method for fiber grating

Technical field

The invention relates to a temperature compensation packaging technology for stabilizing the working wavelength of the fiber grating, which can automatically adjust the working wavelength of the fiber grating to keep it in a stable state.

Background technique

When fiber gratings are made into devices, such as fiber grating filters, fiber grating dispersion compensators, and OADMs (optical add-on/drop-out devices), etc., fiber gratings and their accessories must be packaged. Because the fiber grating is very sensitive to stress and temperature, when the fiber grating is affected by temperature and external force, the working wavelength of the fiber grating will drift, which is very unfavorable for the current application of DWDM (dense wavelength division multiplexing) technology. , or even fail completely. Therefore, to solve the influence of temperature and stress on fiber gratings, temperature compensation and vibration isolation packaging are usually used.

As far as packaging technology is concerned, there are common simple packaging and vacuum packaging technologies at present. Ordinary packaging is just a simple outer packaging, which is equivalent to the case shell of a machine. It is only for decoration and cannot achieve the effect of shock isolation; vacuum packaging technology uses vacuuming to remove the medium that transmits vibration to achieve the purpose of shock isolation, but This technology has many disadvantages such as complex technical process, high economic cost, long production cycle and difficult maintenance.

Contents of the invention

For this reason, we proposed a hydraulic packaging method, which has many advantages such as simple process, low cost, fast production and processing speed, good shock isolation effect and simple maintenance, and can completely overcome and solve the shortcomings of vacuum packaging technology and simple packaging technology.

The technical solution adopted by the present invention to solve its technical problems

The liquid-filled encapsulation method we propose is to seal the fiber grating in a sealed casing and leave an interface to connect with the outside. The sealing liquid is sealed into the sealed casing, and the sealing liquid is maintained at high pressure, and the volume expansion coefficient of the sealing liquid is equal to that of the sealed casing. There is a temperature compensation carrier in the sealed shell to monitor the temperature of the sealed liquid and adjust the temperature in real time to keep the temperature constant. The sealed housing has a liquid injection port for injecting liquid into the sealed chamber; in addition, there is a test pressure gauge interface for real-time monitoring of the pressure of the sealed liquid in the sealed housing.

According to the fiber mode coupling theory, when the forward and reverse light waves are transmitted in the fiber grating, the phase matching condition of the mode coupling satisfies the following Bragg equation

λ _B = 2n _eff Λ (1)

In the formula, Λ is the grating period, n _eff is the effective refractive index, Λ and n _eff are affected by the external environment and change ΔΛ and Δn _eff , resulting in a shift of the reflected wavelength Δλ that meets the Bragg condition. By the Bragg condition, we get

Δλ=2Δn _eff Λ+2n _eff ΔΛ (2)

This equation shows that the reflection wavelength shift is related to the change of the effective refractive index of the fiber core and the grating constant. When the fiber grating is affected by stress or temperature changes, both n _eff and Λ will change. The photoelastic effect under stress causes the refractive index to change, while the deformation changes the grating constant; the photothermal effect caused by temperature changes the effective refractive index, and the thermal expansion coefficient causes the grating constant to change.

1. When the fiber grating is subjected to stress, there is

Δλ _B /λ _B = (1-P)E (3)

Where E is strain, μ is Poisson's ratio, and P is the FBG strain sensitivity coefficient. For silica fibers, advisable

Δλ _B /λ _B = 0.78E (4)

If the external stress can be regarded as the sum of a constant stress and a disturbance stress, correspondingly the strain in the fiber grating can also be expressed as

E＝E ₀ +ΔE (5)

When ΔE<<E ₀ is satisfied, then (4) can be rewritten as

Δλ _B /λ _B ≈0.78E ₀ (6)

That is, when the fiber Bragg grating is placed in a sealed container with high liquid pressure, the pressure in the container is a constant, and the corresponding strain in the fiber Bragg grating is also a constant E ₀ , while the external vibration corresponds to a strain generated on the fiber Bragg grating A small disturbance ΔE, which is negligible relative to the constant strain E ₀ in the fiber grating (realized by adjusting the pressure in the container), this pressure filling method can completely achieve the effect of shock isolation, thereby keeping the optical fiber The working wavelength of the grating remains unchanged; the experimental results show that when there is no shock-isolation package, the center wavelength of the fiber grating changes randomly with the external vibration; when the shock-isolation package is used, when the outer wall of the package is hit, the center wavelength is very stable, thus The correctness of the above theories and techniques is verified.

2. When the fiber grating temperature changes:

Δλ _B /λ _B = (α+ζ)ΔT (7)

Where α is the thermal expansion coefficient and ζ is the thermo-optic coefficient. For germanium-doped silica fiber, α is 5.5×10 ^-7 /℃, ζ is 7.1×10 ^-6 ~ 7.3×10 ^-6 /℃ (in the range of 20 ~ 150℃), 1×10 ^-5 /℃ ( at 400°C). It can be seen from formula (7) that there is a linear relationship between Δλ _B and ΔT.

When the external temperature disturbs the sealed cavity, the temperature compensation carrier (ceramic with negative temperature coefficient) will cause its own length to change due to the temperature change, and then the length of the fiber grating attached to the ceramic will change accordingly, because the fiber grating is sensitive to temperature The change of the fiber grating is equivalent to the change of the refractive index, and the effect of the change of the length of the fiber grating is also equivalent to the change of the refractive index, so the change of the refractive index caused by the change of the length of the fiber grating can be used to offset the change of the refractive index caused by the temperature change of the fiber grating Variety;

3. When the external temperature disturbance of the sealed cavity affects the pressure of the liquid in the sealed cavity, when the volume of the liquid remains unchanged, the pressure of the liquid is also linearly proportional to the temperature of the liquid. When the thermal expansion coefficient of the sealed shell is the same as that of the liquid, the volume change of the liquid will be the same as the volume change of the sealed cavity, so that the volume change can be synchronized with the temperature change, and the pressure of the liquid in the sealed cavity can be kept constant. In the experiment, the material and liquid of the sealed casing we used were duralumin and silicone oil respectively.

4. When the pressure of the sealed cavity changes, there is a test pressure gauge interface to test it. If the pressure is found to have a tendency to decrease, the pressure in the sealed cavity can be kept constant by injecting sealing liquid into the sealed cavity. Through the above three The method is to shield the disturbance of the fiber grating from the outside world, so that the fiber grating works under constant conditions.

The beneficial effect of the invention is that it can completely overcome and solve the shortcomings of vacuum packaging technology and simple packaging technology, and has low cost, good repeatability and good stability.

Description of drawings:

In the picture above, (1) is a cylindrical steel pipe (2) is an external rubber sleeve (3) is a sealing shell (4) is a gum of the oil seal device (5) is a sealing liquid (6) is a gasket (7) is an internal rubber The sleeve (8) is the temperature compensation stage (9) is the fiber grating (10) is the liquid sealed by the inner screw cover (12) of the oil seal device of the fixed gum (11) (13) the outer screw cover of the oil seal device ( 14) The outer rubber gasket (15) of the oil seal device is the optical fiber pigtail (16) is the liquid injection port (17) is the pressure gauge interface

Detailed ways

The sealing shell is cylindrical, and there are liquid injection ports and test pressure gauge ports at both ends of the side wall; the rubber sleeve is also cylindrical, and the rubber sleeve is closely attached to the outer sealing shell. One end is mechanically connected with the gasket by a ring-shaped protrusion to fix the gasket, and the ring protrusion at the other end is directly connected to the temperature compensation carrier for support, and the ring protrusion is in the center of the direction parallel to the main axis of the cylinder There are round holes symmetrically distributed so that the liquid can pass through the left and right cavities; the gasket is mechanically connected with the temperature compensation stage to play a supporting role, and the gasket is symmetrically distributed with round holes in the center of the direction parallel to the main axis of the cylinder so that The liquid can pass through the two left and right cavities; the fiber grating is glued to the temperature compensation carrier by gum; the fiber pigtail is also glued to the steel pipe K by gum;

Oil seal device: There is a circular hole on the side cavity wall of the sealed shell to allow the cylindrical steel pipe to pass through, and a screw hole is coaxial with the circular hole on the inside and outside of the sealed shell, and the two screw holes are not directly connected. , the inner screw hole is sealed with a thin screw cap, in which oil is sealed to isolate it from the sealing chamber; the outer screw hole uses a bolt with the same diameter as the outer diameter of the steel pipe to isolate it from the sealing chamber; the cylindrical One end of the steel pipe inside the sealed casing uses rubber to fix the fiber pigtail and plays the role of isolating the sealed cavity. There are layered rubber gaskets outside the steel pipe outside the sealed casing, which further plays a sealing role, and is wrapped outside the rubber gasket. A rubber holster for convenience and good looks.

Claims (5)

1. a fiber grating liquid is filled the shock insulation method for packing, it is characterized in that: fiber grating, negative temperature compensation pottery, the connection of annular gasket sequential machine also are exposed in the interior highly pressurised liquid of outer package shell, fill liquid outside in the package casing with certain pressure intensity, by in liquid, applying the drift that steady pressure comes limit fibre grating centre wavelength, thereby offset the wavelength disturbance that extraneous random vibration or temperature variation are brought, thereby reach the shock insulation purpose.

2. the method for claim 1, it is characterized in that: adopt the thermal expansivity of outer package shell and the close method of liquid thermal expansion coefficient that the interior sealing of outer package shell is filled, the invariablenes pressure of liquid of seal fluid when realizing temperature variation, thus the pressure in the outer package shell is constant when guaranteeing temperature variation.

3. method as claimed in claim 1 or 2, it is characterized in that: also have a pressure measurement pressure tap in this outer package shell, monitor liquid pressure in the outer package shell by connecting pressure gauge, when pressure reduces, keep invariablenes pressure of liquid in the outer package shell by injection sealing liquid in the outside package casing.

4. method as claimed in claim 1 or 2 is characterized in that: described outer package shell is made by duralumin, and liquid is silicone oil in the described outer package shell.

5. method as claimed in claim 3 is characterized in that: described outer package shell is made by duralumin, and liquid is silicone oil in the described outer package shell.

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