JPS5833522B2 - mechanical light modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to light modulators and, more particularly, to mechanical modulators of light passing through an optical fiber element.

More specifically, conventional light modulation methods include electro-optic light modulation, which utilizes the rotation of the plane of polarization by applying an electric field to a single crystal, and acousto-optic light modulation, which utilizes piezoelectric phenomena to change the refractive index of the medium. has been put into practical use in optical communications, but the present invention relates to a purely mechanical modulation method that modulates the amount of light passing through an optical fiber using a mechanical input such as force or displacement.

FIGS. 1a, b, and c show a conventional method for mechanically modulating the amount of light passing through an optical fiber.

In the figure, 1 indicates an input optical fiber, 2 indicates an output optical fiber, and 3 indicates a shutter.

Figure 1a shows a method of mechanically adjusting the deviation of the shutter 3 to modulate the amount of light passing through the output optical fiber 20. Modulate.

FIG. 1C shows an angle shift type, in which the light is modulated by adjusting the angle θ.

Other methods include modulating the light by adjusting the distance between the end faces of optical fibers whose end faces face each other on the same axis, or using the increase in loss due to bending of the optical fiber. generally have poor sensitivity and are not widely used.

Typical dimensions of the input and output optical fibers 1 and 20 in FIG. 1 are that the core diameter is 100 μm, and the diameter of the cladding, which has a lower refractive index than the core, is often about 150 μm.

For the core and cladding, there are inorganic types using quartz, organic types using acrylic resin, etc., or inorganic and organic combination types using quartz for the core and silicone resin for the cladding. It is used.

There are also multimode step-index fibers in which the refractive index within the core is constant, and multimode gray-sotoindex fibers in which the refractive index is increased at the center of the core.

In addition to these, there are also single-mode fibers with extremely thin core diameters of several micrometers.

Although any of the above-mentioned types of fiber can be used in the present invention, the last single-mode fiber is difficult to align in an optical connector, and therefore has practical difficulties.

Since the outer diameter of the optical fiber including the cladding is about 150 μm, it is difficult to align the optical fiber when configuring the modulation method as shown in FIG.

Even if it fits well, it is equally difficult to maintain it.

It is also vulnerable to dust adhering to the end face of the optical fiber.

Trouble can also occur due to condensation on the end face. Furthermore, when attempting to use the device in water or other liquids, it is a reality that problems occur in a short period of time due to water scale formation, air bubbles adhering to the end surface, and the like.

After all, conventional methods such as those shown in FIGS. 1a, b, and c can only be used for short periods of time in favorable environments such as laboratories.

The present invention has been made in order to eliminate the above-mentioned drawbacks inherent in the prior art, and therefore, the object of the present invention is to eliminate the need for troublesome operations such as alignment, and to maintain stability over time even under adverse environments. The object of the present invention is to provide a novel mechanical modulation device that is highly reliable and does not deteriorate over time.

Another object of the present invention is to obtain a novel optical modulator that can be made compact and inexpensive, and to provide a novel industrial instrument that is inexpensive and highly reliable and operates satisfactorily even under harsh industrial conditions. There is a particular thing.

The above-mentioned objects of the present invention are such that the first and second
An optical fiber is inserted, and a light modulation space in which no optical fiber exists is formed by separating the end faces of the first and second optical fibers by a certain distance, and the light modulation space is passed through by an elastic gap in the light modulation space. This is achieved by a mechanical light modulator that modulates the amount of light.

Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

In the figure, reference number 11 indicates an input optical fiber, 12 indicates an output optical fiber, and 14 indicates a capillary tube through which the optical fibers 11 and 12 pass.

No optical fiber exists between the end faces 15 and 16 of the input and output optical fibers 11 and 12.

As will be described later, since light is modulated in the space between the end faces 15 and 16, this space will hereinafter be defined as a modulation space.

The capillary tube 14 is made of metal, plastic material, or the like.

The input/output optical fibers 11 and 12 have a cladding on the core, but the cladding is omitted in FIG. 2.

Now, if the input optical fiber 11 is fixed and the output optical fiber 12 is bent by an angle θ as shown by the broken line in FIG.
The amount of 0-pass light decreases.

The deflection angle θ of the output optical fiber 12 is expressed as θ−θm at the angular frequency ω.
The case of vibration at sinωt is shown in FIG. 3a.

The amount of transmitted light in this case is shown in FIG.

A specific method for vibrating the deflection angle θ will be described later.

In FIG. 3, curve A shows the case where the inner wall of the capillary tube 14 is blackened by roughening it or painting it with black paint.

Light passes only if the input and output fibers 11,12 are in a straight line as shown in FIG.

If there is a slight deflection angle, the light will be absorbed by the inner wall of the capillary tube, and the amount of output light will become zero, resulting in a sharp pulse-like output as shown by curve A.

Curve B in FIG. 3 shows the case where the degree of blackening of the inner wall of the capillary tube 14 is reduced.

In this case, a portion of the light reflected by the inner wall enters the output optical fiber 12, so the amount of output light increases.

Curve C shows the case where the inner wall of the capillary tube 14 has a substantially mirror surface.

In this case, the amount of passing light further increases, but since there is almost no absorption of light by the inner wall of the capillary, the light passes without loss, and the alternating current component in curve C becomes small.

As will be described later, the present invention utilizes this alternating current component, so curve C is not preferable.

Therefore, it is necessary to have an appropriate degree of blackening, such as thickening the AC component in the output waveform.

As is clear from FIG. 3, the mechanical angular frequency in the present invention is ω, but the angular frequency of the fundamental wave of the AC component in the output light amount is 2ω.

The two points that are practically important in such a deflection angle modulator are that the amount of alternating current in the amount of passing light is large, and that the amount of light changes suddenly at a small deflection angle.

Generally, when a multimode step-index fiber is used as a white light source, the light emitted from the end face 15 in FIG. 2 spreads in a cone shape in the modulation space with an apex angle of about 20 degrees.

Therefore, even if the output fiber is in line with the input fiber, only a small amount of light enters the end face 16 of the output fiber, and most of it is absorbed by the inner wall of the capillary tube 14.

In order to reduce the spread of cone-shaped light, it is effective to place a minute condensing lens adjacent to the end face 15 of the input fiber.

Placing a lens just in front of the end face 16 of the output fiber is also ineffective.

It is also effective to arrange a Rondo lens that functions equivalently to the lens.

It is also effective to fill the space between both end faces of the input and output optical fibers with a transparent solid or liquid whose refractive index matches that of the core.

Such a medium is called a matching agent.

Prevents light spreading and reduces Fresnel reflection loss at the end face.

As shown by the broken line 17 in Fig. 2, when the capillary tube in the modulation space is crushed by a plane perpendicular to the plane of the paper to narrow the optical path, the amount of light changes suddenly with a slight change in the deflection angle, and the output waveform becomes pulse-like. , subsequent waveform shaping becomes advantageous.

Crushing as shown in reference numeral 17 reduces the stress generated on the surface of the capillary tube due to the bending angle θ, and is also advantageous in terms of fatigue failure of the capillary tube due to vibration.

Instead of squishing, the same effect can be obtained by stretching the modulation space and reducing the circular cross-sectional area of the modulation space.

If a reflecting mirror is placed on the end face 16 of the output optical fiber in Fig. 2,
The light from the input optical fiber 11 returns to the input optical fiber 11
Return to

This returning light is also modulated by the deflection angle θ.

Since the returned light can be easily separated from the incident light, this reflection method eliminates the need for the output optical core and fiber 12, the input optical fiber also serves as the output optical fiber, and only one fiber is required.

As is clear from the above explanation, when an optical fiber is passed through a capillary tube, the cores of the input and output optical fibers are automatically matched by the capillary tube, so the troublesome alignment operation required in the past is necessary. do not have.

Since the core and end face of the optical fiber once inserted into the capillary tube are protected by the capillary tube 14, they will not deteriorate over time.

That is, since the modulation space is protected by the capillary tube 14, it will not deteriorate due to dust or condensation, and high reliability can be maintained even under adverse environments.

In addition, by selecting the material of the capillary tube 14, it can operate with sufficient reliability even in corrosive gases and liquids, which has great practical effects.

Furthermore, by collapsing the capillary tubes in the modulation space and narrowing the optical path, light modulation can be achieved with a slight change in the deflection angle, which is extremely advantageous in practice.

Fig. 2 shows the simplest embodiment of the present invention, but if the deflection angle θ is set large and the function of an optical switch is provided, the O
Since R circuits, AND circuits, and other logic circuits can be configured, complex logic circuits that respond to multiple mechanical inputs can be realized.

In such optical switches, the modulation space is bent in advance to block light, and the input and output optical fibers are aligned in a straight line using mechanical input to allow the light to pass (normally closed contact). There is a method (normally open contact) that bends the modulation space using mechanical input, which is the opposite of this.

In the embodiment of the present invention described above, a capillary tube is used for convenience of explanation, but the capillary tube is not essential.

For example, if a modulation space is formed by arranging input and output optical fibers to face each other in an elastic body with pores cut out, and the elastic body is bent, it is clear that light will be modulated in the same way as in a capillary tube.

In FIG. 2, if the end face 16 of the output optical fiber 12 is cut obliquely with respect to the central axis of the output optical fiber 12, the alternating current component of the output light when vibrated at the deflection angle θ-θm5inωt is The fundamental angular frequency can also be set to ω instead of 2ω.

Referring now to FIG. 4, there is shown a reference example of a mechanical light modulation device that can achieve substantially the same objectives as the present invention.

In FIG. 4, 111 is the core of the input optical fiber 11;
Reference numeral 112 indicates the cladding of the input optical fiber 11, 121 indicates the core of the output optical fiber 12, and 122 indicates the cladding of the output optical fiber 12.

In this reference example, the input optical fiber 11 and the output optical fiber 12 are continuous and identical, and the cladding portion of the same optical fiber element is stripped by a length L, and a cladding is attached to the stripped portion. A total reflection preventing material 18 made of a material having a higher refractive index than the material is covered with, for example, a coating.

Here, of the light from the input optical fiber 11, only the light 19 parallel to or very close to the fiber axis reaches the core 12□ of the output optical fiber 12.

This amount of light is about 1/100 or less of the amount of light input into the optical fiber.

Since most of the light is not parallel to the fiber axis, it comes into contact with the inner wall of the total reflection prevention material 18 while passing through the distance.

The refractive index of the total reflection prevention material 18 is cladding 112 or 122.
Since it is larger and closer to that of the core, the light that hits the inner wall of the total anti-reflection material is not totally reflected.
As shown in , it escapes to the outside of the fiber core.

Now, fix the input optical fiber 11 and connect the output optical fiber 12.
When the angle θ of is oscillated at θ=θm5inωt, the amount of passing light is as shown in FIG. 3, as in the case of the present invention.

Waveform A in Figure 3 is when the refractive index of the total reflection prevention material 18 is large and the coating width is long, resulting in a sharp pulsed light quantity, but since the absolute value of the passing light quantity is small, it is necessary for signal processing. requires a large degree of amplification.

Waveform B is the most preferable since the coated portion has an appropriate refractive index, degree of blackening, and width.

Waveform C is a case where the cladding of the optical fiber is not peeled off, and there is almost no loss of light due to bending.

The anti-total reflection material 18 does not necessarily need to be coated, and may be fixed using a mold or the like.

Further, its outer diameter does not need to be the same as that of the cladding.

Furthermore, as shown in Figure 4, it is not necessary to completely peel off the cladding in the section with length L, but it is possible to locally peel it off in many places and coat it with total anti-reflection material. It is clear that the effect is obtained.

In the reference example shown in FIG. 4, the cores of the input and output optical fibers are continuous, so like the present invention described above, there is no need for alignment operations and there is no possibility of deterioration over time. It has the following advantages.

Furthermore, this reference example does not necessarily require a capillary tube, and is generally easy to manufacture.

There are many applications that do not require protection with metallic capillaries.

In such a case, this reference example is more suitable than the present invention.

Similarly to the present invention, if the core of the portion to which the anti-total reflection material is fixed is stretched thinly, light can be modulated by slight bending.

Cut the core at right angles to the axis at the right end of L in Figure 4,
If a mirror is attached to this surface, part of the light from the core 11 will be reflected by the mirror and return to the core 111 again.

It is clear that this returning light is also modulated by the bending angle in the same way as in the present invention.

FIG. 5 is a sectional view showing an example of application of the present invention to a Karman vortex flowmeter.

Figure 6 is a side view when the right pipe in Figure 5 is removed, Figure 7 is a sectional view taken along the 7-γ line in Figure 5 and seen in the direction of the arrow, and Figure 8 is light modulation. It is an enlarged sectional view of a part.

5 to 8, reference numeral 30 indicates a pipe through which fluid flows in the direction of arrow 31. In FIGS.

A ring-shaped gasket 33 is sandwiched between seven flanges 32 formed at the end of the pipe 30 and fixed with bolts 34.

The inner diameter of the ring-shaped gasket 33 is equal to the inner diameter of the pipe 30.

A Karman vortex generator 35 is inserted perpendicularly to the fluid flow and diametrically.

Both ends of the vortex generator 35 are fixed to the ring-shaped gasket 33 by connecting bodies 36.

As shown in FIG. 1, the Karman vortex generator 35 has a trapezoidal cross section and generates a regular Karman vortex street 37 within a certain Reynolds number range.

Here, when the generation frequency of the vortex row 37 is f, the average flow velocity of the fluid in the pipe 30 is V, and the width of the vortex generator 350 is D, the frequency f is expressed as follows.

However, St is a dimensionless quantity called the Stronoll number, and is a constant having a value of about 0.18.

Since the frequency f and the average flow velocity V are directly proportional, the average flow velocity V, that is, the flow rate of the fluid, can be determined by measuring the frequency f.

Conversely, since the frequency f, that is, the modulation frequency, changes by changing the flow rate or velocity of the fluid, it is clear that the present Karman flowmeter can be used as it is as an optical modulation device.

A tail fin 38 is attached to the downstream side of the Karman vortex generator 35.

A constriction 39 is formed at the connection between the tail 38 and the vortex generator 35.

The tail 38 vibrates as indicated by an arrow 40 at a frequency corresponding to the frequency at which the Karman vortex is generated.

The presence of the window 41 further facilitates the vibration of the tail fin 38.

The input optical fiber 11 is passed through the vortex generator 35 as shown by the broken line via an optical connector (not shown).

The input light input from the input optical fiber 11 is also transmitted to the constriction part 3.
The signal is modulated at 9 and taken out from the output optical fiber 12.

FIG. 8 is an enlarged sectional view of the constricted portion 39.

Between the vortex generator 35 and the tail 38 (inside the fin 39, the capillary 1
4 has been passed.

Input optical fiber 11 and output optical fiber 12 are connected to capillary tube 14
A modulation space 42 is formed between the end faces thereof.

Modulation space 420 bending (elastic deformation) due to vibration of tail 38
Therefore, the amount of passing light is modulated.

The material of the vortex generator 35, tail fin 38, etc. will be determined by the fluid to be measured, but plastic is more desirable than metal.

As is clear from FIGS. 5 to 1, the vortex generator 35 and the tail fin 38 are axially symmetrical with respect to the central axis of the pipe 30, so it is easy to integrally mold them from a plastic material.

As the plastic material, polyacecool resin, polypropylene resin, fluororesin, etc. are advantageous in terms of appropriate elastic modulus and corrosion resistance.

Elastomas such as rubber are also suitable.

However, it is undesirable for the vortex generator to vibrate, so in that case it is necessary to insert vibration-preventing ribs.

Although the capillary tube 14 shown in FIG. 8 is not essential, it is easier to mold the optical fiber by passing the optical fiber through the metal capillary tube in advance.

Figures 5 to 7 show examples of measuring the flow velocity in a pipe, but as a modification, if the vortex generating body is formed into a long bar and a tail is attached to the tip, the wind velocity in the atmosphere can also be measured. can.

Furthermore, by attaching a plurality of tail blades to a long vortex generating body, it is possible to measure the flow velocity distribution, which is convenient for measuring the flow velocity distribution in waterways and the like.

In the usage example shown in FIG. 8, the present invention shown in FIG. 2 is used as the light modulation section, but the light modulation section according to the reference example shown in FIG. 4 can be directly replaced. It is clear that there is no need to explain.

Conventional devices of this kind that utilize Karman vortices include those that detect Karman vortices thermally, those that detect them as differential pressure,
There are methods that use ultrasonic waves to detect vibrations, methods that magnetically detect vibrations of the tail blade caused by vortices, and methods that use piezoelectric elements or strain gauges to measure the alternating force that acts on the vortex generator as a reaction to the generation of the Karman vortex.

Each of these methods has its advantages and disadvantages, but the following (1) to (4) are common disadvantages.

(1) Generally complex and expensive.

(2) Because it uses an electrical method, there is a safety problem against explosions.

(3) For the same reason as (2) above, it is vulnerable to electromagnetic induction.

(4) It is difficult to measure the flow rate of small diameters, and the inner diameter is approximately 50mm.
The degree is minimal.

The Karman vortex flowmeter according to this application example solves all of the above drawbacks.

Since it can be integrally formed by molding, it can be constructed at an extremely low cost.

Because it uses an optical method, it is inherently safe against explosions and has no electromagnetic induction.

It can be fully put into practical use for pipes with inner diameters of up to about 10 mm, has the advantage of having few factors that limit the lower limit of the pipe inner diameter, and has great practical effects.

In this usage example, the cross-sectional shape of the Karman vortex generator 35 is formed into a trapezoidal shape, as shown in FIG. In short, any material that stably generates Karman vortices over a wide range of Reynolds numbers is sufficient.

Furthermore, the constriction 39 and window 41 shown in FIGS. 5 to 8 are not essential, and may not be provided.

If an attempt is made to widen the measurement range, the tail fin 38 and constriction 39 will inevitably become weaker.

In order to prevent damage during the production process or when excessive input is applied, it is practically useful to install a stopper that limits the vibration amplitude of the tail fin 38 as necessary.

This stopper has been omitted in the above description.

In this usage example described above, the light is modulated by the constricted portion 39, but it is clear that the light modulating portion may be formed within the tail fin instead by forming the entire tail fin to be soft and bendable.

In addition, although the optical fiber and capillary tube have a circular cross-sectional shape,
It does not necessarily have to be circular; oval, square, etc. will have the same effect and effect.

The only difference is that the circular shape is easier to obtain.

Although the present invention has been described above with reference to its preferred embodiments, it goes without saying that these are merely illustrative and do not have a limiting meaning.

Therefore, without departing from the spirit of the present invention, the present invention may be implemented with various modifications other than those described above, but all such modifications and changes are included within the scope of the present invention. .

[Brief explanation of the drawing]

Figures 1a, b, and c are diagrams explaining the principle of a conventional mechanical light modulation method, Figure 2 is a diagram explaining the principle of an embodiment of the present invention, and Figures 3a and b are detailed diagrams of the present invention. Diagram for explanation, No. 4
The figure is a principle explanatory diagram showing an example of a configuration similar to the present invention for reference.
Fig. 5 is a sectional view showing an example of use when the present invention is applied to a Karman vortex flowmeter, Fig. 6 is a side view of Fig. 5 with the right side pipe removed, and Fig. 7 is a side view of Fig. 5. FIG. 8 is a cross-sectional view taken along line 7-7 and viewed in the direction of the arrow, and is an enlarged cross-sectional view of the light modulation portion. 1.11...Input optical fiber, 111.12,
... Core, 112.122 ... Clad, 2,12 ... Output optical fiber, 3 ...
...Shutter, 14... Capillary, 15, 16-
...End face of optical fiber, 18 ... Total reflection prevention material, 30 ... Pipe, 32 ... Flange, 33 ... Ring-shaped gasket , 34■
・・Bolt, 35・°°・°°Karman vortex generator, 36
...Connection body, 37...Karman vortex, 3
8...Tail, 39...Neck, 41.
...Window, 42...Modulation space.

Claims (1)

[Claims] 1. First and second optical fibers are inserted into the pores of an elastic body, and the optical fibers exist with a certain distance between the end surfaces of the first and second optical fibers. 1. A mechanical light modulation device comprising: a light modulation space in which the light modulation space does not move; and an amount of light passing between the first and second optical fibers is modulated by elastic deformation of the light modulation space. 2. The mechanical light modulation device according to claim 1, further characterized in that a capillary tube made of metal or plastic material is used as the elastic body. 3. The mechanical device according to claim 1 or 2, further characterized in that a transparent liquid or solid whose refractive index matches the refractive index of the core of the optical fiber is sealed in the light modulation space. Light modulator. 4. The mechanical light modulation device according to claim 1 or 2, further characterized in that the light modulation space intra-space lens or Rondo lens is inserted. 5. Claim 1 or 2 further characterized in that the light modulation space is compressed to form a light path.
Mechanical light modulation device as described in . 6. The mechanical light modulation device according to claim 1 or 2, further characterized in that the light modulation space is expanded to narrow the circular cross-sectional area of the light path. 7. The mechanical light modulation device according to claim 1 or 2, further comprising a reflecting mirror inserted at one end of the light modulation space. 8. The mechanical light modulation device according to claim 1 or 2, further characterized in that the end face of the second optical fiber is inclined with respect to the fiber axis. 9. The mechanical light modulation device according to claims 1 to 8, further characterized in that the inner wall of the light modulation space is blackened.