JPS63232386A - Fabry-perot interferometer - Google Patents

Abstract

PURPOSE:To eliminate a variation in an optical distance between mirrors by providing two types of member having different linear expansion coefficients for determining the distance to cancel the variation in the optical distance generated upon temperature change of the refractive index of a medium between the mirrors. CONSTITUTION:Two parallel mirrors 3, 4 and members 1, 2 for determining the distance between the two mirrors are provided, and the two members are so composed as to combine at least two types of materials having different linear expansion coefficients in such a manner that the optical distance represented by the product of the refractive index of the medium between two mirrors and the distance is substantially constant irrespective of the temperature change of the environment. That is, the distance l1 from the connecting surface 5 of mirror holding members 1, 2 to the mirror 3 is not equal to that l2 from the surface 5 to the mirror 4, but the distance l1-l2 between the mirrors can be set to constant by equalizing the temperature changes of the both by utilizing the fact that the linear expansion coefficients are different with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Fabry-Perot interferometer, which is a type of optical resonator with extremely little temperature dependence.

[Prior art] Fabry-Perot interferometers are used not only for ultra-high resolution spectroscopy, but also for narrowing the laser spectral line width by inserting them into laser cavities, for selecting and separating spectral lines, and for applications in astronomy. Recently, it has been applied to frequency stabilized laser devices and the like.

As shown in FIG. 5, the Fabry-Perot interferometer is composed of two partially transmissive mirrors that are parallel to each other and have a plane or curvature. (a) is a parallel plane type, (b)
is called an air gap type, (C) is a confocal type, and (d) is a solid type. In these figures, 3 and 4 are both mirrors.

The single plate-shaped one shown in (d), (a) and (b)
The type shown in ) with fixed mirror spacing is especially called an etalon.

Fabry-Perot interferometers have ultra-high resolution spectroscopic capabilities and are characterized by high efficiency.

One method for stabilizing the laser frequency is to convert the frequency fluctuation of the semiconductor laser into light intensity fluctuation using a frequency discriminator, and after optical-to-electrical conversion, compare it with a reference voltage and calculate the error. A method is used to stabilize the frequency by applying feedback as an error signal by controlling the temperature or drive current of the semiconductor laser.

The transmission spectrum of a Fabry-Perot interferometer is used as such a frequency discriminator. However, because the length between the mirrors of the Fabry-Perot interferometer and the refractive index of the mirror medium change with temperature changes, 1. The transmission spectrum also changes, making it difficult to stabilize the frequency over a long period of time, and causing thermal drift in the transmission spectrum. Therefore, in order to stabilize this, a Fabry-Perot interferometer made of a material with a small coefficient of thermal expansion is used, and the temperature of the Fabry-Perot interferometer is further stabilized.

However, it is not possible to completely eliminate thermal drift, and the Fabric laser has a larger shape than a semiconductor laser.
The drawback was that it was extremely difficult to strictly control the temperature of the Perot interferometer.

In order to solve the above-mentioned drawbacks, the following method is proposed in Japanese Patent Application Laid-Open No. 60-52073 (Wavelength Stabilized Semiconductor Laser). In other words, ``a medium having a refractive index with a temperature coefficient of opposite sign to the temperature coefficient of the refractive index of the active medium of the semiconductor laser is coupled with the semiconductor laser, mirrors are provided at both ends to form an optical resonator, and the length of the medium is The oscillation wavelength of the resonator is made smaller so that the change in the oscillation wavelength due to temperature changes is small.

[Problems to be Solved by the Invention] The "wavelength stabilized semiconductor laser" disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-52073 also has the same problem.

The first problem is that since media with different refractive indexes are connected and used, the end faces of each medium must be coated with anti-reflection coating, and even if this is done, it is not completely anti-reflective. Since light undergoes multiple reflections between these end surfaces, the influence of reflection from the connecting surfaces appears as an error.

The second problem is that the linear expansion coefficient of the medium is often positive;
Therefore, a medium with a negative wavelength coefficient of refractive index is required, and such a medium is Ta (Br.

Only Ce) (KRs-5>, NaCe, BaF, and quartz are disclosed, and some of them have hygroscopic and deliquescent properties, and for practical use, the selection of the medium is further dependent on some of them. limited to those of

The third problem is that the temperature change in the refractive index and the temperature change in the inter-mirror distance due to thermal expansion cannot be individually controlled.

The fourth problem is that the selection range of the medium is very narrow because it is not possible to use a ts material in which the temperature coefficient of refractive index and the coefficient of linear expansion are both of the same sign.

[Means for Solving the Problems] The Fabry-Perot interferometer of the present invention consists of two mutually parallel mirrors and a member for determining the distance between the two mirrors. The member that determines the distance between the two mirrors is a combination of at least two types of materials with different coefficients of linear expansion, so that the optical distance, expressed as the product of the refractive index of the medium between the two mirrors and the distance, changes in response to changes in the surrounding temperature. is configured to remain substantially constant regardless of the

[Function] The distance between the two mirrors changes with temperature so as to cancel out the change in the optical distance '#i (refractive index However, as a result, the optical distance between the mirrors does not change.

[Embodiment] An embodiment of the Fabry-Perot interferometer according to the present invention is shown in FIGS. 1 to 4 and will be described.

The member for determining the distance between the two mirrors is made of a combination of at least two types of materials with different coefficients of linear expansion, and is made of a material different from the medium between the two mirrors. The selection of the medium for determining the refractive index of the medium and the member for determining the distance between the two mirrors can be selected separately. By combining two or more types of materials with different coefficients of linear expansion, the amount of temperature change in the distance between the mirrors can be made positive, negative, or zero even if the individual coefficients of linear expansion are all of the same sign. The rate of temperature change can also be freely determined. If it is made by combining two types of materials with different linear expansion coefficients, it can be made more easily and with higher precision than if it is made by combining three or more types of materials.
It is preferable to use a combination of two types of materials except in special cases.

For example, in FIG. 1, mirror holding members 1 and 2
The distance e1 from the connecting surface 5 to the mirror 3 is not equal to the distance fIie2 from the connecting surface 5 to the mirror 4, but the difference in linear expansion coefficient is used to make the amount of temperature change between the two equal. , the inter-mirror distance e1-e2 can be made constant (Specific Example 1).

As another example, materials with different linear expansion coefficients may be used to cancel out temperature changes in the optical distance caused by temperature changes in the refractive index of the medium between the two mirrors 3 and 4 shown in FIG. They can be configured in combination so that the optical distance is constant as a whole (Specific Examples 2 and 3).

Therefore, the material to be used is characterized in that it can be selected from a wide range of materials without limiting the linear expansion coefficient to a very small range as in the past.

As such materials, in general, various glasses, metals, alloys (invar, super invar, etc. are particularly preferred materials), synthetic resins, and many other materials can be used. However, when using a material that is opaque to the light used, it is necessary to use a transparent material for the portion of the mirror holding member that corresponds to the light path. When using synthetic resin, it can be molded with precision molds at low cost.
And mass production becomes possible. The medium for the light inserted between the two mirrors must change as the distance between the mirrors changes and always exist uniformly between the mirrors. It is desirable to use a fluid such as a gas or liquid that is transparent to the environment, or a vacuum. The fluid such as gas or liquid may be a single component gas or a single component liquid, or may be a mixed gas or a mixed liquid. An anti-reflection coating is applied to the opposite surface (outer surface) of mirrors 3 and 4, and a Fabry-Perot cavity is not formed between this outer surface and the mirror surface as shown in FIGS. As shown in FIG. 2, it is desirable to provide a certain degree of inclination (wedge). Sweeping of the Fabry-Perot interferometer of the present invention can be performed by tilting the Fabry-Perot interferometer from the optical axis.

Specific Example 1 FIG. 1 is a diagram showing a first specific example. 1 is a transparent mirror holding member with a linear expansion coefficient α1, 2 is a transparent mirror holding member with a linear expansion coefficient α2, 3 is a transparent mirror holding member provided on the mirror holding member 1, and 4 is a radius provided on the mirror holding member 2. is rl
Mirrors 3 and 4 have the property of partially transmitting light and are located parallel to each other. The connecting surfaces 5 of the mirror holding members 1 and 2 are provided parallel to the mirrors 3 and 4, and the distance from the connecting surface 5 to the mirror 3 is 21, and the distance from the connecting surface 5 to the mirror 4 is .

The mirror holding members 1 and 2 are connected at a connecting surface 5 to determine the distance between the two mirrors.

In this example, the cavity of the Fabry-Perot interferometer composed of two mirrors 2 and 3 is evacuated and the refractive index n
= 1, and in order to prevent the medium from undergoing temperature changes,
) 1 Place the Burri-Perot interferometer in a vacuum container, or make the connection surface 5 airtight and evacuate the inside. In the Fabry-Perot interferometer configured as described above, the inter-mirror distance e=e1 e2 is ε=co, e1=e1o in a certain standard state (for example, industrial standard state).

If 12=12°, then at the temperature of Haku, 1=e1
e2 -1!1o (1+α1Δd) -t! 2o (1 + α2Δt) = (e10120> + (α1'IO - α21!20)6t (3) Here, 8T is the temperature T and the temperature To (2
0° C.), it can be expressed as ΔT=T−To.

The first term in equation (3) is the distance between the mirrors at ΔT=O, so it is constant, and the second term is the amount of change in the distance between the mirrors due to the temperature change ΔT. Therefore, by setting α1'IO-α2'20=O(4) in the parentheses of the second term, the inter-mirror distance e is always constant regardless of temperature changes. Equation (4) is based on the fact that the difference in expansion (shrinkage) of mirror holding member 1 and mirror holding member 2 in FIG. , which means that the amount of change due to thermal expansion of mirror holding members 1 and 2 is the same. Transforming equation (4), it becomes e10/e20-α2/α1 (4-1>. This relationship is satisfied. Choose the material as shown, and make the length '10.
, 1!20, it is possible to realize a Fabry-Perot interferometer that is not affected by temperature fluctuations. Based on this principle, a 7Brie-Perot interferometer is actually manufactured.

to the mirror holding member 1. Linear expansion coefficient α1=5.5X10
"7/'C quartz glass, α2 to the mirror holding member 2
= 3.2x10-"/'C Pyrex glass, distance between mirrors e. = '1O-e20'1.0
A Fabry-Perot interferometer with a diameter of about 1,000 cm is designed. (4-1) Equation and fear = elo ' 20 = 1.
From 0000, p 1o-1, 20754717ctne 2o= 0
．． 20754717 Cm Here, when processing with precision up to the μm order, '10・'! 20 as e1o=1.2075 art e2o=o, 2075 cm. The change in the inter-mirror distance due to temperature in the Fabry-Perot interferometer thus fabricated is calculated using ΔZ=(α121o−α2′20)ΔT from equation (3). Since the amount of temperature change Δ2 in the distance between mirrors differs depending on the value of ΔT, when Δe was determined by changing the six lenses, the following values were obtained.

Results of specific example 1 ΔT ('C) Δe<cm> +0.1 + 1.25 X10"-o, i
−1,25xio”+1,0+
1.25 X10”-1, 0-1, 25xlO” +3.0 + 3.75 xlO-10-3,
0-3,75XIO" +10.0 + 1.25 XIO'-10,0
-1,25XIO' Specific Example 2 A second specific example is shown in FIG. Mirror 3 with radius r on the inner surface
and 4 are connected by a connecting surface 5 parallel to 4, and the material thereof is quartz glass (linear expansion coefficient α1=5, 5X 10-7/
'C) and Pyrex glass (α2 = 3.2
X10-6/'C).

The mirror holding members 1 and 2 are connected to determine the distance between the two mirrors. When a gas is used as the medium between the mirrors of a Fabry-Perot interferometer, for example, when air is used under industrial standard conditions (20°C, 1 atm),
The refractive index n of air is given by the following equation.

(n-'1)xlO6 = 272.09 + 1.596 (σ2-3)-0
,931(θ-20) + 0.359 (1) −
760>-o, 050(f-10)+0.015(k-
3> (5) Here, σ: Wave number in 1 μm θ: Air temperature ("C) p: Atmospheric pressure (sHq) f: Water vapor pressure (mHO) k: Content rate of CO2 gas (x O, 01% unit) 1 s
HQ = 133.3 p a (Reference: "Fundamentals of Optical Applied Measurement", pages 167-168, edited by the Optical Industry Measurement Research Committee, published by the Society of Instrument and Control Engineers, Inc. Publication date: July 25, 1982). ) From equation (5), it can be seen that air pressure has a relatively large effect. Therefore,
A Fabry-Perot interferometer is equipped with a mechanism (not shown) that controls the air pressure in the cavity inside the interferometer at a constant level, or the cavity is connected to the outside to allow air to enter and exit. It is housed in a container equipped with a control mechanism (not shown) and used with constant air pressure.

In equation (5), n to the temperature coefficient of refractive index is Δn= −0
, 931xlO-6/'C, and the distance between mirrors ff
It can be seen that 1=ffi1+12 needs to be increased (decreased) as the temperature rises (falls).

Therefore, two mirror holding members 1 with different linear expansion coefficients are used.
and 2 are combined to act to cancel out the fluctuations in the optical distance due to temperature fluctuations in the refractive index n. The refractive index n is n = n □ + Δn where no is the refractive index under industrial standard conditions at ΔT=O, 20°C, 1 atm, f=10 Hg, k=3 (
(See formula (5)).

So=e1+1!2=e io (1+α1Δd)+220(1+α2Δ
Therefore, the optical distance ne is nj'-(
n□+Δn＞(glo(1+α1ΔT)+e (1+α
2ΔT)) = n□ (110+ e 20) +n□(α1'IO+α2'20)ΔT+Δn(Zlo
(1+α1ΔT) 10/2o(1+α2ΔT)) (6). (
6) The first term on the right side of the equation is a constant optical distance at ΔT=O that is unrelated to temperature changes, and the sum of the second and third terms is the amount of change in optical distance (at ΔT≠O) due to temperature changes ( Hereinafter, it will be expressed as Δ(n2)), so Δ(ne>=O
Find two conditions such that

Δ(np>-no (α1'IO+α2 e20)Δ
D+Δn[10(1+α1ΔD)+4'20(1+α2ΔT))=0 Kokote, Δrl=-0,931X10-"ΔT (=β
(described below). Therefore, it can be seen from the formula β=-0,931X10-6 (7) that in this specific example, it is not possible to always maintain a constant relationship of "10='20", which is unrelated to the five guns.

Therefore, ΔD = ±0.1. ±1.0. ±3.0. ±10℃
When the relationship '10='20 is determined, the following values are obtained.

Numerical example of formula (7) in specific example 2 ΔT (℃) e1o/12o e1o/e2o (average) + Q, 15.959939857 -0.1 5.959943024 5.959
94144+ 1. Q 5.959925605-
1.0 5.959957274 5.95994
144+3.0 5.95989395 -3.0 5゜959988947 5.95
994144+10.0 5.959783087-
10. 0 5.960099797 5.9
5994144 average 5.9599414
4 5.95994144However, λ-1,3μm (σ= 1/ 1.3) α2= 3.2
X10'/℃ (Linear expansion coefficient of Pyrex glass) β= -0,931 -5,95994144(8'
) That is, by manufacturing so as to satisfy the equation (8), it is possible to manufacture a Fabry-Perot interferometer in which the change in optical distance due to temperature change is extremely small. Based on this principle, we will describe a method for fabricating a Fabry-Perot interferometer.

Optical distance noffio is no eo = no (11o+ /20> =
If it is designed to be 1.0000 CM, no = 1, 000268246, so Z□=t! 10+N20=0.9997318259
(9) is 1n. From equations (8) and (9), 11o=0.85609a e 20=0.14364ca+. That is, it is sufficient to design 2 and e in this way. When actually manufacturing a Fabry-Perot interferometer, when precision processing the mirror holding members 1 and 2 to the μm order, e 1o = 0.8561 c
Let rtt e 20 = 0.1436 cm. The temperature change in the optical distance of the Fabry-Perot interferometer processed with this precision is calculated from equation (6) by Δ(nf>
=n (α1 /10+α2 e20>5 pieces-
0.931X 10 (e 10 (1+α1Δt)
+e2o(1+α2ΔT>)ΔT, so 5 guns are ±0.1℃, ±1.0℃
, ±3.0'C1±10.0℃, the change in optical distance Δ(nZ> is expressed as A in the table below, and similarly, "10 and e20 are processed to the order of 10 μm. Δ(M) when e1o=0.856CM e20−0.144CIA is expressed as 8. For comparison, quartz glass (
Let C be Δ(rl) when processing Pyrex glass (linear expansion coefficient 5.5 x 10'/'C) to 1 μm order, and similarly, process Pyrex glass (linear expansion coefficient 3.2 x 10'/'C) to 1 μm, t- Δ(n) when processed to DA is expressed as D.

Value of Δ(M) in specific example 2 (cm) ΔT +0.1℃ -〇, 1°CA
-9,62XIO+ 9,62XIO"B+ 8.
50XIO”-8,50X10”C-3,81x
lO+ 3.81 x 10'D + 2.27
1O-7-2,27X10'ΔT +1.0℃
-1,O℃A -9,70xlO+9.53X
1O-11B + 8.49 xlO" -8,
51xlO-10C-3, 81xlo + 3.8
1 xlO-7o + 2.27 Xl0-6L
2.27 Xl0-6ΔT +3.0'C-3,0
℃ A -2,96XIO+ 2.81XIO"B
+ 2.54 X10'-2,56XIO'C
-1,14xlO+ 1.14 xlO'-〇D + 6.81 X10' -6,81Xl0
-6ΔT+10.0℃ -10.0℃A -
1,05xlO+ 8.75xlO”B + 8
．． 41xlO'-8,59xlo-9G
-3,81xlO+ 3.81 x10'[) +
2.27 XIO-2, 27
Even in the case of precise processing to the order of magnitude, the change in optical distance Δ(ne) is 3 to 5 orders of magnitude larger than that of the second specific example shown by A and B. That is, it can be seen that the Fabry-Perot interferometer in this specific example 2 is extremely stable against temperature changes.

Concrete Example 3 Instead of making the cavity of the Fabry-Perot interferometer used in Concrete Example 1 a vacuum state, it was heated to 1 atm (76
011tIllHg) air is sealed.

In this specific example, when the temperature of the Fabry-Perot interferometer changes, the volume of the cavity increases and the air pressure also changes. From formula (5), the change in refractive index Δn is Δn= −0,9
31X10-6ΔT +〇, 359X 10-6Δp
Here, Δp is the amount of variation in internal air pressure due to temperature change and volume change.

Δp is determined as follows using the gas equation of state.

1π'20'''20 (1+3α2ΔT))-1 where, po: Internal air pressure (mmHg) when ΔT=O nR:
Constant rlo: Internal radius of mirror holding member 1 at ΔT=O r2o: Internal radius of mirror holding member 2 at ΔT=O (see Figure 1) From equations (11) and (12), Δp= (r1o2 e, .(1-3α1To)r
2e (13α2TO>) XpoΔT/T.

Since Δn in equation (10) is expressed as Δn= -0,931xlO'ΔT + 0.359X
1O-6X [(r1o2 e,.(1-3α1To
)
1+α2ΔT>) =nO('10'20) +e10(noα1ΔminjuΔn(1+α1ΔT)) e 20 (no C20AT +Δn(1+α2ΔT>) The first term on the right side of equation (15) is the optical distance at ΔT=O. Since the distance is constant, the remaining portion is the change in optical distance due to temperature change Δ(ne).

Δ(ne)=e1o(noα1ΔT +Δn(1+α1ΔT>) ff2o(noα2Δd+Δn(1+α28d)) Here, if we find the relationship '10-'20 such that Δ(ne>=O(17)), Similarly to the numerical example of equation (7) in specific example 2, 210/
When the relationship of '20 is determined from equations (14), (16), and (17), the following values are obtained.

Numerical example of elo” 20 in specific example 3 Δc ('C)
R10/120 110/e20<average)+0.
1 5.816844850-0.1 5.
816844606 5.81684473+ 1
, 0 5.816845979-1.0
5.816843476 5.81684473 3.0 5.816848482 -3.0 5.1316840979 5.8
1684473 flat -5,816844735,81
684473 The average value is ff 1o/l 2o= 5.81684473
(18). However, when air in an industrial standard state is sealed inside a Fabry-Perot interferometer, n
o = 1, 000268246α = 5.5X
10'/'C (When using quartz glass for mirror holding member 1) α = 3.2X10'/'C (When using Pyrex glass for mirror holding member 2) '10 = 2.5cm r20 = 2.4cm Calculated using To=293°K (20°C) p□=76011IIllHCJ (1 atm).

By manufacturing while maintaining this relationship, it is possible to realize a Fabry-Perot interferometer that is extremely unaffected by temperature changes. We will describe a method for fabricating a Fabry-Perot interferometer based on this principle.

The optical path length is no e o −1,00000 rat
(19). From equations (18) and (19), 0
When calculating down to ゜1μm, l to = 1, 20728cm j! 20=0.20754cm.

Therefore, when processing with this precision, the change in optical distance Δ(ne) using equations (14) and (16) is calculated and expressed as A in the following table, and similarly, 1
Processed to μm order, e1o = 1.2072 c
Δ(rl) when m e 2o = 0.2075 cm is expressed as B, and similarly, 1
Δ(rl) when processed to the order of 0 μm and e 1o−1, 2070w e 20 = 0.208 cm is expressed as C.

Value of Δ<ne> in specific example 3 (cm) Δ+0.1°C-0,1°C A-3,38xlO"13+3.35xlO
-1313+ 1.13 X10" -1,13X
IO"ΔT +1.0℃ -1,O℃
A -3,51XIO” + 3.23XI
O”B +1.12 Xl0-10-1.13 X1
0"10ΔT +3.0℃ -3,
0℃A -1,14xlO" + 8.82x
lO-128+ 3.38 xlO-10-3,39X
10"ΔT +10.0'C-10,0℃A-
3,84xlo-10+ 1.94xtO-113+
1゜11 Xl0-9-1.14810-9C-1,3
5X10-8+ 1.35 Xl0-8 Specific Example 4 FIG. 3 is a sectional view showing the fourth specific example.

1 and 2 are, for example, optical transparent quartz glass or crown glass (BK-7 Schott, West Germany, 5CHOT
3 and 4 are mirrors provided on the mirror holding members 1 and 2, both of which have the property of partially transmitting light, and are located parallel to each other. .

6 and 7 are cylindrical spacers that determine the distance between the two mirrors and are made of materials with linear expansion coefficients of opposite signs, and are connected at a connecting surface 5. The connecting surface 5 is parallel to the two mirrors, and the distance from the mirror 3 to the connecting surface 5 is el, and the distance from the mirror 4 to the connecting surface 5 is e2.

Mirror holding members 1 and 2. The interior surrounded by spacers 6 and 7 is filled with air at an industrial standard condition and then sealed to prevent air from entering or exiting. Although it is possible to seal by using an adhesive, it is also possible to perform the sealing by an optical contact method.

In this specific example, the spacers 6 and 7 are made of a material having linear expansion coefficients of opposite signs. For example, the spacer 6 is made of a material having a negative linear expansion coefficient, such as glass manufactured by Schott of West Germany. Use ceramic (product name ZERODUR) or Super Invar (X-EL53> manufactured by Tohoku Tokushu M Co., Ltd.).Spacer 7
Materials having a positive coefficient of linear expansion, such as Zerodure, Super Invar (K-EL50), quartz glass, various glasses, ceramics, metals, etc. can be used for the material.

In this specific example, in the Fabry-Perot interferometer explained in specific example 3, by setting r1=r2 and replacing e2 with -R2, the same calculation formula (13), (
14) and (16), Δp=(elo(1-3α1T
o) 10t2o(1-3α2To)) x(plo(1+3α1Δd) +1!20(1+3α2ΔT))−1 XDoΔT/T.

Δn= -0,931X10-6ΔT +〇, 359
x 10-"×[(,.(1-3α1To) +e20(13α2To)) 1+α2ΔT>) (Can be rewritten as 16N.

Next, set the conditional expression % expression % (
16) From the formula, [noToαi(1+3α1Δd) +(1+α1Δd) ×(βT□(1+3α1ΔT) 1γpo(1-3α1To))] (
1+3α2ΔT)) +(1+α1ΔT) ×(βT□(1+3α1ΔT) +rP□ (1-3α1To)) +(1+α2ΔT) ×(βT□ (1+3α2ΔT) +γPo(1-3α2To))] X (e 1o/ e 20) + [no T oα2 (1+3α2,6)+(
1+α2ΔT) ×(βTo(1+3α2ΔT) +γpo(1−3α2To>)]=O(20) However,
β--0,931X 10' γ= 0.359x 10' no= 1.000269500 (λ= 0.852
When 11μm) To=293°K (20'C) P□ = 760mmH! J From equation (20), ! ! Since the value of 10"20 is a function of the 6-piece, it can be seen that it cannot always be constant regardless of ΔT. Therefore, zero dures with negative and positive linear expansion coefficients α1 and α2 are set for spacers 6 and 7, respectively. '1 at ΔT=±0.1.±1.0.±10'C for the case using superinvar and the case using superinvar.
When the value of 0/'20 is determined, the values are shown in the following table.

Even if you change the value of 6 guns! The value of 10''20 does not change significantly, that is, it can be seen that it is possible to fabricate a Fabry-Perot interferometer with extremely little change in optical distance.

110/' 20 value zero dua in specific example 4
Super Invar 0.1 2.05955
3027 0.6154338541-0.1
2.059552993 0.615433852
8+1, 0 2.059553180 0.61
54338599-1.0 2.05955284
0 0.6154338470+ 10 2
．． 059554708 0.6154339177
-10 2.059551313 0.61
54337892 average 2.059553010 0.
6154338535 λ=0.8521
1. czm (in air) n□ = 1.000269
Needle ringing was performed using 500 To = 293°k (20°C) Po = 760 amHD (1 atm).

Next, the distance between the mirrors, e1o+e2o=2. OOOα
Create a Fabry-Perot interferometer. I asked for it first' 10
/ ' 20 and l 1o + l 2o = 2, ooo, the design value of elo-12° is the value in the following table. In reality, machining errors occur, so precision machining is performed to the order of 10 μm, and the length of 110 = ``20'' in the table is [fabricated length, l, l J]. The temperature variation Δ(rl) of the optical distance is as shown in the following table.In other words, it is possible to obtain a Fabry-Perot interferometer that is extremely stable against temperature changes. Linear expansion coefficient α
1 and α2 using zero duers and a case using super invar.

The value of elo and '20 in specific example 4 is zero dua. Super invar linear expansion coefficient (7
℃) Linear expansion coefficient (7℃) Design value (cm>
Design value (cm) ff = 1.3463097
e1o = 0.7619425ri = 0.65
36903 Z2o= 1.2380575'
10" 20 e io/' 202, 05
9955 0.61543385 production
Length (cm)ff1o=1.
346 110 = 0.762e 2o = 0.
654-e2o='1.238ΔT (
'C)Δ(rl)(Cm)Δ(ne)(Cm)+0.1
9.3xlO-13-1, 3xlO-12-0,1
-9,3xlO"' 1.3x10-12+ 1
, 0 9.3xlO"'-1,3xlO-"
-1,0-9,3X10-121.3X10”+10
9.3x10”-1,3xlO-10-1
0-9.3X10" + 1.3X10-10 Specific Example 5 FIG. 4 shows a sectional view of this specific example.

As the material for determining the distance between the two mirrors, materials having linear expansion coefficients of opposite signs (see Example 4) are used,
Make a vacuum inside.

8 is an air vent hole, 9 is a glass pipe connected to an air handling hole, and is connected to a vacuum pump (not shown), which heats the glass pipe 9 while keeping the inside in a vacuum state. The inside of the glass pipe 9 is fused by heating, so it is cut at that part (Fig. 4). The rest is produced in the same manner as in Example 4.

Next, it will be explained using mathematical formulas.

The optical distance ne between mirrors 3.4 is a vacuum inside (refractive index n = 1.000>), so ne = e1 + e2 = ff10 (1 + α1ΔT > 10 and 20 (1 + α2Δ den)
= (e Jo+1! 20) + (α1 !1o+α
2'20>ΔT In the formula (21), as in Example 1,
The first term is the optical distance in the reference state, and the second term is the amount of change in the distance between the mirrors due to the temperature change Δ. Therefore, in the second term, by setting (lt e 1o+ (X 2 e 20 = 0, elo'' 20 = -α2/α1 = constant (22), it becomes unaffected by temperature changes.

In this specific example, by selecting the material so as to satisfy equation (22) and determining the lengths and e, it is possible to realize a Fabry-Perot interferometer that is not affected by temperature changes.

For the spacer 6, a zero dure with a linear expansion coefficient α of −1,2×10−8/”C is used, and for the spacer 7, a zero dure with a linear expansion coefficient α2=−1,7×10−8/”C is used.

Distance between mirrors e ” e 1o+ e 20= 2 C
If li, then from equation (22), e 1o-1,172414 cm e 20-0.827586 cm That is, by creating a spacer as shown in equation (23), a Fabry-Perot interferometer that does not cause temperature changes can be created. .

However, in reality, processing errors occur, so let's try to find the errors.

When processed with precision on the order of 100 μm and 10 μm, 11o = 1.17 as e 2o = 0.8
3 cm and length io = 1.172 cm! ! 20=0.828cm
becomes. The change mΔn in the distance between the mirrors due to the temperature change at this time is calculated from equation (21) by Δ/=(α1'10+α2'20)ΔT (24>
When formula (24) is calculated, the results are shown in the following table.

Machining accuracy on the numerical side of equation (24) in specific example 5 100 μm 10 μmΔT ('
C) Δe<cm) Δe (a>+0.1
, 7x10-121.2x10~12-0.1
'-7X10-12-1.2X10-12+ 1
, 0 7xlO" 1.2xlO-11-
1, 0-7x10”-1,2x10-”+3.0
2.1x10" 3.6x10-11-3.0
-2. lX1O-10-3, 6X10-11+10.
0 7X10"1.2X10"-10.0
-7XiO-1,2X10'', that is, a Fabry-Perot interferometer in which the optical distance between the mirrors changes extremely little due to temperature changes can be manufactured.

Comparison with conventional examples In the air gap type etalon shown in FIGS. 5(a) and (b), the above-mentioned zero duure α=-1,2x10-8/'C was used as a spacer material with a small coefficient of linear expansion. Even in the case where the refractive index of the air changes significantly due to changes in temperature and atmospheric pressure (see equation N5), for example, when the atmospheric pressure is 7.5 mm) - 1 (1 (10 m
bar) change sult, refractive index t, t2.7X 10'
Even if there is no change in the distance between the mirrors, Δ(ne) = 2x 2.7x10' = 5.4
x 1O-6crn/'C will change. Further, the change in refractive index due to temperature change is also expressed as Δn=9.3tXl0-7/'C from equation (5), resulting in a total change of 10-5 to 10-6α/°C.

As is clear from the above specific examples, the Fapuri of the present invention
The bellows interferometer is designed to highly stabilize the optical distance between the mirrors against temperature changes. Compared to the conventional Fapry-Perot interferometer shown, its optical distance change has a stable performance by 3 to 5 orders of magnitude.

For example, if a 1-Brie-Perot interferometer with an optical distance (noNo> of 1 cm) is fabricated using light with a wavelength λ = 1.0 μm, Δ(nt
') to ±10 to ±10-11, and this change in optical distance (±10-8 to ±1O
-11CI! The wavelength change Δλ for 1) is mλo=2
Not.

λo=i, oμm n□j! 0=1cm Than, m = 20000 therefore, Δλ=2Δ(n□　e□　＞　/m = to’xΔ(noeo) Than, Δλ=±10~±10", czm It is possible to stabilize it to a certain extent.

The present invention is not limited to the above specific examples, but includes materials.

The shape, two dimensions, etc. can also be arbitrarily selected.

In addition, in the above specific example, if e10 = '20 is processed more precisely or used in a container or thermostatic oven controlled within △T-±1℃, ∆(nZ) and ∆λ can be roughly stabilized. It is effective because it can be transformed into

In the specific example described above, two types of members with different coefficients of linear expansion were used in combination as members for determining the distance between the two mirrors, but as mentioned earlier, three or more types of members can be used in combination. I'll go. Further, the linear expansion coefficients of the two types of members can be used with the same sign or with different signs, so they can be selected from a wide range of materials.

It goes without saying that the member that determines the distance between the two mirrors may be made of a different material from the member that holds the two mirrors.

In this specific example, an industrial standard state is used as the standard state, but there is no need to limit it to this. In addition, the refractive index was calculated from equation (5) using air as the gas medium between the mirrors, but in general, the (absolute) refractive index n(t, p) of organic or inorganic gas or vapor is = ( n (0℃, 760MRHg) -1)X
(P (0℃, 760mHCJ)) −'Xρ
ct, p) However, t... Air temperature C) α... Expansion rate of gas ρ... Expressed in degree of gas, so it can be calculated using this formula.

Here, the absolute refractive index n(t, p) and expansion coefficient of various gases are as follows: Chemical Handbook Basic Edition ■ Author: Chemical Society of Japan (incorporated association) Publisher: Maruzen Co., Ltd. Publication date: June 1975
20th of the month. It is published on pages 1256 and 688 of . Here, He gas, Ne gas, and the like have a small refractive index, and further, the change in refractive index due to changes in temperature and pressure is small, so it is possible to obtain accuracy that is about one order of magnitude better than when using air.

The 71 Burri-Perot interferometer of the present invention is less affected by temperature changes than conventional ones, and can be produced at low cost since processing accuracy can be lowered to obtain the same performance as conventional ones. be able to.

[Effects of the Invention] In the Fabry-Perot interferometer according to the present invention, the optical distance between the two mirrors is extremely stable against changes in ambient temperature, and the transmission spectrum of the Fabry-Perot interferometer changes due to temperature changes. For example, when used as a frequency discriminator for stabilizing the frequency of a laser, the frequency of the laser can be highly stabilized.

Furthermore, since the medium between the two mirrors and the member that determines the distance between the two mirrors are different materials, the refractive index of the medium and the distance between the mirrors can be set separately.
This has the effect that material selection is easy. Since it is not necessary to select materials in which the sign of the temperature coefficient of the refractive index of the medium and the sign of the linear expansion coefficient of the material of the member that determines the distance between mirrors are opposite to each other, there is a wide range of material selection and low cost. It is possible to select suitable materials, and even if processing accuracy is reduced, it is possible to obtain a Fabry-Perot interferometer with performance comparable to conventional ones. Therefore, the effects of the present invention are extremely large.

[Brief explanation of drawings]

Figure 1 is a sectional view showing one embodiment of the present invention, Figures 2 and 3 are
4 and 4 are cross-sectional views showing other embodiments of the present invention, and FIG. 5 is a cross-sectional view of a conventional 7 appli Perot interferometer. 1.2... Mirror holding member 3.4... Mirror 5... Connection surface 6.7...
・Spacer 8...Air handling hole 9...Pipe.

Claims (8)

[Claims] (1) A first mirror, a second mirror facing parallel to the first mirror at a predetermined distance, and a line that determines the inter-mirror distance between the first mirror and the second mirror. A Fabry-Perot interference device comprising at least two types of members having different expansion coefficients, wherein the optical distance between the first and second mirrors does not substantially change with respect to temperature changes. Total. (2) The Fabry-Perot interferometer according to claim 1, wherein a vacuum is created between the first and second mirrors. (3) The Fabry-Perot interferometer according to claim 1, wherein a fluid having a constant pressure is filled between the first and second mirrors. (4) The Fabry-Perot interferometer according to claim 1, wherein a fluid is sealed between the first and second mirrors. (5) The Fabry-Perot interferometer according to claim 1, wherein the at least two types of members having different coefficients of linear expansion have positive and negative coefficients of linear expansion. (6) The Fabry-Perot according to claim 1, wherein the at least two types of members are a first member that supports the first mirror and a second member that supports the second mirror. Interferometer. (7) The first member has a cylindrical shape, has the first mirror formed at its bottom, and has an opening at the other end, and the second member has a cylinder shape, and has an opening at the other end. 7. The fabric according to claim 6, wherein the part that closes the opening and forms the second mirror is configured to enter a cylindrical part of the first member from the opening.・Perot interferometer. (8) A patent claim in which the cross sections of the first and second members are both U-shaped, and the cross section of the first and second members after they are connected is square-shaped. The Fabry-Perot interferometer according to item 6.