CA2113794C - Interference filter and method of making the same - Google Patents
Interference filter and method of making the sameInfo
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- CA2113794C CA2113794C CA 2113794 CA2113794A CA2113794C CA 2113794 C CA2113794 C CA 2113794C CA 2113794 CA2113794 CA 2113794 CA 2113794 A CA2113794 A CA 2113794A CA 2113794 C CA2113794 C CA 2113794C
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Abstract
A multiple layer film 3 is composed on a substrate 2 by evaporation. The multiple layer film 3 is composed of a lower multiple layer film 31, a cavity layer 32, and an upper multiple layer film 33. The upper and lower layer films 31, 33 are composed by alternately laminating high refractive film layers 31H, 33H, and low refractive film layers 31L, 33L, respectively. In the x-axis direction of the substrate 2, the wavelength .lambda., that is, the film thickness is changed continuously so that all wavelengths may be .lambda./4n (n being the refractive index) with the film thickness corresponding to the transmission wavelength A. Thus, the selective wavelength is changed continuously depending on the incident position of the light.
Description
21~.~'~~t~
Title of the Invention Interference filter and method of making the same Field of the Invention The present invention relates to a variable wavelength type interference optical filter of narrow band, used in optical communication, optical measurement, optical information processing, or the like, and more particularly to a variable wavelength type optical filter not depending on the polarization states capable of varying the transmission wavelength continuous-ly, and a method of making the same.
Background of the Prior Art In a conventional optical filter of narrow band, as a variable wavelength type filter designed to vary the transmission wavelength continuously, a narrow band optical filter possessing a dielectric multiple layer film is used. As such optical fil-ter, for example, a high refractive index material such as Ti02 ZnS and a low refractive index material such as Si02 are applied on a substrate alternately in a multiple layer coating at an optical thickness of .1/4 wavelength exactly. Herein, supposing the transmission wavelength to be ~, and the refractive index of each layer to be n, the optical thickness is expressed as ~,/4n.
By forming such multiple layer coating on the substrate, an ,.
.:. .
' .. , , :, interference optical filter of narrow band is realized.
In this state, the wavelength of the transmission light through the interference optical filter is defined by the optical thickness to be a specific wavelength. However, by varying the angle of incident light into the interference optical filter, the transmission wavelength may be varied continuously. Fig. 10 shows the state of emitting light from a light source not shown, to an optical filter 102 of narrow band through an optical fiber 100 and a collimating lens 101. The transmission light of the optical filter 102 is focused by a focusing lens 103, and enters an optical fiber 104. By varying the incident angle of the light beam into the optical filter 102 by a small angle D from the vertical state shown by solid line in the drawing, for example, in a range of about 0 to 10°, the transmission wavelength ~, can be changed continuously as shown in Fig. 11. At this time, the full width at half maximum(F.W.H.M.) is not changed so much as shown in Fig. 12.
However, as shown in Fig. 11, the transmission center wavelength may be different depending on the polarized states (S
wave, P wave), and the difference is too large to be ignored when the inclination angle is set, for example, at 10° or more.
Moreover, the transmission band width (full width at half maxi-mum) of the interference optical filter also differs individually depending on the polarized states (S wave, P wave). And it changes significantly depending on the inclination angle 8 in P
wave as shown in Fig. 12. The transmissibility is also lowered 2113'~~~~
depending on the inclination angle 0, which was a defect.
Thus, when continuously changing the transmission wavelength by using a conventional interference optical filter, there were many limits in use, and, disadvantageous.
Summary of the Invention The present invention is devised in the light of such conventional problems. Hence a primary object of the present invention is to present a variable wavelength interference opti-cal filter of narrow band capable of changing the transmission wavelength continuously without varying the inclination of the interference optical filter, not depending on the polarized wave, and a method of manufacturing the same.
The variable wavelength interference optical filter of the present invention is able to vary the wavelength of trans-mission light continuously in a specific wavelength range. In the optical filter comprises a substrate composed of a substance for transmitting light in the specific wavelength range, and a multi-ple layer evaporation substance film formed on the substrate, being composed of substance of high transmissiblity for transmit-ting light at wavelength in the specific wavelength range. And the apical thickness of the multiple layer evaporation substance film is composed so as to change continuously along a specific direction of the substrate, and the wavelength of the transmis-sion light is changed by varying the incident position of light to the optical filter along the specific direction of the sub--' - :
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In the invention, by varying the light irradiation posi-tion linearly without changing the inclination of the optical filter, the transmission wavelength can be changed continuously.
The transmission wavelength differs only with the incident posi-tion, and the transmissiblity is not changed by the polarization states so that the same transmissiblity may be obtained in P wave and S wave. Furthermore, the full width at half maximum, the selective characteristic of the light is not changed depending on the light incident position, but remains at a specific value, which is an excellent effect. That is, not depending on the plane of polarization, the full width at half maximum and light transmissiblity are kept constant, and only the wavelength can be changed continuously.
Brief Description of the Drawings Fig. 1 (a) is a sectional view showing the constitution of a variable wavelength type interference optical filter in single cavity structure according to a first embodiment of the invention, Fig. 1 (b) is a graph showing the change of transmis-siblity on the x-axis, and Fig. 1 (c) is a magnified sectional view of a circular part of FIG.1 (a).
Fig. 2 is a graph showing the changes of transmission wavelength, full width at half maximum, and transmissiblity, relative to the incident position of the embodiment.
Fig. 3 is a graph showing the selective characteristic of -~113'~~~~
the wavelength relative to the number of cavity layers.
Fig. 4 is a schematic diagram showing the state of use of variable wavelength type interference optical filter according to the embodiment.
Fig. 5 (a) is a sectional view showing the constitution of a wavelength variable type interference optical filter according to a second embodiment of the invention, Fig. 5 (b) is its front view, and Fig. 5 (c) is a graph showing the changes of its transmissibility.
Fig. 6 is a graph showing the changes of transmission wavelength, full width at half maximum and transmissiblity rela-tive to the rotational angle of the variable wavelength type interference optical filter according to the second embodiment of the invention.
Fig. 7 is a schematic diagram showing a state of use of the variable wavelength type interference optical filter accord-ing to the second embodiment of the invention.
Fig. 8 (a) is a front view showing a combined state of two circular optical filters according to the second embodiment, and Fig. 8 (b) is a front view showing an example of use composed by adhering four different variable wavelength type interference optical filters.
rotary dome.
Fig. 10 is a schematic diagram showing a state of use when varying the transmission wavelength in the conventional interference filter.
Fig. 11 is a graph showing changes of wavelength relative to the incident light angle of the conventional interference filter.
Fig. 12 is a graph showing changes of full width at half maximum by varying the incident angle in the conventional inter-ference filter.
Detailed Description of the Preferred Embodiments Fig. 1 is the diagram showing the constitution of the variable wavelength type interference optical filter of polariza-tion states independent type according to the first embodiment of the invention. The variable wavelength type interference optical filter 1 in the embodiment is composed by evaporating multiple layers on a substrate 2 such as glass and silicon. The substrate 2 is composed of a material high in the transmissiblity of light in the range of the wavelength to be used, and a dielectric material or a semiconductor may be used. In the embodiment, quartz glass is used. Above the substrate 2, a dielectric mate-rial high in transmissiblity of light at the wavelength to be used, a semiconductor, and other substances are formed in multi-ple layers by evaporation to form a multiple layer film 3.
Herein, the multiple layer film 3 is composed of, as shown in the s:
~113'~u drawing, a lower multiple layer film 31, a cavity layer 32, and an upper multiple layer film 33. On the lower surface of the substrate 2, an anti-reflection film 4 is formed by evaporation.
The anti-reflection film 4 is, for example, a two-layer film of Si02 and Ti02, but either one may be used.
Herein, the substance used as evaporation material for the multiple layer film 3 and the anti-reflection film 4 is, for example, Sip2 (refractive index n = 1.46), Ti02 (n = 2.15), Si (n - 3.46), A12(33, Si2N4, MgF, etc. In this embodiment, the multi-ple layer films 31 and 33 are formed by alternately laminating and evaporating a low refractive film and a high refractive film.
The film thickness d, transmission wavelength ~,, and refractive index n are defined in the following formula.
~.=4nd ~ ~ ~ ( 1 ) That is, the optical thickness of each layer of the lower and upper multiple layer 31 and 33 is ~,/4. The cavity layer 32 is composed of the low or high refractive film same as that of the lower and upper multiple layers 31 and 33, and the thickness of the cavity layer do is two times of that of the low or high relative film of the multiple layer 31 and 33, namely ~,=2ndc. By alternately laminating the low refractive film and high refrac-tive film in this way, the full width at half maximum (F.W.H.M.) of the peak of transmissiblity is lowered.
~11.~'~~~~
1 according to the embodiment, having the relation of the trans-mission wavelength and film thickness as shown in the formula (1), is composed with the substrate 2 which is a slender plate, and the optical thickness of the multiple layer film 3 is varied continuously to differ the transmission wavelength ~,. The trans-mission wavelength of the variable wavelength type interference optical filter 1 is set at ~,a to ~,C ( ~,a < ~,c ) , corresponding to the incident position x of the light, and the transmission wave-length of the position at its central position (x = xb) is ~,b.
The upper and lower multiple layer films 31, 33 are composed by alternately laminating a first evaporation substance film with first refractive index nl, and a second evaporation substance film with lower second refractive index n2. That is, As the circular part of Fig. 1 (a) is shown in a magnified view in Fig.
1 (c), the film thickness of the individual multiple layer films is changed continuously. In Fig. 1 (c), the low refractive film of the lower multiple layer film 31 is supposed to be 31L, the high refractive film to be 31H, the high refractive film of the upper multiple layer film 33 to be 33H, and the low refractive film to be 33L. Relative to the transmission wavelength ~,a at the end xa on the x-axis of the interference optical filter 1 in Fig. 1 (a), it is set so that formula (1) may be established in the low refractive film and high refractive film, respectively.
Similarly, relative to the transmission wavelengths ~,b, ~,C at positions xb, xc, the film thickness is set so that formula (1) may be established at individual wavelengths ~.b, ~.c. The film _ g -' .
~ _ .
.
.. : ' ' ~ . .
.' .. ! ~ . ~
SI
' .~,. . : ~.. , :. . ;: ..
r ... '.~' .. : f . .. '' :.. . ~,. ~ ':
~
thickness between them is also set so that the wavelength may change linearly. Therefore, each film thickness of the multiple layer film 3 changes continuously from position xa to xc on the x-axis, and the film thickness increases toward the positive direction of the x-axis.
For example, supposing ~,a to be 1540 nm, ~,c to be 1560 nm, and ~.b to be 1550 nm, by alternately laminating T102 of which first refractive index (high refractive index) nl is 2.15, and Si02 of which second refractive index (low refractive index) n2 is 1.46, the upper and lower low refractive films 31L, 33L have the film thickness d of 263.7 nm at the left end (x = xa), and film thickness of 267.1 nm at the right end (x = xc). The film thickness of the upper and lower high refractive films 31H, 33H
is 179.1 nm at x = xa, and 181.4 nm at x = xc. If using Si of which refractive index n is 3.46 as high refractive films 31H, 33H, the film thickness of high refractive films 31H, 33H is 111.7 nm at x = xa and 112.7 nm at x = xc.
Herein, the change of the film thickness in the x-axis direction is expressed by the function of x, d(x), the wavelength ~. by the function of x, 7~(x), and the refractive index is the variable of x, n(x), and hence their relation is expressed in formulas (2), (3), where x0 is an arbitrary position, for exam-ple, position of x = xa, and A is a constant.
7~(x)=4n(x)d(x) ~~~ (2) _ 9 2~13'~~t~
~,l,x)=~(x0)+EA(x-xB)k ... (3) k=1 In this embodiment, the optical thickness is controlled by controlling the film thickness of the upper and lower multiple layer films 31, 33 and the cavity layer 32. But it is also possi-ble to compose an optical filter by varying the refractive index along the x-axis direction of the substrate while the film thick-ness is unchanged. It is not necessary to change the optical thickness continuously on a straight line, but the film thickness or optical thickness such as refractive index may be varied along an arbitrary line of the substrate.
In a filter of single cavity structure with center wave-length of 1550 nm, by alternately laminating Si02 as low refrac-tive films 31L, 33L, and Ti02 as high refractive films 31H, 33H
on the substrate 2 of quartz glass, when 32 or more layers are formed by laminating upper and lower multiple layer films 31 and 33, a narrow band filter with full width at half. maximum (F.W.H.M.) of 1 nm is formed. Or, in a filter of single cavity structure by laminating Si02 and Si on. the substrate 2 of quartz ~",.. glass, when the upper and the lower multiple layer films 31 and 33 are combined to laminate 24 layers, a narrow band filter with full width at half maximum of l nm is realized. Thus, the great er the difference in the refractive index between the high re >, fractive film and low refractive film, a narrow band filter is realized by the smaller number of layers.
~11~'~~~~
Fig. 2 shows changes of transmission wavelength ~, rela-tive to the incident position x of light in the variable wave-length type interference optical filter in the embodiment, and changes of full width at half maximum, and transmissibility. If composed to vary linearly the transmission wavelength ~, by chang-ing the incident position x in formula (2), the half width at half maximum and transmissiblity do not change corresponding to the position of the x-axis, but it shows a state of constant value. There is also no difference in the polarization states of incident light, and a narrow band optical filter not depending on the polarization states is realized.
The foregoing embodiment relates to the variable wavelength type interference optical filter of single cavity structure, but a filter may be also composed in a mufti-cavity structure by using plural cavity layers. For example, another cavity layer may be formed on the upper multiple layer film 33 in the single cavity structure of the embodiment, and another multi-ple layer film may be formed thereon to compose a variable wave-length type interference optical filter of double cavity struc-ture. In this case, as shown in Fig. 3, the selectivity of the wavelength can be enhanced even by decreasing the number of films of the multiple layer film. In the diagram, m shows the changes of the number of cavities and wavelength selective characteris-tics in the case of using multiple layer films of the same num-ber. As clear from the diagram, the greater the number of cavi-ties, the higher becomes the wavelength selective characteristic.
In such variable wavelength type interference optical filter 1, as shown in Fig. 4, by emitting light, for example, white light to one end of the optical filter 1, it is used to separate the spectrum components of the desired wavelength. In Fig. 4, by emitting light to the interference optical filter 1 through an optical fiber 11 and a collimating lens 12, the light transmitted through a focusing lens 13 and an optical fiber 14 is received. By moving the optical filter ~. in the direction of x-axis, the selected wavelength A is varied. As shown in the drawing, by slightly inclining the variable wavelength type interference optical filter 1, the light reflected by the front face of the interfErence optical filter 1 will not be directly reflected to the light source side, and adverse effects on the light source side can be avoided. This inclination angle should be out of polarization dependent range, for example, 10° or less.
In the embodiment, the filter is a rectangular plate filter, but a circular filter may be also composed. Fig. 5 shows a disk-shaped variable wavelength type interference optical filter 41 forming a multiple layer film 43 and an anti-reflection film 44 on a disk-shaped substrate 42. In this case, too, in proportion to the position of the x-axis direction in Fig. 5, it is composed so that each film thickness changes continuously.
Thus, as shown in Fig. 6 (a) to (c), the transmission wavelength is proportional to cos A, expressing the position in the relation of angle A centered on the origin of the x-axis. Therefore, when the circular filter 41 is rotated, it changes continuously as ~
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i .
~ ." ., , . . ', . ' : . . . .
~ t . , 4~ ,. , .
, . . .
. . .
2113'~~~
shown in the diagram. In this case, too, same as in the forego-ing embodiment, the full width at half maximum and transmissibli-ty are constant, regardless of the rotational angle (cos 0 or 0).
Fig. 7 is a perspective view showing the state of use of such circular variable waveleng~h type interference optical filter. In the diagram, same as in the example of use in Fig. 4, the light entering through the optical fiber 11 is put into the interference optical filter 41 as parallel light through the collimating lens 12. The transmitted light is received by the optical fiber 14 through the focusing lens 13. Herein, the interference optical filter 41 is rotated in the direction of arrow by rotating means not shown herein, for example, a motor, a crank type knob and a reduction gear, or the like. As a result, the wavelength is selected depending on the angle of rotation.
In this case, the wavelength linearized in proportion to cos 8, not rotational angle 8, is selected. Therefore, by preliminarily measuring the angle of rotation and selective wavelength, a desired wavelength can be selected.
In this way, by forming the variable wavelength type interference optical filter in a disk form, and continuously varying the thickness of the multiple layer film 43 by the posi-tion in the x-axis direction as shown in Fig. a (a), the wave-length range.can be selected.by rotating the optical filter by a half circle, that is, in a range of 180°. Therefore, the other optical filter can be composed by gluing together two semicircu-lar variable wavelength type interference optical filters ~lA and 41B differing in the selective wavelength range as shown in Fig.
8 (a). In this case, by mutually varying the selective wave-length, a wavelength selective characteristic in a wide range is achieved. Or, as shown in Fig. 8 (b), it is also possible to composed by using a further multiplicity of variable wavelength type interference optical filters 41A to 41D.
In the circular variable wavelength type interference optical filter, the film thickness of the multiple layer evapo-rated substance film is changed continuously by the position in the x-axis direction, but it is also possible to compose to vary the film thickness continuously corresponding to the angle 0. In this case, the wavelength characteristic depending on the rota-tional angle 8 is obtained.
A manufacturing method of filters shown in the embodiments is described below. In the embodiments, the film thickness of the multiple layer film 3 of the filter 1 must be changed continuously depending on the position of the x=axis.
The manufacturing method for composing the filter having such film thickness is described below while referring to Fig. 9. In Fig. 9 (a), a vacuum vessel 51 for vacuum evaporation contains an evaporation substance 52 as evaporation source such as Si02, Ti02 or Si in the foregoing embodiments in its bottom. In the upper part of the vacuum vessel 51, a parabolic rotary dome 53,opened in the lower side is provided. The rotary dome 53 is rotated at a constant speed in the direction of arrow. A circular substrate 2 is glued to a specific radial position of its inner surface.
f This substrate 2 is not mounted along the inner surface of the rotary dome 53, but is disposed at an inclination of a spe-cific angle a from the inner surface of the rotary dome 53 as shown in Fig. 9 (b). Furthermore, to make the film thickness uniform, the evaporation substance 52 is disposed in the center of the vacuum vessel 51, but in this embodiment its position is at a remote place from the center at a specific distance L.
Thus, the film thickness can be controlled by an evaporation temperature or evaporation time, and moreover by properly setting the angle a and position L of the substance 52, the film thick-ness change can be controlled. Thus, the high refractive film and the low refractive film are evaporated alternately. In this way, the distance from the evaporation substance 52 varies con-tinuously depending on the vertical direction position (x-axis) of the substrate as shown in Fig. 1, and therefore the film thickness changes continuously corresponding to the distance of the evaporation source or the like, by evaporation for a specific time. By sequentially changing over the evaporation substance 52 to Si02, Ti02, etc. in this way, a filter possessing evaporation substances in multiple layer film is composed. In this case, directly, the circular variable wavelength type interference optical filter can be composed as shown in Fig. 5, and by cutting off in a rectangular form along the x-axis in Fig. 5, a variable wavelength type interference optical filter in a rectangular plate form shown in the first embodiment can be constituted.
In this embodiment, the desired film thickness is 211~'~~~~
obtained by mounting the substrate on the inner surface of the rotary dome 53, but when the substrate is disposed at a specific inclination angle from the same film thickness surface equal in the distance from the substance as the evaporation source, it is possible to constitute by sequentially laminating and evaporating evaporation substances of high refractive index and low refrac-Live index. In this case, the film thickness distribution can be controlled by varying the inclination angle a and distance from the evaporation source.
Also in this embodiment, the substrate is mounted on the rotary dome 53 at the inclination, and the evaporation source 52 is located at the position remote from the center of the vacuum vessel 51 by the specific distance L, but it may be achieved only by either inclining the substrate when mounting, or by locating the evaporation substance 52 away from the center of the vacuum vessel 51 by a specific distance L. In this case, too, by prop-erly setting either the inclination angle a or the distance L
from the evaporation source, the film thickness distribution can be controlled.
Title of the Invention Interference filter and method of making the same Field of the Invention The present invention relates to a variable wavelength type interference optical filter of narrow band, used in optical communication, optical measurement, optical information processing, or the like, and more particularly to a variable wavelength type optical filter not depending on the polarization states capable of varying the transmission wavelength continuous-ly, and a method of making the same.
Background of the Prior Art In a conventional optical filter of narrow band, as a variable wavelength type filter designed to vary the transmission wavelength continuously, a narrow band optical filter possessing a dielectric multiple layer film is used. As such optical fil-ter, for example, a high refractive index material such as Ti02 ZnS and a low refractive index material such as Si02 are applied on a substrate alternately in a multiple layer coating at an optical thickness of .1/4 wavelength exactly. Herein, supposing the transmission wavelength to be ~, and the refractive index of each layer to be n, the optical thickness is expressed as ~,/4n.
By forming such multiple layer coating on the substrate, an ,.
.:. .
' .. , , :, interference optical filter of narrow band is realized.
In this state, the wavelength of the transmission light through the interference optical filter is defined by the optical thickness to be a specific wavelength. However, by varying the angle of incident light into the interference optical filter, the transmission wavelength may be varied continuously. Fig. 10 shows the state of emitting light from a light source not shown, to an optical filter 102 of narrow band through an optical fiber 100 and a collimating lens 101. The transmission light of the optical filter 102 is focused by a focusing lens 103, and enters an optical fiber 104. By varying the incident angle of the light beam into the optical filter 102 by a small angle D from the vertical state shown by solid line in the drawing, for example, in a range of about 0 to 10°, the transmission wavelength ~, can be changed continuously as shown in Fig. 11. At this time, the full width at half maximum(F.W.H.M.) is not changed so much as shown in Fig. 12.
However, as shown in Fig. 11, the transmission center wavelength may be different depending on the polarized states (S
wave, P wave), and the difference is too large to be ignored when the inclination angle is set, for example, at 10° or more.
Moreover, the transmission band width (full width at half maxi-mum) of the interference optical filter also differs individually depending on the polarized states (S wave, P wave). And it changes significantly depending on the inclination angle 8 in P
wave as shown in Fig. 12. The transmissibility is also lowered 2113'~~~~
depending on the inclination angle 0, which was a defect.
Thus, when continuously changing the transmission wavelength by using a conventional interference optical filter, there were many limits in use, and, disadvantageous.
Summary of the Invention The present invention is devised in the light of such conventional problems. Hence a primary object of the present invention is to present a variable wavelength interference opti-cal filter of narrow band capable of changing the transmission wavelength continuously without varying the inclination of the interference optical filter, not depending on the polarized wave, and a method of manufacturing the same.
The variable wavelength interference optical filter of the present invention is able to vary the wavelength of trans-mission light continuously in a specific wavelength range. In the optical filter comprises a substrate composed of a substance for transmitting light in the specific wavelength range, and a multi-ple layer evaporation substance film formed on the substrate, being composed of substance of high transmissiblity for transmit-ting light at wavelength in the specific wavelength range. And the apical thickness of the multiple layer evaporation substance film is composed so as to change continuously along a specific direction of the substrate, and the wavelength of the transmis-sion light is changed by varying the incident position of light to the optical filter along the specific direction of the sub--' - :
~ ' _ ' . -. , .
: ::: ; ., ; .
.. >: . . ';: d .. .. '.: ,, , . . :
..,j- ~
I
., y '.. . ,'. ~ ;. v ... ' ~ '.
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' .
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. . ~ . . ~ ;r' . . '..
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. . . ~, ' .. ' . n ~..
Y
strata.
In the invention, by varying the light irradiation posi-tion linearly without changing the inclination of the optical filter, the transmission wavelength can be changed continuously.
The transmission wavelength differs only with the incident posi-tion, and the transmissiblity is not changed by the polarization states so that the same transmissiblity may be obtained in P wave and S wave. Furthermore, the full width at half maximum, the selective characteristic of the light is not changed depending on the light incident position, but remains at a specific value, which is an excellent effect. That is, not depending on the plane of polarization, the full width at half maximum and light transmissiblity are kept constant, and only the wavelength can be changed continuously.
Brief Description of the Drawings Fig. 1 (a) is a sectional view showing the constitution of a variable wavelength type interference optical filter in single cavity structure according to a first embodiment of the invention, Fig. 1 (b) is a graph showing the change of transmis-siblity on the x-axis, and Fig. 1 (c) is a magnified sectional view of a circular part of FIG.1 (a).
Fig. 2 is a graph showing the changes of transmission wavelength, full width at half maximum, and transmissiblity, relative to the incident position of the embodiment.
Fig. 3 is a graph showing the selective characteristic of -~113'~~~~
the wavelength relative to the number of cavity layers.
Fig. 4 is a schematic diagram showing the state of use of variable wavelength type interference optical filter according to the embodiment.
Fig. 5 (a) is a sectional view showing the constitution of a wavelength variable type interference optical filter according to a second embodiment of the invention, Fig. 5 (b) is its front view, and Fig. 5 (c) is a graph showing the changes of its transmissibility.
Fig. 6 is a graph showing the changes of transmission wavelength, full width at half maximum and transmissiblity rela-tive to the rotational angle of the variable wavelength type interference optical filter according to the second embodiment of the invention.
Fig. 7 is a schematic diagram showing a state of use of the variable wavelength type interference optical filter accord-ing to the second embodiment of the invention.
Fig. 8 (a) is a front view showing a combined state of two circular optical filters according to the second embodiment, and Fig. 8 (b) is a front view showing an example of use composed by adhering four different variable wavelength type interference optical filters.
rotary dome.
Fig. 10 is a schematic diagram showing a state of use when varying the transmission wavelength in the conventional interference filter.
Fig. 11 is a graph showing changes of wavelength relative to the incident light angle of the conventional interference filter.
Fig. 12 is a graph showing changes of full width at half maximum by varying the incident angle in the conventional inter-ference filter.
Detailed Description of the Preferred Embodiments Fig. 1 is the diagram showing the constitution of the variable wavelength type interference optical filter of polariza-tion states independent type according to the first embodiment of the invention. The variable wavelength type interference optical filter 1 in the embodiment is composed by evaporating multiple layers on a substrate 2 such as glass and silicon. The substrate 2 is composed of a material high in the transmissiblity of light in the range of the wavelength to be used, and a dielectric material or a semiconductor may be used. In the embodiment, quartz glass is used. Above the substrate 2, a dielectric mate-rial high in transmissiblity of light at the wavelength to be used, a semiconductor, and other substances are formed in multi-ple layers by evaporation to form a multiple layer film 3.
Herein, the multiple layer film 3 is composed of, as shown in the s:
~113'~u drawing, a lower multiple layer film 31, a cavity layer 32, and an upper multiple layer film 33. On the lower surface of the substrate 2, an anti-reflection film 4 is formed by evaporation.
The anti-reflection film 4 is, for example, a two-layer film of Si02 and Ti02, but either one may be used.
Herein, the substance used as evaporation material for the multiple layer film 3 and the anti-reflection film 4 is, for example, Sip2 (refractive index n = 1.46), Ti02 (n = 2.15), Si (n - 3.46), A12(33, Si2N4, MgF, etc. In this embodiment, the multi-ple layer films 31 and 33 are formed by alternately laminating and evaporating a low refractive film and a high refractive film.
The film thickness d, transmission wavelength ~,, and refractive index n are defined in the following formula.
~.=4nd ~ ~ ~ ( 1 ) That is, the optical thickness of each layer of the lower and upper multiple layer 31 and 33 is ~,/4. The cavity layer 32 is composed of the low or high refractive film same as that of the lower and upper multiple layers 31 and 33, and the thickness of the cavity layer do is two times of that of the low or high relative film of the multiple layer 31 and 33, namely ~,=2ndc. By alternately laminating the low refractive film and high refrac-tive film in this way, the full width at half maximum (F.W.H.M.) of the peak of transmissiblity is lowered.
~11.~'~~~~
1 according to the embodiment, having the relation of the trans-mission wavelength and film thickness as shown in the formula (1), is composed with the substrate 2 which is a slender plate, and the optical thickness of the multiple layer film 3 is varied continuously to differ the transmission wavelength ~,. The trans-mission wavelength of the variable wavelength type interference optical filter 1 is set at ~,a to ~,C ( ~,a < ~,c ) , corresponding to the incident position x of the light, and the transmission wave-length of the position at its central position (x = xb) is ~,b.
The upper and lower multiple layer films 31, 33 are composed by alternately laminating a first evaporation substance film with first refractive index nl, and a second evaporation substance film with lower second refractive index n2. That is, As the circular part of Fig. 1 (a) is shown in a magnified view in Fig.
1 (c), the film thickness of the individual multiple layer films is changed continuously. In Fig. 1 (c), the low refractive film of the lower multiple layer film 31 is supposed to be 31L, the high refractive film to be 31H, the high refractive film of the upper multiple layer film 33 to be 33H, and the low refractive film to be 33L. Relative to the transmission wavelength ~,a at the end xa on the x-axis of the interference optical filter 1 in Fig. 1 (a), it is set so that formula (1) may be established in the low refractive film and high refractive film, respectively.
Similarly, relative to the transmission wavelengths ~,b, ~,C at positions xb, xc, the film thickness is set so that formula (1) may be established at individual wavelengths ~.b, ~.c. The film _ g -' .
~ _ .
.
.. : ' ' ~ . .
.' .. ! ~ . ~
SI
' .~,. . : ~.. , :. . ;: ..
r ... '.~' .. : f . .. '' :.. . ~,. ~ ':
~
thickness between them is also set so that the wavelength may change linearly. Therefore, each film thickness of the multiple layer film 3 changes continuously from position xa to xc on the x-axis, and the film thickness increases toward the positive direction of the x-axis.
For example, supposing ~,a to be 1540 nm, ~,c to be 1560 nm, and ~.b to be 1550 nm, by alternately laminating T102 of which first refractive index (high refractive index) nl is 2.15, and Si02 of which second refractive index (low refractive index) n2 is 1.46, the upper and lower low refractive films 31L, 33L have the film thickness d of 263.7 nm at the left end (x = xa), and film thickness of 267.1 nm at the right end (x = xc). The film thickness of the upper and lower high refractive films 31H, 33H
is 179.1 nm at x = xa, and 181.4 nm at x = xc. If using Si of which refractive index n is 3.46 as high refractive films 31H, 33H, the film thickness of high refractive films 31H, 33H is 111.7 nm at x = xa and 112.7 nm at x = xc.
Herein, the change of the film thickness in the x-axis direction is expressed by the function of x, d(x), the wavelength ~. by the function of x, 7~(x), and the refractive index is the variable of x, n(x), and hence their relation is expressed in formulas (2), (3), where x0 is an arbitrary position, for exam-ple, position of x = xa, and A is a constant.
7~(x)=4n(x)d(x) ~~~ (2) _ 9 2~13'~~t~
~,l,x)=~(x0)+EA(x-xB)k ... (3) k=1 In this embodiment, the optical thickness is controlled by controlling the film thickness of the upper and lower multiple layer films 31, 33 and the cavity layer 32. But it is also possi-ble to compose an optical filter by varying the refractive index along the x-axis direction of the substrate while the film thick-ness is unchanged. It is not necessary to change the optical thickness continuously on a straight line, but the film thickness or optical thickness such as refractive index may be varied along an arbitrary line of the substrate.
In a filter of single cavity structure with center wave-length of 1550 nm, by alternately laminating Si02 as low refrac-tive films 31L, 33L, and Ti02 as high refractive films 31H, 33H
on the substrate 2 of quartz glass, when 32 or more layers are formed by laminating upper and lower multiple layer films 31 and 33, a narrow band filter with full width at half. maximum (F.W.H.M.) of 1 nm is formed. Or, in a filter of single cavity structure by laminating Si02 and Si on. the substrate 2 of quartz ~",.. glass, when the upper and the lower multiple layer films 31 and 33 are combined to laminate 24 layers, a narrow band filter with full width at half maximum of l nm is realized. Thus, the great er the difference in the refractive index between the high re >, fractive film and low refractive film, a narrow band filter is realized by the smaller number of layers.
~11~'~~~~
Fig. 2 shows changes of transmission wavelength ~, rela-tive to the incident position x of light in the variable wave-length type interference optical filter in the embodiment, and changes of full width at half maximum, and transmissibility. If composed to vary linearly the transmission wavelength ~, by chang-ing the incident position x in formula (2), the half width at half maximum and transmissiblity do not change corresponding to the position of the x-axis, but it shows a state of constant value. There is also no difference in the polarization states of incident light, and a narrow band optical filter not depending on the polarization states is realized.
The foregoing embodiment relates to the variable wavelength type interference optical filter of single cavity structure, but a filter may be also composed in a mufti-cavity structure by using plural cavity layers. For example, another cavity layer may be formed on the upper multiple layer film 33 in the single cavity structure of the embodiment, and another multi-ple layer film may be formed thereon to compose a variable wave-length type interference optical filter of double cavity struc-ture. In this case, as shown in Fig. 3, the selectivity of the wavelength can be enhanced even by decreasing the number of films of the multiple layer film. In the diagram, m shows the changes of the number of cavities and wavelength selective characteris-tics in the case of using multiple layer films of the same num-ber. As clear from the diagram, the greater the number of cavi-ties, the higher becomes the wavelength selective characteristic.
In such variable wavelength type interference optical filter 1, as shown in Fig. 4, by emitting light, for example, white light to one end of the optical filter 1, it is used to separate the spectrum components of the desired wavelength. In Fig. 4, by emitting light to the interference optical filter 1 through an optical fiber 11 and a collimating lens 12, the light transmitted through a focusing lens 13 and an optical fiber 14 is received. By moving the optical filter ~. in the direction of x-axis, the selected wavelength A is varied. As shown in the drawing, by slightly inclining the variable wavelength type interference optical filter 1, the light reflected by the front face of the interfErence optical filter 1 will not be directly reflected to the light source side, and adverse effects on the light source side can be avoided. This inclination angle should be out of polarization dependent range, for example, 10° or less.
In the embodiment, the filter is a rectangular plate filter, but a circular filter may be also composed. Fig. 5 shows a disk-shaped variable wavelength type interference optical filter 41 forming a multiple layer film 43 and an anti-reflection film 44 on a disk-shaped substrate 42. In this case, too, in proportion to the position of the x-axis direction in Fig. 5, it is composed so that each film thickness changes continuously.
Thus, as shown in Fig. 6 (a) to (c), the transmission wavelength is proportional to cos A, expressing the position in the relation of angle A centered on the origin of the x-axis. Therefore, when the circular filter 41 is rotated, it changes continuously as ~
'~
~
.
~
~~' ' ~.i ,.
' . .y 1 . ' ' : . ~.. , ..
~ . ; .
. . , ., .
.
: ' r '.. . a ~..
!
. ..
i .
~ ." ., , . . ', . ' : . . . .
~ t . , 4~ ,. , .
, . . .
. . .
2113'~~~
shown in the diagram. In this case, too, same as in the forego-ing embodiment, the full width at half maximum and transmissibli-ty are constant, regardless of the rotational angle (cos 0 or 0).
Fig. 7 is a perspective view showing the state of use of such circular variable waveleng~h type interference optical filter. In the diagram, same as in the example of use in Fig. 4, the light entering through the optical fiber 11 is put into the interference optical filter 41 as parallel light through the collimating lens 12. The transmitted light is received by the optical fiber 14 through the focusing lens 13. Herein, the interference optical filter 41 is rotated in the direction of arrow by rotating means not shown herein, for example, a motor, a crank type knob and a reduction gear, or the like. As a result, the wavelength is selected depending on the angle of rotation.
In this case, the wavelength linearized in proportion to cos 8, not rotational angle 8, is selected. Therefore, by preliminarily measuring the angle of rotation and selective wavelength, a desired wavelength can be selected.
In this way, by forming the variable wavelength type interference optical filter in a disk form, and continuously varying the thickness of the multiple layer film 43 by the posi-tion in the x-axis direction as shown in Fig. a (a), the wave-length range.can be selected.by rotating the optical filter by a half circle, that is, in a range of 180°. Therefore, the other optical filter can be composed by gluing together two semicircu-lar variable wavelength type interference optical filters ~lA and 41B differing in the selective wavelength range as shown in Fig.
8 (a). In this case, by mutually varying the selective wave-length, a wavelength selective characteristic in a wide range is achieved. Or, as shown in Fig. 8 (b), it is also possible to composed by using a further multiplicity of variable wavelength type interference optical filters 41A to 41D.
In the circular variable wavelength type interference optical filter, the film thickness of the multiple layer evapo-rated substance film is changed continuously by the position in the x-axis direction, but it is also possible to compose to vary the film thickness continuously corresponding to the angle 0. In this case, the wavelength characteristic depending on the rota-tional angle 8 is obtained.
A manufacturing method of filters shown in the embodiments is described below. In the embodiments, the film thickness of the multiple layer film 3 of the filter 1 must be changed continuously depending on the position of the x=axis.
The manufacturing method for composing the filter having such film thickness is described below while referring to Fig. 9. In Fig. 9 (a), a vacuum vessel 51 for vacuum evaporation contains an evaporation substance 52 as evaporation source such as Si02, Ti02 or Si in the foregoing embodiments in its bottom. In the upper part of the vacuum vessel 51, a parabolic rotary dome 53,opened in the lower side is provided. The rotary dome 53 is rotated at a constant speed in the direction of arrow. A circular substrate 2 is glued to a specific radial position of its inner surface.
f This substrate 2 is not mounted along the inner surface of the rotary dome 53, but is disposed at an inclination of a spe-cific angle a from the inner surface of the rotary dome 53 as shown in Fig. 9 (b). Furthermore, to make the film thickness uniform, the evaporation substance 52 is disposed in the center of the vacuum vessel 51, but in this embodiment its position is at a remote place from the center at a specific distance L.
Thus, the film thickness can be controlled by an evaporation temperature or evaporation time, and moreover by properly setting the angle a and position L of the substance 52, the film thick-ness change can be controlled. Thus, the high refractive film and the low refractive film are evaporated alternately. In this way, the distance from the evaporation substance 52 varies con-tinuously depending on the vertical direction position (x-axis) of the substrate as shown in Fig. 1, and therefore the film thickness changes continuously corresponding to the distance of the evaporation source or the like, by evaporation for a specific time. By sequentially changing over the evaporation substance 52 to Si02, Ti02, etc. in this way, a filter possessing evaporation substances in multiple layer film is composed. In this case, directly, the circular variable wavelength type interference optical filter can be composed as shown in Fig. 5, and by cutting off in a rectangular form along the x-axis in Fig. 5, a variable wavelength type interference optical filter in a rectangular plate form shown in the first embodiment can be constituted.
In this embodiment, the desired film thickness is 211~'~~~~
obtained by mounting the substrate on the inner surface of the rotary dome 53, but when the substrate is disposed at a specific inclination angle from the same film thickness surface equal in the distance from the substance as the evaporation source, it is possible to constitute by sequentially laminating and evaporating evaporation substances of high refractive index and low refrac-Live index. In this case, the film thickness distribution can be controlled by varying the inclination angle a and distance from the evaporation source.
Also in this embodiment, the substrate is mounted on the rotary dome 53 at the inclination, and the evaporation source 52 is located at the position remote from the center of the vacuum vessel 51 by the specific distance L, but it may be achieved only by either inclining the substrate when mounting, or by locating the evaporation substance 52 away from the center of the vacuum vessel 51 by a specific distance L. In this case, too, by prop-erly setting either the inclination angle a or the distance L
from the evaporation source, the film thickness distribution can be controlled.
Claims (6)
1. A variable wavelength and band-pass type interference optical filter of polarization plane independent type for continuously varying the wavelength of transmission light in a specific wavelength range, comprising:
a substrate composed of a substance which transmits light in said specific wavelength range; and a multiple layer evaporation substance film formed on said substrate, being composed of substance of high transmissibility for transmitting light at wavelength in said specific wavelength range;
wherein said multiple layer evaporation substance film is composed by alternately laminating first evaporation substance films of a first refractive index, and second evaporation substance films of a second refractive index, which is lower than said first refractive index, and by inserting at least one cavity layer, and the optical thickness nd of said first and second evaporation substance films respectively changes continuously in the relation of .lambda. = 4nd, and the optical thickness nd of said cavity layer changes continuously in the relation of .lambda.= 2nd, where n is the refractive indices each of said first and second evaporation films and said cavity layer, d is the thickness of each of said first and second evaporation films and said cavity layer, and .lambda., is the transmission wavelength at the incident position, by changing said refractive indices n(x) of said first and second evaporation substance films and cavity layer at the position of x, in a manner to change continuously along a specific direction of said substrate, and said wavelength of the transmission light is changed by varying the incident position of light to said optical filter along the specific direction of said substrate.
a substrate composed of a substance which transmits light in said specific wavelength range; and a multiple layer evaporation substance film formed on said substrate, being composed of substance of high transmissibility for transmitting light at wavelength in said specific wavelength range;
wherein said multiple layer evaporation substance film is composed by alternately laminating first evaporation substance films of a first refractive index, and second evaporation substance films of a second refractive index, which is lower than said first refractive index, and by inserting at least one cavity layer, and the optical thickness nd of said first and second evaporation substance films respectively changes continuously in the relation of .lambda. = 4nd, and the optical thickness nd of said cavity layer changes continuously in the relation of .lambda.= 2nd, where n is the refractive indices each of said first and second evaporation films and said cavity layer, d is the thickness of each of said first and second evaporation films and said cavity layer, and .lambda., is the transmission wavelength at the incident position, by changing said refractive indices n(x) of said first and second evaporation substance films and cavity layer at the position of x, in a manner to change continuously along a specific direction of said substrate, and said wavelength of the transmission light is changed by varying the incident position of light to said optical filter along the specific direction of said substrate.
2, A variable wavelength type interference optical filter of claim 1, wherein for each position of said substrate in the specific direction to be x, and the transmission center wavelength at that position to be .lambda.(x), the film thickness d(x) of said first and second evaporation substance films and the refractive index n(x) of said first and second evaporation substance films refractively satisfy the following formulas, .lambda.(x) = 4n(x) d(x) ~
.lambda.(x) = .lambda.(x0)+ .SIGMA. A (x-x0)k K=1 where A is constant, and film thickness d(x) of said cavity layer satisfy the following formulas .lambda.(x) = 2n(x) d(x) ~
.lambda.(x) = .lambda.(x0)+ .SIGMA. A (x-x0)k k=1.
.lambda.(x) = .lambda.(x0)+ .SIGMA. A (x-x0)k K=1 where A is constant, and film thickness d(x) of said cavity layer satisfy the following formulas .lambda.(x) = 2n(x) d(x) ~
.lambda.(x) = .lambda.(x0)+ .SIGMA. A (x-x0)k k=1.
3. A variable wavelength type interference optical filter of claim 1, wherein said substrate is a rectangular plate substrate, and the position in its longitudinal direction is x, and the optical thickness of said evaporation substance film is changed continuously along the longitudinal direction.
4. A manufacturing method of variable wavelength type interference optical filter comprising the steps of:
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, at an inclination of a specific angle from the inner surface of said dome, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed, disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at a specific distance remote from the rotation center axis of said rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, at an inclination of a specific angle from the inner surface of said dome, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed, disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at a specific distance remote from the rotation center axis of said rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
5. A manufacturing method of variable wavelength type interference optical filter comprising the steps of:
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed;
disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at a specific distance remote from the rotation center axis of said rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed;
disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at a specific distance remote from the rotation center axis of said rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
6. A manufacturing method of variable wavelength type interference optical filter comprising the steps of:
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, at an inclination of a specific angle from the inner surface of said dome, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed;
disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at said rotation center axis of the rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
disposing a substrate in a vacuum vessel, on an inner surface of a rotary dome opened at one side, at an inclination of a specific angle from the inner surface of said dome, said substrate being composed of a substance for transmitting light in a specific wavelength range;
rotating said rotary dome along a center axis of said rotary dome at a specific speed;
disposing a first evaporation source with a first refractive index n1 and a second evaporation source with a second refractive index n2, which is lower than said first refractive index n1, in said vacuum vessel at said rotation center axis of the rotary dome; and evaporating said evaporation sources alternately to evaporate until obtaining a specific film thickness distribution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2631493A JPH06265722A (en) | 1993-01-20 | 1993-01-20 | Wavelength variable type interference optical filter and its production and wavelength variable type interference optical filter device |
| JPHEI5-26314 | 1993-01-20 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2113794A1 CA2113794A1 (en) | 1994-07-21 |
| CA2113794C true CA2113794C (en) | 1999-09-21 |
Family
ID=12189922
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2113794 Expired - Fee Related CA2113794C (en) | 1993-01-20 | 1994-01-19 | Interference filter and method of making the same |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH06265722A (en) |
| CA (1) | CA2113794C (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH09293267A (en) * | 1996-04-23 | 1997-11-11 | Minebea Co Ltd | Recording and reproducing device |
| US6112005A (en) * | 1997-11-12 | 2000-08-29 | Alliance Fiber Optics Products, Inc. | Filter device for use with light and method making the same |
| JP2001111488A (en) * | 1999-10-01 | 2001-04-20 | Nippon Telegr & Teleph Corp <Ntt> | Device for branching wdm signal |
| JP2005043755A (en) * | 2003-07-24 | 2005-02-17 | Seiko Epson Corp | Optical multilayer filter, manufacturing method therefor, optical low-pass filter, and electronic equipment system |
| CN100385264C (en) * | 2004-11-05 | 2008-04-30 | 中国科学院上海技术物理研究所 | Integrated narrow-band filter |
| JP4760011B2 (en) * | 2004-12-24 | 2011-08-31 | セイコーエプソン株式会社 | Optical member |
| US8441710B2 (en) * | 2010-01-08 | 2013-05-14 | Semrock, Inc. | Tunable thin-film filter |
| KR20210094100A (en) * | 2018-12-17 | 2021-07-28 | 어플라이드 머티어리얼스, 인코포레이티드 | Back coating for transparent substrates |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54141149A (en) * | 1978-04-24 | 1979-11-02 | Nec Corp | Interference filter |
| JPS5945406A (en) * | 1982-09-08 | 1984-03-14 | Ulvac Corp | Optical filter |
| JPS5972861A (en) * | 1982-10-19 | 1984-04-24 | Canon Inc | Picture reader |
| JPS62141508A (en) * | 1985-12-16 | 1987-06-25 | Toshiba Corp | Optical parts |
| JPS62164003A (en) * | 1986-01-14 | 1987-07-20 | Toshiba Corp | Optical parts |
| JPS6424202A (en) * | 1987-07-21 | 1989-01-26 | Brother Ind Ltd | Color separation device |
| JPH04233501A (en) * | 1990-12-28 | 1992-08-21 | Fujitsu Ltd | Wavelength filter for projection type display device and its manufacturing device |
| JPH055806A (en) * | 1991-06-27 | 1993-01-14 | Mitsubishi Cable Ind Ltd | Signal light transmission filter module for optical fiber amplifier |
| JPH055805A (en) * | 1991-06-27 | 1993-01-14 | Mitsubishi Cable Ind Ltd | Wavelength variable filter module |
| JP4126201B2 (en) * | 2002-06-04 | 2008-07-30 | アサヒビール株式会社 | Wrap round case |
-
1993
- 1993-01-20 JP JP2631493A patent/JPH06265722A/en active Pending
-
1994
- 1994-01-19 CA CA 2113794 patent/CA2113794C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2113794A1 (en) | 1994-07-21 |
| JPH06265722A (en) | 1994-09-22 |
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