JPH02296205A - Multiplexing/demultiplexing element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a multiplexing/demultiplexing element used in optical communications such as wavelength division multiplexing communications or optical information recording/reproducing devices.

BACKGROUND TECHNOLOGY Although optical communication has become increasingly important in recent years, it is still difficult to say that it has become widespread. This is because optical components are not cheap enough to be compared with electronic components. For example, if LEDs could be used for wavelength division multiplexing communications, it would be possible to reduce their cost and increase their popularity, but in reality, there is no excellent multiplexing/demultiplexing element, making it impossible to use jEDs for wavelength division multiplexing communications.

That is, as an example of a multiplexing/demultiplexing element, there is one using a transmission type diffraction grating as shown in Japanese Patent Application Laid-Open No. 54-5454. More specifically, it consists of a transmission-type hologram that records the interference fringes of two diverging lights, an optical fiber whose end is installed on one side of the hologram, and an optical fiber installed on the other side of the hologram. and two or more optical input/output elements. In this case, one diffraction grating is used.

Problems to be Solved by the Invention In such a configuration, in order to increase the diffraction efficiency, it is necessary to reduce the grating pitch to achieve Bragg diffraction, and to make the depth equal to the pitch. Then,
When splitting broadband light such as LED light, the spot diameter becomes larger than the optical fiber diameter because the pitch is large.

As a result, the coupling loss increases, and there is no point in increasing the diffraction efficiency of the diffraction grating. On the other hand, if the grating pitch is made smaller, although the coupling loss becomes smaller, the diffraction efficiency becomes smaller, so the 11p loss of the entire demultiplexing element ends up increasing. Things like this +
i! 7, even if the diffraction grating described in the above-mentioned publication is also provided with a lens function, there is no difference in terms of wood quality.

That is, the conventional devices do not have both high efficiency and low angular dispersion function, and cannot combine or demultiplex broadband lights such as I and ED lights.

Means to solve the problem The lattice constant of the diffraction grating on the input horn side is 1, the lattice constant of the diffraction grating on the output side is K2, and the angle between the two diffraction gratings is Δθ'
, the diffraction angle by the input-side diffraction grating is O12, and the diffraction angle by the output-side diffraction grating is Oo. It was placed on the optical path for multiplexing or demultiplexing.

Furthermore, the grating constant of the input or output side diffraction grating is 1, the input angle to the diffraction grating is O1, the propagation constant is kB,
At least one diffraction grating was disposed so that each dimension satisfied the following expressions: Δ=, −, and 5 inOi−kB≧0.

Effect If the specifications such as the lattice constant of a double diffraction grating made of at least one pair of diffraction gratings satisfy the above formula, the angular dispersion of wavelength will be small, so such a double diffraction grating etc. By doing so, multiplexing or demultiplexing with both high efficiency and low angular dispersion function becomes possible, and it can also be used for broadband light such as LED light.

Furthermore, by arranging at least one diffraction grating having the specifications as in the second aspect of the invention, an even wider band can be achieved.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 4. The multiplexing/demultiplexing element 1 of this embodiment shown in FIG. 2 has, for example, different wavelengths ^1. It is arranged between an input fiber 2 that outputs input light of λ2 and output fibers 3a and 3b that receive the separated light of wavelengths λ, , λ2. This multiplexing/demultiplexing element 1 has a collimating lens 4, a diffraction grating 5, and a condensing lens 6 arranged in this order from the input fiber 2 side, and the diffraction grating 5 is particularly distinctive.

This diffraction grating 5 has two diffraction gratings 5a and 5b on both sides of the substrate.
It is configured as a transmission type double diffraction grating comprising: These diffraction gratings 5a and 5b are formed so that their grating planes and grating directions are parallel to each other so that their diffraction characteristics are relatively different, but their pitches A, , A are formed in a predetermined relationship. ing. This condition will be explained with reference to the diffraction diagram of the double diffraction grating 5 shown in FIG. Here, the lattice constant of the diffraction grating 5a on the input side is 1, and the output J
The grating constant of the side diffraction grating 5b is K2, and the two diffraction gratings 5
The angle formed by a and 5b is ΔO', the incident angle to the input side diffraction grating 5a is f9i, its diffraction angle is O12, and the diffraction angle by the output side diffraction grating 5b is e.

shall be. Also, the propagation constant. shall be. Then... s
inθi+. 5inOi'=K...
・・・・・・・・・・・・(1). 5in(Oi'-
△0')+. 5in((3o+ΔO')-K.

・・・・・・・・・・・・・・・・・・(2) The following relationship holds true. Solving these equations (1) and (2), 0i' == 5in-(-!L-sinOi)
--To (3).

θ0--Δθ'+5in-' [Tile-(-!Ni-5i
n e 1) cosΔO′. To.

becomes. Therefore, the angular dispersion due to wavelength change can be expressed as O1
'Oo, then 01'-21n. cosQi' ・・・・・・・・・・・・・・・・・・・・・・・・
(6) becomes. However, no is the central refractive index of the diffraction grating. Further, the angles θi' and OO are determined by the above equations (3) and (4).

Here, the fact that the double diffraction grating 5 has a lower angular dispersion than that of only one diffraction grating means that θi'〉OO, so based on equations (5) and (6), the following relational expression is satisfied. , K, and ΔO' are set for each dimension so that. Note that the pitch A1°A2 is 1A, A1=2π/,
=2π/.

Since the multiplexing/demultiplexing element 1 with such a double diffraction grating 5 and high efficiency and low angular dispersion is used, even wideband light such as LED light can be efficiently demultiplexed, and wideband light can be demultiplexed efficiently. The spot diameter does not significantly expand due to

By the way, we will explain how effective it actually is numerically. Now, ignoring the diameter of input fiber 2, 1
It is assumed that a diffraction grating with only one sheet and a two-sheet diffraction grating according to the present embodiment are used, and each value is set as shown in Table 1.

Table 1: Diffraction grating 5a with single set pitch and 1.2 μm pitch
, 5b and 1μ
This is a comparison with the case where a single diffraction grating with only m pitches is used. As a result, the results shown in Table 2 were obtained.

Table 2 Here, the splitting efficiency is the efficiency with which light of each wavelength is diffracted as primary light, and is calculated using S-polarized light, assuming that there is almost no polarization dependence.

The spot diameter is the diameter when the LED light is focused by the condenser lens 6 having a focal length ffl of 10 mm.

In the above results, the noteworthy point is the difference in spot diameter. Now, assuming that the diameter of the input fiber 2 is 200 μm, on the output side, the double diffraction grating 5 of this embodiment has a diameter of 270 μm, and the conventional single grating has a diameter of 64.0 μm. . Therefore, the diameter of the output fiber 3 is set to 2
If the coupling efficiency is simply compared by the ratio of the fiber diameter to the spot diameter, the coupling efficiency of this example method is 2.
~3 times better. This can be said to be an advantageous effect even if the fact that the demultiplexing factor is somewhat inferior is taken into account.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, only the double diffraction grating 7 is shown. In comparison with the double diffraction grating 5 of the embodiment, two diffraction gratings 7a,
The pitch of the diffraction gratings 7b is the same, but by using a wedge-shaped substrate instead of a parallel substrate or plate, the grating planes of the diffraction gratings 7a and 7b are tilted to be non-parallel to each other, thereby creating two diffraction gratings 7a.

7b with relatively different diffraction characteristics.

In this case as well, each dimension of the diffraction grating is set to satisfy the above-mentioned equation (7) (the same applies to the following embodiments), and the same effects as in the above embodiments can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the double diffraction grating 8 itself, which includes the diffraction gratings 8a and 8b, also has a lens function (convergence performance), and by making it serve both as a collimating lens and a condensing lens, the collimating lens 4 and the condensing lens are combined. This eliminates the need for a separate optical component called the lens 6. That is, the multiplexing/demultiplexing element I of this embodiment is composed of one optical component, which is a double diffraction grating 8 including diffraction gratings 8a and 8b.

Furthermore, a fourth embodiment of the present invention will be explained with reference to FIG. In this embodiment, a diffraction grating 10, a collimating lens 11, and a condensing lens 1 are placed on the same substrate 9 using a thick film waveguide structure.
This is an integral structure of 2 and 2. That is, the collimating lens 11 has a waveguide-type cylindrical lens configuration, that is, two-stage waveguide-type collimating lenses Ila and Ilb, and the condenser lens 12 has a cylindrical lens configuration, that is, a two-stage waveguide-type collimating lens 12a. ,
Consisting of 12b. And the waveguide type collimating lens l
A transmission type diffraction grating 10a is provided on the opposite end surfaces of lb and 12a, respectively.
, 10b to form a double diffraction grating 10. Here, the diffraction gratings 10a, 1ob may be of the diffraction gratings 5a, 5b type, or of the diffraction gratings 7a, 7b type. With such a waveguide configuration, light is confined in a direction perpendicular to the surface of the substrate 9 and is demultiplexed in the same manner as in the embodiment described above.

According to this embodiment, the optical elements constituting the multiplexing/demultiplexing element 1 are integrally manufactured on the same substrate 9, so if it is to be duplicated, a mold is made and thermosetting resin and electromagnetic wave hardening material are used. It can be easily reproduced using resin or the like.

Note that the two diffraction gratings constituting the double diffraction grating are not limited to the above-mentioned combination, and even if the grating pitches are different, the grating planes may not be parallel to each other.

In short, it is only necessary to form the diffraction characteristic so that it satisfies the expression (7) depending on the actual configuration of the multiplexing/demultiplexing element.

Further, a fifth embodiment of the present invention will be explained with reference to FIG.

In the embodiment described above, the double diffraction grating was explained as a transmission type, but in this embodiment, two reflection type diffraction gratings 13 are used.
A double diffraction grating 13 consisting of a and 13b is used.

Note that even in such a reflective configuration, the structure, operation, etc. are similar to those of the transmissive configuration.

Furthermore, in these embodiments, the multiplexing function can be achieved by switching the directions of the input and output sides.

Next, a sixth embodiment of the present invention will be described with reference to FIGS. 8 and 9. The multiplexing/demultiplexing element 14 of this embodiment is also arranged between the input fiber 2 and the output fibers 3a and 3b, and in this embodiment, it consists of a condensing lens 15 and a diffraction grating 16 located on the input side. Here, this diffraction grating 16 is constructed as a transmission type double diffraction grating having two diffraction gratings 16a and 16b on both sides of the substrate.

According to the above-mentioned equations (1) and (2), it is also possible to set this deflection angle to O. In this case, the exit angle is the same for each wavelength, but as shown in FIG. 9, each light beam moves in parallel for each wavelength, and in this case as well, it is possible to separate the beams. That is, at this time, the broadband property can be ignored.

In this way, also in this embodiment, the number of wavelengths to be demultiplexed increases, and the degree of multiplexing of wavelength division multiplexing communication can be increased. In particular, since broadband light such as LEDs is also targeted,
This will further contribute to the construction of an inexpensive multiplex communication system. Furthermore, in comparison with the above-mentioned embodiments 1 to 5, the broadband nature of the wavelength of light has only a very slight influence in principle, so efficiency can be further improved, and the optical lens (The condensing lens 15 may be used only on the input side and only on the output side.) There is no need to provide two parts like the lenses 4 and 6. Therefore, it is also small, and the multiplexing/demultiplexing element 14
However, the stability can be increased, and the assembly and adjustment can be made easier.

Furthermore, a seventh embodiment of the present invention will be explained with reference to FIG. In this embodiment, as in the fourth embodiment, a diffraction grating 18 and a condensing lens 19 are integrally formed on the same substrate 17 using a thick film waveguide structure. That is,
The condensing lens 19 has a waveguide type cylindrical lens configuration, that is, two stages of waveguide type collimating lenses 19a, 19.
Consists of b. And the waveguide type collimating lens 19b
A transmission type diffraction grating 18 is provided on the opposite end face of the waveguide 20 and the waveguide 20, respectively.
a and 18b are formed to form a double diffraction grating 18. Here, the diffraction gratings 18a, 18b are the diffraction gratings 16a, 16
Type b is sufficient. With such a waveguide configuration, light is confined in a direction perpendicular to the surface of the substrate 17 and is demultiplexed as in the sixth embodiment.

According to this embodiment, the optical elements constituting the multiplexing/demultiplexing element 14 are integrally manufactured on the same substrate 17. Therefore, in case of duplication, a mold is made and thermosetting resin and electromagnetic wave hardening material are used. It can be easily reproduced using resin or the like.

Next, a fourth embodiment of the present invention is shown in FIGS. 11 to 16.
This will be explained using figures. This embodiment is a further modification of the first to fifth embodiments described above. First, according to the embodiments described above, it is possible to use a wideband multiplexing/demultiplexing element such as an LED. However, since both methods take diffracted light that has been diffracted twice, the light to be demultiplexed needs to have a somewhat similar wavelength, which limits the demultiplexing band. Focusing on this point, in this example, two diffraction gratings 2 as shown in FIG.
1a and 21b, that is, a diffraction grating structurally similar to that shown in the first to fifth embodiments (for example, a double diffraction grating 21 having )
The incoming combined light is split into light with a wavelength that can be diffracted twice and light with a wavelength that can be transmitted twice (it is reversible and is combined in the opposite direction). ) is a thing. A multiplexing/demultiplexing element 22 is constructed using such a double diffraction grating 21 as a main body, for example, in the same manner as in the case of FIG.

For example, when separating short wavelength light λ8 and long wavelength light λ as shown in FIG. 12, short wavelength light λ8 and long wavelength light λ are separated.

passes through the diffraction grating 21 and is converted into 2 by the diffraction gratings 21a and 21b.
The long wavelength light λ is diffracted and becomes λ5(1-1).

passes through the diffraction grating 21 and is converted into 2 by the diffraction gratings 21a and 21b.
λ1. (0-0).

This is achieved by combining the advantage of the double diffraction grating, which has small dispersion of diffraction angles, with the advantage of the micro-pitch 'j+'ll diffraction grating, which allows almost all long wavelength light to pass through. , has been achieved. That is, when the two are combined, it has a feature that the demultiplexing band is wide and the diffraction angle when demultiplexing broadband light such as LED light is small.

Now, FIG. 12 shows a diffraction diagram of the diffraction grating 21 of this example. First, as shown in the above embodiment, a certain light, that is, the light indicated by the propagation constant kA in FIG. 12, is diffracted twice by the diffraction gratings 21a and 21b. On the other hand, the other light, that is, the light indicated by the propagation constant kB, is made non-diffractive. In other words, light with a propagation constant of kB passes through the first diffraction grating 21a.
It is not diffracted by For this purpose, as shown in Fig. 13, Δ=, -kB-sinf91-, ≧0...
If the relationship (8) holds true, light with a propagation constant of 8 becomes completely non-diffractable. Here, as in the previous case, K1 is the grating constant of the first diffraction grating 21a, and 01 is the input angle.

If such a relationship is satisfied, light of a certain wavelength will be diffracted twice by the diffraction grating 21, and light of a certain wavelength will be transmitted twice, so that the output light will be as shown in FIG. will be demultiplexed.

For example, as shown in FIG. 14, short wavelength light λ,
1. The same applies to the case where multiplexed light consisting of a group of λSRI~, λ8n and a long wavelength light λ is demultiplexed, and a group of short wavelength lights λ, 1. λ82. ~． λ, n passes through the diffraction grating 21 and is diffracted (1-1) twice by the diffraction gratings 21a, 21b and is demultiplexed, and the long wavelength light λ, passes through the diffraction grating 21 and is transmitted twice by the diffraction gratings 21a, 21b. λL(0-0
) is separated from the diffracted output light group.

Further, even if the structure is not configured to satisfy the above formula, a similar demultiplexing effect can be obtained if the light whose propagation constant is 8 is significantly different from the Bragg condition.

Furthermore, if there are a plurality of lights that satisfy the above condition, each of the lights in one group passes through the diffraction grating 21 twice and then travels in the same direction. Therefore, these one group of multiplexed lights transmitted through the diffraction grating 21 may be newly demultiplexed using a separate demultiplexing element. At this time, after demultiplexing using the diffraction grating 21 of this embodiment, if the transmitted output light is mixed with light of a plurality of wavelengths, it is sufficient to perform further demultiplexing.

That is, such a demultiplexing step may be repeated as many times as necessary using a plurality of demultiplexing elements.

For example, as shown in FIG. 14, short wavelength light λ8.

^s2. ~． 1 group λsn and long wavelength light λL+1 ^
When demultiplexing multiplexed light consisting of one group of L2°~, λ, and n, two diffraction gratings 23 and 24 equivalent to the diffraction grating 21 may be used. That is, a group of short wavelength lights λ81. λ, 2. ~． λ and n are separated by passing through the diffraction grating 23 and diffracted twice (1-1) by the diffraction gratings 23a and 23b, while long wavelength light λL++ λL
One group of yl to 1 λLn is all transmitted as shown by (0-0) and separated from those on the short wavelength side. After this, a group of long wavelength lights λLll transmitted through the first diffraction grating 23
λLt+ to λLn may be separated by passing through the second diffraction grating 24 and being diffracted twice by the diffraction gratings 24a and 24b.

Now, as a specific example, the diffraction grating 2311 of human power (1!I)
0.5μ+n, 0.6μm at an input angle of 30° in air for the first diffraction grating 23 with a pitch of 0.611 m and a pitch of the output side diffraction grating 23b of 0.62pm.

0.7pm, 1.3pm, 1.41+m, 1. 5μm
Let us consider a case in which multiplexed light of six different wavelengths is manually generated. In this case, the light that is non-diffractive and satisfies the above equation is
1.3pm on the long wavelength side, 1.41+m, 1.
There are three types of light of 5 pm, and these wavelength lights are transmitted through the diffraction grating 23, and the other wavelengths are 0.511+n, 0.6
p.m.

Since the 0.7 μm light is diffracted twice, it is separated from the former. Then, it is necessary to separate the transmitted light again,
In this demultiplexing, the pitch of the diffraction grating 24a on the input side is 1.4 μm, and the pitch of the diffraction grating 24b on the output side is 1.4 μm.
If the second diffraction grating 24 of 5Bim is used, 1,31
The three types of light, Im, 1.4H+m, and 1.5 μm, are each diffracted twice and demultiplexed as in the above embodiment. In this way, the demultiplexing band is expanded and the multiplicity of optical communications etc. can be dramatically improved. In addition, in this example, each double diffraction grating is (7
) is formed to satisfy the conditions of the equation.

If this embodiment is generalized, if there are many more wavelength groups of light, the configuration as shown in FIG. 15 may be adopted in accordance with FIG. 14. That is, the required number of diffraction gratings 24A724N may be provided on the output side of the transmitted light group of the second diffraction grating 24.

If the function shown in FIG. 14 is to be implemented as a thick film waveguide type integrated structure according to FIG. 6, the structure may be configured as shown in FIG. 16. That is, in the configuration shown in FIG. 6, a part of the waveguide type collimating lens 12a is also extended to the optical path side of the light transmitted through the diffraction grating 10, and the condensing lens 25 is installed on the transmission output side of the waveguide type cylindrical lens. The lens structure is integrally composed of two stages of waveguide type collimating lenses 25a and 25b, and transmission type diffraction gratings 26a and 26b are formed on the opposing end surfaces of the waveguide type collimating lenses 12a and 25a, respectively, to achieve double polarization. This becomes a folded lattice 26. That is, this diffraction grating 26
corresponds to the diffraction grating 24, and the diffraction grating 10 corresponds to the diffraction grating 23.
corresponds to

Next, the ninth embodiment of the present invention is shown in FIGS. 17 and 18.
This will be explained using figures. In this embodiment, in order to achieve further miniaturization, two stages of diffraction gratings 27, 28 (or 23, 24) are arranged close to each other, so that the light split by the first diffraction grating 27 passes through the next diffraction grating 28. It is made to be transparent.

In this case as well, if we generalize this example, if there are many more wavelength groups of light, the
It can be configured as shown in the figure. That is, the second diffraction grating 28
The required number of diffraction gratings 28A to 28N (28N
(Only shown in the figure) should be provided.

Furthermore, an embodiment of the present invention will be explained with reference to FIG. In this embodiment, the double diffraction grating structure of the seventh to ninth embodiments is changed to two diffraction gratings 29a,
It is configured as a reflection type double diffraction grating 29 consisting of 29b. The structure itself may remain as shown in FIG. 7, or may be based on the idea of the second embodiment. In any case, some of the combined light is diffracted twice by the diffraction gratings 29a, 29b and output as in the case of FIG. 7, but some of the other light is output by the diffraction gratings 29a, 29. Reflected twice by b (
(corresponding to the above-mentioned transmission), and is output and separated from the former.

Note that in any of the embodiments, the demultiplexing function and the multiplexing function are relative, and if multiplexing is required, input and
All you have to do is replace the output side.

Effects of the Invention As described above, the present invention has the grating constant of the input side diffraction grating as 1, the grating constant of the output side diffraction grating as K2, the angle formed by the two diffraction gratings as Δθ', and the input side diffraction grating as K2. Let θi' be the diffraction angle by Since it is placed on the optical path where the above equation is satisfied, the angular dispersion of the wavelength will be small, achieving high efficiency and low angular dispersion of the wavelength that are impossible with only one diffraction grating. Therefore, even when dealing with broadband light such as LED light, it is possible to perform demultiplexing or multiplexing without expanding the spot diameter, and in particular, to increase the coupling efficiency with output fibers, etc. It is possible to achieve high efficiency as a whole,
Furthermore, as in the invention as claimed in claim 2, when the grating constant of the input side or output side diffraction grating is 1, the input angle to the diffraction grating θ1, and the propagation constant is kB, each dimension is , Δ=K −, by disposing at least one diffraction grating that is set to satisfy the following equation: sin θ1−kB≧0, it is possible to achieve an even wider band.

[Brief explanation of the drawing]

Fig. 1 is a vector diagram of a diffraction grating showing the first embodiment of the present invention, Fig. 2 is a schematic front view, Fig. 3 is a schematic front view showing an enlarged part of the diffraction grating, and Fig. 4 is a schematic front view showing a second embodiment of the invention, FIG. 5 is a schematic front view showing a third embodiment of the invention, and FIG. 6 is a schematic perspective view showing a fourth embodiment of the invention. , FIG. 7 is a schematic front view showing the fifth embodiment of the present invention, FIG. 8 is a schematic front view showing the sixth embodiment of the invention, and FIG. 9 is a schematic front view when the deflection angle is 0. FIG. 10 is a schematic perspective view of an example of an integrated configuration showing a seventh embodiment of the present invention;
FIG. 11 is a schematic front view showing a fourth embodiment of the present invention, FIG. 12 is a vector diagram, FIGS. 13 and 14 are schematic front views showing a multiplexing example, and FIG. 15 is a more generalized one. 16 is a schematic perspective view showing an example of an integrated configuration; FIG. 17 is a schematic front view showing a ninth embodiment of the present invention; FIG.
FIG. 8 is a generalized front view, and FIG. 19 is a schematic front view showing an embodiment of the present invention. 5a, 5b, 7a, 7b, 8a, 8b, 10a. Job, 13a, 13b, 16a, 16b, 18a, 1
8b, 21a, 21b, 23a, 23b. 24a, 24b, 25a, 25b, 27a, 27b, 2
8a, 28b, 29a, 29b--Diffraction grating application
People Rico Co., Ltd. Figure 3.10

Claims (1)

[Claims] 1. The grating constant of the input side diffraction grating is K_1, the grating constant of the output side diffraction grating is K_2, the angle formed by the two diffraction gratings is Δθ', and the diffraction angle by the input side diffraction grating is When θi′ and the diffraction angle by the output side diffraction grating are θ0, each dimension is {K_2^2−[K_1cos(θi′−Δθ′)/c
osθi′]}/cos(θ0+Δθ′)<K_1/c
A multiplexing/demultiplexing element characterized in that at least a pair of diffraction gratings set to satisfy the expression osθi' are disposed on an optical path for multiplexing or demultiplexing light. 2. The grating constant of the diffraction grating on the input side or output side is K_1,
When the input angle to the diffraction grating is θi and the propagation constant is k_B, at least one diffraction grating is arranged so that each dimension satisfies the formula Δ=K_1−k_Bsinθi−k_B≧0. The multiplexing/demultiplexing element according to claim 1, characterized in that: