JPH1123894A - Optical device for optical communication terminal station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device for optical communication terminal station advantageous for making the device compact by using a computer hologram utilizing an optical diffraction phenomenon as the optical element of terminal optical device for wavelength multiplexed transmission. SOLUTION: An optical element except a wavelength selecting filter is composed of computer holograms 21, 22 and a second wavelength component separated from a first wavelength component by the wavelength selecting filter 23 is sent to second input end 24 and output end 23 by means of the light condensing function of the first and second computer holograms 21, 22. A second wavelength component is sent to a second output end 23 by means of the first computer hologram 21 and bi-directional communication between the transmitting source of multiplexed light and an optical element 10 receiving the multiplexed light is enabled by means of the input of a second wavelength component from the second input end 24. The respective computer holograms 21, 22 are optical elements utilizing the diffraction phenomenon and made to be compact by properly and selectively burdening them with or superposing the functions of collimation, convergence, deflection and optical path dividing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device provided in a terminal station for optical multiplex communication in which optical signal media having different wavelength components are superposed, and more particularly, to a computer using an optical diffraction phenomenon as an optical element. The present invention relates to an optical device for an optical communication terminal station incorporating a hologram.

[0002]

2. Description of the Related Art In recent years, in order to enable optical communication with a large communication capacity, an optical fiber is laid to each home.
A plan called e) is underway. According to this, for example, light of each wavelength band of 1.3 μm and 1.55 μm is transmitted to a home communication terminal station as multiplexed light which is superimposed on each other.

[0003] A communication terminal station has a wavelength demultiplexing element for demultiplexing multiplexed light into light of each wavelength, and a bidirectional communication using light of one wavelength separated by the demultiplexing element. And an optical coupler that splits the optical path of one wavelength. With this optical device, the multiplexed light is separated into wavelength components of the respective wavelength bands, and then sent to each terminal device.

[0004] In this type of conventional optical device, in order to reduce the size of the device, for example, a flat package type optical transmission / reception using unadjustable WDM is described in the Proc. module"
As shown in FIG. 1, a wavelength selection filter exhibiting wavelength dependency is used as a wavelength demultiplexing element.

[0005]

However, in the above-mentioned conventional optical device, the optical coupler for handling the light separated by the wavelength selective filter is composed of an optical element based on an optical lens element such as a prism or a shaped lens. Have been. However, miniaturization of optical elements such as these shaped lenses is subject to strong restrictions in manufacturing,
In addition, it is not easy to make the optical device compact from the viewpoint of the alignment of the mutual arrangement relations of the optical elements, that is, from the viewpoint of alignment. Therefore, the appearance of an optical device for an optical communication terminal station that is advantageous for downsizing has been desired.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to an optical element for a terminal station optical device for wavelength division multiplexing transmission using multiplexed light having different wavelengths. Specifically, a computer hologram utilizing the light diffraction phenomenon is used. The computer generated hologram can be appropriately provided with a collimating or condensing function as seen in an optical lens, a deflecting function as seen in a prism, and an optical path dividing function by utilizing a diffraction phenomenon.

<Structure 1> The first aspect of the present invention is to receive a multiplexed light in which lights of different wavelengths are superimposed as a signal medium.
Is inserted into an optical fiber path for guiding the light from the input end of the multiplexed light to the first output end, allowing the light of the first wavelength component of the multiplexed light to pass through to the first output end and of the multiplexed light. A wavelength selection filter that reflects light of the second wavelength component to obtain divergent light, and a second filter that enables bidirectional communication toward the first input end with respect to the divergent light of the second wavelength component A first computer generated hologram for condensing a part of divergent light of a second wavelength component from a wavelength selection filter on a second output terminal in an optical device for an optical communication terminal station having a pair of input terminals and an output terminal. And a second computer generated hologram for guiding the light of the second wavelength component from the second input end to the first input end via the wavelength selection filter to the first input end. Features.

<Function 1> In the optical device according to the present invention, the optical element excluding the wavelength selection filter is constituted by a computer generated hologram, and the second wavelength component separated from the first wavelength component by the wavelength selection filter. Are directed to a second input end and an output end by the converging function of the first and second computer generated holograms. The second wavelength component is directed to the second output terminal by the first computer generated hologram, and the input of the second wavelength component from the second input terminal causes a multiplexed light source and the multiplexed light to be received. Two-way communication with the optical device becomes possible.

Each of the above-mentioned computer generated holograms is an optical element utilizing a diffraction phenomenon, and can perform a collimating function, a condensing function, a deflecting function, and an optical path dividing function in an overlapping or selective manner. It is. Also, by forming the computer generated hologram on a substrate such as a glass substrate and superimposing the substrates on which the computer generated hologram is formed, appropriate alignment between the optical elements can be realized relatively easily. Therefore, it is possible to provide a compact optical device for an optical communication terminal at a lower cost than the conventional optical device without increasing the manufacturing cost.

<Structure 2> In the optical device according to the present invention, the divergent light of the second wavelength component from the wavelength selection filter is supplied to the first computer between the wavelength selection filter and the first or second computer hologram. A third computer hologram that branches to each of the hologram and the second computer hologram can be inserted.

<Function 2> The third computer generated hologram is configured such that the divergent light from the wavelength selection filter does not depend on the spontaneous divergence angle. Make sure the output end is separated. Therefore, the use of the third computer generated hologram is advantageous in reducing the size of the optical device for an optical communication terminal.

<Structure 3> Further, in the optical device according to the present invention, between the wavelength selection filter and the third computer generated hologram, the divergent light of the second wavelength component from the wavelength selection filter is output to the third computer. A fourth computer generated hologram for converting into a parallel light beam directed to the hologram can be inserted.

<Function 3> The fourth computer generated hologram converts the divergent light of the second wavelength component from the wavelength selection filter into a parallel light beam directed to the third computer generated hologram. It is not necessary to handle the diverging light in the condensing function, and the function of condensing the parallel light beam may be considered when designing the third computer generated hologram.
The design and manufacture of the third computer generated hologram becomes easier because it is not necessary to consider the diverging light.

A CAD is used to manufacture a computer generated hologram, and a phase difference function of light in the hologram exhibiting desired diffractive optical characteristics is obtained. This phase difference function is
It is called an optical path difference function ρ (x, y). Optical path difference function ρ
(X, y) is transformed equation [rho (x, y) = a ΣC _N x ^m y ⁿ ... polynomial represented by (1). This polynomial (C _N x ^m y
coefficient C _N of ⁿ⁾ is called an optical path difference coefficient. n and m are positive integers, respectively, and the coefficient C _N is also called a phase coefficient. The following equation holds between N and m, n: N = {(m + n) ² + m + 3n} / 2 (2)

The phase coefficient C _N is obtained as each term coefficient of a Taylor expansion approximation obtained by two-dimensional Taylor expansion,
By substituting it into a CAD program, a photolithography mask pattern required to obtain a desired shape by photolithography can be generated.
One example of such a CAD program is CghCAD from NIPT, California, USA.

In the CAD program, the condition that the sum of m and n is equal to or less than 10 and N is equal to or less than 65 is given from the relation of data processing capacity. Accordingly, an optical path difference function ρ (x, y) showing desired optical characteristics is obtained, and each phase coefficient C _N (C _0-
After obtaining C ₆₅ ), by inputting the data into a CAD program, mask conditions for a computer generated hologram exhibiting desired diffractive optical characteristics can be obtained. Masks are manufactured in accordance with the mask conditions, and a computer generated hologram exhibiting desired diffractive optical characteristics is obtained by a photolithography method using these masks.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a sectional view schematically showing an optical device according to the present invention. The optical device 10 according to the present invention includes a glass substrate 14 in which an optical fiber 13 including a core 11 and a clad 12 surrounding the core is embedded. The refractive index n ₁ of the glass substrate 14 is equal to that of the cladding 12. In FIG. 1, the refractive index of air is shown as n ₂ .

The optical fiber 13 defines an optical fiber path (13) in the glass substrate 14. The optical fiber path 13 is exposed at the opposite end faces of the glass substrate 14 and defines a first input end 15 and a first output end 16 respectively.

The first input terminal 15 has an input optical fiber 1
A multiplexed light is input through the input optical fiber. The multiplexed light is obtained by superimposing light having wavelengths of, for example, 1.3 μm and 1.55 μm, each serving as a signal medium, via the input optical fiber. The multiplexed light is guided via an optical fiber path 13 to an output optical fiber 18 connected to a first output end 16.

The glass substrate 14 has an optical fiber path 13
Is formed, and a wavelength selection filter 20 is inserted in the slit 19.
In the illustrated example, the wavelength selection filter 20 is a dielectric filter composed of a conventionally known dielectric multilayer film. The wavelength selection filter 20 composed of a dielectric filter is called a half mirror.

The wavelength selective filter 20 inserted into the optical fiber path 13 is a wavelength-selective filter of the multiplexed light that enters from the first input end 15 and travels toward the first output end 16 by the guiding action of the optical fiber path 13. Allows the transmission of light of the first component wavelength having a .55 μm. Accordingly, the light of the first wavelength component having a wavelength of 1.55 μm passes through the wavelength selection filter 20 and reaches the first output terminal 16 by the guiding action of the optical fiber path 13, from which the output optical fiber 18 is output. It is taken out by. The light of the first wavelength component transmitted through the wavelength selection filter 20 and extracted from the output optical fiber 18 is sent to a first terminal device for one-way communication such as a television.

On the other hand, the wavelength selection filter 20 reflects the second wavelength component having a wavelength of 1.3 μm of the multiplexed light at a predetermined divergence angle δ. The reflected light of the second wavelength component partially illuminates one surface 14a of the glass substrate 14. A first computer generated hologram 21 is formed on one half of the irradiation area on the surface 14a of the glass substrate 14, and a second computer generated hologram 22 is formed on the other half of the irradiation area on the surface 14a. .

Each computer generated hologram (Computer Generated)
Hologram is hereinafter simply referred to as CGH element. ) 21 and 22 transmit the reflected light of the second wavelength component from the wavelength selection filter 20 to the second output terminal 23 and the second input terminal 24.
It has a light condensing function and a deflecting function for directing light to.

In the example shown, a photodetector 25 connected to a receiving circuit of the telephone is arranged at a second output terminal 23, and a semiconductor detector connected to a transmitting circuit of the telephone is disposed at a second input terminal 24. Laser or light emitting diode 26
Is arranged.

Therefore, the reflected light of the second wavelength component separated by the wavelength selection filter 20 is transmitted to the first CGH element 2.
1, the information included in the light of the second wavelength component is extracted by the receiving circuit of the telephone connected to the photodetector 25 disposed at the second output end 23 and connected to the photodetector.

The second wavelength component of the light emitting diode 26 connected to the transmitting circuit of the telephone is:
When the signal light of 3 μm is emitted, the light of the second wavelength component is directed to the wavelength selection filter 20 by the second CGH element 22, and is connected to the first input terminal 15 through the wavelength selection filter. Guided to the input optical fiber 17.

Thereby, a multiplexed light source (not shown)
Then, two-way communication with the telephone, which is the second terminal device connected to the optical device 10 that receives the multiplexed light via the input optical fiber 17 to the first input terminal 15 becomes possible.

Next, before giving details of the optical characteristics of the CGH elements 21 and 22 according to the present invention, the phase coefficient C _N (of the optical path difference function ρ (x, y) for a general CGH element will be described. C _{0 to} C ₆₅ ) will be described.

Each of the phase coefficients C _{0 to} C ₆₅ is obtained from a two-dimensional Taylor expansion of the two-dimensional optical path difference function ρ (x, y) with respect to the x-axis and the y-axis, and from an approximate expression up to the tenth-order term. Can be. This relationship is represented by equation (3) shown in FIG. Δ in the second term on the right side of Expression (3) is a surplus term in the Taylor expansion, and is a value small enough to be ignored.

FIGS. 3 to 9 show the phase coefficients C _{0 to} C ₆₅ obtained by expanding equation (3), that is, the optical path difference coefficients C ₀ to C ₀ .
FIG. 4 is an explanatory diagram showing C ₆₅ as a relational expression of a general expression ρ (x, y) of an optical path difference function. An optical path difference function ρ (x, y) showing desired optical characteristics is obtained, and this optical path difference function ρ
From (x, y), the optical path difference coefficients shown in FIGS. 3 to 9, that is, the phase coefficients C _{0 to} C ₆₅ are obtained, and these values are calculated by the above-mentioned CA.
By inputting into the D program, mask conditions for a computer generated hologram exhibiting desired diffractive optical characteristics can be obtained.

The details of the first CGH elements 21 and 22 will be examined along the description of the general CGH element described above. First CGH element 21 and second CGH element 22
Are CGH elements each having a point light source and a condensing point.

FIG. 10 shows a computer generated hologram having a point light source (X ₁ , Y ₁ , Z ₁ ) and a condensing point (X ₂ , Y ₂ , Z ₂ ), that is, a diffractive optical element. For simplicity, it is assumed that CGH elements 21 and 22 are on the z-axis and their thickness dimension is small enough to be ignored. These assumptions do not impair generality in calculating the phase coefficient C _N. The refractive index on the point light source side is represented by n ₁ , and the refractive index on the light condensing point side is represented by n ₂ . The optical path difference function ρ (x, y) of the diffractive optical element having the condensing lens function is given by the following equation.

Ρ (x, y) = n ₁ ｛(X ₁ -x) ² + (Y ₁ -y) ² + Z ₁ ² )｝ ^1/2 -n ₁ L ₁ + n ₂ ｛(X ₂ -x) ² + (Y ₂ -y) ² + Z ₂ ² )｝ ^1/2 -n ₂ L ₂ … (5) Here, the distance L ₁ from the origin to the point light source and the distance from the origin to the focal point distance L ₂ are each represented by the following formula. ^{_{L 1 = (X 1 2 +}} Y 1 2 + Z 1 2) 1/2 ... (6) L 2 = (X 2 2 + Y 2 2 + Z 2 2) 1/2 ... (7)

The first and second terms of the equation (5) are computer holograms (21 or 2) in a spherical wave from a point light source.
2) represents a two-dimensional optical path difference in 2). In addition, the third of the equation (5)
The terms and the fourth term represent the two-dimensional optical path difference in the computer generated hologram (21 or 22) in the spherical wave from the origin to the focal point.

First CGH element 21 and second CGH
The phase coefficient C _N for the element 22 can be obtained by substituting Equation (5) into Equations (4-0) to (4-65) shown in FIGS.

FIGS. 11 to 22 show the results of these calculations for each term C _{n in} the form of equations (8-0) to (8-65). The values of C _{0 to} C ₆₅ shown in the equations (8-0) to (8-65) are used as optical path difference coefficients, and CAD
By inputting the optical path difference coefficient C _N shown in equation (1) of the program and executing the program, the first and second CGH elements 21 and 22 represented by equation (5) are formed. Since necessary mask pattern data is obtained, each of the first CGs is used by using the mask pattern.
The H element 21 and the second CGH element 22 can be formed.

According to the optical device 10 of the first embodiment shown in FIG. 1, the optical elements provided in association with the divergent light of the second wavelength component reflected by the wavelength selection filter 20 have a diffractive optical phenomenon. CGH elements 21 and 22 used
, It is possible to provide these CGH elements 21 and 22 with a condensing function including an appropriate deflecting function. In addition, by performing an etching operation using a mask, each of the CGH elements 21 and 22 can be formed relatively easily and with relatively high precision in an appropriate portion of the glass substrate 14. Therefore, accurate alignment can be achieved relatively easily, and a relatively inexpensive and compact optical device 10 can be provided.

<Specific Example 2> In the specific example 1 shown in FIG.
An example has been shown in which the first CGH element 21 and the second CGH element 22 are arranged in the irradiation area by utilizing the natural divergence of the light of the second wavelength component due to the reflection of the wavelength selection filter 20. Instead of spontaneous divergence due to reflection at the wavelength selection filter 20, a third CGH element 27 is inserted between the wavelength selection filter and the two CGH elements 21 and 22, and the third optical path splitting function allows The light reflected by the wavelength selection filter 20 can be distributed to the respective input terminals and output terminals.

In the optical device 110 shown in FIG. 23, the same reference numerals as in the first embodiment denote the same functional parts as in the first embodiment. In the optical device 110, FIG.
As shown in FIG. 3, the glass substrate 14 is provided with an optical fiber path 13 and has the same refractive index n _{1 as the} cladding 12.
Is divided into a first block 14A having a refractive index n ₃ and a second block 14B having a refractive index n ₃ , and the glass substrate 14 is formed by joining the two blocks 14A and 14B. The refractive index n ₃ of the second block 14B can be set equal to the refractive index n ₁ of the first block 14A.

The second block 14 of the first block 14A
A third CGH element 27 that receives the reflected light of the second wavelength component from the wavelength selection filter 20 is formed on the bonding surface to B. Further, the first CGH element 21 and the second CGH element 21 are provided on a surface 14a opposite to the bonding surface of the second block 14B.
The GH element 22 is formed. Thereby, the third C
The GH element 27 includes the wavelength selection filter 20 and the first CG
It is arranged between the H element 21 and the second CGH element 22.

The third CGH element 27 branches 1.3 μm divergent light, which is the second wavelength component, from the wavelength selection filter 20 toward each of the first CGH element 21 and the second CGH element 22. Let it. Further, the first CGH element 21 and the second CGH element 22 condense the respective branched lights split by the third CGH element 27 to the corresponding photodetector 25 and light emitting diode 26.

The optical characteristics of the third CGH element 27 that forms the above-mentioned branched light with respect to the optical path splitting function will be described with reference to FIGS. 24 and 25. The third CGH element 27 is
As shown in FIG. 24, the optical diffraction element (27) having a prism function of deflecting a parallel light beam having an arbitrary deflection angle into a parallel light beam having an arbitrary deflection angle is considered.

For simplification of the description of the diffractive optical element (27) shown in FIG.
It is assumed that H element 27 is in a plane passing through the origin and including the X axis and the Y axis. The parallel light flux incident on the CGH element 27 is a vector component (α ₁ , β ₁ , γ) of the light passing through the origin.
₁ ), and the output parallel light beam is parallel to the vector components (α ₂ , β ₂ , γ ₂ ) passing through the origin.

The incident light side medium 14 in which the incident parallel light flux exists.
A has a refractive index n ₁ , and the output light side medium 14B in which the output parallel light beam exists has a refractive index n ₃ . At this time, the general formula of the optical path difference function ρ (x, y) is as follows:

[0045] ρ (x, y) = n 1 · (α 1 x + β 1 y) / (α 1 2 + β 1 2 + γ 1 2) 1/2) -n 3 · (α 2 x + β 2 y ^{_{) / (α 2 2 + β}} 2 2 + γ 2 2) represented by ^1/2 (9).

Generally, assuming that the number of masks required for manufacturing a computer generated hologram is M, the phase level of the formed computer generated hologram, that is, the number of phase steps is indicated by 2 ^M. Also, depending on the phase level, the required 1
The diffraction efficiency of the second-order diffracted light changes. In a two-phase level computer generated hologram in which one cycle of phase is formed by one mask, as is well known in the art, the amount of light for each 40% of the incident light is divided into the first-order diffracted light and the -1st-order diffracted light, respectively. The remaining 20% of the light is distributed to the other higher-order diffracted lights. Accordingly, by utilizing this phenomenon, that is, by using a computer-generated hologram having two phase levels, as shown in FIG. It can be branched in the direction away.

The third CGH element 27 utilizes the branching action of the above-described computer generated hologram (linear grating), and converts equation (9) into equation (4) shown in FIGS.
−0) to (4-65), the phase coefficient C _N for the third CGH element 27 can be obtained. FIG. 26 shows the results of these calculations as the optical path difference coefficient C _0.
ＣC ₂ .

By executing the CAD program using the operation results shown in FIG. 26, one mask for the third CGH element 27 is generated, and by etching the first block 14A using this mask, Third CGH element 27
Can be formed.

FIG. 27 shows the first CGH element 21 and the second CGH element 2 in the optical device 110 of the second embodiment.
The optical characteristics of the second CGH element 22 (FIG. 27A and the equivalent optical system thereof (FIG. 27B)) are shown as representatives of the second CGH element 22. According to this, as shown in FIG. 27A, the light of the second wavelength component reflected by the wavelength selection filter 20 has a refractive index n
Through the first block 14A ₁ advances vertically the distance D ₁ to toward the third CGH element 27. The reflected light vertically incident on the third CGH element 27 is deflected by an angle Θ by the third CGH element 27, and then passes through the second block 14B having the refractive index n ₃ in the second block 14B. Take the distance D ₂ toward the 22, in the air refractive index n _2, the distance is focused to the second input terminal 24 D ₃ apart.

Regarding the optical characteristics of the second CGH element 22, the second CGH element 22
When the optical path is viewed toward, the optical path is deflected by the third CGH element 27, and the following equation L ₁ = (n ₁ / n ₃ ) D ₁ + D ₂ (11) L ₂ = D ₃ (12) (where L ₁ and L ₂ represent the refractive index n ₃ and the traveling distance at the refractive index n ₂ , respectively, in the equivalent optical system). Figure 2
As shown in FIG. 7 (b), an optical system that advances at the angle な く without bending in the refractive index n ₃ can be equivalently treated. The optical characteristics shown in FIG. 27B are the same as those of the second CGH element 22 shown in FIG.

Accordingly, the optical characteristics of the first CGH element 21 and the second CGH element 22 in the specific example 2 are shown in the same manner as in the specific example 1 by considering the equations (11) and (12). The optical path difference function ρ (x, y) is basically given by the equation (5) except that the refractive index n ₁ is replaced by the refractive index n ₃ , and thus has been described along the specific example 1. Similarly to the above, the first CGH element 21 and the second CGH element 22 of the specific example 2 can be obtained.

In the optical device 110 shown in the second embodiment, the reflected light from the wavelength selection filter 20 is not dependent on the spontaneous divergence angle δ by the filter, and the third CGH element
Accordingly, the light can be positively split into two branch light paths. Thereby, the first CG is output from the wavelength selection filter 20.
Since a relatively short optical path to the H element 21 and the second CGH element 22 can secure a space required for disposing the two CGH elements 21 and 22, it is more advantageous in terms of compactness.

<Embodiment 3> A collimator is provided between the wavelength selection filter 20 in the embodiment 2 shown in FIG. 23 and the third CGH element 27 receiving the reflected light of the second wavelength component from the filter 20. Can be inserted.

In the optical device 120 shown in FIG. 28, the same reference numerals as those in the second embodiment denote the same functional parts as in the second embodiment. In the optical device 120, FIG.
As shown in FIG. 8, the glass substrate 14 is provided with the optical fiber path 13 and has the same refractive index n _{1 as the} cladding 12.
, A second block 14B having a refractive index n _3, and a third block 14C having a refractive index n ₄ , and these three blocks 14A, 14B and 14C The glass substrate 14 is formed by bonding. The refractive indices n ₃ and n ₄ of the second and third blocks 14B and 14C can be set equal to the refractive index n ₁ of the first block 14A.

The second block 14 of the first block 14A
A fourth CGH element 28 that receives the reflected light of the second wavelength component from the wavelength selection filter 20 is formed on the bonding surface to B. In addition, a third surface having an optical path dividing function is provided on a joint surface of the third block 14C to the second block 14B.
Is formed, and the second block 1
A first CGH element 21 and a second CGH element 22 are formed on a surface 14a opposite to the bonding surface of 4B. Thus, the fourth CGH element 28 is arranged between the wavelength selection filter 20 and the third CGH element 27.

The fourth CGH element 28 converts the divergent light of 1.3 μm, which is the second wavelength component from the wavelength selection filter 20, into a parallel light beam directed to the third CGH element 27. The optical characteristics of the fourth CGH element 28 will be described with reference to FIG.

The fourth CGH element 28 is considered to be a CGH element for converting a divergent spherical wave from a point light source into a parallel light beam, as shown in FIG. The CGH element, that is, the diffractive optical element 28 converts a divergent spherical surface from a point light source located at coordinates (X, Y, Z) into a parallel light flux whose vector component passing through the origin is represented by (α, β, γ). .

The first block 14A which is the medium on the incident light side
Is indicated by n ₁ , and the refractive index of the third block 14 </ b> C, which is the exit light side medium, is indicated by n ₄ . For simplicity of explanation, the diffractive optical element 28 is on the z-axis, and its thickness dimension is set to a value small enough to be ignored.
This assumption does not impair generality in calculating the phase coefficient C _N.

The optical path difference function ρ (x,
y) is given by the following equation. ρ (x, y) = n₁・ ｛(X-x)^Two+ (Y-y)^Two+ Z^Two)｝^1/2-n₁L-n_Four・ ｛(Αx + βy) / (α ^Two + β^Two+ γ^Two)^1/2 Ｌ (13) where L is the distance from the light source to the origin, and L = (X^Two + Y^Two + Z^Two )^1/2 .. (14)

The first and second terms of the equation (13) represent a two-dimensional optical path difference in the diffractive optical element 28 for a spherical wave from a point light source. The third term in the equation (13) represents the optical path difference of the deflected parallel light flux (α, β, γ).

The phase coefficient C for the fourth CGH element 28
_N is obtained by calculating Equation (13) from Equations (4-0) to FIGS.
It is obtained by substituting into equation (4-65). FIG.
0 to FIG. 35 show the results of these operations as the terms C _{0 to} C _65.
Are represented in the form of the equations (15-0) to (15-65).

Formulas (15-0) to (15-65)
Using the optical path difference coefficient, that is, the phase coefficients C _{0 to} C ₆₅
By executing the D program in the same manner as described above, the fourth C
Mask data for the GH element 28 can be obtained;
The fourth CGH element 28 is formed using the mask.

As described above, the fourth CGH element 28 converts the divergent light of the second wavelength component from the wavelength selection filter 20 into a parallel light flux. A parallel light beam is incident on the CGH element 27 of FIG.
The first CGH element 21 and the second CGH element 22 substantially receive parallel light beams, respectively.

Therefore, in the third embodiment, the first CGH elements 21 and 22 transmit the parallel light beams to the respective input / output terminals 23.
Since the optical path difference function ρ (x, y) relating to the first CGH elements 21 and 22 has a light condensing function of condensing light onto the first and second CGH elements 21 and 22, the light path difference function ρ (x, y) is basically expressed by Expression (13) Therefore, it can be formed in the same manner as the fourth CGH element 28.

In the optical device 120 of the third embodiment, as described above, the wavelength selection filter 20 and the third CGH element 27 are used.
Between the fourth CGH element 2 having a collimating function
8, the first CGH element 21 and the second CGH element 22 can be CGH elements having the same collimating function as the fourth CGH element 28. It is possible to simplify the design work of the first CGH element 21 and the second CGH element 22 as compared with the first embodiment.

In the above description, an example in which the substrate 14 is formed of glass has been described. However, if the substrate 14 is made of a material having a small optical loss, various substrate materials such as a silicon substrate or a plastic substrate are used. be able to.

[0067]

According to the present invention, as described above, the optical elements excluding the wavelength selection filter are constituted by computer holograms, and these computer holograms include a collimating function, a condensing function, a deflecting function, an optical path splitting function. Since a function can be selectively provided and an appropriate alignment can be obtained relatively easily, a compact optical device for an optical communication terminal capable of two-way communication without increasing the manufacturing cost. Can be achieved. Further, according to the present invention, as described above, it is possible to provide an optical device for an optical communication terminal that can be manufactured at a lower cost than in the past.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing a specific example 1 of an optical device according to the present invention.

FIG. 2 is an explanatory diagram of a Taylor expansion formula according to the present invention.

FIG. 3 is an explanatory diagram (part 1) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 4 is an explanatory diagram (part 2) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 5 is an explanatory diagram (part 3) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 6 is an explanatory diagram (part 4) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 7 is an explanatory diagram (No. 5) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 8 is an explanatory diagram (part 6) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 9 is an explanatory diagram (part 7) of an optical path difference coefficient by Taylor expansion according to the present invention.

FIG. 10 is an explanatory diagram showing optical characteristics of first and second CGH elements.

FIG. 11 is an explanatory diagram (part 1) of an optical path difference coefficient of the first and second CGH elements.

FIG. 12 is an explanatory diagram (part 2) of the optical path difference coefficients of the first and second CGH elements.

FIG. 13 is an explanatory diagram (part 3) of the optical path difference coefficients of the first and second CGH elements.

FIG. 14 is an explanatory diagram (No. 4) of the optical path difference coefficients of the first and second CGH elements.

FIG. 15 is an explanatory view (No. 5) of an optical path difference coefficient of the first and second CGH elements.

FIG. 16 is an explanatory diagram (part 6) of the optical path difference coefficients of the first and second CGH elements.

FIG. 17 is an explanatory diagram (part 7) of an optical path difference coefficient of the first and second CGH elements.

FIG. 18 is an explanatory diagram (No. 8) of the optical path difference coefficients of the first and second CGH elements.

FIG. 19 is an explanatory view (No. 9) of an optical path difference coefficient of the first and second CGH elements.

FIG. 20 is an explanatory diagram (part 10) of an optical path difference coefficient of the first and second CGH elements.

FIG. 21 is an explanatory diagram (11) of an optical path difference coefficient of the first and second CGH elements.

FIG. 22 is an explanatory diagram (part 12) of the optical path difference coefficients of the first and second CGH elements.

FIG. 23 is a longitudinal sectional view schematically showing Example 2 of the optical device according to the present invention.

FIG. 24 is an explanatory diagram showing optical characteristics of a third CGH element.

FIG. 25 is an explanatory diagram of the diffraction order of the CGH element.

FIG. 26 is an explanatory diagram of an optical path difference coefficient of the third CGH element.

FIG. 27 is an explanatory diagram of an equivalent optical system of the second CGH element.

FIG. 28 is a longitudinal sectional view schematically showing Example 3 of the optical device according to the present invention.

FIG. 29 is an explanatory diagram showing optical characteristics of a third CGH element.

FIG. 30 is an explanatory diagram (part 1) of an optical path difference coefficient of a fourth CGH element.

FIG. 31 is an explanatory diagram (part 2) of the optical path difference coefficient of the fourth CGH element.

FIG. 32 is an explanatory diagram (part 3) of the optical path difference coefficient of the fourth CGH element.

FIG. 33 is an explanatory view (No. 4) of the optical path difference coefficient of the fourth CGH element.

FIG. 34 is an explanatory diagram (No. 5) of the optical path difference coefficient of the fourth CGH element.

FIG. 35 is an explanatory view (No. 6) of an optical path difference coefficient of the fourth CGH element.

[Explanation of symbols]

 10, 110, 120 Optical device 13 Optical fiber path 14 Substrate 15 First input terminal 16 First output terminal 20 Wavelength selection filter 21 First CGH element 22 Second CGH element 23 Second output terminal 24 Second Input terminal of 27 Third CGH element 28 Fourth CGH element

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03H 1/08

Claims (7)

[Claims] An optical fiber path for guiding light from a first input end to a first output end, which receives multiplexed light in which light of different wavelengths are superimposed as a signal medium, is inserted into the optical fiber path. A wavelength selection filter that permits transmission of light of a first wavelength component to the first output end and reflects light of a second wavelength component of the multiplexed light to obtain divergent light; An optical device for an optical communication terminal station provided with a second pair of input terminals and an output terminal that enables bidirectional communication toward the first input terminal with respect to divergent light of a wavelength component, A first computer generated hologram for condensing a part of the divergent light of the second wavelength component at the second output end, and a light of the second wavelength component from the second input end to the wavelength selection filter. Through the wavelength selection filter to the first input end And a second computer generated hologram for guiding. 2. The optical fiber path is constituted by an optical fiber embedded in a glass substrate, and the first and second computers are provided on a surface of the glass substrate which is irradiated with divergent light of the second wavelength component. 2. The optical device for an optical communication terminal according to claim 1, wherein a hologram is formed. 3. The first and second computer generated holograms have a condensing function and a deflecting function for directing light of a second wavelength component from the wavelength selection filter to each of the second input / output terminals. Item 2. The optical device for an optical communication terminal according to Item 1. 4. The method according to claim 1, further comprising the step of:
Or a third computer arranged between the second computer generated hologram and a divergent light of the second wavelength component from the wavelength selection filter for branching toward the first computer generated hologram and the second computer generated hologram, respectively. The optical device for an optical communication terminal according to claim 1, further comprising a hologram. 5. The optical device for an optical communication terminal according to claim 4, wherein the third computer generated hologram branches the light of the second wavelength component into first-order diffracted light and −1st-order diffracted light. 6. The hologram device according to claim 1, wherein the divergent light of a second wavelength component from the wavelength selection filter is disposed between the wavelength selection filter and the third computer generated hologram. 5. The optical device for an optical communication terminal according to claim 4, further comprising a fourth computer generated hologram for converting a parallel light beam. 7. The optical communication terminal according to claim 6, wherein the fourth computer generated hologram has a collimating function of directing the divergent light of the second wavelength component from the wavelength selection filter to the third computer generated hologram. Optical device.