JPH10319824A - Optical filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter device comparatively simples in constitution and small in the loss of light quantity by using a computer hologram (CGH) having wavelength dependency in light diffraction phenomenon as a filter element for separating multiplex light in accordance with wavelength. SOLUTION: This optical filter device 10 comprises a filter element 14 for separating light from an incident light fiber 11 receiving multiplex light including wavelength components of, for example, wavelength λ1 , λ2 to first and second outgoing light fibers 12, 13 in accordance with respective wavelength components. The filter element 14 consists of a CGH being a diffraction optical element. The CGH 14 receives outgoing light emitted from the incident fiber 11 through a collimator optical lens 15 for converting it to parallel luminous flux. Also, luminous flux through the CGH 14 is sent to the first and second outgoing light fibers 12, 13 through condensing optical lenses 16, 17. Therefore, the CGH 14 has a prism function deflecting light to parallel luminous flux having an arbitrary deflection angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter device and, more particularly, to an optical filter device suitable for separating multiplexed light into lights of respective wavelengths in optical wavelength multiplex transmission communication in which lights of different wavelengths are superimposed. Related to the device.

[0002]

2. Description of the Related Art A conventional optical filter device of this type includes an optical path distributor such as a half mirror that divides multiplexed light into optical paths corresponding to the number of wavelengths without separating the multiplexed light for each wavelength. A plurality of wavelength filters, each of which is disposed in each optical path and made of a dielectric, each of which exhibits a wavelength dependence of light absorption and a light absorption for mutually different wavelengths.

[0003]

Therefore, in the conventional optical filter device, a wavelength filter is required for each divided optical path, that is, for each wavelength of light to be separated, so that the configuration is complicated. In addition, since the wavelength filter uses the light absorbing effect of a dielectric material exhibiting wavelength dependency, the loss of light amount in the wavelength filter increases. Therefore, the appearance of an optical filter device having a relatively simple configuration and small loss of light amount has been desired.

[0004]

The present invention adopts the following constitution in order to solve the above points. <Structure> The present invention provides an optical filter device for optical wavelength division multiplexing transmission communication using multiplexed light having wavelengths different from each other. It is characterized in that a computer generated hologram showing wavelength dependence is used.

<Operation> A computer-generated hologram can realize a complicated aspheric lens function and a prism function including an axis shift with a single hologram element. In addition, the computer-generated hologram uses a refractive index of a lens and a prism. Unlike such an optical element, since it uses a diffraction phenomenon, it exhibits stronger wavelength dependence than an optical element using a refractive index.

By utilizing the strong wavelength dependency observed in the computer generated hologram, it is possible to cause the computer generated hologram to perform an optical path splitting function and a wavelength separating function without inducing a strong light loss as in the related art. Since a filter element is not required for each optical path, the multiplexed light of the optical wavelength division multiplexing transmission can be efficiently separated into light for each wavelength with a relatively simple configuration without causing a large light loss unlike the conventional one. can do.

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). n and m are positive integers, respectively, and C _N is 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 into a CAD program, a photolithography mask pattern and the like necessary for obtaining a desired shape by photolithography can be generated.
One example of such a CAD program is CghCAD from NIPT, California, USA. Accordingly, the optical path difference function ρ (x,
y) and the respective phase coefficients C _N of the optical path difference function ρ (x, y), and then inputting the data to a CAD program to generate a mask for a computer generated hologram exhibiting desired diffractive optical characteristics. Can be requested. By a photolithography method using these masks, a computer generated hologram exhibiting desired diffractive optical characteristics can be obtained.

According to the computer generated hologram formed in this way, since the computer generated hologram has a strong wavelength dependence that cannot be seen in a shape lens or a prism, it cannot be separated by these refractive optical elements. For example, 20n
The multiplexed light obtained by superimposing light having a very small wavelength difference of m can be effectively separated into light of each wavelength without causing large attenuation.

The computer generated hologram constituting the filter element can be provided with a prism function of deflecting lights of different wavelengths at mutually different angles. Further, the computer hologram constituting the filter element can be provided with a lens function of condensing light of different wavelengths at mutually different image points. Further, the computer hologram constituting the filter element can be provided with both functions of a prism function of deflecting light of different wavelengths at mutually different angles and a lens function of condensing light of different wavelengths at mutually different image points. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. Embodiment 1 FIG. 1 schematically shows the structure of Embodiment 1 of the optical filter device according to the present invention. The optical filter device 10 according to the present invention converts the light from the incident optical fiber 11 receiving the multiplexed light including two wavelength components of, for example, the wavelength λ ₁ and the wavelength λ _{2 into first} and _second light beams according to the respective wavelength components. Includes a filter element 14 for splitting toward the output optical fibers 12 and 13.

The filter element 14 is composed of a computer generated hologram (hereinafter simply referred to as a CGH element) which is a diffractive optical element. In the example shown, the computer generated hologram or CGH 14 is received via a collimator optical lens 15 for converting outgoing light diverging from the incident optical fiber 11 into a parallel light beam. Also, C
The parallel light beams having passed through the GH 14 are respectively condensed optical lenses 1
After passing through 6 and 17, they are sent to first and second outgoing optical fibers 12 and 13, respectively.

Therefore, the CGH 14 has a prism function of deflecting a parallel light beam having an arbitrary deflection angle into a parallel light beam having an arbitrary deflection angle. C having this prism function
The optical characteristics of the GH 14 will be described with reference to FIG. In FIG. 2, for simplicity of description, CGH 14 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 14 is a vector component (α) of light passing through the origin.
₁ , β ₁ , γ ₁ ), and the output parallel light beam is parallel to the vector components (α ₂ , β ₂ , γ ₂ ) passing through the origin.

The medium on the incident light side where the incident parallel light flux exists is:
If the output light side medium having the refractive index n ₁ and the output parallel light beam has the refractive index n ₂ , the optical path difference function ρ (x,
The general formula for y) is

[0015] ρ (x, y) = n 1 · (α 1 x + β 1 y) / (α 1 2 + β 1 2 + γ 1 2) 1/2) -n 2 · (α 2 x + β 2 y ^{_{) / (α 2 2 + β}} 2 2 + γ 2 2) represented by ^1/2 (3). The coefficient of each term of the two-dimensional Taylor expansion equation obtained by the partial differentiation of equation (3) is the phase coefficient C _N of equation (1).
Becomes

A Taylor expansion formula of the optical path difference function ρ (x, y) up to the tenth-order polynomial is shown in FIG. 3 as a formula (3 ′). Δ in the second term on the right side of equation (3 ′) indicates a surplus term when Taylor expansion is performed. The surplus term Δ usually has a value small enough to be ignored.

Expression (3) is Taylor-expanded along expression (3 '). Since expression (3) is a linear expression of x and y, among the phase coefficients C _N , n + m is 2 The phase coefficient C _N corresponding to the partial differential term described above becomes zero. Therefore, with respect to the optical path difference function ρ (x, y) of the equation (3), only the phase coefficients C _{0 to} C ₂ remain as the phase coefficients C _N.

[0018] In other _{words, C 0 = 1 ... (4} ) C 1 = n 1 α 1 / (α 1 2 + β 1 2 + γ 1 2) 1/2) -n 2 α 2 / (α 2 2 + β ^{_{2 2 + γ 2 2) 1/2}} ... (5) C 2 = n 1 β 1 / (α 1 2 + β 1 2 + γ 1 2) 1/2) -n 2 β 2 / (α 2 2 + β ₂ ² + γ ₂ ² ) ^1/2 (6).

Therefore, by executing a CAD program in which each of the equations (4) to (6) is used as the phase coefficient C _N , the mask pattern data necessary for forming the CGH 14 shown in the equation (3) is obtained. Can be The lens material is subjected to an etching process by photolithography using a mask pattern generated by the mask pattern data, whereby the CGH 14 shown in FIG. 1 is obtained.

The wavelength dependence of the diffraction phenomenon of the CGH 14 thus obtained will be described with reference to FIG. The CGH 14 that deflects the incident parallel light beam to an arbitrary angle can be regarded as a grating having a periodic phase distribution.
The optical characteristics of H14 can be explained by a conventionally well-known grating equation.

As shown in FIG. 4, assuming that the incident angle of the CGH 14 with respect to the optical axis is θ ₁ and the emission angle is θ ₂ , the relationship between the grating period r and the wavelength λ is as follows: r = λ / (n ₂ sin θ ₂ −n ₁ sin θ ₁ ) (7) By rearranging equation (7) and obtaining the emission angle θ ₂ for the wavelength λ, the following equation is obtained: sin θ ₂ = λ / (rn ₂ ) + (n ₁ / n ₂ ) · sin θ ₁ (8) .

In equations (7) and (8), the refractive index n ₁
And n ₂ are assumed to be constant irrespective of the wavelength λ, and the change in the refractive index with respect to the wavelength change is not taken into account, but strictly speaking, the respective refractive indices n ₁ and n ₂ are functions of the wavelength. Therefore, for the wavelength λ of the incident light beam and the wavelength λ ′ having a slight shift from this wavelength, the relationship corresponding to each equation (7) is as follows: r = λ / (n _{2 (} λ ₎ sin θ ₂ −n _{1 (} λ ₎ sin θ ₁ ) (9) r = λ ′ / (n _{2 (} λ _′) sin θ ₂ −n _{1 (} λ _′) sin θ ₁ ) (10) Here, n _{1 (} λ ₎ , n _{2 (} λ ₎ , n _{1 (} λ ′ ₎ ,
n _{2 (} λ ′ ₎ means refractive indices n ₁ and n ₂ for wavelengths λ and λ ′, respectively.

The same grating period r, that is, CG
In order to derive the wavelength dependence for H14, the grating period r is eliminated from equations (9) and (10), and
To summarize, the following equation sin θ ₂ ′ = {(1 / n _{2 (} λ _′) ) · (λ ′ / λ) · (n _{2 (} λ ₎ sin θ ₂ −n _{1 (} λ ₎ sin θ ₁ )} + (n _{1 (} λ _′) / n _{2 (} λ _′) ) sin θ ₁ (11) is derived.

Equation (11) shows that the wavelengths λ and λ ′ of the incident light are
Shows the relationship between the angles θ ₂ and θ ₂ ′ of the outgoing light, and shows that the outgoing angle shifts due to the shift in the wavelength of the incident light. Therefore, as shown in FIG.
The multiplexed light of wavelength λ ₁ and wavelength λ ₂ incident on H14 is
Through the CGH14, wavelength lambda ₁ of the light of its multiplexed light is directed to the condensing optical lens 16 by a deflection angle theta _2, the wavelength lambda ₂ of light, focusing optical lens deflection angle theta ₂ ' 1
Pointed at 7.

The prism function by the deflection action of the CGH 14 according to the present invention is used to convert a multiplexed light having a small wavelength difference in optical multiplex communication of, for example, 20 nm, which cannot be separated by a refraction type optical prism, to a wavelength dependence of the deflection angle of the CGH 14. Make it possible to separate based on gender. In addition, the CGH 14 can perform both the function of dividing the optical path and the function of separating the wavelength without exhibiting a strong attenuating function unlike the conventional wavelength filter due to the attenuating function. As a result, the configuration can be simplified as compared with the related art, and the multiplexed light can be separated according to the wavelength without causing a large optical loss unlike the related art.

<Example 2> An optical filter device 20 shown in FIG. 5 converts light from an incident optical fiber 11 diverging multiplexed light containing two wavelength components of wavelengths λ ₁ and λ ₂ into respective wavelength components. A CGH 24 which is a filter element for converging light toward the first and second output optical fibers 12 and 13 accordingly.

In the example shown in FIG. 5, the CGH 24 is arranged such that its object point coincides with the light emitting surface of the incident optical fiber 11, and has different focal lengths according to the wavelength of the CGH 24.
First and second outgoing optical fibers 12 and 1 respectively
Three light receiving surfaces are arranged. A reflecting means 21 such as a mirror is disposed at the short focal point of the CGH 24, and the outgoing optical fiber 12 on the short focal point side passes through the reflecting means 21.
Separated light is sent.

The CGH 24 shown in FIG. 5 is a diffractive optical element having the object point s and the focal point d and exhibiting the function of a condenser lens. The optical characteristics of the CGH 24 having the condensing lens function will be described with reference to FIG. In FIG. 6, for simplicity of description, the CGH 24 is in a plane passing through the origin and including the X axis and the Y axis. The coordinate position of the object point s is represented by (X ₁ , Y ₁ ,
Z ₁ ), assuming that the focal coordinate position is (X ₂ , Y ₂ , Z ₂ ), the refractive index of the medium on the incident light side is n ₁ , and the refractive index of the medium on the outgoing light side is n ₂ , the CGH 24 acting as a condenser lens The optical path difference function ρ (x, y) 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 (12) Here, the distance L ₁ from the origin to the point light source and the distance L ₁ from the origin to the image point the distance L ₂ are each represented by the following formula. ^{_{L 1 = (X 1 2 +}} Y 1 2 + Z 1 2) 1/2 ... (13) L 2 = (X 2 2 + Y 2 2 + Z 2 2) 1/2 ... (14)

Accordingly, the phase coefficient C _N (for example, C _{0 to} C ₆₅ ) is obtained from the coefficient of each term by the Taylor expansion shown in the equation (13 ′) obtained by the partial differentiation of the equation (12).
The respective values of these phase coefficients C _{0 to} C ₆₅ are used as phase coefficients C _N by executing the CAD program similar to that described above.
The mask pattern data necessary for forming the diffractive optical element represented by the formula (12) is obtained. Based on this data, the CGH 24 satisfying the optical characteristics of the formula (12) is obtained in the same manner as in the specific example 1. can get.

The wavelength dependence of the focal length due to the diffraction phenomenon of the CGH 24 will be described with reference to FIG. FIG. 7 shows an example in which an incident parallel light beam is collected for simplification of analysis. The CGH 24 that converges a parallel light beam at the focal length f is a grating of the CGH 24 such that the optical path length from the radius r from the optical axis of each grating to the focal point satisfies the condition of adding the integral multiple of the wavelength to the focal length f. Are formed in the radial direction. Therefore, the focal length f,
The relation between the j-th period and the grating radius r _j is represented by the following equation: r _j ² + f ² = (f + jλ) ² (15)

From the equation (15), the following equation is derived: r _j ² = 2jλf + (jλ) ² (16) Here, the focal length f is in the unit of mm, and the wavelength λ is in the unit of μm.
The second term on the right-hand side of 6) has a sufficiently small value that can be ignored compared to the first term on the right-hand side. Therefore, the following equation r _j ² = 2jλf (17) is obtained as an approximate equation of equation (16). In equation (17), when j = 1, the following equation ^{_{f = r 1 2 / 2λ ...}} (18) is obtained. Expression (18) is a relational expression between the focal length f of the well-known Fresnel lens and the wavelength λ.

The wavelength dependence of the focal length f of such an optical element can be calculated by the following equation (δf / δλ) = − (f / λ) obtained by partially differentiating both sides of the equation (18) with respect to the wavelength λ. Indicated by Therefore, the relationship between the wavelength shift Δλ and the resulting focal length difference Δf is given by the following equation: Δf = − (f / λ) · Δλ (20) Equation (20) shows that for a wavelength λ ₁ longer than the originally designed wavelength λ ₂ for CGH 24, CGH 2
Numeral 4 means that it acts as a condenser lens having a focal length (f + Δf) shorter than the focal length f of the wavelength λ ₂ by | Δf |.

Regarding the specific example 2, in the description of the wavelength dependence along FIG. 7, the refractive index n ₂ is assumed to be 1 for the sake of simplicity, but the obtained focal length is multiplied by the actual refractive index. Is the focal length in the medium.

Therefore, the multiplexed lights of wavelengths λ ₁ and λ ₂ incident on the CGH 24 shown in FIG. 5 are condensed at mutually different object points d ′ and d by passing through the CGH 24, respectively. The light of the wavelength λ ₂ condensed on the object point d enters the output optical fiber 12. Further, the light of wavelength λ ₁ condensed on the object point d ′ is reflected by the reflecting means 21 on the outgoing optical fiber 1.
3 and enters the outgoing optical fiber.

The function of the condenser lens of the CGH 24 according to the present invention is to separate the multiplexed light into light of each wavelength component based on the wavelength dependence of the focal length since the focal length shows the wavelength dependence. Make it possible. Further, similarly to the specific example 1, the CGH 24 can perform both of the function of dividing the optical path and the function of separating the wavelength without exhibiting a strong attenuation function like the conventional wavelength filter by the attenuation function. . This allows
The configuration can be simplified as compared with the related art, and the multiplexed light can be separated according to the wavelength without causing a large optical loss unlike the related art.

<Embodiment 3> The optical filter device 30 shown in FIG. 8 converts light from the incident optical fiber 11 diverging multiplexed light containing two wavelength components of wavelength λ ₁ and wavelength λ ₂ into respective wavelength components. A CGH 34 which is a filter element for converging light toward the first and second output optical fibers 12 and 13 accordingly.

In the example shown in FIG. 8, the CGH 34 is arranged so that its object point coincides with the light emitting surface of the incident optical fiber 11, and the first and second object points correspond to different object points corresponding to the wavelength of the CGH 24. The light receiving surfaces of the outgoing optical fibers 12 and 13 are arranged.

The CGH 34 shown in FIG. 8 is a diffractive optical element having both a condensing lens function having its object point s and a focal point d and a prism function. The optical characteristics of the CGH 34 are basically the same as those described with reference to FIG.
It is represented by an optical path difference function ρ (x, y) similar to that shown in 2). Accordingly, a phase coefficient C _N (for example, C _{0 to} C ₆₅ ) is obtained from the coefficient of each term by Taylor expansion shown in Expression (13 ′) obtained by partial differentiation of Expression (12), and these phase coefficients C ₀ to C ₆₅ are obtained. By executing the same CAD program as described above, using each value of C ₆₅ as a phase coefficient C _N , the equation (12) is obtained.
The data of the mask pattern necessary for the formation of the diffractive optical element represented by the following formula is obtained. Based on this data, as in the first embodiment, C satisfying the optical characteristics of Expression (12).
GH34 is obtained.

The CGH 34 shown in FIG. 8 is considered to have an off-axis type focusing lens for imaging. This CGH3
The wavelength dependence of the diffraction phenomenon 4 will be described with reference to FIG. For light of wavelength λ, the following expression (n ₁ / a) + (n ₂ / b) = (1 / f) (21) is derived from the imaging relational expression of the optical lens. Where a is the distance to the object point,
b is the distance to the image point, and f is the focal length of the CGH 34 in vacuum.

The relationship between the deflection angles θ ₂ and θ ₂ ′ of the outgoing light with respect to the wavelengths λ and λ ′ of the incident light is given by the above equation (1).
As shown in 1), from equation (11), the following equation θ ₂ ′ = sin ⁻¹ {(1 / n _{2 (} λ ′ ₎ ) · (λ ′ / λ) (n _{2 (} λ ₎ sin θ ₂ −n _{1 (} λ ₎ sin θ ₁ ) + (n _{1 (} λ ′ ₎ / n _{2 (} λ ′ ₎ ) sin θ ₁ … (22) is derived. FIG. 9 shows an example in which θ ₁ is zero. Equation (2
2) is a deflection angle θ ₂ due to a wavelength difference between the wavelengths λ and λ ′.
And changes in θ ₂ ′.

When the focal length f at the wavelength λ and the deviation therefrom are Δf, the focal length f ′ at the wavelength λ ′
Is expressed by the following equation: f ′ = f + Δf (23), and equation (23) can be rewritten as f ′ = f (1−Δλ / λ) = f (λ ′ / λ) (24) . Here, Δλ is the difference between the wavelength λ and the wavelength λ ′.

From equations (21) and (24), the wavelength λ '
Is given by the following equation (n ₁ / a) + (n ₂ / b ′) = (1 / f ′) = λ / (fλ ′) (25)

Therefore, according to CGH 34 shown in FIG.
The light of the wavelength component of the wavelength λ is determined by the deflection angle θ ₂ and the expression (2)
It is directed to the output optical fiber 12 with an image point distance b satisfying 1). Further, the light of the wavelength component of the wavelength λ ′ is expressed by the formula (2)
The light is directed to the output optical fiber 13 at a deflection angle θ2 ′ that satisfies 2) and an image point distance b ′ that satisfies the expression (25).

According to the specific example 3 shown in FIG.
As shown in, in addition to being able to effectively separate multiplexed light into its wavelength component light with a relatively simple configuration without causing significant light loss, the luminous flux reaching each object point is not overlapped , From being distinguished from each other,
Higher S / N ratios can be achieved.

In the above description, for the sake of simplicity of description, the diverging spherical wave from the incident optical fiber 11 is adopted as the incident light to the CGHs 14, 24 and 34. A parallel light beam or the like can be appropriately adopted. In addition, the output lights separated from the CGHs 14, 24, and 34 can be appropriately guided to a photodetector, another optical element, or the like. further,
Although the multiplexed light of two wavelength components has been described above, the present invention can be applied to the separation of the multiplexed light for three or more wavelength adjustments.

FIG. 10 shows a subscriber for optical multiplex transmission communication in which the optical filter device (10, 20, or 30) according to the present invention is superimposed with light having wavelengths of 1.3 μm and 1.55 μm, respectively. Application example incorporated in the terminal station 50 for use. The terminal station 50 receives an incoming optical fiber 51 that receives multiplexed light of 1.3 microns and 1.55 microns.
A CGH 54 (14, 24 or 34) for separating the multiplexed light from the fiber into two component light beams 52 and 53 of 1.3 and 1.55 microns;
And a reflecting means 55 composed of a pair of mirrors 55a and 55b for respectively reflecting the lights 52 and 53 of the two component waves separated by the above.

The 1.3-micron-wave light 52 separated by the CGH 54 passes through a pair of mirrors 55a and 55b of the reflection means 55, passes through a CGH 56 having a condensing function, and then becomes a photodetector 58 of an IC 57 having a communication function.
Will be guided to. On the other hand, 1. separated by CGH54.
The light 53 of the 5-micron wave is converted into a CGH 59 having a light collecting function.
, And is guided to the output optical fiber 60.

In the CGH 54 according to the present invention, since the CGH can be provided with a prism function for wavelength separation and a condensing lens function such as a collimation lens, etc., the structure of the terminal station 50 can be simplified and made compact. This is extremely advantageous.

[0050]

According to the present invention, as described above, a computer generated hologram exhibiting a strong wavelength dependency as compared with an optical element utilizing a refractive index and having an optical path dividing function and a wavelength separating function is used as a filter element. Thus, with a relatively simple configuration, the multiplexed light of the optical wavelength division multiplexing transmission can be effectively separated into light of each wavelength without causing a large light loss as in the related art.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing Example 1 of an optical filter device according to the present invention.

FIG. 2 is an explanatory diagram illustrating optical characteristics of a CGH element according to a specific example 1.

FIG. 3 is an explanatory diagram of a Taylor expansion formula according to the present invention.

FIG. 4 is a drawing for explaining a diffraction phenomenon of the CGH element according to the specific example 1.

FIG. 5 is an explanatory view schematically showing Example 2 of the optical filter device according to the present invention.

FIG. 6 is an explanatory diagram illustrating optical characteristics of a CGH element according to a specific example 2.

FIG. 7 is a drawing for explaining a diffraction phenomenon of the CGH element according to the specific example 2.

FIG. 8 is an explanatory view schematically showing Example 3 of the optical filter device according to the present invention.

FIG. 9 is a drawing for explaining a diffraction phenomenon of the CGH element according to Example 3;

FIG. 10 is a sectional view schematically showing an application example of the optical filter according to the present invention.

[Explanation of symbols]

 10, 20, 30 Optical filter device 11, 51 Incident optical fiber 12, 13, 60 Outgoing optical fiber 14, 24, 34, 54 Computer hologram (CGH)

Claims (4)

[Claims] 1. An optical filter device for optical wavelength division multiplexing transmission communication using multiplexed light having different wavelengths from each other, wherein an optical element is used as a filter element for separating the multiplexed light into light of each wavelength. An optical filter device using a computer generated hologram showing wavelength dependence of a diffraction phenomenon. 2. The optical filter device according to claim 1, wherein the computer generated hologram has a prism function of deflecting lights of different wavelengths at mutually different angles. 3. The optical filter device according to claim 1, wherein the computer generated hologram has a lens function of condensing lights of different wavelengths on mutually different image points. 4. The computer-generated hologram has a prism function of deflecting light of different wavelengths at mutually different angles and a lens function of condensing light of different wavelengths at mutually different image points. 2. The optical filter device according to 1.