JPH06317705A - Diffraction element and optical multiplxing/ demultiplxing device using the same - Google Patents

Abstract

PURPOSE:To provide a diffraction element capable of using one element for plural wavelength band and to provide an optical multiplexing/demultiplexing device using the effect of this diffraction element. CONSTITUTION:The diffraction element comprises a transparent substrate 2 having a first and a second surfaces, a periodic groove marked on the first surface, a reflection film 1 provided on the groove and an anti-reflection film 4 provided on the second surface. The multiplexing/demultiplexing device having the diffraction element is provided with a first optical input device 10 making a light beam incident on the first incident plane of the diffraction element (the first surface side provided with the reflection film), a first light receiving device 12 receiving a light beam made incident on the first incident plane and diffracted, a second optical input device 11 receiving a light beam reflected after being made incident on the first incident plane and making it incident on the second incident plane of the diffraction element (the surface provided with the anti-reflection film) and a second light receiving device 13 receiving the light beam made incident on the second surface and diffracted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive element used in a spectroscope or a wavelength division multiplexing optical communication system, and an optical multiplexer / demultiplexer using the same.

[0002]

2. Description of the Related Art In recent years, various forms of a diffractive element and an optical multiplexer / demultiplexer using the same have been proposed and studied as key devices of a wavelength division multiplexing optical communication system. In particular, in high-density wavelength-division multiplex optical communication, the wavelength spacing of the light used is narrow and a large number of wavelengths are multiplexed, so an optical multiplexer / demultiplexer using a diffraction element is considered promising. However, at present, there is generally no diffractive element having a high diffraction efficiency over a wide wavelength range.

FIG. 9 shows the wavelength dependence of the diffraction efficiency of a reflection type diffraction element in which the grating groove has a sawtooth cross section. Fig. 9 shows R.Petit: Electromagnetic
Theory of Gratings <Springer-Verlag Berlin Heidelb
erg New York 1980>. Chap.6, p.164. In FIG. 9, TE polarized light is a component of the light incident on the diffraction element whose polarization direction is parallel to the grating groove direction, and TM polarized light is the light incident on the diffraction element whose polarization direction is the grating groove direction. It is a vertical component. As can be seen from FIG. 9, the diffraction efficiency is greatly affected by the wavelength of the incident light used, the ratio of the wavelength of the incident light to the lattice spacing, and the polarization direction of the incident light. From FIG. 9, the diffraction efficiency is high,
Moreover, it can be seen that the wavelength range in which the difference in diffraction efficiency between TE polarized light and TM polarized light is small is very narrow. For example, the diffraction efficiency is 8
The wavelength range in which the difference in diffraction efficiency between both polarized lights is 5% or more and 10% or less is 40 nm or less when converted with a diffraction grating having a grating groove spacing of 0.8 μm.

Therefore, in order to adjust the wavelength of the light used, it has been proposed to provide a transparent material on the grating groove of the diffraction grating of such a diffraction element. FIG. 10 shows an example thereof. On a substrate 51, a reflection type diffractive substrate 52 in which a grating groove is engraved is formed, and a translucent material 53 is formed thereon.

In the diffractive element having such a structure, light enters from the diffractive element surface 54 and is diffracted by the diffraction grating of the reflection type diffractive substrate 52 via the transmission material 53. The diffracted light is emitted from the diffraction grating surface 54 again via the transmitting material 53. If the refractive index of the transmissive material 53 is n, the light in the transmissive material 53 equivalently has a wavelength of 1 / n. Therefore, the wavelength of the incident light at the time of diffraction can be changed by adjusting the refractive index of the translucent material 53, so that the light can be diffracted in the wavelength band with high diffraction efficiency shown in FIG. 9 ( See, for example, JP-A-62-61002).

An apparatus has also been proposed which performs optical multiplexing / demultiplexing in two types of wavelength bands by using two diffraction gratings having different wavelength regions to be dispersed in combination. For example, Japanese Patent Laid-Open No. 4-282603 describes an optical multiplexer / demultiplexer as shown in FIG. The wavelength-multiplexed light from the input fiber 61 enters the first diffraction grating 64 via the lens 63. Of the wavelength-multiplexed lights, lights λ _{a to} λ _{c in} the short wavelength region are wavelength-dispersed by the first diffraction grating 64 and are output via the lens 63 to the output fiber 62, respectively.
bind to _{a to} 62 _c . On the other hand, light in the long wavelength region λ _d ~ λ
_The wavelength _f is totally reflected by the first diffraction grating 64 without being wavelength-dispersed. The totally reflected light is wavelength-dispersed by the second diffraction grating 65 and enters the first diffraction grating 64. The incident light is totally reflected again by the first diffraction grating 64, and is coupled to the output fibers 62c to 62f via the lens 63, respectively.

[0007]

However, in the above-described conventional technique, in the case of FIG. 10, since light is incident from the diffractive element surface 34 through the transmissive material 33,
Although the spectral characteristic of the incident light can be adjusted to the long wavelength side, the inherent spectral characteristic of the reflection type diffractive substrate 32 is lost by providing the translucent material 33. Also,
Wider wavelength range, for example 0.8μm, 1.3μ
In order to obtain a good spectral characteristic even for light in the m and 1.55 μm band, separate diffractive elements provided with different light-transmitting materials 33 having a refractive index suitable for each wavelength band are prepared separately. It has a problem that it must be. In addition, also in the above-mentioned prior art shown in FIG. 11, two types of diffraction gratings 64 and 65 must be prepared. Diffraction gratings are expensive, and using two diffraction gratings in one device is an obstacle to reducing the overall cost of the device.

Further, in particular, in the case of the one shown in FIG. 11, a device for accurately adjusting the arrangement of the two diffraction gratings is required, and the device inevitably becomes more expensive.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a diffractive element which can be used for a plurality of wavelength bands by one element. To provide an optical multiplexer / demultiplexer using the effect of a leverage element.

[0010]

A diffractive element of the present invention comprises a transparent substrate having first and second surfaces, periodic grooves engraved on the first surface, and the periodic grooves. The first stamped
The reflecting film is provided on the surface of, and a diffraction grating is formed from the periodic grooves and the reflecting film, thereby achieving the above object.

An antireflection film may be formed on the second surface.

The shape of the reflective film is preferably substantially symmetrical with respect to a rotation of 180 degrees about an axis parallel to the groove.

According to one embodiment of the present invention, the first
And the second surface are substantially parallel to each other.

According to another embodiment of the present invention, the first surface and the second surface form a predetermined angle.

The diffractive element of the present invention may have a transparent protective layer provided on the reflective film.

The diffractive element of the present invention may further have another antireflection film provided on the transparent protective layer.

The transparent substrate may have a plurality of portions each having a different refractive index, and the transparent protective layer comprises:
It may have a plurality of portions each having a different refractive index.

An optical multiplexer / demultiplexer according to the present invention has a diffractive element having first and second incident surfaces, and a first light input for making light incident on the first incident surface of the diffractive element. Means for receiving light that is incident on the first incident surface and diffracted by the diffractive element, and means for receiving light that is incident on the first incident surface and reflected by the diffractive element A second light input means for making the light incident on the second incident surface of the diffractive element, and a second light receiving means for receiving the light made incident on the second incident surface and diffracted by the diffractive element. It is provided, and thereby the above-mentioned object is achieved.

According to one embodiment of the present invention, the diffractive element includes a transparent substrate having first and second surfaces, and the first substrate.
And a reflective film provided on the first surface on which the periodic grooves are engraved,
The first incident surface corresponds to the first surface provided with the reflection film, and the second incident surface corresponds to the second surface.

An antireflection film may be formed on the second surface.

The shape of the reflection film of the diffractive element is preferably substantially symmetrical with respect to a rotation of 180 degrees about a predetermined axis parallel to the groove.

The diffractive element may have a transparent protective layer provided on the reflective film.

In the multiplexing / demultiplexing device of the present invention, a first lens arranged in a Littrow arrangement with respect to the first incident surface of the diffractive element and a second lens arranged in a Littrow arrangement with respect to the second incident surface of the diffractive element. The lens may be included.

Preferably, in the first and second light input means, an incident angle θ of the light incident on the first incident surface and the second incident surface is a Littrow angle θ _L , respectively.
The light is made incident such that θ _L −5 ° ≦ θ ≦ θ _L + 5 °, and the wavelength λ of the light that is diffracted by being incident on the first incident surface
₁ and the wavelength λ ₂ of the reflected light (where λ ₂ > λ ₁ )
When the refractive index of the transparent substrate is n, the interval of the grooves (pitch) is _{d, λ 2 -λ 1/2} > d, and n = lambda ₂
The relationship of / λ ₁ is satisfied.

Preferably, the wavelength λ _{1 of} the light that is incident on the first incident surface and diffracted and the wavelength λ ₂ of the reflected light (where λ ₂ > λ ₁ ) are the transparent. refractive index of the substrate is n, the refractive index n ₁ of the transparent protective layer, the interval of the grooves (pitch) is _{d, λ 2 -λ 1/2} > n 1 · d,
And n = n ₁ · λ ₂ / λ ₁ are satisfied.

The multiplexer / demultiplexer of the present invention has a diffractive element having first and second incident surfaces, and light input means for making light incident on the diffractive element, and diffracted by the diffractive element. A light receiving means for receiving light for each wavelength of the diffracted light; and an arranging means for changing the position and / or direction of at least one of the diffractive element, the light inputting means, and the light receiving means. Therefore, the above object is achieved.

According to one embodiment of the present invention, the arrangement means comprises a first arrangement for causing the light from the light input means to be incident on the first incident surface of the diffractive element, and the light input means. A second arrangement in which the light from is incident on the second incident surface of the diffractive element.

The multiplexer / demultiplexer of the present invention preferably comprises a lens for collimating the light from the light input means and condensing the light reflected by the diffraction element on the light receiving means. The first arrangement is a Littrow arrangement with respect to the first entrance surface of the diffractive element, and the second arrangement is a Littrow arrangement with respect to the second entrance surface of the diffractive element.

The arranging means may be provided with a mechanism for rotating the diffractive element, and by rotating the diffractive element, the arrangement may be changed from one of the first and second arrangements to the other.

In one embodiment of the present invention, the diffractive element comprises a transparent substrate having first and second surfaces, periodic grooves engraved on the first surface, and the periodic grooves. A reflective film provided on the first surface on which a typical groove is engraved, and the first incident surface has the first film on which the reflective film is provided.
Surface, and the second incident surface corresponds to the second surface.

An antireflection film may be formed on the second surface.

Preferably, the shape of the reflection film of the diffractive element is substantially symmetrical with respect to a rotation of 180 degrees about an axis parallel to the groove.

The diffractive element may have a transparent protective layer provided on the reflective film.

Preferably, the light input means is the first
Of the incident surface and incident angle of each of the light incident on the second incident face theta is the Littrow angle _{θ L, θ L -5 ° ≦} θ ≦ θ L
The wavelength λ _{1 of} the light which is incident on the first incident surface and is diffracted by the light so that the incident light is + 5 °, and the wavelength λ _{2 of the} light which is incident on the second incident surface and is diffracted. (However, λ ₂ > λ ₁ )
When the refractive index of the transparent substrate is n, the interval of the SL grooves (pitch) is _{d, λ 2 -λ 1/2} > d, and n = lambda ₂
The relationship of / λ ₁ is satisfied.

Further, preferably, the wavelength λ _{1 of} light incident on the first incident surface and diffracted, and the wavelength λ _{2 of} light incident on the second incident surface and diffracted (where λ ₂ > Λ ₁ ) has a refractive index n of the transparent substrate and a refractive index n of the transparent protective layer.
_1. When the groove pitch is d, λ ₂ −λ ₁
/ 2> n ₁ · d and n = n ₁ · λ ₂ / λ ₁ are satisfied.

[0036]

With the above-described structure, the diffractive element of the present invention has the first incident surface of the diffractive element (the side on which the reflective film is provided: the front surface).
Light of two different wavelength bands, that is, the light that is incident on and diffracted on the second incident surface and the light that is incident on the second incident surface (the surface provided with the antireflection film: the back surface) and is diffracted through the transparent substrate Wavelength dispersion. By forming the reflective film in a symmetrical shape between the "front" and the "back", the respective lights incident on the first and second incident surfaces have substantially the same spectral characteristics (diffraction efficiency, etc.). Is wavelength dispersed. By changing the refractive index of the transparent substrate, the wavelength of light that is incident on the second incident surface and diffracted can be adjusted.

When the transparent substrate (and / or the transparent protective layer) has a plurality of portions having different refractive indexes, light in different wavelength bands can be diffracted and wavelength-dispersed.

When the wavelength-multiplexed lights (λ ₁ and λ ₂ ) are input to the first incident surface, one of the wavelength bands (λ ₂ ) of one wavelength band (λ ₂ ) can be obtained by appropriately selecting the conditions such as the wavelength. The light is totally reflected without being diffracted.

According to the optical multiplexer / demultiplexer using the diffractive element of the present invention, the wavelength-multiplexed light incident on the first incident surface from the first optical input device is a light in a certain wavelength band (λ ₁ ). Are wavelength-dispersed and are received by the first light receiving device. Light in other wavelength bands is not diffracted and is totally reflected by the reflective film when certain conditions are met. The totally reflected light (λ ₂ ) is guided to the second incident surface of the diffractive element and is similarly diffracted through the transparent substrate. The light that is incident on the second incident surface and is wavelength-dispersed is received by the second light receiving device.

Another optical multiplexer / demultiplexer using the diffractive element of the present invention should be diffracted by providing an arrangement mechanism for changing the position and / or direction of at least one of the diffractive element, the optical input device and the light receiving device. Wavelength dispersion is performed for light in a plurality of wavelength bands by properly using the first or second incident surface of the diffraction element according to the wavelength.

In particular, when the rotating mechanism for rotating the diffraction element is provided, the angle of the diffraction grating is adjusted by the rear part of the rotating machine so that the light of the desired wavelength is focused on the light receiving device. In particular, when wavelength dispersion is performed on the long wavelength side (λ ₂ ) of the wavelength multiplexed light, the rotating mechanism section diffracts the light so that the light is incident on the second incident surface (back surface) of the diffraction element. The element is rotated so as to turn it over, and the angle is adjusted so that light having a desired wavelength is condensed on the light receiving device.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) FIG. 1A shows the structure of a diffraction element 30 according to the first embodiment of the present invention.
In the diffractive element of this embodiment, grating grooves are engraved on one surface 31 of the transparent substrate 2 at a pitch d, and the reflective film 1 is formed on the grating grooves. The reflective film 1 has characteristics as a reflective film and is formed to have a sufficiently thin film thickness. For example,
The reflective film 1 can be formed by providing a metal film having a high reflectance such as aluminum or a dielectric multilayer film on the lattice surface 31. The reflective film 1 has a film thickness of 50 to 300 n.
If m, preferably about 100 nm, the grooves can be formed uniformly without damaging the shape. The transparent substrate 2 is typically made of glass, and may be any substrate material that is transparent to the wavelength of light used. Less than,
In this specification, the term "transparent" means having a light-transmitting property with respect to the wavelength of light used.

The shape of the lattice grooves on the surface 31 is preferably
The diffraction grating formed on the front surface 31 is engraved so as to be symmetrical on both front and back surfaces. The term "symmetrical" as used herein means a substantially symmetrical shape that overlaps with respect to a rotation of substantially 180 degrees about a predetermined axis parallel to the lattice groove. For example, in FIG. 1 (a), the grating grooves are shown in a sinusoidal shape with the predetermined axis at 0 degrees. However, the shape of the lattice groove is not limited to this.

Next, the operation of the diffractive element 30 will be described with reference to FIG.
A description will be given with reference to (a). When light of wavelength λ ₁ is incident on the reflective film 1 at an angle θ ₀ from above the transparent substrate 2 shown in FIG. 1A, the diffraction element 30 functions as a reflection type diffraction grating. At this time, the angle α of the diffracted light that is first-order diffracted is represented by the following formula (1). Here, the diffraction angle α is the angle that the diffracted light makes with the normal to the lattice plane. In the following discussion, first-order diffracted light will be described.

Sin θ ₀ + sin α = λ ₁ / d (1) Especially, the diffractive element is arranged in 30 Littrow mounts.
In the case of g), the incident angle θ ₀ and the diffraction angle α become almost equal, and the diffraction efficiency can be maximized. At this time,
Approximately θ ₀ = α = θ _L (θ _L : Littrow angle),
From equation (1), sin θ ₀ = λ ₁ / (2d) (2). The incident angle theta ₀ of light is ± about the Littrow angle theta _L
Within the range of about 5 degrees, the diffraction efficiency is high and the polarization efficiency of the diffraction efficiency is small. Under this condition, the light incident on the diffractive element 30 at the angle θ ₀ has a diffraction angle α according to the wavelength λ _1.
Is diffracted by. For example, if the incident light contains a plurality of wavelengths lambda _a wavelength lambda ₁ near, lambda _b, the light of ..., the angle corresponding to each wavelength alpha _a, is diffracted alpha _b, with ... .

On the other hand, in FIG. 1A, consider a case where light of wavelength λ ₂ enters the reflective film 1 from below the transparent substrate 2 through the transparent substrate 2. The light of wavelength λ ₂ is incident on the back surface 32 of the transparent substrate 2 at an angle φ, and is incident on the reflective film 1 in the transparent substrate 2 at an angle θ ₀ ′. The refractive index of the transparent substrate 2 is n
Then, at this time, the relationship between the angles θ ₀ ′ and φ can be expressed by Expression (3) from Snell's law.

N · sin θ ₀ ′ = sin φ (3) Further, the equivalent wavelength λ ₂ ′ of light in the transparent substrate 2 can be expressed by the following equation (4).

Λ ₂ ′ = λ ₂ / n (4) Therefore, the refractive index n and the refractive index n and the wavelength λ ₂ ′ are substantially equal to the wavelength λ ₁ , and θ ₀ ′ is substantially equal to θ _0. By selecting the incident angle φ, the diffraction of the light having the wavelength λ _{2 in} the transparent substrate 2 by the reflective film 1 becomes substantially the same as the diffraction of the light having the wavelength λ ₁ which does not pass through the transparent substrate 2. . The diffractive element 30 functions as a reflection type diffraction grating having the same diffraction efficiency with respect to both lights of wavelengths λ ₁ and λ ₂ .
Further, if the grating grooves are formed symmetrically on the front and back sides, the diffraction element 30 will have the same spectral characteristic with respect to the wavelength λ ₂ as the spectral characteristic with respect to the wavelength λ ₁ .

The back surface 32 of the transparent substrate 2 is preferably flat. The direction (angle) of the back surface 32 with respect to the lattice groove arrangement direction does not necessarily have to be parallel to the lattice groove arrangement direction. For example, it is possible to form the diffraction element 33 by engraving a grating groove on one surface 31 of the transparent base material 21 having a prismatic shape as shown in FIG.

As described above, according to this embodiment, the spectral characteristics can be made the same for the light of different wavelengths incident on both the front and back surfaces of the surface (reflection film 1) on which the grating grooves are engraved. A single element can form a diffraction element that can be used in two or more wavelength bands.

(Embodiment 2) FIG. 2 shows a diffraction element 20 according to a second embodiment of the present invention. The diffractive element 20 includes an antireflection film 4 on the back surface 32 of the transparent substrate 2. The other points are similar to those of the diffraction element 30 described in the first embodiment.

As can be seen from the equation (3), generally, the angle φ at which the light of wavelength λ ₂ enters the back surface 32 (41) of the transparent substrate 2 propagates through the transparent substrate 2 and enters the reflective film 1. Since the angle θ ₀ ′ is larger than the angle θ ₀ ′, the light having the wavelength λ ₂ is easily reflected by the back surface 32. Therefore, by providing the antireflection film 4 on the back surface of the transparent substrate 2 to form the back surface 41, the transmission intensity of light incident on the transparent substrate 2 can be increased.

When the light of wavelength λ ₂ is incident on the reflection film 1 at the incident angle θ ₀ and is diffracted at the diffraction angle α ', the following equation (5) is satisfied similarly to the equation (1).

Sin θ ₀ + sin α ′ = λ ₂ / d (5) Here, if all the light of wavelength λ ₂ is reflected by the reflective film 1 without being diffracted, the diffraction angle α ′ of diffracted light of wavelength λ ₂ Satisfies the following equation (6). However, it is assumed that λ ₂ > λ ₁ .

Sin α ′> 1 (6) When the incident angle θ ₀ is the Littrow angle θ _L , the equation (2) is established. Therefore, substituting the equations (5) and (2) into the equation (6), The following expression (7) is obtained.

[0057] _{λ 2 -λ 1/2> d} (7) Therefore, if the wavelength lambda ₁ and lambda ₂ satisfies the relationship of the equation (7), the light of these wavelengths are multiplexed diffraction element 20
When incident on (or 30), only the light of wavelength λ ₁ is diffracted and the light of wavelength λ ₂ is totally reflected.

On the other hand, when light of wavelength λ ₂ enters from the back surface 41 (32) of the diffractive element 20 (or 30), the refractive index n of the transparent substrate 2 is expressed by the following equation (8) n = λ ₂ / λ ₁ (8) is satisfied, the equivalent wavelength of light of wavelength λ ₂ in the transparent substrate is λ ₁ , so light incident at wavelength λ 2 is diffracted by the reflection film 1 without being totally reflected. It

(Embodiment 3) Next, a diffraction element 34 according to a third embodiment of the present invention will be described with reference to FIG.
In the diffraction element 34, the transparent protective layer 5 is formed on the upper surface of the reflective film 1. The other points are similar to those of the diffraction element 30 described in the first embodiment.

When light of wavelength λ ₃ is incident on the upper surface 51 of the transparent protective layer 5 at an incident angle ψ, propagates through the transparent protective layer 5 and is incident on the reflective film 1 at an incident angle θ ′, the transparent protective layer 5 Refractive index n
Assuming ₁ , the relationship between the incident angle ψ and θ ′ is given by the following equation (9).

N ₁ · sin θ ′ = sin ψ (9) The equivalent wavelength λ ₃ ′ of the light propagating in the transparent protective layer 5 is given by the following expression (10). λ ₃ '= λ ₃ / n ₁ (10) Therefore, using the transparent protective layer 5 having the refractive index n ₁ such that n ₁ = λ ₁ / λ ₃ , θ ′ = θ ₀ (= θ _L ). By adjusting the incident angle ψ so that the light having the wavelength λ ₃ incident on the diffraction grating 34 is the same as the case where the light having the wavelength λ ₁ incident on the diffraction element 30 of the first embodiment is diffracted. Diffracted with diffraction efficiency and spectral characteristics.

The behavior of incident light in the transparent substrate 2 is
When the refractive index of the transparent substrate 2 is n, it can be expressed by equations (3) and (4) as in the first embodiment.

The light of wavelength λ ₂ is diffracted by the diffraction element 3 at the angle ψ.
4 is incident on the upper surface 51, propagates through the protective film 5, and is reflected by the reflective film 1.
The conditions under which the light incident on the light source 3 at the angle θ ′ is totally reflected without being diffracted by the reflective film 1 are the same as those described in the second embodiment.
It is calculated as follows. In the transparent protective layer 5, the equivalent wavelength λ ₂ ″ = λ ₂ / n ₁ and the equivalent wavelength λ ₃ ′ = λ
About ₃ / n ₁ = _{λ 1,} since Equation (7) _{holds, λ 2 -λ 3/2>} n 1 · d (11) n = n 1 · λ 2 / λ 3 (12) According to the present embodiment For example, by providing the transparent protective layer 5 on the reflective film 1, it is possible to block the surface of the grating from the outside air, suppress corrosion, and endure long-term use.

(Embodiment 4) FIG. 4 shows a diffractive element 35 according to a fourth embodiment of the present invention. The diffractive element 35 includes the antireflection film 4 on the back surface 32 of the transparent substrate 2, and further provides the antireflection film 6 on the surface 51 of the transparent protective layer 5. The other points are the same as those of the diffraction element 34 described in the third embodiment.

With such a structure, the reflection of the light incident on the upper surface 52 and the lower surface 41 of the diffraction element 35 can be suppressed and efficiently propagated to the transparent protective layer 5 and the transparent substrate 2.

(Embodiment 5) FIGS. 5A and 5B show diffractive elements 36 and 37 of the fifth embodiment of the present invention. The transparent substrate 2 and the transparent protective layer 5 of the diffractive element 36 are each formed of a plurality of portions having different refractive indexes. Figure 5
As shown in (a), for example, the transparent substrate 2 is formed of two parts, a part having a refractive index n _{3 and} a part having a refractive index n ₄ . The light having the wavelength λ that has entered the portion having the refractive index n _k is diffracted at the equivalent wavelength λ ′ = λ / n _k (k = 3, 4). Area (λ
= N _k λ ₁ , k = 3, 4) can be diffracted.
Similarly, when the transparent protective layer 5 is also formed of two parts, that is, a part having a refractive index n _{1 and} a part having a refractive index n ₂ , the diffractive element 36 has two wavelength regions (λ = n _k λ _{1) which} are incident on the upper surface 51. , K =
The light of 1, 2) can be diffracted. The number of portions having different refractive indexes is not limited to two, and if necessary, it may be provided only on one of the transparent substrate 2 or the transparent protective layer 5.

In the diffraction element 37 shown in FIG. 5B, the antireflection film 4 is provided on the back surface 32 of the transparent substrate 2, and the antireflection film 6 is provided on the surface 51 of the transparent protective layer 5. The other points are similar to those of the diffraction element 36. With such a configuration, reflection of light incident on the upper surface 52 and the lower surface 41 of the diffractive element 35 can be suppressed and efficiently propagated to the transparent protective layer 5 and the transparent substrate 2. The antireflection film may be provided on only one of the upper surface 51 and the lower surface 32.

(Embodiment 6) Next, an optical multiplexer / demultiplexer using the diffraction element of the present invention will be described with reference to FIG.

FIG. 6 shows a diffraction element 2 according to the second embodiment of the present invention.
It is a block diagram of the optical multiplexer / demultiplexer when 0 is used. In addition to this, the diffractive element includes
Alternatively, 34 to 37 may be used. The diffractive element 20, the lens 7, the first input fiber 10, and the first light receiving fiber array 12 are arranged in a Littrow arrangement. Diffractive element 2
The same applies to 0, the lens 9, the second input fiber 11, and the second light receiving fiber array 13. The lens 8 is for guiding the light totally reflected by the reflective film 1 of the diffraction element 20 to the second input fiber 11.

The light emitted from the first input fiber 10 is wavelength-multiplexed and has a spectral distribution as shown in FIG. 7, for example. Wavelength multiplexed light 1 on the short wavelength side
4 is a wavelength band having spectral components of wavelengths λ _a , λ _b , λ _c , and λ _d , and the wavelength-multiplexed light 15 on the long wavelength side is
Is a wavelength band having spectral components of wavelengths λ _e , λ _f , λ _g , and λ _h . Hereinafter, the wavelength band on the short wavelength side will be represented by λ ₁ , and the wavelength band on the long wavelength side will be represented by λ ₂ .

The operation of the optical multiplexer / demultiplexer according to the present invention will be described below. Although the operation of the optical demultiplexer will be described here, the operation of the optical multiplexer can be considered in exactly the same way by reversing the input and output of light.

The light wavelength-multiplexed with wavelengths λ _{a to} λ _h is
Is emitted from the input fiber 10, is collimated by the lens 7, and is incident on the grating surface 19 of the diffractive element 20 provided with the reflection film 1 at an incident angle θ ₀ . The grating surface 19 of the diffractive element 20 provided with the reflection film 1 has a wavelength dispersion ability with high diffraction efficiency for the wavelength multiplexed light 14 in the wavelength region λ ₁ on the short wavelength side. The light having the wavelengths λ _{a to} λ _d is wavelength-dispersed according to the equation (1), and is focused again on each optical fiber of the first light receiving fiber array 12 via the lens 7. In Figure 6,
It is shown schematically for light of wavelength λ _d . In this way, the light having the wavelengths λ _{a to} λ _d is wavelength-separated and output from each optical fiber of the light receiving fiber array 12. On the other hand, since the wavelength-multiplexed light 15 in the wavelength range λ ₂ on the long wavelength side satisfies the inequality of the expression (7), it is totally reflected by the grating surface 19 provided with the reflection film 1 without being diffracted and wavelength-dispersed. It The totally reflected light having the wavelengths λ _{e to} λ _h is guided to the second input fiber 11 via the lens 8.

The wavelength multiplexed light 15 emitted from the second input fiber 11 is collimated by the lens 9 and is incident on the back surface 41 of the diffractive element 20 provided with the antireflection film 4 with an incident angle φ.
Is incident at. Since the refractive index n of the transparent substrate 2 satisfies the expression (6), the wavelength-multiplexed light 15 in the wavelength band λ ₂ is wavelength-dispersed with high diffraction efficiency by the reflective film 1 through the transparent substrate 2 as well. It The wavelength-dispersed light of each wavelength λ _{e to} λ _h is coupled to each optical fiber of the second light receiving fiber array 13 via the lens 9 and output.

The diffraction element 20 has a lattice spacing d of, for example,
When a blazed diffraction grating having a number of grating grooves of 1200 / mm is used, the diffraction efficiency is high. For example, when performing optical demultiplexing of wavelength-multiplexed light such that the wavelength range λ ₁ on the short wavelength side is 0.8 μm band and the wavelength range λ ₂ on the long wavelength side is 1.3 μm band, the transparent substrate 2 The refractive index n may be set to 1.5 to 1.6. In this case, the incident angle θ of the light that enters the diffraction element 20 from the first input fiber 10
₀ is about 30 degrees, and the incident angle of the light entering the diffractive element 20 from the second input fiber 11 is about 54 degrees. As a material for the transparent substrate 2, a dielectric band material such as glass or transparent resin may be used.

As described above, according to this embodiment, by using one diffractive element, it is possible to obtain an optical multiplexing / demultiplexing device having high diffraction efficiency in two wavelength bands. That is, it is possible to configure an optical multiplexing / demultiplexing device that has a low insertion loss of incident light and is capable of wide wavelength band chromatic dispersion.

(Embodiment 7) Next, an optical multiplexer / demultiplexer according to another embodiment of the present invention will be described with reference to FIGS. 8 (a) and 8 (b).

In FIGS. 8A and 8B, the diffractive element 20, the lens 7, the input fiber 10 and the light receiving fiber 16 are arranged in a Littrow arrangement. The light receiving element 20 can be rotated about the rotation axis parallel to the lattice groove direction by the rotation mechanism section 17. That is, both front and back surfaces (19 and 41) of the diffractive element 20 can be used for the light incident through the lens 7, and the incident angle of the light incident on each surface can be adjusted. FIG. 8A shows a configuration for selectively wavelength-dispersing the wavelength division multiplexed light 14 in the wavelength region λ ₁ on the short wavelength side, and FIG. 8B shows a wavelength region λ _{2 in the} long wavelength band.
This is a configuration for selectively wavelength-dispersing the wavelength-multiplexed light 15 of. In addition to this, the diffractive element may be the diffractive element 30 or 34 to 37 in the above-described embodiment.

The operation of the optical multiplexer / demultiplexer configured as described above will be described below with reference to FIGS. 7, 8 (a) and 8 (b).

In FIGS. 8A and 8B, the wavelength λ _a
The light wavelength-multiplexed with ˜λ _h is emitted from the input fiber 10, collimated by the lens 7, and enters the diffraction element 20. In the case of FIG. 8A, the multiplexer / demultiplexer is arranged so that the incident light is incident on the grating surface 19 of the diffraction element 20 provided with the reflection film 1 at the incident angle θ. Incident angle θ is θ
When substantially equal to ₀ , the wavelength division multiplexed light 14 in the wavelength range λ ₁ is wavelength-dispersed with high diffraction efficiency by the diffraction element 20. Since the input fiber 10 and the light receiving fiber 16 are arranged adjacent to each other, only the diffracted light having a wavelength diffracted at the incident angle represented by the equation (2), that is, the Littrow angle is coupled to the light receiving fiber 16. At this time, since the light in the wavelength range λ ₂ is not diffracted by the diffraction element 20, only the light in the wavelength range λ ₁ is selectively chromatically dispersed as follows.

In FIG. 8A, it is assumed that light of wavelength λ _a is coupled to the light receiving fiber 16 when the incident angle θ = θ _a .
The diffractive element 20 is slightly rotated in the counterclockwise direction by the rotation mechanism section 17 and the light of wavelengths λ _b , λ _c , and λ _d is sequentially received as the incident angle is changed to θ _b , θ _c , and θ _d. Can be combined with.

Next, in the case of selectively wavelength-dispersing the wavelength multiplexed light 15 in the wavelength range λ ₂ on the long wavelength side, the rotation mechanism section 1
7, the diffractive element 20 is rotated so as to be turned upside down with respect to the incident light, and is arranged as shown in FIG. As a result, the wavelength multiplexed light emitted from the input fiber 10 is
The light enters the back surface 41 at an incident angle φ and then enters the lattice surface (reflection film 1) through the antireflection film 4 and the transparent substrate 2. And
The wavelength-multiplexed light 15 is wavelength-dispersed with high diffraction efficiency by the diffraction element 20, as in the case of the wavelength-multiplexed light 14. Similarly to the above, by adjusting the incident angle by the rotation mechanism unit 17, it is possible to couple the lights of the desired wavelengths λ _{e to} λ _{h to} the light receiving fiber 16 and selectively output them.

As described above, according to the present embodiment, by rotating one diffractive element, wavelength dispersion with high diffraction efficiency is selectively performed in two wavelength bands, and output from one light receiving fiber. be able to. That is, the insertion loss of incident light is low, and wide wavelength band chromatic dispersion can be performed. Further, as compared with the sixth embodiment, it is not necessary to provide the second input fiber and the second light receiving fiber array. The rotating mechanism 17 can also be implemented by a stepping motor capable of highly accurate positioning, and various driving methods for controlling other rotating mechanisms.

In this embodiment, the example in which the diffraction element 20 is rotated has been described, but the same effect can be obtained by moving the input fiber 10 and the light receiving fiber 16. In this case, it can be realized by using a highly accurate moving mechanism, for example, a laminated piezoelectric element such as a piezo element or a linear actuator applied to an optical pickup.

In this embodiment, the diffractive element 20 is used for explanation. However, for example, when the diffractive element 34 or 35 is used, it is high not only in two wavelength bands but also in more wavelength bands. Wavelength dispersion can be performed with diffraction efficiency. INDUSTRIAL APPLICABILITY The present invention is particularly useful for wavelength division multiplexing optical communication in which the number of multiplexed signals is large in the 0.8 μm band and the 1.3 μm band.

[0085]

As is apparent from the above description,
According to the present invention, one element for a plurality of wavelength bands,
A diffractive element that can be used with high diffraction efficiency can be provided. In addition, by using this diffractive element, it is possible to provide an optical multiplexer / demultiplexer capable of performing wavelength dispersion with high diffraction efficiency for a plurality of wavelength bands. Furthermore, because it is not necessary to use multiple diffraction gratings,
The optical demultiplexer can be provided at a low price with a simple configuration.

[Brief description of drawings]

1A and 1B are diagrams showing a configuration of a diffractive element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a diffractive element according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a diffractive element according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a diffraction element according to a fourth exemplary embodiment of the present invention.

5 (a) and 5 (b) are diagrams showing a configuration of a diffraction element in a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of an optical multiplexer / demultiplexer according to the present invention.

FIG. 7 is a conceptual diagram showing a spectral distribution of wavelength multiplexed light having wavelengths λ _{a to} λ _h .

8A and 8B are diagrams showing the configuration of another optical multiplexer / demultiplexer according to the present invention.

FIG. 9 is a diagram showing wavelength and lattice spacing dependence of diffraction efficiency.

FIG. 10 is a diagram showing a configuration of a conventional diffraction element.

FIG. 11 is a diagram showing a configuration of a conventional optical multiplexer / demultiplexer.

[Explanation of symbols]

 1 Reflective Film 2 Transparent Substrate 4 Antireflection Film 7 Lens 8 Lens 9 Lens 10 First Input Fiber 11 Second Input Fiber 12 First Light-Receiving Fiber Array 13 Second Light-Receiving Fiber Array 20 Diffractive Element

Claims (31)

[Claims] 1. A transparent substrate having first and second surfaces, a periodic groove imprinted on the first surface, and a periodic groove provided on the first surface imprinted with the periodic groove. And a diffraction grating formed from the periodic grooves and the reflection film. 2. The diffractive element according to claim 1, wherein an antireflection film is formed on the second surface. 3. The shape of the reflective film is substantially symmetric with respect to a rotation of substantially 180 degrees about a predetermined axis parallel to the groove. Diffractive element. 4. The diffractive element according to claim 1, wherein the first surface and the second surface are substantially parallel to each other. 5. The diffractive element according to claim 1, wherein the first surface and the second surface form a predetermined angle. 6. The diffractive element according to claim 1, further comprising a transparent protective layer provided on the reflective film. 7. The method according to claim 6, further comprising another antireflection film provided on the transparent protective layer.
The diffraction element according to 1. 8. The diffraction element according to claim 1, wherein the transparent substrate has a plurality of portions each having a different refractive index. 9. The diffraction element according to claim 6, wherein the transparent substrate has a plurality of portions each having a different refractive index. 10. The transparent protective layer has a plurality of portions each having a different refractive index.
The diffraction element according to 1. 11. The transparent protective layer has a plurality of portions each having a different refractive index.
The diffraction element according to 1. 12. The diffractive element according to claim 9, further comprising another antireflection film provided on the transparent protective layer. 13. A multiplexer / demultiplexer having a diffractive element having first and second incident surfaces, the first light input means for making light incident on the first incident surface of the diffractive element, First light receiving means for receiving the light incident on the first incident surface and diffracted by the diffractive element; and light for receiving the light incident on the first incident surface and reflected by the diffractive element, Second light input means for making the light incident on the second incident surface of the element, and second light receiving means for receiving the light made incident on the second incident surface and diffracted by the diffractive element. An optical multiplexing / demultiplexing device. 14. The diffractive element includes a transparent substrate having first and second surfaces, a periodic groove imprinted on the first surface, and the first groove imprinted with the periodic groove. And a reflection film provided on the surface of the first incidence surface, the first incidence surface corresponds to the first surface on which the reflection film is provided, and the second incidence surface is the first incidence surface. The optical multiplexer / demultiplexer according to claim 13, which corresponds to the second surface. 15. The optical multiplexer / demultiplexer according to claim 14, wherein an antireflection film is formed on the second surface. 16. The shape of the reflection film of the diffraction element is
15. Substantially symmetrical about a 180 degree rotation about a predetermined axis parallel to the groove.
The optical multiplexer / demultiplexer described in. 17. The optical multiplexer / demultiplexer according to claim 14, wherein the diffraction element has a transparent protective layer provided on the reflective film. 18. A first lens arranged in a Littrow arrangement with respect to the first incident surface of the diffractive element, and a second lens arranged in a Littrow arrangement with respect to the second incident surface of the diffractive element. The optical multiplexer / demultiplexer according to claim 14, wherein 19. The first and second light input means, wherein an incident angle θ of the light incident on the first incident surface and the second incident surface is a Littrow angle θ _L , respectively.
The light is incident such that θ _L −5 ° ≦ θ ≦ θ _L + 5 °, and the wavelength λ _{1 of} the light diffracted by being incident on the first incident surface,
And the wavelength λ ₂ of the reflected light (where λ ₂ > λ ₁ ) is
Refractive index of the transparent substrate is n, the interval of the grooves (pitch) when it is d, characterized in that it satisfies the _{λ 2 -λ 1/2> d} n = λ 2 / λ 1 of the relationship The optical multiplexer / demultiplexer according to claim 14. 20. A first lens Littrow arranged with respect to the first entrance surface of the diffractive element, and a second lens Littrow arranged with respect to the second entrance surface of the diffractive element. The optical multiplexer / demultiplexer according to claim 17, wherein 21. In each of the first and second light input means, an incident angle θ of the light incident on the first incident surface and the second incident surface is a Littrow angle θ _L ,
The light is incident such that θ _L −5 ° ≦ θ ≦ θ _L + 5 °, and the wavelength λ _{1 of} the light diffracted by being incident on the first incident surface,
And the wavelength λ ₂ of the reflected light (where λ ₂ > λ ₁ ) is
Refractive index n of the transparent substrate, a refractive index n ₁ of the transparent protective layer, the interval of the grooves (pitch) is _{d, λ 2 -λ 1/2} > n 1 · d n = n 1 · The optical multiplexer / demultiplexer according to claim 17, wherein the relationship of λ ₂ / λ ₁ is satisfied. 22. A multiplexer / demultiplexer having a diffractive element having first and second incident surfaces, wherein light input means for making light incident on the diffractive element, and light diffracted by the diffractive element are provided. Light receiving means for receiving each wavelength of the diffracted light, and arranging means for changing the position and / or direction of at least one of the diffractive element, the light inputting means, and the light receiving means. A characteristic optical multiplexer / demultiplexer. 23. The first arranging means causes the light from the light inputting means to be incident on the first incident surface of the diffractive element, and the light from the light inputting means into the diffractive element of the diffractive element. The optical multiplexer / demultiplexer according to claim 22, which enables a second arrangement in which the light is incident on the second incident surface. 24. A lens for collimating the light from said light input means and condensing the light reflected by said diffractive element on said light receiving means, said first arrangement comprising said diffractive element. 24. The optical multiplexer / demultiplexer according to claim 23, wherein the first Littrow arrangement of the diffractive element is a Littrow arrangement and the second arrangement is a Littrow arrangement of the diffractive element. . 25. The arrangement means includes a mechanism for rotating the diffractive element, and by rotating the diffractive element, the arrangement is changed from one of the first and second arrangements to the other. The optical multiplexer / demultiplexer according to claim 23. 26. The diffractive element includes a transparent substrate having first and second surfaces, a periodic groove engraved on the first surface, and the first groove engraved with the periodic groove. And a reflection film provided on a surface of the first incidence surface, the first incidence surface corresponds to the first surface provided with the reflection film, and the second incidence surface is the first incidence surface. 24. The optical multiplexer / demultiplexer according to claim 23, which corresponds to the second surface. 27. An optical multiplexing / demultiplexing device, wherein an antireflection film is formed on the second surface. 28. The shape of the reflection film of the diffraction element is
27. The optical multiplexer / demultiplexer according to claim 26, which is substantially symmetrical with respect to a rotation of 180 degrees about an axis parallel to the groove. 29. The optical multiplexer / demultiplexer according to claim 26, wherein the diffractive element has a transparent protective layer provided on the reflective film. 30. The incident angle θ of each of the lights incident on the first incident surface and the second incident surface is formed by the light input unit.
As the Littrow angle θ _L , the light is made incident such that θ _L −5 ° ≦ θ ≦ θ _L + 5 °, and the wavelength λ _{1 of} the light diffracted by being incident on the first incident surface, and Wavelength λ of light that is incident on the second incident surface and is diffracted
₂ (where lambda _2> lambda ₁₎ when the refractive index of the transparent substrate is n, the interval of the SL grooves (pitch) is _{d, λ 2 -λ 1/2} > d n = λ 2 / λ 1 27. The optical multiplexing / demultiplexing device according to claim 26, wherein 31. The light input means has an incident angle θ of the light incident on the first incident surface and the second incident surface,
The Littrow angle θ _L is such that θ _L −5 ° ≦ θ ≦ θ _L + 5 °, and the wavelength λ _{1 of} the light diffracted by the first incident surface and diffracted. Wavelength λ of light that is incident on the incident surface of 2 and is diffracted
₂ (where λ ₂ > λ ₁ ) is such that the refractive index of the transparent substrate is n, the refractive index of the transparent protective layer is n ₁ , and the groove spacing (pitch)
When There is _{d, λ 2 -λ 1/2} > n 1 · d n = optical multiplexing and demultiplexing device according to claim 27, characterized in that satisfies the n ₁ · λ ₂ / λ ₁ of the relationship .