JP2000111831A - Virtually imaged phased array (VIPA) with spacer member and optical path length adjusting member - Google Patents

Abstract

(57) [Problem] To provide a wavelength demultiplexer capable of simultaneously separating a plurality of carriers from wavelength-division multiplexed light with a simple configuration. A virtual imaged phased array (VIPA) that receives input light of each wavelength and generates spatially distinguishable output light according to the wavelength of the input light.
VIPA has first and second surfaces. The second surface has a reflectance for transmitting a part of incident light. The first and second surfaces are arranged such that input light is reflected multiple times between the first and second surfaces and a plurality of lights are transmitted from the second surface. The plurality of transmitted lights interfere with each other and produce output light that is spatially distinguishable from output light generated for input light having any other wavelength within the continuous range of wavelengths. The spacer member has a coefficient of thermal expansion of approximately 0, and keeps the relative position between the first and second surfaces constant. Preferably, the coefficient of thermal expansion of the spacer member is 10 ⁻⁵ / ° C. or less. More preferably, the thermal expansion coefficient of the spacer member is 1
0 ^-6 / ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a virtual imaged phased array (VIPA),
The present invention relates to a wavelength demultiplexer that receives wavelength division multiplexed light composed of a plurality of carriers and demultiplexes the wavelength division multiplexed light into a plurality of spatially distinguishable light fluxes corresponding to the plurality of carriers.

[0002]

2. Description of the Related Art Wavelength division multiplexing is used in fiber optic communications to transfer relatively large amounts of data at high speeds. That is, each of the plurality of carriers modulated with the information is multiplexed with the wavelength division multiplexed light. The wavelength division multiplexed light is then transmitted to the receiver via one optical fiber. The receiver demultiplexes the wavelength division multiplexed light into individual carriers and detects the individual carriers. Thus, a communication system can transfer a relatively large amount of data via an optical fiber.

[0003] Therefore, the ability of a receiver to accurately demultiplex wavelength division multiplexed light greatly affects the performance of a communication system. For example, even if many carriers are multiplexed with wavelength division multiplexed light, wavelength division multiplexed light should not be transmitted unless the receiver can accurately demultiplex the wavelength division multiplexed light. Therefore, it is desired that the receiver includes a high-precision wavelength demultiplexer.

FIG. 1 is a diagram showing a conventional filter using a multilayer interference film used as a wavelength demultiplexer. According to FIG. 1, the multilayer interference film 20 is formed by a transparent substrate 22. The light 24, which is parallel light, enters the multilayer interference film 20 and is repeatedly reflected inside the multilayer interference film 20. Under the optical conditions determined by the characteristics of the multilayer interference film 20, only the light 26 of the wavelength λ2 can be transmitted. The light 28 including all the light that does not satisfy the optical conditions does not pass through the multilayer interference film 20 and is reflected. Thus, the filter as shown in FIG. 1 is suitable for demultiplexing wavelength division multiplexed light including only two carriers having different wavelengths. But,
Such a filter itself cannot separate wavelength division multiplexed light having more than two carriers.

FIG. 2 is a diagram showing a conventional Fabry-Perot interferometer used as a wavelength demultiplexer. According to FIG. 2, the high reflectivity reflective films 30 and 32 are parallel to each other.
The light 34 as parallel light is incident on the reflection film 30 and is reflected by the reflection film 3.
It is reflected many times between 0 and 32. The light 36 of the wavelength λ2 that matches the transmission condition determined by the characteristics of the Fabry-Perot interferometer passes through the reflection film 32. The light 38 of the wavelength λ1 that does not meet the transmission condition is reflected. Thus, light having two different wavelengths is split into two different lights, each corresponding to two different wavelengths. Thus, like the filter shown in FIG. 1, the conventional Fabry-Perot interferometer is useful for demultiplexing wavelength division multiplexed light containing only two carriers of different wavelengths, λ1 and λ2. However, such a Fabry-Perot interferometer cannot separate wavelength division multiplexed light having more than two carriers.

FIG. 3 is a diagram showing a conventional Michelson interferometer used as a wavelength demultiplexer. According to FIG. 3, the parallel light 40 enters the half mirror 42 and is split into a first light 44 and a second light 46 which are orthogonal to each other. The reflection mirror 48 reflects the first light 44, and
8 reflects the second light 46. The distance between the half mirror 42 and the reflection mirror 48 and the distance between the half mirror 42 and the reflection mirror 50 indicate optical path differences. The light reflected by the reflection mirror 48 is returned to the half mirror 42, and interferes with the light reflected by the reflection mirror 50 and returned to the half mirror 42. As a result, each wavelength λ1
And λ2 lights 52 and 54 are separated from each other. Like the filter of FIG. 1 and the Fabry-Perot interferometer of FIG. 2, the Michelson interferometer of FIG. 3 is useful for demultiplexing wavelength division multiplexed light containing only two carriers of different wavelengths λ1 and λ2. is there. However, such a Michelson interferometer cannot split a wavelength division multiplexed light containing more than two carriers.

[0007] It is possible to combine several filters, Fabry-Perot interferometers and Michelson interferometers into a large array and demultiplex additional wavelength carriers from one wavelength division multiplexed light. However, such an arrangement is expensive, ineffective, and constitutes an unnecessarily large receiver.

[0008] Diffraction gratings or waveguide array gratings are often used to split wavelength division multiplexed light consisting of two or more wavelength carriers. FIG. 4 is a diagram illustrating a conventional diffraction grating for demultiplexing wavelength division multiplexed light. According to FIG. 4, the diffraction grating 56 has an uneven surface 58. The parallel light 60 having a plurality of different wavelength carriers is
The light is incident on the uneven surface 58. Individual wavelength carriers are reflected and interfere with light reflected from different steps of the grating. As a result, carriers 62, 6 having different wavelengths
4 and 66 are output at different angles from the diffraction grating 56 and are separated from each other.

However, the diffraction grating outputs different wavelength carriers with a relatively small angle difference. Therefore, the angular dispersion generated by the diffraction grating is very small. As a result, it is difficult for the receiver to accurately receive the various carrier signals that are split by the diffraction grating. This problem is particularly encountered in a diffraction grating that splits wavelength division multiplexed light having a large number of carriers of relatively close wavelengths.

Further, the diffraction grating is affected by the polarization of the incident light. Therefore, the polarization of the incident light can affect the performance of the diffraction grating. In addition, the uneven surface of the diffraction grating requires a complicated manufacturing process to generate an accurate diffraction grating.

FIG. 5 is a diagram showing a conventional waveguide array grating for splitting wavelength division multiplexed light. According to FIG. 5, light composed of a plurality of different wavelength carriers is received via an entrance 68 and split via a number of waveguides 70.
Light exits 72 are at the ends of the individual waveguides 70 and generate output light 74. The waveguides 70 have different lengths from each other,
Provides light paths of different lengths. Accordingly, the light passing through the waveguide 70 has different optical path lengths and interferes with each other to form an output 74 in different directions for different wavelengths via the exit 72.

In a waveguide array grating, the angular dispersion can be adjusted to some extent by appropriately configuring the waveguide. However, waveguide array gratings are affected by temperature changes and other environmental factors. Therefore, temperature changes and environmental factors make it difficult to properly adjust performance.

Accordingly, an object of the present invention is to provide a simple configuration,
An object of the present invention is to provide a wavelength demultiplexer capable of simultaneously separating a plurality of carriers from wavelength multiplexed light. Another object of the present invention is to provide a wavelength demultiplexer that disperses separated carriers with relatively large angular dispersion and is resistant to changes in environmental conditions.

[0014]

The object of the invention is achieved by providing an apparatus for receiving input light of each wavelength in a continuous range of wavelengths. The apparatus includes an angle dispersion device having a first surface and a second surface. The second aspect is
It has a reflectance such that a part of incident light is transmitted. The first and second surfaces are arranged to reflect the input light a plurality of times between the first and second surfaces such that a plurality of lights are transmitted from the second surface. The plurality of transmitted lights interfere with each other to produce output light that is spatially distinguishable from output light generated for input light of any other wavelength in the continuous range of wavelengths. The spacer member maintains a relative position so that the arrangement of the first and second surfaces is constant, and preferably has a coefficient of thermal expansion of approximately zero. In order to obtain a thermal expansion coefficient of approximately 0, the magnitude of the thermal expansion coefficient of the spacer member is preferably 10 ⁻⁵ / ° C. or less. More preferably, the magnitude of the thermal expansion coefficient of the spacer member is 10 ⁻⁶ / ° C. or less.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention, examples of which are illustrated in the accompanying drawings, are described in detail. In these figures, like reference numbers refer to like components.

FIG. 6 illustrates a virtual imaged phased array (VIP) according to one embodiment of the present invention.
FIG. Further, hereinafter, "wavelength demultiplexer",
"Virtually imaged phased array" and "VIPA" are used interchangeably to describe various embodiments of the present invention.

Referring to FIG. 6, VIPA 76 is preferably made from a thin sheet of glass. The input light 77 is collected on a line 78 by a lens 80, such as a semi-cylindrical lens, and the input light 77 travels into a VIPA 76. Line 78 is
Hereinafter, it is referred to as a “focal line”. Input light 77 propagates radially from focal line 78 within the VIPA. The VIPA 76 outputs a light beam 82 that is collimated light. Here, the output angle of the light beam 82 changes as the wavelength of the input light 77 changes. For example, when the input light 77 has the wavelength λ1,
The VIPA 76 outputs the light flux 82a having the wavelength λ1 in a specific direction. When the input light 77 has the wavelength λ2, VIPA
76 outputs the light beam 82b of the wavelength λ2 in different directions. Accordingly, VIPA 76 generates light beams 82a and 82b that are spatially distinguishable from each other. The input light 77 includes both the wavelengths λ1 and λ2, and the VIPA 76 outputs the light beams 82a and 82b at the same time.

FIG. 7 illustrates V, according to one embodiment of the present invention.
FIG. 3 is a detailed view showing an IPA 76. According to FIG.
A76 is made of, for example, glass, and has a reflective film 122.
And a plate 120 having Reflective film 122
Preferably has a reflectance of approximately 95% or more and less than 100%. The reflection film 124 preferably has a reflectance of approximately 100%. Irradiation window 126 is formed on plate 120 and preferably has a reflectance of approximately 0%.

The input light 77 passes through an illumination window to a lens 80.
Is focused on the focal line 78, and the reflection films 122 and 124
Causes multiple reflections between them. The focal line 78 is preferably on the surface of the plate 120 on which the reflective film 122 is formed. Accordingly, the focal line 78 is essentially through the illumination window 126
This is a line focused on the reflection film 122. The width of the focal line 78 is called the “beam waist” of the input light 77 when condensed by the lens 80. An embodiment of the present invention, as shown in FIG.
The beam waist of the input light 77 is focused on the surface having the reflective film 122). By focusing the beam waist on the far side of plate 120, in this embodiment of the invention,
(I) the area of the input light 77 traveling through the irradiation window 126 (eg, the area “a” shown in FIG. 10, described in more detail below), and (ii) the input light 77 is first reflected by the reflective film 124. When this is done, the likelihood of overlap between regions of light on reflective film 124 (eg, region "b" shown in FIG. 10, described in more detail below) is reduced. It is desirable to reduce such overlap to ensure proper operation of the VIPA.

In FIG. 7, the optical axis 132 of the input light 77
Has a small tilt angle θ ₀ . Assuming that the reflectance of the reflection film 122 is 95%, at the time of the first reflection of the reflection film 122, 5% of the light passes through the reflection film 122 and diffuses after the beam waist, and 95% of the light Is reflected toward the reflection film 124. After being reflected once by the reflective film 124, the light strikes the reflective film 122 again, but is shifted by an amount d. Then, 5% of the light passes through the reflective film 122. Similarly, as shown in FIG. 7, light is split into many paths at a fixed interval d. A beam shape is formed for each pass, and light diffuses from the virtual image 134 of the beam waist. The virtual images 134 are arranged at a constant interval 2t along a vertical line of the plate 120. Here, t is the thickness of the plate 120. The beam waist positions in the virtual image 134 are automatically arranged, and there is no need to adjust the individual positions. Light diffused from the virtual image 134 interferes with each other to form collimated light 136 that propagates in a direction that changes according to the wavelength of the input light 77.

The interval between the optical paths is d = 2tSin θ ₀ , and the difference between the optical path lengths of the adjacent beams is 2tCos θ ₀
It is. The angular variance is the ratio of these two numbers, cot
θ ₀ . As a result, VIPA produces a fairly large angular dispersion.

As can be readily seen from FIG. 7, the phrase "virtual imaged phased array" is:
It comes from the formation of an array of virtual images 134. FIG. 8 illustrates a line VIA of the VIPA 76 of FIG. 6 according to an embodiment of the present invention.
FIG. 8 is a diagram showing a cross section along II-VIII. According to FIG. 8, the plate 120 has reflective surfaces 122 and 124. The reflecting surfaces 122 and 124 are parallel to each other and
Are separated by a thickness t. Reflective surfaces 122 and 12
4 is a reflection film typically provided on the plate 120. As described above, the reflecting surface 124 has a reflectance of approximately 100% except for the irradiation window 126, and the reflecting surface 122
Has a reflectance of about 95% or more. Therefore, the reflection surface 122 has a transmittance of approximately 5% or less, and approximately 5% or less of light incident on the reflection surface 122 is transmitted, and approximately 95%.
The above light is reflected. The reflectivity of the reflective surfaces 122 and 124 can be easily changed depending on the particular application of VIPA. However, in general, the reflective surface 122 must have a reflectance of less than 100% and must transmit incident light.

The reflection surface 124 has an irradiation window 126. The illumination window 126 allows light to pass through and preferably has no or very low reflectivity. Irradiation window 1
26 receives the input light 77 and transmits the input light 77 to the reflection surface 12.
Light is received between 2 and 124 and reflected.

FIG. 8 shows a cross section along the line VIII--VIII of FIG. 6, so that the focal line 78 of FIG.
, It appears as a "point". The input light 77 is
It propagates radially from the focal line 78. Further, as shown in FIG. 8, the focal line 78 is located on the reflection surface 122. The focal line 78 need not be on the reflective surface 122, but the movement of the position of the focal line 78 is
It causes a small change in the characteristics of 76.

As shown in FIG. 8, the input light 77 enters the plate 120 through the area A0 of the irradiation window 126. Here, the point P0 indicates a peripheral point of the area A0. Due to the reflectance of the reflection surface 122, approximately 95% or more of the input light 77 is reflected by the reflection surface 122 and enters the area A1 of the reflection surface 124. Point P1 indicates a peripheral point of the area A1. When reflected from the area A1 on the reflective surface 124, the input light 77 travels to the reflective surface 122 and is partially transmitted through the reflective surface 122 as output light Out1 defined by the ray R1. Thus, as shown in FIG. 8, the input light 77 experiences multiple reflections between the reflective surfaces 122 and 124. Here, each reflection from the reflection surface 122 is
Each output light is transmitted. So, for example,
The input light 77 is reflected from the areas A2, A3, and A4 to generate output lights Out2, Out3, and Out4. Point P2 indicates a peripheral point of area A2, and point P3 indicates area A3.
, And a point P4 indicates a peripheral point of the area A4. The output light Out2 is defined by the ray R2 and the output light O2
out3 is defined by ray R3 and output light Out4.
Is defined by ray R4. FIG. 8 shows the output light Out.
Although only 0, Out1, Out2, Out3, and Out4 are described, more output light actually exists depending on the intensity of the input light 77 and the reflectivity of the reflection surfaces 122 and 124. As described in more detail, the output light interferes with each other and produces a light beam having a direction that varies according to the wavelength of the input light 77.

FIG. 9 illustrates a VI according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating interference generated by a PA. According to FIG. 9, light traveling from the focal line 78 is reflected by the reflecting surface 124. As described above, the reflecting surface 124 is approximately 10
It has a reflectance of 0% and thus essentially functions as a mirror. As a result, output light Out1 can reflecting surfaces 122 and 124 without, can be considered as optically being emitted from the focal line I _1. Similarly, the output light O
ut2, Out3, and Out4 is that they can be considered as optically are respectively emitted from the focal line I _2, I _3, and I _4. I ₂ , I ₃ and I ₄
Is a virtual image of the focal line I ₀ .

Therefore, as shown in FIG.
_1, there is to the focal line I ₀ distance 2t. Here, t is equal to the distance between the reflective surfaces 122 and 124.
Similarly, each subsequent focal line is at a distance 2t from the immediately preceding focal line. Thus, focal line I ₂ is at the focal line I ₁ a distance 2t. Further, the reflection surface 1
Each subsequent multiple reflection between 22 and 124 produces an output light that is less intense than the earlier output light. Therefore, the intensity of the output light Out2 is lower than that of the output light Out1.

As shown in FIG. 9, the output lights from the focal lines overlap and interfere with each other. This interference is caused by the input light 7
7 generates a light beam that travels in a specific direction depending on the wavelength.
The VIPA according to the above embodiment of the present invention has a competitive condition which is a design feature of the VIPA. The constructive conditions increase the interference of the output light and cause it to form a light beam. The condition for constructing VIPA is expressed by the following equation (1).

2t × cos θ = mλ where θ is the propagation direction of the formed light flux measured from a line perpendicular to the surfaces of the reflection surfaces 122 and 124. λ is the wavelength of the input light, t is the distance between the reflecting surfaces 122 and 124, m
Represents an integer.

Therefore, if t is constant and a specific value is given to m, the propagation direction θ of the light beam generated with respect to the input light having the wavelength λ is determined. Further, the input light 77
Diffuse radially at a specific angle from the focal line 78.
Thus, input light having the same wavelength travels from focal line 78 in a number of different directions and is reflected between reflective surfaces 122 and 124. The condition for VIPA reinforcement is such that light traveling in a specific direction reinforces with output light by interference and forms a light beam in a direction corresponding to the wavelength of input light. Light traveling in different directions than the specific direction required by the constructive conditions is weakened by the interference of the output light.

FIG. 10 illustrates an embodiment of the present invention.
FIG. 7 is a cross-sectional view of the VIPA of FIG. 6 taken along line VIII-VIII, showing characteristics of the VIPA for determining an incident angle or an inclination angle of input light.

According to FIG. 10, the input light 77 is condensed by a cylindrical lens (not shown) and converged on a focal line 78. As shown in FIG. 10, the input light 77
Cover an area having a width equal to 26 "a". Input light 7
After the light 7 is reflected once by the reflection surface 122, the input light 7
7 is incident on the reflective film 124 and covers an area of the reflective surface 124 having a width equal to “b”. Further, as shown in FIG. 10, the input light 77 travels along an optical axis 132 inclined at an inclination angle θ ₀ with respect to a perpendicular to the reflection surface 122.

The inclination angle θ ₀ should be set so that the input light 77 does not go out of the irradiation window 126 after being reflected once by the reflection surface 122. In other words,
The tilt angle θ ₀ should be set so that the input light 77 is “trapped” between the reflective surfaces 122 and 124 and does not escape from the irradiation window 126. Therefore, the input light 77 is applied to the irradiation window 12.
6 so that the inclination angle θ ₀ is calculated by the following equation (2).
Should be set according to

The term of the optical axis inclination θ ₀ ≧ (a + b) / 4t (a + b) becomes minimum when a = b. this is,
The situation where the focal line 78 is arranged on the reflection surface 122 is shown.

Accordingly, as shown in FIGS. 6-10, embodiments of the present invention include a VIPA that receives input light having each wavelength within a continuous range of wavelengths. VIPA causes multiple reflections of input light, causes self-interference, and generates output light. The output light is spatially distinguishable from the output light generated for input light having any other wavelength within the continuous range of wavelengths. For example, FIG. 8 shows input light 77 experiencing multiple reflections between reflective surfaces 122 and 124. This multiple reflection causes a plurality of output lights Ou to interfere with each other.
It generates t0, Out1, Out2, Out3, and Out4, and generates a spatially distinguishable light flux for each wavelength of the input light 77.

"Self-interference" is a phrase that indicates the interference caused by multiple beams or beams from the same light source. Therefore, the output light Out0, Out1, Out2, O
The interference between out3 and Out4 is called self-interference of the input light 77. This is because the output light Out0, Out1, Ou
This is because t2, Out3, and Out4 all come from the same light source (that is, the input light 77).

According to the above embodiment of the present invention, the input light may be at any wavelength in the continuous range of wavelengths. Therefore, the input light is not limited to a wavelength having a value selected from a range of discrete values.

Further, according to the above embodiment of the present invention, the output light generated for the input light of a specific wavelength within the continuous wavelength range is such that the input light has a different wavelength within the continuous wavelength range. Is spatially distinguishable from the output light generated when Thus, for example, as shown in FIG. 6, the traveling direction of the light flux 82 (ie, the “spatial characteristic”) is such that when the input light 77 is at a different wavelength within a continuous range of wavelengths,
different. Further, for example, according to FIG.
If all three wavelengths λ1, λ2, and λ3 are included, the light fluxes 82a, 82b, and 82c are generated simultaneously, each traveling in a different direction.

According to the above embodiment of the present invention, the focal line is described as being on the opposite side of the parallel plate on which the input light is incident. However, for example, the focal line may be on the plane of the irradiation window or in a parallel plate in front of the irradiation window.

According to the above embodiment of the present invention, two reflecting films reflect light, and one reflecting film has a reflectance of about 100%. However, the same effect can be obtained by using two reflection films each having a reflectance of less than 100%. For example, both reflective films may have a reflectivity of 95%. In this case, each reflection film transmits light and causes interference. As a result, the light beam traveling in the direction depending on the wavelength is formed on both sides of the parallel plate on which the reflection film is formed. Thus, the various reflectivities of the various embodiments of the present invention can be easily changed according to the required properties of the VIPA.

According to the above embodiment of the present invention, it is described that the waveguide is formed by a parallel plate or by two reflecting surfaces parallel to each other. But,
The plates or reflecting surfaces need not necessarily be parallel.

According to the above embodiment of the present invention, VIPA
Uses multiple reflection to keep the phase difference between the interference lights constant. As a result, the characteristics of VIPA are stable, and the change in optical characteristics due to polarization is suppressed. In contrast, the optical properties of conventional diffraction gratings undergo undesirable changes depending on the polarization of the input light.

The above embodiments of the present invention have been described as providing light beams that are "spatially distinguishable" from each other. “Spatially distinguishable” means that the luminous flux is distinguishable in space. For example, the various luminous fluxes are spatially distinguishable if collimated and travel in different directions or converged to different positions. However, the invention is not intended to be limited to these detailed examples, and there are other ways to make the light beams spatially distinguishable from one another.

FIG. 11 is a diagram illustrating a VIPA used with a receiver, according to an embodiment of the present invention. FIG.
According to 1, the multilayer reflective films 96 and 98 are, for example, 100
It is formed on both sides of a parallel plate 100 made of glass having a thickness t of μm. The parallel plate 100 is 20 to 2000
Preferably, it has a thickness in the range of μm. The reflective films 96 and 98 are preferably multilayer, high-reflectance interference films.

The reflectivity of the reflective film 98 is approximately 100%, and the reflectivity of the reflective film 96 is approximately 95%. But,
The reflectance of the reflective film 96 is not limited to 95%, and may be a different value as long as sufficient light that causes multiple reflection between the reflective films 96 and 98 is reflected from the reflective film 96. Preferably, the reflectance of the reflective film 96 is 80% to 10%.
It is in the range of several percent less than 0%. Further, the reflectivity of the reflection film 98 is not limited to 100%, and may be any value as long as it is sufficient to cause multiple reflection between the reflection films 96 and 98.

The irradiation window 102 receives the input light and is located on the same surface as the reflection film 96 of the parallel plate 100. Irradiation window 1
02 can be formed of a film having a reflectance of approximately 0% of the surface of the parallel plate 100. As shown in FIG. 11, the boundary between the irradiation window 102 and the reflection film 96 is preferably
It is a straight line.

The input light is, for example, an optical fiber (not shown).
And is received by the collimating lens 106. The collimating lens 106 converts the input light into the parallel beam 104 received by the cylindrical lens 108. The cylindrical lens 108 emits the parallel beam 104 to the irradiation window 1.
The light is condensed on the focal line 110 on the reference numeral 02. The focal line 110 is located near and parallel to a straight line boundary between the reflection film 96 and the irradiation window 102. As described above, the input light enters the parallel plate 100 through the irradiation window 102.

The optical axis of the input light 102 is inclined by an inclination angle with respect to the perpendicular of the reflection film 96, and the input light is
After entering 0, it does not escape from the irradiation window 102. Therefore, the tilt angle should be set according to the above equation (2).

Once entering the parallel plate 100, the input light undergoes multiple reflections between the reflective films 96 and 98 (see, for example, FIG. 8).
As shown in). Every time the input light is incident on the reflective film 96, approximately 95% of the light is reflected toward the reflective film 98, and approximately 5% of the light is transmitted through the reflective film 96 and output light (for example, as shown in FIG. 8). (Such as output light Out1). The multiple reflections between the reflective films 96 and 98 form a plurality of output lights. The plurality of output lights interfere with each other and form a light flux 112 having a propagation direction depending on the wavelength of the input light.

The light beam 112 is condensed by a lens 114, and converges the light beam 112 to a converging point. The focal point moves along a linear path 116 for different wavelengths of the input light. For example, as the wavelength of the input light increases, the focal point moves further along a straight path 116. The plurality of receivers 118 are arranged on the linear path 116 and receive the converged light flux 112. Therefore, each receiver 118
It is arranged so as to receive a light beam corresponding to a specific wavelength.

By controlling the distance t between the reflecting films or reflecting surfaces of the VIPA, the phase difference of light reflected between the reflecting films or reflecting surfaces can be shifted by a predetermined amount. Therefore, very good environmental resistance can be realized. Further, the above embodiments of the present invention are only slightly affected by changes in optical characteristics depending on the polarization of light.

FIG. 12 illustrates a VIPA for use with a receiver, according to another embodiment of the present invention. The VIPA shown in FIG. 12 is the VIPA shown in FIG.
And the difference is that the reflectances of the reflection films 96 and 98 are reversed. Further, the VIP shown in FIG.
In A, the reflection film 98 has a reflectance of approximately 95%, and the reflection film 96 has a reflection film of approximately 100%.
As shown in FIG. 12, the light flux 112 is formed through the interference of output light traveling through the reflective film 98. Therefore,
The input light enters from one side of the parallel plate 100, and a light beam 112 is formed on the other side of the parallel plate 100. Otherwise, see FIG.
Operates in the same manner as the VIPA shown in FIG.

FIG. 13 shows an embodiment of the present invention.
It is a figure which shows a waveguide type VIPA. According to FIG. 13, light 138 is output from an optical fiber (not shown) and
The light is received by a waveguide 140 provided at 42. The waveguide 140 is, for example, lithium niobate. Light 1
38 includes an optical signal modulated on a plurality of carriers having different wavelengths.

Light 138 typically diffuses in width when output from an optical fiber. Therefore, the collimating lens 142 converts the light 138 into parallel light. The parallel light is
Then, the light is condensed by the cylindrical lens 144 and converged on a focal line. The light is transmitted through the irradiation window 150 to the focal line 1.
Emitted from 46 into the VIPA 148.

VIPA 148 includes reflective films 152 and 154 on parallel plate 156. The reflection film 154 is formed on the parallel plate 15.
6, the reflection film 152 and the irradiation window 150
It is on the other side of the parallel plate 156. The reflection film 152 is approximately 1
The reflective film 154 has a reflectance of less than 100%. The light beam 158 of the light reflected by the parallel plate 156 is output to the side of the parallel plate 156 opposite to the irradiation window 150.

When the input light 138 includes a plurality of wavelengths, a plurality of light fluxes 158 traveling in different directions depending on the wavelength of the input light 138 are formed. The light beam 158 formed by the VIPA 148 is converged by the lens 160 to a different point depending on the propagation direction of the light beam 158. Therefore, as shown in FIG. 13, the wavelengths λ1, λ2,
And luminous fluxes 158a, 158b and 158 having λ3
c are formed at different light condensing points.

The plurality of light receiving waveguides 162 are provided at the converging point. Each receiving waveguide 162 guides an optical signal and a corresponding carrier having one wavelength. Therefore, a plurality of light beams are received at the same time and transmitted through various channels. Each light receiving waveguide 162 has a corresponding light receiver (not shown) provided at a subsequent stage. The light receiver is typically a photodiode. Therefore, each light receiving waveguide 162
Is guided by a corresponding receiver and then processed.

When manufacturing a VIPA, the reflective surfaces must be held in exactly parallel positions, and the effective distance between the surfaces (this is the optical distance or the physical index multiplied by the refractive index of the medium) Distance) must be adjusted precisely.

Accordingly, FIG. 14 is a diagram illustrating a VIPA according to a further embodiment of the present invention. According to FIG. 14, the spacer member 200 is preferably formed of a material having a thermal expansion coefficient of approximately 0, and holds the reflection films 122 and 124 parallel to each other at a specific distance. In order to obtain a thermal expansion coefficient of approximately 0, for example, the magnitude of the thermal expansion coefficient of the spacer member 200 is preferably 10 ⁻⁵ / ° C. or less. More preferably, the magnitude of the thermal expansion coefficient of the spacer member 200 is 10 ⁻⁶ / ° C. Spacer member 200
Suitable materials with these properties that can be used as
Vycor® and ULE® glass, manufactured by Corning, Corning, New York, USA
And Scho, Duryea, Pennsylvania, USA
tt Zerodur® from Glass Technologies
It is glass. Each of these materials is 7.5 × 1
0 ⁻⁷ / ° C., <3.0 × 10 ⁻⁸ / ° C. and <1.0 × 10 ⁻⁷
/ ° C. However, the spacer member 200 is not limited to being made of a glass material, but may be another material having a required coefficient of thermal expansion.

As described above, the distance of the gap does not change according to the temperature change. In FIG. 14, the VIPA 76 has a transparent block 202 on which reflective films 122 and 124 are formed.
And 204 are shown. Transparent block 2
02 and 204 are not limited to "block" shapes, but any suitable shape is allowed.

The spacer member 200 is formed of the transparent block 20.
Touches 2 and 204. The spacer member 200 is not limited to a specific shape. Preferably, no adhesive is used to secure the spacer member 200 to the transparent blocks 202 and 204. This is because, in general, the adhesive exhibits a corresponding thermal expansion.

In practice, any number of spacer members 200 may be used, and the present invention is not limited to a particular number of spacer members. Further, a gap length adjusting member 206 is inserted between the reflection films 122 and 124. Preferably,
The gap length adjusting member 206 is a thin plate made of a transparent material. For example, when the gap length adjusting member 206 is made of athermal glass, the optical phase of the transmitted light does not change due to a change in temperature. Reflective film 12
The optical distance in the gap between 2 and 124 can be accurately adjusted by tilting the gap length adjusting member 206.

A typical application is as follows.
The material between 24 is simply "air". Further, the gap length adjusting member 206 is preferably made of air or the reflective film 122.
And 124 have a different refractive index from such other materials. As a result, the optical distance between the reflective films 122 and 124 can be changed by moving the gap length adjusting member 206 (for example, by tilting or rotating). Therefore, by adjusting the gap length adjusting member 206, the optical distance between the reflective films 122 and 124 can be adjusted.

The gap length adjusting member 206 is preferably a thin plate having antireflection films on both sides so that reflection does not occur on both sides. Therefore, one reflection film 122 or 12
4, the optical distance to the other reflective film via the gap length adjusting member 206 via the air or other substance between the reflective films becomes the same along the entire length of the gap length adjusting member 206. . However, the optical distance between the reflective films 122 and 124 can be adjusted by changing the angle of the gap length adjusting member 206.

The gap length adjusting member 206 is made of VIPA after manufacturing.
76 and held in place. If the gap length adjusting member 206 can be appropriately moved, rotated, or tilted by the holding mechanism, and the required effect can be obtained, there are various holding mechanisms used to hold the gap length adjusting member 206. Many different types are possible. For example, a metal bar (not shown) can be used to hold gap length adjustment member 206 in place.

Further, the optical distance passing through the gap length adjusting member 206 needs to be such that the temperature does not change. The non-heat glass does not change in temperature and can be used as the gap length adjusting member 206. However, other materials can be used and the invention is not limited to non-heated glass.

The gap length adjusting member 206 is not limited to use for VIPA. Therefore, the gap length adjusting member 206 can be used for another optical element such as a Fabry-Perot interferometer.

In FIG. 14, reflective films 122 and 124 are formed on transparent blocks 202 and 204, respectively.
Therefore, the transparent blocks 202 and 204 are
Of the spacer member 200 and the transparent block 20
2 and 204 are in contact. However, the transparent block 202
And 204 are not required for a particular application, and the invention is not limited to the use of such transparent members. Further, the spacer member 200 includes the reflection films 122 and 12.
It is also possible to position it so as to be in contact with 4.

For example, FIG. 15 shows a spacer member 200 in contact with reflective films 122 and 124 according to an embodiment of the present invention.
FIG. The above embodiments of the present invention can be used with devices that use VIPA to create and compensate for chromatic dispersion.

For example, FIG. 16 illustrates a V having a chromatic dispersion generating and compensating and gap length adjusting member in accordance with an embodiment of the present invention.
It is a top view of the apparatus using IPA. According to FIG. 16, the collimating lens 322a and the semi-cylindrical lens 324a
Are located between input fiber 316 and VIPA 240. The input light proceeds from the input fiber 316 and is generated as collimated light by the collimating lens 322a. The collimated light is converged by the semi-cylindrical lens 324a to a line in the irradiation window of the VIPA. VIPA
The light beam formed by 240 travels to converging lens 252, is focused on mirror 254, and is reflected by mirror 254. In FIG. 16, the converging lens 252 is
It is a "normal" convergent lens. Here, the “normal” convergent lens means a convergent lens that converges light when viewed from the upper surface and the side surface of the convergent lens, and has the same focal length on the upper surface and the side surface.

The collimating lens 322b and the semi-cylindrical lens 324b are located between the output fiber 318 and the VIPA 240. Reflected by mirror 254, VIP
The light returned to the A240 is multiple-reflected in the VIPA 240 and output from the irradiation window of the VIPA 240. VIP
This output light from A240 proceeds to a semi-cylindrical lens 324b and a collimating lens 322b, and the output fiber 318
Converges.

As shown in FIG. 16, the light converged on the mirror 254 is not perpendicular to the mirror 254 when viewed from above. This is because the converging lens 252 is
Of the luminous flux generated by the converging lens 2 as viewed from above
This is because they are arranged so as not to pass through the center of 52. Similarly, light reflected by mirror 254 does not pass through the center of converging lens 252. Preferably, the lens center of the converging lens 252 is shifted from the beam center of the light beam generated by the VIPA 240 and the beam center of the light reflected by the mirror 254 by half the thickness of the beam when viewed from above. . As a result, the converging lens 252 transfers the light to the converging lens 25 on the mirror 254.
The lens is converged at a position where the lens axis of No. 2 is extended. Further, VI
The light 328 that travels from the PA 240 to the converging lens 252 is transmitted from the converging lens 252 to the VIPA for any wavelength.
Parallel to light 330 traveling to 240.

According to the apparatus shown in FIG. 16, input light from input fiber 316 travels a different space than output light received by output fiber 318. Thus, the output light can be coupled to a different fiber than the input fiber. Further, the input light received by the irradiation window of the VIPA 240 is
The device has relatively high performance because it travels in a vertical direction.

In the apparatus shown in FIG. 16, the light received by the output fiber 318 is
Chromatic dispersion is provided to the input light from 16. Thus, the apparatus of FIG. 16 can be used to create and compensate for chromatic dispersion.

The gap length adjusting member 206 is a VIPA 240
Is within. Preferably, as shown in FIG. 16, the gap length adjusting members 206 are respectively provided for the input beam and the output beam.
Is provided so that the optical distance between the reflecting surfaces of the VIPA 240 can be adjusted independently for the input beam and the output beam. However, one gap length adjusting member may be used. One such gap length adjustment member can be designed to affect only one of the input and output beams, or both. Further, the substance between the reflection surfaces of the VIPA 240 may be air holding the gap length adjusting member 206 therein.

FIG. 16 shows two semi-cylindrical lenses 324a and 324b, but one semi-cylindrical lens may be used. For example, FIG. 17 illustrates one semi-cylindrical lens 324 instead of multiple semi-cylindrical lenses 324a and 324b, according to an embodiment of the present invention.

In general, a semi-cylindrical lens is a lens that converges light when viewed from the top or side, and does not have a converging function when viewed from another side. Semi-cylindrical lenses are well known.

Further, the present invention is not limited to the use of collimating lenses, semi-cylindrical lenses, and / or any other particular type of lens. Rather, many other lenses and devices can be used provided the appropriate effect is obtained.

Thus, for example, the apparatus of FIGS. 16 and 17 in accordance with the illustrated embodiment of the invention receives input light and produces a corresponding output light that propagates from the VIPA.
Contains IPA. Optical return devices, such as mirrors,
The output light is received from the VIPA, and the output light is returned to the VIPA. (A) The output light travels from the VIPA to the lens, and is converged by the lens on the optical return device, so that the output light is
(C) from the VIPA, so that output light is returned from the optical return to the VIPA by being directed from the PA to the optical return, (b) the lens from the optical return, and then to the VIPA by the lens; The output light going to the lens is perpendicular to the VIPA on the top surface, and the return output light going from the lens to the VIPA is
The lens is arranged to be perpendicular to the PA. Further, the gap length adjusting member is provided in the VIPA, and provides an optical distance between the reflection surfaces of the VIPA to both or one of the light returning to the optical return device and the light returned to the VIPA from the optical return device. To change.

The VIPA 240 of FIGS. 16 and 17 also includes a spacer member such as, for example, the spacer member of FIG. According to the above embodiment of the present invention, VIPA comprises:
It is described as being formed by a parallel plate or two parallel reflecting surfaces. However, the plates or reflecting surfaces need not necessarily be parallel.

According to the above embodiment of the present invention, light containing a plurality of wavelengths can be branched at the same time. Therefore, it is possible to reduce the size of the receiver used for the wavelength division multiplexing communication.

In the above embodiment of the present invention, the VIP
A can simultaneously demultiplex the wavelength multiplexed light for each wavelength of the input light. Further, the angle of dispersion can be adjusted by the thickness t of the parallel plate forming the VIPA. As a result, the angle of dispersion can be large enough that the receiver can easily receive each split signal. For example, a conventional diffraction grating requires a fine uneven surface due to a large dispersion angle. However, it is very difficult to prepare a fine and fine uneven surface, and the size of the dispersion angle is limited. In contrast, the VIPA according to the above embodiment of the present invention requires changing the thickness of the parallel plate in order to achieve a relatively large dispersion angle.

Further, the VIP according to the above embodiment of the present invention
A produces a larger dispersion angle than a conventional diffraction grating. Therefore, the receiver using the VIPA according to the above-described embodiment of the present invention can accurately receive an optical signal accurately even in wavelength division multiplexing communication that realizes high-level multiplexing processing. Furthermore, such a receiver has a relatively simple configuration and is relatively inexpensive to manufacture.

According to the above embodiment of the present invention, VIPA
Uses multiple reflection to keep the phase difference between the interfering lights constant. As a result, the characteristics of VIPA are stable, and change in optical characteristics due to polarization is suppressed. On the other hand, the optical characteristics of the conventional diffraction grating undergo unnecessary changes depending on the polarization of the input light.

Further, as compared with the waveguide array grating, the VIPA according to the above embodiment of the present invention achieves stable optical characteristics and resistance to changes in environmental conditions with a relatively simple configuration.

In the above embodiment of the present invention, the VIP
A has a reflective film for reflecting light. For example, FIG. 7 shows that reflective films 122 and 124 are used to reflect light.
Is shown. However, VIPA is not limited to the use of a “film” to provide a reflective surface. Rather, the VIPA should simply have a suitable reflective surface, which may or may not be formed by a "film".

Further, in the above embodiment of the present invention,
VIPA includes a transparent glass plate where multiple reflections occur. For example, FIG. 7 shows a VIPA 76 having a transparent glass plate 120 having a reflective film. However, VIPA,
It is not limited to a glass material or any kind of "plate" to separate the reflective surface. Rather, the reflective surface is
They should simply be separated from each other. For example, VI
The reflection surface of PA may simply have “air” instead of a glass plate as long as the reflection surface is stably held by a material such as glass or metal having low thermal expansion. Thus, the reflective surface may be described as having a transparent material such as optical glass or air, for example.

The VIPA according to the above embodiment of the present invention comprises:
It is limited as a wavelength demultiplexer. For example, VIPA is 1
Title of the invention, "OPTICAL APPAR," filed on February 7, 997
ATUSWHICH USES A VIRTUALLY IMAGED PHASED ARR
AY TO PRODUCE CHROMATIC DISPERSION, US application 08 / 796,842 and the title of the invention, "OPTICAL APPARATUS WHICH USE," filed on August 13, 1997
SA VIRTUALLY IMAGED PHASED ARRAY TO PRODUC
US application for "E CHROMATIC DISPERSION" 08/91
0,251, compensate for chromatic dispersion,
Alternatively, VIPA can be used to generate.

While several preferred embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that modifications may be made to these embodiments without departing from the principles or spirit of the invention. Would.

[0090]

According to the present invention, it is possible to provide a wavelength demultiplexer having a relatively large dispersion angle, whose characteristics hardly change due to a temperature change.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional filter using a multilayer interference film.

FIG. 2 is a diagram showing a conventional Fabry-Perot interferometer.

FIG. 3 is a diagram showing a conventional Michelson interferometer.

FIG. 4 is a diagram showing a conventional diffraction grating.

FIG. 5 is a diagram showing a conventional waveguide array grating for demultiplexing wavelength division multiplexed light.

FIG. 6 illustrates a virtual imaged phased array (VIPA) according to one embodiment of the present invention.

FIG. 7 illustrates the VIPA of FIG. 6 according to one embodiment of the present invention.
FIG.

FIG. 8 illustrates a V shown in FIG. 6 according to an embodiment of the present invention.
FIG. 8 is a diagram showing a cross section of the IPA along line VIII-VIII.

FIG. 9 illustrates interference generated by a VIPA, according to one embodiment of the present invention.

FIG. 10 illustrates a line VIA of the VIPA shown in FIG. 6 for determining the tilt angle of the input light according to one embodiment of the present invention.
FIG. 8 is a diagram showing a cross section along II-VIII.

FIG. 11 illustrates a VIPA for use with a receiver, according to one embodiment of the present invention.

FIG. 12 illustrates a VIPA for use with a receiver, according to a further embodiment of the present invention.

FIG. 13 shows a waveguide VI according to one embodiment of the present invention.
It is a figure showing PA.

FIG. 14 illustrates a VIPA having a spacer member and a gap length adjustment member according to a further embodiment of the present invention.

FIG. 15 illustrates a VIPA having a spacer member and a gap length adjustment member according to a further embodiment of the present invention.

FIG. 16 is a front view of a device using a VIPA with a gap length adjustment member to create or compensate for chromatic dispersion, according to one embodiment of the present invention.

FIG. 17 illustrates one collimating lens for a device that uses a VIPA and spacer member to create or compensate for chromatic dispersion, according to one embodiment of the present invention.

[Explanation of symbols]

 76, 148, 240 VIPA 80 Lens 96, 98 Multilayer reflective film 100, 156 Parallel plate 102, 126, 150 Irradiation window 106 Collimate lens 108 Cylindrical lens 114, 160 Lens 118 Light receiver 120 Plate 122, 124, 152, 154 Reflective film 140 Waveguide 142, 322a, 322b Collimating lens 162 Light receiving waveguide 200 Spacer member 202, 204 Transparent block 206 Gap length adjusting member 252 Convergent lens 254 Mirror 316 Input fiber 318 Output fiber 324, 324a, 324b Semi-cylindrical lens

Continuation of the front page (72) Inventor Shira ▲ saki ▼ 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Simon Kao United States, 94538 California, Fremont, CA, Albrace Tree No. 42501, within Avanex Corporation

Claims (38)

[Claims] An apparatus for receiving input light of each wavelength within a continuous range of wavelengths, the apparatus having first and second surfaces, wherein a second surface reflects a portion of incident light. A first surface and a second surface, wherein the input light is reflected multiple times between the first and second surfaces, a plurality of lights are transmitted from the second surface, and the plurality of transmitted lights are: First and second angular dispersion means for interfering with each other to produce output light spatially distinguishable from output light generated for input light of any other wavelength within the continuous range of wavelengths; A spacer means for maintaining a constant relative position between the surfaces and having a coefficient of thermal expansion of 10 ⁻⁵ / ° C. or less. 2. Apparatus according to claim 1, wherein said spacer means has a coefficient of thermal expansion of 10 ⁻⁶ / ° C. or less. 3. The apparatus according to claim 1, wherein said spacer means is made of a material made of glass. 4. The apparatus of claim 1, wherein said first and second surfaces are parallel to each other, and said spacer means keeps said first and second surfaces parallel when the temperature changes. Equipment. 5. The apparatus according to claim 1, wherein said first and second surfaces are separated by a specific distance, and said spacer means keeps said specific distance constant. 6. An apparatus according to claim 1, wherein said spacer means is in contact with said first and second surfaces. 7. Apparatus according to claim 1, further comprising a plurality of spacer means for maintaining a constant relative position between said first and second surfaces. 8. An apparatus according to claim 1, further comprising adjusting means located between said first and second surfaces and capable of adjusting a change in an optical distance between said first and second surfaces. An apparatus according to claim 1. 9. The apparatus according to claim 8, wherein said adjusting means is made of a transparent material. 10. The adjusting means is made of a transparent material and has a first surface and a second surface, and the first surface is provided on the first surface of the angular dispersion means. Being adjacent, the second surface being adjacent to the second surface of the angular dispersion means, and the first and second surfaces of the adjusting means being provided with an anti-reflective coating. The device according to claim 8, characterized in that: 11. The apparatus according to claim 10, wherein said adjusting means is a plate. 12. The apparatus according to claim 8, wherein said adjusting means is rotatable to change said optical distance. 13. The apparatus according to claim 10, wherein said adjusting means is rotatable to change said optical distance.
An apparatus according to claim 1. 14. The apparatus of claim 1, wherein said first surface has a reflectivity of approximately 100%. 15. The input light is wavelength division multiplexed light composed of at least two carriers each having a different wavelength within a continuous range of wavelengths, and the plurality of transmitted lights interfere with each other to form the input light. The apparatus of claim 1, wherein each output light is generated for each carrier, the output light being spatially distinguishable from other output lights. 16. The apparatus has a top view and further receives the output light from the angular dispersion means and the angular dispersion so as to be reflected between the first and second surfaces. A light returning means for returning the output light to the means, and a lens arranged as follows, wherein the output light travels from the angular dispersion means to the lens, and then by the lens to the light returning means. By being converged, the output light is directed from the angular dispersion means to the light returning means, travels from the light returning means to the lens, and is then directed by the lens to the angular dispersion means, thereby providing the output light. The light returning from the light returning means to the angular dispersion means, and the output light traveling from the angular dispersion means to the lens is perpendicular to the angular dispersion means as viewed from the upper surface, and each of the dispersion lights from the lens. The returned output light going to the means is viewed from the top Apparatus according to claim 8, characterized in that it comprises a and said lens disposed to be perpendicular to each of said distributing means. 17. An apparatus for receiving input light of each wavelength and converging it on a line, comprising first and second surfaces, the second surface having a reflectance for transmitting a part of incident light. Wherein the first and second surfaces are arranged such that the input light is emitted from the line and is reflected multiple times between the first and second surfaces, and a plurality of light beams are transmitted through the second surface. And the plurality of transmitted lights interfere with each other and generate output light spatially distinguishable from output light generated for input light of different wavelengths; and the first and second angular dispersion means. A spacer means having a coefficient of thermal expansion of 10 ⁻⁵ / ° C. or less for keeping the relative position between the surfaces constant. 18. The apparatus according to claim 17, wherein said spacer means is made of a material made of glass. 19. The apparatus according to claim 17, wherein said spacer means has a coefficient of thermal expansion of 10 ⁻⁶ / ° C. or less. 20. The method according to claim 17, wherein said first and second surfaces are parallel to each other and said spacer means keeps said first and second surfaces parallel during a temperature change. Equipment. 21. The apparatus according to claim 17, wherein said first and second surfaces are separated by a specific distance, and said spacer means keeps said specific distance constant. 22. Apparatus according to claim 17, wherein said spacer means contacts said first and second surfaces. 23. The apparatus according to claim 17, further comprising a plurality of spacer means for maintaining a constant relative position between said first and second surfaces. 24. Further, it is located between said first and second surfaces,
The apparatus according to claim 17, further comprising adjusting means for adjusting a change in an optical distance between the first and second surfaces. 25. The apparatus according to claim 24, wherein said adjusting means is formed of a transparent member. 26. The adjusting means is composed of a transparent member and has first and second surfaces, and the first surface is adjacent to the first surface of the angular dispersion means. , The second surface is adjacent to the second surface of the angular dispersion means and the first surface of the adjustment means.
25. The apparatus of claim 24, wherein the and the second surface are provided with an anti-reflective coating. 27. The apparatus according to claim 26, wherein said adjusting means is a plate. 28. The apparatus according to claim 2, wherein said adjusting means is rotatable to change said optical distance.
An apparatus according to claim 4. 29. The apparatus according to claim 2, wherein said adjusting means is rotatable to change said optical distance.
7. The apparatus according to 6. 30. The apparatus of claim 17, wherein said first surface has a reflectivity of approximately 100%. 31. The input light is wavelength division multiplexed light composed of at least two carriers having different wavelengths. The plurality of transmitted lights interfere with each other, and each output light is transmitted to each carrier of the input light. 18. The apparatus of claim 17, wherein each output light generated is spatially distinguishable from other output light. 32. The apparatus has a view from the top, further comprising receiving the output light from the angular dispersion means and reflecting the output light from the first and second surfaces. A light returning means for returning the output light to the means, and a lens arranged as follows: the output light travels from the angular dispersion means to the lens, and
By being converged by the lens on the light returning means, the output light is directed from the angular dispersion means to the light returning means and travels from the light returning means to the lens, and then the angular dispersion by the lens. Being directed to the means, the output light is returned from the light returning means to the angular dispersion means, and the output light traveling from the angular dispersion means to the lens, as viewed from the top, is directed to the angular dispersion means Returning the output light that is vertical and travels from the lens to each of the dispersing means, wherein the lens is arranged to be perpendicular to the respective dispersing means when viewed from the top. An apparatus according to claim 24. 33. An apparatus for receiving input light of each wavelength within a continuous range of wavelengths, the apparatus comprising first and second surfaces, the second surface reflecting a portion of incident light. The first and second surfaces have a ratio, wherein the input light is reflected a plurality of times between the first and second surfaces and a plurality of lights are output through the second surface; Said plurality of transmitted lights interfering with each other and generating output light spatially distinguishable from output light generated for input light of any other wavelength within a continuous range of wavelengths; Spacer means for maintaining the relative position of the first and second surfaces constant and made of glass material and having a coefficient of thermal expansion of approximately zero. 34. The apparatus according to claim 33, wherein said spacer means has a coefficient of thermal expansion of 10 ⁻⁵ / ° C. or less. 35. The apparatus of claim 33, wherein said spacer means has a coefficient of thermal expansion of less than 10 ^-6 / ° C. 36. An apparatus for receiving input light of each wavelength and converging it on a line, comprising first and second surfaces, wherein the second surface has a reflectivity for transmitting a part of incident light. Wherein the first and second surfaces are arranged such that the input light is emitted from the line and is reflected multiple times between the first and second surfaces, and a plurality of light beams are transmitted through the second surface. The plurality of transmitted lights interfere with each other and generate output light that is spatially distinguishable from output light generated for input light of different wavelengths; and the first and second dispersion means. And a spacer means which is made of a material made of glass and has a coefficient of thermal expansion of substantially zero. 37. The apparatus according to claim 36, wherein said spacer means has a coefficient of thermal expansion of 10 ⁻⁵ / ° C. or less. 38. Apparatus according to claim 36, wherein said spacer means has a coefficient of thermal expansion of 10 ⁻⁶ / ° C. or less.