JP2000028849A - Virtually imaged phased array (vipa) having surface of changing in reflectivity in order to improve beam profile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the simultaneous sepn. of plural carriers from wavelength division multiplex light with simple constitution by constituting the array in such a manner that input light is reflected plural times between first and second surfaces and that a plurality of the light passes the array via the second surface. SOLUTION: The virtually imaged phased array(VIPA) 76 includes a plate 120 made of, for example, glass and has reflection films 122 and 124 thereon. The input light 77 is focused at a focal line 78 by a lens 80 via an irradiation window and multiple reflection is induced between the reflection films 122 and 124. The reflection surface 124 has approximately 100% reflectivity exclusive of the irradiation window and the reflection surface 122 has approximately 95% or higher reflectivity. Then, the reflection surface 122 has approximately 5% or lower transmissivity to allow the transmission of approximately 5% or lower the incident light on the reflection surface 122 and reflects 95% or more of the light. The reflectivities of the reflection surfaces 122 and 124 are easily changeable if the specific application of VIPA is complied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a virtual imaged phased array (VIPA).
Magnetized phased array, that is, wavelength division multiplexing that receives wavelength division multiplexed light composed of multiple carriers, and that separates the wavelength division multiplexed light into a plurality of spatially distinguishable luminous fluxes corresponding to a plurality of carriers, respectively. About the vessel.

[0002]

2. Description of the Related Art Wavelength division multiplexing is used in fiber optic communications to transmit high speed, relatively large amounts of data. More specifically, a plurality of carriers, each of which is modulated with information, are multiplexed into wavelength 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 each carrier and detects each carrier. As described above, the communication system can transmit a relatively large amount of data using the 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 into wavelength division multiplexed light, such wavelength division multiplexed light is
If the receiver cannot accurately demultiplex the WDM light, it should not be transmitted. Therefore, it is desired that the receiver has a high-precision wavelength demultiplexer.

FIG. 1 is a diagram showing a conventional filter using a multilayer interference film for use as a wavelength demultiplexer. According to FIG. 1, the multilayer interference film 20 includes a transparent substrate 22
Formed on top. Light 24, which must be a collimated light, impinges on film 20, and is then repeatedly reflected within film 20. Depending on the optical conditions determined by the characteristics of the film 20, the light 2 having the wavelength λ2
Only 6 can be transmitted. The light 28 includes all light that does not meet the optical conditions, but does not pass through the film 20 and is reflected. Therefore, the filter shown in FIG. 1 is useful for demultiplexing a wavelength division multiplexed light including only two carriers of different wavelengths λ1 and λ2. However, such a filter, itself,
Wavelength division multiplexed light having more carriers cannot be split.

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, which must be a parallel light, impinges on the reflective film 30 and is reflected between the reflective films 30 and 32 many times. The light 36 having the wavelength λ2 that satisfies the transmission condition determined by the characteristics of the Fabry-Perot interferometer passes through the reflection film 32. Light 38 of wavelength λ1 that does not satisfy the transmission condition is
Is reflected. In this way, light having two different wavelengths can be split into two different lights, each corresponding to two different wavelengths. Thus, like the filter shown in FIG. 1, a conventional Fabry-Perot interferometer is useful for demultiplexing a wavelength division multiplexed light including only two carriers of different wavelengths λ1 and λ2. However, such Fabry-Perot interferometers cannot split wavelength division multiplexed light having more than two carriers.

FIG. 3 shows 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 perpendicular to each other. The reflection mirror 48 reflects the first light 44, and the reflection mirror 50 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 an optical path difference. The light reflected by the reflection mirror 48 is returned to the half mirror 42, reflected by the reflection mirror 50, and interferes with the light returned to the half mirror 42. As a result, the lights 52 and 54 having the wavelengths λ1 and λ2 are separated from each other. The filter in Figure 1
Like 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. However, such a Michelson interferometer cannot split a wavelength division multiplexed light having more than two carriers.

It is possible to combine several filters, Fabry-Perot interferometers or Michelson interferometers into a large array so that additional wavelength carriers can be separated from one wavelength division multiplex. However, such arrays are expensive, inefficient, and result in unexpectedly large receivers.

[0008] Diffraction gratings and waveguide array gratings are often used to split wavelength division multiplexed light consisting of two or more different wavelength carriers. FIG. 4 is a diagram illustrating a conventional diffraction grating for demultiplexing wavelength division multiplexed light. FIG.
According to the above, the diffraction grating 56 has an uneven surface 58. The parallel light 60 having a plurality of different wavelength carriers is applied to the uneven surface 5.
8 is incident. Each wavelength carrier is reflected and interferes between reflected light from different steps of the grating. as a result,
Carriers 62, 64 and 66 of different wavelengths are
6 are output at different angles and are separated from each other.

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

[0010] Furthermore, 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, due to the uneven surface of the diffraction grating, a complicated manufacturing process is required to manufacture an accurate diffraction grating.

FIG. 5 is a diagram showing a conventional waveguide array grating for demultiplexing wavelength division multiplexed light. According to FIG. 5, light consisting of a plurality of different wavelength carriers is applied to the input port 6.
The light is received through the optical waveguide 8 and branched into a number of waveguides 70.
A light output port 72 is provided at an end of each waveguide 70 and has an output light 74.
Is generated. The waveguides 70 have different lengths from each other, and thus provide optical paths of different lengths. Thus, the light passing through the waveguide 70 has different path lengths, and thus interferes with each other through the output port 72, forming an output 74 in different directions for different wavelengths.

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

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 division multiplexed light. A further object of the present invention is to spread the separated carriers with a relatively large angular dispersion, tolerate changes in environmental conditions, and to achieve a desirable beam profile, one of which is for efficient coupling into an optical fiber. It is to provide a wavelength demultiplexer that produces a resulting light beam having a symmetrical beam profile.

[0014]

The object of the invention is achieved by providing an apparatus having first and second surfaces. The second surface has a reflectance such that a part of the incident light is transmitted. The apparatus receives input light at each wavelength within a continuous range of wavelengths. 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 through 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 having any other wavelength within the continuous range of wavelengths. The reflectivity of the second surface varies along the second surface such that the output light has a desired beam profile along the second surface.
The phase adjustment buffer layer can be provided so that light reflected from the second surface to the first surface has a uniform optical phase along the second surface. Further, the phase adjustment layer can be provided to give a plurality of transmitted lights a uniform optical phase along the second surface.

[0015] Another object of the present invention is to provide a semiconductor device having a second surface having a reflectivity for transmitting a part of incident light.
This can also be achieved by providing an apparatus that includes the first and second surfaces. The device receives input light of each wavelength, which is collected on a line. The first and second surfaces are such that the input light is emitted from the line and is reflected multiple times between the first and second surfaces;
Therefore, the plurality of lights are arranged so as to pass through the second surface. The plurality of transmitted lights interfere with each other to generate output light that is spatially distinguishable from output light generated for input light of different wavelengths. The reflectivity of the second surface varies along the second surface such that the output light has a desired beam profile along the second surface.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention will now be described in detail. These examples are illustrated in the accompanying drawings. Like reference numerals refer to like components throughout.

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

In FIG. 6, VIPA 76 is preferably comprised of a thin plate of glass. Input light 77
Is focused on a line 78 by a lens 80, such as a semi-cylindrical lens, and the input light 77 travels into the VIPA 76. Line 78
Is hereinafter referred to as “focal line 78”. The input light 77 is VI
The light propagates radially from a focal line 78 inside the PA 76. VI
Next, the PA 76 outputs the light beam 82 of the collimated light. Here, the output angle of the light flux 82 changes as the wavelength of the input light 77 changes. For example, if the input light 77 has a wavelength λ
In the case of 1, the VIPA 76 has the luminous flux 82a of the wavelength λ1.
Is output in a specific direction. When the input light 77 has the wavelength λ2, the VIPA 76 outputs the light beam 82b having the wavelength λ2 in a different direction. Accordingly, the VIPA 76 generates light fluxes 82a and 82b that are spatially distinguishable from each other. Input light 7
7 includes both wavelengths λ1 and λ2, VI
The PA 76 outputs both the light beams 82a and 82b at the same time.

FIG. 7 illustrates V, according to one embodiment of the present invention.
FIG. 4 is a diagram showing an IPA 76 in detail. According to FIG.
The PA 76 includes, for example, a plate 120 made of glass, and has reflection films 122 and 124 thereon. The reflective film 122 is preferably about 95% or more,
It has a reflectance of less than 100%. Reflective film 124
Preferably has a reflectivity of approximately 100%. The illumination window 126 is formed on the plate 120 and preferably has a reflectance of approximately 0%.

The input light 77 passes through an illumination window,
The light is focused on the focal line 78 by the lens 80,
And 124 are caused by multiple reflections. The focal line 78 preferably corresponds to the plate 120 on which the reflective film 122 is formed.
On the surface. The focal line 78 is essentially a line focused on the reflective film 122 via the irradiation window 126. The width of the focal line 78 can be referred to as the “beam waist” of the input light 77 when collected by the lens 80. Therefore, the embodiment of the present invention shown in FIG. 7 sets the beam waist of the input light 77 to the far surface of the plate 120 (that is, the surface having the reflective film 122 thereon).
Focus on By focusing the beam waist on the far side of the plate 120, this embodiment of the invention provides (i) the area of the input light 77 as it passes through the illumination window 126 (eg, as described in more detail below, FIG.
And (ii) the reflection film 124 when the input light 77 is first reflected by the reflection film 124.
The upper light area (eg, FIG. 1, described in more detail below)
It reduces the likelihood of an overlap with the region "b") shown at 0. 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 reflective film 122 is 95%, at the first reflection of the reflective film 122, 5% of the light passes through the reflective film 122 and diffuses after the beam waist, and 95% of the light is reflected on the reflective film 124. Reflected toward. After being first reflected by the reflective film 124, the light again strikes the reflective film 122, but is shifted by an amount of d. Then, 5% of the light passes through the reflective film 122. Similarly, as shown in FIG. 7, light is split into many paths separated by a fixed distance d. The beam shape of each pass is formed such that the light is diffused from the virtual image 134 of the beam waist. The virtual image 134 is
Are arranged at a constant interval 2t along a line perpendicular to.
Here, t is the thickness of the plate 120. Virtual image 134
The positions of the beam waist in are naturally arranged, and it is not necessary to adjust the respective positions. The light diffused from the virtual image 134 interferes with each other, and the collimated light 136 propagates in a direction that changes according to the wavelength of the input light 77.
To form

The interval between the optical paths is d = 2tSin θ ₀ ,
The difference in path length between adjacent beams is 2tCosθ _0. The angular dispersion is proportional to the ratio of these two numbers,
This ratio is cot θ ₀ . As a result, VIPA
Produces a fairly large angular dispersion.

As can be easily understood from FIG.
The term "y imaged phased array"
From the formation of the sequence of FIG. 8 illustrates a line VIA of the VIPA 76 shown in FIG. 6 according to an embodiment of the present invention.
It is a figure showing the section along II-VIII. According to FIG.
Plate 120 has reflective surfaces 122 and 124 thereon. The reflecting surfaces 122 and 124 are parallel to each other and are separated by a thickness t of the plate 120. The reflection surfaces 122 and 124 are typically reflection films formed on the plate 120. As described above, the reflecting surface 124
Has a reflectivity of about 100% except for the irradiation window, and the reflective surface 122 has a reflectivity of about 95% or more. Therefore, the reflective surface 122 has a transmittance of approximately 5% or less, transmits approximately 5% or less of light incident on the reflective surface 122, and reflects 95% or more of the light. You. The reflectance of the reflecting surfaces 122 and 124 is VI
It can be easily changed according to the special application of PA. However, in general, the reflective surface 122 should have a reflectivity of less than 100% to transmit some of the incident light.

The reflecting surface 124 has an illumination window 126 thereon. Illumination window 126 transmits light 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.
The light is received between 2 and 124 and reflected.

FIG. 8 shows a cross section along the line VIII-VIII in FIG. 6, so that the focal line 78 in FIG.
Appears as a "dot". Input light 77 then propagates radially from focal line 78. Further, as shown in FIG. 8, the focal line 78 is disposed on the reflection surface 122. It is not necessary that the focal line 78 be on the reflective surface 122, but moving the position of the focal line 78 will cause a slight change in the characteristics of the VIPA 76.

As shown in FIG. 8, the input light 77
Is incident on the plate 120 via the area A0 of the irradiation window 126. Here, the point P0 indicates a point around the area A0.

The input light 77 is determined by the reflectance of the reflection surface 122.
Is reflected by the reflecting surface 122 and is incident on the area A1 of the reflecting surface 124. Reflective surface 12
4, the input light 77 is reflected from the reflection surface 1.
22, the output light Ou is partially defined by the ray R1.
The light passes through the reflection surface 122 as t1. Thus, FIG.
, The input light 77 causes multiple reflections between the reflection surfaces 122 and 124. Here, the reflection surface 122
Each reflection from also results in a respective output light being transmitted. Therefore, for example, the input light 77
2, A3 and A4, and output light Out2, Ou
Generate t3 and Out4. Point P2 indicates a point around area A2, point P3 indicates a point around area A3, and point P4 indicates a point around area A4. The output light Out2 is defined by the ray R2, and the output light Out2.
3 is defined by ray R3, and output light Out4 is defined by ray R4. FIG. 8 shows output light Out0,
Although only Out1, Out2, Out3, and Out4 are shown, actually, the power of the input light 77 and the reflection surface 12
Due to the reflectivity of 2 and 124, there is more output light. As described in more detail below, the output lights interfere with each other and produce a light beam having a direction that varies according to the wavelength of the input light 77.

FIG. 9 illustrates VI, according to one 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 reflection surface 124 is approximately 100%
And thus essentially functions as a mirror. As a result, output light Out1 can reflecting surfaces 122 and 124 is no, so that the output light Out1 was emitted from the focal line I _1, can be optically analyzed. Similarly,
The output lights Out2, Out3, and Out4 are
It can be analyzed optically as emitted from the focal lines I ₂ , I ₃ and I ₄ respectively. Focal lines I ₁ , I
₂ , I ₃ and I ₄ are virtual images of the focal line I ₀ .

Therefore, as shown in FIG. 9, the focal line I ₁ is at a distance 2t from the focal line I ₀ . 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 previous focal line. Thus, the focal line I ₂
Is at the focal line I ₁ a distance 2t. Further, each subsequent multiple reflection between the reflective surfaces 122 and 124 produces output light having a lower intensity than the previous output light. Therefore, the output light Out2 has lower intensity than the output light Out1.

As shown in FIG. 9, the output lights from the focal line overlap and interfere with each other. This interference generates a light beam that travels in a specific direction depending on the wavelength of the input light 77. The VIPA according to the above embodiment of the present invention comprises a VIPA
A has the condition of reinforcement, which is a design characteristic of A.
The constructive conditions increase the interference of the output light so that a luminous flux is formed. 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 indicates the wavelength of the input light, t indicates the distance between the reflection surfaces 122 and 124, and m indicates an integer.

Therefore, if t is a constant and m is given a specific value, the propagation direction θ of the light beam formed with respect to the input light having the wavelength λ can be determined. More specifically, input light 77 diverges radially from focal line 78 at a particular angle. Thus, input light of the same wavelength travels in many different directions from focal line 78 and is reflected between reflective surfaces 122 and 124. The condition for VIPA reinforcement is that light traveling in a specific direction reinforces through interference of output light to form a light beam having a direction corresponding to the wavelength of input light. Light traveling in a direction different from the specific direction required by the constructive conditions is weakened by the interference of the output light.

FIG. 10 shows V for determining the incident angle or the inclination angle of the input light according to the embodiment of the present invention.
Line VI of the VIPA illustrated in FIG. 6 showing the characteristics of the IPA.
It is a figure showing the section along II-VIII.

Referring to FIG. 10, input light 77 is collected by a cylindrical lens (not shown) and converged on a focal line 78. As shown in FIG. 10, the input light 77 covers an area on the irradiation window 126 having a width equal to “a”. After the input light 77 is reflected once from the reflection surface 122,
The input light 77 is incident on the reflection surface 124 and is reflected by the reflection surface 124.
Covers an area with a width equal to "b" above. Further, FIG.
As shown in FIG.
Travel along the optical axis 132 at an inclination angle θ _{0 with} respect to the perpendicular to

After the tilt angle θ ₀ is first reflected by the reflecting surface 122, the input light 77
Should be set so as not to get out of
In other words, the inclination angle θ ₀ is such that the input light 77
2 and 124, the capture window 126
Should be set so as not to escape from Therefore, in order to prevent the input light 77 from going out of the irradiation window 126, the inclination angle θ ₀ should be set according to the following equation (2).

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

Accordingly, as shown in FIGS. 6-10, embodiments of the present invention include a VIPA that receives input light having respective wavelengths within a continuous range of wavelengths. VI
The PA causes self-interference by multiple reflection of input light to form output light. The output light is spatially distinguishable from the output light formed for input light of any other wavelength within the continuous range of wavelengths. For example, FIG.
The input light causing multiple reflections between 22 and 124 is illustrated. This multiple reflection is, for each wavelength of the input light 77,
A plurality of output lights Out0, Out1, Out2, Out that interfere with each other so as to generate a spatially distinguishable light flux.
Generate t3 and Out4.

"Self-interference" is a term that refers to interference that occurs between multiple lights or beams from the same light source. Therefore, the output lights Out0, Out1, Out1, and Out4 all come from the same light source (that is, the input light 77) because the output lights Out0, Out1, Out2, Out3, and Out4 all come from the same light source.
The interference of 2, Out3, and Out4 is called self-interference of the input light 77.

According to the above embodiment of the present invention, the input light may be at any wavelength within a 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 beam 82 (ie, the “spatial characteristic”) will be different if the input light 77 is at a different wavelength within a continuous range of wavelengths. Further, for example, referring to FIG. 6, if the input light 77 includes all three wavelengths λ1, λ2, and λ3, the light fluxes 82a, 82b, and 82c are generated simultaneously and travel in different directions.

According to the above embodiment of the present invention, the focal line is described as being on the opposite side of the parallel plate from which input light is input. However, the focal line, for example, in a parallel plate,
It is also possible to be on the surface of the irradiation window or just before the irradiation window.

According to the above embodiment of the present invention, the two reflective films reflect light between them, and the reflectance of one reflective film is approximately 100%. However, a similar effect can be obtained by two reflective films each having a reflectance of less than 100%. For example, both reflective films can have a reflectivity of 95%. In this case, each reflection film transmits light and causes interference. as a result,
A light beam traveling in a 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 characteristics of the VIPA.

According to the above embodiment of the present invention, the waveguide device is described as being formed by a parallel plate or by two reflecting surfaces parallel to each other. However, the plates or reflecting surfaces need not necessarily be parallel.

According to the above embodiment of the present invention, VIPA
Uses multiple reflections to maintain a constant phase difference between the interfering lights. As a result, the characteristics of the VIPA are stable, and as a result, changes in optical characteristics due to polarization are reduced. 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” refers to a light beam that can be distinguished in space. For example, the various luminous fluxes are spatially distinguishable if they are collimated and travel in different directions or are focused at different points. However, the invention is not limited to these detailed examples, and there are other ways to make the light beams spatially distinguishable from one another.

FIG. 11 illustrates an embodiment of the present invention.
FIG. 4 illustrates a VIPA used with a receiver. FIG.
According to 1, the multilayer reflective films 96 and 98 are, for example, 100
It is provided 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
It is desirable to have a thickness in the range of μm. The reflective films 96 and 98 are preferably multilayer high reflectivity interference films.

The reflectance of the reflection film 98 is approximately 100%, and the reflectance of the reflection film 96 is approximately 95%. However, the reflectance of the reflection film 96 is not limited to 95%,
Different values may be used as long as sufficient light is reflected from the reflective film 96 so that multiple reflections occur between the light and the light. Preferably, the reflectivity of the reflective film 96 is between 80% and 100%.
The range is smaller than a few percent. Further, the reflection film 9
The reflectivity of 8 is not limited to 100%, but needs to be high enough to cause multiple reflections between the reflective films 96 and 98.

The irradiation window 102 receives input light and is arranged on the same surface as the reflection film 96 of the parallel plate 100. The irradiation window 102 is formed by a film having a reflectance of approximately 0% on the surface of the parallel plate 100. As shown in FIG. 11, the boundary between the illumination window 102 and the reflective film 96 is preferably 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 a parallel beam received by the cylindrical lens 108. The cylindrical lens 108 irradiates the parallel beam 104 with the irradiation window 1
The light is condensed on the focal line 110 on the reference numeral 02. The focal line 110 is disposed near and parallel to a straight line boundary between the reflective film 96 and the irradiation window 102. Thus, the input light is input to the parallel plate 100 via the irradiation window 102.

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

Once the input light enters the parallel plate 100,
Multiple reflections occur between the reflective films 96 and 98 (eg, as shown in FIG. 8). Each time input light is incident on reflective film 96, approximately 95% of the light is reflected toward reflective film 98 and approximately 5% of the light is transmitted through reflective film 96 to form output light (eg, Output light Out as shown in FIG.
1). Multiple output light is formed by multiple reflection between the reflection films 96 and 98. The multiple output lights interfere with each other,
A light beam is formed in a propagation direction depending on the wavelength of the input light.

The light beam 112 is collected by a lens 114 that converges the light beam to a convergence point. The convergence 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 convergence point moves further along the linear path 116. The plurality of receivers 118 are arranged on the linear path 116 to receive the collected light flux 112. Therefore, each receiver 11
Reference numeral 8 is arranged to receive a light beam corresponding to a specific wavelength.

By controlling the distance t between the reflection films or the reflection surfaces of the VIPA, the phase difference of the light reflected between the reflection films or the reflection surfaces can be shifted by a predetermined amount. Resistance can be realized.
Furthermore, the above embodiments of the present invention make only small changes in optical properties that depend on optical polarization.

FIG. 12 is a diagram illustrating a VIPA for use with a receiver, according to another embodiment of the present invention. FIG.
The VIPA described in FIG. 2 is the same as the VIPA described in FIG. 11 except that the reflectances of the reflection films 96 and 98 are exchanged.
Same as A. More specifically, the V shown in FIG.
In IPA, the reflection film 98 has a reflectance of approximately 95%, and the reflection film 96 has a reflectance of approximately 100%. As shown in FIG. 12, the light flux 112 is formed by interference of output light transmitted through the reflection film 98. Therefore, the input light enters from one side of the parallel plate 100, and the light flux 1
12 is formed on the opposite side of the parallel plate 100. Otherwise, the VIPA described in FIG. 12 is the VIPA described in FIG.
It operates similarly to A.

FIG. 13 illustrates 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 optical signals modulated on a plurality of carriers having different wavelengths.

Light 138 typically has a diffuse width when output from an optical fiber. Therefore, the collimating lens 142 converts the light 138 into parallel light. The parallel light is then collected by a cylindrical lens 144 and converged on a focal line 146. The light then passes through the illumination window 150 from the focal line 146 to the VIP
Emitted into A148.

The VIPA 148 has reflection films 152 and 154 on a parallel plate 156. The reflective film 154 is on one side of the parallel plate 156, and the reflective film 152 and the irradiation window 150 are on the other side of the parallel plate 156. Reflective film 152
Has a reflectance of about 100%, and the reflective film 154 has a reflectance of 10%.
It has a reflectance of less than 0%. The light beam 158 of the light reflected by the parallel plate 156 is output to the opposite side of the parallel plate 156 from the irradiation window 150.

When the input light 138 includes a plurality of wavelengths, a plurality of light beams 158 are formed which travel in different directions depending on the wavelength of the input light 138. The light beam 158 formed by the VIPA 148 is collected by the lens 160 at different points depending on the propagation direction of the light beam 158. Therefore, as shown in FIG.
Light beams 158a, 15 having wavelengths λ1, λ2, and λ3
8b and 158c are formed at different focusing points.

A 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 a single wavelength. Thus, a plurality of light beams are received at the same time and transmitted through various channels. Each light receiving waveguide 162 has a corresponding receiver (not shown) provided at a subsequent stage. The receiver is typically a photodiode. Therefore, each light receiving waveguide 16
The light guided by 2 is received and processed by the corresponding receiver.

However, the VI according to the above embodiment of the present invention
According to PA, the beam profile of the obtained luminous flux is:
The beam profile is not optimal. For example, FIG. 14A is a diagram illustrating an operation of the VIPA 76 in FIG. 7, and FIG. 14B is a diagram illustrating a beam profile of the VIPA.

According to FIGS. 14A and 14B, the input light 77 causes multiple reflections between the reflection films 122 and 124. In this example, it can be assumed that reflective film 124 has a reflectivity of approximately 100% and reflective film 122 has a constant reflectivity of 95%. Reflective films 122 and 124
, The input light 77 is transmitted to the VIPA 76
Weakening in Therefore, the luminous flux generated by the VIPA 76 becomes weaker along the surface of the reflective film 122 as shown in FIG. Therefore, the coupling efficiency of the light beam to the optical fiber is not so high. To solve this problem, it is possible to change the reflectance of the reflection film 122.

For example, FIG. 15A shows the operation of the VIPA 76 according to another embodiment of the present invention, and FIG.
FIG. 15 (B) shows the state of FIG. 15 (A) according to an embodiment of the present invention.
FIG. 4 is a diagram showing a beam profile of VIPA of FIG.

According to FIG. 15A, for example, the reflection film 1
24 can be assumed to have approximately 100% reflectivity. Further, the reflectance of the reflection film 122 is changed, for example, so that the beam profile of the obtained light beam has a substantially symmetrical beam profile such as a substantially bell-shaped curve shown in FIG. For example, the reflection film 12
The reflectance of 2 is such that at the first incident position 180 of the input light 77 of the reflection film 122, the input light multiply reflected by the reflection film 122 is transmitted through the reflection film 122 so that only a small part of the light is transmitted. It is possible to vary so that more light is transmitted through the reflective film 122 at the last incident position 182 of 77. More specifically, the reflectivity of the reflective film 122 preferably has a high reflectivity near the first incident position 180 (thus, a small amount of light can be transmitted through the reflective film 122 at the first incident position 180). And so on, so as to have a low reflectivity near the last incident position 182 (so that more light can be transmitted through the reflective film 122 at the last incident position 182).

For example, the reflective film 122 has a reflectivity of about 99% or more at the first incident position 180, and decreases to about 80% at the last incident position 182. However, the present invention is not limited to this range of reflectivity. The reflective film 122 can be designed such that the reflectivity changes continuously from the first incident position 180 to the last incident position 182.

Therefore, the input light 77 is reflected by the reflection films 122 and 12.
4, the reflection film 1 of the input light 77 is reflected multiple times.
The light incident position on 22 moves from the first incident position 180 to the last incident position 182. The reflectivity decreases along the reflective film 122 from the first incident position 180 to the last incident position, so that the obtained light flux has a substantially symmetric beam profile along the reflective film 122. Such a beam profile is shown in FIG.

According to one embodiment of the present invention, FIG.
FIG. 16A is a graph showing an example of a reflectance curve (r) and a transmittance curve (t) of the reflection film 122, and FIG. 16B is a corresponding power reflection curve (R) and power transmission curve (t). It is a graph which shows T). Here, in general, T = t ² R = r ² (power is the square of amplitude) T + R = 1.

If t is linear, then t = kx. Where k
Is a constant. And T = k^Twox ^Two(Parabolic), R =
1-k^Twox^Two(Parabolic) and r = √ (1-k
^Twox^Two) (Ellipse).

Therefore, referring to FIGS. 16A and 16B, the reflection film 122 has a reflectance as shown by a reflectance curve (r) in FIG. 16A. 16
As shown in the transmittance curve (t) of FIG.
Assume that the amplitude transmittance changes linearly along the plane of 22. Then, since the power is the square of the amplitude, the power transmittance curve (T) in FIG. 16B is parabolic as shown in the above equation. Since the power reflectance is 1 minus the power transmittance, the power reflectance is also parabolic as shown in the power reflectance curve (R) in FIG. By using the power reflectivity curve (R), the output beam couples almost completely to the optical fiber, but has a constant reflectivity VI.
PA has only 20% loss or 80% coupling efficiency.

As shown in the transmittance curve (t),
According to the linear variation of the amplitude transmittance, the output beam profile is not completely symmetric, but is substantially symmetric. However, this practical design gives very high performance. Of course, with a more sophisticated design, a completely symmetric output or a completely Gaussian type can be obtained. However, the complex reflectance curve of such a design is not practical.

Although the reflectivity changes along the reflection film 122, the light phase during reflection by the reflection film 122 is preferably kept constant. FIG. 17 illustrates a phase adjustment buffer layer 1 that keeps the optical phase substantially constant during reflection, ie, uniform, according to one embodiment of the present invention.
FIG. 4 shows a VIPA having a 84. The phase adjustment buffer layer 184 preferably includes the reflective films 122 and 124.
Between, and adjacent to or above the reflective film 122. The thickness of the phase adjustment buffer layer 184 is
It changes along the surface and changes the optical phase of the light transmitted through the phase adjustment buffer layer 184, and
Cancel the change in optical phase through reflection at.

The phase adjustment buffer layer 184 represents a preferred embodiment for changing the phase of the reflected light. However, the invention is not limited to this particular embodiment,
Other configurations can be used to change the phase of the reflected light.

Further, the optical phase of the light transmitted through the reflection film 122 should preferably be kept constant. FIG. 18 illustrates a phase adjustment buffer layer 18 that keeps the optical phase of light transmitted through reflective film 122 substantially constant, ie, uniform, according to one embodiment of the present invention.
6 is a diagram showing a VIPA having a No. 6; FIG. The phase adjustment buffer layer 186 preferably extends along the reflective film 122,
It is arranged on the side opposite to the reflection film 124. The thickness of the phase adjustment buffer layer 186 varies along the surface, canceling out the phase change induced through the reflective film 122.

The phase adjustment buffer layer 186 represents a preferred embodiment for changing the phase of transmitted light. However, the invention is not limited to this particular embodiment, and other configurations can be used to change the phase of the transmitted light.

According to the above embodiment of the present invention, VIPA
Has first and second reflecting surfaces (the reflecting films 124 and 122 in FIG. 15A, respectively). The second surface has a reflectance such that a part of incident light is transmitted. V
The IPA receives input light of each wavelength within a continuous range of wavelengths. The first and second surfaces are arranged such that input light is reflected a plurality of times between the first and second surfaces and a plurality of lights are transmitted through the second surface. The plurality of transmitted lights interfere with each other and are spatially distinguishable from the output light generated for input light of any other wavelength within a continuous range of wavelengths (such as light flux 82a or 82b in FIG. 6). Na). The reflectivity of the second surface changes along the second surface, and the output light has a desired beam profile along the second surface (for example, the reflection film 122 shown in FIG. Fifteen
(See the beam profile in (B)). The phase adjustment buffer layer may be provided to give a uniform optical phase to light reflected from the second surface toward the first surface. Furthermore,
The phase adjustment layer can be provided to give a uniform optical phase to the transmitted light.

According to the above embodiment of the present invention, VIPA
The surface reflectivity is varied to obtain the desired beam profile. In various aspects of the above embodiments of the invention, the desired beam profile is described as being symmetric. However, there may be situations where different beam profiles are required, such as, for example, asymmetric or bilobed profiles. Therefore, the reflectivity is not limited only to obtaining a symmetric beam profile. Rather, the reflectivity is designed to obtain many different types of desired beam profiles, such as, for example, symmetric, asymmetric, Gaussian, generally bell-shaped, or bihedral beam profiles. It is possible to For example, U.S. Pat. S. application
08 / 802,768, entitled "Optical component in which the distribution of the optical field of the received light or the distribution of the optical field of the propagation mode of the light-receiving waveguide is bihedral," and is hereby incorporated by reference.

VIPA combined with a reflection device such as a mirror
Can be used to generate chromatic dispersion. For example, FIGS. 19 to 23 are diagrams illustrating an apparatus that uses VIPA as an angular dispersion unit for generating chromatic dispersion. Such a device is disclosed in U.S. Pat. S. Application 08 / 796,842, "Optical Device Using Virtually Imaged Phased Array to Generate Chromatic Dispersion", filed August 13, 1997, U.S. Pat. S. It is disclosed in more detail in application 08 / 910,251 "Optical device using a virtual imaged phased array to produce chromatic dispersion", which is hereby incorporated by reference.

For example, referring to FIG.
40 has, for example, a first surface 242 having a reflectance of approximately 100%, and a second surface 244 having a reflectance of approximately 98%, for example. VIPA 240 also includes an illumination window 247. However, VIPA24
0 is not limited to this special configuration. Rather, VIPA 240 may take many different configurations, as described herein.

As shown in FIG. 19, light exits fiber 246, is collimated by collimating lens 248, and is line focused by cylindrical lens 250 through illumination window 247 into VIPA 240. VIPA 240 then generates collimated light 251 that is focused by focusing lens 252 onto mirror 254. The mirror 254 is a mirror unit 2 formed on the substrate 258.
56 is sufficient.

The mirror 254 reflects and returns the light through the converging lens 252 into the VIPA 240. The light then undergoes multiple reflections within VIPA 240 and is output from illumination window 247. Light output from illumination window 247 travels through cylindrical lens 250 and collimating lens 248 and is received by fiber 246.

Thus, light is output from VIPA 240, reflected by mirror 254 and returned to VIPA 240. Light reflected by mirror 254 travels in a path exactly in the opposite direction to the path that originally traveled. As will be seen in more detail below, the different wavelength components of the light
The light is collected at four different positions and reflected and returned to the VIPA 240. As a result, different wavelength components travel different distances, thus producing chromatic dispersion.

FIG. 20 illustrates an embodiment of the present invention.
FIG. 20 is a diagram showing the operation of the VIPA of FIG. 19 in more detail. It is assumed that light having various wavelength components is received by the VIPA 240. As shown in FIG.
0 causes a virtual image 260 of the beam waist 262 to be formed,
Each virtual image 260 emits light.

As shown in FIG. 20, the converging lens 252 converges different wavelength components of the collimated light from the VIPA 240 to different points of the mirror 254. More specifically, the long wavelength 264 is converged to point 272, the center wavelength 266 is converged to point 270, and the short wavelength 268 is point 2
74 is converged. Then, the longer wavelength 264 is returned to the virtual image 260 closer to the beam waist 262 than the center wavelength 266. The short wavelength 268 is the center wavelength 2
Compared with 66, the image is returned to a virtual image 260 farther from the beam waist 262. Thus, this arrangement gives a normal variance.

The mirror 254 is designed to reflect only light of a particular interference order, and any other interference order is focused out of the mirror 254. More specifically, as described above, the VIPA outputs collimated light. This collimated light travels in a direction where the path from the virtual image has a difference mλ where m is an integer. The m-th order of interference is defined as the output light corresponding to m.

For example, FIG. 21 is a diagram showing various orders of VIPA interference. According to FIG. 21, VIPA 24
VIPAs such as 0 are collimated lights 276, 278,
Release 280. Each collimated light 276, 278, 280
Correspond to different interference orders. Therefore, for example, when n is an integer, the collimated light 276 is a collimated light corresponding to the (n + 2) -th order of interference, and the collimated light 2
Reference numeral 78 denotes collimated light corresponding to the (n + 1) -th interference order, and collimated light 280 is collimated light corresponding to the n-th interference order. Collimated light 276 is shown as having several wavelength components 276a, 276b, and 276c. Similarly, collimated light 2
78 is illustrated as having wavelength components 278a, 278b, and 278c, and collimated light 280 is illustrated as having wavelength components 280a, 280b, and 280c. Here, the wavelength components 276a, 278a, and 280a have the same wavelength. Wavelength component 276
b, 278b, and 280b have the same wavelength (but different from the wavelengths of wavelength components 276a, 278a, and 280a). The wavelength components 276c, 278c, and 280c are at the same wavelength (but the wavelength components 276a,
78a and 280a, and a wavelength component 276
b, 278b, and 280b). Although FIG. 21 illustrates only collimated light of three different interference orders, the collimated light is also emitted for many other interference orders.

Since collimated light of the same wavelength of different interference orders travels in different directions, and therefore converges to different positions, mirror 254 reflects and returns only light from a single interference order to VIPA 240. can do.
For example, as shown in FIG. 21, the length of the reflecting portion of the mirror 254 should be relatively short so that only light corresponding to a single interference order is reflected. More specifically, in FIG. 21, only the collimated light 278 is
4 reflected. Thus, the collimated light 27
6 and 278 are focused out of mirror 254.

The wavelength division multiplexed light usually includes many channels. Referring again to FIG.
If the thickness t between the first and second surfaces 242 and 244 of the 240 is set to a specific value, this configuration makes it possible to simultaneously compensate for the dispersion of each channel.

More specifically, each channel has a center wavelength. These wavelengths are usually separated by a certain frequency spacing. The thickness t of the VIPA 240 between the first and second surfaces 242 and 244 is such that all of the wavelength components corresponding to the center wavelength have the same output angle from the VIPA 240,
Therefore, it should be set to have the same convergence point on mirror 254. This is because, for each channel, the wavelength component corresponding to the center wavelength is advanced by the thickness t.
The optical path length of the round trip passing through 0 is set to be an integral multiple of the center wavelength of each channel. The amount of this thickness t is hereinafter referred to as “W
It is called "DM matching free spectral range thickness" or "WDM matching FSR thickness".

Further, in this case, the optical path length (2 nt cos θ) of the reciprocation through the VIPA 240 is equal to a value obtained by multiplying the wavelength corresponding to the center wavelength of each channel by a different integer for the same θ. Where n is the first and second surfaces 2
The refractive index, θ, of the member between 42 and 244 indicates the propagation direction of the light beam corresponding to the center wavelength of each channel. More specifically, as described above, θ indicates the propagation direction of the obtained light beam, measured from a line perpendicular to the surfaces of the reflection surfaces 122 and 124.

Therefore, if t is set to a wavelength component corresponding to the center wavelength of each channel, then 2 nt cos θ is set to be an integral multiple of the center wavelength of each channel for an integer different for the same θ. , All of the wavelength components corresponding to the center wavelength have the same output angle from VIPA 240, and thus the same convergent position of mirror 254.

For example, if the reciprocation is a physical length of 2 mm (this is approximately twice the thickness of the VIPA 240 of 1 mm) and the refractive index is 1, 5, all wavelengths at 100 GHz intervals satisfy this condition. it can. As a result, VIPA 24
0 can simultaneously compensate the dispersion of all the channels of the wavelength division multiplexed light.

Therefore, referring to FIG.
When set to DM matching FSR thickness, VIPA24
0 and the converging lens 252 (a) the wavelength component corresponding to the center wavelength of each channel is converged to a point 270 on the mirror 254, and (b) the wavelength component corresponding to the long wavelength component of each channel is on the mirror 254. (C) the wavelength component corresponding to the short wavelength component of each channel is
74 can be converged. Therefore, V
The IPA 240 can be used to compensate for chromatic dispersion of all channels of the WDM light.

FIG. 22 is a graph showing the amount of dispersion of several channels of wavelength division multiplexed light when the thickness t is set to the WDM matching FSR thickness according to the embodiment of the present invention. As shown in FIG. 22, all channels have the same variance. However, the dispersion is not continuous between the channels. Further, the wavelength range for each channel for which VIPA 240 compensates for dispersion can be set by appropriately setting the size of mirror 254.

If the thickness t is not set to the WDM matching FSR thickness, different channels of the wavelength division multiplexed light converge on different points of the mirror 254. For example, the thickness t
Is 、, ３, or some other fraction of the reciprocating optical path length thickness, the convergent points of 2, 3, 4, or more channels are converged on the same mirror. , Each channel converges to a different convergence point. More specifically, if the thickness t is の of the WDM matching FSR thickness, light from the odd channels will be converged to the same point on mirror 254 and light from the even channels will be Converged to the same point. However, light from the even channels is converged to a different point than the odd channels.

For example, FIG. 23 is a diagram illustrating different channels converged at different points on the mirror 254. As shown in FIG. 23, the wavelength component of the center wavelength of the even channel is converged to one point of the mirror 254, and the wavelength component of the center wavelength of the odd channel is converged to a different point. As a result, VI
The PA 240 can sufficiently compensate for the dispersion of all the channels of the wavelength division multiplexed light at the same time.

Referring to FIGS.
Is an input fiber that supplies light to the VIPA 240,
It functions as both output fibers that receive the return light from IPA 240. However, in various designs, the input fiber may be a separate fiber from the output fiber. Thus, the input and output fibers are spatially distinguished from each other.

The second surface 244 of the VIPA 240 of FIGS. 19-23 has been described as having, for example, a reflectivity of approximately 98%. However, VIPAs can be designed to have a surface with varying reflectivity, as described above, to produce a desired beam profile. For example,
The second surface 244 may have a varying reflectivity that minimizes device loss or maximizes coupling efficiency from the input fiber to the output fiber. For example, the second surface 244 may be
To 240, to mirror 254, back to VIPA 240, can have a varying reflectivity to produce the desired beam profile that reduces losses as light travels along the total path back to fiber 246. It is.

In order to reduce the loss and obtain the highest coupling efficiency, it is preferable that the second surface 244 provides a beam profile having a Gaussian shape or a substantially bell-shaped curved shape.

Thus, as described above, VIPAs have a reflective surface with varying reflectivity that produces the desired beam profile. For example, the reflecting surface may have a substantially symmetrical beam profile along the reflecting surface, a substantially bell-shaped curved beam profile along the reflecting surface, a substantially Gaussian beam profile along the reflecting surface, or a bi-bump along the reflecting surface. It can have a varying reflectivity that produces an output beam with a shaped beam profile. Such a beam profile shape will be understood by those skilled in the art. Further, based on the above description, those skilled in the art will recognize how to form a reflective surface that produces a desired beam profile.

According to the above embodiment of the present invention, VIPA
Is described as being formed by a parallel plate or two reflecting surfaces parallel to each other. However, the plates or reflecting surfaces need not necessarily be parallel.

According to the above embodiment of the present invention, light including a plurality of wavelengths is demultiplexed simultaneously. Therefore, the size of the receiver used for the wavelength multiplex communication can be reduced.

According to the above embodiment of the present invention, VIPA
Can simultaneously multiplex wavelength-division multiplexed light for each wavelength of input light. Further, the dispersion angle can be adjusted by the thickness t of the parallel plate forming the VIPA. As a result, the dispersion angle can be large enough so that the receiver can easily receive each demultiplexed 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 uneven surface, and therefore, the size of the dispersion angle is limited. In contrast, the VIPA according to the above embodiment of the present invention
In order to achieve a relatively large dispersion angle, only the thickness of the parallel plate needs to be changed.

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 correctly receive an optical signal without fail 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 reflections and maintains a constant phase difference between the interfering lights. As a result, the properties of the VIPA are stable, thus reducing changes in optical properties caused by polarization. In contrast, the optical properties of conventional diffraction gratings undergo undesirable changes depending on the polarization of the input light.

Furthermore, 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 12 are used to reflect light.
4 shows a VIPA 76 having four. But VIP
A is not limited to using a “film” for providing a reflective surface. Rather, the VIPA should simply have suitable reflective surfaces, and these reflective surfaces
It may or may not be formed as a "film".

Further, in the above embodiment of the present invention,
VIPA includes a transparent glass plate in which multiple reflections occur. For example, FIG. 7 shows a VIPA 76 having a transparent glass plate 120 having a reflective surface thereon. However, VIPA is not limited to using glass members or any type of "plate" to isolate the reflective surface. Rather, the reflecting surfaces should simply be isolated from each other. For example, VIP
The reflecting surface of A is not a glass plate, but has a reflecting surface that is stably held by a member such as glass or metal having a small thermal expansion, and simply has “air” in between. Is possible. Thus, the reflective surface can be described as having a transparent member between it, for example, optical glass or air.

Some preferred embodiments of the present invention are shown,
Although described, those skilled in the art will recognize that these embodiments can be modified without departing from the principles and spirit of the invention, which is defined by the claims and their equivalents.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating 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 details of the VIPA illustrated in FIG. 6, according to one embodiment of the present invention.

FIG. 8 illustrates a cross section of the VIPA illustrated in FIG. 6 along line VIII-VIII, in accordance with an embodiment of the present invention.

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

FIG. 10 illustrates a line VA of the VIPA illustrated in FIG. 6 for determining the tilt angle of the input light, according to one embodiment of the present invention.
It is a figure showing the section along III-VIII.

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

FIG. 12 illustrates a VIPA used with a receiver, according to another 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 operation and a VIPA beam profile, according to one embodiment of the present invention.

FIG. 15 is a diagram showing the operation of the VIPA and the beam profile of the VIPA of FIG. 15A according to one embodiment of the present invention.

FIG. 16 illustrates a VIPA according to an embodiment of the present invention;
5 is a graph showing an example of a reflectance curve (r) and a transmittance curve (t), and a graph showing a corresponding power reflectance curve (R) and a power transmittance curve (T).

FIG. 17 illustrates a VIPA having a phase adjustment buffer layer that keeps the optical phase of the reflected light substantially uniform, according to one embodiment of the present invention.

FIG. 18 illustrates a VIPA having a phase adjustment buffer layer that keeps the optical phase of transmitted light substantially uniform, according to one embodiment of the present invention.

FIG. 19 illustrates an apparatus that uses VIPA as an angular dispersion unit to generate chromatic dispersion, according to one embodiment of the present invention.

20 is a diagram (part 1) illustrating the operation of the apparatus of FIG. 19 according to one embodiment of the present invention.

FIG. 21 is a diagram (part 2) illustrating the operation of the apparatus of FIG. 19 according to one embodiment of the present invention.

FIG. 22 is a diagram (part 3) illustrating the operation of the apparatus of FIG. 19 according to an embodiment of the present invention.

FIG. 23 is a diagram (part 4) illustrating the operation of the apparatus in FIG. 19 according to an embodiment of the present invention.

[Explanation of symbols]

76 VIPA 77 input light 78,110 focal line 80,114 lens 82,112 light flux 96,98 reflective film 100 parallel plate 102 input light 104 parallel light 106 collimating lens 108 cylindrical lens 118 receiver 120 plate 122,124 reflective film 102, 126 Irradiation window 132 Optical axis 134 Virtual image 136, 251, 276, 278, 280 Collimated light 140 Waveguide 142, 258 Substrate 144, 250 Cylindrical lens 146 Focus line 148, 240 VIPA 150, 247 Irradiation window 152, 154 Reflective film 156 Parallel Plate 160 Lens 162 Light receiving waveguides 184, 186 Phase adjustment buffer layer 246 Fiber 248 Collimating lens 252 Converging lens 254 Mirror 256 Mirror

 ──────────────────────────────────────────────────続 き Continuing the front page (72) Inventor Shiro ▲ Saki ▼ 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Simon Kao United States, 94538 Fremont, California , Albula Street 42501, Avanex Corporation

Claims (35)

[Claims] 1. An apparatus comprising a first surface and a second surface, the second surface having a reflectivity for transmitting a portion of light incident thereon, the reflection of the second surface. A rate varying along the second surface, the device receiving input light at each wavelength within a continuous range of wavelengths, wherein the first and second surfaces are configured such that the input light is A plurality of light is reflected between the second surfaces, a plurality of lights are transmitted through the second surface, and the plurality of transmitted lights interfere with each other to form any other wavelength within the continuous range of the wavelength. A device that is arranged to generate output light that is spatially distinguishable from output light generated for input light having: 2. As the input light is reflected a plurality of times between the first and second surfaces, the light incident position of the input light on the second surface is changed from the first incident position to the last incident position. The apparatus of claim 1, moving to an incident position, wherein the reflectivity decreases along the second surface from the first incident position to a last incident position. 3. As the input light is reflected a plurality of times between the first and second surfaces, the light incident position of the input light on the second surface is changed from the first incident position to the last incident position. Moving to an incident position, wherein the reflectivity decreases along the second surface from the first incident position to a last incident position, and the output light is substantially symmetrical along the second surface. 2. The device according to claim 1, wherein the device has a simple beam profile. 4. As the input light is reflected a plurality of times between the first and second surfaces, the reflection by the second surface comprises a plurality of reflections traveling from the second surface to the first surface. The apparatus of claim 1, defining light, the plurality of reflected lights having a uniform optical phase along a second surface. 5. As the input light is reflected a plurality of times between the first and second surfaces, the reflection by the second surface comprises a plurality of reflections traveling from the second surface to the first surface. The apparatus of claim 1, wherein the apparatus further comprises means for defining light and providing a uniform optical phase to the plurality of reflected lights along a second surface. 6. As the input light is reflected a plurality of times between the first and second surfaces, the reflection by the second surface comprises a plurality of reflections traveling from the second surface to the first surface. The apparatus of claim 1, wherein the apparatus further comprises a phase adjustment layer that defines light and provides a uniform optical phase to the plurality of reflected lights along a second surface. 7. The apparatus according to claim 6, wherein the phase adjustment layer is provided along the second surface between the first and second surfaces. 8. The apparatus according to claim 1, wherein said plurality of transmitted lights have a uniform optical phase along said second surface. 9. The apparatus according to claim 1, further comprising a phase adjustment layer for providing a uniform optical phase to the plurality of transmitted lights along the second surface. 10. The apparatus according to claim 9, wherein the phase adjustment layer is provided along the second surface on a side opposite to the first surface. 11. The apparatus of claim 1, further comprising: means for providing a uniform optical phase to said plurality of transmitted lights along said second surface. 12. The apparatus of claim 1, wherein said first surface has a reflectivity of substantially 100%. 13. 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, wherein the plurality of transmitted lights interfere with each other and each of the input lights 2. The apparatus of claim 1, wherein each output light is generated for one of the carriers, and each output light is spatially distinguishable from the other output lights. 14. The apparatus according to claim 14, wherein said input light is converged on a line between said first and second surfaces and is reflected a plurality of times between said first and second surfaces. Item 10. The apparatus according to Item 1. 15. The reflectivity of the second surface varies along the second surface, and the output light has a substantially symmetrical beam profile along the second surface. A substantially bell-shaped curved beam profile along the second surface, a substantially Gaussian beam profile along the second surface, an asymmetric beam profile along the second surface, and a double hump along the second surface. The apparatus of claim 1, having a beam profile that is one of a group of shaped beam profiles. 16. The output light is returned to the second surface and transmitted therethrough, and the returned output light is supplied to the first and second surfaces.
The apparatus of claim 1 further comprising an optical returning device that causes multiple reflections between the surfaces. 17. The apparatus according to claim 16, wherein said optical return device is a mirror. 18. The light returning device, comprising: a mirror; and a lens for condensing the output light on the mirror and guiding the output light reflected by the mirror to the second surface. 17. The apparatus according to claim 16, wherein: 19. The apparatus according to claim 19, wherein said apparatus receives said input light and said returned output light causes multiple reflections between said first and second surfaces, and further comprises a window output from said apparatus. 17. The device according to claim 16, comprising: 20. A semiconductor device comprising a first surface and a second surface, the second surface having a reflectivity for transmitting a portion of light incident thereon, wherein the reflectivity of the second surface is the second surface. The input light of each wavelength is focused on a line, and the first and second surfaces are such that the input light is emitted from the line;
The light is reflected multiple times between the first and second surfaces, so that a plurality of lights are transmitted through the second surface, and the transmitted lights interfere with each other to form another wavelength. An apparatus arranged to generate output light that is spatially distinguishable from output light generated for input light. 21. As the input light is reflected a plurality of times between the first and second surfaces, the input light is reflected on the second surface.
The light incident position of the input light moves from a first incident position to a last incident position, and the reflectance decreases along the second surface from the first incident position to the last incident position. 21. The apparatus according to claim 20, wherein 22. As the input light is reflected a plurality of times between the first and second surfaces, the input light is reflected onto the second surface.
The light incident position of the input light moves from a first incident position to a last incident position, and the reflectance decreases along the second surface from the first incident position to the last incident position. 21. The apparatus of claim 20, wherein said output light has a substantially symmetric beam profile along said second plane. 23. As the input light is reflected a plurality of times between the first and second surfaces, the reflection by the second surface is reflected from the second surface to the first surface. 21. The apparatus of claim 20, further comprising defining a plurality of reflected lights traveling, wherein the apparatus further comprises a phase adjustment layer for providing the plurality of reflected lights with a uniform optical phase along the second surface. An apparatus according to claim 1. 24. The apparatus according to claim 23, wherein the phase adjustment layer is provided along the second plane and between the first and second planes. 25. The apparatus according to claim 20, wherein said plurality of transmitted lights have a uniform optical phase along said second surface. 26. The apparatus according to claim 20, further comprising a phase adjustment layer for providing a uniform optical phase to the plurality of transmitted lights along the second plane. 27. The apparatus according to claim 26, wherein the phase adjustment layer is provided along the second surface on a side opposite to the first surface. 28. The apparatus of claim 20, wherein said first surface has a reflectivity of substantially 100%. 29. The reflectivity of the second surface varies along the second surface, and the output light has a substantially symmetric beam profile along the second surface; A substantially Gaussian beam profile along the second surface, an asymmetric beam profile along the second surface, and a bi-directional beam profile along the second surface. 21. The apparatus of claim 20, wherein the apparatus has one of a group of bump-shaped beam profiles. 30. The method according to claim 30, wherein the output light is returned to the second surface and transmitted therethrough, and the returned light causes multiple reflection between the first surface and the second surface. 21. The device of claim 20, further comprising an optical return device. 31. The apparatus according to claim 30, wherein said optical return device is a mirror. 32. The light returning device, comprising: a mirror; and a lens for condensing the output light on the mirror and guiding the output light reflected by the mirror to the second surface. 31. The apparatus of claim 30, wherein: 33. A light-emitting device comprising a first surface and a second surface, the second surface having a reflectance for transmitting a portion of light incident thereon, and input light of each wavelength being condensed on a line. Wherein the first and second surfaces are such that the input light is emitted from the line;
The light is reflected multiple times between the first and second surfaces, so that a plurality of lights are transmitted through the second surface, and the transmitted lights interfere with each other to form another wavelength. An output light that is spatially distinguishable from an output light generated with respect to the input light, wherein the reflectance of the second surface varies along the second surface; A light beam profile substantially symmetrical along the second surface; a beam profile having a substantially bell-shaped curve along the second surface; a substantially Gaussian beam profile along the second surface; Apparatus characterized by having a beam profile of one of the group consisting of an asymmetric beam profile along a second plane and a bilobed beam profile along the second plane. 34. The method according to claim 31, wherein the output light is returned to the second surface and transmitted therethrough, and the returned light causes multiple reflection between the first surface and the second surface. The apparatus of claim 33, further comprising an optical return device. 35. The apparatus according to claim 34, wherein said optical return device is a mirror.