JP2010134027A - Wavelength selection switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a more compact wavelength selection switch. <P>SOLUTION: The wavelength selection switch includes: an emission part composed of an end face of a fiber, from which light emits; a dispersion element disposed on the light emission side of the emission part; an optical deflection member disposed on the light emission side of the dispersion element; an incident part composed of an end face of the fiber and to which the light from the optical deflection member is made incident; a first optical system disposed in the optical path between the emission part and the optical deflection member; and a second optical system disposed in the optical path between a dispersion element and the optical deflection member, wherein the dispersion element is disposed on the front side focal point position of the second optical system, the optical deflection member is disposed on the rear side focal point position of the second optical system, the optical deflection member is composed of a plurality of deflection elements each of which is independently controlled, the dispersion element has a transmission face through which light passes and a diffraction optical face and the portion between the transmission face and the diffraction optical face is formed of a medium having a refractive index larger than 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavelength selective switch.

  Conventionally, as wavelength selective switches, for example, those proposed in Patent Document 1 and Patent Document 2 are known. Patent Document 1 proposes a transmission-type wavelength selective switch. Patent Document 2 proposes a reflective wavelength selective switch.

Special table 2004-532544 gazette US Pat. No. 6,707,959

  The optical system of the wavelength selective switch is required to be downsized. One of the parameters that determine the size of the optical system of the wavelength selective switch is the focal length of the optical system sandwiched between the dispersion element and the deflection element. Let the focal length of this optical system be f. It is desirable that the beam waist of the beam emitted from the input port to the optical system is relayed in the vicinity of the dispersive element and the deflecting element.

At this time, as shown in FIG. 6, if the distance from the dispersive element to the main surface of the optical system 801 and the distance from the main surface of the optical system 801 to the deflecting element are set to the focal length f, they are in the vicinity of the dispersive element. The beam waist is relayed in the vicinity of the deflection element.
Here, it is assumed that a reflection type grating 810 is used as a dispersion element and a MEMS mirror array is used as a deflection element. In FIG. 6, for convenience of explanation, the reflective grating 810 is depicted as a transmissive grating.

When the reflection grating 810 uses Δθ as the angle difference after diffraction of two signal lights whose frequencies are adjacent to each other and pm as the pitch between the micromirrors M of the MEMS mirror array 802, the following expression is upright.
pm = f · Δθ (1)

  In general, a reflective grating of pg = 1000 lines / mm, that is, pg = 1 μm, used as a dispersion element is taken as an example (pg represents the pitch of the grating). It is assumed that signal lights having two wavelengths of 193.9 THz and 194.0 THz with a C-band 100 GHz spacing are incident on the above-mentioned 1000 lines / mm grating at an incident angle of 50 degrees. At this time, the diffraction angles are 51.229 degrees and 51.157 degrees, respectively. Therefore, Δθ = 0.0722 degrees = 0.000126 rad (see FIG. 7).

As reported in the literature (IEEE / LEOS OPTICAL MEMS 2004 Page 32 A High-Speed Comb-Driven Micromirror Array for 1xN 80-channel Wavelength Selective Switches) When the MEMS mirror is used, the focal length f is 63.46 mm from the above formula (1).
The above is listed in Table 1.

  Therefore, if the optical system of the wavelength selective switch is a transmissive type, the distance from the dispersion element to the deflecting element is at least about 125 mm. With this, a small wavelength selective switch cannot be obtained. In addition, when the optical system of the wavelength selective switch is a reflection type, the distance from the dispersive element to the reflecting mirror exceeds 60 mm.

  Further, in common with both types of wavelength selective switches, the beam diameter is proportional to the focal length of the optical system. For this reason, this also hinders miniaturization.

  The present invention has been made in view of the above, and an object thereof is to provide a more compact wavelength selective switch.

In order to solve the above-described problems and achieve the object, the wavelength selective switch of the present invention includes:
An emission part configured by an end face of the fiber and emitting light;
A dispersive element disposed on the light output side of the optical system;
A light deflection member disposed on the light exit side of the dispersion element;
An incident part configured by an end face of a fiber and receiving light from the light deflection member;
An optical system disposed on the light emitting side with the emitting portion;
A first optical system provided in an optical path between the emitting portion and the light deflection member;
A second optical system provided in an optical path between the dispersion element and the light deflection member;
The dispersive element is provided at a front focal position of the second optical system;
The light deflection member is provided at a rear focal position of the second optical system;
The light deflection member is composed of a plurality of deflection elements,
The plurality of deflection elements can be controlled independently of each other,
The dispersion element includes a transmission surface through which light is transmitted;
Having a diffractive optical surface,
A portion between the transmission surface and the diffractive optical surface is formed of a medium having a refractive index larger than 1.

According to a preferred embodiment of the present invention,
A transmission surface different from the transmission surface,
The transmission surface is an incident surface on which the light is incident,
The another transmission surface is an emission surface from which the light is emitted,
The diffractive optical surface is disposed in an optical path from the incident surface to the exit surface,
The diffractive optical surface is preferably a reflective surface.

According to a preferred embodiment of the present invention,
The dispersive element comprises one medium;
It is desirable that the entrance surface, the exit surface, and the diffractive optical surface are integrally formed on one medium.

According to a preferred embodiment of the present invention,
The dispersion element includes a first medium and a second medium as the medium,
The entrance surface and the exit surface are formed in the first medium,
The diffractive optical surface is preferably formed on the second medium.

  According to a preferred aspect of the present invention, it is desirable that the refractive index of the medium is 1.8 or more.

  According to a preferred aspect of the present invention, it is desirable that the medium is silicon.

  According to a preferred aspect of the present invention, it is desirable that the second optical system is a lens.

  According to a preferred aspect of the present invention, it is desirable that the second optical system is a concave mirror.

  According to the present invention, a more compact wavelength selective switch can be provided.

  First, the dispersion element used for the wavelength selective switch according to the present invention will be described. Next, a wavelength selective switch including this dispersion element will be described.

  First, based on FIG. 8B, the dispersion in the medium in the dispersion element is considered. The incident surface is perpendicular to the incident light, and the incident angle on the diffractive surface is the same as in FIG. The wavelength in the medium 800 is λ / n by dividing the wavelength λ in the atmosphere by the refractive index n of the medium. Therefore, if the pitch of the diffractive surface G is reduced from pg to pg / n, dispersion similar to the example described with reference to FIG.

Next, based on FIG. 8A, consider that this light beam returns to the atmosphere. Refraction occurs at the exit surface from the dispersive element (same as the aforementioned entrance surface) in accordance with Snell's law. That is, the following expression (2) is established.
nsinθ1 = sinθ2 (2)

Here, θ1 is an incident angle on the exit surface, and θ2 is an exit angle from the exit surface. In this example, since θ1 and θ2 can both be regarded as being small, assuming that approximation of sin θ≈θ holds, equation (2) can be approximated as equation (3).
nθ1 = θ2 (3)

  That is, the dispersion angle returned to the atmosphere is n times the dispersion angle in the medium. Even in a region where the approximation of Equation (3) does not hold, the dispersion angle returned to the atmosphere is always larger than the dispersion angle in the medium.

  When silicon is used as the medium of the dispersive element, since the refractive index n at the wavelength illustrated in FIG. 7 is 3.475, the pitch of the diffraction surface G in FIG. 8B is 0.288 μm.

  When the pitch of the MEMS mirror, which is a deflecting element, does not change, that is, when the pitch is constant, if the conventional dispersion element is replaced with a high dispersion element using silicon, the dispersion Δθ is about 3.475 times. become. At this time, the focal length f is approximately 1 / 3.475 times from the equation (1). For this reason, the optical system of the wavelength selective switch can be reduced.

Next, a specific configuration of the dispersion element used in the wavelength selective switch of the present invention will be described.
FIG. 4B shows the dispersive element 200 used in this embodiment. In FIG. 4B, the dispersive element 200 is formed of a medium having a refractive index larger than 1. More specifically, the dispersive element 200 of this embodiment is configured by a prism.

  The prism has an incident surface 201a on which light is incident, an exit surface 201b from which light is emitted, and a diffractive optical surface 201c. Here, the diffractive optical surface 201c is provided in the optical path from the entrance surface 201a to the exit surface 201b. In the dispersive element 200 of the present embodiment, the same surface of the prism is an incident surface 201a and an output surface 201b. A reflective diffraction grating G is formed on the diffractive optical surface 201c. Thus, the dispersive element 200 has a so-called immersion grating configuration.

  As described above, in the dispersive element 200 used in the present embodiment, the light incident side and the diffracting side of the reflection diffraction grating G are filled with a uniform medium transparent to the wavelength used. The medium is generally a solid or a liquid. For example, silicon can be used.

  Further, as shown in FIG. 4C, the dispersive element 200 may have a configuration in which a planar member 230 on which a separate reflection type diffraction grating G is formed is joined to the prism 220. At this time, the planar member 230 and the prism 220 are desirably formed of the same medium.

  As a modification, a transmission grism configuration such as the dispersive element 300 shown in FIG. For reference, FIG. 4D shows a configuration of a normal reflection diffraction grating.

  Next, the dispersive element 200 will be described in more detail with reference to FIG. In FIG. 3, the dispersive element 200 is formed of a medium having a refractive index larger than 1. The dispersive element 200 in FIG. 3 is also formed of a prism. The prism has an incident surface 201a on which light is incident, an exit surface 201b from which light is emitted, and a diffractive optical surface 201c. Here, the diffractive optical surface 201c is provided in the optical path from the entrance surface 201a to the exit surface 201b.

Here, a detailed examination will be made from when light enters the prism until it exits.
In FIG. 3, let us consider a medium and the number of lattices that have an apex angle of 34 degrees, an incident angle of 12 degrees with respect to the incident surface 201a, and an exit surface 201b of 12 degrees.

  First, consider the case where the medium is the atmosphere, that is, a simple reflection type diffraction grating. The number of gratings that achieve the above-described incident angle and output angle is 707.73 lines / mm. Further, the emission angles of the respective wavelengths are as shown in Table 1 below. The dispersion angle is 0.09307 degrees.

  Next, in the dispersive element 200 (prism) used in this embodiment, when the medium is S-BSL7 manufactured by OHARA, the refractive index at the wavelength used is approximately 1.5. The number of lattices at this time is 1075.1 / mm. Further, the emission angle of each wavelength is as shown in Table 1 below, and the dispersion angle is 0.13547 degrees. This dispersion angle is 1.46 times that in the atmosphere.

  Further, in the dispersive element 200 (prism) used in this embodiment, when the medium is S-LAH60 manufactured by OHARA, the refractive index at the wavelength used is approximately 1.8. The number of gratings at this time is 1293.6 / mm, the emission angle of each wavelength is as shown in Table 1 below, and the dispersion angle is 0.16061 degrees. This dispersion angle is 1.73 times that in the atmosphere.

  Further, in the dispersive element (prism) used in this embodiment, when the medium is silicon, the refractive index at the used wavelength is about 3.475. At this time, the number of gratings is 2509.9 / mm, the emission angle of each wavelength is as shown in Table 1 below, and the dispersion angle is 0.23298 degrees. This dispersion angle is 3.28 times that in the atmosphere.

  The number of grids described above can be calculated using the following formula.

  Here, n, θ, m, λ, and p are the refractive index of the medium of the dispersive element 200 (prism) used in the present embodiment, the refraction angle when the light beam having an incident angle of 12 degrees enters the medium, and the diffraction, respectively. The order, wavelength used, and grating pitch.

  For these reasons, the dispersion element 200 used in this embodiment can use a diffraction grating having a larger number of gratings than the conventional reflective diffraction grating 400 (FIG. 4A). For this reason, the dispersion can be increased, that is, a high wavelength resolution can be obtained. Even if the size of the diffractive optical surface G is the same, the number of gratings can be further increased by increasing the refractive index n of the medium of the dispersion element 200. For this reason, a dispersion element with high dispersion (high wavelength resolution) can be realized.

  In the dispersive element used in this embodiment, the surface on which the light ray enters the dispersive element and the surface that exits from the dispersive element are common, and the incident angle and the exit angle on the surface are substantially equal. desirable. In this way, only one type of AR (antireflection) coat is applied to the common surface, and the transmittance can be increased. Also, AR coating can be designed and constructed with only one type.

The number of grooves on the diffractive optical surface G used in this embodiment is preferably 1200 / mm or more.
Further, it is desirable that the wavelength resolution R of the dispersion element of the present embodiment satisfies the following expression.

  Here, λ is a used wavelength, and Δλ is a difference between two adjacent wavelengths to be decomposed. In either case, a high wavelength resolution can be obtained.

(First embodiment)
Next, a wavelength selective switch according to a first embodiment of the present invention will be described with reference to FIG.
This embodiment is a so-called transmission-type wavelength selective switch 500. The wavelength selective switch 500 includes a fiber array 501 composed of a plurality of optical fibers, a microlens array 502, a grating 503, a lens 504, and a MEMS mirror array 505 that is a MEMS module.

  Each optical fiber in the fiber array 501 and each microlens in the microlens array 502 are paired. This pair is arranged in an array. The fiber array 501 functions as an optical input / output port. Wavelength-multiplexed signal light is emitted toward the grating 503 from one of the optical fibers (hereinafter referred to as “first optical fiber”). Light emitted from the optical fiber is converted into a parallel light beam by the microlens array 502.

  As the grating 503, the above-described dispersion element is used. The light emitted from the microlens array enters the grating 503. The grating 503 disperses the wavelength multiplexed light in a band shape.

  The lens 504 guides the light dispersed by the grating 503 to a predetermined position for each wavelength on the MEMS mirror array 505 that is a deflecting member.

  Here, the grating 503 is, for example, a so-called immersion grating in which a reflective grating G is formed on a silicon prism having an apex angle of 34 degrees. The diffraction surface is filled with silicon, and 2500 grooves are formed per 1 mm.

  The MEMS mirror array 505 that is a MEMS module has an array of a plurality of micromirrors M (MEMS mirror array) corresponding to the wavelength of light dispersed in a band shape by the grating 504.

  As described with reference to FIG. 7, the micromirror M can rotate around the local x-axis and y-axis, and the incident direction of the incident light is mainly due to rotation about the y-axis. Reflects in different directions.

  The light reflected by each mirror array in approximately the same direction as the incident direction is integrated on the grating 503 by the lens 504, and after diffraction, becomes the same light flux of multiple wavelength components again.

  On the other hand, light reflected by each mirror array in a direction different from the incident direction is relayed onto the grating 503 by the lens 504, but is not integrated but is diffracted. Then, the light enters one of the fibers in the fiber array 501.

  As described above, the light of the multi-wavelength component emitted from the first optical fiber can be selectively made incident on another fiber depending on the inclination angle of each mirror M of the micromirror array for each wavelength.

  In this embodiment, the coupling from one optical input port to a plurality of optical output ports has been described. However, coupling from a plurality of optical input ports to one optical output port can also be performed.

In the present embodiment, the fiber array 501 includes an emission part from which light is emitted,
The grating 504 is a dispersive element disposed on the light exit side of the fiber array 501.
The MEMS mirror array 505 includes a light deflecting member disposed on the light emitting side of the grating 504,
The fiber array 501 includes an incident portion where light from the MEMS mirror array 505 is incident,
The microlens array 502 includes a first optical system provided in an optical path between the fiber array 501 and the MEMS mirror array 505.
The lens 504 is a second optical system provided in the optical path between the grating 504 and the MEMS mirror array 505.
Furthermore, in this embodiment,
The grating 504 is provided at the front focal position of the lens 504,
The MEMS mirror array 505 is provided at the rear focal position of the lens 504.
In this embodiment, the dispersive element of this embodiment is used instead of the conventional diffraction grating (no prism). Therefore, the optical system can be reduced in size.

(Second Embodiment)
Next, a wavelength selective switch according to a second embodiment of the present invention will be described with reference to FIG. The same members as those in the first embodiment are denoted by the same reference numerals.
The present embodiment is a so-called reflection type wavelength selective switch 600. The wavelength selective switch 600 includes a fiber array 501 composed of a plurality of optical fibers, a macro lens array 502, a grating 503, a reflective optical member 601, and a MEMS mirror array 505 that is a MEMS module.

  Each optical fiber in the fiber array 501 and each microlens in the microlens array 502 form a pair corresponding to one to one. This pair is arranged in an array. The fiber array 501 functions as an optical input / output port. Wavelength-multiplexed signal light is emitted toward the grating 503 from one of the optical fibers (hereinafter referred to as “first optical fiber”). Light emitted from the optical fiber is converted into a parallel light beam by the microlens array 502.

  As the grating 503, the above-described dispersion element is used. Light emitted from the microlens array 502 enters the grating 503. The grating 503 disperses the wavelength multiplexed light in a band shape.

  The reflective optical member 601 guides the light dispersed by the grating 503 to a predetermined position for each wavelength on the MEMS mirror array 505 that is a deflecting member. For example, a concave mirror can be used as the reflective optical member 601.

  Here, the grating 503 is, for example, a so-called immersion grating in which a reflective grating G is formed on a silicon prism having an apex angle of 34 degrees. The diffraction surface is filled with silicon, and 2500 grooves are formed per 1 mm.

  The MEMS mirror array 505 which is a MEMS module has an array of micromirrors M (MEMS mirror array) corresponding to the wavelength of light dispersed in a band shape with the grating 504.

  As described with reference to FIG. 7, the micromirror M can rotate around the local x-axis and y-axis, and the incident direction of the incident light is mainly due to rotation about the y-axis. Reflects in different directions.

  The light reflected by each mirror array in approximately the same direction as the incident direction is integrated on the grating 503 by the reflective optical member 601 and becomes the same light flux of multiple wavelength components again after diffraction.

  In contrast, light reflected by each mirror array in a direction different from the incident direction is relayed on the grating 503 by the reflective optical member 601, but is not integrated and is diffracted. Then, the light enters one of the fibers in the fiber array 501.

As described above, the light of the multi-wavelength component emitted from the first optical fiber can be selectively made incident on another fiber depending on the inclination angle of each mirror M of the micromirror array for each wavelength.
In this embodiment, the coupling from one optical input port to a plurality of optical output ports has been described. However, coupling from a plurality of optical input ports to one optical output port can also be performed.

In the present embodiment, the fiber array 501 includes an emission part from which light is emitted,
The grating 504 is a dispersive element disposed on the light exit side of the fiber array 501.
The MEMS mirror array 505 includes a light deflecting member disposed on the light emitting side of the grating 504,
The fiber array 501 includes an incident portion where light from the MEMS mirror array 505 is incident,
The microlens array 502 includes a first optical system provided in an optical path between the fiber array 501 and the MEMS mirror array 505.
The reflective optical member 601 is a second optical system provided in the optical path between the grating 504 and the MEMS mirror array 505.
Furthermore, in this embodiment,
The grating 504 is provided at the front focal position of the reflective optical member 601.
The MEMS mirror array 505 is provided at the rear focal position of the reflective optical member 601.
Therefore, the optical system can be reduced in size. Further, the optical system can be further downsized as compared with the transmission type wavelength selective switch.

  As described above, the wavelength selective switch according to the present invention is useful in the case of performing spectroscopy with high wavelength resolution and downsizing.

It is a figure which shows the wavelength selective switch concerning 1st Embodiment of this invention. It is a figure which shows the wavelength selective switch concerning 2nd Embodiment of this invention. It is a figure explaining the dispersion element used for this invention. It is another figure explaining the dispersion element used for this invention. It is another figure explaining DMD with which the wavelength selective switch of the present invention is provided. It is a figure explaining the pitch of a deflection | deviation member. It is a figure explaining the diffraction in a reflection type diffraction grating. It is a figure explaining the diffraction and refraction in a reflection type diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 200 Dispersive element 201a Incident surface 201b Ejection surface 201c Diffraction optical surface 220 Prism 230 Planar member 300 Dispersive element 400 Dispersive element 500 Wavelength selection switch 501 Fiber array 502 Microlens array 503 Grating 504 Lens 505 MEMS mirror array 600 Wavelength selection switch 601 Reflection optics Member M Micromirror G Diffraction grating

Claims (8)

An emission part configured by an end face of the fiber and emitting light;
A dispersive element disposed on the light exit side of the exit portion;
A light deflection member disposed on the light exit side of the dispersion element;
An incident part configured by an end face of a fiber and receiving light from the light deflection member;
A first optical system provided in an optical path between the emitting portion and the light deflection member;
A second optical system provided in an optical path between the dispersion element and the light deflection member;
The dispersive element is provided at a front focal position of the second optical system;
The light deflection member is provided at a rear focal position of the second optical system;
The light deflection member is composed of a plurality of deflection elements,
The plurality of deflection elements can be controlled independently of each other,
The dispersion element includes a transmission surface through which light is transmitted;
Having a diffractive optical surface,
A wavelength selective switch characterized in that a space between the transmission surface and the diffractive optical surface is formed of a medium having a refractive index larger than 1. A transmission surface different from the transmission surface,
The transmission surface is an incident surface on which the light is incident,
The another transmission surface is an emission surface from which the light is emitted,
The diffractive optical surface is disposed in an optical path from the incident surface to the exit surface,
The wavelength selective switch according to claim 1, wherein the diffractive optical surface is a reflective surface. The dispersive element comprises one medium;
2. The wavelength selective switch according to claim 1, wherein the entrance surface, the exit surface, and the diffractive optical surface are integrally formed on one medium. The dispersion element includes a first medium and a second medium as the medium,
The entrance surface and the exit surface are formed in the first medium,
The wavelength selective switch according to claim 2, wherein the diffractive optical surface is formed in the second medium.   The wavelength selective switch according to any one of claims 1 to 4, wherein the refractive index of the medium is 1.8 or more.   6. The wavelength selective switch according to claim 5, wherein the medium is silicon.   The wavelength selective switch according to claim 1, wherein the second optical system is a lens. The wavelength selective switch according to any one of claims 1 to 5, wherein the second optical system is a concave mirror.

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