JP2012145373A - Spectroscopic instrument and wavelength selection switch using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectroscopic instrument in which a change in dispersion characteristics is sufficiently small even when a temperature change is generated.SOLUTION: The spectroscopic instrument includes a first group dispersion element and a second group dispersion element which are arranged in the incident order of a forward beam. When it is defined that an emission angle of the forward beam from the first group dispersion element at a first temperature Tis θ, an emission angle of the forward beam from the first group dispersion element at a second temperature Tdifferent from the first temperature Tis θ', a difference θ'-θof the emission angles is Δθ, an emission angle of a beam along an optical path through which the forward beam at the first temperature Tis emitted from the second group dispersion element, which is also a reverse beam at the second temperature T, is θ", an incident angle of the forward beam at the first temperature Ton the second group dispersion element is θ, and the difference θ"-θof the emission angle and the incident angle is Δθ, the Δθis approximately equal to the Δθ.

Description

  The present invention relates to a spectroscopic device and a wavelength selective switch using the spectroscopic device.

  Conventionally, many apparatuses using spectroscopic techniques have been proposed. For example, Patent Document 1 discloses a spectroscopic device using a diffraction grating. For example, Patent Document 2 discloses an endoscope using a diffraction grating. Furthermore, for example, Patent Document 3 discloses a microscope that performs spectroscopy using a prism and a digital micromirror.

  For example, Patent Document 4 discloses a basic configuration of a wavelength selective switch under the name of an optical add / drop multiplexer.

  Here, the wavelength selective switch is a device arranged at a node in ROADM (a system or technology that can be used for branching / inserting wavelength-multiplexed optical signals that are used in a large-capacity network). The wavelength selective switch is an optical switch that switches transmission paths of wavelength-multiplexed optical signals for each wavelength.

  Each node can extract an optical signal having an arbitrary wavelength from the wavelength-multiplexed optical signal, and can mix light having an arbitrary wavelength with the wavelength-multiplexed optical signal by each wavelength selection switch. This wavelength selective switch also uses a diffraction grating.

  Further, for example, in Patent Document 5, a light dispersion device is provided that includes a diffraction element attached adjacent to a prism. There is disclosed a technique in which the effect is canceled by the expansion of the diffraction grating and the change in the refractive index of the adjacent prism, and the emission angle does not change.

JP 2007-187550 A JP 2007-135989 A JP 2000-199855 A Japanese Patent No. 3937403 Special table 2003-509714 gazette

  However, in the prior arts described in Patent Documents 1 to 4, there is no description at all regarding the change in the emission angle when the temperature changes.

Further, for example, in the prior art described in Patent Document 5, a configuration in which the dispersion characteristic changes due to a temperature change is cited as a problem and a countermeasure is proposed. Here, it is assumed that the main cause of the change in dispersion characteristics due to temperature change is the thermal expansion of the substrate of the diffraction grating.
However, the main cause of the change in dispersion characteristics may not be the thermal expansion of the diffraction grating substrate. When the refractive index of the atmosphere changes or when a light beam passes through the dispersion element, a change in the refractive index of the dispersion element itself due to a temperature change can be a main cause of a change in dispersion characteristics.

  The change is particularly great when a material having a high refractive index is used for the dispersive element. For this reason, it has been difficult for conventional spectrometers to have stable dispersion characteristics with respect to temperature changes.

  The present invention pays attention to this point, and an object of the present invention is to provide a spectroscopic device in which a change in dispersion characteristics is sufficiently small even when a temperature change occurs, and a wavelength selective switch using the spectroscopic device.

In order to solve the above-described problems and achieve the object, the spectroscopic device according to the present invention includes:
A first group of dispersive elements and a second group of dispersive elements in the order in which forward light rays are incident;
The outgoing angle of the forward ray from the first group of dispersive elements at the first temperature T ₁ is θ ₄ ,
An outgoing angle of the forward light beam from the first group of dispersion elements at a _second temperature T ₂ different from the _first temperature T ₁ is θ ′ ₄ ,
The difference θ ′ ₄ −θ ₄ of the emission angle is expressed as Δθ ₄ ,
The forward ray at the first temperature T ₁ is a ray along the optical path emitted from the second group of dispersive elements, and the second ray of the reverse ray at the second temperature T ₂ . The exit angle from the group of dispersive elements is θ ″ ₅ ,
The incident angle of the forward ray at the first temperature T _{1 to} the second group of dispersive elements is θ ₅ ,
The difference θ ″ ₅ −θ ₅ between the exit angle and the incident angle is Δθ ₅ ,
And when
Δθ ₄ and Δθ ₅ are substantially equal.

  In another aspect, a wavelength selective switch according to the present invention includes the above-described spectroscopic device.

  According to the present invention, it is possible to provide a spectroscopic device in which a change in dispersion characteristics is sufficiently small even when a temperature change occurs, and a wavelength selective switch using the spectroscopic device.

It is a figure which shows roughly the example of a whole structure of the spectrometer concerning the 1st Embodiment and 2nd Embodiment of this invention. It is a figure which shows the detailed structural example of the spectroscopy part of the spectroscopy apparatus which concerns on 1st Embodiment and 2nd Embodiment. It is a figure which shows the detailed structural example of the spectroscopy part of the spectroscopy apparatus which concerns on the 3rd Embodiment of this invention. It is a perspective view which shows roughly the example of a whole structure of the wavelength selective switch which concerns on the 4th Embodiment of this invention. It is a perspective view which shows the structural example of the micromirror array comprised including the several micromirror which concerns on 4th Embodiment. It is a figure for demonstrating the structure of the lens which guides the dispersed light based on 4th Embodiment. It is a figure for demonstrating the structure of the spectroscopic element in each embodiment. It is a perspective view which shows the structural example of the lens which has two cylindrical lenses in 4th Embodiment.

  Hereinafter, an embodiment according to an aspect of the present invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings. Further, the present invention described in the scope of claims is not limited by this embodiment. That is, all the configurations described in the present embodiment are not necessarily essential configuration requirements of the present invention.

(First embodiment)
FIG. 1 shows a schematic configuration of the spectroscopic device of the first embodiment.
The spectroscopic device condenses the separated light, an incident slit 11 into which light rays are input, a lens 12 that converts light beams 16 having a plurality of wavelengths incident from the incident slit 11 into substantially parallel light, a later-described spectroscopic unit 13, and the like. And a detector array 15 for receiving light of each wavelength band, which is divided in advance. The detector array 15 is configured by arranging a plurality of detector elements.

FIG. 2 shows the configuration of the spectroscopic unit 13. The spectroscopic unit 13 includes a prism 26 and a dispersion element 27. The prism 26 is made of a medium having a refractive index n ₁ and has an apex angle α ₁ . The dispersive element 27 is made of a medium having a refractive index n ₂ and has an apex angle α ₂ , a pitch p, and a diffraction order m.

  The light emitted from the lens 12 enters the prism 26. The prism 26 has a first surface 21 and a second surface 22 in the order in which the incident light 25 is incident and refracted. The dispersive element 27 is disposed at a position where light emitted from the prism 26 enters.

  In the order in which light enters the prism 27 and is refracted or diffracted, it has a first surface 23, a second surface 24 that is a diffractive surface, and a third surface 23 that is common to the first surface. The light emitted from the third surface 23 of the dispersive element 27 is mainly split by the second surface 24 and travels toward the lens 14 in FIG.

  Note that light beams traveling in the order of the prism 26 and the dispersion element 27 are considered as light beams in the forward direction. On the contrary, a light beam traveling in the order of the dispersion element 27 and the prism 26 is considered as a light beam in the reverse direction. More detailed definitions of “forward direction” and “reverse direction” will be described later.

  7A, 7B, 7C, and 7D show the configuration of the dispersion element 27. FIG. FIG. 7A shows details of the cross-sectional configuration of the dispersive element 27. FIG. 7B shows an enlarged cross section of the second surface (diffraction surface) 24. FIG. 7C shows a cross-sectional configuration of the prism 71 constituting the dispersion element 27. FIG. 7D shows a cross-sectional configuration of the grating chip 72 that constitutes the dispersive element 27.

The prism 71 and the grating chip 72 are made of the same glass material. Prism 71 is a prism 26 shown in FIG. 2, it is not necessary shape is identical, with the apex angle alpha _2. The grating chip 72 has grooves formed on one surface of a parallel flat plate at a pitch p. FIG. 7B shows the groove shape.

  The medium of the prism 26 and the medium of the dispersive element 27 are made of the same material, and the material is preferably any one of optical glass, crystal material, resin material, and metal material.

  In the present embodiment, as described above, the medium of the prism 26 and the medium of the dispersion element 27 are both the same silicon.

  The grooves of the grating chip 72 are formed in a direction perpendicular to the paper surface. The dispersive element 27 is configured by joining a joint surface 73 of the prism 71 and a joint surface 74 of the grating chip 72.

  With the above configuration, incident light having a plurality of wavelengths and included in the paper surface enters the first surface 23, reaches the second surface 24, which is a diffraction surface, and is diffracted. Thereby, the incident light diffracted by the second surface 24 is dispersed into light having a plurality of wavelengths, that is, dispersed light. The dispersed light is generated in the same paper surface.

In addition, for the light beam in the forward direction at the _first temperature T1,
The incident angle of the first surface 21 of the prism 26 is defined as an angle θ ₁ ,
The refraction angle of the first surface 21 of the prism 26 is defined as an angle θ ₂ ,
The incident angle of the second surface 22 of the prism 26 is defined as an angle θ ₃ ,
The refraction angle of the second surface 22 of the prism 26 is defined as an angle θ ₄ ,
The incident angle of the first surface 23 of the dispersive element 27 is defined as an angle θ ₅ ,
The refraction angle of the first surface 23 of the dispersive element 27 is defined as an angle θ ₆ ,
The incident angle of the second surface 24 of the dispersive element 27 is defined as an angle θ ₇ ,
The diffraction angle of the second surface 24 of the dispersive element 27 is set to an angle θ ₈ ,
The incident angle of the third surface 23 of the dispersive element 27 is defined as an angle θ ₉ ,
The refraction angle of the third surface 23 of the dispersive element 27 is defined as an angle θ ₁₀ ,
Respectively. The detailed definition of “forward” will be described later.

At this time, it is assumed that the sign of the temperature coefficient dn ₁ / dT of the refractive index n ₁ of the prism 26 and the temperature coefficient dn ₂ / dT of the refractive index n ₂ of the dispersion element 27 are the same.
The second surface 22 of the prism 26 and the first surface 23 of the dispersion element 27 form an angle γ shown in FIG.

For example, when the wavelength λ included in the incident light 25 and the above-described n ₁ , α ₁ , n ₂ , α ₂ , p, m, γ, and θ ₁ are determined at a temperature T ₁ = 20 ° C. The angle θ ₂ to the angle θ ₁₀ are uniquely determined by the equations (1) to (9).

Among these, the formula (1), the formula (3), the formula (5), the formula (7), and the formula (9) are obtained from the Snell's law and the diffraction formula described in the formula (10). Expressions (2), (4), (6), and (8) are merely geometrical relationships.
The mathematical formulas are summarized in Table 7.

For example, when both the prism 26 and the dispersive element 27 are made of silicon, n ₁ , α ₁ , n ₂ , α ₂ , p, m, γ, θ ₁ , dn ₁ / dT, and dn ₂ / dT are as shown in Table 1. Suppose you are given. At this time, the angle θ ₁₀ is obtained from the angle θ ₂ by the equations (1) to (9). The results are listed in Table 2.

Next, consider a case where the temperature T ₂ = 40 ° C.
The change in the refractive index of the medium of the prism 26 accompanying the change from the temperature T ₁ to the temperature T ₂ is Δn ₁ ,
The refractive index change of the medium of the dispersive element 27 accompanying the change of the temperature T ₁ to the temperature T ₂ is Δn ₂ ,
And do each.
Δn ₁ and Δn ₂ are obtained by the equation (12) using the average dn ₁ / dT and dn ₂ / dT between the temperature T ₁ and the temperature T ₂ .

Accordingly, each constant at the temperature T ₂ changes so that only the refractive indexes n ₁ and n ₂ are listed in Table 3 as compared with the values listed in Table 1. At this time, by solving the symbols of the angles θ ₁ to θ _{4 in} the equations (1) to (3) by adding quotation marks “′” (single quotation), the angles θ ′ ₂ to θ ′ ₄ are obtained. I want. The resulting values are listed in Table 4 from angles θ ′ ₂ to θ ′ ₄ .

The light refracted and emitted from the prism 26 at an angle θ ′ ₄ is diffracted by the dispersive element 27. Thereafter, the light is emitted from the dispersive element 27 at an angle θ ′ _{10 shown} in Table 4. The angle θ ′ ₁₀ is the refraction angle of the light beam emitted from the third surface 23 of the dispersion element 27.

Next, assume a reverse ray at a temperature T _2, the forward direction of the light beam. Here, the “forward direction” refers to a direction traveling from the entrance slit 11 toward the detector array 15. Further, “a direction opposite to the forward light beam” refers to a direction traveling from the detector array 15 toward the entrance slit 11.

When the direction of the light beam is reversed with respect to the forward direction, for example, the light beam is incident on the third surface 23 of the dispersion element 27 from the outside (air) side of the dispersion element 27. The incident angle at this time is assumed to be an angle θ ″ _10. Similarly, assuming a light ray in the reverse direction at the temperature T ₂ , the symbols of the angles θ _{5 to} θ ₁₀ defined above are respectively quoted. """(Double quotation) is added and expressed.

The angle theta _"10 at a temperature T _2, the angle theta ₁₀ at a temperature T _1, so as to become equal, it is assumed that is incident the opposite direction of a light ray to the dispersion element 27. At this time, from equation (5) The symbols of the angles θ _{5 to} θ ₁₀ in the equation (9) are respectively solved by reversing the equation (9) by adding double quotation marks “” ”(double quotation). As a result, the angle θ ″ ₅ is obtained from the angle θ ″ ₉ . The resulting values are listed in Table 5.

Here, in Table 2, the angle θ without the quotation mark “′” (single quotation) indicates the angle related to the forward light beam at the temperature T1. Table 4 In quotes "'" angle is denoted by the (single quote) theta' shows the angle in the forward direction of the rays of the temperature T _2. Further, in Table 5, an angle θ ″ given a double quotation mark “” ”(double quotation) indicates an angle with respect to a light ray in the reverse direction of the temperature T2.

The difference between the angle θ _{4 at} the temperature T ₁ in Table 2 and θ ′ _{4 at} the temperature T ₂ in Table 4 is Δθ ₄ (= θ ′ ₄ −θ ₄ ). Further, a difference between θ _{5 at} the temperature T ₁ in Table 2 and θ ″ ₅ at the temperature T ₂ in Table 5 is defined as Δθ ₅ (= θ ″ ₅ −θ ₅ ). The results of the calculation are listed in Table 6.
This value satisfies “the angle Δθ ₄ is substantially equal to the angle Δθ ₅ ”.

As described above, when a set of parameters n ₁ , α ₁ , n ₂ , α ₂ , p, m, γ, θ ₁ , dn ₁ / dT, and dn ₂ / dT is appropriately given, an angle Δθ ₄ and an angle Δθ ₅ can be made substantially equal.

When the angle Δθ ₄ and the angle Δθ ₅ are substantially equal, the angle θ ′ ₅ and the angle θ ″ ₅ are substantially equal. Similarly, the angle θ ′ ₁₀ and the angle θ ″ ₁₀ are substantially equal. Here, as described above, it is assumed that the angle θ ₁₀ and the angle θ ″ ₁₀ are equal when the light beam in the opposite direction is incident on the dispersive element 27. Therefore, the angle θ ₁₀ and the angle θ ′ ₁₀ are substantially equal. It will be.

As described above, by making Δθ ₄ and Δθ ₅ substantially equal, even if a temperature change occurs, the emission angle from the dispersive element 27 can be kept substantially constant with respect to the forward ray. Further, by maintaining the emission angle from the dispersive element 27 to be substantially constant, even if a temperature change occurs, the change in the dispersion characteristic of the spectroscopic unit 13 can be sufficiently reduced.

The light emitted from the spectroscopic unit 13 passes through the lens 14 and then converges on the detector array 15. According to the spectroscopic device having the spectroscopic unit 13 having the above-described characteristics, the light with the wavelength λ is always not affected by the temperature change regardless of the temperature T ₁ and the temperature T _2. Incident on the same array. Similarly, light of other wavelengths different from the wavelength λ is incident on the other arrays in the detector array 15 substantially perpendicularly.
As described above, according to the spectroscopic device of the present embodiment, the condensing position of the light having the same wavelength λ does not substantially change in the detector array 15 regardless of the temperature.

Next, the present embodiment will be described based on different viewpoints. In the present embodiment, when k is calculated from the numerical values in Table 2 and the equation (E), k = 0.961. Further, Δn ₁ / Δn ₂ = 1. The present embodiment satisfies the condition that “k determined by the expression (E) is substantially equal to | Δn ₁ / Δn ₂ |”.

When the condition that “k determined by the equation (E) and the value of | Δn ₁ / Δn ₂ | are substantially equal” is satisfied, the emission angle θ ₁₀ from the dispersive element 27 with respect to the forward ray is equal to the temperature T. Even if it changes, it almost stops changing.

That is, at the temperature T ₁ , a light beam having a wavelength λ is emitted from the third surface (= first surface) of the dispersion element at an angle θ ₁₀ . The emitted light beam is collected by a lens 14 (see FIG. 1) and detected by any detector in the detector array 15.

Further, even when the change in the temperature T _2, the value of the angle theta ₁₀ hardly changes. As a result, the light of wavelength λ can be incident on the same array incident at temperature T ₁ even at temperature T ₂ . Furthermore, light of other wavelengths different from the wavelength λ is collected and incident substantially perpendicularly on another array of detector arrays.

Further, an intersection point between an intersection line of the first surface 21 and the second surface 22 of the prism 26 and an incident plane (paper surface) including a light beam refracted by the second surface 22 of the prism 26 is an intersection point A.
An intersection point between an intersection line of the first surface 23 and the second surface 24 of the dispersion element 27 and an incident plane (paper surface) including a light beam refracted by the second surface 22 of the prism 26 is defined as an intersection point B.

Further, consider a straight line along the optical path of the light beam existing between the prism 26 and the dispersion element 27.
The intersection point A and the intersection point B described above are configured to exist in different regions with respect to the two regions separated by the straight line in the incident plane (paper surface).

In such a configuration, in this embodiment, the refractive index of the prism 26 and the refractive index of the dispersion element 27 are equal. For this reason, when the emission angle of the light beam from the second surface 22 of the prism 26 increases due to the temperature change, the incident angle of the dispersion element 27 on the first surface 23 also increases. For this reason, when the emission angle of the light beam from the second surface 22 of the prism 26 is reduced, the incident angle of the dispersion element 27 on the first surface 23 can also be reduced. This facilitates making the angle Δθ ₄ and the angle Δθ ₅ substantially equal.

  Moreover, the light beam in the forward direction can be one light beam included in the light beam converted into parallel light by the lens 12 of FIG.

  Further, the lens 12 shown in FIG. 1 can be arranged in the optical path on the side where the light beam in the forward direction is incident on the first surface 21 of the prism 26 (incident slit 11 side). Instead of the lens 12, a reflecting mirror having power may be arranged.

  Further, the lens 14 shown in FIG. 1 can be arranged in the optical path on the side (detector array 15 side) from which the forward light beam exits from the third surface 23 of the dispersion element 27. Instead of the lens 14, a reflecting mirror having power may be arranged.

  Furthermore, it is desirable for the lens 14 to telecentric the chief rays of each wavelength after transmission. Thereby, the light of each wavelength after passing through the lens 14 can be configured to enter the array corresponding to each wavelength of the detector array 15 substantially perpendicularly.

In the configuration of the present embodiment, by maintaining the emission angle from the dispersive element 27 substantially constant, even if a temperature change occurs, the change in the dispersion characteristic of the spectroscopic unit 13 can be sufficiently reduced. Thereby, even if a temperature change occurs, there is an effect that a change in dispersion characteristics can be sufficiently reduced.
Furthermore, light of wavelength λ is incident on the same detector array regardless of temperature changes. Therefore, there is an additional effect that light of a predetermined wavelength is not detected by the adjacent detector element due to a temperature change.

  In addition, in the present embodiment, the prism 26 and the dispersive element 27 are arranged in the order in which forward light rays are incident. For this reason, when light of a plurality of wavelengths including light of wavelength λ is incident in the forward direction, dispersion by the prism 26 is small. For this reason, the luminous flux diameter of the light emitted from the prism 26 and incident on the dispersion element 27 does not expand so much. Therefore, the further effect that the dispersive element 27 can be comprised small is also show | played.

  In addition, in the present embodiment, silicon, which is a high refractive index material, is used as the medium constituting the dispersive element 27. For this reason, the difference between the two wavelengths of the refraction angle (= emission angle) when the light having two wavelengths diffracted and dispersed on the second surface 24 of the dispersion element 27 is emitted from the third surface 23 into the air is large. Become. Thereby, the dispersion element 27 itself becomes a high dispersion element. The spectroscopic unit 13 having the dispersive element 27 has an additional effect that high wavelength resolution can be obtained.

  In addition, in the present embodiment, the lens 12 can effectively use the light amount. Therefore, there is a further effect that a spectroscopic device with high detection sensitivity can be obtained.

  In addition, in the present embodiment, the light dispersed by the dispersion element 27 is emitted from the spectroscopic unit 13 at different angles depending on the wavelength. The lens 14 condenses the emitted light at different positions for each wavelength. Thereby, it has the further effect that a spectroscopic device with high wavelength resolution is obtained.

In addition, in the present embodiment, the lens 14 condenses light on the detector array 15 in a telecentric manner. For this reason, the chief rays of light of each wavelength are perpendicularly incident on the detector array 15. Here, an assembly error may occur when the detector array 15 is assembled. When an assembly error occurs, the position of each detector constituting the detector array 15 is different from the set value, and for example, a positional shift in the optical axis direction is caused.
By adopting a configuration in which chief rays of light of each wavelength are perpendicularly incident on the detector array 15, even when the detector array 15 is misaligned in the optical axis direction, the influence of the misalignment can be reduced. . For this reason, there is a further effect that a spectroscopic device with a small detection wavelength deviation can be obtained.

(Modification of the first embodiment)
Next, a modification of the first embodiment described above will be described. In this modification, a so-called immersion grating is used as the dispersive element. The immersion grating is also called a prism grating, a grism, or a carpenter prism.

  A folding mirror may be disposed in the optical path between the prism 26 and the dispersion element 27. In that case, it is desirable to change the angle γ shown in FIG. 2 to an appropriate angle by inserting a folding mirror into the optical path.

The grating chip 72 (see FIG. 7D) may have a trapezoidal cross section, that is, the joint surface 74 and the diffractive surface 24 may be non-parallel. Also in this case, the apex angle α ₂ of the dispersive element 27 is an angle formed by the first surface 23 and the second surface 24 that is a diffraction surface.

  Further, the dispersive element 27 may be manufactured by integral molding. According to the integral molding, a groove is formed directly on the prism 71 (see FIG. 7C) which is a base material.

(Second Embodiment)
Next, a spectroscopic device according to a second embodiment will be described.
The present embodiment is different from the spectroscopic device of the first embodiment described above in that the medium constituting the prism 26 and the dispersive element 27 is different. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The medium of the prism 26 and the medium of the dispersion element 27 are made of different materials, and the material is preferably any one of optical glass, crystal material, resin material, and metal material.

The medium of the prism 26 is F5 (manufactured by SCHOTT), and the medium of the dispersion element 27 is N-BK7 (manufactured by SCHOTT). At this time, the values of the parameters at the temperature T ₁ = 20 ° C. are the values listed in Table 1. Then, the angle θ ₁₀ is obtained from the angle θ ₂ by the equations (11) to (19). The resulting values are listed in Table 2. When k is obtained from the numerical values in Table 2 and the equation (E), k = 1.449.

Next, consider a case where the temperature T ₂ = 80 ° C.
It is assumed that dn ₁ / dT and dn ₂ / dT do not change significantly between the temperature T ₁ and the temperature T ₂ .
The change in the refractive index of the medium of the prism 26 accompanying this change in temperature is Δn ₁ ,
The change in the refractive index of the medium of the dispersion element 27 accompanying the change in temperature is Δn ₂ ,
And do each. At this time, Δn ₁ and Δn ₂ are obtained by Expression (12).

Therefore, the refractive indexes n ₁ and n _{2 of the} constants at the temperature T ₂ change as compared with the values listed in Table 1. The changed values are listed in Table 3.
As a result, in this embodiment, k = 1.2449 and Δn ₁ / Δn ₂ = 1.2449.

Thus, in the present embodiment, the condition that “k determined by the equation (E) and the value of | Δn ₁ / Δn ₂ | are substantially equal” is satisfied.
When this condition is satisfied, the angle θ ₁ to θ _{10 in} the equations (1) to (9) is solved by adding the quotation mark “′” (single quotation) to the angle at the temperature T ₂ . An angle θ ′ ₁₀ is obtained from θ ′ ₂ . The resulting values are listed in Table 4.

When the temperature is T ₁ , a light beam having a wavelength λ is emitted from the third surface 23 (= first surface) of the dispersion element at an angle θ ₁₀ . The emitted light is collected on the detector array 15 by the lens 14 of FIG. The condensed light is detected by any detector element of the detector array 15.

Thus, in the present embodiment, even when the temperature changes to T _2, the value of the angle theta ₁₀ hardly changes. For this reason, the light of wavelength λ at the temperature T ₂ is incident on the same detector element as the detector element in the detector array 15 incident at the temperature T ₁ . Further, light of other wavelengths is also collected and incident substantially vertically on a detector element different from the detector element on which the light of wavelength λ in the detector array 15 is incident.

In the present embodiment, the condition that “k determined by the equation (E) is substantially equal to | Δn ₁ / Δn ₂ |” is satisfied. For this reason, even when a temperature change occurs, the value of the emission angle θ ₁₀ emitted from the dispersive element 27 hardly changes. Thereby, by maintaining the emission angle from the dispersive element 27 substantially constant, even if a temperature change occurs, the change in the dispersion characteristic of the spectroscopic unit 13 can be made sufficiently small. Thereby, even if a temperature change occurs, there is an effect that a change in dispersion characteristics can be sufficiently reduced.

Further, the sign of the temperature coefficient dn ₁ / dT of the refractive index n ₁ of the medium F5 (manufactured by SCHOTT) of the prism 26,
The sign of the temperature coefficient dn ₂ / dT of the refractive index n ₂ of the medium N-BK7 (manufactured by SCHOTT) of the dispersive element 27 is the same.

Further, similarly to the arrangement described in the first embodiment, the above-mentioned intersection A and intersection B are the optical paths of the light rays existing between the prism 26 and the dispersive element 27 in the incident plane (paper surface). The two areas separated by a straight line along the line are configured to exist in different areas.
From Table 2, the angle θ ₁ and the angle θ ₄ are substantially equal. Further, the angle θ ₅ and the angle θ ₁₀ are substantially equal.

  The arrangement of the prism 26 and the dispersion element 27 is the same as that in the first embodiment as described above. In this arrangement, the direction (change direction) of the emission angle of the light beam due to the temperature change of the refractive index is reversed between the prism 26 and the dispersion element 27.

Further, the value of k calculated from the equation (E) is substantially the same as the value of the ratio Δn ₁ / Δn ₂ . For this reason, the magnitude of the deviation (change direction) of the emission angle of the light beam caused by the temperature change of the refractive index is equal. Therefore, the light of wavelength λ is incident on the same detector element in the detector array 15 regardless of the temperature change. Therefore, there is an additional effect that a certain wavelength is not detected by the adjacent detector due to a temperature change.

  In addition, in this embodiment, the medium of the prism 26 and the medium of the dispersion element 27 are both optical glass, but are different. Optical glass has been examined in detail for its physical properties and is supplied stably. For this reason, when manufacturing a spectroscopic device, there exists the further effect that detailed design and stable manufacture are attained.

In addition, the angle θ ₁ and the angle θ ₄ are substantially equal. Further, the angle θ ₅ and the angle θ ₁₀ are substantially equal. For this reason, only one type of anti-reflection (AR) coating can be applied to the first surface 21 and the second surface 22 of the prism 26. Furthermore, the AR coating applied to the first surface 23 of the dispersive element 27 also has a further effect that a coating considering the minimum incident angle dependency is sufficient.

(Third embodiment)
Next, a spectroscopic device according to a third embodiment will be described. The present embodiment differs from the first embodiment in the configuration of the spectroscopic unit 13 in FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

FIG. 3 shows a schematic configuration of the spectroscopic unit 13 of the present embodiment. In the first embodiment described above, the apex angle A of the prism 26 is arranged so as to face the right side of the drawing. Further, the vertical angle B of the dispersive element 27 is arranged so as to face the left direction of the drawing.
On the other hand, in the present embodiment, the apex angle A of the prism 26 is arranged so as to face the left direction of the drawing. Further, the apex angle B of the dispersive element 27 is arranged so as to face the left direction of the paper, similarly to the prism 26.

In this configuration, the angle θ ₁ to the angle θ ₁₀ are defined as in the first embodiment.
At this time, the temperature coefficient _dn 1 / dT of the refractive index _{n 1,} the sign of the temperature coefficient _dn 2 / dT of the refractive index _{n 2} are different.
The second surface 22 of the prism 26 and the first surface 23 of the dispersion element 27 form an angle γ ′ within the paper surface.
The medium of the prism 26 is N-PK51 (manufactured by SCHOTT), and the medium of the dispersion element 27 is N-BK7 (SCHOTT).

At this time, the values of the respective parameters at the temperature T ₁ = 20 ° C. are listed in Table 1. The angle θ ₁₀ is obtained from the angle θ ₂ by the equations (1) to (3), the equations (11), and the equations (5) to (9). The resulting values are listed in Table 2. From the numerical values listed in Table 2 and the equation (E), k is found to be k = 2.9796.

Next, consider a case where the temperature T ₂ = 80 ° C.
It is assumed that dn ₁ / dT and dn ₂ / dT do not change significantly between the temperature T ₁ and the temperature T ₂ .
The change in the refractive index of the medium of the prism 26 accompanying this change in temperature is Δn ₁ ,
The change in the refractive index of the medium of the dispersion element 27 accompanying the change in temperature is Δn ₂ ,
And do each. Δn ₁ and Δn ₂ are obtained by Expression (12).

Therefore, each constant at the temperature T ₂ changes only the refractive indexes n ₁ and n _{2 as} compared with the values listed in Table 1. Table 3 lists the changed refractive indices n ₁ and n ₂ . At this time, the symbols of the angles θ ₁ to θ _{10 in} the expressions (1) to (3), (11), and (5) to (9) are respectively replaced with quotation marks “′” (single quotation). By adding and solving, the angle θ ′ ₁₀ is obtained from the angle θ ′ ₂ . The resulting values are listed in Table 4.

When the temperature is T ₁ , the light beam having the wavelength λ is emitted from the third surface (= first surface) of the dispersion element 27 at an angle θ ₁₀ . The lens 14 condenses the emitted light on the detector array 15. The condensed light is detected by any detector element in the detector array 15.

In the present embodiment, even when the change in the temperature T _2, the value of the angle theta ₁₀ hardly changes. For this reason, the light of wavelength λ is incident on the same detector element as the detector element incident at temperature T ₁ . Further, light of other wavelengths is also collected and incident substantially vertically on a detector element different from the detector element on which the light of wavelength λ in the detector array 15 is incident.

In this embodiment,
From equation (E), k = 2.9976 and Δn ₁ / Δn ₂ = −2.99796.
“K determined by the equation (E) is substantially equal to | Δn ₁ / Δn ₂ |”.
Therefore, even when a temperature change occurs, the value of the emission angle theta ₁₀ of the light emitted from the dispersive element 27 hardly changes. Thus, by maintaining the light emission angle from the dispersive element 27 substantially constant, even if a temperature change occurs, the change in the dispersion characteristic of the spectroscopic unit 13 can be sufficiently reduced. Thereby, even if a temperature change occurs, there is an effect that a change in dispersion characteristics can be sufficiently reduced.

Also, the sign of the temperature coefficient dn ₁ / dT of the refractive index n ₁ of the medium N-PK 51 (manufactured by SCHOTT) of the prism 26 and the temperature of the refractive index n ₂ of the medium N-BK 7 (manufactured by SCHOTT) of the dispersive element 27. It is different from the sign of the coefficient dn ₂ / dT.
Further, the arrangements described in the first and second embodiments are different, and the above-mentioned intersection A and intersection B are the rays of light existing between the prism 26 and the dispersion element 27 in the incident plane (paper surface). The two regions separated by a straight line along the optical path are configured to exist in the same region.

  The arrangement of the prism 26 and the dispersion element 27 is the same as that in the first embodiment as described above. In this arrangement, the direction (change direction) of the emission angle of the light beam due to the temperature change of the refractive index is reversed between the prism 26 and the dispersion element 27.

Further, the value of k calculated from the equation (E) is substantially the same as the value of the ratio Δn ₁ / Δn ₂ . For this reason, the magnitude of the deviation (change direction) of the emission angle of the light beam caused by the temperature change of the refractive index is equal. Therefore, the light of wavelength λ is incident on the same detector element in the detector array 15 regardless of the temperature change. Therefore, there is an additional effect that a certain wavelength is not detected by the adjacent detector due to a temperature change.

(Fourth embodiment)
Next, a wavelength selective switch according to the fourth embodiment will be described.
FIG. 4 shows a schematic configuration of the wavelength selective switch according to the present embodiment.

  The spectroscopic device 500 includes a fiber array 501 composed of a plurality of optical fibers, a microlens array 502, a lens 506, a spectroscopic unit 503, a lens 504, and a micromirror array 505 that is a MEMS (Micro Electro Mechanical Systems) module. It has.

  Each optical fiber in the fiber array 501 and each microlens in the microlens array 502 are configured to be a pair. The pair of optical fibers and microlenses are arranged in an array. The fiber array 501 functions as an optical input / output port.

  Wavelength-multiplexed signal light is emitted toward the spectroscopic unit 503 from one of the plurality of optical fibers (hereinafter, referred to as “first optical fiber” as appropriate). Light emitted from the optical fiber is converted into a parallel light beam by the microlens array 502, passes through the lens 506, and enters the spectroscopic unit 503.

FIG. 8 shows a schematic configuration of the lens 506.
The lens 506 is disposed in the optical path between the microlens array 502 and the spectroscopic unit 503. The lens 506 includes cylindrical lenses 507 and 508 having different powers. Here, the cylindrical lenses 507 and 508 are arranged so that their power directions are perpendicular to each other.

  As the spectroscopic unit 503, a pair of the dispersion element 27 and the prism 26 used in the spectroscopic unit 13 of the first embodiment shown in FIG. The spectroscopic unit 503 disperses incident wavelength multiplexed light in a one-dimensional direction in a band shape. In addition, since the structure and function of the spectroscopic unit 503 are the same as those described in the first embodiment, redundant description is omitted.

  Returning to FIG. 4, the description will be continued. The lens 504 guides the light dispersed by the spectroscopic unit 503 to a predetermined position for each wavelength on the micromirror array 505 that is a light deflection member. On the micromirror array 505, the shape of the condensing point of the light of each wavelength is elliptical because the power of the lens 506 in the chromatic dispersion direction and the fiber array direction is different.

  The micromirror array 505 which 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 spectroscopic unit 503.

More specifically, the center frequency of the ITU grid at the temperature T ₁ is, to be in the center of each micro-mirror M, the individual width and mirror pitch of the mirror of the array of micro-mirror M is set.

  FIG. 5 shows a schematic configuration of the micromirror array 505. The micromirror M can rotate around the local x-axis and y-axis, respectively. The micromirror M reflects incident light in a direction different from the incident direction mainly by rotation about the y-axis.

  In FIG. 4, the light reflected by the plurality of micromirrors M of the micromirror array 505, which is different from the incident direction and reflected in the same direction, for example, the direction D, is incident on the lens 504 again. The light that has entered the lens 504 again is integrated into the spectroscopic unit 503. After being diffracted by the spectroscopic unit 503, it becomes the same light flux with multiple wavelength components again.

  On the other hand, the light reflected by the different micromirrors in the direction different from the incident direction and the direction D is incident on the lens 504 again. The incident light is relayed to the spectroscopic unit 503 by the lens 504. The relayed light is diffracted by the spectroscopic unit 503. Here, the light reflected in the direction D and the light reflected in a direction different from the direction D are not integrated.

  These lights are incident on any other fiber different from the input port of the fiber array 501 (hereinafter referred to as “second optical fiber” as appropriate). The light reflected in the direction D and the light reflected in a direction different from the direction D are incident on different fibers.

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

  In the present 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.

The wavelength selective switch according to this embodiment includes the spectroscopic unit 13 described in the first embodiment. Therefore, the configuration satisfies the condition “Δθ ₄ and Δθ ₅ are substantially equal” as listed in Table 6.

Furthermore, both the prism 26 and the dispersive element 27 of this embodiment are made of silicon. At this time, k = 0.961 and Δn ₁ / Δn ₂ = 1 from the equation (E). From this, it is a configuration satisfying that “the value of k determined by the equation (E) is substantially equal to | Δn ₁ / Δn ₂ |”.

  FIG. 6 shows a cross-sectional configuration of the lens 504. In the lens 504, the glass material of the biconvex positive lens is SK11 (manufactured by SCHOTT), and the glass material of the biconcave negative lens is SF5 (manufactured by SCHOTT). The lens 504 is an achromatic lens configured by joining such a biconvex positive lens and a biconcave negative lens. For this reason, the light of each wavelength emitted from the spectroscopic unit 503 can be condensed at a predetermined position for each wavelength with little chromatic aberration.

(Function and effect)
With the above configuration, the present embodiment has an effect that stable wavelength selection can always be performed because the change in dispersion characteristics is sufficiently small even when a temperature change occurs.
Moreover, the light of wavelength λ is incident on the same MEMS mirror regardless of the temperature change. For this reason, there is an additional effect that a certain wavelength is not reflected by an adjacent mirror that is not intended due to a temperature change.

  In addition, an achromatic lens is used as the lens 504. For this reason, it can condense, making aberration small with respect to the light of each wavelength. As a result, the wavelength selective switch having a high wavelength resolution can be obtained.

  In addition, since the cylindrical lenses 507 and 508 are provided in the optical path between the microlens array 502 and the spectroscopic unit 503, a spot shape having an appropriate aspect ratio can be formed on the MEMS mirror.

  For example, in FIG. 5, a spot having a larger diameter in the x direction than in the y direction is formed. Thereby, there is an additional effect that a wavelength selective switch capable of appropriate switching can be obtained without increasing the rotation angle of the MEMS mirror.

  Further, in FIG. 5, a spot having a smaller diameter in the y direction than in the x direction can be formed. As a result, the wavelength selective switch having a wide pass band, that is, the wavelength selective switch having a wide pass band can be obtained.

In addition, it is desirable for the wavelength selective switch to satisfy the following formula (F).
0.95 <Δθ ₄ / Δθ ₅ <1.05 Formula (F)

When the [Delta] [theta] _{4 /} [Delta] [theta] ₅ below the lower limit of the formula (F), and when it exceeds the upper limit, light having a frequency of ITU grid at temperature T ₂ is, of the individual mirrors of the array of micro-mirrors M center If it hits, it will disappear. As a result, there arises a disadvantage that the passband becomes small.

Note that when the temperature T ₁ is changed to the temperature T ₂ , the prism 26 and the dispersion element 27 can be obtained even when k determined by the equation (E) is substantially equal to the value of | Δn ₁ / Δn ₂ |. The optical path of the light beam passing through changes. As a result, the position where the forward light beam is emitted from the third surface 23 is different.

  In the case of a spectroscopic device, the position where light is condensed through the lens 14 or in the case of a wavelength selective switch depends on the exit angle of the light beam from the third surface 23. For this reason, the positional deviation when the above-mentioned light beam is emitted from the third surface 23 does not affect the performance of the spectroscopic device or the wavelength selective switch.

  All of the modifications described in the first embodiment can also be applied to the spectroscopic unit provided in the wavelength selective switch of the fourth embodiment.

In each of the above-described embodiments, it is described that k determined by the equation (E) is substantially equal to the value of | Δn ₁ / Δn ₂ |. More specifically, it is desirable that 0.9k <| Δn ₁ / Δn ₂ | <1.1k is satisfied.

In addition, the value of | Δn ₁ / Δn ₂ | causes inconvenience both when the value is below the lower limit and when the value is higher than the upper limit. This inconvenience is that in the case of a spectroscopic device, the wavelength accuracy at the temperature T ₂ is deteriorated. In the case of a wavelength selective switch, the light beam having the frequency of the ITU grid at the temperature T ₂ is not irradiated to the center of each mirror of the array of micromirrors M, and the passband is reduced.

  The spectroscopic device according to the first to third embodiments described above can also be used as a spectroscopic device included in a WDM (Wavelent Division Multiplexing) channel equalizer or wavelength blocker of an optical communication module.

  The present invention is not limited to the embodiment of the invention described above, and various modifications can be made without departing from the gist of the present invention.

  As described above, the present invention is useful in the field of using a spectroscopic device in which a change in dispersion characteristics is sufficiently small even when a temperature change occurs and a wavelength selective switch using such a spectroscopic device.

DESCRIPTION OF SYMBOLS 11 Entrance slit 12 Lens 13 Spectrometer 14 Lens (condensing lens)
15 Detector array 16 Light beams with multiple wavelengths 21 First surface (prism)
22 2nd surface (prism)
23 1st surface, 3rd surface (dispersion element)
24 2nd surface (dispersion element)
26 Prism 27 Dispersing element 71 Prism 72 Grating chip 73 Joint surface 74 Joint surface 501 Fiber array 502 Micro lens array 503 Spectroscopic section 504 Lens 505 Micro mirror array (MEMS module)
506 lens

Claims (17)

A first group of dispersive elements and a second group of dispersive elements in the order in which forward light rays are incident;
The outgoing angle of the forward ray from the first group of dispersive elements at the first temperature T ₁ is θ ₄ ,
An outgoing angle of the forward light beam from the first group of dispersion elements at a _second temperature T ₂ different from the _first temperature T ₁ is θ ′ ₄ ,
The difference θ ′ ₄ −θ ₄ of the emission angle is expressed as Δθ ₄ ,
The forward ray at the first temperature T ₁ is a ray along the optical path emitted from the second group of dispersive elements, and the second ray of the reverse ray at the second temperature T ₂ . The exit angle from the group of dispersive elements is θ ″ ₅ ,
The incident angle of the forward ray at the first temperature T _{1 to} the second group of dispersive elements is θ ₅ ,
The difference θ ″ ₅ −θ ₅ between the exit angle and the incident angle is Δθ ₅ ,
And when
A spectroscopic device characterized in that Δθ ₄ and Δθ ₅ are substantially equal. The first group of dispersive elements includes a prism,
The second group of dispersive elements includes dispersive elements;
In the order in which the forward rays are incident,
The prism includes a first surface that is a transmission surface, a second surface that is a transmission surface, and a medium having a refractive index greater than 1 filled in an optical path between the first surface and the second surface. Have
The dispersive element includes a first surface that is a transmission surface, a second surface that is a reflection diffraction surface, a third surface that is a transmission surface in common with the first surface, and the first surface and the second surface. A medium with a refractive index greater than 1 filled in the optical path between
A forward ray of light at the first temperature T ₁ ,
The incident angle of the prism with respect to the first surface is θ ₁ ,
The refraction angle at the first surface of the prism is θ ₂ ,
The incident angle of the second prism surface is θ ₃ ,
The refraction angle of the prism second surface is θ ₄ ,
The incident angle of the first surface of the dispersive element is θ ₅ ,
The refraction angle of the first surface of the dispersive element is θ ₆ ,
The incident angle of the second surface of the dispersion element is θ ₇ ,
The diffraction angle of the second surface of the dispersion element is θ ₈ ,
The incident angle of the third surface of the dispersion element is θ ₉ ,
The refraction angle of the third surface of the dispersion element is θ ₁₀ ,
A change in refractive index of the medium of the prism that occurs when the first temperature T ₁ changes to the _second temperature T ₂ is Δn ₁ ,
A change in the refractive index of the medium of the dispersive element that occurs when the first temperature T ₁ changes to the _second temperature T ₂ is Δn ₂ ,
_2. The spectroscopic apparatus according to claim 1, wherein k determined by the equation (E) is substantially equal to a value of | Δn ₁ / Δn ₂ |.
The medium of the prism and the medium of the dispersion element are made of the same material,
The spectroscopic apparatus according to claim 2, wherein the material is any one of optical glass, crystal material, resin material, and metal material.   The spectroscopic apparatus according to claim 3, wherein the medium of the prism and the medium of the dispersion element are both the same silicon. An intersection point between an intersection line of the first surface and the second surface of the prism and an incident plane including a light beam refracted on the second surface of the prism is an intersection point A,
When the intersection point between the line of intersection of the first surface and the second surface of the dispersion element and the incident plane is an intersection point B,
The intersection point A and the intersection point B are configured to exist in different regions with respect to two regions separated by a straight line along an optical path of a light beam existing between the prism and the dispersion element in the incident plane. The spectroscopic device according to claim 3, wherein the spectroscopic device is provided. The prism medium and the dispersion element medium are made of different materials,
The spectroscopic apparatus according to claim 2, wherein the material is any one of optical glass, crystal material, resin material, and metal material. When the sign of the temperature coefficient dn ₁ / dT of the refractive index n ₁ of the prism medium is the same as the sign of the temperature coefficient dn ₂ / dT of the refractive index n ₂ of the medium of the dispersion element,
An intersection point between an intersection line of the first surface and the second surface of the prism and an incident plane including a light beam refracted on the second surface of the prism is an intersection point A,
When the intersection point between the line of intersection of the first surface and the second surface of the dispersion element and the incident plane is an intersection point B,
The intersection point A and the intersection point B are configured to exist in different regions with respect to two regions separated by a straight line along an optical path of a light beam existing between the prism and the dispersion element in the incident plane. The spectroscopic device according to claim 6, wherein the spectroscopic device is provided. When the sign of the temperature coefficient dn ₁ / dT of the refractive index n ₁ of the prism medium is different from the sign of the temperature coefficient dn ₂ / dT of the refractive index n ₂ of the medium of the dispersion element,
An intersection point between an intersection line of the first surface and the second surface of the prism and an incident plane including a light beam refracted on the second surface of the prism is an intersection point A,
When the intersection point between the line of intersection of the first surface and the second surface of the dispersion element and the incident plane is an intersection point B,
The intersecting point A and the intersecting point B are present on the same side with respect to two regions separated by a straight line along the optical path of the light beam existing between the prism and the dispersive element in the incident plane. The spectroscopic device according to claim 6, wherein the spectroscopic device is configured as follows.   The spectroscopic device according to claim 1, wherein the light beam in the forward direction is one light beam of substantially parallel light.   The spectroscopic device according to claim 9, wherein a lens or a reflecting mirror having power is disposed in an optical path on a side where a forward light beam is incident on the first surface of the prism.   The spectroscopic device according to claim 9 or 10, wherein a reflecting mirror having a lens or a power is disposed in an optical path on a side where a forward light beam is emitted from the third surface of the dispersive element. .   The spectroscopic device according to claim 10 or 11, wherein the lens is an achromatic lens.   12. The lens according to claim 11, wherein the lens makes the chief ray of each wavelength after transmission telecentric, or the reflecting mirror having the power makes the chief ray of each wavelength after reflection telecentric. 12. The spectroscopic device according to 12. The spectroscopic apparatus according to claim ₁ , wherein the angle θ ₁ and the angle θ ₄ are substantially equal. The spectroscopic apparatus according to claim 1, wherein the angle θ ₅ and the angle θ ₁₀ are substantially equal.   A wavelength selective switch using the spectroscopic device according to any one of claims 1 to 15. The wavelength selective switch according to claim 16, wherein the lens includes at least one cylindrical lens.