JP2012145402A - Spectroscope and wavelength selection switch using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectroscope in which variation of dispersion characteristic is sufficiently small even under a temperature change, and a wavelength selection switch using the same.SOLUTION: The spectroscope includes a dispersion element, a prism in which an angle of emission light beam changes by the temperature change, and a light beam angle expansion optical system that is arranged between the prism and the dispersion element and emits a light beam with an angle obtained by proportionally expanding an incident angle of an incident light beam. The wavelength selection switch is configured by including the spectroscope. Consequently, the change of dispersion characteristic is made sufficiently small even under the temperature change.

Description

  The present invention relates to a spectroscope and a wavelength selective switch using the spectrometer.

Conventionally, many apparatuses using spectroscopic techniques have been proposed.
Patent Document 1 discloses a spectroscopic device (spectrometer) using a diffraction grating, and Patent Document 2 discloses an endoscope (spectral endoscope) using a diffraction grating. Patent Document 3 discloses a microscope (spectral microscope) that performs spectroscopy using a prism and a digital micromirror.

  Patent Document 4 discloses a basic configuration of a wavelength selective switch (WSS) under the name of an optical add / drop multiplexer.

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

  In each node, an optical signal having an arbitrary wavelength can be extracted from an optical signal that has been wavelength-multiplexed by using a wavelength selective switch, and light having an arbitrary wavelength can be added to the optical signal that has been wavelength-multiplexed. This wavelength selective switch also uses a diffraction grating.

  Japanese Patent Application Laid-Open No. H10-228561 is a light dispersion device (dispersion element), which includes a diffraction element attached adjacent to a prism. The effect is offset by the expansion of the diffraction grating and the change in the refractive index of the adjacent prism, and the emission angle corrects the change.

  Patent Documents 6 and 7 disclose a wavelength selective switch (WSS + correction prism) using a diffraction grating as a light dispersion element. By disposing a prism in the optical path, changes in the dispersion angle due to temperature changes are corrected.

JP 2007-187550 A JP 2007-135989 A JP 2000-199855 A Japanese Patent No. 3937403 Special table 2003-509714 gazette US Pat. No. 7,058,251 US Pat. No. 7,630,599

  In the prior arts described in Patent Documents 1 to 4, there is no description about the change in the emission angle when the temperature changes.

  In the prior arts described in Patent Documents 5 to 7, a countermeasure is taken up that the dispersion characteristics change due to temperature change. However, the main cause of the change in dispersion characteristics due to temperature changes is sought in the thermal expansion of the substrate of the diffraction grating, but if the refractive index of the atmosphere changes or light passes through the dispersion element, the dispersion element due to temperature change Changes in its own refractive index can be a major cause of changes 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.

An example of a spectrometer using a grism made of silicon having a high refractive index as a dispersive element is shown in FIG.
The grism 150 has a diffraction grating 151 formed on the hypotenuse of the prism 152 as shown in FIG. Since the exit angle θ11 is approximately the refractive index times of the prism of the diffraction angle θ9, the dispersion angle can be made larger than that of a normal diffraction grating. In order to further increase the dispersion angle, it is only necessary to increase the refractive index of the prism, so a silicon prism or the like is used in the infrared. As shown in FIG. 17, a grism or the like in which a silicon chip 172 having a diffraction grating 171 formed thereon is bonded to a silicon prism 170 is used.

  In the spectrometer of FIG. 1, incident light passes through the slit 101, becomes parallel light by the collimator 102, and enters the silicon grism 150. The light is diffracted by the diffraction grating surface 151 of the silicon grism 150 and separated.

  The dispersed light is condensed by the collimator 102 on the light receiving element array 105 for each wavelength. By looking at the output of each element of the light receiving element 105 array, the spectral intensity can be obtained.

  As described above, since the grism uses silicon having a high refractive index, the dispersion angle can be increased and the resolution is high. However, since the refractive index of silicon changes greatly with changes in temperature, the angle of the emitted light changes from the grism with temperature, and the spectral distribution shifts in the wavelength direction.

Table 1 shows the refractive index of silicon and the temperature coefficient of the refractive index. For example, the refractive index n (T, 1.55) at a wavelength of 1.55μm and temperature T ° C is
n (T, 1.55) = 0.00018 × (T-20) + 3.478
It can be calculated with

Further, each angle is defined as shown in FIG.
θ7 = Asin (sin (θ6) / n)
θ8 = α2-θ7
θ9 = Asin (λ / n / p-Sin (θ8))
θ10 = θ9-α2
θ11 = Asin (n sin (θ10))

here,
n: Refractive index at each wavelength and temperature,
p: grating pitch of grism diffraction grating surface,
It is.

  Using the values shown in Table 2, the emission angle from the grism (θ11) is calculated as shown in Table 3. Table 4 shows the results of calculating the wavelength shift amount δλ as shown in the following formula. The graph is as shown in graph 1 (see FIG. 18).

  The shift amount is about 0.75 nm at 10 ° C. For example, in optical communication such as WDM, the wavelength width of one channel is about 0.8 nm or about 0.4 nm, so that the amount of shift is very large as a spectroscope used for measurement in an optical communication device. .

  FIG. 2 shows an example in which correction is performed using a correction prism in the same manner as the methods described in Patent Documents 6 and 7. The angle incident on the grism is changed with the temperature by the correction prism so that the angle emitted from the grism is constant regardless of the temperature.

Each angle is defined as shown in FIG. From Snell's law and diffraction law, there is the following relationship.
θ2 = Asin (sin (θ1) / n)
θ3 = α1-θ2
θ4 = Asin (n sin (θ3))
θ6 = θ4-θ5
θ7 = Asin (sin (θ6) / n)
θ8 = α2-θ7
θ9 = Asin (λ / n / p-Sin (θ8))
θ10 = θ9-α2
θ11 = Asin (n sin (θ10))
here,
n: Refractive index at each wavelength at each temperature p: Grating pitch of the grism diffraction grating surface θ5: θ6 at the reference wavelength and reference temperature (20 ° C, 1.55 μm here) is a value that increases the efficiency of the grism It is stipulated in.
θ6 = 17 degrees, θ5 = θ4 (at 20 ° C., 1.55 μm) −17 degrees.

  Using the values shown in Tables 5 and 6, the emission angle θ11 from the grism with respect to the temperature is calculated. The incident angle θ1 and the apex angle α1 of the correction prism are set so that the change of the emission angle θ11 from the grism is minimal with respect to the temperature change, and the incident angle θ1 and the emission angle θ4 of the correction prism are substantially equal.

  The results are shown in Table 7. Then, as shown in the above [Equation 1], the wavelength shift amount δλ is calculated.

  As a result, the wavelength shift amount is listed in Table 8. The graph is as shown in graph 2 (see FIG. 19). The wavelength shift amount is about 0.05 nm at -20 to 60 ° C. When this spectroscopic device is used for a wavelength selective switch or the like, the wavelength shift reduces the band of one channel. In the case of a WDM system in which one channel is 50 GHz wide, when converted to a wavelength, one channel has a width of about 0.4 nm. The 0.05 nm shift limits the bandwidth by about 10%.

  The present invention has been made in view of such circumstances, 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 there is a temperature change, and a wavelength selective switch using such a spectroscopic device. .

In order to solve the above-described problems and achieve the object, a spectrometer according to the present invention includes:
A dispersive element;
A prism in which the angle of the emitted light changes with respect to temperature changes;
A light beam angle expanding optical system that emits a light beam at an angle that is obtained by proportionally expanding the incident angle of the incident light beam disposed between the prism and the dispersion element;
It is characterized by providing.
A dispersive element is an element that disperses light and whose refractive index changes according to wavelength (an element having a function of dividing light into a spectrum). For example, an optical element such as a prism, a diffraction grating, or a grism is used. It corresponds as an example.

  In the present invention, the dispersive element may be a silicon grism, the prism may be a silicon prism, and the light beam angle expanding optical system may be an afocal optical system.

The spectroscope according to the present invention is
A dispersive element;
A prism in which the angle of the emitted light changes with respect to temperature changes;
An afocal optical system disposed between the correction optical system and the dispersive element;
With
The dispersion element, the afocal optical system, and the correction optical system respectively change the rotation center when the light beam emitted from the prism changes its emission angle due to a temperature change, and change the light beam incident on the dispersion element with a temperature change. It is characterized in that it is arranged so as to have a conjugate relationship with the center of rotation.

  In the present invention, the dispersive element may be a silicon grism, and the correction optical system may be a silicon prism.

The wavelength selective switch according to the present invention is:
At least one input unit for receiving wavelength-multiplexed light;
A prism in which the angle of the emitted light changes with respect to temperature changes;
A dispersing element for dispersing the light;
An afocal optical system disposed between the prism and the dispersive element;
A condensing element for condensing light for each dispersed wavelength;
A light deflecting member having a plurality of deflecting elements capable of independently deflecting the light for each wavelength from the condensing element for each wavelength;
An output unit for receiving the light of each wavelength deflected by the light deflection member;
It is characterized by having.

  The present invention can provide a spectrometer having a sufficiently small change in dispersion characteristics even when there is a temperature change, and a wavelength selective switch using such a spectrometer.

It is a figure which shows an example of the spectrometer which used the grism made from the silicon | silicone with a high refractive index as a dispersive element. It is a figure which shows an example which correct | amends a temperature change using a correction prism. It is a figure which shows the structural example of a grism, and each angle. It is a figure which shows the structural example containing a correction prism, and each angle. 1 is a diagram schematically showing an overall configuration example of a spectroscopic device according to a first embodiment of the present invention. FIG. It is a figure which shows the structural example of the spectroscopy part which concerns on embodiment same as the above. It is a figure which defines each angle in embodiment same as the above. It is a figure explaining the afocal optical system which concerns on embodiment same as the above. It is a figure explaining calculation of wavelength shift amount deltalambda. In the afocal optical system according to the embodiment, when the rotation center (P1) and the rotation center (P2) are not in a conjugate relationship, when there is a temperature change, the emitted light from the grism does not change the angle but is parallel. It is a figure which shows a mode that it moves. In the afocal optical system according to the above embodiment, when the rotation center (P1) and the rotation center (P2) are set in a conjugate relationship, even if there is a temperature change, the emitted light from the grism changes in angle or translates. It is a figure which shows a mode that it radiates | emits without. In the afocal optical system according to the same embodiment, when the rotation center (P1) and the rotation center (P2) are not in a conjugate relationship, when there is a temperature change, the light enters the light receiving element array at an angle. It is a figure which shows a mode. It is a figure which shows the structural example at the time of combining a diffractive lens in the afocal optical system which concerns on embodiment same as the above. It is a perspective view which shows the structure of the wavelength selective switch which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the structure of the mirror array of the wavelength selection switch which concerns on embodiment same as the above. It is a figure which shows the structural example of a grism, and each angle. It is a figure which shows the structural example of a grism which joined the silicon | silicone chip | tip which formed the diffraction grating to the silicon prism, and each angle. FIG. 3 is a diagram showing a graph 1; FIG. 3 is a diagram showing a graph 2; FIG. FIG. 6 is a diagram showing a graph 4; FIG. 6 is a diagram showing a graph 5;

  Embodiments according to the present invention will be described below 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 is not limited to the embodiments.

<First Embodiment>
(Constitution)
As shown in FIG. 5, the prism (spectral device) 300 of the present embodiment has the following configuration.
That is, an incident slit 101 into which a light beam is input, a collimator 102 that converts light beams of a plurality of wavelengths incident from the incident slit 191 into substantially parallel light, a later-described spectroscopic unit 103, and a collimator 104 that collects the dispersed light, respectively. , And a light receiving element array 105 that receives light of each wavelength band divided in advance.

As shown in FIG. 6, the spectroscopic unit has the following configuration.
A correction prism 140 having an apex angle α1 made of a medium having a refractive index n, a grism 150 having an apex angle α2, a pitch p, and a diffraction order 1 made of a medium having a refractive index n, and a correction prism 140 and the grism 150 being arranged between them. And an afocal optical system AL having a focal magnification m.

The afocal optical system AL has the following configuration.
The lens L1 includes a lens L1 having a focal length f1 and a lens L2 having a focal length f2. The afocal magnification m is m = f1 / f2 in the configuration shown in FIG.

  The optical axis of the afocal optical system AL is a light beam at a reference temperature and a reference wavelength. Here, the reference temperature is 20 ° C. and the reference wavelength is 1.55 μm. When the temperature changes, the light beam tilts from the optical axis. The inclination is θ41 when incident on the afocal optical system AL and θ61 when emitted.

  θ41 is the amount of change from the reference ray of the exit angle when exiting from the correction prism 140. Since the amount of change is very small, sin θ can be approximated by θ. The afocal optical system AL is made of ordinary optical glass. The temperature coefficient of refractive index of ordinary optical glass is negligible by two orders of magnitude compared with silicon.

  When the optical communication system is used for measurement or as an apparatus, since the wavelength band is narrow, the refractive index hardly changes in ordinary optical glass. Here, it is assumed that the refractive index hardly changes, and the focal length f of the lens used in the afocal optical system AL is assumed to be constant.

  The light emitted from the collimator 102 in FIG. 5 enters the correction prism 140. The prism 140 has a first surface and a second surface in the order in which the incident light 25 (FIG. 6) strikes. The light exiting the correction prism 140 enters the afocal optical system AL.

  The grism 150 has a first surface, a second surface that is a diffraction grating surface, and a third surface 23 that is common to the first surface (FIG. 7) in the order in which light after passing through the afocal optical system strikes. The light exiting from the third surface of the grating is mainly split by the second surface and travels to the collimator 102 in FIG.

When the angle is defined as shown in FIG. 7, there is the following relationship from Snell's law and diffraction law.
θ2 = Asin (sin (θ1) / n)
θ3 = α1-θ2
θ4 = Asin (n sin (θ3))
θ41 = θ4 (at T ° C, λ)-θ4 (at reference temperature and reference wavelength (here 20 ° C, 1.55μm))
θ61 = m θ41
θ6 = 180-θ61-θ4 (at reference temperature and reference wavelength)-θ5
θ7 = Asin (sin (θ6) / n)
θ8 = α2-θ7
θ9 = Asin (λ / n / p-Sin (θ8))
θ10 = θ9-α2
θ11 = Asin (n sin (θ10))

here,
n: Refractive index at each wavelength and temperature,
p: grating pitch of grism diffraction grating surface,
θ5 is determined such that θ6 at the reference wavelength and the reference temperature (here, 20 ° C., 1.55 μm) increases the efficiency of the grism.
Here θ6 = 17 degrees, reference temperature, and reference wavelength θ61 = 0, so θ5 = 180-θ4 (at 20 ° C, 1.55μm)-17
By setting the incident angle θ1, the apex angle α1, and the afocal magnification m of the correction prism 140 to appropriate values, the light emission angle θ11 from the grism 150 can be made constant regardless of the temperature.

  Using the values in Tables 9, 10, and 11, the light output angle is calculated from the grism as shown in Table 12. Table 13 shows the result of calculating the wavelength shift amount as shown in [Equation 1] above. The graph is shown in graph 3 (see FIG. 20).

  The amount of wavelength shift is about 0.003 nm. When this spectroscopic device is applied to a wavelength selective switch used in a WDM system with a channel width of 50 GHz, the limitation of one channel due to wavelength shift can be suppressed to about 1%.

(Function and effect)
When temperature compensation is performed using only the correction prism, as shown in graph 2 (FIG. 19), the relationship between temperature and wavelength shift becomes a convex graph. When the correction prism and the afocal optical system are used, the shapes differ depending on the afocal magnification, as shown in graphs 3, 4, and 5 (FIGS. 20, 21, and 22). Since the angle of the light beam incident on the afocal optical system is less than 1 degree, the angle change is linearly expanded as shown in FIG. If the magnification is lowered, the case of only the correction prism is approached. When the magnification is increased, the angle change of the light ray incident on the grism changes linearly with respect to the temperature.

  When the magnification is low (−3 times), the graph is convex upward as shown in graph 4 (see FIG. 21), and has the same shape as the correction prism (the shift amount is small).

  When the magnification is large (5 times), a downwardly convex shape is formed as shown in graph 5 (see FIG. 22). The correction prism is convex upward, and the grism is convex downward. Since only the correction prism cannot move the linear component and the nonlinear component independently, when the linear component is corrected, the nonlinear component remains, and when the nonlinear component is corrected, the linear component remains.

  When the correction prism and afocal optical system are combined, the linear component and nonlinear component can be moved independently by moving the afocal magnification and the apex angle of the correction prism. can do. Since the wavelength cannot be corrected independently, a balance can be achieved by correcting the linear components of the reference wavelength and the center wavelength.

  From the above, by performing temperature correction with the correction prism and the afocal optical system, the wavelength shift with respect to temperature change can be reduced to 1/1000 without the correction prism and 1/10 with only the correction prism.

(Modification)
The afocal optical system may be combined with a diffractive lens 160 as shown in FIG. The lens bends light rays with a spherical surface, whereas the diffraction grating 160 bends light rays with a flat surface. For this reason, since the focal length can be shortened even with the same light beam diameter, there is an advantage that the total length of the afocal optical system can be shortened.

  As shown in FIG. 11, the rotation center (P1) where the light beam emitted from the correction prism 140 rotates due to temperature change and the rotation center (P2) where the light beam incident on the grism 150 rotates due to temperature change are an afocal optical system. It is configured to have a conjugate relationship.

  If the relationship is not conjugated, as shown in FIG. 10, when there is a temperature change, the outgoing light from the grism 150 moves in parallel without changing the angle. On the other hand, as shown in FIG. 12, since there is no change in angle, there is no wavelength shift, but the light is incident on the light receiving element array 105 with an angle. Since the sensitivity of PD (photodiode) has angle dependency, the spectrum distribution cannot be measured correctly. If it is conjugated, there is no parallel movement, so there is no angle with respect to the light receiving element array 105, and the spectral distribution can be measured correctly.

<Second Embodiment>
(Constitution)
As shown in FIG. 14, the wavelength selective switch of the second embodiment has the following configuration.
That is, it is configured to include a fiber array 502, a lens array 501, a spectroscopic unit 103, a collimator 504, and a mirror array 505.

  As shown in FIG. 15, the mirror array 505 can rotate an arbitrary mirror M around the Y axis.

  As shown in FIG. 14, light beams having a plurality of wavelengths output from one fiber are converted into parallel light by the lens array 502 and enter the spectroscopic unit 103. Light is emitted after being split from the spectroscopic unit 103, and is collected on the mirror array 505 for each wavelength by the collimator 504.

  The light beam reflected by the mirror array 505 is converted into parallel light by the collimator 504 and returns to the spectroscopic unit 103. By rotating the mirror array 505, the height of the returning light beam can be changed, and the light can enter the arbitrary lens array 502. The lens array 502 can couple a light beam to the fiber 501 and transmit a light beam having an arbitrary wavelength to an arbitrary fiber 501.

As the spectroscopic unit 103, the spectroscopic unit described in the first embodiment can be used.
That is, even if the temperature changes, the angle of the light beam emitted from the spectroscopic unit 103 hardly changes. Accordingly, light of the same wavelength is fixed on the mirror array 505 and does not shift. When the light beam is shifted on the mirror array 505, the band is narrowed accordingly, but in the present embodiment, the band is hardly narrowed.

(Function and effect)
A wavelength selective switch having a wide band of one channel can be realized by using a spectroscope in which the emission angle of the emitted light hardly changes due to temperature change.

  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 can provide a spectroscope having a sufficiently small change in dispersion characteristics even when there is a temperature change, and a wavelength selective switch using such a spectroscopic device, for example, in the field of optical systems. Useful.

DESCRIPTION OF SYMBOLS 101 Slit 102 Collimator 103 Spectrometer 104 Collimator 105 Light receiving element array 140 Correction prism 150 Grism 151 Optical diffraction surface 160 Diffraction lens 300 Spectrometer Lλ1, Lλ2 Light flux AL Afocus optical system L1, L2 Lens M Mirror

Claims (5)

A dispersive element;
A prism in which the angle of the emitted light changes with respect to temperature changes;
A light beam angle expanding optical system that emits a light beam at an angle obtained by proportionally expanding the incident angle of the incident light beam disposed between the prism and the dispersion element;
A spectroscope comprising: The dispersive element is a silicon grism;
The prism is a silicon prism;
2. The spectroscope according to claim 1, wherein the light beam angle expanding optical system is an afocal optical system. A dispersive element;
A prism in which the angle of the emitted light changes with respect to temperature changes;
An afocal optical system disposed between the correction optical system and the dispersive element;
With
The dispersion element, the afocal optical system, and the correction optical system respectively change the rotation center when the light beam emitted from the prism changes its emission angle due to a temperature change, and change the light beam incident on the dispersion element with a temperature change. A spectroscope characterized by being arranged so as to have a conjugate relationship with the rotation center. The dispersive element is a silicon grism;
The spectroscope according to claim 3, wherein the correction optical system is a silicon prism. At least one input unit for receiving wavelength-multiplexed light;
A prism in which the angle of the emitted light changes with respect to temperature changes;
A dispersing element for dispersing the light;
An afocal optical system disposed between the prism and the dispersive element;
A condensing element for condensing light for each dispersed wavelength;
A light deflecting member having a plurality of deflecting elements capable of independently deflecting the light for each wavelength from the condensing element for each wavelength;
An output unit for receiving the light of each wavelength deflected by the light deflection member;
A wavelength selective switch comprising: