JP2005062201A - Spectroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a spectroscope for improving condensation characteristics to an array of photodetectors, or a spectroscope capable of precise measurement by correcting the influence of a dark current when using the photodetectors. <P>SOLUTION: The spectroscope for obtaining a detection signal separated for each wavelength by dispersing measurement light by a wavelength dispersion element for entering the photodetectors is improved. The spectroscope uses the array of photodetectors, where a plurality of photodetectors are arranged in the dispersion direction of wavelengths as the photodetectors, and uses an f-θ lens as a means for condensing light to the array of photodetectors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spectroscopic device, and more particularly to a spectroscopic device useful for optical signal monitoring and evaluation measurement in wavelength division multiplexing optical communication (WDM).

  As a next-generation information communication system, a wavelength multiplexing optical communication system has attracted attention. In monitoring and evaluating measurement of an optical signal in such wavelength division multiplexing optical communication, it is necessary to individually measure each wavelength component of the multiplexed optical signal, and various spectroscopic devices have been proposed.

FIG. 14 is a basic configuration diagram showing an example of such a conventional spectroscopic device.
In the figure, measurement light transmitted through an optical fiber 1 is formed into a parallel beam by a collimating lens 2 and is incident on a diffraction grating (grating) 3 used as a wavelength dispersion element. The output light wavelength-dispersed by the diffraction grating 3 is converged by the focusing lens 4 and is incident on the light-receiving element array 5 in which a plurality of light-receiving elements are arranged in the wavelength dispersion direction.

According to such a configuration, it is not necessary to rotate the diffraction grating 3, and a spectroscopic device excellent in high speed and reliability can be realized.
Here, the optical characteristic of the diffraction grating 3 is expressed by the following equation.

  By designing a spectroscopic device having a narrow wavelength range such as a monitor for a wavelength division multiplexing optical communication system based on such a basic configuration, the optical path spread by wavelength dispersion is smaller than the focal length of the focusing lens 4. When the light receiving element array 5 is arranged in a one-dimensional manner along the wavelength dispersion direction, it is clear that the position of the element and the emission angle are substantially proportional.

However, the relationship between the wavelength λ and the emission angle θ is expressed by the following equation obtained by differentiating Equation 1.

It can be seen that the wavelength λ and the dispersion angle depend on the cosine of the emission angle θ. The emission angle θ can be obtained from Equation 1 based on the wavelength range of the spectroscopic device specification, the grating constant d of the diffraction grating 3 to be used, the focal length f ₂ of the focusing lens 4 and the like.

The wavelength resolution of such a spectroscopic device will be described. Assume that a collimating lens having a focal length f ₁ of 50 mm is used. The use area of the diffraction grating is determined by the numerical aperture NA of the single mode fiber, the focal length f ₁ of the collimating lens, and the incident angle i. In this case, it is an ellipse having a major axis of 11.1 mm. The lattice constant is the line width of the lattice. Since the number of lattices per 1 mm is 1 mm / d, the lattice constant of 1.11 × 10 ⁻⁶ is 900. Since the theoretical resolution (λ / Δλ) based on the Reyleigh standard is obtained by the total number of grooves, in this case, 900 × 11.1 is about 10 ⁴ , and when λ is 1.5 μm, Δλ is obtained as 0.15 nm.

  As described above, it can be seen that the wavelength resolution of the spectroscopic device depends on the size of the region in which the diffraction grating 3 is used. Therefore, in order to increase the wavelength resolution with the basic configuration of FIG. 14, the spectroscopic device must be enlarged.

  As another configuration, as shown in FIG. 15, two monochromatic spectrometers (monochromators) are connected in cascade to increase the total number of grooves of the diffraction grating, increase the wavelength resolution, and stray light superimposed on the original spectrum. There has also been proposed an improvement in the dynamic range of the neighborhood by further dispersing only the above.

  In the figure, measurement light transmitted through an optical fiber 6 is formed into a parallel beam by a first collimating lens 7 and is incident on a first diffraction grating 8. The output light wavelength-dispersed by the diffraction grating 8 is converged by the first focusing lens 9 and enters the slit 10. The output light from the slit 10 is shaped into a parallel beam by the second collimating lens 11 and is incident on the second diffraction grating 12. The output light wavelength-dispersed by the diffraction grating 12 is converged by the second focusing lens 13 and enters the single light receiving element 15 through the slit 14.

  Here, the two diffraction gratings 8 and 12 are rotationally driven in conjunction with each other in order to scan the wavelength of the measurement light. As a result, the total number of gratings in the entire spectroscopic device becomes the sum of the number of gratings of these diffraction gratings 8 and 12, and the wavelength resolution is improved. Then, only the stray light superimposed on the original spectrum is further dispersed by the subsequent monochromator to improve the dynamic range near the original spectrum.

  However, in the configuration of FIG. 15, the two diffraction gratings 8 and 12 must be rotated in an interlocked manner, the configuration becomes complicated, and downsizing is difficult.

Next, temperature characteristics of the spectroscopic device will be described.
When the diffraction grating is used in the air, the temperature characteristic of the emission angle is expressed by the following equation, where n _air is the refractive index of the _air .

Here, the first term in parentheses is the linear expansion coefficient of the diffraction grating, and the second term is the temperature coefficient of the air refractive index.
The temperature coefficient of wavelength is obtained by the following equation.

  For example, at a wavelength of 1.55 μm, when a Pyrex (registered trademark) glass diffraction grating is used in the air, the temperature coefficient is determined to be approximately 3.7 pm / ° C.

  Such a temperature coefficient is not preferable when the temperature of the environment in which the spectroscopic device is used changes, because the measurement light varies depending on the temperature even though the measurement light is stable.

  By the way, as shown in FIG. 16, for example, a concave mirror 16 is often used as an optical system for condensing the light emitted from the diffraction grating 3 on the light receiving element array 5, but the concave mirror is relatively expensive and difficult to reduce in weight. There's a problem. Further, since the optical path is greatly changed by reflection, the space occupied by the optical system is increased, and there is a problem that adjustment is complicated. Furthermore, imaging near both ends of the light receiving element array 5 may be distorted due to the influence of aberration.

On the other hand, when attention is paid to the output current I _S of the light receiving elements, small dark current I _D is generated even in the absence of incident light. The dark current _ID changes greatly depending on the ambient temperature, and there is also some aging.
Therefore, in order to accurately measure based on power of the incident light to the output current I _S of the light receiving element, the magnitude of I _D of the dark current was measured as needed, the dark current I _D from the output current I _S Must be subtracted to obtain a current I _L (= I _S −I _D ) generated only by incident light.

Further, the light emitted from the diffraction grating used as the wavelength dispersion element has a diffraction angle different depending on the wavelength of the incident light.
Therefore, when a light receiving element array in which a plurality of light receiving elements are arranged in the wavelength dispersion direction is used as the light receiving element, a normal lens cannot condense at both ends particularly due to aberrations or the like when condensing on the light receiving element array. There are many cases.

  Further, as shown in FIG. 17, the input side slab waveguide 17 and the output side slab waveguide 18 as the wavelength dispersion element, the input side waveguide 19 for transmitting the measurement light to the input side slab waveguide 17, and the input side slab waveguide A waveguide row 20 for transmitting 17 output light to the output slab waveguide 18 and an output waveguide 21 for transmitting output light of the output slab waveguide 18 to the outside are integrally formed on a common substrate 22. There has also been proposed a spectroscopic device using a waveguide type diffraction grating (AWG; Arrayed Waveguide Grating), in which a light receiving element array 23 is arranged so that the light receiving elements face each port of the output side waveguide 21.

  However, with such an apparatus, although a measurement result as shown in FIG. 18 is obtained, it cannot be identified whether the measurement signal variation ΔP in the measurement result is a variation in optical power or due to a wavelength shift Δλ. Of course, changes in wavelength cannot be detected.

  The present invention pays attention to the problem of a spectroscopic device configured to obtain detection signals separated by wavelength by dispersing the measurement light with a wavelength dispersion element and making it incident on a light receiving element. One of them is to realize a spectroscopic device with improved light collection characteristics on the light receiving element array.

  Another object is to realize a spectroscopic device capable of performing high-accuracy measurement by correcting the influence of dark current when a light receiving element is used.

  Another object is to realize a spectroscopic device capable of improving the temperature characteristics of the entire device.

In order to achieve such an object, claim 1 of the present invention provides:
A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
Using a light receiving element array in which a plurality of light receiving elements are arranged in a wavelength dispersion direction as the light receiving element,
An f-θ lens is used as means for condensing the light receiving element array.

  As a result, even if the diffraction direction differs for each wavelength, the characteristics can be substantially corrected and condensed on the light receiving element array.

Claim 2 of the present invention provides
A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
Using a light receiving element array in which a plurality of light receiving elements are arranged in a wavelength dispersion direction as the light receiving element,
A part of these light receiving elements is used for dark current detection.

  As a result, the dark current can be measured at an arbitrary time point without interrupting the normal measurement, and the incident light power can be measured with high accuracy.

Claim 3 of the present invention provides
A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
An optical element having a refractive index temperature characteristic for correcting a wavelength temperature characteristic of the wavelength dispersion element is provided in an optical path leading to the light receiving element.

  Thereby, the wavelength temperature characteristic of the whole spectroscopic device can be made substantially zero.

The present invention has the following effects.
According to the first aspect of the present invention, it is possible to realize a spectroscopic device with improved light collection characteristics on the light receiving element array.

  According to claim 2 of the present invention, it is possible to realize a spectroscopic device capable of performing high-accuracy measurement by correcting the influence of dark current when a light receiving element is used.

  According to claim 3 of the present invention, a spectroscopic device capable of improving the temperature characteristics of the entire device can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an example of an embodiment of the invention. In the figure, measurement light emitted from an incident end (optical fiber) 101 is formed into a parallel beam by a lens 102 and is incident on a diffraction grating (grating) 103 used as a wavelength dispersion element. A mirror 104 is provided at a position facing the diffraction grating 103 so that the light passes through the diffraction grating 103 twice, specifically, so that the light substantially reciprocates around the center of the lens 102 at the designed center wavelength. It has been. However, since it is usually necessary to separate the incident end 101 and the imaging position, the two are separated by providing an opening of the optical axis in a direction orthogonal to the wavelength dispersion direction. This is shown in the side view, but is omitted from the top view for easy illustration of chromatic dispersion. The light that has substantially reciprocated through the lens 102 is reflected by the mirror 105 and is incident on the light receiving element array 106 in which a plurality of light receiving elements are arranged in the wavelength dispersion direction.

  As a result, since the light passes through the diffraction grating 103 twice, the wavelength resolution is doubled, and a compact spectroscopic device is obtained.

FIG. 2 is an explanatory diagram showing the operation of the wavelength dispersion element in which the diffraction grating 103 and the mirror 104 are combined with the optical axis. The first incident angle to the diffraction grating 103 is θ ₁ , the outgoing angle is θ ₂ , the second incident angle to the diffraction grating 103 is θ ₃ , the outgoing angle is θ ₄ , and the angle formed by the mirror 104 and the diffraction grating 103 is θ ₂₀ is set. The normal of the mirror 104 is assumed to be along the light beam at the center wavelength. The relational expression of 2 degree diffraction is shown below. For simplicity, the refractive index of the medium is 1.

Since the incident angles θ ₁ and θ ₂₀ are constant, the following equation is obtained by differentiating by λ.

If this is arranged with respect to dθ ₄ / dλ, since cos θ ₂₀ = cos θ ₂ = cos θ ₃ at the center wavelength,

となり、２倍の分散角が得られることがわかる。 This

It can be seen that a double dispersion angle can be obtained.

If the incident beam diameter is W ₁ , W _g and W ₂ are expressed as follows.

  Here, since the beam diameter is also kept constant, the wavelength resolution is improved by a factor of two.

  Note that the diffraction efficiency of the diffraction grating 103 changes depending on the polarization state of incident light. In such a configuration of the embodiment, since the light beam passes through the diffraction grating 103 twice, a wave plate (not shown) is inserted between the diffraction grating 103 and the mirror 104 to change the respective polarization states to be orthogonal. Thus, the polarization dependence of the overall diffraction efficiency can be improved.

  FIG. 3 is a block diagram showing another embodiment of the present invention, in which prisms are integrated for improving chromatic dispersion characteristics, and parts common to FIG. 1 are given the same reference numerals. . The prism 107 has a trapezoidal cross-sectional shape. The diffraction grating 103 is in close contact with one surface adjacent to the incident surface, and the mirror 104 is in close contact with the other surface adjacent to the incident surface with the wave plate 108 interposed therebetween. Has been.

FIG. 4 is an explanatory diagram of the operation of FIG.
The incident angle to the prism 107 is θ _i , the refraction angle is θ ₀ , the first incident angle to the diffraction grating 103 is θ ₁ , the outgoing angle is θ ₂ , and the second incident angle to the diffraction grating 103 is θ _3. The exit angle is θ ₄ , the exit angle from the prism 107 is θ ₅ , its refraction angle is θ ₆ , the angle formed by the mirror 104 and the diffraction grating 103 is θ ₂₀ , and the angle formed by the incident surface of the prism 107 and the diffraction grating 103 Is θ _p . The relational expression between these 2 degree diffraction and 2 degree refraction is shown below.

The chromatic dispersion characteristics are obtained by differentiating by λ with θ _i , θ _p and θ ₂₀ being constant.
Since dθ ₀ / dλ = dθ ₁ / dλ = 0,

become. It arranges about d (theta) ₆ / d (lambda). Since cosθ ₂₀ = cosθ ₂ = cosθ ₃ at the center wavelength,

になり、波長分散が２倍になることを示している。 Therefore,

, Indicating that the chromatic dispersion is doubled.

である。 The condition for flattening the chromatic dispersion is as follows: d ² θ ₆ / dλ ² = 0

It is.

The temperature dependence is obtained by differentiating the basic formula by T and arranging for dθ ₆ / dT.

ｄθ_６／ｄＴについて整理すると、 Distinguishes and n _a of the absolute value and n _r to air for refractive index n. relationship n _r and n _a and the air refractive index n _air is shown as follows.

To organize dθ ₆ / dT,

Since cosθ ₂₀ = cosθ ₂ = cosθ ₃ , cosθ ₁ = cosθ ₄ , cosθ ₀ = cosθ ₅ , and cosθ _i = cosθ ₆ at the center wavelength,

となる。

It becomes.

As shown in FIG. 1, by combining the mirror and the diffraction grating so that light passes through the diffraction grating twice, the chromatic dispersion is doubled.
Thereby, the width of the diffraction grating for obtaining the same wavelength dispersion characteristic is halved, and the spectroscopic device can be miniaturized.

  Also, in the case of a dispersive element in which a diffraction grating is bonded to a prism as shown in FIG. 3 to achieve flattening of wavelength dispersion characteristics, a combination of mirrors allows light to pass through the diffraction grating twice so that chromatic dispersion is 2 Therefore, the width of the diffraction grating for obtaining the same wavelength dispersion characteristic is halved, and a compact spectroscopic device can be configured.

  Furthermore, by changing the polarization state between the mirror and the diffraction grating with an appropriate polarization element, a spectroscopic device with improved polarization dependency of diffraction efficiency can be configured.

  FIG. 5 is a block diagram showing another embodiment of the invention. The measurement light emitted from the incident end 109 is shaped into a parallel beam by the lens 110 and is incident on the diffraction grating 111 used as the first wavelength dispersion element. Light emitted from the diffraction grating 111 is collected by a lens 112 and is incident on a digital micromirror element (hereinafter referred to as DMD) 113. Here, the DMD 113 is a monolithically integrated array of a plurality of micromirrors on a semiconductor substrate such as a silicon wafer along the wavelength dispersion direction, and each micromirror can be selectively rotated at an arbitrary angle. . The light emitted from the DMD 113 is again shaped into a parallel beam by the lens 114 and is incident on the diffraction grating 115 used as the second wavelength dispersion element. Light emitted from the diffraction grating 115 is collected by the lens 116 and is incident on the light receiving element 117.

  Compared with the conventional double monochromator shown in FIG. 15, the conventional apparatus scans the wavelength by fixing the intermediate slit 10 and rotating the two dispersive elements 8 and 12 in conjunction with each other. Then, the two dispersive elements 111 and 115 are fixed and the DMD 113 arranged instead of the intermediate slit is operated as a reflection type spatial light modulator, and the micromirrors arranged in the wavelength dispersion direction are sequentially scanned to obtain the corresponding wavelength. The wavelength is scanned by selecting and detecting the spectrum.

As the light receiving element 117, a light receiving element array in which a plurality of light receiving elements are arranged in the wavelength dispersion direction or a single light receiving element is used depending on the application of the spectroscopic device.
When using the light receiving element array, the scan of the DMD 113 and the scan of the light receiving element array 117 are synchronized. That is, the scanning of the light receiving element array 117 is synchronized so that the spectrum of the wavelength selected by the DMD 113 is detected. When a single light receiving element is used, the rotation angle of the micromirror of the DMD 113 is controlled according to the selected wavelength so that each wavelength is incident on the light receiving element.

  In other words, the embodiment of FIG. 5 is a double monochromator and a double polychromator configured by a fixed dispersion element and a spatially moving slit.

  FIG. 6 is a block diagram showing another embodiment of the invention. The measurement light emitted from the incident end 118 is shaped into a parallel beam by the lens 119 and is incident on the diffraction grating 120 used as a wavelength dispersion element. Light emitted from the diffraction grating 120 is collected by the lens 121 and is incident on the DMD 122. The light emitted from the DMD 122 is again shaped into a parallel beam by the lens 121 and is incident on the diffraction grating 120. The light emitted from the diffraction grating 120 is collected by the lens 119 and enters the light receiving element 124 through the slit 123.

  In the embodiment of FIG. 6, the second monochromator to be connected in cascade as shown in FIG. 5 is omitted, and the same effect is obtained by passing the measurement light twice through the first monochromator and returning it to the light receiving element. It is a double pass type configuration. The DMD operates as a slit that moves spatially as in FIG.

5 and 6, the wavelength scanning of the double monochromator is performed by a DMD monolithically integrally formed on a semiconductor substrate such as a silicon wafer, so that a conventional large-scale mechanical movable part is unnecessary. The entire device can be downsized and highly reliable.
In addition, DMD scans can be driven at high speeds up to several MHz, so synchronization with the light-receiving element array is easy. Cascade connection is possible even with a polychromator, and the dynamic range near the measurement wavelength is greatly improved as well as resolution. Can improve.

  FIG. 7 is a block diagram showing another embodiment of the invention. The outgoing light diffracted in the direction corresponding to the wavelength of the incident light by the diffraction grating 125 is condensed by the f-θ lens 126 and imaged on the light receiving element array 127. Note that the f-θ lens 126 is designed so as not to distort the image formation in the vicinity of both ends of the light receiving element array 127.

  By using the f-θ lens 126, it is relatively cheaper than a concave mirror and can be reduced in weight. Further, since the optical path of the diffracted light is not changed, the optical system can be made compact, and the adjustment work can be greatly simplified. Furthermore, the design of the f-θ lens 126 makes it possible to make the intervals between the dispersed wavelengths imaged on the light receiving element array 127 substantially equal, thereby facilitating output signal processing of the light receiving element array 127.

  8 and 9 are specific examples of light receiving element arrays used in the invention for compensating dark current. In the light receiving element array, as described above, a plurality of light receiving elements D are arranged along the wavelength dispersion direction, and a light receiving element D ′ that is not used for light reception is prepared in a part of them, and the dark current is measured. Then, dark current correction calculation processing of the light receiving element D used for other light reception is performed. FIG. 8 shows an example in which elements at both ends in the arrangement direction are not used for light reception, and FIG. 9 shows an example in which light reception elements D ′ not used for light reception are provided separately along the arrangement direction. .

  The light receiving elements D 'that are not used for light reception are shielded from light by covering them with a mask or the like in advance.

An example of dark current correction calculation processing of the light receiving element D will be described.
<Example 1>
Assume that the output current of the light receiving element D used for light reception is measured as 200 pA in a state where the dark current of the light receiving element D ′ not used for light reception is measured as 1 pA. The current IL generated by the incident light of the light receiving element D in this case is
IL = 200-1 = 199 pA
And

<Example 2>
When the dark currents of the light receiving elements D ′ at both ends not used for light reception are measured as 1 pA and 1.1 pA, the dark current of the light receiving element D used for light reception is set to an average value of 1.05 pA.
<Example 3>
When the dark currents of the light receiving elements D ′ at both ends not used for light reception are measured as 1 pA and 1.1 pA, for example, when nine light receiving elements D used for light reception are arranged, the respective dark currents are set to 1.01. , 1.02,... 1.08, 1.09 pA.

<Example 4>
When the dark current of the light receiving element D used for light reception is determined to be 1.1 pA in advance, the dark current of the light receiving element D ′ not used for light reception is measured as 1 pA. Assuming that 2 pA is measured, the dark current of the light receiving element D is
1.1 * (1.2 / 1.0) = 1.32 pA
And

  8 and 9, when measuring dark current, it is necessary to move the light shield on the upper surface of the light receiving element or to mechanically block the incident light of the light receiving element by a part of the optical system reaching the light receiving element. Rather, the power of light incident on the light receiving element D used for light reception can be measured with high accuracy.

  The light receiving element used for light reception is not limited to the light receiving element array, and a plurality of light receiving elements for detecting a single wavelength can be used as long as they have a light receiving element for dark current measurement that is not used for light receiving. The light receiving elements may be two-dimensionally arranged, or a single wavelength may be detected by a single light receiving element.

  FIG. 10 is a block diagram showing another embodiment of the present invention, and the same reference numerals are given to the portions common to FIG. The difference between FIGS. 10 and 14 is that an optical element 128 such as a wavelength temperature characteristic compensating prism or wedge is disposed between the collimating lens 2 and the diffraction grating 3.

The wavelength temperature characteristic compensation operation by the optical element 128 will be described with reference to the light refraction diagram of the wedge plate in FIG.
First, the basic formula corresponding to the light refracted by the wedge plate is as follows.

Assuming that the incident angle θ ₁ is constant, this is differentiated by temperature as follows.

となる。 When these are organized,

It becomes.

になり、 When θ ₃ = θ ₄ = 0,

become,

になる。 When θ ₁ = θ ₂ = 0,

become.

  When the synthetic quartz and Si are calculated at a wavelength of 1.55 μm using the above equation, the result is as shown in FIG.

Next, compensation with the incident light of the diffraction grating 3 will be described.
By combining Equations 1 and 19, it is possible to express the incident light of the diffraction grating 3 with the wedge plate 128 inserted as an optical element.

になる。 Unlike i, since i is no longer constant,

become.

になり、 Substituting Equation 21,

become,

となる。 When θ ₃ = θ ₄ = 0 or θ ₁ = θ ₂ = 0,

It becomes.

が求められる。 In order to set the temperature coefficient dθ / dT = 0, from Equations 26 and 27,

Is required.

Using actual parameters, the value on the left side of Equation 28 is determined to be approximately 3.8 × 10 ^{−6 [} [rad / ° C.], and it can be seen from the results of FIG. 12 that θ _p increases in synthetic quartz. For Si, θ _p is less than 2 °, and it can be seen that this can be realized with a thin wedge plate.

  In FIG. 10, the wedge is arranged on the incident side of the diffraction grating 3 to compensate, but it is obvious that the wedge can be arranged on the emission side of the diffraction grating 3 to compensate.

  FIG. 13 is a block diagram showing another embodiment of the present invention, and parts common to FIG. 17 are given the same reference numerals. The difference between FIG. 13 and FIG. 17 is that the output side waveguide that transmits the output light of the output side slab waveguide 18 to the outside is removed, and the output light of the output side slab waveguide 18 is directly received by each light receiving element of the light receiving element array 23. It is made to inject into, and the polychromator is comprised.

In FIG. 13, the angular dispersion is

m: diffraction order, d: array waveguide pitch, n _s : slab waveguide effective refractive index,
n _c: array waveguide effective refractive index, _{n g:} group index,
ΔL: Waveguide length difference of the arrayed waveguide, λ ₀ : Center wavelength

Therefore, the linear dispersion, that is, the wavelength dependence of the focusing position is

It becomes. Here, f is the focal length of the output side slab waveguide 18.
For example, if n _g = 1.4752, n _s = 1.4529, d = 25 μm, ΔL = 77 μm, f = 100 mm, dx / dλ is almost 201.8 μm / nm, and two spectra at intervals of 0.4 nm Is separated from 201.8 * 0.4 at about 80.7 μm on the light receiving element array.
In other words, assuming that light is received by a light receiving element array in which light receiving elements are arranged at a pitch of 20 μm, about 4 light receiving elements are used per one WDM signal with an interval of 0.4 nm. Measurement is also possible.

At this time, the spatial free spectrum range X _FSR (the distance between the focal positions where the m-th order and (m + 1) -th order diffracted light are collected with respect to the same wavelength) is obtained by X _FSR = λ ₀ f / n _s d. Is about 4.27 mm. Therefore, the wave number that can be demultiplexed is from 4.27 mm / 80.7 μm to almost 52 waves.

According to the configuration shown in FIG. 13, since the main component parts are the solid AWG and the light receiving element array, the size can be reduced and adjustment is not necessary.
And since it is the structure of a polychromator, a wavelength measurement can also be performed.

It is a block diagram which shows an example of embodiment of this invention. It is operation | movement explanatory drawing of FIG. It is a block diagram which shows the other example of embodiment of this invention. It is operation | movement explanatory drawing of FIG. It is a block diagram which shows the other example of embodiment of this invention. It is a block diagram which shows the other example of embodiment of this invention. It is a block diagram which shows the other example of embodiment of this invention. It is a structural example figure of the light receiving element row | line | column used by this invention. It is another structural example figure of the light receiving element row | line | column used by this invention. It is a block diagram which shows the other example of embodiment of this invention. It is operation | movement explanatory drawing of the wedge board of FIG. It is a refractive temperature characteristic figure of the wedge board of FIG. It is a block diagram which shows the other example of embodiment of this invention. It is an example of a conventional spectroscopic device. It is another example of a conventional spectroscopic device. It is another example of a conventional spectroscopic device. It is another example of a conventional spectroscopic device. It is an example of the measurement characteristic of the apparatus of FIG.

Explanation of symbols

101, 109, 118 Incident end 102, 110, 112, 114, 116, 119, 121 Lens 103, 111, 115, 120, 125 Diffraction grating (wavelength dispersion element)
104 Mirror 106, 117, 124, 127 Light-receiving element array 122 DMD
123 Slit 126 f-θ lens 128 Optical element

Claims (3)

A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
Using a light receiving element array in which a plurality of light receiving elements are arranged in a wavelength dispersion direction as the light receiving element,
A spectroscopic device using an f-θ lens as means for condensing light on the light receiving element array. A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
Using a light receiving element array in which a plurality of light receiving elements are arranged in a wavelength dispersion direction as the light receiving element,
A spectroscopic device characterized in that a part of these light receiving elements is used for dark current detection. A spectroscopic device that obtains detection signals separated by wavelength by dispersing measurement light with a wavelength dispersion element and making it incident on a light receiving element,
An optical element having a refractive index temperature characteristic for correcting a wavelength temperature characteristic of the wavelength dispersion element is provided in an optical path leading to the light receiving element.

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