JP7195189B2 - Spectrometer - Google Patents

Description

The present disclosure relates to spectrometers.

2. Description of the Related Art Conventionally, in order to obtain high resolution or sharp filter characteristics in a wavelength region, for example, a multipass spectroscope is known in which light to be measured is made to enter a diffraction grating a plurality of times and pass through a plurality of slits.

For example, Patent Document 1 discloses a multipath spectrometer in which part of scattered light generated in a spectroscopic system before the final spectroscopic system follows the same optical path as diffracted light in the final spectroscopic system. Disclosed is a spectrometer that suppresses the degradation of resolution and dynamic range in spectral characteristics that occurs in .

JP 2009-175038 A

The filter characteristics of multipass spectrometers using conventional technology may be insufficient in measuring the spectral characteristics of optical devices that have been newly developed due to the rapid technological progress of recent years.

An object of the present disclosure is to provide a multi-pass type spectroscope with improved filter characteristics.

A spectroscope according to some embodiments is a spectroscope that disperses incident light under measurement, comprising: a diffraction grating; a collimator that parallelizes the incident light; a plurality of spectroscopic systems each having an optical element arranged at a position where the return light from the diffraction grating of the light incident on the grating is focused and allowing at least part of the return light to pass through; and at least one folding optical system that guides the return light generated in one of the spectral systems to the other spectral system, wherein the folding optical system is one of the optical systems. A first lens for collimating the return light generated in the spectroscopic system, and a second lens for condensing the return light collimated by the first lens with the collimator of the other spectroscopic system. a lens; According to such a spectroscope, filter characteristics are improved in a multi-pass spectroscope. Therefore, such a spectroscope can satisfy the filter characteristics required for measuring recent optical devices.

In one embodiment, the optical element of one of the spectroscopic systems is such that return light from the diffraction grating is focused by the collimator between the collimator of the one of the spectroscopic systems and the first lens. position. Thereby, the spectroscopic system and the folding optical system are completely separated. The folding optical system can return the light dispersed by one spectroscopic system to another spectroscopic system.

In one embodiment, the four spectroscopic systems and the two folding optical systems are provided, and the one folding optical system is a first spectroscopic system through which the light to be measured that enters the spectroscope first passes. The returned light generated in is guided to return toward a second spectral system adjacent to the first spectral system, and the other folding optical system is generated in a third spectral system adjacent to the second spectral system. The returned light may be guided so as to be returned toward a fourth spectroscopic system adjacent to the third spectroscopic system. As a result, when the bandwidth of the filter characteristics of the spectroscope is set to be wide, the spectrum obtained by the entire spectroscope can be improved compared to a spectroscope with four spectroscopes and three folding optical systems. Deterioration of the filter characteristic that is used is suppressed.

In one embodiment, a mirror element is provided on which the return light from the diffraction grating is incident, and the return light that has entered the mirror element is reflected by the mirror element, re-enters the diffraction grating, and passes through the collimator. may be guided to the optical element via. As a result, the light to be measured is dispersed twice by the diffraction grating in each spectroscopic system and passes through each optical element. Therefore, the filter characteristics obtained by the spectroscope become sharper.

In one embodiment, the folding optical system includes a first mirror that reflects the return light collimated by the first lens toward an extending direction of ruled lines of the diffraction grating, and the first mirror. and a second mirror that reflects the reflected return light toward the diffraction grating and guides it to the second lens. Thereby, the folding optical system can return the light dispersed and spectroscopically by one spectroscopic system to the other spectroscopic system.

In one embodiment, the folding optical system includes a first mirror that reflects the return light in an extending direction of ruled lines of the diffraction grating and guides it to the first lens, and the second lens. and a second mirror that reflects the return light toward the diffraction grating. This makes it possible to shorten the total length of the spectroscope in the light propagation direction orthogonal to the extending direction of the ruled lines of the diffraction grating.

According to the present disclosure, it is possible to provide a multi-pass type spectroscope with improved filter characteristics.

1 is a schematic diagram showing the configuration of a spectroscope according to a first embodiment; FIG. FIG. 5 is a schematic diagram showing the configuration of a spectroscope according to a second embodiment; 3 is a graph showing an example of filter characteristics obtained by the spectroscope of FIG. 2; FIG. FIG. 11 is a schematic diagram showing the configuration of a spectroscope according to a third embodiment; 5 is a graph showing an example of filter characteristics obtained by the spectroscope of FIG. 4; FIG. FIG. 11 is a schematic diagram showing the configuration of a spectroscope according to a fourth embodiment; FIG. 7 is a graph corresponding to FIG. 5 and showing an example of filter characteristics obtained by the spectroscope of FIG. 6; 7 is a schematic diagram corresponding to FIG. 6, showing a modification of the spectroscope according to the fourth embodiment; FIG. It is a schematic diagram which shows the 1st modification of a folding optical system. It is a schematic diagram which shows the 2nd modification of a folding optical system. FIG. 4 is a graph showing an example of filter characteristics obtained by a conventional double-pass spectrometer;

For example, as a conventional multi-pass spectroscope used in an optical spectrum analyzer or the like, a Littrow-type double-pass spectroscope as described in Patent Document 1 is known. Such a double pass spectrometer has a diffraction grating, two collimators and two slits. In the double-pass spectrometer, for example, light to be measured emitted from a light guide component such as an optical fiber is collimated by a first collimator and made incident on a diffraction grating. In the double-pass spectroscope, the diffracted light from the diffraction grating is condensed by the first collimator and passed through the first slit. In the double-pass spectrometer, the diffracted light that has passed through the first slit is collimated again by the second collimator and made incident on the diffraction grating. The double-pass spectroscope collects the diffracted light by the second collimator and passes it through the second slit.

As described above, the conventional double-pass spectrometer has a first spectroscopic system that includes the optical path immediately after the light guide component to the first slit, and a second spectroscopic system that includes the optical path after the first slit to the second slit. The light to be measured passes through the first spectroscopic system and the second spectroscopic system in this order. In the conventional double-pass spectroscope having such a configuration, the light under measurement is dispersed and dispersed in the first spectral system, and the light to be measured dispersed and dispersed by the first spectral system is further dispersed and dispersed in the second spectral system. Therefore, a filter characteristic similar to that obtained when two optical filters are arranged in series in the optical path of the light to be measured can be obtained. The filter characteristics are determined based on arbitrary indexes relating to the filter, such as center wavelength, bandwidth, suppression ratio, wavelength slope width, and stopband.

FIG. 10 is a graph showing an example of filter characteristics obtained by a conventional double-pass spectroscope. The vertical axis in FIG. 10 indicates the attenuation rate of light (unit: dB). The horizontal axis of FIG. 10 indicates the offset (unit: nm) from the center wavelength of the light to be measured. In FIG. 10, the thin solid line indicates the optical spectrum of the light under measurement. A dashed-dotted line indicates an example of filter characteristics obtained by the first spectroscopic system. A dashed line indicates an example of filter characteristics obtained by the second spectroscopic system. A thick solid line indicates an example of filter characteristics obtained by the entire double-pass spectroscope when the filter characteristics of the first spectral system and the filter characteristics of the second spectral system are combined. According to the conventional double-pass spectroscope, filter characteristics similar to those obtained when two optical filters are arranged in series are obtained, and filter characteristics as shown in FIG. 10 are obtained.

For example, in the filter characteristics obtained by a conventional double-pass spectroscope, the suppression ratio is increased by synthesizing the filter characteristics of the first spectral system and the filter characteristics of the second spectral system. That is, in the filter characteristics after synthesis, the amount of light attenuation increases more remarkably as the offset from the center wavelength increases, compared to the filter characteristics before synthesis.

On the other hand, the bandwidth of the filter characteristics of the conventional double-pass spectrometer is determined by the bandwidth of the filter characteristics of the first spectroscopic system calculated by the width of the first slit, and is determined by the width of the second slit of the second spectroscopic system. does not depend on That is, the bandwidth of the filter characteristics of the conventional double-pass spectroscope is limited by the bandwidth of the filter characteristics obtained by the first spectroscopic system, no matter how narrow the width of the second slit of the second spectroscopic system. This is because the light to be measured that has undergone dispersion spectroscopy in the first spectroscopic system is subjected to subtractive dispersion spectroscopy in the second spectroscopic system, and the amount of dispersion is canceled in the second slit. More specifically, the position of the beam spot of the diffracted light on the first slit varies according to the rotation of the diffraction grating, but the position of the beam spot of the diffracted light on the second slit varies depending on the diffraction grating. This is because it does not fluctuate even if is rotated and is constant.

For example, the technological development of optical devices in the recent optical fiber communication market has been rapid, and the optical noise level of light-emitting devices has been kept to an extremely low level. For example, the signal-to-noise ratio is 80 dB or more. In order to analyze the internal structure of such an optical device, it is also important to measure the optical spectrum in the vicinity of the emission wavelength. However, the filter characteristics of the multipath spectroscope using the conventional technique may be insufficient for measuring recent optical devices. For example, as shown in FIG. 10, the optical spectrum of the light to be measured is completely buried in the filter characteristics of a conventional multipass spectroscope. Therefore, when the light to be measured is measured while sweeping the center wavelength of the filter using such a spectroscope, the obtained optical spectrum reflects the filter characteristics of the conventional multi-pass spectroscope. In other words, it is difficult to measure the original line width, sideband structure, etc. of the optical spectrum of the light to be measured with the conventional multipath spectroscope.

An object of the present disclosure is to provide a multi-pass spectroscope with improved filter characteristics in order to solve the above problems.

An embodiment of the present disclosure will be mainly described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing the configuration of a spectroscope 1 according to the first embodiment. The configuration of the spectroscope 1 according to the first embodiment will be mainly described with reference to FIG.

The spectroscope 1 according to the first embodiment splits the light to be measured L1 that is emitted from the light guide component 2 such as an optical fiber and is incident on the spectroscope 1, for example. The spectroscope 1 has a diffraction grating 11, a plurality of spectroscopic systems S, and at least one folding optical system T. The spectroscope 1 according to the first embodiment has two spectroscopic systems S and one folding optical system T. As shown in FIG. In the following, when distinguishing between the two optical systems S, they are referred to as a first optical system S1 and a second optical system S2.

The diffraction grating 11 is a reflector plate having a plurality of ruled lines C extending in parallel at regular intervals. The diffraction grating 11 disperses the light incident on the diffraction grating 11 and emits the diffracted light as return light. The diffraction grating 11 can be rotated around a rotation axis R at the center of the diffraction grating 11 extending parallel to the extending direction Y of the ruled lines C by an arbitrary driving mechanism. The diffraction grating 11 can arbitrarily change the apparent intervals of the ruled lines C with respect to the incident light.

Each of the multiple spectroscopic systems S has a collimator 12 that collimates the light incident on the spectroscopic system S. As shown in FIG. The collimator 12 collects the return light from the diffraction grating 11 of the light collimated by the collimator 12 and incident on the diffraction grating 11 . The collimator 12 is arranged between the incident side of the spectroscopic system S and the diffraction grating 11 . Collimator 12 includes, for example, a collimation lens.

The plurality of spectroscopic systems S are arranged at positions where the return light from the diffraction grating 11 of the light collimated by the collimator 12 and incident on the diffraction grating 11 is focused, and is an optical element that transmits at least part of the return light. 13 each. For example, the optical element 13 is arranged at a position where the return light from the diffraction grating 11 is focused by the collimator 12 . The optical element 13 includes arbitrary optical elements such as slits, pinholes, and apertures.

The first optical system S1 is arranged closest to the light guide component 2 in the extending direction Y of the ruled line C. As shown in FIG. That is, the first spectroscopic system S1 allows the light to be measured L1, which is emitted from the light guide component 2 and has entered the spectroscope 1, to pass through first among the plurality of spectroscopic systems S. As shown in FIG. The first optical system S<b>1 has a first collimator 121 and a first optical element 131 . In addition, the first optical system S<b>1 includes an optical path from the optical path portion of the light L<b>1 to be measured immediately after exiting the light guide component 2 to the first optical element 131 .

The light to be measured L<b>1 that is emitted from the light guide component 2 and enters the first optical system S<b>1 while diffusing becomes parallel light by the first collimator 121 . The light to be measured L<b>1 collimated by the first collimator 121 enters the diffraction grating 11 . At this time, diffracted light L2 is generated as the return light from the diffraction grating 11 based on the light to be measured L1 that has entered the diffraction grating 11 . The diffracted light L2 passes through the first collimator 121 and is focused at the position where the first optical element 131 is arranged. At least part of the diffracted light L2 passes through the first optical element 131 .

The second optical system S2 is arranged on the opposite side of the light guide component 2 from the first optical system S1 in the extending direction Y of the ruled line C. As shown in FIG. The second optical system S2 allows the light L3 emitted from the first optical system S1 and the folding optical system T to pass therethrough. The second optical system S2 has a second collimator 122 and a second optical element 132 . In addition, the second optical system S2 includes an optical path from the optical path portion of the light L3 immediately after exiting the folding optical system T to the second optical element 132. FIG.

The light L3 incident on the second optical system S2 is collimated by the second collimator 122 . The light L3 collimated by the second collimator 122 enters the diffraction grating 11 . At this time, diffracted light L 4 is generated as light returned from the diffraction grating 11 based on the light L 3 incident on the diffraction grating 11 . The diffracted light L4 passes through the second collimator 122 and is focused at the position where the second optical element 132 is arranged. At least part of the diffracted light L4 passes through the second optical element 132 .

The folding optical system T guides the return light generated in one of the two adjacent optical systems S to the other optical system S so as to return the light. The folding optical system T includes a first lens 14 for collimating return light generated in one spectroscopic system S, and a collimator 12 of another spectroscopic system S for returning light collimated by the first lens 14 . and a second lens 15 that collects light therebetween.

For example, the folding optical system T guides the diffracted light L2 generated in the first optical system S1 of the adjacent first optical system S1 and the second optical system S2 so as to return it toward the second optical system S2. In the folding optical system T, for example, the first lens 14, the first mirror 16, the second mirror 17, and the second lens 15 are arranged in order from the incident side of the diffracted light L2 toward the exit side.

The first lens 14 collimates the diffracted light L2 generated in the first optical system S1. The first lens 14 is arranged so as to sandwich the first optical element 131 of the first spectroscopic system S1 together with the first collimator 121 of the first spectroscopic system S1. The first mirror 16 reflects the diffracted light L2 collimated by the first lens 14 toward the extending direction Y of the ruled lines C of the diffraction grating 11 . The second mirror 17 reflects the diffracted light L2 reflected by the first mirror 16 toward the diffraction grating 11 and guides it to the second lens 15 . The second lens 15 collects the diffracted light L2 collimated by the first lens 14 between the second collimator 122 of the second spectroscopic system S2 and the second lens 15 .

The diffracted light L2 is focused once at the position where the first optical element 131 of the first optical system S1 is arranged, and then enters the first lens 14 while diffusing. The diffracted light L2 is collimated by the first lens 14 and reflected by the first mirror 16 and the second mirror 17 as parallel light. The diffracted light L2 enters the second lens 15 and is focused between the second collimator 122 of the second spectroscopic system S2 and the second lens 15 .

According to the spectrometer 1 according to the first embodiment, filter characteristics similar to those obtained when two optical filters are arranged in series in the optical path of the light L1 to be measured can be obtained. More specifically, the filter characteristics of the entire spectroscope 1 are obtained by synthesizing the filter characteristics of the first optical system S1 and the filter characteristics of the second optical system S2. For example, the bandwidth BW1 of the filter characteristics of the first optical system S1 and the bandwidth BW2 of the filter characteristics of the second optical system S2 are represented by the following equations 1 and 2, respectively.

[Number 1]
_BW1 = ε1・d/(m・f)・cos(β) (Formula 1)
[Number 2]
BW2 = ε2・d/(m・2f)・cos(β) (Formula ₂ )

Here, ε ₁ and ε ₂ are widths through which light can pass in the first optical element 131 and the second optical element 132, respectively. For example, if the optical element 13 is a slit, ε ₁ and ε ₂ are the slit widths of the corresponding slits. d is the groove interval of the diffraction grating 11, m is the number of diffraction orders, f is the focal length of the collimator 12, and β is the angle between the normal line of the diffraction grating 11 and the output direction of the diffracted light. For example, the slit widths ε ₁ and ε ₂ are determined so that the bandwidth of each filter characteristic satisfies bandwidth BW1>bandwidth BW2.

According to the spectroscope 1 according to the first embodiment as described above, compared with the conventional double-pass spectroscope, the bandwidth and wavelength slope width of the filter characteristics obtained by the entire spectroscope 1 are narrower, and sharper Filter characteristics are obtained. In the spectroscope 1, the light to be measured L1 that has undergone dispersive spectroscopy in the first spectroscopic system S1 is also additively dispersive spectroscopically in the second spectroscopic system S2. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is determined by the narrower of the bandwidths of the filter characteristics obtained by the first optical system S1 and the second optical system S2. For example, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is determined by the bandwidth BW2. Referring to Equation 2 above, the effective doubling of the focal length f of the collimator 12 into the denominator makes the bandwidth BW2 narrower than in a conventional double-pass spectrometer. Become. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is narrowed.

For example, in the filter characteristics obtained by the spectroscope 1 according to the first embodiment, the suppression ratio is increased by synthesizing the filter characteristics of the first optical system S1 and the filter characteristics of the second optical system S2. That is, in the filter characteristics after synthesis, the amount of light attenuation increases more remarkably as the offset from the center wavelength increases, compared to the filter characteristics before synthesis.

(Second embodiment)
FIG. 2 is a schematic diagram showing the configuration of the spectroscope 1 according to the second embodiment. The configuration of the spectroscope 1 according to the second embodiment will be mainly described with reference to FIG.

A spectroscope 1 according to the second embodiment differs from the first embodiment in that it has three spectroscopic systems S and two folding optical systems T. FIG. Hereinafter, when distinguishing between the three optical systems S, they are referred to as a first optical system S1, a second optical system S2, and a third optical system S3. Similarly, when distinguishing the two folding optical systems T from each other, they are referred to as a first folding optical system T1 and a second folding optical system T2. Other configurations, functions, effects, modifications, and the like are the same as those of the first embodiment, and the corresponding description also applies to the spectroscope 1 according to the second embodiment. Below, the same reference numerals are given to the same components as in the first embodiment, and the description thereof will be omitted. Differences from the first embodiment will be mainly described.

The first optical system S1, the first folding optical system T1, and the second optical system S2 are the same as the first optical system S1, the folding optical system T, and the second optical system S2 in the first embodiment, respectively. The first folding optical system T1 has a first lens 141, a second lens 151, a first mirror 161, and a second mirror 171, like the folding optical system T in the first embodiment. In the spectroscope 1 according to the second embodiment, a second folding optical system T2 and a third spectroscopic system S3 are additionally arranged.

For example, the second folding optical system T2 folds the diffracted light L4 generated in the second optical system S2 of the adjacent second optical system S2 and the third optical system S3 toward the third optical system S3. lead. In the second folding optical system T2, for example, the first lens 142, the first mirror 162, the second mirror 172, and the second lens 152 are arranged in order from the incidence side of the diffracted light L4 toward the emission side.

The first lens 142 collimates the diffracted light L4 generated in the second optical system S2. The first lens 142 is arranged to sandwich the second optical element 132 of the second spectroscopic system S2 together with the second collimator 122 of the second spectroscopic system S2. The first mirror 162 reflects the diffracted light L4 collimated by the first lens 142 toward the extending direction Y of the ruled lines C of the diffraction grating 11 . The second mirror 172 reflects the diffracted light L4 reflected by the first mirror 162 toward the diffraction grating 11 and guides it to the second lens 152 . The second lens 152 converges the diffracted light L4 collimated by the first lens 142 between the third collimator 123 of the third spectroscopic system S3 and the second lens 152, which will be described later.

The diffracted light L4 is focused once at the position where the second optical element 132 of the second optical system S2 is arranged, and then enters the first lens 142 while diffusing. The diffracted light L4 is collimated by the first lens 142 and reflected by the first mirror 162 and the second mirror 172 as parallel light. The diffracted light L4 enters the second lens 152 and is focused between the second lens 152 and the third collimator 123 of the third spectroscopic system S3, which will be described later.

The third optical system S3 is arranged on the opposite side of the light guide component 2 from the second optical system S2 in the extending direction Y of the ruled line C. As shown in FIG. The third optical system S3 passes the light L5 emitted from the second folding optical system T2. The third spectroscopic system S3 has a third collimator 123 and a third optical element 133 . In addition, the third optical system S3 includes an optical path from the optical path portion of the light L5 immediately after exiting the second folding optical system T2 to the third optical element 133.

The light L5 incident on the third optical system S3 is collimated by the third collimator 123 . The light L5 collimated by the third collimator 123 enters the diffraction grating 11 . At this time, diffracted light L6 is generated as light returned from the diffraction grating 11 based on the light L5 incident on the diffraction grating 11 . The diffracted light L6 passes through the third collimator 123 and is focused at the position where the third optical element 133 is arranged. At least part of the diffracted light L6 passes through the third optical element 133 .

In the spectroscope 1 according to the second embodiment, the light to be measured L1 is dispersedly dispersed by the first optical system S1, and the light to be measured L1 dispersed by the first optical system S1 is further dispersed by the second optical system S2. Dispersive spectroscopy. Furthermore, in the spectrometer 1 according to the second embodiment, the light to be measured L1 dispersed by the second spectroscopic system S2 is dispersed by the third spectroscopic system S3. Therefore, good filter characteristics similar to those obtained when three optical filters are arranged in series in the optical path of the light L1 to be measured can be obtained.

FIG. 3 is a graph showing an example of filter characteristics obtained by the spectroscope 1 of FIG. The vertical axis in FIG. 3 indicates the attenuation rate of light (unit: dB). The horizontal axis of FIG. 3 indicates the offset (unit: nm) from the center wavelength of the light L1 to be measured. In FIG. 3, the thin solid line indicates the optical spectrum of the light L1 under measurement. A dashed-dotted line indicates an example of filter characteristics obtained by the first optical system S1. A dashed line indicates an example of filter characteristics obtained by the second optical system S2. A dotted line indicates an example of filter characteristics obtained by the third optical system S3. A thick solid line indicates an example of filter characteristics obtained by the entire spectroscope 1 when all the filter characteristics of the first optical system S1, the second optical system S2, and the third optical system S3 are combined.

The filter characteristics of the entire spectroscope 1 are obtained by synthesizing all the filter characteristics of the first optical system S1, the second optical system S2, and the third optical system S3. For example, the bandwidth BW1 of the filter characteristics of the first optical system S1 and the bandwidth BW2 of the filter characteristics of the second optical system S2 are expressed by the above equations 1 and 2, respectively. The bandwidth BW3 of the filter characteristics of the third optical system S3 is represented by Equation 3 below.

[Number 3]
BW3 = _ε3・d/(m・3f)・cos(β) (Formula 3)

Here, ε ₃ is the width through which light can pass in the third optical element 133 . For example, if the _third optical element 133 is a slit, ε3 is the slit width of the corresponding slit. Each of d, m, f, and β is the same as described in Equations 1 and 2. For example, the slit widths ε ₁ , ε ₂ , and ε ₃ are determined so that the bandwidth of each filter characteristic satisfies bandwidth BW1>bandwidth BW2>bandwidth BW3.

According to the spectroscope 1 according to the second embodiment as described above, compared with the first embodiment, the bandwidth and wavelength slope width of the filter characteristics obtained by the entire spectroscope 1 are further narrowed, and sharper Filter characteristics are obtained. In the spectroscope 1 according to the second embodiment, the light to be measured L1 dispersed by the first optical system S1 is additively dispersed by the second optical system S2 and the third optical system S3. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is determined by the narrowest bandwidth among the bandwidths of the filter characteristics obtained by the first optical system S1, the second optical system S2, and the third optical system S3. be done. For example, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is determined by the above bandwidth BW3. Referring to Equation 3 above, the effective tripled focal length f of the collimator 12 is included in the denominator, so that the bandwidth BW3 is narrower than in the first embodiment. Become. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 according to the second embodiment is further narrowed.

For example, as shown in FIG. 3, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is sufficiently narrower than the wavelength interval between the central peak and adjacent sideband peaks in the optical spectrum of the light L1 to be measured. Therefore, when the spectroscope 1 according to the second embodiment is used to measure the light L1 under measurement while sweeping the center wavelength of the filter, the obtained optical spectrum reflects the bandwidth of the filter characteristics of the spectroscope 1. , clearly shows the sideband structure in the optical spectrum of the light L1 to be measured. For example, in order to analyze the internal structure of an optical device, it becomes possible to measure the optical spectrum in the vicinity of the emission wavelength. Thus, the spectrometer 1 according to the second embodiment can also satisfy the filter characteristics required for measuring recent optical devices.

(Third embodiment)
FIG. 4 is a schematic diagram showing the configuration of the spectroscope 1 according to the third embodiment. The configuration of the spectroscope 1 according to the third embodiment will be mainly described with reference to FIG.

A spectroscope 1 according to the third embodiment differs from the first and second embodiments in that it has four spectroscopic systems S and three folding optical systems T. FIG. Hereinafter, when distinguishing between the four optical systems S, they are referred to as a first optical system S1, a second optical system S2, a third optical system S3, and a fourth optical system S4. Similarly, when distinguishing the three folding optical systems T from each other, they are referred to as a first folding optical system T1, a second folding optical system T2, and a third folding optical system T3. Other configurations, functions, effects, modifications, and the like are the same as those of the first and second embodiments, and the corresponding description also applies to the spectroscope 1 according to the third embodiment. Below, the same reference numerals are given to the same components as in the first and second embodiments, and the description thereof will be omitted. Differences from the first embodiment and the second embodiment will be mainly described.

The first optical system S1, the first folding optical system T1, the second optical system S2, the second folding optical system T2, and the third optical system S3 have exactly the same configurations as in the second embodiment. In the spectrometer 1 according to the third embodiment, a third folding optical system T3 and a fourth spectroscopic system S4 are additionally arranged.

For example, the third folding optical system T3 folds the diffracted light L6 generated in the third optical system S3 of the adjacent third optical system S3 and fourth optical system S4 toward the fourth optical system S4. lead. In the third folding optical system T3, for example, the first lens 143, the first mirror 163, the second mirror 173, and the second lens 153 are arranged in order from the incident side of the diffracted light L6 toward the exit side.

The first lens 143 collimates the diffracted light L6 generated in the third optical system S3. The first lens 143 is arranged to sandwich the third optical element 133 of the third spectroscopic system S3 together with the third collimator 123 of the third spectroscopic system S3. The first mirror 163 reflects the diffracted light L6 collimated by the first lens 143 toward the extending direction Y of the ruled lines C of the diffraction grating 11 . The second mirror 173 reflects the diffracted light L6 reflected by the first mirror 163 toward the diffraction grating 11 and guides it to the second lens 153 . The second lens 153 converges the diffracted light L6 collimated by the first lens 143 between the second lens 153 and a fourth collimator 124 of the fourth spectroscopic system S4, which will be described later.

The diffracted light L6 is once focused at the position where the third optical element 133 of the third optical system S3 is arranged, and then enters the first lens 143 while diffusing. The diffracted light L6 is converted into parallel light by the first lens 143 and reflected by the first mirror 163 and the second mirror 173 as parallel light. The diffracted light L6 enters the second lens 153 and is focused between the second lens 153 and the fourth collimator 124 of the fourth spectroscopic system S4, which will be described later.

The fourth optical system S4 is arranged on the opposite side of the light guide component 2 from the third optical system S3 in the extending direction Y of the ruled line C. As shown in FIG. The fourth optical system S4 passes the light L7 emitted from the third folding optical system T3. The fourth optical system S4 has a fourth collimator 124 and a fourth optical element 134 . In addition, the fourth optical system S4 includes an optical path from the optical path portion of the light L7 immediately after exiting the third folding optical system T3 to the fourth optical element 134. FIG.

The light L7 incident on the fourth optical system S4 is collimated by the fourth collimator 124 . The light L 7 collimated by the fourth collimator 124 enters the diffraction grating 11 . At this time, diffracted light L8 is generated as light returned from the diffraction grating 11 based on the light L7 incident on the diffraction grating 11. FIG. The diffracted light L8 passes through the fourth collimator 124 and is focused at the position where the fourth optical element 134 is arranged. At least part of the diffracted light L8 passes through the fourth optical element 134 .

In the spectrometer 1 according to the third embodiment, the light to be measured L1 is dispersedly dispersed by the first optical system S1, and the light to be measured L1 dispersed by the first optical system S1 is further dispersed by the second optical system S2. Dispersive spectroscopy. Further, in the spectrometer 1 according to the third embodiment, the light to be measured L1 dispersed by the second optical system S2 is dispersed by the third optical system S3, and the light to be measured L1 dispersed by the third optical system S3 is dispersed. The measurement light L1 is dispersed and spectroscopically dispersed by the fourth spectroscopic system S4. Therefore, it is possible to obtain good filter characteristics similar to those obtained by arranging four stages of optical filters in series in the optical path of the light L1 to be measured.

The filter characteristics of the entire spectroscope 1 are obtained by synthesizing all the filter characteristics of the first optical system S1, the second optical system S2, the third optical system S3, and the fourth optical system S4. For example, the bandwidth BW1 of the filter characteristics of the first optical system S1, the bandwidth BW2 of the filter characteristics of the second optical system S2, and the bandwidth BW3 of the filter characteristics of the third optical system S3 are expressed by the above equations 1 and 2 , and Equation 3, respectively. The bandwidth BW4 of the filter characteristics of the fourth optical system S4 is represented by Equation 4 below.

[Number 4]
BW4 = ε4・_d /(m・4f)・cos(β) (Formula 4)

Here, ε ₄ is the width through which light can pass in the fourth optical element 134 . For example, if the fourth optical element 134 is a slit, ε ₄ is the slit width of the corresponding slit. Each of d, m, f, and β is the same as described in Equations 1, 2, and 3. For example, the slit widths ε ₁ , ε ₂ , ε ₃ and ε ₄ are determined so that the bandwidth of each filter characteristic satisfies bandwidth BW1>bandwidth BW2>bandwidth BW3>bandwidth BW4.

According to the spectroscope 1 according to the third embodiment as described above, the bandwidth and wavelength inclination width of the filter characteristics obtained by the entire spectroscope 1 are narrower than those of the first and second embodiments. and sharper filter characteristics can be obtained. In the spectrometer 1 according to the third embodiment, the light to be measured L1 dispersed by the first optical system S1 is additively dispersed by the second optical system S2, the third optical system S3, and the fourth optical system S4. be done. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is Determined by the narrowest bandwidth. For example, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is determined by the bandwidth BW4. Referring to Equation 4 above, since the focal length f of the collimator 12 is effectively quadrupled and included in the denominator, the bandwidth BW4 is reduced compared to the first and second embodiments. but narrower. Therefore, the bandwidth of the filter characteristics obtained by the entire spectroscope 1 according to the third embodiment is further narrowed.

In this way, in addition to the case where the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is set to be narrower, for example, depending on the application of the optical spectrum analyzer, the bandwidth of the filter characteristics of the spectroscope 1 may be set to In some cases, it is set to be wide. FIG. 5 shows filter characteristics obtained by the spectroscope 1 according to the third embodiment in such a case.

FIG. 5 is a graph showing an example of filter characteristics obtained by the spectroscope 1 of FIG. The vertical axis in FIG. 5 indicates the attenuation rate of light (unit: dB). The horizontal axis of FIG. 5 indicates the offset (unit: nm) from the center wavelength of the light L1 to be measured. In FIG. 5, the dashed-dotted line indicates an example of filter characteristics obtained by the first optical system S1. A dashed line indicates an example of filter characteristics obtained by the second optical system S2. A dotted line indicates an example of filter characteristics obtained by the fourth optical system S4. A thick solid line indicates an example of filter characteristics obtained by the entire spectroscope 1 when all the filter characteristics of the first optical system S1, the second optical system S2, and the fourth optical system S4 are combined.

Note that the spectroscope 1 according to the third embodiment may have only one of the second optical element 132 and the third optical element 133, for example, as long as good filter characteristics are sufficiently maintained. . FIG. 5 illustrates filter characteristics when the third optical element 133 is omitted, for example, in the spectrometer 1 according to the third embodiment.

For example, when the bandwidth of the filter characteristics of the spectroscope 1 is set to be wide, if the relationship of bandwidth BW1>bandwidth BW2>bandwidth BW4 is to be established, each filter characteristic as shown in FIG. is obtained, and the filter characteristics obtained by the entire spectroscope 1 tend to deteriorate. More specifically, in the filter characteristics obtained by the entire spectroscope 1, the attenuation slope is wavy, and the attenuation of light does not increase smoothly as the offset from the central wavelength increases.

As described above, according to the spectroscope 1 according to the third embodiment, when the bandwidth of the filter characteristics obtained by the entire spectroscope 1 is set to be narrower, the A sharper filter characteristic can be obtained even when compared with . However, when the bandwidth of the filter characteristics of the spectroscope 1 is set to be wide, the filter characteristics tend to deteriorate. A spectroscope 1 according to a fourth embodiment described below solves such new problems.

(Fourth embodiment)
FIG. 6 is a schematic diagram showing the configuration of the spectroscope 1 according to the fourth embodiment. The configuration of the spectroscope 1 according to the fourth embodiment will be mainly described with reference to FIG.

The spectroscope 1 according to the fourth embodiment differs from the third embodiment in that it has a first folding mirror 191 and a second folding mirror 192 instead of the second folding optical system T2. That is, the spectrometer 1 according to the fourth embodiment has four spectroscopic systems S and two folding optical systems T. As shown in FIG. Other configurations, functions, effects, modifications, and the like are the same as those of the third embodiment, and the corresponding description also applies to the spectroscope 1 according to the fourth embodiment. Below, the same reference numerals are given to the same components as in the third embodiment, and the description thereof will be omitted. Differences from the third embodiment will be mainly described.

For example, the first folding mirror 191 is arranged between the second collimator 122 and the second optical element 132 of the second optical system S2. The second folding mirror 192 is arranged between the second optical element 132 of the second optical system S2 and the third collimator 123 of the third optical system S3.

The first folding mirror 191 reflects the diffracted light L4 generated in the second optical system S2 and converged by the second collimator 122 toward the extending direction Y of the ruled line C of the diffraction grating 11 . The second optical element 132 is arranged between the first folding mirror 191 and the second folding mirror 192 at a position where the diffracted light L4 from the diffraction grating 11 is focused by the second collimator 122 . The second folding mirror 192 reflects the diffracted light L 4 , which is reflected by the first folding mirror 191 and diffused after being focused at the position of the second optical element 132 , toward the diffraction grating 11 .

In the spectroscope 1 according to the fourth embodiment, the light to be measured L1 is dispersedly dispersed by the first optical system S1, and the light to be measured L1 dispersed by the first optical system S1 is added by the second optical system S2. dispersive spectroscopy. On the other hand, in the spectroscope 1 according to the fourth embodiment, the light to be measured L1 that has been additively dispersed by the first optical system S1 and the second optical system S2 is divided into the third optical system S3 and the fourth optical system S4. is subtractively dispersive. Therefore, the amount of dispersion is canceled in the third optical element 133 and the fourth optical element 134 . More specifically, the positions of the beam spots of the diffracted light L2 and the diffracted light L4 on the first optical element 131 and the second optical element 132 change according to the rotation of the diffraction grating 11. The positions of the beam spots of the diffracted light L6 and the diffracted light L8 on the optical element 133 and the fourth optical element 134 do not change even if the diffraction grating 11 rotates, and are constant.

FIG. 7 is a graph corresponding to FIG. 5, showing an example of filter characteristics obtained by the spectroscope 1 of FIG. The contents indicated by the vertical axis, the horizontal axis, and each line in FIG. 7 are the same as in FIG. Note that in FIG. 7, the dashed line indicating an example of the filter characteristics obtained by the second optical system S2 and the dotted line indicating an example of the filter characteristics obtained by the fourth optical system S4 are superimposed on each other.

As shown in FIG. 7, the bandwidth of the filter characteristics of the spectroscope 1 according to the fourth embodiment is determined by the bandwidth BW2 of the filter characteristics of the second spectroscopic system S2 calculated by ε ₂ in Equation 2, and the fourth It does not depend on the width ε ₄ through which light can pass through the fourth optical element 134 of the spectroscopic system S4. That is, the bandwidth of the filter characteristics of the spectroscope 1 according to the fourth embodiment is the filter characteristics obtained by the second spectroscopic system S2, no matter how narrow the width ε4 through which light can pass in the _fourth optical element 134. is limited by the bandwidth BW2 of .

For example, even if the filter characteristics of the spectroscope 1 according to the fourth embodiment are set such that the bandwidth of the filter characteristics of the spectroscope 1 is widened as in the third embodiment, It exhibits a smooth attenuation slope while maintaining the same bandwidth as . Therefore, when the bandwidth of the filter characteristics of the spectroscope 1 is set to be wide, deterioration of the filter characteristics obtained by the entire spectroscope 1 is suppressed as compared with the third embodiment.

It will be apparent to those skilled in the art that the present disclosure can be embodied in certain other forms than those described above without departing from the spirit or essential characteristics thereof. Accordingly, the preceding description is exemplary, and not limiting. The scope of the disclosure is defined by the appended claims rather than by the foregoing description. Any changes that fall within the range of equivalence are intended to be included therein.

For example, the shape, arrangement, orientation, number, and the like of each component described above are not limited to the contents illustrated in the above description and drawings. The shape, arrangement, orientation, number, and the like of each component may be arbitrarily configured as long as the function can be realized.

FIG. 8 is a schematic diagram corresponding to FIG. 6, showing a modification of the spectroscope 1 according to the fourth embodiment. FIG. 8 shows a modified example of the spectroscope 1 according to the fourth embodiment, but the same explanation as below also applies to the first to third embodiments.

For example, the spectroscope 1 in the above first to fourth embodiments has been described as being of the Littrow type, but is not limited to this. For example, the spectroscope 1 may further have a mirror element 18 on which return light from the diffraction grating 11 is incident. Mirror element 18 may be, for example, a plane mirror. The return light emitted from the diffraction grating 11 once enters the mirror element 18 , is reflected by the mirror element 18 , and enters the diffraction grating 11 again. The return light incident on the diffraction grating 11 again is guided to the optical element 13 via the collimator 12 .

According to the spectrometer 1 according to such a modified example, the light L1 to be measured is dispersed twice by the diffraction grating 11 in each spectroscopic system S and passes through each optical element 13 . Therefore, the filter characteristics obtained by the spectroscope 1 become sharper.

FIG. 9A is a schematic diagram showing a first modification of the folding optical system T. FIG. The first modification shown in FIG. 9A applies to all spectroscopes 1 according to the first to fourth embodiments.

For example, in the spectrometer 1 according to the first to fourth embodiments described above, the light emitted from the optical element 13 of the spectroscopic system S is described as being incident on the first lens 14 of the folding optical system T. Not limited. Instead of the spectrometer 1 in the above-described first to fourth embodiments in which the spectroscopic system S and the folding optical system T are completely separated, the folding optical system A mode in which T is included is also possible. More specifically, the folding optical system T may be arranged between the collimator 12 and the optical element 13 of the spectroscopic system S, as shown in FIG. 9A. At this time, the optical element 13 is arranged at a position where the return light from the diffraction grating 11 is focused by the second lens 15 of the folding optical system T. FIG.

The light passing through the collimator 12 is focused between the first lens 14 of the folding optical system T and the collimator 12 and then enters the first lens 14 . The light incident on the first lens 14 passes through the folding optical system T as parallel light and is guided to the second lens 15 . The light passing through the second lens 15 is focused at the position where the optical element 13 is arranged.

9B is a schematic diagram showing a second modification of the folding optical system T. FIG. The second modification shown in FIG. 9B applies to all spectroscopes 1 according to the first to fourth embodiments.

For example, in the spectrometer 1 according to the first to fourth embodiments described above, the light emitted from the optical element 13 of the spectroscopic system S is described as being incident on the first lens 14 of the folding optical system T. Not limited. Instead of a mode in which the spectroscopic system S and the folding optical system T are completely separated like the spectroscope 1 in the above-described first to fourth embodiments, a part of the spectroscopic system S and the folding optical system A mode is also possible in which a part of the system T overlaps with each other. More specifically, part of the folding optical system T may be arranged between the collimator 12 and the optical element 13 of the spectroscopic system S, as shown in FIG. 9B. At this time, the optical element 13 is arranged at a position where the return light from the diffraction grating 11 is focused by the second lens 15 of the folding optical system T. FIG.

More specifically, the first lens 14 and the second lens 15 of the folding optical system T may be arranged between the first mirror 16 and the second mirror 17 . At this time, the first mirror 16 reflects the return light generated in the spectroscopic system S toward the extension direction Y of the ruled line C of the diffraction grating 11 and guides it to the first lens 14 . The second mirror 17 reflects the return light that has been condensed by the second lens 15 and passed through the optical element 13 of the spectroscopic system S toward the diffraction grating 11 .

The light passing through the collimator 12 is reflected by the first mirror 16 of the folding optical system T to be focused, and then enters the first lens 14 . The light incident on the first lens 14 passes through the folding optical system T as parallel light and is guided to the second lens 15 . The light passing through the second lens 15 is focused at the position where the optical element 13 of the spectroscopic system S is arranged. The light that has passed through the optical element 13 is reflected by the second mirror 17 and propagates toward the diffraction grating 11 .

For example, in the spectroscope 1 according to the first to fourth embodiments described above, wavelength sweeping is performed by rotating the diffraction grating 11, but the wavelength sweeping method is not limited to this. For example, the arrangement angle of the diffraction grating 11 may be fixed, and the wavelength sweep may be performed by rotating the mirror element 18 in FIG.

1 Spectroscope 11 Diffraction Grating 12 Collimator 121 First Collimator 122 Second Collimator 123 Third Collimator 124 Fourth Collimator 13 Optical Element 131 First Optical Element 132 Second Optical Element 133 Third Optical Element 134 Fourth Optical Element 14, 141 , 142, 143 first lenses 15, 151, 152, 153 second lenses 16, 161, 162, 163 first mirrors 17, 171, 172, 173 second mirror 18 mirror element 191 first folding mirror 192 second folding mirror 2 Light guide component C Ruled line L1 Lights to be measured L2, L4, L6, L8 Diffracted lights L3, L5, L7 Light R Rotational axis S Spectral system S1 First optical system S2 Second optical system S3 Third optical system S4 Fourth Spectral system T Folding optical system T1 First folding optical system T2 Second folding optical system T3 Third folding optical system Y Extension direction

Claims (4)

A spectroscope that disperses the incident light to be measured,
a diffraction grating;
a collimator for collimating incident light; and a position where the light collimated by the collimator and incident on the diffraction grating from the diffraction grating is arranged at a position where at least one of the return lights is focused. a plurality of spectroscopic systems each having an optical element for passing through a portion;
at least one folding optical system for guiding the return light generated in one of the two adjacent spectral systems to the other spectral system;
with
The folding optical system includes a first lens for collimating the return light generated in one of the spectroscopic systems, and a collimator for collimating the return light collimated by the first lens and the collimator of the other spectroscopic system. a first mirror that reflects the return light in the extending direction of the ruled lines of the diffraction grating and guides it to the first lens; a second mirror that reflects the returned light toward the diffraction grating ;
Spectrometer. The optical element of one of the spectroscopic systems is arranged at a position between the collimator of the one of the spectroscopic systems and the first lens so that the return light from the diffraction grating is focused by the collimator. there is
A spectroscope according to claim 1 . Equipped with four said spectroscopic systems and two said folding optical systems,
The one folding optical system directs the return light generated in a first spectroscopic system through which the light under measurement incident on the spectroscope first passes to a second spectroscopic system adjacent to the first spectroscopic system. lead me to turn around,
The other folding optical system guides the return light generated in the third spectral system adjacent to the second spectral system to fold back toward the fourth spectral system adjacent to the third spectral system.
3. A spectrometer according to claim 1 or 2. comprising a mirror element on which the return light from the diffraction grating is incident;
The return light that has entered the mirror element is reflected by the mirror element, re-enters the diffraction grating, and is guided to the optical element via the collimator.
4. A spectrometer as claimed in any one of claims 1 to 3.

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