WO2012073681A1

WO2012073681A1 - Laser light source, interferometer and spectrometer

Info

Publication number: WO2012073681A1
Application number: PCT/JP2011/076155
Authority: WO
Inventors: 祐亮平尾
Original assignee: コニカミノルタホールディングス株式会社
Priority date: 2010-12-03
Filing date: 2011-11-14
Publication date: 2012-06-07

Abstract

A VHG element (42) of a laser light source (40) returns light of a specific wavelength emitted from a semiconductor laser (41) to the semiconductor laser (41), causes resonance to be generated between the semiconductor laser (41) and the actual VHG element (42) to thereby amplify the light, and emits the light. The laser light source (40) comprises a fibre (45) that guides the light of the specified wavelength that is emitted from the VHG element (42) and incident through a lens (43). The fibre (45) is comprises a single-mode fibre or a polarisation plane-maintaining fibre.

Description

Laser light source, interferometer and spectrometer

The present invention relates to a laser light source including a semiconductor laser, an interferometer using the laser light source as a reference light source, and a spectroscope including the interferometer.

In a Michelson two-beam interferometer used for FTIR (Fourier Transform Infrared Spectroscopy) as a spectroscope, infrared light emitted from a light source is divided into two directions, a fixed mirror and a moving mirror, by a beam splitter. A configuration is adopted in which the light reflected and returned by the movable mirror is combined into one optical path by the beam splitter. When the moving mirror is moved back and forth (in the direction of the optical axis of the incident light), the optical path difference between the two divided beams changes, so the intensity of the combined light changes according to the amount of movement of the moving mirror. Measurement interference light (interferogram). By sampling this interferogram and performing AD conversion and Fourier transform, the spectral distribution of the incident light can be obtained, and the intensity of the measurement interference light for each wave number (1 / wavelength) can be obtained from this spectral distribution. it can.

The above interferogram is expressed as a function of the phase difference between the moving mirror and the fixed mirror, that is, the optical path difference between the reflected light from the moving mirror and the reflected light from the fixed mirror. When seeking, it is necessary to constantly monitor the position of the movable mirror. Therefore, normally, the position of the movable mirror is monitored using a reference light source separately from the light source that emits infrared light. Specifically, the reference light emitted from the reference light source is separated by a beam splitter and guided to a moving mirror and a fixed mirror, and each light reflected by the moving mirror and the fixed mirror is synthesized by a beam splitter to be used as reference interference light. The light is guided to a reference light detector for position detection. Since the intensity of the reference interference light changes according to the position of the movable mirror, the position of the movable mirror can be obtained by detecting the intensity change of the reference interference light with the reference light detector.

By the way, for example, due to shock or vibration during transportation of the interferometer, the relative inclination of the optical path of the reflected light from the movable mirror and the optical path of the reflected light from the fixed mirror may deviate from the normal inclination. . Hereinafter, such a deviation in inclination is referred to as an inclination error. If there is a tilt error, the coherence between the reflected light from the movable mirror and the reflected light from the fixed mirror will be reduced, and the contrast of the measured interference light will be reduced. become unable.

Therefore, in Patent Document 1, for example, before the spectroscopic measurement, the tilt error caused by the impact or the like is adjusted by adjusting the angle of the fixed mirror or the movable mirror based on the detection result of the reference interference light by the reference light detector. I am trying to correct. More specifically, the reference light detector is composed of four divided sensors. Based on a total of four signals output from the individual sensors, signals corresponding to the positional deviation of the reference interference light (horizontal and vertical directions). The tilt error is corrected by adjusting the posture of the fixed mirror, for example, based on these phase signals.

Patent Document 1 discloses that, for example, a He—Ne laser is used as a reference light source for an interferometer in a general FTIR. However, since the He—Ne laser is large, the interferometer is enlarged. Invite. In order to realize a small and portable interferometer, it is considered effective to use, for example, a small semiconductor laser as a reference light source.

A semiconductor laser has an oscillation wavelength width of, for example, about 3 nm. By arranging, for example, a volume type diffraction grating at the emission portion of the semiconductor laser, the oscillation wavelength width of the semiconductor laser can be reduced to, for example, 0.1 nm. , The wavelength can be stabilized. A technique for stabilizing the wavelength of a semiconductor laser by combining a semiconductor laser and a volume type diffraction grating in this manner is disclosed in, for example, Patent Document 2. In Patent Document 2, a VBG (Volume Bragg Grating) element is arranged at the emitting portion of the semiconductor laser, and among the laser light emitted from the semiconductor laser, light having a specific wavelength is reflected by the VBG element and returned to the semiconductor laser. The wavelength is locked by resonating between the laser and the VBG element, and the laser beam is emitted from the VBG element.

JP 2004-28609 A (see paragraphs [0002], [0008] to [0020], etc.) US Patent No. 7697589 (see Fig. 1C etc.)

Incidentally, FIG. 7 shows an intensity profile of light emitted from the semiconductor laser 101 through the VBG element 102 in the laser light source 100. In a configuration in which light of a specific wavelength is resonated between the semiconductor laser 101 and the VBG element 102 to lock the wavelength, the intensity profile of the light emitted from the VBG element 102 is returned to the semiconductor laser 101. The intensity is lowered at the position (position reflected by the VBG element 102), and a dark spot 103 is generated in the intensity profile. Since the VBG element 102 has angle selectivity, the position of the dark spot 103 (position where the intensity decreases) varies depending on the wavelength of incident light and the incident angle.

When the laser light source 100 having such an intensity profile is applied to a reference light source of an interferometer, for example, as shown in FIG. 8, a dark spot 202 ( The part where the strength is reduced occurs. Since such a dark spot 202 has an error in the phase signal output from each sensor of the reference light detector 201, the correction of the tilt error (optical path correction) based on the output from the reference light detector 201 is accurate. Can't do well. As a result, it becomes difficult to apply the laser light source 100 to an interferometer or a spectrometer.

The present invention has been made to solve the above problems, and its object is to cause an error in the intensity distribution of the reference interference light in the reference light detector when applied to the reference light source of the interferometer. A small laser light source capable of avoiding dark spots and thereby accurately performing optical path correction based on the output from the reference light detector, and an interferometer and spectroscope to which the laser light source can be applied And to provide.

The laser light source of the present invention is disposed in a semiconductor laser and an emission part of the semiconductor laser, and returns light of a specific wavelength emitted from the semiconductor laser to the semiconductor laser and resonates with the semiconductor laser. A wavelength filter that amplifies and emits, and a single mode fiber or a polarization-maintaining fiber that guides light of the specific wavelength that is emitted from the wavelength filter and enters through a lens.

According to the present invention, the light emitted from the wavelength filter and having a dark spot in the intensity profile is guided by the single mode fiber or the polarization-maintaining fiber, so that the shape is close to the Gaussian distribution, that is, the intensity is most intense near the center. A high rotationally symmetric intensity profile can be obtained. As a result, when a laser light source is applied to a reference light source of an interferometer, for example, it is possible to avoid a dark spot in the intensity distribution of the reference interference light, and the optical path correction based on the intensity distribution of the reference interference light can be accurately performed. It can be carried out. Accordingly, it is possible to realize a laser light source suitable for an interferometer or a spectroscope that performs such optical path correction. In addition, since the semiconductor laser is small, the laser light source, and thus the interferometer and spectroscope, can be configured in a small size.

It is explanatory drawing which shows typically the structure of the outline of the spectrometer of one Embodiment of this invention. It is a top view which shows the structure of the outline of the reference light detector of the interferometer with which the said spectrometer is equipped. It is explanatory drawing which shows two phase signals output from the said reference light detector. It is explanatory drawing which shows the relationship between the phase difference of the said two phase signals, and the relative inclination angle of two optical paths. It is explanatory drawing which shows typically the other structure of the said spectrometer. It is sectional drawing which shows the schematic structure of the laser light source applied to the reference light source of the said interferometer. It is explanatory drawing which shows the intensity profile of the light inject | emitted via a VBG element from a semiconductor laser. It is explanatory drawing which shows typically the intensity distribution of the interference light which isolate | separated and interfered the light with the intensity profile of FIG.

An embodiment of the present invention will be described below with reference to the drawings.

[Configuration of spectrometer and interferometer]
FIG. 1 is an explanatory diagram schematically showing a schematic configuration of the spectroscope (Fourier transform spectroscopic analyzer) of the present embodiment. The spectroscope includes an interferometer 1, a calculation unit 2, and an output unit 3. The interferometer 1 is a two-optical path branching Michelson interferometer, and details thereof will be described later. The calculation unit 2 performs sampling, A / D conversion, and Fourier transform of a signal output from a measurement light detector 18 (to be described later) of the interferometer 1, and a wavelength spectrum included in the measurement light, that is, a wave number (1 / wavelength). ) To generate a spectrum indicating the intensity of light. That is, the calculation unit 2 functions as a spectrum generation unit that generates a spectrum indicating the light intensity for each wavelength based on the detection signal of the measurement interference light. The output unit 3 outputs (for example, displays) the spectrum generated by the calculation unit 2. Hereinafter, details of the interferometer 1 will be described.

The interferometer 1 has a measurement optical system 10, a reference optical system 20, and an optical path correction unit 30. Hereinafter, it demonstrates in order.

(Measuring optical system)
The measurement optical system 10 includes a measurement light source 11, a measurement light collimating optical system 12, a folding mirror M, a BS (beam splitter) 13, a compensation plate 14, a fixed mirror 15, a moving mirror 16, a collecting mirror. An optical optical system 17, a measurement light detector 18, and a drive mechanism 19 are provided. Note that the positional relationship between the fixed mirror 15 and the movable mirror 16 with respect to the BS 13 may be reversed.

The measurement light source 11 emits, for example, near-infrared light or infrared light including a plurality of wavelengths as measurement light, and is configured by a single light source or a fiber coupling optical system in which a light source and an optical fiber are coupled. It consists of The measurement light collimating optical system 12 is an optical system that converts the measurement light emitted from the measurement light source 11 into collimated light and guides it to the BS 13, and is composed of, for example, a collimator lens.

Here, collimated light is a concept that includes substantially parallel light (some convergent light or divergent light) in addition to perfect parallel light. In other words, collimation here refers to guiding light from a light source to a sensor via a BS and a fixed mirror or moving mirror by a collimating optical system, and is not limited to collimation at infinity. In order to facilitate handling as a plane wave, for example, it is desirable to collimate 1 m or more away.

The folding mirror M is provided to bend the optical path between the collimating optical system 12 for measuring light and the BS 13 so as to make the interferometer 1 compact. In the optical path between the folding mirror M and the BS 13 (particularly in the optical path between the optical path combining mirror 23 and the BS 13 described later), a stop A1 for restricting the beam diameter of the measurement light is disposed.

The BS 13 separates incident light, that is, light emitted from the measurement light source 11 into two lights, which are guided to the fixed mirror 15 and the movable mirror 16 and reflected by the fixed mirror 15 and the movable mirror 16, respectively. Each light is combined and emitted as measurement interference light, and is composed of, for example, a half mirror with a branching ratio of 50:50.

The compensation plate 14 is a substrate for correcting an optical path length corresponding to the thickness of the BS 13 and an optical path shift due to refraction when light passes through the BS 13. Depending on how the interferometer 1 is assembled, the compensation plate 14 may be unnecessary.

The condensing optical system 17 is an optical system that condenses the light synthesized and emitted by the BS 13 and guides it to the measurement light detector 18, and is composed of, for example, a focus lens. The measurement light detector 18 receives measurement interference light incident from the BS 13 via the condensing optical system 17 and detects an interferogram (interference pattern).

The drive mechanism 19 moves the movable mirror 16 to the optical axis so that the difference (optical path length difference) between the optical path of the light reflected by the fixed mirror 15 and the optical path of the light reflected by the movable mirror 16 changes. It is a moving mechanism that translates (translates) in the direction, and is composed of, for example, an electromagnetic drive mechanism using a VCM (voice coil motor). The drive mechanism 19 may be a parallel leaf spring type drive mechanism.

In the above configuration, the measurement light emitted from the measurement light source 11 is converted into collimated light by the measurement light collimating optical system 12, then reflected by the folding mirror M and incident on the BS 13. It is separated into two light beams by reflection. One separated light beam is reflected by the movable mirror 16, and the other light beam is reflected by the fixed mirror 15. Each light beam returns to the original optical path and is superimposed by the BS 13, and after passing through the compensation plate 14 as measurement interference light. The sample (not shown) is irradiated. At this time, the sample is irradiated with light while continuously moving the movable mirror 16 by the drive mechanism 19, but the difference in optical path length from the BS 13 to each mirror (movable mirror 16, fixed mirror 15) is an integral multiple of the wavelength. In this case, the intensity of the superimposed light becomes the maximum. On the other hand, when there is a difference between the two optical path lengths due to the movement of the movable mirror 16, the intensity of the superimposed light changes. The light transmitted through the sample is condensed by the condensing optical system 17 and enters the measurement light detector 18 where it is detected as an interferogram. That is, in FIG. 1, the measurement light travels along an optical path indicated by a one-dot chain line.

The computing unit 2 samples a detection signal (interferogram) from the measurement light detector 18 and performs A / D conversion and Fourier transform to generate a spectrum indicating the light intensity for each wave number. The above spectrum is output (for example, displayed) by the output unit 3, and based on this spectrum, the characteristics (material, structure, component amount, etc.) of the sample can be analyzed.

(Reference optical system)
Next, the reference optical system 20 will be described. The reference optical system 20 shares a part of the configuration with the measurement optical system 10 described above. In addition to the BS 13, the compensation plate 14, the fixed mirror 15, and the movable mirror 16, the reference light source 21, A reference light collimating optical system 22, an optical path combining mirror 23, an optical path separation mirror 24, and a reference light detector 25 are provided.

The reference light source 21 is a light source for detecting the position of the movable mirror 16 and generating a timing signal for sampling in the calculation unit 2. In the present embodiment, the reference light source 21 is constituted by a laser light source 40 (see FIG. 6), and details thereof will be described later.

The reference light collimating optical system 22 is an optical system that converts the reference light (laser light) emitted from the reference light source 21 into collimated light and guides it to the BS 13, and is composed of, for example, a collimating lens. A diaphragm A2 is disposed on the light exit side of the reference light collimating optical system 22, and the beam diameter of the collimated light is regulated. It should be noted that the reference light collimating optical system 22 is provided with the function of the aperture A2 by painting the surface of the lens constituting the reference light collimating optical system 22 in black except for the portion that emits the collimated light. It may be.

The optical path combining mirror 23 is a beam combiner that combines the optical paths of the light by transmitting the light from the measurement light source 11 and reflecting the light from the reference light source 21. In the present embodiment, the optical path combining mirror 23 is arranged so that the reference light is incident on the fixed mirror 15 and the movable mirror 16 obliquely. Thereby, the influence of the return light from the fixed mirror 15 and the movable mirror 16 is avoided.

That is, since the optical path of the reference light is tilted with respect to the fixed mirror 15 and the movable mirror 16, the reflected light from the fixed mirror 15 passes through the BS 13, and the direction of the reference light collimating optical system 22 is transmitted by the optical path combining mirror 23. Even if the light reflected by the movable mirror 16 is reflected by the BS 13 and is incident on the optical path synthesis mirror 23 where it is reflected in the direction of the collimating optical system 22 for reference light, The light enters the stop A2 and is blocked there, and does not enter the reference light source 21. Thereby, it is possible to avoid the oscillation at the reference light source 21 becoming unstable due to the incident return light. In FIG. 1, the optical paths of the return light from the fixed mirror 15 and the movable mirror 16 are indicated by broken lines.

The optical path separation mirror 24 transmits the light emitted from the measurement light source 11 and incident through the BS 13, and reflects the light emitted from the reference light source 21 and incident through the BS 13. Is a beam splitter.

The reference light detector 25 is a detector that detects light (reference interference light) emitted from the reference light source 21 and incident on the optical path separation mirror 24 via the BS 13 and reflected there. For example, the response speed is higher than that of the CCD. Is composed of a fast quadrant sensor. A diaphragm A3 is arranged in the optical path between the optical path separation mirror 24 and the reference light detector 25, and the diameter of the reference interference light incident on the reference light detector 25 is regulated by the diaphragm A3. .

FIG. 2 is a plan view showing a schematic configuration of the reference light detector 25. As shown in the figure, the reference light detector 25 includes four light receiving portions 25A to 25D, and the light receiving portions 25A to 25D are arranged in two rows and two columns. The light receiving units of the reference light detector 25 may be arranged in two directions on the light receiving surface of the reference interference light, and the reference light detector 25 includes at least three light receiving units. Such an arrangement can be realized.

In the above configuration, the light emitted from the reference light source 21 is converted into collimated light by the reference light collimating optical system 22, then reflected by the optical path combining mirror 23 and incident on the BS 13, where it is separated into two light beams. The One light beam separated by the BS 13 is reflected by the movable mirror 16, and the other light beam is reflected by the fixed mirror 15. Each light beam returns to the original optical path and is overlapped by the BS 13, and passes through the compensation plate 14 and passes through the optical path. The light enters the separation mirror 24, is reflected there, and enters the reference light detector 25. That is, in FIG. 1, the reference light travels along the optical path indicated by the solid line.

Based on the detection result of the reference interference light by the reference light detector 25, the optical path correction unit 30 described later has a relative inclination error between the optical path of the reflected light from the movable mirror 16 and the optical path of the reflected light from the fixed mirror 15. (Tilt error) is corrected.

(Optical path correction unit)
When the moving mirror 16 is driven by the driving mechanism 19 and the translational property of the moving mirror 19 is lost and the above tilt error occurs, the coherence between the reflected light from the fixed mirror 15 and the reflected light from the moving mirror 16 decreases. The interference intensity (contrast) of the measurement interference light decreases. When the optical path correction unit 30 corrects the tilt error, it is possible to avoid a decrease in the interference intensity of the measurement interference light.

Here, in the present embodiment, the optical axes on the measurement light side and the reference light side are not perfectly coaxial due to the above arrangement of the optical path combining mirror 23, but (1) a measurement light source because the optical axes are close to the same axis. 11, BS 13, moving mirror 16, BS 13, and measurement light detector 18 in the order of light, and measurement light source 11, BS 13, fixed mirror 15, BS 13, light that proceeds in order of measurement light detector 18 and a tilt error ( (Also referred to as a first tilt error) is (2) light traveling in the order of the reference light source 21, BS13, moving mirror 16, BS13, and reference light detector 25, and the reference light source 21, BS13, fixed mirror 15, BS13, reference It is almost close to a tilt error (also referred to as a second tilt error) between light traveling in the order of the photodetector 25. Therefore, the optical path correction unit 30 can correct the first tilt error by correcting the second tilt error based on the light reception signal of the reference interference light from the reference light detector 25.

Specifically, the optical path correction unit 30 includes a signal processing unit 31, an adjustment mechanism 32, and a control unit 33. The control unit 33 is configured by a CPU, for example, and controls the adjustment mechanism 32 based on the detection result of the signal processing unit 31.

The signal processing unit 31 is an inclination detection unit that detects an inclination error based on the intensity of the reference interference light detected by the reference light detector 25. For example, FIG. 3 shows a phase signal (a signal indicating the intensity of light received by the light receiving unit 25A out of the entire reference interference light) output from the light receiving unit 25A of the reference light detector 25 and the light receiving unit 25C. Phase signal (a signal indicating the intensity of light received by the light receiving unit 25C out of the entire reference interference light). In addition, the intensity | strength of the vertical axis | shaft of FIG. 3 has shown the relative value. In this example, there is an inclination error in the direction corresponding to the direction in which the

light receiving portions

25A and 25C are arranged (hereinafter also referred to as the AC direction) by the angle corresponding to the phase difference Δ between these two signals. Become. The relationship between the phase difference between the two signals and the tilt error (tilt angle) is, for example, as shown in FIG.

As described above, the signal processing unit 31 can detect the inclination error in the AC direction based on the phase difference between the signals output from the two

light receiving units

25A and 25C. Further, based on the same idea as described above, the signal processing unit 31 is based on the phase difference between the signals output from the two

light receiving units

25A and 25B, and corresponds to the direction in which the

light receiving units

25A and 25B are arranged (hereinafter referred to as A). (Also referred to as -B direction) can be detected. Therefore, the signal processing unit 31 can detect an inclination error in each of the two directions based on the phase difference between the signals output from the three

light receiving units

25A, 25B, and 25C.

The adjusting mechanism 32 adjusts the tilt of the fixed mirror 15 to tilt one of the two optical paths and correct the tilt error. In the present embodiment, as shown in FIG. 1, the adjustment mechanism 32 has a plurality (at least three) of which the tip is connected to the back surface (surface opposite to the reflection surface) of the fixed mirror 15 and expands and contracts in the optical axis direction. The piezoelectric element 32a, and a drive unit 32b that applies a voltage to the piezoelectric element 32a to expand and contract the piezoelectric element 32a. Based on the detection result of the signal processing unit 31, the control unit 33 controls the voltage applied to each piezoelectric element 32 a and expands and contracts each piezoelectric element 32 a in the optical axis direction, thereby tilting the fixed mirror 15 (fixed mirror). The optical path of the reflected light at 15 can be changed, whereby the tilt error can be corrected.

By performing feedback control that repeats the detection of the tilt error by the signal processing unit 31 and the optical path correction of the reflected light at the fixed mirror 15 by the adjustment mechanism 32, the tilt error is finally brought to zero as much as possible. be able to.

The signal processing unit 31 described above has a function of detecting the position of the movable mirror 16 based on the intensity of the reference interference light detected by the reference light detector 25 and generating a pulse signal indicating the sampling timing. Also have. In the reference light detector 25, the intensity of the reference interference light generally changes between bright and dark according to the position (optical path difference) of the movable mirror 16, and therefore the position of the movable mirror 16 based on the intensity change. Can be detected. The calculation unit 2 samples the detection signal (interferogram) from the measurement light detector 18 in synchronization with the sampling timing of the pulse signal and converts it into digital data.

Incidentally, FIG. 5 is an explanatory view schematically showing another configuration of the spectrometer. As shown in the figure, the adjustment mechanism 32 of the optical path correction unit 30 may correct the tilt error by tilting one of the two optical paths by adjusting the tilt of the movable mirror 16. In this case, the tip of each piezoelectric element 32a is connected to the back surface of the movable mirror 16, and each piezoelectric element 32a is expanded and contracted by the drive unit 32b, whereby the inclination of the movable mirror 16 is changed and reflected by the movable mirror 16. The optical path of light can be corrected. At this time, the drive mechanism 19 of the movable mirror 16 may be connected to the back surface of the drive unit 32b (the side opposite to each piezoelectric element 32a).

[Laser light source]
Next, the detail of the laser light source 40 which comprises the above-mentioned reference light source 21 is demonstrated. FIG. 6 is a cross-sectional view showing a schematic configuration of the laser light source 40. The laser light source 40 includes a semiconductor laser 41, a VHG (Volume Holographic Grating) element 42, a lens 43, and a fiber 44.

The semiconductor laser 41 is an InGaInP-based edge emitting semiconductor laser that emits red light (for example, wavelength 660 nm), and is attached to a CAN type mount. That is, the semiconductor laser 41 is fixed to the side surface of the first mount 47 on the stem 46 having the plurality of lead terminals 45.

Here, the reason why the semiconductor laser 41 is configured to emit red light is as follows.

Many materials often have absorption bands in near-infrared light and infrared light called fingerprint regions, and therefore, spectroscopic analysis is often performed using near-infrared light and infrared light. In such spectroscopic analysis, a light transmission surface (for example, a light transmission surface of the BS 13) in the measurement optical system 10 and the reference optical system 20 is often provided with an antireflection coating (AR coating) to increase the light utilization efficiency.

At this time, due to the design of the antireflection coating, it is difficult to provide antireflection characteristics in a wide band. Further, if the wavelength band for preventing reflection is widened, the reflectance increases in that wavelength band. Therefore, when the measurement light is near-infrared light or infrared light, the reference light is made red light (red semiconductor laser light), and the wavelength band of the reference light and measurement light is made close to make it easy to design the antireflection coating. Can be.

In addition, it is difficult to configure the BS 13 having a predetermined branching ratio (for example, 50:50) in a wide wavelength range. However, as described above, the BS 13 having a predetermined branching ratio (for example, 50:50) has a predetermined branching ratio. It becomes easy to design a BS 13 having a branching ratio of.

Note that the semiconductor laser 41 includes a laser whose reflectance at the emitting portion is extremely low (close to 0%). That is, in general, a semiconductor laser is configured to have a high reflection mirror (reflectance is close to 100%) and a low reflection mirror (reflectance 50%, etc.). For example, an extremely low value of 0.01% or the like can be handled as a semiconductor laser.

The VHG element 42 is a volume type diffraction grating (VBG element) having a function as a wavelength filter, and is formed by exposure of a photosensitive material. The VHG element 42 returns light of a specific wavelength emitted from the semiconductor laser 41 in the direction of the semiconductor laser 41 by diffraction reflection and resonates with the semiconductor laser 41 to amplify the emission wavelength, thereby reflecting reflected diffracted light. Lock to the wavelength of. The wavelength of the reflected diffracted light is determined by the width of the diffraction grating, and the spectral line of the emission wavelength of the semiconductor laser 41 is fixed to a specific mode and narrowed.

The VHG element 42 is provided on the side surface of the second mount 48 fixed on the first mount 47 so as to be positioned at the emitting portion of the semiconductor laser 41. That is, the VHG element 42 is disposed close to the emission surface of the semiconductor laser 41 (position where the laser beam is emitted). By controlling the temperature of the semiconductor laser 41 and the VHG element 42 at the same time, the wavelength fluctuation can be suppressed and stabilized.

In addition to the VHG element 42, it is also possible to configure a wavelength filter using, for example, a multilayer film.

The semiconductor laser 41 and the VHG element 42 are covered with a case 49 on the stem 46. The case 49 is filled with, for example, nitrogen. The case 49 is provided with an opening 49a, and a glass window 50 is fixed so as to close the opening 49a. The light emitted from the VHG element 42 enters the lens 43 through the glass window 50 and the opening 49a.

The lens 43 condenses the light emitted from the VHG element 42 on the light incident surface of the fiber 44. Since the emission light from the semiconductor laser 41 has different emission angles in two directions, it is desirable to use an aspherical lens or the like as the lens 43, but a refractive index distribution type such as a green lens may be used. The lens 43 is held together with the fiber 44 by a fiber holding member 51 fixed to the case 49.

The fiber 44 is an optical fiber that guides light of a specific wavelength that is emitted from the VHG element 42 and is incident through the lens 43, and is configured by a polarization-maintaining fiber in this embodiment. The polarization maintaining fiber guides light while maintaining the polarization plane so that the polarization plane (polarization plane) of the guided light does not change due to birefringence or the like. In the polarization-maintaining fiber, the polarization direction is maintained when the direction of the emission part of the fiber (light emission direction) is determined. Therefore, the interferometer 1 can suppress fluctuations in reflectance and transmittance due to polarization characteristics to be small. it can. As the fiber 44, a single mode fiber can be used in addition to the above-described polarization plane maintaining fiber.

The exit surface 44a of the fiber 44 is inclined about 8 degrees by APC (Angled Physical Contact) polishing with respect to a surface perpendicular to the light guiding direction. As a result, even if the light reflected by the reflection surface downstream of the fiber 44 (for example, the reflection surface of the fixed mirror 15 or the movable mirror 16) is transmitted or reflected by the BS 13 and returns to the fiber 44 again, the emission surface. Since it is reflected by 44a, it does not enter the semiconductor laser 41. Therefore, it is possible to avoid the oscillation of the semiconductor laser 41 from becoming unstable due to the return light.

In this embodiment, the polarization-maintaining fiber as the fiber 44 is made of a silica glass fiber, the MFD (Mode Field Diameter) is 4.5 to 3 μm, and the fiber length is 300 mm or more. ing. Since the fiber 44 is sufficiently long, the fiber 44 can attenuate only a higher-order guided mode and guide only the fundamental mode (LP01 mode), for example.

Thus, in the laser light source 40, the mode guided in the inside of the fiber 44 is only the fundamental mode. In addition, in the polarization maintaining fiber and the single mode fiber, there is no waveguide mode having a different phase as in the case of using the multimode fiber, so that the coherence is not lowered. Accordingly, when light whose intensity profile includes a dark spot (position where the intensity has decreased) is incident on the fiber 44, the incident light is guided through repeated total reflection inside the fiber 44, so that the center intensity is the highest. Light having a high rotational symmetry intensity profile is emitted from the fiber 44. In other words, due to the angle selectivity of the VHG element 42, even when the intensity reduction position in the intensity profile differs depending on the wavelength and the incident angle, the light emitted from the VHG element 42 is guided inside the fiber 44 to be close to a Gaussian distribution. A rotationally symmetric intensity profile can be obtained.

Thereby, even when the laser light source 40 is applied to the reference light source 21 of the interferometer 1, it is possible to avoid the occurrence of a dark spot that causes an error in the intensity distribution of the reference interference light detected by the reference light detector 25. (See FIG. 2), and optical path correction based on the intensity distribution of the reference interference light can be performed with high accuracy. Therefore, the laser light source 40 suitable for the interferometer 1 and the spectroscope that perform such optical path correction can be realized.

Moreover, since the semiconductor laser 41 is smaller than, for example, a He—Ne laser, a small laser light source 40 can be realized. Therefore, using the small laser light source 40, the interferometer 1 and the spectroscope which are small and easy to carry can be realized.

Further, since the laser light source 40 is configured to stabilize the light from the semiconductor laser 41 using the VHG element 42, the laser light source 40 has high robustness and can prevent the influence of disturbance (for example, vibration). Since the movable (portable) interferometer 1 and the spectroscope are required to have higher robustness than the installation type, the laser light source 40 of the present embodiment is small and easy to carry from this point of view. It can be said that this is suitable for the interferometer 1 and the spectroscope.

Furthermore, since the laser light source 40 includes the fiber 44, the semiconductor laser 41, which is a heat source, can be arranged away from the measurement optical system 10. Thereby, performance degradation due to heat of the measurement optical system 10 (degradation of optical performance due to thermal expansion of the member) can be avoided.

Further, since the interferometer 1 can accurately perform optical path correction based on the intensity distribution of the reference interference light as described above, the optical path correction of the measurement interference light in the measurement light detector 18 can be performed by such optical path correction. A decrease can be avoided. Therefore, the spectroscope equipped with such an interferometer 1 can accurately perform the spectral analysis of the measurement interference light based on the spectrum generated by the calculation unit 2.

In the present embodiment, the position of the movable mirror 16 (detection of the optical path difference) is also performed by the signal processing unit 31 based on the signal from the reference light detector 25. However, depending on the configuration of the laser light source 40, reference is made. Since it is possible to avoid the occurrence of dark spots in the intensity distribution of the interference light, the position detection of the movable mirror 16 based on the intensity change of the reference interference light can be performed with high accuracy.

In this embodiment, the VHG element 42, that is, a volume type diffraction grating is used as the wavelength filter. In order to construct a wavelength filter with a narrow line width, the number of laminated diffraction gratings may be increased. However, the VHG element 42 exposes the photosensitive material with two light beams and causes them to interfere with each other. Since it is obtained by alternately forming each layer composed of the low refractive index portion, it is easy to increase the number of laminated diffraction gratings by changing the exposure conditions (exposure time, exposure amount, etc.). Therefore, it is possible to easily realize a wavelength filter with a narrow line width, compared to the case where the wavelength filter is formed of a multilayer film.

Further, since the wavelength filter has a narrow line width, the wavelength stabilization region, that is, the distance (≈cavity length, resonance length) from the semiconductor laser 41 to the wavelength filter necessary to stabilize the wavelength is increased. It can be shortened.

Further, since the fiber 44 has a length that attenuates modes other than the guided mode (fundamental mode), it attenuates higher-order guided modes and guides only the required mode (fundamental mode only). Can be waved. Since only one mode is guided in this way, the intensity profile of the emitted light can be a rotationally symmetric intensity profile close to a Gaussian distribution, regardless of the intensity profile of the incident light.

Further, by obtaining the rotationally symmetric intensity profile as described above in the laser light source 40, the interferometer 1 to which the laser light source 40 is applied has a very small tilt error between the two optical paths as shown in FIG. In a range (for example, a relative inclination angle of 0 to 90 seconds), the phase difference between the two signals output from the two

light receiving units

25A and 25C of the reference light detector 25 and the inclination error are substantially linear. Become. As a result, the signal processing unit 31 can detect the tilt error with high accuracy within the above minute range based on the output from the reference light detector 25.

Further, the interferometer 1 of the present embodiment includes a reference light collimating optical system 22, and light emitted from the fiber end of a laser light source 40 as the reference light source 21 is converted into a plane wave by the reference light collimating optical system 22. Converted. When the reference light is a plane wave, it is not necessary to consider the phase difference between the light beams in the light beam of the reference light (for example, the phase difference between the on-axis light beam and the off-axis light beam). Calculation of the phase difference of the output signal from the photodetector 25 and calculation of the tilt error between the two optical paths based on the phase difference are facilitated.

In the present embodiment, the configuration in which the interferometer 1 includes the measurement light source 11 and obtains the measurement interference light using the measurement light emitted from the measurement light source 11 has been described. However, the measurement light source 11 does not necessarily have to be incorporated. That is, the measurement light for obtaining the measurement interference light may be light emitted from a light source built in the interferometer, or may be light incident from the outside of the interferometer.

Therefore, for example, when (1) light is applied to the sample outside the interferometer and light obtained through the sample is incident on the interferometer to perform spectroscopic analysis, (2) light introduced from the outside of the interferometer When the interference light is generated by the interferometer using the and the spectroscopic analysis is performed by applying the interference light to the sample, (3) the case where the light itself incident from the outside of the interferometer is the object of analysis It is also possible to apply the interferometer of the present invention.

As described above, the laser light source according to the present embodiment is disposed in the semiconductor laser and the semiconductor laser emitting unit, and returns light of a specific wavelength emitted from the semiconductor laser to the semiconductor laser. A laser light source including a wavelength filter that resonates, amplifies, and emits light, and is a single mode fiber or a polarization-maintaining fiber that guides light of the specific wavelength that is emitted from the wavelength filter and incident through a lens May be provided.

According to the above configuration, in the wavelength filter, the light having an intensity profile that decreases the intensity at the position where the light of the specific wavelength is returned to the semiconductor laser is guided to the single mode fiber or the polarization maintaining fiber by the lens. One of the above is guided. In these fibers, there is one mode for guiding the inside of the fiber, and the coherence is not lowered as when a multimode fiber is used. Therefore, regardless of the intensity profile, that is, when the intensity reduction position changes depending on the wavelength or incident angle, light having the intensity profile is guided by total internal reflection. Thus, a shape close to a Gaussian distribution, that is, a rotationally symmetric intensity profile having the highest intensity near the center can be obtained. As a result, even when the laser light source is applied to a reference light source of an interferometer, for example, it is possible to avoid a dark spot that causes an error in the intensity distribution of the reference interference light detected by the reference light detector. Optical path correction based on the intensity distribution of interference light can be performed with high accuracy. Accordingly, it is possible to realize a laser light source suitable for an interferometer or a spectroscope that performs such optical path correction.

Moreover, since the semiconductor laser is smaller than, for example, a He—Ne laser, a small laser light source can be realized. Therefore, by applying the laser light source of the present embodiment to an interferometer or a spectroscope, a small interferometer or spectroscope can be realized, which is easy to carry and improves convenience.

In the laser light source of the present embodiment, it is desirable that the wavelength filter is composed of a volume type diffraction grating.

In this case, since it is easy to increase the number of laminated diffraction gratings by, for example, exposure of a photosensitive material, it is possible to easily realize a wavelength filter having a narrow line width compared to a case where the wavelength filter is formed of, for example, a multilayer film. it can. Further, since the wavelength filter has a narrow line width, it is possible to shorten the wavelength stabilization region, that is, the distance from the semiconductor laser necessary for stabilizing the wavelength to the wavelength filter.

In the laser light source of the present embodiment, it is desirable that the exit surface of the single mode fiber or the polarization-maintaining fiber is inclined with respect to a plane perpendicular to the light guiding direction.

When the laser light source of the present embodiment is applied to, for example, an interferometer, light guided by a single mode fiber or a polarization-maintaining fiber is reflected on an arbitrary reflecting surface (for example, a reflection of a fixed mirror or a moving mirror). Even if the light is reflected again by the surface and is returned to the single-mode fiber or the polarization-maintaining fiber, it is reflected by the exit surface of the fiber and does not enter the semiconductor laser. Therefore, it is possible to avoid the oscillation of the semiconductor laser from becoming unstable due to the return light.

In the laser light source of the present embodiment, it is desirable that the single mode fiber or the polarization-maintaining fiber has a length that attenuates a mode other than the waveguide mode.

If the single-mode fiber or polarization-maintaining fiber has a length that attenuates the higher-order guided mode, for example, the higher-order guided mode is attenuated and only an arbitrary mode (basic mode, LP01 mode) is attenuated. Can be guided. By having one guided mode, a rotationally symmetric intensity profile can be obtained reliably.

The interferometer of this embodiment separates the reference light from the reference light source, the movable mirror and the fixed mirror, and the reference light from the reference light source into two parts, and guides them to the movable mirror and the fixed mirror, respectively. An interferometer comprising a beam splitter for combining and interfering each light reflected by a mirror, and a reference light detector for detecting the interference light combined by the beam splitter as a reference interference light, An optical path correction unit that corrects a relative inclination error between the optical path of the reflected light from the movable mirror and the optical path of the reflected light from the fixed mirror based on a detection result of the reference light detector; The light source is preferably composed of the laser light source of the present embodiment described above.

By applying the laser light source of the present embodiment to the interferometer as a reference light source, it is possible to realize a small interferometer with a configuration capable of optical path correction by the optical path correction unit.

In the interferometer according to the present embodiment, the reference light detector includes at least three light receiving units arranged in two directions on a light receiving surface of the reference interference light, and the optical path correction unit includes: Based on a phase difference between signals output from the three light receiving units, an inclination detection unit that detects an inclination error between the optical paths, and an inclination of the fixed mirror or the movable mirror are adjusted to adjust the optical paths. A configuration may be provided that includes an adjustment mechanism that corrects the tilt error by tilting one of the control unit and a control unit that controls the adjustment mechanism based on a detection result of the tilt detection unit.

The inclination detection unit of the optical path correction unit can detect an inclination error between the two optical paths for each of the two directions based on signals output from the three light receiving units. Thereby, under the control of the control unit, the adjustment mechanism can tilt one optical path in each of the two directions to correct the tilt error between the two optical paths.

In addition, since the intensity distribution of light emitted from the laser light source is close to a rotationally symmetric Gaussian distribution, the phase difference between the two signals output from the two light receiving units, the inclination error, and the inclination error are within a very small range. Are substantially linear, and the inclination detection unit can detect the inclination error with high accuracy.

The interferometer according to the present embodiment may further include a collimating optical system that converts light emitted from the laser light source into collimated light.

The light emitted from the fiber end of the laser light source can propagate through the space as a plane wave through the collimating optical system. Since it can be handled as a plane wave, there is no phase difference between the rays in the collimated light beam. Therefore, the calculation of the phase difference of the output signals from each light receiving unit and the inclination error between the two optical paths based on the phase difference are possible. Calculation becomes easy.

The interferometer of this embodiment separates the measurement light into two by the beam splitter and guides it to the movable mirror and the fixed mirror. The light reflected by the movable mirror and the fixed mirror is separated by the beam splitter. The configuration may further include a measurement optical system that combines and guides the measurement light as measurement interference light to the measurement light detector.

In this configuration, measurement interference light can be measured by the measurement light detector. Further, since the relative inclination error between the two optical paths is corrected by the optical path correction unit, it is possible to avoid a decrease in the contrast of the measurement interference light in the measurement light detector.

The spectroscope according to the present embodiment has a spectrum indicating the light intensity for each wavelength based on the above-described interferometer of the present invention and the measurement interference light detection signal output from the measurement light detector of the interferometer. The structure provided with the spectrum production | generation part to produce | generate may be sufficient.

By applying the laser light source of the present embodiment to the interferometer as a reference light source, the reference interference light can be accurately detected by the reference light detector, and the optical path correction by the optical path correction unit can be accurately performed. Therefore, a spectroscope equipped with such an interferometer can accurately perform spectroscopic analysis of measurement interference light based on the spectrum generated by the spectrum generation unit.

The laser light source of the present invention can be used in a Michelson interferometer and a Fourier transform spectroscopic apparatus for performing spectroscopic analysis using the same.

1 Interferometer 2 Calculation unit (spectrum generation unit)
10 Measurement optics 13 BS (Beam splitter)
DESCRIPTION OF SYMBOLS 15 Fixed mirror 16 Moving mirror 18 Measurement light detector 21 Reference light source 22 Reference light collimating optical system 25 Reference light detector 25A Light receiving part 25B Light receiving part 25C Light receiving part 25D Light receiving part 30 Optical path correction part 31 Signal processing part (Inclination detection part) )
32 Adjustment mechanism 33 Control unit 40 Laser light source 41 Semiconductor laser 42 VHG element (wavelength filter)
43 Lens 44 Fiber (single mode fiber, polarization maintaining fiber)
44a Ejection surface

Claims

A semiconductor laser;
A wavelength filter that is disposed in the emission part of the semiconductor laser, returns light of a specific wavelength emitted from the semiconductor laser to the semiconductor laser, amplifies by resonating with the semiconductor laser, and emits the light,
A single-mode fiber or a polarization-maintaining fiber that guides light of the specific wavelength that is emitted from the wavelength filter and is incident through a lens;
A laser light source comprising:
2. The laser light source according to claim 1, wherein the wavelength filter is constituted by a volume type diffraction grating.
2. The laser light source according to claim 1, wherein an exit surface of the single mode fiber or the polarization-maintaining fiber is inclined with respect to a plane perpendicular to a light guiding direction.
The laser light source according to claim 1, wherein the single mode fiber or the polarization-maintaining fiber has a length that attenuates a mode other than the guided mode.
A reference light source;
And a moving mirror and the fixed mirror,
A beam splitter that separates reference light from the reference light source into two parts, guides them to the movable mirror and the fixed mirror, and combines and interferes with the lights reflected by the movable mirror and the fixed mirror;
A reference light detector for detecting the interference light combined by the beam splitter as a reference interference light;
An optical path correction unit that corrects a relative inclination error between the optical path of the reflected light from the movable mirror and the optical path of the reflected light from the fixed mirror based on the detection result of the reference light detector;
The reference light source is
A semiconductor laser;
A wavelength filter that is disposed in the emission part of the semiconductor laser, returns light of a specific wavelength emitted from the semiconductor laser to the semiconductor laser, amplifies by resonating with the semiconductor laser, and emits the light,
A single-mode fiber or a polarization-maintaining fiber that guides light of the specific wavelength that is emitted from the wavelength filter and is incident through a lens;
An interferometer characterized by comprising:
The reference light detector includes at least three light receiving units arranged in two directions on the light receiving surface of the reference interference light,
The optical path correction unit is
An inclination detection unit for detecting an inclination error between the optical paths based on a phase difference between signals output from the three light receiving units;
An adjustment mechanism that corrects the tilt error by tilting one of the optical paths by adjusting the tilt of the fixed mirror or the movable mirror;
The interferometer according to claim 5, further comprising a control unit that controls the adjustment mechanism based on a detection result of the tilt detection unit.
The interferometer according to claim 5, further comprising a collimating optical system that converts light emitted from the laser light source into collimated light.
The measurement light is separated into two by the beam splitter and guided to the movable mirror and the fixed mirror, and the lights reflected by the movable mirror and the fixed mirror are combined by the beam splitter and measured as measurement interference light. The interferometer according to claim 5, further comprising a measurement optical system that leads to a photodetector.
An interferometer according to claim 8;
A spectroscope comprising: a spectrum generation unit configured to generate a spectrum indicating light intensity for each wavelength based on a detection signal of measurement interference light output from the measurement light detector of the interferometer .