JP2010185726A - Light absorbance analysis device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absorption analyzer capable of stably measuring, with high measurement accuracy. <P>SOLUTION: A negative-feedback amplification type semiconductor optical amplifier 34 is provided between a first optical coupler 18 and a photodetector 20. By subjecting first input light Lin to negative-feedback amplification, the negative-feedback amplification type semiconductor optical amplifier 34 outputs to the photodetector 20, an output light Lout having the same wavelength λ2 as control light Lc and being subjected to intensity modulation by first ambient light Ls1 of the first input light Lin, and thereby light (signal) detected by the photodetector 20 has a waveform strain reduced by the negative-feedback amplification and an S/N ratio heightened thereby. Oscillations in a closed system propagation route of an optical waveguide 14 is not generated, to thereby enable stable absorption analysis. Since the S/N ratio of an attenuation waveform wherein light intensity of pulsing laser light L is attenuated, following an elapse of time is enhanced, and noise contained in the waveform is reduced, measurement accuracy to attenuation of an attenuation curve is fully acquired. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an absorption spectrometer using a semiconductor optical amplifier having a negative feedback amplification function.

  An optical analyzer using a so-called cavity ring-down method is known as an apparatus for analyzing a sample by utilizing the light absorption characteristics of a light-transmitting substance. In this optical analyzer, a laser beam of a predetermined wavelength, for example, having a frequency of about several tens of kHz is circulated in an annular propagation path or provided between mirrors in a propagation path configured in a closed system. Attenuation in which the intensity of pulsed laser light propagating in the light propagation path attenuates over time when a cell filled with a sample is inserted in the closed propagation path after reciprocating in a linear propagation path The waveform is detected using a photodetector, the ring-down time or attenuation rate of the attenuation waveform is obtained, and the number density or absorbance of the sample is measured based on the ring-down time or attenuation rate from a preset relationship. Is done. Based on the number density or absorbance of the sample, a substance contained in the sample is specified or the substance is quantified. For example, the absorption spectrometers described in Patent Document 1 and Patent Document 2 are those.

JP 2004-333337 A JP 2007-093529 A

  By the way, when measuring the attenuation rate of the light intensity of the pulsed laser beam, noise is observed in the attenuation waveform that is observed with a photodetector and the light intensity of the pulsed laser beam attenuates with time. Easy to mix and low S / N ratio. For this reason, the ring-down time, which is the time from the attenuation waveform signal until the light intensity of the pulsed laser beam attenuates to 1 / e, is short and cannot be obtained accurately, or the attenuation rate is also accurately accurate. Since it was not obtained, sufficient measurement accuracy was not obtained.

  On the other hand, as described in paragraph 0033 of Patent Document 2, the intensity of laser light propagating in the light propagation path is increased by inserting an optical amplifier in or outside the closed system propagation path. Thus, it has been proposed to increase the intensity of the signal detected by the photodetector. However, according to such a configuration, noise is also amplified, so that the S / N ratio of the signal is not sufficiently improved, and the laser beam easily oscillates in the closed propagation path, making measurement impossible. Or it may be unstable.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide an absorption spectrometer capable of measuring stably with high measurement accuracy.

  As a result of various studies on the background described above, the present inventors have negatively charged a part of the light detected by the photodetector, that is, the light in the light propagation path extracted from the closed system propagation path. The fact that amplification using an optical amplifier having a feedback amplification function improves the S / N ratio at the same time, and at the same time, does not oscillate in the closed propagation path and enables high-accuracy and stable absorption analysis. I found. The present invention has been made based on such knowledge.

  That is, the invention according to claim 1 for achieving the above object includes: (a) a laser light source that outputs a pulsed laser beam having a predetermined wavelength; and (b) a closed system that repeatedly propagates light by revolving or reciprocating. An optical waveguide having a propagation path; and (c) a pulse-like shape provided in a closed propagation path of the optical waveguide, optically coupled to the laser light source and the optical waveguide, and output from the laser light source. An optical coupler device that inputs laser light into a closed propagation path of the optical waveguide and extracts a part of the pulsed laser light that repeatedly propagates in the closed propagation path; and (d) the optical coupler device A photodetector for detecting a part of the pulsed laser light extracted from the closed system propagation path of the optical waveguide; and (e) provided in the closed system propagation path of the optical waveguide in a state in which a sample is accommodated. The optical waveguide is closed A sample storage device for repeatedly propagating the pulsed laser light through the sample in the system propagation path, and the sample based on an attenuation rate of a part of the intensity of the pulsed laser light detected by the photodetector (F) receiving a part of pulsed laser light propagating in the optical waveguide taken out from the optical coupler device as input light, and the input light is negative feedback amplified A negative feedback amplification type semiconductor optical amplifier for outputting the output light to the photodetector is provided between the optical coupler device and the photodetector.

  According to the absorbance analyzer of the first aspect of the present invention, a negative feedback amplification type semiconductor optical amplifier is provided between the optical coupler device and the photodetector, and the negative feedback amplification type semiconductor optical amplifier includes the light Receiving a part of the pulsed laser light propagating in the optical waveguide taken out from the coupler apparatus as input light, and outputting the output light obtained by negative feedback amplification of the input light to the photodetector, The light detected by the photodetector has a reduced waveform distortion and an increased S / N ratio by negative feedback amplification. For this reason, there is no oscillation in the closed propagation path and stable absorption analysis is possible. Moreover, since the S / N ratio of the observed waveform in which the light intensity of the pulsed laser light decays with time is high and the noise contained in the waveform is reduced, the light intensity of the pulsed laser light from such a signal. Since the time until the dampens, that is, the ring-down time, can be obtained accurately and accurately, the measurement accuracy for the attenuation of the attenuation curve can be sufficiently obtained.

  Preferably, in the absorbance analyzer, the negative feedback amplification type semiconductor optical amplifier receives a part of the pulsed laser beam extracted by the optical coupler device as a first input light, and the optical coupler. Receiving a part of the pulsed laser light propagating in the optical waveguide extracted from the apparatus as second input light, and having negative feedback amplification, thereby having the same wavelength as the second input light, and The output light intensity-modulated by the ambient light of the first input light is output to the photodetector. In this way, the light detected by the photodetector has less waveform distortion due to negative feedback amplification and has an increased S / N ratio, so there is no oscillation in the closed propagation path, Stable absorption analysis becomes possible. Moreover, since the S / N ratio of the observed waveform in which the light intensity of the pulsed laser light decays with time is high and the noise contained in the waveform is reduced, the light intensity of the pulsed laser light from such a signal. Since the time until the dampens, that is, the ring-down time, can be obtained accurately and accurately, the measurement accuracy for the attenuation of the attenuation curve can be sufficiently obtained.

  Preferably, in the absorbance analyzer, the negative feedback amplification type semiconductor optical amplifier amplifies and outputs the first input light which is a part of the pulsed laser light having the predetermined wavelength, and the pulse A first semiconductor optical amplifying element that emits first ambient light other than the wavelength of the pulsed laser light, the intensity of which is inverted with respect to the intensity of the laser light, and the light output from the first semiconductor optical amplifying element A first wavelength selection element that selects all or part of one ambient light; all or part of the first ambient light selected by the first wavelength selection element; and The second input light, which is a part of the pulsed laser light extracted from the closed propagation path, is input, has the wavelength of the second input light, and is intensity-modulated by the ambient light of the first input light. Second to output the output light Of the light radiated from the conductor light amplifying element and the second semiconductor light amplifying element to the output side, the light having the wavelength of the second input light is transmitted, but the wavelength is different from the wavelength of the second input light. A second negative feedback amplification wavelength-selective reflecting element that reflects light and enters the second semiconductor optical amplifying element. If it does in this way, light will be reflected by the wavelength selective reflection element for 2nd negative feedback amplification to the wavelength different from the wavelength of the 2nd input light among the light radiated | emitted from the 2nd semiconductor optical amplifier to the output side. As a result, the light is again incident on the second semiconductor optical amplifying element and a negative feedback amplification action is generated, so that the light (signal light) detected by the photodetector has an S / N ratio due to the negative feedback amplification. It will be enhanced.

  Preferably, in the absorption spectrometer, the second negative feedback amplification wavelength selective reflection element is an end of an output-side optical fiber optically coupled to an output side of the second semiconductor optical amplification element. And a second optical fiber grating part that reflects all or part of the second ambient light emitted from the second semiconductor optical amplifier and re-enters the second semiconductor optical amplifier. In this case, the second negative feedback amplification wavelength-selective reflecting element is provided in the end of the output side optical fiber and is miniaturized, so that the absorption spectrometer is miniaturized.

  Preferably, in the absorbance analyzer, a tip lens is provided on an end surface of the end portion on the second semiconductor optical amplification element side where the second optical fiber grating portion of the output side optical fiber is provided, The output side optical fiber and the second semiconductor optical amplifying element are optically coupled directly via the tip lens. In this way, since no optical component such as a lens for optical coupling is required, the coupling structure is simple and small, and the absorption spectrometer is miniaturized.

  Preferably, in the absorbance analyzer, the second optical fiber grating section transmits light having the wavelength of the output light, and has a band of at least 3 nm or more generated by amplification of the second semiconductor optical amplification element. The second semiconductor optical amplifying element has a reflection characteristic that reflects all or part of light in a short wavelength side and / or long wavelength side of the wavelength of the output light with respect to the amplified light. On the other hand, they are arranged close to each other with a predetermined optical path length LL. In this way, the absorption spectrometer can be miniaturized.

  Preferably, in the absorption spectrometer, the predetermined optical path length LL is such that the refractive index of the optical transmission path between the second semiconductor optical amplification element and the first optical fiber grating portion is n, When the speed of light is c (mm / sec) and the time interval of the pulses of the second input light is t (seconds), LL ≦ (c · t) / (20 · n). In this way, high responsiveness of the second semiconductor optical amplification element can be obtained. Accordingly, since the second ambient light reflected by the first optical fiber grating portion is quickly re-input to the second semiconductor optical amplifier without delay, the distortion of the signal waveform is effectively reduced and a high modulation degree is achieved. Is obtained.

  Preferably, in the absorbance analyzer, the negative feedback amplification type semiconductor optical amplifier is provided on an input side of the first semiconductor optical amplification element, and is input to the first semiconductor optical amplification element. First negative feedback that allows input light to pass but reflects all or part of the first ambient light emitted from the first semiconductor optical amplifier to the input side and re-inputs the first semiconductor optical amplifier to the first semiconductor optical amplifier. A wavelength selective reflecting element for amplification. In this way, a negative feedback action can be obtained also in the first semiconductor optical amplification width element, and the S / N ratio is further increased with less waveform distortion.

  Preferably, in the absorption spectrometer, the first negative feedback amplification wavelength selective reflection element is provided at an end of an input optical fiber optically coupled to an input side of the first semiconductor optical amplification element. A first optical fiber grating portion that is provided and reflects all or a part of the first ambient light emitted from the first semiconductor optical amplifying element and re-enters the first semiconductor optical amplifying element; In this way, the first negative feedback amplification wavelength selective reflection element is provided in the end portion of the output light side fiber 39 and is miniaturized, so that the absorption spectrometer is miniaturized.

  Preferably, in the absorbance analyzer, a tip ball lens is provided on each end surface of the input optical fiber provided with the first optical fiber grating portion on the first semiconductor optical amplification element side. The input optical fiber and the first semiconductor optical amplifying element are directly optically coupled via the tip ball lens. In this case, since a component such as a lens for optical coupling is not required, the coupling structure is further simplified and miniaturized, and the absorption spectrometer is miniaturized.

  Preferably, in the absorbance analyzer, the first optical fiber grating portion transmits light having a first wavelength of the first input light and is generated by amplification of the first semiconductor optical amplification element. With respect to the amplified light in the above band, it has a reflection characteristic that reflects all or a part of the light on the shorter wavelength side and / or longer wavelength side than the wavelength of the first input light, and One semiconductor optical amplification element is arranged in close proximity with a predetermined optical path length LL. In this way, the absorption spectrometer is further downsized.

  Preferably, in the absorption spectrometer, the predetermined optical path length LL is such that the refractive index of the optical transmission path between the first semiconductor optical amplification element and the first optical fiber grating section is n, in vacuum LL ≦ (c · t) / (20 · n) where c (mm / sec) is the speed of light and t (seconds) is the time interval of the pulses of the first input light. In this way, high responsiveness of the first semiconductor optical amplification element can be obtained. Accordingly, since the first ambient light reflected by the first optical fiber grating section is quickly re-input to the first semiconductor optical amplifying element without delay, distortion of the signal waveform is effectively reduced and a high degree of modulation is achieved. Is obtained.

  Preferably, in the absorption spectrometer, the negative feedback amplification type semiconductor optical amplifier is configured such that a part of the pulsed laser light extracted from the closed propagation path of the optical waveguide by the optical coupler device is the first. A second semiconductor optical amplifying element that is input as two-input light and outputs a negative feedback amplified output light having a wavelength of the second input light; and light emitted from the second semiconductor optical amplifying element to the output side Among them, the second negative feedback amplification wavelength that transmits light having the wavelength of the second input light, but reflects the light to a wavelength different from the wavelength of the second input light and enters the second semiconductor optical amplification element. A selective reflection element. In this way, there is no oscillation in the closed-system propagation path, stable absorption analysis is possible, and the S / N ratio of the observed waveform in which the light intensity of the pulsed laser light decays with time is obtained. Since the noise contained in the waveform is high and the time until the light intensity of the pulsed laser beam attenuates from such a signal, that is, the ring-down time is long and accurate, the attenuation curve can be obtained. Measurement accuracy with respect to attenuation is sufficiently obtained. In addition, the absorbance analyzer is configured more simply.

It is the schematic explaining the example of a fundamental structure of the absorption spectrometer of one Example of this invention. It is a circuit diagram explaining the structural example of the laser light source of FIG. It is sectional drawing explaining the principal part of the structural example of the 1st optical coupler of FIG. It is sectional drawing explaining the principal part of the structural example of the sample storage apparatus of FIG. FIG. 2 is a diagram for explaining a main part of a configuration example of the negative feedback amplification type semiconductor optical amplifier of FIG. 1. It is a perspective view explaining the structure of the 1st semiconductor optical amplifier element of FIG. 5, or the 2nd semiconductor optical amplifier element. It is a figure explaining the structural example of the 2nd fiber grating part provided in the edge part of the output side optical fiber of FIG. It is a figure which shows the spectrum of the control light Lc after amplification which is selectively passed by the 2nd optical fiber grating part of FIG. 5, ie, output light Lout. It is a figure which shows the spectrum of 2nd ambient light Ls2 selectively reflected by the 2nd optical fiber grating part of FIG. It is a figure which shows the waveform of the control light (2nd input light) Lc of 1st wavelength (lambda) 1 used in the experiment using the 2nd semiconductor optical amplifier of FIG. FIG. 11 is a diagram illustrating ambient light that is reflected and re-input to the optical fiber grating portion when the input light illustrated in FIG. 10 is input in the second semiconductor optical amplifier of FIG. 5. In the second semiconductor optical amplifying element of FIG. 5, when the input light shown in FIG. 10 is input, the output light (solid line) transmitted by the optical fiber grating portion is compared with the output light (dotted line) without negative feedback. It is a figure shown. It is a figure which shows the measured value of the eye pattern of the 2nd semiconductor optical signal amplification element of FIG. It is a figure which shows the measured value of an eye pattern when there is no negative feedback in the 2nd semiconductor optical signal amplification element of FIG. FIG. 2 is a schematic diagram showing a partial attenuation waveform of pulsed laser light taken out from a closed system propagation path around which pulsed laser light is circulated in the absorption spectrometer of FIG. 1. FIG. 2 is an observation diagram showing a partial attenuation waveform of pulsed laser light extracted from a closed propagation path in the absorption spectrometer of FIG. 1. It is a figure explaining the principal part of the other structural example of the negative feedback amplification type semiconductor optical amplifier in the other Example (Example 2) of this invention. It is a figure explaining the principal part of the other structural example of the negative feedback amplification type semiconductor optical amplifier in the other Example (Example 3) of this invention. It is a figure explaining the principal part of the other structural example of the negative feedback amplification type | mold semiconductor optical amplifier in the other Example (Example 4) of this invention. It is a figure explaining the principal part of the other structural example of the negative feedback amplification type semiconductor optical amplifier in the other Example (Example 5) of this invention. It is a figure explaining the principal part of the other structural example of the negative feedback amplification type semiconductor optical amplifier in the other Example (Example 6) of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings used for the following description, the dimensional ratios of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a schematic diagram showing the main part of the configuration of an absorption spectrometer 10 according to an embodiment of the present invention. In FIG. 1, an absorption analyzer 10 includes: (a) a laser light source 12 that outputs a pulsed laser beam L having a first wavelength λ1 having a predetermined wavelength, for example, 1551 nm; and (b) an annular shape that repeatedly propagates light by rotating. An optical waveguide 14 having a closed propagation path, and (c) an optical waveguide 14 provided in the annular closed propagation path of the optical waveguide 14 and optically coupled between the laser light source 12 and the optical waveguide 14. The pulsed laser light L output from the laser light source 12 is input into the closed propagation path of the optical waveguide 14, and a part of the pulsed laser light L that repeatedly propagates in the closed propagation path is taken out. A first optical coupler 18; and (d) a half of a photodiode, a phototransistor, or the like that detects a part of the pulsed laser light L extracted from the closed propagation path of the optical waveguide 14 by the first optical coupler 18. A photodetector 20 comprising a body photocell, and (e) a sample 22 interposed in an annular closed-system propagation path of the optical waveguide 14 in a state where the sample 22 is accommodated, and the sample in the annular closed-system propagation path of the optical waveguide 14 22 is a container-like sample storage device 24 that repeatedly propagates the pulsed laser light L through 22, and a ring-down time τ or an attenuation indicating the attenuation state of a part of the attenuation waveform of the pulsed laser light L detected by the photodetector 20. A calculation device 26 for calculating the rate k, and calculating the number density n or the absorbance Δk of the sample 22 based on the ring-down time τ or the attenuation rate k; an attenuation curve calculated in the calculation device 26; And the like. The first optical coupler 18 has a coupling coefficient of 20 dB so as to extract a part of the pulsed laser light L that circulates in the closed propagation path of the optical waveguide 14 and repeatedly propagates at a ratio of 99: 1, for example. Yes.

  Further, in the above-described absorption analyzer 10, the optical fiber 30 that guides the pulsed laser light L from the laser light source 12 to the first optical coupler 18 is optically used with a predetermined coupling coefficient (dB) so as to be about 50:50, for example. A second optical coupler 36 is provided that is coupled so that a part of the pulsed laser light L is taken out and input to the negative feedback amplification type semiconductor optical amplifier 34 via the optical fiber 32 as the first input light Lin. ing.

  As shown in FIG. 1, the negative feedback amplification type semiconductor optical amplifier 34 is disposed between the first optical coupler 18 and the second optical coupler 36 and the photodetector 20. The negative feedback amplification type semiconductor optical amplifier 34 receives a part of the pulsed laser light L divided by the second optical coupler 36 and directed from the laser light source 12 toward the optical waveguide 14 as the first input light Lin, and the optical fiber 31. By receiving a part of the pulsed laser light L propagating in the optical waveguide 14 extracted from the first optical coupler 18 guided through the second optical input as the second input light, that is, the control light Lc, and performing negative feedback amplification, Output light Lout having the same wavelength as the control light Lc and intensity-modulated by the first ambient light Ls1 of the first input light (pulse signal light) Lin is output to the photodetector 20 via the optical fiber 39. .

  For example, as shown in FIG. 2, the laser light source 12 has a light emitting layer interposed between a pair of reflecting layers by epitaxially growing a DC power source 12a and, for example, an AlGaAs-based or InGaAsP-based compound semiconductor on a substrate. A laser diode configured in a state, a laser diode 12b outputting a laser beam having a constant wavelength λ1 in accordance with a drive current supplied from the DC power supply 12a, and a drive current supplied from the DC power supply 12a to the laser diode 12b And a pulse generator 12d for outputting an open / close control signal for opening / closing the driver 12c at a predetermined frequency, for example, a first 1551 nm first switch. Having a wavelength λ1 of 20 to 40 ns And it outputs the pulsed laser light L having a frequency of pulse width and 27 to 98kHz.

  The first optical coupler 18 and the second optical coupler 36 are similarly configured from a pair of optical waveguides made of, for example, optical fibers arranged close to each other. For example, as shown in FIG. 3, the first optical coupler 18 is connected to an optical fiber 38 at both ends to form a first waveguide 18a that forms an annular closed propagation path of the optical waveguide 14, and both ends are optical. The main waveguide 18b is optically coupled to each other at a predetermined rate by fixing the fiber 30 and the second waveguide 18b connected to the optical fiber 31 in the main body 18c and being brought close to each other for a predetermined distance. In this case, the light is branched between the first waveguide 18a and the second waveguide 18b. The coupling coefficient is determined according to the approach length between the first waveguide 18a and the second waveguide 18b, the distance between them, and the like. The first optical coupler 18 extracts the coupling coefficient at a rate of 1% (1:99), for example. Thus, the coupling coefficient is set to 20 dB. In the second optical coupler 36, the coupling coefficient is set so as to be extracted at a ratio of 50% (50:50).

  As shown in FIG. 1, the optical waveguide 14 is formed by rotating an optical fiber 38 once or a plurality of times in a ring, and this optical fiber 38 is connected to the first waveguide 18 a of the first optical coupler 18. They are connected in series. The annular optical fiber 38 introduces the pulsed laser light L from the laser light source 12 supplied via the first optical coupler 18 through the optical fiber 38, so that the pulsed laser light L is transmitted through the same path. An annular closed-system propagation path for repeated propagation is formed.

  For example, as shown in FIG. 4, the sample storage device 24 sandwiches the container 24 a interposed in the annular closed propagation path of the optical waveguide 14 in a state in which the sample 22 is stored, and the sample 22 in the container 24 a. A pair of optical fibers 24b whose end faces are opposed to each other, and an optical fiber 38 constituting a closed propagation path is connected in series to the pair of optical fibers 24b. Accordingly, the pulsed laser light L is repeatedly propagated through the sample 22 held in the container 24a in the annular closed propagation path of the optical waveguide 14. The sample storage device 24 is provided with a hole penetrating the core from the side surface in a part of the optical fiber 38 constituting the annular closed propagation path of the optical waveguide 14, and the sample 22 is filled in the hole. You may be comprised with what was made to do.

  When the pulsed laser light L having the first wavelength λ1 is input as the first input light Lin through the optical fiber 32, the negative feedback amplification type semiconductor optical amplifier 34 corresponds to the intensity Iin of the first input light Lin. The light intensity amplification characteristic of the light other than the first wavelength λ1, that is, the first ambient light Ls1 having the first wavelength λ1 is modulated, and the light amplified from the first input light Lin and the intensity Iin of the first input light Lin. The first semiconductor optical amplifying element 40 that outputs light other than the first wavelength λ1 whose intensity has been inverted, that is, the first ambient light Ls1, and the light output from the first semiconductor optical amplifying element 40 are received. The light other than the first wavelength λ1, that is, the first ambient light Ls1 is separated by reflection, and the first ambient light Ls1 is controlled via the optical fiber 31 as the second input light having the second wavelength λ2. Combine and output to the second semiconductor optical amplifying element 42 When the third optical fiber grating device FGD3, which is a long selection element, and the combined light of the ambient light Ls1 from the third optical fiber grating device FGD3 and the control light Lc, which is the second input light of the second wavelength λ2, are input. The control light Lc is modulated by the ambient light Ls1 of the first input light Lin by mutual gain modulation, and the light other than the second wavelength λ2 whose intensity is inverted with respect to the amplified output light Lout and the intensity Ic of the control light Lc, that is, A second semiconductor optical amplifying element 42 that outputs the second ambient light Ls2 and an optical fiber 39 are provided. When light from the second semiconductor optical amplifying element 42 is introduced, control light Lc of the light is introduced. Transmits the output light Lout having the second wavelength λ2 amplified, but reflects the light other than the second wavelength λ2 of the light, that is, the second ambient light Ls2. A negative feedback amplification type three-terminal optical signal amplifier including a second optical fiber grating device FGD2, which is an output optical fiber for re-inputting the reflected light to the second semiconductor optical amplifying element. Light triode).

  The second wavelength λ2 and the first wavelength λ1 are mutually included in the wavelength band of the ambient light, or the second wavelength λ2 and the first wavelength λ1 are the same wavelength. For example, when the first wavelength λ1 is 1551 nm, the second wavelength λ2 is set to a wavelength included in the wavelength band of the first ambient light Ls1 or the same wavelength 1551 nm. If the second wavelength λ2 of the control light Lc is 1549 nm, the wavelength of the output light Lout is 1549 nm. If the second wavelength λ2 of the control light Lc is 1551 nm, the wavelength of the output light Lout is 1551 nm.

  The first semiconductor optical amplifying element 40 and the second semiconductor optical amplifying element 42 are configured in the same manner from, for example, chip-shaped elements shown in FIG. For example, the second semiconductor optical amplifying element 42 is composed of a semiconductor substrate 42a composed of a compound semiconductor, for example, indium phosphorus InP, and a III-V group mixed crystal semiconductor epitaxially grown thereon, and is formed with a predetermined width by photolithography. An optical waveguide 42b composed of a multilayer film having a relatively high refractive index, and a pn junction that constitutes a part of the multilayer film in the optical waveguide 42b, and includes a bulk, a multiple quantum well, a strained superlattice, and a quantum dot. The active layer 42c is composed of any of the above, an upper electrode 42e fixed to the upper surface of the optical waveguide 42b, and a lower electrode 42f fixed to the lower surface of the semiconductor substrate 42a. In a state where an injection current flows between the upper electrode 42e and the lower electrode 42f, the first input light Lin having a predetermined wavelength λ1 is incident and is allowed to pass through the active layer 42c in the process of being propagated through the optical waveguide 42b. When the light is amplified by the induced radiation action, it is output. At the same time, by so-called mutual gain modulation action, the first ambient light (naturally generated) having an ambient wavelength other than the wavelength λ1 centered on the wavelength λ1 and the intensity increasing and decreasing in inverse proportion to the intensity modulation of the first input light Lin. Light) Ls1, and second ambient light having a surrounding wavelength other than the wavelength λ2 centered on the wavelength λ2 and the intensity increasing / decreasing in inverse proportion to the intensity modulation of the control light (second input light) Lc (naturally generated) Light) Ls2 is generated and output as well.

  When the active layer 42c is composed of multiple wells, for example, it is composed of six pairs of InGaAs and InGaP of about 100 nm lattice-matched by epitaxial growth from the semiconductor substrate 42a, and on the active layer 42c, A guide layer (2000 mm) having a GRIN structure in which the composition (refractive index) is changed stepwise is sequentially provided. The device length of the active layer 42c is, for example, about 600 μm.

  A convex lens is provided between the input side end of the first semiconductor optical amplification element 40 of the optical fiber 32 and the second optical fiber grating device FGD2 provided at the end of the optical fiber 39 on the second semiconductor optical amplification element 42 side. And a front spherical lens R functioning as an end face, between the optical fiber 32 and the input side end face of the first semiconductor optical amplifying element 40, and on the output side end face of the optical fiber 39 and the second semiconductor optical amplifying element 42. Are directly optically coupled to each other. That is, no other optical components are interposed between the optical fiber 32 and the input side end face of the first semiconductor optical amplifying element 40 and between the optical fiber 39 and the output side end face of the second semiconductor optical amplifying element 42. The signal light can be directly input or output.

  In order to promptly re-input the second ambient light Ls2 reflected from the second optical fiber grating portion 46 of the second optical fiber grating device FGD2 into the second semiconductor optical amplifying element 42 and improve its response performance, (2) The distance between the output side end face of the semiconductor optical amplifying element 42 and the end face of the second optical fiber grating section 46, that is, the optical path length LL, is n for the refractive index of the optical transmission path between them and c (mm / Sec), when the time interval per pulse of the control light (second input light) Lc is t (sec), LL ≦ (c · t) (20 · n) is set to be satisfied. . The second semiconductor optical amplifying element 42 and the end of the second optical fiber grating device FGD2 and the end of the optical fiber 39 are supported by a bottom or wall of a case (not shown) after predetermined alignment. Accordingly, the positions are relatively fixed.

For example, as shown in FIG. 7, the optical fiber 39 has a substantially cylindrical core 39a made of quartz SiO ₂ doped with germanium Ge, and a substantially cylindrical shape having a refractive index lower than that of the core 39a and covering the outer peripheral surface thereof. And a cladding 39b made of quartz SiO ₂ . The second optical fiber grating device FGD2 uses a phase mask or the like at the end of the core 39a, and periodically refracts typically about 10000 to 20000 layers due to a light-induced refractive index change caused by ultraviolet irradiation. The rate change includes a second optical fiber grating portion 46 formed in one or more groups in the propagation direction of the core 39a of the optical fiber. The refractive index change may have an equal period, but it may be one in which the period is sequentially changed in a chirp shape. The second optical fiber grating portion 46 functions as a second negative feedback amplification wavelength-selective reflecting element for generating a negative feedback amplification action in the second semiconductor optical amplification element 42, and the period of the refractive index thereof. And has a characteristic of selectively reflecting light having a wavelength corresponding to the effective refractive index, for example, transmits light of the second wavelength λ2 centered at 1551 nm, but is at least 3 nm or more different from the second wavelength λ2, for example 6 It functions as a wavelength selective filter that reflects light having a bandwidth of about 5 nm (second ambient light Ls2). FIG. 8 shows a spectrum of the amplified control light Lc (output light Lout) that is selectively passed by the second optical fiber grating unit 46, and FIG. 9 is selected by the second optical fiber grating unit 46. The spectrum of the second ambient light Ls2 that is reflected back is shown.

  FIG. 9 shows the second ambient light Ls2 including the wavelength bands on both sides of the second wavelength λ2, but the reflection characteristic of the second optical fiber grating portion 46 is that of the second ambient light Ls2. A part of them, for example, a wavelength band on one side of the first wavelength λ1 or a part thereof may be reflected. FIG. 9 shows a case where the second wavelength λ2 is 1551 nm, which is the same as the first wavelength λ1.

Similarly to the optical fiber 39, the optical fiber 32 is also composed of a core and a clad made of quartz SiO ₂ having a refractive index lower than that of the core and covering the outer peripheral surface of the core. At the end of the optical fiber, a phase mask or the like is used, and a periodic refractive index change of typically about 10,000 to 20,000 layers due to a light-induced refractive index change caused by ultraviolet irradiation is a propagation direction of the core of the optical fiber. A first optical fiber grating device FGD1 including a first optical fiber grating portion 50 formed in one group or a plurality of groups is disposed. The first optical fiber grating section 50 functions as a first negative feedback amplification wavelength selective reflection element for generating a negative feedback amplification action in the first semiconductor optical amplification element 40. And has a characteristic of selectively reflecting light having a wavelength corresponding to the period of the refractive index and the effective refractive index. For example, light having a first wavelength λ1 centered at 1551 nm is transmitted. It functions as a wavelength selective filter that reflects light (first ambient light Ls1) having a wavelength of at least 3 nm or more different from the wavelength λ1 and having a bandwidth of, for example, about 6.5 nm.

  Further, in order to promptly re-input the first ambient light Ls1 reflected from the first optical fiber grating section 50 of the first optical fiber grating device FGD1 into the first semiconductor optical amplifying element 40 and to improve its response performance, The distance between the input side end face of the first semiconductor optical amplifying element 40 and the end face of the first optical fiber grating section 50, that is, the optical path length LL, is defined as n for the refractive index of the transmission path between them and c for the speed of light in vacuum. mm / sec), and when the time interval per pulse of the first input light Lin is t (sec), LL <(c · t) (20 · n) is set to be satisfied. A predetermined alignment is applied between the first semiconductor optical amplification element 40 and the end of the first optical fiber grating device FGD1 and the end of the optical fiber 39, and then supported by the bottom or wall of a case (not shown). Accordingly, the positions are relatively fixed.

  The first optical fiber grating section 50 and the second optical fiber grating section 46 cause the first ambient light Ls1 in the surrounding wavelength band of the first wavelength λ1 and the second ambient light Ls2 in the surrounding wavelength band of the second wavelength λ2 to be the first semiconductor. By being re-inputted to the optical amplifying element 40 and the second semiconductor optical amplifying element 42, a negative feedback amplification action is generated, so that a stable output can be obtained with little noise, a high degree of modulation.

  According to an experiment using the second semiconductor optical amplifying element 42 by the present inventors, for example, the control light (second input light) Lc and the first ambient light Ls1 having the first wavelength λ1 shown in FIG. When input to the amplifying element 42, the second semiconductor optical amplifying element 42 amplifies the control light Lc of the first wavelength λ1, and generates second ambient light Ls2 other than the wavelength λ1 whose intensity is inverted. And the combined light is output. These lights are output to the second optical fiber grating device FGD2. The second optical fiber grating unit 46 provided therein provides the first wavelength λ1 that is the amplified light of the control light Lc out of the above light. The second ambient light Ls2 having a wavelength other than the first wavelength λ1 is reflected and re-entered into the second semiconductor optical amplifying element 42. The re-input second ambient light Ls2 is inverted in intensity from the output light Lout having the first wavelength λ1 by the mutual gain modulation, so that the control light having the first wavelength λ1 of the second semiconductor optical amplifier 42 is obtained. The gain (amplification factor) for (second input light) Lc is modulated. That is, the re-input second ambient light Ls2 functions as negative feedback light with respect to the control light Lc. FIG. 11 shows the reflected light of the second optical fiber grating section 46 that changes in synchronization with the control light Lc having the first wavelength λ1 shown in FIG. 10 inputted to the second semiconductor optical amplifying element 42, that is, the second semiconductor. The second ambient light Ls2 re-input to the optical amplifying element 42 is shown.

  FIG. 12 shows the output light Lout output from the second optical fiber grating device F GD2 in a dotted line when the second ambient light Ls2 that is negative feedback light is not input to the second semiconductor optical amplifier 42 in the above experiment. When the negative feedback light (second ambient light Ls2) is input to the second semiconductor optical amplifier 42, the output light Lout output from the second optical fiber grating device FGD2 is shown by a solid line. As is clear when the solid line in FIG. 12 is compared with the dotted line, the waveform of the output light (signal light) Lout output from the second optical fiber grating device FGD2 is not distorted, and nonlinear distortion is reduced. It is apparent that the negative feedback effect in the optical amplification is obtained by inputting the negative feedback light (second ambient light Ls2), so that the gain is stabilized and nonlinear distortion is reduced. Further, since the minimum value (signal base line) of the output light output from the second optical fiber grating device FGD2 is set to a value lower than that indicated by the dotted line, the negative feedback light (second ambient light Ls2) As a result, a negative feedback effect in optical amplification is obtained, so that the modulation degree of the output light Lout to be output is increased and the noise is reduced to increase the S / N ratio.

  FIG. 13 shows the output light Lout output from the second optical fiber grating device F GD2 when the second ambient light Ls2 that is negative feedback light is input to the second semiconductor optical amplifier 42 in the above experiment. FIG. 14 shows the result of eye pattern measurement (pattern displayed on an oscilloscope). FIG. 14 shows the second optical fiber when the negative feedback light (second ambient light Ls2) is not input to the second semiconductor optical amplifier 42 in the above experiment. The eye pattern measurement result (pattern displayed on the oscilloscope) of the output light Lout output from the grating device FGD2 is shown. For the eye pattern measurement, a test pattern PEBS31, a mark ratio of 1/2, and a standard mask SYM16 / OC48 (2.48832 GHz) were used. As is apparent from FIG. 13, when negative feedback light (second ambient light Ls2) is input to the second semiconductor optical amplifying element 42, the signal of the output light Lout output from the second optical fiber grating device FGD2 is It has been greatly stabilized.

  Returning to FIG. 5, the third fiber grating device FGD3 is provided in the two optical fibers 52 and 54 connected to the optical fiber 31 and the melt-stretched portion where the end portions on the optical fiber 31 side are melt-stretched. The third optical fiber grating unit 56 is configured to transmit the amplified light of the first input light Lin having the first wavelength λ1 out of the output light of the first semiconductor optical amplifier element 40 input to the optical fiber 52. The first ambient light Ls1 that is light having a wavelength other than the one wavelength λ1 is reflected and input from the optical fiber 54 to the second semiconductor optical amplifier 42. At the same time, the third fiber grating device FGD3 transmits part of the pulsed laser light L transmitted through the optical fiber 31 and propagating through the optical waveguide 14 extracted from the first optical coupler 18, Two-input light, that is, control light Ic is input to the second semiconductor optical amplifying element 42. That is, the third fiber grating device FGD3 functions as a wavelength selection element, receives the output light of the first semiconductor optical amplification element 40, and outputs the first ambient light Ls1 that is light other than the first wavelength of the output light. While being separated by reflection, the first ambient light Ls1 is combined with the control light Lc, which is the second input light having the second wavelength λ2, via the optical fiber 31, and is output to the second semiconductor optical amplifier 42.

  The end surfaces of the two optical fibers 52 and 54 are each provided with a tip lens R that functions as a convex lens, and the output light of the first semiconductor optical amplification element 40 is directly input to the optical fiber 52 from the end surfaces. In addition, the light output from the optical fiber 54 is directly input to the end face of the second semiconductor optical amplifying element 42. That is, between the end face of the optical fiber 52 and the end face of the first semiconductor optical amplifying element 40, and also between the end face of the second semiconductor optical amplifying element 42 and the optical fiber 54, directly without using other optical components. Are combined.

  The melt-stretching portion of the third fiber grating device FGD3 constitutes a so-called fiber coupler in which the cores are mutually melt-stretched over a predetermined length and branch into a Y-type, and the third fiber grating device FGD3 is melted. In the core of the extending portion, similarly to the above-described second optical fiber grating device FGD2, a phase mask or the like is used, and a periodicity of typically about 10,000 to 20,000 layers due to a light-induced refractive index change due to ultraviolet irradiation. By providing the third optical fiber grating portion 56 in which the refractive index change is formed in one group or a plurality of groups in the propagation direction of the core, light of the first wavelength λ1 is transmitted, but other than the first wavelength λ1. The light, that is, the first ambient light Ls1 not including the first wavelength λ1 is reflected.

  In the negative feedback amplification type semiconductor optical amplifier 34 described above, the output light Lout does not simply amplify the first input light Lin having the first wavelength λ1, but the control light (second input light) Lc having the second wavelength λ2. The signal modulated and amplified by the second ambient light Ls2 is transmitted through the second optical fiber grating unit 46 while the output light Lout of the second wavelength λ2 is transmitted through the second optical fiber grating 46, and at the same time, 2 Since the ambient light Ls2 is reflected and re-input to the second semiconductor optical amplifier 42, the gain of the second semiconductor optical amplification element 42 is controlled by the feedback of the second ambient light Ls2 indicating the intensity inversion ( The second input light) is modulated according to Lc to obtain a negative feedback light amplification effect, the output light Lout is effectively reduced in distortion of the signal waveform, and a high modulation degree is obtained with low noise, resulting in an error rate. When (bit error) is about 2 digits lower Cormorants effect can be obtained. Further, a small three-terminal optical signal amplifier (optical triode) that outputs the output light Lout having the first wavelength λ1 modulated by the control light can be obtained.

The arithmetic unit 26 is composed of a so-called microcomputer, which processes the output light Lout of the negative feedback amplification type semiconductor optical amplifier 34 detected by the photodetector 20 in accordance with a program stored in advance, and uses ring-down spectroscopy. Thus, the component of the sample 22 is specified. That is, the arithmetic unit 26 calculates the attenuation waveform of the pulse group obtained from the photodetector 20 when the pulsed laser light L is output when the sample 22 is not yet accommodated in the sample accommodating device 24, and The ring-down time τ ₀ is obtained in advance from the attenuation waveform, and then the pulse group obtained from the photodetector 20 when the pulsed laser beam L is output when the sample 22 is not yet accommodated in the sample accommodating device 24. In addition to calculating the attenuation waveform, the ring-down time τ is calculated from the attenuation waveform. For example, the number of samples 22 is calculated based on the actual ring-down times τ ₀ and τ from the relationship stored in advance in the equation (4). The sample 22 is specified by calculating the density n.

The principle of the spectroscopic measurement used in this embodiment and the method for deriving the above equation (4) will be described below. A part of the pulsed laser light L circulated in the optical fiber 38 constituting the annular closed propagation path in the optical waveguide 14 is transmitted from the first optical coupler 18 at a predetermined ratio, for example, 1/100 each time it circulates. Therefore, every time the pulsed laser beam L is output, the attenuated waveform of the extracted light, that is, the pulse group is observed as shown in FIG. 15, for example. This waveform is attenuated as time elapses, and the attenuation rate changes according to the material state of the sample 22 through which a part of the circulated first input light L is transmitted. The waveform is represented by the time function I (t) of the following equation (1), where the initial intensity is I ₀ .
I (t) = I ₀ exp− (1 / τ ₀ ) t (1)
Here, (1 / τ ₀ ) is an attenuation rate. τ ₀ is a time until the intensity becomes 1 / e, that is, a time constant, and is also referred to as a reference ring down time. When the light extraction ratio in the first optical coupler 18 is R, the speed of light is c, and the cavity length (circumference length) is L, τ ₀ is expressed by the following equation (2).
τ ₀ = L / c (1-R) (2)
Next, if the ring down time τ when the sample is a light-absorbing material, σ is the absorption cross section of the material of the sample, and n is the number density of the material, Equation (1) can be rewritten as Equation (3). Equation (4) is obtained from Equation (2).
I (t) = I ₀ exp− (t / τ ₀ −σnct) (3)
n = 1 / σc (1 / τ−1 / τ ₀ ) (4)
Accordingly, the vibration density transition of a medium such as water whose absorption cross section σ is known is targeted, and τ ₀ and τ are obtained by measurement to calculate the number density n of water using the equation (4). be able to.

  In the absorbance analyzer 10 of the present embodiment configured as described above, a part of the pulsed first laser L that is circulated in the optical fiber 38 that forms the annular closed propagation path in the optical waveguide 14 is obtained. Each time it goes around, it is taken out as control light Lc from the first optical coupler 18 at a predetermined rate, for example, 1/100, and the first input light Lin is modulated by using it in the negative feedback amplification type semiconductor optical amplifier 34. When the signal intensity (power) detected by the photodetector 20 with the output light Lout subjected to negative feedback amplification is observed with an oscilloscope, an attenuation waveform as shown by the solid line in FIG. 16 is obtained. In this attenuated waveform, the frequency characteristic of the oscilloscope is not sufficiently high, so it is not displayed in a pulse shape as shown in FIG. 15, but an envelope of those pulses is displayed. The arithmetic unit 26 measures the ring-down time τ by measuring the time between the initial value time point of the attenuation curve indicated by the solid line and the time point that is 1 / e of the initial value, and from the equation (4), The number density n of the sample 22 is calculated and displayed on the display device 28.

Here, a thick attenuation curve indicated by a one-dot chain line in FIG. 16 indicates an attenuation waveform detected by the photodetector 20 when the negative feedback amplification type semiconductor optical amplifier 34 is not used. In this case, the S / N is low and unstable, and the ring-down time τ _N is significantly short, so that the measurement accuracy as high as that of the present embodiment cannot be obtained.

  As described above, according to the absorbance analyzer 10 of the present embodiment, the negative feedback amplification type semiconductor optical amplifier 34 is provided between the first optical coupler 18 and the photodetector 20, and the negative feedback amplification type semiconductor light is provided. The amplifier 34 receives a part of the pulsed laser light L having the wavelength λ 1 branched by the second optical coupler 36 as the first input light Lin and repeats the inside of the optical waveguide 14 taken out from the first optical coupler 18. By receiving a part of the propagating pulsed laser light L as control light (second input light) Lc and negatively amplifying the first input light Lin, it has the same wavelength λ2 as the control light Lc, In addition, since the output light Lout whose intensity is modulated by the first ambient light Ls1 of the first input light Lin is output to the photodetector 20, the light (signal) detected by the photodetector 20 is obtained by negative feedback amplification. Less waveform distortion and higher S / N ratio It will be. For this reason, there is no oscillation in the closed propagation path of the optical waveguide 14, and stable absorption analysis is possible. In addition, since the S / N ratio of the observed waveform in which the light intensity of the pulsed laser beam L decays with time is high and the noise contained in the waveform is reduced, the signal of the pulsed laser beam L from such a signal is reduced. Since the time until the light intensity is attenuated, that is, the ring-down time τ is long and accurately obtained, the measurement accuracy for the attenuation of the attenuation curve can be sufficiently obtained.

  Further, according to the absorption spectrometer 10 of the present embodiment, the negative feedback amplification type semiconductor optical amplifier 34 amplifies and outputs the first input light Lin that is a part of the pulsed laser light L having the predetermined wavelength λ1. A first semiconductor optical amplifying element 40 that emits first ambient light Ls1 other than the wavelength λ1 of the pulsed laser light L that is inverted with respect to the intensity of the pulsed laser light L, and the first semiconductor optical amplifying element A third optical fiber grating portion (first wavelength selection element) 56 for selecting all or a part of the first ambient light Ls1 from the light output from 40, and a first optical fiber selected by the third optical fiber grating portion 56. All or part of the ambient light Ls1 and control light (second input light) Lc, which is a part of the pulsed laser light L extracted from the closed propagation path of the optical waveguide 14 by the first coupler 18, are input. And its control light a second semiconductor optical amplifying element 42 that outputs an output light Lout having a wavelength λ2 of c and intensity-modulated by the first ambient light Ls1 of the first input light L1, and an output from the second semiconductor optical amplifying element 42 Of the light radiated to the side, the light having the wavelength λ2 of the control light Lc is transmitted, but the second ambient light Ls2 having a wavelength different from the wavelength λ2 of the control light Lc is reflected to the second semiconductor optical amplifier 42. Second optical fiber grating section (second negative feedback amplification wavelength selective reflection element) 46 to be incident, so that the control light Lc of the light emitted from the second semiconductor optical amplification element 42 to the output side is included. Since the second ambient light Ls2 having a wavelength different from the wavelength λ2 is reflected by the second optical fiber grating unit 46, it is incident again on the second semiconductor optical amplifying element 42, and a negative feedback amplification action is generated. Detected by the light detector 20 The emitted light (signal) has an S / N ratio increased by negative feedback amplification.

  Further, according to the absorption spectrometer 10 of the present embodiment, the second optical fiber grating section (second negative feedback amplification wavelength selective reflection element) 46 is optically provided on the output side of the second semiconductor optical amplification element 42. Provided at the end of the coupled output-side optical fiber 39, and reflects all or part of the second ambient light Ls2 emitted from the second semiconductor optical amplifying element 42 and re-enters the second semiconductor optical amplifying element 42. Since the second negative feedback amplification wavelength-selective reflecting element 46 is provided in the end of the output side optical fiber 39 and is reduced in size because it is configured to be incident, the absorption spectrometer 10 is reduced in size. The

  Further, according to the absorbance analyzer 10 of the present embodiment, the front lens R is disposed on the end surface of the output side optical fiber 39 on the side of the second semiconductor optical amplification element 42 provided with the second optical fiber grating portion 46. Since the output side optical fiber 39 and the second semiconductor optical amplifying element 42 are directly optically coupled via the front ball lens R, an optical element such as a lens for optical coupling is provided. Since no parts are required, the coupling structure is simple and small, and the absorbance analyzer 10 is miniaturized.

  Further, according to the absorption spectrometer 10 of the present embodiment, the second optical fiber grating unit 46 transmits light having the wavelength λ2 of the output light Lout and is at least 3 nm or more generated by amplification of the second semiconductor optical amplifier 42. The second semiconductor optical amplifier has a reflection characteristic that reflects all or part of light in the shorter wavelength side and / or longer wavelength side of the output light Lout than the wavelength of the output light Lout. Since the element 42 is disposed close to the element 42 with a predetermined optical path length LL, the absorption spectrometer is further downsized.

  Further, according to the absorbance analyzer 10 of the present embodiment, the predetermined optical path length LL is expressed by the refractive index of the optical transmission path between the second semiconductor optical amplifying element 42 and the second optical fiber grating section 46 being n, LL ≦ (c · t) / (20 · n), where c (mm / sec) is the speed of light in vacuum and t (seconds) is the pulse time interval of the control light Lc (output light Lout). Thus, high responsiveness of the second semiconductor optical amplification element 42 can be obtained. Therefore, the second ambient light Ls2 reflected by the first optical fiber grating 46 is quickly re-input to the second semiconductor optical amplifying element 42 without delay, so that the distortion of the signal waveform is effectively reduced, A high degree of modulation can be obtained.

  Further, according to the absorption spectrometer 10 of the present embodiment, the negative feedback amplification type semiconductor optical amplifier 34 is provided on the input side of the first semiconductor optical amplification element 40 and is input to the first semiconductor optical amplification element 40. The first input light Lin is allowed to pass, but all or part of the first ambient light Ls1 emitted from the first semiconductor optical amplifier element 40 to the input side is reflected and re-input to the first semiconductor optical amplifier element 40. Since the first optical fiber grating section 50 (first negative feedback amplification wavelength-selective reflection element) to be included is included, the first semiconductor optical amplification element 40 can also obtain a negative feedback action, and the waveform distortion is further reduced. The S / N ratio is increased.

  Further, according to the absorption spectrometer 10 of the present embodiment, the first optical fiber grating section 50 (first negative feedback amplification wavelength selective reflection element) is optically connected to the input side of the first semiconductor optical amplification element 40. The first semiconductor optical amplification is provided by reflecting all or part of the first ambient light Ls1 provided at the end of the coupled input optical fiber 32 and emitted from the first semiconductor optical amplification element 40 to the input side. Since the first optical fiber grating section 50 is provided in the end portion of the input side optical fiber 32 and is reduced in size because the light is incident on the element 40 again, the absorption spectrometer 10 is reduced in size.

  Further, according to the absorption spectrometer 10 of the present embodiment, the front lens R is disposed on the end surface of the input side optical fiber 32 provided with the first optical fiber grating section 50 on the first semiconductor optical amplification element 40 side. Since the optical fiber 32 and the first semiconductor optical amplifying element 40 are directly optically coupled via the tip lens R, a lens for optical coupling is provided. Since no components are required, the coupling structure is further simplified and reduced in size, and the absorption spectrometer 10 is reduced in size.

  Further, according to the absorbance analyzer 10 of the present embodiment, the first optical fiber grating section 50 transmits the light having the first wavelength λ1 of the first input light Lin, and is generated by amplification of the first semiconductor optical amplifier element 40. Further, with respect to the amplified light in a band of at least 3 nm or more, it has a reflection characteristic of reflecting all or a part of the light on the shorter wavelength side and / or the longer wavelength side than the wavelength λ1 of the first input light Lin, In addition, since the first semiconductor optical amplifying element 40 is disposed in close proximity with a predetermined optical path length LL, the absorption spectrometer 10 is further downsized.

  Further, according to the absorbance analyzer 10 of the present embodiment, the predetermined optical path length LL is such that the refractive index of the optical transmission path between the first semiconductor optical amplification element 40 and the first optical fiber grating section 50 is n, and the vacuum Since the speed of light in the medium is c (mm / sec) and the time interval of the pulses of the first input light Lin is t (seconds), LL ≦ (c · t) / (20 · n). 1 High responsiveness of the semiconductor optical amplifying element 40 can be obtained. Therefore, since the first ambient light Ls1 reflected by the first optical fiber grating unit 50 is quickly re-input to the first semiconductor optical amplifying element 40 without delay, distortion of the signal waveform is effectively reduced, and A high degree of modulation can be obtained.

  Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments are denoted by the same reference numerals and description thereof is omitted.

  The negative feedback amplification type semiconductor optical amplifier 34 described above may be as follows. For example, in the negative feedback amplification type semiconductor optical amplifier 60 shown in FIG. 17, the input position of the control light Lc is changed in the third fiber grating device FGD3 as compared with the negative feedback amplification type semiconductor optical amplifier 34 of the first embodiment. In other respects, and the others are similarly configured.

  In the third fiber grating device FGD3 of FIG. 17, a branched optical fiber 62 branched from the optical fiber 54 is provided among the two optical fibers 52 and 54 provided in the melt-stretched portion whose one end is melt-stretched. It has been. At the branch point of the branch optical fiber 62, a Y-shaped branch is formed by forming a melt-stretched portion of the core. A similar function is obtained by inputting the control light Lc from the branch optical fiber 62. Therefore, according to the absorption spectrometer 10 provided with the negative feedback amplification type semiconductor optical amplifier 60, the same effect as that of the above-described embodiment can be obtained.

  A negative feedback amplification type semiconductor optical amplifier 64 shown in FIG. 18 has the same function as that of the negative feedback amplification type semiconductor optical amplifier 34 of the first embodiment, but instead of the third optical fiber grating device FGD3, an adder is used. The drop filter 66 is provided, the first input optical fiber 68 provided in the add / drop filter 66 and the first semiconductor optical amplifying element 40, and the output optical fiber 72 provided in the add / drop filter 66. The second semiconductor optical amplifying element 42 is directly coupled to the first input optical fiber 68 and the front spherical lens R functioning as a convex lens formed on the distal end surfaces of the output optical fiber 72. And the second semiconductor optical amplifying element 42 and the first semiconductor optical amplifying element 40 are different from each other in that they are composed of one common chip.

  The add / drop filter 64 has a first input optical fiber 68 to which the output of the first semiconductor optical amplifier element 40 is input, a second input optical fiber 70 to which the control light Lc is input, and a second semiconductor optical amplifier element. And an output optical fiber 72 for output to 42. The add / drop filter 66 reflects the first ambient light Ls1 other than the second wavelength λ1 of the light input from the first input optical fiber 68 to the output optical fiber 72, and the control light input from the second input optical fiber 70. Lc is transmitted to the output optical fiber 72. Therefore, according to the negative feedback amplification type semiconductor optical amplifier 64 of the present embodiment, the same effect as that of the first embodiment can be obtained.

  The negative feedback amplification type semiconductor optical amplifier 74 shown in FIG. 19 has the same function as that of the negative feedback amplification type semiconductor optical amplifier 60 of the second embodiment shown in FIG. 16, but the reflection film 78 (reflection means) is the first. The difference is that the third optical fiber grating device FGD3 is also connected to the optical fiber 32 and used as four terminals. The first semiconductor optical amplifying element 40 functions as a reflective semiconductor optical amplifier having characteristics such as a high degree of modulation by being provided with the reflective film 78.

  The third optical fiber grating device FGD3 of the present embodiment includes a third optical fiber grating portion 56 provided in a melt-stretched portion in which ends of the two optical fibers 52 and 54 are melt-stretched, and a first wavelength λ1. And a third input unit 76 connected to the optical fiber 32 so as to receive the first input light Lin.

  In the negative feedback amplification type semiconductor optical amplifier 74, when the first input light Lin having the first wavelength λ1 is input to the third input unit 76 of the third optical fiber grating device FGD3, the first input light Lin is the third light. The light passes through the fiber grating portion 56 and enters the first semiconductor optical amplification element 40. In the first semiconductor optical amplifying element 40, the first input light Lin having the first wavelength λ1 is amplified and the first ambient light Ls1 not including the first wavelength λ1 whose intensity phase is inverted is generated. The first ambient light Ls1 is output to both sides, but the first ambient light Ls1 directed toward the reflective film 78 is reflected by the reflective film 78 and is incident on the optical fiber 52 of the third optical fiber grating device FGD3. The third optical fiber grating unit 56 reflects the first ambient light Ls1 other than the first wavelength λ1 out of the light input from the optical fiber 52 to the optical fiber 54, and functions as the second input light from the branch fiber 62. The control light Lc having the second wavelength λ2 is input and combined. Then, the combined first ambient light Ls1 other than the first wavelength λ1 and the control light Lc of the second wavelength λ2 are input to the second semiconductor optical amplifier 42. Therefore, according to the negative feedback amplification type semiconductor optical amplifier 74 of the present embodiment, in addition to the same effects as the negative feedback amplification type semiconductor optical amplifier 60 of the second embodiment shown in FIG. Since the optical amplifying element 40 is a reflective semiconductor optical amplifier, there is an advantage that the degree of modulation and the S / N ratio can be further increased.

  The negative feedback amplification type semiconductor optical amplifier 80 of the embodiment shown in FIG. 20 is different from the negative feedback amplification type semiconductor optical amplifier 74 in place of the reflection film 78 fixed to the end face of the first semiconductor optical amplification element 40. For example, the input side optical fiber 32 provided with the first optical fiber grating section 50 of FIG. 5 is provided, and the second semiconductor optical amplifying element 42 and the first semiconductor optical amplifying element 40 are configured from a common one chip. The other points are the same, and the others are similarly configured. In the present embodiment, the first ambient light Ls1 generated in the first semiconductor optical amplifying element 40 is output to both sides, but the first ambient light Ls1 directed to the input side optical fiber 32 is the first optical fiber. Reflected by the grating section 50 and both incident on the optical fiber 52 of the third optical fiber grating device FGD3, the same effect as the negative feedback amplification type semiconductor optical amplifier 74 shown in FIG. 19 is obtained. Further, in this embodiment, since the second semiconductor optical amplifying element 42 and the first semiconductor optical amplifying element 40 are integrated into one chip, there is an advantage that the size is further reduced. In the present embodiment, the first input light Lin may be input from the input-side optical fiber 32 or may be input from the third input unit 76 of the third optical fiber grating device FGD3. In this embodiment, the input side optical fiber 32 provided with the first optical fiber grating section 50 functions as a reflecting means for the first ambient light Ls1.

  The negative feedback amplification type semiconductor optical amplifier 82 of the embodiment shown in FIG. 21 is different from the negative feedback amplification type semiconductor optical amplifiers 34, 60, 74, 80 in that the first semiconductor optical amplification element 40, the first optical fiber grating. The first and second optical fiber grating portions 56 and 56 are removed, and the second semiconductor optical amplification element 42 and the second optical fiber grating portion 46 are different from each other. In the present embodiment, when the control light Lc having the first wavelength λ1 is amplified in the second semiconductor optical amplifying element 42, the second ambient light Ls2 having the surrounding wavelength of the wavelength λ1 of the control light Lc is converted into the second optical fiber grating section. Since the negative feedback amplification is performed by being reflected from 46 and input to the second semiconductor optical amplifying element 42, the stable output light Lout having a high S / N ratio obtained by amplifying the control light Lc is supplied to the second optical fiber grating. Since the light is output through the unit 46, as in the above-described embodiment, there is no oscillation in the closed propagation path of the optical waveguide 14, and stable absorption analysis is possible. In addition, since the S / N ratio of the observed waveform in which the light intensity of the pulsed laser beam L decays with time is high and the noise contained in the waveform is reduced, the signal of the pulsed laser beam L from such a signal is reduced. Since the time until the light intensity is attenuated, that is, the ring-down time τ, can be obtained accurately and accurately, the measurement accuracy for the attenuation of the attenuation curve can be sufficiently obtained. Further, according to the present embodiment, the negative feedback amplification type semiconductor optical amplifier 82 does not include the first semiconductor optical amplification element 40, the first optical fiber grating unit 50, and the third optical fiber grating unit 56, and In the absorbance analyzer 10, the optical fiber 32 and the second optical coupler 36 are not required, so that there is an advantage that the absorbance analyzer 10 is configured more easily.

  As mentioned above, although one Example of this invention was described based on drawing, this invention is applied also in another aspect.

  For example, in the embodiment of FIG. 1 described above, an optical signal amplifier for amplifying an optical signal composed of, for example, an EDFA, and a filter for removing noise are provided as necessary at a position indicated by a dashed square, for example. Can be provided.

  Further, in the embodiment of FIG. 1 described above, the first optical coupler 18 introduces a part of the pulsed laser light L into the optical waveguide 14 at a predetermined ratio, and also circulates in the optical waveguide 14. Although a part of the laser beam L is derived at a predetermined ratio, it may be divided into two parts for introduction and for introduction.

  In the embodiment of FIG. 1 described above, the optical waveguide 14 has an annular closed-system propagation path composed of an optical fiber 38 wound in an annular shape. For example, between the pair of mirrors, It may have a closed propagation path configured to reciprocate along the same path. In this case, by setting the reflectance of one of the pair of mirrors to 99%, a part of the pulsed laser light L that reciprocates in the closed propagation path can be derived at a rate of 1% (1:99). .

  Further, the configurations of the negative feedback amplification type semiconductor optical amplifiers 34, 60, 64, 74, 80, and 82 described above may be variously changed as necessary.

In the embodiment of FIG. 1 described above, the arithmetic unit 26 specifies the substance or physical property of the sample 22 by obtaining the ring-down time τ of the attenuation curve, but the attenuation rate k of the attenuation curve is If it is obtained in advance using the sum of the reference attenuation rate k ₀ and the light absorption rate Δk (= k ₀ + Δk) without 22, the reference attenuation rate k ₀ (= 1 / τ ₀ ) is actually obtained. The light absorption rate Δk of the sample 22 may be calculated from the measured attenuation rate k.

  Further, in the negative feedback amplification type semiconductor optical amplifiers 34, 60, 64, and 80 in the above-described embodiments, the first optical fiber grating section 50 for causing the first semiconductor optical amplification element 40 to perform negative feedback amplification is not necessarily provided. May be. It is sufficient that at least the second semiconductor optical amplifying element 42 performs negative feedback amplification.

  Although not illustrated one by one, the present invention can be implemented in variously modified and improved modes based on the knowledge of those skilled in the art.

10: Absorption spectrometer 14: Optical waveguide 18: First optical coupler (optical coupler device)
20: photodetector 22: sample 24: sample storage device 32: input side optical fibers 34, 60, 64, 74, 80: negative feedback amplification type semiconductor optical amplifier 39: output side optical fiber 40: first semiconductor optical amplification element 42: Second semiconductor optical amplifier 46: Second optical fiber grating section
(Wavelength selective reflection element for second negative feedback amplification)
50: 1st optical fiber grating part
(Wavelength selective reflection element for first negative feedback amplification)
56: Third optical fiber grating (first wavelength selection element)
Lin: first input light Lc: control light (second input light)
Lout: output light LL: optical path length R: tip ball lens

Claims (12)

A laser light source that outputs a pulsed laser beam of a predetermined wavelength; an optical waveguide having a closed propagation path that repeatedly propagates light by revolving or reciprocating; and a closed propagation path of the optical waveguide, A laser light source and the optical waveguide are optically coupled, and pulsed laser light output from the laser light source is input into the closed system propagation path of the optical waveguide, and the inside of the closed system propagation path is repeated. An optical coupler device for extracting a part of the propagating pulsed laser beam, and a photodetector for detecting a part of the pulsed laser beam extracted from the closed propagation path of the optical waveguide by the optical coupler device; A sample storage device that is provided in a closed propagation path of the optical waveguide in a state in which the sample is stored, and repeatedly propagates the pulsed laser light through the sample in the closed propagation path of the optical waveguide A preparative provided, absorption analyzer for analyzing the sample based on the attenuation factor of the intensity of the portion of the pulsed laser light detected by the light detector,
A part of the pulsed laser beam propagating in the optical waveguide taken out from the optical coupler device is received as input light, and the output light obtained by negative feedback amplification of the input light is output to the photodetector. An absorption spectrometer comprising a feedback amplification type semiconductor optical amplifier between the optical coupler device and the photodetector. The negative feedback amplification type semiconductor optical amplifier is:
The first input light, which is a part of the pulsed laser beam having the predetermined wavelength, is amplified and output, and the first wavelength other than the wavelength of the pulsed laser beam whose intensity is inverted with respect to the intensity of the pulsed laser beam. A first semiconductor optical amplifier that emits ambient light;
A first wavelength selection element that selects all or part of the first ambient light from light output from the first semiconductor optical amplification element;
All or part of the first ambient light selected by the first wavelength selection element and part of the pulsed laser light extracted from the closed propagation path of the optical waveguide by the optical coupler device. A second semiconductor optical amplifying element that receives two input lights, has a wavelength of the second input light, and outputs an output light that is intensity-modulated by ambient light of the first input light;
Of the light emitted from the second semiconductor optical amplifying element to the output side, the light having the wavelength of the second input light is transmitted, but the light is reflected at a wavelength different from the wavelength of the second input light and the light is reflected. The absorption spectrometer according to claim 1, further comprising: a second negative feedback amplification wavelength selective reflection element that is incident on the second semiconductor optical amplification element. The second negative feedback amplification wavelength-selective reflection element is provided at an end of an output-side optical fiber optically coupled to the output side of the second semiconductor optical amplification element. The absorption spectrometer according to claim 2, wherein the second optical fiber grating unit reflects all or part of the emitted second ambient light and re-enters the second semiconductor optical amplifier.   A tip lens is provided on an end surface of the output side optical fiber on the side of the second semiconductor optical amplifying element provided with the second optical fiber grating portion, and the output side optical fiber and the second semiconductor light are provided. 4. The absorption spectrometer according to claim 3, wherein the amplifying element is optically coupled directly through the tip ball lens.   The second optical fiber grating portion transmits light having the wavelength of the output light, and with respect to amplified light in a band of at least 3 nm or more generated by amplification of the second semiconductor optical amplification element, from the wavelength of the output light. Has a reflection characteristic that reflects all or a part of light in the short wavelength side and / or long wavelength side band, and is close to the second semiconductor optical amplifying element with a predetermined optical path length LL. The absorption spectrometer according to claim 3 or 4, wherein the absorbance analyzer is arranged. The predetermined optical path length LL includes a refractive index n of an optical transmission path between the second semiconductor optical amplifying element and the first optical fiber grating part, c (mm / sec) a light velocity in vacuum, When the time interval between two input light pulses is t (seconds),
LL ≦ (c · t) / (20 · n)
The absorption spectrometer according to claim 5, wherein The negative feedback amplification type semiconductor optical amplifier is:
The first input light that is provided on the input side of the first semiconductor optical amplifying element and passes through the first semiconductor optical amplifying element is allowed to pass through, but is emitted from the first semiconductor optical amplifying element to the input side. 7. A wavelength selective reflecting element for first negative feedback amplification that reflects all or part of the first ambient light and re-inputs the light to the first semiconductor optical amplifying element. Absorbance analyzer of 1.   The first negative feedback amplification wavelength selective reflection element is provided at an end of an input optical fiber optically coupled to an input side of the first semiconductor optical amplification element, and is emitted from the first semiconductor optical amplification element The absorption spectrometer according to claim 7, wherein the first optical fiber grating unit reflects all or a part of the first ambient light to be incident again on the first semiconductor optical amplifier.   The input optical fiber provided with the first optical fiber grating portion is provided with a tip lens at the end surface of the end portion on the first semiconductor optical amplification element side, and the input optical fiber and the first semiconductor optical amplification 9. The absorption spectrometer according to claim 8, wherein the optical element is directly optically coupled to the element via the tip ball lens.   The first optical fiber grating portion transmits light of the first wavelength of the first input light, and with respect to amplified light in a band of at least 3 nm generated by amplification of the first semiconductor optical amplification element. A reflection characteristic that reflects all or part of light in a shorter wavelength side and / or longer wavelength side than the wavelength of one input light, and a predetermined optical path length with respect to the first semiconductor optical amplifying element; The absorbance analyzer according to claim 8 or 9, wherein LL is arranged in close proximity to each other. The predetermined optical path length LL includes a refractive index n of an optical transmission path between the first semiconductor optical amplifying element and the first optical fiber grating part, c (mm / sec) a light velocity in vacuum, When the time interval of one input light pulse is t (seconds),
LL ≦ (c · t) / (20 · n)
The absorption spectrometer according to claim 10, wherein The negative feedback amplification type semiconductor optical amplifier is:
Part of the pulsed laser light extracted from the closed propagation path of the optical waveguide by the optical coupler device is input as second input light, and negative feedback amplified output light having the wavelength of the second input light A second semiconductor optical amplifying element that outputs
Of the light emitted from the second semiconductor optical amplifying element to the output side, the light having the wavelength of the second input light is transmitted, but the light is reflected at a wavelength different from the wavelength of the second input light and the light is reflected. The absorption spectrometer according to claim 1, further comprising: a second negative feedback amplification wavelength selective reflection element that is incident on the second semiconductor optical amplification element.

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