JP2007193232A - Light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source device that can vary the spectral form of SC (super continuum) light to be emitted. <P>SOLUTION: A light source device 1a is equipped with a pulse light source 2 that emits an optical pulse train P1 of ultrashort pulse light having a pulse width of several femtoseconds, an optical fiber 11 optically coupled with the pulse light source 2 and receiving the light pulse train P1 to emit SC light P2, and an optical axis adjusting unit 3 optically coupled between the pulse light source 2 and the optical fiber 11. The optical axis adjusting unit 3 varies the optical coupling efficiency between the pulse light source 2 and the optical fiber 11 by using misalignment of optical axes between the pulse light source 2 and the optical fiber 11, and thereby varies the maximum power in each pulse included in the pulse train P1. Thus, the spectral form of the SC light P2 can be preferably varied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light source device for outputting super continuum light (SC light).

  The SC light source, which is one of the broadband light sources, is expected as an important light source for various application fields because of its high output power, wide bandwidth, and spectral flatness. Although various types of SC light source devices have been proposed, the configuration generated in the optical fiber is simple, the interaction length can be easily increased, and spectrum control is easy. Generally, it is widely used.

Examples of such an SC light source device include a coherent broadband light source described in Patent Document 1 and a broadband near-infrared pulsed laser light source described in Non-Patent Document 1.
JP-A-11-160744 Okuno et al., “Broadband near-infrared pulsed laser light source applying non-linearity of optical fiber”, Proceedings of the 21st Near-Infrared Forum Lecture, Near-Infrared Study Group, November 2005, p. 173

  The SC light source is characterized in that its spectral shape is gentle over a wide band. However, depending on the application field, it may be desired to change the spectrum shape of the SC light. For example, when the concentration of a plurality of substances is sequentially measured in infrared spectroscopic measurement, if the spectrum shape of the SC light can be changed in accordance with the absorption wavelength specific to each of the plurality of substances, the measurement accuracy is further improved. However, there has been no SC light source device known so far that can vary the spectrum shape of SC light in this way.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a light source device that can vary the spectrum shape of emitted SC light.

  In order to solve the above problems, a first light source device of the present invention includes a seed light source that emits an optical pulse train, and an optical fiber that is optically coupled to the seed light source and that emits SC light upon receiving the optical pulse train. Spectral variable means for changing the spectral shape of light is provided.

  According to the first light source device described above, the spectrum shape of the SC light can be varied by the spectrum varying means. Thus, for example, when measuring the concentration of a plurality of substances in order in infrared spectroscopic measurement, the spectrum shape of the SC light can be changed in accordance with the absorption wavelength specific to each of the plurality of substances, so that the measurement accuracy is further improved. improves.

  Further, the first light source device may be characterized in that the spectrum changing means changes the spectrum shape of the SC light by changing the maximum power of each pulse included in the optical pulse train. Thereby, the spectrum width can be enlarged / reduced, and the wavelength dependence of the spectrum intensity can be changed.

  The first light source device may be characterized in that the spectrum varying means changes the maximum power of each pulse included in the optical pulse train by changing the output power of the excitation laser light source included in the seed light source. Good. The output power of the excitation laser light source can be easily controlled by the amount of current supplied to the excitation laser light source. Therefore, according to this light source device, the maximum power of each pulse included in the optical pulse train can be easily changed using one parameter such as the current amount of the excitation laser light source.

  Further, the first light source device may be characterized in that the spectrum varying means is a variable gain optical amplifier optically coupled between the seed light source and the optical fiber. By amplifying the maximum power of each pulse included in the optical pulse train with an optical amplifier and making the gain variable, the spectral shape of the SC light can be easily controlled. In this case, since the output power of the seed light source may be constant, an optical pulse train can be obtained stably. In this case, the spectral shape of the light incident on the optical amplifier may be different from the spectral shape of the light emitted from the optical amplifier. In addition to the maximum power of each pulse of the optical pulse train incident on the optical fiber, the change in the spectral shape of the optical pulse train in the optical amplifier is also taken into consideration, whereby the spectral shape of the SC light can be made closer to a desired shape.

  Further, the first light source device may be characterized in that the spectrum changing means is a variable attenuation factor optical attenuator optically coupled between the seed light source and the optical fiber. The maximum power of each pulse included in the optical pulse train is attenuated by the optical attenuator and the attenuation factor is made variable, so that the noise characteristics, time waveform, and spectrum shape of the optical pulse train are not affected. The maximum power of each pulse can be controlled. Therefore, according to this light source device, the spectrum shape of the SC light can be controlled with high accuracy.

  In the first light source device, the spectrum varying means changes the optical coupling efficiency between the seed light source and the optical fiber by using the optical axis shift between the seed light source and the optical fiber, thereby changing the optical pulse train. The maximum power of each included pulse may be changed. As a result, the spectral shape of the SC light can be suitably controlled, and the optical loss can be suppressed as compared with the case where an optical amplifier or an optical attenuator is used.

  In the first light source device, the spectrum varying means is optically coupled between the seed light source and the optical fiber, and changes the time waveform of each pulse included in the optical pulse train incident on the optical fiber. The spectral shape of the SC light may be changed. Thereby, the spectrum shape of SC light can be changed suitably.

  In the first light source device, the spectrum changing means is optically coupled between the seed light source and the optical fiber, and the spectral shape of the SC light is changed by changing the center wavelength of the optical pulse train incident on the optical fiber. It is good also as changing. The spectral shape of the SC light is affected by the dispersion characteristics of the optical fiber and the center wavelength of the optical pulse train. Therefore, according to this light source device, the spectral shape of the SC light can be suitably changed.

  In the first light source device, the spectrum varying means is optically coupled between the seed light source and the optical fiber, and the spectral shape of the SC light is changed by changing the spectral shape of the optical pulse train incident on the optical fiber. It is good also as changing. Thereby, the spectrum shape of SC light can be changed suitably.

  In the first light source device, the spectrum varying means is optically coupled between the seed light source and the optical fiber, and the spectrum of the SC light is changed by changing the polarization direction of the optical pulse train incident on the optical fiber. The shape may be changed. The spectrum shape of SC light is affected by the polarization of the optical pulse train and the polarization dependence of the optical fiber. Therefore, according to this light source device, the spectral shape of the SC light can be suitably changed.

  A second light source device according to the present invention includes a seed light source that emits continuous light, and an optical fiber that is optically coupled to the seed light source and receives continuous light to emit SC light. It has a spectrum variable means for making it variable.

  Even if the light incident on the optical fiber is continuous light, SC light can be generated in the optical fiber if the continuous light has a relatively high power. According to the second light source device described above, the spectrum shape of the SC light can be varied by the spectrum varying means. Therefore, for example, when measuring the concentration of a plurality of substances in sequence in infrared spectroscopy, the spectral shape of the SC light can be changed in accordance with the absorption wavelength specific to each of the plurality of substances, so that the measurement accuracy is further improved. To do.

  The second light source device may be characterized in that the power of continuous light incident on the optical fiber is 100 mW or more. Thereby, it is possible to suitably generate SC light having a bandwidth of several tens of nanometers or more in the optical fiber.

  Further, the first or second light source device may be characterized in that a wavelength of 1550 nm is included in a wavelength range of an optical pulse train or continuous light incident on an optical fiber. Thereby, SC light can be efficiently generated in a low-loss region of the optical fiber.

  Further, the first or second light source device may be characterized in that the spectrum variable means is a band variable filter optically coupled to the output end of the optical fiber. Thereby, the spectrum shape of SC light can be easily changed to a shape having a desired bandwidth.

  The first or second light source device may be characterized in that the spectrum changing means changes the spectrum shape of the SC light by controlling the temperature of the optical fiber. Thereby, since the dispersion characteristic of the optical fiber can be suitably changed, the spectrum shape of the SC light can be suitably changed. In this case, the spectrum changing means preferably includes a temperature control element provided in contact with the optical fiber. Thereby, the temperature of the optical fiber can be easily controlled.

  The first or second light source device may be characterized in that the spectrum varying means is a curved portion with a variable curvature formed in an optical waveguide for emitting SC light to the outside of the device. When the optical waveguide of the SC light has such a curved portion, it is possible to give an arbitrary bending loss to the SC light and change the spectrum shape suitably.

  The first or second light source device may further include a detecting unit that is optically coupled to the emission end of the optical fiber and detects the spectral shape of the SC light. By detecting the spectrum shape of the SC light by this detection means, the spectrum variable means can be feedback controlled using the spectrum shape, and the spectrum shape can be controlled with high accuracy and stability.

  Further, the first or second light source device may be characterized in that the spectrum width of the SC light is 10 times or more of the optical pulse train incident on the optical fiber or the spectrum width of the continuous light. When the spectrum width of the SC light becomes 10 times or more of the spectrum width of the optical pulse train (or continuous light), the deformation of the spectral shape of the SC light due to fluctuations in the characteristics (nonlinearity) of the optical pulse train or optical fiber becomes significant. . Therefore, in such a case, it is desirable that the spectrum shape of the SC light can be arbitrarily changed by the spectrum changing means.

  The first or second light source device may be characterized in that the spectral intensity of the SC light at a wavelength of 1400 nm is 3 dB or more larger than the spectral intensity of the SC light at a wavelength of 1600 nm. For example, when infrared spectroscopic measurement is performed on a living body or the like, the wavelength band around 1400 nm is a wavelength band that is absorbed by moisture. By doing so, loss of spectrum information in this wavelength band can be avoided and measurement accuracy can be improved.

  Further, the first or second light source device may be characterized in that the spectrum intensity of the SC light in the vicinity of the wavelength of 1560 nm is flat. For example, when a change in glucose concentration is measured by infrared spectroscopy, a phenomenon in which the absorption peak wavelength shifts in accordance with the glucose concentration in a wavelength band near 1560 nm may be used. At this time, if the spectral intensity of the SC light near the wavelength of 1560 nm is flat, it is possible to measure the change in glucose concentration with high accuracy. Here, “near wavelength 1560 nm” means, for example, a range of wavelength 1530 nm to 1590 nm. “Spectral intensity is flat” means that, for example, the difference between the maximum spectrum intensity and the minimum spectrum intensity in the wavelength range is 50% or less of the maximum spectrum wavelength.

  According to the light source device of the present invention, the spectrum shape of the emitted SC light can be made variable.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a light source device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIGS. 1A and 1B are diagrams respectively showing configurations of light source devices 1a and 1b according to the embodiment of the present invention. Referring to FIG. 1A, the light source device 1 a includes a pulse light source 2, an optical axis adjustment unit 3, an optical fiber 11, a collimator lens 12, and a condenser lens 13. The pulse light source 2 is a seed light source in the present embodiment, and emits an optical pulse train P1 upon receiving power supply from a power supply device (not shown).

  The optical fiber 11 is optically coupled to the pulsed light source 2 via the collimator lens 12 and the condenser lens 13, and receives the optical pulse train P1 and emits a pulsed supercontinuum (SC) light P2. To do. Specifically, the optical fiber 11 generates SC light P2 having a gentle spectral shape over a wide band by expanding the spectral width of the optical pulse train P1 to, for example, twice or more. Note that the wavelength range of the optical pulse train P1 preferably includes 1550 nm, and the center wavelength of the wavelength range is more preferably in the vicinity of 1550 nm. Thereby, SC light can be efficiently generated in a low-loss region of the optical fiber 11.

  The optical axis adjustment unit 3 is a spectrum variable means for changing the spectrum shape of the SC light P2. The optical axis adjustment unit 3 is included in the optical pulse train P <b> 1 by changing the optical coupling efficiency between the pulse light source 2 and the optical fiber 11 using the deviation of the optical axis between the pulse light source 2 and the optical fiber 11. Change the maximum power of each pulse. The optical axis adjustment unit 3 of the present embodiment includes a first drive unit 31 that displaces the condenser lens 13 and a second drive unit 32 that displaces the light incident end of the optical fiber 11. The first drive unit 31 changes the optical coupling efficiency between the pulse light source 2 and the optical fiber 11 by displacing the condensing lens 13 in the optical axis direction and the direction intersecting the optical axis direction. The second drive unit 32 changes the optical coupling efficiency between the pulse light source 2 and the optical fiber 11 by displacing the light incident end of the optical fiber 11 in a direction crossing the optical axis direction.

  Referring to FIG. 1B, the light source device 1 b includes a pulse light source 2, a variable band filter 4, an optical fiber 11, a collimator lens 12, and a condenser lens 13. Among these, the configurations and functions of the pulse light source 2, the optical fiber 11, the collimator lens 12, and the condenser lens 13 are the same as those of the light source device 1a.

  The band variable filter 4 is a spectrum variable means for changing the spectrum shape of the SC light P2. The band-variable filter 4 is optically coupled to the light emitting end of the optical fiber 11 and limits the bandwidth of the SC light P2 emitted from the optical fiber 11, and the bandwidth to be restricted and its center wavelength are variable. ing. The SC light P2 passes through the band variable filter 4 and is emitted to the outside of the light source device 1b.

  Here, FIG. 2 is a diagram illustrating a configuration of a pulse light source 2 a as an example of the pulse light source 2. The pulsed light source 2a is a so-called active mode-locked ultrashort pulsed light source, and is composed of a ring resonator. That is, the pulse light source 2a includes a semiconductor laser element 21, an LN modulator 22a, a signal generator 22b that drives the LN modulator 22a, and a ring-shaped cavity (optical waveguide) 23. The semiconductor laser element 21 is optically coupled to the ring-shaped portion of the cavity 23 through a coupler 23a. The ring-shaped portion of the cavity 23 is optically coupled to the output optical waveguide 23d through the coupler 23c. An erbium-doped optical fiber (EDF) 23 b and an LN modulator 22 a are optically coupled in series to the ring-shaped portion of the cavity 23.

  When the signal generator 22b sends an electrical pulse signal of a certain frequency to the LN modulator 22a, the optical loss in the LN modulator 22a decreases at a period corresponding to the frequency. Excitation light is incident on the ring-shaped portion of the cavity 23 from the semiconductor laser element 21. If the LN modulator 22a is controlled so that oscillation occurs when the phases of the modes contained in the light pumped by the pump light are synchronized, an ultrashort pulse laser beam having a pulse width of about several femtoseconds can be obtained. It is generated and periodically emitted from the output optical waveguide 23d to the outside. In the light source devices 1a and 1b shown in FIGS. 1A and 1B, this periodic ultrashort pulse light is used as the optical pulse train P1. At this time, the repetition frequency of the optical pulse train P1 matches the frequency of the electrical pulse signal sent from the signal generator 22b to the LN modulator 22a.

  FIG. 3 is a diagram showing a configuration of a pulse light source 2b as another example of the pulse light source 2. The pulse light source 2b is a so-called passive mode-locked ultrashort pulsed light source, and is constituted by a ring resonator. That is, the pulse light source 2b includes a semiconductor laser element 21, a ring-shaped cavity (optical waveguide) 23, a reflection mirror 24a, a piezo motor 24b attached to the reflection mirror 24a, and a signal generator 24c for driving the piezo motor 24b. Have The point that the semiconductor laser element 21 is optically coupled to the cavity 23, the point that the cavity 23 has the output optical waveguide 23d, and the point that the EDF 23b is optically coupled to the ring-shaped portion of the cavity 23 are the above-mentioned pulses. This is the same as the light source 2a (FIG. 2).

  In the pulse light source 2b, a reflection mirror 24a is provided in place of the LN modulator 22a of the pulse light source 2a. The reflection mirror 24a constitutes a part of the ring-shaped portion of the cavity 23, and the length of the ring-shaped portion of the cavity 23 changes periodically as the position of the reflection mirror 24a vibrates. The vibration of the reflection mirror 24a is given by the piezo motor 24b. The vibration frequency is controlled by a signal generator 24c that drives the piezo motor 24b.

  When the signal generator 24c sends an electrical pulse signal having a certain frequency to the piezo motor 24b, the length of the cavity 23 varies in a cycle corresponding to the frequency. Excitation light is incident on the ring-shaped portion of the cavity 23 from the semiconductor laser element 21. Then, at the moment when the length of the cavity 23 satisfies the soliton condition, ultrashort pulse laser light having a pulse width of about several femtoseconds is generated. The ultrashort pulse light is periodically emitted from the output optical waveguide 23d to the outside as an optical pulse train P1. At this time, the repetition frequency of the optical pulse train P1 matches the frequency of the electrical pulse signal sent from the signal generator 24c to the piezo motor 24b. In the pulsed light source 2b, periodic ultrashort pulsed light is generated by mechanically driving the reflection mirror 24a. Therefore, the pulsed light source 2b is compared with the pulsed light source 2a configured to electrically drive the LN modulator 22a. Thus, the repetition frequency of the optical pulse train P1 tends to decrease.

  FIG. 4 is a diagram showing a configuration of a pulse light source 2 c as another example of the pulse light source 2. The pulsed light source 2c is a so-called passive mode-locked ultrashort pulsed light source, and is composed of a solid-state laser made of Er: Yb co-doped glass. That is, the pulse light source 2c includes a semiconductor laser element 21, a saturable absorber mirror 25 in which a saturable absorber and a reflector are integrally formed, a collimator lens 26a, prisms 26b and 26c, an output coupler 26d, Mirrors 27a to 27c and an Er: Yb co-added glass plate 28 are included. Among these components, components other than the semiconductor laser element 21 and the collimator lens 26a constitute a cavity CA for laser oscillation.

  Excitation light emitted from the semiconductor laser element 21 reaches the Er: Yb co-doped glass plate 28 via the collimator lens 26a and the mirror 27a, and excites the Er: Yb co-doped glass plate 28. The Er: Yb co-doped glass plate 28 is disposed on a cavity CA including the saturable absorbing mirror 25, prisms 26b and 26c, an output coupler 26d, and mirrors 27a to 27c. The light traveling through the cavity CA reciprocates between the saturable absorber mirror 25 and the output coupler 26d while being amplified by the Er: Yb co-doped glass plate 28.

  The saturable absorbing mirror 25 has a property of absorbing weak light and reflecting strong light. Since the intensity of the light becomes maximum when the phases of the modes included in the light reaching the saturable absorber mirror 25 are synchronized, the saturable absorber mirror 25 functions as a reflecting mirror only at this moment and laser oscillation occurs. . Therefore, this laser light becomes ultrashort pulse light having a pulse width of about several femtoseconds, and is emitted to the outside from the output coupler 26d as an optical pulse train P1. At this time, the repetition frequency of the optical pulse train P1 is a value corresponding to the length of the cavity CA.

  The operation of the light source devices 1a and 1b having the above configuration will be described. The pulse light source 2 having any one of the pulse light sources 2a to 2c shown in FIGS. 2 to 4 emits an optical pulse train P1. The optical pulse train P1 is configured by periodically arranging ultrashort pulse lights having a pulse width of about several femtoseconds. The optical pulse train P <b> 1 is collimated by the collimator lens 12 and then condensed by the condenser lens 13. The maximum power of each optical pulse of the optical pulse train P1 emitted from the pulse light source 2 is a value of, for example, 70 to 80 kW. The repetition frequency of the optical pulse train P1 is a value such as 50 MHz. The pulse width of the optical pulse train P1 is a value such as 300 femtoseconds or less. Further, the time average power of the optical pulse train P1 is a value of, for example, 70 to 80 mW.

  The optical pulse train P <b> 1 is collected by the condenser lens 13 and then incident on the optical fiber 11. Then, the spectral bandwidth of each optical pulse is expanded more than twice by the nonlinear optical effect (adiabatic soliton compression effect) in the optical fiber 11, and the pulsed SC light P2 having a gentle spectral shape over the wide band is generated. . The SC light P2 is emitted from the light emitting end of the light source device 1a to the outside.

  In the light source device 1 a (FIG. 1A), the optical coupling efficiency between the pulse light source 2 and the light incident end of the optical fiber 11 is arbitrarily set by the optical axis adjustment unit 3. Specifically, the amount of deviation between the optical axis of the condenser lens 13 and the optical axis of the incident end of the optical fiber 11 or the amount of deviation between the focal position of the condenser lens 13 and the incident end position of the optical fiber 11 is expressed as follows. By changing by the first and second driving units 31 and 32, the optical coupling efficiency between the pulse light source 2 and the optical fiber 11 is adjusted.

Here, in FIG. 5A, the optical axis of the condenser lens 13 coincides with the optical axis of the incident end of the optical fiber 11, and the focal position of the condenser lens 13 and the incident end position of the optical fiber 11 are the same. If they match (i.e., if the optical coupling efficiency between the light incident end of the pulse light source 2 and the optical fiber 11 is the maximum) in a graph showing an example of an incident waveform P _a to the optical fiber 11. FIG. 5B shows the case where the optical axis of the condenser lens 13 is shifted from the optical axis of the incident end of the optical fiber 11, or the focal position of the condenser lens 13 and the position of the incident end of the optical fiber 11. when the bets are shifted, is a graph showing an example of an incident waveform P _B to the optical fiber 11.

When the optical coupling efficiency between the pulse light source 2 and the light incident end of the optical fiber 11 is the maximum, if the maximum power of each pulse included in the optical pulse train P1 is PW ₁ (see FIG. 5A), the condenser lens When the optical axis of 13 and the optical axis of the incident end of the optical fiber 11 are deviated, or when the focal position of the condenser lens 13 and the position of the incident end of the optical fiber 11 are deviated, the optical pulse train P1. The maximum power of each pulse included in is PW ₂ smaller than PW ₁ (see FIG. 5B). As described above, when the maximum power of each pulse included in the optical pulse train P1 changes, the spectral shape of the SC light P2 generated by the nonlinear optical effect in the optical fiber 11 changes. By utilizing this, in the light source device 1a (FIG. 1A), the optical coupling between the pulse light source 2 and the light incident end of the optical fiber 11 so that the spectrum shape of the SC light P2 becomes a desired shape. Change efficiency.

  Further, in the light source device 1 b (FIG. 1B), the spectral bandwidth of the SC light P <b> 2 emitted from the optical fiber 11 is changed by the band variable filter 4. Here, FIG. 6 shows an example (graph SP1) of the spectrum shape of the SC light P2 emitted from the optical fiber 11, and an example (graphs SP2 and SP3) of the spectrum shape of the SC light P2 that has passed through the band variable filter 4. It is a graph which shows. In FIG. 6, the graph SP3 shows an example in which the pass bandwidth of the band variable filter 4 is smaller than that of the graph SP2. In FIG. 6, the value of the spectral intensity on the vertical axis is normalized. As shown in FIG. 6, in the light source device 1 b (FIG. 1B), the shape mainly related to the bandwidth of the spectrum shape of the SC light P <b> 2 is changed by the band-variable filter 4 so as to become a desired shape. It is preferably changed.

  In the present embodiment, the light source device 1a including the optical axis adjustment unit 3 and the light source device 1b including the band variable filter 4 have been described. However, the light source device according to the present invention includes the optical axis adjustment unit 3 and the band variable filter 4. More preferably, both of these are provided. Thereby, the freedom degree at the time of changing the spectrum shape of SC light P2 increases.

  As described above, according to the light source device 1a or 1b of the present embodiment, the spectrum shape of the SC light P2 can be varied by the optical axis adjustment unit 3 or the band variable filter 4. Thus, for example, when measuring the concentration of a plurality of substances in order in infrared spectroscopic measurement, the spectrum shape of the SC light can be changed in accordance with the absorption wavelength specific to each of the plurality of substances, so that the measurement accuracy is further improved. improves.

  Here, FIGS. 7A and 7B are diagrams for explaining the infrared spectroscopic measurement. As shown in FIG. 7A, first, the object 101 to be measured is irradiated with the SC light P2 emitted from the light source device 1a (1b). Then, the light that has passed through the measurement object 101 is detected by the detector 102. At this time, among the SC light P2 irradiated to the measurement target object 101, the wavelength component that matches the absorption wavelength specific to the substance contained in the measurement target object 101 is the measurement target object according to the concentration of the substance. 101 is absorbed. Therefore, by comparing the spectrum shape of the SC light P2 and the spectrum shape of the light transmitted through the measurement target object 101, the concentration of the substance contained in the measurement target object 101 can be determined.

  FIG. 7B is a graph showing an example of the spectrum shape of the SC light P2 emitted from the light source device 1a or 1b. For example, when the object 101 to be measured includes water (such as a living body), the vicinity of the wavelength of 1400 nm (wavelength A in FIG. 7B) is a wavelength band that is absorbed by water, so By setting the spectrum intensity to be, for example, 3 dB or more larger than other wavelength bands (for example, wavelength 1600 nm), it is possible to avoid missing spectrum information in this wavelength band and improve the measurement accuracy. Therefore, in such a case, the SC is adjusted by the optical axis adjustment unit 3 or (and) the band-variable filter 4 so that the spectrum shape of the SC light P2 becomes, for example, a shape as shown in the graph SP4 in FIG. The spectral shape of the light P2 may be changed.

  By adjusting so that the zero dispersion wavelength is 1400 nm or more and 1600 nm or less and the input wavelength of the optical pulse train is on the longer wavelength side than the zero dispersion wavelength, the spectrum intensity of the SC light at the wavelength 1400 nm is adjusted. It becomes possible to make it 3 dB or more larger than the spectral intensity. Of course, an external filter may be used.

  Further, for example, when measuring a change in the glucose concentration contained in the measurement object 101, the absorption peak wavelength is influenced by the hydrogen bond of water molecules in the wavelength band near 1560 nm (wavelength B in FIG. 7B). In some cases, a phenomenon of shifting depending on the glucose concentration is used (see, for example, JP-A-10-325794). At this time, if the spectrum intensity of the SC light P2 near the wavelength of 1560 nm is flat, even if the absorption peak wavelength changes, the intensity of the SC light P2 at the peak wavelength is almost constant, so the change in glucose concentration is measured with high accuracy. It becomes possible to do. Therefore, even in such a case, the optical axis adjusting unit 3 or (and) the band-variable filter 4 adjusts the SC shape so that the spectrum shape of the SC light P2 becomes a shape like the graph SP4 shown in FIG. The spectral shape of the light P2 may be changed. Thus, since the SC light P2 has a flat spectral intensity characteristic in the vicinity of the absorption peak wavelength of the substance to be measured, a minute change such as a shift of the absorption peak wavelength can be detected with high sensitivity. Note that the flatness of the spectral intensity characteristic at this time is preferably within 50% of the maximum spectral intensity.

  For example, the spectral intensity of the SC light near the wavelength of 1560 nm is flattened by adjusting the input wavelength of the optical pulse train to be 1560 nm or less and adjusting the zero dispersion wavelength of the optical fiber to be shorter than the input wavelength of the optical pulse train. be able to. The spectral intensity of the SC light near the wavelength of 1560 nm can also be flattened by adjusting the input wavelength of the optical pulse train to 1500 to 1620 nm and adjusting the chromatic dispersion value of the optical fiber at the input wavelength to be negative. . Of course, an external filter may be used.

For example, when measuring the glucose concentration, the CO ₂ concentration, or the NO _X concentration contained in the measurement object 101, a wavelength of 2.1 μm (wavelength C in FIG. 7B) in which these substances exhibit large absorption characteristics. It is preferable that the spectral intensity of the SC light P2 in the nearby wavelength band is large. Therefore, in such a case, the spectrum shape of the SC light P2 is changed by the optical axis adjustment unit 3 or (and) the band-variable filter 4 so that the spectrum shape of the SC light P2 becomes a shape like the graph SP5. Good.

  Further, in the light source device 1 a of the present embodiment, the optical axis adjustment unit 3 serving as a spectrum changing unit utilizes the optical axis shift between the pulse light source 2 and the optical fiber 11 to make use of the pulse light source 2 and the optical fiber 11. The maximum power of each pulse included in the optical pulse train P1 is changed by changing the optical coupling efficiency. As a result, the spectral shape of the SC light P2 can be suitably controlled, and the optical loss can be suppressed lower than when an optical amplifier or an optical attenuator is used between the pulse light source 2 and the optical fiber 11.

  Further, in the light source device 1 b of the present embodiment, the band-variable filter 4 serving as a spectrum varying unit is optically coupled to the emission end of the optical fiber 11. Thereby, the spectral shape of the SC light P2 can be easily changed to a shape having a desired bandwidth.

  In the light source device 1a (1b), the spectrum width of the SC light P2 may be 10 times or more the spectrum width of the optical pulse train P1 received by the optical fiber 11. When the spectral width of the SC light P2 becomes 10 times or more the spectral width of the optical pulse train P1, the deformation of the spectral shape of the SC light P2 due to fluctuations in the characteristics (nonlinearity) of the optical pulse train P1 and the optical fiber 11 becomes significant. . Therefore, in such a case, it is desirable to control the spectrum shape of the SC light P2 by the spectrum variable means (in this embodiment, the optical axis adjustment unit 3 and the band variable filter 4).

(First modification)
FIG. 8A is a diagram illustrating a configuration of a light source device 1c according to a first modification of the embodiment. Referring to FIG. 8A, the light source device 1 c of this modification includes a pulse light source 2, a pulse compressor / expander 5, and an optical fiber 11. Among these, since the configurations and functions of the pulse light source 2 and the optical fiber 11 are the same as those in the above embodiment, a detailed description thereof is omitted.

  The pulse compressor / expander 5 is a spectrum variable means for changing the spectrum shape of the SC light P2. Specifically, the pulse compressor / expander 5 is optically coupled between the pulse light source 2 and the optical fiber 11, and the time width and height (maximum power) of each optical pulse included in the optical pulse train P1 are as follows. By changing the pulse shape, the spectral shape of the SC light P2 is changed to a desired shape. As the pulse compressor / expander 5, a dispersion device such as a variable dispersion compensator is preferably used.

  Here, FIG. 8B is a graph showing changes in the spectral shape of the SC light P2 when the time width of each pulse included in the optical pulse train P1 is changed. FIG. 8B is a graph when the length of the optical fiber 11 is 10 m and the time average power of the optical pulse train P1 is 100 mW. In FIG. 8B, graphs SP6 to SP8 show the spectrum shapes when the pulse time widths of the optical pulse train P1 are 200 femtoseconds, 0.5 picoseconds, and 1 picosecond, respectively. In FIG. 8B, the value of the spectral intensity on the vertical axis is normalized.

  As shown in FIG. 8B, the spectral shape (mainly spectral bandwidth) of the SC light P2 is changed by changing the time width of each optical pulse included in the optical pulse train P1 by the pulse compressor / expander 5. It can be changed effectively. Therefore, the spectrum varying means according to the present invention is preferably realized by the pulse compressor / expander 5 of the present modification.

(Second modification)
FIG. 9 is a diagram illustrating a configuration of a light source device 1d according to a second modification of the embodiment. Referring to FIG. 9, the light source device 1 d of the present modification includes a continuous light source 20, a variable attenuation factor optical attenuator 6, an optical fiber 11, and a variable band filter 4. Among these, the configurations and functions of the optical fiber 11 and the variable band filter 4 are the same as those in the above embodiment.

  The continuous light source 20 of this modification is a seed light source that emits continuous light P3. The continuous light source 20 provides continuous light P3 to the optical fiber 11 via the optical attenuator 6. Even if the light incident on the optical fiber 11 is continuous light, the SC light P2 can be generated in the optical fiber 11 if the continuous light has a relatively high power.

  The optical attenuator 6 is a spectral variable means for changing the spectral shape of the SC light P2. Specifically, the optical attenuator 6 changes the spectral shape of the SC light P2 by changing the power of the continuous light P3. That is, when the power of the continuous light P3 incident on the optical fiber 11 is changed, the condition of the pulse (SC light P2) generated in the optical fiber 11 changes, so that the spectrum shape of the SC light P2 also changes. It becomes. The spectrum varying means according to the present invention is preferably realized by the optical attenuator 6 having a variable attenuation factor as in the present modification.

  In the present modification, the power of the continuous light P3 incident on the optical fiber 11 is preferably 100 mW or more. Thereby, the SC light P2 can be suitably generated in the optical fiber 11. Further, as in the present modification, by further arranging the band variable filter 4 on the light output end side of the optical fiber 11, the spectrum shape of the SC light P2 can be made closer to a desired shape.

(Third Modification)
FIG. 10A is a block diagram illustrating a configuration of a light source device 1e according to a third modification of the embodiment. Referring to FIG. 10A, the light source device 1 e of this modification includes a pulse light source 2, a pulse variable unit 7, an optical fiber 11, and a control unit 14. Among these, the configurations of the pulse light source 2 and the optical fiber 11 are the same as those in the above embodiment.

  The pulse varying section 7 is a spectrum varying means for varying the spectrum shape of the SC light P 2, and is optically coupled between the pulse light source 2 and the optical fiber 11. The pulse variable unit 7 includes, for example, the optical axis adjusting unit 3 of the above-described embodiment shown in FIG. 1A, the pulse compressor / expander 5 of the first modification shown in FIG. 8A, or FIG. The optical attenuator 6 of the second modification shown can be applied.

  Further, by applying a band-variable filter to the pulse variable section 7 and changing the spectral shape (in particular, at least one of the spectral width and the central wavelength) of the optical pulse train P1 incident on the optical fiber 11, the spectral shape of the SC light P2 May be changed. Since the spectral shape of the SC light P2 is affected by the dispersion characteristics of the optical fiber 11 and the spectral width and center wavelength of the optical pulse train P1, a band-variable filter is optically coupled between the pulse light source 2 and the optical fiber 11. The spectral shape of the SC light P2 can be suitably changed.

  The pulse variable unit 7 may change the spectrum shape of the SC light P2 by changing the polarization direction of the optical pulse train P1 incident on the optical fiber 11. Since the spectral shape of the SC light P2 is affected by the polarization of the optical pulse train P1 and the polarization dependence of the optical fiber 11, the spectral shape of the SC light P2 is preferably changed by changing the polarization direction of the optical pulse train P1. Can be changed.

The control unit 14 of the present modification also functions as a spectrum changing unit for changing the spectrum shape of the SC light P2. That is, the control unit 14 sends the control signal S ₁ for controlling the output power of the excitation laser light source of the pulse light source 2 (for example, the semiconductor laser element 21 shown in FIGS. 2 to 4) to the pulse light source 2 for excitation. By changing the output power of the laser light source, the maximum power of each pulse included in the optical pulse train P1 is changed. For example, in the second modified example (see FIG. 9), the maximum power of each pulse of the optical pulse train P1 is changed using the optical attenuator 6, but it is also possible to change the output power of the excitation laser light source. The maximum power of each pulse of the optical pulse train P1 can be easily changed. In addition, the output power of the excitation laser light source can be easily controlled by the amount of current supplied to the excitation laser light source. Therefore, with this configuration, the maximum power of each pulse of the optical pulse train P1 can be easily changed using one parameter such as the amount of current of the excitation laser light source.

In addition, the control unit 14 of the present modification functions as a spectrum variable unit that changes the spectrum shape of the SC light P2 by controlling the temperature of the optical fiber 11. That is, the control unit 14 sends a control signal S ₂ for controlling the temperature of the optical fiber 11 to the temperature control element 9 such as a Peltier element provided in contact with the optical fiber 11. Thereby, since the dispersion characteristic of the optical fiber 11 can be changed suitably, the spectrum shape of SC light P2 can be changed suitably. In addition, it is preferable that the temperature of the temperature control element 9 is easily conducted by winding the optical fiber 11 in a coil shape.

Further, the control unit 14 controls the pulse varying unit 7 in order to obtain the SC light P2 having a desired spectral shape. For example, when the pulse variable unit 7 includes the optical axis adjustment unit 3, the control unit 14 controls drive signals for driving the first and second drive units 31 and 32 shown in FIG. Send a signal _{S 3} to the pulse changing unit 7. When the pulse variable unit 7 includes the pulse compressor / expander 5 (FIG. 8A) or when the pulse variable unit 7 includes the optical attenuator 6 (FIG. 9), the control unit 14 A control signal S ₃ for controlling the compressor / expander 5 and the optical attenuator 6 is sent to the pulse variable section 7. Thereby, the SC light P2 having a desired spectral shape can be suitably obtained.

(Fourth modification)
FIG. 10B is a block diagram illustrating a configuration of a light source device 1f according to a fourth modification of the embodiment. Referring to FIG. 10B, the light source device 1f of this modification includes a pulse light source 2 (or continuous light source 20), a spectrum variable unit 8, an optical fiber 11, an optical amplifier 15, and a control unit 16. Prepare. Among these, about the structure of the pulse light source 2 (continuous light source 20) and the optical fiber 11, it is the same as that of the said embodiment.

The optical amplifier 15 is a spectrum variable means for changing the spectrum shape of the SC light P2, and changes the spectrum shape of the SC light P2 by changing the maximum power of each pulse included in the optical pulse train P1. The optical amplifier 15 has a gain variable, light from the control signal S ₄ for controlling the amplification factor received from the control unit 16, pulse light source 2 with an amplification factor in accordance with the control signal S ₄ The pulse train P1 (or continuous light P3 from the continuous light source 20) is amplified.

  As in this modification, the spectrum varying means may be a variable amplification factor optical amplifier 15 optically coupled between the pulse light source 2 (continuous light source 20) and the optical fiber 11. Thereby, the spectrum shape of SC light P2 can be controlled easily. When the pulse light source 2 is used as a seed light source, the maximum power of each pulse of the optical pulse train P1 may be constant, so that the optical pulse train P1 can be obtained stably. In this case, the spectral shape of the light incident on the optical amplifier 15 and the spectral shape of the light emitted from the optical amplifier 15 may be different from each other. In addition to the maximum power of each pulse of the optical pulse train P1 incident on the optical fiber 11, the spectral shape of the SC light P2 is made closer to a desired shape by taking into account the change in the spectral shape of the optical pulse train P1 in the optical amplifier 15. be able to.

The spectrum variable section 8 is another spectrum variable means for changing the spectrum shape of the SC light P2. For example, the band variable filter 4 of the second modification shown in FIG. 9 can be applied to the spectrum variable unit 8. Further, the spectrum variable section 8 may be a curved section having a variable curvature formed in an optical waveguide for emitting the SC light P2 to the outside of the apparatus. Since the optical waveguide for emitting the SC light P2 has such a curved portion, it is possible to give an arbitrary bending loss to the SC light P2 and to suitably change the spectral shape of the SC light P2. Or spectral variable unit 8 receives a control signal S ₅ for controlling the spectral shape of the SC light P2 from the control unit 16 changes the pass band so that the spectral shape corresponding to the control signal S _5, or The curvature of the optical waveguide is changed. Thereby, the spectrum shape of SC light P2 can be controlled suitably.

Control unit 16, in addition to the control signal S ₄ and S ₅ mentioned above, in the same manner as the control unit 14 of the third modification, for controlling the output power of the excitation laser light source of the pulse light source 2 (continuous light source 20) sends the control signals S ₁ to the pulse light source 2 (continuous light source 20), by changing the output power of the excitation laser light source, to change the maximum power of the optical pulse train P1 (continuous light P3). In addition, the control unit 16 changes the dispersion characteristic of the optical fiber 11 by sending a control signal S ₂ for controlling the temperature of the optical fiber 11 to the temperature control element 9 provided in contact with the optical fiber 11. .

(Fifth modification)
FIG. 11 is a block diagram illustrating a configuration of a light source device 1g according to a fifth modification of the embodiment. Referring to FIG. 11, the light source device 1 g of the present modification includes a pulse light source 2, a pulse variable unit 7, an optical fiber 11, a control unit 17, a detector 18, and a duplexer 19. Among these, the configurations of the pulse light source 2, the pulse variable unit 7, and the optical fiber 11 are the same as those in the above embodiment.

  The detector 18 is a detection means for detecting the spectral shape of the SC light P2. The detector 18 is optically coupled to the emission end of the optical fiber 11 via the duplexer 19 and takes in part of the SC light P2. The detector 18 includes a wavelength tunable filter 18a, a light detection element 18b, and a signal processing unit 18c. A part of the SC light P2 taken in by the detector 18 passes through the wavelength tunable filter 18a, and then is photoelectrically converted by the photodetector 18b to become a periodic electrical signal. Based on this electrical signal, the signal processing unit 18c detects the spectrum shape (spectrum intensity for each frequency). The detection result is sent to the control unit 17.

The controller 17 controls the control signal S ₁ for changing the output power of the excitation laser light source of the pulse light source 2 and the temperature control of the optical fiber 11 based on the spectrum shape of the SC light P 2 detected by the detector 18. A control signal S ₂ to be performed and a control signal S ₃ to control the pulse variable unit 7 are generated and sent to the pulse light source 2, the temperature adjustment element 9, and the pulse variable unit 7, respectively. Thus, by detecting the spectrum shape of the SC light P2 by the detector 18, it is possible to feedback control the spectrum variable means (pulse variable unit 7, control unit 17) using the detection result, and the spectrum shape. Can be controlled with high accuracy and stability.

  The light source device according to the present invention described above is not limited to the above-described embodiments and modifications, and various modifications and additions of components are possible. For example, in the above-described embodiments and modifications, various aspects of the spectrum varying unit according to the present invention have been described. However, the light source device according to the present invention combines a plurality of arbitrary units among the above-described spectrum varying units. May be configured.

FIGS. 1A and 1B are diagrams each showing a configuration of a light source device according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of an example of a pulse light source. FIG. 3 is a diagram illustrating a configuration of another example of the pulse light source. FIG. 4 is a diagram illustrating the configuration of another example of the pulse light source. FIG. 5A shows a case where the optical axis of the condensing lens and the optical axis of the incident end of the optical fiber coincide, and the focal position of the condensing lens and the incident end position of the optical fiber coincide. It is a graph which shows an example of the incident waveform to an optical fiber. FIG. 5B shows the case where the optical axis of the condensing lens is shifted from the optical axis of the incident end of the optical fiber, or the focal position of the condensing lens is shifted from the position of the incident end of the optical fiber. It is a graph which shows an example of the incident waveform to the optical fiber in. FIG. 6 is a graph showing an example (SP1) of the spectrum shape of the SC light emitted from the optical fiber and an example (SP2 and SP3) of the spectrum shape of the SC light that has passed through the band-variable filter. FIGS. 7A and 7B are diagrams for explaining infrared spectroscopic measurement. FIG. 8A is a diagram illustrating a configuration of a light source device according to a first modification. FIG. 8B is a graph showing changes in the spectrum shape of the SC light when the time width of each pulse included in the optical pulse train is changed. FIG. 9 is a diagram illustrating a configuration of a light source device according to a second modification. FIG. 10A is a block diagram illustrating a configuration of a light source device according to a third modification. FIG. 10B is a block diagram illustrating a configuration of the light source device according to the fourth modification. FIG. 11 is a block diagram illustrating a configuration of a light source device according to a fifth modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a-1g ... Light source device, 2, 2a-2c ... Pulse light source, 3 ... Optical axis adjustment part, 4 ... Band variable filter, 5 ... Pulse compression / expansion device, 6 ... Optical attenuator, 7 ... Pulse variable part, 8 DESCRIPTION OF SYMBOLS ... Spectrum variable part, 9 ... Temperature control element, 11 ... Optical fiber, 12 ... Collimator lens, 13 ... Condensing lens, 14, 16, 17 ... Control part, 15 ... Optical amplifier, 15 ... Frequency control part, 18 ... Detection 19 ... demultiplexer, 20 ... continuous light source, 21 ... semiconductor laser element, 22a ... LN modulator, 22b, 24c, 52 ... signal generator, 23 ... cavity, 24a ... reflection mirror, 24b ... piezo motor, 25 ... Saturable absorption mirror, 28... Er: Yb co-doped glass plate, 31... First drive unit, 32... Second drive unit, P 1 .. optical pulse train, P 2.

Claims (17)

A seed light source that emits an optical pulse train;
An optical fiber optically coupled to the seed light source and receiving the optical pulse train and emitting supercontinuum light (SC light);
With
A light source device comprising spectrum varying means for varying the spectrum shape of the SC light.   2. The light source device according to claim 1, wherein the spectrum changing unit changes a spectrum shape of the SC light by changing a maximum power of each pulse included in the optical pulse train.   The said spectrum variable means changes the maximum power of each pulse contained in the said optical pulse train by changing the output power of the excitation laser light source contained in the said seed light source, The said power source is characterized by the above-mentioned. Light source device.   3. The light source device according to claim 2, wherein the spectrum varying means is a variable gain optical amplifier optically coupled between the seed light source and the optical fiber.   3. The light source device according to claim 2, wherein the spectrum varying means is a variable attenuation factor optical attenuator optically coupled between the seed light source and the optical fiber.   Each of the spectrum variable means includes each optical pulse train included in the optical pulse train by changing an optical coupling efficiency between the seed light source and the optical fiber by using a deviation of an optical axis between the seed light source and the optical fiber. The light source device according to claim 2, wherein the maximum power of the pulse is changed.   The spectrum variable means is optically coupled between the seed light source and the optical fiber, and changes the time waveform of each pulse included in the optical pulse train incident on the optical fiber to change the SC light. The light source device according to claim 1, wherein a spectrum shape is changed.   The spectrum variable means is optically coupled between the seed light source and the optical fiber, and changes the spectrum shape of the SC light by changing the center wavelength of the optical pulse train incident on the optical fiber. The light source device according to claim 1, wherein:   The spectrum changing means is optically coupled between the seed light source and the optical fiber, and changes the spectrum shape of the SC light by changing the spectrum shape of the optical pulse train incident on the optical fiber. The light source device according to claim 1, wherein:   The spectrum varying means is optically coupled between the seed light source and the optical fiber, and changes the spectrum shape of the SC light by changing the polarization direction of the optical pulse train incident on the optical fiber. The light source device according to claim 1, wherein: A seed light source that emits continuous light;
An optical fiber optically coupled to the seed light source and receiving the continuous light and emitting supercontinuum light (SC light);
With
A light source device comprising spectrum varying means for varying the spectrum shape of the SC light.   The light source device according to claim 1, wherein a wavelength of 1550 nm is included in a wavelength range of the optical pulse train or the continuous light incident on the optical fiber.   The light source device according to claim 1, wherein the spectrum varying unit is a band variable filter optically coupled to an output end of the optical fiber.   The light source device according to claim 1 or 11, wherein the spectrum changing unit changes a spectrum shape of the SC light by controlling a temperature of the optical fiber.   The light source device according to claim 14, wherein the spectrum varying unit includes a temperature control element provided in contact with the optical fiber.   12. The light source device according to claim 1 or 11, wherein the spectrum varying means is a curved portion having a variable curvature formed in an optical waveguide for emitting the SC light to the outside of the device.   The light source device according to any one of claims 1 to 16, further comprising a detection unit that is optically coupled to an emission end of the optical fiber and detects a spectral shape of the SC light.

Images