JP4608402B2 - Wavelength conversion device and fluorescence microscope device - Google Patents

Description

The present invention relates to a wavelength conversion device and a fluorescence microscope apparatus, and more particularly, relates to a fluorescent microscope apparatus that uses the wavelength conversion apparatus and which is Ru can be suppressed noise of the output light.

  In recent years, in order to increase the communication capacity of an optical communication system, a wavelength division multiplexing (WDM) communication system that multiplexes and transmits a plurality of lights having different wavelengths has been actively introduced. In such a WDM communication system, in order to effectively use a limited number of wavelengths, there is a demand for practical use of a wavelength conversion element that converts a signal wavelength into an arbitrary signal wavelength. Conventionally, as a wavelength conversion element for converting the wavelength of light, an element using a semiconductor optical amplifier, an element using four-wave mixing, second harmonic generation by quasi-phase matching, which is a kind of second-order nonlinear optical effect, and sum frequency Wavelength conversion elements using generation and difference frequency generation are known (for example, see Patent Document 1).

FIG. 1 shows a configuration of a wavelength conversion device using a conventional quasi phase matching type wavelength conversion element. The wavelength conversion device combines and outputs the semiconductor laser 11 that outputs the signal light A having the wavelength λ _A , the semiconductor laser 12 that outputs the control light B having the wavelength λ _B , and the signal light A and the control light B. The optical coupler 14 includes a wavelength conversion element 13 that inputs the combined signal light A and control light B and outputs converted light C having a wavelength λ _C. Drive circuits 11a and 12a and temperature control circuits 11b and 12b are connected to the semiconductor lasers 11 and 12, respectively. Further, a fiber grating 15 is inserted between the semiconductor laser 11 and the optical coupler 14.

Since the intensity of the converted light C is proportional to the product of the intensity of the signal light A and the control light B, only the wavelength can be converted from the signal light A to the converted light C if the control light beam is kept at a constant intensity. . For example, when λ _A = 1.55 μm and λ _B = 0.98 μm, λ _C = 0.60 μm is obtained as the sum frequency. When λ _A = 1.31 μm and λ _B = 1.06 μm, λ _C = 0.59 μm is obtained as the sum frequency. Further, when λ _A = 1.55 μm and λ _B = 0.77 μm, λ _C = 1.53 μm is obtained as the difference frequency. Therefore, in order to obtain a specific wavelength, it is necessary to strictly control the wavelengths of the signal light A and the control light B.

  FIG. 2 shows a phase matching curve when wavelength conversion is performed in order to obtain 0.59 μm yellow light by second harmonic generation. Since the phase matching band of the wavelength conversion element is very narrow, a semiconductor laser that oscillates in a single mode is desirable in order to stably output converted light.

  The wavelengths of 1.55 μm and 1.31 μm are long wavelength bands used in optical communication, and a laser diode that oscillates at a single wavelength, such as a DFB laser diode, can be used as a semiconductor laser. On the other hand, the wavelength in the short wavelength band of 0.98 μm, 1.06 μm, and 0.77 μm is very difficult to produce a DFB laser diode and the demand is small. Yes. Therefore, a fiber grating that partially reflects only a specific wavelength is connected to the output of the semiconductor laser, and a part of the output light is reinjected into the semiconductor laser to control the oscillation wavelength to oscillate at the grating wavelength. ing.

JP 2003-140214 A A. Ferrari, et al., “Subkilohertz Fluctuations and Mode Hopping in High-Power Grating-Stabilized 980-nm Pumps,” IEEE J. of Lightwave Tech., Vol.20, pp.515-518, 2002/3

  However, it is known that even when a semiconductor laser and a fiber grating are combined, an unstable region called coherent collapse exists under certain operating conditions, and a state in which the output fluctuates with time (for example, non-coherent collapse occurs). Patent Document 1). Due to coherent collapse, there is a problem that output fluctuation is applied to the wavelength-converted light and noise is generated.

  FIG. 3 shows an output spectrum of a light source combining a conventional semiconductor laser and a fiber grating. It can be seen that temporal output fluctuations appear as discontinuous output spectra. FIG. 4 shows the result of continuously measuring this state and holding the maximum value, and FIG. 5 shows the result of holding the minimum value. Further, FIG. 6 shows the time variation of the output power. Since the maximum value and the minimum value have a continuous spectrum in this way, it can be seen that the output of this light source changes every moment in the order of msec between the maximum value and the minimum value. Therefore, similar noise is also generated in the converted light output from the wavelength converter using the light source that combines the semiconductor laser and the fiber grating.

The present invention has been made in view of such problems, it is an object to provide a fluorescence microscope apparatus using the wavelength conversion device and which Ru can be suppressed noise of the output light It is in.

In order to achieve the above object, the present invention provides a first laser that outputs a first laser beam having a fixed wavelength, and a second laser beam that is output. A wavelength conversion element that inputs a second laser capable of changing the wavelength of the laser, the first laser light, and the second laser light, and outputs converted light having a wavelength different from the wavelength of the laser light Including a fiber grating connected between the first laser and the wavelength conversion element, the fiber grating having the fixed wavelength λ ₁ and the wavelength conversion element A first grating having a reflection band of wavelength λ ₁ within the phase matching band of the wavelength conversion element and outside the phase matching band of the wavelength conversion element,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ LN or _{λ 1 + Δλ 2/2 +} Δλ LN <λ 2
Δλ ₁ <Δλ _LN
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
And a second grating having a reflection band of wavelength λ ₂ having the following relationship: R ₁ and R ₂ are the respective reflectances of the first and second gratings, and Δλ ₁ and Δλ ₂ are the first And the half width of each of the second grating, Δλ _LN is a phase matching band of the wavelength conversion element, G (λ) is a gain at the wavelength λ, and the light of the wavelength λ ₁ reflected by the fiber grating and the wavelength λ maintains the _second optical coherence with each other, the light of wavelength lambda ₁ reflected by the fiber grating with stabilizing the laser oscillation of the first laser, the wavelength lambda ₁ transmitted through the fiber grating light is converted to the converted light by the wavelength conversion element, light of the wavelength lambda ₂ reflected by the fiber grating laser oscillation of the first laser Causes a constant, light of the wavelength lambda ₂ that has passed through the fiber grating is characterized in that is transmitted through the wavelength conversion element.

The invention according to claim 2 is characterized in that the wavelength conversion element according to claim 1 is made of a nonlinear optical crystal having a periodic polarization inversion structure.

The invention according to claim 3 is characterized in that the nonlinear optical crystal according to claim 2 has a waveguide structure.

The invention according to claim 4 includes a light source that emits laser light and a detection unit that detects fluorescence by the laser light from the object to be measured, and is a fluorescence microscope apparatus that analyzes fluorescent protein in a living cell. The light source includes a first laser that outputs a first laser beam having a fixed wavelength, a second laser that can change the wavelength of the second laser beam that is output, and a periodically domain-inverted structure. A wavelength conversion element that inputs the first laser light and the second laser light, and outputs coherent light having a wavelength different from the wavelength of the laser light; with the connected fiber gratings between the laser and the wavelength conversion element, the fiber grating, the a fixed wavelength lambda _1, is within the phase matching band of the wavelength conversion element A first grating having a reflection band of the long lambda _1, there outside the phase matching band of the wavelength conversion element,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ LN or _{λ 1 + Δλ 2/2 +} Δλ LN <λ 2
Δλ ₁ <Δλ _LN
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
And a second grating having a reflection band of wavelength λ ₂ having the following relationship: R ₁ and R ₂ are the respective reflectances of the first and second gratings, and Δλ ₁ and Δλ ₂ are the first And the half width of each of the second grating, Δλ _LN is a phase matching band of the wavelength conversion element, G (λ) is a gain at the wavelength λ, and the light of the wavelength λ ₁ reflected by the fiber grating and the wavelength λ maintains the _second optical coherence with each other, the light of wavelength lambda ₁ reflected by the fiber grating with stabilizing the laser oscillation of the first laser, the wavelength lambda ₁ transmitted through the fiber grating light is converted to the converted light by the wavelength conversion element, light of the wavelength lambda ₂ reflected by the fiber grating laser oscillation of the first laser Causes a constant, light of the wavelength lambda ₂ that has passed through the fiber grating is characterized in that is transmitted through the wavelength conversion element.

  As described above, according to the present invention, since the fiber grating having the reflection band at a wavelength different from the oscillation wavelength of the laser is provided, the output fluctuation of the converted light output from the wavelength converter, that is, the noise is suppressed. It becomes possible to do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, in order to stabilize the operation of the semiconductor laser to which the fiber grating (wavelength λ ₁ , reflectance R ₁ , half-value width Δλ ₁ ) is connected, a new wavelength different from the oscillation wavelength of the semiconductor laser is newly used. A fiber grating (wavelength λ ₂ , reflectance R ₂ , half-value width Δλ ₂ ) having a reflection band is connected.

The time variation in the output of the semiconductor laser indicates that the variation is likely to occur due to the oscillating carrier density. Therefore, it is preferable to further stabilize the fluctuating carrier density. For this purpose, it is necessary to stabilize the carrier density by newly oscillating even at another wavelength, and to maintain the oscillation at the wavelength λ ₁ required for the wavelength converted light.

The laser oscillation conditions are schematically
R _f · R _r · G (λ _LD ) = 1
Determined by. Here, R _f represents the reflectance of the front surface of the semiconductor laser, R _r represents the reflectance of the rear surface of the semiconductor laser, and G (λ _LD ) represents the gain at the oscillation wavelength λ _LD . Since R _f ≦ R ₁ and R ₂ in order to oscillate a fiber laser attached to a semiconductor laser, the oscillation condition determined by FBG is approximately:
R ₁ · R _r · G (λ ₁ ) = 1
R ₂ · R _r · G (λ ₂ ) = 1
Must be. Here, G (λ ₁ ) and G (λ ₂ ) represent gains at wavelengths λ ₁ and λ ₂ . Therefore,
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
Must be met. Furthermore, since it is necessary to make the wavelength λ ₂ outside the full width at half maximum of the other fiber grating,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ 1/2 or _{λ 1 + Δλ 2/2 +} Δλ 1/2 <λ 2
It is necessary to satisfy.

In the wavelength conversion device using the wavelength conversion element, the oscillation condition takes loss into consideration,
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
It is necessary to satisfy. Furthermore, since it is necessary to make the wavelength λ ₂ outside the half width of the other fiber grating and the phase matching band Δλ _LN of the wavelength conversion element,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ LN or _{λ 1 + Δλ 2/2 +} Δλ LN <λ 2
Δλ ₁ <Δλ _LN
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
It is necessary to satisfy.

  By using the semiconductor laser stabilized in this way, it is possible to suppress fluctuations in the output of the converted light output from the wavelength converter, that is, noise.

FIG. 7 shows a configuration of a wavelength conversion device using a stabilized semiconductor laser according to the first embodiment of the present invention. The wavelength converter includes a semiconductor laser 51 that outputs a signal light A having a wavelength λ _A (976.4 nm), a semiconductor laser 52 that outputs a control light B having a wavelength λ _B (1307 nm), a signal light A, and a control light B. And a wavelength conversion element 53 that inputs the combined signal light A and control light B and outputs the converted light C of wavelength λ _C. Drive circuits 51a and 52a and temperature control circuits 51b and 52b are connected to the semiconductor lasers 51 and 52, respectively.

The wavelength conversion element 53 includes a nonlinear optical crystal having a periodic polarization inversion structure, and is any one of LiNbO ₃ , LiTaO ₃ , LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1). Alternatively, it is possible to use a nonlinear optical crystal containing at least one selected from the group consisting of Mg and Zn as an additive. Furthermore, the wavelength conversion element 53 may have a waveguide structure in order to increase the wavelength conversion efficiency.

Fiber gratings 55 and 56 are inserted between the semiconductor laser 51 and the optical coupler 54. The fiber grating 55 has a wavelength λ ₁ = 976.4 nm, a reflectance R ₁ = 8%, and a half width Δλ ₁ = 20 pm, and the fiber grating 56 has a wavelength λ ₂ = 975.1 nm and a reflectance R ₂ = 5%. The full width at half maximum Δλ ₂ = 50 pm. The phase matching band Δλ _LN of the wavelength conversion element 53 is 0.2 nm.

In FIG. 8, the output spectrum of the converted light of the wavelength converter in Example 1 is shown. By providing the fiber grating 56, it can be seen that oscillation occurs at the wavelength λ ₁ (976.4 nm) and the wavelength λ ₂ (975.1 nm). It is the beat that has peaks on the sides of the wavelengths λ ₂ and λ ₁ . At this time, the wavelength lambda _2, since outside the phase matching band [Delta] [lambda] _LN of the wavelength conversion element _{53 (λ 1 + Δλ 2/} 2 + Δλ LN <λ 2), does not contribute to the wavelength conversion by the nonlinear optical effect. The oscillation light and beat light with the wavelength λ ₂ contribute only to the stable operation of the semiconductor laser 51. Since the semiconductor laser 51 oscillates at two wavelengths, even if the oscillation at the wavelength λ ₁ becomes unstable, the oscillation at the wavelength λ ₂ causes the wavelength converted light to be stable.

FIG. 9 shows the time variation of the output power of the wavelength conversion device in the first embodiment. The time fluctuation of the output power of the conversion light of wavelength 560nm output from a wavelength converter is shown. Compared with the conventional wavelength converter shown in FIG. 6, the stability against output fluctuation can be increased to about 10 ⁶ times.

  FIG. 10 shows a configuration of a wavelength conversion device using a stabilized semiconductor laser according to the second embodiment of the present invention. In the first embodiment, the insertion positions of the fiber gratings 55 and 56 are changed. In the second embodiment as well, stable converted light can be output in the same manner as shown in FIGS.

  FIG. 11 shows a configuration of a wavelength conversion device using a stabilized semiconductor laser according to Example 3 of the present invention. In Example 3, a fiber grating 57 having reflection peaks at two wavelengths is used. The fiber grating 57 has, for example, a refractive index change of two different types of grating periods. Therefore, similarly to the first and second embodiments, the configuration is such that two fiber gratings are inserted. In the third embodiment as well, as shown in FIGS. 8 and 9, stable converted light can be output.

  FIG. 12 shows a configuration of a fluorescence microscope apparatus according to an embodiment of the present invention. The fluorescence microscope apparatus incorporates the wavelength conversion apparatus according to Example 1 shown in FIG. 7 as a light source, and the visible light from the light source is measured via an optical system including a lens 1015, a dichroic mirror 1013, and an objective lens 1014. The object 1016 is irradiated. The fluorescence output from the object to be measured is observed by the high-sensitivity camera 1011 via the objective lens 1014, the dichroic mirror 1013, and the prism 1012.

  According to the present embodiment, a visible light source having a modulation function and having a practical light intensity can be produced. Therefore, a fluorescent protein (GFP) fused to another protein gene and introduced into a cell. When used for observation, a specific structure or functional molecule can be fluorescently labeled with high sensitivity in a living cell.

The light sources according to the first to fourth embodiments can superimpose ON / OFF signals by direct modulation in addition to outputting CW light. With reference to FIG. 13, the modulation system of the semiconductor laser of the wavelength conversion device will be described. The semiconductor laser 51 of the wavelength converter (0.98 .mu.m band), conventionally, in order to cause the oscillation of the lambda _1, was subjected to voltage drive by the laser drive current to a fixed. In this embodiment, by changing the pulsed from a low current value than the threshold I _th until the current value out of the high output and superposing the ON / OFF signal, the wavelength converted light, superimposing a stable ON / OFF signal be able to. In the present embodiment, it is also possible to superimpose a signal having an arbitrary waveform and an arbitrary pattern on the wavelength-converted light by current driving.

It is a figure which shows the structure of the wavelength converter using the conventional quasi phase matching type | mold wavelength conversion element. It is a figure which shows the phase matching curve in the case of performing wavelength conversion by 2nd harmonic generation. It is a figure which shows the output spectrum of the light source which combined the conventional semiconductor laser and fiber grating. It is a figure which shows the maximum value of the output spectrum of a DFB laser diode. It is a figure which shows the minimum value of the output spectrum of a DFB laser diode. It is a figure which shows the time fluctuation of the output power of the conventional DFB laser diode. It is a figure which shows the structure of the wavelength converter using the stabilized semiconductor laser concerning Example 1 of this invention. It is a figure which shows the output spectrum of the converted light of the wavelength converter in Example 1. FIG. It is a figure which shows the time fluctuation of the output power of the wavelength converter in Example 1. FIG. It is a figure which shows the structure of the wavelength converter using the stabilized semiconductor laser concerning Example 2 of this invention. It is a figure which shows the structure of the wavelength converter using the stabilized semiconductor laser concerning Example 3 of this invention. It is a figure which shows the structure of the fluorescence microscope apparatus concerning one Embodiment of this invention. It is a figure for demonstrating the modulation system of the semiconductor laser of a wavelength converter.

Explanation of symbols

11, 12, 51, 52 Semiconductor laser 11a, 12a, 51a, 52a Drive circuit 11b, 12b, 51b, 52b Temperature control circuit 13, 53 Wavelength conversion element 14, 54 Optical coupler 15, 55, 56, 57 Fiber grating

Claims (4)

A first laser that outputs a first laser beam having a fixed wavelength; a second laser that can vary the wavelength of the second laser beam that is output; the first laser beam; A wavelength conversion device including a wavelength conversion element that inputs two laser beams and outputs converted light having a wavelength different from the wavelength of the laser beams;
A fiber grating connected between the first laser and the wavelength conversion element;
The fiber grating, said a fixed wavelength lambda _1, a first grating having a reflection band of wavelengths lambda ₁ within the phase matching band of the wavelength converting element, phase matching band of the wavelength conversion element There,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ LN or _{λ 1 + Δλ 2/2 +} Δλ LN <λ 2
Δλ ₁ <Δλ _LN
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
And a second grating having a reflection band of wavelength λ ₂ having the following relationship: R ₁ and R ₂ are the respective reflectances of the first and second gratings, and Δλ ₁ and Δλ ₂ are the first And the half width of each of the second grating, Δλ _LN is a phase matching band of the wavelength conversion element, G (λ) is a gain at the wavelength λ,
The light of wavelength λ _{1 and} the light of wavelength λ ₂ reflected by the fiber grating maintain coherence, and the light of wavelength λ ₁ reflected by the fiber grating is laser oscillation of the first laser. In addition, the light of wavelength λ ₁ transmitted through the fiber grating is converted into the converted light by the wavelength conversion element, and the light of wavelength λ ₂ reflected by the fiber grating is laser oscillation of the first laser. The wavelength conversion device characterized in that the light having the wavelength λ ₂ that has passed through the fiber grating passes through the wavelength conversion element as it is. The wavelength conversion device according to claim 1 , wherein the wavelength conversion element is made of a nonlinear optical crystal having a periodic polarization inversion structure. The wavelength conversion device according to claim 2 , wherein the nonlinear optical crystal has a waveguide structure. A fluorescence microscope apparatus for analyzing a fluorescent protein in a living cell, comprising: a light source that emits laser light; and a detection unit that detects fluorescence by the laser light from an object to be measured.
A first laser that outputs a first laser beam having a fixed wavelength;
A second laser capable of varying the wavelength of the output second laser beam;
A wavelength conversion element made of a nonlinear optical crystal having a periodic polarization inversion structure, which inputs the first laser light and the second laser light and outputs coherent light having a wavelength different from the wavelength of the laser light When,
A fiber grating connected between the first laser and the wavelength conversion element;
The fiber grating, said a fixed wavelength lambda _1, a first grating having a reflection band of wavelengths lambda ₁ within the phase matching band of the wavelength converting element, phase matching band of the wavelength conversion element There,
_{λ 2 <λ 1 -Δλ 2/} 2-Δλ LN or _{λ 1 + Δλ 2/2 +} Δλ LN <λ 2
Δλ ₁ <Δλ _LN
R ₁ · G (λ ₁ ) = R ₂ · G (λ ₂ )
And a second grating having a reflection band of wavelength λ ₂ having the following relationship: R ₁ and R ₂ are the respective reflectances of the first and second gratings, and Δλ ₁ and Δλ ₂ are the first And the half width of each of the second grating, Δλ _LN is a phase matching band of the wavelength conversion element, G (λ) is a gain at the wavelength λ,
The light of wavelength λ _{1 and} the light of wavelength λ ₂ reflected by the fiber grating maintain coherence, and the light of wavelength λ ₁ reflected by the fiber grating is laser oscillation of the first laser. In addition, the light of wavelength λ ₁ transmitted through the fiber grating is converted into the converted light by the wavelength conversion element, and the light of wavelength λ ₂ reflected by the fiber grating is laser oscillation of the first laser. And a light having a wavelength λ ₂ that has passed through the fiber grating passes through the wavelength conversion element as it is.

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