TW201350816A - Wavelength conversion element inspection method and inspection device - Google Patents

Abstract

An inspection device (10) comprises an SC (supercontinuum) light source (110), an optical system (light guide section: 154) and a spectroscopic section (130). The SC light source (110) generates supercontinuum light (SC light) as a first inspection light. The optical system (154) inputs the first inspection light to a wavelength conversion element (20). The wavelength conversion element (20) is a ferroelectric crystal comprising a polarization-reversed structure. The spectroscopic section (130) spectroscopically analyzes output light that has been output from the wavelength conversion element (20), and detects one or multiple first peak wavelengths.

Description

Wavelength conversion element inspection method and inspection device

The present invention relates to an inspection method and an inspection apparatus for a wavelength conversion element having a polarization inversion structure.

In recent years, techniques for performing wavelength conversion using phase-like integration have continued to be developed. The pseudo phase integration is performed using an element in which a ferroelectric crystal periodically forms a pole inversion structure. The wavelength conversion element having the polarization inversion structure changes its characteristics by the structure of the polarization inversion.

Patent Document 1 describes that a plurality of laser beams having mutually different wavelengths are input to a wavelength conversion element, and the output light is analyzed to detect a wavelength integrated by a polarization inversion structure of the wavelength conversion element.

Patent Document 2 describes that the polarization inversion structure is inspected by etching the wavelength conversion element with a step difference between the polarization inversion portion and the other portion.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-69984

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-232826

The inventor of the present invention considered that the above method has the following problems. In the structure described in Patent Document 1, the wavelength of incident light is discrete. Therefore, the optical information necessary for the inspection of the polarization inversion structure cannot be sufficiently obtained. Further, in the structure described in Patent Document 2, actual optical characteristics cannot be inspected.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide an inspection method and an inspection apparatus for a wavelength conversion element which can sufficiently obtain optical information necessary for inspection of a polarization inversion structure.

The inspection method of the wavelength conversion element according to the present invention is as follows. First, the first inspection light generated by the ultra-wideband light source is incident on a ferroelectric crystal having a polarization reversal structure. Next, the emitted light emitted from the wavelength conversion element is analyzed by spectroscopic analysis, and one or a plurality of first peak wavelengths are detected. Further, based on the detected first peak wavelength, the inspection result of the wavelength conversion element is determined.

An inspection apparatus according to the present invention has an ultra-wideband light source, a light guiding portion, and a spectroscopic portion. The ultra-wideband light source generates the first inspection light. The light guiding unit causes the first inspection light to enter the wavelength conversion element. Wavelength conversion element The piece is a ferroelectric crystal having a polarization inversion structure. The spectroscopic unit analyzes the emitted light emitted from the wavelength conversion element by spectroscopic detection, and detects one or a plurality of first peak wavelengths.

According to the present invention, the optical information necessary for the inspection of the polarization inversion structure can be sufficiently obtained.

10‧‧‧Inspection device

20‧‧‧ wavelength conversion components

110‧‧‧SC light source

120‧‧‧stage

130‧‧ ‧Distribution Department

140‧‧‧Control Department

152‧‧‧Spectral adjustment filter

153‧‧‧Variable Wavelength Filter

154‧‧‧Optics

162‧‧‧Optics

164‧‧‧pump cut filter

Fig. 1 is a view showing the configuration of an inspection apparatus according to the first embodiment.

Figure 2 is a flow chart showing the method of using the inspection device.

Fig. 3 is a view showing the configuration of an inspection apparatus according to a second embodiment.

4 is a flow chart showing a method of using the inspection apparatus shown in FIG.

Fig. 5 is a graph showing the frequency dependence of the intensity of light output from the wavelength conversion element.

Fig. 6 is a graph showing how the frequency dependence of the intensity of light output from the wavelength conversion element changes with temperature.

Hereinafter, embodiments of the present invention will be described using the drawings. In the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

(First embodiment)

Fig. 1 is a view showing the configuration of an inspection apparatus 10 according to the first embodiment. The inspection device 10 is an element for inspecting the wavelength conversion element 20. The inspection device 10 includes an SC (Ultra Wide Frequency Light Source) light source 110, an optical system (light guide portion) 154, and a spectroscopic portion 130. The SC light source 110 generates ultra-wideband light source light (SC light) as the first inspection light. The optical system 154 causes the first inspection light to enter the wavelength conversion element 20. The wavelength conversion element 20 is a ferroelectric crystal having a polarization inversion structure. The spectroscopic unit 130 spectrally analyzes the emitted light emitted from the wavelength conversion element 20, and detects one or a plurality of first peak wavelengths. The first peak wavelength is light that is wavelength-converted by the wavelength conversion element 20. SC light is continuous and broadband light. Therefore, compared with the case where a plurality of laser beams having mutually different wavelengths are used as the light for inspection, optical information necessary for the inspection of the polarization inversion structure can be sufficiently obtained. The details will be described below.

In the present embodiment, the inspection apparatus 10 includes an SC light source 110, a spectrum adjustment filter 152, a stage 120, an optical system 162, a pump cut filter 164, a spectroscopic unit 130, and a control unit 140.

The SC light source 110 generates SC light by injecting ultrashort pulse light into the nonlinear optical material. SC light, which is ultrashort pulsed light in a nonlinear optical material, by self-phase modulation, mutual phase modulation, and four-light Produced by nonlinear optical effects such as wave mixing and Raman scattering. That is, the SC light is continuous and broadband pulsed light.

The spectral adjustment filter 152, the SC light emitted from the SC light source 110, removes frequency components unnecessary for inspection by the wavelength conversion element 20. The optical system 154 is constituted by a lens or the like, and guides the SC light transmitted through the spectrum adjustment filter 152 to the incident end surface of the wavelength conversion element 20.

The stage 120 mounts the wavelength conversion element 20. The stage 120 contains a heater to adjust the temperature of the wavelength conversion element 20. The heater of the stage 120 is controlled by the control unit 140.

The optical system 162 directs the light emitted from the wavelength conversion element 20 to a pump cut filter 164. A pump cut filter 164 removes the frequency component of the SC light among the light emitted from the wavelength conversion element 20. The spectroscopic unit 130 splits the light passing through the pump cut filter 164 to detect a wavelength having a peak (first peak wavelength). There are usually a plurality of first peak wavelengths. Next, the spectroscopic unit 130 outputs a plurality of detected first peak wavelengths to a graph of the spectroscopic result, a display unit, and the like. The operation of the spectroscopic unit 130 is controlled by the control unit 140.

The wavelength conversion element 20 is a ferroelectric crystal having a polarization inversion structure as described above. As the ferroelectric crystal, for example, LiNbO _{3 to} which Mg is added is not limited thereto. When the incident light has a specific wavelength component, the wavelength conversion element 20 converts and converts the wavelength component into a wavelength. The wavelength conversion element 20 outputs an output and a frequency (SFG), for example, a second harmonic (SHG), but outputs light generated by parametric conversion, light generated by differential frequency conversion, or by and Light generated by frequency mixing can also be used.

Next, the first method of use of the inspection apparatus 10 will be described. First, the stage 120 is set to a specific temperature. Next, the SC light source 110 is caused to generate SC light. The generated SC light passes through the spectrum adjustment filter 152 and the optical system 154, and then enters the wavelength conversion element 20. The SC light incident on the wavelength conversion element 20 is converted into a wavelength component satisfying the phase integration condition. A pump cut filter 164 removes the wavelength component of the SC light among the light emitted from the wavelength conversion element 20. Therefore, the light incident on the spectroscopic unit 130 mainly includes light whose wavelength is changed by the wavelength conversion element 20. The spectroscopic unit 130 performs spectroscopic analysis to detect the first peak wavelength.

FIG. 2 is a flow chart showing a second method of using the inspection apparatus 10. The wavelength conversion element 20 is placed on the stage 120. First, the control unit 140 sets the stage 120 to a specific temperature (step S12).

Next, the SC light source 110 generates SC light. The generated SC light is incident on the wavelength conversion element 20. The SC light incident on the wavelength conversion element 20 is converted into a wavelength component satisfying the phase integration condition. The spectroscopic unit 130 performs spectroscopic analysis to detect the first peak wavelength. The details of this step are the same as those of the first usage method (step S14).

Next, until the end of the inspection at all the temperatures to be inspected, the temperature of the stage 120 is continuously changed, and the processing of steps S12 and S14 is repeated (step S16). Next, perform wavelength conversion The examiner of the element 20 determines the structure of the wavelength conversion element 20 using the first peak wavelength (step S18). The details of this determination will be described together with the effects of the present embodiment.

Next, the effect of this embodiment will be described. By the above-described processing, the first peak wavelength is efficiently measured at the complex temperature. For example, when the wavelength conversion element 20 outputs the converted light according to the SHG (that is, the second high frequency wave), the phase integration condition of the wavelength conversion element 20 is as shown in the following formula (1).

Here, Λ: polarization reversal period, λ _ω : wavelength of fundamental wave, λ _2ω : wavelength of second harmonic, n _ω : crystal refractive index at fundamental wavelength, n _2ω : second harmonic Crystalline refractive index at wavelength.

Among the incident light, the second harmonic is generated under the condition that the phase integration condition shown in the equation (1) is satisfied. Therefore, in the case where the fine structure of the polarization inversion is uneven, or when the refractive index of the ferroelectric crystal is uneven, the wavelength of the second harmonic changes. By investigating the change in this wavelength, it is possible to recognize the details of the polarization inversion structure of the wavelength conversion element 20 and the unevenness of the refractive index of the ferroelectric crystal. For example, when the polarization reversal period is known, by investigating the temperature of the first peak wavelength Depending on the dependence, it is possible to recognize the distribution of the refractive index dispersion inside the ferroelectric crystal constituting the wavelength conversion element 20.

Further, by using these first peak wavelengths, it is possible to efficiently determine whether or not the wavelength conversion element 20 is set to a certain temperature to obtain a desired wavelength.

In this regard, it is considered to replace the SC light source 110 with a complex laser light source having mutually different wavelengths. The polarization inversion structure of the wavelength conversion element 20 or the refractive index of the ferroelectric crystal has a jagged phenomenon. Therefore, even if the wavelength-converted laser beam is incident on the wavelength conversion element 20, the spectroscopic unit 130 may not detect the first peak wavelength. In this case, it is not known whether or not the wavelength of the laser is shifted in one of the short-wavelength side and the long-wavelength side. Therefore, it is difficult to perform the same inspection as in the case of using the inspection apparatus 10.

(Second embodiment)

Fig. 3 is a view showing the configuration of the inspection apparatus 10 according to the second embodiment. The inspection apparatus 10 according to the present embodiment has the same configuration as that of the inspection apparatus 10 according to the first embodiment except for the following points.

First, the inspection device 10 has a variable wavelength filter 153 instead of the spectral adjustment filter 152. Next, the control unit 140 controls the wavelength transmitted through the variable wavelength filter 153.

4 is a flow chart showing a method of using the inspection apparatus 10 shown in FIG. The stage 120 is set to a specific temperature. Then control The unit 140 sets the wavelength transmitted by the variable wavelength filter 153 to a specific wavelength (step S32). Next, the SC light source 110 is caused to generate SC light. The generated SC light is cut out only by the set wavelength component, and is incident on the wavelength conversion element 20 as the second inspection light.

When the wavelength of the second inspection light incident on the wavelength conversion element 20 satisfies the phase integration condition of the wavelength conversion element 20, a pump cut filter 164 transmits the light emitted from the wavelength conversion element 20. In this case, the spectroscopic unit 130 detects the peak wavelength (second peak wavelength) (step S34).

On the other hand, when the wavelength of the second inspection light does not satisfy the phase integration condition of the wavelength conversion element 20, the pump cut filter 164 cuts off the light emitted from the wavelength conversion element 20. In this case, the beam splitting unit 130 does not detect the peak wavelength (step S34).

The control unit 140 scans the wavelength of the light of the variable wavelength filter 153 while repeating the processing shown in steps S32 and S34 (step S36).

Further, the control unit 140 causes the variable wavelength filter 153 to function in the same manner as the spectrum adjustment filter 152, and causes the SC light to enter the wavelength conversion element 20. Next, the light splitting unit 130 detects the first peak wavelength by the light emitted from the wavelength conversion element 20 (step S38). Next, the examiner who performs the wavelength conversion element 20 compares the first peak wavelength and the second peak wavelength to determine (step S40). Thereby, it is possible to determine the noise component of the polarization inversion period of the wavelength conversion element 20, that is, whether or not there is an unwanted parasitic inversion period.

Specifically, the phase inversion period Λ _{a of the} parasitic formation has a phase integration condition as shown in the following formula (2).

2Πn _out /λ _out =2Π(n ₁ /λ ₁ +n ₂ /λ ₂ +1/Λ _a )‧‧‧(2)

Here, λ _out : wavelength of light converted by the wavelength conversion element 20, n _out : refractive index of the wavelength conversion element 20 at λ _out , λ ₁ , λ ₂ : wavelength of light incident on the wavelength conversion element 20, n ₁ The refractive index of the wavelength conversion element 20 at λ ₁ and the refractive index of the wavelength conversion element 20 at n ₂ : λ ₂ .

This phase integration condition is satisfied when two wavelengths of light (λ ₁ , λ ₂ ) are different from each other. On the other hand, when the first peak wavelength is detected, SC light is incident on the wavelength conversion element 20, and when the second peak wavelength is detected, only a single wavelength of light is incident on the wavelength conversion element 20. That is, the converted light according to the phase integration condition of the formula (2) is included in the first peak wavelength, but is not included in the second peak wavelength.

On the other hand, the desired phase integration condition is satisfied in either of the case where the first peak wavelength is detected and when the second peak wavelength is detected. In other words, by investigating the frequency component included in the first peak wavelength and not included in the second peak wavelength, it is possible to determine whether or not there is a parasitic inversion period of parasitic formation. Further, the process of including the frequency component included in the first peak wavelength but not included in the second peak wavelength may be performed by the control unit 14.

(Example 1)

Using the first inspection method of the first embodiment, a plurality of samples (wavelength conversion elements 20) produced by the same method were examined. Fig. 5 shows the frequency dependence of the intensity of light output from each sample. As can be seen from the figure, the peak wavelengths vary depending on the sample. This shows that the polarization reversal period varies with the sample. Next, by investigating the deviation of this wavelength, the fine structure of the polarization inversion period can be detected.

(Example 2)

Using the second inspection method of the first embodiment, one sample is inspected while changing the temperature of the stage 120. Fig. 6 is a graph showing the frequency dependence of the intensity of light output from a sample, and how it changes with temperature. As can be seen from the figure, as the temperature of the stage 120, that is, the temperature change peak wavelength of the sample becomes different, that is, the wavelength satisfying the phase integration condition is different. Next, the wavelength satisfying the phase integration condition at each temperature can be easily judged.

The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is merely illustrative of the present invention, and various configurations other than the above may be employed.

10‧‧‧Inspection device

20‧‧‧ wavelength conversion components

110‧‧‧SC light source

120‧‧‧stage

130‧‧ ‧Distribution Department

140‧‧‧Control Department

152‧‧‧Spectral adjustment filter

154‧‧‧Optics

162‧‧‧Optics

164‧‧‧pump cut filter

Claims (6)

A method for inspecting a wavelength conversion element, characterized in that a first inspection light generated by an ultra-wideband light source is incident on a wavelength conversion element having a ferroelectric crystal having a polarization inversion structure, and the spectroscopic analysis is performed by the foregoing a first detecting step of detecting a first or a plurality of first peak wavelengths of the emitted light emitted from the wavelength converting element, and a determining step of determining a structure of the wavelength converting element using the first peak wavelength. The method of inspecting a wavelength conversion element according to claim 1, wherein the first detecting step is performed plural times, and the wavelength converting elements are set to mutually different temperatures in each of the detecting steps. The method for inspecting a wavelength conversion element according to the first aspect of the invention, wherein the first inspection light is cut by the first inspection light to generate the second inspection light, and the wavelength scanning the second inspection light is simultaneously incident on the wavelength conversion. Element, spectroscopically analyzing a second detection step of detecting a first or a plurality of second peak wavelengths by the emitted light emitted from the wavelength conversion element; and determining the wavelength conversion by comparing the first peak wavelength and the second peak wavelength The noise component of the component's polarization reversal period. An inspection apparatus comprising: an ultra-wideband light source that generates first inspection light, and the first inspection light is incident on a light guiding unit of a ferroelectric crystal wavelength conversion element having a polarization inversion structure; The spectroscopic analysis is performed by detecting the emitted light emitted from the wavelength conversion element and detecting a first or a plurality of first wavelength peaks. The inspection apparatus of claim 4, further comprising a temperature control unit that controls a temperature of the wavelength conversion element. The inspection apparatus according to claim 4, further comprising: a wavelength filter that generates light for the second inspection by cutting light of a specific wavelength by the first inspection light, and can scan a wavelength of the second inspection light; The second inspection light is guided to the wavelength conversion element, and the spectroscopic unit further spectroscopically analyzes the emitted light when the second inspection light is incident on the wavelength conversion element, and detects one or more of the second plurality. Peak wavelength.