JPH0412407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a spectroscopic device using an electro-optic material having an electro-optic effect, such as PLZT.

[Description of prior art]

FIGS. 1 and 2 are explanatory diagrams showing an example of a conventionally known spectroscopic device.

In the apparatus shown in FIG. 1, light incident from an entrance slit 11 is made into a parallel beam by a concave mirror 12, and is incident on a diffraction grating 13, so that the transmitted light or diffracted light is imaged on a concave mirror 14. In this device, in order to increase resolution, it is necessary to make the slit on the light receiving side thinner, and it is difficult to improve resolution and precision at the same time.

The device shown in FIG. 2 is a spectroscopic device based on the principle of Fourier spectroscopy using a two-beam interferometer, in which light incident from an entrance slit 21 is converted into parallel light by a lens 22, and this parallel light is passed through a half mirror 22. So 2
A bundle of rays and each bundle of rays is reflected by mirrors 24 and 2, respectively.
5, and each of these reflected lights is made to enter a slit 27 via a lens 26. In this device, when one of the reflecting mirrors 24 and 25 is moved in the direction shown by the arrow to change the optical path difference between the two beams, the interface of the signal obtained from the light receiving element 28 that receives the light passing through the slit 27 is changed. An erogram is a Fourier transform of the incident light, and this inverse transform is performed to obtain the original spectral distribution.

Compared to the device shown in Figure 1, this device does not require an entrance slit, can simultaneously measure the entire spectrum of light entering the photodetector, has a high S/N ratio due to the large amount of light, and has high wavelength accuracy. On the other hand, there are drawbacks such as the need to move the reflecting mirror to change the optical path difference, which requires mechanical precision, and the difficulty of miniaturization and integration.

[Object of the present invention]

Here, the present invention aims to realize a spectroscopic device that does not have mechanical components, is small in size, can be integrated, and has good resolution and accuracy.

[Summary of the invention]

The device according to the present invention includes an optical modulator made of an electro-optic material having an electro-optic effect, a light-receiving element that receives light that has passed through the optical modulator, and a light-receiving element that receives a signal from the light-receiving element and modulates the light. It is characterized by the fact that the spectral distribution of the light incident on the optical modulator can be determined by Fourier spectroscopy from the wavelength dependence of the modulation degree of the optical modulator. .

[Explanation of principle]

FIG. 3 is a diagram for explaining the principle of the device according to the present invention, and shows an example of an optical modulator used in the present invention. In the figure, 3 is an electro-optic material having an electro-optic effect (e.g. PLZT or LiNbO ₃ );
31 and 32 are electrodes provided on two parallel surfaces of the electro-optic material 3, and 33 and 34 are polarizers and analyzers that are placed on the light incident side and light output side, respectively, with the electro-optic material 3 in between. The direction of the plane of polarization is
tilted at 45° with respect to the electric field E generated by 1,32,
and are parallel.

In the optical modulator having such a configuration, the electrode 3
When a voltage V is applied between 1 and 32, the incident light P _io
The ratio T=P _OUT /P _io of the output light P _OUT and the output light P OUT can be expressed by equation (1).

T=P _OUT /P _io =kCOS ² {k'/λΔα(V)}...(1) Here, k and k' are constants (k≦1), λ is the wavelength of the incident light, and Δα(V) /λ is the amount of birefringence (rad) due to the electro-optic effect.

In equation (1), 1/λ=f/c (c: speed of light, f:
frequency) and rewriting k'/c as k', we get equation (2).

T=P _OUT /P _io =kCOS ² (k'/λΔα(V)) =k/2{1+COS(2k'fΔα(V)}...(2) In equation (2), the spectral distribution of the incident luminous flux is B
(f), the output light P _OUT becomes as shown in equation (3) (replace P _io with B(f)), similar to equation (2).

P _OUT (V)=∫ ^∞ ₀ B(f)・k/2{1 +COS(2k′fΔα(V)}df=k/2∫ ^∞ ₀ B(f
)df+k/2 ∫ ^∞ ₀ B(f)COS(2k'fΔα(V))df...(3) The second term on the right side of equation (3) is the Fourier cosine transformation of B(f). Therefore, the spectral distribution B(f) of the incident light can be obtained by performing inverse Farier transformation.

Here, since it is easy to select V ₀ as Δα(V ₀ )=0 (usually V ₀ =0), by substituting this into equation (3), equation (4) is obtained.

P _OUT (V ₀ )=k/2∫ ^∞ ₀ B(f)df+k/2
∫ ^∞ ₀ B(f)=k∫ ^∞ ₀ B(f)df...(4) If equation (4) is substituted into equation (3), equation (5) is obtained.

P _OUT (V) = 1/2P _OUT (V ₀ ) + k/2∫ ^∞ ₀
B(f) COS (2k'fΔα(V)) df...(5) As is clear from equation (5), subtract 1/2 P _OUT (V ₀ ) from P _OUT (V) and calculate the remaining If we apply the inverse Fourier cosine transform to the term, we get the spectral distribution B(f) of the incident light P _io
can be known.

[Explanation of Examples]

FIG. 4 is a block diagram showing an example of a device according to the present invention. In this figure, 3 is an optical modulator having the configuration shown in FIG. 3, which satisfies equation (1). 35 is a power source that applies a voltage between the electrodes of this optical modulator, 4 is a light receiving element that receives the light emitted from the optical modulator 3, and 5 is a signal that inputs and stores the signal from this light receiving element. An arithmetic control unit that provides a control signal and controls the voltage applied to the optical modulator 3. For example, it inputs an A/D converter 51 that A/D converts the signal from the light receiving element 4 and a digital signal from this. It consists of a microprocessor 52 and a memory 53 coupled to it. Reference numeral 6 denotes a display device for displaying the calculation results of the calculation control section 5.

The operation of the device configured as described above is as follows. First, the arithmetic control unit 5 sweeps the output voltage of the power supply 35 from V ₁ to V ₂ within a certain range. The optical modulator 3 emits light P _OUT as expressed by equation (5) depending on the voltage applied between the electrodes.
The light receiving element 4 converts the output light P _OUT into an electrical signal,
It is input to the calculation control section 5. The memory means 53 in the arithmetic control section 5 stores the voltage applied to the optical modulator 3 and the signal from the light receiving element 4 at that time from _V1 to _V2 . Here, if necessary, V ₁
Sweep from to V ₂ several times, take some data, and get the average result.
The S/N ratio may be improved.

The data stored in the memory means 53 is subjected to an inverse Fourier transform operation to obtain B(f) from equation (5);
A spectrum of the incident light P _io is obtained by performing correction calculations on the wavelength-sensitivity characteristics of the light receiving element 4 and the wavelength-transmittance characteristics of the optical modulator 3 itself, and the results of this calculation are displayed on the display 6.

FIGS. 5 to 8 are explanatory diagrams showing other configuration examples of optical modulators that can be used in the apparatus of the present invention.

In FIGS. 5 and 6, A is a plan view, and B is a sectional view taken along line X-X in FIG.

The optical modulator shown in FIG. 5 has branched phase modulation/interference type optical waveguides 35 and 36 formed on a dielectric substrate 30, and electrodes 31 and 36 sandwiching the optical waveguide 35.
32 was installed. Here, the substrate 30 and the optical waveguides 35 and 36 may be formed, for example, as follows.

(i) Thermal diffusion of Ti onto the LiNbO ₃ substrate.

(ii) Ag ⁺ and K ⁺ ions are diffused into the LiNbO ₃ substrate. In this case, so-called optical damage can be reduced.

(iii) Diffusion of Cu into the LiTaO ₃ substrate.

(iv) Perform metal ion exchange on the PLZT transparent ceramic substrate.

(v) GaAS and In-P substrates are irradiated with protons.

The optical modulator shown in FIG. 6 is based on the same principle as that shown in FIG. 5, and has branching-phase modulation-interference type optical waveguides 35 and 36 formed on a semiconductor substrate 30. The semiconductor substrate 30 is n-
N-GaAS 30P is epitaxially grown on a GaAS substrate 30n to a thickness of several μm, and ohmic electrodes 31a and 31b are formed thereon.
An ohmic electrode 32 is formed on the entire surface of the GaAS substrate 30n side. In this configuration, when a voltage is applied between the electrodes 31a (31b) and 32 so as to provide a reverse bias to the P-n junction, the depletion layer near the P-n junction expands, and at the same time, the carrier concentration decreases, resulting in
The refractive index increases, and optical waveguides 35 and 36 are selectively formed under the electrode on the P-GaAS substrate 30P side by the applied voltage. Note that the depletion layer is wide on the n-GaAS side and narrow on the P-GaAS side. Here, the electrodes 31, 3
By adjusting the voltage applied between 2, the optical waveguide 3
Since the guided light passing through 5 and 36 undergoes a phase change due to the electro-optic effect of GaAS, a phase difference occurs between the respective guided light, allowing optical modulation.

In this embodiment, GaAS is used as an example, but an n-Inp substrate and a P-Inp epitaxial layer may also be used.

The optical modulators shown in FIGS. 7A and 7B both have a light receiving element 4 integrated on a substrate 30.

In the device shown in A, a transparent electrode 41 is provided at the light output portion of the optical waveguide 35 (36) formed on the substrate 30, and a layer of amorphous silicon (a-Si), CdS, or ZnS is formed on the transparent electrode 41. A photoelectric layer 42 is provided, and an electrode layer 43 made of Al or the like is formed thereon. Here, the transparent electrode 41 is made of a material such as In ₂ O ₃ or SnO ₂ and can be formed by a vacuum evaporation method, a plasma evaporation method, or the like.
The a-Si photoelectric layer 42 has a film thickness of about 0.5 to 1.0 μm, and is made of monosilane (SiH ₄ ), SiF ₄ plasma decomposition, reactive sputtering, or CVD.
It can be created by law etc.

In the one shown in FIG.
n, i-aSi layer 42i and P-aSi layer 42P are formed. Note that the PIN layer is multi-layered (PIN
PIN...) may also be used. Also, a-SiC may be used instead of a-Si.

The optical modulators shown in FIGS. 8A and 8B each have a light receiving element 4 integrated on a semiconductor waveguide.

The one shown in A is a 30n substrate such as n-GaAS.
A layer 30P of P-GaAS or the like is formed on top to create a semiconductor waveguide, and an electrode 43 is provided on this.
This is a photodiode PD using a PN junction.

In the example shown in FIG. 4, a metal material that can be subjected to a Schottky junction is used as the electrode 43, and a Schottky barrier diode SD that utilizes a Schottky junction is constructed.

Although the means for guiding light to the optical modulator 3 was not specifically described in the above embodiments, a known method such as a prism coupler or a grating coupler may be used. Furthermore, the optical modulator 3 may have a structure other than that shown in FIGS. 5 to 8. For example, a structure in which memory means, a microprocessor, etc. are integrated on the substrate constituting the modulator can be used. It can be anything.

[Effects of the present invention]

As described above, according to the present invention, since it does not have mechanical components, it is possible to realize a spectroscopic device that is small in size, can be integrated, and has high reliability. Also,
Since slits and the like are not required, an apparatus with high S/N and good accuracy can be realized.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams showing an example of a conventionally known spectroscopic device, FIG. 3 is a diagram for explaining the principle of the device of the present invention, and FIG. 4 is a diagram showing an example of the device according to the present invention. The configuration block diagrams of FIGS. 5 to 8 are configuration diagrams showing other examples of optical modulators that can be used in the apparatus of the present invention. 3... Light modulator, 4... Light receiving element, 5... Arithmetic control unit, 6... Display device.

Claims (1)

[Scope of Claims] 1. Made of an electro-optic material having an electro-optic effect, the incident light (Pin) with respect to the applied signal (V)
The ratio (T) between the output light and the output light (Pout) is T=(Pout)/(Pin) =k・cos ² {(k ^- /λ)Δα(V)} However, k and k ^- are constants (k ≦1) λ is the wavelength of the incident light, and Δα(V)/λ is the amount of birefringence (rad) due to the electro-optic effect. , a calculation control unit having a function of inputting a signal from the light receiving element and storing the signal, a function of performing calculation, and a function of controlling a voltage signal applied to the optical modulator; The part sweeps the signal applied to the optical modulator from a certain voltage (Vo) to a certain voltage (V), and calculates the incident light by using the following equation related to the output light (Pout) output from the light receiving element at that time. A spectroscopic device characterized in that a spectral distribution B(f) of (Pin) is obtained by performing an inverse Fourier cosine transform operation. Pout (Vo) = (1/2) Pout (Vo) + (k/2)∫ ^∞ _p B (f) cos (2k ^- fΔα (V)) df where f is the frequency.