JPH04172420A - acousto-optic filter - Google Patents

Abstract

PURPOSE:To simultaneously utilize an ordinary ray and an extraordinary ray which are incident at the same angle, whose wave length are the same for an incident ray in a natural polarizing condition by installing a tellurium dioxide crystal and a transducer and setting an optical incident angle and the wave front of a transversal ultrasonic wave in a specified bearing referring to a crystal axis and diffracting the ordinary ray and the extraordinary ray by transversal ultrasonic waves having the same frequencies as both the rays. CONSTITUTION:The surface of an optical incidence of a tellurium oxide crystal 1 inclines by Q1 from an axis (110). A ray of light almost vertically strikes upon that surface, and when diffraction does not occur, the ray of light becomes a transmitted ray of light 1o and goes out. A transducer 2 is adhered to the surface which inclines by alpha from an axis (001), and an electric signal from a high frequency oscillator 3 is changed into an ultrasonic signal by a transducer 2 and is propagated through the inside of an crystal 1. Then, the ultrasonic wave whose wave front tilt angle alpha is transmitted much inclined from the axis (101) because the crystal 1 is anisotropic; and an incident ray is selectively diffracted corresponding to the frequency of ultrasonic wave and an ordinary ray goes out as the filter light I1 of an extraordinary ray whose polarized light is turned by 90 deg., and the extraordinary ray goes out as the filter light I2 of the ordinary ray, respectively. It is thereby possible to use both the rays at the same time for an incident ray whose natural polarizing condition is general, too.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention utilizes the far-axis anisotropic Bragg diffraction phenomenon in an acousto-optic filter that selectively diffracts light using a crystal having optical anisotropy. This invention relates to an acousto-optic filter.

BACKGROUND OF THE INVENTION In recent years, light ranging from visible to near-infrared light has been widely utilized, and acousto-optic filters are used to disperse this light. There are other types of spectroscopy that use optical glass filters, prisms, and diffraction gratings, but these can only select optical wavelengths by mechanical operation, whereas acousto-optic filters can only select the frequency of electrical input. By changing the amplitude, the optical wavelength and output light intensity can be changed, and it can be used as a high-speed, highly stable, and long-life spectrometer with no moving parts. It also has unique functions such as light mixing. This type of acousto-optic filter is shown, for example, in Japan Specification No. 961641 and Japan Specification No. 981883.

Problems to be Solved by the Invention However, since conventional acousto-optic filters of this type diffract at different ultrasonic frequencies for ordinary and extraordinary rays, two wavelengths are used for one frequency. The light will be diffracted, and only one of the above-mentioned light rays can be used to select the optical wavelength. In other words, basically only half the amount of light that is normally incident in a naturally polarized state can be used.

Means for Solving the Problems In order to solve these problems, the present invention is equipped with a tellurium dioxide crystal and a transducer for introducing transverse ultrasonic waves into the tellurium dioxide crystal. The light incident angle and the wavefront of the transverse ultrasonic waves are set so that ordinary and extraordinary rays of the same wavelength that are incident at the same angle are diffracted by the transverse ultrasonic waves of the same frequency.

The configuration will be explained below using the drawings.

FIG. 1 is a wave number vector diagram of a tellurium dioxide crystal. In FIG. 1, if the (11o) axis is the X axis and the (001) axis is the Y axis, the refractive index for ordinary light and extraordinary light is n0. The outer ellipse and inner ellipse are expressed by the following equations (1) and (21) using n, optical activity δ, and optical wavelength λ.

0 is the wave number vector of the ordinary incident light with an incident angle θ, and OC is the diffracted light 'd+ generated in the direction θd by the ultrasonic wave KtL of the angle α from the axis represented by C.
It becomes an abnormal ray. There is a relationship between them according to the law of conservation of momentum as shown in equation (3) below.

(BD) Ordinary ray diffracted light Kd2 (O
D) has the following relationship. Here IKi, I = 2 yr ni□ / A −
---(@lKa+l=2πnd, /λ...
・(6) 1 to 2L, l=2πf, /ma<(Z) ・
...(7) l Ki21 = 2 yr n, /
λ -------・(a) eI IKd21=2πnd0/λ ・・---(9) 1
, 21=2πf2/"m)-=(10).ni□, n-tech. are θi force direction ordinary ray, extraordinary ray refractive index, "do is θ4. The extraordinary ray refractive index of the direction, n,. is θ, the ordinary ray refractive index in two directions, f, f2 are the ultrasonic frequencies,
-) is the propagation speed of the ultrasonic wave in the α direction, and is...(12) -(1S). f,, f' is the law of conservation of momentum (31, (4)
When the formula holds true,...(16)...(16).

The conditions for diffraction by transverse ultrasonic waves of the same frequency are (16)
, (16), it becomes.

As can be seen from Figure 1, this is l', , l==11m
, 21, and an approximate solution can be obtained by finding the combination of α and θi in consideration of the dispersion of no, n, , δ in the optical wavelength band. Then, α and θi that satisfy this condition
In this case, ordinary rays and extraordinary rays of the same wavelength incident on the transverse ultrasonic wave of the same frequency will be diffracted at the same time. Therefore, both of the above-mentioned light rays can be used simultaneously even for general incident light in a naturally polarized state.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. Second
The figure is a basic configuration diagram showing an embodiment of the present invention. 1 is a tellurium dioxide crystal, and the light incidence plane is θ from the (110) axis.
iIt is tilted. When the light having the polarization plane shown in the figure is tilted substantially perpendicularly to this plane and no diffraction occurs, it becomes transmitted light xo and is emitted.

There is a transducer 2 on the surface tilted α from the (001) axis.
is glued. For this transducer 2, an X-plate made of lithium niobate or the like is used.

Furthermore, indium, tin, etc. are suitable for adhesion. The electrical signal from the high frequency oscillator 3 is turned into a super high frequency signal by the transducer 2 and propagated through the crystal 1. At this time, the ultrasonic wave having the wavefront inclination angle α propagates with a large inclination from the anisotropic axis of the crystal 1. Then, the incident light is selectively diffracted according to the frequency of the ultrasonic wave, and the ordinary ray is output as the filter light weight of the extraordinary ray whose polarization plane has been rotated by 90 degrees, and the extraordinary ray is output as the filter light weight of the ordinary ray. do.

Figure 3 shows the tuning characteristics of an embodiment of the present invention, and shows the frequency characteristics for a light wavelength of 1 to 3 μm when the light incident angle θ is 20.2 degrees and the wavefront inclination angle α is 9.1 degrees. . in this case,
The frequency characteristics for ordinary rays and the frequency characteristics for extraordinary rays are almost the same over the entire wavelength range, and light of the same wavelength is filtered light 11. It becomes I2 and emits. This emitted light I,
, I2 can be used by being received by a photodetector, or can be collected into one by using an optical fiber.

Figures 4 and 5 show conventional examples, each with a light incident angle θi
is 20.2 degrees and the wavefront inclination angle α is 8.0 degrees, and θ,
is 20.2 degrees and α is 10.0 degrees. Figure 4,
In FIG. 5, the frequency characteristics for ordinary rays are shown by broken lines, and the frequency characteristics for extraordinary rays are shown by solid lines. In these examples, incident light of the same wavelength will be diffracted by ultrasound waves of different frequencies. For example, incident light with a wavelength of 2 μm is tuned at 0.5 to IM) (z different frequencies for the ordinary ray and extraordinary ray. Also, for ultrasonic waves with the same frequency, the wavelength is 0.1 μm).
Light that is about m away will be diffracted.

Effects of the Invention As described above, the acousto-optic filter of the present invention includes a tellurium dioxide crystal and a transducer that introduces transverse ultrasonic waves into the tellurium dioxide crystal, and adjusts the incident angle of light and the transverse wave in a direction that satisfies specific conditions with respect to the crystal axis. The ultrasonic wavefront is set so that the ordinary and extraordinary rays of the same wavelength that are incident at the same angle are diffracted by the transverse ultrasonic wave of the same frequency, and the ordinary and extraordinary rays of the same wavelength are diffracted at the same time. become. Therefore, both of the above-mentioned light rays can be used simultaneously even for general incident light in a naturally polarized state.

[Brief explanation of the drawing]

Fig. 1 is a wave number vector diagram of a TeA/lv dioxide crystal used to explain the present invention, Fig. 2 is a basic configuration diagram showing an embodiment of an acousto-optic filter according to the present invention, and Fig. 3 shows its tuning characteristics. The figures shown in FIGS. 4 and 6 are diagrams showing the tuning characteristics of the conventional example. 1... Tellurium dioxide U crystal, 2... Transducer, 3... High frequency oscillator. Name of agent: Patent attorney Akira Okaji and two others
+'ml pe4hi Fig. 3 趨音 动子旭铦 (MHz) Fig. 4

Claims (1)

[Claims] It is equipped with a tellurium dioxide crystal and a transducer that injects transverse ultrasonic waves into the tellurium dioxide crystal, and the incident angle of light and the wavefront of the transverse ultrasonic waves are set in a direction that satisfies specific conditions with respect to the crystal axis. An acousto-optic filter utilizing a far-axis anisotropic Bragg diffraction phenomenon, characterized in that ordinary rays and extraordinary rays of a wavelength are diffracted by the transverse ultrasonic wave of the same frequency.