JP5285008B2 - Internal reflection type optical deflector - Google Patents

Description

  The present invention relates to an optical deflector that changes the direction of light.

  Among optical deflectors that change the traveling direction of light, KTN optical deflectors and KLTN optical deflectors that use secondary electro-optic effects, electro-optic optical deflectors that use primary electro-optic effects, and ultrasonic waves Unlike a galvano mirror, a polygon mirror, a MEMS mirror, or the like, an acoustooptic light deflector that utilizes the photoelastic effect is a solid element that does not have a movable part. Accordingly, when changing the deflection angle, there is no need to accelerate or decelerate the mirror having the inertial mass, and therefore no rigidity is required, so that the optical deflector is small and high-speed. These solid-state optical deflectors have the disadvantage that the deflection angle is small and the resolution cannot be increased. However, KTN optical deflectors and KLTN optical deflectors are deflected as the interaction length in the element increases. There is a feature that the angle becomes large, and a device has been devised to extend the interaction length by reciprocating light several times in the element. (See Patent Document 1)

International Publication No. 06/137408 Pamphlet

  However, when a reflecting mirror is used as a means for reciprocating a plurality of times in the element, in order to apply a voltage to the element when the mirror is made of metal, the mirror is separated from the element in order to avoid discharge or voltage drop. Therefore, the light emitted from the high refractive index KTN or KLTN is further deflected in the air by Snell's law and propagates in the air until it reaches the mirror. Light also moves in the voltage application direction due to deflection, but the position is limited by the thickness of the element, and the travelable distance is wasted by propagating through the air.

  When the mirror is made of a dielectric multilayer film, the risk of voltage drop and discharge can be avoided. However, prior to film formation, the dielectric multilayer mirror needs to determine the wavelength used and the incident angle in advance, and is difficult to use except for specific wavelength applications. It means losing generality as a general-purpose product. Furthermore, in the case of simultaneous incidence over a plurality of wavelengths such as a spectroscope, a mirror with a narrow wavelength band cannot be used. On the other hand, the wider the wavelength range and the incident angle range, the greater the number of layers of the multilayer film and the higher the film formation cost. In particular, in order to avoid the propagation of light in the air, when the dielectric multilayer mirror is directly formed on the side of the KTN or KLTN, the total film thickness increases because of the stress on the KTN or KLTN by the film. This means that an increase cannot be avoided and the performance of the device with electrostriction is lowered. Furthermore, there is a concern that the dielectric multilayer film easily peels off due to stress.

  SUMMARY OF THE INVENTION In view of the drawbacks of metal mirrors and dielectric multilayer mirrors, an object of the present invention is to provide an internal reflection type optical deflector based on the principle of interaction length extension due to folding by total reflection in KTN or KLTN crystals. And

  KTN and KLTN are transparent in the wavelength range of 0.4 μm to 4 μm, and the refractive index does not fall below 2.18 at wavelengths of 2 μm or less. When the refractive index is 2.18, the total reflection condition at the interface with air is θ> 27.3 °, so the light inside the KTN or KLTN crystal is at an angle of 27.3 ° or more with the normal of the wall surface. In this case, light having a wavelength of 2 μm or less is totally reflected, and the interaction is repeated within the crystal. In order to create such a situation, an oblique cut surface according to claim 1 for inputting and outputting light is required.

Therefore, in order to achieve the above object, an internal reflection type optical deflector according to claim 1 of the present invention is a KTN (KTa _1-x Nb _x O ₃ ) crystal or KLTN (K _1-y Li). _y Ta _1-x Nb _x O ₃ ) crystal, wherein the KTN crystal or the KLTN crystal is parallel to each other, a pair of electrode surfaces parallel to each other, and perpendicular to the electrode surface pairs, and at least three pairs Ri Do from parallel sides to one another, so that the optical axis of the outgoing light of the incident light projected to the electrode surface are the same, characterized in that the angle and direction of the incident light of the above aspect is adjusted .

Further, in the internal reflection type optical deflector according to claim 2 of the present invention, of the three pairs of side surfaces, the remaining two pairs excluding one pair of incident / exit surfaces are perpendicular to each other, and the two pairs perpendicular to each other The side surface is characterized by totally reflecting the light transmitted through the KTN or KLTN crystal.

  According to the present invention, by adopting the total reflection structure, the beam movement distance in the deflection direction, which is a problem when using the external mirror, is wasted, which causes an increase in cost and stress generation due to the formation of the dielectric multilayer mirror. Without any problem, the interaction length between the crystal and the light can be extended, and the deflection angle can be increased. Alternatively, even when the deflection angle is not increased, the applied voltage required to obtain the necessary deflection angle is reduced, and a reduction in power supply cost can be expected.

It is a figure which shows the basic composition of the optical deflector of Claim 1 of this invention, FIG. 1 (a) is a figure which shows the rectangular parallelepiped of the conventional KTN or KLTN crystal | crystallization, FIG.1 (b) is this figure It is a figure which shows the basic shape of Claim 1 of invention, FIG.1 (c) is explanatory drawing explaining the light input / output direction of this invention. FIG. 3 is a basic configuration diagram of an optical deflector according to claim 2 of the present invention. FIG. 3A is a diagram showing an optical path when the total number of total reflections of the present invention is large, FIG. 3A is a diagram showing an optical path diagram 300 when eight times of total reflection are repeated, and FIG. It is a figure which shows the optical path diagram 310 in the case of repeating 14 times of total reflection. It is a figure which shows the total reflection angle dependence of the crystal width and incident beam width when repeating 6 times of total reflection, fixing the crystal length to 4 mm, and changing the total reflection angle. It is a figure which shows the total reflection angle dependence of interaction length and interaction length / crystal length ratio when repeating total reflection 6 times, fixing a crystal length to 4 mm, and changing a total reflection angle. FIG. 6A is a diagram showing a configuration of an optical deflector according to claims 3 and 4 of the present invention, and FIG. 6A is a diagram showing an optical path diagram 600 when incident light is perpendicularly incident on an incident surface; FIG. 6B is a diagram showing an optical path diagram 610 in the case where the optical axes of incident light and outgoing light coincide. It is a figure which shows the structure of the optical deflector of Example 1 of this invention. It is a figure which shows the structure of the optical deflector of Example 2 of this invention.

  FIG. 1 is a diagram showing a basic configuration of an optical deflector according to claim 1 of the present invention, and FIG. 1A is a diagram showing a conventional rectangular parallelepiped 100 of KTN or KLTN crystal, and FIG. FIG. 1B is a diagram showing the basic shape 110 according to claim 1 of the present invention, and FIG. 1C is an explanatory diagram 120 for explaining the light input / output direction and the voltage application direction of the present invention. A conventional KTN / KLTN device is a rectangular parallelepiped 100 as shown in FIG. 1 (a), and its surface is composed of a pair of electrode surfaces and two pairs of side surfaces perpendicular to the electrode surfaces and parallel to each other. It consists of six sides. In the present invention, the simplest configuration is to additionally form surfaces 102 and 103 which are perpendicular to the electrode surface 101 and parallel to each other.

  As a result, a solid 110 consisting of a total of eight surfaces is formed. The newly formed surfaces 112 and 113 are orthogonal to the electrode surface 111, but not orthogonal to the conventional side surfaces 114, 115, 116, and 117. As shown in FIG. 1C, a part of the rectangular parallelepiped 100 is cut out, and incident light 122 is incident on one of the newly added pair of parallel surfaces 112 and 113, and total internal reflection is performed. The emitted light 123 is emitted repeatedly. Since the applied voltage 124 is applied to the parallel electrode surfaces 121, the beam is deflected in the voltage application direction.

FIG. 2 shows the state of total reflection. In FIG. 2, the optical path is projected in the direction of the electrode surface, and deflection due to voltage application is not visible. Incident light 201 is refracted on the incident surface 202 in accordance with Snell's law, and enters the KTN or KLTN crystal. It is the surfaces 211, 212, 213, and 214 that cause total reflection. First, the incident light is totally reflected by the total reflection portion 204. The angle θ between the normal line of the 211 surface and the light must satisfy sin θ> n, which is a total reflection condition. n is the refractive index of the KTN or KLTN crystal. As described above, since n> 2.18 at a wavelength of 2 μm or less, θ> 27.3 ° is required. Next, the totally reflected light is totally reflected by the total reflection portion 205 on the 213 surface. In this example, since the 211 surface and the 213 surface are orthogonal to each other, the angle φ formed by the normal line of the 213 surface and the light is φ = 90 ° −θ. Since the total reflection condition on the 213 plane is φ> 27.3 °, θ <90 ° −27.3 ° = 62.7 ° must be satisfied. Therefore,
27.3 ° <θ <62.7 ° (1)
Must be satisfied.

  The light incident from the incident surface 202 continues to be totally reflected by the total reflection portions 206, 207, 208, and 209, and is finally emitted from the emission surface 203 to the outside of the crystal. Since the 202 plane and the 203 plane are parallel, when the incident light 201 and the outgoing light 210 are projected onto the electrode surface regardless of whether or not a voltage is applied, the angles are parallel within the projection plane. When a voltage is applied in the normal direction of the electrode surface, it is not parallel. In this figure, the total reflection is repeated six times, but the distance is transmitted through the crystal approximately five times as compared with the case where no reflection is involved. Will result in a deflection angle of.

  FIG. 3 is a diagram showing an optical path diagram when the total number of total reflections is large, FIG. 3A is a diagram showing an optical path diagram 300 when eight times of total reflection are repeated, and FIG. FIG. 36 is a diagram showing an optical path diagram 310 when 14 total reflections are repeated. Incident lights 301 and 311 are incident and outgoing lights 302 and 312 are emitted, respectively. Here, in FIGS. 3A and 3B, numbers are assigned to the total reflection positions in order. As shown in this figure, it is easy to increase the total number of reflections, and hence the deflection angle, as necessary.

  FIG. 4 shows the optimum crystal width (W) when the crystal length (L) in FIG. 2 is fixed to 4 mm, the total number of reflections is fixed to 6, and the total reflection angle (θ) is changed from 31 ° to 45 °. ) And the total reflection angle dependence 400 of the incident beam width. In this case, at each total reflection angle, the angles and lengths of the input / output surfaces 202 and 203 are adjusted so that the incident beam width is maximized. As can be seen from FIG. 4, the incident beam width increases when the total reflection angle is large. However, at the same time, the crystal width (W) also increases, indicating that a larger crystal is required.

  FIG. 5 is a diagram showing the total reflection angle dependence 500 of the distance that light passes through the crystal under the same conditions, that is, the interaction length between the crystal and light, and the interaction length / crystal width ratio. It can be seen that the interaction length increases as θ increases, but the interaction length / crystal width ratio decreases. That is, it can be seen that the deflection angle per crystal unit size is more advantageous as the total reflection angle is smaller.

However, since the reflection is repeated six times in the crystal, if the angle or length of the side surface is deviated from the design value, the beam position is greatly changed at the emission position, resulting in vignetting. The figure of merit (Ξ) as an optical deflector uses the beam diameter (D) and the maximum deflection angle (ξ),
Ξ = Dtanξ (2)
Therefore, even if the deflection angle ξ is increased by the total reflection structure according to the present invention, it is difficult to improve the performance if D decreases due to beam vignetting due to manufacturing errors. Therefore, in determining the size of the total reflection angle, it is necessary to consider the polishing accuracy of KTN or KLTN crystal that can be realized.

  Furthermore, there are at least two types of optically special arrangements in relation to the incident light and the incident surface. One is a case where the incident light described in claim 3 is incident perpendicularly to the incident surface. In this case, there is no chromatic dispersion associated with refraction at the entrance surface. Although wavelength dispersion in the deflection direction, that is, wavelength dependence of the deflection angle is inevitable, there is no wavelength dependence at least in the optical path projected on the electrode surface.

  The other is a case where the optical axes of incident light and outgoing light described in claim 4 coincide in projection onto the electrode surface. Since it is necessary to adjust the refraction angle so that the optical axes coincide with each other, this is realized only when the wavelength is the refractive index at the time of design.

  A diagram relating to these claims 3 and 4 is shown in FIG. FIG. 6A is an optical path diagram corresponding to the third aspect of the present invention, and shows an optical path diagram 600 when incident light is perpendicularly incident on the incident surface. This figure is a projection onto the electrode surface. The thick solid line indicates the side of the KTN or KLTN crystal. A broken line is an optical path. In this case, as long as the total reflection condition is satisfied, the optical path projected on the electrode surface has no wavelength dependency. However, the emitted light is translated with respect to the incident optical axis indicated by the alternate long and short dash line, and may be difficult to handle depending on the application. FIG. 6B is a diagram showing an optical path diagram 600 related to claim 4 in which the optical axis coincidence is prioritized. If the incident light is monochromatic, it is possible to follow the optical path indicated by the broken line and to match the optical axes of the incident light and the emitted light. However, when light including a plurality of wavelengths is incident, an angular shift occurs on the incident surface with the wavelength dispersion of the refractive index. As a result, the exit point may be different, as in the case of the exit light 1 indicated by a thick broken line and the exit light 2 indicated by a thin solid line, so care must be taken when deflecting a plurality of wavelengths. In addition, a non-reflective coating can be applied to the input / output surface as necessary.

Example 1
FIG. 7 shows an embodiment 700 in which incident light is perpendicularly incident on the incident surface. The drawing is a projection onto the electrode surface. The thickness of the KTN or KLTN crystal between the electrode surfaces, that is, in the direction perpendicular to the paper surface is 2 mm. The total reflection angle θ is 31 °. The crystal length (L) is 4 mm, the crystal width (W) is 4.197 mm, and the inclination angle of the incident surface is 31 °, which is the same as the total reflection angle. The shapes of the entrance surface and the exit surface are the same, and the surface interval is 4.665 mm. In this case, the emitted light is shifted by 1.04 mm with respect to the incident optical axis. The interaction length is 22.7 mm. If a deflection angle of 0.25 degrees per 1 mm interaction length is applied by applying an electric field of 150 V / mm, a deflection angle of ± 11.3 ° is obtained by applying ± 300 V.

(Example 2)
FIG. 8 shows an embodiment 800 in which the optical axes of incident light and outgoing light coincide. The drawing is a projection onto the electrode surface. The thickness of the KTN or KLTN crystal between the electrode surfaces, that is, in the direction perpendicular to the paper surface is 2 mm. The total reflection angle θ is 35 °. The crystal length (L) is 4 mm, the crystal width (W) is 4.92 mm, the inclination angle of the incident surface is 24.2 °, and the incident / exit angle is 47.4 ° with respect to the side surface as shown in the figure. is there. The refractive index is 2.25. In this case, the interaction length is 23.8 mm. When a deflection angle of 0.25 ° per 1 mm interaction length is applied by applying an electric field of 150 V / mm, a deflection angle of ± 11.9 ° is obtained by applying ± 300 V.

  As described above, by employing the total reflection structure according to the present invention, the beam movement distance in the deflection direction, which is a problem when using an external mirror, is wasted. Without generating, it is possible to extend the interaction length between the crystal and light and increase the deflection angle. Alternatively, even when the deflection angle is not increased, the applied voltage required to obtain the necessary deflection angle is reduced, and a reduction in power supply cost can be expected.

Claims (2)

In an optical deflector using a KTN (KTa _1-x Nb _x O ₃ ) crystal or a KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ ) crystal,
A pair of electrode surfaces in which the KTN crystal or the KLTN crystal is parallel to each other;
The electrode surface pair is perpendicular, and Ri Do from each other parallel sides of the at least three pairs,
An internal reflection type optical deflector characterized in that the angle of the side surface and the direction of the incident light are adjusted so that the optical axis of the incident light projected onto the electrode surface coincides with the optical axis of the emitted light . Of the three pairs of side surfaces, the remaining two pairs excluding one pair of incident / exit surfaces are perpendicular to each other, and the two pairs of side surfaces perpendicular to each other totally reflect light transmitted through the KTN or KLTN crystal. The internal reflection type optical deflector according to claim 1.

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