CN1405613A - Total internal reflection 1 XN optical switch - Google Patents

Abstract

A 1×N optical switch with total internal reflection is mainly suitable for spatial optical switching and optical exchange of optical communication and optical computing signals. The light beam emitted from the input optical fiber is collimated by the input collimator, enters the input polarizer to form polarized light, passes through a beam modulation and deflection element composed of a polyhedron crystal with an internal reflection surface and 1≤M≤7 pairs of electrode pairs arranged along the crystal optical axis, and then converges to an optical fiber in an optical fiber array composed of N＝M+1 optical fibers through an output focusing lens for output. Compared with the prior art, the present invention uses a crystal to form a beam modulation and deflection element, and realizes a multi-level output optical path of the light beam by total internal reflection and electro-optical modulation. It has a simple and reliable structure, strong anti-interference ability, small insertion loss, and fast switching speed, which can reach the nanosecond level.

Description

Total Internal Reflection 1×N Optical Switch

Technical field:

The invention is a total internal reflection 1×N optical switch, which is mainly used for spatial optical switch or optical exchange of optical communication and optical computing signals.

Background technique:

Optical switching refers to the direct switching of optical signals transmitted by optical fibers. Compared with electronic digital program-controlled switching, optical switching does not need to set up optical transceivers between optical fiber transmission and switches for optical/electrical, electrical/optical conversion, and can also give full play to the high-speed, broadband and non-electromagnetic induction of optical signals during the switching process. The advantage of overcoming the limitation of the electronic bottleneck on the exchange capacity. With the growth of optical signal transmission traffic and the demand for high-capacity and high-speed switching of access network and high-speed data network, the establishment of an all-optical transmission network has become an inevitable trend in the development of optical communication technology. An optical switch is the most basic device in optical switching, and it can perform selective switching operations on optical signals in an optical network system. A 1×N optical switch can have N output optical paths in different positions for an input, and is mainly used in 1) protection switching. Gating a laser beam into one of many fiber channels enables spatial switching of signals. 2) Optical cross connection. Together with other optical switches, it forms an optical switch matrix, enabling the network to have a dynamic configuration function. 3) Device testing. Multiple devices can be tested simultaneously using 1×N optical switches, which simplifies testing and improves efficiency. 4) Network monitoring. A 1×N optical switch is used at the remote monitoring point to connect multiple optical fibers to the network monitoring instrument, and the monitoring of all optical fibers is realized through optical switch switching.

The structure described in the prior art [1] (see P.Pepperl, Opt.Acta., 24(4), 1977, pp.413-425, A solid-state digital light deflector with DKDP polarization switches) is formed by birefringence The optical switch composed of crystal and electro-optic crystal, its working principle is to change the polarization state of light by applying a half-wave voltage on the electro-optic crystal, so that the light is converted between polarized light o light and e light, and the vertically incident o light passes through The direction of the birefringent crystal remains unchanged, but the e light is refracted after entering the birefringent crystal, and deviates from the original optical path. Through multi-level interconnection, a 1×N optical switch can be realized. In order to make the positions of the controllable light beams distributed equidistantly from each other, the size of each birefringent crystal must increase with the increase of the number of stages. There are many difficulties in artificially synthesizing crystals with high optical quality and large size. In addition, this method requires N pieces of electro-optic crystals and N-1 pieces of birefringent crystals to form a 1×N optical switch, so the production and assembly costs are high, the optical path is complicated, the insertion loss is large, and it is not easy to integrate.

Prior art [2] (see H.Yamazaki and M.Yamaguchi.Opt.Lett., 17(17), 1992, pp.1228-1230, Experiments on a multichannel holographic optical switch with the use ofa liquid-crystal display) The structure described in is an array optical switch using liquid crystal phase holography as photoelectric control. Its working principle is to apply a control voltage to a small area of the liquid crystal screen to generate a phase grating, which diffracts the incident light to deflect it to the output port. By controlling the direction and period of the grating, a 1×N optical switch can be realized. However, its switching speed is slow, which is on the order of milliseconds; it will generate second-order diffracted light, and the efficiency is low; the liquid crystal resolution limits the rotation angle and deflection angle of the beam.

Prior art [3] (see L.Y.Lin, E.L.Goldstein and R.W.Tkach, IEEE Photon.Tech.Lett., 10(4), 1998, pp.525-527, Free-space micromachined optical switches with submillisecond switching time for large- The structure described in scale optical crossconnects) is an optical switch using a micro-electromechanical system (MEMS). The basic principle is to mechanically rotate the movable micro-mirror through electrostatic or other control forces to change the propagation direction of the input light. , so as to realize the switching function. Rotation can also be used, that is, the input optical fiber is installed on the rotating arm, and the rotating arm is rotated by a stepping motor to make it turn to different output ports. The speed of such switches is on the order of sub-milliseconds. Since it is exchanged by mechanical rotation, any mechanical friction, wear and external vibration may reduce its reliability.

There are also 1×N optical switches based on other technologies, such as waveguide optical switch devices, etc., but they all have some disadvantages, such as slow speed and so on.

Invention content:

The invention utilizes the double reflection and electro-optic effect of the crystal to form a light beam modulation and deflection element with one crystal, that is, a 1×N optical switch integrating multiple electro-optic modulation reflectors in one crystal.

The structure of the total internal reflection 1×N optical switch of the present invention is shown in Figure 1, including an input optical fiber 1, an input collimator mirror 2, an input polarizer 3, a beam modulation deflection element 4, an output focusing lens 5 and an output optical fiber 6; The light beam emitted from the input fiber 1 is collimated by the input collimator 2, enters the input polarizer 3 to form polarized light, passes through the beam modulation deflection element 4, and then converges to the output fiber 6 through the output focusing lens 5 for output. Said beam modulation and deflection element 4 is composed of a polyhedral crystal ₄₀₁ with internal reflection surfaces D, E, G, B along the direction of the crystal optical axis with 1≤M≤7 pairs of electrodes ₄₀₂ ; The output optical fiber 6 is an optical fiber array composed of N=M+1 optical fibers.

The polyhedral crystal ₄₀₁ of said beam modulating and deflecting element 4 has 1≤n≤4 internal reflection surfaces D, E, G, B, a beam input surface A, a beam output surface F and a beam output surface F relatively parallel to The surface C; the beam input surface A is perpendicular to the optical axis direction of the crystal ₄₀₁ , and the beam output surface F is parallel to the optical axis direction of the crystal ₄₀₁ .

The width of the electrode pair ₄₀₂ placed on the crystal ₄₀₁ along the optical axis of the crystal ₄₀₁ in the beam modulation deflection element 4 is d _m <d/M, where d is the direction perpendicular to the optical axis of the crystal. The distance between the plane F and the plane C parallel to the beam output plane F is called the width of the crystal ₄₀₁ . M is the number of electrode pairs ₄₀₂ ; the length of the electrode pairs ₄₀₂ l≤Ld, where L is the distance between the beam input surface A of the crystal ₄₀₁ and the intersection point O of the first reflection surface D and the second reflection surface E of the crystal ₄₀₁ The distance between them is called the length of crystal 4 ₀₁ . as shown in picture 2.

The light beam entrance surface of each optical fiber in the N=M+1 optical fiber array forming the output optical fiber (6) is placed on the focal plane of the output focusing lens (5), wherein the qth optical fiber is an optical fiber The central fiber of the array (6 _0q ), where q is when N is an even number, q=N/2; when N is an odd number, q=(N+1)/2). The center point (a _q ) of the beam entry surface of the central fiber (6 _0q ) is exactly placed on the focal point (a _q ) of the output focusing lens (5), and the center point of the beam entry surface of the Nth fiber (6 _0N ) The distance between (a _N ) and the center point (a _q ) of the beam entry surface of the central fiber (6 _0q ) a _q a _N = ftan(γ _N -γ _q ), where f is the focal length of the output focusing lens (5), γ _N is the Nth refraction angle of the beam emitted from the beam output surface (F) of the crystal (4 ₀₁ ).

The said crystal ₄₀₁ is a uniaxial crystal with transverse electro-optic modulation performance, such as lithium niobate, lithium tantalate, etc., whose shape is the polyhedron mentioned above, with n=4 reflecting surfaces as a column, and its specific structure is shown in the figure As shown in 2, the optical axis (c-axis) of the crystal is in the crystal plane and the vertical beam input surface A is set as the z-axis on the coordinate axis, the coordinate x-axis is perpendicular to the surface of the electrode pair ₄₀₂ , and its beam input surface A is vertical On the beam output surface F, the first reflective surface D opposite to the beam input surface A is parallel to the third reflective surface G adjacent to the beam input surface A, and the second reflective surface E is adjacent to the other side of the beam input surface A The fourth reflective surface B is parallel, the beam output surface F is opposite to and parallel to the surface C, and the angles a ₁ and a ₂ between the surface C and the first reflective surface D and the fourth reflective surface B are both 135°, the first reflective surface The included angle between D and the second reflective surface E is 90°, the included angle between the third reflective surface G and the fourth reflective surface B is 90°, and the optical axis of the crystal ₄₀₁ is 45° to the perpendicular to the four reflective surfaces. Taking the number M=3 of electrode pairs ₄₀₂ as an example, the crystal ₄₀₁ can be regarded as three parts separated by dotted lines in Figure 2, the width of the first part is _d1 , the width of the second part is _d2 , and the width of the third part is For d ₃ , d ₁ =d ₂ =d ₃ =d/3. The three pairs of electrodes 4 ₀₂₁ , 4 ₀₂₂ , 4 ₀₂₃ are arranged on these three parts along the optical axis of the crystal 4 ₀₁ , so the width of each pair of electrodes 4 ₀₂₁ , 4 ₀₂₂ , 4 ₀₂₃ should be less than d/3, and the length l should be less than or equal to Ld.

(折射角是指光线方向与界面法线之间的夹角，上标t表示是折射角，下标数字表示附图3的分图号，以下同)。给第一电极对4₀₂₁加横向半波电压，光路如图3-2所示：在面B、D之间传播的。偏振光将变为e偏振光，在D面反射后反射角为 (其中上标i表示是入射角，r则表示反射角；下标前一个数字表示附图3的分图号，后一个数字表示第七次反射；以下同)，e光与o光有一个偏离角 ，到F面后因△θ₁小于全反射角折射出于晶体4₀₁，折射角为

。给第二电极对4₀₂₂加横向半波电压，光路如图3-3所示：在面A、D之间传播的o偏振光将变为e偏振光，则在D、E、G、B、D面反射后，e光与o光有偏离角

到F面后因Δθ₂小于全反射角折射出晶体，折射角为

。给第三电极对4₀₂₃加横向半波电压，光路如图3-4所示：在面E、G之间传播的o偏振光将变为e偏振光，则在G、B、D面反射后，e光与o光有偏离角

，到F面后因Δθ₃乱小于全反射角折射出晶体，折射角为

。经过的反射面越多，e光与o光的偏离角Δθ就越大，相应地光在输出面F的折射角δ′也就越大，所以当电极对4₀₂数耳M＝3时，有如下关系Δθ₁＜Δθ₃＜Δθ₂， ${\mathrm{\&delta;}}_1^t<{\mathrm{\&delta;}}_2^t<{\mathrm{\&delta;}}_4^t<{\mathrm{\&delta;}}_3^t.$ 出射角γ_N为光束从晶体4₀₁的光束输出面F射出的第N个折射角，按从小到大的顺序排列，为 ${\mathrm{\&gamma;}}_1={\mathrm{\&delta;}}_1^t,{\mathrm{\&gamma;}}_2={\mathrm{\&delta;}}_2^t,{\mathrm{\&gamma;}}_3={\mathrm{\&delta;}}_4^t,{\mathrm{\&gamma;}}_4={\mathrm{\&delta;}}_3^t$ 。当N＝M+1＝4时，所以q＝2，即中心光纤为6₀₂。使第2输出光束通过输出聚焦透镜5的主轴，将第2根光纤也就是中心光纤6₀₂的光束进入面的中心点a₂：安置在输出聚焦透镜5的后焦点a₂上。如图1所示。若聚焦透镜5的焦距为f，则第一根光纤6₀₁的光束进入面的中心点a₁到中心光纤6₀₂的光束进入面的中心点a₂的距离a₁a₂＝f tan(γ₁-γ₂)，第三根光纤6₀₃的光束进入面的中心点口，到中心光纤6₀₂的光束进入面的中心点a₂的距离a₂a₃＝f tan(γ₃-γ₂)，第四根光纤6₀₄的光束进入面的中心点a₄。到中心光纤6₀₂的光束进入面的中心点a₂的距离a₂a₄＝f tan(γ₄-γ₂)。以后的以此类推。The optical signal emitted from the input optical fiber 1 is collimated by the input collimator 2 and polarized by the input polarizer 3 into a collimated light beam, which is incident on the crystal ₄₀₁ at right angles, and passes through the reflecting surfaces D, E, G, B, D total internal reflection (the optical axis of the crystal is 45° to the normal line of each reflection surface, which is greater than the total reflection angle of the crystal) and then output from the beam output surface F, through different electrode pairs 4 ₀₂₁ , 4 ₀₂₂ , 4 ₀₂₃ …4 _02M Add half-wave voltage to change the polarization state of the input beam, and there will be output beams with different exit angles, thus separating the light in space. In the case of no voltage, the optical path is shown in Figure 3-1: the input o beam is incident vertically from surface A along the optical axis (c axis) of the crystal, and is reflected by surfaces D, E, G, B, and D. The incident angle of o light on the reflective surface is 45°, and the reflection angle is also 45° (incident angle and reflection angle both refer to the angle between the light direction and the interface normal, the same below), and finally along the vertical crystal light The y-axis direction of the axis reaches the beam output surface F, refracted from the crystal 4 ₀₁ beam output surface F, and the refraction angle

(the refraction angle refers to the angle between the light direction and the interface normal, the superscript t represents the refraction angle, and the subscript number represents the sub-figure number of the accompanying drawing 3, the same below). Apply a transverse half-wave voltage to the first electrode pair 4 ₀₂₁ , and the optical path is shown in Figure 3-2: it propagates between surfaces B and D. The polarized light will become e-polarized light, and the reflection angle after being reflected on the D surface is (The superscript i indicates the angle of incidence, r indicates the angle of reflection; the number before the subscript indicates the sub-figure number of Figure 3, and the last number indicates the seventh reflection; the same below), e light and o light have a Angle of deviation , after reaching the F surface, because △θ ₁ is smaller than the total reflection angle, it is refracted out of the crystal 4 ₀₁ , and the refraction angle is

. Apply a transverse half-wave voltage to the second electrode pair 4 ₀₂₂ , and the optical path is shown in Figure 3-3: the o-polarized light propagating between planes A and D will become e-polarized light, then in D, E, G, B , After the reflection of the D surface, the e light and the o light have a deviation angle

After reaching the F surface, the crystal is refracted because Δθ ₂ is less than the total reflection angle, and the refraction angle is

. Apply a transverse half-wave voltage to the third electrode pair 4 ₀₂₃ , and the optical path is shown in Figure 3-4: the o-polarized light propagating between planes E and G will become e-polarized light, and it will be reflected on the planes G, B, and D After that, e light and o light have a deviation angle

, after reaching the F surface, the crystal is refracted because Δθ ₃ is smaller than the total reflection angle, and the refraction angle is

. The more reflective surfaces passed by, the greater the deviation angle Δθ between the e light and the o light, and correspondingly the greater the refraction angle δ' of the light on the output surface F, so when the electrode pair 4 ₀₂ counts M=3, There is the following relationship Δθ ₁ <Δθ ₃ <Δθ ₂ , ${\mathrm{\&delta;}}_1^t<{\mathrm{\&delta;}}_2^t<{\mathrm{\&delta;}}_4^t<{\mathrm{\&delta;}}_3^t.$ The exit angle γ _N is the Nth refraction angle of the beam emitted from the beam output surface F of the crystal ₄₀₁ , arranged in ascending order, as ${\mathrm{\&gamma;}}_1={\mathrm{\&delta;}}_1^t,{\mathrm{\&gamma;}}_2={\mathrm{\&delta;}}_2^t,{\mathrm{\&gamma;}}_3={\mathrm{\&delta;}}_4^t,{\mathrm{\&gamma;}}_4={\mathrm{\&delta;}}_3^t$ . When N=M+1=4, so q=2, that is, the central fiber is 6 ₀₂ . Let the second output beam pass through the main axis of the output focusing lens 5, and place the center point _a2 of the beam entrance surface of the second optical fiber, that is, the central optical fiber ₆₀₂ : on the back focus _a2 of the output focusing lens 5. As shown in Figure 1. If the focal length of the focusing lens 5 is f, then the distance a 1 a 2 from the center point a ₁ of the beam entrance surface of the first optical fiber 6 ₀₁ to the _center point _{a 2} of the beam entrance surface of the central optical fiber 6 ₀₂ =f tan(γ ₁ -γ ₂ ), _the center point of the beam entry surface of the third _optical fiber ₆₀₃ , and the distance a ₂ a ₃ =f tan(γ ₃ -γ ₂ ), the light beam of the fourth optical fiber 6 ₀₄ enters the center point a ₄ of the surface. The distance a ₂ a ₄ =f tan(γ ₄ −γ ₂ ) to the center point a ₂ of the light beam entrance surface of the central optical fiber ₆₀₂ . And so on in the future.

It can be seen that in the 1×4 optical switch with N=4, the light passes through the crystal optical axis 3 times, and is sent to any pair of the 3 pairs of electrodes 4 ₀₂₁ , 4 ₀₂₂ , 4 ₀₂₃ arranged along the direction of the crystal optical axis. Apply a transverse half-wave voltage to make the incident o-polarized light into e-polarized light, and then reflect by different numbers of reflective surfaces, then the e-light and o-light will have different deviation angles Δθ when they reach the exit surface, so there is Different output angles γ, so that there are 4 different output position optical paths for one input light, and a 1×4 optical switch is realized. Let N be the number of light paths output from different positions, N=M+1: M is the number of electrode pairs required for electro-optic modulation, 1≤M≤7. Therefore, to make a 1×N optical switch, there are N≥2 optical channels on which electrode pairs can be arranged along the optical axis of the crystal to form an electro-optic modulator. The number of M is mainly limited by the size of the focusing lens 5 . When N=2, it is a 1×2 optical switch as shown in Figure 4-1. When no voltage is applied, the beam is output perpendicular to the optical axis of the crystal: apply voltage to the electrode pair 4 ₀₂₁ , and the beam deviates from the output. When N=3, it is a 1×3 optical switch as shown in Figure 4-2. When no voltage is applied, the beam is output vertically to the optical axis of the crystal; when voltage is applied to the electrode pairs 4 ₀₂₁ and 4 ₀₂₂ , the beam exits at different angles output. When N=4, it is a 1×4 optical switch as shown in Figure 4-3. When no voltage is applied, the beam is output vertically to the optical axis of the crystal; voltage is applied to the electrode pairs 4 ₀₂₁ , 4 ₀₂₂ , and 4 ₀₂₃ respectively, and the beam is output in different directions. The exit angle output. Extended to when N=N, it is a 1×N optical switch, as shown in Figure 4-4, the input beam is incident vertically from the beam input surface A, and the angle between the first reflective surface D and the second reflective surface E is 90°, The included angle between the third reflective surface G and the fourth reflective surface B is 90°, and the normal line of the reflective surface is 45° with the optical axis. When cutting the crystal, make the two parallel sections C and F perpendicular to the beam input surface A, one of which is the beam output surface F, when no voltage is applied, the beam is output perpendicular to the optical axis of the crystal; the electrode pairs 4 ₀₂₁ , 4 ₀₂₂ , ..., 4 _02M voltages are applied separately, and the beams are output at different exit angles.

对于第二种情况，有：

当光从晶体向空气折射时，如图5-3所示，晶体光轴与界面JI的夹角为θ，e光入射角为δⁱ，波面角为ⁱ，则折射后，e光的折射角δ^t为：在本发明中由于两相邻反射面互相垂直，也就是光在晶体内第k+1次反射时的反射面与第k次反射时的反射面互相垂直，有：

   

其中

指第k+1次反射时的反射角和波面角， 指第k次反射时的入射角和波面角，k≥1。以图3-3为例，给第二电极对4₀₂₂加横向半波电压后，o光变为e光沿晶体光轴入射到第一反射面D，与第一种情况相符，入射角为45°、波面角为90°，代入公式(1)(2)求出反射角

和波面角

；光又入射到第二反射面E，沿近晶体光轴反射，与第二种情况相符，又由于发生第二次反射时的反射面E和发生第一次反射时的反射面D垂直， ，代入公式(3)(4)求出 和 ；光又沿近晶体光轴入射到第三反射面G，与第一种情况相符，又由于发生第三次反射时的反射面G和发生第二次反射时的反射面E垂直，

，代入公式(1)(2)求出 和

；光又入射到第四反射面B，沿近晶体光轴反射，与第二种情况相符，又由于发生第四次反射时的反射面B和发生第三次反射时的反射面G垂直，

，代入公式(3)(4)求出 和 ；光又沿近晶体光轴入射到第一反射面D，与第一种情况相符，又由于发生第五次反射时的反射面D和发生第四次反射时的反射面B垂直， ，代入公式(1)(2)求出

和 ，此时e光与原先的o光就有一个偏离角 最后e光入射到光束输出面F，晶体光轴与面F的夹角θ＝0°，入射角为Δθ₂、波面角为 ，因Δθ₂小于全反射角折射出晶体，代入公式(5)求得折射角

，也就是出射角γ₄。The derivation formulas of the above-mentioned reflection angle and refraction angle of the e-ray are as follows. When a LiNbO ₃ crystal is used, the two main refractive indices are no _{and ne} respectively, and the angle between the crystal optical axis and the interface JI is 45°. When light enters the air from the crystal, if the incident angle is greater than the total reflection angle, total internal reflection will occur on the interface. There are two situations: one is incident along the near-crystal optical axis, as shown in Figure 5-1; the other is reflection along the near-crystal optical axis, as shown in Figure 5-2. Assuming that before reflection, the incident angle of e light is δ ⁱ , and the wavefront angle is ^i (where wavefront angle =90°-α, α is the discrete angle, refer to "Physical Optics" P299, P302), then after reflection, e The light reflection angle is δ ^r , and the wavefront angle is  ^r . δ ⁱ and δ ^r are the included angles between the e-ray and the normal of the interface JI, and both  ⁱ and  ^r are the angles between the advancing direction of the e-ray and the right side of the wave surface. For the first case, there are:

For the second case, there are:

When the light is refracted from the crystal to the air, as shown in Figure 5-3, the angle between the optical axis of the crystal and the interface JI is θ, the incident angle of the e-ray is δ ⁱ , and the wave surface angle is  ⁱ , then after refraction, the angle of the e-ray The refraction angle ^δt is: In the present invention, since two adjacent reflective surfaces are perpendicular to each other, that is, the reflective surface during the k+1 reflection of light in the crystal is perpendicular to the reflective surface during the k reflection, there are:

in

Refers to the reflection angle and wavefront angle at the k+1th reflection, Refers to the incident angle and wavefront angle at the kth reflection, k≥1. Taking Figure 3-3 as an example, after applying a transverse half-wave voltage to the second electrode pair 4 ₀₂₂ , o light becomes e light and enters the first reflection surface D along the optical axis of the crystal, which is consistent with the first case, and the incident angle is 45°, the wavefront angle is 90°, substitute into the formula (1) (2) to find the reflection angle

and wave front angle

; The light is incident on the second reflective surface E and reflected along the near-crystal optical axis, which is consistent with the second case, and because the reflective surface E when the second reflection occurs is perpendicular to the reflective surface D when the first reflection occurs, , substituting into formula (3)(4) to get and ; The light is incident on the third reflective surface G along the near-crystal optical axis, which is consistent with the first case, and because the reflective surface G when the third reflection occurs is perpendicular to the reflective surface E when the second reflection occurs,

, substituting into formula (1)(2) to get and

; The light is incident on the fourth reflective surface B and reflected along the near-crystal optical axis, which is consistent with the second case, and because the reflective surface B when the fourth reflection occurs is perpendicular to the reflective surface G when the third reflection occurs,

, substituting into formula (3)(4) to get and ; The light is incident on the first reflective surface D along the near-crystal optical axis, which is consistent with the first case, and because the reflective surface D when the fifth reflection occurs is perpendicular to the reflective surface B when the fourth reflection occurs, , substituting into formula (1)(2) to get

and , at this time, the e light and the original o light have a deviation angle Finally, the light e is incident on the beam output surface F, the angle between the optical axis of the crystal and the surface F is θ=0°, the incident angle is Δθ ₂ , and the wavefront angle is , because Δθ ₂ is smaller than the total reflection angle, the crystal is refracted out, and the refraction angle is obtained by substituting into formula (5)

, which is the exit angle γ ₄ .

Compared with the prior art: the prior art [1] needs to use N pieces of electro-optic crystals and N-1 pieces of birefringent crystals to be cascaded to realize 1×N optical switch, the cost of manufacture and assembly is high, the optical path is complicated, and the insertion loss is large , It is not easy to integrate, and the switching speed is reduced after multiple cascaded switches. The prior technology [2] uses liquid crystal phase holography as an optical switch for photoelectric control. The speed of liquid crystal is slow and can only reach the order of milliseconds, which will cause secondary diffraction and low efficiency. The prior art [3] is a mechanical optical switch, which realizes optical path switching by mechanical rotation, which has low reliability and slow speed, which is on the order of sub-milliseconds. The above-mentioned structure of the present invention utilizes the total internal reflection effect of a crystal to realize the deflection of multi-level light beams, and the output optical paths of each level use the principle of transverse electro-optical modulation of light propagating along the optical axis of the crystal to realize the rotation of the polarization state of multi-level light beams. The crystal realizes the 1×N optical switch function of multi-level beam deflection and multi-level electro-optic modulation. It has the advantages of simple and reliable structure, not easily affected by the environment, strong anti-interference ability, small insertion loss, and fast switching speed. If LiNbO ₃ crystal is used to make the 1×N optical switch of the present invention, the switching speed can reach nanosecond level.

Description of drawings:

Fig. 1 is a schematic diagram of the structure of the optical switch of the present invention.

FIG. 2 is a structural diagram of crystal ₄₀₁ in FIG. 1 .

Figure 3 is a schematic diagram of the optical path of the 1×4 optical switch used when N=4, M= ₃ : Figure 3-1 is the state of the optical path without voltage; The optical path state of the half-wave voltage; Figure 3-3 is the optical path state when the lateral half-wave voltage is applied to the second electrode pair ₄₀₂₂ ; Figure 3-4 is the optical path state when the lateral half-wave voltage is applied to the third electrode pair ₄₀₂₃ .

Fig. 4 is the 1 * N optical switch optical path structure schematic diagram of the present invention: Fig. 4-1 is the 1 * 2 optical switch optical path schematic diagram when N=2, M=1; Fig. 4-2 is N=3, when M=2 Figure 4-3 is a schematic diagram of the 1×3 optical switch optical path when N=4, M=3; Figure 4(d) is a 1×N optical switch when N=N, M=M Schematic diagram of the switching light path.

Figure 5 is the optical path of light reflection and refraction in the crystal: Figure 5-1 is the incident e-light reflection along the near-crystal optical axis; Figure 5-2 is the e-light reflection along the near-crystal optical axis; Figure 5-3 is Refraction of light rays exiting the crystal-air surface.

Specific implementation plan:

As the structure of the 1×N optical switch of the present invention shown in the above-mentioned Fig. 1, the crystal ₄₀₁ is selected as a LiNbO ₃ crystal sheet, and the slopes D, E, G, and B of 45° and 135° are formed as reflecting surfaces, so that the o light Incident from the input surface A along the optical axis of the crystal, after being reflected by the reflecting surfaces D, E, G, B, D, it is incident on the output surface F along the direction perpendicular to the optical axis of the crystal, and finally the crystal 4 ₀₁ is refracted from the output surface F . The lower the required half-wave voltage, the better, but in order to make the Gaussian beam safely pass through the crystal 4 ₀₁ , the ratio of the thickness h of the crystal 4 ₀₁ to the length l of the electrode pair 4 ₀₂ is actually limited. In this example, considering the processing difficulty of the crystal, L is selected as 50 mm, d is 45 mm, h is 1 mm, and the length l of the electrode pair is 5 mm. The number of electrode pairs 4 ₀₂ is selected as M=3, the number of optical fibers in the output optical fiber 6 is N=4, and the central optical fiber is the second optical fiber 6 ₀₂ .

The wavelength of light output from the input fiber 1 is 1.5 μm. For this wavelength, the two main refractive indices of LiNbO ₃ crystal are _no = 2.2129, _ne = 2.1394, and the transverse half-wave voltage is 2400 volts. Make the polarization direction of the incident light consistent with the o light, and enter the crystal 4 ₀₁ from the input surface A along the optical axis of the crystal 4 ₀₁ ; by applying transverse half-wave voltages to different electrode pairs 4 ₀₂₁ , 4 ₀₂₂ , 4 ₀₂₃ , the light is changed Polarization state; by using the double reflection effect and cascading, the light exits from the crystal ₄₀₁ at different exit angles, so that there are four output light paths at different positions. The data of the specific embodiment is shown in Table 1, wherein δ ^r refers to the reflection angle of the light after the reflection of the reflective surface,  ^r refers to the wavefront angle of the light after the reflection of the reflective surface, and Δθ refers to the arrival of the output surface F, e light The angle of deviation from _the original o light, the refraction angle ^δt refers to the refraction angle of the light refracted out of the crystal from the output surface F, and the exit angle γ _N is the Nth refraction angle ( Arranged in ascending order).

The 1×4 optical switch data implemented in Table 1 Reflective surface no voltage Apply voltage to electrode pair 4 ₀₂₁ Apply voltage to electrode pair 4 ₀₂₂ Apply voltage to electrode pair 4 ₀₂₃ ^δr  ^{r δr}  ^{r δr}  ^{r δr}  ^r The first reflective surface D 45° 90° 45° 90° 46.87° 89.87° 45° 90° Second reflective surface E 45° 90° 45° 90° 40.99° 89.74° 45° 90° The third reflective surface G 45° 90° 45° 90° 50.61° 89.61° 46.87° 89.87° Fourth reflective surface B 45° 90° 45° 90° 36.99° 89.48° 40.99° 89.74° The first reflective surface D 45° 90° 46.87° 89.87° 54.36° 89.36° 50.61° 89.61° The deviation angle Δθ between e light and o light 0° 1.87° 9.36° 5.61° Refraction angle δ ^t 0° 4.29° 21.83° 12.93° Outgoing angle γ _N γ ₁ =0° γ ₂ =4.29° γ ₄ =21.83° γ ₃ =12.93°

When the focal length f=20cm of the focusing lens 5, in the output optical fiber 6, the central point _a2 of the light beam entrance surface of the central optical fiber ₆₀₂ is placed on the focal point _a2 of the output focusing lens 5, and the light beam of the first optical fiber ₆₀₁ enters The distance a ₁ a ₂ =ftan(γ ₁ −γ ₂ )=-1.5cm from the center point a ₁ of the surface to the focal point a ₂ of the output focusing lens 5, the distance a ₃ from the center point a 3 of the light beam entering the surface of the third optical fiber 6 ₀₃ The distance a ₂ a ₃ of the focal point a ₂ of the output focusing lens 5 =ftan(γ ₃ −γ ₂ )=3.03cm, the distance between the center point a ₄ of the beam entrance surface of the fourth optical fiber 6 ₀₄ and the focal point a ₂ of the output focusing lens 5 The distance a ₂ a ₄ = ftan(γ ₄ −γ ₂ )=6.32 cm.

For the 1×8 optical switch used by N=8, M=7, it can be calculated that γ ₁ =0°, γ ₂ =4.29°, γ ₃ =12.93°, γ ₄ =21.83°, γ ₅ =31.22°, γ ₆ =41.47, γ ₇ =53.45°, γ ₈ =24.42°. In the output optical fiber 6, the central point _a4 of the beam entrance surface of the central optical fiber ₆₀₄ is placed on the focal point a4 of the output focusing lens ₅ , and the center point _a1 of the beam entrance surface of the first optical fiber ₆₀₁ is at a distance from the output focusing lens 5 The distance a _{1 a} 4 of the focal point a ₄ =ftan(γ ₁ -γ ₄ )=-8.01cm, the distance a 2 between the center point a ₂ of the light beam entrance surface of the second optical fiber ₆₀₂ and the focal point a ₄ of the output focusing lens ₅ a ₄ =ftan(γ ₂ -γ ₄ )=-6.88cm, the distance a 3 from the center point a ₃ of the light beam entrance surface of the third optical fiber ₆₀₃ to the focal point a ₄ of the output focusing lens 5 a ₃ a ₄ =ftan(γ ₃ -γ ₄ )=-3.13cm, the distance a _{5 a 4} from the center point a 5 of the beam entrance surface of the fifth optical fiber 6 ₀₅ to the focal point a ₄ of the output focusing lens 5 a ₅ a ₄ =ftan(γ ₅ -γ ₄ )=3.27cm , the distance a 6 a ₄ from the center point a ₆ of _the beam entrance surface of the sixth optical fiber 6 06 to the focal point a ₄ of the output focusing lens ₅ = ftan(γ ₆ -γ ₄ )=7.10cm, the seventh optical fiber 6 ₀₇ The distance a ₇ a ₄ = ftan( _{γ 7} -γ ₄ )=12.31cm from the center point a 7 of the light beam entrance surface to the focal point a ₄ of the output focusing lens 5, the center point a ₈ of the light beam entrance surface of the eighth optical fiber ₆₀₈ The distance a ₈ a ₄ from the focal point a ₄ of the output focusing lens 5 =ftan(γ ₈ −γ ₄ )=22.47cm.

Claims (4)

1. A total internal reflection 1×N optical switch, including an input optical fiber (1), an input collimator (2), an input polarizer (3), a beam modulation deflection element (4), and an output focusing lens (5 ) and output optical fiber (6); after the beam emitted by the input optical fiber (1) is collimated by the input collimator (2), it enters the input polarizer (3) to form polarized light, and passes through the beam modulation deflection element (4) Afterwards, it is converged to the output optical fiber (6) for output through the output focusing lens (5), and it is characterized in that said beam modulation deflection element (4) is made of a piece with internal reflection surface (D, E, G, B) The polyhedral crystal (4 01 ) with 1≤M≤7 pairs of electrodes (4 ₀₂ ) placed along the direction of the crystal optical axis is composed of polyhedral crystals (4 ₀₁ ); the output optical fiber (6) is composed of N=M+1 optical fibers fiber optic array. 2. The total internal reflection 1×N optical switch according to claim 1, characterized in that the polyhedral crystal (4 ₀₁ ) constituting the beam modulation and deflection element (4) has 1≤n≤4 internal reflection surfaces (D, E, G, B), a beam input face (A), a beam output face (F) and a face (C) relatively parallel to the beam output face (F); the beam input face (A) is perpendicular to the crystal In the direction of the optical axis of (4 ₀₁ ), the beam output surface (F) is parallel to the direction of the optical axis of the crystal (4 ₀₁ ). 3. The total internal reflection 1×N optical switch according to claim 1, characterized in that said beam modulation and deflection element (4) is placed on the crystal (4 ₀₁ ) along the optical axis of the crystal (4 ₀₁ ) The width d _m of the electrode pair (4 ₀₂ ) on the top is <d/M, where d is the direction perpendicular to the optical axis of the crystal, between the beam output surface (F) and the surface (C) relatively parallel to the beam output surface (F) The distance between is the width of the crystal (4 ₀₁ ); M is the number of electrode pairs (4 ₀₂ ); the length of the electrode pairs (4 ₀₂ ) l≤Ld, where L is the beam input surface of the crystal (4 ₀₁ ) (A ) to the intersection point (O) of the first reflective surface (D) and the second reflective surface (E) of the crystal (4 ₀₁ ), which is the length of the crystal (4 ₀₁ ). 4. The 1×N optical switch of total internal reflection according to claim 1, characterized in that the light beam of each fiber in the N=M+1 fiber array that constitutes the output fiber (6) enters Both surfaces are placed on the focal plane of the output focusing lens (5), wherein the qth optical fiber is the central optical fiber (6 _0q ) of the optical fiber array, where q is when N is an even number, q=N/2, when N is an odd number , q=(N+1)/2; the center point (a _q ) of the beam entry surface of the central fiber (6 _0q ) is just placed on the focal point (a _q ) of the output focusing lens (5), and the Nth fiber The distance a _q a N = ftan( _{γ N} -γ _q ) between the center point (a _N ) of the beam entrance surface of (6 _0N ) and the center point (a _q ) of the beam entrance surface of the central fiber (6 _0q ), where f is the focal length of the output focusing lens (5), and γ _N is the Nth refraction angle of the beam emitted from the beam output surface (F) of the crystal (4 ₀₁ ).

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