JPS63502533A - Voltage tunable optical beam switching device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Voltage tunable optical beam switching device [Technical field of the invention] This invention relates generally to optical information transmission systems, and in particular to optical phase gratings using liquid crystal cells. and an information device for optically switching and dividing information. .

[Related technology] Liquid crystal (LC') cells are generally used in a wide range of applications such as image display devices. used, and recently increasingly used in real-time optical signal processor equipment. Ru. Based on U.S. Pat. No. 4,389,098 (Hori et al.), Contains a liquid crystal layer with dielectric properties and optical anisotropy that partially forms an optical element. A liquid crystal five light valve device and a schlieren light system are disclosed. Enter An electric field with a spatial intensity distribution corresponding to the force image signal is supplied to the liquid crystal to A phase-modulated phase diffraction grating is formed in the liquid crystal layer. The diffracted light is Forms an enlarged image suitable for projection onto a screen. One of the announced examples In Cot, 5, the electrodes on the substrate are arranged in stripes with a predetermined spatial period. It is configured to have a type electrode structure. An electric field is connected across the surface of the substrate. Another layer is supplied to the liquid crystal layer through a periodically shaped high-resistance layer on the electrode. The composition has also been revealed.

In two-dimensional (planar) embodiments, many types of diffraction gratings can be formed in the liquid crystal layer. A photomask and three gratings aligned in different directions are used as a means to conduct photoconductive It is used in layer writing photometry. In another typical image display device As shown, the invention by Hor et al. uses a photoconductive layer to accurately reproduce the input image. . However, optical switching devices require controllable diffraction orders for most of the input power. requires highly efficient beam control to ensure that the star To the coupling device, the intensities of the transmitted power in different diffraction orders are almost the same. must be equal, and its variation is no more than ±10%. In this way voltage or The variation of diffraction intensity of different orders as a function of wavelength is typical for common image displays. This is not considered in the case of optical switching equipment, but is important when considering optical switching equipment. Ru.

As an example of an LC signal processing device, US Pat. No. 4,351,589 can be given. This specification No. 4351589 discloses that a locally variable phase grating is generated. Figure 2 shows a method using an LC light valve operating in a mode of operation. light treatment The variable grid mode (VGM) operation of liquid crystal devices that can be used for Variable Grating ModeLiqui by offerer d Crystal Devlce f’or 0ptical Processes sing”5PIE, Volume 218, Devices and systems for optical signal processing, 81 ~86 pages, published in 1980). In VGM operation , a variable phase grating is formed in a liquid crystal cell. The grating period is determined by the supply voltage and therefore by varying the voltage supplied to the LC cell or photoconductive By adding layers to the cell it can be changed in response to the optical signal. Photoconductive layer as cell Each input signal component is changed according to the optical signal by adding that component generate a local grating structure with a special spatial frequency corresponding to the intensity level of . this In VGM operation, the grating period is fixed or constant throughout the cell. There is no need to worry.

VGM operation of nematic liquid crystal to achieve 1.3 or active dividing device has been used. G,L about this.

"V ariable -G rating-M" by T angonan ode (published by L1quid). In “1φ3” (・ ) is used as a statement to indicate one input port transmitting the same signal to three output ports. used in the to be distinguished from the standard term “NXN” used to indicate the transmission of N signals of receive equal intensity. Star is one input port to N output ports with each output port receiving equal strength N input ports (N-N) are shown for N output ports. fiber optic Disadvantages of commercial VGM LC devices include lack of sufficient efficiency and grid failure at high electric fields. Contains completeness issues. Furthermore, the reported results show that the VGM light valve operates dC. This indicates that the voltage required is as follows.

Rapidly develop the field of optical communications and draw more attention to fiber optic communications. A switch that can optically split the information transmitted optically into various channels. The need arises for In the past, electrical switching devices were commonly used. It was The optical signal is first converted to an electrical signal that is switched to a new path.

The electrical signals are then used to modulate the output of the semiconductor lasers, which convert them into optical It is converted back into an optical signal that is transmitted by a fiber. This kind of electrical switch The main drawback is that the effective communication bandwidth is limited.

U.S. Pat. No. 4,518,837 discloses that an arbitrarily polarized incident light beam A polarizing beam splitting cue is used to split the beam into polarized components that propagate along parallel paths. “E Electro-Optical S” using a beam and reflector witch for U polarized Optlcal Signa ls”. The polarization rotator polarizes the unpolarized beam of light in parallel paths. installed in the path of the reflected component to rotate the plane of polarization of the light beam component that is coplanar with the plane. be placed. Two beams emerge at one or more desired outputs Liquid crystal nematic reflector transmitter array confined between prismatic bodies as are deflected simultaneously or individually by selectively energizing the electrodes.

As discussed in Cot, 8. ``optically transparent electrode'' means one optically transparent electrode opposite the individually segmented electrode. Two parallel with a single uniform liquid crystal film confined between electrodes and electrode layers They are preferably arranged in rows. This example allows you to independently scan either beam. switch an array of four parallel LC cells to produce eight possible outputs. providing.

A two-way coupling device using a star coupling device and two phase transmission gratings is U, “Binary Phase Grating f” by Mr. Klllat et al. or Couplers Used in Fiber-Optic Commu nlcation”. The ideas appearing in this literature are B1nary PhaseGrating f’o by Mr. Ranini 111at r 5tar Couplers with Hlgh SpHttingRa tio”. In these documents, the authors use How can two phase transmission gratings with a certain number of central diffraction orders to N (i.e. 1×N) and N to N (i.e. NXN). It discusses what it is used to do. These devices are passive phase grating devices . Passive gratings are suitable for use in equipment requiring fixed or unchanging divisions. Ru. However, active grids reduce the fraction of divisions that are not available with passive grids. The ability to actively control data partitioning when the data bus is overloaded. Dynamically reduce the number of active star terminals in the distribution network. therefore active The switching device is particularly suitable for use in data distribution networks.

By holographic means to connect two NxN matrices of optical fibers. a diffraction grating recorded in a light-sensitive crystal (preferably blue lead silicon oxide). A holographic optical switch that deflects a light beam using It is shown in Application No. 4543682. This light switch is electrical Rather than being holographic, it overcomes the bandwidth limitations of electrical switches. However, once the grating is holographically recorded in the crystal, the device is a passive optical scanner. works as a switch. The orientation and spatial frequency of the grating are then Changed only when erasing and rewriting the grid. Hence the erasure of the existing grid and a new grid record for each time a change in the switching pattern is desired. must be done once in a while. This is a problem when controlling a large number of beams. Formation requires the use of multiple lasers. Furthermore, the holographic switch is N XN switching, but also a variety of telecommunications, signal processing and data communications In the communication region, 1·N switching is required.

[Summary of the invention] The present invention comprises a layer of liquid crystal material sandwiched between two substrates of transparent material such as glass. The present invention provides an LC optical switch using an LC cell. The base is a transparent conductive electrode layer. A grating pattern is formed on one of the substrates of the LC cell. The device has the same voltage It operates as a tunable phase grating, whose grating strength is determined by an externally supplied electric field. controlled by

An advantage of the present invention is the provision of an optical switch for 1·N division with equal output power.

Another advantage of the present invention is that the present invention provides one-dimensional and two-dimensional The switching consists in the use of liquid crystal cells.

A further advantage of the invention is that the segmentation is performed in a single stage.

Yet another advantage of the present invention utilizes active star networks and power diversity. It is a possibility.

[Brief explanation of the diagram] These advantages and features of the invention will be further apparent from the following detailed description and accompanying drawings. will become clear.

FIG. 1a is a cross-sectional view of the LC cell of the present invention, and FIG. 1b is a cross-sectional view of the LC cell of the present invention. FIG. 1c is a perspective view of the constituent parts of the cell shown in FIG. Figures 5 to 5 show various diffraction patterns when various operating voltages are supplied to the device of the invention. Figure 6a shows the results of the order of magnitude for two-dimensional switching using the present invention. showing the device; FIG. 6b shows two-dimensional switching achieved using the apparatus shown in FIG. 6a. This is the display result from .

[Example] FIG. 1a is a sectional view showing the basic structure of the LC cell 10 of the present invention. glass two transparent materials, preferably having a thickness of the order of 1+nn+, of a material such as The smooth plates 1 and 3 are inscribed to provide conductive electrode surfaces 5 and 7. It is covered with a transparent conductive material such as dium tin oxide (ITO).

Homogeneous alignment of liquid crystal molecules in a resting state can be achieved by rubbing or ion radiation etching. caused by conventional methods such as chiming alignment. Homogeneously aligned L At C, the rest-state alignment is parallel to the bounding surface. LC material 9 is commonly performed It is sandwiched between plates 1 and 3 as a thin layer so that the about 6μm Thick liquid crystal layers provide effective electro-optic modulation in conventional cells, and considerably lower drive It is used to supply voltage (<10V).

A grating pattern as shown in Figure 1b is then photolithographically printed on the mask. and then masked using conventional ion beam sputtering. 170 is formed in the ITO layer 5 by removing the unused portion 170. other Any suitable conventional technique can also be used to form the grid pattern. Electrode 5 of the present invention is a typical grid of several parallel lines of constant and equal width, uniformly spaced They are arranged in pattern 11. The selected grid line width and grid spacing are determined by stem requirements and the following general design considerations. LC layer is thick The lower the voltage, the lower the required operating voltage. Furthermore, line 11 is abnormal (e.g. 5μIl+) and their spacing is the same or wider. In some cases, the electric field they output can be applied to the LC layer 9, which is approximately 6 to 12 μm thick. It only poorly locally repositions the molecular alignment in the region. However, the line For example, if it is 25 μm wide and the spacing is the same or wider , the electric field output by the relatively wide electrode wire is more effectively installed and has a wide range The molecular alignment is performed again over the period. Therefore, the magnitude of voltage, field efficiency, molecular alignment The region of the domain where column rearrangement occurs, and the operating voltage and zero molecule orientation. Design consideration for the balance between electric field efficiency and electric field efficiency when generating a This affects the dimensioning of the lattice pattern.

The LC cell 10 of the present invention may be any of the types commonly used in liquid crystal electro-optical device technology. It can also be formed by technology. LC cell 10 of the present invention and conventional liquid crystal electrical/optical device The fundamental difference is that the voltage-tunable phase grating is suitable for electrical and optical switching. The method of patterning the electrode structure to provide any suitable nematic fluid can be used as the LC layer 9. The birefringence B of liquid crystal is very large, for example B -0.2, and the thickness of the LC cell is generally less than 12 μm as mentioned earlier. In this case, strong electrical-optical interactions occur even at low operating voltages.

The LC cells described above are driven by conventional external circuitry in a known manner.

An LC cell according to the invention was assembled for testing. Referring to Figure 1a, the test section Each layer has a thickness of 3mm and is made of transparent and conductive IT with a thickness of 700mm. Assembled using two glass plates 1 and 3 covered with O layers 5 and 7 It is being Coated glass plate to ensure even homogeneous alignment of liquid crystal molecules After rubbing 1 and 3, commercially available (BDH Chemicals, Ltd. , Poole, Dorset, England) nematic LC mixture. (BDH) layer is separated by a mylar spacer to a thickness of 12 μm. It was formed between lath plates 1 and 3. The ITO layer 5 is then The mask is formed photolithographically and the mask is formed using ion beam sputtering. patterned by removing the leftover ITO exposed by the . A grating pattern 11 having lines 25 μm wide at 25 μm intervals is formed.

The orientation of the LC molecules is determined by the optical axis of the liquid crystal, referred to as director L. This is a direction parallel to the grid lines 11. The LC cell 10 uses the apparatus shown in FIG. 1C. He Ne (0,83 μl1) and Ga At As (0,82 tested at a wavelength of .mu.m).

The polarization direction of the input light with respect to the grating lines is divided into the same 1.5 with a specific voltage for each wavelength. adjusted to carry out. Initially, the supplied voltage v-0 causes the LC molecules to They are homogeneously aligned parallel to the L direction, ie parallel to the boundary surface. supplied The voltage applied is typically a 10KHz aC signal in the 0-20V range.

No analyzer is used on the output. Instead, voltage regulation, monitoring and The light transmitted by the LC cell lO to assist in quantitative measurements is (retlcon). The reticon output is displayed on the oscilloscope. It will be done. This device performs 1·N splitting and monitors the voltage dependence of the diffraction order.

Referring to Figure 2, the oscilloscope transmits optical power for an operating voltage of 3.5V. Cope display shows that the maximum transmitted intensity corresponds to the zero order, 0.9d A weak tap condition in the order of B is the two first taps on either side of the zero order. Indicates that it exists in the order.

4. The oscilloscope display of the transmitted light for the operating voltage of the OV is the third As shown in the figure. The three maxima clearly correspond to zero and first order. , with a weak tap state in the second order. The intensity of the diffracted light is However, if we are limited to the maximum of these three, a division of 1.3 can be obtained with a loss on the order of ldB. It will be done.

As can be seen from Fig. 4, the five maxima are at zero for an operating voltage of 4.2 V. b, clearly corresponds to the first and second orders, and is weaker in the third order. With tap state. In this way, 1.5 division has a loss of only 0.7dB or less. It will be done.

The above loss numbers include losses of an undesired order.

Experimental observations show that the splitting effect is high. This is about a total loss of 1 dB. This is because the LC grating forms diffraction orders of equal intensity. this Such latter formation is clearly shown in FIGS. 3 and 4. output strength It is observed that the distribution in is of the order of 1150. Cell transmission is generally 95% and reflections are ignored.

In the output device shown in FIG. 3, the LC cell 10 of the invention has one output. N-2 diffraction orders are formed for each light beam from the power port. that Therefore, 2N-1 or 3 output ports are required to collect all these light beams. It becomes necessary. Similarly, five output ports correspond to N-3 in FIG. required to collect the light transmitted by O.

Referring to Figure 5, for an operating voltage of 4.75V, the first order is zero and the It is observed that weak tap states exist in the 2nd, 3rd and 4th orders.

In different cells with different proportions of LC alignment, the 1.7 division is ± in the output intensity. It is observed that there is a variation of 20%.

There is no departing from the scope of the invention in using a grid electrode pattern. rather than the actual dimensions of the LC cell and grating pattern, the polarization direction of the input light and It will be appreciated that the output and output collection means may be varied in other embodiments. cormorant. The experimental observations described here are for illustrative purposes only and are beyond the technical scope. It is not limited to.

A coupling device with a higher splitting factor than those discussed above is can be obtained by intersecting two grids. 2D using intersecting grid The concept of switching is known (e.g. previously referenced by K. Illuminated B1nary Phase Gratlngs for 5tar C uplers with High Splitting Ratio” 18 (See pages 3-7). Klllat et al. intersect at an angle of BO'' or 90°. We report results obtained with two grids. They have a tangent diameter of 50 μm 1 with a total loss on the order of a few dB using graded index fibers. ・We were able to achieve 35 coupling devices. This, to the best of their knowledge, was achieved at the time. This was the highest split rate ever achieved.

A two-dimensional switching embodiment for the present invention is shown in Figure 6a. Kl A conventional double phase grating 12 or other suitable The phase grating is 60″ for the voltage tunable phase grating LC cell 10 of the present invention. or at an angle of 90''.The electric current supplied to the LC cell 10 In the absence of pressure, the dual phase grating 12 only performs passive switching. appropriate voltage is supplied to the LC cell 10, the active grid is energized and has a high splitting ratio. A two-dimensional partitioning is realized, which allows active addressing of a large number of output ports. be done. For example, passive 1/3 division can be achieved by etching a glass slide. This is achieved using a conventional double phase grating formed. The division is φ-2rad Control the etching time until the appropriate phase shift (in radians) is achieved. It is known that this corresponds to a division ratio of 1.3. 1・ The voltage tunable phase grating 10 of the present invention, which is adjusted to perform a division by seven, is a passive It is arranged at an angle of 90' with respect to the grating 12. 8v operating voltage is 1.5dB It has been found that it is most preferable to divide the area into 1.7 parts to ensure uniformity of strength. Also a book At lower power intensities, the device of the invention performs a 1.3 or 1.5 split. It was also approved to perform 1.7 division at a certain degree. Voltage controlled phase grating lO is operated at 4v, the three output spots generated by the passive grating 12 are , is transformed into a two-dimensional 3×7 pattern as shown in FIG. 6b. That's why it happened , conversion of 1.3 division into 1.21 is realized. In this example, the two-dimensional output Fiber arrays can be effectively addressed by a combination of active and passive gratings. It is possible to Different output states change the voltage settings of phase gratings 10 and 12. The intersection angle of the grating can be varied or used in this example. The dividing characteristics of the passive grating 12 can be changed, and the operating characteristics of the LC cell 10 can be adjusted appropriately. It should be noted that this is achieved by changing the

In yet another embodiment, the two-dimensional partitioning is essentially the same as the apparatus discussed above. Both can be formed with active intersecting grids in the same device.

The specific embodiments of the invention shown and described herein are merely illustrative.

Numerous modifications and variations of the present invention are possible in view of what has been set forth above, and These may be realized without departing from the technical scope of this invention as set forth in the claims. It is possible.

-1OI　-3-2-10123 Fig, 6b.

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Claims (14)

[Claims] 1. In a voltage tunable optical beam switching device, the This is different from a liquid crystal cell with transparent electrodes forming a voltage-tunable phase grating. connected to the liquid crystal cell for supplying a voltage to the liquid crystal cell through the electrode. an input optical beam from the input port; is characterized by being switched to one or more output ports after passing through a capable phase grating. Optical beam switching device. 2. The liquid crystal cell consists of two flat plates of transparent material and a space between the plates. a liquid crystal material sandwiched between the plates, and the plate is covered with a transparent conductive electrode material. and the conductive coating on the plate includes transparent conductive coatings arranged in a grid pattern. 2. A device according to claim 1, wherein the device is suitably treated to form an electrode. 3. 3. The apparatus of claim 2, wherein said plate is made of glass. 4. 3. The device of claim 2, wherein said liquid crystal is nematic. 5. Claims wherein the transparent conductive coating is a mixed oxide of indium and tin. The device according to paragraph 2. 6. orders diffracted from the input beam passing through the voltage tunable phase grating Claims further comprising display means connected to the liquid crystal cell for displaying the intensity distribution between The device according to item 1. 7. 2. The apparatus of claim 1, wherein said input port is an optical fiber. 8. Claim 1, wherein the one or more output ports are one or more optical fibers. Apparatus described in section. 9. Active optical switch for optically coupling one input port to multiple output ports In a etching device, a liquid crystal cell with transparent electrodes arranged in a grid pattern and the appropriate polarization at the appropriate angle with respect to the orientation of said grating pattern. means for inputting light of the liquid; means for supplying a variable voltage to the electrode; and a means for inputting the light of the liquid; and means at the output port for receiving the output of the crystal cell. etching device. 10. Claims further comprising display means connected to the liquid crystal cell at the output port. The device according to paragraph 9. 11. Claim 9, wherein said input and output ports are optical fibers. Device. 12. In a voltage-tunable two-dimensional optical beam switching device, a double phase grating intersected at an angle with respect to the optical axis of the liquid crystal cell; A liquid crystal cell with transparent electrodes arranged in a grid pattern and a variable voltage applied to the liquid crystal the cell through the electrodes to form a voltage tunable phase grating; and voltage supply means connected to the liquid crystal cell, The light beam from the input port is diffracted by the crossed phase grating in two dimensions. It is characterized by realizing optical connection of multiple output ports and input ports. Two-dimensional optical beam switching device. 13. Voltage tunable two-dimensional optical beam switching with two or more liquid crystal cells In the device, said cell having transparent electrodes arranged in a grid pattern; voltage supply that provides a variable voltage, thereby forming a voltage-adjustable phase grating. the two or more voltage tunable phase gratings having respective optical axes at an angle with each other; The light beams from the input ports are crossed in two dimensions. is diffracted by the crossed phase grating, and the optical A two-dimensional optical beam switching device characterized by realizing connection. 14. Multidimensional with two or more said liquid crystal cells in a crossed structure Claim 1 constituting a voltage tunable optical beam switching device of Optical beam switching device by.