JP3222567B2 - Hologram type optical switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram type optical switch which can switch an input optical signal and output the signal from one or more arbitrary output ports.

[0002]

2. Description of the Related Art A conventional hologram type optical switch which can be used in an optical signal exchange system in an optical communication system is configured as shown in FIG.

As shown in FIG. 3, a liquid crystal display
The driver 11 selects and writes arbitrary information from a plurality of hologram information stored in the image memory 13 by the driver 12. Reference numeral 14 denotes an output port surface, and the output port surface 14 has a plurality of, for example, four output ports 14a, 14b,.
An input optical signal incident on the liquid crystal display 11 is diffracted by the liquid crystal display 11, and any one of the output ports 14a, 14b, 14c, 14c is provided.
The output is switched to d.

Here, the hologram written on the liquid crystal display 11 is a binary phase type hologram having a phase difference of π radians, and has a parallel lattice structure with an equal pitch. With this lattice structure having a phase difference of π radians,
The zero-order light of the light transmitted through the hologram disappears. Although ± 1st-order light and higher-order diffracted light are generated, the + 1st-order light is used for the optical switch, so that the other diffracted lights need to be cut by a mask or the like.

The direction in which light is diffracted is perpendicular to the direction of the hologram grating, and the angle of diffraction is determined by the pitch of the grating. That is, in order to increase the diffraction angle, the pitch of the grating may be reduced.

Further, since the liquid crystal display 11 is used as a phase modulator for transmitted light, the polarizing plate is removed and only the liquid crystal plate is used. By controlling the voltage applied to each pixel of the liquid crystal display 11, an electric field distribution is formed on the liquid crystal display 11, and a corresponding refractive index distribution is formed. Then, from the difference in the refractive index of each pixel, it is possible to give the light transmitted through the liquid crystal display 11 a phase distribution proportional to the difference in the refractive index.

Therefore, in order to form a desired phase distribution, the driver 12 may apply a necessary voltage to each pixel of the liquid crystal display 11. This voltage information is stored in the image memory 13 and switches the optical switch shown in FIG. 3, that is, the input optical signal is transmitted to the other output ports 14b and 14b.
In the case of switching to c and 14d for output, the driver 12 sets the voltage based on the voltage information read from the image memory 13 based on
The corresponding voltage is applied to the liquid crystal display 11. That is, the switching of the optical switch is given by the operation of the driver 12.

In the above configuration, when a light beam is applied to the hologram written on the liquid crystal display 11, the wavefront of the light of the hologram changes and is diffracted. The diffraction direction and the diffraction angle are determined by a hologram written on the liquid crystal display 11. That is, by rewriting the hologram on the liquid crystal display 11 with a different hologram in real time, the optical path is switched in real time, and an optical switch is configured.

Therefore, the output optical paths can be selected by the number of hologram types to be rewritten, and a one-input / multi-output switch (1 × N switch) can be realized in principle. Also,
By combining N such 1 × N switches, a multi-input multi-output (N × N switch) is configured.

FIGS. 4 to 7 show the operation concept of the 1 × 4 switch. For example, when the optical path is switched to the output port 14a, that is, when switching is performed, FIG.
Nothing is written on the liquid crystal display 11 as shown by. On the other hand, when switching to the other output ports 14b, 14c, 14d, three types of binary phase holograms are used as shown in FIGS. 5, 6, and 7.
11 formed on.

[0011]

In such a conventional optical switch, one of N output ports can be selected and output for one input.
It cannot switch to any output port beyond the point.

An object of the present invention is to provide an arbitrary input for one input.
It is an object of the present invention to provide a hologram type optical switch capable of switching to one or an arbitrary plurality of output ports.

[0013]

SUMMARY OF THE INVENTION A hologram type optical switch according to the present invention is a hologram type optical switch for outputting an input optical signal by switching a plurality of output ports. A memory for storing a pattern to be written to the liquid crystal display, and a Fourier transform lens arranged with a focal length between the liquid crystal display and the output port, wherein the hologram has a periodic structure, and during one cycle, The diffraction order from -I / 2 to I / 2 is assigned to each output port for the number of pixels 2I, and the distribution of the phase of each pixel is an odd function. The input optical signal can be switched to an arbitrary output port by arbitrarily switching and writing the corresponding hologram to the liquid crystal display. It is.

[0014]

According to the present invention, the hologram has a periodic structure,
For the number of pixels 2I in one cycle, the diffraction orders from -I / 2th to I / 2th are assigned to the output ports, respectively, and
The distribution of the phase of each pixel is an odd function, a plurality of preset phase distributions are arbitrarily switched, the corresponding hologram is written to the liquid crystal display, and the input optical signal is switched to an arbitrary output port. , And outputs an optical signal to any one or more of the output ports.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the hologram type optical switch according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of an optical switch. In FIG. 1, reference numeral 21 denotes a liquid crystal display. The liquid crystal display 21 has a function as a phase modulator using holograms, and is arranged in a matrix. A predetermined hologram is written by controlling the voltage applied to these pixels.

Since the liquid crystal display 21 is used as a phase modulator as described above, the polarizing plate is removed and only the liquid crystal plate is used. In addition, this liquid crystal display 21 includes:
The pattern stored in the memory 23 is written via the driver 22 for driving. That is, a plurality of patterns, that is, voltage information for obtaining a phase distribution, are stored in the memory 23. An arbitrary pattern is read by the driver 22, and a hologram corresponding to this pattern is written to the liquid crystal display 21.

On the other hand, reference numeral 24 denotes a Fourier transform lens, and the Fourier transform lens 24 is disposed between the liquid crystal display 21 and an output surface 25 having a plurality of output ports (not shown) while maintaining a focal length.

FIG. 2 is a sectional view of the hologram. This hologram has a periodic structure. Here, one period is set to "1". FIG. 2 shows the phase distribution of the hologram for one period, L represents the size of a pixel, and a represents the size of an opening. When the aperture ratio is b, b = L /
a is defined. The phase amount has different multivalued values in each pixel, and the distribution of the phase is an odd function.

Here, assuming that the number of pixels is I and the amount of phase in each pixel is φ _i (where i = 0,..., I), φ _i = −φ− _i . On the other hand, in FIG.
Since the vertical axis is in the range of ２2π radians, φ− _i =
−φ _i + 2π.

The number of output ports is determined by the number of pixels in one cycle. That is, by assigning each of the diffraction orders from the −I / 2 order to the I / 2 order to one output port, the number N of output ports becomes N = I + 1.
At this time, the number of pixels included in one cycle of the hologram is 2
I.

Next, the phase distribution of the hologram and the output surface 25
Equation 1 shows the relationship with the amplitude Am of the diffracted light at. Note that the subscript m represents the diffraction order.

[0023]

(Equation 1) Here, Equation 2 is defined.

[0024]

(Equation 2) Then, the intensity of the diffracted light can be obtained by squaring Equation 1. Therefore, it is necessary to determine in advance the phase amount φ _i for generating the intensity distribution necessary for switching using Expression 1. Note that the intensity distribution is set so that, when there are a plurality of output ports to be connected, that is, in a so-called ON state, the input light is distributed to the corresponding plurality of output ports with equal intensity. In addition, the light intensity of the output port that is not connected and is in an off state is set to zero.

In the above configuration, when an input optical signal is incident on the liquid crystal display 21, the input optical signal is diffracted by the hologram written on the liquid crystal display 21.
Since this hologram can diffract light to an arbitrary diffraction order with equal intensity, an input optical signal is output to arbitrary n arbitrary output destinations among N output ports for one input. be able to. That is, by changing the hologram to be written, 2 ^N switching patterns can be selected. The information of ^2N kinds of holograms designed in accordance with this switching pattern is stored in the image memory 23 shown in FIG.
By switching the hologram on the liquid crystal display 21, the switching to an arbitrary output port is performed.

Hereinafter, a specific example will be described. First, Table 1 to Table 6 show design values of the phase distribution necessary for configuring the 1 × 9 switch as an optical switch by the system shown in FIG. 1 with the number N of output ports being N = 9. At this time, the opening ratio b is set to b = 0.711. Note that this value is based on the liquid crystal display used for the function test.
The aperture ratio is 21. The -4th-order (-I / 2-order) diffracted light is set as the output port 1, and the output ports are sequentially allocated, and the quaternary (I / 2-order) diffracted light is set as the ninth output port. In this design, the phase of the hologram for performing the desired switching was obtained by using the least square method.

Here, Table 1 shows a phase distribution for turning off all the output ports, Table 2 shows a phase distribution when only the ninth output port is switched on,
Table 3 shows the phase distribution when the second and sixth output ports are switched on. Table 6 below shows the relationship between the output ports switched on and the phase distribution. Then, a corresponding voltage is applied to the liquid crystal display 21 by the driver 22 to form the phase distribution of the design value.

[0028]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[0029]

According to the hologram type optical switch of the present invention, the hologram has a periodic structure and has a diffraction order from -I / 2 to I / 2 with respect to the number of pixels 2I in one cycle. Assigned to each output port, and the distribution of the phase of each pixel is an odd function, arbitrarily switches a plurality of preset phase distributions, writes the corresponding hologram to the liquid crystal display, and inputs the input optical signal to any output port. By switching, for one input, an optical signal is output to any one or more output ports among the output ports. Therefore, for one input, for example, an arbitrary n out of N output ports is output.
Optical signals can be output to any number of output ports,
2 ^N switching patterns can be selected, and the signal strength at each output port can be made equal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a hologram type optical switch according to the present invention.

FIG. 2 is a cross-sectional view of the hologram.

FIG. 3 is a block diagram showing a conventional optical switch.

FIG. 4 is a diagram showing a switching state of the optical switch.

FIG. 5 is a diagram showing another switching state of the optical switch.

FIG. 6 is a diagram showing another switching state of the optical switch.

FIG. 7 is a diagram showing still another switching state of the optical switch.

[Explanation of symbols]

 21 LCD display 22 Driver 23 Memory 24 Fourier transform lens 25 Output surface

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-134418 (JP, A) JP-A-5-273606 (JP, A) JP-A-1-502304 (JP, A) Journal of Optical Society of America A, Vol. 9, No. 3 (March 1992) Rick L. MORR ISON, "Symmetries that simply the design of the sample phase gratings," pp. 464-471 IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 2, No. 6 (June 1990) J. CLOONAN, et. al. “An All-Optical Implementation of a 3-D Crossover Switching network” pp. 438-440 (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/31 G02F 1/13 505 JICST File (JOIS)

Claims (1)

(57) [Claims] 1. A hologram type optical switch for outputting an input optical signal by switching a plurality of output ports, comprising: a liquid crystal display on which a hologram is written; a memory for storing a pattern written on the liquid crystal display; A Fourier transform lens disposed between the display and the output port while maintaining a focal length, wherein the hologram has a periodic structure, and the number of pixels 2I in one cycle is -I / 2 second order. The diffraction order up to the I / 2 order is assigned to each output port, and the phase distribution of each pixel is an odd function, and a plurality of preset phase distributions are arbitrarily switched to write a corresponding hologram to the liquid crystal display. The hologram type optical switch, wherein the input optical signal is switched to an arbitrary output port.