JPS6144293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for switching the optical path of an optical signal modulated by information by an optical pulse of another wavelength.

Conventionally, there have been two types of optical switches for changing the optical path of optical signals in optical communications, etc.: mechanical switches and switches that use electro-optic or acousto-optic effects.

In switches using the electro-optic effect or the acousto-optic effect, an electric field is used to switch the optical path of the optical signal (LiNbO ₃ is also used to generate sound waves in the acousto-optic effect).
A common method is to generate sound waves by applying an electric field using a crystal such as . In addition, even if a mechanical optical switch is used, unless it is done manually, the optical switch is operated by an electrical signal in the method of moving an optical fiber or rotating a reflecting mirror. However, one of the purposes for using optical signals, particularly for fiber communications in which optical signals are transmitted within optical fibers, is to avoid being affected by electromagnetic induction. Even if an optical switch is installed in a place with little electromagnetic induction, if the electrical signal that operates the optical switch is transmitted through a place with a lot of electromagnetic induction, the probability that the optical switch will malfunction increases.

Optical signals also need to be used to operate optical switches, but there have been no concrete proposals to date.

An object of the present invention is to provide a device that controls the operation of an optical switch using light of a wavelength different from that of the optical signal carrying information, and that not only the information signal but also the control signal is not affected by electromagnetic induction. There is a particular thing.

That is, the present invention provides an optical modulator in which an electro-optic crystal is provided with a plurality of periodic electrodes that increase or decrease, a means for changing the optical path depending on the polarization state of the light, and a means for spatially separating information light and control light. and a means for photoelectrically converting the control light, and a bistable circuit operated by the electrical output from the means, and the information-modulated light and the control light are incident from substantially the same direction. The bistable circuit is operated depending on the presence or absence of control light or a light pulse train, and its output is applied to the optical modulator to switch the polarization state of the incident light and switch the optical path of the information light. .

Conventionally, optical modulators employ the principle of applying a phase difference to perpendicularly polarized light using an electro-optic effect and emitting the light in a polarization state different from that of the incident light. However, such optical modulators utilize the phase difference of light, and the modulation sensitivity differs depending on the wavelength. In other words, the voltage values required to make the polarizations orthogonal are different. The optical modulator used in the present invention is
This is an optical modulator that eliminates such wavelength dependence (Patent Application No. 52-8534, Electro-Optical Optical Modulator).

In other words, in this optical modulator, a comb-shaped electrode is provided on an electro-optic crystal such as lithium tantalate (LiTaO ₃ ) along the direction of light propagation, and when no voltage is applied to this comb-shaped electrode, the polarization of the incident light is preserved. It has the property of emitting light in a state of polarization perpendicular to the polarization of the incident light when a certain voltage is applied. The electrode period of this comb-shaped electrode is 2π/Λ=2
If it is selected to satisfy π|ne−no|/λ (ne and no are the refractive indexes for orthogonal polarized light, and λ is the optical wavelength), the polarized light for ne will be 100% converted into the polarized light for no. By selecting the electrode period Λ to increase or decrease, the above equation can be satisfied even for different wavelengths. Light of different wavelengths
By changing the component ratio of semiconductor lasers such as Al _x G _a-1-x A _s , GaA _s1-x P _x , I _o1-x G _ax A _s , any wavelength from 0.6 to 3 μm (spectral width of several 10 Å) can be achieved. Therefore, if multiple wavelengths are required, it is sufficient to provide semiconductor lasers with different component ratios for the required number of wavelengths.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention,
Reference numeral 1 denotes the aforementioned optical modulator, which is provided with different electrode periods so as to have the same modulation sensitivity for polarized light of a plurality of wavelengths. A comb-shaped structure as shown in the figure is suitable for the electrode period. In this optical modulator, by applying a voltage to a comb-shaped electrode, the polarization of incident light is orthogonalized and the polarized light is emitted. Numeral 2 is a calcite-like crystal whose direction of propagation of light varies depending on the polarization state of the light, and is provided behind the optical modulator 1 with its optical axis aligned. In this embodiment, light polarized parallel to the plane of the paper travels straight through the crystal, and light polarized perpendicular to the plane of the paper is refracted within the crystal and exits. 3 is the light λ with a wavelength that controls the optical switch of the present invention. ₁ is the reflected light λ that is modulated with information.
₀ is a transmitting filter and is provided behind the crystal 2 at an angle with respect to the optical axis. The photoelectric conversion element 4 is installed at a position where it can receive the control light λ ₁ reflected by the filter 3, converts the received control light λ ₁ into an electrical signal, operates the flip-flop 5 with this signal, and polarizes the incident light. This is to apply to the optical modulator 1 the voltage necessary to make the light beams orthogonally emit the light. The flip-flop 5 maintains two states of applying or removing voltage depending on the trigger input. In this embodiment, the filter 3 is the crystal 2.
Although it is installed on the output side of the optical modulator 1, the same effect can be obtained even if it is installed in a place other than this, for example, between the optical modulator 1 and the crystal 2, or on the input side of the optical modulator 1.
The same can be said of the second embodiment.

Next, the operation of this embodiment will be explained.

Information light λ obtained by directly modulating a semiconductor laser
₀ 10 is incident in a polarized state parallel to the plane of the paper, and assuming that no voltage is applied to the optical modulator 1 from the flip-flop 5, it travels straight through the crystal 2, passes through the filter 3, and becomes the output light 11. Next, the control light λ ₁
20, the flip-flop 5 operates via the photoelectric conversion element 4 reflected by the filter 3, and a voltage is applied to the optical modulator. Then, the polarization state of the information light 10 emitted from the optical modulator 1 becomes perpendicular to the plane of the paper, and the information light 10 is refracted by the crystal 2 and becomes an emitted light 12. At this time, the polarization state of the control light λ ₁ 20 and the position of the reflected light on the filter 3 change, but if the size of the photoelectric conversion element 4 is made sufficiently large, this effect will not have any adverse effect on the operation of the optical switch. do not have. Since the flip-flop 5 is used, the control light _λ1 can be applied in the form of a pulse.

It can be easily understood from the operating principle of the flip-flop 5 that when the output light is initially in the state 12, the state of the output light becomes 11 when the control light pulse 20 is input. That is, the optical switch of the present invention returns to its original state with two control light pulses 20.

When a large number of optical switches of the present invention are installed and operated, first, in order to operate all the optical switches through which the information light passes with the same control light λ ₁ , the characteristics of the filter 3 must be adjusted so that a part of the control light 20 is reflected. This can be achieved by transmitting the other portions and by making the information light λ ₁ and the control light λ ₁ incident in the same polarization state.

In addition, in order to operate all the optical switches through which the information light passes independently, each of the n multi-stage optical switches must have a different control wavelength λ ₀ ......, λ _o
If the filter of each optical switch reflects only the assigned wavelength, the operation of any number of optical switches at any location can be controlled by selecting the control wavelength. ,
There is an advantage that all the light having wavelengths unique to each optical switch can be transmitted through the same optical fiber. In this case as well, it is necessary that the light be of the same polarization as the information light and that it be incident from substantially the same direction. Also, the optical modulator has λ ₁ ...
...It is necessary to select the electrode period so that it has the same modulation sensitivity for polarized light of wavelengths up to λ _o .

Another embodiment in which n multi-stage optical switches are operated independently is shown in FIG. 1, 2, 3, 4, and 5 are the optical modulator, crystal, filter, photoelectric conversion element, and flip-flop described in the embodiment of FIG. 6
is a register with fixed contents that stores the address of the corresponding optical switch as a binary code. 7 is a register for accumulating the optical pulse train signal of control light λ ₁ ; 8 is a register that compares the contents of fixed register 6 and register 7; if they match, operates flip-flop 5 and applies voltage to the optical modulator; This is a comparison circuit that performs a removing operation. In this embodiment, the control light 20 and the information light 10 are the same polarized light and enter from the same direction, and a portion of the control light 20 is made to enter the photoelectric conversion element 4 through the filter 3 . The control light 20 is modulated as an optical pulse train with a signal corresponding to the address of the optical switch to be operated.
Since the contents are stored in the register 7, only the optical switch that matches the contents of the fixed register 6 can operate and change the optical path of the information light 10. Since the control light 20 also transmits the same optical path as the information light 10, the optical path of the information light 10 can be effectively selected.

As explained above, in this embodiment, even if the control light for controlling n optical switches has only one wavelength, any optical switch can be controlled by the pulse train of the control light.

In the above explanation, the information light and the control light are input at the same time, but the information light is input first, and the control light may be input to switch this optical path, or the control light may be input first. After light is input to operate each optical switch, information light may be input to perform information transmission. Furthermore, using the light emitted from an optical fiber as the incident light and making the light emitted from an optical switch enter the optical fiber can be easily achieved by providing a matching lens between the optical fiber and the optical switch. can.

As described above, according to the present invention, the operation of an optical switch that changes the transmission path of an optical signal can be performed using optical pulses, so that it is completely free from the effects of electromagnetic induction.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing an embodiment of the present invention. In the figure, 1 is an optical modulator, 2 is a separating means, and 3 is a light modulator.
1 is a filter, 4 is a photoelectric conversion element, 5 is a flip-flop, 6 and 7 are registers, 8 is a comparison circuit, and 10, 11, 12, and 20 are optical signals, respectively.

Claims (1)

[Claims] 1. An electro-optic light modulator provided with different periodic electrodes, a means for changing the optical path depending on the polarization of the light, and a means for spatially separating the information light and the control light are arranged in series, and the control light is converted into a photoelectronic light modulator. 1. An optical switch comprising a photoelectric conversion means and a flip-flop that operates depending on the presence or absence of electrical output from the photoelectric conversion means, and is operated by an optical trigger.