JPH0230492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for converting parallel bit electrical signals into serial optical signals, mainly in digital signal optical transmission.

In digital signal transmission, signals processed by a computer or transmitted signals such as A/D conversion output are basically multiple bit signals output in parallel, and these are It is necessary to convert it into a serial signal (P-S conversion) and transmit it, and for this purpose, P-S conversion is essential. This parallel signal differs depending on the type of computer, but 4 to 32 bits are usually used. The same applies to PCM signal transmission and the like. In recent years, processing speeds have increased dramatically, and transmission speeds have also increased significantly. For example, if a parallel 8-bit signal is processed at 30Mbps, the serial transmission speed is
240 Mbps, which requires extremely high speeds in terms of P-S conversion processing speed and driving speed of light emitting elements during optical transmission.

The purpose of the present invention is to:
The present invention provides a high-speed PS conversion device that electrically uses only parallel signals and performs PS conversion using light.

An optical PS converter according to an embodiment of the present invention will be described below with reference to FIG. 1, which is a schematic diagram of the basic configuration. An output 5 from a light emitting element 1 that regularly emits pulse light at a certain period is led to an optical random access coupler 2. Parallel electrical signals a ₁ to a _o to be transmitted are output from the transmitted signal generating section 3 . The optical random access coupler 2 has optical output terminals b ₁ to b _o corresponding to the electrical signals a ₁ to a _o , and the presence or absence of optical output from each terminal b ₁ to b _o depends on the corresponding electrical input. Signal a ₁ ~ _{a o}
determined by the level of Here, the operation of the optical random access coupler 2 will be described based on the configuration diagram shown in FIG. Figure 2 b ₀ is the optical input, and the first
is input into the waveguide 11 of This optical random access coupler 2 sequentially forms a first waveguide 11 and a second waveguide 12 on a substrate 10 made of GaAs or InP, and these two waveguides form a coupling waveguide. , the degree of coupling is controlled by voltage, and the degree of coupling of light from the first waveguide 11 to the second waveguide 12 is changed to extract light.

Reference numerals 13 to 16 in FIG. 2 are electrodes, and a voltage is applied between these electrodes and the substrate 10 to change the refractive index and the degree of coupling. In this example, it is assumed that light can be extracted from the first waveguide 11 to the second waveguide 12 when voltage is applied. The light guided to the second waveguide 12 is extracted to the outside by grading couplers 17 to 20 arranged beside each electrode.

In FIG. 2, the number of electrodes is four, and the number of light emitting ends is also four, but by increasing the number of electrodes and the number of gratings, it is possible to accommodate a case with more than this number. In FIG. 2, a ₁ to _{a 4} are parallel electrical signal application terminals, and b ₁ to b ₄ indicate the light extracted by each electrical signal level.

Now, returning to FIG. 1, the optical outputs b ₁ to b _o from the optical random access coupler 2 are as follows:
It is guided to an optical fiber or waveguide 6 corresponding to each output, and coupled to a transmission optical fiber or waveguide 7 by a coupler 4.

Next, the operation of converting an electrical parallel signal into an optical serial pulse train using this configuration will be explained. Figure 3 shows a time chart. FIG. 3A shows a light pulse output from the light emitting element 1. In the diagram
b It shall emit light only during the period indicated as ₀ . Figure 3 (b) is the output signal of the optical coupler 4, b ₁ to _{b 4} in the figure.
The optical pulse train corresponds to the optical outputs b ₁ to _{b 4} of the optical random access coupler 2 shown in FIG. When the output optical pulse _b0 of the light emitting element 1 enters the optical random access coupler 2, for example, when all the parallel electrical signals are at high level, the coupling waveguide formed under the first electrode 13 first passes through the coupling waveguide formed under the first electrode 13. A part of the light is taken out from the waveguide 11 to the second waveguide 12, and the light is taken out to the outside by the grating 17 and becomes _b1 . As the light pulse b ₀ passes under each electrode one after another, light is outputted one after another in time, such as first b ₁ , then b ₂ , and so on. Therefore, if the light is guided into one fiber or waveguide, a serial pulse train of light is generated. Moreover, the presence or absence of this optical pulse is determined by the level of the parallel electric signal applied to each electrode. In other words, a parallel electrical signal is converted into a serial pulse train of light.

Further, the strength of coupling of light from the first waveguide 11 to the second waveguide 12 varies depending on the coupling length, the refractive index difference, the distance between the waveguides, and the like. For P-S conversion, it is ideal that the optical output powers of b ₁ to _{b o} be the same. Therefore, instead of making the degree of bonding of each bond constant, it is better to make the degree of bonding larger in the later parts. The simplest method for this purpose is to set the voltages applied to terminals a ₁ to _{a 4} so that the voltages applied to terminals a 1 to a 4 become higher little by little.

In the optical random access coupler 2 shown in Fig. 2,
Since the delay time of light is determined by the spacing between the electrodes 13 to 16, the period of the light pulse _b0 becomes very small. Changing the size of the element in order to appropriately select the period of the optical pulse b ₀ reduces the degree of freedom. Therefore, as shown in FIG. 4, there is a method in which the optical outputs b ₁ to _{b 4} of the optical random access coupler 2 are coupled to the optical coupler 4 via a delay element having a certain delay time. 21-24 are delay elements, which may be, for example, a length of fiber or waveguide. Determine the delay time connected to b ₁ as τ ₁ , and the delay time connected to b ₂ as τ ₂ below. The time relationship between the optical pulse input b ₀ and the optical coupler output c at this time is shown in FIG. C in the figure is the optical input pulse _b0 , and D in the figure is the optical coupler output c. Based on the time when the light pulse b ₀ was incident,
After a delay of τ ₁ , b' ₁ enters the optical coupler 4, then after a delay of τ ₂ , b' _{2 .} . . , and so on. At this time, since the light emitting element 1 only needs to oscillate in pulses, it also has the advantage of being able to extract more peak power than when outputting continuously.

As described above, the present invention simultaneously applies electrical parallel signals from the transmitted signal generator to the optical random access coupler, and connects the light beam from the common light emitting element to each signal constituting the parallel signal. and sequential modulation to obtain a time-series optical pulse signal. That is, since the present invention makes it possible to directly convert an electrical parallel signal into an optical serial pulse train, it is possible to perform parallel-to-serial conversion that is compact and capable of extremely high-speed operation.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a device for converting parallel electrical signals into serial optical signals in an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the configuration of an optical random access coupler, which is a component of FIG. 1. , FIG. 3 is a timing chart for explaining the operation of the configuration shown in FIG.
This figure is a basic configuration diagram of an optical signal serial-to-parallel converter according to a different embodiment of the present invention, and FIG. 5 is a timing chart for explaining the operation of the configuration shown in FIG. 4. DESCRIPTION OF SYMBOLS 1... Light emitting element, 2... Optical random access coupler, 3... Transmitted signal generating section, 4... Coupler, 6, 7... Waveguide, 21-24... Delay element.

Claims (1)

[Scope of Claims] 1. A light emitting element that emits pulsed light at a predetermined period, and an optical random access coupler that sequentially branches the pulsed light from the light emitting element for each bit according to the state of each bit of a parallel electric signal. and a multiplexing coupler which is coupled to the optical random access coupler via a plurality of waveguides and inputs a plurality of output lights for each bit of the optical random access coupler into one fiber. A device that converts parallel electrical signals consisting of 2 to serial optical signals. 2. The plurality of waveguides provided between the optical random access coupler and the multiplexing coupler are waveguides each having a different delay time. A device that converts into optical signals.