Optical analog/digital conversion system

The present invention relates to an optical analog / digital converter, and more particularly to an optical analog / digital converter that converts an optical analog amount of an optical signal into a digital value.

Conventionally, in order to convert the analog amount of an optical signal into a digital value of an electric signal, first, the optical analog amount is converted into an electric analog amount through an optical detector such as a photodiode, and then the electric analog amount is electrically converted. It was converted to the final digital value using an analog / digital converter (hereinafter referred to as an electrical analog / digital converter).

However, in the method of once converting the optical analog amount to the electric analog amount, there is a limit to the speedup due to the limitation of the conversion speed of the electric analog / digital converter, and a linear signal is input to the electric analog / digital converter. Therefore, it was also necessary to correct the non-linearity of the light detector. Furthermore, the power consumption of such an electric analog / digital converter could not be ignored.

Further, there is also known a technique of converting an electric analog amount to be converted into a digital value into a digital signal by utilizing the characteristics of light (optical phase modulation) (for example, Patent Document 1 and Patent Document 2). However, such a technique does not directly convert an optical analog signal into an electric digital signal, and is limited to use only in a single mode.

Further, there is also known a technique for deriving an electric digital signal by once converting an input electric analog signal into an optical signal and comparing the light intensity with an optical signal in a plurality of stages (for example, Patent Document 3). ). However, focusing on the inputs and outputs of such technology, it merely shows electrical analog-to-digital conversion, and requires an optical reference signal and two photodetectors for each signal. The configuration becomes very complicated.

<patcit num="1"><text>Japanese Patent Application Laid-Open No. 61-282826</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 62-011835</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 63-131128</text></patcit>

<p> The present invention has been made in view of the above-mentioned problems of the conventional method for detecting a digital value from an optical analog amount, and an object of the present invention is to input without referring to an optical signal as a reference. It is to provide a new and improved optical analog / digital converter capable of directly deriving the optical analog amount of the optical signal as a digital value.</p>

<p> In order to solve the above problems, according to a certain viewpoint of the present invention, an input optical signal is divided into a divided waveguide that divides the input optical signals at predetermined division ratios that are different from each other; the divided optical signals are detected. An optical analog-to-digital converter is provided, which comprises a plurality of photodetectors for converting into an electric signal; and is characterized by directly deriving a digital value of the input optical signal. The digital value that can be derived is two or more steps, preferably three or more steps.</p><p> The present invention generates a divided optical signal having a predetermined ratio by dividing an optical signal into predetermined division ratios different from each other, and determines whether or not each divided optical signal reaches a threshold value of the input optical signal. Digital values can be detected.</p><p> With such a configuration, it is possible to directly derive the optical analog amount of the input optical signal as a digital value without going through a process such as once deriving the electric analog amount. Therefore, since there is no delay in the electric analog / digital converter whose conversion speed is limited, high-speed conversion similar to that of a 1-bit optical analog / digital converter is possible, and cost reduction is also possible.</p><p> In addition, the photodetector according to the present invention is not used to detect the amount of electrical analog corresponding to the conventional amount of optical analog, but only detects discrete values such as on / off. There is no need to consider non-linearity.</p><p> The divided waveguide may be formed by dividing the waveguide into a predetermined number of unit waveguides having the same amount of optical analog passing through, and synthesizing the unit waveguides so as to have the above division ratio. In the unit waveguide, for example, the amount of optical analog passing through can be made uniform by making the material and cross-sectional area of the waveguide equal.</p><p> With such a configuration, it is not easily affected by dimensional errors in the process of forming the waveguide, and the division ratio of the optical signal can be obtained with high accuracy. It is also possible to adjust the amount of light of the divided optical signal by providing an extra unit waveguide, cutting an arbitrary unit waveguide and blocking the optical signal passing through the unit waveguide.</p><p> When the digital value to be derived has n steps, the predetermined number may be equal to or greater than the numerator value when the result of Equation 1 is reduced. The above n steps represent the number of numerical values that can be distinguished as digital values. For example, the digital value represented by the four values of "0,1,2,3" has four steps. At this time, the formula 1 is calculated to be 23/15, and this numerator 23 is the number of unit waveguides.<maths num="1"><img file="JP2007024924A_D0001.tif" /></maths>... (Formula 1)</p><p> With such a configuration, the minimum number of unit waveguides in carrying out the present invention can be calculated, and cost reduction can be maintained.</p><p> The divided waveguide may be formed by providing a predetermined stage of a binary divided waveguide that equally divides the amount of optical analog, and synthesizing the outputs from the binary divided waveguide so as to have the above division ratio. The binary split waveguide is a waveguide that simply divides the input of the optical signal of 1 into the outputs of 2, and the amount of light is evenly divided between the two outputs. By continuously connecting such binary split waveguides, a uniform amount of light is output 2ⁿLight output end can be obtained. In addition, since it is not easily affected by dimensional errors in the process of creating the waveguide, the division accuracy can be further improved. Further, since the binary division waveguide is divided while maintaining the phase of the incident light, it can be used in a single mode.</p><p> A surplus waveguide formed by synthesizing the surplus of the binary divided waveguide; and a surplus light detection unit for detecting an optical signal output from the surplus waveguide; may be further provided. With such a configuration, the surplus waveguide can be used for calibration of the analog / digital converter, error detection, test signal application, backup, and the like.</p><p> When the digital value to be derived is n steps, the number of the above predetermined steps is log.₂(Value of numerator when the result of Equation 1 is reduced) It may be more than or equal to. With such a configuration, the minimum number of stages of the unit waveguide can be calculated when the present invention is implemented, and the cost reduction can be maintained.<maths num="2"><img file="JP2007024924A_D0002.tif" /></maths>... (Formula 1)</p><p> The plurality of photodetectors may have substantially the same photodetection characteristics. For the predetermined number and the predetermined number of stages, a threshold value is set for the analog amount corresponding to the intermediate value of each digital value in order to accurately derive the state of the optical analog amount. Therefore, although a certain degree of detection error of the photodetector can be tolerated, the amount of optical analog can be detected more accurately by making the detection characteristics of the photodetector equal.</p><p> A plurality of comparators for comparing the electric signals from the plurality of photodetectors with the reference signal; and a decoder for converting the output signal from the comparator into a binary signal; may be further provided. With such a configuration, it is possible to detect the amount of optical analog more accurately by adjusting the reference signal as well as simply reading the detection signal from the photodetector.</p><p> Further, an optical signal receiving device provided with the above-mentioned optical analog / digital conversion device and receiving an optical signal from an optical transmission line is also provided.</p>

<p> As described above, according to the present invention, the digital value of the input optical signal is directly derived without referring to the optical signal as a reference or using an electric analog / digital converter having a slow conversion speed. can do. This makes it possible to digitally convert an optical signal at high speed.</p>

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

First, before explaining the embodiment of the present invention, a brief description of the analog / digital conversion device for optical signals will be given.

FIG. 1 is a schematic diagram for explaining an analog / digital conversion of an optical signal that has been conventionally used. Here, the optical signal from the signal source LD is input to the photodetector PD via the optical transmission line 10 such as an optical fiber, and is once converted into an electric analog signal by the photodetector PD. Then, the digital value of the optical signal is derived by the electric analog / digital converter 20.

The analog-to-digital converter 20 inputs the electrical analog signal converted by the photodetector PD and each threshold value obtained by dividing the reference voltage Vref by the resistor unit 30 into the comparator 40. Then, according to the comparison result of the comparator 40, that is, the output of the comparator 40 for which the input electric analog signal is determined to be larger than each threshold value is read, and the binary / binary converter 50 reads the 2-bit digital signal. Is replaced by. Here, four states of the comparator optical signal can be detected.

In the detection of the digital value of such a conventional optical signal, the optical analog amount is once converted into an electric analog amount through an optical detector such as a photodiode, and the electric analog amount is finally converted into an electric analog / digital converter. It was converted to a typical digital value.

However, in the above method through the derivation process of the amount of electric analog, there is a limit to the speed increase due to the limitation of the conversion speed of the electric analog / digital converter, and a linear signal is input to the electric analog / digital converter. Therefore, it was also necessary to correct the non-linearity of the light detector. Furthermore, the power consumption of such an electric analog / digital converter could not be ignored.

There is also known a technique for converting an electrical analog signal to be converted into a digital value into a digital signal by utilizing the characteristics of light (optical phase modulation). However, in such a technique, since optical phase modulation is used, it is necessary to use a fixed output single laser, and it is not possible to use a multimode light source or a light source simply using LEDs. Therefore, it was not possible to directly convert the power (amplitude) of a simple optical signal or the change of the PAM (Pulse Amplitude Modulation) signal into an electric digital signal.

Further, a technique is also known in which an input electric analog signal is once converted into an optical signal, the intensity of the light is compared with a fixed multi-stage optical signal, and an electric digital signal is derived. However, such technology is merely an electrical analog / digital signal in the context of input and output. In addition, the configuration is to simply compare the signal with the optical reference weighted by the filter and the input signal with two light receiving elements, and the configuration of the flash type electrical analog / digital converter is simply replaced with light. Absent.

(First Embodiment: Analog / Digital Converter) In the embodiment according to the present invention, an optical analog / digital converter is provided, and the basic concept of the conversion theory will be described here.

FIG. 2 is a block diagram for explaining the operating principle of a normal electric analog / digital converter. Here, the flash type 2-bit analog / digital converter 100 is listed.

The electric analog / digital converter 100 includes a resistance unit 110, a comparator 120, and a decimal / binary converter 130.

The resistance unit 110 divides the reference voltage Vref into a predetermined voltage. Here, the resistors R / 2, R, R, R / 2 generate a voltage that is 1/6, 3/6, 5/6 times the reference voltage Vref.

The comparator 120 compares the analog voltage input Vin to be analog / digital converted with each threshold voltage divided by the resistance unit 110, and detects whether the analog voltage input Vin is equal to or higher than the threshold voltage. .. For example, when the analog voltage input Vin is 3/6 or more and less than 5/6 of the reference voltage Vref, "1" and "2" of the comparator 120 output an on signal, and "3" is not output. In this case, the analog signal has a digital value of "2".

The decimal / binary converter 130 receives the output from the comparator 120, determines which comparator 120 outputs the on signal, and outputs a 2-bit digital signal. For example, as described above, when only "1" and "2" of the comparator 120 output an on signal and "3" is not output, it is judged as "2" in decimal. At this time, the output of the decimal / binary converter 130 is the binary number "10". With the above 2-bit digital signal, four states of the input analog signal can be detected.

FIG. 3 is an explanatory diagram for explaining the threshold value due to the resistance division of the resistance portion 110. According to the analog-to-digital converter 100, the digital value to be detected is 2 bits, that is, four states, and is represented by "0,1,2,3" in FIG.

In order to distinguish such "0,1,2,3" states, the threshold value should be set to "0.5,1.5,2.5" in order to improve the detection accuracy. Therefore, the threshold value is 1/6, 3/6, 5/6 times the maximum value of "3" of the analog voltage input Vin. This division ratio is obtained by dividing the reference voltage Vref by resistors R / 2, R, R, R / 2 connected in series.

By setting the above threshold, if the analog voltage input Vin is less than 0.5, that is, if the digital value to be judged is less than the LSB (here, "1") x (1/2), it is "0", LSB x (1). / 2) or more and less than LSB × (3/2) is "1", LSB × (3/2) or more and less than LSB × (5/2) is "2", LSB × (5/2) ) If it is above, it can be judged as "3".

In this analog-to-digital converter 100, the range of the voltage value of the reference voltage Vref input to the comparator 120 is wide, and the linearity and reaction speed are improved at high and low voltage values in the detection range of the comparator 120. There was a problem.

FIG. 4 is a block diagram for explaining the operating principle when the configuration of the analog / digital converter shown in FIG. 2 is changed. Here, the flash type 2-bit analog / digital converter 200 is listed.

The analog / digital converter 100 in FIG. 2 detected the digital value by comparing the analog voltage input Vin with the thresholds of a plurality of stages, but the analog / digital converter 200 had a constant threshold ( The digital value is detected by comparing the reference voltage Vref) with the analog voltage input Vin changed to multiple levels.

The analog / digital converter 200 includes a resistance unit 210, a comparator 220, and a decimal / binary converter 230.

The resistance section 210 converts the analog voltage input Vin into a plurality of voltage levels. Here, the resistance division by 4R and R and the resistance division by 2R and R generate a voltage that is 1,1/3, 1/5 times that of the analog voltage input Vin.

The comparator 220 compares a plurality of signals whose levels of the analog voltage input Vin are changed with a constant reference voltage Vref, and determines whether each changed analog voltage input Vin is equal to or higher than the reference voltage Vref. To detect. For example, if the value obtained by multiplying the analog voltage input Vin by 1/3 is equal to or higher than the reference voltage Vref, "1" and "2" of the comparator 220 output an on signal, and the analog voltage input Vin is multiplied by 1/5. If the value is less than the reference voltage Vref, "3" of the comparator 120 is not output. In this case, the analog signal has a digital value of "2".

The decimal / binary converter 230 receives the output from the comparator 220, determines which comparator 220 is outputting the on signal, and outputs a 2-bit digital signal. For example, if the input decimal number indicates the digital value "2" as described above, the binary number "10" is output. With the above 2-bit digital signal, four states of the input analog signal can be detected.

FIG. 5 is an explanatory diagram for explaining the level of the analog voltage input Vin due to the resistance division of the resistance portion 210. According to the analog / digital converter 200, the analog value to be detected is 2 bits, that is, four states, and is represented by "0,1,2,3" in FIG.

In order to distinguish such "0,1,2,3" states, the level of the analog voltage input Vin itself is multiplied by 1,1 / 3,1 / 5, and the analog voltage input Vin LSB × (1 /). Compare with the reference voltage Vref corresponding to 2). This is compared with the analog voltage input Vin by multiplying the value of 1/6 times the reference voltage Vref, which is LSB × (1/2) of the analog voltage input Vin in Fig. 2, by 1,3,5. Similar results can be obtained.

For example, when the analog voltage input Vin corresponds to the digital value 1, it indicates a value equal to or higher than the reference voltage Vref. Therefore, "1" of the comparator 220 outputs an on signal, but 1/3 of the analog voltage input Vin, Since the 1/5 times signal is less than the reference voltage Vref, the other comparator 220 does not output the on signal. When the analog voltage input Vin corresponds to the digital value 2, the signal of 1,1 / 3 times indicates the value equal to or higher than the reference voltage Vref, so "1" and "2" of the comparator 220 output the on signal. However, since the signal 1/5 times the analog voltage input Vin is less than the reference voltage Vref, the other comparator 220 "3" does not output the on signal. Similarly, if the analog voltage input Vin corresponds to a digital value of 3, the comparator 220 outputs all on signals, and if the analog voltage input Vin corresponds to a digital value of 0, the comparator 220 does not output any on signal. ..

In the analog / digital converter 200 of FIG. 4, since all of the comparators 220 compare a constant reference voltage Vref and an analog voltage input Vin, the center value of the detection range of the comparator 220, that is, a straight line. It can be detected in a good place. Moreover, since the reaction speed of the comparator 220 is high near the center value of the detection range, the reaction speed is higher than that of the analog / digital converter 100. In this way, the analog / digital conversion speed can be improved.

The optical analog / digital converter of the embodiment according to the present invention is formed by utilizing the latter principle of the analog / digital converter 200 of FIG. That is, the input optical signal itself is decomposed into a plurality of levels, and the digital value is derived by comparing the level with a constant reference signal.

(Second Embodiment: Optical Analog / Digital Converter 300) FIG. 6 is a configuration diagram showing a schematic configuration of the optical analog / digital converter according to the second embodiment. The optical analog-to-digital converter 300 includes a split waveguide 310 and a plurality of photodetector PDs.

In the divided waveguide 310, the optical signal from the signal source LD or the optical signal input via the optical transmission line such as an optical fiber is divided into different predetermined division ratios, for example, 1 in the example of FIG. Divide at a ratio of 1: 3: 1/5. Dividing at this ratio of 1: 1/3: 1/5 means that the cross-sectional area of the branch path of the optical signal is 15: 5: 3.

The photodetector PD detects each of the divided optical signals divided by the divided waveguide 310. The amount of electricity detected by the photodetector PD may be gradually increased according to the amount of light per unit area.

Further, in order to accurately derive the state of the optical analog amount for the predetermined number of lines and the predetermined number of stages, which will be described later as another embodiment of the divided waveguide 310, a threshold value is set for the analog amount corresponding to the intermediate value of each digital value. There is. Therefore, a certain degree of detection error of the photodetector PD can be tolerated. However, by making the photodetection characteristics of all the photodetector PDs substantially equal, it is possible to detect the amount of optical analog more accurately.

The optical analog-to-digital converter 300 can directly derive the digital value of the input optical signal according to the detection states of the plurality of photodetectors 320. The digital value that can be derived is two or more steps, preferably three or more steps.

In the present embodiment, a divided optical signal having a predetermined ratio is generated by dividing the optical signal by predetermined division ratios different from each other, and the optical signal input depending on whether or not each divided optical signal reaches a threshold value. Digital value of can be detected.

For example, in the case of FIG. 6, the input optical analog quantity is divided into 15: 5: 3 in the divided waveguide 310. Therefore, 15/23 of the input optical analog amount is output to the photodetector PD1, 5/23 is output to the photodetector PD2, and 3/23 is output to the photodetector PD3. Then, when the unit (1LSB) of the digital value to be detected is 1, the photodetectors PD1, PD2, and PD3 set the optical analog amount of (15/23) × (1/2) = 15/46 as the threshold value for receiving light. It should be done. With such a configuration, when the amount of optical analog is 0, all the photodetector PDs are turned off, when it is 1, only the photodetector PD1 is turned on, when it is 2, the photodetectors PD1 and PD2 are turned on, and when it is 3, the photodetectors PD1 and PD2 are turned on. All photodetector PDs turn on.

With such a configuration, it is possible to directly derive the optical analog amount of the input optical signal as a digital value without going through a process such as once deriving the electric analog amount. Therefore, since there is no delay in the electrical analog / digital converter whose conversion speed is limited, high-speed conversion is possible and cost reduction is also possible.

In addition, the photodetector PD does not use it to detect the amount of electrical analog corresponding to the conventional amount of optical analog, but only detects discrete values such as on / off, so the non-linearity of the photodetector There is no need to consider gender.

(Third Embodiment: Optical analog / digital converter 400) FIG. 7 is a configuration diagram showing another configuration of the optical analog / digital converter. As in the second embodiment, the optical analog-to-digital converter 400 includes a split waveguide 410 and a plurality of photodetector PDs. Since the photodetector PD has substantially the same function as the photodetector PD already described in the second embodiment, duplicate description will be omitted.

The divided waveguide 410 is formed by dividing the divided waveguide 410 into a predetermined number of unit waveguides 420 having the same amount of optical analog passing through, and synthesizing the unit waveguide 420 so as to have a predetermined division ratio. The unit waveguide 420 makes the amount of optical analog passing through uniform, for example, by making the materials and cross-sectional areas of the waveguides equal.

Also in such a divided waveguide 410, a division ratio equal to that of the divided waveguide 310 is set. Therefore, the optical signal from the signal source LD or the optical signal input via the optical transmission line such as an optical fiber is divided into predetermined division ratios different from each other, for example, 1: 1/3: in the example of FIG. Divide at a ratio of 1/5. Dividing at this ratio of 1: 1/3: 1/5 means that the cross-sectional area of the branch path of the optical signal is 15: 5: 3, that is, dividing into 23 unit waveguides 420. Is. Then, the unit waveguide 420 divided into 15 lines: 5 lines: 3 lines is combined in the divided units.

In the present embodiment, as in the second embodiment, the light amount is expressed by a predetermined ratio by dividing the optical signal by a predetermined division ratio different from each other, and it is input depending on whether or not each divided optical signal reaches the threshold value. It is possible to detect the amount of optical analog of the optical signal.

For example, in the case of FIG. 7, the input optical analog quantity is divided into 15: 5: 3 in the divided waveguide 410 via 23 unit waveguides 420. Therefore, 15/23 of the input optical analog amount is output to the photodetector PD1, 5/23 is output to the photodetector PD2, and 3/23 is output to the photodetector PD3. Then, if the detected digital unit (1LSB) is 1, the photodetectors PD1, PD2, and PD3 receive the optical analog amount of (15/23) × (1/2) = 15/46. It may be set to the threshold value of. With this configuration, when the amount of optical analog is 0, all the photodetector PDs are turned off, when it is 1, only the photodetector PD1 is turned on, when it is 2, the photodetectors PD1 and PD2 are turned on, and when it is 3, the photodetectors PD1 and PD2 are turned on. All photodetector PDs turn on.

The above-mentioned predetermined number can be calculated by using the formula 1 shown below. That is, when the digital value to be derived is n steps, it is the numerator value when the result of Equation 1 is reduced, or an integral multiple of that value.<maths num="3"><img file="JP2007024924A_D0003.tif" /></maths>... (Formula 1)

For example, if the digital value to be derived as described above is in 4 stages ("0,1,2,3"), 1+ (1/3) + (1/5) = 23/15, which is the predetermined number. Is 23 as shown in the molecule. If the number of digital values to be derived is 5 levels, 1 + (1/3) + (1/5) + (1/7) = 176/105, and the predetermined number is 176. The minimum required number of unit waveguides can be calculated by the above formula 1, and the cost can be reduced.

FIG. 8 is an explanatory diagram illustrating the relationship between the derived digital value and the number of unit waveguides. In FIG. 8, the "digital value" determines the number of detectable steps, the "level" determines all the levels that can be detected, the "divided branch number" determines the number of branches of the divided waveguide, and the "divided voltage" determines the digital value. "Voltage division-&gt; light amount conversion" is the threshold of the amount of light for outputting the maximum input voltage and digital value, and "the number of unit waveguides" is the unit lead required to maintain the division ratio. "Number of stages" indicates the number of stages of the binary split waveguide, and "A / D resolution" indicates the resolution of the digital value.

With reference to Fig. 8, it can be seen that when the digital value to be derived is three values, the number of unit waveguides is four, and when the six values are six, 563 are required.

Explaining in detail the "voltage division light amount conversion" in FIG. 8 above, for example, when the input of the maximum input voltage corresponding to 3 ("voltage division") is multiplied by 1/5 ("light amount conversion"), the light is emitted. It suffices if the detection unit detects the light. That is, for the input of the signal corresponding to 3 in the electric analog / digital converter, the reference signal (1/6 of the maximum value 3) that is 1/2 times the signal corresponding to 1 is output by the photodetector. Set to the threshold. For example, if the threshold is defined as 1/6 times the maximum input voltage, 3/5, which is 1/5 times the maximum input voltage 3, becomes 3 × (1/6) or more, and the input voltage 3 is detected. Become.

However, as described above, in an actual optical analog-to-digital converter, such 1/5 times corresponds to 3/23 times, and the maximum input voltage 3 can be detected by setting the threshold value to 15/46.

With the above configuration of the optical analog / digital converter 400, it is possible to directly derive the optical analog amount of the input optical signal without going through the electrical analog / digital converter that detects the electrical analog amount. Become. Therefore, since there is no delay in the electrical analog / digital converter whose conversion speed is limited, high-speed conversion is possible and the cost can be reduced.

Furthermore, it is not easily affected by dimensional errors in the process of creating a waveguide, and an accurate division ratio of an optical signal can be obtained with high accuracy. It is also possible to adjust the amount of light of the divided optical signal by providing an extra unit waveguide, cutting an arbitrary unit waveguide, and blocking the optical signal passing through the unit waveguide.

(Fourth Embodiment: Optical analog / digital converter 500) FIG. 9 is a configuration diagram showing another configuration of the optical analog / digital converter. As in the second embodiment, the optical analog-to-digital converter 500 includes a split waveguide 510 and a plurality of photodetector PDs. Since the photodetector PD has substantially the same function as the photodetector PD already described in the second embodiment, duplicate description will be omitted.

The divided waveguide 510 is formed by providing a binary divided waveguide 520 that equally divides the amount of optical analog and synthesizing the outputs from the binary divided waveguide 520 so as to have the above division ratio. The binary split waveguide 520 is a waveguide that simply divides the input of the optical signal of 1 into the outputs of 2, and the amount of light is evenly divided between the two outputs. Further, although it is stated here that the amount of optical analog is equally divided into two, it is not limited to such a case, and it may be equally divided into integers of 3 or more.

Also in such a divided waveguide 510, a division ratio equal to that of the divided waveguide 310 is set. Therefore, the optical signal from the signal source LD or the optical signal input via the optical transmission line such as an optical fiber is divided into predetermined division ratios different from each other, for example, 1: 1/3: in the example of FIG. Divide at a ratio of 1/5. Dividing at this ratio of 1: 1/3: 1/5 means that the cross-sectional area of the branch path of the optical signal is 15: 5: 3, that is, the binary split waveguide 520 is continuously divided into five stages. Provided, 2⁵= 32 branch paths are formed, 23 are extracted from them, and 15: 5: 3 are combined.

In the present embodiment as well, as in the second embodiment, the light amount is expressed by a predetermined ratio by dividing the optical signal by a predetermined division ratio different from each other, and it is input depending on whether or not each divided optical signal reaches the threshold value. It is possible to detect the amount of optical analog of the optical signal.

For example, in the case of FIG. 9, the input optical analog quantity is divided into 32 lines in the divided waveguide 510 and combined so as to have a division ratio of 15: 5: 3. Therefore, 15/32 of the input optical analog amount is output to the photodetector PD1, 5/32 is output to the photodetector PD2, and 3/32 is output to the photodetector PD3. Then, the optical detection units PD1, PD2, PD3 receive the optical analog amount of (15/32) × (1/2) = 15/64, assuming that the detection unit (1LSB) of the input optical analog amount is 1. It may be set to the threshold value of. With such a configuration, when the amount of optical analog is 0, all the photodetector PDs are turned off, when it is 1, only the photodetector PD1 is turned on, when it is 2, the photodetectors PD1 and PD2 are turned on, and when it is 3, the photodetectors PD1 and PD2 are turned on. All photodetector PDs turn on.

The number of the above predetermined stages can be calculated by using the formula 1 shown below. That is, when the digital value to be derived is n steps, log₂(The value of the numerator when the result of Equation 1 is reduced) Take the above value.<maths num="4"><img file="JP2007024924A_D0004.tif" /></maths>... (Formula 1)

For example, if the digital value to be derived as described above is in 4 stages ("0,1,2,3"), 1+ (1/3) + (1/5) = 23/15, which is the minimum. The required number of branch paths is 23 molecules. Therefore, log₂23 = 4.52, and the number of stages is 5. If the digital value to be derived has 5 stages, 1 + (1/3) + (1/5) + (1/7) = 176/105, and the required number of branch paths is 176, and the number of stages is It will be 8 steps. Another example of such a number of stages is shown as the number of stages in FIG. 8, similar to the number of unit waveguides in the third embodiment.

By continuously connecting the binary split waveguides as described above, a uniform amount of light is output 2ⁿLight output end can be obtained. In addition, since it is not easily affected by dimensional errors in the process of creating the waveguide, the division accuracy can be further improved.

Moreover, in the example of FIG. 9, since only 23 of the 32 branch roads are used, the surplus branch road can be used for other purposes. In the present embodiment, the surplus waveguide 530 formed by synthesizing the surplus of the binary divided waveguide 510 and the surplus light detection unit PDX for detecting the optical signal output from the surplus waveguide 530 are further provided. With such a configuration, the surplus branch path can be used for calibration of the analog / digital converter, error detection, test signal application, backup, and the like.

For example, by using the surplus waveguide 530 with the surplus 9 branch paths shown in FIG. 9, it is possible to obtain an optical analog amount of 3/5 in terms of division ratio. Therefore, it barely reacts to the digital value "1". This makes it possible to detect a failure of the photodetector PD1.

In addition, the surplus waveguide 530 can be connected to an electrical analog / digital converter (not shown) and referred to as a reference value for calibration of optical analog amount detection. At this time, it is expected that the conversion speed will be slow because the configuration of the residual light detector PDX and the electrical analog / digital converter is used, but the above configuration is used as a test signal and is suitable for normal use. Does not affect.

In FIG. 9, all the surplus branch paths are combined as the surplus waveguide 530, but the case is not limited to this, and one or more lines may be selected and combined to provide a plurality of surplus waveguides 530. ..

(Fifth Embodiment: Optical analog / digital converter 600) FIG. 10 is a configuration diagram showing another configuration of the optical analog / digital converter. The optical analog-to-digital converter 600 is the optical analog-to-digital converter 500 according to the fourth embodiment, to which a plurality of comparators 610 and a decimal / binary converter 620 as a decoder are added. is there. Since the functions of the optical analog / digital converter 500 already described in the fourth embodiment are substantially the same, duplicate description will be omitted.

The comparator 610 compares electrical signals from a plurality of photodetector PDs with reference signals. Such a reference signal can be adjusted for the entire comparator 610 at once or individually by the division ratio of the divided waveguides. For example, in the divided waveguide 510 in the fourth embodiment, the input optical analog is used. Assuming that the quantity detection unit (1LSB) is 1, the light receiving thresholds of the photodetectors PD1, PD2, and PD3 are (15/32) × (1/2) = 15/64 optical analog quantities. Therefore, when the optical analog amount of 15/64 is input to the photodetectors PD1, PD2, PD3, a reference signal is selected so that the output of the comparator 610 is surely turned on. It is also possible to control the reference signal in real time according to the standard of the input optical signal.

Further, as described in the first embodiment, since all the comparators 610 are compared with one reference signal, the region of the comparator having good linearity and a high reaction rate (for example, the center of the detection range). By setting the reference signal to), the reaction speed can be increased as compared with the case where the conventional analog / digital converter is used.

The decimal / binary converter 620 as the decoder converts the output signal from the comparator 610 into a binary signal. With such a configuration of the comparator 610 and the decimal / binary converter 620, not only the detection signal from the photodetector PD is simply read, but also the reference signal is adjusted to more accurately obtain the amount of optical analog. It becomes possible to detect.

FIG. 11 is an explanatory diagram showing the relationship between the input from the photodetector PD and the output of the decimal / binary converter 620. Referring to FIG. 11, the decimal / binary converter 620 outputs the binary number "00" when all the photodetector PDs are off, and outputs the binary number "11" when all are on. In this way, it is possible to discriminate between the four states of the input optical analog amount.

With reference to the above-described embodiment, the optical analog-to-digital converter according to the present invention receives an input optical signal without referring to an optical signal as a reference or using an electric analog-to-digital converter having a slow conversion speed. The optical analog amount can be directly derived, and the optical signal can be digitally converted at high speed.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, which naturally belong to the technical scope of the present invention. Understood.

For example, in the fifth embodiment, the split waveguide of the fourth embodiment is referred to as the split waveguide that converts the optical analog amount into the signal of the photodetector, but the second embodiment is not limited to this case. Alternatively, it can be formed with reference to the divided waveguide in the third embodiment.

Further, the above-mentioned decoder is not limited to the decimal / binary converter described in the fifth embodiment, and can convert an electric signal output from the photodetector into a binary number in relation to the amount of optical analog and the threshold value. It can also take various configurations.

Further, by providing the optical analog / digital conversion device in the optical signal receiving device connected to the optical fiber, it is possible to directly derive the optical analog amount of the input optical signal as a digital amount.

<figref num="1">It is a schematic diagram for demonstrating the analog-to-digital conversion of a conventional optical signal.</figref><figref num="2">It is a block diagram for demonstrating the operation principle of an electric analog-to-digital converter.</figref><figref num="3">It is explanatory drawing for demonstrating the threshold value by resistance division of a resistance part.</figref><figref num="4">It is a block diagram for demonstrating the operation principle when the composition of an analog / digital converter is changed.</figref><figref num="5">It is explanatory drawing for demonstrating the level of the analog voltage input Vin by the resistance division of a resistance part.</figref><figref num="6">It is a block diagram which showed the schematic structure of the optical analog-to-digital conversion apparatus by 2nd Embodiment.</figref><figref num="7">It is a block diagram which showed the other configuration of an optical analog-to-digital converter.</figref><figref num="8">It is explanatory drawing which illustrated the digital value to be derived and the number of unit waveguides.</figref><figref num="9">It is a block diagram which showed the other configuration of an optical analog-to-digital converter.</figref><figref num="10">It is a block diagram which showed the other configuration of an optical analog-to-digital converter.</figref><figref num="11">It is explanatory drawing which showed the relationship between the input from a photodetector and the output of a decimal / binary converter.</figref>

Code description

310,410,510 Divided waveguide 420 Unit waveguide 530 Residual waveguide 610 Comparator 620 Decoder PD1, PD2, PD3 Photodetector PDX Residual residual light detector