JP2006203873A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiver which has an improved level of coupling efficiency and reception performance, without causing the frequency response characteristics to deteriorate. <P>SOLUTION: Optical signals emitted from an optical transmitter is received individually and are converted into electrical signals by a plurality of photodetectors 12a. A plurality of amplifiers 13a individually amplify the electrical signals converted by the respective corresponding photodetectors 12a. A plurality of identification sections 14a individually identify the multivalued digital data of the optical signal, based on the amplified electrical signals outputted from the respective corresponding amplifiers 13a. A determination section 15 comprehensively examines all of a plurality of pieces of digital data outputted by the plurality of identification sections 14a, to determine the digital data which are outputted from the optical receiver 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical receiver that performs data communication using an optical signal.

  Conventional optical transmission systems include optical fiber transmission that transmits an optical signal using an optical fiber, and optical space transmission that transmits an optical signal in free space without using an optical fiber. When considering optical receivers used in these optical transmission systems, the problem is how to efficiently receive the optical signal from the transmission side with a light receiving element (PD; photo detector). In particular, in optical space transmission, the light output from the optical transmitter is accurately controlled by accurately aligning the optical axis between the optical transmitter and the optical receiver, and suppressing the spread of the light beam using a lens or the like. It is necessary to couple the signal with the light receiving element of the optical receiver.

As a method of aligning the optical axis, apart from the optical signal on which the data signal is superimposed, an optical signal for optical axis alignment is transmitted to perform optical axis alignment in advance, and after this optical axis alignment is completed, the data signal There has been proposed a method for realizing optical space transmission by transmitting an optical signal in which is superimposed (for example, see Patent Document 1).
JP-A-5-183513

  In the conventional method for aligning the optical axis in advance as described above, in order to increase the coupling efficiency between the optical signal and the light receiving element, it is necessary to narrow the diameter of the light beam emitted from the optical transmitter. However, it is technically difficult to narrow the diameter of the light beam until the coupling efficiency is effectively increased, and even if the light beam is narrowed in a certain positional relationship, the coupling efficiency decreases if the positional relationship is shifted. End up. Therefore, the method of narrowing the diameter of the light beam is not very realistic.

  Therefore, considering the case where the diameter of the light beam is large, the coupling efficiency cannot be increased unless the light receiving diameter of the light receiving element 100 is increased as shown in FIG. However, when the light receiving diameter of the light receiving element 100 is increased, the capacity of the light receiving element 100 is increased. As a result, the frequency response characteristic is deteriorated and the transmission rate of the data signal is limited (the transmission speed is reduced). is there.

  As a countermeasure when the diameter of the light beam is large, a method is conceivable in which a plurality of light receiving elements having a small light receiving diameter are used, and signals obtained by the plurality of light receiving elements are added after being preamplified. However, this analog method has a problem that the added signal after the pre-amplification has a large amplitude, and a very large dynamic range is required for the subsequent circuit. Further, since the added signal has a large amplitude, there is a problem that the power consumption of the optical receiver is increased.

  Therefore, an object of the present invention is to provide an optical receiver capable of improving the coupling efficiency and reception performance of the optical receiver without degrading the frequency response characteristics of the light receiving element.

  The present invention is directed to an optical receiver that performs data communication using an optical signal. In order to achieve the above object, the optical receiver of the present invention includes a plurality of light receiving elements, a plurality of amplification units, a plurality of identification units, and a determination unit. The plurality of light receiving elements receive an optical signal. The plurality of amplifiers are provided corresponding to the plurality of light receiving elements, and amplify signals output from the respective light receiving elements. The plurality of identification units are provided corresponding to the plurality of amplification units, and respectively identify the digital data of the optical signal based on signals output from the amplification units. The determination unit inputs a plurality of identified digital data output from the plurality of identification units, and determines digital data to be output based on the plurality of identified digital data.

  It is preferable that the determination unit determines the most identified digital data among the plurality of identified digital data as the output digital data. Typically, the plurality of identification units identify binary digital data.

  Moreover, you may further provide the some detection part provided corresponding to several amplification part, and each detecting the amplitude level of the signal output from each amplification part. In this case, the determination unit can weight each of the plurality of identified digital data according to the amplitude level detected by the detection unit and perform the determination process. Alternatively, the determination unit can perform the determination process using only the identified digital data in which the amplitude level detected by the detection unit is greater than the specified value.

  The identification unit stops outputting digital data to the determination unit when the amplitude of the signal output from the amplification unit is smaller than the specified value, and the determination unit detects the identified digital data output from the identification unit. The determination process may be performed using only. In this case, the operation of the corresponding light receiving element and the amplifying unit can be further stopped.

  Furthermore, a light receiving power detection unit for detecting the light receiving power of the light receiving element, and a light receiving current output for stopping output from the light receiving element to the amplifying unit when the light receiving power detected by the light receiving power detecting unit is smaller than a specified value A switching unit may be further provided. In this case, the light reception current output switching unit can further stop the operations of the corresponding amplification unit and identification unit.

  According to the present invention, the coupling efficiency and reception performance of the optical receiver can be improved without degrading the frequency response characteristics of the light receiving element.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an optical receiver 1 according to the first embodiment of the present invention. In FIG. 1, the optical receiver 1 according to the first embodiment includes a light receiving unit 12, a preamplifier 13, a data identification unit 14, and a determination unit 15.

  An optical signal emitted from an optical transmitter (not shown) is received by the light receiving unit 12 and is photoelectrically converted. The light receiving unit 12 includes a plurality of light receiving elements (PD; photodetector) 12a, and each light receiving element 12a individually receives an optical signal and converts it into an electrical signal. Each light receiving element 12a has a light receiving area that has sufficient frequency response characteristics with respect to the modulation speed of the optical signal. In order to increase the coupling efficiency of the light receiving element 12a, the light receiving diameter of the light receiving element 12a may be increased. However, as described in the prior art, the frequency response characteristic deteriorates as the light receiving diameter increases. For this reason, in this invention, the form which uses the some light receiving element 12a is employ | adopted. FIG. 1 illustrates an example in which the light receiving unit 12 is configured by five light receiving elements 12a.

The preamplifier 13 includes a plurality of amplifiers 13a corresponding to the plurality of light receiving elements 12a of the light receiving unit 12, and individually amplifies the electric signals converted by the light receiving elements 12a.
The data identification unit 14 includes a plurality of identification units 14a corresponding to the plurality of amplification units 13a of the pre-amplification unit 13, and based on the amplified electrical signals output from the amplification units 13a, Each value digital data is identified individually. For example, when the data identification unit 14 identifies binary digital data, each identification unit 14a has a specified value in advance, and if the amplified electrical signal exceeds the specified value, the digital data “1” is exceeded. If not, it is possible to identify it as digital data “0”.

  The determination unit 15 comprehensively determines a plurality of digital data output from the plurality of identification units 14 a of the data identification unit 14 and determines the digital data output from the optical receiver 1. The following method is mentioned as a typical determination method performed by the determination unit 15. Of the plurality of digital data output by the plurality of identification units 14a, the digital data having a large number is determined as the digital data output from the optical receiver 1. For example, when the plurality of digital data output by the five identification units 14a is “1, 1, 0, 0, 1”, “1” having a large number is determined as the digital data.

At this time, since the plurality of amplifying units 13a of the preamplifying unit 13 generate noise independently, even if the code error rate characteristics with respect to the received light power of each amplifying unit 13a are the same, the code error at the same timing is Each will occur independently. Here, it is assumed that the light receiving power of each light receiving element 12a of the light receiving unit 12 is the same, and the code error rates of the (2n + 1) amplifying units 13a constituting the preamplifying unit 13 at that time are all the same “Pe1”. In other words, the code error rate Pe as the optical receiver 1 is given by the following equation (1). In the following formula (1), it is assumed that noise generated in each amplification unit is dominant compared to noise present in the received optical signal.
Pe≈n (2n + 1) [Pe1] ^{n + 1} (1)

For example, consider the calculation when the number of amplifiers 13a is five (n = 2) as in the optical receiver 1 illustrated in FIG. The code error rate Pe of the optical receiver 1 when n = 2 is calculated as follows.
Pe = Pe1 * Pe1Pe1 * Pe1 * (1-Pe1)
+ Pe1 * Pe1 * Pe1 * (1-Pe1) * Pe1
+ Pe1 * Pe1 * (1-Pe1) * Pe1 * Pe1
+ Pe1 * (1-Pe1) * Pe1 * Pe1 * Pe1
+ (1-Pe1) × Pe1 × Pe1 × Pe1 × Pe1
+ Pe1 * Pe1 * Pe1 * (1-Pe1) * (1-Pe1)
+ Pe1 * Pe1 * (1-Pe1) * Pe1 * (1-Pe1)
+ Pe1 * (1-Pe1) * Pe1 * Pe1 * (1-Pe1)
+ (1-Pe1) × Pe1 × Pe1 × Pe1 × (1-Pe1)
+ Pe1 * Pe1 * (1-Pe1) * (1-Pe1) * Pe1
+ Pe1 * (1-Pe1) * Pe1 * (1-Pe1) * Pe1
+ (1-Pe1) * Pe1 * Pe1 * (1-Pe1) * Pe1
+ Pe1 * (1-Pe1) * (1-Pe1) * Pe1 * Pe1
+ (1-Pe1) * Pe1 * (1-Pe1) * Pe1 * Pe1
+ (1-Pe1) × (1-Pe1) × Pe1 × Pe1 × Pe1
+ Pe1 * Pe1 * Pe1 * Pe1 * Pe1
= 10 [Pe1] ³ -15 [Pe1] ⁴ -6 [Pe1] ⁵
≒ 10 [Pe1] ³ (∵ [Pe1] ³ >> [Pe1] ⁴ >> [Pe1] ⁵ )

  Here, if Pe1 is 1E-3, the code error rate Pe as the optical receiver 1 is about 1E-8, which is improved. This code error rate characteristic is shown in FIG. In FIG. 2, the code error rate characteristics when the number of light receiving elements and amplifying units is one are indicated by a solid line, the code error rate characteristics when the number is three, and the code error rate characteristics when the number is five by a dotted line. It is indicated by a one-dot chain line. As can be seen from FIG. 2, the minimum light receiving power (light receiving power with a code error rate of 1E-12) is improved by about 2 dB when there are three light receiving elements and amplifying units, and by about 3 dB when there are five light receiving elements and amplifiers.

  As described above, according to the optical receiver 1 according to the first embodiment of the present invention, the coupling efficiency and the reception performance can be improved without deteriorating the frequency response characteristics of the light receiving element 12a.

[Second Embodiment]
FIG. 3 is a block diagram showing the configuration of the optical receiver 2 according to the second embodiment of the present invention. In FIG. 3, the optical receiver 2 according to the second embodiment includes a light receiving unit 12, a preamplifier 13, a data identification unit 14, a determination unit 25, and an amplitude detection unit 26.
As illustrated in FIG. 3, the optical receiver 2 according to the second embodiment is different from the optical receiver 1 according to the first embodiment in the configuration of the determination unit 25 and the amplitude detection unit 26. Hereinafter, the same reference numerals are given to the same components and the description thereof will be omitted, and the optical receiver 2 according to the second embodiment will be described with respect to the different configurations.

  The amplitude detector 26 includes a plurality of detectors 26a corresponding to the plurality of amplifiers 13a of the preamplifier 13, and detects the amplitude level of the electrical signal output from each amplifier 13a. Information on the detected amplitude level is transmitted to the determination unit 25. The determination unit 25 determines the plurality of digital data output from the plurality of identification units 14 a of the data identification unit 24 in consideration of the weighting according to the amplitude level information received from the amplitude detection unit 26, and from the optical receiver 2. Determine the digital data to be output.

  Typically, a weighting coefficient corresponding to the amplitude level of the electric signal is given to each digital data (for example, if the amplitude level is equivalent to the ninth power level, the weight is increased, and the amplitude level corresponding to the third power level is used). If so, reduce the weight). Then, the total value of the weighting coefficients added for each digital data is determined, and digital data having a large total value is determined as digital data to be output from the optical receiver 2.

  Alternatively, only the top few digital data having a large amplitude level may be determined using a specified value or the like, and the large number of digital data may be determined as the digital data output from the optical receiver 2. At this time, the power consumption can be suppressed by stopping the operations of the amplifying unit 13a and the identifying unit 14a that process the invalid digital data. The number of valid data may be determined based on whether the sum of the amplitude levels is a predetermined value, for example, whether the code error rate is equal to or higher than error free (1E-12), instead of a specified value.

  As described above, according to the optical receiver 2 according to the second embodiment of the present invention, if the amplitude level of the electrical signal output from the amplifying unit 13a is large, it is determined that the reliability of the signal is high, and the signal Increase the weight of. Thereby, the value of the digital data received by the light receiving unit 12 can be determined more accurately.

[Third Embodiment]
FIG. 4 is a block diagram showing the configuration of the optical receiver 3 according to the third embodiment of the present invention. In FIG. 4, the optical receiver 3 according to the third embodiment includes a light receiving unit 12, a preamplifier 13, a data identification unit 34, and a determination unit 35.
As shown in FIG. 4, the optical receiver 3 according to the third embodiment differs from the optical receiver 1 according to the first embodiment in the configuration of a data identification unit 34 and a determination unit 35. Hereinafter, the same reference numerals are given to the same components and the description thereof will be omitted, and the optical receiver 3 according to the third embodiment will be described with respect to the different configurations.

  The data identification unit 34 includes a plurality of identification units 34a corresponding to the plurality of amplification units 13a of the pre-amplification unit 13, and based on the amplified electrical signals output from the amplification units 13a, Each value digital data is identified individually. The identification unit 34a has a predetermined specified value, and performs the identification process only when the amplified electrical signal is equal to or greater than the specified value. The digital data obtained by the identification process is output to the determination unit 14 together with an “output possible” signal indicating that the data is output. On the other hand, when the amplified electrical signal is less than the specified value, the identification unit 34a stops outputting the digital data to the determination unit 14 and outputs an “output impossible” signal indicating that no data is output. And the operation is stopped by controlling the light receiving element 12a and the amplifying unit 13a to the power-off state. This operation stop is continuously performed for a predetermined period (according to the optical signal output cycle on the optical transmitter side), and when the predetermined period elapses, the original power-on state is restored for the next optical reception process. To do.

  The determination unit 35 determines that only the digital data for which the “output enabled” signal is notified among the plurality of digital data output from the plurality of identification units 34 a of the data identification unit 34 is valid data for determination. The digital data output from the optical receiver 3 is determined. By this processing, it is possible to block a signal from the light receiving element 12a having a low light receiving power among the plurality of light receiving elements 12a in the light receiving unit 12, and as a result, it is possible to reduce the cause of the code error.

  As described above, according to the optical receiver 3 according to the third embodiment of the present invention, if the amplitude level of the electrical signal output from the amplifying unit 13a is small, it is determined that it causes a code error, and the electrical signal is generated. The output of the signal is stopped, and the operation of the associated light receiving element 12a and the amplifying unit 13a is stopped. Thereby, the reception performance of the optical receiver 3 can be improved and the power consumption can be reduced.

  In the third embodiment, the case where the data identification unit 34 determines the output signal amplitude of the preamplifier 13 and stops the operations of the light receiving element 12a and the amplifier 13a has been described. The determination unit 25 described in the embodiment may be provided with the same operation stop function of the light receiving element 12a and the amplification unit 13a. In this case, the operation of the identification unit 34a may be stopped simultaneously.

[Fourth Embodiment]
FIG. 5 is a block diagram showing a configuration of an optical receiver 4 according to the fourth embodiment of the present invention. In FIG. 5, the optical receiver 4 according to the fourth embodiment includes a light receiving unit 42, a preamplifier 13, a data identification unit 14, and a determination unit 15.
As illustrated in FIG. 5, the optical receiver 4 according to the fourth embodiment is different from the optical receiver 1 according to the first embodiment in the configuration of the light receiving unit 42. Hereinafter, the same reference numerals are given to the same components and the description thereof will be omitted, and the optical receiver 4 according to the fourth embodiment will be described with respect to the different configurations.

  The light receiving unit 42 includes a plurality of light receiving elements 42a, and a light receiving power detection unit 42b and a light receiving current output switching unit 42c provided corresponding to the plurality of light receiving elements 42a. Each light receiving element 42a individually receives an optical signal and converts it into an electrical signal. Each light receiving power detector 42b detects the light receiving power (light receiving current) of the corresponding light receiving element 42a, and determines whether or not the light receiving power is equal to or greater than a predetermined value. When the received light power is equal to or greater than a predetermined value, the received light power detection unit 42b controls the received light current output switching unit 42c so as to output the received light power obtained by the light receiving element 42a to the preamplifier unit 13. . On the other hand, when the received light power is less than a predetermined value, the received light power detection unit 42b sets the received current output switching unit 42c so as not to output the received light power obtained by the light receiving element 42a to the preamplifier unit 13. Control. The light reception current output switching unit 42c switches the output operation / output stop from the light receiving element 42a to the amplification unit 13a in accordance with the control of the light reception power detection unit 42b. At the same time, the light reception current output switching unit 42c may stop the operations of the amplification unit 13a and the identification unit 14a.

  As described above, according to the optical receiver 4 according to the fourth embodiment of the present invention, the light receiving power of the light receiving element 42a is determined, and the output of the light receiving power is stopped. Thereby, the reception performance of the optical receiver 4 can be improved.

Next, structural examples in the case where the optical receivers 1 to 4 according to the first to fourth embodiments described above are actually incorporated into a substrate will be described with reference to FIGS. 6 to 9.
FIG. 6 is a diagram illustrating a structural example in which the optical receiver 1 according to the first embodiment is incorporated in the substrate 50. In this structure example, the five light receiving elements 12a are arranged in a cross shape so that an optical signal having a beam profile (shaded portion in FIG. 6) can be received efficiently.

  Here, when the five light receiving elements 12a are arranged in a cross shape as shown in FIG. 6, the wiring lengths from the respective light receiving elements 12a to the determination unit 15 are not the same. This causes a difference in the time until the signal received by each light receiving element 12a reaches the determination unit 15. Therefore, as shown in FIG. 7, it is preferable to provide a delay unit 17 including a delay element 17 a that absorbs a time difference between the data identification unit 14 and the determination unit 15.

  Further, as shown in FIG. 8, a condensing lens 18 for condensing the optical signal transmitted from the optical transmitter may be provided on the light receiving surface side of the plurality of light receiving elements 12a. With such a structure, an optical signal can be efficiently received by the plurality of light receiving elements 12a.

  Furthermore, as shown in FIG. 9, if the substrate 50 is a substrate that can be mounted on both sides, a plurality of light receiving elements 12a are mounted on one surface (front surface), and a plurality of amplifiers 13a are mounted on the other surface (back surface). A structure in which a plurality of light receiving elements 12a and a plurality of amplifying units 13a are connected through a through hole or the like is also conceivable.

  The optical receiver of the present invention can be used in a system for transmitting an optical signal in a free space, particularly when it is desired to improve the coupling efficiency and the reception performance without deteriorating the frequency response characteristics of the light receiving element. Useful for.

1 is a block diagram showing a configuration of an optical receiver 1 according to a first embodiment of the present invention. The figure which shows the code error rate characteristic of the optical receiver 1 of FIG. The block diagram which shows the structure of the optical receiver 2 which concerns on the 2nd Embodiment of this invention. The block diagram which shows the structure of the optical receiver 3 which concerns on the 3rd Embodiment of this invention. The block diagram which shows the structure of the optical receiver 4 which concerns on the 4th Embodiment of this invention. The figure which shows the structural example which incorporated the optical receivers 1-4 of this invention in the board | substrate 50 The figure which shows the structural example which incorporated the optical receivers 1-4 of this invention in the board | substrate 50 The figure which shows the structural example which incorporated the optical receivers 1-4 of this invention in the board | substrate 50 The figure which shows the structural example which incorporated the optical receivers 1-4 of this invention in the board | substrate 50 The figure for demonstrating the subject in the conventional optical receiver

Explanation of symbols

1 to 4 Optical receivers 12 and 42 Light receivers 12a, 42a, 100 Light receiver 13 Preamplifier 13a Amplifiers 14 and 34 Data identifiers 14a and 34a Identifiers 15, 25 and 35 Determination unit 17 Delay unit 17a Delay element 18 Condensing lens 26 Amplitude detection unit 26a Detection unit 42b Light reception power detection unit 42c Light reception current output switching unit 50 Substrate

Claims (9)

An optical receiver that performs data communication using an optical signal,
A plurality of light receiving elements for receiving the optical signal;
A plurality of amplifying units that are provided corresponding to the plurality of light receiving elements and amplify signals output from the respective light receiving elements;
A plurality of identification units provided corresponding to the plurality of amplification units, each for identifying digital data of the optical signal based on a signal output from each amplification unit;
An optical receiver comprising: a plurality of identified digital data output from the plurality of identification units; and a determination unit that determines digital data to be output based on the plurality of identified digital data.   2. The optical receiver according to claim 1, wherein the determination unit determines digital data identified most among the plurality of identified digital data as output digital data. 3.   The optical receiver according to claim 1, wherein the plurality of identification units identify binary digital data. A plurality of detection units provided corresponding to the plurality of amplification units, each detecting an amplitude level of a signal output from each amplification unit;
The optical receiver according to claim 1, wherein the determination unit weights each of the plurality of identified digital data according to an amplitude level detected by the detection unit, and performs determination processing. . A plurality of detection units provided corresponding to the plurality of amplification units, each detecting an amplitude level of a signal output from each amplification unit;
The optical receiver according to claim 1, wherein the determination unit performs the determination process using only the identified digital data whose amplitude level detected by the detection unit is greater than a specified value. When the amplitude of the signal output from the amplification unit is smaller than a specified value, the identification unit stops digital data output to the determination unit,
The optical receiver according to claim 1, wherein the determination unit performs determination processing using only the identified digital data output from the identification unit.   The identification unit further stops the operation of the corresponding light receiving element and the amplification unit when the amplitude of the signal output from the amplification unit is smaller than a specified value. Optical receiver. A light receiving power detector for detecting a light receiving power of the light receiving element;
The light according to claim 1, further comprising: a light reception current output switching unit that stops output from the light receiving element to the amplification unit when the light reception power detected by the light reception power detection unit is smaller than a specified value. Receiver. The light reception current output switching unit further stops the operation of the corresponding amplification unit and the identification unit when the light reception power detected by the light reception power detection unit is smaller than a predetermined value. Item 9. The optical receiver according to Item 8.

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