JPH02155321A - Optical receiver - Google Patents

Abstract

PURPOSE:To expand the dynamic range by controlling an optical input suppression section provided to a pre-stage of a photodetector with an excess optical input detection control section and suppressing an optical signal level inputted to the photodetector when an input optical signal is at an excess level. CONSTITUTION:An excess optical input detection control section 4 detects an output signal of an amplifier section 3 and an output signal of a photodetector to discriminate whether or not the level is an excess optical input level and in the case of the excess optical input level an optical input suppression section 1 to suppress the input level to the photodetector 2 to a proper value. Since the excess optical input level is inputted to the photodetector 2 as a proper value, it is possible to increase the optical reception sensitivity to expand the dynamic range.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical receiving device with an expanded dynamic range, optical input suppression that can suppress the level of an input optical signal is aimed at expanding the dynamic range without deteriorating the optical receiving sensitivity. a light-receiving element that converts the input optical signal inputted through the optical input suppression part into an electrical signal; an amplifying part that amplifies the output signal of the light-receiving element; and detecting an excessive level of the input optical signal. and an excessive light human power detection control section that controls the light input suppression section and suppresses the input level to the light receiving element.

[Industrial application field]

The present invention relates to an optical receiving device with an expanded dynamic range.

Optical reception 'AM' in optical communication systems has the function of converting an input optical signal into an electrical signal and making the level of the converted output signal constant. By controlling the magnification and the gain of the amplifier, the output signal level is kept constant even when the input optical signal level fluctuates. In this case, it is desired to widen the variation range of the input optical signal level in which the output signal level can be made constant, that is, to expand the dynamic range.

[Conventional technology]

As mentioned above, conventional optical receivers have a configuration in which the multiplication factor is controlled by controlling the reverse bias voltage of the APD as a light receiving element in order to maintain a constant received output signal level, and a configuration in which the output signal of the light receiving element is controlled. A configuration that controls the gain of a gain control amplifier that performs amplification is known, and a configuration that combines these is also known.

For example, FIG. 7 shows a configuration in which control of the multiplication factor of the light receiving element and gain control of the gain control amplifier are combined,
71 is a light receiving element such as an avalanche photodiode (APD), 72 is a preamplifier, 73 is a gain control amplifier, 74
75 is a peak detection circuit, 75 is a gain control circuit, and 76 is an optical fiber transmission line. The optical signal input via the optical fiber transmission line 76 is converted into an electrical signal by the light receiving element 71, amplified by the preamplifier 72, further amplified by the gain control amplifier 73, and output as a received output signal. .

FIG. 8 is a gain control characteristic curve diagram showing the relationship between input optical signal level (dBm) and relative gain (dB). In the range where the input optical signal level is below P, the reverse bias voltage of the light receiving element 71 is controlled by the gain control circuit 75 so that the peak value of the output signal detected by the peak detection circuit 74 is constant. The multiplication factor of the light receiving element 71 is controlled as shown in FIG. For example, the light receiving element 71
The multiplication factor of the light receiving element 71 is controlled within the range of 12 to 2, and when the input optical signal level exceeds P, the multiplication factor of the light receiving element 71 reaches the minimum value of 2.
will be maintained. Then, as shown in curve B, the gain of the gain control amplifier 73 is controlled so that the gain decreases as the level of the human-powered optical signal increases.
Therefore, it is controlled within a range of about 10 dB in terms of the input optical signal level. Through such control, the output signal level becomes a set constant value.

[Problem to be solved by the invention]

As mentioned above, the dynamic range of the optical receiver by controlling the multiplication factor and amplification gain was about 20 dB.

Therefore, in an optical receiving device designed to have high optical receiving sensitivity and to prevent code errors from occurring even in the case of a weak input optical signal, if the length of the optical fiber transmission line 76 is short or If the optical output of the optical transmitter is large, the input optical signal level will be so high that the preamplifier 72 etc. will be saturated, resulting in code errors.

In such a case, conventionally, a fixed optical attenuator is used as the light receiving element 7.
A configuration is adopted in which the optical signal is provided at the front stage of 1 to attenuate the excessive human power optical signal level. In an optical receiver equipped with a fixed optical attenuator as described above, the optical reception sensitivity becomes low. Either the optical attenuator must be removed or replaced with a fixed optical attenuator that provides an amount of attenuation that corresponds to the input optical signal level. That is, it is necessary to replace the fixed optical attenuator each time depending on the length of the optical fiber transmission line 76, etc., and there is a drawback that a great deal of effort is required for adjustment.

The present invention aims to expand the dynamic range without deteriorating the optical reception sensitivity.

[Means to solve the problem]

The optical receiver of the present invention suppresses excessive optical input by detecting excessive optical input, and will be described with reference to FIG.

An optical input suppressing section 1 that can suppress the level of an input optical signal, a light receiving element 2 that converts the input optical signal inputted through the optical input suppressing section 1 into an electrical signal, and amplifying the output signal of this light receiving element 2. and an excessive optical input detection control section 4 that detects an excessive level of the input optical signal and controls the optical input suppressing section 1 to suppress the input level to the light receiving element 2. .

[Function] The excessive light input detection control section 4 detects the output signal of the amplification section 3, the output signal of the light receiving element, etc., determines whether or not there is an excessive light input level, and in the case of an excessive light input level, The input suppressing section 1 is controlled to suppress the level of human power applied to the light receiving element 2 to an appropriate value.

Further, the optical input suppressing unit l can be configured using, for example, the configuration of an optical switch, and suppresses the optical signal input to the light receiving element 2 by a control signal from the excessive optical input detection control unit 4. A part of the signal is branched to input an optical signal at an appropriate level to the light receiving element 2.

Therefore, the excessive light input level can be automatically converted into an appropriate value and inputted to the light receiving element 2, so that the light reception sensitivity can be increased and the dynamic range can be expanded.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of the first embodiment of the present invention.
1 is an optical input suppression section, 12 is a light receiving element such as an APD, 13 is a preamplifier, 14 is a gain control amplifier, 15 is a peak detection circuit, 16 is a gain control circuit 17 is an excessive optical input detection section, 1
8 is an optical fiber transmission line.

The preamplifier 13 and the gain control amplifier 14 correspond to the amplification section 3 in FIG.
6 and the excessive light input detection section 17 correspond to the excessive light input detection control section 4 in FIG. Further, the output signal of the light receiving element 12 is amplified by the preamplifier 13, further amplified by the gain control amplifier 14 to obtain a received output signal, and the peak value of the received output signal is detected by the peak detection circuit 15. Gain control circuit 16 so that the difference from the set value is zero.
Accordingly, for example, the multiplication factor of the light receiving element 12 is controlled according to the gain control characteristic shown in FIG. 8, and the gain of the gain control amplifier 14 is controlled to make the peak value of the received output signal constant. Such operation is similar to the conventional example.

Further, the excessive light input detection section 17 uses a control signal for controlling the gain of the gain control amplifier 14 from the gain control circuit 16, an output signal of the light receiving element 12, or an output signal of the preamplifier 13 to transmit light to the light receiving element 12. It detects whether the input optical signal level is excessive, and in the case of an excessive optical input level, controls the optical input suppressing section 11 to reduce the input level to the light receiving element 12.

The optical input suppressing section 11 can use the configuration shown in FIG. 3, for example. That is, a waveguide-type optical switch is constructed by forming intersecting pattern waveguides 22 by diffusing Ti or the like on an electro-optic effect crystal substrate 21 such as 1, i N b Oz, etc., and forming electrodes 23 and 24 at the intersections. Can be used. In the optical input suppressing unit 11 having this configuration, the optical signal incident on the boat P1 from the optical fiber transmission line 25 is suppressed from -P3. It can be distributed to P4. Therefore, for example, when the level of the input optical signal to the light receiving element 26 arranged at baud 1-P3 is not excessive, the optical signal incident from the boat PI is directly output from baud) P3 and input to the light receiving element 26, and when the input optical signal level is not excessive, If the level is boat P3. Boat P3 by distributing to P4
Excessive input optical signal level can be suppressed by reducing the output level of the optical signal.

Further, the optical input suppressing section 11 can also be configured by an optical switch that utilizes the Bragg diffraction phenomenon, a distributed coupling type optical switch, or the like.

Therefore, when the optical receiving sensitivity is designed to be high when the input optical signal level is not suppressed, the optical input suppressing section 11 can reduce the excessive input optical signal level when performing a test by directly connecting an optical transmitter. Since it can be suppressed, code errors will not occur.

That is, the dynamic range can be expanded. It is also possible to make the determination of the excessive level in the excessive optical input detection section 17 in a plurality of stages, and to control the degree of suppression of the input optical signal level in the optical input suppression section 11 in correspondence with each stage. In this case, for example, the electrode 2 in a waveguide optical switch
Since the distribution ratio of the input optical signal is controlled by controlling the voltage applied between 3.24 and 24 in accordance with the excessive level level, the degree of suppression can be controlled.

FIG. 4 is a block diagram of a second embodiment of the present invention, in which an optical input suppressor 31, a light receiving element 32, a preamplifier 33, a gain control amplifier 34, a peak detection circuit 35, and a gain control circuit 3
6 is the same as in the previous embodiment. In this embodiment, the excessive light input detection section 37 is connected to a comparison circuit 39 and a reference voltage 4.
0, the control voltage for controlling the gain of the gain control amplifier 34 from the gain control circuit 36 is compared with the base voltage 40 in the comparison circuit 39, and an excessive level of the input optical signal is detected. It is.

The gain control by the gain control amplifier 34 is approximately 10 dB in terms of the input optical signal level. Therefore, if the optical signal level input via the optical fiber transmission line 38 is excessive, the multiplication factor of the light receiving element 32 will be reduced. Even if the gain of the gain control amplifier 34 is minimized and the gain of the gain control amplifier 34 is minimized, the peak value of the received output signal will be higher than the set value. Therefore, the gain control amplifier 3
A comparison circuit 39 compares the control voltage for controlling the gain of 4 with a reference voltage 40, and when the value that minimizes the gain of the gain control amplifier 34 is reached, it is determined that the input optical signal level has become excessive, and the optical input signal level is determined to be excessive. The suppressor 31 is controlled to suppress the input optical signal level.

Furthermore, when the human input optical signal level drops considerably below the excessive level, the optical input suppressing section 31 stops suppressing the input optical signal level, and by providing the comparator circuit 39 with hysteresis characteristics, it is possible to easily reduce the input optical signal level. The optical input suppressor 31 can be controlled by detecting a decrease in the optical signal level.

FIG. 5 is a block diagram of a main part of a third embodiment of the present invention, in which a bias voltage is applied to a light receiving element 42 via a resistor 44, and a current flowing through the light receiving element 42 is detected by a current detecting section 45. The comparison circuit 46 compares the excessive optical input identification level 47 with the detected current value, and in the case of an excessive optical input level, controls the optical input suppressing section 41 to suppress the optical input through the optical fiber transmission line 48. suppresses the input optical signal level that is
By preventing saturation of the preamplifier 43, it is possible to prevent code errors from occurring. Therefore, the dynamic range can be expanded.

In this embodiment as well, by providing the comparator circuit 46 with hysteresis characteristics, it is possible to detect a case where the input optical signal drops from an excessive level and control the optical input suppressing section 41.

Further, the multiplication factor of the light receiving element 42, etc. are determined from the above-mentioned No. 1. As in the second embodiment, it is controlled by a gain control circuit (not shown).

FIG. 6 is a block diagram of the main part of the fourth embodiment of the present invention, in which the output signal of a preamplifier 53 that amplifies the output signal of the light receiving element 52 is applied to an excessive optical power detection section 55, and the output signal is transmitted through an optical fiber. It detects whether the optical signal input via the path 56 has an excessive level, and in the case of an excessive level, controls the optical input suppressing section 51 to suppress the input optical signal level,
This prevents the preamplifier 53 from becoming saturated.

Note that the multiplication factor of the light receiving element 52 and the gain of the gain control amplifier 54 are controlled by a gain control circuit (not shown) as in the first and second embodiments.

The present invention is not limited to the above-described embodiments, and various additions and changes can be made.

〔Effect of the invention〕

As explained above, in the present invention, the excessive optical input detection control section 4 controls the optical input suppressing section 1 provided before the light receiving element 2, and when the input optical signal is at an excessive level, the optical input suppressing section 1 This suppresses the level of the optical signal input to the light receiving element 2 and expands the dynamic range.Even if the optical reception sensitivity is designed to be low, code errors will occur if the input optical signal level becomes excessive. Since it is possible to automatically take measures to prevent this from occurring, it becomes possible to use the same optical receiver under various conditions.

Therefore, there is no need to replace the fixed optical attenuator depending on the usage conditions, so the scope of application of the optical receiver can be expanded, and costs can be reduced through mass production. There are advantages that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a block diagram of a first embodiment of the present invention, FIG. 3 is an explanatory diagram of an example of an optical input suppressing section, and FIG. The block diagram of the second embodiment, FIGS. 5 and 6 are the block diagrams of the third embodiment of the present invention. FIG. 7 is a block diagram of the main part of the fourth embodiment, FIG. 7 is a block diagram of the conventional example, and FIG. 8 is a gain control characteristic curve diagram. 1 is a light input suppressor, 2 is a light receiving element 1. 4 is an excessive light input detection control section. 3 is the amplification section

Claims (1)

[Claims] An optical input suppressing section (1) capable of suppressing the level of an input optical signal; and a light receiving element (1) converting the input optical signal inputted via the optical input suppressing section (1) into an electrical signal. 2), an amplifying section (3) that amplifies the output signal of the light receiving element (2), and an amplifier section (3) that detects an excessive level of the input optical signal and controls the optical input suppressing section (1), 2) An optical receiver comprising an excessive optical input detection control section (4) that suppresses an input level to the optical receiver.