JP3396793B2 - Optical receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver in an optical communication system including an optical amplifier. In an optical communication system, an optical amplifier such as an erbium (Er) -doped optical fiber amplifier that amplifies an optical signal as it is is applied.
When such an optical amplifier is applied to a repeater of an optical communication system, an optical signal is converted into an electric signal for amplification, synchronization,
Since a configuration such as waveform equalization and conversion to an optical signal is not required, the configuration is simplified, amplification is possible regardless of the transmission speed of the optical signal, and the wavelength-multiplexed optical signal can be amplified as it is.

When applied as an optical booster amplifier in the output stage of an optical transmitter, it is easy to transmit a large output optical power, and there is an advantage that a difference between transmission and reception levels can be widened. Further, when it is applied as an optical preamplifier in the preceding stage of the optical receiving device, there is an advantage that it is possible to achieve a receiving sensitivity above the noise limit generated in an electric circuit. However, in such an optical amplifier, an optical surge occurs due to restoration after the interruption of the optical input. There is a demand for protective measures against this light surge.

[0003]

2. Description of the Related Art In an optical amplifier of each part in an optical communication system, for example, a semiconductor laser for pumping is controlled so as to keep an optical output level constant, and the optical power for pumping from the semiconductor laser controls the optical amplifier. A constant light output control method in which the gain is controlled is applied. Therefore, the gain of the optical amplifier is increased due to the optical input interruption or the level drop caused by the incorrect insertion / removal of the optical connector, the obstacle or switching of the optical transmission line, and the optical surge is output by the subsequent optical input.

FIG. 8 is an explanatory diagram of an optical communication system.
1 is an optical transmitter, 82 is an optical receiver, 83 is a relay,
Reference numeral 84 is an optical transmission line, 85 is an electro-optical conversion unit, 86 is a photoelectric conversion unit, and 87, 88 and 89 are optical amplifiers. Optical repeater 8
3 includes an optical amplifier 89, and is arranged at every predetermined distance between the optical transmitter 81 and the optical receiver 82.

The optical transmitter 81 includes an optical amplifier 8 which forms an optical boost amplifier with an electro-optical converter 85 including a semiconductor laser.
7 and the like, the transmission data is converted into an optical signal by the electro-optical conversion unit 85, and the optical signal is amplified by the optical amplifier 87.
4 is sent. The optical repeater 83 is arranged at every predetermined distance of the optical transmission line 84, and the optical signal attenuated by the optical transmission line 84 is amplified by the optical amplifier 89.

Further, the optical receiving device 82 includes an optical amplifier 88 forming an optical preamplifier and a photoelectric conversion unit 86 including a light receiving element such as a pin photodiode or an avalanche photodiode.
Etc., the optical signal amplified by the optical amplifier 88 is converted into an electric signal by the photoelectric conversion unit 86, and transferred to a receiving circuit (not shown).

FIG. 9 is an explanatory view of the optical amplifier, showing a main part of an example of the optical amplifiers 87 to 89 of FIG. 8, 91 is an optical fiber amplifying section made of an erbium (Er) -doped optical fiber, and 92 is a multiplexing. , 93 is a demultiplexer, 94 is a control circuit, 9
Reference numeral 5 is a semiconductor laser for excitation, and 96 is a light receiving element for detection.

The pumping light from the semiconductor laser 95 enters the optical fiber amplifier 91 through the multiplexer 92, the optical signal is amplified in accordance with the pumping light power, and is sent out through the demultiplexer 93. It A part of the amplified optical signal output is demultiplexed by the demultiplexer 93 and incident on the light receiving element 96, the amplified optical signal output level is detected, and the control circuit 94 makes the amplified optical signal output level constant. In addition, the output power of the semiconductor laser 95 is controlled. That is, the control circuit 94
Is for controlling the semiconductor laser 95 according to a constant light output control method.

FIG. 10 is an explanatory view of the occurrence of optical surge.
(A) shows the relationship between the input level to the optical amplifier and time t, (b) shows the relationship between the gain of the optical amplifier and time t,
(C) shows the relationship between the output level of the optical amplifier and the time t. As shown in (a), at time t1, when the input level to the optical amplifier drops to 0 or is extremely reduced as indicated by the dotted line, the gain of the optical amplifier keeps the output level constant as shown in (b). Increase to.

The response speed of the optical amplifier is about 1 to 10 ms, and even if the input level suddenly drops, the gain cannot be increased following it. Then, when the input level is restored at time t2, the gain of the optical amplifier gradually decreases. In this case, if the input level is 0 or the time T during which the input level is extremely lowered is about 0.1 ms to 0.5 ms, the input level is restored when the gain of the optical amplifier becomes relatively large, and the gain is large. Since the optical signal is amplified by the optical amplifier, the output level of the optical amplifier instantaneously becomes an output level equal to or higher than the set output level as shown in (c). That is, the optical surge PS occurs.

[0011]

In an optical communication system, due to a momentary interruption of an optical signal due to an incorrect insertion / removal of an optical connector, a momentary interruption of an optical signal due to a temporary failure of an optical transmission line, or an active pre-switching, etc. When an instantaneous interruption of the optical signal occurs, the optical surge of the above-mentioned type occurs due to the provision of the optical output constant control type optical amplifier. In particular, when the optical amplifiers are cascade-connected via the optical transmission line, a large optical surge is output from the optical amplifier corresponding to the final stage.

When such a light surge is incident on the light receiving element of the optical receiving device, an excessive photocurrent may flow and the light receiving element may be destroyed. Therefore, there has been proposed a configuration that detects an instantaneous interruption of an optical signal to prevent the gain of the optical amplifier from increasing, but there is a problem that the configuration of each optical amplifier in an optical communication system becomes complicated, and It is difficult to protect the light receiving element. It is an object of the present invention to protect a light receiving element against a light surge with a simple structure.

[0013]

The optical receiving device of the present invention comprises:
Referring to FIG. 1, (1) in an optical receiver in an optical communication system including an optical amplifier such as an optical preamplifier, an optical booster amplifier, or an optical inline amplifier, the power supply terminals are connected in series. The load impedance, the light receiving element 1, and the output resistance 2 are provided, the output terminal 4 is connected to the connection point between the light receiving element 1 and the output resistance 2, and the load impedance is the absolute rated reverse current value of the light receiving element 1 or its vicinity. In the above value, the voltage applied to the light receiving element 1 is selected to be substantially zero.

(2) The load impedance of the light receiving element 1 is a resistor 3, the resistance value of the resistor 3 is R, and the power supply voltage is V.
d, the built-in voltage of the light receiving element is V _bi , the applied voltage of the light receiving element is V ₀ , the limit current value at the time of light surge input is I _L , and the current value during steady operation is I ₀ , R = (V _bi + V ₀ ) / (I _L −I ₀ ) Vd = (I ₀ · V _bi + I _L · V ₀ ) / (I _L −I ₀ ) The resistance value R of the resistor 3 is selected so as to satisfy the relational expression. To do.

(3) Further, the load impedance connected in series between the power supply terminals, the light receiving element 1 and the output resistance 2 are provided, the output terminal 4 is connected to the connection point between the light receiving element 1 and the output resistance 2, and the light receiving A capacitor may be connected in parallel to the element 1 and the output resistor 2.

(4) The output terminal 4 is connected to the load impedance connected in series between the power supply terminals, the light receiving element 1 and the output resistor 2, and the connection point between the light receiving element 1 and the output resistor 2, and the light receiving element 1 is connected. And a capacitor connected in parallel to the output resistor 2, the load impedance is a resistor, the resistance value of this resistor is R, the power supply voltage is Vd, the built-in voltage of the light receiving element is V _bi , and the built-in voltage of the light receiving element is The applied voltage is V ₀ ,
The limit current value at the time of light surge input is I _L , the current value at the time of steady operation is I ₀ , the time constant due to the resistor and the capacitor is τ, the limit time at the time of light surge input is t _L, and R = (V _bi + V ₀ ) / (I _L · P−I ₀ ) Vd = (I ₀ · V _bi + I _L · P · V ₀ ) / (I _L · P −
I ₀ ) P = {1-Y · (1-exp (−1 / Y)} Y = τ / t _L The resistance value R of the resistor and the capacitance value of the capacitor are selected so as to satisfy the relational expression. be able to.

(5) Further, a load resistance, an inductance, a light receiving element and an output resistance are connected between the power supply terminals, an output terminal is connected to a connection point between the light receiving element and the output resistance, and a light receiving element and an output resistance are connected. A capacitor may be connected in parallel to the series circuit of.

(6) Further, the load impedance can be a field effect transistor having a connection configuration of constant current characteristics.

(7) The load impedance may be a bipolar transistor, and the base bias voltage of the bipolar transistor can be adjusted.

[0020]

[Action]

(1) The optical surge generated by the optical amplifier has a surge waveform in which the level rapidly increases with the passage of time and decreases in a short time. The current flowing through the light receiving element 1 is increased as the optical level increases. Increase. A voltage drop due to the load impedance occurs as the current increases. By selecting this load impedance, the photocurrent value is limited by setting the applied voltage of the light receiving element 1 to substantially zero at the absolute rated reverse current value of the light receiving element 1 or a value in the vicinity thereof to protect the light receiving element 1. You can

(2) Further, when the input level of the optical signal is in a steady state, the light receiving element 1 is operated in a state where the junction capacitance is reduced to ensure a desired frequency characteristic and an optical surge is input. At this time, when the preset limit current value I _L is reached, in this case, if the current value flowing through the light receiving element 1 in the steady state is I ₀ and the built-in voltage of the light receiving element 1 is V _bi , R = (V _bi + V ₀ ) / (I _L −I ₀ ). Further, the power supply voltage Vd needs to be a low voltage if the limit current value I _L is set small, and Vd = (I ₀ · V _bi
+ I _L · V ₀ ) / (I _L −I ₀ ).

(3) Further, by setting the load impedance, the current flowing through the light receiving element 1 is restricted against the optical surge, and the capacitor connected in parallel with the light receiving element 1 and the output resistor 2 is in a steady state. The power supply impedance is lowered to improve the frequency characteristic of the light receiving element 1.

(4) The load impedance is a resistance,
Let CR be the time constant of τ and t _{L be} the time constant of the resistor (R) and the capacitor (C), and t be Y = τ / t _L , and P =
If {1-Y · (1-exp (-1 / Y)}, the resistance value R satisfies the relational expression of R = (V _bi + V ₀ ) / (I _L · P−I ₀ ). By making a selection, it is possible to limit the transient current, and in this case as well, the power supply voltage Vd needs to be a low voltage if the limit current I _L is set small, and therefore Vd = (I ₀ · V _bi + I _L · P ·
It is selected according to the relational expression of V ₀ ) / (I _L · P−I ₀ ).

(5) Further, when a large current flows through the light receiving element due to the optical surge input, the voltage drop due to the inductance as well as the voltage drop due to the resistance becomes large. Therefore, the voltage applied to the light receiving element is only due to the resistance. It becomes large in comparison. Therefore, it is possible to suppress an excessive current flowing through the light receiving element due to the optical surge input.

(6) Further, the load impedance is a field effect transistor, and the gate and drain of this field effect transistor are connected to have a constant current characteristic, and an excessive current flowing to the light receiving element due to an optical surge input is set to a constant current characteristic configuration. It can be suppressed by a field effect transistor.

(7) Further, the load impedance is a bipolar transistor, and an excessive current flowing in the light receiving element at the time of light surge input is suppressed by the bipolar transistor.
In addition, the base bias voltage can be adjusted to select the limit current value without depending on the power supply voltage Vd.

[0027]

1 is an explanatory view of a first embodiment of the present invention, in which (A) is a main circuit diagram, (B) is an operation characteristic curve diagram, and FIG.
(C) is a relationship curve diagram between a light surge and a current. As the light receiving element 1, a pin photodiode, an avalanche photodiode, or the like can be used, and an optical signal is input via an optical transmission path including an optical amplifier. An output resistor 2 and a resistor 3 as a load impedance are connected in series with the light receiving element 1 and a power supply voltage Vd is applied. The output terminal 4 is connected to the connection point between the light receiving element 1 and the output resistor 2. The reception processing circuit 5 is connected to the output terminal 4 to process received data.

In a steady state, the operation is performed at point B in the operation specifying curve diagram of (B) in which the horizontal axis is voltage V and the vertical axis is current I.
That is, a voltage having a value obtained by subtracting the voltage drop due to the resistor 3 from the power supply voltage Vd is applied to the light receiving element 1, and the current I ₀ flows. Then, if the light surge is input, increases the current to be directed to the operating point A from the operating point B becomes the in current I _L to the operating point A.

FIG. 3 is a curve diagram showing the relationship between the optical surge and the current in (C), where the horizontal axis is time t and the vertical axis is the input optical signal P _in , and the current in the light receiving element 1 is proportional to the input optical signal P _in. When I (t) flows, the optical signal P _{0 in the} steady state becomes the maximum input optical signal P _max due to an optical surge, and when the input is again in the steady state, the current flowing through the light receiving element 1 is as shown by the dotted line. Changes to. That is, the current flowing in the light receiving element 1 increases due to the optical surge input, but the voltage drop due to the resistor 3 increases accordingly. By selecting the resistance value R of the resistor 3, the current flowing in the light receiving element 1 becomes I _L Limited to.

Voltage drop e due to the aforementioned limit current I _L
Is e = I _L · R, where R is the resistance value of the resistor 3. In this case, in order to approximate the voltage applied to the light receiving element 1 to 0V, this voltage drop e needs to be equal to the power supply voltage Vd. Note that it is necessary to consider the built-in voltage V _bi of the light receiving element 1, and therefore the relationship of Vd + V _bi = I _L · R needs to be established, and the resistance value R of the resistor 3 is required.
Becomes R = (Vd + V _bi ) / I _L (1)

On the other hand, in the steady state, the voltage applied to the light receiving element 1 needs to be a predetermined value V ₀ . Therefore,
Assuming that the current of the light receiving element 1 at constant time is I ₀ , V ₀ = Vd−I ₀ · R (2), and from the formulas (1) and (2), R = (V _bi + V ₀ ) / _{(I L -I 0) ... (} 3) Vd = relational expression _{(I 0 · V bi + I} L · V 0) / (I L -I 0) ... (4) is obtained. That is, the resistance value R of the resistor 3 and the power supply voltage Vd are set so as to satisfy the relational expressions of the equations (3) and (4), so that the light receiving element 1 can receive light surges. To the desired limit current I _L
To protect the optical receiver.

2A and 2B are explanatory views of a second embodiment of the present invention. FIG. 2A is a circuit diagram of a main part, and FIG. 2B is an operation characteristic curve diagram. The same reference numerals as those in FIG. 1 denote the same portions, and show the case where the load impedance connected in series with the light receiving element 1 is the variable resistor 6. In this embodiment, by adjusting the voltage Vd applied to the light receiving element 1, the equivalent capacitance value of the light receiving element 1 changes, and the light receiving frequency characteristic can be adjusted to some extent. In that case, since will change the limit current I _L in accordance with the change in the power supply voltage Vd, is adjusted to maintain the limit current I _L to a predetermined value by the variable resistor 6.

In the operating characteristic curve diagram (B), the horizontal axis represents the voltage V, the vertical axis represents the current I, and V _bi represents the built-in voltage of the light receiving element 1. When the steady-state operating point when the power supply voltage is Vd1 is B, a current I ₀ flows through the light receiving element 1. Then, as described above, when an optical surge is input,
Although the current flowing through the light receiving element 1 increases toward the operating point A, it is limited to the limit current value of I _L1 . Also when the power supply voltage is Vd2 (> Vd1), the light surge is input, the current flowing through the light receiving element 1 is increased toward the operating point D from the operating point C, the current limit of I _L2. In this case, I _L1 <I _L2 . Therefore, when the power supply voltage is increased to Vd2 by adjusting the variable resistor 6, the operating point in the steady state is set to E. As a result, when an optical surge is input, the current increases toward the operating point A and is limited to the same limit current value of I _L1 as when the power supply voltage is Vd1.

3A and 3B are explanatory views of a third embodiment of the present invention. FIG. 3A is a circuit diagram of a main part and FIG. 3B is an equivalent circuit. In this embodiment, a light receiving element 1, an output resistor 2 and a resistor 3 as a load impedance are connected in series to apply a power supply voltage Vd, and an output terminal 4 is connected to a connection point between the light receiving element 1 and the output resistor 2. The capacitor 7 is connected in parallel to the series circuit of the light receiving element 1 and the output resistor 2. Normally, the capacitor 7 is charged by the power supply voltage Vd through the resistor 3, but the charged electric charge is supplied to the light receiving element 1 at the time of light surge input, and the power supply impedance can be equivalently lowered. .

(B) shows an equivalent circuit of (A) at the time of optical surge input, and the current i flowing through the light receiving element 1 is i = i ₁ + i
_The output resistance 2 is about 50 Ω and can be ignored. Matahikari the rate of increase in input power of the surge I _P
If it is / a, it can be expressed as follows. I ₂ / C + R · (di ₂ / dt) = R · I _P / a Current i ₂ flowing from the differential equation in the capacitor C _{is, i 2 = τ · I P} / a · {1-exp (-t / τ)} ... a (5). Here, τ indicates the time constant of CR.

The voltage drop e (t) due to the resistor 3 as the load impedance is: e (t) = R · _IP / a · [t−τ · {1-exp (−t / τ)}] (6 ).

FIG. 4 is a diagram for explaining the operation of the third embodiment of the present invention. (A) is the current i ₂ , (B) is the current i ₁ , (C).
Indicate the changes in the current i when the optical surge is input.
In (B), the dotted line shows the increase in the current flowing through the resistor 3 when the capacitor 7 is not connected, and the solid line shows the increase in the current when the capacitor 7 is connected.

The limit time t _L until the predetermined limit current I _L is reached is expressed by t _L = I _L · a / I _P (7), and the voltage drop of the resistor 3 at the limit time t _L Is approximated to the power supply voltage Vd, and a predetermined limit current I _L
To satisfy Y = τ / t _L, and P = [1-Y · {1
−exp (1− / Y)}], Vd + V _bi = I _L · R · P (8) Accordingly, the resistance value R becomes _{R = (Vd + V bi)} / I L · P ... (9).

On the other hand, in a steady state, it is necessary to set the voltage applied to the light receiving element 1 to be a predetermined voltage V ₀ , so that V ₀ = Vd−I ₀ · R (10) Therefore, from the equations (9) and (10), R = (V _bi + V ₀ ) / (I _L · P−I ₀ ) ... (11) Vd = (I ₀ · V _bi + I _L · P · V ₀ ) / (I _L · P−I ₀ ) ... (12), and by setting the resistance value R and the power supply voltage Vd so as to satisfy these conditions, when an optical surge is input , (C), the current can be limited to I _L for protection.

5A and 5B are explanatory views of the fourth embodiment of the present invention. FIG. 5A is a circuit diagram of a main part and FIG. 5B is an operation characteristic curve diagram. In this embodiment, an output resistor 2, a resistor 3 as a load impedance, and an inductance 8 are arranged in series with the light receiving element 1.
And the power supply voltage Vd are applied, the output terminal 4 is connected to the connection point between the light receiving element 1 and the output resistance 2, and the capacitor 7 is connected in parallel to the series circuit of the light receiving element 1 and the output resistance 2. It is a thing.

In the operating characteristic curve diagram (B), the horizontal axis represents the voltage V, the vertical axis represents the current I, and V _bi is the built-in voltage of the light receiving element 1. During the constant time, the current I ₀ flows due to the power supply voltage Vd. In the case where the inductance 8 is not connected and an optical surge is input, the current increases along the operation curve shown by the dotted line and becomes the limit current of I _La .
However, since the inductance 8 is connected, the voltage drop due to the inductance 8 is added to the voltage drop due to the resistance 3, and the operation curve shown by the solid line is obtained. Therefore, it becomes the limit current of I _Lb , and the current flowing when the optical surge is input can be limited to protect the optical receiving device.

6A and 6B are explanatory views of the fifth embodiment of the present invention. FIG. 6A is a circuit diagram of a main part and FIG. 6B is an operation characteristic curve diagram. In this embodiment, the field effect transistor 10 is used as a load impedance connected in series to the light receiving element 1, and the field effect transistor 10 is connected so as to have a constant current characteristic. Also, the light receiving element 1 and the output resistance 2
The output terminal 4 is connected to the connection point with.

In the steady state, in the operation characteristic curve diagram of (B), the current I ₀ is set so as to flow by the power supply voltage Vd. When an optical surge is input, the current flowing in the light receiving element 1 is set. However, the constant current connection configuration of the field effect transistor 10 limits the current to the limit current of I _L. Therefore, the current flowing when the light surge is input is limited by the field effect transistor 10, and the light receiving device can be protected.

7A and 7B are explanatory views of a sixth embodiment of the present invention, FIG. 7A is a circuit diagram of a main portion, and FIG. 7B is an operation characteristic curve diagram. In this embodiment, a bipolar transistor 11 is used as a load impedance connected in series to the light receiving element 1, a bias voltage is applied to the base by a resistor 12 and a variable resistor 13, and a connection point between the light receiving element 1 and the output resistor 2 is added. Connect the output terminal 4 to.

In the steady state, in the operation characteristic curve diagram of (B), the current I ₀ is set to flow by the power supply voltage Vd, and when an optical surge is input, the current I ₀ flows to the light receiving element 1. Although the current will increase, the bipolar transistor 11 will limit it to the limit current of I _L corresponding to the bias voltage. Therefore, even if an optical surge is input, the current flowing through the light receiving element 1 is limited and the optical receiving device can be protected. Further, since the bias voltage can be adjusted by the variable resistor 13, the limit current I _L can be adjusted to a predetermined value regardless of the power supply voltage Vd.

[0046]

As described above, according to the present invention, in an optical receiver in an optical communication system including an optical amplifier, when an optical surge is output from the optical amplifier due to a momentary interruption of an optical signal. The advantage that the voltage applied to the light receiving element 1 is reduced by the voltage drop due to the load impedance connected in series to the light receiving element 1 so that an excessive current does not flow and the optical receiving device can be protected There is.

Further, the load impedance is a resistor 3,
The resistance value R is set so that the conditions of the expressions (3) and (4) are satisfied.
By setting the power supply voltage Vd and the power supply voltage Vd, there is an advantage that an excessive current due to a light surge can be suppressed. Further, when the capacitor 7 is connected in parallel to the series circuit of the light receiving element 1 and the output resistor 2, the power source impedance is reduced to improve the frequency characteristic, and the transient excessive current when the light surge is input is used. Is also based on the CR time constant (1
By selecting the resistance value R, the power supply voltage Vd, and the capacitance C of the capacitor so as to satisfy the conditions of the equations (1) and (12), it is possible to suppress an excessive current due to a light surge. There is.

When the load impedance is composed of the resistor 3 and the inductance 8, a steep rising current due to an optical surge flows through the light receiving element 1. However, since the inductance 8 limits the load impedance, it is more than the case of the resistor 3 alone. Can suppress an excessive current due to a light surge.

When the load impedance is constituted by the field effect transistor 10 or the bipolar transistor 11, the current flowing in the light receiving element 1 can be limited by the active load characteristic thereof, so that an excessive current due to a light surge is suppressed. There is an advantage that can be done.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a sixth embodiment of the present invention.

FIG. 8 is an explanatory diagram of an optical communication system.

FIG. 9 is an explanatory diagram of an optical amplifier.

FIG. 10 is an explanatory diagram of occurrence of optical surge.

[Explanation of symbols]

1 Light receiving element 2 output resistance 3 Resistance as load impedance 4 output terminals

Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04B 10/28 (72) Inventor Hiroshi Hamano 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor, Tsuyoshi Ihara Kawasaki, Kanagawa Prefecture 1015 Kamiodadanaka, Nakahara-ku, Fujitsu Ltd. (72) Inventor Kazuo Hagimoto 1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo Tokyo Telegraph and Telephone Corporation (72) Inventor, 1-chome, Uchiyuki-cho, Chiyoda-ku, Tokyo No. 6 in Nippon Telegraph and Telephone Corporation (56) Reference JP 61-163738 (JP, A) JP 4-180315 (JP, A) JP 5-206765 (JP, A) JP JP 4-183124 (JP, A) JP-A-7-162369 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14 / 08

Claims (2)

(57) [Claims] 1. An optical receiver in an optical communication system including an optical amplifier such as an optical preamplifier, an optical booster amplifier, or an optical inline amplifier, and a load impedance, a light receiving element and an output connected in series between power supply terminals. A resistor, and a configuration in which an output terminal is connected to a connection point between the light receiving element and the output resistor, wherein the load impedance is a resistor, and the resistance value of the resistor is
R, power supply voltage Vd, built-in voltage of the light receiving element
V _bi , the applied voltage of the light receiving element is V ₀ , when an optical surge is input
Current limit I _L, the current value during normal operation and I ₀ for
_{And, R = (V bi + V} 0) / (I L -I 0) Vd = (I 0 · V bi + I L · V 0) / to satisfy (I _L -I ₀₎ relationship, the Select the resistance value R of the resistor
Optical receiver, characterized in that the. 2. An optical preamplifier or an optical booster amplifier or
Optical communication system equipped with optical amplifier such as optical in-line amplifier
In the optical receiver in the optical system, load impedance and light reception connected in series between the power supply terminals
An element and an output resistance, wherein the light receiving element and the output resistance
Connect the output terminal to the connection point of the
There is a configuration in which a capacitor is connected in parallel with the force resistance.
The load impedance as a resistance, and the resistance value of the resistance is
R, power supply voltage Vd, built-in voltage of the light receiving element
V _bi , the applied voltage of the light receiving element is V ₀ , when an optical surge is input
The limit current value of I _L , the current value during steady operation I ₀ ,
The time constant of the resistor and capacitor is τ,
Letting the limit time at the time of force be t _L , R = (V _bi + V ₀ ) / (I _L · P−I ₀ ) Vd = (I ₀ · V _bi + I _L · P · V ₀ ) / (I _L · P −I ₀ ) P = {1-Y · (1-exp (−1 / Y)} Y = τ / t _{L so that} the relational expression of the resistance R and
An optical receiver characterized in that the capacitance value of the capacitor is selected .