JPH0697888A - Optical level adjusting circuit - Google Patents

Abstract

PURPOSE:To quickly set the reception level of an optical receiver and the transmission level of an optical transmitter to optimum levels. CONSTITUTION:The optical level adjusting circuit which detects the level of the optical signal passing an optical variable attenuator 11 by a photodetector 12 and adjusts the extent of attenuation of the optical variable attenuator 11 in accordance with the output level of the photodetector 12 is characterized by using a field absorption type modulator as the photodetector 12 and using the DC, which flows in accordance with the DC voltage applied to this field absorption type modulator and the optical level, for adjustment of the extent of attenuation of the optical variable attenuator 11 and adjusting the optical output transmitted through the field absorption type modulator into a certain value and is characterized by providing the means which uses the DC of the photodetector 12 to read the optical output level of the photodetector 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical level adjusting circuit, and more particularly to a circuit using an electroabsorption modulator as an optical variable attenuator or a light receiving element. Generally, an optical receiver is required to have a wide dynamic range of light, but it is very difficult to improve the minimum receiving input level and the maximum receiving input level at the same time. Therefore, there is a method of expanding the dynamic range of light by adding an optical attenuator element in the front stage of the optical receiver and adjusting the maximum reception input level.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a conventional optical level adjusting circuit. In the figure, 1 is a light receiving element, 2 is a preamplifier circuit, 3 is a feedback circuit, 4 is an optical attenuator, and each of the elements 1 to 4 is a component of an optical receiver (referred to as OR). The optical input signal 101 is converted into an electric signal by the light receiving element 1 via the optical attenuator 4 and sent to the preamplifier circuit 2. The electric signal amplified by the preamplifier circuit 2 is output as the output signal 102 and is also input to the feedback circuit 3. The feedback circuit 3 outputs the level control signal 103 corresponding to the input of the output signal 102, and changes the attenuation amount of the optical attenuator 4. As a result, the level of the output signal 102 converges within a predetermined range.
As an example of the conventional technique, refer to Japanese Patent Application No. Hei 1-164424, which was published as a patent application on Feb. 4, 1991.

[0003]

Since the conventional light detecting element incorporated in the receiver is used for the detection of the optical level, the receiving level cannot be directly read and the optimum receiving level cannot be detected. There is a drawback that the holding is not performed reliably, and it is not suitable for the purpose of independently using a constant level optical signal.

On the other hand, the conventional variable optical attenuator mainly has a structure in which the light transmittance is mechanically changed as shown in FIG. 8, but since there are movable parts, the adjustment speed is slow and the shape is small. It becomes big. In addition to this, although not shown in the figure, a method utilizing an electro-optical effect or a magneto-optical effect is also conceivable. However, the former requires a relatively high control voltage, and the latter requires current control to change the magnetic field. Both of them have a problem in that a relatively large-scale control circuit is required as the device becomes smaller.

[0005]

FIG. 1 is a diagram for explaining the principle of the present invention. In the figure, 11 is a first electro-absorption modulator (referred to as EA) that attenuates the optical input signal 101, and 12 is a second EA, which is an optical signal attenuated by the first EA 11.
It detects 104 light levels.

[0006]

As shown in FIG. 2 (a), the light transmittance of EA (the ratio of the optical power appearing at the optical output end after passing through the EA to the optical power input from the optical input end) is applied. Voltage (refers to the DC voltage V _D applied between the modulation electrodes)
It depends on the value of. Further, as shown in FIG. 2B, when the optical input level (which is the value of power) is changed while the applied voltage is kept constant, the current flowing through the EA increases or decreases depending on the optical input level. That is, it is shown that the EA has a function as a light receiving element whose sensitivity can be adjusted depending on the value of the applied voltage.

In the configuration of FIG. 1, the first EA 11 is used as an optical variable attenuator and the second EA 12 is used as a light receiving element. The optical input signal 101 undergoes a certain amount of attenuation at the first EA11 and is input to the second EA12 as an optical signal 104. The light receiving sensitivity is adjusted by adjusting the applied voltage 106 of the second EA 12. The control amplifier 14 regulates the voltage of the first EA 11 until the current of the second EA 12 matches the value corresponding to the reference value of the output level 105. as a result,
The level of the optical output signal 105 is maintained at the set constant value.

Further, as is apparent from FIG. 2 (b), the current of the second EA12 is changed by an appropriate means, for example, a stable DC amplifier,
After amplification, the optical signal level can be read after amplification by a suitable display means, for example an ammeter. Therefore, even if the receiver input level (that is, the optical signal level from the transmission line) fluctuates, by inserting the circuit of FIG. 1 into the input of the receiver, the input level of the receiver can be arbitrarily set. It is possible to maintain a constant value of.

[0009]

FIG. 3 is a block diagram of the first embodiment of the present invention. In the figure, 11 is an optical variable attenuator, which changes the amount of attenuation given to an optical signal electrically, magnetically or mechanically, 12 is E
A is a light receiving element, and 14 is a DC amplifier for amplifying the DC current fluctuation of the EA 12 used as a light receiving element to change the applied voltage (or current) of the variable optical attenuator 11. Optical signal 101 input to the variable optical attenuator 11
Is the voltage (or current) applied to the variable optical attenuator 11.
To become an optical signal 104. The attenuated optical signal 104 is input to the EA 12, and a DC current is output according to the value of the DC voltage 106 applied to the EA, and at the same time, a constant attenuated optical signal 105 is output. E
Although the amount of attenuation of A changes depending on the DC applied voltage, the sensitivity can be adjusted at the same time. Therefore, the output level can be set to a target value by adjusting the applied voltage. Of course, it is possible to set the level in a wider range by inserting a separate optical attenuator in the optical path.

FIG. 4 is a block diagram of the second embodiment of the present invention. In the figure, 11 is the one used as an optical variable attenuator in the first EA, 12 is the one used as the light receiving element in the second EA, 105 is an optical output signal, 21 is an optical receiver, and the optical signal is electrically supplied. It is converted into a signal. Others are the same as FIG. In the case of this configuration, when the optical level from the transmission line (hereinafter referred to as the reaching level) is high, the attenuation amount of the EA automatically increases, and when the reaching level is low, the EA The amount of attenuation is automatically reduced so that the input level of the receiver can always be kept at the optimum level. On the other hand, when the reached level changes suddenly, unlike the conventional adjusting means, the adjustment is rapidly performed and the optimum input level is immediately returned.

In the case of the configuration diagram of this embodiment, the first EA 11 and the second EA 12 can be integrated, which is extremely useful for miniaturization and high performance. FIG. 5 is a block diagram of the third embodiment of the present invention. In the figure, 11 is used as an optical variable attenuator in the first EA, 12 is used as a light receiving element in the second EA, 105 is an optical output signal, and 22 is an optical transmitter (O
Say S. ), The electrical signal is converted into an optical signal. Others are the same as FIG. In the case of this configuration, the optical output level of the optical transmitter 22 can be arbitrarily set, as in the case of the second embodiment.

In the case of the present embodiment configuration example, the first EA 11 and the second EA 12 can be integrated as well as the third embodiment configuration example, and further, the modulator of the optical transmitter 22 can be further incorporated. It can also be integrated with a laser diode or the like, which is extremely useful for downsizing and high performance of an optical transmitter having a built-in level adjustment function. FIG. 6 is a block diagram of the fourth embodiment of the present invention. Reference numeral 15 in the drawing denotes a display section drive circuit, which is used for the display section 16 to display a level corresponding to the value of the light output level 105. Others are the same as in the case of the second embodiment.

In the above embodiment, the level adjustment is performed by proportional control for convenience of explanation, but the same effect can be obtained by other control methods.

[0014]

As described above, according to the present invention,
It is possible to easily set the reception level of the optical receiver to the optimum level, and it is possible to quickly adjust to rapid changes in the reaching optical signal level, and to stabilize the transmission level of the optical transmitter. It is useful, and by integrating EA, it is extremely useful for downsizing and high performance of optical transmitters and receivers. Furthermore, there is an effect that it can be used for independent level measurement.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a characteristic example of EA used in the practice of the present invention.

FIG. 3 is a configuration diagram of a first embodiment of the present invention.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 7 is a conventional configuration example.

FIG. 8 is a principle diagram of a conventional variable optical attenuator.

[Explanation of symbols]

 1, 12 Light receiving element 2 Preamplifier 3 Feedback circuit 4, 11 Optical variable attenuator 14 Control amplifier 15 Display drive circuit 16 Display 21 Optical receiver (OR) 22 Optical transmitter (OS)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Ken Onishi 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Kazuhiro Suzuki, 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor ▲ Masahiro Tada 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (3)

[Claims] 1. An optical level adjusting circuit for detecting the level of an optical signal that has passed through an optical variable attenuator with a light receiving element and adjusting the attenuation amount of the optical variable attenuator according to the output level of the light receiving element. An electroabsorption modulator is used as the element (12), and the attenuation amount of the variable optical attenuator (11) is adjusted by using the DC voltage applied to the electroabsorption modulator and the DC current flowing according to the optical level. Then, the optical level adjustment circuit is characterized in that the optical output transmitted through the electro-absorption modulator is adjusted to a constant value. 2. The optical level adjusting circuit according to claim 1, wherein an electroabsorption modulator is used as the variable optical attenuator (11). 3. A light level adjusting circuit according to claim 1, further comprising means for reading the light output level of the light receiving element (12) by utilizing the direct current of the light receiving element (12).