JPH06188834A - DC coupled optical receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the reception level of an optical receiver and reduce the skew for optical input changes. [Composition] A device for generating DC light and a multiplexer are provided, and DC light is superimposed on input light. [Effect] Since the direct-current light can be superimposed on the signal light by adjusting the light quantity of the direct-current light generator, the minimum light receiving level of the optical receiver can be improved and the skew can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the receiving performance of an optical receiver used for optical communication.

[0002]

2. Description of the Related Art In optical fiber communication for transmitting burst signals such as machine control signals and computer data signals, the ability to receive light from direct current to high frequency components is required.
In such a DC direct-coupled receiver, the receiving sensitivity of the receiver is generally determined not by the noise generated by the preamplifier but by the set value of the threshold level of the discriminator. This is because it is difficult to add an automatic gain control circuit to long bit series close to DC,
This is because it is necessary to avoid the risk of code error due to amplifier noise. In addition, as an example of a method for ensuring transmission quality by superimposing DC light on an optical signal to be transmitted,
Proceedings of the 1992 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers B-69
There is a description in 3.

[0003]

However, in the conventional direct current direct coupling type optical receiver, the receiving sensitivity is determined by the set value of the discrimination level, and depending on the set value, it is much larger than the performance of the preamplifier. It is often impossible to receive at the level. Therefore, it is necessary to replace the receiver itself when extending a transmission line of a communication system already installed or when temporarily branching an optical path.

When a plurality of optical fibers are used to secure the transmission capacity by parallel transmission, the fiber length is adjusted to reduce variations in transmission delay amount of each channel, that is, skew, and the light receiving level is reduced. It was necessary to arrange.

An object of the present invention is to provide an optical receiver for improving the receivable level or reducing the skew with respect to the change of the optical input level according to the usage condition of the device.

[0006]

In order to solve the above-mentioned problems, the present invention is provided with a device for generating DC light of a certain level and a multiplexer, and the device superimposes DC light on signal light. Has become. Further, the wavelength of the DC light to be combined is substantially the same as the wavelength of the received signal light.

[0007]

The optical multiplexer has a function of superposing the DC light from the DC light generator on the signal light. Further, by making the wavelength of the DC light to be multiplexed substantially equal to the wavelength of the received signal light, the photodetector can convert both the signal light and the DC light into an electric current. The photocurrent from the photodetector is amplified by the preamplifier and then discriminated and reproduced by the discriminator. The discrimination operation at this time is performed by comparing the high level of light with the discrimination level of the discriminator. Therefore, reception becomes impossible at an optical input level below the identification level. However, if a constant DC light is superposed in this state, the DC component can be sensed and the optical high level can be made higher than the discrimination level, so that the signal can be received. This state is shown in FIG. Figure (a)
Shows the case where there is no DC light, and FIG. In addition, a signal to be transmitted always has a rising time and a falling time. Therefore, in parallel transmission, when one of the two channels has a large optical input and the other has a small input just for identification, a large skew (t
1) occurs. However, since the level difference of the input light can be reduced by superimposing the DC light, the skew can be alleviated (t2).

[0008]

EXAMPLE An example of the present invention will be described with reference to FIG. In
A GaAs-PIN photodiode receiver 1 with pigtail fiber, a transimpedance type preamplifier 2 of, for example, about 1 kilo ohm and 100 MHz, and a differential amplification type discriminator 3 having a discrimination level of 0.1 volt are respectively DC coupled. The receiver is configured by using the same and is mounted in the same metal case. The direct current light source 4 and the light output control circuit 5 which are the laser diode modules having the wavelength of 1.55 μm constitute a direct current light generating section. The multiplexer 6 including the dielectric multilayer filter multiplexes the signal input light of 1.3 μm and the DC light of 1.55 μm and inputs the multiplexed light to the receiving unit. These are mounted on a single printed board.

By adjusting the light output level of the light output control circuit of the DC light generating section, the minimum level of light that can be received can be improved as compared with the case where DC light is not superimposed. Moreover, when high-speed modulated signal light is input, the skew of the reproduced waveform due to the change of the optical input level can be reduced. At this time, even if the wavelength of the DC light is substantially the same as the wavelength of the signal light, it is sufficiently effective to use a coupler with little loss. Further, although the laser diode is used as the light source of the DC light, other light sources can be used.

[0010]

According to the present invention, it is possible to superimpose DC light on signal light by adjusting the light quantity of the DC light generator.
The minimum light receiving level of the optical receiver can be improved, and the skew due to the change of the optical input level can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment according to the present invention.

FIG. 2 is a diagram illustrating an operation according to the present invention.

[Explanation of Codes] 1 ... Photoreceiver, 2 ... Preamplifier, 3 ... Discriminator, 4 ... DC light source, 5 ... Optical output control circuit, 6 ... Multiplexer.

Claims (3)

[Claims] 1. An optical receiver having a light receiver, a preamplifier, and a discriminator, which is capable of detecting an optical modulation signal and a direct current component,
Equipped with a device that generates a certain level of DC light and a multiplexing device,
A DC-coupled optical receiver having a function of adjusting reception sensitivity of an optical receiver by superimposing DC light on signal light by the device. 2. The DC coupled optical receiver according to claim 1, wherein the wavelength of the DC light to be combined is substantially equal to the wavelength of the received signal light. 3. An optical receiver according to claim 1, wherein the optical receiver has a function of adjusting a skew at the time of reception.