JPH05268169A - Optical receiver - Google Patents

Abstract

PURPOSE:To provide an optical receiver for which amplification is implemented over a broad band with low noise and waveform distortion is more completely corrected in a process in which the frequency component of a reception signal is split into some frequency bands and each frequency component is amplified. CONSTITUTION:A received signal light 101 is split into 5 frequency bands by an optical frequency decomposing device 1 at an optical frequency region. The signal light split to each frequency band is amplified by an optical amplifier array 2. The output light is converted into an electric signal by a photoelectric converter array 3, subjected to a proper delay respectively, the resulting signals are summed by an adder 4 and an equalizing signal 102 is obtained. Furthermore, the frequency passing characteristic of the optical filter in the optical frequency decomposing device is controlled via a wavelength control circuit 5 by detecting the output of the photoelectric converter array 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for optical fiber communication, optical information processing and the like.

[0002]

2. Description of the Related Art In optical fiber communication, an intensity modulated signal obtained by modulating a current injected into a semiconductor laser with a signal source is transmitted through an optical fiber serving as a transmission line, and a photoelectric conversion element such as a PIN diode is used. Intensity modulation-direct detection communication devices received by an optical receiver are mainly used. In this communication device, in the 1.5 μm band transmission, which is the wavelength band in which the loss of the optical fiber is the minimum, if the communication is performed at a transmission speed of gigabit or more, the dispersion of the optical fiber may influence the quality deterioration after the transmission. Known (M. Sh
ikada et al. , "Long-Distan
ce Gigabit-Range Optical
Fiber Transmission Experi
mens Employing DFB-LD's
and InGaAs-APD's, "IEEE Jo
local if LightwaveTechnol
ology, Vol. LT-5, No. 10, pp. 148
8-1497).

In recent years, research on optical amplifiers has been carried out, and direct amplification relay systems using optical amplifiers have also been actively studied (S. Yamamoto et al., “516k”).
m2.4Gb / s Optical Fiber Tr
MISSION EXPERIMENT USI
ng 10 Semiconductor Laser
Amplifiers and Measurememe
nt of Jitter Accumulatio
n, "17th Conference on Inte
grated Optics and Optical
Fiber Communication, Post-
Deadline Papers 20PDA-9). In such a direct amplification repeater system, loss can be compensated and the transmission distance can be extended, and therefore, the possibility of transmission over a very long distance is expected. In such ultra-long-distance transmission, the distortion of the received waveform due to the influence of the dispersion of the above-mentioned optical fiber is the main factor that limits the transmittable distance.

As a conventional technique for correcting received waveform distortion due to optical fiber dispersion, for example, as shown in FIG. 4, an optical frequency decomposer is used to divide the frequency components contained in the received signal into several frequency bands. , There is a method of obtaining an equalized signal by receiving each of them by a photoelectric converter and converting them into an electric signal, appropriately multiplying and delaying each electric signal, and adding them.

[0005]

In the conventional waveform equalizing means described above, the frequency component of the received signal is divided into several frequency bands, and a wide band is obtained in the process of amplifying each frequency component. An electric amplifier is required, and it is difficult to realize an electric amplifier that has a flat frequency characteristic from DC to high frequencies. Also, since the electric circuit becomes complicated and the circuit noise increases, the waveform distortion can be corrected, but the signal pair There is a drawback that the noise ratio is reduced.

It is an object of the present invention to perform wide band and low noise amplification in the process of amplifying a received signal divided into each frequency band to more completely correct waveform distortion.

[0007]

The optical receiving apparatus of the present invention comprises:
An optical frequency decomposing unit that divides an optical reception signal into n frequency bands (n is an integer of 2 or more) to generate an optical signal for each frequency band, and each of the optical frequency decomposing units divided into frequency bands by the optical frequency decomposing unit. N optical amplifiers that change the intensity of optical signals, n photoelectric converters that receive the outputs of these optical amplifiers, and n delay devices that delay the output signals of these photoelectric converters, respectively. And an adder that adds the outputs of these n delay devices, and compensates the waveform distortion of the received signal by adjusting the amplification factor of the optical amplifier and the delay amount of the delay device. ..

[0008]

In the optical receiving apparatus of the present invention, the received signal is divided into several frequency bands in the optical frequency domain, each frequency-divided optical signal is appropriately multiplied, and then received by the photoelectric converter. To do. Appropriate delay is applied to the output signal of each photoelectric converter, and each is added to obtain a signal close to the transmission source signal, suppressing the sensitivity deterioration of the optical receiver due to the dispersion of the transmission path that occurs after transmission. Moreover, since the light is amplified by the optical amplifier before being received by the photoelectric converter, it is possible to have the effect of improving the reception sensitivity by increasing the multiplication factor of the optical amplifier.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an optical receiving device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reception is performed in the following procedure. First, the transmitted signal light 101 has five frequencies in the optical frequency range by the optical frequency decomposing device 1 including the optical branching device 6 and the Fabry-Perot type optical filters 21 to 25 shown in FIG. Divided into bands. The signal light divided into each frequency band is amplified by an optical amplifier array 2 using semiconductor optical amplifiers arranged in an array. The output light is converted into an electric signal by a photoelectric converter array 3 using photodiodes arranged in an array, and each electric signal is delayed appropriately. Then, each signal is added by an adder 4 using a power branching element. And the equalized signal 102 is obtained. The frequency pass characteristics of the optical filters 21 to 25 are controlled via the wavelength control circuit 5 by detecting the output of the photoelectric converter array 3.

In this configuration, an optical signal with a center wavelength of 1.5 μm band ideally intensity-modulated by a LiNbO ₃ external modulator with a random pattern of 10 Gb / s is 1.
An optical fiber having a zero-dispersion wavelength of 3 μm is transmitted after being transmitted for 100 km. First, in order to obtain a reception characteristic similar to that of an ordinary receiver, the gains of the five semiconductor amplifiers in the optical amplifier array are made the same and the delay amounts of the variable delay units 11 to 15 are made the same. Intersymbol interference occurs in the output, causing a large waveform distortion, which makes reception impossible. Then, the optical signal 101 is received by the optical receiving device of the present invention using the optical filters 21 to 25 in the optical frequency decomposing device as shown in FIG. When the amplification factor of the semiconductor amplifier and the delay amounts of the variable delay devices 11 to 15 were adjusted, it was possible to reproduce the waveform close to the transmission signal. The amount of deterioration of the reception sensitivity at this time was about 0.5 dB as compared with the reception sensitivity of back-to-back, and good reception characteristics were obtained. Further, when the amplification factor of the optical amplifier is increased, the optical amplifier operates as an optical preamplifier, which is different from the conventional receiving apparatus shown in FIG. 4 which is configured by an electric amplifier without using the optical amplifier. , As a receiving sensitivity improvement effect of 13 dB
Was obtained.

The present invention has various modifications other than the above. As a signal to be received, a method of directly modulating an injection current of a semiconductor laser can be used as a modulation method, and a transmission signal speed is not limited to 10 Gb / s, and a transmission signal speed of 20 Gb / s or more and 5 Gb / s or less But good. In addition, the signal light wavelength is not limited to the 1.5 μm band but 1.3 μm.
It may be in the m band, or may have another wavelength. Further, a light source other than coherent light such as a light emitting diode may be used.

The optical fiber, which is a transmission line that gives distortion to the signal light during transmission, is not limited to a dispersion fiber, but may be a dispersion shift fiber, and the length is not limited to 100 km and may be more or less.

The optical filter is not limited to the Fabry-Perot type, but may be a Mach-Zehnder type or any other type of optical filter. Further, the frequency division is not limited to five, but may be more than ten or less than four.

The number of optical amplifiers, the number of variable delay devices, and the number of photoelectric converters are not limited to those in this embodiment, and may be more or less depending on the number of divisions.

The optical amplifiers are not limited to the semiconductor optical amplifier array, but may be individual ones, or Er-doped optical fiber amplifiers and other rare earth-doped optical fiber amplifiers.

The photoelectric converter is not limited to an array type using photodiodes, but may be an individual one, a photoconductive device, or another photoelectric conversion element.

The variable delay device may be a waveguide type variable delay element, and the length of the delay line may be fixed if the delay amount is determined.

As the adder, an adder circuit which can be realized by a conventional electric circuit technique can be used instead of using the power branching element.

[0019]

As described above, according to the present invention, it is possible to easily and stably perform the optical reception that compensates the influence of the dispersion even in the high-speed / long-distance transmission in which the influence of the dispersion of the transmission line is great. In addition to the effect that the device can be obtained, it also has the effect of improving the reception sensitivity. Also, the multiplication factor,
By changing the delay amount, an effect as an optical filter can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an optical frequency decomposing device.

FIG. 3 is a diagram showing characteristics of an optical filter.

FIG. 4 is a block diagram of a conventional method.

[Explanation of symbols]

 1 Optical Frequency Decomposing Device 2 Optical Amplifier Array 3 Photoelectric Converter Array 4 Adder 5 Wavelength Control Circuit 6 Brancher 11-15 Variable Delay Device 21-25 Optical Filter 31-35 Photoelectric Converter 41-45 Electric Amplifier 101 Signal Light 102 Equalized signal

Claims (1)

[Claims] 1. An optical frequency decomposing device for dividing an optical received signal into n frequency bands (n is an integer of 2 or more) to generate an optical signal for each frequency band, and a frequency band by this optical frequency decomposing device. N optical amplifiers that change the intensity of each of the divided optical signals, n photoelectric converters that receive the outputs of these optical amplifiers, and the output signals of these photoelectric converters are delayed. n delay devices and these n
An optical receiver including an adder for adding the outputs of the delay devices, and compensating the waveform distortion of the received signal by adjusting the amplification factor of the optical amplifier and the delay amount of the delay device.