JPS5848513A - Optical amplifier for wave shaping - Google Patents

Abstract

PURPOSE:To obtain a waveform suitable for long-distance transmission and time division for an ultrahigh speed signal shaping and amplifying the waveform of an optical pulse, by providing an optical fiber inducing and scattering amplifying medium and an optically exciting mode synchronizing laser. CONSTITUTION:A part of an optical pulse 1 is transmitted by an optical branching device 2 to a timing extracting circuit 3. The circuit 3 extracts a clock frequency of the pulse 1, controls an optically exciting mode synchronizing laser 5 and synchronizes a mode synchronizing optical pulse 6 to the clock frequency. The pulses 1 and 6 are superimposed and made incident to an optical fiber inducing and scattering amplifying medium 8. From the exit light, an excited light transmitted at an optical branching device 9 is eliminated to obtain an optical pulse code train wave-shaped and amplified as an output signal 10.

Description

[Detailed Description of the Invention] Kinmei has developed a waveform-shaping optical amplification device for ultra-high-speed optical communications that completely shapes and amplifies the waveform of an optical pulse (relating to Since loss and dispersion occur in the optical transmission path, the optical pulse is attenuated and its pulse width is widened. This widening of the pulse width causes band deterioration and limits the bit rate that can be transmitted.

Generally, for long-distance optical communications, an optical repeater must be installed in the middle of the transmission line. The optical repeater has
There are two types of regenerative repeaters: one is a regenerative repeater that converts an optical signal into an electrical signal and then returns it to an optical signal, and the other is an optical amplification repeater that directly amplifies the optical signal. M juxtaposition disease is used. However, although the optical modulator used for external modulation is capable of high-speed modulation, it is not suitable for long-distance transmission because of its large insertion loss. On the other hand, direct modulation of a laser light source does not cause any problems in terms of optical output; however, for example, in the case of a semiconductor laser, 1. There is a drawback that it becomes difficult to stably perform high-speed modulation when the frequency exceeds IGHz.
Therefore, regenerative repeaters are not suitable for the purpose of multiplexing optical pulses using methods such as time division multiplexing and transmitting high-speed, large-capacity signals over long and short distances.In contrast, optical amplification Repeaters can directly amplify time-division multiplexed light due to their broadband properties, so if the possible transmission distance is limited due to loss limitations, optical amplification can be used. By using nine optical amplification repeaters, long-distance transmission of ultra-high-speed signals is partially possible.

However, since laser amplifiers have traditionally been used exclusively as optical amplification repeaters, dispersion of the optical transmission line
In the case where the band deteriorates and the signal width widens, no countermeasures can be taken, and in such cases there is a drawback that appropriate aerial relay cannot be carried out. [Objective of the present invention] It is to provide a waveform shaping optical amplification device suitable for an optical repeater for long-distance transmission of ultrahigh-speed signals, which eliminates the above-mentioned conventional drawbacks and shapes and amplifies the waveform of an optical pulse. K〇Another object of the present invention is to increase the peak value of the optical pulse obtained by directly modulating a laser light source, and narrow the pulse width to make it sharp), making it suitable for time division multiplex communication, etc. An object of the present invention is to provide a waveform shaping optical amplification device capable of generating signal light pulses with sharp waveforms. A sharp, large-amplitude optical pulse can be obtained as an output. Furthermore, it is possible to narrow the pulse width of a wide optical pulse obtained by directly modulating a laser light source and amplify it, thereby increasing the output of six sharp optical pulses.

Next, the waveform shaping optical amplification device according to the present invention will be explained in detail with reference to two drawings.

FIG. 1 shows the configuration of one embodiment of this invention.

This is shown in the figure below.

In FIG. 1, l is a binary-encoded optical pulse as an input signal, with a wavelength of 1.55 μm and a wavelength of 1.55 μm.

The frequency, or pit rate, is 1.6 Gb/a. The input signal l propagating through the optical transmission line has a pulse width of 9
．． The signal level spreads to 5f18, and the peak value of the signal is as weak as 30 dBm. 2 is an optical multiplexer, by which a part of the input signal 1 is sent to the tie power extraction circuit 3, and the output of the other branch is sent to the optical multiplexer 7 to the optical multiplexer 7 and the optical fiber 7 to the optical fiber guided scattering amplification circuit. The timing extraction circuit 3 coupled to the medium 8 extracts the clock frequency of 1.6 GHz from the input signal l, controls the mode-locked laser 5 for optical excitation with this clock frequency, and controls the mode-locked laser 5 for optical excitation. The mode-locked optical pulse 6 generated from the laser beam f5 is synchronized to the black and white frequencies.

This mode-locked optical pulse 60 has a wavelength of 132 am and a pulse width of 6. It is Ins. 4 is a variable delay circuit].

Input signal 1 at optical multiplexer 7 using multilayer interference filter
It is used to adjust the timing w4 so that the peak of the optical pulse 6 and the beat of the mode-locked optical pulse 6 overlap.

The input signal "l" outputted from the optical multiplexer 7 and the mode-locked light pulse 6 for excitation are superimposed and input into the optical fiber stimulated scattering amplification medium 8. The output light from the optical fiber stimulated scattering amplification medium 8 is is guided to an optical demultiplexer 9 using a multilayer interference filter, and the transmitted excitation light is removed.
As output signal 10.

Pal; "IA power, Ins, peak value is OdBm
An optical pulse code sequence whose waveform is shaped and amplified is obtained.

Regarding optical amplification using stimulated scattering in optical fibers, see, for example, Elec, August 14, 1980) a 2/
x V 31-s (Electronics Let
ters).

Please refer to the article by Utsugo' et al., one of the inventors of this invention, published in Volume 16, pages 658-666. If a single mode fiber is used as the optical fiber and is strongly pumped at a wavelength with low dispersion and low loss, a small signal amplification gain of 4j+aa or more can be easily obtained with a pumping input of about several tens of W. − Wave number difference ν゛2 between the pumping light (frequency) and the amplified signal source (frequency νS), which is large even with amplification gain
-v8 can be changed from 100cIL"8K to 3.8K by changing the core diameter and refractive index distribution of the optical fiber to change the dispersion characteristics of the original fiber and thereby controlling the phase matching conditions.
Q
-The response time for OFPK is determined by the longitudinal relaxation time TIK of the medium, so it is difficult to achieve high-speed switching of less than a nanosecond in the case of a semiconductor laser. However, the response time for S scattering is determined by the coherent time of the medium. It is almost determined by this, and when the medium is an original 7-Iber, a high-speed response on the order of picoseconds is possible.9) This is also sufficient even if a narrow optical pulse of 1 klIa, such as a mode-locking optical pulse, is used as the excitation light pulse. can follow. Fermentation gain changes exponentially with the intensity of excitation light, so if you excite with a sharp mode-locked light pulse with little background light component, you can narrow the pulse width of a wide pulse width signal input and amplify it. Ru.

For example, 1 as a mode-locked laser for excitation of 5.

The wavelength is 1.32 JmONd: YAG v-fttMjhrue. In this case, the dispersion characteristics of the single-mode fiber must be changed), and the wavelength can be changed from 1.35 μm to 13 μm.
It is possible to amplify light from a semiconductor laser up to 5 am. Therefore, it is extremely convenient in the design of the optical transmission system. ◇ If it is difficult to increase the mode-locked optical pulse 60 repetition frequency, use it outside the laser oscillator.

For example, multiplexing using a semi-transparent mirror and an optical delay circuit.

It is preferable to use a method that increases the repetition of light pulses.

This increases the repetition rate of the excitation light pulse for the 80-element fiber induced scattering filter.

As described above, according to Jin's invention, it is possible to obtain a waveform shaping optical amplification device that shapes and amplifies the waveform of an optical pulse and is suitable for long-distance transmission and time division multiplexing of ultrahigh-speed signals.

Note that the present invention is not limited to the configuration shown in the above-described embodiment, and of course, several modifications can be made.

For example, the variable delay circuit 4 is provided between the timing extraction circuit 3 and the excitation mode-locked laser 5.

Similar effects can also be obtained by providing an optical delay circuit between the excitation mode-locked laser 5 and the optical multiplexer 7 instead. Furthermore, an optical delay circuit is provided between the optical multiplexer 2 and the optical multiplexer 7, and by delaying the input signal l here, the timing of the input signal l and the mode-locked optical pulse 6 can be matched. can.

In addition, in this embodiment, the optical multiplexer 7 and the optical demultiplexer 9
9 using a multilayer interference filter.

Alternatively, a diffraction grating spectrometer, for example, may be used.

In addition, when using the waveform shaping optical amplification device of the present invention for the purpose of increasing the peak value of the transmitted optical pulse and narrowing the optical pulse width in the optical transmitter, the timing extraction circuit 3 described in the above embodiment is set to W. There is no need to use it, and the timing signal may be brought directly from the transmitter.

In addition, in the embodiment of the present invention, as an optical pulse encoded by pulse amplitude modulation, 21 [described in the case of using an encoded optical pulse], but as an optical pulse, multi-level encoding is used. Of course, it does not matter whether it is a pulse or an optical pulse with an analog value.

[Brief explanation of drawings]

FIG. M1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, l-...input signal, 2...
・−・Optical splitter, 3・・・・−Timing extraction circuit, 4
. . . Variable delay circuit, 5 . . . Mode-locked laser for optical excitation, 6 . . . Mode-locked optical pulse,
7--Optical multiplexer, 8-- Optical fiber guided number 4 amplification medium, 9-- Optical demultiplexer.

Claims (1)

[Claims] A waveform shaping optical amplification device that shapes and amplifies the waveform of an encoded optical pulse by pulse amplitude modification 11 includes an optical fiber stimulated scattering amplification medium and a mode-locked laser for optical excitation, and A mode-locked optical pulse generated from the optically pumped laser-locked laser and the optical pulse are superimposed and input into the optical fiber stimulated scattering enhancement medium, and the waveform of the optical pulse is shaped and amplified. Waveform shaping optical amplification device 0 characterized by