JP2002152133A - Optical signal format converter - Google Patents

Abstract

(57) [Summary] To convert an RZ signal light into an NRZ signal light by an all-optical system. SOLUTION: An RZ signal light S having a pulse width of 25 ps and four pump lights Sp1 to Sp1 having different wavelengths.
When Sp4 is input to the wavelength converter 101, a converted signal light Sh having the same waveform as the signal light S and including each wavelength component light of the pump lights Sp1 to Sp4 is output. When the converted signal light Sh is passed through the wavelength-dispersive optical fiber 102, the transmission speed differs for each wavelength component light, and from the output end of the optical fiber 102, the converted signal light Shw of the NRZ format having a pulse width of 100 ps is obtained. Can be Since the light receiving device 6 receives the signal light Shw in the NRZ format, the band may be narrow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal format converter, and more particularly, to a non-return-to-zero (NRZ) signal light without converting a signal light of a return-to-zero (RZ) format without photoelectric conversion.
It is devised so that it can be converted to signal light of the zero) format. Thereby, the band required for the light receiving device for receiving the signal light can be narrowed.

[0002]

2. Description of the Related Art Generally, an optical transmission system has a hierarchical structure as shown in FIG. 4, 1001 to 1008 are end users, 1009 and 1010 are local networks, 1011
Is an upper network accommodating a plurality of local networks. Generally, in a local network, a transmission band required by each user is about 10 Gb / s.

[0003] The optical transmission system is an erbium doped optical fiber amplifier (effective band 1530 to 1560).
nm: 1.55 micron band)
It has developed mainly in the 1.55 micron band. This means that, for example, assuming wavelength multiplexed signal light, if wavelength multiplexing is performed at 1 nm intervals, for example, only about 30 wavelengths can be used. That is, in the local network, a total throughput of 10 Gb / s × 30 = 300 Gb / s can be expected.

Incidentally, the upper network accommodates a plurality of, for example, four user networks. In the upper network, the usable wavelength remains the same at about 30 wavelengths. Therefore, in order to prevent congestion from occurring, the transmission band must be set to, for example, 40 in the upper network.
It is necessary to increase to Gb / s.

FIG. 5 shows a conventional optical transmission system for expanding a transmission band of a transmission optical fiber to 40 Gb / s by converting a 10 Gb / s NRZ signal light into an RZ signal light. .

As shown in FIG. 1, an optical signal format converter 2 is connected to the transmission side of the transmission optical fiber 1, and a duplexer 3 is connected to the reception side of the transmission optical fiber 1. I have. The optical signal format converter 2 on the transmitting side is connected to the signal light S1 having the wavelength λ1 and the signal light S1 having the wavelength λ2 via the input optical fiber 4.
, A signal light S3 having a wavelength of λ3, and a signal light S3 having a wavelength of λ3.
The fourth signal light S4 is wavelength-multiplexed and input. Each of the signal lights S1 to S4 is an NRZ 10 Gb / s signal light having a pulse width of 100 ps.

The optical signal format converter 2 first performs a clipping process to convert the pulse width of each of the NRZ signal lights S1 to S4 into a 1/4 pulse width of 25 ps, and thereby to convert the RZ signal lights S11 to S14. To Further, the signal light S11
The signal light S12 is delayed by 25 ps with respect to the signal light S1.
After delaying the signal light S3 by 50 ps and delaying the signal light S14 by 75 ps, the signal light S11 to S14 are combined to form a transmission signal light S, and the transmission signal light S is input to the transmission optical fiber 1. The signal light S for transmission has a pulse width of 25.
ps, which is 40 Gb / s signal light in RZ format.

The transmitted signal light S for transmission is split by the duplexer 3 on the receiving side according to the wavelengths λ1, λ2, λ3, λ4, the signal light S11 is output to the output fiber 5a, and the signal light S12 is output. The output light 5b, the signal light S13 is output to the output fiber 5c, and the signal light S14 is output to the output fiber 5d.
And the light receiving devices 6a, 6b, 6c, 6
sent to d. The light receiving devices 6a to 6d have a pulse width of 25.
The information can be obtained by photoelectrically converting the signal light S11 to S14 in the RZ format which is ps.

[0009]

Since each of the light receiving devices 6a to 6d must receive the RZ signal light S11 to S14 having a pulse width of 25 ps, each of the light receiving devices 6a to 6d receives the signal light S11 to S14. Requires a band of 40 GHz. In other words, each of the light receiving devices 6a to 6b includes a light receiver and an electric amplifier, and the light receiver and the electric amplifier require a wide band of 40 GHz. Such a broadband light receiving device is expensive, which has led to an increase in cost when constructing an optical transmission system.

SUMMARY OF THE INVENTION In view of the above prior art, the present invention provides an optical signal format converter capable of reducing the bandwidth required for a light receiving device used on the receiving side while widening the transmission band in a transmission optical fiber. The purpose is to provide.

[0011]

According to a configuration of the present invention that achieves the above object, when a signal light of RZ format and a plurality of pump lights having different wavelengths are input, each of the pump light includes each wavelength component light of the pump light. A wavelength converter for outputting a converted signal light having the same waveform as the signal light, and an optical transmission medium having a chromatic dispersion characteristic for transmitting the converted signal light output from the wavelength converter.

In the configuration of the present invention, the wavelength converter is a mutual gain modulation type wavelength converter or a mutual phase modulation type wavelength converter, and the optical transmission medium is an optical fiber having chromatic dispersion characteristics. It is characterized by being.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an optical signal format converter 100 according to an embodiment of the present invention.
The optical signal format converter 100 includes a wavelength converter 101 and a wavelength dispersion type optical fiber 102 as main members. As the wavelength converter 101, mutual gain modulation (X
A GM (Cross Gain Modulation) type wavelength converter and a cross phase modulation (XPM: Cross Phase Modulation) type wavelength converter are employed. Wavelength dispersion type optical fiber 102
Has a dispersion characteristic of 25 ps / nm / Km, that is, a time difference of 25 ps occurs when light having a wavelength difference of 1 nm is transmitted for 1 km. The length of the wavelength dispersion type optical fiber 102 is 1 km.

The optical signal format converter 100 is arranged on the receiving side of the optical transmission system. More specifically, it is provided at the subsequent stage of the splitter connected to the receiving side of the transmission optical fiber, and receives the split signal light S. For example, the signal light S is an RZ 10 Gb / s signal light having a pulse width of 25 ps and a wavelength of 1555 nm. This signal light S is input to the wavelength converter 101.

In the wavelength converter 101, in addition to the signal light S in the RZ format, a pump light Sp1 (wavelength 1550) which is a continuous light is provided.
nm), Sp2 (wavelength 1551 nm), Sp3 (wavelength 1
552 nm) and Sp4 (wavelength 1553 nm) are input. The XGM or XPM wavelength converter 101 causes the pump lights Sp1 to Sp4 to act on the signal light S,
In addition to having the same waveform as the signal light S, the pump light Sp1
RZ converted signal light Sh including each wavelength component light of Sp4
Is output. The principle of wavelength conversion by the XGM or XPM wavelength converter 101 will be described later.

That is, the converted signal light Sh has the same waveform (same waveform or inverted waveform) as the signal light S, but the converted signal light having a wavelength of 1550 nm and the same waveform (same waveform or inverted waveform) as the signal light S. A converted signal light having an inverted waveform but having a wavelength of 1551 nm; a converted signal light having the same waveform (same or inverted waveform) as the signal light S but having a wavelength of 1552 nm; The converted signal light having the same waveform as S (same waveform or inverted waveform) but having a wavelength of 1553 nm is a signal light superimposed in the same phase.

A plurality of wavelength component lights (wavelength 1550 nm, 1
551 nm, 1552 nm, 1553 nm) is input to the wavelength dispersion type optical fiber 102 and transmitted through the optical fiber 102. The wavelength dispersion type optical fiber 102 has a length of 1 km and a dispersion characteristic of 25 ps / nm / km.
Therefore, the output end of the converted signal light Sh has a wavelength of 1553 nm with respect to the signal light of 1553 nm.
The signal light of the wavelength component of 52 nm is delayed by 25 ps and 1551.
The signal light of the wavelength component of nm is delayed by 50 ps and 1550 nm.
Is delayed by 75 ps. Therefore, the pulse width from the output end of the chromatic dispersion type optical fiber 102 is 1 pulse width.
The converted signal light Shw of 10 Gb / s spread to 00 ps is output. Since the pulse width is widened in this manner, the converted signal light Shw becomes an NRZ signal light.

The light receiving device 6 is provided with a converted signal light Sh of the NRZ format.
w is received and converted into an electric signal. The light receiving device 6
Detects the presence / absence of information based on the presence / absence of light. Therefore, even if the converted signal light Shw including a plurality of frequency component lights is input, the state in which an optical pulse is present is determined to be 1, and there is no optical pulse. Only when the state is determined to be 0, the converted signal light Shw is detected (determination of 1, 0) without being affected by the wavelength.

The light receiving device 6 has a 10 Gb / s NRZ format converted signal light Shw having a pulse width of 100 ps.
Is input, the transmission band required for the light receiving device 6 is only 5 GHz. By the way, if the pulse width is 25 ps and 10
When trying to receive Gb / s signal light S in the RZ format, the light receiving device requires a band of 40 GHz.

As described above, the optical signal format converter 100 converts the RZ signal light S into the NRZ converted signal light Sh.
Since it is converted to w and input to the light receiving device 6, the band required for the light receiving device 6 is narrowed,
Can be adopted.

In the above embodiment, an optical fiber is used as the optical transmission medium having chromatic dispersion characteristics. However, another optical transmission medium having chromatic dispersion characteristics, such as a fiber Bragg grating, may be used.

Here, cross gain modulation (XGM: Cross Ga
The principle of wavelength conversion by the wavelength converter of the (in Modulation) type will be described with reference to FIG. Semiconductor optical amplifier 15
The pump light Sp having the wavelength λp is input to 0 to keep the semiconductor optical amplifier 150 in a saturated state. At this time, when the signal light S having the wavelength λs is input, the amplification degree of the pump light Sp at the wavelength λp decreases when the intensity of the signal light S is high. When the signal light S is cut by the filter 151, the converted signal light S having the wavelength λp and having the inverted waveform of the signal light S is output.
h is obtained. If a plurality of pump lights having different wavelengths are used as the pump light Sp, the converted signal light Sh becomes a signal light including wavelength component lights of the plurality of pump lights.

Next, cross phase modulation (XPM: Cross Phas)
The principle of wavelength conversion by a wavelength converter of the (e Modulation) type will be described with reference to FIG. In this XPM type wavelength conversion, when light is input to a semiconductor optical amplifier, the refractive index changes,
This is based on the fact that the optical length changes. FIG.
As shown in the figure, two semiconductor optical amplifiers 160A and 160
B is connected with a splitter and a coupler. Pump light S of wavelength λp
p is input to the two semiconductor optical amplifiers 160A and 160B. On the other hand, only from the opposite side to the semiconductor optical amplifier 160A,
The signal light S having a wavelength of λs is input. At this time, the signal light S
Is high, the refractive index of the semiconductor optical amplifier 160A changes, and the pump light Sp
Changes. Since the phases of the semiconductor optical amplifier 160A and the semiconductor optical amplifier 160B are different, the pump light Sp that has passed through the semiconductor optical amplifier 160A and the semiconductor optical amplifier 1
When the pump light Sp that has passed through 60B is coupled by a coupler at the output end, a phase change appears as an intensity change. Therefore, at the output end, the converted signal light Sh having the same waveform as the signal light S and having the wavelength of λp is output. When a plurality of pump lights having different wavelengths are used as the pump light Sp, the converted signal light Sh becomes a signal light including wavelength component lights of the plurality of pump lights.

[0024]

As described above in detail with the embodiments, in the present invention, the RZ signal light is wavelength-converted into converted signal light including a plurality of wavelength component lights, and this converted signal light is converted into a wavelength-converted signal light. An NRZ with a wider pulse width transmitted to an optical transmission medium having dispersion characteristics and shifted for each wavelength component light
It can be a type of signal light. As described above, the RZ-format signal light can be converted to the NRZ-format signal light by the all-optical method, so that an inexpensive device with a narrow band can be adopted as the light receiving device, and the optical transmission system can be manufactured at low cost. Can contribute to the construction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical signal format converter according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing the principle of a wavelength converter of a mutual gain modulation type.

FIG. 3 is a configuration diagram showing the principle of a cross-phase modulation type wavelength converter.

FIG. 4 is a system diagram showing an optical transmission system.

FIG. 5 is a configuration diagram showing an optical transmission system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission optical fiber 2 Optical signal format conversion part 3 Demultiplexer 4 Input fiber 5a-5d Output fiber 6,6a-6d Light receiving device 100 Optical signal format conversion device 101 Wavelength converter 102 Wavelength dispersion type optical fiber

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Suzuki 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Noboru Ishihara 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 F-term in Nippon Telegraph and Telephone Corporation (reference) 2K002 AA02 AB12 BA01 CA13 DA06 EA28 HA01 5K002 CA03 CA09 CA13 DA06 FA01

Claims (3)

[Claims] 1. A wavelength converter that receives an RZ signal light and a plurality of pump lights having different wavelengths and outputs a converted signal light having the same waveform as the signal light, including each wavelength component light of the pump light. A converter, for transmitting the converted signal light output from the wavelength converter,
An optical signal format converter comprising: an optical transmission medium having a wavelength dispersion characteristic. 2. The optical signal format converter according to claim 1, wherein said wavelength converter is a cross gain modulation type wavelength converter or a cross phase modulation type wavelength converter. 3. The optical signal format converter according to claim 1, wherein said optical transmission medium is an optical fiber having chromatic dispersion characteristics.