JPH06194697A - Wavelength multiplex reference light source - Google Patents

Abstract

PURPOSE:To provide the wavelength multiplex reference light source by which light rays of respective modes are stable oscillated at arbitrary wavelength intervals. CONSTITUTION:This wavelength multiplex reference light source consists of a light source 1 of a wavelength lambda1, a light source 2 of a wavelength lambda2, a one-to-one optical multiplexer 3 and an optical ring resonator 4. The optical ring resonator 4 is provided of an optical demultiplexer 5, an optical demultiplexer 6, a dispersion shift fiber 7 and an erbium doped fiber optical amplifier 8 and mixedly inputs the light of the wavelength K 1 and the light of the wavelength lambda2 to the optical ring resonator 4. The light of the frequency fm=f1+ or -nDELTAf (m, n are integers) regulated by a differential frequency DELTAf: ¦f1-f2¦ between f1=c/lambda1, f2=c/lambda2 (c is a light velocity) is generated within the optical fiber 7 within the optical ring resonator. This wavelength multiplex light is the light stable at the respective modes at equal frequency intervals within the band of the optical amplifier 8 within the optical ring resonator 4. The wavelength multiplex reference light source which can drastically decrease the number of the light sources as compared with the degrees of multiplexing and can arbitrarily set the wavelength intervals of the resulted light is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission light source in an optical wavelength division multiplexing optical communication system.

[0002]

2. Description of the Related Art An optical fiber communication system is expected as a large capacity communication system utilizing the wide band property of light. However, in the currently practically used system, transmission is performed by a single signal light wavelength, and it cannot be said that the broadband property of light is fully utilized. In order to make full use of the broadband property of light, an optical wavelength transmission technique for multiplexing and transmitting a number of signal light wavelengths is effective. In the optical wavelength division multiplexing transmission, the capacity can be increased without increasing the transmission rate per wavelength. For example, if 100 waves of light with a transmission rate of 10 Gb / s per wavelength are multiplexed, the total transmission rate is 1 Tb / s.
It is possible to build a large capacity transmission system.

Conventionally, in order to perform wavelength division multiplexing transmission, as many light sources as the number of wavelengths to be multiplexed are required. For example, 199
April, 2nd year, E, E, I, C, E Transactions on Communications, E75-
Volume B, Issue 4 (IEICETRANSACTIONS
on Communications, Vol. E75
-B, No. 4, April, 1992) reported that multiple wavelengths of 100 wavelengths were transmitted by 100 stabilized semiconductor lasers having different wavelengths.

Further, as a technique for reducing the number of light sources for optical wavelength division multiplexing transmission, Japanese Patent Laid-Open No. 63-203026 discloses an emission light of a multimode oscillation laser whose wavelength is stabilized as one wavelength mode. A technique is described in which each of the light sources is separated and used as a wavelength division multiplexing transmission light source.

[0005]

As a light source in a conventional optical wavelength division multiplexing optical communication system in which a number of light sources are prepared and each of which is stabilized, as many light sources as the number of wavelengths to be multiplexed are required. Each light source had to be stabilized.

In the case of using a laser that oscillates in multiple modes as a light source, there is a problem that the obtained wavelength interval is determined and fixed by the laser used and the power in each mode is unstable.

An object of the present invention is to provide a wavelength multiplex reference light source that stably oscillates light of each mode at arbitrary wavelength intervals.

[0008]

A wavelength multiplexing reference light source according to the present invention comprises a light source group for outputting a plurality of light beams of different wavelengths, a multiplexer for multiplexing light beams from the light source group, an optical fiber and an optical fiber. It is composed of an optical ring resonator with an amplifier,
By inputting the output light multiplexed by the multiplexer into the optical ring resonator, the sum / difference frequency of the plurality of light source output frequencies of the light source group is output.

[0009]

In this case, the case where there are two light sources will be described as an example. The operation does not change even if the number of light sources is three or more. Light of wavelength λ1 and light of wavelength λ2 are mixed and input to the optical ring resonator. This results in f1 = c / λ1 and f2 = c / λ2 in the optical fiber in the optical ring resonator.
A beat signal defined by a difference frequency Δf = | f1-f2 | of (c is the speed of light) is generated. With this beat signal, frequency f1,
The light of f2 undergoes phase modulation, and the frequencies f1 ± Δf and f2 ±
A signal component of Δf is generated (four-wave mixing). The signal lights of the frequencies f1 ± Δf and f2 ± Δf generated by the four-wave mixing are further phase-modulated by the beat of Δf and the frequency f1 ± 2Δ.
f, f2 ± 2Δf. This effect is repeated until light with a frequency fm = f1 ± nΔf (m and n are integers and m = 2n + 1 when the compound sign is + and m = 2n when the sign is −) is generated. This wavelength-multiplexed light is stable light at equal frequency intervals and in each mode within the band of the optical amplifier in the optical ring resonator.

Further, the polarization state in the optical fiber changes intricately due to the fact that the optical fiber does not have a perfect circular cross section, the external force applied to the optical fiber, and the twist. As a result, the plane of polarization changes intricately within the optical ring resonator, causing fluctuations in the intensity of the emitted light. Therefore, if a polarization-preserving fiber is inserted in the optical ring resonator as a polarization control element or an optical fiber in the ring resonator to make the polarization direction in the optical ring resonator constant, the intensity fluctuation due to a complicated change in polarization will occur. Can be suppressed, and the obtained wavelength-multiplexed light can be further stabilized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
This light source comprises a light source 1 which is a DFB laser having a wavelength of 1.5589 μm, a light source 2 which is a DFB laser having a wavelength of 1.5592 μm, a one-to-one optical multiplexer 3, and an optical ring resonator 4.
The optical ring resonator 4 is composed of a one-to-one optical demultiplexer 5, a one-to-one optical demultiplexer 6, a zero dispersion wavelength 1.5591 μm, a dispersion shift fiber 7 having a length of 25 km, and an erbium-doped fiber optical amplifier 8. It

As a result, when the incident light levels of the light source 1 and the light source 2 are 0 dBm and the amplifier output is 0 dBm or more, the spectrum waveform of the obtained emitted light is shown in FIG. 15 wavelengths (f1 to f15) of wavelength-multiplexed light having a level difference of 3 to 8.5 dB adjacent to the level of the incident light within 30 dB can be synthesized including the incident light. The frequency interval between them is 37 GHz. Further, by inserting a polarization controller into the ring resonator 4 to make the polarization direction in the optical ring resonator constant, it is possible to suppress intensity fluctuation due to a complicated change in polarization, and obtain the obtained wavelength division multiplexing. The light could be further stabilized.

From the above results, it is difficult for the conventional means for obtaining the wavelength-division-multiplexed wave to significantly reduce the number of light sources as compared with the multiplicity and to arbitrarily set the wavelength interval of the obtained light. It has been shown that this can be achieved by using the present invention.

The present invention has many other variations. The wavelength interval between the light source 1 and the light source 2 can be widened to 1 nm or more, or conversely narrowed to 0.2 nm or less. Within the band of the optical amplifier, wavelength-division multiplexed light of an arbitrary wavelength can be obtained by using dispersion-shifted fibers having different zero-dispersion wavelengths and the light sources 1 and 2 having wavelengths near the zero-dispersion wavelength. Further, the optical amplifier is not limited to the erbium-doped fiber optical amplifier, but may be a semiconductor optical amplifier or a Raman optical amplifier.

If the optical fiber in the optical ring resonator is a normal fiber and the optical amplifier is a 1.3 μm band semiconductor optical amplifier, or the praseodymium-doped fiber optical amplifier is a light source 1 and the light source 2 is a 1.3 μm band wavelength band. 1.
The wavelength-multiplexed reference light source is not limited to the 55 μm band but can be a 1.3 μm band.

The polarization state in the optical ring resonator can be stabilized by using a polarization control element or a polarization-maintaining fiber as the optical fiber in the optical ring resonator in the optical ring resonator.

[0017]

As described above, the optical wavelength division multiplexing reference light source in the optical wavelength division multiplexing transmission optical communication system according to the present invention uses the wavelength division multiplexed light from the sum / difference frequency of two input lights by the nonlinear four-wave mixing in the optical fiber. Therefore, the wavelength interval can be set arbitrarily and stable light can be obtained in each mode.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a spectrum diagram of wavelength multiplexed light obtained by the present invention.

[Explanation of symbols]

 1, 2 DFB laser light source 3 Optical multiplexer 4 Optical ring resonator 5 and 6 Optical demultiplexer 7 Dispersion shift fiber 8 Erbium-doped fiber optical amplifier

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01S 3/094 3/10 Z 8934-4M

Claims (2)

[Claims] 1. A light source group that outputs a plurality of different wavelength lights, a multiplexer that multiplexes the lights from the light source groups, and an optical ring resonator having an optical fiber and an optical amplifier, A wavelength multiplex reference light source, which outputs the sum / difference frequency of a plurality of light source output frequencies of the light source group by inputting the output light multiplexed by the multiplexer into the optical ring resonator. 2. A polarization controller is inserted in an optical ring resonator having an optical fiber and an optical amplifier, or a polarization-maintaining fiber is used as the optical fiber in the optical ring resonator. Item 3. The wavelength division light source according to item 1.