JP3200630B2 - Apparatus and method for generating multi-wavelength phase modulated optical pulse train - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-wavelength phase-modulated optical pulse train generator and a method for generating the same. In particular, it is used in a wavelength division multiplex digital phase modulation code communication system in optical communication, and proposes a new multi-wavelength digital phase modulation optical pulse train generation device and a generation method thereof.

[0002]

2. Description of the Related Art In a conventional multi-wavelength digital phase modulation optical pulse train generation method, after a multi-wavelength optical pulse train is generated,
Each was digitally phase-modulated.

FIG. 4 shows a typical configuration of a conventional multi-wavelength digital phase modulation optical pulse train generator. In this configuration, pulse light sources 41-1, 41-2 having different oscillation wavelengths,
... 41-n (n indicates an apparatus for the n-th wavelength)
Are prepared by the number of wavelengths necessary for the intended wavelength division multiplexing communication, and the phase modulators 42-1, 42-2,.
By digitally modulating the signals with n (n indicates the device for the n-th wavelength) and multiplexing them by the multiplexer 43,
A multi-wavelength digital phase modulation optical pulse train is generated. In this conventional multi-wavelength digital phase modulation optical pulse train generation apparatus, the pulse light sources 41-
1, 41-2,... 41-n and the digital phase modulator 4
.., 42-n must be prepared, and the configuration is very complicated.

Further, a multi-wavelength ultrashort pulse light source that generates a multi-wavelength pulse train from one pulse light source without preparing a required number of pulse light sources having the required number of wavelengths is disclosed in Japanese Patent Laid-Open No. 6-29.
1398, or JP-A-8-1
This is disclosed in Japanese Patent No. 22833. If the configurations disclosed in these publications are combined with the above-described configurations, a multi-wavelength optical pulse train is generated by the configurations disclosed in these publications, and each optical pulse train is digitally phase-modulated by the above-described conventional method. Thus, it is possible to easily generate a multi-wavelength digital phase modulation optical pulse train. However, even in this method, it is necessary to prepare a digital phase modulator having a necessary number of wavelengths, and the configuration is still complicated.

[0005]

As described above, in the conventional multi-wavelength digital phase modulation optical pulse train generation method, the configuration of the generation apparatus is complicated.

SUMMARY OF THE INVENTION The present invention has been proposed in view of this point, and provides a multi-wavelength phase-modulated optical pulse train generating apparatus and a generating method capable of generating a multi-wavelength digital phase-modulated optical pulse train with a simple configuration. With the goal.

[0007]

According to a first aspect of the present invention, there is provided an apparatus for generating a multi-wavelength phase-modulated optical pulse train, comprising: a pulse light generating section for generating a series of optical pulse trains; An optical phase modulator 12 that digitally modulates an optical pulse train, an optical spectrum spreader 13 that performs an operation to increase the spectrum width of the phase-modulated optical pulse train, and a bandwidth that is narrower than the spread optical spectrum width. There is disclosed an optical pulse train generating device including an optical filtering unit 14 for obtaining a plurality of optical pulse train signal trains.

[0008] The invention described in claim 2 is the first invention.
In addition to the configuration of the invention described in the above, the optical spectrum spreading unit 13
Uses an optical fiber, and in particular, is characterized in that the spectrum of the optical pulse train is broadened using supercontinuum light generated when the optical pulse train propagates in the optical fiber. An optical pulse train generating apparatus is disclosed.

According to a third aspect of the present invention, in addition to the configuration of the third aspect of the invention, the optical fiber is a dispersion flat fiber having a small change in chromatic dispersion with respect to wavelength at a pump wavelength. And the variance is-
An optical pulse train generator using an optical fiber in a normal dispersion region of 1.0 to 0.0 ps / nm / km.

The invention according to claim 4 discloses a method for generating a multi-wavelength phase-modulated optical pulse train, generating a series of optical pulse trains, digitally modulating the optical pulse trains, and performing the phase modulation. An operation of expanding the spectrum width of the optical pulse train is performed, and an optical pulse train generating method is characterized in that a plurality of optical pulse train signal trains having a bandwidth smaller than the optical spectrum width are filtered from the optical pulse train having a broadened spectral width. .

[0011]

FIG. 1 shows an embodiment of the present invention. First, an optical pulse train is generated by the pulse light generating unit 11 in FIG. 1, then the optical pulse train is phase-modulated by the optical phase modulation unit 12, and the spectrum width of the optical pulse train phase-modulated by the optical spectrum spreading unit 13 is widened. A plurality of phase-modulated optical pulse trains are simultaneously obtained by dividing the optical pulse trains into light pulse trains having relatively close light wavelengths in the optical filtering unit.

Next, a more specific embodiment is shown in FIG. In FIG. 2, a pulse light source 21 first generates an optical pulse train, then digitally modulates the optical pulse train with a phase modulator 22, and amplifies the optical pulse train with high intensity by an optical amplifier 23 belonging to an optical spectrum spreading unit. After that, the spectral width of the optical pulse train phase-modulated by the supercontinuum generating optical fiber 24 is widened, and the optical wavelengths relatively close to each other by the optical filter array 25, wavelength ♯1, wavelength ♯2,.
By dividing into wavelengths ♯n (n indicates the type of wavelength of the optical pulse train output from the optical filter array 25),
A plurality of phase-modulated optical pulse trains are obtained at the same time.

FIG. 2 shows a specific configuration in which a pulse light source 21 oscillating at a pump wavelength is a hybrid mode synchronous semiconductor laser having an emission wavelength of 1550 nm and a pulse width of 3p.
s, and the average output power is 1 mW. The output optical pulse train is input to the phase modulator 22. The phase modulator 22 is a digital optical phase modulator and has a repetition frequency of 20G.
Hz digital phase modulation is performed to generate a digital phase modulated optical pulse train. This is amplified to high intensity by an optical amplifier 23 using an optical fiber. The input to the optical amplifier 23 is 0.1 mW in average power and 3.3 m in peak power.
W. On the other hand, the output from the optical amplifier 23 is 1.4 W in average power and 47 W in peak power.

The optical pulse train amplified in this manner is incident on a supercontinuum generating optical fiber 24. As shown in FIG. 2A, the bandwidth at the time of incidence is 2 nm, which is a bandwidth defined by a wavelength reduced by -20 dB from the highest light intensity at the center wavelength. The super continuum generating optical fiber is a dispersion flat normal dispersion optical fiber having a length of 2 km and a dispersion value of -0.19 at 1550 nm.
2 ps / nm / km. Also, this variance is −
It could be used in the range of 1.0 to 0.0 ps / nm / km.

Since the pulse train after passing through the supercontinuum generating optical fiber 24 has a very large frequency chirping, the optical spectrum width is very wide due to the nonlinear effect, as shown in FIG. 3 (b). In addition, the bandwidth was 20 nm or more in a -20 dB bandwidth defined by a wavelength weakened by -20 dB from the highest light intensity near the center wavelength. This spectrum width increases as the peak power to the supercontinuum generating optical fiber 24 increases. AWG (Arr) from within this spread spectrum band
The center wavelength is 1545 nm by the optical filter array 25 using the ayed waveguide grating.
FIG. 3C shows a digital phase-modulated pulse train of (wavelength # 1) and 1555 nm (wavelength # 2) generated.

An advantage of the present apparatus and method is that a plurality of digital phase modulated pulse trains having different wavelengths can be simultaneously generated using one pulse light source while preserving the digital phase information from one digital phase modulator. is there. Thus, the light source can be greatly simplified as compared with the conventional method.

[0017]

Since the present invention has the above-described configuration,
The following effects can be obtained.

According to the first aspect of the present invention, by performing digital phase modulation before broadening the spectrum width to obtain multiple wavelengths by the filter, a multi-wavelength phase-modulated optical pulse train can be formed with a simpler configuration than in the prior art. Now you can get it.

According to the second aspect of the present invention, in addition to the first aspect of the present invention, the use of an optical fiber in the optical spectrum spreading section makes it possible to achieve a relatively simple wave number approach with a simpler structure than in the prior art. A plurality of digital phase-modulated optical pulse trains can be obtained.

Further, according to the third aspect of the present invention, in addition to the third aspect of the present invention, by defining the dispersion value of the optical fiber, even in the current technical level of optical amplification, it is relatively easy. This makes it possible to obtain a plurality of digital phase-modulated optical pulse trains with similar wave numbers.

Further, according to the present invention, in the method for generating a multi-wavelength phase-modulated optical pulse train, a series of optical pulse trains is generated, and the optical pulse trains are digitally phase-modulated.
An optical pulse train characterized by performing an operation of increasing the spectrum width of the phase-modulated optical pulse train and filtering a plurality of optical pulse train signal trains having a bandwidth narrower than the optical spectrum train from the light pulse train having a widened spectral width. The present invention discloses a method of generating a digital phase-modulated optical pulse train having a relatively close wave number.

An advantage of the multi-wavelength phase-modulated optical pulse train generating apparatus and method of the present invention is that a multi-wavelength phase-modulated optical pulse train can be simultaneously generated from a series of digital phase-modulated optical pulse trains. Since a plurality of pulsed light sources and a plurality of optical modulators are not used unlike the conventional generation method, the apparatus can be greatly simplified.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram for specifically illustrating an embodiment of the present invention.

FIG. 3 is a diagram showing a spectrum of an optical pulse train in the embodiment of the present invention. (a) is the spectrum of the optical pulse train input to the optical fiber 24. (b) is the spectrum of the optical pulse train output from the optical fiber 24. (c) is an optical spectrum of the optical multi-wavelength digital phase-modulated pulse train output from the optical filter array 25.
1 (1545 nm) and wavelength♯2 (1555 nm).

FIG. 4 is a schematic diagram showing a conventional multi-wavelength digital phase modulation optical pulse train generation apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Pulse light generation part 12 Optical phase modulation part 13 Optical spectrum spreading part 14 Optical filtering part 21 Pulse light source 22 Phase modulator 23 Optical amplifier 24 Super continuum light generation optical fiber 25 Optical filter array 41-1 and 41 -2,... 41-n pulse light source (n
Indicates an apparatus for the n-th wavelength. 42-1, 42-2,... 42-n Phase modulator (n
Indicates the device for the n-th wavelength.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-291398 (JP, A) JP-A-8-234249 (JP, A) European Patent Application Publication 859266 (EP, A2) (58) Field (Int.Cl. ⁷ , DB name) G02F 1/35 H01S 3/10 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A pulse light generator 1 for generating a series of optical pulse trains in a multi-wavelength phase modulated optical pulse train generator.
1, an optical phase modulator 12 that digitally modulates the optical pulse train, an optical spreader 13 that performs an operation to increase the spectrum width of the phase-modulated optical pulse train, and a bandwidth narrower than the expanded optical spectrum width An optical pulse train generator comprising an optical filtering section 14 for obtaining a plurality of optical pulse train signal trains. 2. The multi-wavelength phase-modulated optical pulse train generating apparatus according to claim 1, wherein the optical spectrum spreader uses an optical fiber, and particularly generates the optical pulse train when the optical pulse train propagates through the optical fiber. An optical pulse train generating apparatus characterized in that the spectrum of the optical pulse train is broadened using super continuum light. 3. The multi-wavelength phase-modulated optical pulse train generating apparatus according to claim 2, wherein said optical fiber is a dispersion flat fiber having a small change in chromatic dispersion with respect to wavelength at a pump wavelength. 0 to 0.0 ps
An optical pulse train generator using an optical fiber in a normal dispersion region of / nm / km. 4. A method for generating a multi-wavelength phase-modulated optical pulse train, comprising the steps of generating a series of optical pulse trains, digitally modulating the optical pulse trains, and expanding the spectrum width of the phase-modulated optical pulse trains. A method for generating an optical pulse train, characterized in that a plurality of optical pulse train signal trains having a bandwidth narrower than the optical spectrum width are filtered from the optical pulse train having the widened optical pulse train.