JP2000295201A - Optical frequency mutliplexing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To array an optical modulation wave signal at narrow frequency intervals which is difficult for wave division by respectively dividing equal frequency interval multiplex-wave length lights into respective light waves, modulating the divided light waves by means of a transmission signal, synthesizing the obtained optical modulation wave signals and generating light signals where the respective light waves are mutually multiplexed at optical frequency intervals. SOLUTION: A second optical demultiplexer 4 is constituted of an array waveguide diffraction grating AWG like the first optical demultiplexer 2. The second optical demultiplexer 4-1 demultiplexes the light waves multiplexed by a wave multiplexing device 3-1 into the light waves at frequency interval λ and outputs them to optical modulators 5-11 to 5-1m arranged at every demultiplexing. The optical modulators 5-11 to 5-1m input the respective light waves with a wavelength λ1 supplied from the second optical demultiplexer 4-1 as a center, modulates them by an electric signal and generates the optical modulation signals. The generated optical modulation wave signals are supplied to the optical multiplexer 6-2. Besides, the optical modulators 5-k1 to 5-2m input the respective light waves supplied from the second optical demultiplexer 4-2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density optical frequency multiplexing optical transmission system in which interference between adjacent optically modulated waves becomes a problem due to wavelength fluctuations, and to use dual multi-wavelength technology. Thus, the present invention relates to an optical frequency multiplexing apparatus that reduces the number of transmission light sources and does not require optical frequency interval control.

SUMMARY OF THE INVENTION The present invention is an optical transmission system in which a plurality of signals are transmitted by optical frequency division multiplexing (hereinafter, simply referred to as "optical frequency multiplexing"). In the case where light waves are optically frequency-multiplexed at a narrow frequency interval F for which optical demultiplexing is difficult to the extent that coherent optical detection is required for selective reception, an optical sideband at an optical frequency interval ∧ or a Multi-wavelength light waves (hereinafter, operations such as optical phase modulation performed to generate optical sidebands or multi-wavelength light waves are referred to as "multi-wavelength", and a multi-wavelength light source is referred to as a "multi-wavelength light source." Is generated and demultiplexed. From each lightwave, another sideband with an optical frequency interval of λ is generated by another multi-wavelength generation and demultiplexed, and each lightwave is modulated with an electric signal to be transmitted. After that, all the light modulated wave signals By appropriately selecting the frequency intervals Λ and λ, it is possible to combine optical modulated wave signals with narrow and equal optical frequency intervals, which are difficult to separate with an optical filter or optical demultiplexer. This is to generate optical signals arranged without using control.

[0003]

2. Description of the Related Art A signal distribution system using optical frequency multiplexing as shown in FIG. 3 is conventionally known.

In this signal distribution system, each of the optical transmitters (first optical transmitter 101-1 to k-th optical transmitter 101-k) is connected to the optical combiner / distributor 102, while the optical receiver (first Each of the optical receivers 103-1 to 103-n) is configured to be connected to the optical combiner / distributor 102. Each optical transmitter 101 includes a light source and an external optical modulator, modulates the light source light with a transmission signal, generates an optical signal, and outputs the optical signal to the photosynthetic distributor 102. Each of the optical receivers 103 includes a lightwave selector and a photodetector, selects and receives a desired optical signal from the optical signals supplied from the photosynthetic distributor 102, and reproduces the received signal.

In the above-described signal distribution system, when the wavelength multiplexing system is adopted, a tunable optical filter is used as the lightwave selector for selecting a desired lightwave in each optical receiver 103. In this wavelength multiplexing method, since the wavelength interval is wide, strict wavelength management is not required. On the other hand, in the above signal distribution system, when a coherent reception method using a local light source is adopted, it is possible to selectively receive wavelengths narrower than wavelength multiplexing, that is, light waves arranged at optical frequency intervals. However, in this case, strict management of the optical frequency of each optical transmitter 101 is required to prevent interference between light waves.

As one method of managing the optical frequency of an optical transmitter, as shown in FIG. 4, a method of individually controlling the optical frequency of a transmission light source based on an absolute optical frequency standard (such as acetylene gas) is known. (For example, Electron. Lett., Vol. 2
5, No. 9, pp. 574-576 (1989)).

As shown in FIG. 4, this prior art example has a semiconductor laser 111-1 which generates light waves of wavelengths λ1 to λk.
To 111-k and these semiconductor lasers 111-1 to 111-111.
-k drive control and optical frequency control to execute optical frequency control and optical frequency controllers 112-1 to 112-k, and lasers of wavelengths λ1 to λk emitted from semiconductor lasers 111-1 to 111-k, respectively. Optical frequency standard devices 113-1 to 113-k for inputting light and generating light, and semiconductor lasers 111-1 to 111-1
External modulators 114-1 to 114-k for inputting light waves having wavelengths λ1 to λk output from 11-k and modulating them with a predetermined transmission signal
And an optical multiplexer 115 that outputs an optical signal obtained by synthesizing optical modulation wave signals output from the external modulators 114-1 to 114-k to an optical transmission system. Then, the semiconductor lasers 111-1 to 111-k are controlled based on the light to generate lightwaves having wavelengths λ1 to λk, and the lightwaves having wavelengths λ1 to λk are modulated by a predetermined transmission signal to generate a light modulation wave signal. After that, an optical signal obtained by combining these optical modulation wave signals is generated and output to the optical transmission system.

However, this method requires a semiconductor laser to be a light source for each wavelength, and requires optical frequency control by an optical frequency standard device 113 and an optical frequency controller 112 for each light source. There is a disadvantage that the configuration is complicated and large-scale.

On the other hand, a technique of a multi-wavelength light source for generating a plurality of light waves having the same frequency interval from one light source is also known. This technology uses a mode-locked laser (eg, K. Sat
OK. Wakita, I. Kotaka, I. Kondo, and M. Yamamoto, “Mon
olithic strained-InGaAsP multiple-quantum-well las
ers with integrated electroabsorption modulators f
or active mode locking, ”Appl.Phys.Lett., Vol.65, N
o.1, pp. 1-3 (1994)) or an optical frequency comb generator (eg, M. Kourogi, K. Nakagawa, and M. ohtsu, “Wide-span o
ptical frequency comb generator for accurate optic
al frequency differency measurement, ”IEEE J.Quant
um Electron., Vol. 29, No. 10, pp. 2693-2701 (1993)).

[0010] The multi-wavelength light obtained by these mode-locked lasers or optical frequency comb generators is demultiplexed,
By modulating each lightwave with a transmission signal and then multiplexing, a plurality of signals can be transmitted from one light source, and frequency interval control can be eliminated.

For example, as an example in which a mode-locked laser is used, as shown in FIG. 5, the output of a mode-locked laser 122 in a state in which a specific oscillation light frequency is tuned to the reference laser 121 by injection locking of the reference laser 121. Light (optical sideband signal) is converted into an arrayed waveguide diffraction grating (AWG) 1
The LN light intensity modulators 124-1 through 12-1 are divided into 16 waves at intervals of 50 GHz by 23 and provided for each of the wavelengths λ1 through λ16.
Transmission experiments with modulation and transmission at 124-16 have been conducted (Yasaka Yasaka, Mitsuhiro Teshima, Hiroaki Sanjo, Yuzo Yoshikuni, "Multiwavelength light source with equal wavelength and reference wavelength for lightwave networks," 1
997 IEICE General Conference SC-4-3).

A method has also been proposed in which light waves of one multi-wavelength light source are distributed to respective transmission points, different wavelengths are extracted at each transmission point, modulated with a transmission signal, and then combined (Katsu Iwashita, Ishida) Osamu, Noboru Kochio, "Lightwave Network Using Wavelength Division Multiplexing Technology," Institute of Electronics, Information and Communication Engineers Optical Communication Systems Study Group OCS95-33 (1995)).

However, when a one-stage multi-wavelength light source is used, it is necessary to extract one lightwave so that external modulation can be performed on the transmission signal. In the above-mentioned method, however, the frequency is narrower than the selectivity of the optical demultiplexer. Light waves cannot be arranged at intervals.

As an attempt to double the frequency utilization efficiency, 2
Prepare two light sources, multi-wavelength at equal frequency intervals, 2
There is a report that the output wavelengths of two multi-wavelength light sources are arranged to be interleaved after multiplexing (R. Monnard, AKSrivastav
a, CRDoerr, R.-J.Essiambre, CHJoyner, LWStulz, M.
Zirngibl, Y. Sun, JWSulhoff, JLZyskind, and C.Wol
f, “Demonstration of A 16 × 10Gb / s Long-Haul Transm
ission with 50-GHz Channel Spacing Using Two Multi
frequency Lasers, ”ECOC'98,20-24 September 1998, Ma
drid, Spain, pp.193-194)).

However, this method also has a disadvantage that the frequency interval between the two sets of multi-wavelength light sources must be controlled.

As a method of arranging light waves modulated without using frequency division control and without using an optical demultiplexer, subcarrier multiplex transmission techniques (for example, R. Olshansky, VALanzisera,
andP.M.HiIl, “Subcarrier multiplexed lightwave sy
stems for broadband distribution, ”J.Lightwave.Tec
hnol., Vol. 7, No. 9, pp. 1329-1342 (1989)).

In the conventional example shown in FIG. 6, the output light of the laser light source 131 of the optical frequency f0 is optically modulated by the optical modulator 132 with the modulation signal obtained by multiplexing the sine wave electric signals of the frequencies fl and f2, and the modulation generated. One side of the sideband is used. If the sine wave is modulated by an electric signal, the optical sideband can be regarded as an optical frequency multiplexed optically modulated wave. As an example of this, a signal wave optically phase-modulated with a signal obtained by frequency-multiplexing two QPSK modulated waves modulated by an electric stage is subjected to local oscillation and heterodyne synchronous detection (for example, PMHill, and R. Olshansky, “8Gb / s
Subcarrier multiplexed coherent lightwave syste
m, ”IEEE Photon.Technol.Lett., Vol.3, No.8, pp.764-76
6 (1991)).

However, since optical frequency multiplexing in a wide wavelength range cannot be performed due to the limitation by the modulation band of the light source or the external optical modulator, and the magnitude of the optical modulation degree is limited due to the need to suppress the generation of modulation distortion. There is a disadvantage that the use efficiency of light frequency and light wave energy is poor.

Further, when optical frequency multiplexing is extended by using a plurality of light waves, as shown in FIG. 6, it is necessary to extract and use only one optical sideband (for example, upper sideband) with an optical filter or the like. Therefore, when the number of multiplexed signals is increased in a limited frequency band, an optical filter having a steep demultiplexing characteristic is newly required.

[0020]

As described above, in each of the above-described prior arts, strict frequency control is required, a large number of light sources are required, or the use efficiency of the optical frequency and the light wave energy is poor. There is a defect, and there is no known technique similar to the present invention.

The present invention has been made in view of the above circumstances, and makes it possible to arrange optically modulated wave signals at narrow frequency intervals where demultiplexing is difficult as expected in coherent optical transmission without using optical frequency interval control. It is an object of the present invention to provide an optical frequency multiplexing optical transmission device.

[0022]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an optical frequency division multiplexed optical wave to the extent that coherent optical detection is required when selectively receiving one optical wave from a plurality of optical waves. An optical frequency multiplexing apparatus for generating an optical signal multiplexed at a narrow frequency interval F in which optical demultiplexing is difficult, wherein a first light source generates a multi-wavelength light having an equal frequency interval に よ り from a single light source by multi-wavelength conversion. Wavelength converting means, first demultiplexing means for demultiplexing the multi-wavelength multi-wavelength light having the same frequency interval に into each light wave, and performing multi-wavelength conversion on each of the demultiplexed light waves to obtain the same frequency interval. a second multi-wavelength generating means for generating multi-wavelength light of λ (λ と), and an equal frequency interval λ obtained by performing multi-wavelength conversion.
Second demultiplexing means for demultiplexing the multi-wavelength light into each lightwave, a modulation means for modulating each demultiplexed lightwave with a transmission signal, and an optical modulation wave signal obtained by the modulation, and An optical signal generating means for generating an optical signal in which light waves are alternately light-wave multiplexed at the light frequency interval F.

According to the above configuration, the multi-wavelength and demultiplexing are performed twice for a single light source, modulated by an electric signal to be transmitted, and then combined, so that optical frequency interval control is not used. The optically modulated wave signals are arranged at narrow frequency intervals in which demultiplexing is difficult as expected in coherent optical transmission.

[0024]

FIG. 1 is a block diagram showing an embodiment of an optical frequency multiplexing apparatus according to the present invention.

This optical frequency multiplexing apparatus has a multi-wavelength light source 1
, A first optical demultiplexer 2, and a multi-wavelength device 3 (3-1, 3-2,
, 3-k) and the second optical demultiplexer 4 (4-1, 4-2, ..., 4-
k), an optical modulator 5 (5-11, 5-12,..., 5-km), an optical multiplexer 6 (6-1, 6-2,..., 6-k), And Further, the multi-wavelength device 3 and the second optical demultiplexer 4
, The optical modulator 5 and the optical multiplexer 6 are provided as a set, and a total of k types are provided, and these are provided for each transmission point. Then, in an optical transmission system that transmits a plurality of signals by optical frequency multiplexing, optical demultiplexing is difficult to the extent that coherent photodetection is required when selectively receiving one lightwave from a plurality of lightwaves multiplexed. In the case where light waves are multiplexed at a narrow frequency interval F, the optical sidebands of equal frequency interval 波 generated from a single light source by multi-wavelength separation are split by the first optical splitter 2 and extracted. The obtained lightwave is subjected to additional multiwavelength processing by the multiwavelength conversion device 3, and the obtained optical sidebands at equal frequency intervals λ (λ ≠ Λ) are demultiplexed by the second optical demultiplexer 4 and transmitted. By using an electric signal to be modulated as an optical carrier, an appropriate frequency interval is set so that each optical sideband is alternately optically multiplexed at an optical frequency interval F when all the optically modulated wave signals are combined. And multiple wavelengths are applied by λ

The multi-wavelength light source 1 is composed of a mode-locked laser and has multi-wavelength lights λ 1 and λ with a frequency interval Λ = 70 GHz.
, .Lambda.k, and outputs this multi-wavelength light to the first demultiplexer 2 via an optical fiber.

The first optical demultiplexer 2 is composed of an arrayed waveguide diffraction grating (AWG), and outputs multi-wavelength light (λ1, λ2,..., Λk) supplied from the multi-wavelength light source 1 via an optical fiber. The light beams having the wavelengths λ1, λ2, and λk are respectively demultiplexed and supplied to the respective multi-wavelength converting devices 3 (3-1, 3-2,..., 3-k).

The multi-wavelength converting devices 3 are each constituted by an optical frequency comb generator, and the multi-wavelength converting device 3-1 has a multi-wavelength device having a wavelength interval of λ = 25 GHz around the wavelength λ1. Multi-wavelength light generated by the multi-wavelength conversion device 3-k
Is the center of the wavelength λk and the frequency interval before and after that is λ =
The multi-wavelength light having a wavelength of 25 GHz is generated.
Each of the multi-wavelength lights having the multi-wavelengths is supplied to a second demultiplexer 4 (4-1, 4-2,..., 4-k) provided separately.

Each of the second optical demultiplexers 4 is, similarly to the first optical demultiplexer 2, composed of an arrayed waveguide diffraction grating (AWG), and the second optical demultiplexer 4-1 is a multi-wavelength conversion device 3 The multi-wavelength lightwave divided by -1 is divided into lightwaves having a frequency interval of λ and output to optical modulators 5-11,..., 5-1m provided for the respective demultiplexers. The optical modulator 4-2 splits the lightwave multi-wavelength-converted by the multiwavelength converting device 3-2 into lightwaves having a frequency interval of λ, and optical modulators 5-21,. Further, the second optical demultiplexer 4-k demultiplexes the lightwave multi-wavelength-converted by the multi-wavelength conversion device 3-k into lightwaves having a frequency interval λ, and the light provided for each demultiplexing. Output to modulators 5-k1, ..., 5-km.

The optical modulators 5-11,..., 5-1m receive the respective optical waves centered on the wavelength λ1 supplied from the second optical demultiplexer 4-1 and modulate them with electric signals to perform optical modulation. A wave signal is generated, and the generated optical modulation wave signal is supplied to the optical multiplexer 6-1. Also, the optical modulators 5-21,.
Each of the light waves centered on the wavelength λ2 supplied from the optical demultiplexer 4-2 is input and modulated by an electric signal to generate a light modulated wave signal. The generated light modulated wave signal is an optical multiplexer. 6-2. Further, the optical modulators 5-k1,..., 5-km
Is for inputting each light wave centered on the wavelength λk supplied from the second optical demultiplexer 4-k and modulating it with an electric signal to generate a light modulated wave signal. Is supplied to the optical multiplexer 6-k.

Each optical multiplexer 6-1 is connected to each optical modulator 5-11,
,... 5-1m are input and combined, and the combined optical signal is output to the combiner / distributor 7. Also,
The optical multiplexer 6-2 inputs and combines the respective optical modulation wave signals supplied from the respective optical modulators 5-21,..., 5-2m, and outputs the combined optical signal to the multiplexer / distributor 7. Further, the optical multiplexer 6-k is
Each of the optical modulators 5-k1,..., And 5-km is input and combined, and the combined optical signal is output to the combiner / distributor 7.

The multiplexer / demultiplexer 7 includes multiplexers 6-1, 6-2,.
All the combined optical signals supplied from 6-k are multiplexed, and the multiplexed optical signal is output to the optical network. It should be noted that, in place of the multiplexer / distributor 7, this can be constituted by a multiplexer and a distributor.

Next, the operation of this embodiment will be described.

In the multi-wavelength light source 1, the frequency interval ∧, the wavelength λ
1, .lambda.2,..., .Lambda.k are generated.
Are supplied to the first optical demultiplexer 2. In the first optical demultiplexer 2, the multi-wavelength light (λ1, λ2,.
The light is demultiplexed into lightwaves having wavelengths of 1, λ2, and λk, and supplied to the respective multiple wavelength converting devices 3.

In the multi-wavelength conversion device 3, the multi-wavelength conversion is performed again. At this time, the lightwave of wavelength λx generated at a frequency interval λ from the lightwave of wavelength λ1 has a positional relationship with the lightwave of wavelength λy similarly generated from the lightwave of wavelength λ2 when the output of the combiner / distributor 7 is shown in FIG. Side by side like the spectrum shown in
They are arranged at frequency intervals F. This utilizes the fact that the profiles of the outputs of the multiple wavelength converting device 3 overlap. Similarly, the light wave of the wavelength λz generated from the wavelength λ3 is further adjacent to the light wave of the wavelength λy at the frequency interval F. For this reason, each optical wave can be split by an optical filter, but after optical frequency multiplexing, is multiplexed at a narrower optical frequency interval.

In this embodiment, as described above, the first example of the multi-wavelength light source 1 uses a mode-locked laser, and the second-stage multi-wavelength device 3 uses an optical frequency comb generator. This will be described.

The first optical splitter 2 and the second optical splitter 4 are AW
In the case of G, the second-stage frequency interval λ is set to 25 GHz in consideration of the current AWG technology. For example, as shown in FIG. 2, when the frequency interval 初 of the first stage is set to 70 GHz, the number of light waves generated by the second-stage multiwavelength device 3 is set to a maximum of 14 waves in consideration of the overlapping of light waves. Can be. Here, the frequency intervals ∧ and λ are optical frequency intervals that can be split by the first and second optical splitters 2 and 4. FIG.
Is an example in which the first stage is shown as three waves. The demultiplexed light waves of wavelengths λx, λy, and λz are adjacently multiplexed at an optical frequency interval F (= 5 GHz) that cannot be demultiplexed by the second optical demultiplexer 4.

In this case, the first stage has 32 waves (about 17n).
m range), assuming that a maximum of 44
Eight light waves can be used in a state where each wavelength is managed at a frequency interval of 5 GHz. These light waves are equivalent to one channel of Hi-Vision, and are optical D having a transmission rate of 1.485 Gbps.
It can be applied to an optical carrier that optically multiplexes a BPSK wave (Mikio Maeda et al., "Experiment on DPSK coherent optical transmission using a phase diversity scheme", IEICE Technical Committee on Optical Communication Systems, OCS 96-126, 1997).

In the above embodiment, the case where λ <Λ has been described. However, it is clear that the same object can be achieved when λ> Λ.

[0040]

As described above, according to the present invention, without using optical frequency interval control, an optically modulated wave signal is arranged at a narrow frequency interval in which demultiplexing is difficult as expected in coherent optical transmission. It is possible to do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical frequency multiplexing device according to the present invention.

FIG. 2 is an explanatory diagram illustrating an example of an arrangement of light waves generated in an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a conventionally known optical transmission system.

FIG. 4 is a block diagram illustrating an example of a conventional optical frequency multiplexing device.

FIG. 5 is a block diagram showing a conventional optical frequency multiplexing apparatus for realizing a multi-wavelength light source using a mode-locked laser.

FIG. 6 is a block diagram showing a conventional example of an optical frequency multiplexing apparatus using a subcarrier multiplex transmission technique.

[Explanation of symbols]

 Reference Signs List 1 multi-wavelength light source 2 first optical demultiplexer 3 (3-1 to 3-k) multi-wavelength conversion device 4 (4-1 to 4-k) second optical demultiplexer 5 (5-11 to 5-km) ) Optical modulator 6 (6-1 to 6-k) Optical multiplexer 7 Multiplexer

Claims (1)

[Claims] 1. An optical signal multiplexed at a narrow frequency interval F in which optical demultiplexing is difficult to the extent that coherent optical detection is required when one optical wave is selectively received from a plurality of optical frequency multiplexed optical waves. An optical frequency multiplexing apparatus that generates multi-wavelength light having an equal frequency interval に よ り from a single light source by multi-wavelength generation; and a multi-wavelength equal frequency interval Λ multi-wavelength device. A first demultiplexing unit for demultiplexing the wavelength light into each light wave, and a second demultiplexing unit for performing multi-wavelength generation for each demultiplexed light wave to generate multi-wavelength light having an equal frequency interval λ (λ ≠ Λ). Wavelength demultiplexing means; second demultiplexing means for demultiplexing the multi-wavelength light having the same frequency interval λ obtained by performing multi-wavelength division into respective light waves; and modulation for modulating each demultiplexed light wave with a transmission signal. Means for synthesizing an optically modulated wave signal obtained by the modulation so that each light wave is An optical frequency multiplexing apparatus, comprising: an optical signal generating unit that generates an optical signal that is alternately light-wave multiplexed at several intervals F.