JP3971049B2 - Optical frequency multiplexer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a high-density optical frequency multiplexing optical transmission system in which interference between adjacent optical modulation waves becomes a problem due to wavelength fluctuations. The present invention relates to an optical frequency multiplexing apparatus in which the optical frequency interval control is unnecessary.
[0002]
[Summary of 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”), and coherent optical detection is performed when one optical wave is selectively received from a plurality of optical waves. In the case where optical waves are optical frequency multiplexed at a narrow frequency interval F where optical demultiplexing is difficult to the extent necessary, a single side light source optical sideband of optical frequency interval ∧ or similar multiwavelength light waves (hereinafter, Operations such as optical phase modulation performed to generate this optical sideband or multi-wavelength light wave are called “multi-wavelength”, and a multi-wavelength light source is called “multi-wavelength light source”). The optical sidebands of the optical frequency interval λ are generated and separated from each optical wave by different multi-wavelengths, and each optical wave is modulated with an electrical signal to be transmitted, and then all optical modulated waves It is designed to synthesize signals By appropriately selecting the frequency intervals Λ and λ, the optical modulation wave signals with narrow and equal optical frequency intervals that are difficult to separate with optical filters and optical demultiplexers are arranged without using optical frequency interval control. A signal is generated.
[0003]
[Prior art]
Conventionally, a signal distribution system using optical frequency multiplexing as shown in FIG. 3 is known.
[0004]
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 optical receiver). Each of the optical receivers 103-1 to 103-n) is also 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 optical combiner / distributor 102. Each optical receiver 103 includes a light wave selector and a light receiver, selects a desired optical signal from among the optical signals supplied from the light combining / distributing device 102, and reproduces the received signal.
[0005]
In the above signal distribution system, when the wavelength multiplexing system is adopted, a tunable optical filter is used as the light wave selector for selecting a desired light wave in each optical receiver 103. In this wavelength multiplexing system, since the wavelength interval is wide, strict wavelength management is not required. On the other hand, in the signal distribution system, when a coherent reception method using a local light source is adopted, it is possible to selectively receive light waves arranged at a wavelength narrower than wavelength multiplexing, that is, 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 the light waves.
[0006]
As a method for managing the optical frequency of the optical transmitter, as shown in FIG. 4, a method of individually controlling the optical frequency of the transmission light source based on an absolute optical frequency standard (acetylene gas or the like) is known (for example, Electron. Lett., Vol. 25, No. 9, pp. 574-576 (1989)).
[0007]
As shown in FIG. 4, this conventional example includes semiconductor lasers 111-1 to 111-k that generate light waves of wavelengths λ1 to λk, and drive control and optical frequencies of these semiconductor lasers 111-1 to 111-k, respectively. Each of the drivers and optical frequency controllers 112-1 to 112-k that execute the control and the laser beams of wavelengths λ1 to λk emitted by the semiconductor lasers 111-1 to 111-k are respectively input to emit light. An optical frequency standard device 113-1 to 113-k to be generated and an external modulator 114- that receives light waves of wavelengths λ1 to λk output from the semiconductor lasers 111-1 to 111-k and modulates them with a predetermined transmission signal 1 to 114-k and an optical multiplexer 115 that outputs an optical signal obtained by synthesizing the optical modulation wave signals output from the external modulators 114-1 to 114-k to the optical transmission system. Then, based on the light, the semiconductor lasers 111-1 to 111-k are controlled to generate light waves of wavelengths λ1 to λk, and the light waves of wavelengths λ1 to λk are modulated with a predetermined transmission signal to generate an optical modulation wave signal After that, an optical signal obtained by synthesizing these optical modulation wave signals is generated and output to the optical transmission system.
[0008]
However, this method requires a semiconductor laser as a light source for each wavelength, and requires optical frequency control by the optical frequency standard device 113 and the optical frequency controller 112 for each light source, resulting in a complicated apparatus configuration. And has the disadvantage of becoming large.
[0009]
On the other hand, a technique of a multi-wavelength light source that generates a plurality of light waves with equal frequency intervals from one light source is also known. This technique is based on mode-locked lasers (eg, K. Sato, K. Wakita, I. Kotaka, I. Kondo, and M. Yamamoto, “Monolithic strained-InGaAsP multiple-quantum-well lasers with integrated electroabsorption modulators for active mode locking. , “Appl. Phys. Lett., Vol. 65, No. 1, pp. 1-3 (1994)) or optical frequency comb generator (eg, M. Kourogi, K. Nakagawa, and M. ohtsu,“ Wide -span optical frequency comb generator for accurate optical frequency difference measurement, "IEEE J. Quantum Electron., Vol. 29, No. 10, pp. 2693-2701 (1993)).
[0010]
By demultiplexing the multi-wavelength light obtained by these mode-locked lasers or optical frequency comb generators, and then multiplexing each light wave with a transmission signal, multiple signals can be sent from one light source, And frequency interval control can be made unnecessary.
[0011]
For example, as an example using a mode-locked laser, as shown in FIG. 5, the output light (light) of the mode-locked laser 122 in which a specific oscillation light frequency is tuned to the reference laser 121 by injection locking of the reference laser 121. (Sideband signal) is demultiplexed into 16 waves at intervals of 50 GHz by an arrayed waveguide diffraction grating (AWG) 123, and LN light intensity modulators 124-1 to 124-16 provided for the respective wavelengths λ1 to λ16. Experiments are being conducted to transmit modulated signals (Hiroshi Yasaka, Mitsuhiro Teshima, Hiroaki Sanjo, Yuzo Yoshikuni, “Reference Wavelength / Equal Optical Frequency Spacing Multiwavelength Light Source for Lightwave Networks,” 1997 IEICE General Conference SC-4-3).
[0012]
Also proposed is a method of distributing light waves from one multi-wavelength light source to each transmission point, extracting different wavelengths at each transmission point, modulating them with a transmission signal, and then combining them (Katsushi Iwashita, Osamu Ishida, Kochio) Noboru, “Lightwave Network Using Wavelength Multiplexing Technology,” IEICE Optical Communication System Study Group OCS 95-33 (1995)).
[0013]
However, when a one-stage multi-wavelength light source is used, it is necessary to extract one light wave so that external modulation can be performed on the transmission signal. However, in the above method, the light wave has a frequency interval narrower than the selectivity of the optical demultiplexer. Cannot be arranged.
[0014]
In an attempt to double the frequency utilization efficiency, there are reports that two light sources are prepared, multiple wavelengths are arranged at equal frequency intervals, and the output wavelengths of the two multi-wavelength light sources are arranged so that they are interleaved after multiplexing (R. Monnard, AKSrivastava, CRDoerr, R.-J.Essiambre, CHJoyner, LWStulz, M.Zirngibl, Y.Sun, JWSulhoff, JLZyskind, and C.Wolf, “Demonstration of A 16 × 10Gb / s Long-Haul Transmission with 50-GHz Channel Spacing Using Two Multifrequency Lasers, “ECOC'98, 20-24 September 1998, Madrid, Spain, pp.193-194)).
[0015]
However, this method also has a drawback that the frequency interval between the two sets of multi-wavelength light sources must be controlled.
[0016]
Subcarrier multiplexed lightwave systems for broadband (for example, R. Olshansky, VALanzisera, and PMHiIl, “Subcarrier multiplexed lightwave systems for broadband”) is a method for arranging modulated light waves without using an optical demultiplexer. distribution, “J. Lightwave. Technol., Vol. 7, No. 9, pp. 1329-1342 (1989)) can be used.
[0017]
In the conventional example shown in FIG. 6, the output light of the laser light source 131 having the optical frequency fO is optically modulated by the optical modulator 132 with a modulation signal obtained by multiplexing the sinusoidal electric signals having the frequencies fl and f2, and the modulation sideband generated. One side is used. If the sine wave is modulated by an electric signal, the optical sideband can be regarded as an optically modulated wave obtained by optical frequency multiplexing. As an example of this, a signal wave that is optically phase-modulated with a signal obtained by frequency-multiplexing two QPSK modulated waves modulated by the electrical stage is subjected to local light emission and heterodyne synchronous detection (for example, PMHill, and R. Olshansky, “8Gb / s Subcarrier multiplexed coherent lightwave system, “IEEE Photon. Technol. Lett., Vol. 3, No. 8, pp. 764-766 (1991)).
[0018]
However, 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 because it is necessary to suppress the occurrence of modulation distortion. There is a disadvantage that the utilization efficiency of light wave energy is bad.
[0019]
Furthermore, when extending optical frequency multiplexing using a plurality of light waves, as shown in FIG. 6, it is necessary to extract and use only one optical sideband (for example, the upper sideband) with an optical filter or the like. If the number of multiplexed signals is increased within a limited frequency band, an optical filter having a steep demultiplexing characteristic is newly required.
[0020]
[Problems to be solved by the invention]
As described above, each of the above-described conventional techniques has problems such as requiring strict frequency control, requiring a large number of light sources, or poor utilization efficiency of optical frequency and light wave energy. There is no known technique similar to.
[0021]
In view of the above circumstances, the present invention is an optical frequency that enables optical modulated wave signals to be arranged at narrow frequency intervals that are difficult to demultiplex as expected in coherent optical transmission without using optical frequency interval control. An object of the present invention is to provide a multiplexed optical transmission apparatus.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a narrow optical frequency at which optical demultiplexing is difficult to the extent that coherent optical detection is required when selectively receiving one optical wave from a plurality of optical waves multiplexed in optical frequency. An optical frequency multiplexing device that generates optical signals multiplexed at an interval F, and generates a first multi-wavelength light that generates multi-wavelength light having an equal frequency interval Λ that can be demultiplexed from a single light source by multiple wavelengths. Means, first demultiplexing means for demultiplexing the multi-wavelength light having the same frequency interval Λ, which has been made into multi-wavelengths, into N (N is an integer of 2 or more) light waves, and each of the demultiplexed N light waves each multi-wavelength of performing multi-wavelength equal frequency intervals capable optical demultiplexing λ (λ ≠ λ, the integer multiple of the difference or the sum of an integral multiple and lambda of lambda is a relationship of an integral multiple of F) of a second multiple wavelength means for generating each light, the multi-wavelength light M (M equal frequency intervals λ obtained by subjecting a multi-wavelength is 2 or more A second duplexer means for respectively demultiplexing the respective light waves integer) pieces each, modulation for modulating the plurality of light waves each having a required wavelength of the maximum N × M pieces of the light wave demultiplexed by the transmission signal And optical signal generation means for synthesizing the optical modulation wave signals obtained by the modulation and generating optical signals in which the respective optical waves are alternately optically multiplexed at the optical frequency interval F. .
[0023]
According to the above configuration, coherent light can be generated without using optical frequency interval control by performing multi-wavelength multiplexing and demultiplexing for a single light source, and combining after modulation with an electrical signal to be transmitted. Optical modulated wave signals are arranged at narrow frequency intervals that are difficult to demultiplex as expected in transmission.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of an optical frequency multiplexing apparatus according to the present invention.
[0025]
This optical frequency multiplexing device includes a multi-wavelength light source 1, a first optical demultiplexer 2, a multi-wavelength device 3 (3-1, 3-2,..., 3-k), and a second optical demultiplexer. 4 (4-1, 4-2,..., 4-k), an optical modulator 5 (5-11, 5-12,..., 5-km), and an optical multiplexer 6 (6-1, 6-). 2, ..., 6-k) and a combiner / distributor 7. Further, the multi-wavelength device 3, the second optical demultiplexer 4, the optical modulator 5, and the optical multiplexer 6 are provided as a set, and a total of k expressions are provided for each transmission point. It shall be arrange | positioned. In an optical transmission system that transmits a plurality of signals by optical frequency multiplexing, optical demultiplexing is difficult to the extent that coherent optical detection is required when selectively receiving one light wave from a plurality of light waves multiplexed. When light waves are multiplexed at a narrow frequency interval F, the optical sidebands of equal frequency interval Λ generated by a multi-wavelength from a single light source are demultiplexed by the first optical demultiplexer 2 and extracted. The optical wavelength is subjected to additional multi-wavelength by the multi-wavelength device 3, and the obtained optical sidebands with the equal frequency interval λ (λ ≠ Λ) are demultiplexed by the second optical demultiplexer 4 and transmitted. By using the desired optical signal as an optical carrier wave to modulate, when all the optical modulation wave signals are combined, the respective optical sidebands are optically multiplexed with the optical frequency interval F alternately. And λ are doubled for multiple wavelengths.
[0026]
The multi-wavelength light source 1 is composed of a mode-locked laser, generates multi-wavelength light λ1, λ2,..., Λk with a frequency interval Λ = 70 GHz, and sends this multi-wavelength light to the first demultiplexer 2 through an optical fiber. Output.
[0027]
The first optical demultiplexer 2 is composed of an arrayed waveguide diffraction grating (AWG), and multiwavelength light (λ1, λ2,..., Λk) supplied from the multiwavelength light source 1 via an optical fiber has a wavelength λ1, Each of the light waves having the wavelengths λ2 and λk is demultiplexed and supplied to the different multi-wavelength devices 3 (3-1, 3-2,..., 3-k).
[0028]
Each of the multi-wavelength devices 3 is composed of an optical frequency comb generator, and the multi-wavelength device 3-1 is a multi-wavelength multi-wavelength having a wavelength interval of λ = 25 GHz around the wavelength λ1. The multi-wavelength generating device 3-k generates multi-wavelength light having a multi-wavelength with a frequency interval of λ = 25 GHz around the wavelength λk. Each multi-wavelength light converted to multi-wavelength is supplied to a second demultiplexer 4 (4-1, 4-2,..., 4-k) provided separately.
[0029]
As with the first optical demultiplexer 2, each second optical demultiplexer 4 is composed of an arrayed waveguide diffraction grating (AWG, and the second optical demultiplexer 4-1 is a multi-wavelength device 3-1. The multi-wavelength light waves are demultiplexed into light waves having a frequency interval λ and output to the optical modulators 5-11,..., 5-1m provided for each demultiplexing, and the second optical demultiplexer 4- 2 demultiplexes the light wave that has been multi-wavelength by the multi-wavelength device 3-2 into light waves with a frequency interval λ, and outputs them to the optical modulators 5-21,. Further, the second optical demultiplexer 4-k demultiplexes the light wave that has been multi-wavelength by the multi-wavelength device 3-k into light waves having a frequency interval λ, and is provided for each demultiplexing. -k1, ..., output to 5-km.
[0030]
The optical modulators 5-11,..., 5-1m input each light wave centered on the wavelength λ1 supplied from the second optical demultiplexer 4-1, and modulate the light wave by modulating an electric signal. The generated optical modulation wave signal is supplied to the optical multiplexer 6-1. The optical modulators 5-21,..., 5-2m receive the respective optical waves centered on the wavelength λ2 supplied from the second optical demultiplexer 4-2, and modulate the optical waves with electrical signals to modulate the optical waves. A signal is generated, and the generated optical modulation wave signal is supplied to the optical multiplexer 6-2. Further, the optical modulators 5-k1,..., 5-km receive the respective optical waves centered on the wavelength λk supplied from the second optical demultiplexer 4-k, and modulate the optical waves with electrical signals to modulate the optical waves. A signal is generated, and the generated optical modulation wave signal is supplied to the optical multiplexer 6-k.
[0031]
Each optical multiplexer 6-1 receives and synthesizes the optical modulated wave signals supplied from the optical modulators 5-11,..., 5-1m, and outputs the combined optical signal to the multiplexer 7. . Further, the optical multiplexer 6-2 inputs and synthesizes the optical modulated wave signals supplied from the optical modulators 5-21,..., 5-2m, and outputs the synthesized optical signal to the multiplexer 7. To do. Further, the optical multiplexer 6-k inputs and synthesizes the optical modulation wave signals supplied from the optical modulators 5-k1,..., 5-km, and outputs the combined optical signal to the multiplexer 7. To do.
[0032]
The multiplexer 7 multiplexes all the combined optical signals supplied from the multiplexers 6-1, 6-2,..., 6-k, and outputs the multiplexed optical signals to the optical network. In addition, it can replace with this combiner | distributor 7 and can also comprise this with a multiplexer and a divider | distributor.
[0033]
Next, the operation of this embodiment will be described.
[0034]
In the multi-wavelength light source 1, light waves having a frequency interval ∧ and wavelengths λ 1, λ 2,..., Λk are generated, and each output light wave of the multi-wavelength light source 1 is supplied to the first optical demultiplexer 2. In the first optical demultiplexer 2, the multi-wavelength light (λ 1, λ 2,..., Λ k) is demultiplexed into light waves having wavelengths λ 1, λ 2, and wavelength λ k and supplied to each multi-wavelength device 3. .
[0035]
In the multi-wavelength device 3, the multi-wavelength is performed again. At this time, the light wave of the wavelength λx generated at the frequency interval λ from the light wave of the wavelength λ1 has the positional relationship with the light wave of the wavelength λy similarly generated from the light wave of the wavelength λ2 when the combiner 7 outputs, as shown in FIG. As shown in the spectrum shown in FIG. This utilizes the fact that the profiles of the outputs of the multi-wavelength device 3 overlap. Similarly, the light wave having the wavelength λz generated from the wavelength λ3 is further adjacent to the light wave having the wavelength λy at the frequency interval F. For this reason, each optical wave can be demultiplexed by an optical filter, but is multiplexed at a narrower optical frequency interval after optical frequency multiplexing.
[0036]
In this embodiment, as described above, the first-stage multi-wavelength light source 1 uses a mode-locked laser, and the second-stage multi-wavelength device 3 uses an optical frequency comb generator. explain.
[0037]
When the first optical demultiplexer 2 and the second optical demultiplexer 4 are configured by AWG, the frequency interval λ of the second stage is set to 25 GHz in consideration of the current AWG technology. For example, as shown in FIG. 2, when the frequency interval Λ of the first stage is set to 70 GHz, the number of light waves generated by the multi-wavelength device 3 in the second stage should be a maximum of 14 waves in consideration of the overlapping of light waves. Can do. Here, the frequency intervals ∧ and λ are optical frequency intervals that can be demultiplexed by the first and second optical demultiplexers 2 and 4. FIG. 2 is an example showing the first stage as three waves. The demultiplexed 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.
[0038]
In this case, assuming that the first stage can output up to 32 waves (within a range of about 17 nm), a maximum of 448 light waves can be used in the final stage in a state where each wavelength is managed at a frequency interval of 5 GHz. These optical waves can be applied to an optical carrier that optically multiplexes optical DBPSK waves with a transmission speed of 1.485 Gbps equivalent to one channel of HDTV (Mikio Maeda et al. “Phase Diversity DPSK Coherent Optical Transmission Experiment”, IEICE) Optical Communication System Study Group, OCS 96-126, 1997).
[0039]
In the above embodiment, the case of λ <Λ has been described. However, it is obvious that the same object can be achieved also in the case of λ> Λ.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to arrange optical modulation wave signals at narrow frequency intervals that are difficult to demultiplex as expected in coherent optical transmission without using optical frequency interval control. Become.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an optical frequency multiplexing apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing an arrangement example of light waves generated in the embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of a conventionally known optical transmission system.
FIG. 4 is a block diagram showing an example of a conventional optical frequency multiplexing device.
FIG. 5 is a block diagram showing a conventional optical frequency multiplexing device that realizes 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 multiplexing transmission technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Multi-wavelength light source 2 1st optical demultiplexer 3 (3-1 to 3-k) Multi-wavelength 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 / distributor

Claims (1)

Light that generates an optical signal multiplexed at a narrow optical frequency interval F, in which optical demultiplexing is difficult to the extent that coherent optical detection is required when selectively receiving one optical wave from among a plurality of optical waves multiplexed in optical frequency A frequency multiplexing device,
First multi-wavelength generating means for generating multi-wavelength light with equal frequency interval Λ capable of optical demultiplexing by multi-wavelength from a single light source;
First demultiplexing means for demultiplexing the multiwavelength light having the equal frequency interval Λ, which has been made multiwavelength, into N (N is an integer of 2 or more) light waves;
An equal frequency interval λ (λ ≠ Λ, an integer multiple of Λ and an integer multiple of λ, or the sum of the integer multiples of F is equal to an integer that can be demultiplexed to each of the N light waves that have been demultiplexed. Second multi-wavelength generating means for generating multi-wavelength light each having a double relationship ),
Second demultiplexing means for demultiplexing multi-wavelength light of equal frequency interval λ obtained by performing multi-wavelength into M (M is an integer of 2 or more) light waves;
Modulation means for modulating a plurality of optical waves each having a required wavelength among the demultiplexed maximum N × M optical waves with a transmission signal;
Optical signal generating means for combining optical modulated wave signals obtained by modulation and generating optical signals in which the respective optical waves are alternately optically multiplexed at the optical frequency interval F;
An optical frequency multiplexing apparatus comprising:

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