JP4699413B2 - Wavelength multiplexer - Google Patents

Description

  The present invention relates to an optical transmitter / receiver of a wavelength division multiplexing optical communication system.

  FIG. 1 shows a configuration example of a conventional WDM-PON (Wavelength Division Multiplexing-Passive Optical Network). FIG. 1A is a configuration example in which a wavelength splitter is used in a branch portion of a transmission path, and FIG. 1B is a configuration example in which a power splitter is used in a branch section of the transmission path.

  As shown in FIG. 1, a plurality of optical signals having different wavelengths from a transmitter arranged in an OLT (Optical Line Terminal) 10 are multiplexed by a wavelength multiplexing circuit and sent to a transmission line as a downlink signal. This downstream signal is received by ONUs (Optical Network Units) 14-1 to 14-n via the wavelength splitter 12 or the power splitter 16 of the transmission path. In the case of FIG. 1A, the downstream signal is demultiplexed for each wavelength by the wavelength splitter 12, and each ONU receives the downstream signal of a predetermined wavelength. In the case of FIG. 1B, the downlink signal is branched by the power splitter 16, and each ONU selects and receives a predetermined wavelength of the downlink signal.

  On the other hand, a plurality of optical signals having different wavelengths from the transmitters arranged in each of the ONUs 14-1 to 14-n are sent to the transmission line as uplink signals. This upstream signal is received by the OLT 10 via the wavelength splitter 12 or the power splitter 16 in the transmission path. In OLT, an upstream signal is separated for each wavelength by a wavelength separation circuit and received by each receiver.

  Conventionally, in such a WDM-PON, an optical signal has been generated by direct modulation of a DFB-LD (Distributed Feedback-Laser Diode).

H. Suzuki, et al., “A Remote Wavelength Setting Procedure based on Wavelength Sense Random Access (λ-RA) for Power-splitter-based WDM-PON,” ECOC2009, We3, P.157, Sept. 2006 Sang-Mook Lee, et al., “Dense WDM-PON Based on Wavelength-Locked Fabry-Perot Laser Diodes,” IEEE Photonics Technology Letters, Vol. 17, No. 7, July 2005

  However, in the case of direct modulation of DFB-LD, the optical spectrum is expanded beyond the modulation band B of the optical signal by chirping. Here, when wavelength multiplexing is performed with the number of wavelengths N, the optical frequency utilization efficiency is η (≦ 1), and the required bandwidth of the optical region is N · B / η. That is, the influence of the decrease in the optical frequency utilization efficiency due to the spread of the optical spectrum is expanded N times by wavelength multiplexing.

  In order to avoid this problem, if the CW (Continuous Wave) light obtained from the DFB-LD is modulated by an external modulator, the spread of the optical spectrum can be reduced, but this method also separates the upstream signal from the downstream signal. It is difficult to avoid the dead band W of the optical filter used for multiplexing. The band of the optical region required in this case is (W + N · B / η) as shown in FIG.

  By the way, the power splitter type WDM-PON of FIG. 1B can share a transmission line by wavelength multiplexing with an existing TDMA type PON (for example, G-EPON or G-PON) ( Non-patent document 1). In that case, it is necessary to allocate the Future Band (1555-1625 nm), which is an unused wavelength band of the existing PON, to the uplink and downlink signals of the WDM-PON. Therefore, a technique capable of reducing the required optical band (W + N · B / η) for a predetermined number N of wavelengths is desired.

  As shown in FIG. 3, in an OLT of a power splitter type WDM-PON (Non-patent Document 2), an AWG (Arrayed Waveguide Grating) 22 is applied to a wavelength division multiplexing circuit for WDM, and its FSR (Free Spectral Range) is applied. By using this, it is possible to avoid the dead band W of the optical filter for demultiplexing the uplink signal and the downlink signal. However, in this case, optical filters 24-1 to n for wavelength selection are required for all receivers of OSUs (Optical Subscriber Units) 20-1 to 20-n arranged in the OLT 10, which is not economical.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wavelength division multiplex transmission technique for reducing a wavelength band required for WDM-PON.

In order to achieve such an object, the present invention provides a wavelength multiplexing apparatus, a wavelength multiplexing circuit for multiplexing a plurality of DPSK signals having different wavelengths, and the multiplexed DPSK. An optical delay circuit that generates an optical duobinary signal from the signal, and an optical receiver that receives a plurality of DPSK signals having different wavelengths as optical duobinary signals via the optical delay circuit , and each DPSK signal includes a bit Either a rate R DPSK signal or a bit rate nR (n is an integer) DPSK signal, and the optical delay circuit provides an optical duobinary from the multiplexed DPSK signal by providing a delay amount of 1 / R. A signal is generated .

The invention according to claim 2 is the wavelength multiplexing device according to claim 1, wherein each DPSK signal is one of a plurality of different bit rate DPSK signals, and the wavelength multiplexing device A wavelength multiplexing circuit and an optical delay circuit are provided for each different bit rate, and the wavelength multiplexing apparatus further includes an optical coupler for multiplexing optical duobinary signals from the optical delay circuit.

The invention according to claim 3 is the wavelength multiplexing device according to claim 1, wherein each DPSK signal is one of a plurality of DPSK signals having different bit rates, and the wavelength multiplexing device A wavelength multiplexing circuit and an optical delay circuit are provided for each different bit rate, and the wavelength multiplexing apparatus further includes a wavelength multiplexing circuit for multiplexing optical duobinary signals from the optical delay circuit.

The invention according to claim 4 is the wavelength multiplexing apparatus according to claim 1, wherein each DPSK signal is one of two DPSK signals having different bit rates, and the wavelength multiplexing apparatus A wavelength multiplexing circuit and an optical delay circuit are provided for each different bit rate, and the wavelength multiplexing apparatus further includes an interleaver for multiplexing optical duobinary signals from the optical delay circuit.

The invention according to claim 5 is the wavelength multiplexing device according to claim 4 , wherein the odd-numbered wavelength of the DPSK signal includes one of the DPSK signals having the two different bit rates, and is an even number. The second wavelength includes the other of the DPSK signals of the two different bit rates.

The invention described in Claim 6 is the wavelength multiplexing transmission network, and the wavelength multiplexing device according to any one of claims 1 to 5, for each wavelength, the optical duo-binary signal from the wavelength multiplexer characterized in that e Bei an optical receiver for receiving.

The invention described in Claim 7, a wavelength multiplexing transmission network according to claim 6, and further comprising a power splitter for splitting the optical duobinary signal from the wavelength division multiplexer.

The invention of claim 8 is a wavelength multiplexing transmission network according to claim 6, characterized in that it further comprising a wavelength splitter for demultiplexing an optical duobinary signal from the wavelength multiplexer .

The invention according to claim 9 is a method in a wavelength division multiplexing apparatus, which multiplexes a plurality of DPSK signals having different wavelengths and generates and transmits an optical duobinary signal from the multiplexed DPSK signal. And receiving a plurality of DPSK signals having different wavelengths into optical duobinary signals , each DPSK signal having a DPSK signal having a bit rate R and a DPSK signal having a bit rate nR (where n is an integer). And generating the optical duobinary signal includes combining each DPSK signal with a 1 / R delay amount .

The invention according to claim 10 is the method according to claim 9 , wherein each DPSK signal is one of a plurality of DPSK signals having different bit rates, and the optical duobinary signal is generated. Is further characterized by combining each DPSK signal with a delay amount corresponding to each bit rate.

  According to the present invention, the wavelength band required for WDM-PON can be economically narrowed, and wavelength resources can be effectively utilized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 4 shows a configuration example of the WDM-PON according to the first embodiment of the present invention. The WDM-PON is composed of one OLT 100 and a plurality of ONUs 140-1 to 140-n connected to the OLT via the power splitter 120. The OLT 100 has OSUs 200-1 to 200-n corresponding to each ONU, a wavelength demultiplexing circuit 210 that performs wavelength demultiplexing of upstream signals, a wavelength demultiplexing circuit 212 that performs wavelength multiplexing of downstream signals, and a predetermined delay. And an optical delay circuit 220 composed of a Mach-Zehnder interferometer. The OSU 200 includes an optical transmitter that transmits a DPSK (Differential Phase Shift Keying) modulated optical signal and an optical receiver that receives an optical duobinary signal. Each ONU 140 includes an optical filter 310 for wavelength selection, an optical transmitter that transmits a DPSK signal, and an optical receiver that receives an optical duobinary signal.

  The optical transmitter of the OSU 200 generates a precoded DPSK signal (bit rate R) to generate an optical duobinary signal. This DPSK signal is multiplexed by a wavelength demultiplexing circuit, then delayed for each wavelength by an optical delay circuit, and converted into an optical duobinary signal (bit rate R). Here, the delay amount of the optical delay circuit 220 is set to a value equal to the delay amount given by the precoding of the DPSK signal. The optical duobinary signal is wavelength-selected by the ONU optical filter 310 via the power splitter 120 and demodulated by the receiver.

  The optical transmitter of each ONU 140 generates a DPSK optical signal (bit rate R), passes through the optical filter 310, and is received by the OLT 100 via the power splitter 120. In the OLT 100, the DPSK optical signal is delay-detected by the optical delay circuit 220, converted into an optical duobinary signal, wavelength-separated by the wavelength demultiplexing circuit 210, and received by the OSU receiver for each wavelength.

  As described above, since the upstream and downstream optical signals are multiplexed / demultiplexed by the optical delay circuit 220, the dead band W does not occur. FIG. 5 shows the relationship between the transmission characteristics of the wavelength demultiplexing circuit and the optical delay circuit and the upstream and downstream optical signal spectra. As shown in FIG. 5, there is no need to set the dead band W between the upstream and downstream wavelength bands. In addition, since an optical duobinary signal obtained by delay detection of a DPSK signal and a DSPK signal is used as an optical signal, the modulation band is about half that of NRZ, which is a normal optical intensity signal, and the required bandwidth of the optical region Can be reduced.

(Second Embodiment)
FIG. 6 shows a configuration example of a WDM-PON according to the second embodiment of the present invention. This WDM-PON uses a wavelength splitter 160 instead of the power splitter 120 in the first embodiment. In this configuration example, the optical filters 312-1 to 31-n mounted on the ONUs 140-1 to n are for separating upstream and downstream optical signals.

  FIG. 7 shows the relationship between the transmission characteristics of the wavelength separation circuit, the optical delay circuit, and the wavelength splitter, and the upstream and downstream optical signal spectra. As shown in FIG. 7, the same effects as those of the first embodiment can be obtained in this embodiment.

(Third embodiment)
FIG. 8 shows a configuration example of a WDM-PON according to the third embodiment of the present invention. This WDM-PON is the same as the configuration example of the first embodiment, except that the bit rate R is an integer multiple n depending on the wavelength. In this configuration example, the delay amount (delay time) of the optical delay circuit 220 is set to 1 / R, and the delay amount (delay time) of a transmitter having a bit rate of nR is set to 1 / R (n-bit). Give delay). Thereby, it is possible to configure a WDM-PON in which a plurality of bit rates are mixed.

(Fourth embodiment)
FIG. 9 shows a configuration example of a WDM-PON according to the fourth embodiment of the present invention. This WDM-PON uses a wavelength splitter 160 instead of the power splitter 120 in the third embodiment.

(Fifth embodiment)
FIG. 10 shows a configuration example of a WDM-PON according to the fifth embodiment of the present invention. This WDM-PON has a different bit rate depending on the wavelength. Wavelength demultiplexing is performed for each wavelength having the same bit rate, and a delay amount (delay time) corresponding to the bit rate is given by the optical delay circuits 220-1 to 220-N. That is, the bit rate R _k: relative (k integer of 1 to N), sets the delay amount of the optical delay circuit 220-k to 1 / R _k. In this case, the delay amount of the precoder of the corresponding transmitter (delay time) is also set to 1 / R _k. The N optical delay circuits 220 are multiplexed by the optical coupler 240 and connected to the transmission path. Thereby, it is possible to configure a WDM-PON in which a plurality of bit rates are mixed.

(Sixth embodiment)
FIG. 11 shows a configuration example of a WDM-PON according to the sixth embodiment of the present invention. This WDM-PON is obtained by replacing the power splitter 120 in the fifth embodiment with a wavelength splitter 160.

(Seventh embodiment)
FIG. 12 shows a configuration example of a WDM-PON according to the seventh embodiment of the present invention. This WDM-PON uses an AWG 260 instead of the optical coupler 240 in the fifth embodiment. FIG. 13 shows the relationship between the transmission characteristics of the AWG and the upstream and downstream optical signal spectra in this configuration example. As shown in the figure, the wavelengths of the upstream and downstream signals can be arranged using the AWG FSR.

(Eighth embodiment)
FIG. 14 shows a configuration example of a WDM-PON according to the eighth embodiment of the present invention. This WDM-PON uses a wavelength splitter 160 instead of the power splitter 120 in the seventh embodiment.

(Ninth embodiment)
FIG. 15 shows a configuration example of a WDM-PON according to the ninth embodiment of the present invention. This WDM-PON uses an interleaver 280 instead of the optical coupler 240 when the bit rate is two types (N = 2) in the fifth embodiment. In this configuration example, 2 × n AWGs are used for the wavelength splitters 214 and 216 that perform wavelength demultiplexing in the OLT 100.

  FIG. 16 shows an example of a 2 × n AWG. Due to the circulatory nature of the AWG, if the input port is different even at the same wavelength, the output port is also different. Therefore, when the odd-numbered wavelength is assigned to one port on the 2-port side and the even-numbered wavelength is assigned to the other port, the odd-numbered and even-numbered adjacent wavelengths are one port every other port on the n-port side. Assigned to. Such an AWG is used as the wavelength splitters 214 and 216.

FIG. 17 shows an example of the wavelength arrangement of the upstream and downstream optical signals in this configuration example. Two wavelengths adjacent to each of the OSUs 200-1 and 200-2 are assigned in the wavelength arrangement as shown in the figure. Specifically, the receiver of each OSU 200 includes an upstream even-numbered wavelength λ _2k (k: integer of ₁ to n) having _one bit rate R ₁ and an upstream having the other bit rate R ₂ . An odd-numbered wavelength λ _{2k + 1} is assigned. In addition, each OSU200 transmitter bit rate even-numbered wavelengths down with R ₁ λ _'2l: and (l integer of 1 to n), the odd-numbered wavelengths downlink having a bit rate R ₂ lambda' Assign _{2l + 1} .

Further, the upstream even-numbered wavelength λ _2k is allocated to the transmitter of the ONU 140a set to the bit rate R ₁ , and the downstream even-numbered wavelength λ ′ _2l is allocated to the receiver. The upstream odd-numbered wavelength λ _{2k + 1} is allocated to the transmitter of the ONU 140b set to the bit rate R ₂ , and the downstream odd-numbered wavelength λ ′ _{2l + 1} is allocated to the receiver. In FIG. 15, only the ONU 140a set to the bit rate R ₁ and the ONU 140b set to the bit rate R ₂ are shown, but other ONUs 140 that can select the bit rate may be used.

  In this way, by assigning different bit rates to even-numbered and odd-numbered wavelengths, downlink signals transmitted from each OSU 200 are wavelength-multiplexed at different ports of the 2 × n AWG 216 according to the bit rate (wavelength). The Then, the optical delay circuits 220a and 220b are given delay amounts according to the respective bit rates, and are sent to the transmission line via the interleaver 280. In this case, the delay amount of the precoder of the corresponding transmitter is also set according to the bit rate. Each ONU 140 selects a corresponding downstream signal with the optical filters 310a and 310b, and receives a signal with a corresponding bit rate.

  On the other hand, each ONU 140 transmits an upstream signal having an even or odd wavelength according to the bit rate. This upstream signal is multiplexed by the power splitter 120 and demultiplexed by the interleaver 280 according to the even or odd wavelength (that is, according to the bit rate). The demultiplexed upstream signal is given delay amounts according to the respective bit rates by the optical delay circuits 220a and 220b, and is wavelength-separated into different ports of the 2 × n AWG 214 according to the respective wavelengths. Each OSU 200 receives the wavelength-separated uplink signal with a corresponding bit rate receiver.

  As described above, according to this configuration, it is possible to configure a WDM-PON in which two types of bit rates are mixed using the interleaver 280.

(10th Embodiment)
FIG. 18 shows a configuration example of a WDM-PON according to the tenth embodiment of the present invention. This WDM-PON uses a wavelength splitter 160 instead of the power splitter 120 in the ninth embodiment. FIG. 19 shows an example of the wavelength arrangement of the upstream and downstream optical signals in this configuration example.

  While the present invention has been described with respect to several specific embodiments, the embodiments described herein are merely illustrative in view of the many possible embodiments to which the principles of the present invention can be applied. It is not intended to limit the scope of the invention. For example, the wavelength demultiplexing circuit and the optical delay circuit of the OLT in the above embodiment can be integrated on a PLC (Planer Lightwave Circuit), and the OLT can be realized economically. Therefore, the configuration and details of the embodiment exemplified herein can be changed without departing from the spirit of the present invention. Further, the illustrative components and procedures may be changed, supplemented, or changed in order without departing from the spirit of the invention.

It is a figure which shows the structural example of the conventional WDM-PON, FIG. 1 (a) is a structural example which used the wavelength splitter for the branch part of a transmission line, FIG.1 (b) is a branch part of a transmission line. This is a configuration example using a power splitter. It is a figure for demonstrating the dead band of the optical filter for isolation | separation of the upstream signal and downstream signal used by the conventional WDM-PON. FIG. 3A is a diagram for explaining a WDM-PON without a dead band, FIG. 3A shows a configuration example of the WDM-PON, and FIG. 3B shows the transmission characteristics of the AWG and the optical filter, the uplink and The relationship with the spectrum of a downstream signal is shown. It is a figure which shows the structural example of WDM-PON by 1st Embodiment of this invention. FIG. 5 is a diagram showing the relationship between the transmission characteristics of the wavelength demultiplexing circuit and the optical delay circuit of FIG. 4 and the upstream and downstream optical signal spectra. It is a figure which shows the structural example of WDM-PON by 2nd Embodiment of this invention. It is a figure which shows the relationship between the transmission characteristic of the wavelength separation circuit of FIG. 6, an optical delay circuit, and a wavelength splitter, and an upstream and downstream optical signal spectrum. It is a figure which shows the structural example of WDM-PON by 3rd Embodiment of this invention. It is a figure which shows the structural example of WDM-PON by 4th Embodiment of this invention. It is a figure which shows the structural example of WDM-PON by 5th Embodiment of this invention. It is a figure which shows the structural example of WDM-PON by 6th Embodiment of this invention. It is a figure which shows the structural example of WDM-PON by 7th Embodiment of this invention. It is a figure which shows the relationship between the transmission characteristic of AWG of FIG. 12, and an upstream and downstream optical signal spectrum. It is a figure which shows the structural example of WDM-PON by 8th Embodiment of this invention. It is a figure which shows the structural example of WDM-PON by 9th Embodiment of this invention. It is a figure which shows the wavelength characteristic of 2 * n AWG in the structural example of FIG. FIG. 16 is a diagram illustrating a wavelength arrangement example of upstream and downstream optical signals in the configuration example of FIG. 15. It is a figure which shows the structural example of WDM-PON by 10th Embodiment of this invention. It is a figure which shows the example of wavelength arrangement | positioning of the upstream and downstream optical signal in the structural example of FIG.

Explanation of symbols

10 OLT
12 Wavelength splitter 14 ONU
16 Power splitter 20 OSU
22 wavelength demultiplexing circuit 24 optical filter 100 OLT
120 power splitter 140 ONU
160 Wavelength splitter 200 OSU
210 Wavelength demultiplexing circuit 212 Wavelength multiplexing circuit 214 2 × n wavelength demultiplexing circuit 216 2 × n wavelength demultiplexing circuit 220 Optical delay circuit 240 Optical coupler 260 Wavelength splitter 280 Interleaver 310, 312 Optical filter

Claims (10)

A wavelength multiplexing circuit for multiplexing a plurality of DPSK signals having different wavelengths;
An optical delay circuit for generating an optical duobinary signal from the multiplexed DPSK signal ;
An optical receiver that receives a plurality of DPSK signals having different wavelengths as optical duobinary signals via the optical delay circuit ;
Each DPSK signal is either a bit rate R DPSK signal or a bit rate nR (n is an integer) DPSK signal,
The optical delay circuit generates an optical duobinary signal from the multiplexed DPSK signal by giving a delay amount of 1 / R. The wavelength division multiplexing apparatus according to claim 1,
Each DPSK signal is one of a plurality of DPSK signals having different bit rates, and the wavelength multiplexing device includes a wavelength multiplexing circuit and an optical delay circuit for each of the different bit rates,
The wavelength multiplexing apparatus further includes an optical coupler that multiplexes optical duobinary signals from the optical delay circuit. The wavelength division multiplexing apparatus according to claim 1,
Each DPSK signal is one of a plurality of DPSK signals having different bit rates, and the wavelength multiplexing device includes a wavelength multiplexing circuit and an optical delay circuit for each of the different bit rates,
The wavelength multiplexing apparatus further comprises a wavelength multiplexing circuit for multiplexing optical duobinary signals from the optical delay circuit. The wavelength division multiplexing apparatus according to claim 1,
Each DPSK signal is one of two different bit rate DPSK signals, and the wavelength multiplexing device includes a wavelength multiplexing circuit and an optical delay circuit for each of the different bit rates,
The wavelength multiplexing apparatus further includes an interleaver that multiplexes optical duobinary signals from the optical delay circuit. The wavelength multiplexing device according to claim 4 , wherein
The odd-numbered wavelength of the DPSK signal includes one of the DPSK signals having the two different bit rates, and the even-numbered wavelength includes the other of the DPSK signals having the two different bit rates. Multiplex device. A wavelength multiplexing transmission network,
A wavelength division multiplexing apparatus according to any one of claims 1 to 5,
An optical receiver for receiving an optical duobinary signal from the wavelength multiplexing device for each wavelength ;
Wavelength multiplexing transmission network, characterized in that example Bei a. The wavelength division multiplexing transmission network according to claim 6,
A wavelength division multiplexing transmission network, further comprising a power splitter for branching an optical duobinary signal from the wavelength division multiplexer. The wavelength division multiplexing transmission network according to claim 6,
A wavelength division multiplexing transmission network further comprising a wavelength splitter for demultiplexing an optical duobinary signal from the wavelength division multiplexing apparatus. A method in a wavelength division multiplexing apparatus, comprising:
Multiplexing a plurality of DPSK signals having different wavelengths;
Generating and transmitting an optical duobinary signal from the multiplexed DPSK signal ;
Converting a plurality of DPSK signals having different wavelengths into optical duobinary signals ,
Each DPSK signal is either a bit rate R DPSK signal or a bit rate nR (n is an integer) DPSK signal,
The method of generating the optical duobinary signal includes combining each DPSK signal with a delay amount of 1 / R. The method of claim 9 , comprising:
Each DPSK signal is one of a plurality of different bit rate DPSK signals,
The method of generating the optical duobinary signal further comprises combining each DPSK signal with a delay amount corresponding to each bit rate.

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