JPH04247729A - Wave length selector - Google Patents

Abstract

PURPOSE:To simultaneously synchronize an AM-FDM signal with an FM-FDM signal by inputting wave length incorporating the AM-FDM signal to an optical multiplexer and wave length incorporating no signal to an optical switch while the optical demultiplexer are outputting wave length to respective ports. CONSTITUTION:A video signal group is electrooptically converted by the light source for transmitting wave length lambda1. A frequency band is electrooptically converted by the light source for transmitting wave length lambda2-lambdan. Respective wave lengths are multiplexed by the optical multiplexer 13 and branched to a 1XM optical coupler 14 through an optical fiber 5 so as to be transmitted to the house of a user. Then, a different single wave length is outputted to (n) output ports by the n-wave optical demultiplexer 16 and wave length lambda1 incorporating the AM-FDM signal is inputted to the optical multiplexer 18 and lambda2-lambdan incorporating no signal to the (n-1)X1 optical switch 17. Even if the optical switch 17 changes over lambdag, the used frequency band is different from lambda1 so that video signal reception is not affected and respective terminals switch independently channels.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength selector that is compact and operates stably.

0002

2. Description of the Related Art Conventionally, in an optical CATV system, a patent has been filed for a selector (Japanese Patent Application No. 165929/1999) as a configuration example of a wavelength selector that selects any one channel from a group of multi-channel input signals. ing. This is shown in FIG. In the system shown in this figure, the video signal of each channel in the CATV head end 1 is first subjected to FDM by FM modulating and multiplexing carrier waves f1 to fm in an electrical stage, and then FDMed by optical wavelengths λ1 to
The signal is WDMed at λn and input to the optical fiber 5. The n-wavelength multiplexed signal transmitted through the optical fiber 5 is branched into M by the optical splitter 14. One of the M branched outputs is input to the n-wavelength demultiplexer 11, and different single wavelengths are output to each of the n output ports of 11. This output signal is n×
1 optical switch 12, and only one wavelength is output. The crosstalk characteristics required for an n×1 optical switch are as follows. When transmitting an AM-modulated video signal using a coaxial cable, the D/U ratio, which is the electrical signal level ratio between the desired wave D and the interference U, is required to be 50 dB or more (corresponding to 25 dB in the optical domain). (Cable Television Technology Research Committee “Survey Report on Cable Television Broadcasting Facilities”)

0003

[Problems to be Solved by the Invention] Therefore, when providing an AM modulated video signal using the system shown in FIG.
1 to λn use the same frequency band, so n×1
Crosstalk characteristics of optical power between each port of the fiber selector 14 (Kobayashi, Sugita: "Quartz-based optical waveguide and applied circuit components" IEICE Technical Report OCS 89-10S, Dec.
．． 19.1989), the required D/U ratio cannot be met and beat disturbance occurs. Therefore, when using the selector shown in Fig. 3, FM-FDM
Signals can be provided, but coaxial CA, which has been provided conventionally,
It has become difficult to provide AM-FDM signals used in TV services and the like.

The object of the present invention is to provide an optical demultiplexer, an optical switch,
The object of the present invention is to provide a wavelength selector that can simultaneously provide an AM-FDM signal and an FM-FDM signal by combining an optical multiplexer.

[0005]

[Means for Solving the Problems] This wavelength selector inputs the wavelength containing the AM-FDM signal to the optical multiplexer without inputting it to the optical switch during the output from each port of the optical demultiplexer, and also inputs the wavelength containing the AM-FDM signal to the optical multiplexer, and
The configuration is such that wavelengths that do not include FDM signals are input to an optical switch, and a selected single wavelength is input to an optical multiplexer together with wavelengths that do not pass through the switch and include AM-FDM signals. Therefore, users can receive conventional services by adding this wavelength selector to their conventional receiving equipment, and the switching of the optical switch will not affect receiving terminals for conventional services, but as shown in the figure. The conventional selector shown in No. 3 differs in that it cannot receive services including AM-FDM signals.

[0006]

[Operation] That is, as shown in FIG.
However, this switch 12 has only 20 dB of crosstalk between the lights. In the FM-FDM method, in which the signal from signal source 2 is FM-modulated and then frequency-multiplexed based on the difference in carrier frequencies, this value is sufficient, but after AM-modulating the signal from signal source 2,
AM frequency multiplexed by different carrier frequencies
- For FDM systems, this value is insufficient. The reason why the above 20dB is insufficient is that the required D/U ratio = 50dB
(equivalent to 25 dB for light). Therefore, in order to transmit the AM-FDM system signal to the system of FIG. 3, the AM-FDM system signal (λ1 in FIG. This prevents AM-FDM from passing through.
Prevents signal D/U deterioration.

[0007]

[Embodiment] FIG. 1 is a diagram illustrating an embodiment of the invention, and is an example in which a new FM-FDM signal service is provided simultaneously with conventionally provided services such as coaxial CATV and satellite broadcasting. It is. FIG. 2 shows the frequency bands used at each wavelength when services are provided with the configuration shown in FIG. f1 to fh indicate the frequency band used in coaxial CATV, and fk to fl indicate the intermediate frequency band (BS-IF or CS-I) in satellite broadcasting.
Corresponds to F. ) is shown. fi~fj and fo~
fp is a region excluding the above frequency band. In FIG. 1, video signal groups f1 to fh and fk to fl are electrically/optically exchanged by a transmission light source having a wavelength λ1. fi~f
Frequency bands j and fo to fp are electrically/optically exchanged by a transmitting light source having wavelengths λ2 to λn. Each wavelength is multiplexed by 13 and input to 5. The n wavelength multiplexed signal transmitted through 5 is branched into M at 14. User home 1
If there is only one 5, 14 is unnecessary. One of the M branched outputs is input to the n-wavelength demultiplexer 16, and different single wavelengths are output to the n output ports of the 16. Among this output, AM-F, which is typified by coaxial CATV,
The wavelength λ1 containing the DM signal is input to the optical multiplexer 18. Wavelengths λ2 to λn that do not include AM-FDM signals are (n
-1) Input to ×1 optical switch 17, select only one wavelength λg, and input to 18.

Here, the transmitting light source 4 includes DFB and DBR.
High sub-mode suppression ratio (sub-mode suppression ra) such as single longitudinal mode semiconductor lasers such as
tio ≥ 30 dB), the high-order modes of the light source from λ2 to λn (especially λ2) leak into the λ1 passband in the demultiplexer or multiplexer and are included in λ1. No deterioration of the D/U ratio of AM-FDM signals occurs. It goes without saying that the same light source as used in 4 is used as the transmitting light source 22. λ
1 and λg are multiplexed by 18 and optically/electrically exchanged by 6. 7 is a multi-channel FM-FDM signal receiver that selects one channel from a group of video signals multiplexed into λ1 to λn, 8 is a control circuit that drives 17, 9 is a channel selection remote control, and 19 is a satellite controller. TV with built-in tuner (some receivers have built-in AM and FM tuners and can receive FM signals simultaneously while receiving AM signals)20
1 is a coaxial CATV reception tuner, and 10 is a television monitor.

[0009] These can be connected in the form of a bus. Since λ1 and λ2 to λg have different frequency bands, only one optical/electrical exchange unit 6 is required. If you switch λg at step 17 while receiving video using the four types of terminals shown in Figure 1, the effect of switching λg will be that the video signal group of λ1 is not received because λ1 and λg use different frequency bands. However, each terminal can switch channels independently. Also, AM-FDM
When the signal is included in each wavelength of λ1 to λa, as shown in FIG.
It goes without saying that λa is input to the n-wavelength multiplexer via a (na)×1 optical switch. Note that FIG. 5 shows the wavelength selector when a=1 in FIG. 4. In addition, in this embodiment, the n-wave optical demultiplexer 16
, (n-1)×1 optical switch 17, and n-wave optical multiplexer 18 constitute a wavelength selector shown in the claims of the present invention. Furthermore, although a plurality of wavelength selectors are provided as shown in FIG. 1, it is preferable that these plurality of wavelength selectors are integrated on the same Si substrate with a quartz waveguide structure.

0010

[Effects of the Invention] As explained above, by using the wavelength selector shown in the present invention and the frequency array shown in FIG. 2, it is possible to simultaneously provide a new multi-channel service in addition to the conventionally provided CATV service. can be,
Needless to say, users do not need to change the terminal they are using, and can receive new services by preparing a tuner for multi-channel reception.

[Brief explanation of the drawing]

FIG. 1 is a diagram that best represents the present invention, and is a configuration diagram of a system that simultaneously provides coaxial CATV and satellite broadcasting services as well as new multi-channel services.

FIG. 2 is a diagram showing frequency bands used at the wavelength of the light source in FIG. 1;

FIG. 3 is a system configuration diagram when a conventional selector is used.

[Fig. 4] Claim (1) adopted in the system of Fig. 1.
) wavelength selector.

FIG. 5 shows a wavelength selector when a=1 in FIG. 4;

[Explanation of symbols]

1 Head end 2 Information source such as video source 3 FM modulator for FDM 4 Light source for N-channel transmission 5 Single mode optical fiber 6 Optical/electrical exchange section 7 Tuner for multi-channel FM-FDM signal reception 8
Optical switch control unit 9 Channel selection remote control 10 TV monitor 11 Optical demultiplexer 12 n×1 optical switch 13 Optical multiplexer 14 1×M optical coupler 15 User home 16 N-wave optical demultiplexer 17 (n-1)×1 optical Switch 18 N-wave optical multiplexer 19 TV monitor with built-in satellite tuner 20 Coaxial CATV reception tuner 21 FDM AM modulator 22 L channel transmission light source 23 (n-a) x 1 optical switch

Claims (2)

[Claims] [Claim 1] Among the n output ports of the n-wave optical demultiplexer, (n
-a) Input the output to a (na)×1 optical switch, and connect the output port of the optical switch to the output port of the optical demultiplexer that does not input to the (na)×1 optical switch. 1. A wavelength selector characterized in that the wavelength selector is configured to input to a wavelength selector (where n>a). 2. A wavelength selector characterized in that the wavelength selector having the structure set forth in claim 1 is integrated on the same Si substrate with a quartz waveguide structure.