JPH01500240A - optical transmission equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] optical transmission equipment 〔Technical field〕 The present invention relates to optical transmission equipment, and more particularly to multiple access equipment.

[Background technology] When transmitting information from multiple channels over a single link, it is necessary to separate the signals at the receiving end. It is necessary to To achieve this, the bandwidth used is separated into separate slots for each addition. or allow each subscriber to occupy the entire band and use it for various transmissions. The transmitted signals are orthogonalized in some way so that the signals do not interfere with each other.

The latter is a spread spectrum technique. (UQE), which is attracting attention especially in radio frequency transmission. space with optical equipment A method has been proposed to use the tractram spreading method, e.g. Generates a pseudorandom electrical signal modulated with information and feeds it into a laser or other light source Techniques have been proposed to provide this. At this time, different channels are code division multiplexed. It will be done. However, generating pseudorandom signals and code multiplexing both require complex techniques. It is a technique.

If the coherence time of the optical signal is relatively short, add a time delay longer than the coherence time. Channels can be multiplexed by doing this. Coherent interference as a technology for optical transmission equipment A device has been proposed that branches the output signal of a signal source with a short interval into a plurality of components. this place In this case, each component is split into two, one modulated and the other delayed. these parts component is combined with another component, that is, a component that has been previously branched out and has been modulated and delayed differently. and send it. At the receiving end, the combined signal is split again and each Split into two parts, delay one part, and recombine these parts. This causes the change Equal parts of the delay between the modulated and unmodulated signals combine and this Detected. The disadvantage of this device is the high loss in the detection stage, and the half of the modulated signal and half of the unmodulated signal are lost. related to this Direct detection techniques also have high losses.

The purpose of the present invention is to provide a more effective spread spectrum optical transmission device. do.

[Disclosure of the invention]

According to a first aspect of the invention, an optical carrier signal is divided into at least two signal paths. , the optical carrier signal in at least one of the signal paths is modulated with information, and then split. The recombined signals are recombined by delay multiplexing, and a part of this recombined signal is transmitted to the above optical carrier. For hetero gain detection by coupling to a local oscillation signal whose frequency is shifted from the wave signal. In an information transmission method using a broadband optical carrier signal that receives information from Before coupling part of the combined signal to the above local oscillation signal, the above local oscillation signal is It is characterized in that it is delayed by a time corresponding to the delay of the delay multiplexing.

The local oscillator signal must have the same spread spectrum characteristics as the optical carrier. do not have. The local oscillator signal may be generated at a location remote from the receiver or at a distribution point, or uses a signal that is split from the carrier wave, either in a separate signal path or in a recombined modulated signal. The signal is multiplexed and transmitted on the same signal path as the signal. Is it a carrier wave signal as a local oscillation signal? It is desirable to use a signal whose frequency is shifted by dividing the signal. The frequency deviation is It is convenient to do this before transmitting, since most of the dynamic elements are placed on the transmitter side. Tradition For transmission purposes, it is desirable to polarization multiplex the local oscillation signal.

Preferably, the signal path includes an optical fiber or other optical waveguide.

As a preferred embodiment of the present invention, the split/recombined signal and the local oscillation signal are mixed. This is used as the carrier wave signal for the returned message, and this carrier wave signal is divided into two signal paths. modulates one of them with the return message, and after this modulates the other return message by delay multiplexing. can be recombined with the sage signal path.

According to a second aspect of the invention, the carrier wave is divided into a plurality of signal paths, and the plurality of signal paths The frequency of the carrier wave is shifted in one of the signal paths to generate a local oscillation signal, and the other modulating the signal in at least one of the signal paths of the signal path to generate an information signal; In addition, different delays are caused in the other signal paths, and at least the other signals are The recombined signals are recombined to generate a recombined signal, and this recombined signal and the local oscillation signal A method of transmitting information using a spread spectrum optical carrier for transmitting signals is provided.

Angle modulation is preferable as the modulation method.

Another aspect of the invention is an apparatus for implementing the method described above, in which a plurality of channels are Coherence using a broadband optical carrier with a means to generate a superimposed carrier signal In optical transmission equipment that performs wave detection, at least one channel is modulated with information. channel by adjusting the delay of the local oscillator signal at the receiver. and means for selecting.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Brief explanation of the drawing] FIG. 1 is a diagram showing the basic configuration of an optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a fourth embodiment in which the present invention is applied to two-way transmission.

FIG. 5 is a diagram showing a fifth embodiment of the present invention.

[Best mode for carrying out the invention]

The basic operation of this device will be explained with reference to the basic configuration shown in FIG. - pieces The output light of the laser light source 1 is frequency modulated to generate a spread spectrum signal, and the signal is It is fed to local node 10 via line 2. In this node 10, signal line 2 The above signal is fed to beam splitter 3, which outputs two outputs. A signal is supplied to signal line 4.5. On the signal line 4, the signal is further divided into n component signal paths. It is branched in the n direction along. The signal path of each component is connected to a different modulator M1, M,... ・Connect to M (n=4 in the figure). These modulators M,,M.

″...As Ml, it is convenient to use a lithium niobate phase modulator. The input signals I, , 1 .・Modulate the signal of each component by -1, . The modulators M, , M, . . . Ml are connected to delay lines 1, . 12...t, Continued. The delay characteristics of each delay line are different from all other delay lines. output end of delay line Then, the n modulated and delayed component signals are recombined and supplied to the signal line 6. Faith The signal on line 5 passes through frequency shifter 8 and, without being recombined, the signal on reference number It passes through the distribution point indicated by 7. The combined modulated signal also passes through the distribution point 7.

At the distribution point 7, each signal on the signal lines 5 and 6 is branched into n pieces, and the signals from the signal line 5 are The signal and the signal from signal line 6 are combined into pairs. This pair of signals is detected by the detector. Ishiri. supplied to Each detector has a Then, delay lines L I', j2't,,' corresponding to the modulators are connected.

The signal branched from signal line 5 passes through this delay line, and then branches from signal line 6. It enters the coupler 9 together with the detected signal, where it is paired for hetero gain detection. combined.

The output channel of the detector depends on the amount of delay provided by the connected delay line. Exists. Therefore, by choosing a specific delay that corresponds to the transmitter delay , each receiver terminal can be assigned a separate channel, and also variable Delays can also be used to make the terminal tunable.

A variety of different waveforms may be used to provide a suitable spread spectrum signal to node 10. is used to modulate the output frequency of light source 1. Triangle or sawtooth as modulating waveform Waves are particularly suitable. In addition, the relaxation oscillation frequency is close to or equal to the relaxation oscillation frequency of the laser light source. You can also use a sine wave oscillating at a new frequency to maximize the "chirp" .

Instead of directly frequency modulating the laser source, a fixed frequency laser source is used. A modulator can also be provided separately. In that case, the modulator is replaced by an M-sequence generator. drive

Moreover, a laser light source with a wide line width can also be used. In this case, frequency modulation This eliminates the need to match delay lines between transmitter and receiver fairly accurately. It is necessary to Such delays can be obtained with short lengths of single-mode optical fiber. Ru. The delay at the transmission end can also be applied before modulation rather than after.

In the embodiment described with reference to FIG. 1, the signal path from the transmitter to the distribution point 7 is , two fiber optic signal paths (signal lines 5.6) are required. Heterogeneous gain detection In order to do this, it is necessary to control the polarization of the signal. For this purpose, a polarization-maintaining optical fiber is used. The use of bars should be avoided. Therefore, active polarization control, polarization modulation or polarization Diversity reception is generally required. Another channel from signal line 5.6 at the distribution point. polarization feedback control (e.g., as described with reference to Figure 3). You can also do that. The active part of this 3-way polarization control is located at node 10. In that case, along one of the signal lines 5 or 6 in the return direction. to transmit a side control signal.

FIG. 2 shows another embodiment. This example device uses a single fiber to locally The oscillation signal and the delay multiplexed and modulated signal are transmitted. Up to final coupler 20 uses a polarization-maintaining optical fiber, after which the polarization of the various signals changes in the same way. It can be assumed that The local oscillator signal is delay multiplexed with other signals (the frequency is shifted). ) to reach the distribution point. To detect different information signals, the signal on signal line 6 is Branch in N directions, branch each further, delay one, then recombine . However, this detection method is difficult to detect because half of the signal and half of the local oscillator signal are lost. There is a point.

FIG. 3 shows a third embodiment of the invention. This embodiment device uses a local oscillation signal and a coupling The delay multiplexed and modulated signals are combined and transmitted through a single optical fiber. Ru. Local oscillator signals are shared by a common transmission so that strong local oscillator signals can be separated at the distribution point. Polarization multiplexed on the fiber. Accurate orthogonal alignment using non-polarization-maintaining optical fiber To obtain polarized light, one signal arm performs polarization control before polarization multiplexing.

To explain the embodiment shown in FIG. 3 in more detail, the local node 10 The beam splitter 3, modulator, delay line and station are similar to those shown in FIG. A partial oscillation frequency shifter 8 is provided. The local oscillation signal path 5 includes a polarization control circuit 11. , from here, the local oscillation signal is input to the polarization splitting coupler 12, and this polarization splitting/coupling The local oscillator signals are multiplexed onto the transmission fiber with orthogonal polarizations by the transmitter 12. distribution At point 7, the polarization splitter 13 demultiplexes the local oscillation signal and branches it in the N+1 direction. do. Of the branched local oscillation signals, n series are the same as in the embodiment shown in Figure 1. , respectively, and are combined into the n branched modulation signals to form a heterogeneous signal. In-detected. The n+1th branched modulation signal is further delayed. The local oscillator is reconnected to the (n+1)th signal branched from the local oscillator without any interruption. this The decoded signal is returned to the polarization control circuit 11 in the opposite direction along the outer signal path 6'.

In FIG. 3, the signal path 6 and the signal path 6' are shown separately for simplicity.

However, in practice, both signal paths are implemented using a single optical fiber, and output delay multiplexing is performed. Both signals and return polarization control signals can be transmitted.

To realize a two-way transmission device, a coupler 9 at each receiver (e.g. For the return message, the second output of used as a carrier wave. FIG. 4 shows its configuration.

In this embodiment, the second output is provided to return modulator 16. Return strange 'Sub station 16 is equipped with a beam splitter 14, and one output signal of this beam splitter 14 is Then, the modulator 15 modulates the signal using an input signal (indicated by R). after this , recombining the previously branched signals and recombining them with the signals from the other return modulators 16; It is sent to the signal line 17. At the receiving end of the return message, the combined return signal is Branch in the direction. Branch each branched signal again and apply an appropriate delay to one side. Add. Thereafter, the branched signals are recombined and directly input to the detector 18.

A delay t, , is added to one of the branched signals for return, which is important. isn't it. This delay may be added in the same signal path as modulator 15. heterodyne interest Since there is no gain, the forward signal path does not require any sensitivity in the return transmission signal path.

Various methods are available for generating spread spectrum signals.

It is also possible to use a wide linewidth light source that outputs naturally random wavelengths; The source may be swept or modulated. When using a laser light source with a fixed wavelength , modulated by the output of a pseudorandom signal generator. Reproduces laser power and modulation local oscillator signals may be placed locally at the receiver rather than at the transmitter. local oscillation when using fixed frequency lasers and M-sequence generators. It is easy to generate the signal locally.

This type of device is shown in FIG. In this embodiment, under the control of the M-sequence generator 22, The signal from the light source 1 is modulated by the modulator 21 before being input to the node 10. child In the embodiment, node 10 is not provided with a frequency shifter. remote distribution point , a local oscillation signal whose frequency is shifted with respect to the first light source 1 is transmitted from the second light source 23. The signal is transmitted to the second M-sequence generator 25 which is phase-locked to the first M-sequence generator 22. is supplied via a modulator 24 which is controlled by

With reference to the distributed network shown in Figure 1, the estimated network Let's explain the parameters.

Assume the output from the common light source is +3 dBm. Operates at 140Mtiit/s -23 dBm local oscillation power (local oscillation power when not suppressed) is theoretically -63 dBm), the optimal PSK heterodyne receiver The sensitivity is -59 dBm. Branches the output power into a signal path and a local oscillation signal path. Ru. The signal path is branched in N directions with an insertion loss of, for example, 2 dB. Here N is 1 Let it be 20. Each signal is modulated by a phase modulator; The total loss from the fiber to the output fiber is, for example, 3 dB. Everything from the modulator All outputs recombine with a loss of 101 ogN + 2 dB. network Assume that the transmission loss is 5 dB. The loss of the distributor is 101ogN + 2dB. It will be done. The voltage of the recombined signal and local oscillator signal before entering the photodetector Assume that the loss is 3 dB for the field. In the local oscillator signal path, the acoustic There is a 3dB loss when passing through the optical frequency shifter, and in addition, the polarization control circuit 3dB loss when passing through (if used). In the local oscillator signal path Other transmission losses and distribution losses shall be the same as for the signal path.

Regarding the laser linewidth, when using conventional heterodyne detection, it is faster than ASK. PSK is used. However, if both the modulation signal and the local oscillation signal are transmitted from a common light source, If we derive from It does not matter whether ASK or PSK is used to perform the verification.

With the above parameters, the network speed of 20X 140Mhit/s with 20 terminals is The size of the network is maximum in terms of power.

Another factor that limits the size of the network is the issue of maximum FM deviation of the laser source. There is a problem. The instantaneous channel spacing is 5 x intermediate frequency bandwidth, and the intermediate frequency band Assuming a width of 2 x bit rate, to achieve a 20 channel configuration, approximately 2 It is necessary to sweep the entire optical frequency at 8 GHz. This level of current control frequency cha laser beams have been proposed by several groups studying distributed feedback lasers.

The modulation frequency used determines the length of fiber required for the delay. I For a modulation rate of MHz, the maximum length of the delay fiber is about 10 m. child The length of is considered a little difficult to handle. To significantly shorten the required delay signal path uses a sweep frequency of the order of 611z. This moves the laser light source to its relaxation period. This can be achieved by driving at a wave number, for example, 1 to 2 GHz. In this case , not only can perform frequency modulation with large frequency deviation, but also has some desired Undesirable amplitude modulation occurs, but this amplitude modulated signal is within the receiver's intermediate frequency band. It's outside.

It can also be used for analog transmission.

Broadband traveling wave laser amplifiers are installed at key points in both the signal path and the local oscillation signal path. This allows you to expand your network. Use a high power laser amplifier transmits optical carrier signals from − swept laser sources to an unlimited number of fibers. can be branched. Combining multiple spread spectrum devices with traditional wavelength multiplexing technology In addition, the network can be further expanded. This kind of distributed network The ultimate capacity of the arc is only limited by the fiber's inherent transmission bandwidth.

[Industrial applicability]

The present invention uses spread spectrum heterogain detection to achieve coherent transmission. The present invention provides a new locally distributed network system and transmission device that performs this. This new Components of a Basic Network Naturally, it is necessary to implement a basic network. In order to Means for fixing the laser frequency are unnecessary, and narrowband optical filters are also unnecessary. Cha Channel selection can be achieved simply by using matching optical delay elements (homodyne detection It is not necessary to match the phase delay exactly because it is a heterodyne detection rather than a standard data rate <14014 hit/s), the standard PIN ET can be used. This device applies conventional WDM technology and It can be easily expanded by using the amplifier. Basically, wideband signal dispersion network, we will reconfigure this device to use a separate light source for each terminal. It is also possible to provide a low capacity return channel without the need for

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Claims (16)

[Claims] 1. An optical carrier signal is divided into at least two signal paths, and at least one of the signal paths is After modulating the optical carrier signal of the route with information, the divided signals are delayed and multiplexed. A part of this recombined signal is shifted in frequency with respect to the optical carrier signal. information is received by heterodyne detection by coupling it to the local oscillation signal In an information transmission method using a broadband optical carrier signal, a part of the recombined signal Before combining the local oscillation signal with the local oscillation signal, the local oscillation signal is delay by the amount of time corresponding to An information transmission method characterized by: 2. The local oscillator signal is generated from a light source that is separate from the light source used to generate the optical carrier signal. The information transmission method according to claim 1. 3. A local oscillation signal is generated by frequency-shifting the signal split from the optical carrier signal. 2. The information transmission method according to claim 1, wherein the information transmission method generates the following information. 4. The local oscillator signal is polarization multiplexed on the same transmission line along with the recombined delay multiplexed signal. 4. The information transmission method according to claim 3. 5. Return message by mixing part of the recombined signal and part of the local oscillator signal generate a carrier signal for This return message carrier signal is divided into two signal paths, one of which is used for the return message. message and recombines to other return message paths via delay multiplexing. An information transmission method according to any one of claims 1 to 4. 6. Split the carrier wave into multiple signal paths, Local oscillation is generated by shifting the frequency of the carrier wave in one of these multiple signal paths. generate a number, When a signal is modulated in at least one of the other signal paths to generate an information signal. In addition, different delays are caused in the other signal paths, recombining at least the signals of the other signal paths to generate a recombined signal; Information transmission using a broadband optical carrier wave that transmits this recombined signal and the above local oscillation signal. Shipping method. 7. Claim 6, wherein the local oscillation signal is recombined with the signal from the other signal path and transmitted. information transmission method. 8. Information transmission according to claim 7, wherein the local oscillation signal is polarization multiplexed with respect to the recombined signal. Method. 9. The broadband optical carrier signal is generated by modulating a light source. 8. The information transmission method according to any one of 8. 10. 10. The information transmission method according to claim 9, wherein the carrier signal is modulated by a triangular wave. 11. Broadband with means for generating a carrier signal in which multiple channels are delay multiplexed In an optical transmission device that performs coherent detection using a diffused optical carrier wave, means for modulating at least one channel with information; and means for modulating at least one channel with information; means for selecting a channel by adjusting the delay of the oscillation signal; An optical transmission device characterized by comprising: 12. A light source and means for modulating the light source are provided to generate a broadband optical carrier wave. 12. The optical transmission device according to claim 11. 13. The means for modulating the light source is by a triangular wave to generate a broadband optical carrier signal. 13. The optical transmission device according to claim 12, wherein the optical transmission device is configured to perform modulation. 14. Generates a local oscillation signal by shifting part of the frequency of a broadband optical carrier signal The optical transmission device according to claim 11, further comprising means. 15. A method of polarization multiplexing and transmitting a local oscillation signal along with a delay multiplexed carrier signal. The optical transmission device according to claim 14, further comprising a stage. 16. Multiple channels mix part of the delay multiplexed signal with part of the local oscillator signal. to generate a carrier wave signal for the return message, and this carrier wave signal for the return message is divided into two signal paths, one of which is modulated by the return message, and delay multiplexing is performed. further comprising a return message transmitting means for re-coupling to another return message signal path. The optical transmission device according to any one of claims 11 to 15.