JPH0831841B2 - Optical frequency multiplexing signal transmission circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency multiplex signal transmission circuit, and more particularly to a method for stabilizing the channel spacing of an optical frequency multiplex signal.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional method for stabilizing the channel spacing of an optical frequency multiplexed signal includes a plurality of laser (hereinafter referred to as LD) drive circuits 11 to 14 and LDs thereof.
A plurality of LDs 21 to 24 driven by a drive circuit, a star coupler 30 which outputs the outputs of these LDs as optical frequency multiplex signals from a terminal 40, and an arbitrary optical frequency is selected from the optical frequency multiplex signals. An optical frequency selection switch 41, a Mach-Zehnder type optical frequency discriminator (MZF) 42 that outputs a frequency error optical signal between the selected optical frequency and a reference optical frequency, and an optical receiver 43 that converts the frequency error optical signal into an electrical signal. A control unit 44 for selecting an optical signal of a desired frequency and an LD drive circuit, and a switching unit 45 for selecting an arbitrary LD drive circuit by the control unit 44.

The operation of this circuit is such that the outputs of the LDs 21 to 24 are the 2 × 2 couplers 30-1 to 30- in the star coupler 30.
3 to multiplex to make an optical frequency multiplexed signal. Control unit 4
4 is an optical frequency selection switch 4 for an arbitrary optical frequency selection command
1 and select an arbitrary optical signal from the optical frequency division multiplexed signal. The selected optical signal is input to the optical frequency discriminator 42, and a frequency error optical signal between the optical frequency of the optical signal and the reference optical frequency is obtained. This frequency error optical signal is converted into an electrical frequency error signal by the optical receiving unit 43, and is fed back to the LD drive circuit selected by the switcher 45 so that the frequency error signal is minimized.

By repeating the above process for each LD one by one, the channel interval is matched with the cycle of the optical frequency discriminator 42 and the channel interval is kept constant.

[0005]

This conventional method for constant channel spacing of optical frequency multiplexed signals requires the use of optical waveguides such as an optical frequency selection switch and an optical frequency discriminator.
There is a problem that the reference frequency is unstable over time and a strict temperature adjustment circuit is required.

Apart from the above example, Japanese Patent Laid-Open No. 60-24273.
There is a frequency-multiplexing optical transmitter as shown in Japanese Patent Publication No. 9, but this device has a problem that it requires a detector and a control unit for each light source.

Further, there is also a method in which optical heterodyne reception is performed using a wavelength tunable local laser, and one channel is selected by sweeping the local laser to stabilize the frequency. There was a problem that there was a need.

[0008]

An optical frequency multiplexed signal transmission circuit of the present invention includes a plurality of LD drive circuits, a plurality of LDs driven by these LD drive circuits, and a plurality of 2 × 2 couplers. A star coupler that optical-frequency-multiplexes the plurality of LD outputs and sends an optical frequency-multiplexed signal, an optical switcher that selects an arbitrary optical signal from the 2 × 2 coupler in the star coupler, and a selected optical signal An optical receiver for converting the signal, a frequency discriminator for outputting a frequency error signal between the frequency of the converted electric signal and a reference frequency, a switcher for selecting any of the LD drive circuits, the optical switcher, and The control unit controls the switching device.

The star coupler includes a plurality of first 2 × 2 couplers that receive two laser outputs of the plurality of lasers and two of the plurality of first 2 × 2 coupler outputs. A plurality of second 2 × 2 couplers having an output as an input are included, and one of the outputs of the plurality of second 2 × 2 couplers is selected by the optical switch.

[0010]

Next, the present invention will be described with reference to the drawings. FIG. 1 shows one embodiment of the present invention. Here, as an example of considering an N-channel optical frequency multiplex signal, a 4-channel optical frequency multiplex signal is simply shown as shown in the figure.

The LD drive circuits 11-14 are used to drive the LDs 21-24.
Drive each of them and output the 4 outputs to a 4 × 1 star coupler 1
Optical frequency multiplexing is performed at 5. Normally, there are only 2 × 2 couplers 15-5, 15-7, and 15-8 in the 4 × 1 star coupler, but in this embodiment, the 2 × 2 couplers 15-1 to 15- are used.
By adding 4 (first 2 × 2 coupler) and 2 × 2 coupler 15-6, the output of 2 × 2 coupler 15-5 is L
Beat signal of D21 and LD22 is 2 × 2 coupler 15-
The beat signal of LD22 and LD23 is 2x at the output of 6
The beat signals of the LD 23 and LD 24 are output to the output of the 2-coupler 15-7, respectively.

Therefore, the 2 × 2 couplers 15-5 to 15-7
The output signal of the (second 2 × 2 coupler) is LD21.
.About.24 channel spacing optical signals. The output is 3 × 1
It is input to the optical switch 16 to select the channel-interval optical signal to be controlled. Next, the channel interval optical signal is received by the optical receiver 17, converted into an electric signal, and amplified by the amplifier 18. Frequency discriminator 1 for the amplified channel spacing signal
By inputting to 9, the channel spacing error signal is obtained. The control unit 20 minimizes this channel interval error signal.
To return to any LD drive circuit 11-14.

By repeating the above operation for each LD one by one, the channel intervals of four channels can be made constant. For example, when it is desired to keep the channel spacing between the LD 21 and the LD 22 constant, the 3 × 1 optical switch 16 selects the output of the 2 × 2 coupler 15-5, the 1 × 3 switch 25 selects the LD 22, and the feedback is performed. Just do it.

[0014]

As described above, since the optical heterodyne reception is performed by using the star coupler and the laser of its own, the channel spacing can be fixed without using the local oscillation laser of the wide band wavelength tunable, and the optical heterodyne reception is performed. Since the control is performed by means of the above, there is an effect that the channel spacing can be made highly accurate and there is no need to use an optical waveguide component whose frequency is unstable over time.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of a conventional optical frequency multiplex signal transmission circuit.

[Explanation of symbols]

11-14 LD drive circuit 21-24 LD 15,30 Star coupler 15-1-15-8, 30-1-30-3 2x2 coupler 16 3x1 optical switcher 17,43 Optical receiving part 18 Amplifier 19 Frequency discriminator 20 Control unit 25 1 × 3 switch

Claims (2)

[Claims] 1. A plurality of laser drive circuits, a plurality of lasers driven by these laser drive circuits, and a plurality of lasers.
A star coupler for optical frequency multiplexing the plurality of laser outputs including a × 2 coupler and transmitting an optical frequency multiplexed signal; an optical switcher for selecting an arbitrary optical signal from the 2 × 2 coupler in the star coupler; An optical receiver for converting the optical signal into an electric signal, a frequency discriminator for outputting a frequency error signal between the frequency and the reference frequency of the converted electric signal, a switcher for selecting an arbitrary laser drive circuit, and An optical frequency multiplex signal transmission circuit, comprising: an optical switch and a controller for controlling the switch. 2. The optical frequency multiplex signal transmission circuit according to claim 1, wherein the star coupler has a plurality of first 2 × 2 inputting two laser outputs of the plurality of lasers.
A coupler and a plurality of second 2 × 2 couplers having two outputs of the plurality of first 2 × 2 coupler outputs as inputs, and one of the outputs of the plurality of second 2 × 2 couplers An optical frequency multiplex signal transmission circuit, characterized in that one of the optical frequency switching signals is selected by the optical switch.