JPH04346525A - Coherent light transmitter - Google Patents

Abstract

PURPOSE:To stabilize the frequency of a beat signal. CONSTITUTION:An optical connector 9 connects the signal light received from a transmitter 1 to the signal light of a local oscillation semiconductor laser 16. A photodetecting circuit 10 converts two signal light beats, i.e., the output of the connector 9 into the electric signals. A filter 11 separates the carrier component obtained when the optical frequency is modulated by a semiconductor laser 7 from a first side wave component and extracts both components out of the output signal of the circuit 10. A mixer 12 secures the product of both components, and a detection circuit 14 detects the amplitude of a pilot signal. A control circuit 15 controls the optical frequency of the signal light of the laser 16 so as to ensure the largest amplitude of the pilot signal. An electric FM modulation circuit 13 demodulates an angle modulation signal, i.e., the output signal of the mixer 12.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides electrical angle modulation (F
The present invention relates to a coherent optical transmission device that optically frequency modulates the output light of a semiconductor laser using a signal (M, PM, etc.) and transmits the signal light.

0002

2. Description of the Related Art Conventionally, an optical FM coherent optical transmission apparatus disclosed in Japanese Patent Application No. 2-159028 has been proposed as this type of optical transmission apparatus. In this coherent optical transmission device, a transmitting device inputs an electrically FM or PM original signal to a semiconductor laser, performs optical frequency modulation on the output light, and a receiving device performs heterodyne detection of the light. , the product of the carrier wave component signal obtained by optical frequency modulation and the first side wave component signal is taken, and the original signal is obtained through a band pass filter.

[0003] By the way, as a conventionally used method of suppressing the frequency fluctuation of the beat signal after optical heterodyne detection, for example, ``Minemura et al., Optical Heterodyne Detection Technology for Long Distance Communication'' (NEC Technical Report Vol. 39, No.12,
pp. 100-108, 1986), a part of the beat signal output from the light receiving circuit is extracted, its frequency is discriminated, and the frequency fluctuation is converted into an electrical signal to determine the optical frequency of the local oscillation semiconductor laser. There is a way to control it.

[0004] In addition, as a conventional method for selecting optical signals from a plurality of transmitting devices, for example, “Kitajima et al.
“Beat Count Optical Tuning Method for Optical Frequency Division Multiplexing Transmission” (1990 Institute of Electronics, Information and Communication Engineers Spring National Conference, B
997), there is a beat counting method in which a desired channel is selected by reading the number of beat signals while scanning the optical frequency of locally oscillated light.

[0005]

[Problem to be Solved by the Invention] The above-mentioned conventional coherent optical transmission device has a method of controlling the optical frequency of a local oscillation semiconductor laser by frequency-discriminating the beat signal and converting the frequency fluctuation into an electrical signal, and then performing heterodyne detection of the light. If the above conventional method of suppressing the frequency fluctuation of the beat signal is adopted,
The following problems arise. That is, the frequency band of the beat signal after optical heterodyne detection is more than twice the maximum frequency of the signal output from the angle modulation circuit in the transmitting device, and is a very wide band. Therefore, the output signal of the frequency discrimination circuit fluctuates greatly, and the frequency fluctuation of the beat signal cannot be sufficiently suppressed. When the frequency of the beat signal fluctuates greatly, the carrier wave component and the first side wave component of the optical frequency modulated signal fall out of the band of the filter that extracts the respective components, resulting in a deterioration of the S/N ratio.

[0006] Furthermore, in the conventional beat counting method described above, if there is no signal light from a certain transmitting device or the signal light is extremely small, errors may occur when selecting a channel. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coherent optical transmission device that can stabilize the frequency of a beat signal or reliably tune signal light from a plurality of transmitting devices. shall be.

[0007]

Means for Solving the Problems The invention according to claim 1 provides a plurality of angle modulation circuits having mutually different carrier wave frequencies, an oscillator that generates a pilot signal of a frequency different from all the carrier wave frequencies, and a plurality of angle modulation circuits having different carrier wave frequencies. A transmitting device is provided that includes an adder that combines the output signal from the modulation circuit and the pilot signal, and a transmitting semiconductor laser that performs optical frequency modulation according to the output signal of the adder. a laser, an optical coupler that couples the signal light sent from the transmitter and the signal light of the local oscillation semiconductor laser, and converts the beats of the two signal lights output from the optical coupler into electrical signals. a light-receiving circuit that converts the output signal of the light-receiving circuit into a carrier wave component and a first side wave component obtained by optical frequency modulation by the transmitting semiconductor laser, and a filter that separates and extracts each of the carrier wave component and the first side wave component; a mixer that takes the product of the first side wave component; a detection circuit that detects the amplitude of the pilot signal; and a mixer that adjusts the optical frequency of the signal light of the local oscillation semiconductor laser so that the amplitude of the pilot signal is maximized. The present invention is characterized in that it includes a receiving device including a control circuit for controlling the mixer and a demodulating circuit for demodulating the angle modulated signal that is the output signal of the mixer.

[0008] The invention according to claim 2 includes: a plurality of angle modulation circuits having mutually different carrier frequencies; an oscillator generating a pilot signal having a frequency different from all the carrier frequencies;
A plurality of transmitting devices are provided, including an adder that combines the output signals from all of the angle modulation circuits and the pilot signal, and a transmitting semiconductor laser that performs optical frequency modulation in accordance with the output signal of the adder. In addition, a first optical coupler for multiplexing signal lights from each of these transmitting devices is provided, and further,
a local oscillation semiconductor laser; a second optical coupler that couples the signal light sent from the first optical coupler with the signal light of the local oscillation semiconductor laser; and the second optical coupler. a light receiving circuit that converts the beats of the signal light from the first optical coupler and the signal light from the local oscillation semiconductor laser, which are the outputs of the light receiving circuit, into electrical signals; a filter that separates and extracts a carrier wave component and a first side wave component when the optical frequency is modulated by a laser; a mixer that takes the product of the carrier wave component and the first side wave component; and a mixer that takes the product of the carrier wave component and the first side wave component; a frequency detection circuit that detects the frequency; a tuning circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the output signal of the frequency detection circuit; and an angle modulation signal that is the output signal of the mixer. A receiving device including a demodulation circuit for demodulating is provided, the frequencies of pilot signals in each of the transmitting devices are different from each other, and the optical frequencies of the signal lights from the respective transmitting devices are different from each other. There is.

According to a third aspect of the invention, a plurality of angle modulation circuits having different carrier wave frequencies, an oscillator that generates a signal of a frequency different from all of the carrier wave frequencies, and a channel signal having certain specific information are provided. a pilot signal generation circuit that modulates the oscillator signal to generate a pilot signal, an adder that combines the output signals from all the angle modulation circuits and the pilot signal, and an optical A plurality of transmitting devices each having a transmitting semiconductor laser that performs frequency modulation is provided, a first optical coupler is provided that multiplexes signal light from each of these transmitting devices, and the local oscillating semiconductor laser and the above-mentioned transmitting semiconductor laser are provided. a second optical coupler that couples the signal light sent from the first optical coupler with the signal light of the local oscillation semiconductor laser; and the first optical coupler that is the output of the second optical coupler. a light receiving circuit that converts the beat of the signal light from the optical coupler and the signal light from the local oscillation semiconductor laser into an electrical signal; a filter that separates and extracts a carrier component and a first side component; a mixer that takes the product of the carrier component and the first side component; a channel detection circuit that demodulates the pilot signal; A receiving device comprising a tuning circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the output signal of the channel detection circuit, and a demodulation circuit that demodulates the angle modulation signal that is the output signal of the mixer. The present invention is characterized in that the channel signal information is mutually different between the respective transmitting devices, and the optical frequencies of the signal lights from the respective transmitting devices are mutually different.

0010

[Operation] In the coherent optical transmission device according to claim 1,
The plurality of angle modulation circuits have different carrier frequencies. An oscillator generates a pilot signal at a frequency different from all carrier frequencies. The adder combines the output signals from all angle modulation circuits and the pilot signal. The transmitting semiconductor laser performs optical frequency modulation according to the output signal of the adder. The optical coupler combines the signal light sent from the transmitter and the signal light from the local oscillation semiconductor laser. The light receiving circuit converts the beats of the two signal lights output from the optical coupler into electrical signals. The filter separates and extracts a carrier wave component and a first side wave component obtained by optical frequency modulation by the transmitting semiconductor laser from the output signal of the light receiving circuit. The mixer multiplies the carrier component and the first side component. The detection circuit detects the amplitude of the pilot signal. The control circuit controls the optical frequency of the signal light of the local oscillation semiconductor laser so that the amplitude of the pilot signal is maximized. The demodulation circuit demodulates the angle modulation signal that is the output signal of the mixer.

In the coherent optical transmission device according to the second aspect of the present invention, the plurality of angle modulation circuits have different carrier frequencies. An oscillator generates a pilot signal at a frequency different from all carrier frequencies. The adder combines the output signals from all angle modulation circuits and the pilot signal. The transmitting semiconductor laser performs optical frequency modulation according to the output signal of the adder. The first optical coupler multiplexes signal lights from each transmitter. The second optical coupler couples the signal light sent from the first optical coupler with the signal light from the local oscillation semiconductor laser. The light receiving circuit converts the beat of the signal light from the first optical coupler, which is the output of the second optical coupler, and the signal light from the local oscillation semiconductor laser into an electrical signal. The filter separates and extracts a carrier wave component and a first side wave component obtained by optical frequency modulation by the transmitting semiconductor laser from the output signal of the light receiving circuit. The mixer multiplies the carrier component and the first side component. The frequency detection circuit detects the frequency of the pilot signal. The tuning circuit controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the output signal of the frequency detection circuit. The demodulation circuit demodulates the angle modulation signal that is the output signal of the mixer. The frequencies of pilot signals in each transmitting device are different from each other, and the optical frequencies of signal lights from each transmitting device are different from each other.

In the coherent optical transmission device according to claim 3, the plurality of angle modulation circuits have different carrier frequencies. The oscillator generates a signal at a frequency different from all carrier frequencies. The pilot signal generation circuit generates a pilot signal by modulating the oscillator signal with a channel signal having specific information. The adder combines the output signals from all angle modulation circuits and the pilot signal. The transmitting semiconductor laser performs optical frequency modulation according to the output signal of the adder. The first optical coupler multiplexes signal lights from each transmitter. The second optical coupler couples the signal light sent from the first optical coupler with the signal light from the local oscillation semiconductor laser. The light receiving circuit converts the beat of the signal light from the first optical coupler, which is the output of the second optical coupler, and the signal light from the local oscillation semiconductor laser into an electrical signal. The filter separates and extracts a carrier wave component and a first side wave component obtained by optical frequency modulation by the transmitting semiconductor laser from the output signal of the light receiving circuit. The mixer multiplies the carrier component and the first side component. A channel detection circuit demodulates the pilot signal. The channel selection circuit controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the output signal of the channel detection circuit. The demodulation circuit demodulates the angle modulation signal that is the output signal of the mixer. Channel signal information is different for each transmitting device, and optical frequencies of signal lights from each transmitting device are different from each other.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram of a coherent optical transmission device according to Embodiment 1 of the present invention, and this embodiment is as claimed in claim 1.
It corresponds to This coherent optical transmission device includes a transmitting device 1 and a receiving device 2. The transmitter 1 includes an electric FM circuit 3 as an example of an angle modulation circuit,
4, an oscillator 5, an adder 6, and a semiconductor laser 7 for transmission.
, a light receiving circuit 10, a filter 11, a mixer 12,
Electric FM demodulation circuit 13 as a demodulation circuit and detection circuit 1
4, a control circuit 15, and a local oscillation semiconductor laser 16. The carrier wave frequency of the electric FM circuit 3 is f1, and the carrier wave frequency of the electric FM circuit 4 is f2. Oscillator 5 generates a pilot signal with a frequency fP. The semiconductor laser 7 outputs signal light A, and the local oscillation semiconductor laser 16 outputs local oscillation light B.

Next, the operation will be explained. Electric FM circuit 3, 4
are electric FMs with carrier frequencies f1 and f2, respectively.
Output a signal. Oscillator 5 outputs a pilot signal with a frequency fP. Note that the frequencies of the above three signals are different from each other. These signals are combined by an adder 6 and supplied to a semiconductor laser 7. The frequency of the light emitted from the semiconductor laser 7 shifts depending on the input signal current. That is, frequency modulation is applied at the frequency of light. This optical frequency modulated signal light A is transmitted to the receiving device 2.

The signal light A transmitted to the receiving device 2 is
The light enters the optical coupler 9. The optical coupler 9 couples the local oscillation light B from the local oscillation semiconductor laser 16 to the signal light A. The two laser beams combined by the optical coupler 9 are supplied to a light receiving circuit 10. The light receiving circuit 10 outputs both beat signals as electrical signals. This electrical signal is filtered by filter 1
The carrier wave component and the first side wave component generated by the optical frequency modulation by the semiconductor laser 7 are separated and each is supplied to the mixer 12 . The mixer 12 multiplies the carrier component and the first side component and supplies the product to the electric FM demodulation circuit 13 and the detection circuit 14 . Electric FM demodulation circuit 1
3 demodulates the electric FM signal of the output signal of the mixer 12. On the other hand, the detection circuit 14 detects the amplitude of the pilot signal and supplies the information to the control circuit 15. The control circuit 15 controls the optical frequency of the local oscillation light B by supplying a control signal to the local oscillation semiconductor laser 16 so that the signal from the detection circuit 14 is always maximized. Furthermore, control circuit 1
Examples of signal processing algorithms used in 5 include the hill climbing method. Further, as a method of controlling the optical frequency of the local oscillation light B, there are, for example, a method of changing the current flowing through the local oscillation semiconductor laser 16, the temperature, and the resonator length of the laser.

As described above, the frequency of the beat signal from the optical coupler 9 fluctuates, and the carrier wave component and the first side wave component of the optical frequency modulated signal deviate from the band of the filter 11 that extracts the respective signals. When this happens, the amplitude of the carrier wave component or the first side wave component becomes smaller, and the signal from the mixer 12 becomes smaller. At the same time, the amplitude of the pilot signal from the mixer 12 also decreases, but since the control circuit 15 controls the optical frequency of the local oscillation semiconductor laser 16 so that the amplitude increases, the frequency of the beat signal can be stabilized. . (Embodiment 2) FIG. 2 is a block diagram of a coherent optical transmission device according to Embodiment 2 of the present invention, and this embodiment is as claimed in claim 2.
It corresponds to This coherent optical transmission device includes transmitting devices 21, 22, and 23, an optical coupler 24 as a first optical coupler, and a receiving device 25. Each of the transmitting devices 21, 22, and 23 has the same configuration as the transmitting device 1 of the first embodiment, and is provided with an oscillator 26, respectively. The receiving device 25 includes an optical coupler 28 as a second optical coupler.
, a light receiving circuit 29, a filter 30, a mixer 31,
An electric FM demodulation circuit 32 as a demodulation circuit and a detection circuit 3
3, a control circuit 34, a local oscillation semiconductor laser 35, a frequency detection circuit 36, and a tuning circuit 37. The oscillators 26 of the transmitting devices 21, 22, 23 are
fP1, fP2, fP3 whose frequencies are different from each other
generates a pilot signal. Each transmitter 21, 22,
Optical frequency ν1 of signal lights C, D, and E emitted from 23
, ν2 and ν3 are different from each other. The optical coupler 24 outputs the signal light F, and the local oscillation semiconductor laser 35 outputs the local oscillation light G.

Next, the operation will be explained. Transmitting devices 21, 22
, 23, the signal lights C, D, E are sent to the optical coupler 2.
4 and transmitted to the receiving device 25 as signal light F. In the receiving device 25, a control signal is supplied from the tuning circuit 37 to the local oscillation semiconductor laser 35 to change the optical frequency of the local oscillation light G. The light receiving circuit 29 receives three signal lights C.
, D, and E is subjected to optical heterodyne detection. The filter 30 and mixer 31 demodulate the optical frequency modulation signal subjected to optical heterodyne detection. The detection circuit 33 detects the amplitude of the pilot signal and sends the information to the control circuit 34.
supply to. The control circuit 34 supplies a control signal to the local oscillation semiconductor laser 35 to control the optical frequency of the local oscillation light G so that the signal from the detection circuit 33 is always at the maximum. The output level of the frequency detection circuit 36 changes depending on the frequency of the pilot signal. Therefore, by making a one-to-one correspondence between the output level of the frequency detection circuit 36 and the frequencies of the pilot signals of the transmitting devices 21, 22, and 23, it is possible to determine which transmitting device the signal light currently being received comes from. can be determined. The tuning circuit 37 supplies a control signal to the local oscillation semiconductor laser 35 based on the information from the frequency detection circuit 36, controls the optical frequency of the local oscillation light G, and transmits the signal light from the desired transmitter. Select a channel.

In this way, each transmitting device 21, 22, 23
The frequencies of the pilot signals are made to differ from each other, and the frequency detection circuit 36 of the receiving device 25 detects the frequency of the pilot signal to determine which transmitting device is currently receiving the signal light, and based on that information. Since the optical frequency of the local oscillation light G from the local oscillation semiconductor laser 35 is controlled, the signal lights from the plurality of transmitters 21, 22, and 23 can be reliably tuned. Of course, the same effects as in the first embodiment can be obtained in this second embodiment as well. (Embodiment 3) FIG. 3 is a block diagram of a coherent optical transmission device according to Embodiment 3 of the present invention, and this embodiment is as claimed in claim 3.
It corresponds to This coherent optical transmission device includes transmitting devices 41, 42, and 43, an optical coupler 44 as a first optical coupler, and a receiving device 45. The receiving device 45 includes an optical coupler 47 as a second optical coupler, a light receiving circuit 48, a filter 49, a mixer 50, an electric FM demodulation circuit 51 as a demodulation circuit, and a detection circuit 52.
, a control circuit 53 , a local oscillation semiconductor laser 54 ,
It is composed of a channel detection circuit 55 and a channel selection circuit 56. Each of the transmitting devices 41, 42, 43 includes electric FM circuits 58, 5 as an example of an angle modulation circuit as shown in FIG.
9, an oscillator 60, a pilot signal generation circuit 61,
It is composed of an adder 62 and a semiconductor laser 63 for transmission. The electric FM circuits 58, 59 of each transmitting device 41, 42, 43 have carrier frequencies f1, f2, respectively.
Outputs an electric FM signal. Oscillator 60 outputs a signal with a frequency fP. The frequencies of the above three signals are different from each other. Pilot signal generation circuit 61 modulates the output signal from oscillator 60 with channel signal a to generate pilot signal b. Each transmitter 41, 42, 43
The channel signals a supplied to the pilot signal generation circuits 61 of the two are different from each other. In addition, each transmitting device 41
, 42, 43, the optical frequencies ν1, ν2, ν3 of the signal lights H, I, J are also different from each other. Optical coupler 4
4 emits signal light K, and local oscillation semiconductor laser 54 outputs local oscillation light L.

Next, the operation will be explained. Electric FM circuit 58,
The two output signals of 59 and the pilot signal b are combined by an adder 62 and supplied to a semiconductor laser 63. The frequency of the light emitted from the semiconductor laser 63 shifts depending on the input signal current from the adder 62. That is, the optical frequency is frequency modulated, and the optical frequency modulated signal light is output from the semiconductor laser 63 of each transmitting device 41, 42, 43.

Signal lights H, I, and J emitted from the transmitters 41, 42, and 43 are multiplexed by an optical coupler 44, and transmitted as signal light K to a receiver 45. In the receiving device 45, a control signal is supplied from the tuning circuit 56 to the local oscillation semiconductor laser 54, and the optical frequency of the local oscillation light L is changed. The light receiving circuit 48 performs optical heterodyne detection on one of the three signal lights H, I, and J. The filter 49 and the mixer 50 demodulate the optical frequency modulation signal subjected to optical heterodyne detection. The detection circuit 52 detects the amplitude of the pilot signal from the signal from the mixer 50 and supplies the information to the control circuit 53. The control circuit 53 is the detection circuit 52
A control signal is supplied to the local oscillation semiconductor laser 54 to control the optical frequency of the local oscillation light L so that the signal from the local oscillation light L is always maximized. The channel detection circuit 55 includes a mixer 5
The pilot signal is demodulated by the signal from 0 to reproduce the channel signal. The channel selection circuit 56 supplies a control signal to the local oscillation semiconductor laser 54 based on the channel signal from the channel detection circuit 55, controls the optical frequency of the local oscillation light L, and selects a signal light from a desired transmitter. Select a channel.

In this way, each transmitting device 41, 42, 43
In this step, a channel signal having information specific to the transmitting device is placed on the pilot signal, and the channel detection circuit 55 of the receiving device 45 detects the channel signal to determine from which transmitting device the signal light is currently being received. Since the optical frequency of the local oscillation light L from the local oscillation semiconductor laser 54 is controlled based on the information, the plurality of transmitting devices 41
, 42, 43 can be reliably tuned. Of course, the same effects as in the first embodiment can be obtained in this third embodiment as well.

In each of the above embodiments, the electric FM circuits 3, 4, 58, and 59 are used as angle modulation circuits, but the modulation method may be PM, FSK, or PSK in addition to FM. Furthermore, these modulation methods may be mixed. Further, the number of installed electric FM circuits 3, 4, 58, 59 and transmitting devices 1, 21, 22, 23, 41, 42, 43 can be set arbitrarily.

[0023]

As explained above, according to the present invention, a plurality of angle modulation circuits having mutually different carrier frequencies, an oscillator that generates a pilot signal of a frequency different from all the carrier frequencies, and all angle modulation circuits are provided. A transmitting device is provided that includes an adder that combines an output signal from the adder with a pilot signal, and a transmitting semiconductor laser that performs optical frequency modulation according to the output signal of the adder, and a local oscillating semiconductor laser; An optical coupler that combines the signal light sent from the transmitting device and the signal light of the local oscillation semiconductor laser, and a light receiving circuit that converts the beats of the two signal lights that are output from this optical coupler into electrical signals. , a filter that separates and extracts the carrier wave component and the first side wave component when optical frequency modulation is performed by the transmitting semiconductor laser from the output signal of the light receiving circuit, and the product of the carrier wave component and the first side wave component. a mixer that detects the amplitude of the pilot signal, a detection circuit that detects the amplitude of the pilot signal, a control circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser so that the amplitude of the pilot signal is maximized, and the output signal of the mixer. Since the receiving device is equipped with a demodulation circuit that demodulates the angle modulation signal, a pilot signal is added to the signal to be transmitted, and the receiving device detects the amplitude of this pilot signal to control the optical frequency of the locally oscillated light. Therefore, it is possible to stabilize the frequency of the beat signal.

Furthermore, a plurality of angle modulation circuits having mutually different carrier frequencies, an oscillator that generates a pilot signal of a frequency different from all the carrier frequencies, and an addition circuit that combines the output signals from all the angle modulation circuits and the pilot signal. a first optical coupler that includes a plurality of transmitting devices each including a transmitter and a transmitting semiconductor laser that performs optical frequency modulation according to the output signal of the adder, and multiplexes signal light from each of these transmitting devices; Further, a semiconductor laser for local oscillation,
a second optical coupler that couples the signal light sent from the first optical coupler with the signal light of the local oscillation semiconductor laser; and a first optical coupler that is the output of the second optical coupler. A light receiving circuit converts the beat of the signal light from the device and the signal light from the local oscillation semiconductor laser into an electrical signal, and the output signal of this light receiving circuit is converted into a carrier wave component and a frequency modulated by the transmitting semiconductor laser. A filter that separates the first side wave component and extracts each side wave component, a mixer that takes the product of the carrier wave component and the first side wave component, a frequency detection circuit that detects the frequency of the pilot signal, and an output of this frequency detection circuit. Each transmitting device is equipped with a receiving device equipped with a tuning circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the signal, and a demodulating circuit that demodulates the angle modulation signal that is the output signal of the mixer. By configuring the structure in which the frequencies of the pilot signals in the transmitting devices are different from each other and the optical frequencies of the signal lights from the respective transmitting devices are different from each other, the frequencies of the pilot signals in the transmitting devices are made to be different from each other, and the frequencies of the pilot signals in the receiving device are different from each other. By detecting the frequency, it is possible to determine from which transmitter the signal light is currently being received, and to control the optical frequency of the local oscillation light based on that information, ensuring that the signal light is received from the desired transmitter. You can select a channel.

In addition, a plurality of angle modulation circuits having different carrier frequencies, an oscillator that generates a signal with a frequency different from all the carrier frequencies, and a pilot signal is generated by modulating the oscillator signal with a channel signal having specific information. A pilot signal generation circuit that generates a signal, an adder that combines the output signals from all the angle modulation circuits and the pilot signal, and a transmitting semiconductor laser that performs optical frequency modulation according to the output signal of this adder. A first optical coupler for multiplexing signal light from each of these transmitting devices is provided, and a local oscillation semiconductor laser;
a second optical coupler that couples the signal light sent from the first optical coupler with the signal light of the local oscillation semiconductor laser; and a first optical coupler that is the output of the second optical coupler. A light receiving circuit converts the beat of the signal light from the device and the signal light from the local oscillation semiconductor laser into an electrical signal, and the output signal of this light receiving circuit is converted into a carrier wave component and a frequency modulated by the transmitting semiconductor laser. A filter that separates the first side wave component and extracts each, a mixer that takes the product of the carrier wave component and the first side wave component, a channel detection circuit that demodulates the pilot signal, and an output signal of the channel detection circuit. A receiving device is provided that includes a tuning circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the frequency of the local oscillation semiconductor laser, and a demodulation circuit that demodulates the angle modulation signal that is the output signal of the mixer. By configuring each transmitting device to have a different optical frequency and the optical frequency of the signal light from each transmitting device to be different from each other, in each transmitting device, a channel signal having information unique to that transmitting device is added to the pilot signal. The receiving device detects this channel signal, determines which transmitting device is currently receiving the signal light, and can control the optical frequency of the local oscillation light based on that information. This has the excellent effect of being able to reliably tune the light.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a coherent optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a coherent optical transmission device according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a coherent optical transmission device according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a transmitting device provided in a coherent optical transmission device according to a third embodiment of the present invention.

[Explanation of symbols]

1 Transmitting device 2 Receiving device 3 Electric FM circuit 4 Electric FM circuit 5 Oscillator 6 Adder 7 Semiconductor laser 9 Optical coupler 10 Photo receiving circuit 11 Filter 12 Mixer 13 Electric FM demodulation circuit 14 Detection circuit 15 Control circuit 16 Semiconductor laser for local oscillation 21 Transmitting device 22 Transmitting device 23 Transmitting device 24 Optical coupler 25 Receiving device 26 Oscillator 28 Optical coupler 29 Photo receiving circuit 30 Filter 31 Mixer 32 Electric FM demodulation circuit 35 Semiconductor laser for local oscillation 36 Frequency detection circuit 37 Tuning circuit 41 Transmitting device 42 Transmitting device 43 Transmitting device 44 Optical coupler 45 Receiving device 47 Optical coupler 48 Light receiving circuit 49 Filter 50 Mixer 51 Electric FM demodulation circuit 54 Semiconductor laser for local oscillation 55 Channel detection circuit 56 Tuning circuit 58 Electric FM circuit 59 Electric FM circuit 60 Oscillator 61 Pilot signal generation circuit 62 Adder 63 Semiconductor laser

Claims (3)

[Claims] 1. A plurality of angle modulation circuits having mutually different carrier frequencies, an oscillator that generates a pilot signal of a frequency different from all of the carrier frequencies, and output signals from all of the angle modulation circuits and the pilot signal. A transmitting device is provided, which includes an adder for synthesizing the signals, and a transmitting semiconductor laser that performs optical frequency modulation according to the output signal of the adder, and a local oscillating semiconductor laser and the transmitting device. an optical coupler that couples the signal light with the signal light of the local oscillation semiconductor laser; a light receiving circuit that converts the beats of the two signal lights that are output from the optical coupler into electrical signals; A filter that separates and extracts a carrier wave component and a first side wave component when the output signal is optically frequency modulated by the transmitting semiconductor laser, and calculates the product of the carrier wave component and the first side wave component. a mixer, a detection circuit that detects the amplitude of the pilot signal, a control circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser so that the amplitude of the pilot signal is maximized, and an output signal of the mixer. What is claimed is: 1. A coherent optical transmission device comprising a receiving device including a demodulation circuit that demodulates an angle modulated signal. 2. A plurality of angle modulation circuits having mutually different carrier frequencies, an oscillator that generates a pilot signal of a frequency different from all of the carrier frequencies, and output signals from all of the angle modulation circuits and the pilot signal. A plurality of transmitting devices each including an adder for synthesizing the signals, and a transmitting semiconductor laser for performing optical frequency modulation according to the output signal of the adder are provided, and a first transmitter for multiplexing the signal light from each of these transmitting devices further includes a local oscillation semiconductor laser, and a second optical coupler that couples the signal light sent from the first optical coupler and the signal light of the local oscillation semiconductor laser. a light receiving circuit that converts the beat of the signal light from the first optical coupler, which is the output of the second optical coupler, and the signal light from the local oscillation semiconductor laser into an electrical signal; A filter that separates and extracts a carrier wave component and a first side wave component when optical frequency modulation is performed by the transmitting semiconductor laser from an output signal of the circuit, and a product of the carrier wave component and the first side wave component. A mixer that takes
a frequency detection circuit that detects the frequency of the pilot signal; a tuning circuit that controls the optical frequency of the signal light of the local oscillation semiconductor laser based on the output signal of the frequency detection circuit; and an output signal of the mixer. A receiver equipped with a demodulation circuit that demodulates the angle modulation signal is provided, and the frequencies of the pilot signals in each of the transmitting devices are different from each other, and the optical frequencies of the signal lights from the respective transmitting devices are different from each other. A coherent optical transmission device characterized by: 3. A plurality of angle modulation circuits having mutually different carrier frequencies, an oscillator that generates a signal with a frequency different from all the carrier frequencies, and a channel signal having certain information that modulates the signal of the oscillator. a pilot signal generation circuit that generates a pilot signal using the angular modulation circuit; an adder that combines the output signals from all the angle modulation circuits with the pilot signal; and a transmitter that performs optical frequency modulation according to the output signal of the adder. A plurality of transmitting devices each having a reliable semiconductor laser are provided, a first optical coupler for multiplexing signal light from each of these transmitting devices is provided, and a local oscillation semiconductor laser and the first optical coupler are provided. a second optical coupler that couples the signal light sent from the device with the signal light of the local oscillation semiconductor laser; a light receiving circuit that converts the beat of the signal light and the signal light from the local oscillation semiconductor laser into an electric signal; a carrier wave component when the output signal of the light receiving circuit is optically frequency modulated by the transmitting semiconductor laser;
a filter that separates the side wave components and extracts each;
a mixer that takes the product of the carrier wave component and the first side wave component; a channel detection circuit that demodulates the pilot signal; and a signal light beam of the local oscillation semiconductor laser based on the output signal of the channel detection circuit. A receiving device including a tuning circuit for controlling a frequency and a demodulating circuit for demodulating an angle modulated signal that is an output signal of the mixer is provided, and information on the channel signal is mutually different in each of the transmitting devices, and A coherent optical transmission device characterized in that the optical frequencies of signal lights from each transmitting device are different from each other.