JPH0287729A - Optical information transmission method - Google Patents

Abstract

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

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical information transmission method.

[Conventional technology]

Conventional optical information transmission methods include, for example, modulating a semiconductor laser with an information signal, transmitting the intensity-modulated optical signal through an optical waveguide such as an optical fiber, detecting it with a photodetector, and converting it into an electrical signal. There is something to do. When transmitting digital signals using the above method, one optical pulse corresponds to one bit. In this method, when it is necessary to increase the amount of information transmitted per unit time, this is handled by increasing the generation rate of optical pulses. As a method that does not require the generation speed of optical pulses to be increased, there is also a wavelength division multiplexing transmission method. This method modulates multiple semiconductor lasers with different emission wavelengths separately, and guides the output optical modulation signals through an optical multiplexing element to a leading wave path such as an optical fiber. Information on multiple modulated lights is transmitted in the leading wavepath, and in the detection section, the multiple wavelengths are separated into individual wavelengths using a demultiplexer, and then detected using a photodetector and converted into electrical signals. . With this method, even if the information transmission per pharyngeal time per wavelength is not increased,
Overall, the amount of information transmitted per medium time can be increased by the number of wavelengths.

(Problem to be Solved by the Invention) However, among the above conventional examples, in the optical transmission system using one wavelength, in order to increase the amount of information transmitted per unit time, it is necessary to increase the number of pulses generated per unit time. For this purpose, it is necessary to increase the speed of the modulation electronic circuit, which has the disadvantage of making the electronic circuit complicated. Furthermore, the wavelength multiplexing optical transmission system has the disadvantage that it requires a number of laser modulation circuits corresponding to the number of wavelengths multiplexed, making the configuration complicated. Furthermore, a multiplexer is required to input the light emitted from multiple lasers into one leading wavepath, but it is difficult to multiplex multiple lights with high efficiency, and the disadvantage is that there is a large loss of optical power. There was also.

[Means to solve the problem]

A typical outline of the present invention is as follows. That is, a transmitting section that transmits an optical pulse having a wavelength uniquely corresponding to a multi-level encoded electrical signal, and a receiving section that receives the multi-wavelength optical pulse and converts it into a multi-level encoded electrical signal are provided. This allows the amount of information transmitted per unit time to be increased without increasing the pulse sending speed or degrading the error rate. The transmitting section may include, for example, one semiconductor laser capable of oscillating a plurality of wavelengths, and may modulate and drive this as appropriate.

[Effect]

By assigning a corrupted wavelength to each 9th level of a multilevel code and transmitting it, the amount of information per pulse can be increased1.In addition, if digital communication is used, it is resistant to noise and timing extraction is easy. Become.

[Embodiment] FIG. 1 is a block diagram showing the configuration of a system when carrying out an embodiment of the present invention.

In the figure, 1 is a wavelength selection circuit, 2 is a variable wavelength semiconductor laser, 3 is a pulse generator, 4 is an optical fiber, 22 is an optical amplifier using a semiconductor laser, 5 is a demultiplexer, and 6 is a photodetector. 7 is an output selection circuit. For example, the Japanese Journal of
Applied Physics Volume 27 No. 4 (L[1
93-695), and its structure is shown in FIG. In FIG. 2, 9 is a semiconductor substrate made of, for example, n-type InP, and 10 is made of, for example, Ga1nAs.
It is a waveguide layer (guide layer) made of P, and a first-order diffraction grating is formed on its surface. 11 is, for example, Ga1nAsP
12 is a cladding layer made of, for example, P[nP], 13.14 is a current confinement region, 13 is made of,
It is made of type InP, and 14 is made of n-type 1nP. 15 is an electrode contact layer made of, for example, P-type InP. 19 is a first electrode, 16 and 17 are wavelength control electrodes, and 18 is an active region electrode. The tunable wavelength semiconductor laser having the configuration shown in FIG. 2 changes the refractive index of the waveguide layer IO by injecting a current through the wavelength control electrode, and the optical As the pitch changes, the wavelength showing the maximum reflectance of the distributed reflection mirror formed by the case r of the waveguide layer to) changes, and the wavelength at which the laser oscillates changes.

Next, an outline of the operation of the present invention will be explained.

For example, in the case of transmitting 3-value information, 3-value information "0", "1"
Separate oscillation wavelengths for “, 2”., λ1
．． By transmitting information by assigning λ2, and recognizing which wavelength has been transmitted at the detector, 3
It recognizes which value information has been sent and converts it into an electrical signal.

Next, the present invention will be explained in detail with reference to FIG. The electrical multi-value signal (n-value) to be transmitted is manually input to the wavelength selection circuit 1. In the wavelength selection circuit, the wavelength control electrode 1 of the tunable wavelength semiconductor laser 2 is configured such that the tunable wavelength semiconductor laser 2 outputs light with a wavelength corresponding to the input multilevel information.
6. Adjust the amount of current flowing to 17. The pulse generator 3 is
Pulse currents are always injected into the active region electrode 18 of the tunable wavelength semiconductor laser 2 at regular intervals, and these pulses are synchronized with the multilevel encoding pulses. By doing the above,
The optical output from the tunable wavelength semiconductor laser 2 is as shown in FIG. 3 (in FIG. 3, three values are given as an example).

The optical pulse train output as described above is transmitted using the optical fiber 4. In the receiving section, the signal is sent to the photodetector array 6 via the demultiplexer 5 . The output of the photodetector array 6 is input to the output selection circuit 7. This output selection circuit 7 recognizes that an optical pulse with a wavelength corresponding to the largest output among the outputs of the photodetector array 6 has been transmitted, and selects one of the multilevel codes corresponding to the recognized wavelength. , output as an electrical signal.

In the above embodiment, the wavelength selection circuit 1 is used, but the value-encoded electrical signal is directly transmitted to the tunable wavelength semiconductor laser 2.
The same effect can be obtained by inputting to the wavelength control electrodes 1fi, 17.

Further, in the above embodiment, the optical amplifier 22 is used before the demultiplexer 5, but the same effect as in this embodiment can be obtained even if the input is directly input to the demultiplexer 5 without using the optical amplifier 22. .

In addition, in the above embodiment, a ternary encoded information transmission method has been described, but n-ary encoding (n
It is obvious that the same can be done for positive integers).

FIG. 4 is a block diagram of a system implementing another embodiment of the invention. In FIG. 4, 20 is a voltage controlled oscillator (V(:O)), 21 is an acousto-optic modulator 1 and 4 are optical fibers, 23 is a combiner constituted by, for example, a beam splitter, and 24 is a continuously oscillating laser. light source, 25
is a photodetector consisting of, for example, a PTN photodiode, 2
6 is a PLL detection circuit whose configuration is shown in FIG. In FIG. 5, 27 is a phase detection circuit, for example, a 16G044.28H inversion circuit manufactured by Gigabit Logic, 29 is an adder, 3o is a low-pass filter, and 31 is a voltage controlled oscillator (VCO).

First, the operation of the PLI and detection circuit 26 shown in FIG. 5 will be explained. A sine wave voltage (signal) with an arbitrary wave number and a sine wave voltage (reference signal) from the VCO 31 are input to the phase detection circuit 27, and the output of the phase detection circuit 27 is determined according to the difference between the signal and the reference signal. Two types of pulse trains are output. By taking the difference between these two types of pulse trains and passing it through the low-pass filter 30, an error voltage for controlling the VCO 31 is output. This error voltage is generated such that when the frequency of the signal is higher than the frequency of the reference signal, the voltage applied to the VCO 31 becomes larger.
The frequency of the reference signal output from the VCO 31 increases. It functions to eliminate such a difference in frequency between the signal and the reference signal, and eventually the frequencies of the signal and the reference signal match, and a voltage corresponding to that frequency is output.

Next, the operation of this embodiment will be explained. The multilevel encoded electrical signal is manually input to a voltage control oscillator (VCO) 20.
Generates a sine wave voltage with a frequency corresponding to the electrical signal. For example, in the case of 4-value encoding, 60M corresponds to 0"
1lz, “1” corresponds to 65MHz, “2”
70Mtlz corresponding to 75MH7 corresponding to 3”
Outputs a sine wave signal. The sine wave signal output from the VCO 20 is input to the acousto-optic modulator 21 to frequency-modulate the continuous wave laser beam having a wavelength of 850 nm, for example, which is input to the acousto-optic modulator 21 . The modulated laser light is transmitted using the optical fiber 4. In the receiving section, the light is combined with light from a laser light source 24 having a wavelength of 850 nm in a combiner 23, and square detection (heterodyne detection) is performed in a photodetector 25. The output voltage from the photodetector 25 is a sine wave voltage of 2 MHz to 8 MHz corresponding to information. When the sine wave voltage from the photodetector 25 is input to the PLL detection circuit 26, the PLL detection circuit 26 generates a multi-level encoded electric pulse corresponding to the frequency of the manually input sine wave voltage. I can get a signal.

(Effect of the invention) As explained above, when transmitting multi-level coded information using light, by assigning different wavelengths to each predetermined level of the multi-level code and transmitting it, it is possible to In addition, since pulses are constantly being sent out, timing extraction becomes easier.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an optical information transmission system implementing the present invention, Fig. 2 is a diagram showing the structure of a tunable wavelength semiconductor laser, and Fig. 3 explains the basic concept of the optical signal transmission system of the present invention. 4 is a diagram showing the configuration of an optical information transmission system corresponding to another embodiment of the present invention, and FIG. 5 is a diagram showing the configuration of an optical information transmission system corresponding to another embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of a detection circuit. DESCRIPTION OF SYMBOLS 1... Wavelength selection circuit, 2... Tunable wavelength semiconductor laser, 3... Pulse generator, 4... Optical fiber, 5...
...Demultiplexer, 6...Photodetector array 7...
- Output selection circuit, 22... optical amplifier.

Claims (1)

[Claims] 1. After converting a multilevel encoded electrical signal into an optical pulse with a wavelength corresponding to the multilevel amount and transmitting the optical pulse via an optical waveguide, An optical information transmission method that detects the wavelength of an optical pulse, converts it into a multi-level encoded electrical signal, and demodulates the signal. 2. By injecting a current into the distributed feedback region of a distributed feedback semiconductor laser, a wavelength tunable semiconductor laser whose oscillation wavelength can be changed is used to generate a current proportional to a multilevel encoded electrical signal. By injecting into the distributed feedback region of a wavelength tunable semiconductor laser, an optical pulse with a wavelength corresponding to the multilevel code is generated, the optical pulse is transmitted via a transmission path, and the transmitted optical pulse signal is separated. An optical information transmission method in which the signals are demultiplexed by a wave detector, converted into electrical signals by a photodetector, converted into multi-level encoded electrical signals by a discrimination circuit, and demodulated. 3. Frequency modulate the continuously oscillated laser light by applying a sinusoidal voltage corresponding to the multi-level code to the acousto-optic modulation element, transmit the frequency modulated light via the optical transmission path, and transmit the frequency modulated light through the optical transmission path. An optical information transmission method that uses heterodyne detection to convert an optical signal into a multi-level encoded electrical signal and demodulate it.