JPH036136A - Optical transmitting and receiving circuit - 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 [Object of the Invention] (Industrial Application Field) The present invention relates to an optical transceiver circuit that converts a frequency multiplexed signal such as an analog video signal into an optical signal using a semiconductor laser and transmits the optical signal.

(Prior Art) Conventionally, two types of devices have been proposed for optically transmitting frequency-multiplexed analog video signals using semiconductor lasers: an AM-FDM system and an FM-FDM system. Regardless of the type, the conventional analog video signal optical transmitter/receiver circuit uses a frequency band of several hundred MHz to 1.3 GHz.

For example, the intermediate frequency of broadcasting satellites is standardized as the BS-IF interface, and the frequency band is 1.0359.
It is selected to be 8 to 1.33150 GHz. As shown in FIG. 3, a conventional optical transmitter/receiver circuit converts an electric signal (analog video signal in a high frequency band as described above) applied to an input terminal 1 into an electric/optical converter transmitter 2 using a semiconductor laser.
The optical modulation signal is input as is, the obtained optical signal is transmitted to the optical/electrical conversion receiver 4 via the optical fiber 3, and the optical/electrical converted signal is sent to the output terminal 5. Therefore, the optical modulation signal is extremely It was in the high IGHz band.

(Problem to be solved by the invention) As mentioned above, in the conventional system that converts electricity to light and transmits the high frequency band, the characteristics of the optical transmission system deteriorates, and there are very few measures to improve it. It was becoming a hassle.

In other words, it is known that the harmonic distortion Dn characteristic of a semiconductor laser deteriorates as the modulation frequency increases and the modulation degree increases (a measurement example is shown in FIG. 4). In addition, the input equivalent noise current density 1 nT of the optical/electrical conversion receiver also deteriorates as the frequency increases (a measurement example is shown in FIG. 5).

Therefore, the Dn characteristics of the semiconductor laser and the relative noise intensity RIN
The requirements for semiconductor lasers have become extremely strict, and selection of semiconductor lasers is essential. In addition, in order to suppress the generation of mode hopping noise, automatic temperature control circuit A using a Peltier element
It was necessary to add a TC to the semiconductor laser drive section. Further, in order to suppress deterioration of RIN characteristics and Dn characteristics due to the influence of light reflected back to the semiconductor laser, a special optical connector called a diagonal polished connector has been used. (1989
IEICE Spring National Conference B-787-789,
"Semiconductor Laser and Application Technology" by Hiroo Yonezu, published by Kogakusha) Furthermore, in order to compensate for the deterioration of the InT characteristics of the optical/electrical conversion receiver, an avalanche photodiode, which is expensive and requires complicated adjustment, must be used as a light receiving element. I had to.

All of the above drawbacks increase costs and impede mass production.

In addition, as a method to improve the RIN characteristics and Dn characteristics of semiconductor lasers, we have developed a technology that detects the monitor light of the semiconductor laser and provides negative feedback to the laser drive circuit (optical/electrical conversion negative feedback circuit).
is known, but this method cannot be applied to very high frequency bands either. Due to the capacitance of the photodetector for monitoring light detection and the phase rotation in the feedback loop, it does not work as desired in high frequency bands. (W, ZSCHUNKE etal
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Japan, vol, E68. (No. 3.1985) Therefore, the above-mentioned negative feedback circuit could not be employed in a conventional circuit that converts and transmits electricity to light in a high frequency band.

This invention was made in view of the conventional problems mentioned above, and its purpose is to significantly relax the requirements for semiconductor lasers and to make it possible to mass-produce optical transmitter/receiver circuits with excellent characteristics at low cost. be.

[Structure of the invention]

(Means for Solving the Problems) Accordingly, in this invention, after frequency-converting a frequency-multiplexed human-powered electric signal to an arbitrary low frequency band, it is converted into an optical signal by an electric/optical conversion transmission section using a semiconductor laser, and then transmitted. However, this optical signal is converted into an electrical signal by an optical/11-channel conversion receiver, and then the frequency is converted to an arbitrary high frequency band and output.

(Operation) An electrical signal frequency-converted to a low frequency band is inputted to the electrical/optical conversion transmitter, and an optical signal modulated with the low frequency band signal is transmitted to the optical/14-channel converter receiver.

(Embodiment) FIG. 1 shows a basic embodiment of the present invention. A frequency-multiplexed high frequency band electrical signal is applied to the input terminal 1 . This input electrical signal is frequency-converted into an electrical signal in a low frequency band by the first frequency converter 6, and then input to the electrical/optical conversion transmitter 2 using a semiconductor laser. The optical signal from the transmitting section 2 is transmitted to the optical/electrical conversion receiving section 4 via the optical fiber 3. The electrical signal output from the receiving section 4 is input to the second frequency converting section 7, where the frequency is converted to a higher frequency band, and then output to the output terminal 5.

Therefore, the electrical/optical conversion transmitter 2, the optical fiber 3, the optical/optical
The electrical conversion receiver 4 will operate in a low frequency band. Therefore, as is clear from FIG. 4(a), the transmitter 2
The harmonic distortion Dn characteristics of the semiconductor laser itself are improved. Furthermore, as is clear from FIG. 4(b), since the modulation amplitude can be increased within a range that satisfies the Dn characteristic, the C/N characteristic can be improved. Also the second
As is clear from the figure, since the characteristic of the input equivalent noise current density ln■ of the receiving section 4 is improved, the desired characteristic can be ensured with smaller received optical power.

This leads to a relaxation of the requirements for the semiconductor laser in the transmitter 2, as well as a relaxation of the requirements for the light-receiving element in the receiver 4. characteristics can be realized.

FIG. 2 shows a second embodiment of the invention, which is similar to the first embodiment.
An optical/electrical conversion negative feedback section 8 is added to the electrical/optical conversion transmission section 2 in the illustrated embodiment to detect the monitor light of the semiconductor laser and provide negative feedback to the laser drive circuit. Since the input frequency band of the transmitter 2 is lowered by the frequency converter 6,
The negative feedback section 8 functions effectively, and the Dn characteristics and RIN characteristics of the semiconductor laser are significantly improved. Therefore, it is possible to eliminate the special obliquely polished connector for suppressing reflected return light, and the reflection characteristics of the connection portion of the optical fiber line can be relaxed.

〔Effect of the invention〕

As explained in detail above, the present invention has a configuration in which an input signal is converted to a lower frequency band before electrical/optical conversion is performed by a semiconductor laser, and the frequency is reconverted to a higher frequency after the optical/electrical conversion is performed by a light receiving element. Therefore, ■ The harmonic distortion characteristics of the semiconductor laser are improved. ■ The noise characteristics of the receiving section are improved. ■ The harmonic distortion and RIN characteristics of the semiconductor laser are improved because it can be used in conjunction with optical/electrical conversion negative feedback technology. Therefore, the requirements for each component of the optical transmission system are relaxed, and it becomes possible to mass-produce optical transceiver circuits with excellent characteristics at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical transmitter/receiver circuit according to a first embodiment of the present invention, FIG. 2 is a block diagram of the second embodiment, and FIG.
The figure is a block diagram of a conventional optical transmitter/receiver circuit, and FIGS. 4 and 5 are characteristic diagrams for explaining problems in the prior art and details of the present invention.

Claims (2)

[Claims] (1) A first frequency converter that converts the frequency of the frequency-multiplexed input electrical signal into an arbitrary low frequency band, and converts the output electrical signal of this converter into an optical signal using a semiconductor laser and sends it to the optical transmission line. an electrical/optical conversion transmitting unit that converts the optical signal input from the optical transmission line into an electrical signal;
An optical transceiver circuit comprising an electrical conversion receiver and a second frequency converter that frequency converts the electrical signal output from the receiver into an arbitrary high frequency band. (2) The electrical/optical conversion transmitting section includes an optical/electrical conversion negative feedback section that converts the monitor light of the semiconductor laser into an electrical signal and provides negative feedback to the drive circuit of the semiconductor laser. The optical transmitter/receiver circuit according to claim (1).