JPH0697549A - Light transmitting equioment - Google Patents

Abstract

PURPOSE:To compensate the distortion generated by a laser diode itself as well as a laser diode driving circuit, by installing a means which chancels the distortion generated by an amplifying means and a light emitting element. CONSTITUTION:A first light emitting element 6 is driven by an electric signal, and generates a light signal. A first amplifying means 5 generates an electric signal for driving the first light emitting element 6. A first canceling signal generating means 100 generates a first canceling component which cancels the distortion generated in the first amplifying means 5, and adds the component to electric signals inputted in the element 6 and the amplifying means 5. A second canceling signal generating means 200 generates a second canceling component which cancels the distortion which is generated in the first light emitting element 6 and adds the component to the inputted electric signal. The first amplifying means 5 receives and amplifies the electric signal to which the first and the second canceling components are added, and generates an electric signal for driving the first light emitting element 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter having a distortion compensating circuit for compensating for distortion in an optical transmitter for transmitting multi-channel high frequency analog signals. In an optical transmitter that transmits a multi-channel high frequency analog signal, a distortion compensation circuit that compensates for distortion caused by interference between signals of a plurality of channels has been proposed. It is desired to compensate for the distortions that occur in laser diodes.

[0002]

2. Description of the Related Art FIG. 3 shows a distortion component generated in a transmission side device when a high frequency analog signal is multi-channel transmitted (that is, modulated with a plurality of carrier frequencies, frequency division multiplexed and transmitted). is there. For example, C
In the ATV system, high-frequency analog signals of a plurality of channels are frequency-division-multiplexed and transmitted, but these plurality of channels interfere with each other, and for example, distortion components as shown in FIG. To occur.

FIG. 4 shows the configuration of a conventional optical transmitter having a function of compensating for distortion that occurs during multi-channel transmission of high frequency analog signals. In FIG.
Reference numeral 1 is a distributor, 2'is a distortion generator, 3 is a delay circuit, 4 is a coupler, 5 is an amplifier, and 6 is a laser diode. Figure 4
In the distortion generator 2'of FIG. 1, 7 is an amplifier, 9 is a delay circuit, 10 is a combiner, and 14 is an attenuator.

The signal e _i input to the configuration of FIG. 4 is distributed in three directions by the distributor 1, and the signals in two directions are distorted by the distortion generator 2 '.
In addition, the other one-way signal passes through the delay circuit 3 and the coupler 4
It becomes one input of. Of the two-direction signals input to the distortion generator 2 ′, the first signal is input to the amplifier 7 and the second signal is input to the delay circuit 9. The amplifier 7 is assumed to have the same characteristics as the amplifier 5 that drives the laser diode 6, and when the above-mentioned first signal is input, a distortion component that is substantially the same as that generated by the amplifier 5 that drives the laser diode 6 is generated. Output as a signal containing. For example, when considering up to the third-order distortion component, this signal is G ₁ (e _i + αe
_i ² + βe _i ³ ...). Here, G ₁ is the gain of the amplifier 7. The output of the amplifier 7 is the attenuator 14
Is attenuated by 1 / G ₁ at the signal (e _i + αe _i ² + β
e _i ³ ...) is obtained. The delay circuit 9 applies a delay to the input signal of the delay circuit 9 so that the output signal of the delay circuit 9 is 180 ° out of phase with the output signal of the attenuator 14. In the combiner 10, the output signal (e of the attenuator 14 from the delayed second signal e _i
i + αe _i ² + βe _i ³ ...) Is subtracted, and a signal − (αe _i ² + βe _i ³ ...) With the distortion component inverted is output. A signal obtained by inverting this distortion component − (αe _i ² +
βe _i ³ ...) In the combiner 4, the signal (e _i −αe _i ² −βe _i ³ ...) Is combined with the above signal input to the combiner 4 via the delay circuit 3. Is output. The delay circuit 3 is for giving a delay such that the output signal of the delay circuit 3 is 180 ° out of phase with the output signal of the distortion generator 2 ′ to the signal input to the delay circuit 3. . The signal (e _i −αe _i ² −βe _i ³ ...
.) Is amplified by the amplifier 5 with substantially the same characteristics as the amplifier 7, and the distortion-removed signal G ₂ (e _i + e _i ² + e _{i)
^{3 ···) (e i -αe i}} 2 -βe i 3 ···) ≒ G 2
Output e _i . Therefore, the laser diode 6
It is driven by the signal G ₂ e _i from which this distortion has been removed.

[0005]

However, the configuration of FIG. 4 has a problem that the distortion generated by the laser diode itself driven by the distortion-compensated signal is not compensated. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical transmitter for transmitting a multi-channel high frequency analog signal, which compensates for distortion generated by not only the laser diode drive circuit but also the laser diode itself.

[0006]

FIG. 1 shows the basic principle of the present invention. As shown in FIG. 1, a first light emitting element 6'which is driven by an electric signal to generate an optical signal, and a first amplifier which generates an electric signal to drive the first light emitting element 6 '. Means 5 ', first canceling signal generating means 100 for generating a first canceling component for canceling the distortion generated in the first amplifying means 5'and adding it to the inputted electric signal, and the first canceling signal generating means 100. The second canceling signal generating means 200 for generating a second canceling component for canceling the distortion generated in the light emitting element 6'and adding it to the inputted electric signal.
And the first amplifying means 5'includes the first
And an electric signal to which the second canceling component has been added is input and amplified to generate an electric signal for driving the first light emitting element 6 '.

[0007]

More specifically, in the present invention, as shown in FIGS. 1 and 2, when a signal corresponding to a main signal containing distortion is generated in the distortion generator 2, the optical transmission is performed. A light emitting element 11 having substantially the same characteristics as the light emitting element 6 that transmits an optical signal on the road, and a light receiving element 12 that receives the optical signal generated by the light emitting element 11 and converts the optical signal into an electric signal are provided. The signal corresponding to the main signal including is also configured to include the distortion component that may be generated in the light emitting element 6.

With the above structure, the distortion generator 2 generates a signal that also includes a component that cancels the distortion component that may occur in the light emitting element 6, and adds this to the signal that drives the light emitting element 6. Therefore, the distortion component actually generated in the light emitting element 6 is canceled, and the output of the light emitting element 6 outputs an optical signal that does not include the distortion component generated by the light emitting element 6 itself.

[0009]

FIG. 2 shows the configuration of an optical transmitter having a distortion compensation function according to the present invention. In FIG. 2, reference numeral 2 is a distortion compensating unit, and the configuration other than the distortion compensating unit 2 is the same as that of FIG. In the distortion compensator 2, the amplifier 7, the delay circuit 9, the coupler 10, and their functions are the same as those in the configuration of FIG. 4, but instead of the attenuator 14 of FIG. An optical array link portion indicated by a broken line 8 in FIG. 2 is provided. Further, the delay circuit 9 applies a delay to the input signal of the delay circuit 9 so that the output signal of the delay circuit 9 is 180 ° out of phase with the output signal of the optical array link unit 8.

In the optical array link section 8, the laser diode 1 having substantially the same characteristics as the laser diode 6 is provided.
1, a photodiode 12 that receives an optical signal generated by the laser diode 11 and converts it into an electric signal, and an amplifier 13 that amplifies an output signal of the photodiode 12. Here, the laser diode 11 having substantially the same characteristics as the laser diode 6 is formed, for example, on the same semiconductor substrate as shown in FIG. 2, and in particular, the two laser diodes described above are located relatively close to each other. It can be connected by designing. The distortion generated by the photodiode 12 is sufficiently smaller than the distortion generated by the laser diode. Further, the amplifier 13 also uses a low distortion, and its gain is
3 output is distortion generated in the amplifier 5, and
A signal that also includes distortion that approximates the distortion of the laser diode 6.
(e _i + α′e _i ² + β′e _i ³ ...) Here, e _i is an input signal of the distortion compensation circuit of FIG.

Thus, the same as in the above-mentioned configuration of FIG.
Similarly, in the coupler 10, the output signal e of the delay circuit 9 is output.
_iFrom the output of (the amplifier 13 of) the optical array link unit 8 described above.
Force signal (e_i+ Α'e_i ²+ Β'e_i ³...)
Signal minus the distortion component- (α'e_i ²+ Β '
e_i ³...) is output. Invert this distortion component
Signal- (α'e_i ²+ Β'e_i ³...) is the coupler 4
, The main signal input to the coupler 4 via the delay circuit 3
The signal (e_i-Αe_i ²-Βe _i ³・ ・
・) Is output. This signal is sent to amplifier 5
It is amplified with a characteristic similar to that of No. 7 and is generated in the amplifier 5.
Wax distortion is removed and generated by laser diode 6.
An electrical signal containing a component that cancels the distortion that would occur
To drive the laser diode 6
It Thus, the optical signal output from the laser diode 6
Signal to eliminate the distortion that would occur in the laser diode 6.
It may be canceled and less distorted.

[0012]

As described above, according to the optical transmitter of the present invention, not only the laser diode driving circuit but also the distortion generated by the laser diode itself can be compensated. In particular, multichannel analog signals can be compensated. There is an effect that the characteristics of optical transmission can be greatly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic principle of an optical transmitter of the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of an optical transmitter of the present invention.

FIG. 3 is a diagram showing an example of distortion generated in a transmission side device in multi-channel transmission of analog signals.

FIG. 4 is a diagram showing a configuration of a conventional optical transmitter having a distortion compensation function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Distributor 2, 2 '... Distortion generating part 3, 9 ... Delay circuit 4, 10 ... Coupler 5, 7, 13 ... Amplifier 6,6 ... Laser diode 8 ... Optical array link part 14 ... Attenuator

Claims (4)

[Claims] 1. A first light emitting element (6) which is driven by an electric signal to generate an optical signal, and a first amplifying means (5) which generates an electric signal for driving the first light emitting element (6). ), A first canceling signal generating means for generating a first canceling component for canceling the distortion generated in the first amplifying means (5) and adding it to the inputted electric signal, and the first light emitting element. A second canceling signal generating means for generating a second canceling component for canceling the distortion generated in (6) and adding the second canceling component to the input electric signal; and the first amplifying means (5). The optical transmission device is characterized in that the electric signal added with the first and second canceling components is inputted and amplified to generate an electric signal for driving the first light emitting element (6). 2. The optical transmitter according to claim 1, wherein the second canceling signal generating means includes a second light emitting element (11) having substantially the same characteristics as the first light emitting element (6). . 3. The optical transmitter according to claim 1, wherein the first canceling signal generating means includes a second amplifying means (7) having substantially the same characteristics as the first amplifying means (5). . 4. A distribution means (1) for distributing an inputted electric signal into first, second and third electric signals, and a first amplification means (7) for amplifying the first electric signal. )
A first light emitting element (11) for converting an electric signal output from the first amplifying means (7) into an optical signal; and receiving the optical signal generated by the first generating element (11). A photoelectric conversion element (12) for converting into an electric signal, a second amplification means (13) for amplifying the electric signal output by the photoelectric conversion element (12) with a predetermined gain, and the second electric For the signal, the first electrical signal is
The first light emitting element (12), the photoelectric conversion element (1
2), and first delay means (9) for giving a delay obtained by adding a phase shift of 180 ° to the delay received while passing through the first amplification means (13), A first coupling means (10) for electrically coupling the output signal of the first delay means (9) and the output signal of the second amplification means (13); and to the third electrical signal, The second amplification means (1
Second delay means (3) for giving a delay that gives a phase different from the phase of the output signal of 3) by 180 °, the output signal of the second delay means (3), and the first coupling means (10) Output signal of the second coupling means (4) having substantially the same characteristics as the second coupling means (4) for electrically coupling the output signal of the second coupling means (4). A third amplifying means (5) for inputting and amplifying, and having substantially the same characteristics as the first light emitting element (11), driven by an output signal of the third amplifying means (5),
An optical transmitter, comprising: a second light emitting element (6) for generating an optical signal according to the output signal.