JP4708890B2 - Optical transmission unit - Google Patents

Description

  The present invention relates to an integrated optical transmission unit having optical branching and amplifier functions.

  Recently, FTTH has been known in which a coaxial cable transmission line for transmitting a high-frequency broadband signal is laid to each household instead of an optical fiber. In this system, the electrical signal is divided into several parts at the transmission end of the optical transmission line, and then the distributed electrical signal is converted into an optical signal and transmitted to each household as an optical signal. .

  This system first amplifies a broadband electric signal with a high frequency amplifier, then distributes it with a distributor, converts each distributed electric signal into an optical signal with an optical transmitter, and outputs it to an optical fiber. In addition, an optical amplifier that optically amplifies an optical signal output from the optical transmitter is provided at a subsequent stage of the optical transmitter to compensate for a loss caused by distribution.

  On the other hand, a laser diode is used for the optical transmitter. In order to suppress the wavelength transition depending on the temperature of the laser diode, as described in the prior art of Patent Document 1 below, The temperature is detected by a thermistor, and the temperature of the laser diode is controlled to be constant so that the detected temperature does not fluctuate. However, due to the correlation error between the temperature error to be detected and the oscillation wavelength, even if the temperature is controlled, it is not always possible to stably control the desired wavelength. Therefore, in Patent Document 1, the temperature of the laser diode is controlled so that the wavelength becomes a predetermined value by directly measuring the wavelength of the laser oscillated by the laser diode.

  Further, as described in Patent Document 2 below, the temperature of the electroabsorption modulator is controlled by a temperature control circuit to an optimum temperature corresponding to the wavelength of the carrier light input to the electroabsorption optical modulator. Has been done.

JP-A-9-18413 JP-A-2005-45548

  However, when an electrical signal is converted into an optical signal by an optical transmitter after distributing a broadband electrical signal, it is necessary to provide an optical transmitter for each optical fiber system. In the optical transmitter, wavelength control is required. Therefore, there is a problem that the manufacturing cost increases.

  The present invention has been made to solve the above-described problems, and the object thereof is to enable branching of an optical signal into many optical fibers without increasing the number of optical transmitters having high manufacturing costs. A single optical transmission unit is configured.

In order to solve the above-mentioned problem, the invention according to claim 1 converts a wideband signal including a multi-channel high-frequency television signal into an optical signal, branches the optical signal into a plurality of optical signals, and then branches the optical signal. The optical transmission unit for transmitting each optical signal to each optical fiber has one first laser diode whose temperature is controlled so that the oscillation wavelength is constant at a predetermined value, and the light oscillated by the first laser diode is transmitted. One optical transmitter that modulates the intensity with an electrical signal, an optical splitter that splits the optical signal output from the optical transmitter, and a non-temperature-controlled second laser diode that oscillates pumping light for optical amplification An optical amplifier for optically amplifying the optical signal output from the optical branching device, a first temperature detecting device for detecting the temperature of the second laser diode, and an ambient temperature at which the optical amplifier dissipates heat, the ambient temperature being Accompanying change A second temperature detector for detecting ambient temperature to a heating device for heating an optical amplifier, when the detected temperature by the first temperature detector is higher than a predetermined temperature, by energizing the second laser diode, the first oscillating It is determined whether or not the ambient temperature detected by the control device and the second temperature detection device is lower than each different predetermined value set stepwise, and if it is lower than each predetermined value, it corresponds to each predetermined value And a second control device that feeds each of the electric power increasing step by step to the heating device .

  According to the present invention, the optical transmission unit is provided with one optical transmitter whose wavelength needs to be controlled with high accuracy, and after branching the optical signal output from the optical transmitter, the wavelength of the optical transmission unit is highly accurate. An optical amplifier using a laser diode is provided as a pumping light source that does not require controllability. Therefore, by using this optical transmission unit, it is possible to obtain an optical signal branched into a large number using a single optical transmitter.

  In addition, since a laser diode used as an excitation light source in an optical amplifier is not required to have high-precision temperature stability, simple temperature control may be realized to such an extent that the light emission state can be stabilized. Therefore, the manufacturing cost of the optical amplifier can be reduced, and the optical transmission unit can be provided at a low cost.

  The best mode for carrying out the present invention will be described.

  FIG. 1 is a block diagram showing a configuration of an optical transmission unit 7 according to a specific embodiment of the present invention. The optical transmission unit 7 is provided with an optical transmitter 3 for intensity-modulating light having a wavelength oscillated by a laser diode by a high-frequency broadband electric signal including a multi-channel TV signal. This laser diode is temperature-controlled so that the wavelength becomes a desired value accurately.

  The optical signal output from the optical transmitter 3 is input to the optical branching device 6 and a part of the optical signal is branched. The branched optical signal is optically amplified by the optical amplifier 5, is output to the optical fiber 40b, and is output from the optical transmission unit 7 via the optical output terminal 4b. On the other hand, the optical signal output from the optical branching unit 6 is output to the optical fiber 40a and output from the optical transmission unit 7 via the optical output terminal 4a.

  In this embodiment, the number of branches by the optical branching device 6 is 1. However, for example, many branches of 2 or more may be performed. In that case, an optical amplifier 5 is provided in each branch system.

  FIG. 2 is a block diagram showing a detailed configuration of the optical amplifier 5. A laser diode 8 serving as an excitation light source is disposed on the temperature control plate 12. The temperature control plate 12 is heated by energizing the heating element 11 (Peltier element) joined to the back surface of the temperature control plate 12. This Peltier element is provided in the housing of the optical transmission unit 7. By using the Peltier element, when energized, the thermal resistance increases, heat dissipation from the back surface side on the temperature control plate 12 side is suppressed, and the heating power of the optical amplifier can be suppressed. Further, when the Peltier element is not energized, the thermal resistance of this element is small, so the heat generated by the optical amplifier is dissipated from the back surface of the temperature control plate 12 to the casing of the optical transmission unit 7 via the Peltier element. The temperature increase of the optical amplifier can be prevented. In order to detect the ambient temperature of the optical amplifier 5, a temperature sensor 9 b is provided in contact with the housing of the optical transmission unit 7. The output of the temperature sensor 9b is input to the comparators 10b, 10c, and 10d, and the reference voltages are input to the comparators 10b, 10c, and 10d from the temperature setting reference input terminals 13b, 13c, and 13d, respectively. The outputs of the comparators 10b, 10c, and 10d are input to the heating element control circuit 14. The heating element control circuit 14 supplies the heating element 11 with power corresponding to the outputs of the comparators 10b, 10c, and 10d. As a result, the optical amplifier 5 is heated and its temperature rises.

  On the other hand, a temperature sensor 9 a is provided to detect the temperature of the laser diode 8. The temperature detected by the temperature sensor 9a is input to the comparator 10a, and a reference voltage is input to the comparator 10a from the temperature setting reference input terminal 13a. In response to the output of the comparator 10a, energization to the laser diode 8 is started.

  Reference voltages that increase in order are input to the reference input terminals of the comparators 10b, 10c, and 10d. In this state, when the ambient temperature detected by the temperature sensor 9b decreases, a voltage corresponding to the temperature is output from the temperature sensor 9b. For example, when the ambient temperature is 10 ° C. or higher, the voltage output from the temperature sensor 9b is higher than any of the reference voltages of the comparators 10b, 10c, and 10d, so that the outputs of all the comparators are at a low level. In this state, the heating element control circuit 14 does not supply power to the heating element 11. However, when the ambient temperature falls below 10 ° C., only the output of the comparator 10b becomes high level. The heating element control circuit 14 inputs this high level signal and supplies the first stage power to the heating element 11, and the heating element 11 heats the temperature control plate 12. As a result, the temperature of the optical amplifier 5 becomes thermal equilibrium and stable at 20 ° C., which is 10 ° C. higher than the ambient temperature.

  In this state, when the outside air temperature further decreases, the heat release to the surroundings becomes larger than the heat absorption by the heating element 11, and the temperature of the optical amplifier 5 decreases as the outside air temperature decreases. When the ambient temperature becomes lower than 5 ° C., the voltage output from the temperature sensor 9b decreases to be lower than the reference voltage of the comparator 10c, and the outputs of the comparators 10b and 10c become high level. When the heating element control circuit 14 inputs these two high level signals, the second stage power is supplied to the heating element 11 to increase the heating capacity. Thereby, the heat absorption of the optical amplifier 5 becomes higher than the heat dissipation, the temperature of the optical amplifier 5 rises, and a thermal equilibrium state is reached at 35 ° C.

  Next, when the outside air temperature further decreases, heat radiation from the optical amplifier 5 to the surroundings increases, and the temperature of the optical amplifier 5 decreases as the outside air temperature decreases. When the ambient temperature reaches −16 ° C., the voltage output from the temperature sensor 9b is lower than the reference voltage of the comparator 10d, and the output of the comparator 10d is inverted to a high level. When the heating element control circuit 14 inputs these three high level signals, the third stage power is supplied to the heating element 11 to increase the heating capacity. Thereby, the heat absorption of the optical amplifier 5 becomes higher than the heat dissipation, the temperature of the optical amplifier 5 rises, and a thermal equilibrium state is reached at 35 ° C.

  In this way, the temperature of the laser diode 8 of the optical amplifier 5 is controlled according to the ambient temperature as shown in FIG. That is, the temperature of the laser diode 8 can be maintained at 5 ° C. or higher even when the outside air temperature is lowered, and stable oscillation is realized. Thereby, optical amplification can be stably performed.

  On the other hand, when the temperature output from the temperature sensor 9a is lower than 5 ° C., the output of the comparator 10a is at a low level and the laser diode 8 is not energized. When heated or when the outside air temperature is high and the temperature output from the temperature sensor 9a is 5 ° C. or higher, the output of the comparator 10a becomes high level, energization of the laser diode 8 is started, and laser oscillation occurs. Light increase starts. As described above, energization is started only when the temperature of the laser diode 8 becomes equal to or higher than a temperature at which stable oscillation is possible.

In this embodiment, since the temperature of the optical amplifier 5 is controlled as described above, stable optical amplification can be realized with a simple configuration.
The optical transmitter uses a temperature-controlled laser diode, but it is possible to optically amplify an optical signal whose intensity is modulated by the laser diode even if the laser diode is not temperature-controlled. is there.

  The present invention is effective for use in an FTTH system for broadband transmission.

The block diagram of the optical transmission unit which concerns on one specific Example of this invention. The block diagram which showed the structure of the optical amplifier used for the optical transmission unit. The characteristic view which showed the relationship between the energization start timing to the laser diode for optical excitation of an optical amplifier, and ambient temperature. The characteristic view which showed the relationship between the ambient temperature of an optical amplifier, the electric power feeding timing to a heating element, and the temperature of the optical amplifier by heating.

DESCRIPTION OF SYMBOLS 3 ... Optical transmitter 4a, 4b ... Optical output terminal 5 ... Optical amplifier 6 ... Optical branching device 8 ... Laser diode 9a, 9b ... Temperature sensor 11 ... Heating element 12 ... Temperature control board 10a-10d ... Comparator 14 ... Heating element control circuit

Claims (1)

In an optical transmission unit that, after converting a broadband signal including a multi-channel high-frequency television signal into an optical signal, branching the optical signal into a plurality of optical signals, and then sending each branched optical signal to each optical fiber ,
One optical transmitter having one first laser diode whose temperature is controlled so that the oscillation wavelength is constant at a predetermined value, and intensity-modulating the light oscillated by the first laser diode with an electric signal;
An optical branching device for optically branching an optical signal output from the optical transmitter;
An optical amplifier having a non-temperature-controlled second laser diode that oscillates excitation light for optical amplification, and optically amplifies the optical signal output from the optical splitter;
A first temperature detecting device for detecting a temperature of the second laser diode;
A second temperature detection device for detecting an ambient temperature at which the optical amplifier dissipates heat, the ambient temperature changing with an outside air temperature ;
A heating device for heating the optical amplifier;
A first controller for energizing and oscillating the second laser diode when a temperature detected by the first temperature detector is equal to or higher than a predetermined temperature;
It is determined whether or not the ambient temperature detected by the second temperature detection device is lower than each predetermined value set in a stepwise manner, and if it is lower than each predetermined value, it corresponds to each predetermined value. A second control device for supplying power to the heating device in a stepwise manner.
An optical transmission unit comprising:

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