JP2004111526A - Optical communication module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication module in which high output signal light can be sent from a fiber exit even when an operating temperature of a semiconductor laser which is a signal light source changes. <P>SOLUTION: Laser beams 13 and 14 of signal light emitted from a plurality of semiconductor lasers 11 and 12 on which emitted light wavelengths in a common temperature are mutually different are made incident to one multi-mode optical fiber 18 of which the propagation loss changes in accordance with the wavelength of propagating light, and the laser beams 13 and 14 are commonly modulated by a modulation means 20. Temperatures of the semiconductor lasers 11 and 12 are then detected by a temperature detecting means 22, and a semiconductor laser of which the emitted light wavelength in the detected temperature becomes a wavelength minimizing the propagation loss is selected and driven in the plurality of semiconductor lasers 11 and 12 by a drive switching means 21 which receives a signal S2 indicating the detected temperature from the temperature detecting means 22. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical communication module that modulates a laser beam emitted from a semiconductor laser and transmits the modulated laser beam via a multimode optical fiber.
[0002]
[Prior art]
Conventionally, a single-mode optical fiber or a multi-mode optical fiber mainly made of quartz glass has been used as a light propagation path in optical communication. The diameter of this type of optical fiber is 200 μm or less, and high-precision alignment in the order of microns is required for alignment. For this reason, fiber laying work in a general environment such as a construction site is not easy, and this greatly hinders further spread. Recently, various plastic fibers with large diameters have been developed. Non-Patent Document 1 discloses one such plastic fiber.
[0003]
On the other hand, as a light source for generating light propagating through an optical fiber, many semiconductor lasers that are small and light and can be directly modulated are applied.
[0004]
[Non-Patent Document 1]
Supervised by Yasuhiro Koike and Kiyozo Miyata, “Basics and Practice of Plastic Optical Fiber”, NTS Corporation, 2000, p. 84-87
[0005]
[Problems to be solved by the invention]
However, in the case of a plastic fiber using PMMA (polymethylmethacrylate) as a basic material, the wavelength suitable for transmission is limited to around 650 nm, and the following problems are recognized when a semiconductor laser is used as a light source.
[0006]
As a basic property of a semiconductor laser, it is well known that the emission wavelength changes as the operating temperature changes. Specifically, in a GaAs semiconductor laser, the emission wavelength increases at a rate of about 0.2 nm / ° C. as the operating temperature increases. This change in emission wavelength causes the following problems.
[0007]
FIGS. 8A and 8B show the optical output at the optical fiber entrance and exit, respectively, but use a semiconductor laser that emits light at a wavelength at which the propagation loss of the optical fiber is low (that is, the propagation efficiency is high) at room temperature. In such a case, as indicated by a solid line in the drawings, the light output at the fiber exit is large at room temperature, and good communication is possible. However, the operating temperature of the semiconductor laser is not constant because the environmental temperature naturally changes according to the season and the like, and the temperature rises due to the heat generated by the device itself where the semiconductor laser is installed. For example, when the environmental operating temperature of the semiconductor laser rises, the emission wavelength changes to the longer wavelength side as shown by the broken line in the figure. As a result, the optical wavelength deviates from the optimum wavelength that can be propagated with low loss, and the optical output is greatly reduced at the fiber exit, making communication difficult.
[0008]
There is also a method to compensate for the decrease in light output due to the above-mentioned reasons by increasing the drive current of the semiconductor laser and increasing the light output, but in that case, the life of the semiconductor laser is shortened. Cause problems.
[0009]
In addition, by controlling the operating temperature of the semiconductor laser using a Peltier element or the like, it is conceivable to maintain the emission wavelength at the optimum wavelength, but in that case, a large cost is required for temperature control, This becomes a factor that increases the communication cost.
[0010]
SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an optical communication module capable of transmitting high-power signal light from a fiber outlet even when the operating temperature of a semiconductor laser as a signal light source changes. .
[0011]
[Means for Solving the Problems]
A first optical communication module according to the present invention comprises:
One multimode optical fiber whose propagation loss varies with the wavelength of the propagating light;
A plurality of semiconductor lasers having different emission wavelengths under a common temperature, in which a laser beam as signal light is incident on the multimode optical fiber,
Modulating means for commonly modulating the laser beams respectively emitted from the plurality of semiconductor lasers based on predetermined information;
Temperature detecting means for detecting the temperature of the semiconductor laser;
Drive that receives a signal indicating a detection temperature from the temperature detection means and selects and drives a semiconductor laser whose emission wavelength under the detection temperature is a wavelength that minimizes the propagation loss from among the plurality of semiconductor lasers And a switching means.
[0012]
The second optical communication module according to the present invention includes:
One multimode optical fiber whose propagation loss varies with the wavelength of the propagating light;
A plurality of semiconductor lasers having different emission wavelengths under a common temperature, in which a laser beam as signal light is incident on the multimode optical fiber,
The laser beam emitted from each of the plurality of semiconductor lasers comprises modulation means for commonly modulating each of the laser beams based on predetermined information.
[0013]
【The invention's effect】
The first optical communication module according to the present invention uses a plurality of semiconductor lasers having different emission wavelengths under a common temperature as a light source, and the emission wavelength under a detection temperature is a multimode among these semiconductor lasers. Since it is configured to select and drive the semiconductor laser with the wavelength that minimizes the propagation loss of the optical fiber, it always sends out high-power signal light from the fiber outlet even if the operating temperature of the semiconductor laser changes. Is possible.
[0014]
Hereinafter, the above points will be described in more detail with reference to the drawings. Two semiconductor lasers are used as an example, and one semiconductor laser A emits light at a wavelength that minimizes the propagation loss of the multimode optical fiber at the first temperature (hereinafter referred to as “optimum wavelength”), and another semiconductor laser. B emits light at the optimum wavelength at a second temperature higher than the first temperature. Incidentally, since the emission wavelength of a semiconductor semiconductor laser generally becomes longer as the temperature rises, when the semiconductor lasers A and B are driven at the same temperature, the former emits light on the longer wavelength side and the latter emits light on the shorter wavelength side. Become.
[0015]
The drive switching means switches the semiconductor laser to be driven at a predetermined temperature set between the first temperature and the second temperature (of course, the semiconductor is near the first temperature. The laser A is driven near the second temperature to drive the semiconductor laser B). More specifically, desirably, when the semiconductor lasers A and B are both driven, as shown in FIG. 2 showing the optical output at the optical fiber inlet and outlet, respectively, in (a) and (b), the laser beams from them are The vicinity of the temperature at which propagation occurs with the same degree of loss is selected as the switching temperature. In FIG. 2 and FIGS. 3 to 5 described later, the optical outputs of the semiconductor lasers A and B are indicated as A and B, respectively. 3 to 5 also show the optical output at the optical fiber entrance and exit, respectively, as in FIG.
[0016]
Next, the operation in the above configuration will be described. Here, a case where the operating environment temperature changes from a low temperature to a high temperature will be described. First, in the low temperature region, the semiconductor laser A is driven (solid line in FIG. 3). At this time, since the emission wavelength is in the low loss region of the fiber, good communication is performed. If the semiconductor laser B emits light, the emission wavelength indicated by the broken line in FIG.
[0017]
When the operating environment temperature rises from there, the emission wavelength of the semiconductor laser A changes to the longer wavelength side accordingly. When the temperature reaches the switching temperature in this way, the semiconductor laser B is driven as shown in FIG. As described above, the semiconductor laser B originally emits light at an optimum wavelength when the temperature is higher than the switching temperature. Therefore, even if the temperature further rises, as is apparent from FIG. 5, a stronger signal light is emitted from the fiber outlet than when the semiconductor laser A is driven, and a good communication state is maintained.
[0018]
Even if the semiconductor lasers to be driven are switched as described above, the semiconductor lasers are commonly modulated with each other based on predetermined information. Therefore, even if this switching is performed, the communication itself is not performed. It can be done normally without incurring errors or interruptions.
[0019]
The second optical communication module according to the present invention has a configuration in which the temperature detecting means and the drive switching means are omitted from the first optical communication module. In other words, in the second optical communication module, in addition to the signal light having the optimum wavelength or a wavelength close to it propagating through the multimode optical fiber, the signal light having a wavelength other than that is also transmitted in the multimode with a relatively large loss. In this case, the above-described effect that high-intensity signal light can be transmitted from the multimode optical fiber in the range from low temperature to high temperature can be obtained as it is.
[0020]
As described above, according to the present invention, it is possible to supply signal light having a wavelength that can reduce the loss of the optical fiber from a low temperature to a high temperature without using an expensive part such as a Peltier element, and good communication can be performed. Can be maintained. By using such an optical communication module of the present invention, large-capacity optical communication using a large-diameter optical fiber is also possible.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0022]
FIG. 1 shows a schematic configuration of an optical communication module according to a first embodiment of the present invention. This module for optical communication uses a first semiconductor laser 11 and a second semiconductor laser 12 as well as laser beams 13 and 14 as signal lights emitted from these semiconductor lasers 11 and 12 as divergent lights, respectively. The collimator lenses 15 and 16 to be converted, the condensing lens 17 for converging the parallel laser beams 13 and 14 to one point, and the incident end 18a located at the convergence position of the laser beams 13 and 14. And a multi-mode optical fiber 18 disposed in the middle.
[0023]
A modulation drive signal S1 output from one modulation drive circuit 20 is alternatively input to one of the semiconductor lasers 11 and 12 via the drive switching circuit 21. The drive switching circuit 21 is connected to a temperature detecting means 22 comprising, for example, a thermistor for detecting the temperature of the semiconductor lasers 11 and 12. The drive switching circuit 21 is configured to switch the semiconductor lasers 11 and 12 to which the modulation drive signal S1 is input based on the temperature detection signal S2 output from the temperature detection means 22.
[0024]
Therefore, when the modulation drive signal S1 is input to the semiconductor laser 11, the laser beam 13 as signal light modulated based on the modulation drive signal S1 enters the core 18b of the multimode optical fiber 18 and propagates there. When the modulation drive signal S1 is input to the semiconductor laser 12, the laser beam 14 as signal light modulated based on the modulation drive signal S1 enters the core 18b of the multimode optical fiber 18 and propagates there. To do.
[0025]
Here, the multimode optical fiber 18 is, for example, a plastic fiber having PMMA as a basic material, and has a diameter of 1 mm, a core diameter of about 200 to 500 μm, and a length of 100 m. The propagation loss of the multimode optical fiber 18 changes according to the wavelength of the propagation light, and the optimum wavelength at which the propagation loss is minimum is 650 nm. When the propagation light wavelength is shifted by 5 nm from this optimum wavelength, the propagation efficiency is the same as that at the optimum wavelength. If it is shifted by 10 nm to about 40%, the propagation efficiency is reduced to about 15% at the optimum wavelength. In addition, it is desirable to use a graded index type as the plastic fiber, and the diameter is preferably about 800 μm or more in general.
[0026]
In this embodiment, the operating environment temperature is set in the range of -20 to 80 ° C, the semiconductor laser 11 is operated in the range of -20 ° C or higher and lower than 30 ° C, and the semiconductor laser 12 is operated in the range of 30 to 80 ° C. That is, the drive switching circuit 21 drives the semiconductor laser 11 when the temperature indicated by the temperature detection signal S2 is less than 30 ° C., and drives another semiconductor laser 12 when the temperature is 30 ° C. or higher.
[0027]
These semiconductor lasers 11 and 12 have different emission wavelengths at a common temperature. Specifically, the emission wavelengths of the semiconductor laser 11 are 645 nm, 650 nm, and 655 nm at −20 ° C., 5 ° C., and 30 ° C., respectively. In contrast, the emission wavelengths of the semiconductor laser 12 are 645 nm, 650 nm, and 655 nm at 30 ° C., 55 ° C., and 80 ° C., respectively. As apparent from the above, the temperature characteristics of the emission wavelengths of the semiconductor lasers 11 and 12 are both 0.2 nm / ° C.
[0028]
The operation of this optical communication module will be described below. First, when the semiconductor laser 11 is driven on the low temperature side, the emission wavelength is 645 nm when the operating environment temperature is −20 ° C., and the propagation efficiency of the multimode optical fiber 18 is about 40% of the optimum wavelength. As the temperature rises, the emission wavelength of the semiconductor laser 11 shifts to the longer wavelength side, the loss of the multimode optical fiber 18 gradually decreases (the propagation efficiency increases), the operating environment temperature is 5 ° C., and the emission wavelength is 650 nm. Then, the loss becomes the lowest. When the emission wavelength is almost 655 nm at 30 ° C., the propagation efficiency is about 40% of the optimum wavelength. In this way, the propagation efficiency of the multimode optical fiber 18 is kept at about 40% or more of the optimum wavelength at the lowest in the range where the operating environment temperature is −20 ° C. or higher and lower than 30 ° C.
[0029]
On the other hand, when the operating environment temperature is 30 ° C. or higher, the semiconductor laser 12 is driven, the emission wavelength is 645 nm at 30 ° C., and the propagation efficiency of the multimode optical fiber 18 is about 40% at the optimum wavelength. When the temperature rises from there, the emission wavelength of the semiconductor laser 12 shifts to the longer wavelength side, the loss of the multimode optical fiber 18 gradually decreases, and when the operating environment temperature is 55 ° C. and the emission wavelength becomes 650 nm, the loss becomes the lowest, When the emission wavelength is 655 nm at 80 ° C., the propagation efficiency is about 40% of the optimum wavelength. In this way, even when the operating environment temperature is in the range of 30 to 80 ° C., the propagation efficiency of the multimode optical fiber 18 is kept at about 40% or more of the optimum wavelength at the minimum.
[0030]
As described above, in the present embodiment, the propagation efficiency of the multimode optical fiber 18 is kept at about 40% or more at the optimum wavelength at the minimum in the operating temperature range of −20 to 80 ° C. On the other hand, when operating with a single semiconductor laser in the range of −20 to 80 ° C., a wavelength change of +/− 10 nm occurs, so that the optical output from the multimode optical fiber 18 is the worst. In this case, it is reduced to 15% at the optimum wavelength. Under such conditions, it is difficult to perform good communication.
[0031]
Note that if the driving of the semiconductor lasers 11 and 12 is switched at a certain predetermined temperature, if the operation happens to occur near the temperature, the switching frequently occurs, which may hinder communication. Therefore, although this is a commonly used technique, this frequent switching can be avoided by providing hysteresis.
[0032]
That is, a first temperature and a second temperature slightly higher than the first temperature are set, and the low temperature semiconductor laser 11 is switched to the high temperature semiconductor laser 12 at the second temperature, and the high temperature semiconductor laser 12 is switched to the low temperature semiconductor laser 11. Is switched at the first temperature. In such a configuration, once the low temperature semiconductor laser 11 is operated, the low temperature semiconductor laser 11 is operated as it is even if the temperature fluctuates in the vicinity of the first temperature. Then, when the temperature rises to the second temperature, it switches to the high-temperature semiconductor laser 12 for the first time. Thus, once the high temperature semiconductor laser 12 operates, the low temperature semiconductor laser 12 operates as it is even if the temperature fluctuates in the vicinity of the second temperature.
[0033]
In addition, when two semiconductor lasers 11 and 12 are used as described above, there is a concern that the laser beams 13 and 14 can be sufficiently input to the multimode optical fiber 18, but light is coupled to an optical fiber having a small core diameter. Unlike the case, it is not a big problem for plastic fibers with a large core diameter.
[0034]
Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 6, the same elements as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted unless necessary (the same applies hereinafter).
[0035]
The optical communication module of the second embodiment is different from that of FIG. 1 in that the drive switching circuit 21 and the temperature detection means 22 are omitted. That is, in this embodiment, the two semiconductor lasers 11 and 12 are driven simultaneously. In the apparatus of FIG. 1, the laser beam 13 or 14 having a wavelength in the range of 645 to 655 nm propagates through the multimode optical fiber 18, whereas in this embodiment, the wavelength is 645 nm or less in addition to such a laser beam. The laser beam 14 or the laser beam 13 having a wavelength of 655 nm or more also only propagates through the multimode optical fiber 18. In this case as well, high intensity signal light is transmitted from the multimode optical fiber 18 in the range from low temperature to high temperature. The effect of the present invention that it can be sent out can be obtained as it is.
[0036]
Next, a third embodiment of the present invention will be described with reference to FIG. In the optical communication module according to the third embodiment, one condensing lens 30 is used as an alternative to the two collimator lenses 15 and 16 and the condensing lens 17 as compared with the one shown in FIG. Is different. By using such a condenser lens 30, the configuration of the optical system can be simplified.
[0037]
Although the embodiment using two semiconductor lasers has been described above, the number of semiconductor lasers used in the present invention is not limited to these two, and how many semiconductor lasers are used by two or more. Also good.
[0038]
In the above embodiment, a plurality of individually formed semiconductor lasers are used. However, a plurality of semiconductor lasers manufactured on the same substrate can also be used.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an optical communication module according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining the operation of the optical communication module of the present invention. FIG. 4 is an explanatory diagram illustrating the operation of the optical communication module of the present invention. FIG. 5 is an explanatory diagram illustrating the operation of the optical communication module of the present invention. FIG. 7 is a schematic configuration diagram showing an optical communication module according to a second embodiment of the present invention. FIG. 7 is a schematic configuration diagram showing an optical communication module according to a third embodiment of the present invention. Explanatory drawing explaining problems in modules [description of symbols]
11 and 12 Semiconductor lasers 13 and 14 Laser beams 15 and 16 Collimator lens 17 Condensing lens 18 Multimode optical fiber 20 Modulation drive circuit 21 Drive switching circuit 22 Temperature detection means 30 Condensing lens

Claims (2)

One multimode optical fiber whose propagation loss varies with the wavelength of the propagating light;
A plurality of semiconductor lasers having different emission wavelengths under a common temperature, in which a laser beam as signal light is incident on the multimode optical fiber,
Modulating means for commonly modulating the laser beams respectively emitted from the plurality of semiconductor lasers based on predetermined information;
Temperature detecting means for detecting the temperature of the semiconductor laser;
Drive that receives a signal indicating a detection temperature from the temperature detection means and selects and drives a semiconductor laser whose emission wavelength under the detection temperature is a wavelength that minimizes the propagation loss from among the plurality of semiconductor lasers An optical communication module comprising switching means. One multimode optical fiber whose propagation loss varies with the wavelength of the propagating light;
A plurality of semiconductor lasers having different emission wavelengths under a common temperature, in which a laser beam as signal light is incident on the multimode optical fiber,
An optical communication module comprising modulation means for commonly modulating laser beams respectively emitted from the plurality of semiconductor lasers based on predetermined information.

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