JPH0897800A - Optical transmission method - Google Patents

Abstract

PURPOSE: To set optionally an optical wavelength of each transmission station within each wavelength control range by allowing deteriorated quality of a signal due to beat to hardly take place, selecting a wavelength interval to be narrow and minimizing kinds of light sources used for an optical transmitter having lots of transmission stations. CONSTITUTION: A light source 3 of plural transmission stations 11 , 12 ,... has a means controlling its center wavelength and a control range of the center wavelength of two light sources 3 or over among plural light sources 3 is selected to be equal and the control range is made different from the control range of the center wavelength of the other light sources 3. The control range of the plural light sources 3 whose center wavelength control range is set identically is not overlapped with the control range of the center wavelength of other light sources. The center wavelength of the light source 3 is controlled by applying temperature control to a semiconductor laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission method using an optical CATV system, an optical ITV system or the like.

[0002]

2. Description of the Related Art There are various optical transmission methods using an optical CATV system, an optical ITV system, etc. As one of the optical transmission methods, conventionally, an optical transmission apparatus shown in FIG. 7A is used. there were. In the optical transmission device shown in FIG. 7A, a single receiving station 2 receives images from a plurality of (n locations) transmitting stations 1 ₁ , 1 _2, ... Arranged at a distance of several hundred meters to several km. This is an optical transmission system that enables collective monitoring. Figure 7 each transmission station ₁ 1 (a), 1 ₂ such as video imaging camera to ... of the signal source 11, the modulator 12, the light source 3, an optical multiplexer 14 is installed, the transmission stations ₁ 1, The optical signal from 1 ₂ ... Is sent to the receiving station 2 by the optical fiber trunk line 15,
Terminal device 1 such as light receiver 16, demodulator 17, monitor TV
8 is received by the installed receiving station 2.

[0003] The video signal of each transmission station 1 _1, 1 ₂ ... in Fig. 7 (a) entrained in a carrier wave of a specific frequency f ₁ ~f _n by the modulator 12, it is generated from the semiconductor laser by the signal The optical signal is modulated. The frequency band of the carrier wave varies depending on the optical transmission system, but is in the range of 0.4 to 2 GHz in the optical transmission device of FIG. Figure 7
The optical signals from the respective transmitting stations 1 ₁ , 1 _2, ... Of (a) are guided to the optical fiber trunk line 15 through the optical multiplexer 14, and are transmitted to the optical fiber trunk line 15.
As shown in (b), they are multiplexed and received by the light receiver 16 of the receiving station 2 at once. Then, the electric signal from the light receiver 16 is selected by the demodulator 17 according to the carrier frequency, and the monitor television 18 monitors the image for each transmitting station. In addition, the solid line arrow in FIG. 7A indicates the flow of an electric signal transmitted by a coaxial cable or the like, and the broken line arrow indicates the flow of an optical signal transmitted by an optical fiber.

[0004]

As shown in FIG. 7 (a), when a plurality of optical signals are multiplexed and multiplexed and detected by the photodetector 16, the wavelength difference of each optical signal is detected. A beat occurs at the frequency position. Moreover, if the frequency position where the beat is generated coincides with the frequency band of the carrier, the beat will impair the quality of the signal. Therefore, in this case, the light wavelength intervals of the respective light sources 3 must be set so that the quality of the signal can be ensured to a predetermined level or more.

The center frequency of the beat is 1.55 μ of the optical wavelength.
Since approximately 125GH _Z per optical wavelength difference 1nm in m band, for example, when there is a combination of a light source comprising a wavelength difference of 0.01nm beat occurs in the vicinity of 1.25GH _Z,
It matches the frequency band of the carrier. In addition, the wavelength difference is 0.1
In the case of nm, the center wavelength of the beat is 12.5GH
_Although it becomes _Z , which is separated from the frequency band of the carrier wave, the beat has a skirt over a relatively wide frequency range, and therefore it is necessary to design the wavelength array in consideration of this.

Since the conventional multiplex transmission number in the above optical transmission apparatus is several channels, the light source 3 has been used so far.
It was possible to prevent the wavelengths from approaching each other by the selection of 1. However, the method of selecting the light source 3 has a limit to the future demand for expanding the number of channels. Therefore, in order to solve the problem of beat, it is necessary to design the wavelength intervals of the combined laser lights to be sufficient so that no beat occurs in the frequency band of the carrier.

The beat noise can be solved by making the wavelength spacing sufficiently wide, but if the wavelength spacing is unnecessarily widened, on the other hand, some practical problems arise. For example, when the wavelength interval is set to 2 nm in an optical transmission device that combines optical signals of 50 waves, it becomes necessary to control the wavelength of the semiconductor laser within a width of 100 nm. However, in the manufacturing process of the semiconductor laser, the cost is extremely high for manufacturing such a semiconductor laser having a wide width and different wavelengths. Therefore, it is necessary to design the above-mentioned wavelength interval as narrow as possible so that the beat does not deteriorate the quality of the signal, rather than being unduly wide.

An object of the present invention is to minimize the wavelength interval within the range where signal quality deterioration due to beats does not occur, and to minimize the number of light sources used in transmitting stations even in an optical transmission apparatus with many transmitting stations. Can be suppressed, and also
An object of the present invention is to provide an optical transmission method in which the optical wavelength of each transmitting station can be arbitrarily set within its wavelength control range.

[0009]

The optical transmission method according to claim 1 of the present invention is, as shown in FIG. 1, a plurality of transmitting stations 1 ₁ , 1 _2.
.. each of the light sources 3 generates an optical signal modulated by the transmitted signal, and the plurality of optical signals are generated by the receiving station 2.
In the optical transmission method of simultaneously receiving and demodulating in a plurality of transmitting stations 1 ₁ , 1 _2, ...
Has a means for controlling the center wavelength thereof, and makes the control ranges of the center wavelengths of two or more light sources 3 of the plurality of light sources 3 equal, and this control range is different from the control ranges of the center wavelengths of the other light sources 3. This is the method.

In the optical transmission method according to claim 2 of the present invention, as shown in FIG. 1, the optical signal modulated by the transmitted signal is transmitted from each of the light sources 3 of the plurality of transmitting stations 1 ₁ , 1 _2, ... In the optical transmission method in which the plurality of optical signals generated and received at the receiving station 2 are simultaneously demodulated,
A plurality of transmitting stations 1 _1, 1 ₂ ... light source 3 has a means for controlling the center wavelength, two or more central control range of the wavelength of the light source 3 among the plurality of light sources 3 is equal, the The control range does not overlap with the control ranges of the central wavelengths of the other light sources 3.

In the optical transmission method according to claim 3 of the present invention, a semiconductor laser is used as the light source 3 in the optical transmission method according to claim 1 or 2, and the central wavelength of the semiconductor laser is controlled by controlling the temperature of the semiconductor laser. The control is performed.

In the optical transmission method according to claim 4 of the present invention, one light source 3 in the optical transmission method according to claim 1 or 2 is formed by arranging a plurality of semiconductor lasers having different wavelengths. Light source 3 by switching the semiconductor laser
The central wavelength of is controlled.

In the optical transmission method according to claim 5 of the present invention, a semiconductor laser is used as the light source 3 in the optical transmission method according to claim 2, and the central wavelengths of two or more semiconductor lasers having the same central wavelength control range are used. Control range does not overlap with the control range of the center wavelength of other semiconductor lasers, and the upper limit of the control range of the former center wavelength and the lower limit of the control range of the latter center wavelength, or the lower limit of the control range of the former center wavelength. And the wavelength difference between the latter and the upper limit of the control range of the center wavelength is 0.1 nm or more.

[0014]

The optical transmission method according to claim 1 of the present invention, comprises means for a plurality of transmitting stations 1 _1, 1 ₂ ... light source 3 to control the center wavelength, two or more of these light sources 3 Light source 3
Since the control ranges of the central wavelengths of are equal and the control ranges of the central wavelengths of the other light sources 3 are different,
The central wavelengths of the semiconductor lasers having the same central wavelength control range are changed by means such as temperature control, and the optical wavelengths of the plurality of transmitting stations 1 ₁ , 1 ₂ ... (For example, about 0.3 nm), and good transmission quality can be obtained without being affected by beat noise. Moreover, since the same light source 3 can be used by a plurality of transmitting stations 1 ₁ , 1 _2, ..., It is possible to minimize the type of the light source 3 used by the transmitting station 1.

In the optical transmission method according to claim 2 of the present invention,
And means in which a plurality of transmitting stations 1 _1, 1 ₂ ... light source 3 to control the center wavelength, and two or more centers control range of the wavelength of the light source 3 of the light sources 3 equivalent, this control range Since it does not overlap with the control range of the central wavelength of the other light source 3, beat noise is less likely to occur and good transmission quality can be obtained.

According to the optical transmission method of claim 3 of the present invention,
Since the semiconductor laser is used as the light source 3 in the transmitting station 1 and the central wavelength of the semiconductor laser is controlled by the temperature control of the semiconductor laser, the central wavelength can be easily controlled.

In the optical transmission method according to claim 4 of the present invention,
One light source 3 in the transmitting station 1 is formed by arranging a plurality of semiconductor lasers having different wavelengths, and the central wavelength of the light source 3 is controlled by switching the plurality of semiconductor lasers. The center wavelength can be controlled easily with.

In the optical transmission method according to claim 5 of the present invention,
A semiconductor laser is used as the light source 3 in the transmitting station 1, the control ranges of the center wavelengths of two or more semiconductor lasers having the same control range of the center wavelength do not overlap with the control ranges of the center wavelengths of other semiconductor lasers, and the former The upper limit of the control range of the center wavelength and the lower limit of the control range of the latter center wavelength, or the wavelength difference between the lower limit of the control range of the former center wavelength and the upper limit of the control range of the latter center wavelength is 0.1 nm or more. Therefore, beat noise is less likely to occur and good transmission quality can be obtained.

[0019]

Embodiment 1 FIG. 1 shows an example of an optical transmission apparatus used in the optical transmission method of the present invention, and the present invention will be described in detail based on this. The optical transmission device shown in FIG. 1 has a plurality of (n locations) transmitting stations 1 ₁ , 1 ₂ , which are arranged at a distance of several hundred meters to several km.
..Signal source 11 such as video camera, modulator 12,
The light source 3 and the optical multiplexer 14 are installed, and each transmitting station 1 ₁ , 1 ₂
The optical signals from ... are simultaneously sent to the receiving station 2 by the optical fiber trunk line 15, and are simultaneously received by one receiving station 2 in which the light receiver 16, the demodulator 17, and the terminal device 18 such as a monitor TV are installed. Is done.

In FIG. 1, there are 16 transmitting stations 1 ₁ , 1 _2, ... And the light source 3 has a different control range of the center wavelength.
Semiconductor lasers LD _{1 to} LD ₄ of various types are used. Among them, 6 stations of transmitting stations 1 ₁ to ₁₆ are semiconductor lasers LD ₁ , 5 stations of transmitting stations 1 ₇ to ₁₁ are semiconductor lasers LD ₂ and transmitting stations are 1 station. The semiconductor laser LD ₃ is installed at four stations 1 ₁₂ to 1 ₁₅ , and the semiconductor laser LD ₄ is installed at the transmitting station 1 ₁₆ .

The wavelength control of each semiconductor laser of FIG. 1 can be performed by various methods. One method is to control the temperature of the semiconductor laser. In the case of temperature control, the temperature control range of the semiconductor laser is set to 25 ± 10 ° C., which is within the range where the life of the semiconductor laser is not impaired, as shown in FIG. The wavelength band is 1.
In the case of a 55 μm band semiconductor laser (for example, DFB laser), the relationship between wavelength and temperature is as shown in FIG.
Since the wavelength changes at about 0.09 nm / ° C. with respect to temperature change, in this case, a wavelength control range of about ± 0.9 nm can be obtained. Therefore, within this wavelength control range, six transmission stations 1 ₁ using LD ₁ with the same center wavelength control range are used.
Light wavelengths of up to ₁₆ can be arranged at intervals of 0.3 nm or more, and good transmission quality can be obtained without being affected by beat noise.

In the case of FIG. 1, for example, the upper limit value of the wavelength of LD _{1 and} the lower limit value of the wavelength of LD ₂ are almost the same, but rather the former tends to exceed the latter, and the control ranges overlap. When the wavelength is not used, there is no possibility that the wavelengths will approach each other in this vicinity, and there is no problem.

[0023]

Second Embodiment In a system in which the life of the semiconductor laser may be sacrificed to some extent, the temperature control range is about 25.
By setting the temperature to ± 20 ° C, the wavelength control range is approximately ± 2 nm.
It is possible to extend the wavelength range to a higher level, which allows a larger wavelength interval to be set. When the wavelength spacing is 0.3 nm, which is the same as in the first embodiment, the same semiconductor laser can be used for more transmitting stations.

[0024]

Third Embodiment The light output of the semiconductor laser fluctuates as shown in FIG. 5 due to temperature control. The fluctuation of the optical output can be corrected by adjusting the current supplied to the semiconductor laser. However, when the fluctuation of the optical output affects the transmission quality, the temperature control range can be adjusted as shown in FIG. By setting the temperature to 5 ° C., the output fluctuation can be suppressed to the minimum. Also in this case, it is possible to set the transmitting stations ₁₁ to ₁₆ at six locations by using one kind of semiconductor laser with a wavelength interval of about 0.2 nm. Good transmission quality is maintained even if the wavelength interval is 0.2 nm.

When the wavelength control range is narrow, the control range is used to the maximum extent so that wavelengths do not approach each other among a plurality of transmitter stations 1 ₁ , 1 _2, ... Using the same laser as much as possible. There is a need to. For this purpose, it becomes necessary to use the upper limit side and the lower limit side of the control range, but in this case it is necessary to set the wavelength control range so that wavelengths do not approach between transmitting stations with different wavelength control ranges. There is.

As a result of a detailed examination on the transmission quality, it is confirmed that the influence of the beat noise is sharply increased when the wavelength interval becomes 0.1 nm or less. There is no problem because the wavelength difference of is set to be larger than this.

[0027]

[Embodiment 4] FIG. 6 shows another example of an optical transmission apparatus used in the optical transmission method of the present invention. In this optical transmission apparatus, 16 transmission stations 1 ₁ , 1 _2, ... Are divided into two blocks, and each block is separately connected to two optical fiber trunk lines 15. Are arranged in front of the receiving station 2 and a wavelength tunable filter 19 is arranged in front of the receiving station 2 so that adjacent wavelengths can be removed and the influence of beat noise can be avoided. . In this case, even if there is the wavelength tunable filter 19,
There is a limit value for the wavelength spacing approach depending on the resolution,
Finally, it becomes necessary to control the light wavelength of the light source 3 of the transmitting station 1. The control of the light wavelength of the light source 3 in this case is also performed in the same manner as in the above-described first to third embodiments.

[0028]

[Embodiment 5] Although the wavelength control is performed by temperature in each of the above embodiments, the wavelength control in the present invention is not limited to this, and a plurality of semiconductors having different wavelengths are used as one light source 3. It is also possible to use an array of lasers and control the wavelength of the light source 3 by switching among these semiconductor lasers. This method can be easily implemented by using a semiconductor laser array.

[0029]

Other Embodiments The wavelength control in the present invention can also be performed by using a wavelength tunable laser with current control or a wavelength tunable laser with an external diffraction grating.

In the embodiment shown in FIG. 1, four types of lasers L _{1 to} L _{4 are} arranged in order from the receiving station 2 to the transmitting station 1 ₁ closer to the laser.
However, there is no particular need for this, and several kinds of lasers may be randomly assigned.

Although the modulation method of the above-mentioned embodiment is FM, AM may be used or digital modulation method may be used.

The transmitted signal in FIGS. 1 and 2 is a video signal from the camera 11 for capturing a video, which can be monitored by the monitor television 18 of the receiving station 2, but the transmitted signal is not limited to this. Instead, it may be a voice signal or a data signal. In these cases, the monitor TV 18 of the receiving station 2 in FIG. 1 is replaced with a speaker or a computer.

Although the temperature control range of the semiconductor laser of the present invention is set to ± 5 ° C., ± 10 ° C., and ± 20 ° C. in Examples 1 to 3, the temperature control range of the present invention may be other than these. Further, although the wavelength control range is ± 0.9 nm, ± 2 nm, and ± 0.5 nm in Examples 1 to 3, the wavelength control range in the present invention may be other than these.

[0034]

In the optical transmission method according to claim 1 of the present invention, since the light sources 3 of the plurality of transmitting stations 1 ₁ , 1 _2, ... Have means for controlling the central wavelength, the plurality of transmitting stations 1 ₁ 1 ₂
The same light source 3 can be used for ...
Even with a large number of optical transmission devices, it is possible to minimize the types of light sources 3 used in the transmission station 1, which is economical. Further, since the influence of the beat can be avoided by controlling the wavelength, good transmission quality can be obtained.

In the optical transmission method according to claim 2 of the present invention,
Since the control ranges of two or more light sources 3 having the same control range of the center wavelength do not overlap with the control ranges of the center wavelengths of the other light sources 3, beat noise is less likely to occur,
Good transmission quality is obtained.

In the optical transmission method according to claim 3 of the present invention,
Since the central wavelength of the semiconductor laser used as the light source 3 of the transmitting station 1 is controlled by the temperature control of the semiconductor laser, the central wavelength can be easily controlled.

In the optical transmission method according to claim 4 of the present invention,
Since a plurality of semiconductor lasers having different wavelengths arranged is used as one light source 3 in the transmitting station 1, the central wavelength of the light source 3 can be easily controlled only by switching the plurality of semiconductor lasers.

In the optical transmission method according to claim 5 of the present invention,
The control ranges of the center wavelengths of two or more semiconductor lasers having the same control range of the center wavelength used as the light source 3 of the transmitting station 1 do not overlap with the control ranges of the center wavelengths of other semiconductor lasers, and When the upper limit of the control range of the center wavelength and the lower limit of the control range of the latter center wavelength, or the wavelength difference between the lower limit of the control range of the former center wavelength and the upper limit of the control range of the latter center wavelength is 0.1 nm or more. Therefore, beat noise is less likely to occur, and good transmission quality can be obtained.

In any of the first to fifth aspects, the optical wavelength of each transmitting station 1 can be arbitrarily set within the respective wavelength control range, so that the design and operation of the optical transmission device to which the present invention is applied are designed and operated. The degree of freedom of is improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of an optical transmission method of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a temperature control range and a wavelength control range in the optical transmission method of the present invention, where the temperature range is 2
Explanatory drawing when it is 5 ± 10 ° C.

FIG. 3 is an explanatory diagram showing a relationship between a temperature control range and a wavelength control range in the optical transmission method of the present invention, where the temperature range is 2
Explanatory drawing when it is 5 ± 5 ° C.

FIG. 4 is an explanatory diagram showing an example of the relationship between the temperature of a semiconductor laser and the output light wavelength.

FIG. 5 is an explanatory diagram showing an example of the relationship between the temperature and output of a semiconductor laser.

FIG. 6 is an explanatory diagram showing a second embodiment of the optical transmission method of the present invention.

7A is an explanatory diagram showing an embodiment of a conventional optical transmission method, and FIG. 7B is an explanatory diagram of an optical signal at point F in FIG. 7A.

[Explanation of symbols]

1 ₁ 1 ₂ ... is a transmitting station 2 is a receiving station 3 is a light source such as a semiconductor laser

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04B 10/02 10/18 H04B 9/00 M

Claims (5)

[Claims] 1. An optical signal modulated by a transmitted signal is generated from each of the light sources (3) of a plurality of transmitting stations (1 ₁ , 1 ₂ ...), and the plurality of optical signals are received by the receiving station (2 ), The light sources (3) of a plurality of transmitting stations (1 ₁ , 1 ₂ ...) Have means for controlling the center wavelength of the plurality of transmitting stations (1 ₁ , 1 ₂ ...). Of the light sources (3), the control ranges of the central wavelengths of two or more light sources (3) are made equal, and the control ranges of the other light sources (3) are different from the control ranges of the central wavelengths. Optical transmission method. 2. An optical signal modulated by a transmitted signal is generated from each of the light sources (3) of a plurality of transmitting stations (1 ₁ , 1 ₂ ...), and these plurality of optical signals are received by the receiving station (3). In the optical transmission method of simultaneously receiving and demodulating in ₂ ), the light sources (3) of the plurality of transmitting stations (1 ₁ , 1 _2, ...) Have means for controlling the central wavelength, The control ranges of the central wavelengths of two or more light sources (3) among the light sources (3) are made equal, and the control ranges are not overlapped with the control ranges of the central wavelengths of the other light sources (3). Optical transmission method. 3. The optical transmission method according to claim 1 or 2, wherein a semiconductor laser is used as the light source (3), and the central wavelength of the semiconductor laser is controlled by controlling the temperature of the semiconductor laser. 4. A single light source (3) is formed by arranging a plurality of semiconductor lasers having different wavelengths, and the central wavelength of the light source (3) is controlled by switching the plurality of semiconductor lasers. The optical transmission method according to claim 1 or 2. 5. A semiconductor laser is used as a light source (3), and the control ranges of the center wavelengths of two or more semiconductor lasers having the same control range of the center wavelength do not overlap with the control ranges of the center wavelengths of other semiconductor lasers. And the wavelength difference between the upper limit of the control range of the center wavelength of the former and the lower limit of the control range of the center wavelength of the latter, or the wavelength difference between the lower limit of the control range of the center wavelength of the former and the upper limit of the control range of the latter center wavelength. 3. The optical transmission method according to claim 2, wherein the optical transmission length is 1 nm or more.