JPH09211508A - Incoherent light source and light transmitter formed by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain incoherent light of desired spectra with the high-output powder of the output light efficiently converted from power of exciting light. SOLUTION: An optical multiplexer/demultiplexer 102 with which light output Pa from one surface is connected to a rare earth added optical fiber 103 mixed with rare earths and an exciting light source 101 is connected to the other surface of this optical multiplexer/demultiplexer 102. An optical band-pass filter 105 is connected to the rare earth added optical fiber 103. A light reflector 106 is connected to this optical band-pass filter 105. Optical amplification is executed by the rare earth added optical fiber 103 and the incoherent light having the desired wavelength and spectral width is efficiently obtd. by this constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an incoherent light source used for optical fiber communication and an optical transmitter using the same.

[0002]

2. Description of the Related Art In optical fiber communication, a semiconductor laser or the like is used as its light source. These light sources generally have a narrow emission spectrum width and high coherency. However, in some cases, high coherency can be an obstacle to transmission.

For example, the higher the coherency of a light source, the more the reflected waves at a plurality of connecting portions such as an optical connector interfere with each other to generate noise. Alternatively, it becomes more susceptible to nonlinear effects of the optical fiber such as stimulated Brillouin scattering. Furthermore, when optical signals of the same wavelength are multiplexed (in each optical signal, for example, electrical signals are superimposed using different subcarrier frequencies), beat noise is generated due to interference between signal lights. There is a problem such as.

In order to avoid this problem, an incoherent light source with a certain broad spectrum width is required,
Furthermore, when wavelength multiplexing is performed, a light source capable of wavelength control is required. The structure of a conventional light source that satisfies such requirements will be described below. FIG. 7 is a block diagram showing an example of a conventional incoherent light source.

An optical band pass filter 202 and an optical amplifier 203 are sequentially arranged on the optical path of the broadband light source 201. The broadband light source 201 generally includes a white light source such as a lamp, an LED (Light Emitting Diode), an SLD (Su
per Luminescent Diode), or spontaneous emission light from an excitation medium is used. The broadband light source 201 has a sufficient spectral width, and the light is passed through the optical bandpass filter 20.
By passing it through 2, an output signal light having a desired center wavelength and spectrum width can be obtained.

Output light obtained by filtering the broadband light source 201 may not have sufficient light intensity. Therefore, the output light of the optical bandpass filter 202 is amplified by the optical amplifier 203 and the intensity of the signal light is increased to obtain the signal light output Po. By using the incoherent light source as shown in FIG. 7, various problems caused by the coherent light source can be avoided.

FIG. 8 shows another conventional incoherent light source.
It is a block diagram which shows an example. Broadband light source 301_-1, 301_-2
... 301_-nHave the same specifications and a sufficient spectral width
As described above, the white light source, LED, S
For example, LD or spontaneous emission light from the excitation medium. Wide band
Area light source 301_-1, 301_-2... 301 _-nLight on each of
Bandpass filter 302_-1, 302_-2... 302_-n
Of the optical bandpass filter 30
2_-1, 302_-2... 302_-nOptical amplifier 30 for each
3_-1, 303_-2... 303_-nIs connected. Change
Optical amplifier 303_-1, 303_-2... 303_-nLight on
A multiplexer / demultiplexer 304 is connected, and from this optical multiplexer / demultiplexer 304
The signal light output Po is output.

In the configuration of FIG. 8, the broadband light source 301
_-1 , 301 _-2 ... 301 _-n output lights are individually passed through the optical bandpass filters 302 _-1 , 302 _-2 ... 302 _-n , respectively, and specific centers different from each other are passed. The n output signal lights having the wavelength and the spectral width are obtained. Further, these output signal lights are converted into optical amplifiers 303 _-1 , 303 _-2 ... 3
After being optically amplified by 03- _n , it is multiplexed by the optical multiplexer / demultiplexer 304 to obtain the signal light output Po.

[0009]

However, according to the conventional incoherent light source, when the pass band width of the optical bandpass filter is set relatively narrow, most of the output light from the broadband light source is generated by the optical bandpass filter. Since it is removed, there is a problem of inefficiency. This problem can be compensated by an optical amplifier, but this leads to a complicated structure and an increase in cost.
In particular, in the configuration of FIG. 8, it is necessary to individually control the wavelength of each signal by the optical bandpass filter, and the control accuracy of each optical bandpass filter becomes strict, so a great amount of time must be taken for adjustment. .

Therefore, an object of the present invention is to provide an incoherent light source which is easy to adjust, efficient, and inexpensive, and an optical transmitter using the same.

[0011]

In order to achieve the above object, the incoherent light source according to the present invention emits a rare earth-doped optical fiber doped with a rare earth and a pumping light for exciting the rare earth-doped optical fiber. An excitation light source, an optical multiplexer / demultiplexer that supplies the excitation light to the rare earth-doped optical fiber, and supplies amplified light from the rare earth-doped optical fiber to an output end, and an optical bandpass filter connected to the rare earth-doped optical fiber. Alternatively, a Fabry-Perot type optical filter and an optical reflector for reflecting the light from any one of the filters to the filter are provided.

According to this structure, the rare-earth-doped optical fiber is excited by the excitation light source, and the spontaneous emission light generated from the rare-earth-doped optical fiber at that time is reflected by the optical reflector through the optical bandpass filter or the Fabry-Perot optical filter. When returning to the rare earth-doped optical fiber, the light from the light reflector is amplified by the rare earth-doped optical fiber. Therefore, incoherent light having a desired wavelength and spectrum width can be efficiently obtained.

Further, to achieve the above object, the incoherent light source according to the present invention comprises a rare earth-doped optical fiber doped with a rare earth, and a first optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber. A pumping light source connected to the first optical multiplexer / demultiplexer for emitting pumping light for pumping the rare earth-doped optical fiber; a second optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber; A first optical reflector for reflecting light from one surface of the second optical multiplexer / demultiplexer to the second optical multiplexer / demultiplexer, and an optical bandpass connected to the other surface of the second optical multiplexer / demultiplexer A filter, and a second reflecting the light from the optical bandpass filter to the optical bandpass filter
And a light reflector of.

According to this structure, the pumping light from the pumping light source that has passed through the rare earth-doped optical fiber is separated by the second optical multiplexer / demultiplexer, and the separated pumping light is reflected by the first optical reflector. The pumping light is reused by returning to the rare earth-doped optical fiber through the second optical multiplexer / demultiplexer. Therefore,
Incoherent light can be obtained more efficiently.

In each of the above incoherent light sources, the excitation light source generates excitation light having a wavelength corresponding to the excitation level of the rare earth ion added to the rare earth added optical fiber. According to this configuration, since the generated light of the excitation light source has a wavelength corresponding to the excitation level of the rare earth ion added to the rare earth-doped optical fiber, the energy level of the rare earth ion is excited by the excitation light from the excitation light source. Since the population inversion is formed, the spontaneous emission light generated in the rare earth-doped optical fiber is transmitted to the end while being amplified by the stimulated emission phenomenon due to the population inversion of the energy level. Therefore, incoherent light can be efficiently obtained.

Further, the above object is to provide a rare earth-doped optical fiber doped with rare earth, an optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, and a rare earth-doped optical fiber connected to the optical multiplexer / demultiplexer. An excitation light source that emits excitation light that excites a fiber, an optical bandpass filter connected to the rare earth-doped optical fiber, and an optical reflector that reflects light from the optical bandpass filter to the optical bandpass filter, It is also achieved by an optical transmitter having a configuration including an external modulator that modulates incoherent light output from the optical multiplexer / demultiplexer.

According to this structure, by optically modulating the incoherent light obtained with high efficiency, signal transmission can be performed with a simple structure. In order to achieve the above-mentioned object, the optical transmitter according to the present invention is a rare earth-doped optical fiber, a first optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, Pump light source connected to the optical multiplexer / demultiplexer 1 for emitting pumping light for exciting the rare earth-doped optical fiber, a Fabry-Perot optical filter connected to the rare-earth-doped optical fiber, and the Fabry-Perot optical filter An optical reflector for reflecting the light from the optical fiber to the Fabry-Perot optical filter; a second optical multiplexer / demultiplexer for demultiplexing the light from the first optical multiplexer / demultiplexer into light of a plurality of different wavelengths; A configuration including a plurality of optical modulators that optically modulate each output light of the second optical multiplexer / demultiplexer, and a third optical multiplexer / demultiplexer that multiplexes the plurality of lights output from the optical modulator I have to.

According to this configuration, by optically modulating the incoherent light obtained with high efficiency, the signal transmission of the signal light output having a plurality of output peaks of different wavelengths is performed by one light with a simple configuration. It can be done via fiber.

[0019]

1 is a block diagram showing a first embodiment of an incoherent light source according to the present invention. An optical multiplexer / demultiplexer 102 is connected to the pumping light source 101, and a rare earth-doped optical fiber 103 is connected to one output surface thereof,
The optical isolator 104 is connected to the other output surface. An optical bandpass filter 105 for setting a specific center wavelength and a specific spectral width is connected to an end of the rare earth-doped optical fiber 103, and an optical reflector 106 is connected to the optical bandpass filter 105.

In the above structure, the excitation light source 101 has a wavelength corresponding to the excitation level of the rare earth ion added to the rare earth-doped optical fiber 103, and the rare earth ion is excited by the excitation light from the excitation light source 101 to have an energy level. An inversion distribution of is formed. Therefore, the spontaneous emission light generated in the rare earth-doped optical fiber 103 reaches both ends of the rare earth-doped optical fiber 103 while being amplified by the stimulated emission phenomenon due to the population inversion. The spontaneous emission light amplified by the rare earth-doped optical fiber 103 is ASE (Amplif
ied Spontaneous Emission) Called light.

The ASE light that has reached the optical bandpass filter 105 side from the rare earth-doped optical fiber 103 passes through the optical bandpass filter 105, is reflected by the optical reflector 106, and is returned to the optical bandpass filter 105 again. ASE passing through the optical bandpass filter 105 from the opposite direction
The light is further amplified as it passes through the rare earth-doped optical fiber 103. The amplified ASE light goes straight through the optical multiplexer / demultiplexer 102, and is further extracted as the signal light output Po via the optical isolator 104. The optical isolator 104 functions so as to prevent a part of the signal light output Po from being reflected and returned to the rare earth-doped optical fiber 103 again, thereby causing laser oscillation.

AS generated in the rare earth-doped optical fiber 103
If the spectral width of the E light is sufficiently wide and the gain in the excited rare earth-doped optical fiber 103 is sufficiently large, the wavelength and the spectral width of the signal light output Po are determined by the pass characteristics of the optical bandpass filter 105. . Therefore, by optimizing the pass characteristic of the optical bandpass filter 105, a light source having a desired spectrum can be obtained. Furthermore, the energy of the pumping light is efficiently converted into the ASE light that has passed through the optical bandpass filter 105 via the pumping medium. Therefore, if the power of the pumping light is high to some extent, the signal light output Po of sufficient intensity is obtained. Can be obtained.

As described above, according to the configuration of FIG. 1, the rare earth-doped optical fiber 103 is excited, and the spontaneous emission light generated from the rare earth-doped optical fiber 103 is reflected at one end through the optical bandpass filter 105, and again. By amplifying and outputting from the other end, it is possible to efficiently obtain a plurality of incoherent light beams having desired wavelength intervals and spectral widths.

FIG. 2 is a block diagram showing a second embodiment of the incoherent light source according to the present invention. This optical transmitter includes an optical multiplexer / demultiplexer 110 between the rare earth-doped optical fiber 103 and the optical bandpass filter 105 in the configuration of FIG.
A (second optical multiplexer / demultiplexer) is provided, and an optical reflector 111 is connected to the optical multiplexer / demultiplexer 110. With such a configuration, the pumping light that is given to the rare earth-doped optical fiber 103 via the optical multiplexer / demultiplexer 102 (first optical multiplexer / demultiplexer) and has passed through the rare earth-doped optical fiber 103 is combined with the optical multiplexer / demultiplexer 110. And a part of the incident light is branched to the light reflector 111 (first light reflector). Light reflector 1
The light sent to 11 is reflected by the light reflector 111, passes through the optical multiplexer / demultiplexer 110 again, and is returned to the rare earth-doped optical fiber 103. In addition, A that has passed through the optical bandpass filter 105
SE light is reflected by the light reflector 106 (second light reflector),
It is returned to the rare earth-doped optical fiber 103 and amplified.

According to the configuration of FIG. 2, the utilization efficiency of the excitation light is improved, and the incoherent light can be obtained with higher efficiency. FIG. 3 is a configuration diagram showing a third embodiment of the incoherent light source according to the present invention. While the incoherent light source of FIG. 1 has the optical bandpass filter 105 between the rare earth-doped optical fiber 103 and the light reflector 106, the incoherent light source of FIG. 3 has a Fabry-Perot type light. The filter 107 is used.

The structure is as follows: pumping light source 101, optical multiplexer / demultiplexer 102 connected to this pumping light source 101, rare earth-doped optical fiber 103 connected to one output surface of this optical multiplexer / demultiplexer 102, optical multiplexer / demultiplexer. Optical isolator 104 connected to the other output surface of 102, rare earth-doped optical fiber 10
Optical bandpass filter 105 sequentially connected to the end of
And a light reflector 106.

In the structure shown in FIG. 3, the excitation light source 101 has a wavelength corresponding to the excitation level of the rare earth ion added to the rare earth-doped optical fiber 103, and the rare earth ion is excited by the excitation light from the excitation light source 101 to an energy level. A population inversion is formed. Therefore, the spontaneous emission light generated in the rare earth-doped optical fiber 103 reaches both ends of the rare earth-doped optical fiber 103 while being amplified by the stimulated emission phenomenon due to the population inversion. The spontaneous emission light amplified by the rare earth-doped optical fiber 103 is ASE (Amplif
ied Spontaneous Emission) Called light.

The ASE light that has reached the Fabry-Perot type optical filter 107 side from the rare earth-doped optical fiber 103 passes through the Fabry-Perot type optical filter 107, is then reflected by the optical reflector 106, and is again Fabry-Perot type optical filter 1.
Returned to 07. The ASE light that has passed through the Fabry-Perot type optical filter 107 from the opposite direction is amplified when it further passes through the rare earth-doped optical fiber 103. Amplified AS
The E light travels straight through the optical multiplexer / demultiplexer 102 and is further extracted as a signal light output Po through the optical isolator 104. The optical isolator 104 functions so as to prevent a part of the signal light output Po from being reflected and returned to the rare earth-doped optical fiber 103 again, thereby causing laser oscillation.

AS generated in the rare earth-doped optical fiber 103
If the spectral width of the E light is sufficiently wide and the gain in the pumped rare earth-doped optical fiber 103 is sufficiently large, the wavelength and the spectral width of the signal light output Po are determined by the pass characteristics of the Fabry-Perot optical filter 107. It
Therefore, by optimizing the pass characteristic of the optical bandpass filter 105, a light source having a desired spectrum can be obtained.

FIG. 4 shows a Fabry-Perot type optical filter 107.
, And has periodic characteristics with respect to wavelength. Therefore, the signal light output Po from the optical isolator 104 is equivalent to a plurality of light sources having equal wavelength intervals. That is, with the configuration shown in FIG.
1 _-1 , 301 _-2 ... 301 _-n Optical bandpass filters 302 _-1 , 302 _-2 ...
It is possible to obtain a light source having the same function as the combination of 302 _-n . In this case, the wavelength interval and the spectral width are the cavity length and Q of the Fabry-Perot type optical filter 107.
The light source having a desired wavelength interval and spectrum width can be obtained by appropriately setting these. Further, the energy of the pumping light is efficiently converted into the ASE light that has passed through the Fabry-Perot type optical filter 107 via the pumping medium. Therefore, if the power of the pumping light is high to some extent, the output signal light of sufficient intensity is obtained. Is obtained.

As described above, according to the configuration of FIG. 3, the rare earth-doped optical fiber 103 is excited, and spontaneous emission light generated from the rare earth-doped optical fiber 103 is reflected at one end through the Fabry-Perot optical filter 107, By amplifying again and then outputting from the other end, it is possible to efficiently obtain a plurality of incoherent lights having desired wavelength intervals and spectral widths.

An optical transmitter can be constructed by using the incoherent light source of the present invention described above. FIG.
Alternatively, since the signal light output Po obtained by the incoherent light source shown in FIG. 3 is CW (Continuous Wave), it must be modulated in order to be used for signal transmission (optical communication). An optical transmitter for signal transmission can be configured by adding a modulation means to the incoherent light source shown in FIG. 1 or 3.

FIG. 5 is a block diagram showing a first example of the optical transmitter according to the present invention. Note that, in FIG. 5, the same reference numerals are used for the same components as those shown in FIG. 1, and thus duplicated description will be omitted below. As shown in FIG. 5, an optical multiplexer / demultiplexer 102 is connected to the pumping light source 101,
The rare earth-doped optical fiber 103 is connected to one of the output surfaces, and the optical isolator 104 is connected to the other output surface. At the end of the rare earth-doped optical fiber 103,
An optical bandpass filter 105, an optical reflector 106, and an optical modulator 108 as an external modulator are sequentially connected.
Further, a modulation signal source 109 is connected to the optical modulator 108.

As the optical modulator 108, one using the electro-optical effect of a ferroelectric crystal such as LiNbO ₃ or one utilizing the change in absorption wavelength characteristic due to the Stark effect of a semiconductor can be used. In this optical transmitter, the incoherent light obtained as described in FIG. 1 is modulated by the optical modulator 108 by the modulation signal given from the modulation signal source 109.

FIG. 6 is a block diagram showing a second example of the optical transmitter according to the present invention. The optical transmitter in FIG.
01, optical multiplexer / demultiplexer 10 connected to the pumping light source 101
2 (first optical multiplexer / demultiplexer), a rare earth-doped optical fiber 103 connected to one output surface of the optical multiplexer / demultiplexer 102, an optical isolator 104 connected to the other output surface of the optical multiplexer / demultiplexer 102, Fabry-Perot type optical filter 107 connected to the end of the rare earth-doped optical fiber 103, and optical reflector 10 connected to the Fabry-Perot type optical filter 107.
6. Optical multiplexer / demultiplexer 112 (second optical multiplexer / demultiplexer) connected to the output side of the optical isolator 104, and this optical multiplexer / demultiplexer 11
N optical modulators 113 _-1 , 113 _-2 ...
113 _-n , modulation signal sources 114 _-1 , 114 _-2 ... 114 _-n for applying a modulation signal to each of these optical modulators,
Each of the optical modulators _113-1 , _113-2, ... 113- _n is provided with an optical multiplexer / demultiplexer 115 (third optical multiplexer / demultiplexer).

In the optical transmitter of FIG. 6, the incoherent light obtained as described in FIG.
The light is demultiplexed by 12 and each of the demultiplexed lights
3 ₋₁ , 113 ₋₂ ... 113 _−n , and the intensity of each demultiplexed light is modulated. Optical modulator 113 _-1 , 113 _-2
The output light from each of the 113 _-n is the optical multiplexer / demultiplexer 11
5, the signal light output Po having a plurality of output peaks of different wavelengths is outputted again from one optical fiber as shown in FIG.

[0037]

As is apparent from the above, according to the present invention, the power of the pumping light is efficiently converted into the output light, and the incoherent light of the desired spectrum can be obtained with the high output power. In addition, ASE of rare earth doped optical fiber
The length of the rare earth-doped optical fiber can be shortened by the configuration in which the light is reflected and the light is again incident on the rare earth-doped optical fiber.

Further, in the incoherent light source using the Fabry-Perot type optical filter, the wavelength intervals are all equal, it is not necessary to set individual center wavelengths, and a plurality of wavelength intervals and spectral widths having the desired wavelength are provided. Incoherent light can be obtained with a simple configuration. Furthermore, by configuring an optical transmitter using the incoherent light source according to the present invention, signal transmission with high-power incoherent light becomes possible with a simple configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an incoherent light source of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the incoherent light source of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the incoherent light source of the present invention.

FIG. 4 is a characteristic diagram showing transmission characteristics of a Fabry-Perot type optical filter.

FIG. 5 is a configuration diagram showing a first example of an optical transmitter according to the present invention.

FIG. 6 is a configuration diagram showing a second example of the optical transmitter according to the present invention.

FIG. 7 is a configuration diagram showing an example of a conventional incoherent light source.

FIG. 8 is a configuration diagram showing another example of a conventional incoherent light source.

[Explanation of symbols]

101 pump light source 102, 110, 112, 115 optical multiplexer / demultiplexer 103 rare earth-doped optical fiber 104 optical isolator 105 optical bandpass filter 106 optical reflector 107 Fabry-Perot type optical filter 108 optical modulator 109, 114 _-1 , 114 _-2 ... 114 _-n modulation signal source 113 _-1 , 113 _-2 ... 113 _-n optical modulator

Claims (6)

[Claims] 1. A rare-earth-doped optical fiber, a pumping light source that emits pumping light that pumps the rare-earth-doped optical fiber, and the rare-earth-doped optical fiber that supplies the pumping light to the rare-earth-doped optical fiber. An optical multiplexer / demultiplexer that supplies amplified light from the fiber to the output end, an optical bandpass filter or a Fabry-Perot optical filter connected to the rare earth-doped optical fiber, and the light from any one of the filters is reflected to the filter. An incoherent light source, comprising: 2. The incoherent light source according to claim 1, wherein the pumping light source generates pumping light having a wavelength corresponding to a pumping level of a rare earth ion doped in the rare earth doped optical fiber. 3. A rare earth-doped optical fiber doped with rare earth, a first optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, and a rare earth doped optical fiber connected to the first optical multiplexer / demultiplexer. A pumping light source that emits pumping light that pumps an optical fiber, a second optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, and light from one surface of the second optical multiplexer / demultiplexer is supplied to the second optical multiplexer / demultiplexer. A first optical reflector for reflecting the light to the optical multiplexer / demultiplexer, an optical bandpass filter connected to the other surface of the second optical multiplexer / demultiplexer, and light from the optical bandpass filter. And a second light reflector for reflecting the light to the optical transmitter. 4. The incoherent light source according to claim 3, wherein the pumping light source generates pumping light having a wavelength corresponding to the pumping level of the rare earth ion doped in the rare earth doped optical fiber. 5. A rare earth-doped optical fiber doped with a rare earth, an optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, and an excitation connected to the optical multiplexer / demultiplexer to excite the rare earth-doped optical fiber. An excitation light source that emits light, an optical bandpass filter connected to the rare earth-doped optical fiber, an optical reflector that reflects light from the optical bandpass filter to the optical bandpass filter, and the optical multiplexer / demultiplexer And an external modulator that modulates the incoherent light output from the optical transmitter. 6. A rare earth-doped optical fiber doped with rare earth, a first optical multiplexer / demultiplexer connected to the rare earth-doped optical fiber, and a rare earth doped optical fiber connected to the first optical multiplexer / demultiplexer. An excitation light source that emits excitation light that excites an optical fiber, a Fabry-Perot optical filter connected to the rare-earth-doped optical fiber, and light that reflects the light from the Fabry-Perot optical filter to the Fabry-Perot optical filter. A reflector, a second optical multiplexer / demultiplexer that splits the light from the first optical multiplexer / demultiplexer into a plurality of lights having different wavelengths, and outputs the output light of each of the second optical multiplexer / demultiplexers. An optical transmitter comprising: a plurality of optical modulators for modulating; and a third optical multiplexer / demultiplexer for multiplexing a plurality of lights output from the optical modulators.