JPH0675254A - Optical filter - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide an optical filter having a wavelength dependence of a characteristic opposite to the wavelength dependence of a gain of a fiber amplifier and capable of varying transmission loss. To do. According to a first aspect of the present invention, an optical filter includes a control light emitting unit that can change at least one of an optical output and a wavelength of the emitted control light, and a control light input from the control light emitting unit. And a light amplification means for changing the absorption degree of the input light, which is combined with the control light by the multiplexer, according to at least one of the optical output and the wavelength of the control light. Consists of The second invention of the present application is
First light amplifying means for optically amplifying input light, control light emitting means capable of changing at least one of optical output and wavelength of emitted control light, and control light input from the control light emitting means And a second optical amplifying means for performing optical amplification by changing the amplification characteristic so as to have a wavelength dependence of an inverse characteristic to the amplification characteristic of the first optical amplifying means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter used in, for example, an optical transmission system or optical signal processing.

[0002]

2. Description of the Related Art The basic configuration of a conventional optical filter is shown in the block diagram of FIG. The optical filter F shown in FIG.
As the dielectric multilayer filter, a dielectric multilayer filter, an etalon plate, a fiber coupler type filter, or the like is appropriately used. FIG. 12 shows an example of the transmission loss of the input light when a dielectric multilayer filter is used for the optical filter F, for example. As is clear from the example shown in FIG. 12, the wavelength dependence of the transmission loss of the optical filter F usually shows a simple shape such as a trapezoid, and the value of the transmission loss is fixed.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a wavelength dependence of a characteristic opposite to the wavelength dependence of the gain of a fiber amplifier and can make transmission loss variable. An object is to provide an optical filter.

[0004]

In order to achieve the above object, the first invention of the present application is a control light emitting means capable of changing at least one of an optical output and a wavelength of emitted control light, and this control light. Depending on at least one of the optical output and wavelength of the control light, the combiner for combining the input light with the control light from the emission means and the absorption of the input light combined with the control light by this combiner The present invention is characterized in that it has an optical amplifying means for changing it.

The second invention of the present application is the first optical amplifying means for optically amplifying the input light, and the control light emitting means capable of changing at least one of the optical output and the wavelength of the emitted control light. A second light for amplifying the light by changing the amplification characteristic so as to have a wavelength dependence of the amplification characteristic of the first light amplifying means and the opposite characteristic according to the change of the control light inputted from the control light emitting means. The gist is to have an amplifying means.

[0006]

With the above arrangement, the optical filter according to the first aspect of the present invention can be used in the optical amplifying means by changing at least one of the optical output and the wavelength of the control light emitted from the control light emitting means. The absorption of the input light can be changed according to the control light.

In the optical filter of the second invention of the present application, the amplification characteristic of the second optical amplification means is reversed from that of the first optical amplification means by changing the control light output from the control light emission means. It can be improved by changing the characteristics so as to have wavelength dependence and flattening the gain at the time of optical amplification.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining the principle of the optical filter according to the present invention.

First, the principle of the optical filter according to the present invention will be described with reference to FIG. The input light is guided to the optical amplification medium 3 for the optical filter via the multiplexer 1, and is output via the demultiplexer 5. On the other hand, the control light emitted from the optical filter control light source 7 is guided to the optical amplification medium 3 for the optical filter via the multiplexer 1. Although FIG. 1 shows the case where the control light is incident from the A side, the control light may be incident from the B side or both the A side and the B side.

Here, the input light receives a wavelength-dependent loss due to the optical amplifying medium 3 for the optical filter. Depending on the wavelength λcont of this control light and the optical output (optical power) Pcont,
Laser upper level occupation ratio Pu of the optical amplification medium 3 for optical filter
Changes.

For example, here, the input light wavelength is λin and the optical output is Pin, and the absorption and stimulated emission cross sections of the optical amplifying medium 3 for optical filter at the wavelength λ are σabs (λ), respectively.
And σemi (λ). When Pcont is sufficiently large, the laser upper level occupation ratio Pu is Pu = σabs (λcont) / σemi (λcont) (≡R (λ
cont)).

When R (λcont) <R (λin), the input light receives a loss due to the optical amplifying medium 3 for the optical filter. Therefore, by selecting the wavelength λcont of the control light and the optical output Pcont to be large so as to satisfy the relationship of R (λcont) <R (λin), the laser upper level occupation ratio Pu of the optical amplifying medium 3 for optical filter can be determined. You can control. The loss of the optical amplifying medium 3 for an optical filter changes according to the change of the laser upper level occupation ratio Pu.

That is, the wavelength dependence of the loss of the optical amplifying medium for optical filter 3 depends on the wavelength absorption characteristic of the amplifying medium, and the amount of loss of the optical amplifying medium for optical filter 3 depends on the laser resonance. It can be adjusted arbitrarily by the adjuster of the vessel.

A concrete example of the transmission loss of this optical filter is shown in FIG.
Shown in. The transmission loss changes like curves a and b in the figure. Thus, compared to the conventional case shown in FIG.
It can be seen that the wavelength dependence of the transmission loss has the inverse characteristic of the wavelength dependence of the optical amplifier, and the transmission loss is variable.

Next, basic configuration examples according to the present invention are shown in FIGS. 3 to 6, respectively. 3 shows a case where a ring type laser resonator and an optically pumped optical amplification medium for a laser resonator are used, FIG. 4 shows a case where a repetitive type laser resonator and an optically pumped optical amplification medium for a laser resonator are used, and FIG. Shows a case where a ring type laser resonator and a laser diode for a laser resonator are used, and FIG. 6 shows a case where a repetitive type laser resonator and a laser diode for a laser resonator are used.

That is, FIGS. 3 and 5 show the case where a ring type laser resonator is used, FIGS. 4 and 6 show the case where a repetitive type laser resonator is used, and FIGS. 3 and 4 show the optical excitation light for the laser resonator. When an amplification medium is used, FIGS. 5 and 6 show the case where a laser diode for laser resonance is used.

Here, the ports through which the input light of the multiplexer 1 and the demultiplexer 5 does not pass are installed in the optical path of the laser resonator, and the laser light propagating in the laser resonator is the laser light of the laser resonator. The wavelength and the optical output are adjusted by the adjuster 71.

In FIGS. 3 and 4, the pumping light remover 73
A and 73B are arranged so that pumping light does not enter the optical pumping light amplifying media 75A and 75B for laser resonators, respectively. Further, in FIGS. 4 and 6, the mirrors 81B, 81
D is provided so that the laser resonator causes laser oscillation.

In the above structure, a rare earth-doped optical fiber or a semiconductor laser medium (for example, a laser diode) is used as an optical amplifying medium for an optical filter as an optical amplifying means, and a multiplexer, a demultiplexer, and A fiber coupler or a dichroic mirror is used as the multiplexer of the pumping light, and an optical bandpass filter or an optical attenuator is used as the adjuster of the fiber laser.

Next, the configuration of an embodiment according to the present invention will be described with reference to FIG. It should be noted that this embodiment corresponds to the basic configuration shown in FIG. 3, and the same embodiment as in FIG. 3 can be constructed with respect to FIGS. 4 to 6.

In this embodiment, the optical isolator OI is used.
The wavelength of the signal light input via the laser diode is 1.533 μm, and the wavelength of the laser light emitted from the laser diode LD is 0.98 μm. Further, the multiplexer FC1 and the demultiplexer FC2 are composed of fiber couplers, and the optical amplification medium for the optical filter is composed of an erbium-doped optical fiber (EDF-att) of 16.5 m.

The optically pumped light amplification medium for the laser resonator is an erbium-doped optical fiber (EDF-f1),
The pumping light source is a 1.48 μm laser diode LD, the pumping light multiplexer is a dichroic mirror DM, the pumping light remover is an optical isolator OI, the laser resonator adjuster is an optical isolator OI, and an optical bandpass with a bandwidth of 3 nm. It is a filter OBPF.

The optical isolator OI as the adjuster of the laser resonator limits the propagation direction of the laser light in the laser resonator to the arrow direction in FIG. The laser resonator is adjusted by changing the central wavelength of the optical bandpass filter OBPF.

The signal light of 1.533 μm is 20.0
The optical pumping light amplifying medium EDF1 of m and the optical pumping light amplifying medium EDF2 of 13.0 m are amplified in two stages.

The excitation light in the vicinity of 0.98 μm emitted from the optical excitation light amplification medium EDF1 is the input light to the optical filter. FIG. 8 shows the pumping light wavelength dependence of the signal light gain of the optically pumped light amplification medium EDF1 and the optically pumped light amplification medium EDF2. As shown by the signal light gain of the optical pumping light amplification medium EDF1, the pumping light wavelength dependency is not flat in the one-stage amplification.

Therefore, as shown in FIG. 8, the pumping light is passed through an optical filter so that the pumping light wavelength dependence of the signal light gain of the optically pumping light amplifying medium EDF2 is shown.
Of the optical pumping light amplification medium EDF1
The gain of the two-stage optical amplifier including the optical pumping light amplification medium EDF2 is flattened. The flattened signal light gain (total gain) is shown in FIG.

The transmission loss of the optical filter with respect to the input light in the vicinity of 0.98 μm is determined by the optical bandpass filter OBPF.
Center wavelengths of λ _C = 1540, λ _B = 1546, λ _A =
FIG. 9 shows the case of 1550 nm. Also, FIG.
Signal gain of the optical amplifier of the optical bandpass filter OB
The central wavelength of PF is λ _C = 1540, λ _B = 1546, λ
FIG. 10 shows the case of _A = 1550 nm. When the center wavelength of the optical bandpass filter OBPF is 1546 nm, the signal light gain is independent of the pumping light wavelength near 0.98 μm.

As described above, the optical filter of this embodiment is effective for realizing an optical amplifier having a signal light gain independent of the pumping light wavelength.

[0029]

As described above, the optical filter of the present invention has the wavelength dependence of the characteristic opposite to the wavelength dependence of the gain of the fiber amplifier and the transmission loss can be made variable. Can be flattened.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the principle of the present invention.

FIG. 2 is a diagram showing wavelength dependence of transmission loss of an optical filter in the present invention.

FIG. 3 is a block diagram showing a basic configuration of an embodiment according to the present invention, showing a case where a ring type laser resonator and an optically pumped optical amplification medium for a laser resonator are used.

FIG. 4 is a block diagram showing a basic configuration of an embodiment according to the present invention, showing a case where a repetitive laser resonator and an optically pumped optical amplification medium for a laser resonator are used.

FIG. 5 is a block diagram showing a basic configuration of an embodiment according to the present invention, showing a case where a ring type laser resonator and a laser diode for a laser resonator are used.

FIG. 6 is a block diagram showing a basic configuration of an embodiment according to the present invention, showing a case where a repetitive laser resonator and a laser diode for a laser resonator are used.

FIG. 7 is a block diagram specifically showing an embodiment according to the present invention.

FIG. 8 is a diagram showing pump light wavelength dependence of gains of EDF1 and EDF2 in FIG.

9 is a diagram showing the excitation light wavelength dependence of the optical filter transmission loss in FIG.

10 is a diagram showing pump light wavelength dependency of optical amplifier gain in FIG.

FIG. 11 is a diagram showing a basic configuration of a conventional technique.

FIG. 12 is a diagram showing wavelength dependence of transmission loss of an optical filter in a conventional technique.

[Explanation of symbols]

 1 multiplexer 3 optical amplification medium for optical filter 5 demultiplexer 7 optical filter control light source 71 regulator 73 excitation light remover 75 optical excitation light amplification medium 77 excitation light multiplexer 79 excitation light source 81 mirror 83 laser diode 85 current drive circuit 87 High reflectance end face

Claims (2)

[Claims] 1. A control light emitting means capable of changing at least one of an optical output and a wavelength of the emitted control light, and a multiplexer for multiplexing the input light with the control light from the control light emitting means. An optical filter comprising: an optical amplifying unit that changes the degree of absorption of the input light multiplexed with the control light by the multiplexer according to at least one of the optical output and the wavelength of the control light. 2. A first light amplifying means for optically amplifying input light, a control light emitting means capable of changing at least one of an optical output and a wavelength of the emitted control light, and a control light emitting means. A second optical amplifying means for changing the amplifying characteristic so as to have a wavelength dependence of an opposite characteristic to the amplifying characteristic of the first optical amplifying means in response to a change of the input control light. Characteristic optical filter.