JPH05257177A - Optical amplifier noise characteristics measurement method - Google Patents

Abstract

(57) [Abstract] [Objective] Regarding a measurement method of noise characteristics of an optical amplifier, even when noise of a signal light source and noise of the optical amplifier are similar to each other, such as in an optical power amplifier, noise characteristics of the optical amplifier, For example, the purpose is to make it possible to measure the spontaneous emission coefficient. It is another object of the present invention to provide a method for easily measuring the noise characteristic, especially the spontaneous emission light coefficient n _sp even when the input signal light power is small. A modulation means 3 for applying pulse modulation to input light from a signal light source 1 at a modulation speed in a range where a gain of an optical amplifier 2 and a spontaneous emission light coefficient are determined by an average power of modulated signal light, and the modulation means. The control means 3 controls the light output of the optical amplifier 2 when the modulated signal light is in the “H” state, and the light blocking means 4 is provided to receive the output when the input signal light is in the “L” state. And measure the noise power.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the noise characteristics of optical amplifiers.
Regarding the measurement method, especially in the case of an optical power amplifier, for example,
Of noise characteristics in optical amplifiers that output various output signal lights
It is possible to adjust the input signal light level when it is low.
Noise characteristics, especially spontaneous emission coefficient n _spEasy to measure
To do.

In recent years, research and development of optical communication systems have been vigorously pursued, but the importance of booster amplifiers, repeaters, and preamplifiers utilizing optical amplification technology has been clarified, and in designing optical communication systems. Therefore, it is indispensable to understand the noise characteristics of these optical amplifiers.

[0003]

2. Description of the Related Art As an optical amplifier, a semiconductor laser amplifier in which an end face of a semiconductor laser is non-reflectively coated to suppress oscillation and an optical fiber amplifier using a rare earth-doped optical fiber such as erbium have been studied. In such an optical fiber amplifier, light from a pumping light source is input to the optical fiber together with signal light, and stimulated emission is performed in the optical fiber to realize an optical amplification effect.

As one of the methods for measuring the noise characteristics of an optical amplifier, amplified signal light and spontaneous emission light are passed through an optical bandpass filter and then received by a photodetector (PIN-PD).
In the method of measuring the noise power (to be referred to as a direct detection method), the signal light incident on the optical amplifier is P _i , the gain of the optical amplifier is G, the spontaneous emission coefficient is n _sp , and the bandwidth of the optical filter is Is Δν _ASE , the coupling loss on the output side is η _L , and the quantum efficiency of the photodetector is η, the received photocurrent is

[0005]

[Equation 1]

[0006] Here, e is the electron charge amount, h is Planck's constant, and ν is the frequency of the signal light. Also, the root mean square noise current, that is, the noise spectral density is

[0007]

[Equation 2]

[0008] Where Δν _ASE and Δν _ASE-ASE are the equivalent noise bandwidth of ASE shot noise and ASE, respectively.
-Equivalent noise band of ASE beat noise. The noise figure of the optical amplifier is given by the ratio of the SNR due to the shot noise of the input signal light and the SNR on the output side, and the noise figure F [dB] is obtained from the following equation.

[0009]

[Equation 3]

Here, Be is the bandwidth of the receiver. Normally, an optical amplifier is used with a gain of 15 dB or more, and ηη _L is 1
If it is close to, the measured total noise can be approximated by beat noise. Especially when G is about 20 dB or more,

[0011]

[Equation 4]

Since the approximation of <i _n ² >
Can be approximated as follows.

[0013]

[Equation 5]

Therefore, F is

[0015]

[Equation 6]

Is given by Furthermore, when the input light is large or Δν _ASE-ASE is small, measurement is performed at the Sig-ASE beat noise limit that can be approximated by the first term on the right side of Eq. (9), and it is an important parameter that determines the noise characteristics of the optical amplifier. It is easy to obtain a certain spontaneous emission coefficient n _sp from this measuring method.

[0017]

However, it has been difficult to measure a high output signal such as a power amplifier. Because, in the direct detection method, the relative intensity noise (RIN) of the signal light source is added to the noise generated by the optical amplification, and the relative intensity noise becomes larger in some cases, so that the noise generated by the optical amplification cannot be accurately measured.

On the other hand, the maximum input light power of the photoreceiver has an upper limit.
There is about 0 dBm in PIN-PD. example
For example, G is 10 dB and output light power is +10 dBm.
Consider measuring the noise characteristics of a width box. PD maximum entry
Effective quantum efficiency η to keep the upper limit of force power_Lη is 0.
If 1, the shot noise power is η_Lproportional to ηG,
Noise power is (η_LηG)²Since both are proportional to
The same power level, and the above-mentioned beat noise
Approximation of power alone does not hold, and shot noise component is also considered
Need to occur. The noise power of relative intensity noise is also beat noise
Like the power (η _LηG)²Proportional to. In this way,
When the output optical power of the power amplifier is about +10 dBm or more
, Beat noise power, relative intensity noise power and shot
Noise power is almost the same, and measurement is difficult.
However, there is a problem that it is difficult to improve the measurement accuracy.
It was

Next, problems of the heterodyne (homodyne) detection method as a method for measuring noise power will be described. The heterodyne detection method is, in principle, local light-ASE
This is a method of measuring n _sp from the beat noise power. A wide range from the small signal region to the saturation region, with a beat noise limit of n
_sp can be measured and dual balance type optical receiver (DB
If OR) is used, it is possible to suppress the relative intensity noise of the signal light and the local light. However, there is a problem that the measurement system becomes complicated, such as the need for two light sources of signal light and local light.

According to the present invention, even when the noise of the signal light source and the noise of the optical amplifier are similar to each other as in the case of the optical power amplifier, or when the noise of the signal light source is larger than the noise of the optical amplifier, The purpose is to enable measurement of noise characteristics of an amplifier.

It is another object of the present invention to facilitate the measurement of noise characteristics, especially the spontaneous emission coefficient n _sp even when the input signal light level is low.

[0022]

1 to 7 are block diagrams of the principle of the present invention. These figures are principle block diagrams of the noise characteristic measuring method of the optical amplifier 2 for amplifying the input signal light from the signal light source 1.

FIG. 1 is a principle block diagram of the first and second inventions. In the figure, the modulation means 3 is a signal light source 1.
The signal light output from the optical modulator 2 is pulse-modulated at a modulation speed within a range in which the gain of the optical amplifier 2 and the spontaneous emission light coefficient are determined by the average power of the modulated signal light. This modulation speed is such that when an erbium (Er) -doped fiber is used as the optical amplifier 2, the population inversion distribution of the Er-doped fiber is about several tens of msec. Therefore, the gain and the spontaneous emission coefficient are several MHz or more. However, the modulation speed is determined in such a frequency range because it is determined by the average optical power without following the change of the optical signal.

The light blocking means 4 is, for example, an optical shutter, and in the first aspect of the invention, by controlling the modulation means 3, when the modulated signal light is in the H level, the amplified output by the optical amplifier 2 is blocked and modulated. The signal light is transmitted when it is in the L level state, the output of the light blocking means 4 is converted into an electric signal by the optical / electrical converter 16, and noise is measured by using the noise power measuring device 17, for example, an RF spectrum analyzer. By measuring the power, the noise when the input signal light is in the “L” state is measured.

In the second invention, contrary to the first invention, the light blocking means 4 transmits the amplified output of the optical amplifier 2 when the modulated signal light is in the "H" state and in the "L" state. The only difference is that it sometimes shuts off.

FIG. 2 is a principle block diagram of the third and fourth inventions. In the first and second aspects of the invention, the amplified output of the optical amplifier 2 is transmitted by the light blocking means 4 when the modulated signal light is at the “L” or “H” level, and the light is converted into an electric signal to cause noise. Although the electric power was measured, in the third and fourth inventions, the light of the'L 'or'H' level is converted by passing the electric switch after converting the output of the optical amplifier 2 into an electric signal. The noise power is measured using the generated electrical signal.

In the third invention, the optical receiver 18 receives the optical signal output from the optical amplifier 2, converts the optical signal into an electric signal and outputs the electric signal. Also, the electric signal interruption means 19
Is, for example, an electric switch or a gate circuit, which cuts off the electric signal output from the optical receiver 18 when the modulated signal light is in the “H” state and keeps it when the modulated signal light is in the “L” state by the control of the modulation means 3. And the output is measured by the noise power measuring device 17.

In the fourth invention, as in the second invention, the electric signal blocking means 19 outputs the electric signal output from the optical receiver 18 as it is when the modulated signal light is in the "H" state, It differs from the third invention only in that it shuts off when in the “L” state.

FIG. 3 is a block diagram of the principle of the fifth invention. In the figure, the optical demultiplexing means 6 is, for example, an optical coupler and branches the output of the optical amplifier 2 into two. The optical delay means 7 is, for example, a delay loop made of a fiber, and delays one of the lights output from the optical demultiplexing means 6 with respect to the other of the outputs in time until it becomes uncorrelated. The optical multiplexing means 8 is, for example, an optical coupler, and combines the output of the optical delay means 7 and the output of the optical demultiplexing means 6 which is not input to the optical delay means 7.

The output of the optical multiplexing means 8 is received by, for example, a dual balance type optical receiver (DBOR) 9, and the noise power measuring device 17 measures the noise power. FIG. 4 is a block diagram showing the principle of the sixth invention. Comparing this figure with FIG. 3 showing the principle of the fifth invention, it is different in that a frequency shift means 10 is added after the optical delay means 7. The frequency shift means 10 is the optical demultiplexing means 6
The frequency shift means 10 may be inserted between the optical demultiplexing means 6 and the optical delay means 7 in the sense that the frequency of any one of the lights outputted by It may be inserted on the optical path side of the direct connection between the wave means 6 and the optical multiplexing means 11. And the optical multiplexing means 11 is
The two lights as a result of the action of the optical delay means 7 and the frequency shift means 10 on the two outputs of the optical demultiplexing means 6 are combined, and for example, a dual balance type optical receiver (DBO).
R) 9 will be output.

FIG. 5 is a block diagram showing the principle of the seventh invention. Comparing this figure with FIG. 4 showing the principle of the sixth invention,
Between the optical demultiplexing means 6 and the optical multiplexing means 13, the light transmitting means 12 is provided.
The difference is that is added. The light transmitting unit 12 is, for example, an optical bandpass filter, and blocks the frequency of the signal light contained in either one of the two lights output from the light demultiplexing unit 6 and allows the spontaneous emission light to pass therethrough. .. The light transmitting means 12 may be inserted between the optical demultiplexing means 6 and the optical multiplexing means 13 in the same manner as the optical delaying means 7 and the frequency shifting means 10, and the optical multiplexing means 13 may perform the optical Optical delay means 7, frequency shift means 10, and light transmission means 12 for the two outputs of the demultiplexing means 6.
Will combine the two lights as a result of the action.
FIG. 6 shows a principle block of the eighth invention. In the same figure, the light transmitting means 12 is, for example, an optical bandpass filter, like the light transmitting means 12 in FIG. 5 showing the principle of the seventh invention, and shows the frequency of the signal light included in the output of the optical amplifier 2. Blocks and transmits spontaneous emission light. Further, the optical combining means 15 combines the output of the light transmitting means 12 and the local light 14 which is a light source different from the signal light source 1, and the dual balance type optical receiver ( DB
OR) is used to measure the noise power.

FIG. 7 is a block diagram showing the principle of the ninth invention. In the same figure, the light transmission means 12 is, for example, an optical bandpass filter, as in FIG. 6 showing the principle of the eighth invention, and blocks the wavelength of the signal light in the output of the optical amplifier 2 to naturally The emitted light is transmitted, and the noise power is measured as the spontaneous emission light power per unit frequency by inputting the output of the light transmission means 12 to, for example, an optical power meter.

[0033]

In the first invention whose principle is shown in FIG. 1,
The optical amplifier 2 includes an optical shutter that constitutes the light blocking unit 4.
Only low-level light as a result of pulse-modulation of the output light of is input to, for example, an optical receiver, and noise power is measured. In this way, the average input light power that determines the gain of the optical amplifier 2 and the difference between the high level and the low level of the output light can be set separately. For example, if the low-level optical power measured as noise power is set to a level that is the beat noise limit, the spontaneous emission light can be easily received without being affected by the relative intensity noise as the intrinsic noise of the signal light source 1. It is possible to measure the coefficient. On the contrary, when the average power of the modulated signal light input to the optical amplifier 2 is low, only the high level light is transmitted to, for example, the optical receiver by the optical shutter which constitutes the light blocking means 4 according to the second invention. By inputting, the measurement can be performed at the beat noise limit even when the average input light power is low.

In the third and fourth inventions, the principle of which is shown in FIG. 2, instead of directly blocking the light of'H 'or'L' level by the light blocking means 4 in the first and second inventions. The noise power is measured for the modulated signal light converted into the electric signal that has passed through the electric signal cutoff means 19, for example, the gate circuit. The setting of the average input light power that determines the gain of the optical amplifier 2 and the like and the difference between the high level and the low level of the output light is the same as in the first and second inventions.

In the fifth invention whose principle is shown in FIG. 3, for example, one of the optical signals branched into two by the optical coupler forming the optical demultiplexing means 6 is delayed until there is no correlation with each other. , Which is used as local light in homodyne detection. This eliminates the need to prepare a new light source as the local light, and the homodyne detection using the DBOR 9 makes it possible to measure the noise characteristics without being affected by the relative intensity noise of the signal light and the local light. Further, since the output of the optical amplifier 2 is branched and received by a plurality of light receivers, the input light power to the light receivers can be reduced without lowering the quantum efficiency.

In the sixth invention whose principle is shown in FIG. 4, the frequency of either one of the two signal lights branched by the optical coupler forming the optical demultiplexing means 6 is shifted, and as a result, Is used as local light. Further, either one of the signal lights is delayed until the two signal lights are no longer in phase with each other, as in the fifth aspect of the invention, and the output of the optical coupler forming the optical multiplexing means 11 is input to the DBOR 9 to perform heterodyne detection. By doing so, it becomes possible to measure the noise characteristic that is not affected by the relative intensity noise and reduce the input light power to the photodetector as in the fifth aspect of the invention.

In the seventh invention whose principle is shown in FIG. 5, for either one of the two signal lights outputted by the optical demultiplexing means 6, the wavelength of the signal light is further blocked and the spontaneous emission light is eliminated. An optical bandpass filter as a light transmitting means 12 for transmitting light is inserted, and two lights that have been delayed, frequency-shifted, and acted as a signal light wavelength blocker are combined by an optical coupler forming the optical combining means 13. The result is input to the DBOR 9 and the heterodyne detection is performed to measure the noise characteristic. In this measurement, the frequency shift amount and the center wavelength of the optical filter are set so that the frequency of the signal light subjected to the frequency shift (or the wavelength of the light) matches the center wavelength of the optical bandpass filter.

In FIG. 6 showing the principle of the eighth invention,
Of the output of the optical amplifier 2, the wavelength of the input signal light is blocked by the light transmitting means 12, the transmitted spontaneous emission light is combined with the separately prepared local light 14, and the combined output is DBO.
It is input to R9 and the noise characteristics can be measured. Also, since the signal light of the measured light is blocked, the power of the light input to the light receiver can be reduced.

In the ninth invention whose principle is shown in FIG. 7, the wavelength of the input signal light is blocked by the optical bandpass filter constituting the light transmitting means 12, and, for example, a natural wavelength having a wavelength near the signal light wavelength is blocked. By inputting the emitted light into the optical power meter, the noise power is measured as the spontaneous emission light power per unit frequency. In this method, n _sp at a desired input signal light level can be determined from the spontaneous emission light power. Note that G is assumed to be obtained in advance from the conventional method.

As described above, according to the present invention, without being affected by the relative intensity noise of the signal light or the local light,
It is possible to measure the noise characteristic of the optical amplifier.

[0041]

FIG. 8 shows an embodiment of the first invention. FIG. 3A is a configuration block diagram of the embodiment, in which the modulator 22 is applied to the signal light output from the signal light source 21.
Is modulated by. The modulation speed of this modulation will be described with reference to FIGS.

FIG. 9 shows the gain and noise figure (NF) characteristics of an erbium (Er) -doped fiber optical amplifier,
FIG. 10 shows an example of the actual measurement. In the first and second inventions, the case where an erbium-doped fiber is mainly used as an optical amplifier together with a pumping light source will be described.
Since the population inversion distribution of the r-doped fiber is as slow as several tens of msec, the gain G and the spontaneous emission coefficient n _sp of the Er-doped fiber optical amplifier are such that the change (modulation speed) of the optical signal is several MH.
When it becomes z or more, the change cannot be followed, and it is determined by the average value P _ave of the optical power. In the present embodiment, the noise figure NF in FIG. 9B and FIG.
The purpose is to measure the noise figure at the average value P _B of the optical power that is the minimum, that is, the beat noise limit, but conventionally, when the power of the output signal light becomes large, the relative intensity noise as the inherent noise of the signal light source. Became large, and it was difficult to measure the noise of the optical amplifier itself.

Therefore, the input signal light is changed as shown in FIG.
To adjust, that is, the value of low level power is shown in FIG. 9 (b).
P shown in_BAnd the average value of the input optical power
To Pave. The modulation speed is high level and
And the low-level time should be 0.1 μs, respectively.
By setting the repetition frequency to 5MHz, Er-doped
Gain G of fiber amplifier and spontaneous emission coefficient n
_spIs the average value P of the optical power _aveAs determined by
To

In FIG. 8, the output light of the signal light source 21 modulated as described above is amplified by the optical amplifier 23 and input to the optical shutter 25 via the optical bandpass filter (BPF) 24. The optical shutter 25 is the modulator 22.
With the control of the RF spectrum analyzer 26, the shutter is opened only when the output of the optical amplifier 23 is at a low level.
Only low-level light is input to.

FIG. 8B shows the relationship between signal power and frequency. For example, when 1/2 of one cycle τ is a low-level time width, the signal power becomes 0 when 2 / τ, 4 / τ, 6 / τ, ... For example, S _ig. It becomes possible to perform noise measurement without influence of relative intensity noise even though the optical power average value P _ave is large, and the measurement is always performed at the beat noise limit regardless of the input optical power. Be seen.

The beat noise limit corresponds to the case where the logarithm of the noise figure explained in the equation (9) is only the first term “2n _sp ”, and noise measurement is performed at the beat noise limit. This facilitates the measurement of the spontaneous emission light coefficient n _sp , and also improves the accuracy.

The optical BPF 24 shown in FIG. 8A removes the spontaneous emission light component contained in the output of the optical amplifier 23 to facilitate or enable noise measurement at the beat noise limit. The operation will be described with reference to FIGS.

FIG. 12 is an explanatory diagram of input / output of the optical amplifier according to the first invention. The figure (a) shows an input, the input has P _ave as an average value thereof, and the wavelength of the input signal light is, for example, the wavelength of the laser light.

On the other hand, the output is the spontaneous emission light (AS) having a wide range of wavelengths as shown by the broken line in FIG.
E) is included, and by inputting this output to the optical BPF 24, it becomes possible to suppress the spontaneous emission light component only within the band width Δf of the filter without affecting the signal light component.

FIG. 13 shows spontaneous emission light (A
It is a figure which shows the influence of (SE) component. As shown in the figure, if the ASE passing through the filter is large, the beat noise limit cannot be achieved. In this case, therefore, it is necessary to remove the ASE component by the optical BPF 24 and input the signal light to the optical shutter 25.

A block diagram of the embodiment of the second invention is shown in FIG.
Similar to (a), the optical shutter 25 receives only high level light by the PIN-PD and outputs it to the RF spectrum analyzer 26, contrary to the first invention. That is, in the second invention, when the input light power is small, the high level value of FIG. 11 is set to P _B, and only the high level light is received, whereby the measurement at the beat noise limit is performed.

Regarding the third and fourth embodiments of the invention, in FIG. 8 showing the embodiment of the first invention, an optical receiver for converting an optical signal into an electric signal is provided at a stage subsequent to the optical bandpass filter 24. Is inserted, the optical shutter 25 is an electric switch,
Alternatively, it is replaced by a gate circuit, and is described by FIGS. 8 to 13 except that the output of the electric switch or the gate circuit is measured by a noise power measuring device, for example, an RF spectrum analyzer.

In the third and fourth inventions, unlike the first and second inventions, an electric switch or a gate circuit is used instead of the light blocking means 4, for example, an optical switch, but the advantages in this case Compared with the drawbacks, the electric switch has the advantage that it can operate at a higher speed than the optical switch and the signal loss in the switch part is small, and the disadvantage is that both high and low level light is the optical receiver of FIG. There is a limitation that the value of the'H 'level of the output of the optical amplifier 2 must be set below the allowable maximum input optical power of the optical receiver 18 in order to be received by the optical amplifier 18. However, this comparison is based on current technology and the third and fourth inventions can also be considered as different alternatives to the first and second inventions.

As described above, the first and second inventions are mainly intended to use the Er-doped optical fiber amplifier as the optical amplifier. This is because the population inversion life of the semiconductor optical amplifier is several nanoseconds, which is 1 compared with the case of Er-doped optical fiber.
⁶ times faster than the modulation speed of the modulator 22 of FIG.
This is because it must be sufficiently faster than the reciprocal frequency of ec, that is, several tens of GHz or more. On the other hand, the third to ninth inventions whose embodiments will be described later are applicable to both the optical fiber amplifier and the semiconductor optical amplifier.

FIG. 14 is a block diagram showing the configuration of the fifth embodiment of the invention. In the figure, the light from the signal light source 21 is amplified by the optical amplifier 23, and branched into two by the coupler 28. One of the two branched lights is output to the coupler 31 via the delay loop 29 and the polarization controller 30, and the other light is directly output to the coupler 31.
The two lights are combined into a dual balanced optical receiver (DB
OR) 32.

The delay loop 29 delays one of the two lights output from the coupler 28 until they are uncorrelated with each other. This allows delay loop 2
The light output from 9 is used as local light, and optical homodyne detection is performed. The DBOR 32 corresponds to a differential amplifier in an electric system, and by using the same, the in-phase component of the light input to the two photodiodes is suppressed, so that the relative intensity noise of the signal light and the local light is suppressed. Will be.

The polarization controller 30 in FIG. 14 is for adjusting the polarization state of the output light of the delay loop 29 used as the local light and the polarization state of the light under measurement, and by using this, the measurement under test can be performed efficiently. The light can be detected. Further, this polarization controller is not necessary for an optical fiber amplifier that does not have polarization dependence on the emitted spontaneous emission light, but is necessary for an optical semiconductor amplifier that has polarization dependence.

FIG. 15 is a block diagram showing the configuration of the sixth embodiment of the invention. Comparing this figure with FIG. 14 showing the embodiment of the fifth invention, it is different in that a frequency shifter 33 is inserted between the delay loop 29 and the polarization controller 30. The frequency shifter 33 shifts one frequency of the light split into two by the optical coupler 28.
For example, an A / O modulator capable of changing the traveling direction of light by diffraction based on an acousto-optic effect and performing a frequency shift that is an integral multiple of the frequency of a sound wave is used. Due to this, the local light becomes different from the frequency of the input signal light,
Optical detection will be performed by the heterodyne detection method. Although the frequency shifter 33 is inserted for the light on the same side as the delay loop 29, the frequency shifter 33 is inserted for the other optical path, that is, between the couplers 28 and 31 so that it acts on the other light. It is also possible to insert into.

FIG. 16A is a block diagram showing the configuration of the seventh embodiment of the invention. Comparing this figure with FIG. 15 showing the embodiment of the sixth invention, of the optical signals split into two by the optical coupler 28, the optical bandpass filter is applied to the optical signal directly output to the coupler 31. The difference is that (BPF, center wavelength λ _c ) 35 is inserted. As shown in FIG. 16B, this optical bandpass filter suppresses signal light (wavelength λ _sig ) and transmits only spontaneous emission light. The spontaneous emission light and the frequency shifter 33 are used.
Local light whose frequency is shifted by, and DBOR
32 measures the noise power. Therefore,
The wavelength of local light and λ _c are set to match. Since the output light of the optical bandpass filter 35 does not include the signal light, it is possible to reduce the input light power to the light receiver. In FIG. 16, of the two lights branched by the coupler 28, the optical hand-pass filter 35 is provided on one side and the delay loop 29 and the frequency shifter 33 on the other side.
However, it is sufficient that all of them are applied to only one of the two lights branched by the optical coupler 28, and the insertion position is not limited to this embodiment, and for example, the delay loop 29 Can be inserted in the front stage of the optical BPF 35.

FIG. 17 is a block diagram showing the structure of the embodiment of the eighth invention. In the figure, a light BPF 35 that blocks the frequency of the signal light and transmits only spontaneous emission light is connected to the output side of the optical amplifier 23, and a local light source 36 that is completely different from the signal light source is used, and its wavelength λ _Local and optical BP
The noise power is measured by setting the center wavelength λ _{c of} F35 equal. The output of the DBOR 32 is input to the RF spectrum analyzer 37.

FIG. 18 is a block diagram showing the configuration of the embodiment of the ninth invention. In the figure, the light B for suppressing the signal light from the output light of the optical amplifier 23 is output to the output side of the optical amplifier 23.
An optical BPF is provided by the power meter 38 provided with the PF 35.
The power of the spontaneous emission light output by is measured. Then, using the measured spontaneous emission power P _ASE , for example,
The spontaneous emission light coefficient n _sp of the Er-doped fiber optical amplifier is obtained by the following equation.

2n _sp = P _ASE / [ηhν (G-1) Δf] (10) If the gain G and the bandwidth Δf of the optical bandpass filter 35 are known from the above equation, spontaneous emission The light coefficient can be measured. Note that η is a coupling loss from the output end of the optical amplifier 23 to the optical power meter 38.

FIG. 19 is a configuration block diagram of an embodiment in which the output of the optical amplifier is branched into 2n lines in the fifth invention whose embodiment is shown in FIG. In the figure, the coupler 2
The output of the optical amplifier 23 branched into two by 8 is further branched into two by the coupler 41, and each two outputs of the coupler 41 are subjected to the same operation as in FIG. Are combined by
Received by the DBOR 42 each including an amplifier,
The outputs are added by the adder 43 and output as noise power.

FIG. 20 is a configuration block diagram of an embodiment in which the output of the optical amplifier is branched into 2n lines in the sixth invention whose embodiment is shown in FIG. In FIG.
Similarly, the output of the coupler 28 is branched into two by the coupler 41, and the two outputs are combined by the coupler 31 after receiving the same action as in FIG. 15, received by the DBOR 42, and added. Bowl 43
Are added and output as noise power.

FIG. 21 shows the seventh embodiment shown in FIG.
FIG. 4 is a configuration block diagram of an embodiment in which the output of the optical amplifier is branched into 2n lines in the invention of FIG. Comparing FIG. 20 with FIG. 20, the optical BPF 35 is inserted into the signal light directly input to the coupler 31 among the optical signals branched into two by the coupler 41, as in FIG. The point is different.

In FIG. 21, the signal light is split into two by using the coupler 41, and the delay loop 29
Instead of using the frequency shifter 33 to create the local oscillation light, as in the embodiment of the eighth invention shown in FIG. 17, using the local oscillation light which is completely different from the signal light, the homodyne detection or the heterodyne detection method is used. Embodiments in which power is measured are also conceivable.

[0067]

As described above in detail, according to the present invention, it is possible to measure the noise characteristic of the optical amplifier without being affected by the relative intensity noise as the inherent noise of the signal light or the local light. Become. Further, it becomes possible to easily measure the noise characteristics accurately at a high signal light level of +10 dBm or more without preparing a signal light source with a low relative intensity noise. Moreover, the input signal light power is small and the conventional method uses ASE-ASE. Even if the beat noise power cannot be ignored,
By this measuring method, n _sp can be easily measured, and a great contribution can be expected to an optical communication system using an optical amplifier.

[Brief description of drawings]

FIG. 1 is a principle block diagram of first and second inventions.

FIG. 2 is a principle block diagram of third and fourth inventions.

FIG. 3 is a principle block diagram of a fifth invention.

FIG. 4 is a principle block diagram of a sixth invention.

FIG. 5 is a principle block diagram of a seventh invention.

FIG. 6 is a principle block diagram of an eighth invention.

FIG. 7 is a principle block diagram of a ninth invention.

FIG. 8 is a diagram illustrating an embodiment of the first invention.

FIG. 9 is a diagram showing gain and noise figure characteristics of an Er-doped fiber optical amplifier.

FIG. 10 is a diagram showing an example of measurement results of gain and noise figure characteristics of an Er-doped fiber optical amplifier.

FIG. 11 is a diagram showing an example of a modulation pattern of signal light.

FIG. 12 is a diagram illustrating input / output of the optical amplifier according to the first invention.

FIG. 13 is a diagram illustrating the influence of a spontaneous emission component on the noise figure.

FIG. 14 is a block diagram showing a configuration of an example of the fifth invention.

FIG. 15 is a block diagram showing a configuration of an example of the sixth invention.

FIG. 16 is a diagram illustrating an embodiment of the seventh invention.

FIG. 17 is a block diagram showing a configuration of an eighth embodiment of the invention.

FIG. 18 is a block diagram showing a configuration of an exemplary embodiment of the ninth invention.

FIG. 19 is a block diagram showing the configuration of an embodiment in which the output of the optical amplifier is branched into 2n lines in the fifth invention.

FIG. 20 is a block diagram showing a configuration of an embodiment in which an output of an optical amplifier is branched into 2n lines in a sixth invention.

FIG. 21 is a block diagram showing the configuration of an embodiment in which the output of the optical amplifier is branched into 2n lines in the seventh invention.

[Explanation of symbols]

1, 21 Signal light source 2, 23 Optical amplifier 3 Modulating means 4 Optical blocking means 6 Optical demultiplexing means 7 Optical delaying means 8, 11, 13 Optical multiplexing means 9 Dual balance type optical receiver (DBO)
R) 10 frequency shifting means 12 light transmitting means 14 local light 15 optical combining means 16 optical / electrical converter 17 noise power measuring instrument 18 optical receiver 19 electrical signal blocking means 22 modulator 24 optical bandpass filter 25 optical shutter

Claims (20)

[Claims] 1. A noise characteristic measuring method of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein the input signal light has a gain of the optical amplifier (2) and a spontaneous emission coefficient. Is a modulation means (3) for performing pulse modulation at a modulation speed within a range determined by the average power of the modulated signal light, and an amplified output of the modulated signal light by the optical amplifier (2) by the control of the modulation means (3). And a light blocking means (4) for blocking the modulated signal light when it is in the “H” state and transmitting it when it is in the “L” state, and receives the light when the input signal light is in the “L” state. A method for measuring the noise characteristic of an optical amplifier, which is characterized in that the noise power is measured. 2. The modulation means (3) changes the difference between the values of the “H” level and the “L” level of the modulated signal light or the duty to change the input signal light to the optical amplifier (2). 2. The noise characteristic measuring method for an optical amplifier according to claim 1, wherein the average power is changed to measure the noise power. 3. After the optical amplifier (2), further comprising:
An optical hand-pass filter for transmitting the modulated signal light component of the output light of the optical amplifier (2), blocking spontaneous emission light and inputting it to the light blocking means (4) is provided. A method for measuring noise characteristics of an optical amplifier according to claim 1. 4. A noise characteristic measuring method of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein the input signal light has a gain of the optical amplifier (2) and a spontaneous emission coefficient. Is a modulation means (3) for performing pulse modulation at a modulation speed within a range determined by the average power of the modulated signal light, and an amplified output of the modulated signal light by the optical amplifier (2) by the control of the modulation means (3). And a light blocking means (4) for blocking the modulated signal light when it is in the “L” state and transmitting it when it is in the “H” state, and receives the light when the input signal light is in the “H” state. A method for measuring the noise characteristic of an optical amplifier, which is characterized in that the noise power is measured. 5. The average power of the input signal light to the optical amplifier (2), wherein the modulating means (3) changes the difference or duty between the'H 'level and the'L' level of the modulated signal light. The noise characteristic measuring method for an optical amplifier according to claim 4, wherein the noise power is measured by changing 6. The optical amplifier (2) after the optical fiber, further comprising:
An optical hand-pass filter for transmitting the modulated signal light component of the output light of the optical amplifier (2), blocking spontaneous emission light and inputting it to the light blocking means (4) is provided. A method of measuring noise characteristics of an optical amplifier according to claim 4. 7. A noise characteristic measuring method of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein the input signal light has a gain and a spontaneous emission coefficient of the optical amplifier (2). A modulation means (3) for performing pulse modulation at a modulation speed within a range determined by the average power of modulated signal light, and an optical signal output from the optical amplifier (2) are received, and the optical signal is converted into an electrical signal. The optical signal output from the optical receiver (18) is cut off when the modulated signal light is in the “H” state by the control of the optical receiver (18) that operates and the modulating means (3). It is characterized in that it is provided with an electric signal cutoff means (19) for outputting as it is in the state of "L", and measures the noise power using the electric signal obtained by converting the light when the input signal light is in the state of "L". Noise characteristics measurement method for optical amplifiers. 8. The modulation means (3) changes the difference between the values of the “H” level and the “L” level of the modulated signal light or the duty to change the input signal light to the optical amplifier (2). The noise characteristic measuring method for an optical amplifier according to claim 7, wherein the average power is changed to measure the noise power. 9. The optical amplifier (2) is provided at a subsequent stage, further comprising:
The modulated signal light component of the output light of the optical amplifier (2) is transmitted, spontaneous emission light is blocked, and the optical receiver (1
8. An optical amplifier noise characteristic measuring method according to claim 7, further comprising an optical hand-pass filter to be inputted to 8). 10. A noise specific measurement method for an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein the input signal light has a gain of the optical amplifier (2) and a spontaneous emission coefficient. And a modulation means (3) for performing pulse modulation at a modulation speed within a range determined by the average power of the modulated signal light, and an optical signal output from the optical amplifier (2) is received to convert the optical signal into an electrical signal. By controlling the optical receiver (18) for conversion and the modulating means (3), the electric signal output from the optical receiver (18) is blocked when the modulated signal light is in the “L” state. An electric signal blocking means (19) for outputting the signal as it is in the H state is provided, and the noise power is measured by using an electric signal obtained by converting the light when the input signal light is in the H state. Measuring method for noise characteristics of optical amplifiers. 11. The modulation means (3) changes the difference between the values of the “H” level and the “L” level of the modulated signal light or the duty to change the input signal light to the optical amplifier (2). 11. The noise characteristic measuring method for an optical amplifier according to claim 10, wherein the average power is changed to measure the noise power. 12. The optical receiver (2) is further provided downstream of the optical amplifier (2) to transmit the modulated signal light component of the output light of the optical amplifier (2) and block spontaneous emission light. The method for measuring noise characteristics of an optical amplifier according to claim 10, further comprising an optical hand-pass filter for inputting to (18). 13. A method of measuring a noise characteristic of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein an optical demultiplexing means (6) for branching an output of the optical amplifier (2) into two. ) And an optical delay means (7) for delaying one of the lights output from the optical demultiplexing means (6) until the other of the outputs becomes uncorrelated with each other, and the optical delay means (7). The optical multiplexing means (8) is provided with an output and an optical multiplexing means (8) for multiplexing the output of the optical demultiplexing means (6) that is not input to the optical delay means (7). Output is a dual-balanced optical receiver (DBO
R) A method for measuring the noise characteristic of an optical amplifier, characterized by receiving the noise power by (9) and measuring the noise power. 14. The optical demultiplexing means (6) branches the output of the optical amplifier (2) into an even number (2n), and outputs the even number (2n), and outputs the 2n output of the optical demultiplexing means (6). N optical delay means (7) for delaying one of the n sets of light, each of which is two sets, until they are uncorrelated with the other of the outputs of each set; And n optical multiplexing means (8) for multiplexing the output of the means (7) and the light that is not input to the respective optical delay means (7) of the respective sets of light, 14. The output of the optical multiplexing means (8) is measured by n dual-balanced optical receivers (DBOR) (9), and the noise power is measured by adding the measurement results.
A method for measuring the noise characteristics of the optical amplifier described. 15. A method for measuring a noise characteristic of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), and an optical branching means (6) for branching an output of the optical amplifier (2) into two. And an optical delay means (7) for delaying one of the lights output from the optical demultiplexing means (6) until the other of the outputs is uncorrelated with each other, and the optical demultiplexing means (6) Frequency shift means (10) for shifting the frequency of either one of the output lights, the optical delay means (7) for the two outputs of the optical demultiplexing means (6), and the frequency shift means (10). And an optical combining means (11) for combining two lights as a result of the action of (1), the output of the optical combining means (11) is received by a dual balance type optical receiver (DBOR) (9), and noise is generated. Noise characteristics measurement of optical amplifier characterized by measuring power Method. 16. The optical demultiplexing means (6) branches the output of the optical amplifier (2) into an even number (2n), and outputs the even number (2n), and outputs the 2n output of the optical demultiplexing means (6). N optical delay means (7) for delaying each one of the n sets of light as two of them, respectively, until they are uncorrelated with the other output of each set, and N number of the frequency shift means (10) for shifting the frequency of any one of the lights, the respective optical delay means (7) for the n sets of outputs of the optical demultiplexing means (6), and the respective frequencies And n optical combining means (11) for combining two light beams of n sets respectively as a result of the action of the shift means (10), and outputs of the n optical combining means (11) respectively. Measure with n dual-balanced optical receivers (DBOR) (9) and add the measurement results 2. The noise power is measured.
5. The method for measuring the noise characteristic of the optical amplifier according to 5. 17. A noise characteristic measuring method for an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein an optical demultiplexing means (6) for branching an output of the optical amplifier (2) into two. ), And an optical delaying means (7) for delaying one of the lights output from the optical demultiplexing means (6) until it is uncorrelated with the other of the outputs, and the optical demultiplexing means (6). Frequency shift means (10) for shifting the frequency of any one of the lights output from the signal light, and the signal light as a component of one of the lights output from the optical demultiplexing means (6) Light transmission means (12) for blocking the wavelength of light and transmitting spontaneous emission light, the optical delay means (7) for the two outputs of the optical demultiplexing means (6), the frequency shift means (10), and the light. Optical combining means (for combining two lights as a result of the action of the transmitting means (12) ( 3) and provided with, light multiplexing means (13) dual balanced optical receiver the output (DBOR) (9) noise characteristic measurement method of an optical amplifier, characterized in that receiving and measuring the noise power by. 18. The optical demultiplexing means (6) branches the output of the optical amplifier (2) into an even number (2n) and outputs the 2n output of the optical demultiplexing means (6). N optical delay means (7) for delaying one of the n sets of light, each of which is two sets, until the other of the outputs of the set is uncorrelated with each other; N frequency shift means (10) for shifting the frequency of any one of the lights, and blocking the wavelength of the signal light as a component of any one of the lights of each set. N said light transmitting means (12) for transmitting spontaneous emission light, said respective optical delay means (7) for said n sets of outputs of said optical demultiplexing means (6), each frequency shift means (10), and Each of the n sets of 2 as a result of the action of each light transmitting means (12)
And n optical multiplexing means (13) for multiplexing two lights, and outputs of the n optical multiplexing means (13) are respectively output by n dual-balanced optical receivers (DBOR) (9). 18. The method for measuring the noise characteristic of an optical amplifier according to claim 17, wherein the noise power is measured by measuring and adding the measurement results. 19. In a noise characteristic measuring method of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), a wavelength of the signal light included in an output light of the optical amplifier (2) is blocked. A light transmitting means (12) for transmitting spontaneous emission light, a local light (14) as a light source different from the signal light source, and an optical combination for multiplexing the output of the light transmitting means (12) and the local light (14). An optical multiplexing means (1)
5) Output of dual balance type optical receiver (DBOR)
A method for measuring the noise characteristic of an optical amplifier, characterized in that the noise power is measured according to (9). 20. A noise characteristic measuring method of an optical amplifier (2) for amplifying an input signal light from a signal light source (1), wherein a wavelength of the signal light is blocked in an output of the optical amplifier (2). A noise characteristic measurement of an optical amplifier, comprising: a light transmission means (12) for transmitting spontaneous emission light, and measuring the noise power as the spontaneous emission light power per unit frequency by the output of the light transmission means (12). method.