JPH08146473A - Optical signal processor - Google Patents

Abstract

PURPOSE: To provide an optical signal processor using a nonlinear loop mirror to enable ultra-high speed switching without increasing a pulse width. CONSTITUTION: This optical signal processor is composed of a 3dB coupler 1 having a coupling rate of 1:1 and an optical fiber loop (nonlinear loop) 7 consisting of a zero dispersion dispersion flat optical fiber connected to both output terminals 1c, 1d of the 3dB coupler 1. The one phase of the signal light 4 branched by the 3dB coupler 1 is changed by the nonlinear optical effect of the control light 5 entering via a wavelength multiplex coupler 2 and is propagated through the nonlinear loop 7 in directions opposite to each other and is then recoupled by the 3dB coupler 1. The signal light 4 is thus switched by the presence or absence of the control light 5 and is emitted from the terminal 1b. As a result, the ultra-high speed light signal processing is made possible and the ultra-high speed optical signal processor and more particularly optical DEMUX device are inexpensively provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to signal processing of optical signals, and more particularly to an optical signal processing device capable of performing ultra-high-speed time demultiplexing of optical communication signals.

[0002]

2. Description of the Related Art In recent years, with the demand for a large amount of information,
The transmission speed of optical communication is steadily increasing due to the wide band property of optical fibers. For example, 100 Gbit /
It is not difficult to transmit an ultrahigh-speed optical signal exceeding s in an optical fiber. Further, the speed of the optical modulator, the photodetector, and the relay device, which are the sending and receiving of the optical communication path, has been remarkably increased, but at present, the operating speed of these electric circuits is about 10 to 20 Gbit / s and transmission is possible. There is a difference between the optical signal and the operating speed of the electrical circuit.

Further, in order to receive an ultrahigh-speed optical communication signal with an existing electric circuit, a so-called optical separation technique in which the optical signal is separated as it is into a relatively low-speed optical signal in the receiving section is indispensable. Becomes

As a high-speed optical separation technique, an optical separation technique (also called an optical DEMUX) using a nonlinear loop mirror utilizing a nonlinear optical effect in a fiber has been reported.

Further, this technique can be used for high-speed optical signal processing such as optical sampling, optical switch, optical operation, optical branching and the like.

Here, the conventional optical separation technique using a non-linear loop mirror will be briefly described. Figure 6
FIG. 3 is a configuration diagram showing an optical signal processing device using a conventional nonlinear loop mirror. In the figure, 1 is 3 with a coupling ratio of 1: 1.
dB coupler (also called a directional coupler), 2 is a wavelength multiplexing coupler, 3 is a non-linear loop (optical fiber loop), 4
Is high-speed signal light (hereinafter referred to as signal light), 5 is control light,
Reference numeral 6 denotes an optical filter, and the 3 dB coupler 1 and the non-linear loop 3 constitute a non-linear loop mirror.

Here, the 3 dB coupler 1 converts the signal light 4 into 5
It is separated into 0:50, and the wavelength multiplexing coupler 2 is a 3 dB coupler 1.
One of the signal light and the control light 5 separated by is multiplexed.

When the control light 5 is not input, the signal light 4 incident from the terminal 1a of the 3 dB coupler 1 is the 3 dB coupler 1
Are propagated counterclockwise and clockwise through the non-linear loop (optical fiber loop) 3 which is divided into the terminals 1c and 1d, and both are incident on the 3 dB coupler 1 again at the same time. At this time, the 3 dB coupler 1 outputs the signal light only to the terminal 1 a and does not output it to the terminal 1 b due to the interference of the signal lights propagating counterclockwise and clockwise in the nonlinear loop (optical fiber loop) 3. That is, when viewed from the input side of the signal light 4, the signal light 4 is reflected by the non-linear loop mirror including the 3 dB coupler 1 and the non-linear loop 3. This is the reason why it is called a loop mirror.

When a strong pulsed control light 5 is input, the portion of the signal light 4 propagating counterclockwise from the terminal 1c of the 3 dB coupler, which overlaps the control light 5, is propagating through the optical fiber loop 3. In addition, the phase change proportional to the intensity of the control light 5 occurs due to the mutual phase modulation effect which is one of the nonlinear optical effects.

Since the non-linear optical effect is used, this optical fiber loop 3 is called a non-linear loop. Then, when the light enters the 3 dB coupler 1 again, only the portion where the phase change occurs is output to the terminal 1 b due to the interference in the 3 dB coupler 1. That is, only the portion of the signal light 4 overlapping the control light 5 can be separated into the terminal 1b. The optical filter 6 is an optical wavelength filter for removing the control light 5 from the signal light output from the terminal 1b of the 3 dB coupler 1 and transmitting and extracting only the separated signal light portion.

In order to perform ultra-high-speed light separation, the optical switch speed is limited by the control light pulse width, so a thin (narrow) pulse is required as the control light 5.

Further, in order to perform an ultrahigh-speed optical switch, the difference in the propagation speed between the control light 5 and the signal light 4 (referred to as walk-off) must be small. Because,
This is because if the overlapping portion of the control light 5 and the signal light 4 is displaced during propagation, the gate width of the switch will be widened accordingly.

Therefore, a dispersion-shifted fiber having a delay time characteristic as shown in FIG. 7 has been used as the non-linear loop 3. In FIG. 7, the horizontal axis represents the wavelength of light, and the vertical axis represents the delay time and group velocity dispersion of light in the nonlinear loop 3.

That is, the delay time of the signal light 4 and the control light 5 are used by using the dispersion shift fiber in which the zero-dispersion wavelength of the dispersion shift fiber is set between the signal light 4 and the control light 5.
To make the delay times of the two equal.

As a result, the control light 5 and the signal light 4 do not shift during the propagation, so that the light can be separated at a speed determined by the pulse width of the control light 5. Here, the group velocity dispersion shown in FIG. 7 is the group velocity (proportional to the reciprocal of the delay time).
Of the pulse width, and represents the degree of spread of the pulse at that wavelength.

[0016]

However, in the method of using the dispersion-shifted fiber in which the zero-dispersion wavelength is set in the middle of the signal light 4 and the control light 5 as the nonlinear loop 3 as described above, the group velocity is Since the dispersion value has a slope of about 0.065 ps / km / nm ² ,
The group velocity dispersion values at the wavelengths of the signal light 4 and the control light 5 do not become zero. For this reason, the pulse of the signal light 4 or the control light 5 spreads during propagation through the nonlinear loop 3, and there is a drawback that a switch as fast as the incident pulse width cannot be realized.

On the other hand, in the region where the group velocity dispersion is negative, it is possible to prevent or narrow the pulse width by the self-phase modulation effect, but in the region where the group velocity dispersion is positive, the pulse width is widened. In the conventional method in which either the signal light 4 or the control light 5 is always the positive group velocity dispersion region,
We have not been able to realize an ultra-high-speed switch that does not widen the incident pulse width.

When a Gaussian pulse having an incident pulse width t _in is incident on a nonlinear loop having a length L, the pulse width t _out after leaving the nonlinear loop 3 is expressed by the following equation (1) t _out = [t _in ² + {(2ln2 / π) (1 / t _in ) (λ ² / c) DL} ² ] ^1/2 ... (1) Here, λ is the wavelength, c is the speed of light, and D is the group velocity dispersion.

When the signal light wavelength is 1.552 μm and the control light wavelength is 1.532 μm, the zero-dispersion wavelength of the dispersion shift fiber used as the nonlinear loop 3 is 1.542 μm in order to equalize the delay times. The group velocity dispersion at the control light wavelength is about 0.65 ps / km / nm. As a numerical example, the incident pulse width is 500 fs (1 fs
= 10 ⁻¹⁵ seconds) and L = 100 m, the pulse width t _out after leaving the non-linear loop 3 expands to 818 fs.

In the above simple estimation, the nonlinear loop 3
It does not take into account the broadening of the pulse spectrum due to the nonlinearity within. Taking this into consideration, the pulse width t _out after leaving the nonlinear loop 3 is 1 which is twice the incident pulse width.
It spreads to about ps (1 ps = 10 ⁻¹² seconds).

In view of the above problems, it is an object of the present invention to provide an optical signal processing device using a non-linear loop mirror in which the pulse width does not widen and an ultra-high speed switch is possible.

[0022]

To achieve the above object, the present invention comprises an optical coupler having a coupling ratio of 1: 1 and an optical fiber loop connected to both output terminals of the optical coupler. By changing one phase of the signal light branched by the optical coupler by a non-linear optical effect due to the incidence of control light, by propagating the optical fiber loop in mutually opposite directions and then recombining in the optical coupler, In a nonlinear loop mirror type optical signal processing device that switches the signal light depending on the presence or absence of the control light, an optical signal processing device is proposed in which the optical fiber loop is configured by using a zero-dispersion dispersion flat optical fiber.

[0023]

According to the present invention, when there is no control light input, for example, the signal light incident from the first terminal of the optical coupler is separately output to the third and fourth terminals of the optical coupler, Propagate counterclockwise and clockwise respectively in the optical fiber loop,
Both of them simultaneously enter the optical coupler again. At this time, the optical coupler outputs the signal light only to the first terminal but not to the second terminal due to the interference of the signal light propagating counterclockwise and clockwise in the optical fiber loop. That is, when viewed from the input side (first terminal side) of the signal light, the signal light is reflected by the nonlinear loop mirror including the optical coupler and the optical fiber loop.

On the other hand, when there is strong pulsed control light input, for example, in the portion of the signal light propagating counterclockwise from the third terminal of the optical coupler, which overlaps the control light, the optical fiber loop is provided. A phase change proportional to the intensity of the control light occurs due to the mutual phase modulation effect, which is one of the nonlinear optical effects, during propagation. Then, when the light enters the optical coupler again, only the portion where the phase change occurs is output to the second terminal due to the interference in the optical coupler. That is, only the portion of the signal light that overlaps the control light is separated and output to the second terminal.

Since the optical fiber loop is composed of a zero-dispersion dispersion flat optical fiber, the delay times of the control light and the signal light are equal (the walk-off is zero). For this reason, the super-high-speed switch can be performed without shifting the overlapping portion of the control light and the signal light during the propagation through the optical fiber loop. Furthermore, since the group velocity dispersions at the wavelength of the control light and the wavelength of the signal light are both substantially zero, the pulses of the control light and the signal light do not spread during the propagation through the optical fiber loop. Therefore, an extremely high-speed switch that is determined by the incident pulse width becomes possible.

Even if the wavelengths of the control light wavelength and the signal light wavelength are slightly deviated, since the difference in delay time and the group velocity dispersion value are almost zero over a wide wavelength range, the wavelengths of the control light wavelength and the signal light wavelength are small. A wider range of choices.

[0027]

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 showing an embodiment of the present invention.
In the figure, the same components as those in the conventional example described above are represented by the same reference numerals. Further, the difference between this embodiment and the conventional example is that a nonlinear loop 7 using a zero dispersion dispersion flat optical fiber is used instead of the nonlinear loop 3 of the conventional example. That is, 1 is a 3 dB coupler, 2 is a wavelength multiplexing coupler, 4 is high-speed signal light, 5 is control light, 6 is an optical filter, and 7 is a non-linear loop using a zero-dispersion flat optical fiber. Here, the 3 dB coupler 1 and the non-linear loop 7 constitute a non-linear loop mirror. The zero-dispersion flat optical fiber is an optical fiber having the characteristics of both the zero-dispersion optical fiber and the dispersion-flat optical fiber, as is well known.

Further, the wavelength multiplexing coupler 2 is not limited to the wavelength multiplexing coupler and may be a 3 dB coupler or a 6: 4 coupler as long as it combines one of the signal light separated by the 3 dB coupler 1 and the control light 5. good.

The operating principle of this embodiment is similar to that of the ordinary nonlinear loop mirror described in the prior art, but the control light 5 is used.
The feature is that the walk-off between the signal light 4 and the signal light 4 is small, and the pulse spread of the control light 5 and the signal light 4 is small.

FIG. 2 is a diagram showing an example of delay time and group velocity dispersion characteristics of a zero-dispersion dispersion flat optical fiber used as the nonlinear loop 7, which is the most important feature of the present invention. This example has ideal characteristics as a zero-dispersion flat optical fiber.

The features of the present invention will be described with reference to FIG. In FIG. 2, the horizontal axis represents the wavelength of light and the vertical axis represents the delay time and group velocity dispersion of light in the nonlinear loop 7. In the nonlinear loop 7, the wavelength of the control light 5 and the signal light 4
Since the wavelengths of (1) and (2) have the same delay time (the walk-off is zero), the super-high-speed switch can be performed without shifting the overlapping portion of the control light 5 and the signal light 4 during propagation through the nonlinear loop 7. Furthermore, since the group velocity dispersions at the wavelength of the control light 5 and the wavelength of the signal light 4 are both zero, the pulses of the control light 5 and the signal light 4 do not spread during propagation through the nonlinear loop 7. Therefore, an extremely high-speed switch that is determined by the incident pulse width becomes possible.

Further, even if the wavelength of the control light and the wavelength of the signal light are not at the positions shown in FIG. 2 and even if they are slightly deviated, the delay time difference and the group velocity dispersion value are zero over a wide wavelength range. It also has a feature that the range of selection of the wavelength and the wavelength of the signal light is expanded.

FIG. 3 shows another example of delay time and group velocity dispersion characteristics of the zero dispersion dispersion flat optical fiber used as the nonlinear loop 7, which is the most important feature of the present invention. This example is a characteristic that is relatively easy to make as a zero-dispersion dispersion flat optical fiber and is a realistic characteristic.

The features of the present invention will be described with reference to FIG. In FIG. 3, the horizontal axis represents the wavelength of light, and the vertical axis represents the delay time and group velocity dispersion of light in the nonlinear loop 7. In the non-linear loop 7, the wavelengths of the control light 5 and the signal light 4 have the same delay time (the walk-off is zero). Further, the group velocity dispersion at the wavelength of the control light 5 and the wavelength of the signal light 4 is much smaller than that of the conventional example shown in FIG. 7 which uses a dispersion shift fiber. The spread of the pulse becomes very small, and a very short pulse propagates with its pulse width. For this reason, a very high-speed switch determined by the incident pulse width becomes possible.

The pulse width t of the output is calculated by using the above-mentioned numerical values.
Estimating _out is as follows. That is, the wavelength of the signal light 4 is 1.552 μm, and the wavelength of the control light 5 is 1.532.
.mu.m, the group velocity dispersion at the wavelength of the control light 5 is about 0.059 ps / km / nm, and the group velocity dispersion at the wavelength of the control light 5 is 1/10 or less as compared with the case where the dispersion shift fiber is used. Become.

As a numerical example, the incident pulse width is 50
If 0 fs (1 fs = 10 ⁻¹⁵ seconds) and the length L of the non-linear loop 7 is 100 m, the pulse width of the output can be estimated to be 502 fs, and the non-linear loop 7 uses a zero-dispersion flat optical fiber. The spread of the pulse due to the mirror is so small that it can be ignored, and the incident pulse width t
it can be seen that the propagation remain _in.

Further, since the gradient of the group velocity dispersion is very small, the control light wavelength and the signal light wavelength are not located exactly as shown in FIG. 3, and even if they are slightly deviated, the difference in delay time and the group velocity dispersion. Since the value is very small, it has a feature that the range of selection of the control light wavelength and the signal light wavelength is widened.

In other words, in the case where the control light wavelength and the signal light wavelength have a certain fixed wavelength, if a slight pulse spread and a slight walk-off (these mean a decrease in the switch speed) are allowed, the zero dispersion dispersion is allowed. A relatively wide range of wavelengths can be allowed as the zero dispersion wavelength of the flat optical fiber. Therefore, the zero-dispersion flat optical fiber can be manufactured with less precision in the zero-dispersion wavelength, and the production yield of the zero-dispersion flat optical fiber used in the present invention can be improved.

Although the control light wavelength is set to the short wavelength side and the signal light wavelength is set to the long wavelength side so far, the control light wavelength is set to the long wavelength side and the signal light wavelength is set to the short wavelength side. The invention is effective.

Next, an actual experimental example is shown to demonstrate that the present invention is capable of ultra-high speed operation. FIG. 4 shows the delay time and group velocity dispersion characteristics of the zero-dispersion dispersion flat optical fiber used as the nonlinear loop 7 in the actual experiment. Here, the wavelength of the signal light 4 is set to 1.525 μm, and the wavelength of the control light 5 is set to 1.545 μm. Since zero-dispersion flat optical fiber is used, signal light 4 and control light 5
The difference in the delay time between and is 500 fs / km (a shift of 500 fs occurs when propagating 1 km), which is very small.

The length L of the nonlinear loop 7 used in the experiment is 1
Since the difference (deviation) in the delay time between the signal light 4 and the control light 5 is about 50 fs, which is extremely small, there is no decrease in the operating speed due to the deviation between the signal light 4 and the control light 5, and the speed is very high. It is possible to operate.

The group velocity dispersion at the wavelength of the signal light 4 is 0.05 ps / km / nm, and the group velocity dispersion at the wavelength of the control light 5 is -0.08 ps / km / nm. The value is about 1/10 of the value of the non-linear loop 3 using the dispersion-shifted fiber that is used, and the control light pulse and the signal light pulse of 1 ps or less hardly spread.

Therefore, the operation speed does not decrease due to the spread of the control light pulse and the signal light pulse, and the extremely high speed switching operation in the femtosecond range becomes possible. As described in the section of the conventional technique, in the optical signal processing device using the non-linear loop 3 using the conventional dispersion-shifted fiber,
Ultra-high speed operation was impossible because it spreads over 1 ps during propagation through the loop.

FIG. 5 shows the result of an experiment using the present invention. 5A shows the control light pulse, and FIG. 5B shows the switched signal light. It should be noted that this experiment is an experiment for showing the performance of the ultrahigh-speed optical signal processing device of the present invention, and continuous light is incident as the signal light instead of the high-speed signal.

The apparatus configuration in this experiment is similar to that shown in FIG. When continuous light was made incident as the signal light 4 and an optical pulse having a pulse width of 605 fs was made incident as the control light 5, a pulse of 770 fs was obtained as the switched signal light. The control light 5 has a pulse width reduced by the self-phase modulation effect while propagating through the nonlinear loop 7,
The pulse width is 40 fs, and the operation speed does not decrease due to the spread of the control light 5. Further, since the switched signal light has a pulse width similar to that of the incident control light 5, the difference in propagation speed between the control light 5 and the signal light and the spread of the signal light are small.

As described above, by operating the optical signal processing device of the present invention and using a zero-dispersion flat optical fiber as the non-linear optical fiber loop 7 by experiments,
Actually, it was shown that the pulse widths of the control light 5 and the signal light 4 did not widen and there was no difference in the propagation speed of the control light 5 and the signal light 4, and it was clarified that the operating speed did not decrease. And, according to the present invention, it is impossible to realize by the conventional technique.
It has been demonstrated that ultra-high-speed signal processing of ps or less, that is, femtosecond order is possible.

[0047]

As described above, according to the present invention, the pulse widths of the control light and the signal light are not widened, and there is no difference in the delay time between the control light and the signal light, in other words, a very high speed. It enables signal processing, especially optical DEMUX.
There is an advantage that extremely high-speed signal processing is possible, which is impossible with the conventional technology.

As a result, it becomes possible to carry out an ultrahigh-speed optical signal processing, and to provide an ultrahigh-speed optical signal processing device, particularly an optical DEMUX device, at a low cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical signal processing device using a nonlinear loop mirror according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of delay time and group velocity dispersion characteristics of a zero-dispersion flat optical fiber used as a non-linear loop, which is the most important feature in one embodiment of the present invention.

FIG. 3 is a diagram showing an example of delay time and group velocity dispersion characteristics of a zero-dispersion flat optical fiber used as a non-linear loop, which is the most important feature in one embodiment of the present invention.

FIG. 4 is a diagram showing delay time and group velocity dispersion characteristics of a zero dispersion dispersion flat optical fiber used as a nonlinear loop in an actual experiment using the present invention.

FIG. 5 is a diagram showing an experimental result using the present invention.

FIG. 6 is a configuration diagram showing an optical signal processing device using a non-linear loop mirror according to a method of a conventional example.

FIG. 7 is a diagram showing an example of delay time and group velocity dispersion characteristics of a dispersion shift fiber used as a non-linear loop in the conventional method.

[Explanation of symbols]

1 ... 3 dB coupler, 1a ... 3 dB coupler terminal, 1b ... 3
dB coupler terminal, 1c ... 3dB coupler terminal, 1d ... 3d
B coupler terminal, 2 ... Wavelength multiplex coupler, 3 ... Non-linear loop, 4 ... High-speed signal light, 5 ... Control light, 6 ... Optical filter, 7
... A non-linear loop using a zero-dispersion dispersion flat optical fiber.

Claims (1)

[Claims] 1. An optical coupler having a coupling ratio of 1: 1 and an optical fiber loop connected to both output terminals of the optical coupler, wherein one phase of a signal light branched by the optical coupler is a control light. The non-linear loop mirror type that switches the signal light depending on the presence or absence of the control light by changing the nonlinear optical effect due to the incidence of light and propagating the optical fiber loops in opposite directions and then recombining them in the optical coupler. 2. The optical signal processing device according to claim 1, wherein the optical fiber loop is configured by using a zero-dispersion dispersion flat optical fiber.