JP2848933B2 - Optical data latch method - Google Patents

Description

[Description of the Invention] [Summary] [Technical Field] [Technical Field] [Industrial Application Field] [Prior Art] Problems to be Solved by the Invention Means and Actions for Solving the Problems Embodiments Effect of the Invention Overview Regarding the optical data latch system for extracting only desired data from the optical data sequence multiplexed above, even if the phases of the optical data pulse and the optical frame pulse are relatively changed, the optical data pulse and the optical frame pulse are not changed. It is an object of the present invention to provide an optical data latch system in which the time of being superimposed and input to the optical bistable element can be made constant and the pulse width of the latched optical signal can be made constant. A first optical coupler that splits and outputs the second optical frame pulse, and adds and outputs the input optical data pulse and the first optical frame pulse; And second optical coupler, the light from the second optical coupler is input, the first in the optical data pulse
An optical bistable element that transitions from an off state to an on state when the optical frame pulse is superimposed, and the second optical frame pulse is input, and the optical bistable element passes a predetermined time after the rise of the optical frame pulse. A reset signal generating circuit for providing a stable element with a reset signal for causing the element to transition from an on state to an off state, wherein the pulse width of the optical frame pulse is T _f , and the pulse width of the optical data pulse is T _d
Then, it is configured as T _f <T _d .

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical data latch system for extracting only desired data from a data sequence of light multiplexed on a time axis using an optical bistable element.

With the development of optical communication networks, optical signal processing technology that performs signal processing between optical transmission lines and optical terminals, such as subscribers, without changing optical-to-electrical conversion means or electric-to-optical conversion means. Is considered as one measure to cope with an increase in the amount of signal processing, and various studies have been made on the method. As one of them, an optical signal sequence asynchronously input from an optical transmission line or a terminal to a transmission processing node that performs signal processing on an optical signal sequence transmitted by an optical transmission line is transmitted to an optical frame or the like in the node. There is a synchronous optical signal processing method for processing in synchronization with an optical clock or the like. In this type of synchronous optical signal processing system, an optical frame pulse generated in a node is superimposed on a desired optical data pulse in an optical data pulse train transmitted by an optical transmission line, and the superimposed light is transmitted. Is input to the optical bistable element or the like, and the processing is performed. Therefore, generally, the rising of the optical data pulse and the rising of the optical frame pulse are not completely synchronized.
Therefore, in implementing the above method, regarding the timing between the optical data pulse and the optical frame pulse, a condition that enables a stable signal processing operation without fine timing adjustment if there is an approximate timing is provided. Required to be set.

2. Description of the Related Art Conventionally, as shown in FIG. 1, a first optical coupler 1 for splitting an input optical frame pulse into first and second optical frame pulses and outputting the same, as shown in FIG. A second optical coupler 2 that adds and outputs a data pulse and the first optical frame pulse, and a light from the second optical coupler 2 is input and an optical frame pulse is superimposed on the optical data pulse. The optical bistable element 3 that transitions from the off state to the on state, and the second optical frame pulse is input, and after a lapse of a predetermined time from the rise of the optical frame pulse, the optical bistable element 3 is switched from the on state to the optical bistable element 3. An optical data latch system including a reset signal generation circuit 4 for providing a reset signal for transitioning to an off state is known. Then, the pulse width of the optical data pulse (temporal pulse width,
Regarding the relationship between _Td and the pulse width _Tf of the optical frame pulse, proposals have been made on the assumption that _Td ≦ _Tf .

FIG. 8 shows that the pulse width of the optical data pulse and the pulse width of the optical frame pulse in the conventional method are equal (T _d =
12 is a timing chart when T _f ) and the optical data pulse is completely synchronized with the optical frame pulse. In the figure, (a) is a pulse waveform of an optical data pulse given in the RZ code format, (b) is a pulse waveform of an optical frame pulse also given in the RZ code format, and (C) is an optical data pulse and an optical frame. (D) is a waveform of a reset signal given by adjusting the bias current when the optical bistable element is a bistable semiconductor laser,
(E) shows the waveform of the latched optical signal (latch optical signal). In this figure or in the following description, in other figures, T _B is the time of one time slot in the optical data pulse, _TF is the time of one time slot in the optical frame pulse, and T _d is the pulse width of the optical data pulse. , T _f is the pulse width of the optical frame pulse, T _high is the time during which the optical data pulse and the optical frame pulse are superimposed, specifically, the optical data pulse and the optical frame pulse are superimposed and the superimposed optical power is optically bistable The time during which the threshold value of the device is exceeded, T _fr is the time from the rise time of the optical frame pulse to the fall time of the reset signal (the rise time depending on the form of the reset signal), and T _M is the pulse width of the latch optical signal. (Memory time).

As shown in FIG. 8, synchronized optical data pulse and an optical frame pulse is the same, and if these pulse widths are equal, becomes _{T high = T d = T f} , T high is constant, T _high There is no fear of unstable operation of the optical bistable element due to the fluctuation of the optical bistable element.

However, since the temporal phase of an optical data pulse input from an optical transmission line fluctuates due to a change in the laying environment of the optical transmission line and the like, generally, the rising of the optical data pulse and the rising of the optical frame pulse generally occur. Are not perfectly synchronized. As an example, FIG. 9 shows a timing chart when the rising time of the optical data pulse is slightly earlier than the rising time of the optical frame pulse when T _d = T _f . In this figure or the following description and other figures, T _fd is the time from the rising time of the optical frame pulse to the rising time of the optical data pulse.
_fd indicates that the rise of the optical frame pulse is prematurely with respect to the rise of the optical data pulses in the case of a positive value, the optical frame is the rise of the optical data pulses in the case of T _fd takes a negative value This indicates that the pulse is advanced with respect to the rise of the pulse. In FIG. 9, since the rising time of the optical data pulse is earlier than the rising time of the optical frame pulse by the time | T _fd |, the following problem occurs. That is, in this case, T _high = T _d − | T _fd | = T _f − | T _fd |, and T _high is smaller than in the case of FIG.
In other words, when the pulse width of the optical data pulse is equal to the pulse width of the optical frame pulse, the optical data pulse and the optical frame pulse are superimposed when the phases of the optical data pulse and the optical frame pulse relatively change. Therefore, the time T _high input to the optical bistable element cannot be kept constant. If T _high is not constant, the energy of the optical signal input to the optical bistable device exceeding its operating threshold (the product of the power of the optical signal input above the operating threshold and T _high )
Fluctuates, and the operation of the optical bistable element becomes unstable.

In order to eliminate the instability of the operation of the optical bistable element, as shown in FIG.
_Tf is made larger than the pulse width _Td of the optical data pulse, and within a predetermined phase variation range, even if the temporal phase relationship between the optical frame pulse and the optical data pulse changes, _Thigh
It has been proposed to keep this from changing. As shown in the figure, if the pulse width T _f of the optical frame pulse is equal outlined in time T _B of one time slot in the optical data pulse, T _fd (optical data pulses to T _high is constant and light The fluctuation range allowed for the phase shift of the frame pulse) is 0 <T _fd <T _f −T _d ≒ T _B −T _d . However, in general, the reset signal is provided after a predetermined time T _{fr has} elapsed from the rise of the optical frame pulse. Therefore, if T _fd fluctuates within the above range, the pulse width of the latch optical signal, The time T _M ′ in which data is stored is T _M ′ = T _fr −T _fd <T _fr , whereas T _M = T _fr (constant) in FIG. 8 and the like. Such a change in T _M ′ depending on T _fd when the phases of the optical data pulse and the optical frame pulse relatively change is not desirable in configuring a system.

The present invention has been made in view of such a technical problem, and even when the phases of the optical data pulse and the optical frame pulse are relatively changed, the optical data pulse and the optical frame pulse are superimposed to form an optical bistable. Time T input to element
the _high constant, the pulse width of the latch optical signal, i.e., the desired data is intended to provide an optical data latch system can be kept constant time T _M is the memory (T _M ').

Means and Action for Solving the Problems FIG. 1 is a block diagram showing a device configuration for explaining the principle of the present invention.

According to the optical data latch system of the present invention, a first optical coupler 1 for splitting an input optical frame pulse into first and second optical frame pulses and outputting the same, an input optical data pulse and the first optical frame A second optical coupler 2 for adding and outputting a pulse, and an OFF state when light from the second optical coupler 2 is input and the first optical frame pulse is superimposed on the optical data pulse. Optical bistable element 3 that changes from the ON state to the ON state, and the second optical frame pulse is input, and after a lapse of a predetermined time from the rise of the optical frame pulse, the optical bistable element 3 switches the element 3 from the ON state to the ON state. and a reset signal generating circuit 4 to give a reset signal shifts to the oFF state, the pulse width of the pulse of the optical frame T _f, the pulse width of the optical data pulses when the T _d, T _f <T _d One in which the.

FIG. 2 and FIG. 3 are an operation characteristic diagram and a timing chart, respectively, for explaining the principle of the present invention. The optical bistable element has, under certain conditions, an ON state “H” in which the optical output is large relative to a predetermined optical input level, and an OFF state “L” in which the optical output is relatively small compared to the ON state. It has stable optical bistability. Operation characteristics of the optical bistable device, as shown in FIG. 2 (a), abruptly optical output P when the optical signal input level P _in exceeds the threshold P _{th
Even when OUT} becomes large and the optical signal input level becomes 0, the optical output continues to maintain a high ON state "H" (threshold characteristic, optical bistable characteristic). In order to make a transition from the ON state “H” to the OFF state “L”, operating conditions such as an injection current bias are changed. Fig. 2 (a)
The optical data pulse and the optical frame pulse satisfying the following conditions as shown in FIG. 4B are input to the optical bistable element 3 in the state exhibiting the following characteristics and in the off state "L". I do. This condition sets the level of the optical data pulse to P
_data, the level of light frame pulse when the _{P f, P f, P data} <P th and, P _f + P _data> is P _th. Under this condition, an optical frame pulse is input so as to substantially coincide with a desired optical data pulse (shown in FIG. 3) in the input optical data pulse train, and the first optical coupler 1 converts the optical frame pulse into an optical frame pulse. The second optical coupler 2 superimposes one of them (the first optical frame pulse) on the desired optical data pulse and inputs the same to the optical bistable element 3.
In this case, the optical bistable element 3 transitions to the ON state only when the optical data pulse on which the optical frame pulse is superimposed is the mark signal, so that a desired optical data pulse can be latched. In this state, the optical bistable element 3 keeps the ON state, and is returned to the OFF state by the reset signal. Latch optical signal obtained rises in rise time T _f of the optical frame pulse, it is assumed that falls with the falling time t _r of the reset signal, the pulse width T _M of the latch optical signal, T _M = t _r -t _f (= T _fr ). Therefore, in the case of the present invention, even if the phases of the optical data pulse and the optical frame pulse relatively change, the pulse width T _M of the latch optical signal is constant.

On the other hand, the allowable variation width of the temporal phase shift T _fd between the optical data pulse and the optical frame pulse is given by T _f −T _d <T _fd <0 under the condition that T _high is constant. . That is, as long as T _fd is within this range, T _high is kept constant even if the temporal phase relationship between the optical data pulse and the optical frame pulse fluctuates. Therefore, according to the present invention, even when the temporal phase of the optical data pulse fluctuates from the initial setting condition with respect to the temporal phase of the optical frame pulse due to fluctuations in the laying environment conditions of the optical transmission line, T _high = The operating condition of T _f (constant) is secured.

In the present invention, the code format of the optical data pulse and the optical frame pulse is not particularly limited in order to satisfy the condition of T _f <T _d . For example, it is clear from the description with reference to the drawings that the above condition can be satisfied when the code format of the optical data pulse and the optical frame pulse is the RZ code format. On the other hand, as shown in FIG. 4 (a), when the code format of the optical data pulse is the NRZ code format and the code format of the optical frame pulse is the RZ code format, the data normally given in the NRZ code format is used. And the construction of the system is facilitated. still,
In this case, the T _d = T _B, and T _f <T _d. Further, in this case, as shown in FIG. 4 (b), 50% duty ratio of the optical frame pulse with respect to time width T _B corresponding to one time slot of the optical data pulses
So that the normal duty ratio is 50
%, And the generation of the optical frame pulse based on the clock is facilitated.

The effectiveness of the present invention will be described in more detail with reference to FIG.
FIG. 5 is a graph showing changes in T _high and T _M with respect to a change in a temporal phase relationship between an optical data pulse and an optical frame pulse. FIG. 9A corresponds to, for example, the case of FIG. 9 in which the code format of the optical data pulse and the optical frame pulse are both RZ code format, and FIG. 5B is a diagram in which the code format of the optical data pulse is RZ code format. 5 corresponds to the case of FIG. 10 in which the code format of the optical frame pulse is the NRZ code format, and FIG. 5C shows that the code format of the optical data pulse is the NRZ code format and the code format of the optical frame pulse is RZ
This corresponds to the case of the present invention which is a code format. In the case of the RZ code format, the duty ratio is set to 50%. The horizontal axis T _fd, and the vertical axis normalized by the time T _B of one time slot indicates the T _M of T _high left normalized by T _B, right normalized by T _fr. The region where T _fd / T _B <0 indicates that the rise of the optical data pulse is earlier in time than the rise of the optical frame pulse. 5 (b) and 5 (c), the part shown by the broken line is T
_{Although high} ≠ 0, a sufficiently stable operation cannot be expected because the optical frame pulse overlaps another optical data pulse immediately before or immediately after the desired optical data pulse, or is considered in a preferred embodiment of the present invention. The area is excluded from the target. By comparing FIGS. 5 (a), (b) and (c), it can be seen that according to the present invention, T _high and T _M are kept constant even if T _fd changes within a predetermined range. it is obvious.

EXAMPLES Examples of the present invention will be described below.

FIG. 6 is a block diagram of an optical data latch device showing an embodiment of the present invention. In this embodiment, a bistable semiconductor laser 30 is used as an optical bistable element, and the power of light input to the bistable semiconductor laser 30 from the second optical coupler 2 is adjusted by an attenuator (ATT) 11. The reason why the attenuator 11 is used is to adjust the optical input power of the bistable semiconductor laser 30 to a region where the required optical bistability is generated. Also, the reset signal generation circuit 4
The optical frame pulse branched by the first optical coupler 1 (the second
An optical-to-electrical conversion circuit 12 for performing optical-to-electrical conversion of an optical frame pulse, a current level switch 14 for level-switching the bias current of the bistable semiconductor laser 30 based on the output of the conversion circuit 12, A delay circuit that delays the output of 12 for a predetermined time and supplies it to the current level switch 14.
13 is provided. According to the configuration of the reset signal generation circuit, a system in which a required memory time T _M (= T _fr ) is set can be constructed by arbitrarily setting the delay time of the delay circuit 13.

Bistable semiconductor laser 30, as shown in FIG. 7 (a), in the state of the light input P _in = 0, when it exceeds the first threshold value I _ON when Yuku increase the current input I _IN When the optical output P _OUT sharply increases and laser oscillation starts (transition to the ON state), and the current input I _IN decreases, the second
When the threshold value becomes equal to or less than the threshold value I _OFF , the optical output P _OUT sharply decreases to stop laser oscillation (transition to an off state). Further, the bistable semiconductor laser 30 is shown in FIG.
As shown in the figure, the first threshold value I _ON and the second threshold value I _ON
The current input I _B corresponding to the value located in the middle between _OFF when supplied as a bias sharply optical output P _OUT when exceeding the optical threshold P _th when Yuku to increase the light input P _IN
Increases to start laser oscillation (transition to the ON state),
When the optical input _PIN is lowered, the laser has a characteristic of continuing laser oscillation even when the optical input _PIN becomes zero.
Therefore, it is clear that the present invention can be implemented by adopting the apparatus configuration shown in FIG.

In practicing the present invention, as the first and second optical couplers, those configured using a half mirror can be adopted in addition to those configured using an optical directional coupler. .

As described above, according to the present invention, even when the phases of the optical data pulse and the optical frame pulse are relatively changed, the optical data pulse and the optical frame pulse are superimposed and input to the optical bistable element. This makes it possible to provide an optical data latch system capable of keeping the operating time constant and keeping the pulse width of the latch optical signal constant.
As a result, the operation of the optical bistable element can be stabilized, and the construction of the system can be facilitated, which greatly contributes to the realization of synchronous optical signal processing.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus configuration for explaining the principle of the present invention, FIG. 2 is an operation characteristic diagram for explaining the principle of the present invention, and FIG. 3 is a timing for explaining the principle of the present invention. Chart, FIG. 4 is a diagram for explaining an example of a code format of an optical data pulse and an optical frame pulse in the present invention, FIG. 5 is a diagram for explaining the effectiveness of the present invention, and FIG. 6 is a present invention. FIG. 7 is a characteristic diagram of a bistable semiconductor laser used in the embodiment of the present invention, and FIGS. 8 to 10 are timing charts in the conventional system. DESCRIPTION OF SYMBOLS 1 ... 1st optical coupler, 2 ... 2nd optical coupler, 3 ... Optical bistable element, 4 ... Reset signal generation circuit, 12 ... Opto-electric conversion circuit, 13 ... Delay circuit, 14 …… Current level switch, 30 …… Bistable semiconductor laser.

Claims (4)

(57) [Claims] An input optical frame pulse is converted into first and second optical frame pulses.
A first coupler (1) for branching and outputting an optical frame pulse, and a second optical coupler (2) for adding and inputting the input optical data pulse and the first optical frame pulse, and An optical bistable element (3) that receives light from the second optical coupler (2) and transitions from an off state to an on state when the first optical frame pulse is superimposed on the optical data pulse; The second optical frame pulse is input, and after a lapse of a predetermined time from the rise of the optical frame pulse, a reset signal for causing the optical bistable element (3) to transition from the on state to the off state is supplied to the optical bistable element (3). and a reset signal generating circuit (4), the pulse width of the optical frame pulse when T _f, the pulse width of the optical data pulse and T _d, the light, characterized in that the T _f <T _d Data latch method. 2. The optical bistable device (3) is a bistable semiconductor laser (30), and the reset signal generating circuit (4) is an optical-electrical device that optically-electrically converts the second optical frame pulse. Conversion circuit (12)
A current level switch (14) for level-switching the bias current of the bistable semiconductor laser (30) based on the output of the conversion circuit (12); and a delay of the output of the photoelectric conversion circuit (12) for a predetermined time. 2. The optical data latch system according to claim 1, further comprising a delay circuit (13) for providing the current level switch (14) to said current level switch (14). 3. The optical data latch system according to claim 1, wherein the code format of the optical data pulse is an NRZ code format, and the code format of the optical frame pulse is an RZ code format. 4. The optical data latch system according to claim 3, wherein a duty ratio of said optical frame pulse is 50% with respect to a time width corresponding to one time slot of said optical data pulse.