Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-06-12
2003-12-30
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C375S375000
Reexamination Certificate
active
06671074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical receiver for use in optical communication system, and more particularly an optical receiver for a system such as an ATM-PON optical subscriber system in which burst transmission is carried out.
BACKGROUND OF THE INVENTION
A configuration example of the conventional optical receiver corresponding to burst transmission is shown in FIG.
1
. The 2R regenerator
1
shown in this example is the one published in B-1034 at the 1996 General Conference of the Communications Society of the IEICE (Institute of Electronic, Information and Communication Engineers).
Also, the bit synchronizer
2
is the one published in B-844 at the 1996 General Conference of the Communications Society of the IEICE. The above-mentioned 2R regenerator
1
is an optical signal receiver having functions of waveform regenerating and waveform reshaping against received light, in which a received optical signal is converted to a voltage signal through a photodiode
10
and a pre-amplifier
11
. A binary signal is output after an ATC circuit
12
discriminates the signal in an amplitude direction.
ATC circuit
12
is provided with an automatic threshold value control function to discriminate and detect level ‘1’ and level ‘0’ by setting a threshold level in the middle of the received signal. A reset circuit
13
is provided for resetting the preset threshold value of ATC circuit
12
.
Bit synchronizer
2
inputs the output signal of this 2R regenerator
1
, to sample at multiphase timing using a system clock CLK being externally input. Further, using this sampled result, bit synchronizer
2
detects a rise change point (edge) and a fall change point on both sides of the input data to select the center phase therebetween to output as the optimal phase for data sampling.
More specifically, the output of 2R regenerator
1
is commonly input to a plurality of timing adjustment circuits (delay line)
200
-
20
n
. The outputs of timing adjustment circuits
200
-
20
n
are further input to the corresponding flip-flop circuits
210
-
21
n
. Here, the output data of 2R regenerator
1
are latched in multiphase at the inputs of flip-flop circuits
210
-
21
n
at the timing determined by the external clock CLK.
The outputs of flip-flop circuits
210
-
21
n
are input to the corresponding shift registers
220
-
22
n
, as well as to an edge detection circuit
20
.
Edge detection circuit
20
detects change points of the input signal, namely both a rise edge and a fall edge of the output of 2R regenerator
1
, from the outputs of flip-flop circuits
210
-
21
n.
Accordingly, based on the detection result of the rise edge and the fall edge, a phase selection circuit
21
controls a selector
22
so as to select a shift register output corresponding to the data being latched at the timing of the center phase of the detected edges.
Here, in the above-mentioned configuration, the signal output of 2R regenerator
1
is inclined to fall into the state of varied pulse width caused by either nonlinear circuit operation or an error in setting a discrimination threshold value by an ATC circuit
12
.
There may also be a case that the pulse width itself of the optical signal data received from the transmission side to input to 2R regenerator
1
has already been varied for such a reason as the characteristic of a laser on the transmission side. Therefore, bit synchronizer
2
is required to cope with such pulse width degradation in the input data.
Considering this issue, in the conventional configuration example shown in
FIG. 1
, a measure has been taken to cope with pulse width degradation by detecting the both edge sides, or a rise edge and a fall edge of the data, to determine the center phase therebetween as a discrimination phase.
However, the method of detecting both edge sides has a limit from the viewpoint of tolerance against the pulse width deterioration.
One example resulting from varied data width is shown below: Consider a case of an NRZ signal data having a pattern of ‘0100’ being input with a duty ratio of 170%, and a case of a data with a pattern of ‘0110’ being input with a duty ratio of 70%. It is not possible to distinguish these two cases as shown in
FIG. 2
which illustrates a problem in the conventional optical receiver configuration.
Namely, as shown in FIGS.
2
(
a
) and
2
(
b
), for the cases of receiving ‘0100’ and ‘0110’ with a duty of 100%, consider that these data width are deteriorated resulting in such conditions that the respective data have duties of 170% and 70% as shown in FIGS.
2
(
c
) and
2
(
d
). In such cases the NRZ signal patterns become identical.
As a result of edge detection in edge detection circuit
20
, there are two sets of the rise timing in phases ø
2
and ø
3
, and also two sets of the fall timing in phases ø
15
and ø
16
.
Therefore, the timing position of phase ø
9
being located at the center of those two positions is determined as the sampling position for each bit. As a result, in the case shown in FIG.
2
(
d
), it is determined as ‘0’ in the third bit, thus producing an error.
In order to circumvent the above-mentioned problem, there has been taken in such a conventional method a measure of restricting the tolerable pulse width variation value within the range of 50% to 150% for signals being input to bit synchronizer
2
.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide an optical receiver having an extended tolerable variation value of input signal pulse width for use in a system such as ATM-PON optical subscriber system in which burst transmission is carried out.
As a basic feature, the optical receiver to attain the object of the present invention includes; an optical signal receiver for receiving an optical signal in burst transmission to regenerate and reshape waveform of the received optical signal; and a bit synchronizer for detecting a rise change point and a fall change point of the signal being output from the optical signal receiver using an externally-input clock to determine a discrimination phase according to the detected change points, and to discriminate to output the received optical signal at the timing of the determined discrimination phase.
The above-mentioned optical signal receiver further includes an amplitude detector for detecting the received optical signal intensity, and also the above-mentioned bit synchronizer further includes a phase selector for selecting the discrimination phase timing corresponding to the received optical signal intensity detected by the amplitude detector.
Moreover, as a preferred embodiment of the present invention, the optical receiver includes; an opt-electric converter for converting a received optical signal into an electric signal; a pre-amplifier for amplifying the electric signal; an amplitude detector for detecting amplitude intensity of a signal output from the pre-amplifier; a main amplifier for amplifying the pre-amplifier output signal as well as for setting a discrimination threshold value to discriminate in the amplitude direction; a multiphase sampler for splitting an output signal of the main amplifier into a plurality of branch signals to apply mutually different delays to the each branch signal and thereafter to discriminate an input signal using the identical externally-input clock; a change-point detector for detecting a rise change point and/or a fall change point of a signal output from the multiphase sampler; a selection phase controller for outputting a control signal to determine a signal discrimination phase according to both the change point detection result from the change-point detector and a value detected by the amplitude detector; and a selection signal output portion for outputting a signal discriminated by the discrimination phase corresponding to the control signal being output from the selection phase controller,
The above-mentioned selection phase controller generates a control signal for determining a signal output from the selection signal output portion according to the recept
Chan Jason
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Li Shi K.
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