What is claimed is:
1. A digital filter made from optical components that enables an optical signal to be manipulated in an optical domain without needing to convert the optical signal into an electrical domain.
2. The digital filter of claim 1, wherein said digital filter is an infinite impulse response filter.
3. The digital filter of claim 1, wherein said digital filter is a finite impulse response filter.
4. The digital filter of claim 1, wherein said optical components are incorporated onto a lightwave optical circuit.
5. The digital filter of claim 1, wherein said optical components can process a 500 GHz or less optical signal.
6. The digital filter of claim 1, wherein said optical components can process a dynamic optical signal.
7. A digital filter that synthesizes a digital signal processing difference equation:
5
H
(
z
)
=
Y
(
z
)
X
(
z
)
=
i
=
0
r
L
i
z
–
i
1
+
j
=
1
m
K
j
z
–
j
where:
H(z)Z-transform of filter response
Y(z)Z-transform of output response
X(z)Z-transform of input response
rNumber of input sample coefficients
mNumber of output sample coefficients
LiGain (tap weights) for the input sample data
KjGain (tap weights) for the output sample data
ziZ-transform of the discretized version of an input delayed by i samples
zjZ-transform of the discretized version of an output delayed by j samples
said digital filter is synthesized by replacing elements of said digital signal processing difference equation with an optical component as follows:
each memory element zi and zj is replaced with a delay unit;
each sum block is replaced with a combiner;
each gain block element Li and Kj is replaced with an amplifier or an attenuator; and
each T-junction between each pair of delay units is replaced with a splitter.
8. The digital filter of claim 7, wherein each delay unit is a piece of optical fiber.
9. The digital filter of claim 7, wherein each combiner is a tap or an interferometer.
10. The digital filter of claim 7, wherein each splitter is a tap or an interferometer.
11. The digital filter of claim 7, wherein:
each amplifier is an semiconductor optical amplifier, an electro-absorptive modulator or an erbium-doped fiber amplifier; and
each attenuator is an optical attenuator if the gain is scaled to a value less than one.
12. The digital filter of claim 7, wherein said digital filter is an infinite impulse response filter.
13. The digital filter of claim 7, wherein said digital filter is a finite impulse response filter when m is set to zero.
14. The digital filter of claim 7, wherein said optical components are incorporated onto a lightwave optical circuit.
15. The digital filter of claim 7, wherein said digital filter manipulates an optical signal that has a sample rate less than or equal to 500 GHz.
16. The digital filter of claim 7, wherein said digital filter manipulates an optical signal that has a dynamic sample rate.
17. A method for synthesizing a digital filter that implements a digital signal processing difference equation:
6
H
(
z
)
=
Y
(
z
)
X
(
z
)
=
i
=
0
r
L
i
z
–
i
1
+
j
=
1
m
K
j
z
–
j
where:
H(z)Z-transform of filter response
Y(z)Z-transform of output response
X(z)Z-transform of input response
rNumber of input sample coefficients
mNumber of output sample coefficients
LiGain (tap weights) for the input sample data
KjGain (tap weights) for the output sample data
ziZ-transform of the discretized version of an input delayed by i samples
zj32 Z-transform of the discretized version of an output delayed by j samples
said digital filter is synthesized by replacing elements of said digital signal processing difference equation with an optical component in accordance with the following steps:
replacing each memory element zi and zj with a delay unit;
replacing each sum block with a combiner;
replacing each gain block element Li and Kj with an amplifier or an attenuator; and
replacing each T-junction between each pair of delay units with a splitter.
18. The method of claim 17, wherein:
each delay unit is a piece of optical fiber;
each combiner is a tap or an interferometer;
each splitter is a tap or an interferometer; and each amplifier is a semiconductor optical amplifier, an electro-absorptive modulator or an erbium doped fiber amplifier; and
each attenuator is an optical attenuator if the gain is scaled to a value less than one.
19. The method of claim 17, wherein said optical components are incorporated onto a lightwave optical circuit.
20. A digital filter that synthesizes a digital signal processing difference equation:
7
H
(
z
)
=
Y
(
z
)
X
(
z
)
=
i
=
0
r
L
i
z
–
i
1
+
j
=
1
m
K
j
z
–
j
where:
H(z)Z-transform of filter response
Y(z)Z-transform of output response
X(z)Z-transform of input response
rNumber of input sample coefficients
mNumber of output sample coefficients
LiGain (tap weights) for the input sample data
KjGain (tap weights) for the output sample data
ziZ-transform of the discretized version of an input delayed by i samples
zjZ-transform of the discretized version of an output delayed by j samples
said digital filter is synthesized by replacing elements of said digital signal processing difference equation with an analog component as follows:
each memory element zi and zj is replaced with a delay unit that delays a presented voltage for a predetermined amount of time;
each sum block is replaced with an analog power combiner;
each gain block element Li and Kj is replaced with an analog amplifier, a resistor divider network or an attenuator; and
each T-junction between each pair of delay units is replaced with an analog power splitter.
21. The digital filter of claim 20, wherein each delay unit that delays a presented voltage for a predetermined amount of time is a length of cable or a filter.
22 The digital filter of claim 20, wherein said digital filter is an infinite impulse response filter.
23. The digital filter of claim 20, wherein said digital filter is a finite impulse response filter when m is set to zero.
24. The digital filter of claim 20, wherein said digital filter manipulates an optical signal that has a sample rate in the range of 1 GHz.
25. A method for synthesizing a digital filter that implements a digital signal processing difference equation as follows:
8
H
(
z
)
=
Y
(
z
)
X
(
z
)
=
i
=
0
r
L
i
z
–
i
1
+
j
=
1
m
K
j
z
–
j
where:
H(z)Z-transform of filter response
Y(z)Z-transform of output response
X(z)Z-transform of input response
rNumber of input sample coefficients
mNumber of output sample coefficients
LiGain (tap weights) for the input sample data
KjGain (tap weights) for the output sample data
ziZ-transform of the discretized version of an input delayed by i samples
zjZ-transform of the discretized version of an output delayed by j samples
said digital filter is synthesized by replacing each element of said digital signal processing difference equation with an analog component in accordance with the following steps:
replacing each memory element zi and zj with a delay unit that delays a presented voltage for a predetermined amount of time;
replacing each sum block with an analog power combiner;
replacing each gain block element Li and Kj with an analog amplifier, a resistor divider network or an attenuator; and
replacing each T-junction between each pair of delay units with an analog power splitter.
26. The method of claim 25, wherein each delay unit that delays a presented voltage for a predetermined amount of time is a length of cable or a filter.
27. The method of claim 25, wherein said digital filter manipulates an optical signal that has a sample rate in the range of 1 GHz.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method for determining a cut-off wavelength of an optical fibre, the method comprising:
i) providing a spectral measurement setup,
ii) carrying out a spectral measurement on the optical fibre using the spectral measurement setup at a specific wavelength,
iii) bending the optical fibre,
iv) carrying out a spectral measurement on the bent optical fibre, using the spectral measurement setup, at the specific wavelength,
v) determining a bend attenuation on a basis of measuring results obtained in steps ii) and iv), and
vi) determining a cut-off wavelength of the optical fibre based on the bend attenuation and a mode field diameter of the optical fibre by correlating the cut-off wavelength of the optical fibre to the bend attenuation and the mode field diameter of the optical fibre on the basis of a previously determined correlation between bend attenuation and cut-off wavelength.
2. A method according to claim 1, wherein said correlation is determined by:
vii) determining a mode field diameter of a plurality of optical fibres,
viii) measuring an attenuation of the plurality of optical fibres at said specific wavelength,
ix) bending the plurality of optical fibres, measuring the attenuation of the plurality of bent optical fibres at said specific wavelength, and determining a bend attenuation,
x) determining the cut-off wavelength of the plurality of optical fibres by carrying out a spectral attenuation measurement at a number of wavelengths around the cut-off wavelength, in which the optical fibre has a specific bent position, and
xi) correlating the bend attenuation and a mode field diameter of the plurality of optical fibres to the cut-off wavelength for the plurality of optical fibres.
3. A method according to claim 2, wherein said specific wavelength lies outside the wavelength region around the cut-off wavelength.
4. A method according to claim 1, wherein the spectral measurement setup is a backscatter apparatus.
5. A method according to claim 4, wherein the bending iii) takes place at a point spaced by a distance L from the position where the optical fibre to be measured is connected with a fibre present in the backscatter apparatus.
6. A method according to any one of the preceding claims, wherein the bending of the optical fibre is carried out in a manner that the deformation of the fibre axis at the bend corresponds to the deformation of the fibre.
7. A device for determining the cut-off wavelength of an optical fibre, comprising:
means for bending an optical fibre,
a spectral measurement setup suitable for carrying out a spectral measurement on an optical fibre, said spectral measurement setup configured to carry out a spectral measurement on the optical fibre at a specific wavelength and to carry out a spectral measurement on the optical fibre after the optical fibre is bent by the means for bending at the specific wavelength, wherein bend attenuation is measured by said measurement setup from spectral measurements made prior to and after the bending of the optical fiber being carried out, and
means for relating the cut-off wavelength to the bend attenuation and a mode field diameter of the optical fibre.
8. A device for introducing a bend into an optical fibre as used in the device according to claim 7, comprising:
means for introducing at least one bend into an optical fibre,
means for guiding the optical fibre between at least two rows of vertical pins, and
means for moving said rows of vertical pins towards each other so as to obtain a defined bend in the optical fibre.