Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
2001-12-20
2003-11-04
Hellner, Mark (Department: 3663)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S341320, C359S341330
Reexamination Certificate
active
06643058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to an optical pumping unit comprising a first and a second pump source for providing two pump radiations, and a common coupling section for coupling a first, a second and a third radiation.
The present invention also relates to an optical amplifier comprising said optical pumping unit and an optical communication line and an optical communication system comprising said optical pumping unit or said optical amplifier.
The present invention also relates to a coupling section and a method for coupling two pump radiations and a signal radiation.
2. Technical Background
In the present description and claims, the expression
“insertion losses undergone by a pump radiation”, referred to a pumping unit, is used to indicate the difference, expressed in dB, between the power of the radiation emitted by a pump source of the pumping unit and the power in output from the pumping unit;
“100%&lgr; optical coupler” is used to indicate an optical coupler comprising two optical paths coupled to one another and adapted to let pass substantially 100% of power of a radiation of wavelength &lgr; from one optical path to the other, and to substantially maintain 0% of power along the same optical path;
“100%&lgr;x/0%&lgr;y WDM optical coupler” is used to indicate an optical coupler comprising two optical paths coupled to one another and adapted to let pass from one optical path to the other substantially 100% of power of a radiation at wavelength &lgr;x, and substantially 0% of power of a radiation at wavelength &lgr;y by maintaining substantially 0% of power of the radiation at wavelength &lgr;x and substantially 100% of power of the radiation at wavelength &lgr;y along the same optical path;
“50%&lgr;x/0%&lgr;y WDM optical coupler” is used to indicate an optical coupler comprising two optical paths coupled to one another and adapted to let pass from one optical path to the other substantially 50% of power of a radiation at wavelength &lgr;x and substantially 0% of power of a radiation at wavelength &lgr;y by maintaining substantially 50% of power of the radiation at wavelength &lgr;x and substantially 100% of power of the radiation at wavelength &lgr;y along the same optical path;
“50%&lgr;x/100%&lgr;y WDM optical coupler” is used to indicate an optical coupler comprising two optical paths coupled to one another and adapted to let pass from one optical path to the other substantially 50% of power of a radiation at wavelength &lgr;x and substantially 100% of power of a radiation at wavelength &lgr;y by maintaining substantially the remaining 50% of power of the radiation at wavelength &lgr;x and substantially 0% of power of the radiation at wavelength &lgr;y along the same optical path;
“optical transmission fibre” is used to indicate an optical fibre used in an optical communication line or system for transmitting optical signals from a point to another placed at an appreciable distance.
In the above definitions, the expression “substantially 100%” of power coupling is preferably used for indicating a power coupling at least equal to 90%; “substantially 0%” of power coupling, is preferably used for indicating a power coupling that is less than or equal to 10%, and “substantially 50%” of power coupling is preferably used for indicating a power coupling comprised between 45% and 55%.
A 100%&lgr;WDM, 100%&lgr;x/0%&lgr;y WDM, 50%&lgr;x/0%&lgr;y WDM, 50%&lgr;x/100%&lgr;y WDM optical coupler can be realised in micro-optics, fused fibre, integrated optics or through any other technique which allows the formation of waveguides at the optical frequencies.
An optical amplifier typically consists of an active means (for example, an optical fibre or a planar waveguide doped with a rare earth) and a pumping unit.
In turn, the pumping unit typically consists of a pump source (for example, a laser diode) adapted to provide a pump radiation at wavelength &lgr;p to the active means, and of a wavelength division multiplexing (or WDM) device for coupling the pump radiation at wavelength &lgr;p with a signal radiation to be amplified at wavelength &lgr;s.
Typically, the WDM device is a WDM optical coupler of the 100%&lgr;p/0%&lgr;s or 100%&lgr;s/0%&lgr;p type, with two inputs and two outputs, and it is adapted to couple—into one of the two outputs—substantially all the power of the pump radiations at wavelength &lgr;p and of the signal radiations at wavelength &lgr;s at its two inputs.
With the advent of WDM optical communication systems, there is the need of increasing the pump power of optical amplifiers, so as to effectively amplify a WDM optical signal.
A WDM optical signal is a signal comprising a plurality of N optical signals independent of one another, each at a predetermined central wavelength &lgr;
1
, &lgr;
2
. . . &lgr;N different from that of the other signals. The signals can also be both digital and analogue, and they have a certain spectral width around the value of the central wavelength.
Typically, in a WDM system, the various optical signals are generated by a plurality of optical sources, multiplexed so as to form a WDM signal, transmitted along the same optical transmission line (for example an optical fibre line) and then demodulated so as to be each received by a receiver.
Optical amplifiers used in transmission, reception and/or along a transmission line of a WDM optical system need high pump powers to efficiently amplify the plurality of optical signals forming the WDM optical signal.
For the purpose of meeting said requirement, the use of a pumping unit with two pump sources has been proposed.
More in particular, it has been proposed to combine two pump radiations provided by two pump sources in a single total pump radiation, and to combine said total pump radiation with the signal radiation.
For example, the use of a wavelength combiner or of a polarisation combiner—upstream of a WDM device used for coupling the total pump radiation with the signal radiation—has been proposed to combine the two pump radiations.
In the first case (FIG.
1
), the pumping unit
10
comprises two laser diodes
11
,
12
, two optical fibre gratings
15
,
17
respectively connected to the two lasers
11
and
12
, a wavelength combiner
14
and a fused fibre 100%&lgr;p/0%&lgr;s WDM optical coupler
16
. According to this solution, the pump radiations emitted by the two laser diodes
11
,
12
have slightly different wavelengths (typically, by some nm) and the two optical fibre gratings
15
,
17
are adapted to stabilise said wavelengths.
Since the wavelengths of the two pump radiations are very close to one another (by some nm), the wavelength combiner
14
is typically realised in micro-optics. In fact, a fused fibre 100%&lgr;p/0%&lgr;s WDM optical coupler of the type used for coupling the total pump radiation and the signal radiation (which typically have different wavelengths from one another, in the range of dozens or hundreds nm), is not adapted to combine wavelengths that are very close to one another (in the range of nm).
Considering Bragg gratings currently available on the market by JDS, E-TeK, Innovative Fibers, Sumitomo, Bragg Photonics, 3M, Optical Technologies Italia (having insertion losses that are more than or equal to about 0.2 dB) and micro-optics wavelength combiners and fused fibre 100%&lgr;p/0%&lgr;s WDM optical couplers currently available on the market by JDS, E-TeK, Oplink and Gould (having insertion losses that are respectively higher than or equal to about 0.6 dB and 0.3 dB), the Applicant has noted that in the pumping unit of
FIG. 1
each pump radiation undergoes insertion losses higher than about 1.1 dB (that is, higher than about 23%).
Moreover, as the pumping unit of
FIG. 1
consists of the micro-optics wavelength combiner
14
, the two optical fibre gratings
15
,
17
and the fused fibre 100%&lgr;p/0%&lgr;s WDM optical coupler
16
, it is realised using different technologies. This makes the pumping unit less reliable and more expensive than a unit that is entirely realised with the same technolo
De Donno Marco
Milanese Paolo
Pianciola Aurelio
Avanex Corporation
Hellner Mark
Paglierani Ronald J.
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