Rare earth polymers, optical amplifiers and optical fibers

Details Rare earth polymers, optical amplifiers and optical fibers Rare earth polymers, optical amplifiers and optical fibers

2000-02-18

2001-09-18

Hellner, Mark (Department: 3662)

Optical: systems and elements

Optical amplifier

Optical fiber

C372S006000, C501S045000, C252S30140P

Reexamination Certificate

active

06292292

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to rare earth polymer compositions, optical fibers, optical waveguides, and particularly to optical amplifier waveguides and splitters.
2. Description of the Related Art
Optical communication systems based on glass optical fibers (GOFs) allow communication signals to be transmitted not only over long distances with low attenuation but also at extremely high data rates, or bandwidth capacity. This capability arises from the propagation of a single optical signal mode in the low-loss windows of glass located at the near-infrared wavelengths of 0.85, 1.3, and 1.55 &mgr;m. Since the introduction of erbium-doped fiber amplifier (EDFA), the last decade has witnessed the emergence of single-mode GOF as the standard data transmission medium for wide area networks (WANs), especially in terrestrial and transoceanic communication backbones. In addition, the bandwidth performance of single-mode GOF has been vastly enhanced by the development of dense wavelength division multiplexing (DWDM), which can couple up to 160 channels of different wavelengths of light into a single fiber, with each channel carrying gigabits of data per second. Moreover, in a recent demonstration, a signal transmission of 1 terabit (10
12
bits) per second was achieved over a single fiber on a 100-channel DWDM system. Enabled by these and other technologies, the bandwidth capacities of the communication networks are increasing at rates of as much as an order of magnitude per year.
The success of single-mode GOF in long-haul communication backbones has given rise to the new technology of optical networking. The universal objective is to integrate voice video, and data streams over all-optical systems as communication signals make their way from WANs down to smaller local area networks (LANs), down to the curb (FTTC), home (FTTH), and finally to the end user by fiber to the desktop (FTTD). Examples are the recent explosion of the Internet and use of the World Wide Web, which are demanding vastly higher bandwidth performance in short- and medium-distance applications. Yet as the optical network nears the end user starting at the LAN stage, the system is characterized by numerous fiber connections, splices, and couplings, especially those associated with splitting of the input signal into numerous channels. All of these introduce enormous optical loss. To compensate for the unacceptably high loss penalty, current solutions rely on expensive EDFAs that are bulky at fiber lengths of about 40 m. The cost of a typical commercial EDFA can reach many tens of thousands of dollars. Thus, to complete the planned build-out for FTTC, FTTH, and FTTD in the US would require millions of amplifiers and hundreds of billions of dollars.
An EDFA module is made up of a number of key components. One of the most critical components in the module is the erbium doped silica fiber (EDF). Present EDF is limited by low concentrations of erbium atoms, clustering that leads to quenching of photoluminescence, a relatively narrow emission band, a highly wavelength dependent gain spectrum, and an inability to be fabricated in a compact, planar geometry. Efforts have been directed toward the use of other rare earth ions in both fused silica glass hosts and other glasses including fluoride, tellurite and phosphate glasses. To this point, these efforts have been limited by the fundamental materials properties of these glass media with regard to their ability to dissolve rare earth atoms, mechanical properties, thermal stability, and other key properties.
The benefits of the present invention are based on the development of rare earth fluorphosphinate polymer material that have the following preferred properties:
compatibility with a broad range of rare earths that enable coverage of the full 1500 to 1600 nm window (and beyond) using a common host platform;
very high concentrations of rare earth elements without associated quenching and upconversion penalties, allowing for very short lengths of fiber to be used as small as centimeters and less;
very low intrinsic optical loss;
capable of being drawn into single mode optical fiber; and
capable of being cast into films for planar waveguide applications.
Cost effective, compact integrated optics is a preferred solution to this problem, but currently none exists.
It is an object of the present invention to provide novel optical waveguide materials that are easy to process using standard silicon VLSI (very large scale integration) fabrication methods and optical fiber drawing processes.
It is a further objective of the present invention to produce a fiber amplifier and material therefor having low-loss in short and medium distance communications network systems.
It is an object of the present invention to produce an integrated optical component that is a low-loss splitter that combines amplification and splitting of the input light signal while maintaining a high signal-to-noise ratio.
SUMMARY OF THE INVENTION
Disclosed are cost-effective, compact, optically pumped, high gain, rare earth polymer materials such as, erbium (Er
3+
) fluorophosphinate polymers, optical fibers made from the materials and optical amplifiers made from the materials having low-loss at telecommunications wavelengths for operation in data communications network systems. The polymer amplifier is based on the use of novel high performance rare earth (RE) polymer materials. The highly transparent RE polymer materials are directly synthesized at high RE ion concentrations (~10
20−
10
21
rare earth ion/cm
3
~10% wt) with each metal ion encapsulated and physically buffered by insulating, covalently bonded, perfluorinated phosphate ligands that then form the high temperature stable, polymer backbone matrix. This is distinctly different from widely studied inorganic glasses and single crystals where RE ion salts are doped directly into the host but only to relatively low levels (<0.1% wt).
The RE polymer material as depicted in
FIG. 1
is designed for use in an integrated optical circuit element utilizing numerical modeling and computer simulations. Utilizing this RE polymer material, the polymer amplifier length can be as short as several cm because of the ultra high gain coefficient of >5 dB/cm. As a complement to the cost effective VLSI methods utilized for the planar waveguide architecture, standard low-cost fiber drawing methods are used to fabricate the fiber amplifier element to further realize significant cost reduction of the final integrated optical device.
The use of RE polymer materials affords the devices several unique properties and advantages. These include high RE ion concentrations with homogeneous distribution, enhanced optical transition moments, controllable decay rates and branching ratios, novel energy transfer effects, and relatively low optical loss across the near infrared region. The combination of these critical features is not available in standard RE-doped silica glasses and inorganic crystals.
RE polymer systems have many outstanding materials properties. These include simple two-step synthesis by standard organic methods; ease of synthesis modification; ease in fiber and planar waveguide fabrication by standard methods; compatibility with various cladding materials; high thermal, mechanical, and photostabilities; and room temperature operation. Further, the new RE polymers easily form highly transparent thin films both by simple casting and standard spin coating methods. For compact optical amplification devices, the processing properties of silica glass and inorganic crystal systems are inferior to the RE polymer materials.
The successful realization of RE-containing polymers is not straightforward, and the reasons for this are fundamental and intrinsic. Common organic polymers contain high-frequency optical phonons, such as O—H stretch (~3600 cm
−1
) and C—H stretch (~3200 cm
−1
) vibrations. These vibrations play the dominant role in phonon-assisted, nonradiative removal of electronic excitation energy

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