Coherent light generators – Particular beam control device – Mode locking
Reexamination Certificate
2002-04-15
2004-04-20
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Mode locking
C372S034000
Reexamination Certificate
active
06724784
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to optical devices and, more specifically, to an optical wavelength locker module having an electrically nonconductive material with a high thermal conductivity and methods of manufacture and operation thereof.
BACKGROUND OF THE INVENTION
In current technology, optical fiber communication systems provide for low loss and very high information carrying capacity. In practice, the bandwidth of optical fiber may be utilized by transmitting many distinct channels simultaneously using different carrier wavelengths. The associated technology is called wavelength division multiplexing. In a dense wavelength division multiplexing (DWDM) system, different wavelengths are closely spaced to increase fiber transmission capacity. If it becomes necessary to add further channels to an existing optical fiber, even denser wavelength spacing may be used in the future.
A wavelength stabilized laser is a recently developed component of DWDM systems. In a DWDM system, a single semiconductor laser device may be used to provide light at several predetermined wavelengths, each corresponding to a different channel. Unfortunately, some laser sources, for example, distributed feedback (DFB) lasers, exhibit wavelength drift over time, in excess of the requirements for DWDM. As a result, the wavelength of the device tends to change with aging under continuous power. Thus, to maximize the number of channels, lasers with stable and precise wavelength control are employed to provide narrowly spaced, multiple wavelengths. As the wavelength spacing decreases, wavelength stabilization takes on a more important role.
Typically, lasers are tuned by varying the wavelength or, equivalently, the laser frequency by providing a feedback circuit employing an optical interferometer. In many conventional DWDM systems, a stable optical interferometer, such as an etalon, is used in a feedback circuit to provide the necessary wavelength stabilization. Those who are skilled in the art understand that an etalon is an interferometer typically consisting of a plate of silica having two parallel faces that create an optical interference by reflecting a portion of each ray of light incident upon the faces. Since laser wavelength is a function of laser temperature, lasers are typically tuned by altering their temperature with a thermoelectric cooler (TEC). Unfortunately, although the temperature of the lasers may be monitored and altered as needed, the resulting temperature changes of the lasers may also dramatically affect the temperature of the etalon mounted near the laser.
A change in the temperature of an etalon often limits the precision of the wavelength stabilization of the laser because etalons are typically manufactured from temperature sensitive materials. A change in the temperature will lead to changes in refractive index and thickness of each etalon fabricated from the temperature sensitive materials, allowing optimal functioning only under a very stable temperature environment. Thus, the etalon's temperature stability is of integral concern in the wavelength stabilization of the lasers in optoelectronic devices. In current packaging techniques, etalons are typically mounted on the same platform or substrate of an application specific carrier (ASC) as the laser, where both are mounted in a package having its temperature monitored and altered by a TEC. Thus, although the etalon is within the same temperature-controlled environment as the laser, a temperature gradient still typically exists between the surface of the etalon mounted directly to the substrate and those surfaces not in direct contact with the substrate due to the low thermal conductivity of the etalon material. Typically, a change in the temperature of the surrounding environment will result in a change in the etalon temperature.
Attempts to correct this temperature gradient of the optical interferometers (e.g., etalons) employed in DWDM systems have met with marginal results. One approach has been to construct the etalons from materials that are not as temperature sensitive as those typically employed. Unfortunately, excessive costs in manufacturing etalons using less temperature sensitive materials discourage wavelength locker manufacturers from employing such materials. More specifically, these exotic low temperature sensitivity materials are typically fragile, difficult and expensive to initially manufacture, and difficult to process into a finished etalon.
Another approach has been to employ an “air-gap” etalon as the wavelength locker in the DWDM system. Air-gap etalons include two plates of silica, or similar material, positioned parallel to each other with a small air-gap in between them. The air-gap has a refractive index, which is less sensitive to temperature than materials such as fused silica. However, these special etalons are also costly and time consuming to manufacture since four sides (two sides on each silica plate) must be polished to create the necessary interference. In addition, the two plates must be precisely aligned parallel to each other to provide interference of the incoming light at the appropriate wavelength, a task not easily achieved.
Accordingly, what is needed in the art is an apparatus for maintaining the temperature of a wavelength locker used in optoelectronic laser devices that does not suffer from the deficiencies found in the prior art.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides an improved optical wavelength locker module. In one embodiment, the wavelength locker module includes an optical interferometer or filter, such as an etalon. In addition, the wavelength locker module also includes an electrically nonconductive material having a high thermal conductivity substantially surrounding the etalon.
In another embodiment, the present invention provides a method involving an optical wavelength locker module. In one embodiment, the method includes providing an optical interferometer or filter, such as an etalon. Also, the method provides placing an electrically nonconductive material having a high thermal conductivity substantially around the etalon, where the material is capable of reducing a temperature gradient across the etalon.
In yet another embodiment, the present invention provides an optical assembly. In one embodiment, the optical assembly includes a substrate having conductive traces, and an optical subassembly mounted on the substrate and having a laser therein. In this embodiment, the laser is configured to generate a beam of light. The optical assembly further includes an optical wavelength locker module positioned on the substrate to receive the beam of light from the laser. The wavelength locker module includes an optical interferometer or filter, such as an etalon, and an electrically nonconductive material having a high thermal conductivity substantially surrounding the etalon.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.
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Bylsma Richard B.
Cheng Ling
Eshelman Mark A.
Meyers Mark
Verma Kaushal
Agere Systems Inc.
Jr. Leon Scott
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