Athermalized integrated optical waveguide devices

Details Athermalized integrated optical waveguide devices Athermalized integrated optical waveguide devices

2001-01-10

2003-02-11

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

Integrated optical circuit

C385S122000, C385S130000, C385S132000, C385S142000

Reexamination Certificate

active

06519380

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to integrated optical waveguide devices in which the light transmitting properties are insensitive to temperature variations and fluctuations. More particularly, the present invention is directed to athermalized integrated planar optical waveguide devices with organic-containing overclads containing silicate glasses, polymers, and/or hybrid (organic/inorganic) sol-gels.
BACKGROUND OF THE INVENTION
Integrated optical waveguide devices, such as integrated optical circuits, combine miniaturized waveguides and optical devices into a functional optical system incorporated onto a small planar substrate. Such integrated optical waveguide devices are utilized in, for example, optical communications systems, usually by attaching optical waveguide fibers that transmit light signals to the integrated optical waveguide device as inputs and outputs. The integrated optical waveguide device performs a function or process on the transmitted light in the optical communications system.
Integrated optical devices which incorporate optical path length differences can be used as, for example, wavelength multiplexing and demultiplexing devices. Such integrated optical devices are particularly useful as wavelength division multiplexers (WDM)/demultiplexers, and may incorporate a phased array made from a plurality of different waveguide core arms which have differences in optical path length.
Wavelength division demultiplexers include, in particular, at least one input waveguide, which transmits N optical signals at N different wavelengths (&lgr;
1
, &lgr;
2
, . . . &lgr;
N
), and at least N output waveguides, each transmitting one of the N optical signals at a predetermined wavelength &lgr;
i
(i=1, 2, . . . N). Conversely, wavelength division multiplexers include at least N input waveguides, each transmitting one of the N optical signals at the wavelengths &lgr;
1
, &lgr;
2
, . . . &lgr;
N
and at least one output waveguide, which transmits the N optical signals. The wavelengths &lgr;
1
, &lgr;
2
, . . . &lgr;
N
of the N optical signals preferably are equal to the channel center wavelengths, where the transmission spectra of the real device show the lowest losses. Any perturbation inducing a change in the channel center wavelengths of the device is preferably avoided.
WDMs, such as phasars, require precise control of the optical path difference (OPD) between adjacent waveguide paths of the phased array. The OPD can be expressed as n×&Dgr;L, where n is the effective index of the fundamental mode in the optical waveguide path, and &Dgr;L is the physical path length difference between adjacent waveguide paths. The mean channel wavelength &lgr;
0
is determined by m&lgr;
0
=OPD=n×&Dgr;L, where m is the diffraction order. Any shift of the mean channel wavelength induces the same shift on the channel center wavelengths. Since n and &Dgr;L usually both depend on temperature, the available integrated optical waveguide devices require temperature regulation to avoid a wavelength shift with temperature. Although such devices provide good performance at consistent standard room temperatures, the devices exhibit poor performance when used in environments where they are exposed to thermal variations and fluctuations in temperature. In such integrated devices, thermal shifts of the channel center wavelengths of greater than one tenth of the channel spacing at a transmitting wavelength in the 1550 nm range can limit their usefulness in environments of differing temperature. Silica-based phasars show a channel wavelength shift of about 0.01 nm/° C., while channel spacings are currently of 0.4 to 1.6 nm, which limits their use to small temperature ranges. Thus, use of integrated optical waveguide devices is limited by their temperature dependence.
Presently, the application of integrated optical waveguide devices has been hindered by the requirement to consistently maintain the temperature of the device such as by actively heating or cooling the device. While such costly and energy consuming heating and cooling may suffice in a laboratory setting, there is a need for an integrated optical waveguide device that is manufacturable and can be deployed in the field and operate properly when subjected to temperature changes. Accordingly, the present invention is directed to athermalized integrated optical devices that can be manufactured, packaged, and/or used without the requirement for temperature control.
SUMMARY OF THE INVENTION
The present invention is directed, in part, to an integrated optical waveguide device that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art. The present invention provides, in part, an athermalized integrated optical waveguide device comprising a thermal shift compensating negative dn/dT organic-containing overclad, such as a polymer or sol-gel, which inhibits the shifting of channel wavelengths due to variations in operating temperature within a predetermined operating temperature range. In a preferred embodiment of the invention, an athermalized phased array wavelength division multiplexer/demultiplexer is provided.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus, compositions, and methods particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described, the invention provides an integrated optical waveguide circuit device that includes a doped silica waveguide circuit core supported on a planar substrate. The planar substrate is preferably a solid flat substrate (such as a silica wafer or a silicon wafer) which may further include an underclad or buffer layer (such as an undoped or lightly doped silica layer). The doped silica waveguide circuit core has a first waveguide path and at least a second waveguide path, wherein the waveguide paths have a difference of &Dgr;L of path length that is selected to provide an optical path difference which corresponds to suitable channel wavelengths &lgr; in the range of 1500-1600 nm and to a suitable free spectral range (with respect to the number of channels and to the channel spacing).
Preferred optical waveguide devices of the invention include a thermal shift compensating negative dn/dT organic-containing overclad, such as a polymer or sol-gel, which may be used in combination with a doped silica (or silicate glass) partial overclad. The organic-containing overclad (together, if applicable, with the doped silica partial overclad) clads the doped silica waveguide circuit core. The organic-containing overclad is preferably made of a polymer material, or of a sol-gel material, and is preferably used in combination with a silicate glass as a local overclad, a bi-layer overclad, or a hybrid overclad. The overclad covers and encapsulates the waveguide circuit core. Preferably, the organic-containing overclad has a negative variation in refractive index versus temperature (dn/dT). The organic-containing material and the geometrical parameters of the device are selected such that the organic-containing material's negative variation in refractive index versus temperature (dn/dT) restricts the shift in the channel center wavelengths to less than 0.10 nm, preferably less than 0.05 nm, when the device is subjected to a temperature variation within the operating range of 0° C. to 70° C.
In a preferred embodiment of the invention, the device is a wavelength division multiplexer/demultiplexer with the waveguide paths forming a phased array. In other preferred embodiments of the invention, the athermalized integrated optical phased array wavelength division multiplexer/demultiplexer comprises a dop

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