Thermo-optic tunable optical attenuator

Details Thermo-optic tunable optical attenuator Thermo-optic tunable optical attenuator

2001-05-14

2003-07-01

Kim, Robert H. (Department: 2882)

Optical waveguides

Accessories

Attenuator

C385S045000, C385S001000, C385S002000, C385S003000

Reexamination Certificate

active

06587632

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an integrated optical technology; and, more particularly, to a thermo-optic tunable attenuator has a wide range of light attenuation region, a linear operating characteristic and a polarization independence characteristic for an input electrical signal, and the ability to operate at a speed of milliseconds.
DESCRIPTION OF THE PRIOR ART
In general, an optical attenuator serves to attenuate an intensity of an input optical signal and a tunable attenuator serves to control a degree that the optical signal is attenuated in an electrical and mechanical manner.
A conventional tunable attenuator includes an opto-mechanical optical attenuator, an optical attenuator using a micro electro mechanical system (MEMS) and a thermo-optic optical waveguide type of optical attenuator.
The opto-mechanical optical attenuator utilizes a technique which spaces two optical fibers at a small interval from one another and mechanically moves a variable absorption filter or a shielding film over the interval, to thereby absorb or shut off a portion of incident light, or a technique which collocates two side-polished optical fibers with each other and controls an interval therebetween, to thereby adjust an intensity of light to be transmitted through. Although, however, the opto-mechanical optical attenuator may have extremely good characteristics including an optical attenuation range higher than 50 dB, a reduced insertion loss and a linearity of 0.1 dB, it suffers from a drawback that it requires numerous bulky discrete components to decrease the operational speed on a second basis.
In addition to an excellent operation characteristic of the opto-mechanical optical attenuator, the MEMS based optical attenuator also has merits including an increased operation speed of microseconds and a reduced operation power. Unfortunately, the MEMS based optical attenuator suffers from a drawback that it is difficult to integrate with another optical waveguide device.
The thermo-optic optical waveguide type of optical attenuator is implemented through the use of operation characteristics of a thermo-optic modulator or thermo-optic switch, which may be used in an integrated optical circuit. The thermo-optic tunable attenuator using silica or polymer has been published, which can precisely control an optical attenuation degree in an operation speed of milliseconds, a polarization independence and powers less than several hundreds mW.
In practice, as the opto-mechanical optical attenuator and the MEMS based optical attenuator, an optical attenuator using an asymmetric Y-branch optical switch has a digital-like operational characteristic in which the optical attenuation degree is continuously decreased with an external drive signal to reach to a saturation state, extends the optical attenuation degree over 30 dB, and increases a degree of fault tolerance to facilitate fabrication processes. For this reason, studies of the optical attenuator using the asymmetric Y-branch optical switch are actively in progress.
In
FIG. 1
, a schematic pictorial view of a conventional tunable attenuator using a thermo-optic device is illustrated. As shown in
FIG. 1
, the conventional tunable attenuator includes an optical modulator having an asymmetric Y-branch waveguide
11
and a drive electrode
12
for applying a power, a main output port
13
for outputting an attenuated output from the optical modulator, a monitor port
14
for extracting a portion of the main output port
13
to monitor extracted results, and a dummy drain port
15
, which is branched from the asymmetric Y-branch waveguide
11
in a curve shape, for removing a portion of input optical power. The conventional tunable attenuator has been published in the following paper: “Polymeric Tunable Attenuator with an Optical Monitoring Tap for WDM Transmission Network”, IEEE Photonics Technology Letters, Vol. 11, No.5, p590, May 1999, Sang-shin Lee, et.al.
As mentioned above, the conventional optical attenuator including the asymmetric Y-branch waveguide
11
and the drive electrode
12
attenuates an intensity of output light beam responsive to an applied power using a mode evolution scheme and feeds back a portion of output light beam to thereby stabilize the output light beam.
However, the conventional thermo-optic tunable attenuator suffers from a drawback that since a change in optical attenuation degree for an applied power is non-linear, it causes a considerable amount of power consumption at an initial change in the optical attenuation degree, thereby adversely affecting the energy efficiency of the tunable attenuator.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a thermo-optic tunable attenuator which is capable of preventing a considerable amount of power consumption due to a non-linear change in optical attenuation degree for a power applied externally, to thereby achieve a high linearity, a wide range of optical attenuation region higher than 35 dB, an operation speed of milliseconds, a polarization independence and be configured for use in an integrated optical circuit.
In accordance with a preferred embodiment of the present invention, there is provided a thermo-optic tunable attenuator, which comprises a single mode channel optical waveguide; an optical waveguide of a Mach-Zehnder interferometer structure coupled with the single mode channel optical waveguide, the optical waveguide including two symmetric Y-branches; and two metal heating wires for applying power to one side of each of the two symmetric Y-branches, wherein the two metal heating wires are in a facing relationship with each other, wherein a refractive index of the optical waveguide is changed in response to a power applied to any one of the two metal heating wires.
Preferably, the thermo-optic tunable attenuator further comprises a first metal electrode for connecting the two metal heating wires in a series fashion; and a pair of second metal electrodes, each of which being connected to a corresponding one in the metal heating wires, for applying the power to the metal heating wires.


REFERENCES:
patent: 5502780 (1996-03-01), Rangaraj
patent: 5696855 (1997-12-01), Skeie
patent: 5841568 (1998-11-01), Miyakawa
patent: 5917974 (1999-06-01), Tavlykaev et al.
patent: 6181456 (2001-01-01), McBrien et al.
patent: 6320692 (2001-11-01), Notargiacomo
IEEE Photonics Technology Letter, vol. 12, No. 4, Apr. 2000, pp. 407-409.
IEEE Photonics Technology Letters, vol. 11, No. 5, May 1999, pp. 590-592.

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