Optical waveguides – Temporal optical modulation within an optical waveguide – Electro-optic
Reexamination Certificate
2000-12-18
2003-03-04
Nasri, Javaid (Department: 2839)
Optical waveguides
Temporal optical modulation within an optical waveguide
Electro-optic
Reexamination Certificate
active
06529647
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical device with optical waveguides having a variable optical attenuation function, and more particularly to an optical device with optical waveguides capable of electrically controlling the attenuation of light passing through an optical waveguide circuit.
2. Description of the Related Art
U.S. Pat. No. 5,956,437 (Japanese Patent Laid-open No. Hei 11-249089) discloses an electrically controllable optical attenuator including a first Mach-Zehnder type optical interference unit and a second Mach-Zehnder type optical interference unit cascaded with each other. The first Mach-Zehnder type optical interference unit includes a pair of optical waveguide arms having different lengths. That is, one of the optical waveguide arms in the first Mach-Zehnder type optical interference unit is longer than the other. Similarly, the second Mach-Zehnder type optical interference unit includes a pair of optical waveguide arms having different lengths. That is, one of the optical waveguide arms in the second Mach-Zehnder type optical interference unit is longer than the other. The longer optical waveguide arm in the first Mach-Zehnder type optical interference unit is provided with phase control means, and the shorter optical waveguide arm in the second Mach-Zehnder type optical interference unit is provided with phase control means. In each optical interference unit, the builtin phase or initial phase of light passing through the longer optical waveguide arm is delayed by &pgr; or 2&pgr; from the phase of light passing through the shorter optical waveguide arm.
In the case that the initial phase delay is set to &pgr;, a maximum attenuation, or maximum loss is obtained when the phase delay by the phase control means is 0, whereas a minimum attenuation, or minimum loss is obtained when the phase delay by the phase control means is &pgr;. In the case that the initial phase delay is set to 2&pgr;, a minimum attenuation, or minimum loss is obtained when the phase delay by the phase control means is 0, whereas a maximum attenuation, or maximum loss is obtained when the phase delay by the phase control means is &pgr;.
Silica is used for each optical waveguide arm, and an electric heater is used for each phase control means. When power to be injected into the electric heater is increased, the temperature of the optical waveguide arm on which the electric heater is mounted rises to cause an increase in refractive index. As a result, the phase delay of light passing through the optical waveguide arm on which the electric heater is mounted increases, so that when the initial phase delay is set to &pgr;, the attenuation is decreased, whereas when the initial phase delay is set to 2&pgr;, the attenuation is increased. In the conventional electrically controllable optical attenuator described in the above publication, the attenuation characteristics of the first and second Mach-Zehnder type optical interference units are added together to realize an optical attenuator superior in wavelength flatness.
In the case of using a heater as each phase control means, the phase changes by &pgr; when a maximum power of about 500 mW is injected into each heater (a total maximum power of about 1 W for the two heaters), and the attenuation can be controlled from a minimum value to a maximum value. In the conventional optical attenuator described in U.S. Pat. No. 5,956,437 mentioned above, substantially the same quantity of energy is injected into each heater to control the attenuation, so that a change in injected power according to the attenuation becomes large. As a result, a change in heat value in the whole of the optical device becomes large. Such a large change in heat value causes a problem that the temperature of the optical attenuator and its peripheral device easily change. Thus, the optical attenuator described in the above publication has the problem that the temperature easily changes with a change in attenuation.
Further, in wavelength division multiplex (WDM) communication, a variable optical attenuator is used as an equalizer for equalizing the powers of a plurality of light sources. In this case, the variable optical attenuator is arranged downstream of each light source, and the powers of the light sources are equalized by setting the attenuation to the light source having the lowest optical power to 0 and attenuating the powers of the other light sources. In the case that the variable optical attenuator is used as such an equalizer for WDM communication, it is operated in a wavelength region where the loss is relatively low. In the conventional electrically controllable optical attenuator described in the above publication, the loss is minimum when the power input into each heater is maximum. Accordingly, in the case of using this conventional optical attenuator as an equalizer for WDM communication, it is operated in a wavelength region where the power consumption becomes substantially maximum. For example, in the case of using this conventional optical attenuator as an equalizer for WDM communication having 32 channels, the maximum power consumption becomes about 32 W.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical device with optical waveguides which can electrically control an attenuation with a reduction in power consumption.
It is another object of the present invention to provide an optical device with optical waveguides which can electrically control an attenuation with a reduction in change in heat value according to the attenuation.
It is a further object of the present invention to provide a manufacturing method for an optical device with optical waveguides.
In accordance with an aspect of the present invention, there is provided an optical device comprising a first Mach-Zehnder type optical interference unit including a first input optical waveguide, a first input 3-dB optical coupler optically connected in tandem with said first input optical waveguide, first and second interference optical waveguide arms optically connected in tandem with said first input 3-dB optical coupler opposite to said first input optical waveguide, said second optical waveguide arm having a length shorter than that of said first optical waveguide arm, a first output 3-dB optical coupler optically connected in tandem with said first and second interference optical waveguide arms, and a first output optical waveguide optically connected in tandem with said first output 3-dB optical coupler opposite to said first and second interference optical waveguide arms; a second Mach-Zehnder type optical interference unit including a second input optical waveguide, a second input 3-dB optical coupler optically connected in tandem with said second input optical waveguide, third and fourth interference optical waveguide arms optically connected in tandem with said second input 3-dB optical coupler opposite to said second input optical waveguide, a second output 3-dB optical coupler optically connected in tandem with said third and fourth interference optical waveguide arms, and a second output optical waveguide optically connected in tandem with said second output 3-dB optical coupler opposite to said third and fourth interference optical waveguide arms; first phase control means provided on said first interference optical waveguide arm; and second phase control means provided on any one of said third and fourth interference optical waveguide arms; the lengths of said third and fourth interference optical waveguide arms being adjusted so that the phase difference of light having a given wavelength passing through said third and fourth interference optical waveguide arms becomes 2n&pgr; where n is an integer greater than or equal to 0; said first and second Mach-Zehnder type optical interference units being optically connected in tandem with each other.
The lengths of said first and second interference optical waveguide arms are adjusted so that the phase difference of light havi
Katten Muchin Zavis & Rosenman
Nasri Javaid
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