Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-02-08
2004-07-20
Glick, Edward J. (Department: 2882)
Optical waveguides
With optical coupler
Particular coupling structure
C385S050000, C385S049000, C385S009000, C385S122000, C438S030000, C438S031000, C438S065000
Reexamination Certificate
active
06766082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure in which a surface-normal optical (or photonic) device or material is mounted on an optical fiber or waveguide, in which the surface-normal optical device or material has a function of controlling the intensity, phase, polarization of light, or a function of receiving, emitting, or modulating light. In particular, the present invention relates to a technique for inserting a thin and surface-normal active optical device into a trench which is formed perpendicularly to a substrate on which an optical fiber or waveguide is mounted.
2. Description of the Related Art
Optical communication using optical fibers has been rapidly spreading because it can transmit large amounts of data at high speed.
Optical waveguides are used in order to perform separating, coupling, switching, wavelength-division multiplexing, or wavelength-division demultiplexing of light. Optical waveguides are made of glass or polymeric material and are thus basically passive devices. However, the refractive index of an optical waveguide can be partially changed by providing a local heater or the like so as to obtain a thermo-optical effect. Accordingly, the phase and polarization of light can be controlled, thereby realizing an optical switch, variable optical attenuator, variable optical filter, or the like.
However, when a heater is provided on a substrate for waveguides, the distance between the heater and the core of the waveguide is large. Therefore, if a plurality of heaters having required high power are provided on a substrate, the temperature of the entire substrate is increased.
In addition, when a device or material having a function of emitting or processing light is provided at an optical waveguide, conventionally, the device or material is mounted on the optical waveguide. More specifically, when a semiconductor chip or the like having such a function is mounted on an optical waveguide, a relevant portion of the waveguide is removed, and the semiconductor device (i.e., chip) is mounted on that portion in parallel to the surface of the waveguide. Therefore, the distance between the divided waveguides is large, and thus transmission loss is large. In addition, it is very difficult to adjust a core (through which light passes) of the semiconductor chip to the core of the waveguide.
When a surface-normal optical device such as a semiconductor laser or an optical detector is mounted on an optical waveguide, the device is put on the same surface of the optical waveguide and the direction of light is changed by 45° by using a mirror. This structure is suitable for forming electrodes and being integrated. However, the distance between the device and the waveguide is large and the light is diffused; thus, a condenser such as a micro lens is necessary.
In addition, a technique for inserting a passive optical device such as a filter or a wavelength plate (typically, a half- or quarter-wave plate) into a trench formed in the waveguide is known. However, when an active surface-normal optical device is inserted into such a trench, necessary electrodes cannot be formed and obtained.
In most conventional optical devices used for optical communication, light output from an optical fiber is collimated so as to make the light pass through a surface-normal optical device, which can be selected from various kinds of surface-normal optical devices (i.e., optically-functional devices). This light is collimated again using a collimating lens so as to allow input into an optical fiber for outputting the light. However, many problems occur in this case, for example, the surface-normal optical device is relatively large and is expensive.
FIGS. 38A
to
38
D show typical optical devices using collimating fibers, where each collimating fiber has a collimator.
In the figures, reference numeral
19
-
1
indicates an optical fiber having an input collimator, reference numeral
19
-
2
indicates an optical fiber having an output collimator, reference numeral
19
-
3
indicates a rotatable half-wave plate, reference numeral
19
-
4
indicates a rotatable quarter-wave plate, and reference numeral
19
-
5
indicates a rotatable or movable ND filter. Reference numeral
19
-
6
indicates a homogeneous liquid crystal device, a TN liquid crystal device, a liquid crystal variable-wavelength filter in which a liquid crystal is inserted in a Fabry-Perot interferometer, or a piezo-controlled Fabry-Perot interferometer-type variable-wavelength filter. Reference numeral
19
-
7
indicates a first polarizer, reference numeral
19
-
8
indicates a second polarizer, and reference numeral
19
-
9
indicates a Faraday rotator.
In typical polarization control devices, a quarter-wave plate and a half-wave plate are inserted between the collimating fibers, and the polarization state of incident light can be changed by rotating such wavelength plates without any limitation (refer to FIG.
38
A). The wavelength plates are manually rotated in most laboratories. However, in practical systems, motor-controlled rotation is employed.
In variable optical attenuators, mechanical attenuators are known, in which a planar ND filter is rotated or moved with respect to collimated incident light (refer to FIG.
38
B). The planar ND filter can be manually adjusted or can be controlled using a motor.
The following devices are also known: (i) phase modulators in which a liquid crystal having a homogeneous alignment is inserted between collimating lenses, (ii) polarization switching devices for switching the polarization direction between 0° and 90°, in which a TN liquid crystal is inserted between collimating lenses, (iii) liquid crystal variable-wavelength filters in which a liquid crystal is inserted in a Fabry-Perot interferometer-type filter, and (iv) Fabry-Perot interferometer-type variable-wavelength filters in which a filter gap is adjusted using a piezo element (refer to FIG.
38
C).
Additionally, known optical isolators have a structure in which a Faraday rotator is inserted between polarizers whose polarization directions differ by 45° from each other, where collimated light is transmitted between the polarizers (refer to FIG.
38
D). In order to provide polarization-insensitive characteristics in this structure, a polarization separating element must further be employed.
In addition, optical fiber amplifiers are known, in which an excited optical beam is input into an optical fiber via a free-space optical beam system.
In the above-explained conventional devices, it is generally difficult to perform coupling and adjustment of the optical beam. In addition, such devices generally provide a single channel system, and the device is large. Therefore, it is difficult to reduce the costs of relevant optical elements.
When a trench having a width of 10 to 100 &mgr;m is formed in a substrate on which an optical waveguide or an optical fiber is provided and a functional device as explained above is vertically inserted into the trench, the optical device (including the functional device) which can be realized in a free-space optical beam system can also be realized as a waveguide-type device. In such a small width of 10 to 100 &mgr;m, radiation loss of light due to the presence of the trench is smaller than the power loss in the free-space optical beam system. In particular, if the width of the trench is equal to or less than 40 &mgr;m, the radiation loss is very small, approximately 0.2 dB.
The inventors have realized a variable optical attenuator by filling a trench, which is formed in a substrate on which an optical waveguide or fiber is fixed, with a liquid crystal material. In optical waveguides, a wavelength plate made of polyimide may be inserted so as to cancel the polarization dependence, or a dielectric mirror formed on a polyimide material may be inserted so as to perform wavelength-division multiplexing of light. That is, a liquid or an elastic material can be relatively easily inserted into a trench as explained above.
However, when a solid surface-normal op
Amano Chikara
Hirabayashi Katsuhiko
Glick Edward J.
Nippon Telegraph and Telephone Corporation
Suchecki Krystyna
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