Optical waveguides – Having nonlinear property
Reexamination Certificate
2000-02-22
2002-10-22
Bovernick, Rodney (Department: 2874)
Optical waveguides
Having nonlinear property
C385S132000, C385S009000, C385S040000
Reexamination Certificate
active
06470125
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a channel optical waveguide type optical device, driving method of the same optical device and manufacture of the same optical device which may be applied to switching of optical path such as an optical fiber and to an optical logical circuit and an optical memory and more specifically to an optical device, a matrix type optical device formed by arranging the plural optical devices, driving method of the same optical device and manufacture of the same optical device which may be driven with high response characteristic, low drive voltage, low crosstalk and low insertion loss and assures to maintain the constant characteristic by utilizing the hysteresis characteristic even under the condition that a voltage is not applied.
2. Description of the Related Art
An optical communication network is now being developed, from a point-to-point optical communication which is individually connecting nodes, to the Add_Drop Multiplexing optical communication which is realized between points and moreover to optical communication which is connecting among the plural nodes in direct with optical signal without conversion to an electrical signal. Therefore, development of various kinds of optical parts required for such communication such as optical branching/coupling device, optical multiplexing/demultiplexing device and optical switch or the like is very important and particularly a matrix type optical switch utilizing the plural optical switches (or optical gates) is one of the most important parts among various kinds of optical parts because it is used for switching the plural optical fibers depending on demands or for switching the fibers to assure the alternative route when a failure occurs in the network.
A type of optical switch can be sorted as a bulk type and optical waveguide type switches. A bulk type switch is used to switch the optical path by mechanically driving a prism, mirror or fiber or the like and has the merits in less dependence on wavelength and comparatively low loss but also has problems that switching speed is rather low, reduction in size is difficult, that structure is not suitable for matrix type arrangement and that assembling and adjusting process are rather complicated to result in considerable difficulty in mass production and cost reduction. The optical waveguide type switch has excellent merits in the switching speed, reduction in size and integration and mass production and therefore the optical waveguide type matrix optical switch is widely discussed.
The optical waveguide type matrix optical switch can roughly be sorted to two kinds of mode. In the first mode, a branching type channel optical waveguide for connecting an input port and output port is switched through combination of plural sets of the optical switches or optical gates based on a certain principle. In the second mode, an optical deflector is provided between the input port and output port to deflect the optical beam of input port toward the output port. In these modes, the optical waveguide type optical switch of the first mode is now discussed most widely from the viewpoint of flexibility of design and less amount of loss.
In the optical waveguide type optical switch, a channel optical waveguide is generally formed on LiNbO
3
, compound semiconductor, quartz or polymer and an optical switch for electrically controlling the traveling direction of optical beam or an optical gate for electrically controlling the switching of traveling of optical beam is provided at the crossing areas of respective optical paths.
The optical waveguide type optical switch utilizing quartz or polymer has a merit that the core size can be set almost equal to the mode field diameter of an optical fiber and insertion loss can be set small because optical coupling efficiency from the optical fiber is good, but also has a problem that a response rate is rather slow because a current is applied to a heater provided at the surface of optical waveguide in order to switch the traveling direction of optical beam by changing refractive index due to the thermo—optical effect. For example, it is disclosed in the J. Lightwave Tech. 16(1998) 1049 by T. Watanabe et al. That the response rate is extended up to 6 ms. Moreover, this optical switch also has a problem that only one electrode requires the power consumption as much as several hundreds of mW and its application field is limited because the heating system by heater is employed.
In addition, an optical waveguide type optical switch formed of an organic non-linear optical material is also proposed. In general, the optical waveguide can be formed of an organic non-linear optical material by doping organic non-linear molecule into the polymer or by giving the non-linear structure to the side chain or main chain portion of polymer to attain the electric field alignment polymer to which poling has been conducted through application of electric field. However, as disclosed in the reference, O plus E, 186(1995), 98 by Kainoh, the electric field alignment polymer has a problem of temperature stability in comparison with the oxide ferroelectric material and development of an element which may be enough for practical use is not yet insufficient in current.
In the case of the optical waveguide type switch utilizing a compound semiconductor or quantum well, high speed response can be realized but it also has a problem, as disclosed in the reference Optoelectronics 24 (1995) 324 by Koizumi, that a core size is small and optical coupling efficiency from an optical fiber is rather bad and thereby insertion loss becomes large. Accordingly, various effects have been made for this optical waveguide type optical switch. Moreover, this optical switch has the problems that the switching characteristic is deteriorated because optical absorption is generated simultaneously with the switching by the electrical field application and that it is difficult to form a large size matrix optical switch because the wafer size is limited.
In the case of the LiNbO
3
which is the most typical optical switch material and is one of the oxide ferroelectric material, optical condition changes at a high speed when a voltage is applied to the electrode of optical switch because the refractive index changes due to the electro-optic effect and the traveling direction of optical beam changes depending on the setting of optical condition. Therefore, each optical switch is capable of selectively outputting the light beam from a couple of input ends to a couple of output ends. Accordingly, when the traveling direction of the optical beam is adequately set in each stage, the light beam from the input port can be sent to the desired output port.
Moreover, in an optical switch using LiNbO
3
, a Ti diffusion type optical waveguide and a proton exchange type optical waveguide is formed to a single crystal wafer, but since the core size may be determined equal to the mode field diameter of an optical fiber and optical coupling efficiency from optical fiber is good, insertion loss becomes small. Accordingly, this optical switch is known as the optical switch for the level of practical use.
However, since a voltage is applied in the structure by providing a coplanar type electrode to the surface of optical waveguide, the distance between electrodes becomes long and an ideal field profile cannot be attained and the drive voltage as high as 40 volts is required in order to eliminate dependence on polarization disclosed, for example, in the Electron. Lett. 29 (1993) 765 by H. Okayama and M. Kawahara. Moreover, since the optical waveguide is formed by the Ti diffusion and proton exchange on the single crystal wafer, an effective refractive index of the channel optical waveguide cannot sufficiently be set higher than that of the peripheral area and therefore the difference of the refractive index cannot be set large. Accordingly, it is also required to assure the radius of curvature of S-shape channel optical waveguide as large as 50 mm and the s
Morikawa Takashi
Nakamura Shigetoshi
Nashimoto Keiichi
Bovernick Rodney
Fuji 'Xerox Co., Ltd.
Stahl Mike
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