Optical switch with liquid-air-liquid switch assembly

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical switch, and particularly to an optical switch employing a piezoelectric element to perform optical switching function.

[0004] 2. Description of Related Art

[0005] With the increasing development of optical telecommunications, the development of optical switches has become vital for better performance. A typical optical switch has one or more light input port(s) and at least two light output ports. Using these ports, the switch performs switching or logical operations on optical signals in a light transmitting link/system or in an integrated optical circuit. Measures for assessing the capability of an optical switch include low insertion bss (IL, <1 db), good isolation performance (>50 db), and fast switching speed (normally, tens of milliseconds).

[0006] Optical switches are commonly catergorized into mechanical type and non-mechanical type. In principle, a mechanical type optical switch has a number of advantages over a non-mechanical type optical switch when switching speed is not a critical factor for performance consideration. The mechanical type optical switches offer low insertion losses, high degree of immunity against backscattering of light from the switch back down the input fiber, low cross-talk, and insensitivity to wavelength of light.

[0007] Some conventional mechanical switches operate by moving an input fiber relative to a plurality of output fibers. Examples of such designs are disclosed in U.S. Pat. Nos. 4,303,302, 4,896,935 and 5,175,776. However, these optical switches share a common problem. They require high precision parts to obtain precise positioning control and low insertion loss. This results in high cost and complicated manufacturing process. Moreover, moving fibers repeatedly to and fro is apt to damage or even break the fibers.

[0008] Other kinds of conventional mechanical optical switches perform their optical switching functions by moving optical elements of the switches, such as ferrules with attached input/output fibers, reflectors, and lenses. U.S. Pat. No. 4,261,638 discloses an optical switch as shown in FIG. 5 of the attached drawings, comprising a rotatable reflector 3. The switching function is performed by rotating the reflector 3. The reflector 3 can be rotated around different axes, such as axis 2-2′, to switch the transmission of light coming from an input fiber 1 between selected output fibers 6. The switching speed of this optical switch is determined by the rotating speed of the reflector 3 and corresponding controlling mechanisms of the reflector 3. Since the optical switch is operated by rotating the reflector 3 around different rotating axes, the design and manufacturing of the optical switch are complicated. resulting in high cost.

[0009] A main object of the present invention is to provide an optical switch with high switching speed and low insertion loss.

[0010] An optical switch in accordance with an embodiment of the present invention comprises an input port and first and second output ports. An optical switching subassembly is arranged between the input port and the output ports. The input port and the first and second output ports are arranged in a T-shaped configuration with the input port and the second output port substantially aligned with each other forming an optical path. The first output port is arranged perpendicular to the optical path. The optical switch further comprises a shell enclosing the input and output ports and the optical switching subassembly.

[0011] The optical switching subassembly includes a first optical transmitting medium and a second optical transmitting medium respectively having first and second surfaces spaced from and opposing each other. A switching means is movably retained between the first and second surfaces of the transmitting media. The switching means comprises two optical transmitting liquid sections between the surfaces and an air section between the liquid sections. A piezoelectric (PZT) element is in physical engagement with one of the liquid sections and can be electrically biased to move the switching means between first and second positions.

[0012] The first and second optical transmitting media have the same first refractive index N₁. The first and second transmitting liquid sections have the same refractive index N₂which is approximately equal to N₁.

[0013] When the switching means is at the first position, the air section is coincident with the optical path between the input port and the second output port. Thus, light from the input port will be fully reflected by the first surface of the first optical transmitting medium and re-directed to the first output port. When the switching means is at the second position, the air section is moved out of the optical path and one of the liquid sections is moved to the optical path between the input port and the second output port. Since the second refractive index N₂is approximately equal to the first refractive index N₁, light from the input port is transmitted directly through the first transmitting medium, the liquid section and the second transmitting medium, and exits the optical switch via the second output port.

[0014] FIG. 1 is a cross-sectional schematic view of an optical switch in accordance with the present invention;

[0015] FIG. 2 is a cross-sectional schematic view of the optical switch of FIG. 1 showing a light signal transmitted from an input port to a first output port;

[0016] FIG. 3 is a cross-sectional schematic view similar to FIG. 2 but showing a light signal transmitted from the input port to a second output port;

[0017] FIG. 4 is a diagram showing an optical switch assembly/system containing more than one optical switch and defining more than two output ports/paths thereof; and

[0018] FIG. 5 is a schematic view of a conventional optical switch.

[0019] Referring to FIG. 1, an optical switch 100 in accordance with the present invention comprises a shell 40 enclosing an optical switching subassembly (not labeled). The shell 40 has an input port 10 and first and second output ports 50, 60 arranged in a T-shaped configuration wherein the input port 10 and the second output port 60 are substantially aligned with each other along an optical path. The switching subassembly is arranged at a center (an intersection) of the T-shape between the input port 10 and the output ports 50, 60. The first output port 50 is arranged perpendicular to the optical path between the input port 10 and the second output port 60. The input port 10, and the first and second output ports 50, 60 each comprise an input/output fiber 11 (12, 13) and a collimating lens 14 (15, 16).

[0020] The optical switching subassembly includes a first optical transmitting medium 21 having a triangular cross section and a first surface, a second optical transmitting medium 22 having a second surface spaced from and opposing the first surface, and a switching means 30 sandwiched between the first and second surfaces of the transmitting mediums 21, 22. The switching means 30 comprises an enclosure 33 having a first portion 34 outside the shell 40 and a second portion 35 arranged in the space between the first and second transmitting media 21, 22 and in communication with the first portion 34. The switching means 30 comprises first and second transmitting liquid sections 231, 232 which are properly enclosed so that the optical characteristics of the liquid are not affected. The liquid sections 231, 232 are movably retained in the second portion 35 of the enclosure 33 between the first and second transmitting media 21, 22. The liquid sections 231, 232 are spaced from each other to define an air section 233 therebetween. A piezoelectric (PZT) element 31 is contained in the first portion 34 of the enclosure 33 and is in physical engagement with the second liquid section 232 therein. The PZT element 31 is electrically connected to a power source 32 whereby the PZT element 31 can be selectively biased by the power source 32 and thus changes between a non-biased, first condition and a biased, second condition. The change of the PZT element 31 between the first and second conditions moves the liquid sections 231, 232 and the air section 233 between first and second positions with respect to the transmitting media 21, 22.

[0021] The first and second transmitting mediums 21, 22 have the same refractive index N₁. The first and second transmitting liquid sections 231, 232 also share the same refractive index N₂. N₂is approximately equal to N₁and preferably satisfies the following inequality relationship: N₁sin 45>N₂. It is more preferable if the inequalities: N₂>N₁and |(N₁−N₂)/N₁|>0.05 are also satisfied. The air section 233 has a refractive index N₃which meets the requirements: N₃<N₁, N₃<N₂, and θ>arcsin (N₃/N₁), where θ is the incident angle of light from the first transmitting medium 21 to the air section 233. The second portion 35 of the enclosure 33 has a refractive index approximately equal to N₁of the first and second transmitting mediums 21, 22, thereby having little or even no influence on the performance of the optical switch.

[0022] Referring to FIG. 2, in the first condition where the PZT element 31 is not biased, the air section 233 is in the first position that is coincident with the optical path from the input port 10 to the second output port 60. Light passing through the first transmitting medium 21 from the input port 10 is fully reflected by the first surface of the first transmitting medium 21 and is redirected to the first output port 50.

[0023] Referring to FIG. 3, in the second condition where the PZT element 31 is biased, the second transmitting liquid section 232 and the air section 233 are moved to the second position where the second transmitting section 232 is located on the optical path while the air section 233 is not. In other words, the second transmitting liquid section 232 replaces the air section 233 in the optical path from the input port 10 toward the second output port 60. Under this condition, light from the input port 10 is transmitted directly through the first transmitting medium 21, the second transmitting liquid section 232 and the second transmitting medium 22, and exits the optical switch via the second output port 60.

[0024] The PZT element 31 can also be designed to change in a reversed direction when it is biased. In this situation, the air section 233 is replaced by the first transmitting liquid section 231 in the optical path from the input port 10 to the second output port 60. Since the first transmitting liquid section 231 also has the refractive index N₂, the same effect as described above with the respect to the second transmitting liquid section 232 can be achieved.

[0025] In the embodiment illustrated in FIGS. 1, 2 and 3, the PZT element 31 is generally located outside the shell 40 of the optical switch. However, the PZT element 31 can also be designed to be completely received within the shell 40. Furthermore, the switching means can also be embodied in other arrangements and still accord with the present invention.

[0026] FIG. 4 shows an optical switch assembly/system having a plurality of optical switches and defining more than two output ports.

[0027] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.