Optical switch

1. Field of the Invention

The present invention relates to an optical switch for use in fiber communication and optical network technology, and particularly to a mechanically operated optical switch with a GRIN (graded index) lens and at least one mirror as a switching element.

2. Description of Related Art

Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optical fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals.

In optical fiber systems, various methods have been previously developed for switching optical signals between fiber cables. Among these previously developed methods, one important category is mechanical optical switches.

Mechanically operated optical switches come in two different designs: in one design, the optical components move, and in the other design, the fibers move. Factors for assessing the capability of an optical switch include low insertion loss (<1 dB), good isolation performance (>50 dB) and bandwidth capacity compatible with the fiber network the switch is supporting.

Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a light beam from one fiber end to another under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses which expand the light beam coming from the fibers, and then, using moving prisms or mirrors, redirect the expanded light beam to other fibers, as required by the switching process.

The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small fraction of the fiber core diameter for two fibers to precisely collimate to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes the fibers less flexible, increasing the force required to manipulate each fiber into alignment. Thus these moving fiber switches share a common problem of requiring high precision parts to obtain precise position control and low insertion loss. This results in high cost and complicated manufacture of the switches. Moreover, frequently moving fibers to and from is apt to damage or even break the fibers.

The moving optical component switches, in contrast, have less stringent movement control tolerance requirements. The presence of the collimating lenses allows relaxation of the tolerance requirements.

As illustrated in FIG. 14 and FIG. 15, U.S. Pat. No. 5,742,712 describes a mechanical optical switch, which relies on a mirror 420 being moveable into an optical path between a first and second fixed collimating lenses ( 428 , 436 ). When the moveable mirror 420 is displaced out of the optical path (FIG. 14 ), the light signals from a first input fiber 422 are transmitted to a second output fiber 432 and the light signals from a second input fiber 430 are transmitted to a first output fiber 424 through the first and second collimating lenses ( 428 , 436 ). However, when the moveable mirror 420 is moved into the optical path (FIG. 15 ), the light signals from the first input fiber 422 are reflected back through the first collimating lens 428 into the first output fiber 424 , which is parallel to and in close proximity with the first input fiber 422 . The light signals from the second input fiber 430 are likewise reflected back through the second collimating lens 436 into the second output fiber 432 , which is parallel to and in close proximity with the second input fiber 430 .

In this mechanical optical switch, the gap between the two collimating lenses ( 428 , 436 ), must be sufficiently large to allow movement of the movable mirror 420 between the two collimating lenses. However, this gap has a significant effect on insertion losses across the switch. For this reason, the gap is preferably less than about 2.0 mm. In addition, in a fixed collimator system initially without a mirror, the insertion of a two-surface mirror will introduce an insertion loss in an input/output port proportional to a thickness of the two-surface mirror.

For the above reasons, an improved optical switch is desired. In particularly, an optical switch is desired which has high optical efficiency and which does not require precise alignment or movement of the optical fibers themselves.

An object of the present invention is to provide an optical switch in which the optical fibers don't move.

Another object of the present invention is to provide an optical switch which allows easy alignment of associated fibers and which has a low insertion loss.

Yet another object of the present invention is to provide an optical switch which uses a GRIN lens as a switching element.

An optical switch in accordance with one embodiment of the present invention comprises a housing, a driver, a first I/O (input/output) port, a second I/O port and a switching element. The housing holds the first I/O port and the second I/O port in alignment with one another and supports the driver on the housing substrate. The switching element is rotationally attached to the driver and has a first and second mirrors and a rod lens. The driver drives the switching element between a first position, wherein the rod lens aligns with the I/O ports, and a second position, wherein the mirrors align with the I/O ports.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of an optical switch according to the present invention;

FIG. 2 is a cross-sectional view taken along the line 2 — 2 in FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 3 — 3 in FIG. 1;

FIG. 4 is an optical elements cross-sectional view of the optical switch of FIG. 1 in a first position;

FIG. 5 is an essential optical path of the optical switch in FIG. 1 in the first position;

FIG. 6 is a beam trace in GRIN lenses of the optical switch in FIG. 1 in the first position;

FIG. 7 is a second beam trace in the GRIN lenses of the optical switch in FIG. 1 in the first position;

FIG. 8 is an optical elements cross-sectional view of the optical switch of FIG. 1 in a second position;

FIG. 9 is an essential optical path of the optical switch in FIG. 1 in the second position;

FIG. 10 is an optical elements cross-sectional view of a second embodiment optical switch in a first position;

FIG. 11 is an essential optical path of the second embodiment optical switch of FIG. 10 in the first position;

FIG. 12 is an optical elements cross-sectional view of the second embodiment optical switch of FIG. 10 in a second position;

FIG. 13 is an essential optical path of the second embodiment optical switch of FIG. 10 in the second position;

FIG. 14 is an optical elements cross-sectional view of a prior art mechanical optical switch in a first position;

FIG. 15 is an optical elements cross-sectional view of the prior art switch of FIG. 14 in a second position.

Referring to FIG. 1, an optical switch 99 according to the present invention comprises a housing 10 , a first I/O port 20 , a second I/O port 40 , a driver 50 and a switching element 32 . The housing 10 comprises a substrate 11 forming a base of the housing 10 , two upright beams 12 extending upward at a front of the substrate 11 and a stopper 13 extending upward from the substrate 11 between the two upright beams 12 . The driver 50 is fixed to and extends upward from a rear of the substrate 11 .

The switching element 32 comprises a moving arm 503 having a rear end (not labeled) adapted for connecting with the driver 50 , a cross beam 321 attached to a forward end of moving arm 503 , and a pair of fixing arms 325 extending downward from either end of the cross beam 321 . A first and a second mirrors 322 , 323 are fixed at opposite side ends of the cross beam 321 , and a rod lens 324 is accommodated between and through the fixing arms 325 . The rod lens 324 is a half pitch GRIN lens.

The first I/O port 20 includes a first DFP (dual fiber pigtail) 25 , and a first collimator 27 . The first DFP 25 has an angled front surface 252 and the first collimator has an angled back surface 272 . The first DFP 25 and the first collimator 27 are held in fixed relation by using epoxy or solder between the angled front and back surfaces 252 , 272 . The first collimator 27 is a quarter pitch GRIN lens, or can instead be a 0.23 pitch GRIN lens.

Referring to FIG. 2, the first DFP 25 is an elongate tube having a hollowed out interior aperture 251 extending longitudinally therethrough. The aperture 251 accommodates a first input fiber 21 and a first output fiber 22 while constraining two centers of the first input fiber 21 and the first output fiber 22 to remain respectively on points A and B.

FIGS. 1 and 3 show that the second I/O port 40 is just like the first I/O port 20 , having a second collimator 47 , angled front surface 452 , angled back surface 472 , and a second DFP 45 . An aperture 451 of the second DFP 45 accommodates a second input fiber 41 and a second output fiber 42 , and constrains centers of the second input fiber 41 and the second output fiber 42 to remain respectively on points B′ and A′.

In assembly, the first I/O port 20 and the second I/O port 40 are engaged with corresponding upright beams 12 , which hold the first and second I/O ports 20 , 40 in alignment with each other. The driver 50 is fixed to and extends upward from a rear of the substrate 11 . The switching element 32 is rotationally attached to the driver 50 at a rear end of the moving arm 503 .

When the driver 50 is actuated, the switching element 32 is either moved up into a first position, wherein the rod lens 324 aligns with the two I/O ports 20 , 40 , or down into a second position, wherein the mirrors 322 , 323 align with the two I/O ports 20 , 40 . Downward movement of the switching element 32 is limited by the fixing arms 325 striking the stopper 13 .

FIGS. 4-9 illustrate the operation of the optical switch 99 . In the first position (FIGS. 4 and 5 ), the switching element 32 is in the upward position with the rod lens 324 aligned with the first and second collimators 27 , 47 . Light beams from the first and second input fibers 21 , 41 transmit through the first collimator 27 and the second collimator 47 , respectively. Each light beam is transmitted in opposite directions from each other through the rod lens 324 , and then through the second collimator 47 and the first collimator 27 , and then through the second output fiber 42 and the first output fiber 22 , respectively.

FIGS. 6 and 7 show tracings of light beams through the switch 99 when the switch 99 is in the first position. Note that light beams input through the points A and B′ are output through the points A′ and B, respectively, after transmitting two quarter pitch GRIN lenses 27 , 47 and a half pitch GRIN lens 324 . The two quarter pitch GRIN lenses 27 , 47 (the first and second collimators 27 , 47 ) have the effect of a half pitch GRIN lens which has been split into two equal parts.

In the second position (FIGS. 8, 9 ), the switching element 32 is in the downward position, where the first and second mirrors 322 , 323 sit in the optical path and align with the two I/O ports 20 , 40 . In this position, light beams from the first and second input fibers 21 , 41 are transmitted through the first and second collimators 27 , 47 and reflect off of the first and second mirrors 322 , 323 , to transmit back through the first and second collimators 27 , 47 and then through the first and second output fibers 22 , 42 , respectively.

FIGS. 10-13 show drawings describing operation of a second embodiment of an optical switch 99 ′ in accordance with the present invention. The optical switch 99 ′ makes use of a first mirror 322 ′ and a rod lens 324 ′ to realize alternate switching optical paths. The mirror 322 ′ and the rod lens 324 ′ move between a first position, wherein the rod lens 324 ′ aligns with a first and second collimators 27 ′, 47 ′, and a second position, wherein the first mirror 322 ′ aligns with the first collimator 27 ′.

In the first position (FIGS. 10, 11 ), the rod lens 324 ′ aligns with the first and second collimators 27 ′, 47 ′. A light beam from a first input fiber 21 ′ transits the first collimator 27 ′ and is then transmitted by the rod lens 324 ′ to the second collimator 47 ′ to the second output fiber 42 ′.

In the second position (FIGS. 12, 13 ), the first mirror 322 ′ aligns with the first collimator 27 ′. A light beam from the first input fiber 21 ′ is reflected by the first mirror 322 ′ to transmit through the first collimator 27 ′ and then through the first output fiber 22 ′.

The optical switch 99 of the present invention uses a moving GRIN lens and mirrors as switching elements, thereby avoiding the need to move fibers. Alignment is easily realized and low insertion loss is achieved by using the switching element 32 with two mirrors 322 , 323 and the rod lens 324 to replace the two reflecting-surface mirror of the prior art.

Advantages of the optical switch 99 of the present invention over those of the prior art include the following. First, only optical components of the switch move; no fibers move. Second, the first and second I/O ports are easily aligned with one another. Third, operation of the switch leaves only small gaps between moving optical components, rather than the relatively large gap left between the two opposing collimating lenses of the prior art design when the mirror is moved out of the gap between the collimating lenses. Thus, insertion loss in the design of the present invention is minimized. Basically, insertion loss is minimized by replacing an air gap left by the prior art design with the rod lens of the present design.

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. For example, the diameter of the DFP 25 , 45 could be altered to accommodate more than two fibers to produce a double 1×2 optical switch or a double 2×2 optical switch.