Multi-fiber optical connect

An optical connector comprises a first block having a channel for accommodating a first set of optical cables and a second block having a channel for accommodating a second set of optical cables. Each block has three protrusions, each adapted to be engaged to a respective one of the three protrusions from the other block in an end-to-end fashion and having a channel for accommodating one of the optical cables. The connector further comprises a spring biasing the two blocks to maintain the end-to-end engagement a longitudinal direction between the protrusions three spacers. The connector also includes limiter disk having three slots arranged in a Y-pattern, each slot width-wise closely fitting an opposing pair of the protrusions. The limiter disk thus constrains the relative shifting or rotation between the two blocks in any direction transverse to the longitudinal direction. The connector further includes a fastener attached to the two blocks for securing the two blocks together. A kinematic support is thus provided for stable optical connection across an optical connector.

FIELD OF THE INVENTION

The invention relates generally to fiber optical systems. More particularly, the invention relates to an optical connector and method for reliably connecting optical fibers.

BACKGROUND OF THE INVENTION

Optical connectors are important components in fiber optical systems. Stable, intimate contacts between optical cables are crucial for reliable transmission of signals across the connection. The ability of two cable ends that are to be secured together by a connector to move relative to one another is often characterized by the degrees-of-freedom one end has relative to another. A cable end totally unconstrained relative to another has six degrees-of-freedom, which are often expressed in terms of three translational and three rotational coordinates. Ideally, the ends being connected have no degree-of-freedom relative to each other.

Optical cables are typically spliced in an end-to-end fashion. The connectors typically are designed to hold the opposing ends of optical cables to be spliced in compressive stress when the cables are connected. Typically in the prior art, to achieve stable contact between the ends of the optical cables, the ends of the cables and the areas surrounding the ends are made planar. However, any unevenness in the planar surfaces or contaminant particles, which may be introduced during the process of splicing the cables, will tend to give the connected cable end added degrees-of-freedom, i.e., to permit the ends to tilt relative to one another. The added degrees-of-freedom is generally undesirable for both optical connections that are relatively immobile (such as those for buried optical cables) and those that tend to be flexed or moved often (such as those connecting handheld optical probes to base stations). However, it is particularly undesirable for the latter as the movement of the connections will more likely expose the connector to impact and cause the connected cable ends to rock or shift relative to one another when the connector is moved.

The invention disclosed herein is aimed at providing a method and device for establishing reliable connection between optical cables, substantially without the drawbacks of the conventional approaches.

SUMMARY OF THE INVENTION

Generally, the invention provides a stable contact between two halves of an optical connector by employing an essentially kinematic engagement between the two. The essentially kinematic engagement is formed by maintaining a three-footed contact between the two halves of the connector in a longitudinal direction and constraining the relative shifting and rotation between the two in directions transverse to the longitudinal direction. More specifically, an optical connector according to the invention comprises a first block have a channel for accommodating a first optical cable; a second block have a channel for accommodating a second optical cable; three spacers, each positioned between the first and second blocks and engaging both blocks when the blocks are pressed against each other by a biasing force in a first (longitudinal) direction, the three spacers being positioned and adapted to balance substantially the entire biasing force; and a plurality of limiters arranged to constrain relative motion between any portion of the first block and any portion of the second block in all directions transverse to the first direction. In one embodiment each of the three spacers comprises a protrusion extending from either one of the first and second blocks and adapted to be engaged to the other one of the first and second blocks when the blocks are pressed against each other by the biasing force in the first direction. The limiters in one embodiment comprise slots for receiving the protrusions, the slots being arranged in a Y-pattern to prevent substantial movement of one of the blocks relative to the other in directions transverse to the longitudinal direction. The optical cables run through some or all of the three spacers (or protrusions), which are secured to the optical cables.

A connector according to the invention can also including a resilient member, such as a spring for providing a biasing force engaging the first block to the second block. The connector also includes a fastener having a first portion attached to the first block and a second portion attached to the second portion, the two portions being adapted to be connected to each other to maintain the biasing force engaging the two blocks to each other. The fastener in embodiment comprises a first shell adapted to house the first block and a second shell adapted to house the second block. The two shells are coupled together with a bayonet (pin-and-slot) mechanism.

In another embodiment, an optical connector further has a space for receiving an electrical device, such as an integrated-circuit chip, having a conductive terminal, and further comprises an electrode, such as a spring-loaded pin adapted to be in electrical contact with the conductive terminal when the two blocks are engaged to each other.

According to another aspect of the invention, an optical system comprises optical cables coupled together with a connector described above.

The invention further provide an optical device, such as an optical probe designed to be detachably connected to a base station, that includes and optical head, the device-side portion of an optical connector described above and an optical cable linking the optical head and the device-side portion of an optical connector. The device-side portion of the connector can further include a cavity for receiving an electrical device.

The invention also provides a method for coupling optical cables, the method comprising securing a first optical cable to a first block; securing a second optical cable to a second block; biasing the first block against the second block in a longitudinal direction at three locations while engaging an end of the first optical cable to an end of the second optical cable in one of the three locations; and constraining the relative movement between the first and second blocks in directions transverse to the longitudinal direction.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring toFIG. 1, an illustrative embodiment of the invention is a connector100for connecting a first set of optical cables10,12and14(see alsoFIG. 4) to a second set of three optical cables (not shown). Each set is enclosed in a protective shield (16and18, respectively). The first set of cables extend from the connector100to an end optical device (not shown), such as a handheld optical probe for measuring the spectral response characteristics of the subject of investigation (e.g., human tissues). An example of such a probe is disclosed U.S. patent application Ser. No. 10/698,751, which is commonly owned with the present application and is incorporated herein by reference. Each optical cable carries a desired number of individual optical fibers. For example, optical cable10is an input optical cable for transmitting light of different wavelengths to an optical emitter in the probe and includes a number of (e.g., four) optical fiber bundles 0.75 mm in diameter, each bundle to carry light of a different wavelength. Each bundle includes a number of optical fibers 50 μm in diameter. Optical cables12and14are, respectively, received-signal cable for collecting emitted light transmitted through the tissues and reference-signal cable for directly collecting emitted light. Each of cables12and14in this example includes an optical fiber 400 μm in diameter.

The second set of optical cable extend from the connector100to a base station, which provides any optical and electrical power supplied to the probe and performs signal processing and analysis functions.

The connector100includes the following components: a first block210on the probe side; a second block910on the station side; a spring310as a resilient biasing member engaging the first block210to the second910in a longitudinal direction110; a limiter disk410for constraining the relative motion between the first and second blocks in any direction transverse to the longitudinal direction110; an integrated-circuit chip610and its mounting board620to be positioned in the first block210; spring-loaded conductive pins1010and their holder1020to be positioned in the second block910; a probe-side shell510(in two halves510a,510b) for receiving the first block210and spring310; a station-side shell1210(in two halves1210a,1210b) for receiving the second block910; and a retainer nut (or probe-side-engaging nut)1220, which in cooperation with the probe-side shell, maintains the engagement between the first and second blocks.

FIG. 17shows the connector100in its fully assembled and connected state.

Referring further toFIGS. 2–5, reliable and stable connection between optical cables are provided by an essentially kinematic engagement, i.e., a combination of three-footed contact to prevent significant rocking motion between the blocks210,910and a limiter to prevent significant shift or rotation between the two blocks210,910. The probe-side block210has three cylindrical protrusions212,214and216on the portion218that faces the station-side block910; similarly, the station-side block910has three cylindrical protrusions912,914and916on the portion918that faces the probe-side block910. A three-footed contact is established by pair-wise engagement of the protrusions212,214and216to the protrusions912,914and916, respectively. Each protrusion includes an opening to accommodate and hold the end portion of its respective optical cable. Thus, for example, the protrusion212holds the end of the input optical cable10, and the protrusions214and216hold (e.g., by an adhesive) the ends of the received signal cable12and reference-signal cable14, respectively. The cables held by the station-side block910are arranged in a corresponding configuration. The ends of the protrusions212,214and216, together with the respective optical cables secured in the protrusions, are polished so that they are smooth and coplanar. Likewise, the ends of the protrusions912,914and916, together with the respective optical cables secured in the protrusions, are polished so that they are smooth and coplanar.

The main body of the probe-side block210comprises longitudinally three coaxial, cylindrical or truncated cylindrical (solid or otherwise) sections218,220and230, the axis of a truncated cylindrical section being defined as that of an imaginary cylindrical section without truncation. The centers of the protrusions212,214and216in this illustrative embodiment are positioned through the apexes of an equilateral triangle centered on the common axis of the main body. Similarly, the main body of the station-side block910comprises longitudinally three coaxial, cylindrical or truncated cylindrical sections918,920and930. The planar side surfaces in the truncated cylindrical sections (e.g., surfaces250,940and950) are designed to prevent rotation of either block relative to the shells510and1210. The middle section220is a flange, which the biasing spring310engages to push the first block210towards the second block910, and which acts as a stop, retaining the first blocks210in the shell510when the first block210is detached from the second block910. The middle section920is a flange, which the retainer nut1220engages to push the second block910towards the first block910.

The centers of the protrusions912,914and916in this illustrative embodiment are positioned through the apexes of an equilateral triangle centered on the common axis of the main body. Such a symmetrical configuration facilitates a balanced distribution of forces borne by the protrusions.

The limiter disk410in this illustrative embodiment has three slots412,414and416through its thickness for accommodating the pair-wise engaged protrusions (212,912), (214,914) and (216,916), respectively. The thickness of the disk410is greater than the tallest of the protrusions but no greater than the smallest combined height of any engaged pair of protrusions. Thus, when the two blocks210and910are pressed against each other such that the protrusions are pair-wise aligned, the protrusions are allowed to be engaged, preferably with space330left between the blocks210,910and the disk410. At the same time, both protrusions of any opposing pair are captured by one of the three slots412,414and416.

Each of the slots412,414and416has a width sufficient to accommodate the pair of protrusions intended to be position in that slot. The width, however, is not substantially greater than the diameter of the protrusions. That is, the width is not greater than the diameter of the protrusions by more than an amount of relative shift allowable between the opposing ends of the optical cables for adequate optical signal transmission across the interface between the ends of the optical cables. Preferably, the protrusions fit exactly in their respective slots within the manufacturing tolerances of the relevant parts. The slots412,414and416are further arranged in a Y-pattern. Thus, when the protrusions from the two blocks210and910are pair-wise engaged, the protrusions (and therefore the optical cables) are constrained in directions transverse to the longitudinal direction110. That is, the protrusions, and therefore the optical cables, are not allowed to move a significant amount (again, defined as more than the amount of relative shift allowable between the opposing ends of the optical cables for adequate optical signal transmission across the interface between the ends of the optical cables) relative to each other in any direction transverse to the longitudinal direction110.

An essentially kinematic engagement is thus formed. The finite contact areas between the polished ends of the protrusions and the manufacturing tolerances in the fit between the protrusions and the slots in the limiter disk results in a deviation from an ideal kinematic engagement. However, the small contact areas between the opposing ends of the protrusions and the limiter disk ensures a good approximation of an ideal kinematic engagement.

The spring310is slipped over the tail portion230of the probe-side block210. The probe-side shell510comprises retaining surfaces520and522for catching the flange portion220and the tail end312of the spring310, respectively. When the spring310and block210are received by the shell510, the spring310is compressed between the flange portion220and the retaining surface522, thereby exerting a biasing force on the block210. When the connector100is in its disconnected state, the retaining surface520stops the flange portion220, thereby preventing the block210from falling out of the shell510. When the connector100is in its connected state, the probe-side block210is displaced toward the spring310by a small distance320by the station-side block910. The protrusions (212,912), (214,914) and (216,916) are thus maintained in pair-wise engagement by the biasing force provided by the biasing spring310.

One of the advantages that the spring310provides is that a significant amount of deformation of external portions of the connector100is allowed while the intimate contacts between the ends of the opposing optical cables are maintained by the spring310. This feature allows the wider use of softer, and often more economical, materials, such as certain plastics, in portions of the connector100without compromising the integrity of the optical connections between optical cables. It also allows certain portions of the connector100be made with less precision than would otherwise be required without compromising the optical connections. The use of such materials makes certain application more feasible. For example, in applications such as medical examinations, it may be desirable to use disposable optical probes. Using plastic materials for certain portions, such as the block210, shell510and spring310, on the probe side of the connector100, serves to make the probes more affordable. In addition, the increased tolerance to deformation makes the connector more adapted to applications where the connector often is moved or experiences impact.

Referring in addition toFIGS. 6,7and8, the connector100further comprises an opening260for receiving an electrical device, which in this example is an integrated-circuit chip610bonded to the top of a mounting board620. The chip610has pins612a,612band612c, which are bonded (by soldering, for example) to the conductive pads622a,622band622c, respectively. At least some of the conductive pads, in this case622aand622b, are connected to conductive terminals, which in this case are the conductive pads628aand628b, respectively formed on the opposite sides of the mounting board620from the chip610. The electrical connections through the board620are made through “vias” (metal plugs filling holes through the board620) or, other conductive paths, between the top contact points624aand624b, and the bottom contact points626aand626b, respectively. The conductive pad622cin this example is a dummy pad for strengthening the bonding between the chip610and mounting board620but can be of any other suitable use, such as the ground plane of the circuitry.

The chip610can be designed to perform a variety of function as dictated by the particular applications. In one embodiment of the invention, where the length of time period a probe has been used can be monitored, one of the pins612aand612bis the power line and the other data line. The chip610further includes a circuitry having a timing counter that begins counting after the chip has been powered up for a set period of time (e.g., two minutes). The signals from the timing counter are transmitted to the base station via a conductive pin (to be described below) in contact with the conductive pad628aor628b. The base station is programmed to take proper actions in response to the signals from the timing counter. In another embodiment, data obtained from probe calibration are stored in the chip610and available to the base station.

The electrical device in this example is placed in the opening260with the conductive pads628aand628bfacing the station-side block. The opening has a step270along the periphery to seat the mounting board620.

Referring further toFIGS. 9 and 10, the connector100also comprises an opening960for receiving electrodes1010aand1010band an electrode holder1020. The electrodes1010aand1010bin this example are spring loaded electrodes, available from Everett Charles Technologies, Pomona, Calif., but can be of any suitable form, particularly of a resilient type. The holder1020, typically made of a plastic material, has a flange portion1022, which allows the holder1020to be seated in the opening960, which has a step970(seeFIG. 2).

Thus, as shown inFIG. 11, when the blocks210and910are pressed together to pair-wise engage the protrusions and optical cables, the pins1010aand1010bare pushed back by, and in contact with, the conductive pads628aand628b, respectively.

Referring further toFIG. 12, the tail portion930of the station-side block910has grooves980on the arcuate portions of the side surface for engaging the station-side shell1210. The station-side shell1210is in two halves and has inwardly protruding portions1212that fit in the grooves980. The shell1210also has a flat inner surface portions1214for engaging the flat side surfaces940to prevent the block910from rotating relative to the shell1210. The shell1210further comprises a strain relief portion1216, which grips the protective shield18encasing the optical cables running from the connector100to the base station.

Referring further toFIGS. 12–16, the connector100further comprises a retaining nut slipped over the tail portion930and flange portion920of the station-side block910to engage the probe-side shell510in a bayonet fashion. The retaining nut910in the example comprises a rigid nut1230, which can be made of a variety of suitable materials, including stainless steel, brass and hard plastics, and a cover1240, which can be a soft plastic over-mold or any other suitable material.

The rigid nut1230comprises a cylindrical ring portion1231and a flange portion1232projecting inwardly from the ring portion1231for engaging the flange portion920of the station-side block910. It also has pins1238a,1238band1237(only1238ais shown; seeFIG. 15) mounted in the dowel holes1234a,1234band1236, respectively and protruding inward from the ring1231. The pins can also be formed integrally with the ring portion1231. Two pins1238aand1238bare positioned to engage the slots512aand512b(only512ais shown), respectively, on the outside surface of the probe-side shell510(seeFIGS. 1,15and16) to lock the two halves of the connector100together. Each slot, using slot512aas an example, has a longitudinal segment514aand an essentially circumferential, slightly helical segment516a. In operation, the pin1238afirst enters the longitudinal segment when the retaining nut1220is pushed longitudinally toward the probe-side half of the connector100, against the biasing force from the biasing spring310. When the retaining nut1220is then twisted, the pin1238atravels along the essentially circumferential segment, thereby locking the two halves of the connector100. The third pin1237is positioned to engage a slot990of a finite length on the block910to limit the range of rotation of the rigid nut.

Other mechanisms to for locking the two halves of the connector100can be used. For example, the probe-side shell510and retaining nut1220can have mating threaded portions so that the two halves of the connector100can be screwed together, or snap-lock mechanisms so that the two halves can be snapped together.