Abstract: The invention relates to a method of measuring the wavelength of an optical signal such as a light beam. The optical signal is directed toward a detector where its intensity is detected and stored. Several optical elements each having a different wavelength dependence are moved into the path of the optical beam one at a time and for each intensity is detected and stored. The wavelength of the optical signal is then approximately determined based upon the ratio of the detected intensity of the optical signal in the absence of any optical elements and the detected intensities of the optical signal in the presence of each optical element.

Abstract: A bandpass optical filter is provided that is formed within an optical fiber in the form of a Bragg grating. The grating includes multiple Fabry Perot cavities disposed along the waveguide. Each of the cavities includes a pair of reflectors. Each reflector comprises alternating high-low index regions within the waveguide, each region having a thickness of one quarter-wave at a bandpass wavelength, each alternate region being of a different index of refraction than an adjacent region. A multiple odd quarter-wave or quarter-wave high or low index region is sandwiched between each pair of reflectors. The number of high/low regions within a reflector is selected in accordance with the refractive index difference between two alternate adjacent regions.

Abstract: An optical filter is provided having first and second graded index (GRIN) lenses preferably disposed in a coaxial relationship so that they have a common optical axis. Each of the GRIN lenses have an endface providing a port at predetermined location. The ports are disposed on opposite sides of the optical axis and each of the ports are substantially equidistant from the optical axis, so as to be oppositely offset from the optical axis by a same amount. The filter also includes an optical interference filter disposed between other endfaces of the first and second graded index lenses. By changing the location of the ports by a same small amount, the center wavelength of the filter changes by a small amount, thus in manufacture, the filter is tunable. After tuning the filter to a desired wavelength, the locations of the ports are fixed.

Abstract: A multi-wavelength optical filtering device for optical signal transmission, capable for functioning as a multiplexer or a demultiplexer. The device has at least one (first) optical circulator having at least four ports including an input port and a plurality of sequential ports, the last of said sequential ports being an output port, and an in-fiber Bragg grating (wavelength selective means) coupled to each of said sequential ports except said output port. The circulator may be branched off to a number of other circulators, the number depending on the number of the sequential ports of the first circulator, through the Bragg grating rather than through the output port of the first circulator. The other circulators, which are preferably also at least four-port circulators with wavelength selective means at the sequential ports, can also be branched off in an analogous manner as the first circulator.

Abstract: The apparatus extracts from an optical transmission path bidirectionally-propagating groups of wavelength-division multiplexed optical signals, arranges the groups to propagate unidirectionally via an output port, receives a corresponding unidirectional group via an input port, sorts the corresponding unidirectional group into two groups corresponding to those extracted from the transmission path, and returns the two corresponding groups of wavelength-division multiplexed signals to the transmission path so that each group propagates in its original direction. The apparatus comprises first and second bidirectional ports for coupling in series between first and second sections of the transmission path, and a series of optical devices each comprising first, second, third and fourth ports and an optical bandpass filter or other wavelength-selective element. Each of the filters selects a different wavelength.

Abstract: An opto-mechanical switch suitable for use in optical telecommunications systems comprises an input port and two output ports interconnected by an optical path, an optical element and an actuation mechanism for moving the optical element relative to the optical path so as to change coupling of light beams between the input port and the output ports. The optical element is supported by a flexible suspension unit comprising a pair of mutually-spaced twin elongate flexures. Each of the pair of flexures is attached at one end to an anchorage and at its other end to a mounting for optical element. The flexures are identical in length and flexibility and are spaced apart in the direction of displacement of the optical element. In use, when the actuator displaces the optical element, the flexures flex in common in the direction of displacement of the optical element. The optical element may be an optical fiber, a mirror, a prism, and so on.

Abstract: An optical connector ferrule is provided having an standard single mode optical fiber therein whose mode field diameter is approximately 10 .mu.m along its length. An end portion and the end face of the optical fiber are heated to thermally expanded the mode field diameter to approximately 20 .mu.m or greater for reducing power density at the end face. By providing an expanded mode field diameter at the end face of the fiber, the power density is lessened, thereby lessening the probability that any dirt or debris at the end face will become heated sufficiently to damage the optical fiber.

Abstract: An integrated optical isolator arrangement is described that is capable of isolating an input optical signal and coupling a pump signal. The coupler includes a pair of lenses with an isolator disposed therebetween. The isolator is sandwiched between a splitter/filter and a wavelength selective device. An end face of each lens has an input and an output port for receiving and transmitting optical signals. The splitter/filter is selected to transmit some of the input signal on a first input port and to reflect the remaining untransmitted portion of the input optical signal to a first output port proximate to the first input port. The wavelength selective device allows the input signal from the first input port to pass through it to a second output port, and in addition, reflects a pump signal transmitted on the second input port to the second output port for combination with the input optical signal.

Abstract: A non-reciprocal optical device for interconnecting single mode optical fiber waveguides so that a light beam can pass between the fibers in a forward direction but a reverse beam, such as might be caused by unwanted reflections, is displaced away the input fiber, includes a focussing lens unit and at least one non-reciprocal optical element in series between respective ends of an input optical fiber and an output optical fiber. The focussing lens unit has a focal length such that a light beam from the input optical fiber will be focussed onto the end of the output optical fiber. The focussing lens unit may comprise, for example, a half-pitch grin-rod lens. The non-reciprocal device is positioned adjacent one or other of the foci of the focussing lens unit. The focussing lens unit may comprise several lens elements, for example a pair of quarter pitch collimating lenses, allowing additional optical elements, such as filters, to be interposed.

Abstract: The optical circulator according to the present invention comprises two birefringent crystal end-plates, non-reciprocal Faraday rotators inserted between birefringent crystal plates, and a pair of matched birefringent crystal plates disposed between the rotators. The first birefringent crystal end-plate functions as a dividing and combining means for dividing a beam into two beams of orthogonal electric field vectors from different paths into one on the same path. The pair of matched birefringent crystal plates serve as beam path determining means shifting a beam to a different direction depending on the direction of the electric field vector and the propagation. The pair of crystal plates are substantially identical but oppositely oriented, such that the pair of means have opposite beam shifted directions.

Abstract: A chromatic dispersion compensation device is provided in the form of an etalon having first partially reflecting mirror providing an input and output port for porting a signal into and out of the etalon cavity. A second partially reflective mirror parallel to and spaced apart from the first mirror, being more reflective than the first mirror provides a monitoring port for monitoring energy within the cavity. Means are optionally provided for controlling a parameter related to the cavity in dependence upon a signal ported from the monitoring port. Means may be provided to control a transmitting laser in dependence upon the signal ported from the monitoring port.

Abstract: A method and apparatus is provided for injecting an optical test pulse mid-stream into an optical path to be tested by providing a switch that in normal transmitting and receiving of data includes two lenses separated by a gap. Data is usually transmitted across the gap from one lens to the other. In a test mode where OTDR is to be performed, a prism functioning in a similar manner to a periscope is moved into the gap between the lenses to couple/inject a test pulse into one of the lenses. An arrangement is described wherein either side of transmission line on either side of the gap can be tested.

Abstract: A device for splitting an optical beam into two beams propagating along different optical paths, is provided. The device includes a pair of graded index collimating lenses having their planar collimating ends aligned such that they are both inwardly facing and share a common optical axis. A partially transmitting partially reflective material is disposed between the lenses. At least one of the planar endfaces of the collimating ends are wedge shaped such that a non-zero angle is formed between the two endfaces. This non-zero angle reduces the effect of unwanted optical interference.

Abstract: A device is provided for controllably moving an optical element such as an attenuator, into one of a plurality of positions. The device includes a rotatable, cylindrical member having a face cam that is an endless cammed surface for supporting and moving a cam follower. As the cammed surface is rotated, the cam follower resting upon it moves the optical element in a controlled manner. A gearing means in the form of a toothless planetary gear box is coupled to the cylindrical member and provides fine control over the range of movement of the device.

Abstract: An tunable optical filter of the kind used, for example, in wavelength-division multiplexing (WDM) optical communication systems and tunable source applications, has an interference filter element which is pivotable to adjust the operating wavelength of the filter. In order to reduce polarization dependency as the angle of the interference filter element changes, the light beam to be filtered is passed through the filter element twice, the second time with its polarization state shifted, specifically orthogonal, relative to the polarization state during the first pass. As a result, polarization dependent effects are equalized.

Abstract: In order to reduce the number of components and avoid relatively long optical lengths, a non-reciprocal device such as a circulator comprises a plurality of ports at one end of the device, a mirror at an opposite end of the device, and a series of optical elements disposed between the ports and the mirror. The optical elements include a first element which spatially separates first and second orthogonally-polarized components of a light beam leaving one of said plurality of ports and passing through the device in a forward direction, and recombines the first and second components as they pass through the device in a reverse direction after reflection. A second optical element, disposed between the separating and recombining element and the mirror, selectively displaces and rotates the light beam components such that the recombined light beam is coupled to a different one of the plurality of ports.

Abstract: A polarization-independent optical detection apparatus for measuring light output from optical fibers comprises an optical detector having an input port for receiving input light by way of an optical path and an output for a corresponding detection signal. A polarization-transformation element is rotatably mounted in the optical path so that the input light passes through the element to reach the input port. A drive motor rotates the polarization-transformation element in a plane extending transversely of the optical path. The polarization-transforming element is selected to transform the polarization state of the input light reaching the detector, as the element spins, so that, for any given input polarization state, the time averaged electrical signal from the detector is approximately the average electrical signal from the detector over all input polarization states.

Abstract: A multi-port tunable fiber-optic etalon filter (MTFET) having two spaced partially reflective mirrors, has three or more ports, with at least two on one side and at least one on the other side of the etalon. A single signal can be filtered with the reflected signal being received, forming a wavelength division multiplexor, or a plurality of signals can be filtered, with or without the reflected signals being received. A series of filters can be arranged in a cascade for sequential filtering a series of wave bands. A signal can be processed in two directions sequentially for a higher filter efficiency. A first signal can be monitored and controlled by a second signal. Various other arrangements can be provided. Integral optical processing functions can be incorporated, for example a blocking filter.

Abstract: A moving fiber optical fiber switch is formed by mounting one or more optical fibers on support surfaces of two spaced support members, one or both of which are laterally movable. After mounting of the fiber or fibers, a transverse fine cut across the fiber or fibers produces a conventional gap, but providing extremely accurate positioning. A pivot member moved by a coil mounted on a lever extension, in conjunction with magnets, moves one or both support members via rods or similar members extending between the pivot member and the support members, one on each side of the pivot axis of the pivot member. Adjustment means coactive with the free end of the lever provides easy and accurate control of the pivoting of the pivot member and of the support members and fibers. A large lever differential obtained by the lever provides for the ease and accuracy of control.

Abstract: A graded index lens having one end-surface thereof adapted for connection to an optical fiber or the like characterized by an axially asymmetrically tapered end portion terminating in the end-surface.