Abstract: A tunable optical filter comprises an optical switch having a single first optical port and a plurality of second optical ports; a plurality of band pass filters, each one of the band pass filters optically coupled to a respective second optical port; and an optical multiplexer having a plurality of inputs and a single output, each input optically coupled to a respective band pass filter, wherein the optical switch delivers a plurality of optical channels to a selected one of the band pass filters, the selected band pass filter transmitting a single selected optical channel to an input of the optical multiplexer. Alternatively, the multiplexer may be substituted by a second optical switch. Optionally, the band pass filters may reflect other channels back to the plurality of second optical ports.

Abstract: The present invention relates to a multiple access space laser communications optical system. According to the present invention, multiple optical signals containing a number of channels are simultaneously received and demultiplexed at a multiple access communication device. Separate communication signals may be multiplexed by the multiple access communication device, and transmitted through the same or a different telescope optical assembly used to receive communication signals. Double-pass reflection is used to selectively polarize signals and to ensure that signals are substantial normal to optical bandpass filters, to avoid large shifts in the wavelengths transmitted by the optical bandpass filters. The system is capable of providing discrete communications with a number of communication endpoints, regardless of where the communication endpoints are located within the field of view of the telescope optical assembly.

Abstract: Laser light emitted from a vertically confined surface emitting laser (VCSEL) is incident on a side surface near an end region of an optical waveguide. The end region of the optical waveguide is processed by polishing to taper at an angle of 45 degrees, and an optical modulator is formed on the polished surface. The optical modulator is a Fabry-Perot modulator using a linear electro-optical effect. The modulator has a thick transparent electro-optical layer which is deposited by using an aerosol deposition method.

Abstract: A bi-directional (BiDi) electrical to optical converter (transceiver) module is described that contains means for communicating in a full duplex fashion over one fiber. Furthermore, an automatic fail-over capability is included which allows redundancy to be build in to the transceiver. In one configuration, a BiDi transceiver module contains two lasers at different wavelengths and a means for establishing which wavelength to communicate with. An example of an application for the described invention is a storage area network application which requires redundant links and are currently bound by the number of fibers connecting to the front panels of switches.

Abstract: A bi-directional path switched ring optical transmission node has simple configuration which reduces the influence of a wave reflected by an obstacle on optical line.The BPSR optical transmission node connects to a first optical line through which an odd channel signal and an even channel signal are transmitted to and from the BPSR optical transmission node in direction opposite to each other. The BPSR optical transmission node further connects to a second optical line through which the odd channel signal and the even channel signal are transmitted from and to the BPSR optical transmission node in direction opposite to each other.

Abstract: A tunable add/drop&continue or drop&continue module comprises two optical filters where at least one is tunable and that are arranged following one another between a branching unit for optical signals and an insertion unit follow a branching unit for optical signals. The reflection attenuation of the one tunable optical filter is lower and the transmission attenuation higher than that of the other optical filter, as a result of which the drop&continue function of the module can be realized without high circuit-oriented expense.

Abstract: Improved designs of optical devices for processing optical signals with one or more specified wavelengths are disclosed. According to embodiment, a filter mirror assembly appears an “L” shape and provides a filtering function as well as a reflecting function. The filter mirror assembly is so mounted that a rotation thereof will not alter the optical path the beam positions of signals resulted from a rotation of the filter mirror assembly. To cancel or minimize a lateral shift introduced to a light beam going through an optical filter, an optical compensator is introduced and rotates oppositely whenever the optical filter rotates.

Abstract: This invention provides a system that combines a wavelength multiplexer with an FM discriminator for chirp reduction and wavelength locker in a filter to produce a wavelength division multiplexed signal with reduced chirp. A partially frequency modulation laser signal is converted into a substantially amplitude modulation laser signal. This conversion increases the extinction ratio of the input signal and further reduces the chirp. A wavelength division multiplexing (WDM) method is used for transmitting high capacity information through fiber optics systems where digital information is carried on separate wavelengths through the same fiber. Separate transmitters normally generate their respective signals that are transmitted at different wavelengths. These signals are then combined using a wavelength multiplexer to transmit the high capacity information through the fiber optic system.

Abstract: An optical multi-filter discriminator suitable for treating optical signals from an optical signal source, e.g., a direct modulated laser (“DML”), comprises a first optical filter, a second optical filter optically coupled to the first optical filter, an input port operative to receive optical signals from an optical signal source and oriented to launch the optical signals directly or indirectly to the first optical filter, and an output port oriented to receive optical signals treated by the multiple optical filters and operative to pass the optical signals directly or indirectly to an optical waveguide “downstream” of the discriminator. The first filter is transmissive (i.e., at the angle of incidence received from the input port) of at least a first wavelength band having a first center wavelength and reflective (again, meaning in this instance at the angle of incidence received from the input port) of at least a second wavelength band different from the first wavelength band.

Abstract: A flexible waveband deaggregator/aggregator design is disclosed, including an embodiment that utilizes flexible band tunable filters and an embodiment that utilizes tunable interleavers. An optical cross-connect design is also disclosed which utilizes the flexible waveband deaggregators and which can replace a core all-optical switch with a fiber interconnect matrix.

Abstract: A switchless optical add/drop module (OADM) includes: a first variable optical splitter (VOS) for splitting a composite optical signal including a plurality of channels into a first portion and a second portion; a first multi-channel variable optical attenuator (MCVOA) optically coupled to the first VOS, where the first MCVOA blocks dropped channels of the first portion, transmits express channels of the first portion, and balances power levels of each of the transmitted express channels of the first portion; a second VOS optically coupled to the first MCVOA opposite to the first VOS for combining the transmitted express channels of the first portion and added channels; and a second MCVOA optically coupled to the first VOS, where the second MCVOA blocks express channels of the second portion, transmits dropped channels of the second portion, and balances power levels of each of the transmitted dropped channels of the second portion.

Abstract: A bidirectional optical add-drop multiplexer adds and drops optical signals having specific wavelengths among the WDM optical signals transmitted bidirectionally through one of the optical transmission lines connected between neighbor nodes in a bidirectional WDM ring network.

Abstract: An optical wavelength locking system is provided that includes a plurality of optical signal generating units for generating optical signals corresponding to a plurality of channels, and an optical wavelength locking unit for receiving the optical signals corresponding to the plurality of channels and sequentially controlling a wavelength fluctuation exhibited by the optical signal of each channel. Since one optical wavelength locking unit is used for a plurality of optical sources, production costs are reduced, a better utilization of available space can be achieved and the reliability of the system is improved.

Abstract: A wavelength division element includes a first filter and a second filter. The first filter has incident angle-to-transmission wavelength characteristics and separates multiplexed lights in a plurality of wavelength bands into first lights that are in a first wavelength band and first reflected lights. The first filter allows the first lights to pass through in a first direction and reflects the first reflected lights in a second direction. The second filter is located in the second direction and separates the first reflected lights into second lights that are in a second wavelength band and second reflected lights. The second filter allows the second lights to pass through in a third direction and reflects the second reflected lights in a fourth direction.

Abstract: The invention relates to a planar lightwave circuit including a two stage optical filter for use in a bi-directional transceiver. A first stage includes a non-dispersive optical filter, which enables light within in a certain wavelength range, e.g. a signal channel from a laser source, to be launched onto an input/output waveguide, while light within another wavelength range, e.g. one or more detector channels, will be directed from the input/output waveguide to a second stage. The second stage includes a reflective diffraction grating with a higher resolution than the first stage providing passbands 2 to 5 times thinner than the first stage.

Abstract: In an optical wavelength division multiplexed access system, a center unit (OSU) and n optical network units (ONUs) are connected together via a wavelength splitter and optical fiber transmission lines, and downstream optical signals from the OSU to the ONUs and upstream optical signals from the ONUs to the OSU are transmitted in both directions, the wavelength spacing ??d (optical frequency spacing ?fd) of the downstream optical signals is set to twice or more the wavelength spacing ??u (optical frequency spacing ?fu) of the upstream optical signals, each ONU transmits an upstream optical signal whose optical spectral width is twice or more ??u (?fu), and the wavelength splitter spectrum slices the upstream signals transmitted from the ONUs into wavelengths (optical frequencies) whose optical spectral widths are mutually different within ??u (?fu), and wavelength-division multiplexes them and transmits to the OSU.

Abstract: The invention relates to a system for conveying digital signals inside a space vehicle between a transmitter and a receiver. In the invention, the link between the transmitter and the receiver comprises a first portion made of optical fiber and a second portion in which infrared radiation propagates without guidance. A particular application lies in conveying remote control and telemetry signals within a satellite between a control module and a piece of equipment.

Abstract: The first present invention provides an optical switch including the following elements. At least a plurality of optical transmission lines are provided for transmissions of optical signals. Each of the at least plurality of optical transmission lines have at least an impurity doped fiber. At least an excitation light source is provided for emitting an excitation light.

Abstract: A reconfigurable optical add-drop multiplexer is disclosed including an optical splitter receiving an input optical signal and splitting the input optical signal into a dropped optical signal and an express optical signal; a wavelength blocker optically coupled to the optical splitter, the wavelength blocker blocking particular wavelengths in the express optical signal; a cassette having a plurality of slots capable of accepting a plurality of pluggable optical filters; at least one pluggable optical filter optically coupled to the optical splitter, the pluggable optical filter filtering wavelengths so as to output a particular wavelength channel from the dropped optical signal; and an optical combiner optically coupled to the wavelength blocker and to an optical add path on which an optical add signal may be carried, the optical combiner combining the express optical signal having particular wavelengths expressed by the wavelength blocker and the optical add signal.

Abstract: The present invention propose an optical filter for filtering out at least a part of one of two spectral side-bands of a coded optical signal spectrum having a carrier wavelength, the first of said side-bands which is to be transmitted by said filter being called transmitted side-band, the second of said side-bands which is to be filtered out by said filter being called vestigial side-band, said optical filter having a transmission response in intensity, having a maximum value at a central filter wavelength distinct from said carrier wavelength and located in said transmitted side-band, and said response being divided into two parts, a first filter part associated to a wavelength region including said carrier wavelength, a second filter part associated to a wavelength region which does not include said carrier wavelength where at a given value of transmittance distinct from said maximum value, said second filter part has a filter width smaller than the filter width of said first filter part.

Abstract: The present invention describes a structure and method for a multi-ports WDM device for compensating the filter distortion while reducing insertion loss. The multi-ports WDM device comprises a 4-fiber collimator having a grin lens and a 2-fiber collimator having a lens where the focal plane of the second lens is shorter than the focal plane of the first grin lens Ands with aspheric surface. When a light signal travels through the first lens in the 4-fiber collimator to a filter, the film on the filter causes distortion to the light signal resulting in a large insertion loss. To compensate for the insertion loss, the lens on the 2-fiber collimator has a aspheric function and a shorter focal plane than the grin lens on the 4-fiber collimator. The type of grin lens used in the 4-fiber collimator is different than the lens used in the 2-fiber collimator. Effectively, the lens in the 2-fiber collimator operates to de-focus a light signal relative to the grin lens in the 4-fiber collimator.

Abstract: Disclosed is a dense wavelength division multiplexing-passive optical network (DWDM-PON) system utilizing self-injection locking of Fabry-Perot laser diodes, in which output optical signals of different wavelengths are partially fed back by a partial mirror, so as to injection-lock the Fabry-Perot laser diodes, respectively. In accordance with this system, inexpensive Fabry-Perot laser diodes can be used as respective light sources of a central office and optical network units (ONUs). Accordingly, it is possible to minimize the system construction costs, as compared to conventional optical networks.

Abstract: A method and an apparatus are provided to demultiplex an optical signal having a plurality of channels at a predetermined channel spacing having demultiplexing means with a frequency spacing larger than the predetermined channel spacing for receiving the optical signal and for dividing the optical signal by wavelength into a plurality of wavelength streams broader than the predetermined channel spacing, time domain demultiplexing means for receiving one of the plurality of wavelength streams and for dividing the one of the plurality of wavelength streams into a plurality of time domain demultiplexed wavelength streams, and optical filtering means for demultiplexing one of the plurality of time domain demultiplexed wavelength streams into a single channel. Advantageously, splitting means are provided to split the optical signal into sub-signals before launching them into the demultiplexing means.

Abstract: An optical signal transmitter is disclosed that transmits an optical signal with corresponding Wavelength Division Multiplexing (WDM) channels and Time Division Multiplexing (TDM) channels. The transmitter is comprised of a laser, a dispersion system, and a modulator. The laser generates and transmits a narrow laser pulse comprised of a plurality of wavelength channels. The dispersion system broadens the narrow laser pulse into a wide laser pulse. The modulator modulates the wide laser pulse based on an electric modulation signal comprised of a plurality of time slot channels wherein the time slot channels in the electric modulation signal correspond to the wavelength channels in the wide laser pulse respectively. The modulator transfers a modulated wide laser pulse. Channels of the modulated wide laser pulse are hybrid wavelength and time slot channels. The transmitter singularly transmits a WDM optical signal comprised of multiple wavelength channels.

Abstract: An optical delay circuit includes a plurality of defect waveguides arranged in parallel and including a line-shaped defect in a periodic refractive-index distribution structure of a photonic crystal. The defect waveguides include a multiplexing/demultiplexing portion in which the defect waveguides are arranged close to each other to multiplex and demultiplex light; and an optical delay portion extending from the multiplexing/demultiplexing portion, in which the defect waveguides are arranged with a predetermined distance therebetween so that light propagating in any of the defect waveguides does not interfere with light propagating in the other defect waveguides. Each of the waveguides has a different configuration.

Abstract: A tunable dispersion compensator whose passband center wavelength changes when the amount of dispersion compensation is changed is suitably adjusted. The relationship between temperature for keeping the center wavelength constant and the amount of dispersion compensation is stored in advance. After controlling the amount of dispersion compensation to achieve best or optimum transmission quality, the amount of dispersion compensation is converted into temperature in accordance with the stored relationship and, based on that, the temperature is controlled to keep the center wavelength constant.

Abstract: A light branching/inserting apparatus which can easily control light signal wavelengths, and which can branch, insert or transmit light signals having an optional wavelength and optional multiplexed number, by using a wavelength selection filter utilizing acousto-optic effects.

Abstract: AOTF controller that monitors output power of a plurality of wavelengths of an AOTF and scans the frequency of corresponding RF input signals to an AOTF acoustic transducer and searches for the RF frequency corresponding to each desired wavelength that provides maximum optical output for each wavelength. The controller includes a plurality of sensor inputs for monitoring the power of each wavelength output from the AOTF, and alternatively, also monitors other AOTF parameters such as temperature and/or reads AOTF identification performance data that can be stored in a EPROM on a AOTF housing. The controller includes facility for input of modulation data, and in response to the data modulates the corresponding wavelength parameter such as power. A USB bus is provided for input of programming to the controller, and for output of performance data from the controller.

Abstract: A system for matching a optical filter characteristic of a first filter tunable in wavelength with an optical first signal comprises a modulator for modulating at least a part of the first signal with a modulation signal before being applied to the first filter. An analyzing unit derives a control signal for tuning the first filter by analyzing the modulated first signal after passing the first filter in conjunction with the modulation signal.

Abstract: The present invention relates to an optical signal shaping device such as an optical filter having a profile such that transmission of light through the device varies as a function of frequency over a selected bandwidth. The optical signal shaping device of the present invention includes a frequency dependent disperser that disperses the input optical signal to form a dispersed signal having a plurality of frequencies, a frequency selective modulator that modulates at least one of the plurality of frequencies and a frequency dependent combiner that combines the frequencies to form a modulated output signal.

Abstract: A monolithically integrated optic triplexer is described herein that can be mounted in one transistor outline (TO) can and can be used in a passive optical network. The monolithically integrated optic triplexer includes: an emitting laser; at least a first photodiode that is capable of receiving an optical signal; and a thin film filter that is located between the emitting laser and the first photodiode. In addition, the monolithically integrated optic triplexer may include a thin film filter that is located between the first photodiode and a second photodiode. Also described herein is a method for making the monolithically integrated optic triplexer.

Abstract: Techniques for calibrating tunable optical devices using a probing signal as a reference so as to achieve an accurate control over an absolute wavelength of the tunable optical devices. A probing signal being a calibrated optical signal with a spectrum centered at a desired add/drop channel or wavelength is introduced into an N-port circulator coupled between two tunable optical devices. When the two tunable optical devices are tuned not exactly at the desired wavelength, a portion of probing signal will be reflected or dropped out by the two tunable optical devices. The dropped probing signal is detected and coupled to a signal processor or circuitry configured to generate adjustments to or the control signals for controlling the tunable optical devices in accordance with the reflected probing signal being maximized.

Abstract: An optical ring network architecture including a number (N) of multi-add/drop filters, such as filters formed using symmetrical pairs of frequency routers. Each multi-add/drop filter is coupled to two other multi-add/drop filters using N?2 transmission media, such as optical fibers, to form a ring. The network also includes a number (N) of terminal stations associated with the multi-add/drop filters. A terminal station (p) is coupled with, and receives information from, its associated multi-add/drop filter (p) through a single optical fiber. In addition, the terminal station p is coupled with, and transmits information in a first direction around the ring to, a multi-add/drop filter p+1 through a single optical fiber. Communications from terminal station p to each other terminal station in the first direction are assigned one of N?1 wavelengths such that no two wavelengths on a given optical fiber are associated with communications between terminal stations in the same direction.

Abstract: Two set of filter chips on the upper and lower surfaces, each of which has a wavelength characteristic corresponding to each wavelength component of wavelength-multiplexed light, are mounted on a transparent substrate to make an optical filter element. When the wavelength-multiplexed light is inputted to the optical filter element via an optical fiber and when the same light components as those having the wavelengths demultiplexed by an optical fiber is also inputted, the demultiplexed light and the replaced wavelength-multiplexed light will be obtained at another optical fibers, respectively.

Abstract: An all optical network for optical signal traffic has at least a first ring with at least one transmitter and one receiver. The first ring includes a plurality of network nodes. At least a first add/drop broadband coupler is coupled to the first ring. The broadband coupler includes an add port and a drop port to add and drop wavelengths to and or from the first ring, a pass-through direction and an add/drop direction. The first add/drop broadband coupler is configured to minimize a pass-through loss in the first ring and is positioned on the first ring.

Abstract: A configuration of acousto-optical tunable filters (AOTF) having stable output characteristics so that the output does not significantly vary with time. The configuration includes a plurality of AOTFs cascaded together. Each AOTF generates a surface acoustic wave in an optical waveguide in accordance with RF signals applied to the AOTF. A phase of a beat generated by the RF signals applied to one of the plurality of AOTFs is different from a phase of a beat generated by the RF signals applied to a different AOTF of the plurality of AOTFs.

Abstract: The present invention relates to a method using a node, a system comprising a node and a node for filtering signals in a wavelength division multiplexing (WDM) optical communications system, especially for re-configurably adding and dropping signals to and from an optical fibre path. The node comprising a drop filter, an add filter, a signal channel receiver, and a signal channel transmitter each being connected to a switch for signal channel relaying between said network, and signal channel dropping and adding from and to said network. The node provides low loss for relayed signals by allowing the drop filter to have a low crosstalk isolation, and provides high crosstalk isolation for dropped signal channels by connecting said receiver to the switch through an additional filter with high filtering characteristics for at least one predetermined signal channel of said signal.

Abstract: An input port of an add/drop node receives a plurality of optical channels. An add/drop port transmits a first drop channel of the plurality of channels when in a first channel mode and a second drop channel of the plurality of optical channels during a second channel mode. When the add/drop node is tuned from the first channel to the second channel, the output port transmits the plurality of channels spectrally located between the first channel and the second channel.

Abstract: There is provided a WDM optical transmission system and transmission method that have excellent spectral efficiency. The WDM optical transmission system is provided with: an optical transmitting section having an optical transmitter that generates N wave (wherein N is an integer of 2 or greater) optical signals with an optical frequency spacing ?f [Hz] and modulated by a modulation bit rate B [bit/s] (wherein B/?f?1 [bit/s/Hz]) using a modulation device, and having a coupler that couples the optical signals; an optical receiving section provided with an optical DFT circuit of a sampling frequency ?f [Hz] that is equal to the optical frequency spacing; and a bit phase adjustor that makes bit phases of respective wavelength division multiplexed signals synchronous at an input of the optical DFT circuit.

Abstract: A method and apparatus for filter spectrum deconvolution and reshaping include providing a filter output of a spectrum signal and determining the intensity and wavelength of the spectrum signal at each spectral peak. The filter output is characterized as an integral of convolution of a spectrum signal function and a filter function. Transformation are then performed on the filter output to deconvolve and remove the undesirable filter function and add a desirable filter function to reshape the output filter spectrum.

Abstract: An architecture is proposed for an optical node in a wavelength division multiplexed network. The optical node may be an optical add/drop node. Conventional add/drop nodes utilize a broadcast or blocking architecture. In a broadcast architecture, a copy of an optical signal is dropped to a drop path of a node while another copy continues on a through path. Thus, channels that occupy a specific portion of wavelengths (or spectrum) prior to the node are not available for use subsequent to the add/drop connectivity. In a blocking architecture, at least the through path (and often the drop path) is spectrally filtered. This permits wavelength reuse for add/drops in subsequent portions of the network. Disclosed is an optical node architecture that enables starting with a low cost approach, such as broadcast, but includes connections to permit ‘in-service’ upgrade to more capable architecture. Increasing spectral reuse is enabled through the architecture.

Abstract: The invention provides an optical module that enables to increase the optical coupling efficiency without being dependent on the thickness of a substrate. The optical module, detachably coupled to a connector provided at one end side of an optical fiber, can include a substrate having a first hole, a translucent layer arranged so as to cover, at least, the first hole on one surface side of the substrate, and an optical element that is arranged inside the first hole and on the translucent layer and carries out transmission or reception of light signal to/from the optical fiber through the translucent layer.

Abstract: The present invention is directed towards an optical transmitter including a noise generator. The noise generator provides noise signals that are filtered to below a frequency spectrum. The filtered noise signals are combined with RF signals to provide continuous modulation of a laser. The combined signals are converted to optical signals by the laser and transmitted over an optical link.

Abstract: An optical demultiplexer includes a first light bandpass filter that receives an input light beam at a first angle of incidence, passes a first light wavelength, and reflects a reflected beam, and a second light bandpass filter that receives the reflected beam at a second angle of incidence and passes a second light wavelength. A beam redirection element such as a reflective surface receives the reflected beam from the first light bandpass filter and redirects the reflected beam toward the second light bandpass filter at the second angle of incidence.

Abstract: A planar lightwave circuit (PLC) (1; 20) comprises an optical device, where the optical device comprises at least one piece of waveguide structure (5; 24), in particular one piece of fiber, which has at least one thin film layer deposited on an end facet (9; 28). Thus, a thin film filter can be integrated in a PLC with minimized insertion loss and high mechanical stability for athermalization.

Abstract: Disclosed herein is a bidirectional wavelength division multiplexed self-healing ring network. The ring network includes a central office and a plurality of remote nodes. Two optical fibers each connect the central office and the remote nodes in a ring form to allow optical signals to be bidirectionally received and transmitted between the central office and the remote nodes. One of the two optical fibers is a drop fiber for transmitting optical signals from the central office to the remote nodes, while the other is an add fiber for transmitting optical signals from the remote nodes to the central office.

Abstract: An add/drop node for an optical network comprises a passive splitter to split an ingress signal from the network into a first ingress signal and a second ingress signal. A first amplified splitter stages module is operable to passively split and amplify the first ingress signal into a plurality of drop signals. A filter module is operable to filter the second ingress signal to provide a filtered pass-through signal. A second amplified splitter stages module is operable to passively combine a plurality of add signals into a combined add signal and to combine the combined add signal with the filtered pass-through signal to create an egress signal forwardable to the network.

Abstract: A system and apparatus for dropping and adding optical data streams in an optical communication network uses a photonic switching fabric for dropping but not adding optical data streams, and uses a combiner external to this photonic switching fabric for combining passed optical data streams from the photonic switching fabric together with added optical data streams. The added optical data streams are not limited to the wavelengths of the dropped optical data streams. The photonic switching fabric may be a Micro Electro Mechanical System (MEMS) that uses single-sided mirrors configurable to drop but not add optical data streams.

Abstract: A fiber optic device comprises an optical lens element having a focal length greater than 2 mm, and an optical signal source or receiver mounted at the focal plane of the optical lens element and operative to communicate optical signals with a selectively transparent interference filter through the optical lens element. Methods for the production and use of the fiber optic devices are also disclosed.

Abstract: A reconfigurable optical add/drop module (ROADM) for dynamically adding or dropping various wavelengths of an optical signal without having to physically replace the module with a wavelength-specific add/drop module, and corresponding methods. A multiplexed optical signal in an optical network enters the reconfigurable optical add/drop module. Filters on the module separate various wavelengths of the optical signal along the module's various waveguides and a reconfigurable switching matrix directs the various wavelengths of the optical signal to be added, dropped and/or combined with other wavelengths.