Abstract: A new type of fiber filter is useable in optical communication systems. In particular, the fiber filter may be used to flatten the gain of erbium-doped fiber amplifiers (EDFAs). Such gain flattening is important for long-haul, dense (wavelength dependent multiplexed) WDM communication systems. The filter includes a periodic mechanical structure pressed against the side of a single-mode fiber to induce a wavelength-dependent loss in a signal propagating in the fiber core by coupling the signal to fiber cladding modes. The mechanical structure is a periodic comb of small ridges. Each ridge induces a local index change in the fiber via the photoelastic effect. For coupling to the right cladding modes, the period of the grating (and the comb) is in the range of few hundreds of microns. Thus, the grating is easy to fabricate with standard machining equipment.

Abstract: The present invention is to provide a multi-channel variable optical attenuator with a small size and a simple control circuitry, which requires a short time for adjusting the attenuation level of signal lights. The optical attenuator comprises an optical attenuating portion 10, a control circuitry 20 and a master control circuitry 21. The optical attenuating portion includes a plurality of optical waveguides 121-12N and a plurality of attenuation adjusting portions 131-13N, both of which is formed in a substrate 11. A signal light of a specific wavelength &lgr;i, which is derived from the wavelength multiplexed light, transmits in a respective waveguide 12i and is attenuated by a specific amount at the attenuation adjusting portion 13i. The control circuitry 20outputs a plurality of control signals 141-14N to attenuation adjusting portions 131-13N so that the attenuation in each optical waveguides 121-12N is varied by the specific amount to the master control 22 sent from the master control circuitry 21.

Abstract: In accordance with the invention, an optical waveguide grating with adjustable chirp comprises a waveguide grating in thermal contact with an electrically controllable heat-transducing body which varies the temperature along the length of the grating. The heat-transducing body can generate heat on the fiber or remove heat from the fiber to establish a temperature gradient along the grating. In an exemplary embodiment, the heat-transducing body is a resistive film coating whose local resistance varies along the length of the grating. Electrical current passed through the film generates a temperature gradient along the grating approximately proportional to the local resistance of the film, and the amount of chirp can be adjusted by the current. The resulting devices are simple, compact and power efficient.

Abstract: A tunable chirped grating device for an optical fiber, wherein the grating has equal spacings between index perturbations. A piezoelectric element is bonded to the optical fiber for changing the perturbation spacings according to an applied voltage, and a voltage source applys the voltage to the piezoelectric element. Since a predetermined piezoelectric element is bonded to an optical fiber provided with a grating having regular spacings and the perturbation spacings can be differently deformed by applying different electric field to respective perturbation positions by the piezoelectric element, then the resulting in a chirped grating device, whose manufacturing procedure is simple and which has flexibility, can provide adjustable chirping rates of the reflected wavelengths waves.

Abstract: Optoelectronic and photonic devices are formed by employing polymer materials that have a lower glass transition temperature (Tg) than the nominal operating temperature. By using such materials, the local or segmental mobility is increased so that local stress is eliminated or minimized on the polymer material, making performance more robust. The current invention involves use of a polymer in an optical device in an operating temperature range in the region above Tg, where the polymer segments between crosslinks are allowed local freedom of movement; however, large-scale movement of the material may be restricted by the crosslinked structure of the polymer material.

Abstract: An aspect of the present invention is an optical spectrometer for detecting a spectral signature of a input optical signal, including: (a) a collimating lens having an optical axis and focal plane, for collimating the input optical signal; (b) an input optical system, for directing the input optical signal to the collimating lens; (c) a diffraction grating, for scattering the collimated input optical signal, positioned in the path of collimated light from the collimating lens, oriented to reflect a majority of the scattered light through the collimating lens; and (d) a detector, in a focal plane of the collimating lens. Another aspect of the invention is a fiber-based sensing system using the optical spectrometer of the invention.

Abstract: The present invention relates generally to electro-optically active waveguide segments, and more particularly to the use of a selective voltage input to control the phase, frequency and/or amplitude of a propagating wave in the waveguide. Particular device structures and methods of manufacturing are described herein.

Abstract: A method for monitoring the interaction of molecular species utilizes a sensor device comprising a substrate (1) with a waveguide (2) formed on the surface thereof. A grating (3) is formed in one of the surfaces of the waveguide (2). A beam of light (6) is incident on the grating (3) and the angle of incidence at which maximum reflection occurs is monitored. A first molecular species is immobilized on the waveguide (2). Changes in the angular position of the reflection maximum provide an indication of interaction of the first molecular species with a second molecular species contained in a sample brought into contact with the sensor device.

Abstract: External cavity micro laser apparatus comprises at least one multimode micro laser having an emission aperture with a relatively long dimension lying in a slow axis plane and a relatively short dimension lying in a fast axis plane. The laser produces multiple transverse lasing modes, the multiple modes having multiple lasing lobe components. External cavity means embracing the laser has an output section including spatial filter means, which may be the input aperture of an optical waveguide, for effectively selecting at least one of the transverse lasing lobe components. The cavity output section includes imaging means for imaging at the spatial filter means a far field spatial frequency distribution in the slow axis plane of the emission aperture, at which distribution the lasing lobe components are spatially distinguishable.

Abstract: A class of opto-electronic mechanical devices that include a planar optical waveguide having a cladding in which there is carried an evanescent electric field by a light beam traveling along the waveguide and a mechanical micro-element controllably coupled into the evanescent field for varying locally the properties of the waveguide in a wavelength dependent fashion. The devices described include optical switches and WDM add/drop apparatus.

Abstract: A Bragg grating device (10) is provided including a semiconductive optical waveguide (12) with a Bragg grating structure (14) formed along its length. A first plurality of electrodes (16) are disposed on a first surface (18) of the optical waveguide (12) and individually communicate with select members of the Bragg grating structure (14). A second plurality of electrodes (20) are disposed on a second surface (22) of the optical waveguide (12) and individually communicate with select members of the Bragg grating structure (14) such that individual electrodes of the second plurality of electrodes (20) are electrically coupled to individual electrodes of the first plurality of electrodes (16) via the Bragg grating structure (14). As such, a plurality of addressable portions (30) of the Bragg grating device (6) are defined.

Abstract: A frequency division multiplexed bar code scanner system includes a plurality of radiation sources for simultaneously providing a plurality of source beams, and a modulator circuit for modulating the intensity of each source beam at a different frequency. The source beams are combined and directed along a path to a bar code to be read; the return combined reflected light patterns are amplitude modulated by the bar code and are detected and the amplitude modulation of at least one of these patterns is detected to obtain a representation of the bar code read. The phase shift between the source beam and at least one of the reflected light patterns is used to determine the distance to the barcode bearing object. Distance information may be used to improve barcode reading performance.

Abstract: A method and an apparatus for stretching an optical pulse and shaping its spectrum. The method includes the step of: providing a an optical fiber element having a first long length fiber Bragg grating having a refractive index perturbation of varying periodicity. The optical pulse is launched into the fiber Bragg grating, wherein the Bragg grating reflects the pulse in a chromatically dispersed output. The reflected output is coupled with an optical modulator programmed to temporally modify the amplitude of the chromatically dispersed output to attenuate selected optical frequencies in a desired pattern. The apparatus for stretching and arbitrarily shaping the spectrum of an optical pulse with a desired wavelength resolution &Dgr;&lgr;res includes a routing optical device and an optical fiber element having a Bragg grating. The routing optical device routs energy between different waveguides, and has an input port to receive the optical pulse.

Abstract: A reflectivity-tunable fiber reflector is disclosed. The Bragg reflectivity of the fiber grating is modulated by exciting the transverse vibration of the fiber through an acoustic wave. The excitation of the transverse vibration, leading to fiber grating tilting and fiber micro-bending, induces the coupling of the fiber core mode into cladding modes. This leads to the reduction of core-mode power and hence that of Bragg reflection. This mechanism is applied by this invention to control the reflectivity of a fiber optic Bragg grating after fabrication. The fiber reflector is suitable for fiber-compatible acousto-optical switching.

Abstract: An optical fiber used as the active amplifying medium in a fiber laser is arranged to have a high insertion loss at an undesired frequency, while retaining a low insertion loss at a desired lasing frequency. In one embodiment, loss at a Raman-shifted frequency is introduced by using an optical fiber which has multiple claddings with an index profile that includes an elevated index region located away from the core, but within the evanescent coupling region of the core. A distributed loss, which can be enhanced by bending, is produced at the Raman frequency which effectively raises the threshold at which Raman scattering occurs in the fiber and therefore results in a frequency-selective fiber. In another embodiment, an absorbing layer is placed around the core region. The absorbing layer is chosen to have a sharp absorption edge so that it absorbs highly at the Raman-shifted wavelength, but minimally at the desired lasing wavelength.

Abstract: A device for compensating the temperature sensitivity normally associated with an integrated optical waveguide grating device has a temperature compensating slab waveguide region. This compensating region is provided within the slab waveguide region normally present in the grating device by modifying a sub-region of a predetermined shape and dimension to change its temperature coefficient of refractive index. This method and device can be applied to reflective and transmissive diffraction gratings and to phased array waveguide gratings.

Abstract: A method of scanning a plurality of display elements or pixels of a display and an apparatus capable of performing the method of scanning, allow energy propagating along a primary path to be diverted sequentially by a series of energy diverting devices to a plurality of secondary paths in a scanning direction depending upon the finite turn-on and turn-off times of the energy diverting devices.

Abstract: A device for changing the power levels of signals transmitted by an optical fiber, along with signal modulation and wavelength routing, comprises a length of optical fiber in which for a predetermined section of the length of the fiber, the fiber core is surrounded by a cladding having one or more variable refractive index (VRI) regions disposed therein in close proximity to the core. The VRI regions are fabricated with a material having an index of refraction higher than that of the cladding and may comprise a variable attenuator.

Abstract: An optical arrangement comprising a plurality of cells arranged in a two-dimensional array on, into, or partly into an optical medium, each said cell having a pattern structure comprising a number of grooves which are parallel to each other and which form a grating. The grating of each cells forms at least two sections which are displaced in relation to each other by a predetermined distance in a direction which is essentially perpendicular to the longitudinal direction of the grooves. The grooves of two or more adjacent cells are unaligned with one another for controlling the phase or amplitude of one or more incident optical waves when the cells receive the incident optical waves.

Abstract: A flat panel display is based on a new switching technology for routing laser light among a set of optical waveguides and coupling that light toward the viewer. The switching technology is based on poled electro-optical structures. The display technology is versatile enough to cover application areas spanning the range from miniature high resolution computer displays to large screen displays for high definition television formats. The invention combines the high brightness and power efficiency inherent in visible semiconductor diode laser sources with a new waveguide electro-optical switching technology to form a dense two-dimensional addressable array of high brightness light emissive pixels.

Abstract: A long-interval grating in an optical fiber is designed to enable the making of a mode-coupling filter. In particular, it has periodic variations of the diameter of the optical fiber and a symmetry of revolution.

Abstract: An optical fiber used as the active amplifying medium in a fiber laser is arranged to have a high insertion loss at an undesired frequency, while retaining a low insertion loss at a desired lasing frequency. In one embodiment, loss at a Raman-shifted frequency is introduced by using an optical fiber which has multiple claddings with an index profile that includes an elevated index region located away from the core, but within the evanescent coupling region of the core. A distributed loss, which can be enhanced by bending, is produced at the Raman frequency which effectively raises the threshold at which Raman scattering occurs in the fiber and therefore results in a frequency-selective fiber. In another embodiment, an absorbing layer is placed around the core region. The absorbing layer is chosen to have a sharp absorption edge so that it absorbs highly at the Raman-shifted wavelength, but minimally at the desired lasing wavelength.

Abstract: A device for changing the power levels of signals transmitted by an optical fiber, along with signal modulation and wavelength routing, comprises a length of optical fiber in which for a predetermined section of the length of the fiber, the fiber core is surrounded by a cladding having one or more variable refractive index (VRI) regions disposed therein in close proximity to the core. A grating region is disposed along the length of the fiber overlapping the VRI region. The VRI regions have an index of refraction lower than that of the core to change the effective index of the guided light and thereby define a tunable grating.

Abstract: An optical device for splitting up a multi-wavelength light beam into a plurality of individual beams, each comprising light of a different wavelength or a narrow beam of wavelengths. The optical device includes an optical grating and an optical system for directing the incident beam onto the optical grating. The incident beam is divided into two portions, and one portion is directed onto the grating in one direction, while the other portion is directed onto the grating along an opposite direction. Preferably the grating is formed in two parts and one beam portion is directed through the two grating parts in succession in one direction while the other beam portion is directed through the two grating parts in succession along an opposite direction. A common mirror may be used to direct light towards the grating and to receive light returning from the grating. The device may also be used as a multiplexer by reversing the direction of light transmitted through the device.

Abstract: The use of regularly repeated small sections of pattern in making a complete optical grating may generate unwanted effects, such as side lobes, as a result of the regular repetition of defects in the small sections. Methods are described for disrupting the regularity of the occurrence of such defects in a grating made of a plurality of sections, thereby minimizing the likelihood of the occurrence of unwanted side lobes, for example.

Abstract: A flat panel display is based on a new switching technology for routing laser light among a set of optical waveguides and coupling that light toward the viewer. The switching technology is based on poled electro-optical structures. The display technology is versatile enough to cover application areas spanning the range from miniature high resolution computer displays to large screen displays for high definition television formats. The invention combines the high brightness and power efficiency inherent in visible semiconductor diode laser sources with a new waveguide electro-optical switching technology to form a dense two-dimensional addressable array of high brightness light emissive pixels.

Abstract: A fiber Bragg grating is used to stabilize the intensity and frequency fluctuations of a diode laser. The diode laser is connected with an opto-mechanical apparatus to the fiber which contains the grating. The grating is formed in the guided-mode region of the optical fiber. The wavelength of maximum grating reflectivity is selected to lie near the maximum of the diode laser gain bandwidth. The magnitude and bandwidth of the grating reflectivity stabilizes the diode laser output without appreciably reducing the optical output power from the end of the fiber. The bandwidth of the optical spectrum of the diode laser is selected depending on the distance of the grating from the diode laser.

Abstract: The invention is a temperature compensating structure for a fiber Bragg grating (FBG) contained in optical fiber. The structure comprises two plates made of materials having different temperature coefficients of expansion and bonded together. The optical fiber is bonded to the exposed surface of the plate having the lower temperature coefficient. The structure bends with changes in temperature and produces an elongation of the fiber with decreasing temperature.

Abstract: Optical plasmon-wave attenuator and modulator structures for controlling the amount of coupling between an guided optical signal and a surface plasmon wave. Optical power coupled to the plasmon wave mode is dissipated in varying amounts producing an intensity modulation effect on the optical signal. For electrical modulation, an additional dielectric (or polymer) layer with variable refractive index in optical contact with a metal layer supporting at least one plasmon wave mode is used to perturb or vary the propagation constant of plasmon wave. Propagation constant variation results in the power coupling variation between the surface plasmon wave and the optical wave. The refractive index variation of the dielectric (or polymer) layer can be accomplished via an electro-optic traveling-wave, a lump-element, or any other integrated optics modulator configuration situated to affect the layer, thereby permitting data rates into tens of GHz.

Abstract: A resonant grating structure in a waveguide and methods of tuning the performance of the grating structure are described. An apparatus includes a waveguide; and a subwavelength resonant grating structure embedded in the waveguide. The systems and methods provide advantages including narrowband filtering capabilities, minimal sideband reflections, spatial control, high packing density, and tunability.

Abstract: Method of fabricating a wavelength filter on a substrate in which a phase mask having corrugations is placed over a polymeric substrate composed of at least two comonomers having different indexes of refraction and passing light through the phase mask to form light into two beams corresponding to different diffraction orders to form refractive gratings capable of reflecting light of a selective wavelength. Optical signal devices employing gratings fabricated in this manner are also disclosed.

Abstract: An array of optical fiber bundles includes one or more diffractive elements positioned above gaps between adjacent bundles. Incident radiation produces mathematically determinative diffraction patterns on the respective input faces of the adjacent bundles. Radiation intensity values for areas between and along the abutting edges of adjacent optical fiber bundles can be determined using the diffraction patterns. These intensity values can be assigned to other pixels so that precise, seamless images can be reconstructed.

Abstract: An RF optical signal processing system that can provide various filter functions by way of tapped delay lines with fiber Bragg gratings, variable weight taps, positive and negative taps and a short coherent length optical source. Such an RF optical signal processing systems is advantageous over corresponding RF electronic systems and offer the increased bandwidth and lower power consumption making the RF optical signal processing system suitable for various application such as avionics and satellite communications.

Abstract: A tunable filter comprises either an internal or an external grating proximal to a variable index of refraction material. This variable index of refraction material may vary upon the application of an external electrical potential or the application of a change in temperature of the polymer. Additionally, the grating may comprise a periodic modulation of the index of refraction, this periodic modulation comprising an isoplanar modulation of the index of refraction at an angle to the central axis of the waveguide, thereby causing conversion of fundamental mode waves to second mode waves, and by reciprocity, conversion of second mode waves to fundamental mode waves.

Abstract: The present invention relates to a wavelength selective switch. Said switch comprises at least one MMI waveguide, at least one Mach Zehnder waveguide, at least one phase control element and at least one Bragg grating, where said Mach Zehnder waveguide comprises said phase control element and said Bragg grating and is arranged in connection to at least one MMI waveguide. The invention further comprises a method for switching wavelength channels by using the above mentioned wavelength selective switch.

Abstract: In a transmission system, a control circuit (4) receives an input binary sequence (T) representing data to be transmitted. The circuit encodes the sequence using a phase alternation code which differs from the phase inversion duobinary code in that the phase shifts applied to a carrier wave are less than 90 degrees. For this purpose, a semiconductor chip (3) includes a laser transmitter and an electro-absorption modulator having two segments. The chip generates said carrier wave and modulates it using the encoded sequence. An optical fiber (54) conveys the modulated wave. And a detector diode (58) receives the conveyed wave and performs intensity discrimination thereon so as to restore the input binary sequence.

Abstract: An optical isolator, which has: a medium through which a light transmits and in which a dynamic diffraction grating that periodically repeats a refractive index distribution is formed; wherein the dynamic diffraction grating causes a propagation loss difference between an incident light which is supplied into the medium and a returning light which is supplied into the medium in a direction reverse to the incident light.

Abstract: An image display apparatus capable of displaying a clear image without a prominent vacancy between pixels, even when a luminance distribution is present within each of the pixels, has a display device for displaying a plurality of pixels, each having a luminance distribution and an optical element for diffusing each of the pixels displayed by the display device so that each of the pixels has a plurality of peaks in the luminance distribution.

Abstract: A nonlinearly chirped fiber grating for achieving tunable dispersion compensation, chirp reduction in directly modulated diode lasers, and optical pulse manipulation. A dynamical dispersion compensation mechanism can be implemented in a fiber communication system based on such a nonlinearly chirped fiber grating.

Abstract: A flat panel display is based on a new switching technology for routing laser light among a set of optical waveguides and coupling that light toward the viewer. The switching technology is based on poled electro-optical structures. The display technology is versatile enough to cover application areas spanning the range from miniature high resolution computer displays to large screen displays for high definition television formats. The invention combines the high brightness and power efficiency inherent in visible semiconductor diode laser sources with a new waveguide electro-optical switching technology to form a dense two-dimensional addressable array of high brightness light emissive pixels.

Abstract: A device for adding and/or dropping a signal to a transmission line. First and second optical circulators are connected by at least one switchable grating reflector, whereby a grating reflector can be switched into or out of the connecting path between the two circulators. A plurality of optical signals, each centered about a different wavelength, is coupled to a first port of the first circulator; these signals appear at the second port thereof. If a grating reflector capable of reflecting .lambda..sub.i is switched into the circuit, the signal centered about .lambda..sub.i propagates from the second port of the first circulator and reflects from the grating reflector back into the second port and out of the third port. The remainder of the input signals that are not reflected by grating reflectors propagate into the first port and from the second port of the second circulator as an output thereof. Also, a signal at wavelength .lambda..sub.

Abstract: A variety of optical components or nodes are provided which components are formed utilizing holographically polymerized polymer/liquid crystal composites, and which components include free space/unguided wave switches, guided wave switches, out/in couplers, reflection nodes/reflection filters and guided wave interconnect nodes. Selected ones of these nodes may be designed to operate either in a single wavelength mode or in a multiwavelength WDM mode. All of the components are switchable so as to able to modify the component output to which an optical signal received on a component input is applied as a function of an electric field applied across the component, and to vary the channel outputted on a given output for WDM operation.

Abstract: The invention concerns a planar electro-optical light-beam deflector with a line of prismatic deflectors, arranged side by side, exhibiting electrodes to which an electric voltage can be applied. It is essential to the invention that the light beam is conveyed in a Z-cut lithium niobate or lithium tantalate crystal, preferably in a monomodal layer waveguide extending along the surface of the latter, the prismatic deflectors each consisting of two triangular or prismatic zones in which a largely uniform polarization direction is generated by inversion of the polarization direction determined by the E-field vector in domains with spontaneous polarization in the opposite direction, each triangular zone exhibiting polarization in the direction opposite to that of the one adjacent to it, and that a rectangular electrode covering the triangular zones is attached to the upper side of the crystal and a counterelectrode to the lower side of the same.

Abstract: A flat panel display is based on a new switching technology for routing laser light among a set of optical waveguides and coupling that light toward the viewer. The switching technology is based on poled electro-optical structures. The display technology is versatile enough to cover application areas spanning the range from miniature high resolution computer displays to large screen displays for high definition television formats. The invention combines the high brightness and power efficiency inherent in visible semiconductor diode laser sources with a new waveguide electro-optical switching technology to form a dense two-dimensional addressable array of high brightness light emissive pixels.

Abstract: A Brag reflective Mach-Zehnder filter has arms that introduce a .pi. phase difference in transmission but not in reflection. In one embodiment a .pi. phase difference is introduced in one of the two arms between the Bragg grating and one of the couplers. In another embodiment, a phase difference of .pi./2 is introduced in one arm both before and after the grating and the location of the grating in the other arm is shifted. The transmission of the resulting filter is substantially independent of the degree of coupling at the input and the output. WDM systems employing the new filters are also disclosed.

Abstract: A new class of energy interaction devices, particularly optical energy transfer devices and energy guiding devices, use an energy field, particularly an electric field, applied to a poled structure to control energy propagation in a solid material. The poled structures, which may form gratings in thin film or bulk configurations, may be combined with waveguide structures to guide energy beams such as optical or acoustic beams. Electric fields applied to the poled structures, such as electrically-activated gratings, control routing of optical energy. Optical devices include but are not limited to, frequency-selective switchable- and adjustably-tunable reflectors, splitters, directional couplers, frequency-tunable switches and efficient beam combiners, as well as polarized beam combiners, am and fm modulators, mode selectors, energy transfer devices, optical data readers, panel display devices, and waveguide/reflector switching arrays.

Abstract: The present invention relates to an optical fiber grating as an optical component comprising an optical fiber having a core and a cladding, and a grating photowritten in the optical fiber. In particular, in the optical fiber grating in accordance with the present invention, the optical fiber into which the grating periodically changing the refractive index in the waveguide along the advancing direction of light is photowritten has a depressed cladding type refractive index profile. Accordingly, when the configuration of the optical fiber having a depressed cladding type refractive index, employed as the object in which the grating is photowritten, is changed, the stability in characteristics as the optical component or the like can easily be improved.

Abstract: An electro-optical waveguide element with reduced DC drift phenomena is presented. The waveguide element is made up of an optical waveguide formed on a substrate possessing electro-optical effects, at least a pair of electrodes closely attached to the optical waveguide with a buffer layer sandwiched between the substrate and the electrodes, and a driver circuit for applying a voltage between the electrodes. The buffer layer is made of a material having a dielectric constant in the range of 20-1000. The buffer layer is more preferably made of a material having a dielectric constant in the range of 20-200. The material of the buffer layer is selected from the group consisting of HfO.sub.2, TiO.sub.2, SrTiO.sub.3, BaTiO.sub.3, LiNbO.sub.3, LiTaO.sub.3, Pb(Zr, Ti)O.sub.3, and (Pb, La)(Zr, Ti)O.sub.3.

Abstract: An optical add/drop multiplexer device which is capable of extracting or inserting optical signals of arbitrary wavelength and having a wavelength selection characteristic with a narrow bandwidth, and which is compact in size and highly reliable. The device is formed by a substrate member; a plurality of optical waveguides, formed over the substrate member in layers with a prescribed interval along a direction perpendicular to a plane of the substrate member, each optical waveguide having a portion arranged in parallel and in proximity to an adjacent optical waveguide to form a coupling section; and a diffraction grating member, provided at the coupling section and having a prescribed period along a light propagation direction, for reflecting light signals with a specific wavelength among light signals entered from one of adjacent optical waveguides to another one of the adjacent optical waveguides.

Abstract: An integrated tunable optical filter comprising a substrate made of a semiconducting material. The substrate includes first and second sections. The first section forms a tunable transmission filter, based on a codirectional coupler having a low selectivity. The second section forms a reflection filter with a reflection spectrum containing a number of peaks. A first injector, designed for current injection into said first section, is provided. Thus, the filter response of the first section is shifted in wavelength over a large wavelength range. There is also a second injector, designed for current injection into the second section. As a result, the reflective spectrum of the second section is slightly shifted in wavelength, in such a way that one reflection peak of the reflection spectrum corresponds to the coupling wavelength of the first section. Consequently, the total filter response has a very narrow bandwidth and wide tunability.