Abstract: A Bragg grating has a local reflection strength which varies with position along the length of the grating so as to generate a non-uniform wavelength reflection spectrum, enabling compensation for a non-uniform gain profile of the gain section of a tunable laser. In another aspect, a Bragg comb grating is modulated by an envelope function which can also compensate for a non-uniform gain profile. The comb grating may be a phase change grating, with the envelope function shape being controlled by the length between phase changes and/or size of the phase changes.

Abstract: The present invention concerns tunable distributed Bragg reflector (DBR) semiconductor lasers, in particular a DBR laser with a branched optical waveguide 5 within which a plurality of differently shaped lasing cavities may be formed, and a method of operation of such a laser. The laser may comprise a phase control section (418), gain section (420, 422), a sampled grating DBR (412) giving a comb-line spectrum and two tunable, chirped DBRs (414, 416) for broadband frequency training and a coupling section (410).

Abstract: A Bragg reflector grating comprises a plurality of chirped grating sections (65-72), in which at least a first chirped grating section and a second chirped grating section have differing ranges of grating pitches. The combined range of grating pitches provided by the first and second chirped grating sections includes at least one discontinuity, such that the first and second chirped grating sections have one or more grating pitches in common and/or there are one or more ranges of grating pitches within the combined range of grating pitches that are absent.

Abstract: A Bragg grating has a local reflection strength which varies with position along the length of the grating so as to generate a non-uniform wavelength reflection spectrum, enabling compensation for a non-uniform gain profile of the gain section of a tunable laser. In another aspect, a Bragg comb grating is modulated by an envelope function which can also compensate for a non-uniform gain profile. The comb grating may be a phase change grating, with the envelope function shape being controlled by the length between phase changes and/or size of the phase changes.

Abstract: A tunable laser comprises a gain section and two or more reflectors. At least one of the reflectors is a Bragg grating comprising a reduced strength section comprising a base order periodic pattern of marks and spaces from at which at least some of the marks or spaces are missing. This enables the reflective strength of the grating to be controlled relative to the other reflector. The Bragg grating may be a phase change grating with individual sections being reduced in strength by line removal.

Abstract: A Bragg grating has a local reflection strength which varies with position along the length of the grating so as to generate a non-uniform wavelength reflection spectrum, enabling compensation for a non-uniform gain profile of the gain section of a tunable laser. In another aspect, a Bragg comb grating is modulated by an envelope function which can also compensate for a non-uniform gain profile. The comb grating may be a phase change grating, with the envelope function shape being controlled by the length between phase changes and/or size of the phase changes.

Abstract: An apodised Bragg grating comprises a base grating section formed by a base order 5 periodic pattern of marks and spaces. The Bragg grating further comprises one or more apodised grating sections that are formed by a periodic pattern of marks and spaces, each defined by the base order pattern from which at least some of the marks are missing. The determination of which marks are missing may be performed by combining the base order pattern with a higher order modulation envelope function.

Abstract: A Bragg reflector grating comprises a plurality of chirped grating sections (65-72), in which at least a first chirped grating section and a second chirped grating section have differing ranges of grating pitches. The combined range of grating pitches provided by the first and second chirped grating sections includes at least one discontinuity, such that the first and second chirped grating sections have one or more grating pitches in common and/or there are one or more ranges of grating pitches within the combined range of grating pitches that are absent.

Abstract: A tuneable laser includes a gain section (50) bounded by two mirrors (51 and 52) at least one mirror being a chirp grating. At least one of the mirrors includes a plurality of selectable electrodes (59 to 65) to enable the grating to be selectively activated to produce a selective reflection at a predetermined wavelength.

Abstract: A tunable laser comprises a gain section and two or more reflectors. At least one of the reflectors is a Bragg grating comprising a reduced strength section comprising a base order periodic pattern of marks and spaces from at which at least some of the marks or spaces are missing. This enables the reflective strength of the grating to be controlled relative to the other reflector. The Bragg grating may be a phase change grating with individual sections being reduced in strength by line removal.

Abstract: A Bragg grating has a local reflection strength which varies with position along the length of the grating so as to generate a non-uniform wavelength reflection spectrum, enabling compensation for a non-uniform gain profile of the gain section of a tunable laser. In another aspect, a Bragg comb grating is modulated by an envelope function which can also compensate for a non-uniform gain profile. The comb grating may be a phase change grating, with the envelope function shape being controlled by the length between phase changes and/or size of the phase changes.

Abstract: A tuneable laser having an active section, a phase section and a Bragg reflector comprising a plurality of discrete grating units, at least two of which gratings have a different pitch, wherein current is applicable to at least the grating having a longer pitch, such that the effective wavelength of the grating having a longer pitch can be tuned to the wavelength of the grating having a shorter pitch. A chirp grating can provide the difference in pitch.

Abstract: A tuneable laser having an active section, a phase section and a Bragg reflector comprising a plurality of descrete grating units, at least two of which gratings have a discrete pitch, wherein at least two of the gratings having a different pitch are each provided with a plurality of independently actuable electrodes.

Abstract: The laser comprises an active layer (4) with edges cleaved and/or dry etched so that the electromagnetic radiation undergoes total internal reflection. The layer is bounded on one face by a laser substrate (7) and on the other by a Bragg grating having lattices extending in second (11) and first (12) orthogonal directions, each of pitch related to that of the other and to the desired wavelength of the laser. Adjacent the substrate (7) is a heat sink (40), which acts as return path for electrical energy. Adjacent the grating (11, 12) is an electrode layer (24) having a window (26) through which the output laser energy (42) is radiated.

Abstract: A tuneable laser having an active section, a phase section and a Bragg reflector comprising a plurality of discrete grating units, at least two of which gratings have a different pitch, wherein current is applicable to at least the grating having a longer pitch, such that the effective wavelength of the grating having a longer pitch can be tuned to the wavelength of the grating having a shorter pitch. A chirp grating can provide the difference in pitch.

Abstract: A tuneable laser having an active section, a phase section and a Bragg reflector comprising a plurality of descrete grating units, at least two of which gratings have a discrete pitch, wherein at least two of the gratings having a different pitch are each provided with a plurality of independently actuable electrodes.

Abstract: A multi-wavelength optical reflector comprises a diffraction grating structure (18) which comprises a plurality of repeat grating units (20) in which each grating unit (20) comprises a series of adjacent diffraction gratings (22, 24, 26) having the same pitch. The grating units (20) and adjacent gratings within a grating unit are separated by a phase change (28) of substantially pi (&pgr; radians). The lengths of the gratings (22, 24, 26), which are different for each grating within a grating unit, are selected so as to provide a predetermined comb reflection spectrum which comprises a plurality of reflection maxima of substantially equal reflectivity.

Abstract: A scanning system which includes a rotatable multifaceted polygon, the faceted surfaces of which are optically reflective; a recording means spaced-apart from the said polygon and adapted to move in a direction parallel to the rotational axis of the polygon; light generating means for generating at least one pair of light beams, the light beams of each pair being directed at different angles onto the faceted surface in a manner whereby the regions of the faceted surface illuminated by the beams are in contact with each other in a non-overlapping relationship; modulating means for modulating the said at least one pair of light beams; and focussing means interposed between the said polygon and the said recording means for focussing each pair of light beams reflected from the said polygon onto the said recording means.