Optical line printhead and an LED chip used therefor

An optical beam source for producing a plurality of optical beams, comprising:

• a support substrate having an upper major surface;
• a plurality of light emitting diode chips provided on said upper major surface of said support substrate so as to be aligned in a row, each of said light emitting diode chips comprising:
• a substrate of a single crystal semiconductor material doped to a first conductivity type and having upper and lower principal surfaces;
• a bottom electrode covering said lower principal surface of said substrate;
• a plurality of light emitting diodes disposed on said upper principal surface of said substrate so as to be aligned in a row, said plurality of light emitting diodes thereby forming a light emitting diode array;
• each of said light emitting diodes having an identical construction and comprising:
• a first cladding layer doped to said first conductivity type and provided on said substrate epitaxially with respect to said substrate, said first cladding layer having a first bandgap;
• an active layer of undoped semiconductor material provided on said first cladding layer epitaxially with respect to said first cladding layer, said active layer having a second bandgap smaller than said first bandgap;
• a second cladding layer doped to a second, opposite conductivity type and provided on said active layer epitaxially with respect to said active layer, said second cladding layer having a third bandgap larger than said second bandgap;
• and a top electrode provided on said second cladding layer for injecting carriers of a first polarity thereto;
• each of said light emitting diodes having a front edge facing a common, first direction perpendicular to a direction of a hypothetical normal drawn to said upper principal surface of said substrate and a rear edge opposing said front edge, each of said light emitting diodes emitting an optical beam at said front edge in said first direction, in response to electric energization applied across said top electrode and said bottom electrode;
• and
• monitoring means provided on said upper principal surface of said substrate for monitoring the optical power of said optical beams produced by said light emitting diodes forming said light emitting diode array, said monitoring means comprising:
• a monitoring-purpose light emitting diode having a construction substantially identical with the construction of said light emitting diodes that form said light emitting diode array, said monitoring-purpose light emitting diode having a front edge for emitting an optical beam therethrough, said monitoring-purpose light emitting diode being disposed on said upper principal surface of said substrate such that said front edge of said monitoring-purpose light emitting diode faces a second direction perpendicular to said first direction and the direction of the hypothetical normal drawn to said upper principal surface of said substrate so that said optical beam produced by said monitoring-purpose light emitting diode is emitted in said second direction through said front edge of said monitoring-purpose light emitting diode;
• and a photodiode having a construction substantially identical to the construction of said light emitting diodes forming said light emitting diode array, said photodiode having a front edge facing said front edge of said monitoring-purpose light emitting diode for receiving said optical beam emitted from said monitoring-purpose light emitting diode, said photodiode producing an output signal indicative of the optical power of said optical beam produced by said monitoring-purpose light emitting diode, said output signal being produced across said top electrode of said photodiode and said bottom electrode;
• said monitoring means being disposed behind said rear edges of said light emitting diodes forming said light emitting diode array;
• said plurality of light emitting diode chips being disposed on said support substrate so as to produce said optical beam in a common direction;
• and
• a plurality of feedback control circuits provided in a one-to-one correspondence with said plurality of light emitting diode chips, said feedback control circuit drives, in each of said plurality of light emitting diode chips, said monitoring-purpose light emitting diode with energization determined in response to said output signal of said photodiode, such that said optical beam produced by said monitoring-purpose light emitting diode has a predetermined optical power, said feedback control circuit driving said light emitting diodes forming said light emitting diode array on said light emitting diode chip by energization corresponding to the energization of said monitoring-purpose light emitting diode.

A light emitting diode, comprising:

• a substrate having upper and lower major surfaces, said substrate comprising a semiconductor material doped to a first conductivity type;
• first electrode means provided on said lower major surface of said substrate;
• a first cladding layer having upper and lower major surfaces and provided on said substrate, said first cladding layer comprising a semiconductor material doped to said first conductivity type and having a first bandgap;
• an active layer having upper and lower major surfaces and provided on said first cladding layer, said active layer comprising an undoped semiconductor material having a second bandgap smaller than said first bandgap, said active layer producing optical radiation as a result of recombination of carriers, said active layer having an edge surface generally perpendicular to said upper major surface of said substrate for emitting said optical radiation as a first optical beam;
• a second cladding layer having upper and lower major surfaces and provided on said active layer, said second cladding layer comprising a semiconductor material doped to a second, opposite conductivity type and having a third bandgap larger than said second bandgap;
• and
• second electrode means provided on said upper major surface of said second cladding layer and having upper and lower major surfaces, said second electrode means passing said optical radiation produced in said active layer generally in a direction perpendicular to said upper major surface of said second electrode means, as a second optical beam.

An optical beam source for producing a plurality of optical beams, which comprises:

• a case member having a first substrate positioned therein;
• at least one light emitting diode chip positioned on said first substrate, said at least one light emitting diode chip having;
• a second substrate of a single crystal semiconductor material doped to a first conductivity type and having upper and lower principal surfaces;
• a bottom electrode covering said lower principal surface of said second substrate;
• a plurality of light emitting diodes disposed on said upper principal surface of said second substrate so as to be aligned in a row;
• each of said light emitting diodes having a first cladding layer doped to said first conductivity type and provided on said substrate epitaxially with respect to said substrate, said first cladding layer having a first bandgap;
• an active layer of undoped semiconductor material provided on said first cladding layer epitaxially with respect to said first cladding layer, said active layer having a second bandgap smaller than said first bandgap;
• a second cladding layer doped to a second, opposite conductivity type and provided on said active layer epitaxialy with respect to said active layer, said second cladding layer having a third bandgap larger than said second bandgap;
• and a top electrode provided on said second cladding layer for injecting carriers of a first polarity thereto;
• each of said light emitting diodes having a front edge facing a common, first direction perpendicular to a direction of a hypothetical normal drawn to said upper principal surface of said substrate and a rear edge opposing said front edge, each of said light emitting diodes emitting an optical beam at said front edge in said first direction in response to electric energization applied across said top electrode and said bottom electrode;
• and
• monitoring means provided on said upper principal surface of said second substrate for monitoring an optical power of said optical beams produced by said light emitting diodes forming said light emitting diode array, said monitoring means further including at least one monitoring-purpose light emitting diode having a front edge for emitting an optical beam therethrough, said at least one monitoring-purpose light emitting diode being disposed on said upper principal surface of said second substrate such that said front edge of said at least one monitoring-purpose light emitting diode faces a second direction perpendicular to said first direction so that said optical beam produced by said at least one monitoring-purpose light emitting diode is emitted in said second direction through said front edge of said at least one monitoring-purpose light emitting diode;
• and at least one photodiode associated with said at least one monitoring-purpose light emitting diode, said at least one photodiode having a front edge facing said front edge of said at least one monitoring-purpose light emitting diode for receiving said optical beam emitted from said at least one monitoring-purpose light emitting diode, said at least one photodiode producing an output signal indicative of an optical power of said optical beam produced by said at least one monitoring-purpose light emitting diode, said output signal being produced across said top electrode of said at least one photodiode and said bottom electrode;
• and
• means positioned within said case member for focusing and directing light emitted from said at least one light emitting diode chip to a recording surface.

An optical beam source for producing a plurality of optical beams, comprising:

• a substrate having upper and lower major surfaces;
• a plurality of light emitting diodes provided on said upper major surface of said substrate so as to align in a row in a first direction, each of said plurality of light emitting diodes having an edge surface facing a common, second direction substantially perpendicular to said first direction for emitting a first optical beam generally in said second direction, each of said light emitting diodes further having an upper principal surface for emitting a second optical beam therethrough generally in a third direction perpendicular to said upper principal surface of said light emitting diode;
• an optical system for focusing said optical beams on a recording surface, said optical system comprising:
• first reflection means for deflecting said first optical beams produced by said light emitting diodes in a fourth direction which is different from said second direction and which is generally perpendicular to said first direction;
• second reflection means for deflecting said first optical beams deflected by said first reflection means in a fifth direction which is generally perpendicular to said first direction and which is generally opposite to said second direction, said second reflection means further deflecting said second optical beams in a sixth direction which is generally perpendicular to said first direction and which is generally opposite to said second direction;
• third reflection means for causing first and second successive reflections in said first optical beams that have been deflected by said second reflection means, such that said first optical beams are deflected by substantially 90 degrees in each of said first and second reflections, such that said first optical beams travel in a seventh direction generally perpendicular to said first direction and generally opposite to said fifth direction, said third reflection means further causing third and fourth successive reflections in said second optical beams that have been deflected by said second reflection means, such that said second optical beams are deflected by substantially 90 degrees in each of said third and fourth reflections, such that said second optical beams travel in an eighth direction generally perpendicular to said first direction and generally opposite to said sixth direction;
• a plurality of lenses aligned, with a predetermined pitch, in said first direction to form a lens array, said plurality of lenses being disposed in a path of said first and second optical beams traveling away from said third reflection means for focusing the same on an image plane;
• and
• fourth reflection means disposed in a path of said first optical beams passed through said lens array after reflection by said third reflection means, for deflecting said first optical beams in a ninth direction that is generally perpendicular to said first direction and pointing towards said image plane, such that said first optical beams are focused at respective, corresponding focal points of said second optical beams.

A light emitting diode for emitting optical beams in mutually different directions, comprising:

• a substrate of a semiconductor material having upper and lower major surfaces and doped to a first conductivity type;
• first cladding layer of a semiconductor material doped to said first conductivity type and having a first bandgap, said first cladding layer having upper and lower major surfaces and provided on said upper major surface of said substrate;
• an active layer of an undoped semiconductor material having a second bandgap smaller than said first bandgap, said active layer having upper and lower major surfaces and provided on said upper major surface of said first cladding layer, said active layer producing optical radiation as a result of recombination of carriers taking place in said active layer;
• second cladding layer of a semiconductor material doped to a second, opposite conductivity type and having a third bandgap larger than said second bandgap, said second cladding layer having upper and lower major surfaces and provided on said upper major surface of said active layer;
• said first cladding layer and said second cladding layer forming, together with said active layer, a layered structure having an upper major surface and an edge surface extending substantially perpendicularly to said upper major surface of said substrate, said layered structure outputting a first optical beam from said active layer at said edge surface as a result of said optical radiation produced in said active layer;
• lower electrode means provided on said lower major surface of said substrate for injecting carriers of a first polarity into said active layer;
• and
• upper electrode means provided on said upper major surface of said layered structure for injecting carriers of a second, opposite polarity into said active layer, said upper electrode means being substantially transparent to said optical radiation produced in said active layer for emitting a second optical beam therethrough in a direction generally perpendicular to said upper major surface of said layered structure.