Gain-clamped optical amplifier

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• and
• a plurality of gain clampers disposed alone the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by grating structures arranged in an in-axis form along the amplifier axis, and the gain clamping efficiencies of the grating structures declining from the input facet to the output facet,
• wherein the more the grating structures approach the output facet, the more the oscillation wavelength of the grating structures matches the peak of the spectrum of the gain medium, thereby realizing declining effect of the gain clamping efficiencies of the grating structures and
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• a plurality of gain clampers disposed along the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by laser cavities, each of the laser cavities being defined by a pair of mirrors disposed beside the gain medium, said mirrors facing each other and arranged in an off-axis form along the amplifier axis;
• wing structures disposed between each of said mirrors and the gain medium, respectively, wherein the optical gain coefficient of the wing structures increases from the input facet to the output facet, thereby making the clamped local carrier densities of the gain medium of the optical amplifier decline to satisfy the round trip condition of the corresponding laser cavities;
• and
• a series of longer laser cavities with wing structures inserted thereinto to realizing the declining effect of the local carrier densities, and a series of shorter laser cavities containing no wing structures, to determine the carrier response time,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• and
• a plurality of gain clampers disposed along the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by laser cavities, each of the laser cavities being defined by a pair of mirrors disposed beside the gain medium, said mirrors facing each other and arranged in an off-axis form along the amplifier axis;
• and
• photon detectors for receiving output optical powers from said gain clamping laser cavities, wherein the photon currents output by the photon detectors indicate signal power levels at the portions of the gain medium corresponding to said gain clamping laser cavities,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• and
• a plurality of gain clampers disposed along the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by grating structures arranged in an in-axis form alone the amplifier axis, and the gain clamping efficiencies of the grating structures declining from the input facet to the output facet,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal, and
• wherein the optical amplifier is a semiconductor optical amplifier, said semiconductor optical amplifier comprising:
• a slab waveguide region sandwiching said gain medium, said grating structure placed close to said slab waveguide region for defining in-axis laser cavities;
• electronic contacts placed on and under the semiconductor optical amplifier for directing pumping currents into the semiconductor optical amplifier;
• and
• a wafer base for supporting the respective components,
• wherein the grating pitches of the grating structure are uniform, and the grating structure is getting closer to the slab waveguide region toward the output facet.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• and
• a plurality of gain clampers disposed along the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by laser cavities, each of the laser cavities being defined by a pair of mirrors disposed beside the gain medium, said mirrors facing each other and arranged in an off-axis form along the amplifier axis, and wherein the products of reflectivities of the peak wavelength of the amplifier gain spectrum of the mirror pairs of the gain clamping laser cavities increase toward the output facet, thereby making the gain clamping efficiencies of the laser cavities decline from the input facet to the output facet,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal, and
• wherein the optical amplifier is a semiconductor optical amplifier, said semiconductor optical amplifier comprising:
• a slab waveguide region sandwiching said gain medium;
• distributed Bragg reflector (DBR) regions disposed beside the slab waveguide region for acting as mirrors to define off-axis surface emission laser cavities;
• electronic contacts placed on and under the semiconductor optical amplifier for directing pumping currents into the semiconductor optical amplifier;
• and
• a wafer base for supporting the respective components,
• wherein at least one DBR region has a thickness varying along the waveguide region, and the DBR mirrors are constructed so that the local resonate frequency of the DBR mirrors gradually approaches to the peak frequency of the gain medium toward the output facet.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• and
• a plurality of gain clampers disposed alone the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by laser cavities, each of the laser cavities being defined by a pair of mirrors disposed beside the gain medium, said mirrors facing each other and arranged in an off-axis form along the amplifier axis, and wherein the products of reflectivities of the peak wavelength of the amplifier gain spectrum of the mirror pairs of the gain clamping laser cavities increase toward the output facet, thereby making the gain clamping efficiencies of the laser cavities decline from the input facet to the output facet,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal, and
• wherein the optical amplifier is a semiconductor optical amplifier, said semiconductor optical amplifier comprising:
• a gain medium having input and output facets;
• a slab waveguide region sandwiching said gain medium;
• distributed Bragg reflector (DBR) regions disposed as pairs beside the slab waveguide region for acting as mirrors to define off-axis surface emission laser cavities;
• electronic contacts placed on and under the semiconductor optical amplifier for directing pumping currents into the semiconductor optical amplifier;
• and
• a wafer base for supporting the respective components,
• wherein the DBR mirror pairs are constructed so that the products of reflectivity of the DBR mirror pairs decline from the input facet to the output facet.

An optical amplifier for amplifying optical signals, said optical amplifier having an input facet and an output facet, said optical amplifier comprising:

• a gain medium defining an amplifier axis;
• a plurality of gain clampers disposed along the amplifier axis to control the local carrier density distribution of the gain medium of the optical amplifier, each of said gain clampers being constructed by laser cavities, each of the laser cavities being defined by a pair of mirrors disposed beside the gain medium, said mirrors facing each other and arranged in an off-axis form along the amplifier axis;
• and
• wing structures disposed between each of said mirrors and the gain medium, respectively, wherein the optical gain coefficient of the wing structures increases from the input facet to the output facet, thereby making the clamped local carrier densities of the gain medium of the optical amplifier decline to satisfy the round trip condition of the corresponding laser cavities,
• wherein the whole carrier density distribution of the optical amplifier is controlled by the gain clampers, the whole carrier density distribution of the optical amplifier declines from the input facet to the output facet, and the resulting local saturation photon density is larger than the local photon density of the amplified optical signal, and
• wherein the optical amplifier is a semiconductor optical amplifier, said semiconductor optical amplifier comprising:
• a slab waveguide region disposed along said gain material;
• electronic contacts placed on and under the semiconductor optical amplifier for directing pumping currents into the semiconductor optical amplifier;
• a plurality of off-axis gain-clamping lasers, whose laser mirrors are composed by crystal surfaces, each off-axis gain-clamping laser comprising at least one wing structures, each wing structure having bias electrodes so that the gain coefficient of the wing structure is controlled by the biasing electrodes;
• and
• a wafer base for supporting the respective components,
• wherein the cross-cavity gain-clamping lasers are controlled so that the gain coefficient of the wing structures increases from the input facet to the output facet, making the clamped local densities of the gain materials of the optical amplifiers declining toward the output facet.