Semiconductor laser device having plurality of layers for emitting lights of different wavelengths and method of driving the same

a method of driving a semiconductor laser device of the type having:

• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers, the band gap and the thickness of said barrier layer being determined to be large enough to create, in response to injection of carriers to said light-emitting layers, a state in which the carrier density in said second light-emitting layer is made higher while the carrier density in said first light-emitting layer is made lower than those which would be obtained when said barrier layer is omitted;
• a pair of cladding layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said cladding layers having smaller refractive index values than said first and second light-emitting layers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• said method comprising the steps of:
• injecting, through said electrode means, an electrical current of a level slightly lower than an emission threshold current of said laser;
• causing an external light of a wavelength near the laser emission wavelength to be incident to said device;
• and
• taking a light of the same wavelength as the incident light out of said device.

A method of driving a semiconductor laser device of the type having:

• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers, the band gap and the thickness of said barrier layer being determined to be large enough to create, in response to injection of carriers to said light-emitting layers, a state in which the carrier density in said second light-emitting layer is made higher while the carrier density in said first light-emitting layer is made lower than those which would be obtained when said barrier layer is omitted;
• a pair of cladding layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said cladding layers having smaller refractive index values than said first and second light-emitting layers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• said method comprising the steps of:
• injecting, through said electrode means, an electrical current of a level slightly lower than an emission threshold current of said laser;
• causing an external light of a light having a photon energy greater than the band gaps of said first and second light-emitting layers to be incident to said device;
• and
• taking a light of a wavelength different from that of the incident light out of said devices.

A semiconductor laser device comprising:

• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers;
• a pair of separate confinement layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said separate confinement layers having band gaps greater than those of said first and second light-emitting layers but smaller than that of said barrier layer;
• a pair of cladding layers sandwiching therebetween said separate confinement layers, said cladding layers having smaller refractive index values than said separate confinement lasers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers.

A method of driving a semiconductor laser device of the type having:

• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers;
• a pair of separate confinement layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said separate confinement layers having band gaps greater than those of said first and second light-emitting layers but smaller than that of said barrier layer;
• a pair of cladding layers sandwiching therebetween said separate confinement layers, said cladding layers having smaller refractive index values than said separate confinement lasers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• said method comprising the steps of:
• injecting, through said electrode means, an electrical current of a level slightly lower than an emission threshold current of said laser;
• causing an external light of a wavelength near the laser emission wavelength to be incident to said device;
• and
• taking a light of the same wavelength as the incident light out of said device.

A method of driving a semiconductor laser device of the type having:

• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers;
• a pair of separate confinement layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said separate confinement layers having band gaps greater than those of said first and second light-emitting layers but smaller than that of said barrier layer;
• a pair of cladding layers sandwiching therebetween said separate confinement layers, said cladding layers having smaller refractive index values than said separate confinement lasers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• said method comprising the steps of:
• injecting, through said electrode means, an electrical current of a level slightly lower than an emission threshold current of said laser;
• causing an external light of a light having a photon energy greater than the band gaps of said first and second light-emitting layers to be incident to said device;
• and
• taking a light of a wavelength different from that of the incident light out of said device.

A semiconductor laser array comprising:

• (a) a first semiconductor laser including:
• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers, the band gap and the thickness of said barrier layer being determined to be large enough to create, in response to injection of carriers to said light-emitting layers, a state in which the carrier density in said second light-emitting layer is made higher while the carrier density in said first light-emitting layer is made lower than those which would be obtained when said barrier layer is omitted;
• a pair of cladding layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said cladding layers having smaller refractive index values than said first and second light-emitting layers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• (b) a second semiconductor laser device formed on the same substrate as said first semiconductor laser device in a monolithic manner and having the same construction as said first semiconductor laser device;
• and
• (c) said electrode means of the first and second semiconductor laser devices having different lengths from each other in the direction of the laser resonance.

A semiconductor laser array comprising:

• (a) a first semiconductor laser including:
• a substrate;
• a first light-emitting layer provided on said substrate comprising a first resonant cavity;
• a second light-emitting layer provided on said substrate comprising a second resonant cavity and having a greater band gap than said first light-emitting layer;
• a barrier layer disposed between said first and second light-emitting layers and having a band gap greater than those of said first and second light-emitting layers, the band gap and the thickness of said barrier layer being determined to be large enough to create, in response to injection of carriers to said light-emitting layers, a state in which the carrier density in said second light-emitting layer is made higher while the carrier density in said first light-emitting layer is made lower than those which would be obtained when said barrier layer is omitted;
• a pair of cladding layers sandwiching therebetween said first light-emitting layer, said barrier layer and said second light-emitting layer, said cladding layers having smaller refractive index values than said first and second light-emitting layers;
• and
• an electrode means for supplying electrical currents to said first and second light-emitting layers;
• (b) a second semiconductor laser device formed on the same substrate as said first semiconductor laser device in a monolithic manner and having the same construction as said first semiconductor laser device;
• and
• (c) first and second diffraction gratings provided in said first and second semiconductor laser devices, respectively, said first and second diffraction gratings having different pitches from each other.