A unipolar-doped light emitting diode or laser diode is described. The diode includes a bottom region having an n-type layer, a top region having an n-type layer, and a middle region between the top and bottom regions having at least one material different from the top or bottom region forming two or more heterojunctions. The top and bottom regions create light emission by interband tunneling-induced photon emission. Systems including the unipolar-doped diode including LIDAR are also taught.

A tunable multi-mode laser is configured to generate a multi-mode optical signal at a tuned wavelength. The laser includes a semiconductor optical gain region, a feedback region, and a phase modulation region between the gain and feedback regions. Each of the regions may be monolithically integrated. A feedback loop is coupled to the tunable laser to receive the optical signal and includes at least one delay line. The delay line may also be monolithically integrated. An output of the delay line is fed back to the tunable multi-mode laser in order to provide at least one of self-injection locking and self-phase locked looping for the multi-mode tunable laser. Each of the optical gain region and phase modulation region of the laser is biased by the output of the delay line in order to reduce phase drift of the optical signal.

A semiconductor light emitting element has a laminated structure formed by laminating a first compound semiconductor layer, an active layer, and a second compound semiconductor layer. The semiconductor light emitting element satisfies I.sub.2>I.sub.1, where I.sub.1 is an operating current range when the temperature of the active layer is T.sub.1, and I.sub.2 is the operating current range when the temperature of the active layer is T.sub.2 (where T.sub.2>T.sub.1). The semiconductor light emitting element satisfies P.sub.2>P.sub.1, where P.sub.1 is a maximum optical output emitted when the temperature of the active layer is T.sub.1, and P.sub.2 is the maximum optical output emitted when the temperature of the active layer is T.sub.2 (where T.sub.2>T.sub.1).

A unipolar-doped light emitting diode or laser diode is described. The diode includes a bottom region having an n-type layer, a top region having an n-type layer, and a middle region between the top and bottom regions having at least one material different from the top or bottom region forming two or more heterojunctions. The top and bottom regions create light emission by interband tunneling-induced photon emission. Systems including the unipolar-doped diode including LIDAR are also taught.

A surface-emitting laser includes an active layer; multiple reflectors sandwiching the active layer; and an electrode pair connected to a power supply, through which a current is injected into the active layer. The surface-emitting laser emits at least one laser beam during a current injection period when the current injected into the active layer through the electrode pair during the current injection period is a first current and emits at least one laser beam during a current decrease period when the current injected into the active layer through the electrode pair during the current injection period is a second current exceeding the first current. The current decrease period is after the current injection period. The current injected into the active layer during the current decrease period is lower than the current injected into the active layer during the current injection period.

A laser light-source apparatus includes: a fiber amplifier and a solid-state amplifier to amplify pulse light output from a seed light source serving as a first light source; a nonlinear optical element to perform wavelength conversion on the pulse light output from the solid-state amplifier; an optical switching element to permit or stop propagation of the pulse light from the fiber amplifier to the solid-state amplifier; a second light source disposed on an upstream side of the solid-state amplifier and is configured to output laser light able to be combined with the pulse light output from the seed light source; and a control unit to control the optical switching element in such a manner that the propagation of light is stopped and to perform control in such a manner that the second light source oscillates, at least in an output period of the pulse light from the seed light source.

A laser light-source apparatus includes: a fiber amplifier and a solid-state amplifier to amplify pulse light output from a seed light source serving as a first light source; a nonlinear optical element to perform wavelength conversion on the pulse light output from the solid-state amplifier; an optical switching element to permit or stop propagation of the pulse light from the fiber amplifier to the solid-state amplifier; a second light source disposed on an upstream side of the solid-state amplifier and is configured to output laser light able to be combined with the pulse light output from the seed light source; and a control unit to control the optical switching element in such a manner that the propagation of light is stopped and to perform control in such a manner that the second light source oscillates, at least in an output period of the pulse light from the seed light source.

A surface-emitting laser includes a resonator and an electrode pair connected to a power supply, through which a current is injected into an active layer. The resonator includes the active layer to oscillate a laser beam; a first reflector; and a second reflector facing the first reflector with the active layer therebetween. The resonator has an optical thickness 1.5 times or more than a wavelength of the laser beam in a vacuum. The surface-emitting laser does not oscillate the laser beam during a current injection period in which the power supply injects the current into the active layer through the electrode pair; and oscillates and emits the laser beam during a current decrease period after the current injection period. The current injected into the active layer during the current decrease period is lower than the current injected into the active layer during the current injection period.

Light with a short pulse width is emitted using a simple structure. A light source 101, a differentiation circuit 102, and a switch 103 are connected in series. When the switch 103 is switched on, inrush current flows in a capacitor 102b forming the differentiation circuit 102, and accordingly the light source 101 is supplied with electric current and thereby emits light. When the capacitor 102b is charged, electric current flows in a resistor 102a, and voltage drops at the resistor 102a. Then, the voltage applied to the light source 101 is decreased, whereby the light source 101 stops emitting light. By using the inrush current at the capacitor 102b, light with a short pulse width can be generated.

A semiconductor light emitting element has a laminated structure formed by laminating a first compound semiconductor layer, an active layer, and a second compound semiconductor layer. The semiconductor light emitting element satisfies I.sub.2>I.sub.1, where I.sub.1 is an operating current range when the temperature of the active layer is T.sub.1, and I.sub.2 is the operating current range when the temperature of the active layer is T.sub.2 (where T.sub.2>T.sub.1). The semiconductor light emitting element satisfies P.sub.2>P.sub.1, where P.sub.1 is a maximum optical output emitted when the temperature of the active layer is T.sub.1, and P.sub.2 is the maximum optical output emitted when the temperature of the active layer is T.sub.2 (where T.sub.2>T.sub.1).