Abstract: An improved gain-clamped optical amplifier is disclosed. A series of laser cavities are placed along the amplifier axis. The laser cavities are designed such that the carrier densities of the amplifier decline toward the signal output end. Since the gain clamping amplitudes at positions along the amplifier can be different, we have the freedom to optimize the optical gain at all location, to minimize the noise impact at the signal input end, and to maximize the saturation output power at the signal output end. In addition, carrier levering effect realized by gain/loss wings further lowers the noise figure, and extends the optical gain and saturation output power. An ideal optical amplifier with high linear gain, small noise figure, and large saturation output power and extended dynamic range is then achieved. Energy saving is the bonus of using the invented amplifiers.

Abstract: A unitary two-section semiconductor optical amplifier including a first active region, a second active region, and a passive region integrally connected between the first and second active regions to minimize optical loss therebetween. The arrangement of the two-section semiconductor optical amplifier is advantageous in that the gain in the first active region may be increased in order to maintain a substantially constant input power level to the second active region over a relatively wide dynamic range of input power levels to the first active region.

Abstract: An optical coupling system couples an optical fiber to an optical semiconductor device. A beam expander is disposed within the optical semiconductor so as to receive light from or transmit light into the optical fiber. The coupling is accomplished by disposing a layer of an index matching gel or epoxy on either surface of the semiconductor optical device or the end portion of the optical fiber and another layer of an antireflective material adjacent to the index matching gel or epoxy. The semiconductor device may include an array of optical devices, each coupled to a corresponding optical fiber via the arrangement that comprises the index matching gel and the antireflective material. The semiconductor device may also include an array of waveguides, each configured to receive light from a corresponding optical fiber.