An optical transmission apparatus includes a first multilevel optical phase modulator and a first semiconductor optical amplifier. The first semiconductor optical amplifier includes a first active region having a first multiple quantum well structure. Assuming that a first number of layers of a plurality of first well layers is defined as n.sub.1 and a first length of the first active region is defined as L.sub.1 (μm): (a) n.sub.1=5 and 400≤L.sub.1≤563; (b) n.sub.1=6 and 336≤L.sub.1≤470; (c) n.sub.1=7 and 280≤L.sub.1≤432; (d) n.sub.1=8 and 252≤L.sub.1≤397; (e) n.sub.1=9 and 224≤L.sub.1≤351; or (f) n.sub.1=10 and 200≤L.sub.1≤297.

A semiconductor optical integrated element according to the present disclosure includes:; a first optical amplifier which amplifies a signal beam inputted from a first end surface; a first passive optical waveguide which guides the amplified signal beam toward a direction different from a direction of the optical waveguide; an optical splitter which splits the guided signal beam into a plurality of signal beams; a phase modulator which is connected to the first passive optical waveguide and performs phase modulation on the plurality of signal beams; a second passive optical waveguide which guides each phase-modulated signal beam toward the direction of the optical waveguide; an optical multiplexer which multiplexes the plurality of phase-modulated signal beams into one signal beam; and a second optical amplifier which amplifies the signal beam guided by the second passive optical waveguide, and whose saturated beam output is smaller than that of the first optical amplifier.

An optical semiconductor device includes an optical modulator provided on a substrate, an optical waveguide provided on the substrate, one end of the optical waveguide being connected to a light emission side of the optical modulator and another end of the optical waveguide being present at an end portion of the substrate, a phase adjusting unit provided on a path of the optical waveguide and an optical amplification unit provided on the path of the optical waveguide, wherein a minimum value or a maximum value of a transmittance spectrum having a ripple that periodically fluctuates with respect to a frequency because of multiple reflection of light that occurs between the one end and the other end of the optical waveguide is matched with a wavelength of the light input to the optical modulator by phase adjustment of the phase adjusting unit, and an error vector amplitude is minimized.

An optical device includes an optical amplifier that optically amplifies incident light, a first isolator that is arranged on an input stage of the optical amplifier and inputs the incident light to the optical amplifier, and a second isolator that is arranged on an output stage of the optical amplifier and receives input of incident light that has been optically amplified by the optical amplifier. The first isolator inputs, to the optical amplifier, first linearly-polarized incident light that is converted from randomly-polarized incident light and that has been transmitted. The second isolator, when reflected light of the first linearly-polarized incident light that has been optically amplified by the optical amplifier is input from a reverse direction, converts reflected light of the first linearly-polarized incident light to reflected light of second linearly-polarized light that is orthogonal to the reflected light of the first linearly-polarized incident light.

An integrated optical beam steering device includes a planar dielectric lens that collimates beams from different inputs in different directions within the lens plane. It also includes an output coupler, such as a grating or photonic crystal, that guides the collimated beams in different directions out of the lens plane. A switch matrix controls which input port is illuminated and hence the in-plane propagation direction of the collimated beam. And a tunable light source changes the wavelength to control the angle at which the collimated beam leaves the plane of the substrate. The device is very efficient, in part because the input port (and thus in-plane propagation direction) can be changed by actuating only log.sub.2 N of the N switches in the switch matrix. It can also be much simpler, smaller, and cheaper because it needs fewer control lines than a conventional optical phased array with the same resolution.

A programmable two-dimensional simultaneous multi-beam optically operated phased array receiver chip is manufactured based on silicon-on-insulator (SOI) and indium phosphide (InP) semiconductor manufacturing processes, including the SiN process. The InP-based semiconductor is used for preparing a laser array chip and a semiconductor optical amplifier array chip, the SiN is used for preparing an optical power divider, and the SOI semiconductor is used for preparing a silicon optical modulator, a germanium-silicon detector, an optical wavelength multiplexer, a true delay line, and other passive optical devices. The whole integration of the receiver chip is realized through heterogeneous integration of the InP-based chip and the SOI-based chip. Simultaneous multi-beam scanning can be realized through peripheral circuit programming control. The chip not only can realize two-dimensional multi-beam scanning, but also has strong expansibility, such that the chip can be used for ultra-wideband high-capacity wireless communication and simultaneous multi-target radar recognition systems.

A photonic chip. In some embodiments, the photonic chip includes a waveguide; and an optically active device comprising a portion of the waveguide. The waveguide may have a first end at a first edge of the photonic chip; and a second end, and the waveguide may have, everywhere between the first end and the second end, a rate of change of curvature having a magnitude not exceeding 2,000/mm.sup.2.

An optical coherent transceiver comprising a polarization and phase-diversity coherent receiver and a polarization and phase-diversity modulator on the same substrate interfaced by three grating couplers, one grating coupler coupling in a signal, one grating coupler coupling in a laser signal, and a third grating coupler coupling out a modulated signal.

A photonic chip. In some embodiments, the photonic chip includes a waveguide; and an optically active device comprising a portion of the waveguide. The waveguide may have a first end at a first edge of the photonic chip; and a second end, and the waveguide may have, everywhere between the first end and the second end, a rate of change of curvature having a magnitude not exceeding 2,000/mm.sup.2.

A semiconductor laser source including a Mach-Zehnder interferometer including first and second arms. Each of these arms being divided into a plurality of consecutive sections. The first and second arms each include a gain-generating section forming first and second gain-generating waveguides, respectively. The laser source includes power sources able to deliver currents through the gain-generating waveguides such that the following condition is met: $\underset{n=1}{\overset{N_2}{.Math.}}{L}_{2,n}{\mathrm{neff}}_{2,n}-\underset{n=1}{\overset{N_1}{.Math.}}{L}_{1,n}{\mathrm{neff}}_{1,n}=k_f{\lambda }_{\mathrm{Si}}$
where: k.sub.f is a preset integer number higher than or equal to 1, N.sub.1 and N.sub.2 are the numbers of sections in the first and second arms, respectively, L.sub.1,n and L.sub.2,n are the lengths of the nth sections of the first and second arms, respectively, neff.sub.1,n and neff.sub.2,n are the effective indices of the nth sections of the first and second arms, respectively.