A GaN based LED, with an active region of the LED containing one or more quantum wells (QWs), with the QWs separated by higher energy barriers, with the barriers doped, may be part of an optical communications system.

A space optical coupling apparatus, including M first couplers, a phase adjustment apparatus, N beam splitters, M second couplers, a coupling apparatus, and a controller. The first coupler receives a beam, and couples the beam to the phase adjustment apparatus. The phase adjustment apparatus includes M phase adjusters, N beam splitters, and N detectors. Each beam splitter is configured to split a received beam into two beams, one sent to a corresponding detector and the other sent to a corresponding phase adjuster. The second coupler receives output light from the coupling apparatus, and transmits the output light into the space. The coupling apparatus is configured to couple a beam onto a single-mode fiber. The controller is configured to control, based on the beam intensity detected by the detector and the beam intensity on the single-mode fiber, the M phase adjusters to adjust the phases of the received beams.

A coherent receiver comprising: a signal port receiving the signal light that has two polarization components at right angles each other; a polarization dependent beam splitter (PBS) that splits the signal light into two portions depending on the polarizations contained in the signal light; a beam splitter (BS) that splits the local light into two portions; a multi-mode interference (MMI) device that interferes between one of the two portions of the signal light and one of the two portions of the local light; optical components provided between the PBS and the MMI device; and wherein the PBS splitting a first wavelength range of the signal light and a second wavelength range outside the first wavelength range.

A communication network includes a coherent optics transmitter, a coherent optics receiver, an optical transport medium operably coupling the coherent optics transmitter to the coherent optics receiver, and a coherent optics interface. The coherent optics interface includes a lineside interface portion, a clientside interface portion, and a control interface portion.

A method and structure for tap centering in a coherent optical receiver device. The center of gravity (CG) of the filter coefficients can be used to evaluate a proper convergence of a time-domain adaptive equalizer. However, the computation of CG in a dual-polarization optical coherent receiver is difficult when a frequency domain (FD) adaptive equalizer is adopted. In this case, the implementation of several inverse fast-Fourier transform (IFFT) stages is required to back time domain impulse response. Here, examples of the present invention estimate CG directly from the FD equalizer taps and compensate for an error of convergence based off of the estimated CG. This estimation method and associated device architecture is able to achieve an excellent tradeoff between accuracy and complexity.

A reception device 20 is configured to include a separation means 21 and a plurality of optical reception means 22. Each optical reception means 22 further includes an optical/electrical conversion means 23, a reception coefficient computation means 24, and a band restoration means 25. The separation means 21 separates a multiplexed signal into which signals of respective channels to which spectral shaping that narrows bandwidth to less than or equal to a baud rate is applied as band narrowing filter processing on the transmission side, based on characteristics of a transmission line are multiplexed at spacings less than or equal to the baud rate. Each band restoration means 25 applies processing having inverse characteristics to those of the band narrowing filter processing to a reception signal, based on the band narrowing parameter acquired by the reception coefficient computation means 24 and thereby restores the band of the reception signal.

Aspects of a symmetric coherent optical mixer are described. In one example, the coherent optical mixer includes a group of symmetric MMI couplers and a group of symmetric bend waveguides optically coupled between the MMI couplers. The group of symmetric MMI couplers can include an input for a local light reference signal, an input for a modulated light signal, and outputs for detection of data from the modulated light signal. The group of symmetric MMI couplers can include four MMI couplers, each of which comprises a 22 MMI coupler of symmetric dimension. The group of symmetric bend waveguides can include a symmetric layout of four 90 bend waveguides optically coupled between the four MMI couplers. The coherent optical mixer, which can be implemented as a Silicon Photonics (SiPh) device, provides better performance as a 90 degree optical hybrid than prior mixer devices due to its symmetric layout.

An optical network communication system utilizes a coherent passive optical network (PON). The system includes an optical line terminal (OLT) having a downstream transmitter and an upstream receiver system configured for time-wavelength division coherent detection. The system further includes a splitter in operable communication with the OLT, and a plurality of optical network units (ONUs) in operable communication with the splitter. Each of the plurality of ONUs is configured to (i) receive downstream coherent burst signals from the OLT, and (ii) transmit at least one upstream burst signal to the OLT. The upstream receiver system further includes a power control module and a local oscillator (LO) configured to generate an optical LO signal The power control module is configured to adaptively control, in real-time, a power level of the optical LO signal.

An optical reception apparatus (1) of the present invention includes: a local oscillator (11) outputting local oscillation light (22); an optical mixer (12) receiving a multiplexed optical signal (21) and the local oscillation light, and selectively outputting an optical signal (23) corresponding to the wavelength of the local oscillation light from the multiplexed optical signal; a photoelectric converter (13) converting the optical signal (23) output from the optical mixer into an electric signal (24); a variable gain amplifier (15) amplifying the electric signal (24) to generate an output signal (25) whose output amplitude is amplified to a certain level; a gain control signal generating circuit (16) generating a gain control signal (26) for controlling the gain of the variable gain amplifier (15); and a monitor signal generating unit (17) generating a monitor signal (27) corresponding to the power of the optical signal (23) using the gain control signal (26).

A method and structure for a coherent optical receiver device. Timing recovery (TR) is implemented after channel dispersion (i.e., chromatic dispersion (CD) and polarization mode dispersion (PMD)) compensation blocks. This architecture provides both improves performance and reduces power consumption of the device. Also, a TR loop is provided, enabling computing, by an error evaluation module, a first sampling phase error (SPE) and computing, by a timing phase information (TPI) module coupled to the error evaluation module, a second SPE from a plurality of CD equalizer taps PMD equalizer taps. The first and second SPE are combined into a total phase error (TPE) in a combining module, and the resulting TPE is filtered by a timing recovery (TR) filter coupled to an interpolated timing recovery (ITR) module and the combining module. The ITR module then synchronizes an input signal of the coherent optical receiver according to the TPE.