Device for modulating the intensity of an optical signal on four levels, this device comprising: a first resonant ring modulator comprising an output port capable of delivering a first modulated optical signal, a second resonant ring modulator comprising an output port capable of delivering a second modulated optical signal, an optical assembler comprising: a first input optically coupled to the output port of the second resonant ring modulator, a second input optically coupled to the output port of the first resonant ring modulator, and an output capable of delivering the optical signal of which the intensity is modulated on four different levels constructed by combining the optical signals received on its first and second inputs.

An outphasing power management circuit for radio frequency (RF) beamforming is disclosed. The outphasing power management circuit includes a first outphasing amplifier branch consisting of a plurality of first power amplifiers and a second outphasing amplifier branch consisting of a plurality of second power amplifiers. A controller operates the first outphasing amplifier branch and the second outphasing amplifier branch as a pair of outphasing power amplifiers. The first outphasing amplifier branch generates a plurality of first output signals, and the second outphasing amplifier branch generates a plurality of second output signals. The first output signals and the second output signals are transmitted in an RF beam without being combined. As such, it is possible to support RF beamforming with a reduced number of power amplifiers and/or direct current (DC) to DC converters, thus helping to improve efficiency and reduce cost.

A bias control apparatus and method of a modulator of an optical transmitter and an optical transmitter, in which by performing mutual interference on driving signals of two Mach-Zehnder modulators constituting the modulator of the optical transmitter, output optical fields of the two Mach-Zehnder modulators are correlated. Hence, an output power signal of the modulator of the optical transmitter contains information on phase bias. Thus, the phase bias may be controlled by using the output power signal, sensitivity of the bias control may be efficiently improved, and various types of modulation formats may be applied.

An optical IQ modulator with automatic bias control is disclosed. A dither signal is applied to the modulator bias and its signature detected in light tapped from an output of the modulator using a phase sensitive dither detector such as a lock-in amplifier. The detected signal is processed using pre-recorded information defining the direction of the detected signal change relative to a change in the modulator bias, and the bias is adjusted in the direction determined using the information. The IQ phase bias is controlled by dithering I and Q optical signals in quadrature to produce opposite-sign single subband modulation of output light at two different dither frequencies, and detecting an oscillation at a difference frequency using a lock-in detector.

An optical communication apparatus includes: a light-receiving device that receives an optical signal transmitted from another optical communication apparatus through an optical fiber and converts the optical signal into an electrical signal; a first measurement circuit that measures an average power and a modulation power of the optical signal based on the electrical signal; a light-emitting device that transmits the optical signal to the another optical communication apparatus by emitting light in accordance with a driving current; a driver that causes the light-emitting device to transmit the optical signal according to a transmission signal by controlling the driving current based on the transmission signal; and a processor that adjusts the driving current based on the average power and the modulation power.

A single-channel phase conjugation apparatus includes a spatial light modulator and a single-channel optical sensing and generating unit. The spatial light modulator receives a light having a wavefront scattered by a scattering object. The single-channel optical sensing and generating unit senses a phase control wavefront of an output light focused by the spatial light modulator and outputs a light having a phase conjugation wavefront by changing a direction of the output light in a reverse direction depending on the phase control wavefront.

Provided are a device and method for free space coherent optical communications by means of an automatic compensation for phase noise in atmosphere using a femtosecond laser optical comb, and more particularly, a device and method for free space coherent optical communications by means of an automatic compensation for phase noise in atmosphere using a femtosecond laser optical comb, in which a phase shift value due to atmospheric turbulence is obtained from reflected light of transmission light generated from a femtosecond laser optical comb and the transmission light is pre-distorted on the basis of the phase shift value, thereby pre-compensating, in a transmission end, for phase noise due to atmospheric turbulence.

A method of generating a signal being phase-shifted at a predetermined phase-shift division factor relative to a reference signal is disclosed. The method comprises: using the predetermined phase-shift division factor for selecting a modulation amplitude, modulating a control signal at the selected modulation amplitude, and combining the reference signal and the control signal to form the phase-shifted.

An architecture for an optoelectronic oscillator uses Stimulated Brillouin Scattering (SBS) to seed, filter and amplify the oscillation signal in an overlapped oscillator loop for both a RF modulated optical sideband and a SBS signal. By phase matching the RF modulated optical sideband generated by SBS with the SBS signal, the feedback will collapse the bandwidth of the SBS signal and in turn the bandwidth of the Brillouin frequency signal, which also serves as a filter to filter out multiple undesired OEO loop modes. The embodiments herein result in reduced phase noise and increased stability.

Systems, methods, and computer-readable media for providing adaptive feedback in downhole telemetry in a wellbore. A feedback system includes a source assembly, which can be located on the surface or downhole, and a receiving assembly, which can likewise be located on the surface or downhole. The source assembly includes a source device that transmits a light signal having a first phase, and an encoder coupled to the source device. The receiving assembly comprising an oscillator that transmits an oscillator having a second phase, a coupler that couples the light signal with the oscillator signal, a detector and difference amplifier that detect and determine the difference between the first phase and second phase and a processor that receives the difference between the phases and provides the difference to an encoder so that the encoder can adjust the oscillator phase.