A forward optical intensity modulation signal, generated by optical intensity-modulating a laser signal using a forward microwave phase modulation signal, is transmitted from a base to a remote station. A backward microwave phase modulation signal, in which frequency of the forward microwave phase modulation signal is changed by demodulating the forward optical intensity modulation signal, is generated, and a backward optical intensity modulation signal, generated by optical intensity-modulating the laser signal using the backward microwave phase modulation signal, is transmitted from the remote station to the base. The backward microwave phase modulation signal is extracted by photoelectric converting the backward optical intensity modulation signal, a round trip timing is extracted by demodulating the backward microwave phase modulation signal, and transmission delay is determined from a difference between the timing and the round trip timing.

Free-space optical (FSO) wireless transmission, including optical communications, remote-sensing, power beaming, etc., can be enhanced by replacing conventional laser sources that operate in the infrared portion of the optical spectrum with ultra-short pulsed laser (USPL) sources having peak pulse powers of one kWatt or greater and pulse lengths of less than one picosecond. Specifically, it has been observed that under these conditions the attenuation of an USPL beam having the same average optical power as a conventional laser in a lossy medium, such as the atmosphere, is substantially less than the attenuation of a conventional laser beam having a lower peak pulse power and/or a longer pulse width. The superior system performance when using an USPL can be translated into an increased distance between a laser source in a transmitter and a photodetector in receiver and/or a higher reliability of system operation in inclement weather conditions.

RF processing systems and methods. An RF processing system includes an optical storage module, a processing module, and an electro-optical modulation module. The electro-optical modulation module is configured to receive the first signal from the optical storage module, receive the modulation signal from the processing module, and electro-optically modulate the first signal based on the modulation signal.

An adjusting method for stabilizing optical characteristic parameters applicable to transmitter optical subassemblies with silicon photonic chips is provided. The adjusting method might include: sensing an initial optical signal emitted by the transmitter optical subassembly with first control component, controlling phase setting parameter of the silicon photonic chip with the first control component to change the transmitter optical subassembly from emitting the initial optical signal to emitting a first modified optical signal, transmitting a power target value to second control component when the first modified optical signal conforms to the phase target value and sensing the first modified optical signal with the second control component, and controlling a bias current of the transmitter optical subassembly according to the first modified optical signal and the power target value to change the transmitter optical subassembly from emitting the first modified optical signal to emitting a second modified optical signal.

Free-space optical (FSO) wireless transmission, including optical communications, remote-sensing, power beaming, etc., can be enhanced by replacing conventional laser sources that operate in the infrared portion of the optical spectrum with ultra-short pulsed laser (USPL) sources having peak pulse powers of one kWatt or greater and pulse lengths of less than one picosecond. Specifically, it has been observed that under these conditions the attenuation of an USPL beam having the same average optical power as a conventional laser in a lossy medium, such as the atmosphere, is substantially less than the attenuation of a conventional laser beam having a lower peak pulse power and/or a longer pulse width. The superior system performance when using an USPL can be translated into an increased distance between a laser source in a transmitter and a photodetector in receiver and/or a higher reliability of system operation in inclement weather conditions.

A local oscillation light output unit; a phase adjustment unit; a polarization control unit; a multiplexing unit; a photoelectric conversion unit; a demodulation unit; and a control unit. The phase adjustment unit adjusts the phase of local oscillation light. The polarization control unit controls polarization rotation of an optical signal. The multiplexing unit multiplexes the local oscillation light output from the phase adjustment unit with the optical signal output from the polarization control unit. The demodulation unit performs a demodulation process based on an electric signal obtained through conversion performed by the photoelectric conversion unit. The control unit, on the basis of information about the reception status of the optical signal, controls the execution of at least one of the phase adjustment of the local oscillation light in the phase adjustment unit and the polarization rotation of the optical signal in the polarization control unit.

Systems, methods, and devices are disclosed for implementing photonic links. Methods include transmitting light using an optical emitter, splitting, using an input coupler, the light into a first path and a second path, the first path being provided to a modulator, and the second path being provided to a phase shifter, and combining, using an output coupler, an output of the modulator and an output of the phase shifter. Methods further include identifying a modulator phase angle that reduces a third order distortion at an output of the output coupler, applying a first bias voltage to a modulator to maintain the identified modulator phase angle, and applying a control signal to the phase shifter to maintain a phase difference between an output of the modulator and an output of a phase shifter.

A method of interference suppression with intermodulation distortion mitigation includes processing an RF signal comprising an RF signal of interest and an RF interfering signal to produce a first and second RF drive signal each with a desired RF interference signal power and having a 90 degree relative phase. The first RF drive signal is imposed onto a first optical signal with a modulator to generate a first modulated optical signal so that the modulator has a large-signal behavior that is characterized by a Bessel function of the first kind J.sub.1(ϕ), wherein the desired power at a frequency of the interference signal of the first drive signal is chosen to correspond to a zero of the Bessel function of the first kind J.sub.1(ϕ). The second RF drive signal is imposed onto a second optical signal with a modulator to generate a second modulated optical signal so that the modulator has a large-signal behavior that is characterized by a Bessel function of the first kind J.sub.1(ϕ), wherein the desired power at a frequency of the interference signal of the second drive signal is chosen to correspond to another zero of the Bessel function of the first kind J1(ϕ). The first and second modulated optical signal are combined with an optical power ratio that is selected to suppress third-order intermodulation distortion products in an electrical signal generated by detecting the optically combined first and second modulated optical signals.

An optical transmitter includes a bias supplying unit configured to supply a first bias voltage, a second bias voltage and a third bias voltage to an optical modulator. The bias supplying unit acquires a first voltage value at which an average value of an optical output signal becomes maximum by sweeping the first bias voltage, acquires a second voltage value at which an average value of the optical output signal becomes maximum by sweeping the second bias voltage, and acquires a third voltage value at which an average value of the optical output signal becomes maximum by sweeping the third bias voltage. The bias supplying unit determines a value of the first bias voltage based on the first voltage value, determines a value of the second bias voltage based on the second voltage value, and determines a value of the third bias voltage based on the third voltage value.

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.