A free-space optical communication method is provided. An example method may include generating an optical frequency comb comprising a first tone and a second tone different from the first tone. The method may include modulating, by a first modulator of a first device, the first tone to generate a first signal comprising data. The method may include modulating, by a second modulator of the first device, the second tone to generate a second signal that is a phase conjugate of the first signal. The method may include transmitting, via free-space and to a second device, a communication signal having the first signal and the second signal.

An EDFA may include an input photodiode configured to generate a control signal based on an input signal. The EDFA may include a blind stage configured to generate an amplified signal based on the control signal and the input signal. The EDFA may include a non-blind stage configured to generate an output signal based on the amplified signal within the blind stage, the control signal, and a feedback signal. The EDFA may include a filter configured to generate a filtered signal based on the output signal. The EDFA may include an output photodiode configured to generate the feedback signal based on the filtered signal. The EDFA may include an alarm device. A signal within the non-blind stage may be generated based on the feedback signal and the control signal. The alarm device may be configured to generate an alarm signal when the signal exceeds a threshold value.

Described herein are photonic integrated circuits (PICs) comprising a semiconductor optical amplifier (SOA) to output a signal comprising a plurality of wavelengths, a sensor to detect data associated with a power value of each wavelength of the output signal of the SOA, a filter to filter power values of one or more of the wavelengths of the output signal of the SOA, and control circuitry to control the filter to reduce a difference between a pre-determined power value of each filtered wavelength of the output signal of the SOA and the detected power value of each filtered wavelength of the output signal of the SOA.

An optical repeater is a C+L-band repeater inserted between a first transmission path fiber and a second transmission path fiber. The optical repeater includes: a first optical fiber amplifier inserted in a first line, for amplifying a C-band signal; a second optical fiber amplifier inserted in a second line, for amplifying an L-band signal; a third optical fiber amplifier inserted in a third line, for amplifying a C-band signal; a fourth optical fiber amplifier inserted in a fourth line, for amplifying an L-band signal; and a first loopback means provided between an input to the first optical fiber amplifier or an output from the first optical fiber amplifier and an input to the third optical fiber amplifier or an output from the third optical fiber amplifier.

An optical node device includes: a multicore optical amplification unit that amplifies collectively light transmitted along a multicore fiber; a separation unit that inputs the amplified light in each core to each of a plurality of input-side single-core fibers; an optical cross-connect switch that attenuates the light input from each of the plurality of input-side single-core fibers through an optical attenuator, separates the light in accordance with a wavelength, and outputs the separated light to an output-side single-core fiber of a plurality of output-side single-core fibers related to a respective output destination; a plurality of single-core optical amplification units that amplify the light transmitted along the corresponding output-side single-core fibers; and an output unit that outputs the light transmitted along each of the plurality of output-side single-core fibers to a multicore fiber. A control unit controls the optical attenuator and the single-core optical amplification unit based on input signal optical power and output optical signal power.

A fiber-optic communication system includes a first optical transceiver and a second optical transceiver. First, the first optical transceiver is configured to transmit signals to the second optical transceiver using an optical transmission power having an initial value. When the optical receiving power inputted into the second optical transceiver is larger than the expected input power of the second optical transceiver, a power compensation value is acquired according to the optical receiving power and the expected input power. The first optical transceiver is configured adjust its optical transmission power according to the power compensation value and then transmit signals to the second optical transceiver using the adjusted optical transmission power.

A method and apparatus for controlling an optical switch. The switch includes a switching fabric and optical amplifiers for amplifying optical signals. A configuration for the switching fabric is generated and implemented. The configuration indicates a set of optical paths between switching fabric input ports and the output ports. Optical path losses through the switching fabric vary based on the configuration. An amplifier control signal for controlling gains of the optical amplifiers, is also provided. The configuration for the switching fabric is generated based on the gains of the optical amplifiers, the amplifier control signal is generated based on the configuration for the switching fabric, or both.

An optical node device includes: a multicore optical amplification unit that amplifies collectively light transmitted along a multicore fiber; a separation unit that inputs the amplified light in each core to each of a plurality of input-side single-core fibers; an optical cross-connect switch that attenuates the light input from each of the plurality of input-side single-core fibers through an optical attenuator, separates the light in accordance with a wavelength, and outputs the separated light to an output-side single-core fiber of a plurality of output-side single-core fibers related to a respective output destination; a plurality of single-core optical amplification units that amplify the light transmitted along the corresponding output-side single-core fibers; and an output unit that outputs the light transmitted along each of the plurality of output-side single-core fibers to a multicore fiber. A control unit controls the optical attenuator and the single-core optical amplification unit based on input signal optical power and output optical signal power.

In order to improve reception sensitivity of a response signal at a terminal station, an optical transmission device includes a reception unit that receives a control signal including a predetermined instruction and a main signal, via an optical transmission path connected to the terminal station, a control unit that performs the predetermined instruction of the received control signal, an extraction unit that extracts light in a band of the control signal, a response signal generation unit that modulates the extracted light in the band of the control signal, and outputs a response signal, and a multiplexing unit that multiplexes and outputs the response signal and the main signal. The control unit controls modulation by the response signal generation unit according to the control signal.

In order to improve reception sensitivity of a response signal at a terminal station, an optical transmission device includes a reception unit that receives a control signal including a predetermined instruction and a main signal, via an optical transmission path connected to the terminal station, a control unit that performs the predetermined instruction of the received control signal, an extraction unit that extracts light in a band of the control signal, a response signal generation unit that modulates the extracted light in the band of the control signal, and outputs a response signal, and a multiplexing unit that multiplexes and outputs the response signal and the main signal. The control unit controls modulation by the response signal generation unit according to the control signal.