A communication system including a first detector; a first scattering medium; a second detector; an intensity modulator; a second scattering medium; wherein electromagnetic radiation transmitted from a first spot at the first scattering medium, and scattered by and through the first scattering medium and then the second scattering medium, forms a first speckle pattern detected by the second detector. The intensity modulator outputs a second spot of electromagnetic radiation representing the ones in a data stream at locations of the bright speckles (or at locations of the dark speckles to represent the zeros in the data stream) so that the electromagnetic radiation, transmitted from the second spot and scattered by and through the second scattering medium and then the first scattering medium, forms one or more second bright or dark speckles on the first detector. The data stream can be constructed from the second bright or dark speckles.

A communication system including a first detector; a first scattering medium; a second detector; an intensity modulator; a second scattering medium; wherein electromagnetic radiation transmitted from a first spot at the first scattering medium, and scattered by and through the first scattering medium and then the second scattering medium, forms a first speckle pattern detected by the second detector. The intensity modulator outputs a second spot of electromagnetic radiation representing the ones in a data stream at locations of the bright speckles (or at locations of the dark speckles to represent the zeros in the data stream) so that the electromagnetic radiation, transmitted from the second spot and scattered by and through the second scattering medium and then the first scattering medium, forms one or more second bright or dark speckles on the first detector. The data stream can be constructed from the second bright or dark speckles.

According to examples, a channel checker optical time-domain reflectometer (OTDR) may include a laser source to emit a laser beam. An optical switch may be optically connected to the laser source to receive the laser beam and to selectively transmit the laser beam to a circulator that is optically connected to a device under test (DUT). A first coupler may be optically connected to a first photodiode and to the circulator. A second coupler may be optically connected to the first coupler, the optical switch, and a second photodiode.

According to examples, a channel checker optical time-domain reflectometer (OTDR) may include a laser source to emit a laser beam. An optical switch may be optically connected to the laser source to receive the laser beam and to selectively transmit the laser beam to a circulator that is optically connected to a device under test (DUT). A first coupler may be optically connected to a first photodiode and to the circulator. A second coupler may be optically connected to the first coupler, the optical switch, and a second photodiode.

An apparatus includes multiple ports configured to be coupled to multiple optical fibers and to transmit first optical signals and receive second optical signals over the optical fibers. The apparatus also includes a signal source configured to generate a first additional optical signal for inclusion with the first optical signals. The apparatus further includes a signal detector configured to detect a second additional optical signal included with the second optical signals. In addition, the apparatus includes a switch configured to selectively couple the signal source to one of the ports. The switch is configured to couple the signal source to different ones of the ports in different configurations of the switch.

Techniques for transmitting an optical signal through optical fiber with an improved cost effective stimulated Brillouin scattering (SBS) suppression include externally modulating a light beam emitted from a light source with a high frequency signal. The light beam is also modulated externally with an RF information-carrying signal. The high frequency signals are at least twice a highest frequency of the RF signal. The high frequency signals modulating the light source can be gain and phase adjusted by the first set of gain and phase control circuit to achieve a targeted spectrum shape. The adjusted high frequency signals then are split, providing a portion of the split signals to modulate the light source and another portion of the split signals to the second set of phase and gain control circuit for adjusting a phase/gain. The output of second set of phase and gain control circuits can be applied to the external modulator to eliminate intensity modulation caused by the corresponding high frequency signals that modulate the light source. The spread spectrum for SBS suppression or the optical transmitter's SNR is further improved by cancelling a beat between SBS suppression modulation tones and out of band distortion spectrum of information bearing RF signal.

Techniques for transmitting an optical signal through optical fiber with an improved cost effective stimulated Brillouin scattering (SBS) suppression include externally modulating a light beam emitted from a light source with a high frequency signal. The light beam is also modulated externally with an RF information-carrying signal. The high frequency signals are at least twice a highest frequency of the RF signal. The high frequency signals modulating the light source can be gain and phase adjusted by the first set of gain and phase control circuit to achieve a targeted spectrum shape. The adjusted high frequency signals then are split, providing a portion of the split signals to modulate the light source and another portion of the split signals to the second set of phase and gain control circuit for adjusting a phase/gain. The output of second set of phase and gain control circuits can be applied to the external modulator to eliminate intensity modulation caused by the corresponding high frequency signals that modulate the light source. The spread spectrum for SBS suppression or the optical transmitter's SNR is further improved by cancelling a beat between SBS suppression modulation tones and out of band distortion spectrum of information bearing RF signal.

In the embodiments of the present disclosure, a transmit apparatus generates a to-be-processed optical signal and a quantum optical signal, where the to-be-processed optical signal includes at least a classical optical signal; and the transmit apparatus couples the to-be-processed optical signal and the quantum optical signal, to obtain a coupled optical signal, and sends the coupled optical signal. Because a wavelength of the classical optical signal is in an L band and/or a C band and a wavelength of the quantum optical signal is in an S band, a wavelength in the band of the classical optical signal is greater than a wavelength in the band of the quantum optical signal.

In the embodiments of the present disclosure, a transmit apparatus generates a to-be-processed optical signal and a quantum optical signal, where the to-be-processed optical signal includes at least a classical optical signal; and the transmit apparatus couples the to-be-processed optical signal and the quantum optical signal, to obtain a coupled optical signal, and sends the coupled optical signal. Because a wavelength of the classical optical signal is in an L band and/or a C band and a wavelength of the quantum optical signal is in an S band, a wavelength in the band of the classical optical signal is greater than a wavelength in the band of the quantum optical signal.

A Raman amplifier having an optical pump configured to generate pump bands, each of which is spectrally aligned with a respective wavelength channel of a frequency grid in a manner that enables the pump bands to coexist in an optical fiber with data-carrying signals of other wavelength channels of the frequency grid without causing unworkable levels of inter-channel interference. In an example embodiment, the optical pump comprises a laser whose single-mode output is modulated to sufficiently suppresses stimulated Brillouin scattering in the optical fiber while still keeping the optical power of each of the resulting pump bands spectrally compact, e.g., substantially contained within the slot width of the respective wavelength channel. In some embodiments, at least some pump bands can be spectrally interleaved with some of the data-carrying signals to increase the data-throughput capacity of the corresponding optical transport system.