Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for optical communications. In one aspect, an optical amplifier includes an input port, a wavelength division multiplexing fiber coupled to a pump source and to a bar-cross switch, a first gain stage optically coupled between a first port of the bar-cross switch and to an output port, the first gain stage including a first gain flattening filter, and a secondary gain stage optically coupled between a second port and a third port of the bar-cross switch, the secondary gain stage including a second gain flattening filter. When in a bar-state of the bar-cross switch, the secondary gain stage is bypassed. And when in a cross-state of the bar-cross switch, the secondary gain stage and the first gain stage are applied to an input light beam.

Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link. The received optical signal contains a modulated unique frequency tone. The method also includes mixing the modulated unique frequency tone with a reference signal to provide a mixed output signal and determining a signal strength of the modulated unique frequency tone based on the mixed output signal. The reference signal includes a same frequency as the modulated unique frequency tone. The method adjusts an optical head of the first communication terminal to establish acquisition and optical beam pointing with the second communication terminal based on the signal strength of the modulated unique frequency tone received from the second communication terminal.

Abstract: A communication method includes combining first and second optical signals into a third optical signal, processing the third optical signal, and separating the third optical signal back into the first and second optical signals. The method includes sending the first optical signal out a first system port, sending the second optical signal out a second system port, receiving a fourth optical signal in the first system port, and receiving a fifth optical signal in the second system port. The method also includes combining the fourth and fifth optical signals into a sixth optical signal, processing the sixth optical signal, and separating the sixth optical signal back into the fourth and fifth optical signals.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link. The received optical signal contains a modulated unique frequency tone. The method also includes mixing the modulated unique frequency tone with a reference signal to provide a mixed output signal and determining a signal strength of the modulated unique frequency tone based on the mixed output signal. The reference signal includes a same frequency as the modulated unique frequency tone. The method adjusts an optical head of the first communication terminal to establish acquisition and optical beam pointing with the second communication terminal based on the signal strength of the modulated unique frequency tone received from the second communication terminal.

Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link and determining a receiving power for the optical link based on the first optical signal. The method further includes adjusting an output amplification at the first communication terminal based on the receiving power for the optical link. The output amplification is adjusted to provide a second optical signal with a minimum transmission power for maintaining the optical link. The method transmits the second optical signal from the first communication terminal to the second communication terminal through the optical link.

Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link. The received optical signal contains a modulated unique frequency tone. The method also includes mixing the modulated unique frequency tone with a reference signal to provide a mixed output signal and determining a signal strength of the modulated unique frequency tone based on the mixed output signal. The reference signal includes a same frequency as the modulated unique frequency tone. The method adjusts an optical head of the first communication terminal to establish acquisition and optical beam pointing with the second communication terminal based on the signal strength of the modulated unique frequency tone received from the second communication terminal.

Abstract: A communication system includes a transparent refractive optical wedge, a steerable mirror, a position feedback device, and a transceiver. The transparent refractive optical wedge has first and second faces angled with respect to each other and receives first and second optical signals through both the first and second faces. The first and second optical signals travel along parallel or common paths through the first face and diverge at a deflection angle with respect to each other through the second face. The steerable mirror is in optical communication with the first face of the optical wedge, the position feedback device, and the transceiver. The position feedback device adjusts a position of the steerable mirror to maintain the alignment of the reflected signal with the position feedback device. The transceiver has an optical transmitter transmitting one of the optical signals and an optical receiver receiving the other optical signal.

Abstract: A communication system includes a first optical system and a second optical system optically connected to a clamping laser and a pump laser. The first optical system includes first and second optical splitters. The first optical splitter is configured to receive a clamping laser signal from the clamping laser and split the signal into split clamping laser signals. The second optical splitter is configured to receive a pump laser signal from the pump laser and split signal into split pump laser signals. The second optical system is optically connected to the first optical system and includes amplifier systems. Each amplifier system is configured to receive a multiplexed signal. The second optical system includes first and second combiners optically connected to an erbium-doped fiber. The first combiner is optically connected to the first splitter, and the second combiner is optically connected to the second splitter.

Abstract: A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link. The received optical signal contains a modulated unique frequency tone. The method also includes mixing the modulated unique frequency tone with a reference signal to provide a mixed output signal and determining a signal strength of the modulated unique frequency tone based on the mixed output signal. The reference signal includes a same frequency as the modulated unique frequency tone. The method adjusts an optical head of the first communication terminal to establish acquisition and optical beam pointing with the second communication terminal based on the signal strength of the modulated unique frequency tone received from the second communication terminal.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link and determining a receiving power for the optical link based on the first optical signal. The method further includes adjusting an output amplification at the first communication terminal based on the receiving power for the optical link. The output amplification is adjusted to provide a second optical signal with a minimum transmission power for maintaining the optical link. The method transmits the second optical signal from the first communication terminal to the second communication terminal through the optical link.

Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for optical communications. In one aspect, an optical amplifier includes an input port, a wavelength division multiplexing fiber coupled to a pump source and to a bar-cross switch, a first gain stage optically coupled between a first port of the bar-cross switch and to an output port, the first gain stage including a first gain flattening filter, and a secondary gain stage optically coupled between a second port and a third port of the bar-cross switch, the secondary gain stage including a second gain flattening filter. When in a bar-state of the bar-cross switch, the secondary gain stage is bypassed. And when in a cross-state of the bar-cross switch, the secondary gain stage and the first gain stage are applied to an input light beam.

Abstract: A method of free-space optical communication includes guiding, by focusing optics, an optical communication beam emitted from an optical transmitter into a double-clad optical fiber. The optical communication beam carrying data. The double-clad optical fiber has first and second ends, where the first end is arranged to receive the optical communication beam. The double-clad optical fiber includes a fiber core, a first cladding, and a second cladding. The method also includes directing, by collimating optics, the optical communication beam from the second end of the double-clad optical fiber toward an optical receiver of a communication terminal. the second portion of the optical communication beam arranged concentrically around the first portion of the optical communication beam, the first portion of the optical communication beam having a higher intensity than the second portion of the optical communication beam.

Abstract: A communication system includes a transparent refractive optical wedge, a steerable mirror, a position feedback device, and a transceiver. The transparent refractive optical wedge has first and second faces angled with respect to each other and receives first and second optical signals through both the first and second faces. The first and second optical signals travel along parallel or common paths through the first face and diverge at a deflection angle with respect to each other through the second face. The steerable mirror is in optical communication with the first face of the optical wedge, the position feedback device, and the transceiver. The position feedback device adjusts a position of the steerable mirror to maintain the alignment of the reflected signal with the position feedback device. The transceiver has an optical transmitter transmitting one of the optical signals and an optical receiver receiving the other optical signal.

Abstract: A method includes receiving a first optical signal at a first communication terminal from a second communication terminal through a free space optical link and determining a receiving power for the optical link based on the first optical signal. The method further includes adjusting an output amplification at the first communication terminal based on the receiving power for the optical link. The output amplification is adjusted to provide a second optical signal with a minimum transmission power for maintaining the optical link. The method transmits the second optical signal from the first communication terminal to the second communication terminal through the optical link.