A cascading microwave isolator (cascade) includes a set of Josephson devices, each Josephson device in the set having a corresponding operating bandwidth of microwave frequencies. Different operating bandwidths have different corresponding center frequencies. A series coupling is formed between first Josephson device from the set and an n.sup.th Josephson device from the set. The series coupling causes the first Josephson device to isolate a signal at a first frequency from a frequency multiplexed microwave signal (multiplexed signal) in a first signal flow direction through the series coupling and the n.sup.th Josephson device to isolate a signal at an n.sup.th frequency from the multiplexed signal in the first signal flow direction through the series.

A cascading microwave isolator (cascade) includes a set of Josephson devices, each Josephson device in the set having a corresponding operating bandwidth of microwave frequencies. Different operating bandwidths have different corresponding center frequencies. A series coupling is formed between first Josephson device from the set and an n.sup.th Josephson device from the set. The series coupling causes the first Josephson device to isolate a signal at a first frequency from a frequency multiplexed microwave signal (multiplexed signal) in a first signal flow direction through the series coupling and the n.sup.th Josephson device to isolate a signal at an n.sup.th frequency from the multiplexed signal in the first signal flow direction through the series.

A cascading microwave isolator (cascade) includes a set of Josephson devices, each Josephson device in the set having a corresponding operating bandwidth of microwave frequencies. Different operating bandwidths have different corresponding center frequencies. A series coupling is formed between first Josephson device from the set and an n.sup.th Josephson device from the set. The series coupling causes the first Josephson device to isolate a signal at a first frequency from a frequency multiplexed microwave signal (multiplexed signal) in a first signal flow direction through the series coupling and the n.sup.th Josephson device to isolate a signal at an n.sup.th frequency from the multiplexed signal in the first signal flow direction through the series.

A cascading microwave isolator (cascade) includes a set of Josephson devices, each Josephson device in the set having a corresponding operating bandwidth of microwave frequencies. Different operating bandwidths have different corresponding center frequencies. A series coupling is formed between first Josephson device from the set and an n.sup.th Josephson device from the set. The series coupling causes the first Josephson device to isolate a signal at a first frequency from a frequency multiplexed microwave signal (multiplexed signal) in a first signal flow direction through the series coupling and the n.sup.th Josephson device to isolate a signal at an n.sup.th frequency from the multiplexed signal in the first signal flow direction through the series.

A cascading selective microwave isolator (cascade) includes a set of Josephson devices, each Josephson device in the set having a corresponding operating bandwidth of microwave frequencies. Different operating bandwidths have different corresponding center frequencies. A series coupling is formed between first Josephson device from the set and an n.sup.th Josephson device from the set. The series coupling causes the first Josephson device to isolate a signal at a first frequency from a frequency multiplexed microwave signal (multiplexed signal) in a first signal flow direction through the series coupling and the n.sup.th Josephson device to isolate a signal of an n.sup.th frequency in a second signal flow direction through the series, where the second signal flow direction is opposite of the first signal flow direction.

One aspect of the present invention is a signal detection device including a mode demultiplexer configured to convert N (N is a natural number) spatial mode signals including a plurality of higher modes excited in a transmission path fiber into N base modes and output the N basis modes, a frequency conversion unit configured to convert N optical signals into frequencies different from each other, a multiplexing unit configured to multiplex the N optical signals having frequencies that have been converted, and a reception unit configured to photoelectrically convert a multiplexed optical signal while maintaining modulation information for a phase and polarization, perform digital signal conversion and signal processing, and demodulate an original information sequence.

A method for multiplexing optical signals for transmission over a communication link includes receiving a set of input optical signals. Each input optical signal has an optical intensity at a given time in one of at least two amplitude states. The method further includes selectively adjusting the optical intensity of the input optical signals so that each input optical signal has a respective specific optical intensity for each of the at least two amplitude states. The respective specific optical intensity of each input optical signal in the at least two amplitude states differs such that the respective specific optical intensity of each input optical signal in the at least two amplitude states has a magnitude in which any combination of the input optical signals at any given time sums to a different combined magnitude. The input optical signals are combined to form a combined beam for transmission.