A transmission device includes: a first wavelength conversion circuit configured to convert a wavelength band of a wavelength multiplexed signal light based on a wavelength of a second excitation light by performing four-wave mixing on the second excitation light and the wavelength multiplexed signal light inputted to a second nonlinear medium; and a second wavelength conversion circuit configured to convert the wavelength band of the wavelength multiplexed signal light based on a difference between frequencies of a third excitation light and a fourth excitation light by performing four-wave mixing on the third excitation light and the fourth excitation light and the wavelength multiplexed signal light inputted to a third nonlinear medium.

A transmission device includes: a first wavelength conversion circuit configured to convert a wavelength band of a wavelength multiplexed signal light based on a wavelength of a second excitation light by performing four-wave mixing on the second excitation light and the wavelength multiplexed signal light inputted to a second nonlinear medium; and a second wavelength conversion circuit configured to convert the wavelength band of the wavelength multiplexed signal light based on a difference between frequencies of a third excitation light and a fourth excitation light by performing four-wave mixing on the third excitation light and the fourth excitation light and the wavelength multiplexed signal light inputted to a third nonlinear medium.

One embodiment is directed towards a resonator fiber optic gyroscope (RFOG) including a resonator, one or more light sources coupled to the resonator, and resonance tracking electronics coupled to the resonator. The one or more light sources are configured to produce at least two light beams for input into the fiber coil, the at least two light beams including a first light beam at a first frequency and a second light beam at a second frequency, the first and second frequencies locked to nearby resonance modes of the resonator. The resonance tracking electronics are configured to process output light from the resonator and generate a signal therefrom, the signal indicative of a rotation rate of the resonator. The fiber coil has approximately zero total accumulated chromatic dispersion at the first frequency and the second frequency of the first light beam and the second light beam.

Example systems and nodes are provided. An example system includes a first node, a second node, and an optical fiber that connects the first node and the second node. A zero-dispersion wavelength (ZDW) of the optical fiber belongs to a ZDW region. The optical fiber is configured for transmission of N first-direction wavelength channels and N second-direction wavelength channels. N is an integer greater than 2. At least two first-direction wavelength channels and at least one second-direction wavelength channel, or at least two second-direction wavelength channels and at least one first-direction wavelength channel, are located in the ZDW region. The first-direction wavelength channel and the second-direction wavelength channel that are in the ZDW region are mixedly distributed. The first-direction wavelength channel is sent by the first node to the second node, and the second-direction wavelength channel is sent by the second node to the first node.

There is provided a single mode optical fiber including a core layer, a first cladding layer, and a second cladding layer, in which when a refractive index of a center portion of the core layer is set as no, a radial position where a refractive index becomes n.sub.00.45 is set as r.sub.CORE, a minimum value of a refractive index of the first cladding layer is set as n.sub.3, and a radial position where a refractive index becomes the n.sub.3 is set as r.sub.3, a relative refractive index difference of the first cladding layer is reduced continuously and gently from the r.sub.CORE to the r.sub.3.