Efficient In-Band Pumping of Holmium-Doped Optical Fiber Amplifiers

An optical system for providing amplified spontaneous emission in an eye-safe wavelength band, comprising:

• a section of Ho-doped optical gain fiber which exhibits a gain coefficient G and an absorption coefficient α that both vary as a function of an applied pump wavelength λP;
• and
• a pump source coupled to the section of Ho-doped optical gain fiber and configured to provide pump light at a pump wavelength λP within an absorption-dominant wavelength region where α(λP)>G(λP), the pump light operating at an absorption-dominant pump wavelength interacting with the Ho ions present in the Ho-doped optical gain fiber to as to generate as an output amplified spontaneous emission centered at a wavelength within the eye-safe wavelength band.

A multi-stage optical amplifier for operation at an eye-safe input signal wavelength λs within the 2 μm region, comprising:

• a plurality of N sections of Ho-doped optical fiber disposed in a concatenated configuration such that an input optical signal applied to a first amplifier stage propagates through the plurality of N sections of Ho-doped optical fiber and exits as an amplification optical output signal, each section of Ho-doped optical fiber characterized by a gain coefficient G(λ) and an absorption coefficient α(λ) that vary as a function of a wavelength of the pump light applied thereto;
• and
• a pump source providing pump light at a defined absorption-dominant pump wavelength λP selected from a wavelength region where α(λP)>G(λP), the pump light applied as an input to each amplifier stage of the multi-stage optical fiber amplifier.