Researchers have designed an integrated on-chip optical device that couples an aluminum gallium arsenide on insulator wavelength converter with an erbium-ytterbium co-doped waveguide amplifier to bridge telecommunication C-band signals and the 2 μm infrared band. Documented optical wavelength converters relying on aluminum gallium arsenide on insulator waveguides have routinely faced conversion efficiencies falling below minus 20.0 dB when shifting signals between these two distinct spectral windows. To resolve the performance deficit that typically necessitates bulky external optical fiber amplifiers, the research team structured a self-contained device incorporating dedicated loss-compensation stages directly into the photonic chip architecture.
The interest in expanding optical technology toward the 2 μm wavelength band stems from multiple critical technical applications, notably greenhouse gas sensing, atmospheric remote sensing, and expanding optical telecommunications bandwidth beyond the conventional Shannon limit. Gases such as methane and carbon dioxide exhibit strong characteristic absorption spectral lines around 2 μm, providing an optical mechanism for highly sensitive environmental monitoring. Concurrently, the 2 μm window serves as an atmospheric transmission window characterized by high optical penetration power, while offering an expansion domain for telecommunications networks facing capacity bottlenecks in existing fiber channels.
Despite these technological motivations, the widespread deployment of comprehensive 2 μm transceiver systems has been restricted by the limited availability and high development costs of native 2 μm commercial hardware, including specialized semiconductor laser sources, optical modulators, and detectors. Traditional implementations attempting to bridge communication bands have relied on four-wave mixing processes within nonlinear waveguides, but these conventional approaches generally depend on extensive waveguide lengths or supplementary external fiber amplifiers to recover optical power losses. Such external equipment enlarges total physical dimensions, increases power consumption, and introduces system complexity that counters the benefits of integrated photonics.
To overcome these system constraints, the proposed chip design employs an integrated bidirectional architecture that allows standard commercial C-band transmission equipment and photodetectors to drive and monitor 2 μm optical signals. At the transmission end, optical emission from an off-the-shelf C-band laser enters a first erbium-ytterbium co-doped waveguide amplifier before mixing with pump light inside an aluminum gallium arsenide wavelength converter, which translates the optical signal into the 2 μm band. At the receiving end, incoming 2 μm signals pass through a second wavelength converter that shifts the light back into the C-band, after which a secondary waveguide amplifier boosts the recovered signal prior to measurement by a commercial C-band detector.
The wavelength conversion mechanism is governed by degenerate four-wave mixing, an optical nonlinear process where effective conversion across wide spectral separations demands rigorous phase matching. Because shifting frequencies from the C-band near 1.55 μm to the 2 μm band requires spanning a broad optical frequency gap, the researchers incorporated fourth-order waveguide dispersion considerations alongside second-order dispersion parameters in their analytical models. By tuning the waveguide dispersion so that the pump wavelength operates in a normal dispersion region with a negative fourth-order dispersion parameter, the researchers ensured phase matching occurs only in the far pump wavelength region, suppressing near-pump phase-matching points that generate detrimental quantum noise.
The material platform for the wavelength converter takes advantage of aluminum gallium arsenide on insulator, which provides a high Kerr nonlinear refractive index and substantial second-order optical susceptibility alongside a broad optical transparency window ranging from 0.9 to 17 μm. By varying the aluminum fraction in the material, the bandgap energy can be tuned to mitigate two-photon absorption effects during high-power pumping. Furthermore, the strong refractive index contrast between the aluminum gallium arsenide core and the underlying silicon dioxide substrate establishes tight optical mode confinement, enabling precise geometric control over waveguide dispersion characteristics while lowering linear transmission propagation losses.
Through systematic numerical simulations of waveguide geometries, the authors established that an aluminum gallium arsenide waveguide with a cross-sectional width of 0.40 μm and a height of 0.95 μm provides the targeted near-zero normal second-order dispersion and negative fourth-order dispersion when driven by a pump wavelength near 1.76 μm. Under an evaluated linear propagation loss of 1 dB per centimeter and an applied pump power of 100 mW, simulation curves tracking conversion efficiency relative to waveguide length demonstrated that a 3 cm long converter achieves a single-stage conversion efficiency of minus 15.54 dB, representing a significant baseline improvement over unoptimized waveguides.
To compensate for the optical losses inherent in the nonlinear conversion step, the authors incorporated an integrated waveguide amplifier based on an active glass host composed of 5 Er2O3, 5 Yb2O3, 44 La2O3, and 46 Al2O3. In this co-doped glass system, trivalent ytterbium ions absorb 980 nm pump light with a cross section substantially larger than that of trivalent erbium ions, exciting them from the ground state to an upper excited state before transferring energy non-radiatively to adjacent erbium ions. The resulting rapid population inversion between intermediate energy levels produces optical gain around the signal wavelength while lanthanum oxide doping suppresses rare-earth ion clustering and sets the refractive index near 1.97 at 1.55 μm.
Rate equations and power transmission equations solved via the fourth-order Runge-Kutta algorithm determined the performance profile of the amplifier section. With an initial optical input power of 10 μW and a modest pump power of 15 mW, a 10 mm long erbium-ytterbium waveguide section yields an optical signal gain of 18.77 dB, providing sufficient amplification to overcome upstream converter losses.
Because the aluminum gallium arsenide waveguide has a refractive index of approximately 3.28 whereas the active amplifier glass features an index of 1.97, directly butting the two sections would induce severe Fresnel reflection and modal mismatch. To resolve this interface problem, the researchers designed an adiabatic double-layer tapered coupler consisting of an inverted aluminum gallium arsenide taper separated from the overlying active waveguide by a silicon dioxide spacer layer. As the lower core tapers down to an 80 nm tip width over a length of 114 μm with a 175 nm spacer thickness, the optical mode transitions smoothly into the upper waveguide, yielding a calculated transfer efficiency of 91.79 percent.
By combining the conversion efficiency of the nonlinear core, the internal gain of the active amplifier, and the transition efficiency of the intermediate coupler, the integrated system achieves an overall net device efficiency of 2.86 dB at an input power of 10 μW. Operating both the transmitter and receiver ends simultaneously requires 100 mW of pump power for each wavelength converter and 15 mW for each amplifier stage, bringing the total operational power budget of the four active elements on the monolithic chip to 230 mW without drawing upon external laboratory optical fiber amplifiers.
The evaluation of the receiving architecture also incorporated comprehensive noise modeling, accounting for quantum noise generated during nonlinear conversion, amplified spontaneous emission within the active medium, and photodetector shot and inherent noise. When evaluating the electrical signal-to-noise ratio across varying input signal levels, indirect detection utilizing the integrated converter and a commercial C-band receiver demonstrated superior signal-to-noise metrics compared to most standard direct mid-infrared photodetectors. Although high-performance direct detectors can theoretically offer marginal signal-to-noise advantages under specific conditions, they often demand cryogenic cooling and exhibit slower response times, whereas indirect conversion maintains room-temperature operation with high responsiveness.
The findings indicate that embedding active rare-earth gain elements alongside tailored nonlinear semiconductor waveguides provides a viable path toward compact, low-power mid-infrared photonic transceivers. By overcoming the physical interface losses between distinct optical materials on a shared substrate and neutralizing four-wave mixing attenuation, this dual-material integrated platform demonstrates how complex multi-band optical processing can be achieved entirely within a chip-scale footprint, opening practical avenues for robust field sensing and high-capacity communication links.
Subject of Research: Integrated on-chip wavelength conversion between C-band and 2 μm band assisted by waveguide amplification
Article Title: Design of an on-chip wavelength conversion device assisted by an erbium-ytterbium co-doped waveguide amplifier
Article References: Zhou, C., He, X., Xiao, M., Ma, D., Chen, W., & Zhou, Z. (2024). Design of an on-chip wavelength conversion device assisted by an erbium-ytterbium co-doped waveguide amplifier. Frontiers of Optoelectronics, 17(1), Article 16. https://doi.org/10.1007/s12200-024-00118-2
Image Credits: AI Generated
DOI: 10.1007/s12200-024-00118-2
Keywords: Wavelength Conversion, Four-Wave Mixing, Waveguide Amplifier, Erbium-Ytterbium Co-Doping, AlGaAs Photonic Integrated Circuits, Mid-Infrared Optics, Optical Telecommunications, Integrated Photonics, Dispersion Engineering, Phase Matching, Gas Detection Sensing, Silicon Photonics, Optical Coupler, Photodetectors, Optical Amplification, Nonlinear Optics, Semiconductor Waveguides
News Source: Denise Maddox. (November 13, 2026). Integrated Photonic Chip Achieves High Efficiency Wavelength Conversion Without External Optical Amplifiers. Scienmag.
