Front Cover: An Efficient Diamond Raman Amplification Scheme Based on Adaptive Temporal Synchronization (Adv. Photonics Res. 2/2026)

Dispersion-compensating fibers (DCF) are the most widely used technology for dispersion compensation. The idea to additionally use the DCF as a Raman gain medium was originally proposed by Hansen et al. in 1998 [1]. This was quickly followed by Emori et al., [2], who demonstrated a broadband lossless DCF using multiple-wavelength Raman pumping. DCF is a good Raman gain medium, due to a relatively high germanium doping level and a small effective area. Normally, a discrete Raman amplifier will contain several kilometers of fiber, adding extra dispersion to the system that must be handled in the overall dispersion management. Dispersion-compensating Raman amplifiers integrate two key functions, dispersion compensation and discrete Raman amplification, into a single component.

A study was initiated to understand requirements for widening and flattening the gain spectra of tellurite-based glasses for their application as new gain media for photonic devices. For this purpose, two Raman active components, WO3 and P2O5, were added either separately or jointly to a TeO2-BaO-SrO-Nb2O5 (TBSN) glass system, and the Raman spectral evolution in response to this addition was studied. Raman scattering cross sections of the TBSN glasses were increased with an increase in the WO3 content and decreased with an increase in the P2O5 content. The Raman intensity and bandwidth increased when WO3 and P2O5 were jointly added in TBSN. The bandwidths of the Raman gain coefficient spectra of the present tellurite glasses were more than twice that of a conventional TeO2-Bi2O3-ZnO-Na2O glass and 70% larger than that of silica glass. The new glasses are expected to be candidates for ultrabroadband fiber Raman amplifiers.

Many species alter their acoustic signals in response to environmental or anthropogenic factors. Differential use of frequency bands may occur as a result of overlapping biotic and abiotic sounds that interfere with communication signals between conspecifics. Singing humpback whales produce units with frequencies ranging from 30 Hz to over 10,000 Hz, but may favor specific frequency bands during song production. We tested the prediction that singing humpback whales consistently produce units with energy focused in specific spectral bands by measuring the consistency of peak frequency bands in the southeastern Pacific stock G population of humpback whales in the Gulf of Tribuga, Colombian Pacific. Songs recorded from 2013-2016 in the Gulf of Tribuga, Colombian Pacific suggest that not only do singers favor specific frequencies, but that they consistently concentrate their sound production within three frequency bands across years. One band spanning frequencies between 250-475 Hz is the most stable and consistently used band. These findings will allow for further spatial and temporal comparisons across distinct population segments, and can be used in future studies to assess whether singers change their use of frequency bands in response to increased anthropogenic noise or as themes evolve over time.Many species alter their acoustic signals in response to environmental or anthropogenic factors. Differential use of frequency bands may occur as a result of overlapping biotic and abiotic sounds that interfere with communication signals between conspecifics. Singing humpback whales produce units with frequencies ranging from 30 Hz to over 10,000 Hz, but may favor specific frequency bands during song production. We tested the prediction that singing humpback whales consistently produce units with energy focused in specific spectral bands by measuring the consistency of peak frequency bands in the southeastern Pacific stock G population of humpback whales in the Gulf of Tribuga, Colombian Pacific. Songs recorded from 2013-2016 in the Gulf of Tribuga, Colombian Pacific suggest that not only do singers favor specific frequencies, but that they consistently concentrate their sound production within three frequency bands across years. One band spanning frequencies between 250-475 Hz is the most stable and cons...

In this study we report the physical properties and spontaneous Raman scattering spectra of nine oxide tellurite and fluorotellurite glasses from three glass systems—sodium–zinc–tellurite (TZN), tungsten–tellurite, and fluorotellurite. Raman gain and surface damage threshold at 1064 nm are also shown for a selection of these glasses, which all exhibited high gain and damage resistance. Raman gain spectra were directly measured and accurately calculated for selected TZN and fluorotellurite glasses after Fresnel, internal solid angle, and Bose–Einstein corrections. The calculated gain showed good fits to the Raman gain measurements made using a calibrated nonlinear optics apparatus. Infrared and UV‐Vis absorption spectra, characteristic temperatures obtained by differential thermal analysis, densities acquired by the Archimedes principle and refractive indices measured by spectroscopic ellipsometry are also given. The ternary systems TeO 2 –WO 3 –Bi 2 O 3 and TeO 2 –Na 2 O–ZnF 2 and the quaternary system TeO 2 –Na 2 O–ZnO–PbO show promise as Raman amplifiers as they are relatively easy to draw into optical fiber and to these authors' knowledge, this is the first time Raman gain has been presented on halide containing tellurite glasses. The oxyfluoride system studied here, TeO 2 –Na 2 O–ZnF 2 , exhibited a dependence on the peak Raman intensity with ZnF 2 addition. Calculations of preform geometry for mono‐ and multimode guidance and stresses in similar and dissimilar (core suction) core–clad pairs are shown. Dispersion in the mid‐infrared and initial fiber drawing studies are also reported with fibers showing reasonable unclad losses.

Raman amplification is added to a transmission system to provide an increase in power budget allowing for a four-fold upgrade in capacity either by TDM or WDM. Here, a TDM upgrade from 2.5 to 10 Gb/s and a WDM upgrade from a single 10-Gb/s channel to four channels of 10 Gb/s each were experimentally verified with an improvement in the power budget of 7.4 dB. Raman gain is an attractive upgrade method for installed systems requiring no changes to the fiber span.

Optical amplification in silicon photonic integrated circuits remains a challenge and stimulated Raman scattering has been proposed as a means of achieving optical gain in silicon. In this work, we experimentally investigate silicon Raman amplifiers optimized for fabrication with open-access foundry sub-micron silicon platform. We discuss and experimentally validate the importance of considering the non-reciprocal Raman-gain by using counter-propagating or co-propagating pumps and probes, different amplifier lengths, input pump powers and nonlinear loss values. We demonstrate a Raman-assisted loss-less optical circuit in a 1.2-cm-length waveguide that reaches zero net-gain with only 60 mW continuous-wave pumping. A 5.5 dB stimulated Raman scattering (SRS) gain yielding 0.5 dB net-gain is also demonstrated with a 115 mW pump in a 3.25-cm waveguide. Furthermore, we examine the nonlinear loss of silicon waveguides to estimate free carrier lifetime (FCL) with different bias voltages applied to the waveguide <i>p-i-n</i> structure. Accounting for non-reciprocal Raman amplification by using the two dataset of co- and counter-propagating SRS gain, we extract the Raman gain coefficient of this 220 nm thick silicon photonic waveguide. We perform the curve fitting over the whole input pump power range using the extracted FCL, and over the low power range where only linear loss is expected. We find a good agreement in the extracted Raman gain coefficients. We use these key parameters as input to a silicon photonic Raman amplifier model to find the optimum performance based on the available footprint and pump power.

A new and practically applicable scheme of optimally configuring backward multiple pumps in optical fiber Raman amplifiers is presented based on the characteristics of Raman gain spectra and the fact that different pump powers and wavelengths have different impact on the gain slope by using Optiamplifier 4.0 simulating software, which is made in Optiwave Corporation, Canada. We use the idea to optimize a distributed Raman amplifier pumped by 2-walvelength sources. The optimized design contained signal channels between 1490 and 1530 nm with 4-nm separations. The fiber used as the gain medium was a 50-km single-mode fiber (SMF) with 9.9e-14m/W peak Raman-gain coefficient. After calculating 11 times optimum pump wavelengths 1390nm, 1427nm are obtained. The achieved gain flatness is 1.46dB and the maximum forward on/off gain is 10.43 dB, which is much better than initial un-optimized gain flatness 5 dB. Then after 24 calculations we get the optimum pump powers. The final optimized pump sources are 1390nm 300mW, 1427nm 290mw. Gain ripple less than 1.2 dB in 40nm and maximum Raman on/off gain about 10.1 dB are obtained. Finally the factors of the noise figure are analyzed and ASE is found to be the main noise source.

In our method of anti-Stokes generation at stimulated Raman scattering (SRS) with quasi-phase-matched conditions we took into account the generation of high-order Stokes and anti-Stokes components. The dependence of Raman gain dispersion on SRS generation was studied using numerical simulation. The possibility of an effective periodical structure for hydrogen was determined. For a multiwave media model we found that the efficiency of first anti-Stokes generation reached ~40%. We determined that for transient SRS the maximum efficiency of quasi-phase-matching anti-Stokes generation does not depend on pulse duration while the medium length greatly increases as transience increases. Our calculations showed that for hydrogen and barium nitrate if the duration of interacted pulses is 3 ns and more then we can neglect the influence of transitivity on quasi-phase-matching conditions. The results of our research can be used for the creation of new effective nonlinear optical frequency converters and Raman amplifiers.

The Raman properties of triangular photonic crystal fibers (PCFs) are analyzed in order to design a fiber for Raman amplification with enhanced performances. By casting the Raman intensity propagation equations, the Raman effective area and the Raman gain coefficient are introduced - two meaningful parameters that take into account the overlap between the pump and signal profiles. The behavior of these two parameters is examined in silica PCFs as a function of the geometrical characteristics of the triangular lattice. The numerical results show that a proper design of the hole diameter and the spacing between air holes can minimize the Raman effective area and maximize the Raman gain coefficient. The paper then focuses on PCFs with a germania-doped core. It is found that, for a given PCF cross section and dimension of the doped region, the Raman gain coefficient increases linearly with germania concentration. Moreover, by enlarging the doped region, it is discovered that a PCF with a germania-doped area internally tangent to the first ring of air holes has a maximum Raman gain coefficient. Finally, the calculated values of the Raman gain coefficient are compared with those of other highly nonlinear fibers presented in the literature, showing that a well-designed triangular PCF can significantly improve Raman gain performance.

In this paper, we present new structures based on ring, conventional photonic crystal and hybrid PhC for enhanced Raman amplification. The structures consist of two separate entrances for the pump and signal. In this way, only pump is coupled into the ring and signal passes through the amplified pump without creating coupling noise. Using engineered nano holes filled with optofluidic materials in the signal and pump paths, we reduce pump and signal group velocity to improve the structure and achieve larger Raman gain and less dispersion. The time evolution and propagation of picosecond signal pulses and dispersion inside the device are analyzed and Raman gain, Raman bandwidth and bit rate are studied in one-ring and two-ring structures. To model Raman amplification in these structures, Maxwell equations are solved using finite difference time domain method considering optical nonlinear parameters like two photon absorption, free carrier absorption and Kerr effect.

We perform Raman amplification in a high-pressure methane cell seeded by a low-threshold liquid Raman oscillator. The Raman frequency of the oscillator medium, dimethyl sulfoxide (DMSO), is tuned when it is mixed with water to fit the Raman frequency of methane. The Raman gain in this configuration is not so sensitive to the methane pressure, and the conversion efficiency is high. Using this configuration, we measure the polarization dependence of the Raman amplifier. An experiment is performed for three typical polarization states. Complete gain suppression is expected in some polarization states, but there is a little gain because of the incompleteness of the polarization state. Theoretically the results are analyzed when the x and the y components of the scattered waves are coupled.

We demonstrate a wavelength-tunable semiconductor pump diode for Raman amplification. Thediode is stabilized by a fiber Bragg grating (FBG) that can be continuously tuned over more than 20 nm. Tuning of the diode output wavelength is achieved by varying the center wavelength of the FBG, since the diode preferentially lases within the FBG bandwidth. We investigate the effects of wavelength tuning on the diode spectrum on its corresponding Raman gain, and on pump-pump four-wave mixing in fiber having zero-dispersion wavelength coincident with the Raman pumps.

Raman amplification characteristics of the GaP-AlxGa1-xP heterostructure waveguide have been measured by fine tuning the pump light frequency. The Raman gain and the Raman gain bandwidth are 0.03 × 10-6 W-1 cm-1 and 23.5 GHz, respectively. The amplified signal light can be detected even at the pump light power level of 10 mW. This result shows that the semiconductor Raman amplifier is suitable for demodulators based on light frequency discrimination in wideband optical communication systems.

We model the TPA-induced free carrier absorption effect in silicon Raman amplifiers and quantify the conditions under which net gain may be obtained. The achievable Raman gain strongly depends on the free carrier lifetime, propagation loss, and on the effective Raman gain coefficient, through pump-induced broadening.

In this paper, some patents on silicon Raman amplifiers are investigated. These patents emphasize on the length reduction of amplifiers compared with the silica ones. However, the bandwidth of the amplifier in these patents is very low. In addition, while the pump wavelength is constant, the central frequency remains unchanged. The germanium doping leads to tuning of central frequency and bandwidth enhancement of Raman gain spectrum. Thus, the effect of germanium doping on the characteristics of major patents on silicon Raman amplifiers is investigated in this paper. Amplifier gain depends on various parameters such as the Raman gain coefficient. The effects of germanium doping on the impressive parameters of the silicon Raman amplifiers are also presented. By usage of the variable germanium concentration waveguides, the bandwidth of amplifiers is enhanced which has a great effect on communication systems. Furthermore, the characteristics of waveguide are estimated in order to achieve a flat gain amplification in silicon germanium on insulator (SiGe-OI) waveguides. Keywords: Continuous wave pumping, free carrier absorption, free carrier lifetime, pulsed pumping, Raman amplification, ring resonator, silicon germanium (SiGe), two photon absorption, SiG-OI Waveguides, Frequency, SiGe Raman Amplifiers, Amplifiers, resonator, insulator, waveguides