# Review of Soliton Crystal Kerr Optical Microcombs

David Moss

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# Review of Soliton Crystal Kerr Optical Microcombs

**David J. Moss** email: dmoss@swin.edu.au

Optical Sciences Center, Swinburne University of Technology, Hawthorn, VIC 3122, Australia.

**Abstract:** Soliton crystal microcombs, as a new type of Kerr frequency comb, offer advantages such as higher energy conversion efficiency and a simpler generation mechanism compared to traditional soliton microcombs. They have a wide range of applications in fields like microwave photonics, ultra-high-speed optical communication, and photonic neural networks. In this review, we discuss recent developments of soliton crystals microcombs and analyze the advantages and disadvantages of generating soliton crystal microcombs utilizing different mechanisms. First, we briefly introduce the numerical model of optical frequency combs. Then, we introduce the generation schemes for soliton crystal microcombs based on various mechanisms, such as utilizing an avoided mode crossing, harmonic modulation, bi-chromatic pumping, and the use of saturable absorbers. Finally, we discuss the progress of research on soliton crystal microcombs in the fields of microwave photonics, optical communication, and photonic neural networks. We also discuss the challenges and perspectives of soliton crystal microcombs.

**Keywords:** soliton microcombs; soliton crystal microcombs; microwave photonics; optical communication; photonic neural networks

## 1. Introduction

Over the last twenty years, advancements in photonic nanofabrication technology have given rise to a variety of sophisticated integrated microcomb devices, providing considerable benefits regarding compactness, reduced weight, lower power consumption, and economic efficiency [1]. Microcombs, a special type of light source, exhibit a series of coherent spectral lines in the frequency domain with uniform spacing. This pattern manifests in the time domain as optical pulses that occur at regular intervals [2]. Thanks to their high coherence and stability, soliton microcombs exhibit great potential in applications such as spectroscopy [3-6], optical clocks [7,8], astronomical detection [9,10], ultra-high capacity communications [11-14], frequency synthesis [15], and photonic neural networks [16-19]. Additionally, soliton microcombs provide a novel physical platform for studying interactions between light and matter [20,21].

Dissipative Kerr solitons (DKSs) are self-sustaining waves that can be produced in nonlinear optical microresonators. The study of DKSs originated in 2004 with the initial experimental observation of several discrete comb lines in high-quality factor silica microcavities [22]. The cascaded four-wave mixing in a silica toroid microcavity was reported in 2007, creating a broadband optical frequency comb with uniformly spaced lines in the frequency domain. This pioneering research achievement marks the official birth of microcavity optical frequency comb technology [23]. In 2010, back-to-back reports on optical frequency combs based on high index doped Silica [24] and silicon nitride (SiN) [25] platforms were published, marking the first on-chip integration of microcavities with coupled waveguides and pioneering the field of integrated on-chip microcombs. In 2014, the
formation of mode-locked DKSs was first observed within a magnesium fluoride crystal cavity, which displayed anomalous dispersion [26]. These solitons are combined effects of optical loss, gain, nonlinearity, and dispersion within the microresonator. This discovery opened up a new field of research for soliton microcomb. Compared to previous microcavity optical frequency combs, soliton microcombs eliminate the effects of modulation instability (MI), thus offering high coherence and stability advantages.

During the last ten years, soliton microcombs have seen considerable advancements in both their theoretical foundations and applications, becoming one of the important research directions in the field of photonics. However, there are still some challenges in the generation of soliton microcombs that need to be addressed urgently. The generation of DKSs requires adjusting the pumping wavelength from the short-wavelength region to the long-wavelength region of the resonance mode. However, the accumulation of thermal effects during this transition impedes the microcomb's shift from MI state to single soliton state stability [26-28], which necessitates a complex pump laser control mechanism for the generation of DKSs. In order to overcome the thermal effects during the generation process of DKSs, researchers have adopted a variety of strategies, such as the power-kicking method [29], thermal tuning method [30], auxiliary laser thermal stabilization method [31-33], and the photorefractive effect in lithium niobate microresonators [34]. Moreover, the efficiency of transforming the energy of the pump light into the optical comb within traditional DKS is approximately 1%.

Soliton crystals (SC) are composed of a series of closely spaced solitons arranged in a well-ordered, crystal-like formation and exhibit a highly organized spectral pattern [35]. When transitioning from the MI state to the SC state, the solitons are closely packed within the microcavity, and the intracavity optical power is very close to the spatiotemporal chaos that precedes its formation in the experimental setup, encompassing the entire angular domain of the resonator [35]. Therefore, the generation of SC microcombs does not require complex wavelength control mechanisms and can be produced by slowly tuning the laser wavelength. Until now, leveraging sophisticated experimental techniques, soliton crystal microcombs have been successfully demonstrated across a variety of material platforms [21,36-54], such as yttria-stabilized zirconia (YSZ) microdisk [36], Aluminum Gallium Arsenide (AlGaAs) microring [37], Silica microdisk and microrod [35,38,39], graphene-nitride heterogeneous microring[40], SiNₓ microring [21,41-46], lithium niobate (LN) microring [47], aluminum nitride (AlN) microring [48], and high index doped silica microring [49-54]. The following Table 1 provides a concise summary of some typical SC microcombs realized on various material platforms, each with its unique cavity characteristics.

In this paper, we provide an overview of the latest advancements in SC microcombs and present the outlook on the future perspectives of soliton crystal microcombs. The subsequent sections of this paper are arranged in the following manner: Section 2 briefly introduces the fundamental principles of optical frequency combs. Section 3 summarizes several methods for generating SC. Section 4 presents the applications of SC microcombs
in the fields of microwave photonics, optical communication, and photonic neural networks. The challenges and perspectives of SC microcombs are discussed in Section 5. Finally, conclusions are given in Section 6.

<table><caption>**Table 1.** Typical specifications for reported SC microcombs.</caption><thead><tr><th>Material platform</th><th>Structure</th><th>FSR (GHz)</th><th>Wavelength Range (nm)</th><th>Crystal Types</th><th>Refs.</th></tr></thead><tbody><tr><td>YSZ</td><td>microdisk</td><td>~74.5</td><td>1530-1580</td><td>PSC<sup>1</sup></td><td>36</td></tr><tr><td>AlGaAs</td><td>microring</td><td>~1018</td><td>1400-1700</td><td>PSC</td><td>37</td></tr><tr><td>SiO<sub>2</sub></td><td>microrod</td><td>~25.6</td><td>1535-1565</td><td>Defected SC</td><td>38</td></tr><tr><td>SiO<sub>2</sub></td><td>microdisk</td><td>~26</td><td>1530-1570</td><td>Multiple SC</td><td>35</td></tr><tr><td>SiO<sub>2</sub></td><td>microrod</td><td>~60.7</td><td>1500-1600</td><td>PSC</td><td>39</td></tr><tr><td>Graphene–Nitride</td><td>microring</td><td>~90</td><td>1400-1900</td><td>PSC</td><td>40</td></tr><tr><td>SiN<sub>x</sub></td><td>microring</td><td>~200</td><td>1400-1800</td><td>PSC</td><td>41</td></tr><tr><td>LN</td><td>microring</td><td>~199.7</td><td>1480-1640</td><td>PSC</td><td>47</td></tr><tr><td>AlN</td><td>microring</td><td>~374</td><td>1150-2300</td><td>PSC</td><td>48</td></tr><tr><td>High Index Doped Silica</td><td>microring</td><td>~49</td><td>1500-1650</td><td>Defected SC</td><td>49</td></tr><tr><td>High Index Doped Silica</td><td>microring</td><td>~49</td><td>1500-1650</td><td>PSC</td><td>50</td></tr><tr><td>High Index Doped Silica</td><td>microring</td><td>~48.9</td><td>1450-1650</td><td>Flat spectral SC</td><td>51</td></tr><tr><td>High Index Doped Silica</td><td>microring</td><td>~48.9</td><td>1500-1600</td><td>'Palm-like' SC</td><td>52</td></tr><tr><td>High Index Doped Silica</td><td>microring</td><td>~48.9</td><td>1500-1600</td><td>Multiple SC</td><td>53</td></tr></tbody></table>

## 2. Numerical Model of Soliton Microcombs

The nonlinear dynamics of Soliton microcombs involve the decay, dispersion, continuous optical pumping, and third-order nonlinear effects experienced by each comb tooth. This nonlinear process can be articulated through mathematical formulations in the frequency domain or the time domain. In the frequency domain, a differential equation can be formulated for each tooth of the microcomb optical frequency comb, with the various differential equations coupled together through four-wave mixing terms. This set of differential equations is collectively referred to as the coupled mode equations (CMEs) [55,56]. When describing the nonlinear dynamics of microcombs using the CMEs, the frequency dependence of various parameters can be fully taken into account, leading to more accurate results. When conducting coupled mode analysis, it is assumed that the optical field of each comb line is $A_j$, with the corresponding resonant frequency $\omega_j$. The optical field of the pump mode is $A_{j_0}$, and the resonant frequency of the pump mode is $\omega_p$. Since microcombs are typically centered around the pump light and extend bilaterally in the frequency domain, the relative mode number $\mu = j - j_0$ is introduced, with the pump mode's relative mode number being 0. The dynamical equation for the optical field $A_\mu$ can be expressed as:

<footnote n="1">¹ Perfect Soliton Crystals.</footnote>
$$ \frac{dA_{\mu}}{dt} = -(i\omega_{\mu} + \kappa/2)A_{\mu} + \delta_{0,\mu} \sqrt{\frac{\kappa_{\text{ext}} P_{\text{in}}}{\hbar\omega_{0}}} e^{-i\omega_{p}t} + ig \sum_{\mu_1, \mu_2, \mu_3} A_{\mu_1} A_{\mu_2} A_{\mu_3}^* \quad (1) $$

Where $\omega_{\mu} = \omega_0 + D_1\mu + D_2\mu^2/2! + D_3\mu^3/3! + \cdots$, $\kappa$ represents the overall decay rate of the cavity, which encompasses both the intrinsic decay rate and the rate due to coupling losses $\kappa_{\text{ext}}$. $P_{\text{in}}$ represents the pump power. The nonlinear coupling coefficient $g = \hbar\omega_0^2 cn_2/n_0^2 V_{\text{eff}}$, where $n_0$ and $n_2$ denote the linear and nonlinear refractive indices, respectively. $V_{\text{eff}}$ represents the cavity's effective modal volume, while $c$ denotes the speed of light in vacuum, and $\hbar$ signifies the reduced Planck constant.

The CMEs illustrate the intricate nonlinear behavior of microcombs in the frequency domain. By applying a discrete Fourier transform, these equations can be reinterpreted in the time domain, resulting in the formulation of the Lugiato-Lefever equation (LLE). When performing numerical simulations of steady-state SC microcombs, it is common to introduce a local dispersion shift in the LLE to model mode coupling, which can be described in the frequency domain by the following equation[35, 57-59]:

$$ \frac{dA_{\mu}}{dt} = -\left(\frac{\kappa}{2} + i\delta\omega\right) A_{\mu} + iD_{\text{int}}^{\text{AMX}}(\mu)A_{\mu} + ig\mathcal{F}[|A|^2A]_{\mu} + \sqrt{\frac{\kappa_{\text{ext}} P_{\text{in}}}{\hbar\omega_0}} \delta_{0\mu} \quad (2) \\ D_{\text{int}}^{\text{AMX}}(\mu) = D_{\text{int}}(\mu) - \delta_{\mu\mu_0} \Delta\omega_{\text{AMX}} $$

### 3. Generating Schemes for Soliton Crystals Microcombs

Various schemes for generating SC microcombs have been developed, such as utilizing avoided mode crossings (AMXs), harmonic modulation, bi-chromatic pumping, and saturable absorbers. In this part, we offer an exhaustive summary of these cutting-edge approaches.

#### 3.1. Avoided mode crossing

The formation of SC is observed to correlate with the expanded background wave, resulting from the interference between the mode that gains surplus power due to mode crossing and the pump laser. Enough solitons coexist in the microcavity for the total intracavity energy to approach the level of chaotic MI states. Typical SC steps appear at the top of the intracavity power curve and exhibit excellent thermal interference resistance. The fluctuations of temperature within the cavity are comparatively minor, having a minimal impact on the resonance frequency, thus allowing for the stable formation of SC utilizing a slow-speed adjusting method without the need for complex methods to overcome thermo-optic effects.

Figure 1(a) illustrates several typical material platforms for generating soliton crystal microcombs utilizing AMXs. The dispersion curve on the top right of Figure 1(a) contains an obvious AMX point. Figure 1(b) shows that we classified the typical SC microcombs listed in Ref. [35]. We can roughly divide them into the following categories: PSC, Solitons with vacancies, Solitons with a shifted pulse, Solitons with irregular spacings, and Solitons with periodicity over multiple scales (superstructure). PSC, a distinctive state of SC, features solitons uniformly distributed within the cavity, resulting in comb lines spaced
by integer multiples of the free spectral range (FSR). The comb repetition rate of PSC is related to the number of solitons, which depends on the spacing between the pump wavelength and AMXs. When there are a larger number of solitons within the cavity, PSC can increase the FSR to above THz. Furthermore, the generation of PSCs does not require excessively high power. A pump power threshold has been identified below which photonic soliton crystals can be generated deterministically [41]. SC with a single vacancy exhibits a spectrum that is a superposition of a single soliton microcomb and PSC microcomb. SC with two vacancies exhibits a frequency domain that is a superposition of two-soliton microcombs and PSC, with spectral characteristics related to the number of solitons between the two vacancies. Crystals that exhibit a superstructure, also known as 'palm-like' SC, feature a large number of solitons within the cavity, with a power level nearly equivalent to that of the MI state, and their spectral characteristics display a single FSR. Compared to traditional single-soliton microcombs, palm-like SC microcombs have higher energy conversion efficiency, are less susceptible to thermal effects, and are easier to generate.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** (a) Material platform for SC microcombs generation. Reproduced with permission [37, 41, 47, 48, 54]. (b) Spectral and temporal characteristics of several typical SC microcombs. Reproduced with permission [35].</figcaption></figure>

## 3.2. *Harmonic modulation*

Single-soliton microcombs have been successfully generated by employing the sub-harmonic phase-modulation scheme (SPS) [60]. In 2020, the method of achieving PSCs using SPS was numerically explored [61]. Figure 2 illustrates how the interaction between side bands and cavity modes was adjusted through modulation to generate PSC micro-combs. The modulation frequency was meticulously designed and optimized to achieve the desired outcome. The results demonstrate that adjustable repetition frequencies ranging from approximately 50 to 200 GHz can be achieved using a doped silica microcavity with an FSR of 10 GHz. Within this approach, phase modulation of the pump light is achieved via an electro-optic modulator (EOM), followed by being amplified with an er-bium-doped fiber amplifier (EDFA). Conceptually, for the formation of an n-soliton PSC, the modulation frequency ought to correspond to a ratio of n/m of the microcavity's FSR. Figure 2(a) demonstrates the vernier effect, with the modulated sidebands represented in dark blue and the cavity modes depicted in red. Consistent with the resonant criteria [62],
interferometric enhancement within the microcavity occurs exclusively for those modulated comb lines that match the cavity resonance modes. As a result, the effective pump signal for creating an n-soliton PSC has a frequency spacing of n times the FSR. As depicted in Figure 2(b), they realized PSC microcombs with soliton counts between 5 and 20 through numerical simulation, accomplishing this by fine-tuning the pump power.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** Sub-harmonic phase-modulation scheme. (a) Controllable PSC generation scheme diagram and methods for controlling the number of solitons in PSC. (b) Simulation results of controllable PSC generation. Reproduced with permission [60].</figcaption></figure>

### 3.3. *Bi-chromatic pumping*

The bi-chromatic pumping method is widely used to counteract the effects of thermo-optic effects in single soliton microcombs [31-33]. The principle is as follows: Initially, the auxiliary light is tuned to the blue detuning region of the resonance peak, and then the pump light is tuned to the red detuning direction by coupling into the micro-ring resonator (MRR) in the opposite direction. As the pump light is tuned beyond the MI state, the auxiliary laser offsets the drop in intracavity power, maintaining the cavity's resonant state. Thus, transitioning from the MI state to soliton states becomes feasible without the need for a particular tuning rate.

<figure><img src="image_4.png" /><figcaption>**Figure 3.** Bi-chromatic pumping scheme. The (a) setup, (b) conceptual, and (c) experimental optical spectrum of deterministic PSC synthesis. Reproduced with permission [50].</figcaption></figure>

The bi-chromatic pumping technique for deterministic PSC synthesis operates on distinct mechanical principles compared to the previously mentioned approaches. Figure
3(a) shows a typical experimental setup with control and pump lasers propagating in opposite directions through a high-index doped silica microresonator [48]. Figure 3(b) depicts the concept of deterministic SC synthesis. In this approach, an additional laser acts as a control beam. A fraction of the control light is reflected opposite to the pump, forming a modulated background field. This modulated background is used to regulate the generation of PSC microcombs. The period of the potential field corresponds to the difference in the number of modes between the pump and control lasers. As illustrated in Figure 3(c), by adjusting the spacing between the two lasers, a comprehensive set of PSC microcombs with repetition rates spanning from 1×FSR to 32×FSR of the microcavity can be deterministically generated with a high degree of reproducibility.

### 3.4. Saturable absorber

PSC can be deterministic and produced within a system incorporating a saturable absorber (SA) [63]. In previous schemes [64], it has been proven that the structure with carbon nanotubes deposited on a silica microresonator, as shown in Figure 4(a), can achieve the saturable absorption effect. Figure 4(b) demonstrates the principle of achieving PSCs using the SA effect, where the system transitions directly from the Turing state to the PSC state, skipping the chaotic state. This happens as the nonlinear absorption curbs the development of sub-pulses and noise, maintaining a stable waveform. Furthermore, the SA effect enhances the modulation depth of the Turing patterns. Consequently, the system transitions directly from the Turing patterns to the DKS state, bypassing the chaotic phase [63]. This can also be interpreted as the presence of the SA effect being instrumental in creating the periodic potential wells necessary for the formation of PSC [63]. Figure 5 presents the relevant numerical simulation results. As shown in Figures 5(a) - 5(d), without the introduction of the SA effect, the system successively experiences the turing state, chaotic state, and ultimately enters the DKS state. When the SA effect is introduced (Figures 5(e) -5(h)), the system bypasses the chaotic state and directly enters the PSC state.

<figure><img src="image_5.png" /><figcaption>**Figure 4.** Deterministic generation scheme for PSC utilizing the SA effect. Reproduced with permission [61].</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Figure 5.** The numerical simulation result is (a-d) without the SA effect and (e-h) with the SA effect. (a), (b), (e), and (f) represent frequency domain characteristics, while (c), (d), (g), and (h) represent time domain characteristics. Reproduced with permission [63].</figcaption></figure>

## 4. Applications

Benefiting from high energy conversion efficiency and simple generation methods, SC microcombs have been widely applied in fields such as microwave photonics [66-80], optical communication [14,81], and photonic neural networks [16,19,82]. In this section, we summarize the applications realized by the 'palm-like' SC microcomb generated from the doped silica microresonator, as shown in Figure 6.

<figure><img src="image_7.png" /><figcaption>**Figure 6.** (a) Generation schematic diagram of the SC microcomb, (b) Microring chip based on high index doped silica, (c) Optical spectrum of 'palm-like' SC microcomb.</figcaption></figure>

### 4.1. Microwave Photonics

SC microcombs can supply numerous wavelength sources for microwave photonics, enabling diverse processing capabilities. In particular, SC microcombs have the advantage of low-phase noise, and a lot of research focuses on the application of microwave photonics based on SC microcombs.
<figure><img src="image_8.png" /><figcaption>Figure 7. (a)Experimental setup of microwave photon filters. Reproduced with permission [66]. (b) Experimental setup of true time delay line. Reproduced with permission [70].</figcaption></figure>

In 2020, Tan M. et al. proposed an arbitrary fractional order differentiator ranging from 0.15 to 0.90 utilizing SC [66]. They conducted experiments to characterize the radio frequency (RF) amplitude and phase response in the frequency domain when the temporal response with a Gaussian pulse input. The experimental setup and results are shown in Figure 7(a) and Figure 8, respectively.

<figure><img src="image_9.png" /><figcaption>Figure 8. Experimental and simulated results of the photonic RF fractional differentiator. Reproduced with permission [66].</figcaption></figure>
Firstly, a palm-shaped SC microcomb is produced by tuning the pump wavelength, and the lines of the comb are smoothed by the first waveshaper (WS). Subsequently, the comb lines were modulated by the input RF signal, which was then distributed across the wavelength channels to create duplicates. The RF duplicates were transmitted via conventional optical fiber, achieving a cumulative time delay of 29.2ps between neighboring wavelengths. The second WS fine-tunes the coefficients by controlling the power of the comb lines, and the outcome is then measured by the balanced photodetector, yielding the aggregate of both positive and negative coefficients.

In 2021, Tan M. et al. demonstrated three kinds of fractional-order Hilbert transformers utilizing SC micro-combs within the identical experimental setup (Figure 7(a)) [67], such as the lowpass Hilbert transformers and bandpass Hilbert transformers with phase shifts of 90 and 45 degrees. Figure 9(a) presents the optical spectra of these fractional-order Hilbert transformers as both designed and measured. Figures 9(b-d) show the simulated and experimental results of these fractional-order Hilbert transformers. The results show that the bandwidth of the lowpass Hilbert transformer, 45-degree phase shift bandpass Hilbert transformer, and 90-degree phase shift bandpass Hilbert transformer can be adjusted in 1.2-7.1 GHz, 3.5-15.2 GHz, and 3.4-15.3 GHz, respectively.

<figure><img src="image_10.png" /><figcaption>**Figure 9.** Results from simulations and experiments on the adjustable Hilbert transformers. Reproduced with permission [67].</figcaption></figure>
Except for the microwave photon filter, SC microcombs have the potential to achieve an RF arbitrary waveform generator using the experimental systems in Figure 7(a). In 2020, by utilizing SC microcombs, Tan M. et al. provided over 80 channels and successfully achieved various arbitrary waveform shapes [68]. As depicted in Figure 10, they created square waves with adjustable duty cycles from 10% to 90%, sawtooth waves with adjustable slope ratios between 0.2 and 1, and symmetric concave quadratic chirp signals in the sub-GHz frequency range. That same year, utilizing up to 60 wavelength channels from the microcomb, Xu X. et al. obtained a substantial pulse compression ratio, peaking at 30 [69]. Figure 11 illustrates the working principle of phase encoding and the test results of reconfigurable phase encoding rates. By altering the duration of each phase encoding, adjustments can be made between 1.98 to 5.95 Gb/s.

<figure><img src="image_11.png" /><figcaption>**Figure 10.** Design and test results of square waves and sawtooth waves: (a) optical spectra; (b) RF waveforms. Reproduced with permission [68].</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Figure 11.** (a) Operating principle of the phase encoder. (b) Configuration of the range gates within the radar system's receiver. (c) The optical spectra and phase-encoded RF waveform have different phase codes and sequence lengths. Reproduced with permission [69].</figcaption></figure>

In phased array antenna applications [70], as illustrated in Figure 7(b), the SC microcomb is used as a premium source of multi-wavelength light for the true time delay line, modulating the microwave signal across various wavelengths, followed by dispersion introduction through single-mode fiber (SMF), thereby creating a delay difference between
adjacent channels. Subsequently, a waveform shaper is employed to weight the individual channels, with each channel being separated by a wavelength division multiplexer. Following photoelectric detection, microwave signals with diverse time delays are input into the antenna array. Finally, as shown in Figure 12, the essential performance metrics for the phased array antenna utilizing the device have been determined.

<figure><img src="image_13.png" /><figcaption>**Figure 12.** (a,b) Measurement results of the TTDLs. (c-f) Calculated results for the phased array antenna. Reproduced with permission [70].</figcaption></figure>

## 4.2. Optical Communication

Emerging technologies such as 5G-A/6G, big data, and artificial intelligence are experiencing exponential growth in demand for transmission capacity, posing unprecedented challenges to existing optical communication technologies. Wavelength division multiplexing technology can significantly enhance data transmission efficiency, requiring a large number of equally spaced frequency parallel laser sources as optical carriers. By leveraging advanced encoding techniques to modulate their amplitude and phase precisely, high-speed information transmission can be achieved. Thanks to the large number of parallel wavelength channels provided by the 'palm-like' SC microcombs, several milestones have been achieved, including ultra-high data transmission over 75 kilometers of standard optical fiber and the implementation of a broadband RF channelizer.

The system setup for ultra-high bandwidth optical communication is shown in Figure 13(a) [14]. Corcoran B. et al. selected 80 comb lines from the SC microcomb within the C-band using a WS, and by employing single-sideband modulation, they increased the comb line count to 160, resulting in a 24.5 GHz line spacing and an improved spectral efficiency. The implementation of 64 QAM across the entire comb spectrum was achieved at 23 Gigabaud, efficiently utilizing 94% of the available spectrum. Figures 13 (b, c) show the SC microcomb spectra following flattening, modulation, and passage through either 75 km of lab fiber or the field trial connection. Figure 13 (d) presents constellation diagrams of the received signals under different conditions, including back-to-back (directly connecting the transmitter to the receiver), through 75 km of in-lab fiber, and through the
76.6 km field trial link. These constellation diagrams reveal the signal quality under various transmission conditions, including parameters such as bit error rate (BER) and signal quality ($Q^2$). The results demonstrate that the system can maintain a low BER and exhibit good transmission performance even after long-distance transmission.

<figure><img src="image_14.png" /><figcaption>Figure 13. (a) The experimental setup of ultra-dense optical data transmission. Spectra of the comb at key points: (b) back-to-back; (c) in-lab fiber; (d) over the field trial network. (e) Constellation diagrams for the signal at 194.34 THz. Reproduced with permission [14].</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Figure 14. (a) The experimental setup of the designed broadband RF channelizer. (b, c) The measured RF spectra. Reproduced with permission [81].</figcaption></figure>
The setup for the broadband RF channelizer, depicted in Figure 14(a), incorporates two MRRs with closely aligned FSRs of around 49 GHz [81]. The active MRR generates an SC microcomb that provides up to 92 comb lines in the operating band, while the other MRR acts as an intensity modulator. Xu X. et al. utilized the vernier effect between the two to segment the broadband RF spectrum with a high resolution of 121.4 MHz, thereby achieving continuous channelization at a rate of 87.5 MHz per channel. Shown in Figs. 14(b, c), their experiments confirmed an instantaneous RF operating bandwidth of 8.08 GHz.

### 4.3. Photonic Neural Network

With the development of big data, network convergence, and the Internet of Things, artificial intelligence has attracted widespread attention worldwide, achieving significant results in fields such as computer vision, medical diagnosis, molecular and materials science, and speech recognition. Against this backdrop, the world generates massive amounts of data at an exponential growth rate, necessitating faster and more efficient processing methods. However, traditional electronic neural networks face a series of technical bottlenecks, including long latency and high power consumption. With its advantages of high speed, high bandwidth, and low crosstalk, photonic technology can significantly enhance computational speed by introducing optical processing mechanisms to construct photonic neural networks.

In 2021, Xu X. et al. proposed a microcomb-based photonic convolutional accelerator [16], which utilizes time, wavelength, and spatial interleaving technology to achieve a photonic neural network with a computing speed of 11.3 TOPS (Tera-ops per second). As shown in Figure 15, the convolutional kernel is unfolded into a weight vector $W$, and each element of the weight vector is mapped onto lines of the SC microcomb by a waveform shaper. Next, the image data matrix is one-dimensionalized and unfolded into a one-dimensional vector, where each pixel of the image is transformed into a part of a time-sequence digital signal. The symbols correspond one-to-one with the vector elements, with each symbol lasting for a duration of $\tau$. Subsequently, this digital signal is modulated onto the microcomb by an electro-optic Mach-Zehnder modulator, and then it is input into a single-mode fiber, where a fixed time delay is introduced. Eventually, the delayed optical signal is detected by a photodetector, and the time-domain signal sequence is collected on an oscilloscope. During the photoelectric detection process, the detector sums the optical power of all frequency components, which essentially is a convolution process of the weight matrix and the input data. Under the same experimental conditions, a photonic convolutional neural network containing ten output neurons was constructed in sequence, and this network achieved an accuracy rate as high as 88% in the task of recognizing handwritten digital images. This achievement not only demonstrates the potential of optical convolutional neural networks in the field of image recognition but also proves the scalability and trainability of the method, which is expected to be applied to more complex network structures and scenarios with more stringent requirements.
<figure><img src="image_16.png" /><figcaption>**Figure 15.** (a) Principle of the convolutional accelerator principle. (b)Experimental diagram of a convolutional neural network based on the SC microcomb. Reproduced with permission [16].</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>**Figure 16.** Operation principle of the photonic signal processor for film processing. Reproduced with permission [82].</figcaption></figure>
In 2023, Tan M. et al. designed a photonic processor for video processing utilizing the time-wavelength convolutional accelerator [82]. This system achieves ultra-high-speed performance, reaching 17 terabits per second (Tbs/s), simultaneously processing approximately 399,061 video signals and performing up to 34 different image processing functions on each signal. Figure 16 illustrates the working principle of the photonic signal processor based on an SC microcomb, which includes the following key steps: (1) The creation of the SC microcomb is achieved by utilizing a microring resonator made of doped silica platform, with the comb lines of the microcomb acting as signal processing carriers. (2) Shaping of the optical signal produced by the microcomb using a WS to form the required weights. (3) Modulation of the shaped optical signal through an EOM, which is driven by the analog input film signal, encoding the information of the film signal into the optical signal. (4) Utilization of SMF to serve as an optical delay line, enabling the introduction of precise time delays for various wavelength channels. These controlled delays are essential for performing signal processing operations, including convolution. (5) The processed optical signal is detected by a photodetector, transforming it back into an electrical signal. (6) The detected electrical signal undergoes resampling and digital conversion to rebuild digital video frames, constituting the system's digital output signal.

## 5. Challenges and Perspectives

Over the past few years, the study of SC microcombs has rapidly advanced, with enhancements in their performance and an expansion of their application scope. In this section, we discuss the current challenges and prospects faced in the generation and applications of SC microcombs.

Despite numerous works having achieved the deterministic generation and switching of PSC microcombs[37-48,50], their application is still limited due to the large FSR of the PSC microcombs, which results in a smaller number of available wavelength channels within specific bands, especially the communication C band. For single FSR 'palm-like' SC microcombs, their generation is limited by the position and intensity of the AMX. This poses a challenge because variations in fabrication can influence the positioning and intensity of AMXs in microresonators.

AMXs arise from the interactions between distinct mode families and are prevalent in rings with anomalous dispersion. Waveguides exhibiting anomalous dispersion typically feature a larger cross-sectional area and often facilitate the coexistence of multiple modes, leading to the possibility of inter-modal crossings. The dispersion characteristics of the mode family undergo significant alterations in the vicinity of the AMX. For devices without cladding, their dispersion and AMXs can be tuned after fabrication [81], but for integrated single-resonator devices, the dispersion and AMXs are difficult to tune over large ranges. For instance, experimental results in Ref. [84] indicated that in two high-index doped silica micro-rings, by altering the temperature, the position of the AMX shifted by 0.88 and 0.55 resonances within the 10-40°C range, respectively. Furthermore, a study [44] has experimentally demonstrated that as the pump power increases, both the fundamental and higher-order modes undergo a redshift with differing shifts, decreasing
the frequency gap and inducing minor alterations in the AMX's location and intensity. For dual-ring devices, the auxiliary ring, acting as a source of additional modes, can facilitate the occurrence of mode crossings [85-89]. The AMX can be tuned across an extensive range by independently tuning two micro-rings with on-chip heaters. Therefore, the dual-ring structure has the potential to generate 'Palm-like' SC microcombs with arbitrary tuning of the pump wavelength.

The automated generation technology of soliton microcombs is crucial in practical applications. Despite the traditional automated generation of soliton microcombs facing the challenge of microcavity thermal effects and still requiring complex generation mechanisms, these issues are being gradually resolved with the advancement of SC microcombs. Because the intracavity power of the SC state is very close to that of the chaotic state, there will be no significant change in the cavity temperature when transitioning from the chaotic state to the SC state [35]. This temperature stability is crucial for achieving automated generation, as it reduces the risk of soliton state instability caused by thermal effects. Subsequently, with the setup of specific pump wavelength scanning, SC microcombs have the potential to achieve automatic or programmable-controlled generation.

In the applications mentioned in Section 4, the spectral control of SC microcombs is all achieved by using non-integrated devices (such as commercial programmable optical processors). The bulky volume of these devices limits their use in subsequent applications that urgently require miniaturization and integration. Fortunately, a variety of innovative on-chip spectral shaping devices [90-97] have recently emerged, offering significant potential for miniaturization essential for compact device applications. For example, PICs composed of MZI coupler arrays and linearly incremental delay lines can be programmed to perform various signal processing functions as needed [90-92]. PICs based on MRR arrays [93-97] can also process input signals. By independently controlling each MRR with thermo phase shifters, these PICs can achieve high precision in optical power control. Additionally, with the advancements in photonic nanofabrication and heterogeneous integration technologies, it will be possible in the future to achieve the co-integration of MRRs with other on-chip active and passive devices, such as integrated lasers[98], high-performance modulators[99-101], photodetectors[102,103], and so on, to achieve monolithic integration of diverse systems. This will be aided with the use of novel 2D materials [104-134] that will be extremely useful for all forms of microcombs [135-199] with the use of novel designs [200-208] for a wide range of applications to classical and quantum nonlinear optics. [209-286]

## 5. Conclusion

In this article, we examine the recent developments in soliton crystal microcombs. Firstly, we briefly introduce the numerical model of the Kerr optical frequency comb. Secondly, we introduce several typical schemes for generating soliton crystals. Then, we summarized the applications of palm soliton crystal microcombs in the fields of microwave photonics, optical communication, and photonic neural networks. Ultimately, we analyzed the current challenges and prospects faced by SC microcombs.
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109. Yuning Zhang, Jiayang Wu, Linnan Jia, Yang Qu, Baohua Jia, and David J. Moss, "Graphene oxide for nonlinear integrated photonics", *Laser and Photonics Reviews* **17** 2200512 (2023). DOI:10.1002/lpor.202200512.

110. Jiayang Wu, H.Lin, David J. Moss, T.K. Loh, Baohua Jia, "Graphene oxide for electronics, photonics, and optoelectronics", *Nature Reviews Chemistry* **7** (3) 162-183 (2023). doi.org/10.1038/s41570-022-00458-7.
111. Yang Qu, Jiayang Wu, Yuning Zhang, Yunyi Yang, Linnan Jia, Baohua Jia, and David J. Moss, "Photo thermal tuning in GO-coated integrated waveguides", Micromachines Vol. 13 1194 (2022). doi.org/10.3390/mi13081194

112. Yuning Zhang, Jiayang Wu, Yunyi Yang, Yang Qu, Houssein El Dirani, Romain Crochemore, Corrado Sciancalepore, Pierre Demongodin, Christian Grillet, Christelle Monat, Baohua Jia, and David J. Moss, "Enhanced self-phase modulation in silicon nitride waveguides integrated with 2D graphene oxide films", IEEE Journal of Selected Topics in Quantum Electronics Vol. 29 (1) 5100413 (2023). DOI: 10.1109/JSTQE.2022.3177385

113. Yuning Zhang, Jiayang Wu, Yunyi Yang, Yang Qu, Linnan Jia, Baohua Jia, and David J. Moss, "Enhanced spectral broadening of femtosecond optical pulses in silicon nanowires integrated with 2D graphene oxide films", Micromachines Vol. 13 756 (2022). DOI:10.3390/mi13050756.

114. Jiayang Wu, Yuning Zhang, Junkai Hu, Yunyi Yang, Di Jin, Wenbo Liu, Duan Huang, Baohua Jia, David J. Moss, "Novel functionality with 2D graphene oxide films integrated on silicon photonic chips", Advanced Materials Vol. 36 2403659 (2024). DOI: 10.1002/adma.202403659.

115. Di Jin, Jiayang Wu, Junkai Hu, Wenbo Liu1, Yuning Zhang, Yunyi Yang, Linnan Jia, Duan Huang, Baohua Jia, and David J. Moss, "Silicon photonic waveguide and microring resonator polarizers incorporating 2D graphene oxide films", Applied Physics Letters vol. 125, 000000 (2024); doi: 10.1063/5.0221793.

116. Yuning Zhang, Jiayang Wu, Linnan Jia, Di Jin, Baohua Jia, Xiaoyong Hu, David Moss, Qihuang Gong, "Advanced optical polarizers based on 2D materials", npj Nanophotonics Vol. 1, (2024). DOI: 10.1038/s44310-024-00028-3.

117. Junkai Hu, Jiayang Wu, Wenbo Liu, Di Jin, Houssein El Dirani, Sébastien Kerdiles, Corrado Sciancalepore, Pierre Demongodin, Christian Grillet, Christelle Monat, Duan Huang, Baohua Jia, and David J. Moss, "2D graphene oxide: a versatile thermo-optic material", Advanced Functional Materials 34 2406799 (2024). DOI: 10.1002/adfm.202406799.

118. Yang Qu, Jiayang Wu, Yuning Zhang, Yunyi Yang, Linnan Jia, Houssein El Dirani, Sébastien Kerdiles, Corrado Sciancalepore, Pierre Demongodin, Christian Grillet, Christelle Monat, Baohua Jia, and David J. Moss, "Integrated optical parametric amplifiers in silicon nitride waveguides incorporated with 2D graphene oxide films", Light: Advanced Manufacturing 4 39 (2023). https://doi.org/10.37188/lam.2023.039.

119. Di Jin, Wenbo Liu, Linnan Jia, Junkai Hu, Duan Huang, Jiayang Wu, Baohua Jia, and David J. Moss, "Thickness and Wavelength Dependent Nonlinear Optical Absorption in 2D Layered MXene Films", Small Science 4 2400179 (2024). DOI:10.1002/smsc202400179;

120. Linnan Jia, Jiayang Wu, Yuning Zhang, Yang Qu, Baohua Jia, Zhigang Chen, and David J. Moss, "Fabrication Technologies for the On-Chip Integration of 2D Materials", Small: Methods Vol. 6, 2101435 (2022). DOI:10.1002/smtd.202101435.

121. Yuning Zhang, Jiayang Wu, Yang Qu, Linnan Jia, Baohua Jia, and David J. Moss, "Design and optimization of four-wave mixing in microring resonators integrated with 2D graphene oxide films", Journal of Lightwave Technology Vol. 39 (20) 6553-6562 (2021). DOI:10.1109/JLT.2021.3101292.

122. Yuning Zhang, Jiayang Wu, Yang Qu, Linnan Jia, Baohua Jia, and David J. Moss, "Optimizing the Kerr nonlinear optical performance of silicon waveguides integrated with 2D graphene oxide films", Journal of Lightwave Technology Vol. 39 (14) 4671-4683 (2021). DOI: 10.1109/JLT.2021.3069733.

123. Yang Qu, Jiayang Wu, Yuning Zhang, Yao Liang, Baohua Jia, and David J. Moss, "Analysis of four-wave mixing in silicon nitride waveguides integrated with 2D layered graphene oxide films", Journal of Lightwave Technology Vol. 39 (9) 2902-2910 (2021). DOI: 10.1109/JLT.2021.3059721.
124. Jiayang Wu, Linnan Jia, Yuning Zhang, Yang Qu, Baohua Jia, and David J. Moss, "Graphene oxide: versatile films for flat optics to nonlinear photonic chips", Advanced Materials Vol. 33 (3) 2006415, pp.1-29 (2021). DOI:10.1002/adma.202006415.

125. Y. Qu, J. Wu, Y. Zhang, L. Jia, Y. Yang, X. Xu, S. T. Chu, B. E. Little, R. Morandotti, B. Jia, and D. J. Moss, "Graphene oxide for enhanced optical nonlinear performance in CMOS compatible integrated devices", Paper No. 11688-30, PW210-OE109-36, 2D Photonic Materials and Devices IV, SPIE Photonics West, San Francisco CA March 6-11 (2021). doi.org/10.1117/12.2583978

126. Yang Qu, Jiayang Wu, Yunyi Yang, Yuning Zhang, Yao Liang, Houssein El Dirani, Romain Crochemore, Pierre Demongodin, Corrado Sciancalepore, Christian Grillet, Christelle Monat, Baohua Jia, and David J. Moss, "Enhanced nonlinear four-wave mixing in silicon nitride waveguides integrated with 2D layered graphene oxide films", Advanced Optical Materials vol. 8 (21) 2001048 (2020). DOI: 10.1002/adom.202001048. arXiv:2006.14944.

127. Yuning Zhang, Yang Qu, Jiayang Wu, Linnan Jia, Yunyi Yang, Xingyuan Xu, Baohua Jia, and David J. Moss, "Enhanced Kerr nonlinearity and nonlinear figure of merit in silicon nanowires integrated with 2D graphene oxide films", ACS Applied Materials and Interfaces vol. 12 (29) 33094-33103 June 29 (2020). DOI:10.1021/acsami.0c07852

128. Jiayang Wu, Yunyi Yang, Yang Qu, Yuning Zhang, Linnan Jia, Xingyuan Xu, Sai T. Chu, Brent E. Little, Roberto Morandotti, Baohua Jia, and David J. Moss, "Enhanced nonlinear four-wave mixing in microring resonators integrated with layered graphene oxide films", Small vol. 16 (16) 1906563 (2020). DOI: 10.1002/smll.201906563

129. Jiayang Wu, Yunyi Yang, Yang Qu, Xingyuan Xu, Yao Liang, Sai T. Chu, Brent E. Little, Roberto Morandotti, Baohua Jia, and David J. Moss, "Graphene oxide waveguide polarizers and polarization selective micro-ring resonators", Paper 11282-29, SPIE Photonics West, San Francisco, CA, 4-7 February (2020). doi: 10.1117/12.2544584

130. Jiayang Wu, Yunyi Yang, Yang Qu, Xingyuan Xu, Yao Liang, Sai T. Chu, Brent E. Little, Roberto Morandotti, Baohua Jia, and David J. Moss, "Graphene oxide waveguide polarizers and polarization selective micro-ring resonators", Laser and Photonics Reviews vol. 13 (9) 1900056 (2019). DOI:10.1002/lpor.201900056.

131. Yunyi Yang, Jiayang Wu, Xingyuan Xu, Sai T. Chu, Brent E. Little, Roberto Morandotti, Baohua Jia, and David J. Moss, "Enhanced four-wave mixing in graphene oxide coated waveguides", Applied Physics Letters Photonics vol. 3 120803 (2018). doi: 10.1063/1.5045509.

132. Linnan Jia, Yang Qu, Jiayang Wu, Yuning Zhang, Yunyi Yang, Baohua Jia, and David J. Moss, "Third-order optical nonlinearities of 2D materials at telecommunications wavelengths", Micromachines (MDPI), 14, 307 (2023). https://doi.org/10.3390/mi14020307.

133. Linnan Jia, Dandan Cui, Jiayang Wu, Haifeng Feng, Tieshan Yang, Yunyi Yang, Yi Du, Weichang Hao, Baohua Jia, David J. Moss, "BioBr nanoflakes with strong nonlinear optical properties towards hybrid integrated photonic devices", Applied Physics Letters Photonics vol. 4 090802 vol. (2019). DOI: 10.1063/1.5116621

134. Linnan Jia, Jiayang Wu, Yunyi Yang, Yi Du, Baohua Jia, David J. Moss, "Large Third-Order Optical Kerr Nonlinearity in Nanometer-Thick PdSe2 2D Dichalcogenide Films: Implications for Nonlinear Photonic Devices", ACS Applied Nano Materials vol. 3 (7) 6876-6883 (2020). DOI:10.1021/acsanm.0c01239.

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156. Yang Sun, Jiayang Wu, Mengxi Tan, Xingyuan Xu, Yang Li, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Applications of optical micro-combs", *Advances in Optics and Photonics* **15** (1) 86-175 (2023). https://doi.org/10.1364/AOP.470264.

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158. Antonio Cutrona, Maxwell Rowley, Debayan Das, Luana Olivieri, Luke Peters, Sai T. Chu, Brent L. Little, Roberto Morandotti, David J. Moss, Juan Sebastian Totero Gongora, Marco Peccianti, Alessia Pasquazi, "High Conversion Efficiency in Laser Cavity-Soliton Microcombs", Optics Express Vol. 30, Issue 22, pp. 39816-39825 (2022). https://doi.org/10.1364/OE.470376.
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160. A. Cutrona, M. Rowley, A. Bendahmane, V. Cecconi, L. Peters, L. Olivieri, B. E. Little, S. T. Chu, S. Stivala, R. Morandotti, D. J. Moss, J. S. Totero-Gongora, M. Peccianti, A. Pasquazi, "Nonlocal bonding of a soliton and a blue-detuned state in a microcomb laser", Nature Communications Physics 6 Article 259 (2023). https://doi.org/10.1038/s42005-023-01372-0

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162. A. Cutrona, M. Rowley, A. Bendahmane, V. Cecconi, L. Peters, L. Olivieri, B. E. Little, S. T. Chu, S. Stivala, R. Morandotti, D. J. Moss, J. S. Totero-Gongora, M. Peccianti, A. Pasquazi, "Stability Properties of Laser Cavity-Solitons for Metrological Applications", Applied Physics Letters vol. 122 (12) 121104 (2023); doi: 10.1063/5.0134147.

163. X. Xu, J. Wu, M. Shoeiby, T. G. Nguyen, S. T. Chu, B. E. Little, R. Morandotti, A. Mitchell, and D. J. Moss, "Reconfigurable broadband microwave photonic intensity differentiator based on an integrated optical frequency comb source," APL Photonics, vol. 2, no. 9, 096104, Sep. 2017.

164. Xu, X., et al., Photonic microwave true time delays for phased array antennas using a 49 GHz FSR integrated micro-comb source, Photonics Research, vol. 6, B30-B36 (2018).

165. X. Xu, M. Tan, J. Wu, R. Morandotti, A. Mitchell, and D. J. Moss, "Microcomb-based photonic RF signal processing", IEEE Photonics Technology Letters, vol. 31 no. 23 1854-1857, 2019.

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189. Xingyuan Xu, Weiwei Han, Mengxi Tan, Yang Sun, Yang Li, Jiayang Wu, Roberto Morandotti, Arnan Mitchell, Kun Xu, and David J. Moss, "Neuromorphic computing based on wavelength-division multiplexing", *IEEE Journal of Selected Topics in Quantum Electronics* **29** (2) 7400112 (2023). DOI:10.1109/JSTQE.2022.3203159.

190. Yunping Bai, Xingyuan Xu,1, Mengxi Tan, Yang Sun, Yang Li, Jiayang Wu, Roberto Morandotti, Arnan Mitchell, Kun Xu, and David J. Moss, "Photonic multiplexing techniques for neuromorphic computing", Nanophotonics vol. 12 (5): 795-817 (2023).
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191. Chawaphon Prayoonyong, Andreas Boes, Xingyuan Xu, Mengxi Tan, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, David J. Moss, and Bill Corcoran, "Frequency comb distillation for optical superchannel transmission", Journal of Lightwave Technology vol. 39 (23) 7383-7392 (2021). DOI: 10.1109/JLT.2021.3116614.

192. Mengxi Tan, Xingyuan Xu, Jiayang Wu, Bill Corcoran, Andreas Boes, Thach G. Nguyen, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Integral order photonic RF signal processors based on a soliton crystal micro-comb source", IOP Journal of Optics vol. 23 (11) 125701 (2021). https://doi.org/10.1088/2040-8986/ac2eab
193. Yang Sun, Jiayang Wu, Yang Li, Xingyuan Xu, Guanghui Ren, Mengxi Tan, Sai Tak Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Optimizing the performance of microcomb based microwave photonic transversal signal processors", Journal of Lightwave Technology vol. 41 (23) pp 7223-7237 (2023). DOI: 10.1109/JLT.2023.3314526.

194. Mengxi Tan, Xingyuan Xu, Andreas Boes, Bill Corcoran, Thach G. Nguyen, Sai T. Chu, Brent E. Little, Roberto Morandotti, Jiayang Wu, Arnan Mitchell, and David J. Moss, "Photonic signal processor for real-time video image processing based on a Kerr microcomb", Communications Engineering vol. 2 94 (2023). DOI:10.1038/s44172-023-00135-7

195. Mengxi Tan, Xingyuan Xu, Jiayang Wu, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Photonic RF and microwave filters based on 49GHz and 200GHz Kerr microcombs", Optics Communications, vol. 465, Article: 125563 (2020). doi:10.1016/j.opt-com.2020.125563. doi.org/10.1063/1.5136270.

196. Yang Sun, Jiayang Wu, Yang Li, Mengxi Tan, Xingyuan Xu, Sai Chu, Brent Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Quantifying the Accuracy of Microcomb-based Photonic RF Transversal Signal Processors", IEEE Journal of Selected Topics in Quantum Electronics vol. 29 no. 6, pp. 1-17, Art no. 7500317 (2023). 10.1109/JSTQE.2023.3266276.

197. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Bill Corcoran, Xingyuan Xu, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, "Processing accuracy of microcomb-based microwave photonic signal processors for different input signal waveforms", *MDPI Photonics 10*, 10111283 (2023). DOI:10.3390/photonics10111283

198. Caitlin E. Murray, Mengxi Tan, Chawaphon Prayoonyong, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, David J. Moss and Bill Corcoran, "Investigating the thermal robustness of soliton crystal microcombs", *Optics Express* 31(23), 37749-37762 (2023).

199. Yang Sun, Jiayang Wu, Yang Li, and David J. Moss, "Comparison of microcomb-based RF photonic transversal signal processors implemented with discrete components versus integrated chips", *MDPI Micromachines* 14, 1794 (2023). https://doi.org/10.3390/mi14091794

200. Hamed Arianfard, Saulius Juodkazis, David J. Moss, and Jiayang Wu, "Sagnac interference in integrated photonics", *Applied Physics Reviews 10* (1) 011309 (2023). doi: 10.1063/5.0123236.

201. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, and David J. Moss, "Optical analogs of Rabi splitting in integrated waveguide-coupled resonators", *Advanced Physics Research 2* 2200123 (2023). DOI: 10.1002/apxr.202200123.

202. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, and David J. Moss, "Spectral shaping based on optical waveguides with advanced Sagnac loop reflectors", Paper No. PW22O-OE201-20, SPIE-Opto, Integrated Optics: Devices, Materials, and Technologies XXVI, SPIE Photonics West, San Francisco CA January 22 - 27 (2022). doi: 10.1117/12.2607902

203. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, David J. Moss, "Spectral Shaping Based on Integrated Coupled Sagnac Loop Reflectors Formed by a Self-Coupled Wire Waveguide", IEEE Photonics Technology Letters vol. 33 (13) 680-683 (2021). DOI:10.1109/LPT.2021.3088089.

204. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, "Three Waveguide Coupled Sagnac Loop Reflectors for Advanced Spectral Engineering", Journal of Lightwave Technology vol. 39 (11) 3478-3487 (2021). DOI: 10.1109/JLT.2021.3066256.

205. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, "Advanced Multi-Functional Integrated Photonic Filters based on Coupled Sagnac Loop Reflectors", Journal of Lightwave Technology vol. 39 Issue: 5, pp.1400-1408 (2021). DOI:10.1109/JLT.2020.3037559.

206. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, "Advanced multi-functional integrated photonic filters based on coupled Sagnac loop reflectors", Paper 11691-4, PW21O-OE203-44, Silicon Photonics XVI, SPIE Photonics West, San Francisco CA March 6-11 (2021). doi.org/10.1117/12.2584020
207. Jiayang Wu, Tania Moein, Xingyuan Xu, and David J. Moss, "Advanced photonic filters via cascaded Sagnac loop reflector resonators in silicon-on-insulator integrated nanowires", Applied Physics Letters Photonics vol. 3 046102 (2018).
DOI:/10.1063/1.5025833

208. Jiayang Wu, Tania Moein, Xingyuan Xu, Guanghui Ren, Arnan Mitchell, and David J. Moss, "Micro-ring resonator quality factor enhancement via an integrated Fabry-Perot cavity", Applied Physics Letters Photonics vol. 2 056103 (2017). doi: 10.1063/1.4981392.

209. MD Pelusi, F Luan, E Magi, MRE Lamont, DJ Moss, BJ Eggleton, ... et al., "High bit rate all-optical signal processing in a fiber photonic wire", Optics Express vol. 16 (15), 11506-11512 (2008).

210. M Shokooh-Saremi, VG Ta'Eed, NJ Baker, ICM Littler, DJ Moss, ... et al., "High-performance Bragg gratings in chalcogenide rib waveguides written with a modified Sagnac interferometer", JOSA B vol. 23 (7), 1323-1331 (2006).

211. T Ido, H Sano, DJ Moss, S Tanaka, A Takai, "Strained InGaAs/InAlAs MQW electroabsorption modulators with large bandwidth and low driving voltage", IEEE photonics technology letters vol. 6 (10), 1207-1209 (1994).

212. D Freeman et al., "Chalcogenide glass photonic crystals", Photonics and Nanostructures-Fundamentals and Applications vol. 6 (1), 3-11 (2008).

213. C Grillet, C Smith, D Freeman, S Madden, B Luther-Davies, EC Magi, ... "Efficient coupling to chalcogenide glass photonic crystal waveguides via silica optical fiber nanowires", Optics Express vol. 14 (3), 1070-1078 (2006).

214. E Ghahramani, DJ Moss, JE Sipe, "Second-harmonic generation in odd-period, strained, (Si(Ge/Si superlattices and at Si/Ge interfaces", Physical Review Letters vol. 64 (23), 2815 (1990).

215. TD Vo, et al., "Silicon-chip-based real-time dispersion monitoring for 640 Gbit/s DPSK signals", Journal of Lightwave Technology vol. 29 (12), 1790-1796 (2011).

216. C Monat, C Grillet, B Corcoran, DJ Moss, BJ Eggleton, TP White, ..., et al., "Investigation of phase matching for third-harmonic generation in silicon slow light photonic crystal waveguides using Fourier optics", Optics Express vol. 18 (7), 6831-6840 (2010).

217. L Carletti, P Ma, Y Yu, B Luther-Davies, D Hudson, C Monat, ..., et al., "Nonlinear optical response of low loss silicon germanium waveguides in the mid-infrared", Optics Express vol. 23 (7), 8261-8271 (2015).

218. MRE Lamont, VG Ta'Eed, MAF Roelens, DJ Moss, BJ Eggleton, DY Choi, ... et al., "Error-free wavelength conversion via cross-phase modulation in 5cm of As2S3 chalcogenide glass rib waveguide", Electronics Letters vol. 43 (17), 945-947 (2007).

219. C Grillet, C Monat, CLC Smith, BJ Eggleton, DJ Moss, S Frédérick, ... et al., "Nanowire coupling to photonic crystal nanocavities for single photon sources", Optics Express vol. 15 (3), 1267-1276 (2007).

220. M Rochette, JN Kutz, JL Blows, D Moss, JT Mok, BJ Eggleton, "Bit-error-ratio improvement with 2R optical regenerators", IEEE Photonics Technology Letters vol. 17 (4), 908-910 (2005).

221. MW Lee, C Grillet, CLC Smith, DJ Moss, BJ Eggleton, D Freeman, "Photosensitive post tuning of chalcogenide photonic crystal waveguides", Optics Express vol. 15 (3), 1277-1285 (2007).

222. DJ Moss, HM Van Driel, JE Sipe, "Third harmonic generation as a structural diagnostic of ion-implanted amorphous and crystalline silicon", Applied physics letters vol. 48 (17), 1150-1152 (1986).

223. VG Ta'Eed, MRE Lamont, DJ Moss, BJ Eggleton, DY Choi, S Madden, ... et al., "All optical wavelength conversion via cross phase modulation in chalcogenide glass rib waveguides", Optics Express vol. 14 (23), 11242-11247 (2006).

224. TM Monro, D Moss, M Bazylenko, CM De Sterke, L Poladian, "Observation of self-trapping of light in a self-written channel in a photosensitive glass", Physical Review Letters vol. 80 (18), 4072 (1998).

225. C. Mazoukh, L. Di Lauro, I. Alamgir1 B. Fischer, A. Aadhi, A. Eshaghi, B. E. Little, S. T. Chu, D. J. Moss, and R. Morandotti, "Genetic
algorithm-enhanced microcomb state generation", *Nature Communications Physics* Vol. 7, Article: 81 (2024). DOI: 10.1038/s42005-024-01558-0.

226. Mengxi Tan, David J. Moss, "The laser trick that could put an ultraprecise optical clock on a chip", *Nature* **624**, (7991) 256-257 (2023).
doi.org/10.1038/d41586-023-03782-0.

227. Junkai Hu, Jiayang Wu, Di Jin, Sai Tak Chu, Brent E. Little, Duan Huang, Roberto Morandotti, and David J. Moss, "Thermo-optic response and optical bistability of integrated high index doped silica ring resonators", *MDPI Sensors* **23** 9767 (2023).
https://doi.org/10.3390/s23249767.

228. M. Zerbib, V.T. Hoang, J. C. Beugnot, K. P. Huy, B. Little, S. T. Chu, D. J. Moss, R. Morandotti, B. Wetzel, and T. Sylvestre, "Observation of Brillouin scattering in a high-index doped silica chip waveguide", *Results in Physics* **52** 106830 (2023).
https://doi.org/10.1016/j.rinp.2023.106830.

229. Stefania Sciara, Hao Yu, Farzam Nosrati, Piotr Roztocki, Bennet Fischer, Mario Chemnitz, Christian Reimer, Luis Romero Cortés, William J. Munro, David J. Moss, Rosario Lo Franco, Alfonso C. Cino, Lucia Caspani, Michael Kues, Zhiming Wang, José Azaña, and Roberto Morandotti, "Generation of integrated quantum frequency combs on microring resonators for the realization of complex entangled two-photon states", Early Access *IEEE Journal of Selected Topics in Quantum Electronics* **28** (2022).

230. Linnan Jia, Yang Qu, Jiayang Wu, Yuning Zhang, Yunyi Yang, Baohua Jia, and David J. Moss, "Third-order optical nonlinearities of 2D materials at telecommunications wavelengths", *Micromachines*, **14** 307 (2023). https://doi.org/10.3390/mi14020307.

231. Alberto Della Torre, Remi Armand, Milan Sinobad, Kokou Firmin Fiaboe, Barry Luther-Davies, Stephen Madden, Arnan Mitchell, Thach Nguyen, David J. Moss, Jean-Michel Hartmann, Vincent Reboud, Jean-Marc Fedeli, Christelle Monat, and Christian Grillet, "Mid-Infrared Supercontinuum Generation in a Varying Dispersion Waveguide for Multi-Species Gas Spectroscopy", *IEEE Journal of Selected Topics in Quantum Electronics* **29** (1) 5100509 (2023). DOI: 10.1109/JSTQE.2022.3185169.

232. Andrew Cooper, Luana Olivieri, Antonio Cutrona, Debayan Das, Luke Peters, Sai Tak Chu, Brent Little, Roberto Morandotti, David J Moss, Marco Peccianti, and Alessia Pasquazi, "Parametric interaction of laser cavity-solitons with an external CW pump", *Optics Express* **32** (12), 21783-21794 (2024).

233. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Chaoran Huang, Jiayang Wu, Kun Xu, David J. Moss, and Xingyuan Xu, "Photonic RF Channelization Based on Microcombs", *IEEE Journal of Selected Topics in Quantum Electronics* **30** (5) 7600417 (2024).
DOI:10.1109/JSTQE.2024.3398419.

234. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Xingyuan Xu, Mengxi Tan, Sai Chu, Brent Little, Roberto Morandotti, Arnan Mitchell, and David Moss, "Feedback control in micro-comb-based microwave photonic transversal filter systems", *IEEE Journal of Selected Topics in Quantum Electronics* Vol. **30** (5) 2900117 (2024). DOI: 10.1109/JSTQE.2024.3377249.

235. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Yuhua Li, Xiaotian Zhu, Yanni Ou, Feifei Yin, Roberto Morandotti, Brent E. Little, Sai Tak Chu, Xingyuan Xu, David J. Moss, and Kun Xu, "Dual-polarization RF Channelizer Based on Microcombs", *Optics Express* **32**, No. 7, 11281-11295 (2024). DOI: 10.1364/OE.519235.

236. Mengxi Tan, Xingyuan Xu, Andreas Boes, Bill Corcoran, Thach G. Nguyen, Sai T. Chu, Brent E. Little, Roberto Morandotti, Jiayang Wu, Arnan Mitchell, and David J. Moss, "Photonic signal processor for real-time video image processing based on a Kerr microcomb", *Nature Communications Engineering* **2** 94 (2023). DOI:10.1038/s44172-023-00135-7.

237. Kues, M. et al. "Quantum optical microcombs", Nature Photonics vol. 13, (3) 170-179 (2019). doi:10.1038/s41566-019-0363-0

238. C.Reimer, L. Caspani, M. Clerici, et al., "Integrated frequency comb source of heralded single photons," *Optics Express*, vol. 22, no. 6, pp. 6535-6546, 2014.
239. C. Reimer, et al., "Cross-polarized photon-pair generation and bi-chromatically pumped optical parametric oscillation on a chip", Nature Communications, vol. 6, Article 8236, 2015. DOI: 10.1038/ncomms9236.

240. L. Caspani, C. Reimer, M. Kues, et al., "Multifrequency sources of quantum correlated photon pairs on-chip: a path toward integrated Quantum Frequency Combs," Nanophotonics, vol. 5, no. 2, pp. 351-362, 2016.

241. C. Reimer et al., "Generation of multiphoton entangled quantum states by means of integrated frequency combs," Science, vol. 351, no. 6278, pp. 1176-1180, 2016.

242. M. Kues, et al., "On-chip generation of high-dimensional entangled quantum states and their coherent control", Nature, vol. 546, no. 7660, pp. 622-626, 2017.

243. P. Roztocki et al., "Practical system for the generation of pulsed quantum frequency combs," Optics Express, vol. 25, no. 16, pp. 18940-18949, 2017.

244. Y. Zhang, et al., "Induced photon correlations through superposition of two four-wave mixing processes in integrated cavities", Laser and Photonics Reviews, vol. 14, no. 7, pp. 2000128, 2020. DOI: 10.1002/lpor.202000128

245. C. Reimer, et al., "High-dimensional one-way quantum processing implemented on d-level cluster states", Nature Physics, vol. 15, no.2, pp. 148-153, 2019.

246. P.Roztocki et al., "Complex quantum state generation and coherent control based on integrated frequency combs", Journal of Lightwave Technology vol. 37 (2) 338-347 (2019).

247. S. Sciara et al., "Generation and Processing of Complex Photon States with Quantum Frequency Combs", IEEE Photonics Technology Letters vol. 31 (23) 1862-1865 (2019). DOI: 10.1109/LPT.2019.2944564.

248. Stefania Sciara, Piotr Roztocki, Bennet Fisher, Christian Reimer, Luis Romero Cortez, William J. Munro, David J. Moss, Alfonso C. Cino, Lucia Caspani, Michael Kues, J. Azana, and Roberto Morandotti, "Scalable and effective multilevel entangled photon states: A promising tool to boost quantum technologies", Nanophotonics vol. 10 (18), 4447-4465 (2021). DOI:10.1515/nanoph-2021-0510.

249. L. Caspani, C. Reimer, M. Kues, et al., "Multifrequency sources of quantum correlated photon pairs on-chip: a path toward integrated Quantum Frequency Combs," Nanophotonics, vol. 5, no. 2, pp. 351-362, 2016.

250. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Yuhua Li, Xiaotian Zhu, Yanni Ou, Feifei Yin, Roberto Morandotti, Brent E. Little, Sai Tak Chu, David J. Moss, Kun Xu, and Xingyuan Xu, "Complex-valued optical neuromorphic convolution accelerator based on microcombs", *Nature Communications* (2024).

251. H. Yu, S. Sciara, M. Chemnitz, N. Montaut, B. Fischer, R. Helsten, B. Crockett, B. Wetzel, T. A. Göbel, R. Krämer, B. E. Little, S. T. Chu, D. J. Moss, S. Nolte, W.J. Munro, Z. Wang, J. Azaña, R. Morandotti, "Quantum key distribution with high-dimensional entangled photons", *Nature Communications* (2024).

252. Luigi di Lauro, Stefania Sciara, Bennet Fischer, Junliang Dong, Imtiaz Alamgir, Benjamin Wetzel, Goëry Genty, Mitchell Nichols, Armaghan Eshaghi, David J. Moss, Roberto Morandotti, "Optimization Methods for Integrated and Programmable Photonics in Next-Generation Classical and Quantum Smart Communication and Signal Processing", *Advances in Optics and Photonics* (2023).

253. Bill Corcoran, Arnan Mitchell, Roberto Morandotti, Leif K. Oxenlowe, and David J. Moss, "Microcombs for Optical Communications", *Nature Photonics* (2024).

254. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Roberto Morandotti, Xingyuan Xu, Mengxi Tan, Arnan Mitchell, and David J. Moss, "Performance analysis of microwave photonic spectral filters based on optical microcombs", *Advanced Physics Research 3* (9) (2024). DOI:10.1002/apxr.202400084.
255. Andrew Cooper, Luana Olivieri, Antonio Cutrona, Debayan Das, Luke Peters, Sai Tak Chu, Brent Little, Roberto Morandotti, David J Moss, Marco Peccianti, and Alessia Pasquazi, "Parametric interaction of laser cavity-solitons with an external CW pump", *Optics Express* **32** (12), 21783-21794 (2024).

256. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Chaoran Huang, Jiayang Wu, Kun Xu, David J. Moss, and Xingyuan Xu, "Photonic RF Channelization Based on Microcombs", *IEEE Journal of Selected Topics in Quantum Electronics* **30** (5) 7600417 (2024). DOI:10.1109/JSTQE.2024.3398419.

257. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Xingyuan Xu, Mengxi Tan, Sai Chu, Brent Little, Roberto Morandotti, Arnan Mitchell, and David Moss, "Feedback control in micro-comb-based microwave photonic transversal filter systems", *IEEE Journal of Selected Topics in Quantum Electronics* Vol. **30** (5) 2900117 (2024). DOI: 10.1109/JSTQE.2024.3377249.

258. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Yuhua Li, Xiaotian Zhu, Yanni Ou, Feifei Yin, Roberto Morandotti, Brent E. Little, Sai Tak Chu, Xingyuan Xu, David J. Moss, and Kun Xu, "Dual-polarization RF Channelizer Based on Microcombs", *Optics Express* **32**, No. 7, 11281-11295 / 25 Mar 2024 / (2024). DOI: 10.1364/OE.519235.

259. Aadhi A. Rahim, Imtiaz Alamgir, Luigi Di Lauro, Bennet Fischer, Nicolas Perron, Pavel Dmitriev, Celine Mazoukh, Piotr Roztocki, Cristina Rimoldi, Mario Chemnitz, Armaghan Eshaghi, Evgeny A. Viktorov, Anton V. Kovalev, Brent E. Little, Sai T. Chu, David J. Moss, and Roberto Morandotti, "Mode-locked laser with multiple timescales in a microresonator-based nested cavity", *APL Photonics* **9** 031302 (2024); DOI:10.1063/5.0174697.

260. C. Mazoukh, L. Di Lauro, I. Alamgir, B. Fischer, A. Aadhi, A. Eshaghi, B. E. Little, S. T. Chu, D. J. Moss, and R. Morandotti, "Genetic algorithm-enhanced microcomb state generation", Special Issue Microresonator Frequency Combs - New Horizons, *Nature Communications Physics* Vol. 7, Article: 81 (2024). DOI: 10.1038/s42005-024-01558-0.

261. Yonghang Sun, James Salamy, Caitlin E. Murry, Brent E. Little, Sai T. Chu, Roberto Morandotti, Arnan Mitchell, David J. Moss, Bill Corcoran, "Enhancing laser temperature stability by passive self-injection locking to a micro-ring resonator", *Optics Express* **32** (13) 23841-23855 (2024) https://doi.org/10.1364/OE.515269.

262. C. Khallouf, V. T. Hoang, G. Fanjoux, B. Little, S. T. Chu, D. J. Moss, R. Morandotti, J. M. Dudley, B. Wetzel, and T. Sylvestre, "Raman scattering and supercontinuum generation in high-index doped silica chip waveguides", Nonlinear Optics and its Applications, edited by John M. Dudley, Anna C. Peacock, Birgit Stiller, Giovanna Tissoni, SPIE Vol. 13004, 130040I (2024). SPIE-0277-786X doi: 10.1117/12.3021965

263. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Roberto Morandotti, Xingyuan Xu, Mengxi Tan, Arnan Mitchell, and David J. Moss, "Performance analysis of microwave photonic spectral filters based on optical microcombs", *Advanced Physics Research* **3** (9) (2024). DOI:10.1002/apxr.202400084.

264. Kues, M. et al. "Quantum optical microcombs", Nature Photonics vol. 13, (3) 170-179 (2019).

265. C. Reimer et al., "Generation of multiphoton entangled quantum states by means of integrated frequency combs," Science, vol. 351, no. 6278, pp. 1176-1180, 2016.

266. M. Kues, et al., "On-chip generation of high-dimensional entangled quantum states and

267. C. Reimer, et al., "High-dimensional one-way quantum processing implemented on d-level cluster states", Nature Physics, vol. 15, no.2, pp. 148-153, 2019.

268. H. Yu, S. Sciara, M. Chemnitz, N. Montaut, B. Fischer, R. Helsten, B. Crockett, B. Wetzel, T. A. Göbel, R. Krämer, B. E. Little, S. T. Chu, D. J. Moss, S. Nolte, W.J. Munro, Z. Wang, J. Azaña, R. Morandotti, "Quantum key distribution implemented with d-level time-bin entangled photons", Nature Communications Vol. 16, 171 (2025). DOI:10.1038/s41467-024-55345-0.
269. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Yuhua Li, Xiaotian Zhu, Yanni Ou, Feifei Yin, Roberto Morandotti, Brent E. Little, Sai Tak Chu, David J. Moss, Xingyuan Xu, and Kun Xu, "TOPS-speed complex-valued convolutional accelerator for feature extraction and inference", Nature Communications Vol. 16, 292 (2025). DOI: 10.1038/s41467-024-55321-8.

270. Yonghang Sun, James Salamy, Caitlin E. Murray, Xiaotian Zhu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, Sai T. Chu, David J. Moss, Bill Corcoran, "Self-locking of free-running DFB lasers to a single microring resonator for dense WDM", Journal of Lightwave Technology, (2024). DOI: 10.1109/JLT.2024.3494694.

271. Zhihui Liu, Haoran Zhang, Yuhang Song, Xiaotian Zhu, Yunping Bai, Mengxi Tan, Bill Corcoran, Caitlin Murphy, Sai T. Chu, David J. Moss, Xingyuan Xu, and Kun Xu, "Advances in Soliton Crystals Microcombs", Photonics Vol. 11, 1164 (2024). https://doi.org/10.3390/photon-ics11121164.

272. Di Jin, Jiayang Wu, Sian Ren, Junkai Hu, Duan Huang, and David J. Moss, "Modeling of complex integrated photonic resonators using scattering matrix method", Photonics Vol. 11, 1107 (2024). https://doi.org/10.3390/photonics11121107.

273. Yonghang Sun, James Salamy, Caitlin E. Murry, Brent E. Little, Sai T. Chu, Roberto Morandotti, Arnan Mitchell, David J. Moss, Bill Corcoran, "Enhancing laser temperature stability by passive self-injection locking to a micro-ring resonator", Optics Express Vol. 32 (13) 23841-23855 (2024). https://doi.org/10.1364/OE.515269.

274. C. Khallouf, V. T. Hoang, G. Fanjoux, B. Little, S. T. Chu, D. J. Moss, R. Morandotti, J. M. Dudley, B. Wetzel, and T. Sylvestre, "Raman scattering and supercontinuum generation in high-index doped silica chip waveguides", Nonlinear Optics and its Applications, edited by John M. Dudley, Anna C. Peacock, Birgit Stiller, Giovanna Tissoni, SPIE Vol. 13004, 130040I (2024). doi: 10.1117/12.3021965

275. Yang Li, Yang Sun, Jiayang Wu, Guanghui Ren, Roberto Morandotti, Xingyuan Xu, Mengxi Tan, Arnan Mitchell, and David J. Moss, "Performance analysis of microwave photonic spectral filters based on optical microcombs", Advanced Physics Research Vol. 3 (9) 2400084 (2024). DOI:10.1002/apxr.202400084.

276. Di Jin, Jiayang Wu, Junkai Hu, Wenbo Liu1, Yuning Zhang, Yunyi Yang, Linnan Jia, Duan Huang, Baohua Jia, and David J. Moss, "Silicon photonic waveguide and microring resonator polarizers incorporating 2D graphene oxide films", Applied Physics Letters Vol. 125, 053101 (2024). doi: 10.1063/5.0221793.

277. Jiayang Wu, Yuning Zhang, Junkai Hu, Yunyi Yang, Di Jin, Wenbo Liu, Duan Huang, Baohua Jia, David J. Moss, "Novel functionality with 2D graphene oxide films integrated on silicon photonic chips", Advanced Materials Vol. 36 2403659 (2024). DOI: 10.1002/adma.202403659.

278. Yuning Zhang, Jiayang Wu, Linnan Jia, Di Jin, Baohua Jia, Xiaoyong Hu, David Moss, Qihuang Gong, "Advanced optical polarizers based on 2D materials", npj Nanophotonics 1 (2024). DOI: 10.1038/s44310-024-00028-3.

279. Junkai Hu, Jiayang Wu, Wenbo Liu, Di Jin, Houssein El Dirani, Sébastien Kerdiles, Corrado Sciancalepore, Pierre Demongodin, Christian Grillet, Christelle Monat, Duan Huang, Baohua Jia, and David J. Moss, "2D graphene oxide: a versatile thermo-optic material", Advanced Functional Materials Vol. 34 2406799 (2024). DOI: 10.1002/adfm.202406799.

280. Di Jin, Wenbo Liu, Linnan Jia, Junkai Hu, Duan Huang, Jiayang Wu, Baohua Jia, and David J. Moss, "Thickness and Wavelength Dependent Nonlinear Optical Absorption in 2D Layered MXene Films", Small Science Vol. 4 2400179 (2024). DOI:10.1002/smsc202400179.

281. Andrew Cooper, Luana Olivieri, Antonio Cutrona, Debayan Das, Luke Peters, Sai Tak Chu, Brent Little, Roberto Morandotti, David J Moss, Marco Peccianti, and Alessia Pasquazi, "Parametric interaction of laser cavity-solitons with an external CW pump", Optics Express Vol. 32 (12), 21783-21794 (2024).

282. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Chaoran Huang, Jiayang Wu, Kun Xu, David J. Moss, and Xingyuan Xu, "Photonic RF Channelization Based on Microcombs", Special Issue on Microcombs IEEE Journal of Selected Topics in Quantum Electronics Vol. 30 (5) 7600417 (2024). DOI:10.1109/JSTQE.2024.3398419.
283. Y. Li, Y. Sun, J. Wu, G. Ren, X. Xu, M. Tan, S. Chu, B. Little, R. Morandotti, A. Mitchell, and D. J. Moss, "Feedback control in micro-comb-based microwave photonic transversal filter systems", IEEE Journal of Selected Topics in Quantum Electronics Vol. 30 (5) 2900117 (2024). DOI: 10.1109/JSTQE.2024.3377249.

284. Weiwei Han, Zhihui Liu, Yifu Xu, Mengxi Tan, Yuhua Li, Xiaotian Zhu, Yanni Ou, Feifei Yin, Roberto Morandotti, Brent E. Little, Sai Tak Chu, Xingyuan Xu, David J. Moss, and Kun Xu, "Dual-polarization RF Channelizer Based on Microcombs", Optics Express 32, No. 7, 11281-11295 / 25 Mar 2024 / (2024). DOI: 10.1364/OE.519235.

285. Aadhi A. Rahim, Imtiaz Alamgir, Luigi Di Lauro, Bennet Fischer, Nicolas Perron, Pavel Dmitriev, Celine Mazoukh, Piotr Roztocki, Cristina Rimoldi, Mario Chemnitz, Armaghan Eshaghi, Evgeny A. Viktorov, Anton V. Kovalev, Brent E. Little, Sai T. Chu, David J. Moss, and Roberto Morandotti, "Mode-locked laser with multiple timescales in a microresonator-based nested cavity", APL Photonics Vol. 9 031302 (2024). DOI:10.1063/5.0174697.

286. C. Mazoukh, L. Di Lauro, I. Alamgir, B. Fischer, A. Aadhi, A. Eshaghi, B. E. Little, S. T. Chu, D. J. Moss, and R. Morandotti, "Genetic algorithm-enhanced microcomb state generation", Special Issue Microresonator Frequency Combs - New Horizons, Nature Communications Physics Vol. 7, Article: 81 (2024) (2024). DOI: 10.1038/s42005-024-01558-0.