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Abstract The proliferation of computation-intensive technologies has led to a significant rise in the number of datacenters, posing challenges for high-speed and power-efficient datacenter interconnects (DCIs). Although inter-DCIs based on intensity modulation and direct detection (IM-DD) along with wavelength-division multiplexing technologies exhibit power-efficient and large-capacity properties, the requirement of multiple laser sources leads to high costs and limited scalability, and the chromatic dispersion (CD) restricts the transmission length of optical signals. Here we propose a scalable on-chip parallel IM-DD data transmission system enabled by a single-soliton Kerr microcomb and a reconfigurable microring resonator-based CD compensator. We experimentally demonstrate an aggregate line rate of 1.68 Tbit/s over a 20-km-long SMF. The extrapolated energy consumption for CD compensation of 40-km-SMFs is ~0.3 pJ/bit, which is calculated as being around 6 times less than that of the commercial 400G-ZR coherent transceivers. Our approach holds significant promise for achieving data rates exceeding 10 terabits.

On-chip optical dispersion compensation and wavelength division multiplexing/demultiplexing (WDM) are highly demanded functions for optical communications. In this work, we proposed a multichannel dispersion compensation structure based on chirped multimode grating within a counter-directional coupler (CMG-CDC). Simultaneous wavelength division multiplexing and demultiplexing can be realized within a compact footprint. A device design for four-channel CMG-CDC at the C/L (1530–1565 nm) band is presented with a channel spacing of 20 nm assisted by a grooved multimode waveguide structure. The average dispersion for all channels is about −2.25 ps/nm with a channel bandwidth of about 3.1 nm. The device is highly compact and highly scalable, which makes it rather convenient for increasing the group velocity dispersion (GVD) and channel number, indicating flexible applications for versatile systems, including typically coarse wavelength division multiplexer four-lane (CWDM4) transceivers.

Silicon photonic optical phased arrays are promising solutions for solid-state LIDAR. But the nonlinear absorption significantly saturates the optical power in the waveguides at 1.5-μm wavelengths. Besides, the high refractive index contrast of silicon grating exhibits a strong diffraction strength of the antenna, which results in a limited aperture of the device. These ultimately place a limit on the detection accuracy and reach. Here, a shallow etched two-dimensional subwavelength grating structure is proposed to improve the efficiency and aperture of the waveguide antenna. A reduction of diffraction strength is achieved via nanohole structure instead of conventional grating lines. Thus, a millimeter-long optical antenna is demonstrated with a peak efficiency of 71%. The far-field diffracted beam width of 0.035° and vertical field-of-view of 17.5° are achieved within 100 nm wavelengths range from 1.95 μm to 2.05 μm. The operation at 2-μm waveband also guarantees better eye-safety and significantly reduces the nonlinear absorption in silicon waveguide compared with conventional 1.5-μm band.

The transparent window in optical fiber at 2-μm waveband enables a huge potential for fiber optical communications. Intensive efforts have been devoted to pursuit of photonic devices in this new band. The arrayed waveguide grating (AWG) is one of the key components for various functionalities like wavelength multiplexer, optical filter, spectrometer and so forth. However, the integrated and wavelength tunable AWG has not been realized in the 2-μm wavelength range yet. Here, we demonstrate an 8-channel thermo-optic tunable AWG at 2 μm via silicon photonic multi-project wafer shuttle run. The device is fully compatible with standard foundry fabrication process without customization. The TiN heater is designed for uniform waveguide heating and wavelength detuning. Experiments show that the fabricated AWG has a dense channel spacing of 1.6 nm and a minimum insertion loss of 6.1 dB. The wavelength tuning efficiency is measured to be 6.4 nm/W.

Optical technology is one of the key technologies that have been widely used for communication, computing and sensing [...]

Nonlinear distortion for single-sideband (SSB) signals will significantly reduce the performance of Kramers–Kronig (KK) receiver-based optical transmission. In this work, we present a proof-of-concept study of stimulated Brillouin scattering (SBS)-induced nonlinear distortion for 10 Gbaud and 28 Gbaud SSB QAM16 transmission over 80 km standard single mode fiber (SSMF) based on a KK receiver. Significantly reduced bit error rate (BER) has been experimentally observed due to the SBS and the threshold of SBS at about 7 dBm is detected for such an 80 km SSMF link. With left sideband (LSB) modulation of SSB, together with optical filtering, reduced SBS nonlinear distortion has been achieved with ~2 dB power tolerance improvement. The results reveal an important issue of SBS-induced nonlinear distortion, which would be of great significance for KK receiver-based optical transmission applications.

On-chip mode-division multiplexing has many challenges including crosstalk, losses, and footprint. Here the authors use a nanohole metastructure to create multiplexed bends and crossings for photonic data communications circuit routing with high density that combats these challenges.

In this paper, dyadic probabilistic shaping (PS) for pulse amplitude modulation (PAM) has been investigated and experimentally demonstrated for intensity-modulation and direct-detection optical interconnection systems. Improved achievable information rate can be obtained under the condition of limited bandwidth and signal-to-noise ratio (SNR). Theoretical investigations of generalized mutual information have been performed. 0.61- and 1.74-dB SNR gains by dyadic PS can be obtained for PAM-4 and PAM-8, respectively, to achieve error free assuming optimal 20% FEC. Meanwhile, such fixed distributions can offer a considerably broad SNR range (10.3-16.7 dB for PAM-4 and 13.4-24.6 dB for PAM-8) with positive gain. Moreover, experimental investigations have been carried out over optical multimode fiber (MMF) links at 850 nm using a commercial-product-level vertical-cavity surface-emitting laser (VCSEL) chip. PAM-8 signaling by PS at the net rate of 75 Gb/s has been realized with 100-m OM3 fiber transmission. Energy efficient signaling can be achieved with up to 46% theoretical power reduction by PS. Experimentally, we obtained 16% reduction of optical power for the VCSEL-MMF optical link. The dyadic distribution of PS, due to its simplicity of coding, as well as considerable shaping gain and energy efficiency, is expected to be an opportune solution for the cost-sensitive short-reach scenarios.

We demonstrate the absorption-based fiber humidity sensors working near 1950 nm wavelength which is a strong water absorption peak. No additional coating of humidity-sensitive material is needed for the proposed relative humidity (RH) fiber sensors. Two sensor structures including a taper fiber and a microfiber knot resonator are fabricated. For the taper fiber sensor, upto 0.18 mW/% RH sensitivity has been achieved via direct power measurement. For the fiber knot sensor, the RH variations induce both extinction ratio change and wavelength shift. The optical spectra of the fiber knot resonator under different RH are measured, and the extinction ratio and wavelength shift sensitivity are measured to be 0.034 dB/% RH and 10 pm/% RH, respectively. The response time for the tapered fiber is 1.13 s for RH increasing from 28.6% to 53.4% and 2.27 s for the reverse operation. The microfiber knot sensor can respond in 0.8 and 1.55 s accordingly. The sensor performance for the two structures is also investigated under different temperatures from 25 °C to 45 °C and the results indicate negligible impact from the temperature variations. We believe the simple fabrication and low cost of the sensor will make it potential and practical for the RH measurement.

As for vertical-cavity surface-emitting lasers (VCSEL)-based optical pulse amplitude modulation (PAM) interconnection system, apart from the universal signal distortions like Gaussian noise and fiber dispersion, direct modulation of VCSEL specially induces level nonlinearity and level-dependent noise. To mitigate these two specific distortions in VCSEL-based link, a k-means assisted PAM-4 signal receiver including equalization and soft decision (SD) is proposed. Based on learned mean values and standard deviations for individual levels through k-means approach, probability density function of nonlinearly distorted PAM-4 symbols can thus be approximated more precisely than conventional SD, leading to improved decision performance. In addition, depending on k-means result, least means square (LMS) equalization with adapted levels can converge to a lower error value than conventional LMS, thanks to level nonlinearity mitigation. Consequently, by using proposed k-means equalization and SD, improved signaling performance can be obtained by mitigating the level nonlinearity and level-dependent noise. Both simulation and experiment are performed for evaluating the proposed method in a 100-Gb/s VCSEL-MMF PAM-4 optical interconnection system, by comparing with conventional means.

The 2 μm waveband is considered to have great potential in optical communications. Driven by the demands on high-performance functional devices in this spectral band, various integrated photonic components have been demonstrated. In this work, an analog and digital topology optimization method is proposed to design an ultra-broadband polarization beam splitter at the 2 μm waveband. Within an optical bandwidth of 213 nm, the excess losses of TE and TM modes are 16.5 dB and 18.1 dB. The device has a very compact footprint of only 2.52 µm × 5.4 µm. According to our best knowledge, this is a benchmark demonstration of an ultra-broadband and ultra-compact polarization beam splitter enabled by the proposed optimization method.

Optical communication refers to the communication mode with optical signal as a carrier [...]

We demonstrate integrated 1 × 4 power splitters at 2-μm spectral range with arbitrary power-splitting ratios. The devices are based on digital meta-structures that are designed by algorithm. Four devices with split ratios of 1:1:1:1, 2:2:1:1, 2:2:2:1, and 4:3:2:1 are inversely designed to conceptually prove the capability of arbitrary split ratios. Up to four design objectives including both efficiency and power ratios between the four outputs of each device have been jointly optimized. The total transmission efficiencies of all the algorithm-optimized splitters are above 80%, which is predicted by simulations. The power ratios are well consistent with the design targets as well. Then, the devices are fabricated on silicon-on-insulator platform with the device footprint of only 3.6 μm × 3.6 μm. The fabricated splitters are characterized at wavelength range from 1945 to 1975 nm. The total transmission efficiencies of all the splitters are measured to be higher than 70%, and the power ratios agree with the simulation results.

Chromatic dispersion engineering of photonic waveguide is of great importance for Photonic Integrated Circuit in broad applications, including on-chip CD compensation, supercontinuum generation, Kerr-comb generation, micro resonator and mode-locked laser. Linear propagation behavior and nonlinear effects of the light wave can be manipulated by engineering CD, in order to manipulate the temporal shape and frequency spectrum. Therefore, agile shapes of dispersion profiles, including typically wideband flat dispersion, are highly desired among various applications. In this study, we demonstrate a novel method for agile dispersion engineering of integrated photonic waveguide. Based on a horizontal double-slot structure, we obtained agile dispersion shapes, including broadband low dispersion, constant dispersion and slope-maintained linear dispersion. The proposed inverse design method is objectively-motivated and automation-supported. Dispersion in the range of 0–1.5 ps/(nm·km) for 861-nm bandwidth has been achieved, which shows superior performance for broadband low dispersion. Numerical simulation of the Kerr frequency comb was carried out utilizing the obtained dispersion shapes and a comb spectrum for 1068-nm bandwidth with a 20-dB power variation was generated. Significant potential for integrated photonic design automation can be expected.

Distributed Raman amplifier (DRA) has been widely studied in recent decades because of its low noise figure and flexible gain. In this paper, we present a novel scheme of DRA with broadband amplified spontaneous emission(ASE) source as pump instead of discrete pump lasers. The broadband pump is optimized by machine learning based inverse design and shaped by programmable waveshaper, so as to realize the ultrafine, dynamic and arbitrary gain spectrum shaping of Raman amplification. For the target of flat gain spectrum, the maximum gain flatness of 0.1086 dB is realized based on the simulation results. For the target of arbitrary gain spectrum, we demonstrate four gain profiles with maximum root mean square error (RMSE) of 0.074 dB. To further measure the performance of arbitrary gain spectrum optimization, the probability density functions (PDF) of RMSE and Errormax are presented. Meanwhile, the numeral relationship between the bands of broadband pump and signal is also explored. Furthermore, this work has great application potential to compensate the gain distortion or dynamic change caused by other devices in communication systems.

Dispersion engineering of microresonators is very important for applications, such as optical comb generation which desires wideband flat and small dispersion. In this paper, dispersion investigation has been carried out for whispering gallery mode (WGM) microresonators fabricated by laser micromachining. The dispersion properties of WGM microresonators fabricated by CO2 and femtosecond lasers have been comprehensively studied by finite element method for different geometries. Significantly flattened dispersion curves have been obtained for both microresonators fabricated by CO2 laser and femtosecond laser with optimized geometries. The belt-like resonator fabricated by femtosecond laser has better flattened small dispersion which is only between 0 and 4 ps/(nm · km) within the wavelength range from 1300 to 1800 nm, comparable to that of a zero dispersion flattened fiber. The results are of great significance for guiding the WGM microresonator fabrication for optical comb generation applications.

Aluminum nitride (AlN) is an emerging platform for a wide range of on-chip applications. One promising feature is that both the second- and third-order nonlinearities are available in crystalline AlN waveguides. We design an AlN slot waveguide with a flat and low dispersion over an ultrawide spectral range from near-infrared to mid-infrared. A dual-slot structure is designed and the flattened group velocity dispersion within -13 and +11 ps/(nm·km) over 2000-nm-wide bandwidth with three zero dispersion wavelengths is achieved. The impacts of the structural parameters are analyzed in detail and the phase-matching condition in four-wave mixing process is investigated as well. A 3-dB conversion bandwidth of 1200 nm and -28-dB conversion efficiency are predicted in a 1-cm-long horizontal dual-slot AlN waveguide with the pump power of 2 W.

It is well known that optical fiber communications support the global communication networks nowadays, which originates from Charles K [...]

Advanced modulation formats with intensity modulation and direct detection (IM/DD) have shown promise in a short-reach optical communication system like data center interconnect. However, the conventional fiber transmission spectral window is mostly located at 850, 1310, and 1550 nm. Here, we experimentally demonstrated an amplifierless IM/DD link at the 2-μm spectral band. The signal is encoded with pulse amplitude modulation (PAM) and 3-D carrier-less amplitude and phase modulation (3-D-CAP). The encoded signal is transmitted through a 100 m-long solid-core fiber designed for single mode at 2-μm. We achieve a transmission with bit-rate of 40 Gbit/s using PAM-4 and 24 Gbit/s using CAP16. The measured bit error rates of both formats are below the forward error correction (FEC) limit of 3.8 × 10-3. This study is the first demonstration of PAM4 and CAP transmission at 2-μm, and the results show a significant potential of advanced modulation for 2-μm optical communication.

All-optical signal processing based on four wave mixing (FWM) in a highly nonlinear fiber (HNLF) to enhance the sensitivity of a fiber sensor is demonstrated and comprehensively reviewed in this paper. The principle is based on the frequency chirp magnification (FCM) by FWM. Degenerated FWM, cascaded two-stage FWM and pump-pulsed FWM with optical parametric amplification (OPA) are experimentally utilized for magnifying the frequency chirp. By using the pump pulse modulation to increase the peak power, OPA can be induced with the use of a dispersion-optimized HNLF. Therefore, ultra-highly efficient FWM can be realized due to the high peak power and OPA. By using the fiber Bragg grating (FBG) laser as the FWM pump, the wavelength drift of the FBG can thus be magnified due to the FCM. We obtain a sensing performance of 13.3 pm/με strain sensitivity and 141.2 pm/°C temperature sensitivity for a conventional FBG, which has an intrinsic strain sensitivity of only ~1 pm/με and an intrinsic temperature sensitivity of only ~10 pm/°C, respectively.

We demonstrate a novel method for obtaining high spatial resolution optical frequency domain reflectometry (OFDR) utilizing recirculating frequency shifter for broadening the optical frequency sweeping. Twelve times broadened optical frequency sweeping is achieved. We obtain 0.97 cm spatial resolution over 710-m measurement range with modulation frequency sweeping span of 882 MHz. Such a spatial resolution corresponds to a frequency sweeping span of 10.31 GHz. The experimental results indicate that the measurement range can be extended to 10 km, based on the proposed method.