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We report the fabrication of a first electro-absorption modulated widely tunable DBR lasers (TEML) based on InGaAlAs multi-quantum well (MQW) material, which is superior than InGaAsP MQWs for the fabrication of both modulators and lasers. The device is fabricated by using butt-joint material growth technology and operates at a wavelength of 1.5 μm. An over 12 nm wavelength tuning range can be obtained. The characteristic temperature of the device is 83 K, which is notably higher than that for a laser based on InGaAsP MQWs. At 25°, the electro-absorption modulator (EAM) of the device has a small signal modulation bandwidth exceeding 27 GHz, which is notably higher than the bandwidth for a TEML device having the same structure but InGaAsP MQW active material. At 25 Gb/s NRZ data modulation, to achieve 10E-10 bit error rate (BER), the power penalty after 5 and 10 km fiber transmission are 1 and 3 dB, respectively. The device is a promising low-cost light source for future high-capacity wavelength division multiplexing (WDM) optical communication systems.

A novel wavelength triplexer based on Channel-Shaped Multimode Interference (C-MMI) structures on the InP platform is proposed for multi-channel integration compatibility in a 50G passive optical network (PON) system. Performance analysis of the proposed device is carried out by using the 3D Beam Propagation Method (3D-BPM), which shows excellent properties with insertion loss < 0.5 dB and low crosstalk < −14 dB for the 1342 nm in the Original band (1260–1360 nm), 1490 nm in the Short wavelength band (1460–1530 nm), and 1577 nm in the Long wavelength band (1565–1625 nm), also known as the OSL wavelengths band. Furthermore, the passbands of the three downlink channels of 1342 nm, 1490 nm, and 1577 nm, reach 14 nm, 20 nm, and 64 nm, respectively, which is wide enough to meet the 50G PON optical line terminal (OLT) requirement. Additionally, the proposed device is extremely compact with a total length of only 448 μm, making it attractive in the monolithic integrated laser chip and OLT packaged module.

The inert radioactive gas radon-222, ubiquitous in the environment, is the first cause of lung cancer in non-smokers and a powerful asset to trace geological fluids and constrain atmospheric transport models. In all of these applications, radon flux (RF) from the ground needs to be estimated. However, obtaining a large-scale representative estimate of RF in continental land is a challenging task and a starting basis is to focus on large countries in the world. Here, we collected a total of 2622 direct RF measurements carried out in continental China from 1988 to 2021 using 69 publications in a 494-document pool. Over the whole dataset, the RF results were classified into geographical provinces, time periods and substratum types. Mean RF values yield 180±32, 36.9±4.8, 31.1±1.0, 66.1±1.6 and 1510±100 mBq m−2 s−1 in metamorphic and igneous (n=71), sedimentary (n=24), Quaternary (n=585), faulted areas (n=832) and uranium-related sites (n=898), respectively. Considering geology only, mean RF for China (66±11 mBq m−2 s−1) is larger than most large-scale estimates worldwide. To account for the distribution of soil thickness, RF values were extrapolated to representative soil thickness values per lithology using a scaling law inferred from natural sites. The inferred corrected mean RF for China yields 20.2±6.1 mBq m−2 s−1, corresponding to a total radon-222 emission of (191±43)×109 Bq s−1, and appears compatible with available large-scale estimates in Europe or at global scale. Potential sources of systematic bias and variability, such as vegetation cover, meteorological and seasonal effects, remain. The contribution of urban areas, estimated for the first time, was found significant. Our study suggests future research directions to better constrain the RF source to the atmosphere in China, and, more generally, to extract robust global-scale representative RF values from direct RF measurements.

National innovation is important for driving a country’s long-term economic growth and identifying social problem solutions. However, while some countries maintain favorable policies for promoting innovation, some seem to fall behind. In addition, a country’s innovation policies may change over time. In this study, we examine when and why policy-makers change innovation policies. Specifically, we draw on performance feedback theory to theorize how aspirations for national innovation may affect a country’s innovation policies. Based on the data of member states of the Organization for Economic Co-operation and Development (OECD), we find that when national innovation output is below the level of aspiration, policy-makers improve policies to attract private R&D investment (expand public R&D investment) if national private R&D investment (national public R&D investment) is also below the aspiration levels. However, the shortfalls in national private or public R&D investment alone do not motivate policy-makers to take any action. Such findings provide strong implications for policy-makers and innovators in both the private and public sectors.

A differential multi-frequency laser Doppler velocimetry is demonstrated, utilizing the synchronized multimode of a mode-locked distributed Bragg reflector laser. This scheme enables the simultaneous detection of multiple Doppler frequency shifts. Multiple differential Doppler shifts of 0.6 Hz, 1.3 Hz, and 1.9 Hz are obtained, with an average speed of 3.677 mm/s and a standard deviation of 0.122 mm/s, demonstrating a cross-referenced velocity measurement capability. The measurement results are also compared with the dual-frequency laser Doppler velocimetry scheme using electro-optical modulation.

A tunable narrow-linewidth photonic terahertz (THz) carrier generation scheme using a distributed-Bragg-reflector-based mode-locked laser diode (MLLD) with optical feedback and mode filtering technique is proposed and experimentally demonstrated. Photonic terahertz carrier covering the D-band (110–170 GHz), and H-band (220–325 GHz) was obtained. With the assistance of the feedback loop, the optical linewidth of the MLLD was reduced from MHz to kHz level, and the heterodyning photonics carrier linewidth was reduced from 121.7 kHz to 2.1 kHz, satisfying the linewidth tolerance in the THz communication system with high-order modulation formats.

Internet-based companies such as Amazon, Facebook, and Tencent hold an enormous amount of consumer data that are utilized to create business value via big data analytics. Although some companies use big data to provide professional services, such as targeted advertising and product recommendations, according to the current CAS, IFRS, and U.S. GAAP accounting standards, these assets are not recognized as assets since they are generated internally. This paper starts with a discussion of how Amazon, Facebook, Tencent, and Walmart use big data to create value for their businesses and then argues why it makes sense to recognize big data as intangible assets. Possible methods of data asset evaluation and their implications for business managers are also explored.

The optical feedback tolerance (OFT) of a distributed Bragg reflector (DBR) laser was investigated experimentally. The static and modulation performance of the DBR laser under optical feedback was examined by evaluating its relative intensity noise (RIN) and bit error rate (BER). It is shown that the OFT of the DBR laser is closely related to its peak wavelength detuning relative to the Bragg wavelength. A high tolerance to optical feedback was demonstrated, both in the continuous wave (CW) and the direct modulation (DM) states, when the DBR laser was red-detuned relative to the Bragg wavelength. The excess RIN induced by optical feedback was well suppressed to a level of −140 dB/Hz at a feedback level of −9 dB in the CW state. In a 10 Gbps direct modulation state, bit error rates (BER) below 1 × 10−9 and 3 × 10−7 were obtained under a feedback level of −15 dB and −9 dB, respectively, for the case of back-to-back transmission. After 20 km fiber transmission, the BER still maintained below 1 × 10−7 under a feedback level of −15 dB, with a power penalty of less than 1 dB.

We report an electro-absorption modulator integrated with a distributed feedback Bragg laser fabricated by butt-joint technology. The lasing wavelength of the EML laser was 1311.71 nm, the output power was 10.04 mW when the current of the DFB section was 100 mA, the side-mode suppression ratio was greater than 50 dB, and the small-signal bandwidth was 29.40 GHz when the bias voltage of the modulator was −2 V. A 50 Gb/s data transmission over a single-mode fiber of up to 10 km was realized, which could be used as a light source for 50 G passive optical network systems.

A frequency-tunable and low-timing-jitter O-band regenerative mode-locked laser (RMLL) using an optoelectronic oscillation configuration and electric-controlled yttrium iron garnet (YIG) bandpass filter is proposed and demonstrated. In this scheme, an O-band semiconductor optical amplifier (SOA) is used as the gain medium of the RMLL to realize a dispersion-management-free operation during frequency tuning. With a polarization-maintaining fiber loop of 300 m, we produced a robust frequency-tunable RMLL with a pulse width below 16 ps, phase noises below −123 dBc/Hz at a 10-kHz frequency offset from the carrier frequency, and timing jitter less than 12 fs (integrated in 1-kHz to 1-MHz range) in a frequency tuning range between 10 GHz and 22 GHz.

We present data transmission using a directly modulated distributed Bragg reflector (DBR) laser having an integrated Ti thin film heater in the DBR section and butt-jointed InGaAsP as DBR material. By combining DBR current tuning and thermal tuning effects, an over 16 nm wavelength tuning range is obtained. 5 Gb/s data transmissions are conducted at up to 25 km distance and different wavelengths. In the fabricated device, the butt-jointed InGaAsP material is also used for the formation of an integrated photodiode for monitoring the light power of the device.

Synchronized dual-wavelength narrow-linewidth lasers and a wideband frequency-tunable optoelectronic oscillator are simultaneously realized using mutual-injection-locked distributed feedback (DFB) lasers. The two laser modes serve as the seeding light and a microwave photonic filter for the optoelectronic oscillation. Mutual-injection locking between the two DFB lasers through a delay fiber loop results in synchronized narrow-linewidth operation. Microwave tuning from 19 to 41 GHz has been obtained through thermal-tuning of the DFB lasers, with the single-sideband phase noises below -100 dBc/Hz at a 10-kHz frequency offset from the carrier. Laser linewidth has been reduced from several-MHz to kHz with a linewidth reduction factor over 104.

With the deployment of the fifth generation of mobile networks (5G), 25 and 100 Gb/s directly modulated lasers and modules will become the mainstream optical transmitters. A directly modulated InGaAlAs/InP distributed Bragg reflector (DBR) laser is fabricated by butt-joint technology. A 25 Gb/s data transmission over a single-mode fiber of up to 10 km is demonstrated, and a wavelength tuning range of 14.28 nm is achieved through injection current tuning of a DBR section and temperature control of a thermoelectric cooler (TEC), which is the best candidate of colorless light sources for wavelength-division-multiplexed passive optical network (WDM-PON) systems.

The rapid progress of optical fiber communication makes it become the key technology for the information society.The active and passive optoelectronic devices are the foundation of the optical communication.The progress and development trend of the key active optoelectronic devices were reviewed,including DFB laser,photonic integrated circuit,980 nm high power laser for EDFA pumping,compound semiconductor photodetector and Si-based long wavelength photodetector.

We report a low-cost arrayed waveguide grating (AWG) based mode-locked semiconductor laser designed for multichannel synchronous ultrashort pulse generation. Both the fabrication process and chip characterization results are discussed in detail. By deploying a bundle active-passive photonic integration technique, only one regrowth step is required to monolithically integrate a semiconductor optical amplifier array, an AWG, and a common saturable absorber on a single InP substrate. Combined with a shallow ridge waveguide structure common for both active and passive sections and formed in a single dry etching process, our process allows the fabrication of the monolithic photonic integrated circuit chip in a much simplified process. The fabricated device demonstrated multichannel mode-locking operation at a repetition frequency of 4.1 GHz in a fundamental mode-locking regime under both passive mode-locking and synchronous hybrid mode-locking conditions. Timing jitter as low as 1 ps was obtained, and preliminary pulse chirping characteristics were analyzed by a frequency-resolved optical gating technique. The exhibited performance makes our device a promising candidate as a multichannel ultrashort pulse optical source for future cost-effective high-speed optical networking and signal processing applications.

Modulation bandwidth enhancement of directly modulated semiconductor lasers (DMLs) has attracted broad interest to accommodate the tremendously growing demand for network traffic. In this paper, a monolithically integrated mutually coupled (IMC) laser for the O-band is demonstrated both numerically and experimentally. The direct modulation bandwidth was enhanced utilizing a photon–photon resonance (PPR) effect based on the mutual injection-locking technique. The IMC laser consisted of two distributed feedback (DFB) laser sections with a semiconductor optical amplifier (SOA) section in between. The relationship between the PPR frequency and SOA length was analyzed numerically to achieve a flat modulation response by optimizing the SOA length. Then, an enhanced 3-dB bandwidth of 38.7 GHz was realized experimentally, a nearly threefold enhancement over the modulation bandwidth of a solitary DFB laser at the same bias. Moreover, clear open eyes up to 40 Gb/s transmission over a 25-km single-mode fiber were achieved. Although the dynamic extinction ratio of the eye diagram was 1.1 dB, it can be further improved by increasing the mutual injection locking range of the IMC laser.

A widely tunable optoelectronic oscillator (OEO) based on a directly modulated monolithic integrated dual-mode amplified feedback laser (AFL) is proposed and experimentally demonstrated. In this OEO scheme, the functions of the laser source, the intensity modulator, and the tunable high- $Q$ RF filter are all realized through an AFL chip. On one hand, the beating frequency of the two modes defines the central oscillating frequency, which functions as an active tunable microwave photonic filter. On the other hand, by taking advantage of the photon–photon resonance, the laser has high modulation efficiency around the beating frequency that is far beyond the intrinsic modulation bandwidth of the lasers. It eliminates the use of high-speed external modulators and dramatically reduces the threshold gain of the oscillator. By tuning the injection currents of the laser sections, stable microwave signals that are continuously tunable from 28 to 41 GHz with signal-sideband phase noise below −106 dBc/Hz (at a 10-kHz offset) and threshold electronic gain no more than 27 dB are experimentally realized.

We demonstrate a widely tunable and high-modulation-bandwidth distributed Bragg reflector (DBR) laser. With the selected butt-joint material (λg = 1.44 μm) and butt-joint angle (45°) for the grating section, a widely tuning range of 13.88 nm with 19 consecutive channels is obtained for the two-section DBR laser. Furthermore, a small-signal modulation bandwidth of 16 GHz with in-band flatness of ±3 dB is realized at 10 °C. A uniform modulation bandwidth of more than 13 GHz is obtained for ten consecutive channels at 25 °C. Meanwhile, the DBR laser shows a high linearity, with an input 1-dB compression point of 17 dBm and an input third-order intercept point of 30 dBm at 13 GHz.

An Indium-phosphide-based monolithically integrated photonic chip comprising of an amplified feedback laser (AFL) and a photodetector was designed and fabricated for on-chip photonic and microwave generation. Various waveforms including single tone, multi-tone, and chaotic signal generation were demonstrated by simply adjusting the injection currents applied to the controlling electrodes. The evolution dynamics of the photonic chip was characterized. Photonic microwave with frequency separation tunable from 26.3 GHz to 34 GHz, chaotic signal with standard bandwidth of 12 GHz were obtained. An optoelectronic oscillator (OEO) based on the integrated photonic chip was demonstrated without using any external electrical filter and photodetector. Tunable microwave outputs ranging from 25.5 to 26.4 GHz with single sideband (SSB) phase noise less than −90 dBc/Hz at a 10-kHz offset from the carrier frequency were realized.