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A laser scanner is a powerful tool for 3-D geometry measurement. The amplitude-modulated continuous-wave (CW) laser scanner, which benefits from high accuracy measurement operating in the intermediate range, is suitable for high-precision 3-D industrial inspection. However, due to the limited dynamic range, laser scanners suffer from data loss and deterioration. This poses challenges for 3-D modeling, conversion of 3-D point cloud data to 3-D solid data, and so on. We chose the operation wavelength in the 1530-nm region. The dynamic range of an amplitude-modulated CW laser scanner was enhanced by the implementation of a combination of a low-noise and high-gain optical preamplifier and p-i-n photodiodes, a pellicle beamsplitter, and automatic gain control using a polarization-independent high-speed variable optical attenuator based on electrooptic ceramics in the receiver. In these manners, receiver sensitivity of −72 dBm was achieved and receiver dynamic range of around 37 dB was realized. We expect that our results contribute to high-definition industrial inspection for Industry 4.0.

Frequency modulated continuous-wave (FMCW) radar systems suffer from permanent leakage from the transmitted signal into the receiver, which will reduce the dynamic range of the system and degrade the receiver sensitivity. Herein, a photonic-assisted leakage cancellation method for a wideband FMCW radar transceiver is proposed and experimentally demonstrated. At the remote antenna unit (RAU), a local oscillator (LO) signal, and a leakage signal are converted to optical signals with orthogonally polarization states by using a polarization-division-multiplexed Mach–Zehnder modulator (PDM-MZM). After the transmission of 10 km single mode fiber (SMF), the leakage signal is cancelled by using a variable optical attenuator (VOA), a variable optical delay line (VODL), and a balanced photodetector (BPD) at central office (CO). Compared with other analog cancellation methods, the proposed one has wider sweeping bandwidth and simpler structure. In the experiment, the LO signal and leakage signal are emulated by using an arbitrary waveform generator (AWG), a power divider, and two different length radio frequency lines. Then, experimental results show that a leakage cancellation depth of 17.5 dB at the carrier frequency of 15 GHz with a sweeping rate of 2 GHz/4 us is achieved.

In the proposed work, we fabricated a liquid crystal cladding waveguide-based variable optical attenuator. The waveguide is realized using a negative photoresist (AZ15nXT) core on indium tin oxide (ITO) coated glass substrates. The device is characterized at two wavelengths, 633 nm and 520 nm. The transverse magnetic (TM) modes get attenuated on the application of the electric field across the waveguide. The maximum extinction ratio achieved is 6.85 dB.

In this paper, we propose a radio-over-fiber system with no filters and generate 80 and 160 GHz millimeter (mm) waves via two Mach–Zehnder modulators (MZMs). The two MZMs, biased at the maximum transmission point, are used to suppress odd-order sidebands. By controlling the phase difference between the RF driving signal of the two MZMs, the ± ( 4 n − 2 ) -order is canceled. By adjusting the optical attenuator and phase shifter, the 0-order sideband is canceled, so only the ± 4 n -order sidebands are left. The simulation results show that using a 10 GHz RF signal to drive the MZMs, we obtain an 80 GHz mm wave signal with a 36.59 dB optical sideband suppression ratio (OSSR), a 30.27 dB radio frequency sideband suppression ratio (RFSSR), and a 160 GHz mm wave signal with a 30.34 dB OSSR and 24.77 dB RFSSR. The results are consistent with the theoretical analysis. Because no optical filter is employed and only two MZMs are used, the system exhibits a simple structure, good performance and is low cost.

A novel switchable multi-wavelength erbium-doped fiber laser based on random distributed feedback is demonstrated in this paper. Based on loop mirror to form a half-opened laser cavity, typical random laser radiation is achieved with an obvious threshold behavior as a function of pump power. Switchable multi-wavelength lasing operation is also achieved by changing attenuation value through the variable optical attenuator. Due to the efficient gain from the pumped erbium-doped fiber, a low threshold power of 22 mW is achieved, which is much lower in magnitude than that of previously reported conventional random fiber lasers.

A switchable multi-wavelength fiber laser with tunable wavelength spacing is proposed. It is based on a structure filter composed of a phase-shifted fiber Bragg grating (PSFBG) and a Mach-Zehnder interferometer (MZI), and the MZI is fabricated by splicing a section of polarization-maintaining fiber with two segments of multi-mode fibers. By adjusting the variable optical attenuator in the cavity and slightly changing the temperature, stable single-, dual-, triple- and quadruple-wavelength emissions can be obtained. The minimum wavelength spacing of adjacent peaks is 0.176 nm, and the maximum is 17.86 nm. The laser line emissions can be switched from 1527.684 nm to 1550.224 nm with optical signal to noise ratio of more than 50 dB. The maximum wavelength fluctuation of the fiber laser is less than 0.025 nm over 50 min. When the strain applied to the filter is changed, the tunable wavelength spacing can be achieved. The wavelength spacing of dual-wavelength laser can be continuously tuned from 21.82 nm to 22.69 nm by applying strain of 0–258 μe to the filter.

In this paper Ridge, S-bend waveguide design and analysis has been performed for C-band using various materials like Silica (SiO 2 ), Silicon Nitride (Si 3 N 4 ), Barium Fluoride (BaF 2 ) and Titanium Dioxide (TiO 2 ). We have performed a comparative study and identified Si 3 N 4 as the most suitable material for silicon photonics platform based on lower insertion and propagation losses. Si 3 N 4 based ridge waveguide reduces insertion loss to 5.68dB and propagation loss to less than 1dB/cm. These designed waveguides will be used in variable optical attenuator. Here in this paper, we also propose a variable optical attenuator based on the configurations of a Si 3 N 4 -BaF 2 and TiO 2 -Si 3 N 4 S-bend waveguides. The thermo-optic characteristics of Si 3 N 4 and BaF 2 materials are fully utilized for making variable optical attenuator (VOA). After performing software simulation, simulation results are verified with theoretical results. We get Optical attenuation of 1 to 50 dB with an applied electrical voltage of 0 to 20 V for length of 100 um device with low insertion loss.

A novel tunable Erbium-doped fiber ring laser (EDFRL) with a cascaded-chirped long-period fiber grating (C-CLPG) as a wavelength selection filter is proposed from the viewpoint of the sensor use, in which a variable optical attenuator (VOA) is employed as an intracavity loss modulator to change the oscillation wavelength region so that the resultant tuning wavelength range is widened. In the demonstrative experiment for temperature measurements, oscillation over the wavelength range of 12.85 nm (1557.62~1570.47 nm), which is more than three times range of the previously presented laser and is equivalent to 64 °C in terms of temperature change, was achieved, while a single-wavelength oscillation was maintained. In addition, a practical technique for realizing a temperature measurement by combining with the VOA control is also discussed.

We present the concept and design, and we report on the experimental performance of a broadband Variable Optical Attenuator (VOA) for integration with large-core rectangular multimode waveguides. Operation of an individual 221 mu m x 111 mu m optical waveguide channel employing a MEMS actuated dual-shutter to continuously modulate the intensity of the optical input signal is demonstrated experimentally. The MEMS actuated dualshutter is fabricated in a 211 mu m thick device layer of a Silicon-On-Insulator wafer by Deep Reactive Ion Etching. Electrostatic comb drive actuators allow a displacement of more than 63 mu m at 86 V, resulting in a continuously tunable attenuator efficiency of up to 99.97% at an operating wavelength of 532 nm with a reconfiguration time < 0.5 ms.

Passively mode-locked semiconductor lasers are promising for a wide variety of chip-scale high-speed and high-capacity applications. However, the phase noise/timing jitter of such light sources are normally high, which restricts their applications. A simple and low-cost chip-scale solution to address this issue is highly desired. In this work, a two-section GaSb-based passively mode-locked laser (MLL) emitting in the 2 µm wavelength band with a fundamental repetition frequency of ∼ 13.35 G H z is presented. Dramatic phase noise reduction is achieved through its hybrid integration with a silicon photonic circuit which provides chip-scale optical feedback to the MLL. Under a fixed laser bias condition, more than 50 × improvement of radio frequency linewidth to sub-kilohertz level is realized by carefully adjusting the feedback strength (via a p-i-n junction-based variable optical attenuator) and optical length of the feedback loop (via integrated heater on the silicon waveguide). The phase noise reaches − 113 d B c / H z at 1 MHz offset with integrated timing jitters of 274 fs (100 kHz to 100 MHz) and 123 fs (4 to 80 MHz). At the same time, the pulse-to-pulse jitter reaches as low as 7.8 fs/cycle. These values are record low for 2 µm passively mode-locked semiconductor lasers. Our results prove the feasibility of MLL noise reduction with the chip-scale hybrid III-V/silicon integration method, bringing low-noise light sources to the silicon platform. Moreover, this work also suggests the potential miniaturization of various other functional setups with the same method.

We propose a cost-effective method for temperature measurement range changing of the Ethernet-based optical fiber sensing system, and also show experimental results about the temperature measurement range changeability with a variable optical attenuator.

A tunable metamaterial (MM)-based silicon (Si) waveguide is presented that is composed of an MM nanodisk array on a Si-on insulator substrate. A significant modulation efficiency of transmission intensity could be realized by elevating individually or simultaneously the column number of MM nanodisks. For a convenient description, an MM-based Si waveguide with one, two, three, four, and five columns of MM nanodisks are denoted as MM-1, MM-2, MM-3, MM-4, and MM-5, respectively. Transmission intensity of MM-based Si waveguides could be switched between on and off states by driving different columns of MM nanodisks on the Si waveguide surface. Transmission intensities could be attenuated from 100% to 56%, 24%, 6%, 1%, and 0% for MM-1, MM-2, MM-3, MM-4, and MM-5, respectively, at the wavelength of 1.525 µm. Furthermore, the MM-5 device is exposed to an ambient environment with different refraction indices. It exhibits a linear relationship of resonance dips and refraction indexes. The proposed design of the MM-based Si waveguide provides potential possibilities in an optical switch, variable optical attenuator, and sensor applications.

A directly ghost imaging method based on a feedback loop is proposed. The image of an object is reconstructed directly by actual optical devices, rather than a post processing of a large number of data. A voltage-controlled optical attenuator and a voltage reverse amplifier are added to the ghost imaging system. The voltage-controlled optical attenuator is set in front of reference arm camera. The signal of the object arm, which is detected by the bucket detector, passes through the voltage inverting amplifier and is connected to the control port of the optical attenuator. Thus the reference speckles are controlled by the bucket signal, and a feedback loop is formed. By adjusting the exposure time of the reference arm camera, these devices complete a simple fluctuations correlation operation, and the image of the object is reconstructed directly via the reference arm camera. Results show that, by using cameras and detectors of common level, this new ghost imaging method can achieve the object image recovery within a time of less than one second.

A novel tunable and switchable Erbium-doped fiber ring laser (EDFRL) is constructed from the viewpoint of sensor applications. The laser consists of a cascaded-chirped long period fiber grating (C-CLPG) and a variable optical attenuator (VOA). The oscillation wavelength is used for sensing a measurand. As a result, wavelength range selecting over about 1557.57 ~ 1570.68 nm with the tuning range within ~5.6 nm is demonstrated, and the sensitivity of ~ −0.22 nm/°C is recorded.

Wavelength modulation spectroscopy (WMS) with second harmonic detection is an extremely effective technique to detect gases in site applications. However, the significant levels of nonlinear effects in a system give rise to high background signals that either limit detection sensitivity or distort the harmonic signals. This paper outlines the theory of WMS-involved background signals and focuses on the elimination of undesirable effects in the background. A real-time, long-distance methane sensor using a tunable diode laser near 1653.7 nm is developed to continuously monitor methane by using a variable optical attenuator to suppress the background. Trace methane detection experiments verify that the minimum detection limit of the system can be increased by 47.5 times compared to the traditional WMS method.

Free Space Optics (FSO) communication technology substantially increases its presence in the growing satellite constellations as well as for deep space applications. The current work provides an overview over a demonstration of deeper space optical links beyond Lunar distance, reaching planets Mars and Venus (that is partly accomplished in frame of ESA's Hybridised Optical/RF Payload Data Transmitter study). By means of Poisson point processes (PPPs), the introduced space-to-ground downlink is simulated in Matlab programming language and in a later phase, it is modeled with a self-developed laboratory testbed (implementing also different atmospheric effects and influences). In order to comply with CCSDS standards, the High Photon Efficiency (HPE) communication link relies on $N_{r}$ -array Superconducting Nanowire Single-Photon Detector (SNSPD) unit. Along with BER performance, the dependence on SNSPD's recovery time and array size as well as Pulse Position Modulation (PPM) order and adverse atmospheric conditions are investigated, plotted and verified. The consistence of the theoretical predictions with the real downlink are tested based on laboratory FSO testbed investigating the performance of a 2-array SNSPD receiver unit. Apart from the SNSPD, an approach with space-to-ground downlink emulator based on fibre-coupled Variable Optical Attenuator (VOA) and a few fixed attenuators, which reproduce a Poisson channel, is considered and analysed.

A spectrally tunable monochromatic integrating sphere photon source (ISPS) was built based on a laser driven plasma light source, a monochromator, an optical attenuator, and an integrating sphere. The wavelength of ISPS output photons can be tuned from 300 nm to 800 nm with a spectral bandwidth of 1 nm ~ 5 nm; the spectral optical radiant power into the integrating sphere can be adjusted over three decades through the optical attenuator; the diameters of the inner wall and the exit port of the integrating sphere are 100 mm and 50 mm, respectively. The spectral photon radiance of the ISPS can be measured by a photomultiplier-tube (PMT) based photon counter and two precision apertures. An integrating sphere was utilized in front of the PMT-based photon counter and the non-uniformity of the spectral optical radiant power responsivity was reduced to be ~0.5% over a 5-mm-diameter effective detection area. Two precision apertures were adopted to define the effective detection area and the solid angle extended for the field-of-view. The ISPS can be directly applied to calibrate the spectral photon radiance responsivity of a few-photon imaging system, which was demonstrated on a digital color camera and a focusing lens. The spectral photon radiance responsivity of a given imaging system can be effectively validated based on this ISPS apparatus.

Many quantum key distribution systems employ a laser followed by an optical attenuator to prepare weak coherent states in the source. Their mean photon number must be pre-calibrated to guarantee the security of key distribution. Here we experimentally show that this calibration can be broken with a high-power laser attack. We have tested four fiber-optic attenuator types used in quantum key distribution systems, and found that two of them exhibit a permanent decrease in attenuation after laser damage. This results in higher mean photon numbers in the prepared states and may allow an eavesdropper to compromise the key., 12 pages, 12 figures

Optical refractive index (RI) sensors exploiting selective co-integration of plasmonics with silicon photonics in Lab-on-achip configurations are expected to disrupt Point-of-Care (POC) diagnostics, delivering performance and economic breakthroughs. Propagating surface-plasmon-polariton modes offer superior sensitivity due to their extreme overlap with the surrounding medium. In parallel, low-loss photonics act as the hosting platform with which the plasmonic losses can be sustained while allowing for multiplexed layouts via in-plane SPP excitation schemes. However, merging plasmonics with silicon photonics in a cost-effective manner, requires a truly CMOS-compatible manufacturing process. Herein, we demonstrate experimentally, the highest bulk-sensitivity among all the plasmo-photonic interferometric RI sensors, while taking the leap forward in the development of a CMOS-manufactured plasmo-photonic sensing platform merging Si3N4 photonics and aluminum plasmonics. The proposed structure relies on a butt-coupled interface between Si3N4 waveguides and a 70 μm long plasmonic stripe, deployed in one branch of a Mach-Zehnder Interferometer (MZI) serving as the sensing transducer that detects local changes in the refractive index. The lower MZI arm (reference arm) exploits the low-loss Si3N4 platform to deploy a MZI-based variable optical attenuator followed by a thermo-optic phase shifter to optimize the sensor performance achieving resonance extinction ratio values at the MZI output of more than 35 dB. Experimental evaluation of a gold-based sensor revealed a bulk refractive index sensitivity of 1930 nm/RIU. In addition, we experimentally demonstrate that the proposed plasmo-photonic waveguide platform can migrate from gold (Au) to Aluminum (Al), demonstrating the first step towards a fully CMOS compatible plasmo-photonic interferometric sensor.

We design and simulate a robust integrated optical attenuator involving an air-filled trench and deep trench which is resilient to crosstalk. Further, a 50% more power efficient thermal phase shifter is presented on silicon platform.

The structure optimization for a binary reconfigurable true time delay lines (RTTDL) based on the Mach–Zehnder interferometer (MZI) switches is proposed. Firstly, the number of the variable optical attenuator (VOA), which is generally used to make up for the imperfectness of the MZI switch and improves the RTTDL ’s flatness of broadband amplitude response and the delay accuracy, is minimized. Meanwhile, by adopting a pair of photoelectric detectors (PD) between every two MZI switches for power monitoring, the initialization time can be greatly reduced owing to the realization of the parallel initialization. On the other hand, with the help of the PDs, a continuously adjustable delay scheme is put forward by adjusting the allocation ratio of the last MZI switch. The proof-of-principle calculations are carried out to verify the optimization. The results show that the proposed optimization not only reduces the power consumption, the optical link loss and the integration volume caused by the VOAs, but also solves the problem that the binary RTTDL has only discrete delay states.

Variable optical attenuation and optical modulation are essential operations in integrated photonic circuits. A new graphene plasmonic gap waveguide structure, which possesses the functions of variable optical attenuator and modulator, is proposed and numerically investigated. The propagation and attenuation modes of the structure can be realized by tuning the gate-voltage. The result shows that it can achieve great modulation depth per micrometer and the working frequency range of 8 THz or more for the variable optical attenuator and the modulator. It also has the advantages of high tolerance, large attenuation range/ modulation depth, wide bandwidth and high integration without crosstalk, which would be promising for high integrated optical circuits.

Based on the epsilon-near-zero (ENZ) effect of indium tin oxide (ITO), we numerically demonstrate a high efficiency ITO phase/intensity modulator by exploiting ultra-thin silicon strip waveguide configuration. Heavily n-doped indium tin oxide is used as the semiconductor together with p-doped silicon and hafnium oxide (HfO2) to form a MOS waveguide. Due to the special feature of the ultra-thin silicon waveguide structure, the propagating transverse electric (TE) mode is less confined to the silicon core and penetrates deeper into the cladding layer, which will enhance the interaction between the active material and the optical mode. The combination of the ultra-thin silicon strip waveguide and ITO material exhibits high modulation efficiency together with broad optical bandwidth. When the modulator operates as a phase modulator, the effective refractive index change can reach the value 8:95x10-3 for the light wavelength λ = 1550 nm when the applied voltage is 6 V. Thus, the phase shifter length which can induce a π phase shift is supposed to be only about 97 µm, giving a corresponding VπL of 0.58 V∙mm. The effective index change even keeps > 7:32 x 10-3 with the wavelength increasing from 1300 nm to 1800 nm, indicating the broad modulation bandwidth. Meanwhile, the modulator can also operate as a variable optical attenuator or an intensity modulator. The modulation depth (MD) is about 0.074 dB/µm at 9 V when the wavelength is 1550 nm. This device confirms electrical phase shifting in ITO enabling its use in applications such as compact phase shifters, sensing, and phased array applications for LiDAR.

A novel in-fiber Mach-Zehnder interferometer based on cascaded up-down-taper (UDT) structure is proposed by sandwiching a piece of polarization maintaining fiber between two single-mode fibers (SMF) and by utilizing over-fusion splicing method. The dual up tapers respectively act as fiber splitter/combiner, the down taper acts as an optical attenuator. The structure parameters are analyzed and optimized. A larger interference fringe extinction ratio ~15 dB is obtained to achieve refractive index (RI) sensing based on intensity demodulation. The experimental results show that the RI sensitivity is &minus, 310.40 dB/RIU with the linearity is improved to 0.99 in the range of 1.3164&ndash, 1.3444. The corresponding resolution can reach 3.22 &times, 10&minus, 5 RIU, which is 6.8 times higher than wavelength demodulation. The cross sensitivity which caused by temperature fluctuation is less than 1.4 &times, 4.

Graphene has been widely utilized in optoelectronic applications due to its high carrier mobility, and extremely fast optical response. Microcavity-integrated graphene waveguide structure is one basic module of integrated photonic devices which can greatly improve the light-matter interaction strength. The enhanced optical absorption in the undoped graphene layer results from the light trapping and the corresponding long light-graphene interaction length. Tuning the Fermi energy level of the graphene layer enables the electro-optical modulation. We report the realization of reconfigurable electro-optical attenuator and switch with unity-order modulation depth in light reflection and transmission at near-infrared frequency. The transformation from a lossy absorber to a quasi-perfect transparent condition of the monolayer graphene by tuning the Fermi level leads to the unity-order tunability of the electro-optical attenuator and switch. We investigate theoretically and numerically the absorption properties of the designed microcavity-integrated graphene with respect to different graphene Fermi levels. Electro-optical attenuator with attenuating coefficient from 10% to 98.29% is fulfilled. On-off electro-optical switching with a switching contrast larger than 21 dB is demonstrated. Our approach provides the possibilities of graphene photonics applied in communications, and sensing.

Graphene metasurface has attracted a lot of attentions due to the unique tunability for exotic electromagnetic properties. In this work, we propose and numerically investigate a tunable metasurface with two non-coplanar and inter-perpendicular graphene nanoribbon arrays. The variation of transmission at different substrate thickness and the coupled mode are analyzed. It is shown that the Rabi-like splitting can be achieved by the coupling between localized and delocalized graphene surface plasmon polaritons. Tunable coupling strength and positions with different gate-voltages have been discussed. The effect of relaxation time and oblique incidences to resonant responses are also investigated. Additionally, we find an optical analogue of a spring, where the spectral dip vibrates around its equilibrium position at a certain wavelength. Our study suggests that the proposed structure is potentially attractive for realization of tunable double-channel filter, optical switch, and variable optical attenuator based on the graphene metasurface.

In this study, we construct a photomultiplier calibration system. This calibration system can help scientists measuring and establishing the characteristic curve of the photon count versus light intensity. The system uses an innovative 10-fold optical attenuator to enable an optical power meter to calibrate photomultiplier tubes which have the resolution being much greater than that of the optical power meter. A simulation is firstly conducted to validate the feasibility of the system, and then the system construction, including optical design, circuit design, and software algorithm, is realized. The simulation generally agrees with measurement data of the constructed system, which are further used to establish the characteristic curve of the photon count versus light intensity.

Vertical comb drives are critical for electrostatic optical switches and variable optical attenuators (VOAs), but fabricating vertical comb drives requires the formation of two levels of comb fingers and thus suffers from the difficulty of dealing with the comb-finger alignment. This paper presents a vertical comb drive design and its micro-fabrication method that can realize self-aligned two-level comb fingers. The self-aligned vertical comb fingers are enabled by a novel vertically-elevated flat-end (VEFE) bimorph structure. Both the stator and rotor fingers of the vertical comb drive are formed by the same photomask and the same silicon etching step, which automatically ensures accurate alignment of the stator and rotor fingers. The vertical separation between the stator and rotor is created by the VEFE structure. A 1mm-aperture MEMS mirror with the proposed VEFE comb drive has been fabricated using SOI wafers with buried cavities. The mirror rotates 0.94° at 8 Vdc. The resonant frequency is 1.428 kHz. The MEMS mirror has been assembled into a VOA module. Measurements show that the VOA achieved a dynamic range of 55 dB and an insertion loss of less than 0.4 dB and met the telecommunications standards on shock, vibration and long-term stability.

Recently, an optical attenuator has been important in fiber optic communication systems, because a transmission power in fiber has become higher due to a channel increment in wavelength division multiplexing transmission. A photonic crystal fiber (PCF) optical attenuator is fabricated by air hole diameter reduction in a part of PCF in which radiations are caused in the air hole diameter reduced part of PCF. A PCF optical attenuator has a high power resistance feature due to its radiation-induced operation of optical attenuation. In this paper, we proposed a variable PCF optical attenuator in which a bend was applied to the air hole diameter reduced part in PCF optical attenuator that was fabricated by CO2 laser irradiation. In PCF optical attenuator fabrication, the attenuation was adjusted by the reduced air hole diameter with laser irradiation time control. It was demonstrated that 10.6–13.5 dB of variable attenuation was obtained at 1550 nm-wavelength with 0°–90° bending angle applied to the air hole diameter reduced part in PCF optical attenuator.

This paper presents a method to estimate the optical attenuator according to the false firing percentage of Geiger Mode Avalanche Photodiode array detection system only under background light. The effect of the dark current and the gate setting are discussed. The efficiency of the Geiger mode avalanche photodiode detection system is improved by the optical attenuator by simulation analysis, that the false probability is reduced in all cases, and the detection probability increases accorindgly when the signal is larger than the total noise. Finally, the imaging simulation experiments show that the average ranging accuracy increase by using optical attenuator.

A large-scale monolithic silicon nanophotonic phased array on a chip creates and dynamically steers a high-resolution optical beam in free space, enabling emerging applications in sensing, imaging, and communication. The scalable architecture leverages sub-array structure, mitigating the impact of process variation on the phased array performance. In addition, sharing control electronics among multiple optical modulators in the scalable architecture reduces the number of digital-to-analog converters (DACs) required for an $N^{2}$ array from $\mathcal {O}(N^{2})$ to $\mathcal {O}(N)$ , allowing a small silicon footprint. An optical phased array for 1550-nm wavelength with 1024 uniformly spaced optical grating antennas, 1192 optical variable phase shifters, and 168 optical variable attenuators is integrated into a 5.7 mm $\times$ 6.4 mm chip in a commercial 180-nm silicon-on-insulator RF CMOS technology. The control signals for the optical variable phase shifters and attenuators are provided by 136 DACs with 14-bit nonuniform resolution using 2.5-V input-output transistors. The implemented phased array can create 0.03° narrow optical beams that can be steered unambiguously within ±22.5°.

A hybrid integrated photodetector array receiving module with multiple optical chips is demonstrated, which can be used for a multi-channel high uniformity optical communication system. The receiving module includes a 100 GHz PLC type arrayed waveguide grating, a variable optical attenuator chip with 8-channel, a photodetector chip array, power regulation, an impedance matching circuit, etc. With the hybrid-integration technology and high-precision coupling process, the experimental results show that the coupling loss of the module is 3.40 dB. The crosstalk between the adjacent channels is -30 dB. And the adjustable range of the electric power is up to 20 dB.

We demonstrate a wavelength tunable, Q-switched Er-doped fiber laser using a mixture of gold nanorods and nanospheres as a saturable absorber. The laser has a very low Q-switched threshold pump power of 22 mW, and at a pump power of 47.86 mW, a pulse with a maximum pulse energy of 36.01 nJ, repetition rate of 37.50 kHz, and pulse width of $2.74~\mu \text{s}$ was obtained. In addition, by using a tapered fiber as a variable attenuator (ATT), the central wavelength of the laser could be tuned continuously from 1560.97 to 1554.74 nm. The experimental results further verify that a tapered fiber ATT possesses potential advantages for applications in stable, wavelength tunable, all-fiber laser systems.

We demonstrate an L-band wavelength-tunable passively mode-locked fiber laser using a single long-period fiber grating (LPFG) as a narrow-band optical attenuator (NBOA). Through bending the LPFG, the central wavelength can be continuously tuned from 1582.02 to 1597.29 nm, while the output power only varies from 1.465 to 1.057 mW, approximately a rate of 22 µW/nm variation. This is the first time that LPFG is functioned as a NBOA in mode-locked fiber lasers, showing the great advantage of less impact on output power variation reduction. Besides, the total cavity length is 5.08 m, which is the shortest length yet reported in wavelength-tunable mode-locked fiber lasers. The wavelength tuning could also be realized at harmonic mode locking with tuning range of 14.69 nm under 5th harmonic.

A new technique for tripling the frequency of a microwave signal is presented. It is based on an integrated dual-parallel Mach–Zehnder modulator, which generates two orthogonally polarised RF modulated optical signals with different modulation indexes, and a polarisation-dependent optical attenuator. The photodetector output fundamental RF components generated by the two orthogonally polarised RF modulated optical signals have the same amplitude but an opposite phase, which are cancelled, leaving the frequency tripled microwave signal and the unwanted fifth order harmonic. The new frequency tripler has a simple structure, a wide bandwidth, and a high electrical spurious suppression ratio. Experimental results are presented demonstrating three times frequency multiplication of different-frequency microwave signals with electrical spurious suppression ratio of over 20 dB. The phase noise and the stability performance of the frequency tripler are also investigated experimentally.

Automotive optical gigabit Ethernet is a technology that is expected to realize autonomous driving cars with notable benefits: electromagnetic interference free, lighter weight, and higher data communication. Plastic optical fibers have been used in automotive optical networks since 1998. To secure a higher data rate, two issues must be considered: the need for modal power distribution (MPD) control and the lack of link margin. Here, we performed a combined study of MPD and the frequency characteristics of a 15-m optical fiber cable with multiple connections. The results reveal that the links have transmission directivity and the number of connections influences the bandwidth with different MPDs, as shown in encircled angular flux (EAF) profiles. We also show that automotive optical connections typically contain an air gap that generates higher mode radiation. To minimize this radiation, we filled the gap with a cured gel. We found that the EAF profile shifts from 13.8° to 15.4° at 50% EAF with a 1.75-dB insertion loss improvement based on the shift at z/a = 3.1 (where z indicates the axial misalignment at the connection, and a is the core radius). The approach presented here is an effective solution for facilitating the rapid realization of automotive optical gigabit communication.