Increased modulation depth of submicron gratings produced by photoelectrochemical etching of GaAs

AbstractGraphene has been widely used in silicon-based optical modulators for its ultra-broadband light absorption and ultrafast optoelectronic response. By incorporating graphene and slow-light silicon photonic crystal waveguide (PhCW), here we propose and experimentally demonstrate a unique double-layer graphene electro-absorption modulator in telecommunication applications. The modulator exhibits a modulation depth of 0.5 dB/μm with a bandwidth of 13.6 GHz, while graphene coverage length is only 1.2 μm in simulations. We also fabricated the graphene modulator on silicon platform, and the device achieved a modulation bandwidth at 12 GHz. The proposed graphene-PhCW modulator may have potentials in the applications of on-chip interconnections.

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VS2 as saturable absorber for Q-switched pulse generation

Nanophotonics ◽

10.1515/nanoph-2020-0128 ◽

2020 ◽

Vol 9 (8) ◽

pp. 2569-2576 ◽

Cited By ~ 4

Author(s):

Lu Li ◽

Lihui Pang ◽

Qiyi Zhao ◽

Yao Wang ◽

Wenjun Liu

Keyword(s):

Saturable Absorber ◽

Nonlinear Optical ◽

Modulation Depth ◽

Signal To Noise Ratio ◽

Transition Metal Dichalcogenides ◽

Laser Cavity ◽

Pulse Generation ◽

High Signal ◽

Power Pulse ◽

Metal Dichalcogenides

AbstractTransition metal dichalcogenides have been widely utilized as nonlinear optical materials for laser pulse generation applications. Herein, we study the nonlinear optical properties of a VS2-based optical device and its application as a new saturable absorber (SA) for high-power pulse generation. Few-layer VS2 nanosheets are deposited on the tapered region of a microfiber to form an SA device, which shows a modulation depth of 40.52%. After incorporating the microfiber-VS2 SA into an Er-doped fiber laser cavity, passively Q-switched pulse trains could be obtained with repetition rates varying from 95 to 233 kHz. Under the pump power of 890 mW, the largest output power and shortest pulse duration are measured to be 43 mW and 854 ns, respectively. The high signal-to-noise ratio of 60 dB confirms the excellent stability of the Q-switching state. To the best of our knolowdge, this is the first illustration of using VS2 as an SA. Our experimental results demonstrate that VS2 nanomaterials have a large potential for nonlinear optics applications.

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Dynamics of carbon nanotube-based mode-locking fiber lasers

Nanophotonics ◽

10.1515/nanoph-2020-0269 ◽

2020 ◽

Vol 9 (9) ◽

pp. 2731-2761 ◽

Cited By ~ 1

Author(s):

Lin Huang ◽

Yusheng Zhang ◽

Xueming Liu

Keyword(s):

Carbon Nanotube ◽

Fiber Lasers ◽

Modulation Depth ◽

Laser System ◽

Physical Nature ◽

Mode Locking ◽

Environmental Stability ◽

Saturation Intensity ◽

Soliton Dynamics ◽

Deep Modulation

AbstractCarbon nanotube (CNT) can work as excellent saturable absorber (SA) due to its advantages of fast recovery, low saturation intensity, polarization insensitivity, deep modulation depth, broad operation bandwidth, outstanding environmental stability, and affordable fabrication. Its successful application as SA has promoted the development of scientific research and practical application of mode-locked fiber lasers. Besides, mode-locked fiber laser constitutes an ideal platform for investigating soliton dynamics which exhibit profound nonlinear optical dynamics and excitation ubiquitous in many fields. Up to now, a variety of soliton dynamics have been observed. Among these researches, CNT-SA is a key component that suppresses the environmental perturbation and optimizes the laser system to reveal the true highly stochastic and non-repetitive unstable phenomena of the initial self-starting lasing process. This review is intended to provide an up-to-date introduction to the development of CNT-SA based ultrafast fiber lasers, with emphasis on recent progress in real-time buildup dynamics of solitons in CNT-SA mode-locked fiber lasers. It is anticipated that study of dynamics of solitons can not only further reveal the physical nature of solitons, but also optimize the performance of ultrafast fiber lasers and eventually expand their applications in different fields.

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A 40 Mb/s VLC System Reusing an Existing Large LED Panel in an Indoor Office Environment

Sensors ◽

10.3390/s21051697 ◽

2021 ◽

Vol 21 (5) ◽

pp. 1697

Author(s):

Xicong Li ◽

Zabih Ghassemlooy ◽

Stanislav Zvánovec ◽

Paul Anthony Haigh

Keyword(s):

Modulation Depth ◽

Light Emitting Diode ◽

Low Cost ◽

Data Communication ◽

Experimental System ◽

Digital Signal ◽

Visible Light Communication ◽

Cost Driver ◽

Limiting Factors ◽

Light Sources

With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm2. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed.

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Film Thickness-Profile Measurement Using Iterative Peak Separation Structured Illumination Microscopy

Applied Sciences ◽

10.3390/app11073023 ◽

2021 ◽

Vol 11 (7) ◽

pp. 3023

Author(s):

Kejun Yang ◽

Chenhaolei Han ◽

Jinhua Feng ◽

Yan Tang ◽

Zhongye Xie ◽

...

Keyword(s):

Modulation Depth ◽

Thickness Distribution ◽

Detection Threshold ◽

Profile Measurement ◽

Structured Illumination ◽

Structured Illumination Microscopy ◽

Separation Algorithm ◽

Peak Separation ◽

Lower Detection ◽

Depth Response

The surface and thickness distribution measurement for transparent film is of interest for electronics and packaging materials. Structured illumination microscopy (SIM) is a prospective technique for measuring film due to its high accuracy and efficiency. However, when the distance between adjacent layers becomes close, the peaks of the modulation depth response (MDR) start to overlap and interfere with the peak extraction, which restricts SIM development in the field of film measurement. In this paper, an iterative peak separation algorithm is creatively applied in the SIM-based technique, providing a precise peak identification even as the MDR peaks overlap and bend into one. Compared with the traditional method, the proposed method has a lower detection threshold for thickness. The experiments and theoretical analysis are elaborated to demonstrate the feasibility of the mentioned method.

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Highly Stable Passively Q-Switched Erbium-Doped All-Fiber Laser Based on Niobium Diselenide Saturable Absorber

Molecules ◽

10.3390/molecules26144303 ◽

2021 ◽

Vol 26 (14) ◽

pp. 4303

Author(s):

Ping Hu ◽

Jiajia Mao ◽

Hongkun Nie ◽

Ruihua Wang ◽

Baitao Zhang ◽

...

Keyword(s):

Fiber Laser ◽

Saturable Absorber ◽

Pulse Width ◽

Nonlinear Optical ◽

Modulation Depth ◽

Transition Metal Dichalcogenide ◽

Center Wavelength ◽

Niobium Diselenide ◽

Erbium Doped ◽

Layered Transition Metal

A saturable absorber (SA) based on niobium diselenide (NbSe2), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe2 nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm2, and 14%, respectively. By using the as-fabricated NbSe2 SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 μs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe2 SA in a Q-switched fiber laser.

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