In this paper, for the first time, we propose a large-broadband orbital angular momentum (OAM) mode converter based on helical long period fiber grating (HLPG) working at turning point (TP). Owing to the combination of dual-resonance peaks at TP, an OAM mode converter with 3-dB bandwidth of ~287 nm is readily obtained, and a high coupling efficiency of ~100% is achieved. We believe that this OAM mode converter will play a key role in fiber communication and other fields.
Using rolling shutter effect of the CMOS camera can increase the data rate of camera-based visible light communication (VLC) system. However, when fewer pixel columns represent one bit, the grayscale value fluctuation becomes serious, which leads to data logic not being correctly defined by the threshold, and therefore degrades the demodulation performance. In this paper, a thresholding scheme based on adjacent pixel grayscale value to reduce the influence of grayscale value fluctuation is proposed, which sets threshold using the grayscale values of the forward and backward pixels adjacent to the current pixel. And combining with segment downsampling, experimental results show that the proposed demodulation algorithm can achieve a bit-error-rate (BER) performance well below the forward error correction (FEC) limit of 3.8×10-3 with the bit resolution of 2.962 pixel/bit, and the net data rate can reach 10.56 kbit/s.
As the demand for higher capacity and longer reach of optical access networks is garnering momentum in recent years,
coherent access technology attracts renewed interests in high-capacity optical networking. In this paper, designs of
various coherent access networks are investigated and compared. From our results, it may be the most promising solution with high capacity at optimized cost. When coherent detection is employed in access network, the laser linewidth is a key design issue for optimized performance and cost as laser phase noise is larger with lower bit rate. One of our objectives is to examine the feasibility of employing a conventional DFB as carrier sources. We evaluated the
performance of ultra-dense WDM access networking system. Experimental results show that 2.5GB/s QPSK data can be
transmitted over 35-km SMF-28 with 6.5GHz channel spacing using DFB lasers.
An efficient bit-to-symbol mapping method for star 16-quadrature amplitude modulation (16-QAM) is proposed in this
paper, which is similar to Gray coding for square 16-QAM. With the consideration of optimal ring ratio of constellation,
our simulation results show that a linewidth of 3MHz per laser can be tolerated for star 16-QAM optical coherent
systems with SNR penalty of 1dB at BER of 10-3, which is much better than that of square 16-QAM. Further
optimization possibility with variable number of points on each of the rings for star 16-QAM constellation is also
Ultracompact wave plate (UWP) will be one of the key elements in future all-optical photonic integrated circuits (PICs).
In this paper, we propose UWPs based on periodic dielectric waveguides (PDWs) with air holes in conventional
dielectric waveguides. The mode characteristics (for both TE and TM) and birefringence of PDWs are calculated by
plane wave method (PWM). The transmission efficiencies and phase changing of TE and TM waves in PDW are
obtained by finite-difference time-domain (FDTD) scheme. Based on the PDWs, the quarter-wave plates (QWPs) and
half-wave plates (HWPs) are designed. Calculating results show that the proposed PDW has large birefringence (Δn>1)
and can introduce 2π phase difference with a short length being less than λ. The size of low order UWPs are compact.
The transmission efficiency of PDW is improved by taper structure. Based on the taper PDW, ultra-wide band (>100 nm)
achromatic QWP is designed. Profiting from the waveguide guiding, the UWPs have low beam divergence and can be
easily integrated with other photonic components. The UWPs have many potential applications in future PIC systems
such as optical communications, optical measurements and sensors.
In order to achieve higher output powers, double-clad fibers (DCF's) are widely used by optical fiber lasers and amplifiers. In this paper, we present a comprehensive mathematical model for the novel multi-mode (MM) double-clad (DC) Er: Yb co-doped hexagonal fiber, Based on the rate and propagation equations, the pump light and forward and backward-amplified spontaneous emissions (ASE±) light transmission in the fiber are analyzed numerically and measured. The simulative and experimental results show that pump power was absorbed almost completely when the length of the fiber is about 3.5~4 m, the suitable length of the fiber in optical fiber lasers is 2~2.5 m. and the 2 m long fiber emits at 1535 and 1543 nm simultaneously, and the peak-value wavelength of ASE+ changes to the long wavelength with the increase of the pump power. The results investigated are useful for the design of optical fiber lasers.