PbS quantum dot fiber amplifier based on a tapered SMF fiber

A PbS quantum dot coated (QD-coated) tapered fiber amplifier with a broad bandwidth is theoretically demonstrated. The QD layer is coated on the surface of a tapered fiber and is excited by the evanescent wave of a pump. An optical gain of 10.5 dB, with a 160-nm broad bandwidth of at 1530-nm center wavelength, is achieved. The gain efficiency is over 4 dB/cm. This QD-tapered fiber amplifier has a concentration control of the QDs, a lower insertion loss, and shows good suppression of amplified spontaneous emission (ASE), while its structure is also quite simple. Therefore, the proposed fiber amplifier has great potential in fiber-optic communication systems.     

Research on phosphor-conversion laser-based white light used as optical source of VLC and illumination

Visible light communication (VLC) based on light emitting diodes (LEDs) or laser diodes (LDs) has attracted considerable interest in recent years. Due to the advantages of laser diodes based on nitrides, such as small size, high brightness, visible light and high bandwidth, it can be applied to illumination and communication at the same time. In this paper, blue laser and yellow phosphors were employed to synthesize white light. And “efficiency droop” is not observed in the LIV characteristics of LD-based white light either. The bandwidth measurement system with high reliability was set up. The bandwidth of blue laser diode and phosphor-conversion laser-based white light was measured. The maximum of optical ?3 dB bandwidth of blue LD is around 1.8 GHz at 80 mA and maximum of optical ?3 dB bandwidth of white light is about 1.3 GHz at 60 mA. The color parameters of the synthetic white light were characterized through integrating sphere. Moreover the trends of test data with injection current were analyzed in detail. The problem of thermal degradation of yellow phosphors has been improved by a special design that can keep a certain distance between the blue laser diode and phosphors. The experiment results verified that laser diodes based on nitrides have promising applications in lighting and communications.     

Experimental study of an actively mode-locked fiber ring laser based on in-fiber amplitude modulation

We report an experimental study of an actively mode-locked fiber ring laser based on the development of an efficient in-fiber amplitude modulator. Intermodal coupling induced by standing flexural acoustic waves permits the implementation of broad bandwidth (1.5 nm), high modulation depth (72%), low-insertion-loss (0.75 dB), in-fiber amplitude modulators, operating in the MHz frequency range. The experimental characterization of the laser as a function of the radio frequency voltage that controls the modulator, the length of the active fiber, and the optical bandwidth of an intracavity filter implemented with a fiber Bragg grating has led to an improved performance of the Erbium-doped fiber laser: optical pulses of 34-ps temporal width, 1.4-W peak power, and 4.75-MHz repetition rate.     

Tunnel injection transistor laser for optical interconnects

Transistor laser (TL) is already an established potential candidate for high speed optical interconnects and present day optical communication networks. This paper investigates theoretically the possibility of having lower base threshold current density and enhanced modulation bandwidth by inserting a tunnel injection structure in a TL having multiple quantum wells (MQW) in the base of the heterojunction bipolar transistor. Transfer of injected charge carriers from bulk to low dimensional nano-structure is assumed to occur via virtual energy states, which contributes to the terminal current. Small signal modulation response is obtained by solving the Statz–De Mars laser rate equations. The optimum threshold base current, confinement of carrier, light power outputs etc. are estimated for three QWs positioned at distances of 39, 59, and 79 nm from the emitter-base junction across the base. Incorporation of tunneling structure substantially lowers the base threshold current and increases the modulation bandwidth as compared to usual MQW transistor laser structure. The changes are more prominent with increasing tunneling probability.     

Multi-frequency AOM for multi-beam laser scanning exposure system

Digital printing systems recorded on films or computer to plates (CTPs) have been required to improve their productivity and image quality. Under the circumstance, a printing technology of the multi-beam laser scanning for the drum capstan system, which is almost the same as optics configuration as the flat bed system, was developed using a newly developed multi-frequency acousto–optic modulator (AOM) as a key device instead of ultra-fast scanning devices toward a main scan direction. The multi-frequency AOM was developed with phased array-type transducers, achieving a wider bandwidth of over 160 MHz. The design consisted of a simultaneous three beams generation with interlace scan to avoid the beat effect by adjacent Doppler-shifted beams, which consequently attained the fastest recording speed of 5.0 mm/s compared with 2.0–3.0 mm/s of existing systems in those days. Furthermore, a couple of critical parameters of the multi-frequency AOM are studied, for example, a treatment of third-order intermodulation and also beat effect in connection with photosensitive media. As a result, the necessity of interlaces scanning to obtain good image quality without beat effect and also to allow a lower laser power to apply is proposed.     

Characterisation of the potential of frequency modulation and optical feedback locking for cavity-enhanced absorption spectroscopy

A combination of optical feedback self-locking of a continuous-wave distributed feedback diode laser to a V-shaped high finesse cavity, laser phase modulation at a frequency equal to the free spectral range of the V-cavity and detection of the transmitted laser beam at this high modulation frequency is described for the possible application in cavity-enhanced absorption spectroscopy. In order to estimate the noise level of an absorbance baseline, the triplet of frequency modulated light, i.e. the central laser frequency and the two sidebands, were transmitted through both the V-cavity in open air and a 1.5-cm long optical cell placed behind the cavity output mirror and filled with acetylene (C₂H₂) at low pressure. The performance of the setup was evaluated from the measured relative intensity noise on the cavity output (normalised by the bandwidth) and the frequency modulation absorption signals induced by C₂H₂ absorption in the 1.5-cm cell. From these data, we estimate that the noise-equivalent absorption sensitivity of 2.1 × 10^?11 cm^?1 Hz^?1/2—by a factor of 11.7 above the shot-noise limit—can be achieved for C₂H₂ absorption spectra extracted from the heterodyne beat signals recorded at the transmission maxima intensity peaks of the successive TEM₀₀ resonances.     

Circuit model for analysis of SOA-based photonic switch

This paper presents an equivalent lumped element electric circuit model for traveling wave semiconductor optical amplifier (SOA) in integrated circuit applications. The model facilitates incorporation of chip and package parasitic elements of SOA. The model is used to represent an all optical 2 × 2 switch based on cross gain modulation in SOA capable of operating at an ultra fast speed. SPICE simulation of the switch with the proposed circuit model provides bit error rate (BER) values at the switch output which agrees well with the experimentally measured values at 10 Gb/s. The degradation of switching performance has been examined in terms of bit error rate, modulation bandwidth and switching time in the presence of chip parasitic elements of SOA.     

5 × 10 Gbps WDM-CAP-PON based on frequency comb using OFDM with blue LD

Presently, optical access networks are in great demand to meet the bandwidth requirement due to rapid growth in high speed applications for smart devices, cloud computing, big data analysis and other 5G applications. In this paper, 5?×?10 Gb/s wavelength division multiplexing carrier-less amplitude phase modulation-passive optical network (WDM-CAP-PON) with frequency comb is proposed and demonstrated. Also, 450 nm blue laser diode having bandwidth 0.8 GHz is used for visible light communication using 6 m FSO link to support cost effective high data rate optical network. The WDM-CAP-PON employing orthogonal frequency division multiplexing has been analysed in terms of tolerance to the fiber non-linearities through the effect of variations in launch power (??5 to 4 dBm), datarate (2.5–40 Gb/s) and distance (20–110 km) on Q-factor and error vector magnitude (EVM%) by considering pre-, post- and symmetrical-dispersion compensation schemes. It is reported that post-compensation is superior to pre- and symmetrical-compensation schemes to achieve the minimum 3.8?×?10^?3 BER under 7% forward error correction (FEC). The faithful transmission distance achieved for 10 Gb/s WDM-CAP-PON using post dispersion compensation scheme is 110 km.     

气源MBE外延自组装GeSi量子点光致荧光研究

利用气源分子束外延设备（MBE）制作了GeSi自组装量子点样品。利用原子力显微镜（AFM）和光致荧光（PL）光谱研究了量子点的形貌和光学性质。气源MBE在较低温度下生长的量子点材料具有较高的量子点覆盖度。200K以下载流子以局域激子形式束缚在量子点中,激子束缚能约为17meV。升温至200K,载流子的输运过程发生变化。对量子点PL积分强度与温度关系曲线进行拟合得到量子点中空穴跃迁至浸润层的热激活能为129meV。     

A novel reconfigurable radio-over-fiber system based on flexible optical devices

In this paper, a reconfigurable Radio over Fiber system based on optical switches, optical multimode interference power splitter and tunable optical filters is designed, which can achieve quadrature phase shift keying wireless modulation in optical domain and switch carrier frequency between 30 and 60 GHz. The scheme can make good use of bandwidth resource and realize signal transmission in fiber within 10 km.     

用于Rb原子冷却系统的半导体激光放大(TPA)装置

报道了我们最近研制的780 13m半导体激光放大装置.激光放大管采用Eagleyard公司生产的(EYP-TPA-0780-01000)半导体锥形放大器,当输入的种子源激光功率为25 mW时,放大器输出的激光功率达600mW左右,该光束经过透镜整形,声光调制器频移,然后耦合到单模保偏光纤后,输出功率达110 mW.该激光放大装置可很好的用于高密度冷原子的俘获.     

Actively mode-locked fiber ring laser by intermodal acousto-optic modulation

We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth (187 GHz), easy tunability in the optical wavelength, and low insertion losses (0.7 dB). The narrowest optical pulses obtained were of 95 ps time width, 21 mW peak power, repetition rate of 4.758 MHz, and 110 mW of pump power.     

Optical Coherence Tomography Implemented by Photonic Crystal Fiber

We report a photonic crystal fiber (PCF)-based optical coherence tomography (OCT) system, in which conventional single-mode fiber for the transmission line and the fiber coupler for the beam splitter/combiner are replaced with PCF and PCF coupler. The PCF coupler fabricated using the fused biconical tapered (FBT) method showed a nearly flat coupling ratio over a broad spectral bandwidth of 400 nm, which provided an axial resolution of 3-μm for OCT imaging. With a white-light source, the 8-μm thick air gap between two stacked cover glasses was measured, and with a conventional superluminecent diode (SLD) source, the in vitro images of rat eye and Misgurnus mizolepis skin were successfully obtained. The PCF and PCF coupler might enable a white-light as the source for the cost effective and high-resolution OCT system.     

Optical access transmission with improved channel capacity using non-orthogonal frequency quadrature amplitude modulation

A new modulation scheme that improves the bandwidth efficiency of an optical access link is proposed in this paper. It is implemented using non-orthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM) simultaneously. We call the proposed technique non-orthogonal frequency quadrature amplitude modulation (NOFQAM). Especially, non-orthogonal FSK based on digital signal processing (DSP) is proposed for the first time. DSP-aided non-orthogonal FSK allows us to select RF carrier frequency irrespective of the channel bandwidth to allocate FSK symbols, unlike the existing orthogonal FSK. The non-orthogonality is implemented using a sequential correlation, where a received NOFQAM signal is correlated with only one RF carrier at a time by using DSP. After the sequential correlation is completed, both the FSK and the QAM symbols are recovered successfully and merged to generate the NOFQAM symbols. For experimental verification, a 20-km optical access link, which can transmit a 64-NOFQAM signal sampled at 10 Gsample/s, is implemented. We observed no increase in occupied channel bandwidth and a power penalty <0.5 dB compared to the 16-QAM scheme. A bit error rate lower than 10^?11 was obtained for the frequency spacing considered herein, which corresponds to 3% of the used RF carrier (1.5 GHz) when there are 50 sampling points per 64-NOFQAM symbol.     

Broadband four-wave optical parametric amplification in bulk isotropic media in the ultraviolet

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF₂. Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.     

Measurement of the velocity inside an all-fiber DBR laser by self-mixing technique

The self-mixing interference for optical velocity sensing is experimentally investigated in an all-fiber configuration distributed Bragg reflector laser. Simultaneously, theory model of self-mixing interference laser Doppler velocimeter based on quasi-analytical method. The experimental results show Doppler shift frequency is linearly proportional to the value of the velocity which agrees well with theory analysis. The results preserve an enough signal-to-noise ratio around 40 dB in the range from 39.3–317.0 mm/s (measurement range depending on bandwidth of circuit) for velocity measurement. Additionally, the cutoff circuit is used in our system to get a stable Doppler signal and reduces the error rate to 0.136 % in practical measurement.     

Design of 1060nm tapered lasers with separate contacts

Numerical simulations have been used to produce advanced designs of high brightness gain guided tapered lasers emitting at 1,060 nm. The simulations predicted high modulation efficiency in devices with separate contacts and low front facet reflectivity. The devices fabricated following these design guidelines demonstrated high internal quantum efficiency in Broad Area lasers, output power of 3 W with good beam quality in tapered lasers with common contacts, and modulation efficiencies up to 20 W/A in tapered lasers with separate contacts, in good agreement with the simulation predictions.     

Watt-level red-emitting diode lasers and modules for display applications

Red-emitting lasers for display applications require high output powers and a high visibility. We demonstrate diode lasers and modules in the red spectral range based on AlGaInP with optical output powers up to 1 W and a nearly diffraction limited beam. These high-luminance light sources based on tapered lasers are well suited for laser TVs and projectors for virtual reality simulators based on the flying spot technology. Additionally, we developed diode lasers with internal distributed Bragg reflector (DBR) surface gratings. These DBR tapered lasers and master-oscillator power-amplifiers based on DBR ridge-waveguide lasers and tapered amplifiers feature high power, single mode emission with coherence lengths up to several meters, which are suitable for the next-generation 3D displays based on holography.     

High speed intracavity-contacted vertical cavity surface emitting lasers with separated quantum wells

In this work, the simulation of the 980 nm InGaAs intra-cavity-contacted oxide-confined vertical-cavity surface-emitting lasers (ICOC VCSELs) with separated triplets of quantum wells (STQW) is presented. We analyze the thermal, electrical and optical properties of such devices. Results of simulations show the larger optical power efficiency and higher modulation bandwidth for devices with included STQW.