Signal Light Power Research Articles

Optical duobinary transmitter based OQPSK line coding phase offset for the prediction of OWC channel systems performance efficiency

Abstract This work demonstrates the optical duobinary transmitter based optical quadature phase shift keying line coding phase offset for the prediction of optical fiber wireless channel systems performance efficiency. The max signal light power variations with the spectral wavelength variations for different degree phase offsets based optical quadrature phase shift keying (OQPSK) transmitter are clarified. The max signal light power variations with the time variations for various degrees phase offset based OQPSK transmitter are demonstrated. The total power lighted after OWC channel for various degree phase offset based OQPSK transmitter are indicated. The max electrical power signal amplitude variations with the time variations for various degree phase offset based OQPSK transmitter are observed. Total electrical power signal after optical receiver for various degree phase offset based OQPSK transmitter is clarified. Total optical power variations after OWC channel for various degrees phase offset based OQPSK transmitter is studied.

An idler light power measurement temperature sensor based on the four-wave mixing in a highly nonlinear fiber

In this study, an idler light power measurement temperature sensor based on four-wave mixing (FWM) is designed and analyzed experimentally. In the experiments, the FWM effect is realized in a highly nonlinear fiber (HNLF). The FWM conversion efficiency of the proposed sensor is calculated, and its temperature sensing is evaluated by changing the pump wavelengths and the signal light powers. Unlike previous studies on the FWM temperature sensors, this work uses the idler light power as sensing basis. The experimental results show that the output power of the idler light varies significantly with the temperature at different pump wavelengths. In the experiment, a temperature sensor with a measurement range from 20 ℃ to 80 ℃ is used. The results show that at a wavelength of 1540 nm, the average signal light power is 60 mW, and the proposed sensor’s sensitivity is 0.1295 dB/℃. The proposed sensor is easy to operate and allows performing measurements conveniently. In addition, it provides an improved measuring method for FWM-based temperature sensing.

Time advancement and distortionless of optical pulses via stimulated Brillouin scattering by broadband pump in optical fibers

The broadening Brillouin absorption spectrum of stimulated Brillouin scattering (SBS) in optical fibers by multiple monochromatic pumps is investigated. The results show that the bottom of the effective absorption spectrum becomes flatter with increasing the number of spectrum lines, and the spectral bandwidth is effectively expanded by multiple monochromatic pumps. but the spectral spacing should be tailored reasonably to ensure a broad linear range of the refractive index to reduce the pulse distortion. The time advancement and the pulse distortion induced by SBS pumped by broadband Gaussian and rectangular spectra are demonstrated respectively. The simulation results indicate that the pulse distortion induced by broadband rectangular spectral pump is smaller than that of broadband Gaussian spectral pump, and the time advancement can be improved effectively by increasing signal light power. We believe that these results are very promising for designing optical buffering or sensing components based on SBS fast light.

Design and Application of Waveguide Microwave Electron Synthesis Power Amplifier Using Er3+−Yb3+ Co-Doped Nanocrystalline

The solid-state power device has the advantages of small size, light weight and low working voltage, but the output power of the device is limited and cannot meet the engineering needs of power synthesis. Based on the characteristics of erbium (Er3+)-doped optical waveguide amplifier (EDWA), Er3+-ytterbium (YB3+) nanocrystalline were introduced into the design of solid-state power devices, and then nanoelectronic devices were designed to improve the output power of the device. First, NaYF4: 8%Er3+, 16%Yb3+ nanocrystalline were prepared. SU-8 UV glue was used to prepare NaYF4: Er3+. Yb3+ nanocrystalline doped polymer waveguide amplifier was designed and used to observe the waveguide morphology and its performance was tested. Then, the power synthesis amplification technology was studied, and the power distribution-synthesis network based on waveguide E–T junction was designed. The waveguide-microstrip transition structure adopted ridge waveguide transition. On this basis, the 4-stage waveguide E-plane stepped structure was introduced and its structure was simulated. In the design of the power synthesis amplifier, the signal gain of the synthesis amplifier was tested by using the nanocrystal-doped polymer waveguide amplifier as the power unit device. The experimental results show that the output signal light of the nanocrystal-doped polymer waveguide amplifier can be received by an infrared detector. When the pump light power at 980 nm is 200 mW and the signal light power is only 0.1 mW, the maximum relative gain is 4.7 dB in a 1.2 cm long waveguide. The saturated output power of the power unit device is 19.3 dB~19.8 dB, which is close to the saturated output power required by the chip manual. The gain curve of the power synthesis amplifier is relatively flat, that is, the use of nanocrystal-doped polymer waveguide electronic devices effectively improves the synthetic signal gain and reduces the adverse impact of power distribution-synthetic passive network loss.

Analytical Evaluation of Signal-to-Noise Ratios for Avalanche- and Single-Photon Avalanche Diodes

Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM-APDs or APDs) and Geiger-mode APDs or single-photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low-light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal-to-noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologically achievable photodiode parameters. In this article, analytical methods are used to obtain a universal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detector. LM-APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time-dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a common framework.

Analysis on light power and three-dimentional temperature distribution characteristics of gain guided and index alternate-guided fiber lasers

Gain guided and index alternate-guided (GGIA-G) fiber was suggested by our group recently. In this work, the improved rate equations of the GGIA-G fiber laser were established and solved. The pump and signal light power distribution along the fiber longitudinal axis were simulated under the conditions of forward, backward and bidirectional pump. Furthermore, a theoretical three-dimensional temperature distribution model of the GGIA-G fiber laser was established, and the temperature distribution characteristics along both the fiber longitudinal axis and radius were simulated and compared when the fiber was pumped with different methods. The research results show that different pump method has obvious influence on both signal light power distribution and the fiber temperature. When the fiber is forward pumped, the signal light power in the fiber is the highest, and when the fiber is bidirectionally pumped, the temperature of the fiber is the lowest. The research conclusions are helpful in the application of the GGIA-G fiber.

Experimental verification of coherent tracking system based on fiber nutation.

We report a coherent tracking system based on fiber nutation for inter-satellite beaconless laser communication, which uses a piezo-electric ceramic tube (PCT) to drive the end face of single mode fiber (SMF) for nutation, and uses coherent demodulation method to directly calculate the boresight error from the intensity envelope fluctuation of signal light. The method is given theoretically and verified experimentally. Under the condition of fiber nutation frequency is 2000Hz and nutation radius is 1.1um, the experimental verification results in our interested range of signal light power (1nW-10nW) meet our design requirements. The receiving field of view (FOV) of tracking system is more than 300urad, and the closed-loop tracking bandwidth (-3dB) is about 115 Hz. When the boresight error is fixed at 80urad, the real calculation error is less than 10%. The closed-loop performance of tracking system is insensitive to the change of signal light power. Our coherent tracking system is of great significance to the inter-satellite beaconless laser communication.

Tunable optical delay with low intensity loss in a cascade structure Er3+-doped optical fiber amplifier

In this paper, we propose a new pumping scheme-a dual-frequency laser-pumped cascade structure of Er3+-doped optical fiber based on the theory of coherent population oscillation. While realizing slow light transmission, the loss of output signal light power is reduced. Using numerical simulation, we compare the effects of a single fiber without pumping, a 980nm single pumping single fiber, and a dual-frequency laser-pumped cascade structure of Er3+-doped optical fiber on signal light intensity loss coefficient τ and maximum time delay with the increase of input signal light power. The results show that the signal light intensity loss coefficient τ of the three structures decreases gradually with the increase of input signal light power. However, the transmission of lower signal light intensity loss coefficient τ=0.0823 and a larger time delay of 0.15ms can be obtained under the dual-frequency laser-pumped cascade structure of Er3+-doped optical fiber. On the basis of the dual-frequency laser-pumped cascade structure of Er3+-doped optical fiber, the signal light intensity loss coefficient τ decreases gradually with the increase of pump ratio M (M=P1480∶P980) and the decrease of length ratio N (N=L2∶L1; L1 and L2 represent the length of the first and second cascaded optical fibers, respectively). Moreover, we compare the effects of ion density of the Er3+-doped optical fiber on the time delay of three structures. The dual-frequency laser-pumped cascade structure of Er3+-doped optical fiber can provide a larger time delay and smaller signal light intensity loss coefficient τ at low ion density of the Er3+-doped optical fiber.

Broad-band, reversible nonreciprocal light transmission based on a single nanocavity.

We present a general yet simple method for achieving broad-band, high-contrast-ratio, and reversible all-optical diodes. The mechanism is based on the controllable photonic transitions inside a nonlinear nanocavity, triggered by only one pulse. We demonstrate that the interaction between the signal, pump pulse, and the cavity mode plays a crucial role in dynamically controlling the nonreciprocal light transmissions. Using this mechanism, we show that the nonreciprocal light transmission can be controllably reversed without changing the signal light's wavelength or power, with a broad operation bandwidth over 7.5nm and a transmission contrast rate over 20dB. This approach provides a promising avenue in flexible manipulation of on-chip all-optical signal processing.

Polymer waveguide thermo-optical switch with loss compensation based on NaYF4: 18% Yb3+, 2% Er3+ nanocrystals**Project supported by the National Natural Science Foundation of China (Grant Nos. 61475061 and 61575076).

A polymer waveguide thermo-optical switch with loss compensation based on NaYF4: 18% Yb3+, 2% Er3+ nanocrystals, fabricated by traditional semiconductor processes, has been investigated. NaYF4: 18% Yb3+, 2% Er3+ nanocrystals were prepared by a pyrolysis method. The morphology and luminescent properties of the nanocrystals were characterized. The nanocrystals were doped into SU-8 as the core material of an optical waveguide amplifier. The size of the device was optimized for its optical and thermal fields as well as its transmission characteristics. The device was fabricated on a silica substrate by spin coating, photolithography, and wet etching. The insertion loss of the switch device is ∼ 15 dB. The rise and fall times of the device are 240 μs and 380 μs, respectively, as measured by application of a 304 Hz square wave voltage. The extinction ratio of the device is about 14 dB at an electrode-driving power of 7 mW. When the pump light power is 230 mW and the signal light power is 0.1 mW, the loss compensation of the device is 3.8 dB at a wavelength of 1530 nm. Optical devices with loss compensation have important research significance.

Investigation of signal power splitting ratio for BPSK homodyne receiver with an optical Costas loop

We demonstrate influences of the power splitting ratio of the quadrature-arm to the input signal on both receiver sensitivity and residual phase error for a 10-Gb/s binary phase-shift keying coherent receiver based on an optical homodyne Costas loop. Fine adjustment of the signal power splitting ratio (Ks) is realized by tuning the polarization state of the input signal light of a dual-polarization optical 90-deg hybrid, leading to the precise control of the power distribution on two orthogonal states of polarization that are used for in-phase and quadrature arm, respectively. When the phase error is negligible (<10 deg) under different Ks, the sensitivity is improved by 2.65 dB and the Ks is optimized around 0.05. Based on loop bandwidth maintaining, the requirement on laser linewidth is also relaxed, i.e., 5.26 times larger linewidth is permitted at Ks = 0 . 05 than that without loop bandwidth maintaining. To fully utilize the signal light power and to avoid excess losses of the dual-polarization hybrid, homodyne Costas coherent receiver with a free-space optics-based 90-deg hybrid is also proposed. All experimental and theoretical results demonstrate the potential of approaching shot noise limited sensitivity for a Costas coherent receiver with an optimum Ks. It is significant to increase power budget and transmission span for satellite optical communication and free-space optical communication.

3D thermal analysis of end-pumped Nd3+-doped index-crossover gain guided–index antiguided fiber laser

Improved rate equations are established for the new model of index-crossover gain guided-index antiguided (IGG-IAG) fiber, then the pump and signal light power distribution along the IGG-IAG fiber are investigated. Based on the thermal conduction equations, the 3D temperature distributions of a one-end-pumped and dual-end-pumped Nd3+-doped IGG-IAG fiber laser are further analyzed. The simulation results show that many factors have an important influence on fiber temperature. The temperature of the fiber with the dual-end-pump method is obviously lower than that with the one-end-pump method, and the temperature distribution is more uniform. The larger the R value, the lower the fiber temperature, and the smaller the −Δn, the lower the fiber temperature. Thus proper fiber parameters and pump scheme may help to reduce the fiber temperature.

Intracavity KTP OPO pumped by a doubly Q-switched laser with AOM and a monolayer graphene saturable abosorber

An intracavity KTiOPO4 (KTP) optical parametric oscillator (IOPO) pumped by a doubly Q-switched YVO4/Nd:YVO4 laser with an acousto-optic modulator (AOM) and a monolayer graphene saturable absorber has been realized for the first time. The average output power, the pulse duration, single pulse energy and the peak power of signal light versus incident pump power have been measured. At an incident pump power of 11.7W and an AOM repetition rate of 10kHz, the shortest pulse duration of 1.24ns was obtained, corresponding to a single pulse energy of 9.5μJ and a peak power of 7.9kW. In comparison, the doubly IOPO (DIOPO) pumped by doubly Q-switched laser with AOM and graphene saturable absorber can generate pulses with narrower pulse width and higher peak power than the singly IOPO (SIOPO) pumped only by AOM Q-switched laser.

OOK-to-QPSK modulation-format conversion based on two gain-transparent SOAs

In this paper, the system scheme of on–off keying (OOK) to quadrature phase-shift keying (QPSK) format conversion is proposed, which is based on two gain-transparent semiconductor optical amplifiers (GT-SOA). GT-SOA is used as a simple all-optical phase modulator, which is no effects of cross gain modulation and four-wave mixing existing in conventional SOA. The assistant light is used to speed up the SOA carrier recovery time. The principles of OOK to QPSK format conversion are expounded. The influences of the assistant light power and signal light power on the conversions are numerically analyzed. The OOK signal can still be exactly converted to the QPSK signal with the power of OOK signal being changed within a certain range.

Study on a Methane and Acetylene Spectrum Absorption Mode Gas Sensor with Optical Fiber

The gas monitor with optical fiber is developed in this paper based on the principle that the absorption light changes with gas intensity under absorptive peak wavelength. The LED of driving light source is selected by the absorptive peak wavelength of measured gas. The light source driving circuit with the different frequency is used to detect the varied gas in real time. The techniques of phase-sensitive detected and ratio between measured signal and reference signal is used to ensure measurement accuracy. The examination system chooses low loss 50cm-long quartz optical fiber as long distance transmitting channel. The light source adopts low power pulse modulation semiconductor LED. 50cm-long absorption gas room is used to ensure measurement sensitivity. The system adopts the technique to carry out scheme combining optical fiber sensing technique with computer data handling technique. Uniting sensing light signal and stimulating light power transfer and measured parameter sensing, the advantages of optical fiber system, micro-electron electric circuit and computer compatibility can be sufficiently realized. The entire measurement system can attain light, the engine and electricity integration, and realize multi-parameter and multi-function. The experiment result of methane and acetylene intensity indicates that the system has higher detected sensitivity and detected accuracy. The system is not only used to detect the methane and acetylene intensity, but also to detect other gas intensity under a little structure parameter change.

Study of Nd3+-doped polarization maintaining fiber amplifier

The distribution of pump light and signal light power of Nd3+-doped fiber amplifier along the fiber is numerically simulated. The Nd3 +-doped polarization-maintaining fiber amplifier is experimentally studied, which is pumped by 808nm semiconductor laser. The enlargement factor of small-signal is 300（the gain is 25dB）, and the steady 5W amplificatory pulse is obtained by using the self-made Nd:YAG passive mode-locking laser as seed source. The 86142B-type spectrograph and TDS5104 oscillograph are employed to detect the output laser, and the output power is measured by power meter.

Michelson Interferometer-Type Wavelength Converter Integrated with Multimode Interference Coupler; Fundamental Characteristics

We proposed and investigated a Michelson interferometer-type wavelength converter with a multimode interference coupler (MIWC-MMIC) as one of the key devices in future DWDM photonic switching networks. The MIWC-MMIC is compact and efficient due to its Michelson interferometer-like structure, which uses an MMIC simultaneously as input and output-side couplers. The dependence of the output characteristics on structural parameters, such as the power-division ratio of the MMIC and the reflection coefficient at semiconductor optical amplifier (SOA) ends, was analyzed to optimize the structure for operation with a low excess loss and a low signal light power. The device was actually fabricated and its preliminary static characteristics were measured. The cross modulation of the converted light by 9.0 dB was attained by introducing a signal light with a power of about -5 dBm.

Measurement of Dimensions Using Robot Constructed Utilizing Optical Fiber Signal Transmission System Having Reference Capability.

This paper describes the optical signal transmission system constructed using direct intensity modulation technique which is capable of transmitting a signal through a movable optical fiber, and its application to the measurement of dimensions using a robot. When the optical fiber is bent, the optical power losses are increased, and however, the power loss at 830nm was almost the same as that at 660nm. So, the light at 660nm can be used as a reference light to correct the intensity error of the signal light at 830nm which is caused by the optical fiber bending. This system simultaneously transmits the signal and reference from a transmitter to a receiver through a movable optical fiber. At the receiver, the signal is normallized by the reference to provide the correct output signal. When the optical fiber was bent with a bending radius of 10mm at a bending angle of 180 degrees, the transmission error rate was 0.28 in the conventional single-path system. This error was caused by the bending loss of the signal light power. Under the same bending conditions, the error rate was improved to 0.03 in the proposed system due to the reference capability. This system was experimentally applied to transmit data from the displacement sensor attached to the arm of the robot through the movable optical fiber installed in the arm of the robot. The proposed system having the reference capability can transmit an optical distance signal with the minimum error through a movable optical fiber. The experiment was successful.

A Holographic Optical Element for an Integrated Optical Head

Diffraction efficiencies of a reflection-type blazed holographic optical element (HOE) are analyzed and optimized for use in a totally integrated optical head. The HOE, consisting of four-step phase levels, was fabricated by a double-etching process. By controlling each etching depth, signal light power efficiency was maximized to 16% and the power ratio of noise components relative to signal light power was suppressed to 21%. Diffraction efficiencies were made uniform over the entire HOE in oblique positioning by controlling the respective step widths of the HOE.

Broad-range tunable wavelength conversion of high-bit-rate signals using super structure grating distributed Bragg reflector lasers

Tunable wavelength conversion of a 10 Gb/s signal over a broad wavelength range of about 90 nm is achieved by using a super structure grating distributed Bragg reflector laser. The extinction ratio dependence of converted signal light on input signal light power and bias current to the laser active region is discussed. The extinction ratio becomes large when the input signal light power increases and the bias current decreases. Bit error rate measurements show that error-free, penalty-free wavelength conversion is achieved when the extinction ratio is large (12.5 dB) and that the bit rate which error-free wavelength conversion is possible increases as the input signal light power increases. Twenty Gb/s signal wavelength conversion is also demonstrated.