A long-reach WDM passive optical network enabling broadcasting service with centralized light source

We propose a long-reach wavelength-division-multiplexed (WDM) passive optical network (PON) to provide conventional point-to-point (P2P) data and downstream broadcasting service simultaneously by superimposing, for each WDM channel, the differential-phase-shift-keying (DPSK) broadcasting signal with the subcarrier multiplexing (SCM) modulated downstream P2P signal, at the optical line terminal (OLT). In the optical network units (ONUs), by re-modulating part of the downstream signal with a reflective semiconductor optical amplifier (RSOA), we realize color-less ONUs for upstream data transmission. The proposed scheme is numerically verified with a 5 Gb/s downstream P2P signal and broadcasting services, as well as 2.5 Gb/s upstream data through a 60 km bidirectional fiber link. In particular, the influence of the downstream lightwave's optical carrier–subcarrier ratio (OCSR) on the system performance is also investigated.     

Influence of guard band on performance of absolute polar duty cycle division multiplexing over a single wavelength and wavelength division multiplexing system

For the first time to the best of our knowledge the effect of guard band (GB) on the performance of 40 Gb/s Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) over a single wavelength and wavelength division multiplexing (WDM) are investigated and reported. It is demonstrated that the spectral width occupied by 40 Gb/s AP-DCDM with GB is 100 GHz (with minimum spectral efficiency of 0.4 b/s/Hz) whereas, this value can be reduced to around 80 GHz for AP-DCDM without GB (with minimum spectral efficiency of 0.5 b/s/Hz). In addition to better spectral efficiency, this amount of saving in the spectral width leads to ～60 ps/nm improvement in chromatic dispersion tolerance. In this paper, characteristics of AP-DCDM with and without GB over WDM system are compared at the speed of 40 Gbit/s per WDM channel, for the tolerance to narrow optical filtering and minimum allowed channel spacing. The AP-DCDM without GB has narrower spectral width than AP-DCDM with GB, which makes its implementation in WDM system advantageous.     

Simulation of 16 × 10 Gb/s WDM system based on optical amplifiers at different transmission distance and dispersion

In this paper, the 16 channel WDM systems at 10 Gb/s have been investigated for the various optical amplifiers and hybrid optical amplifiers and the performance has been compared on the basis of transmission distance and dispersion. The amplifiers EDFA and SOA have been investigated independently and further compared with hybrid optical amplifiers like RAMAN-EDFA and RAMAN-SOA. It is observed that hybrid optical amplifier RAMAN-EDFA provides the highest output power (12.017 and 12.088 dBm) and least bit error rate (10^?40 and 9.08 × 10^?18) at 100 km for dispersion 2 ps/nm/km and 4 ps/nm/km respectively.     

Performance evaluation of 64 × 10 Gbps and 96 × 10 Gbps DWDM system with hybrid optical amplifier for different modulation formats

In this paper, we investigated the performance of multi terabits DWDM system consisting of hybrid optical amplifier RAMAN-EDFA for different data format such as non-return to zero (NRZ), return to zero (RZ) and differential phase shift keying (DPSK). We find that in 64 × 10 and 96 × 10 Gbps, RZ is more adversely affected by nonlinearities, where as NRZ and DPSK is more affected by dispersion. We further show that RZ provide good quality factor (13.88 dB and 15.93 dB for 64 and 96 channels), less eye closure (2.609 dB and 3.191 dB for 64 and 96 channels) and acceptable bit error rate (3.89 × 10⁸ and 1.24 × 10⁹ for 64 and 96 channels) at the respective distance as compare to other existing modulation format. We further investigated the maximum single span distance covered by using existing data formats.     

An optical continuous phase FSK modulation scheme with an arbitrary modulation index over long-haul transmission fiber link

This paper presents an optical continuous phase frequency shift keying (CPFSK) modulation scheme with an arbitrary modulation index. The detailed principle on the optical CPFSK generation is derived and analyzed, which includes the special case of the minimum-shift keying (MSK) with a modulation index h = 1/2. The differential detection and the coherent detection of CPFSK are also depicted. The performances of the four kinds of the optical CPFSK modulated system with a 40 Gb/s modulation rate whose modulation index are h = 1/2, h = 2/3, h = 3/4 and h = 1 are simulated via the spectral efficiency and the receiver sensitivity over fiber link respectively. In addition, comparison with the differential phase shift keying (DPSK) is taken. Through the calculation of the spectral efficiency of each modulation formats, CPFSK has higher spectral efficiency than DPSK with the same optical devices. The transmission performances of our CPFSK over the fiber link change better as the modulation index increases under the condition of the first order dispersion of the fiber link is completely compensated. Through simulations, a 1200 km transmission distance can be achieved with a modulation index h = 1.     

Performance analysis of optical network based on optical add drop multiplexers with different MZI techniques

This paper presents an investigation on the performance of an optical network in terms of crosstalk based on optical add drop multiplexers with Mach–Zehnder interferometer (MZI), MZI-semiconductor optical amplifier (SOA) and MZI-fiber Braggs gratings (FBG) techniques obtained at 8 × 10 Gbps with 0.1 nm channel spacing wavelength division multiplexing (WDM) transmission with optical add drop multiplexer (OADM) placed at the 20 km point of a 40 km link. It is found that the signal can be transmitted with least BER and better Q-factor with MZI-FBG based OADM and the worst case is found with the MZI-SOA based OADM.     

High speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20 GHz and 40 GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~ 1.5 ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~ 610 fs for 20 GHz pulse train and ~ 570 fs for 40 GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30 dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission.     

Proposal for a 4-channel all optical demultiplexer using 12-fold photonic quasicrystal

In this work, 12-fold photonic quasicrystal (PQC) with cross section equals to 138 μm² has been used to design a 4-channel optical demultiplexer. The size of structure promises its applications in optical integrated circuits (OICs) and also, wavelength division multiplexing (WDM) communication devices. Finite difference time domain (FDTD) method has been employed in order to investigate the structure's band gap and output waveforms of each channel. Four channels, with spacing less than 1 nm and cross-talk level better than ? 2.8 dB have been separated by introducing defects in L-shaped and line defect waveguides (LDWs) in the crystal's structure. It has been shown that, L-shaped waveguides (LWs) are quite more frequency selective than line defect waveguides. Also, it has been found that the exact tuning of the central wavelength of each channel is possible by making use of defects with different radiuses and sites in the waveguides.     

Sub-THz continuous wave generation scheme using high-order harmonics modulated lightwave

We propose a sub-THz continuous wave (CW) generation scheme using a high-order harmonics modulated lightwave (HML) to reduce an electronic dependency of a conventional double sideband suppressed carrier (DSB-SC) scheme. The electronic dependency should be overcome to increase frequency tunability of the conventional DSB-SC scheme. This is because the frequency of a local oscillator (LO), f_LO, should be one-half frequency of the frequency of a desired sub-THz CW in the conventional DSB-SC scheme. The proposed scheme is formed by adding an optical feedback loop to the conventional DSB-SC scheme. In order to verify our proposed scheme, a 120 GHz CW is generated using the LO with f_LO = 20 GHz. Based on our experimental results, we have found that the frequency of the LO can be reduced by our proposed scheme up to one-sixth (20 GHz) of 120 GHz. The 120 GHz CW generated by the proposed scheme has 52 dB higher photomixed output power with narrow spectral linewidth than that of the 120 GHz CW generated by the conventional DSB-SC scheme using the LO with f_LO = 20 GHz. Consequently, our proposed scheme can be helpful to reduce the electronic dependency of the conventional DSB-SC scheme.     

A Reconfigurable Microwave Photonic Channelized Receiver Based on Dense Wavelength Division Multiplexing Using an Optical Comb

A photonic approach to implementing a microwave channelized receiver based on dense wavelength division multiplexing using an optical comb is proposed. In the approach, a flat optical comb with 11 comb lines is generated using two cascaded Mach-Zehnder modulators. Frequency analysis of a microwave signal with multiple-frequency components is realized by using the optical comb together with an optical etalon with a periodic transfer function, a wavelength division multiplexer (WDM) and a photodetector array. The system is investigated numerically. Frequency measurement of a multi-frequency signal with a measurement range from 0.5-11.5 with an accuracy of ± 0.5 GHz is achieved. The reconfigurability of the system realized by tuning the comb-line spacing and the peak positions of the etalon is also evaluated. The improvement of the dynamic range of the system using an optimized periodic filter is also discussed.     

Novel 60 GHz RoF system with optical single sideband mm-wave signal generation and wavelength reuse for uplink connection

In order to improve RF frequency to achieve higher bandwidth and larger capacity, we propose a novel scheme to generate optical single sideband (SSB) millimeter-wave, in which frequency doubling of local radio frequency (RF) is obtained by using one integrated Mach–Zehnder modulator (MZM), and we theoretically investigate the generating principle of SSB. The optical SSB modulation scheme is employed to generate 60 GHz optical mm-wave and the 2.5 Gb/s baseband signal is simultaneously up-converted at the central station (CS) for downlink transmission, and the optical carrier is reused for uplink connection at the base station (BS). The full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF-28) for both uplink connection and downlink connection with less than 2-dB power penalty. Results show the novel 60 GHz RoF system with optical SSB mm-wave signal generation using optical frequency doubling is feasible and we can obtain simple cost-efficient configuration and good performance over long-distance transmission.     

Theoretical ultraslow bright and dark optical solitons in cascade-type GaAs/AlGaAs multiple quantum wells

We show the formation of ultraslow bright and dark optical solitons in a cascade-type three-level system of GaAs/AlGaAs multiple quantum wells (MQWs) structure based on the biexciton coherence in the transient optical response, and study analytically and numerically with Maxwell–Schrödinger equations. The calculated velocity of bright and dark optical solitons are V_g = 2.7 × 10⁴ ms^? 1 and V_g = 8.91 × 10⁴ ms^? 1, respectively. Such investigation of ultraslow optical solitons in MQWs may provide practical applications such as high-fidelity optical delay lines and optical buffers in semiconductor quantum wells structure, because of its flexible design.     

10 Gb/s optical carrier distributed network with W-band (0.1 THz) short-reach wireless communication system

Millimeter-wave (mm-wave) operated in W-band (75 GHz–0.11 THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10 Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1 THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10 Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10 Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20 km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed.     

Microfabrication of solenoid-type RF SMD chip inductors with an Al2O3 core

We investigated micron size, high-performance, and solenoid-type radio-frequency surface-mounted device (SMD) chip inductors with a low-loss Al₂O₃ core for a GHz drive microwave circuit application. Copper coils with a diameter of 27 μm were used and the chip inductors fabricated in this study are 0.86 × 0.46 × 0.45 mm³. The high-frequency characteristics of the inductance (L), quality factor (Q), and impedance (Z) of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). The developed inductors have a self-resonant frequency of 3.7–5.2 GHz and exhibit L of 15–34 nH. The inductors have Q of 38–49 over the frequency ranges of 900 MHz–1.7 GHz. The calculated data obtained from the equivalent circuit and the derived equation of Q described the high-frequency data of L, Q, and Z of the inductors developed quite well.     

Infrared broadband emission of bismuth–thulium co-doped lanthanum–aluminum–silica glasses

The Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission was investigated by the optical absorption and photoluminescence spectra. The super broadband near-infrared emission from 1000 to 2100 nm, which covered the whole O, E, S, C and L bands, was observed in the Bi–Tm co-doped samples, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm^{3+ 3}H₄→³F₄ transition (1440 nm) as well as Tm^{3+ 3}F₄→³H₆ transition (1800 nm). Relative luminescence intensity at 1270, 1440 and 1800 nm wavelength varied depending on the mixing ratio of Bi and Tm and the full-width at half-maximum (FWHM) extending from 1000 to 1600 nm could be 400 nm. These results indicated that Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ glasses could provide potential applications in tunable lasers as well as the broadband optical amplifiers in WDM system.     

High LO-to-RF isolation 94 GHz coplanar monolithic down-converter for FMCW radar sensor applications

This paper presents a 94 GHz monolithic down-converter with low conversion loss and high local oscillator (LO)-to-RF isolation using the 0.1 μm T-gate metamorphic high electron-mobility transistor (MHEMT) technology. The down-converter consists of a one-stage amplifier and a single-balanced mixer based on the high-directivity tandem coupler structure using the air-bridge crossovers, thereby amplifying the RF signals and maximizing the LO-to-RF isolation by using an inherent S₁₂ isolation characteristic of the amplifier and good phase balance of the tandem coupler. The fabricated one-stage amplifier using a 30 μm × 2 MHEMT shows a small signal gain of 7 dB at 94 GHz. The single-balanced mixer comprising two 20 μm × 2 MHEMT Schottky diodes and the tandem coupler with an additional λ/4-length line exhibits the conversion loss less than 7.8 dB and the LO-to-RF isolation higher than 30 dB in a RF frequency range of 91–96 GHz. Two circuits designed both for a 50 Ω impedance system are integrated into the down-converter of a 2.6 × 2.5 mm² chip size, and it shows a low conversion loss of ∼1 dB at 94 GHz and excellent LO-to-RF isolation above 40 dB in a frequency range of 90–100 GHz. This is the best isolation among the W-band monolithic down-converters reported to date.     

Tunable single-longitudinal-mode operation of a sandwich-type YAG/Ho:YAG/YAG ceramic laser

We present a 2.09 μm single-longitudinal-mode sandwich-type YAG/Ho:YAG/YAG ceramic laser pumped by a Tm-doped fiber laser for the first time. A pair of F-P etalons was used to achieve tunable single-longitudinal-mode operation. The maximum single-longitudinal-mode output power of 530 mW at 2091.4 nm was obtained with an absorbed pump power of 8.06 W, corresponding to an optical conversion efficiency of 6.6% and a slope efficiency of 12.7%. Wavelength tunable was achieved by tuning the angle of etalons and the wavelength could be tuned from 2091.1 nm to 2092.1 nm, corresponding to a tuning frequency of 68 GHz. The M² factor was measured to be 1.23.     

Crystallographic orientation-dependent optical properties of GaInSb mid-infrared quantum well laser

The optical properties of compressively strained GaInSb/GaInAlSb quantum well (QW) laser are numerically studied in different crystal orientations solving envelope function equation using finite difference method. The simulation results demonstrate that there is a strong correlation between the optical gain and its emission wavelength with crystal orientation of the QW. The maximum and minimum optical gains are evaluated in the (1 1 3) and (1 1 1) crystal orientations, respectively, due to band mixing effects. The peak emission wavelength can be tuned from 2.4 μm to 2.25 μm by changing the crystal orientation from (1 1 0) to (1 1 1). Typical optical gains are evaluated 3115, 3080, 2790, 3415, and 2940 cm^?1 in (0 0 1), (1 1 0), (1 1 1), (1 1 3), and (1 3 1) crystal orientations, respectively, when the injection carrier density is 3.5 × 10¹⁸ cm^?3. The highest optical power and lower threshold current are obtained in (1 1 3) orientation for the number of quantum wells three.     

Fiber-fault protection WDM-PON using new apparatus in optical networking unit

In this study, we propose and experimentally demonstrate a simple self-protection architecture for WDM passive optical network (PON) by adding a novel 2 × 2 optical switch design in each optical networking unit (ONU). Two adjacent ONUs are interconnected into a group. By using the proposed protection architecture, the affected traffic can be restored immediately against fiber fault in the feeder and distributed fibers. Moreover, the performance of proposed self-protection WDM-PON is also discussed and analyzed.     

Performance comparison between 160 Gb/s WDM and TDM systems

The performances of 160 Gb/s time-division multiplexing (TDM) and 4 × 40 Gb/s wavelength-division multiplexing (WDM) signals are comparatively studied in the nonzero-dispersion shifted fibers (NZDSFs). TDM format is superior to WDM, and with the increase of distance, this advantage is enhanced. In the case of adopting the dispersion managed soliton transmission and dispersion flattened fibers (DFFs) technique, the Q values of both formats change little when the channel space varies. So, TDM technique is applicable to the dense and very long haul transmissions. Only by utilizing the conventional loss and dispersion compensation schemes (NZDSFs + DCFs + EDFAs), the available transmission distance of dense WDM signals reaches 1000 km, and for TDM format, it even extends to 2000 km. Both systems have the analogue characteristics: a higher pulse power benefits system's working; ASE noise is the dominant impact factor of system performance; both format's system performances are improved for the case of less channel number; the channel space and duty cycle of return zero pulse have little effect on Q; the impact of duty cycle relates to the filter bandwidths, XPM induced sidebands and pulse broadening effect; the influence of channel space is determined by the walk-off effect.