Optical Frequency Shift Keying Research Articles

Secure FSO communication based on optical frequency-hopping technology using delay interferometers

—A novel optical frequency-hopping (OFH) scheme using optical delay interferometers (DI) is proposed and demonstrated for secure transmission in free space. By performing carrier suppression modulation on the light wave emitted by the laser and connecting the phase modulator (PM) and DI in series, the conversion of the light wave modulated by the Mach-Zehnder modulator (MZM) from phase modulation to intensity modulation can be realized, and finally output the desired optical frequency-shift-keying (OFSK) carrier signal. Meanwhile, by controlling the positions of the frequencies of the positive and negative first-order sideband light waves on the DI frequency response curve, the OFSK signals output by the two ports of the DI can be complemented in the time domain. For the proposed OFH scheme, we carried out simulation experiments of 5 km free-space link transmission and back-to-back transmission with a communication rate of 10 Gbps, and the simulation results proved the feasibility of the scheme. Additionally, we also analyze the security performance of the proposed scheme and give the security space based on the eavesdropping probability.

Photonic Generation of Microwave Frequency Shift Keying Signals

A novel approach to generating microwave frequency shift keying (FSK) signals using a polarization modulator (PolM) and a dual-polarization Mach–Zehnder modulator (DPol-MZM) is proposed and experimentally demonstrated. In the proposed system, the PolM is employed to modulate the polarization state of an input linearly polarized lightwave to switch between two orthogonal directions, leading to the generation of a polarization shift keying (PolSK) signal. Then the PolSK signal is sent to a DPol-MZM, which is made up of two polarization multiplexed sub-MZMs by a polarization controller (PC). Two microwave signals with different frequencies are applied to the sub-MZMs. After aligning the orthogonal directions of the PolSK signal with the axes of the DPol-MZM by the PC, the PolSK signal can be converted into a microwave FSK signal. A proof-of-concept experiment is carried out to verify the proposed system. When the sub-MZMs in the DPol-MZM are biased at a quadrature point, a double sideband microwave FSK signal at 3/6.5 GHz with a bit rate of 1.25 Gb/s is generated and transmitted over 10 km of single-mode fiber. When the sub-MZMs are biased at minimum point, an optical carrier suppression microwave FSK is achieved at frequency-doubled 6/14 GHz with a bit rate of 2.5 Gb/s.

High-speed optical FSK demodulator using plasmonic nanorods

An optical frequency-shift keying (FSK) demodulator with ultrasmall plasmonic nanorods that can filter the coherent optical frequency is developed. Since the filtering efficiency depends strongly on the position and number of the plasmonic nanorods in the array, binary teaching–learning-based optimization (BTLBO) algorithm is proposed to design an array of the plasmonic nanorods in order to achieve maximum absorption coefficient spectrum. In BTLBO, a group of learner consists of a matrix with binary entries; control the presence (‘1’) or the absence (‘0’) of the nanoparticles in the array.

Investigation on the combined orthogonal FSK/ASK labeled signal based on cross gain modulation in a SOA

An optical frequency shift keying (FSK) transmitter performed by the cross gain modulation (XGM) in a semiconductor optical amplifier (SOA) is used in an optical label switching (OLS) system with 622 Mbit/s FSK label and 10 Gbit/s amplitude shift keying (ASK) payload. The key parameters in this system are optimized to achieve the best performance of FSK/ASK signal, including the input power of LD, the extinction ratio (ER) of the control light and that of the ASK payload. Besides, the transmission performance of ASK payload and FSK label is also investigated after propagating in the 50 km single-mode fiber (SMF).

Optical homodyne receiver utilizing image rejection in FSK/ASK re-modulation WDM-PON

Optical frequency shift keying (FSK) homodyne detection utilizing image rejection in FSK/amplitude shift keying (ASK) re-modulation wavelength-division-multiplexed passive optical network (WDM-PON) is proposed and demonstrated. Image rejection is adopted to achieve better performance. We show the result in back-to-back and 40-km distance respectively and apparent improvement is obtained in the latter situation by using image rejection. Several factors which affect the image rejection receiver are analyzed in order to find out the optimum parameters. Result shows that the presented scheme is suitable for super long reach access network, especially for future metro access network.

High speed optical transmission utilizing constant envelope modulation based on frequency shift keying and minimum-shift keying (Invited Paper)

A novel 40-Gb/s constant envelope optical frequency shift keying (FSK) transmitter and the transmission characteristics are investigated both by simulation and experiment. Meanwhile, to increase the spectrum efficiency of FSK, we propose a novel optical minimum-shift keying (MSK) scheme and analyze its performance compared with other MSK schemes and other traditional modulation formats. Simulation and experimental results show that the novel FSK scheme could be a potential candidate for the future high speed transmission and label switching systems. And the novel MSK scheme deserves future deep research for its potential excellent performance.

Investigation of high-speed optical FSK generation scheme based on carrier suppression and phase modulation

We propose and numerically investigate a novel high-speed (40-Gb/s and above) optical frequency shift-keying (FSK) transmitter scheme. By optical carrier-suppressed modulation and differential phase-shift-keying (DPSK) to intensity modulation (IM) conversion, only one light source is needed in the proposed scheme to generate high-speed optical FSK signals. By using a Mach–Zehnder modulator (MZM) as phase modulator and an additional delay interferometer (DI) cascaded after the carrier-suppressed MZM to suppress the remaining carrier, the performance of our scheme can compete with the double-light-source counterparts. The transmission performances of the FSK signal generated with the proposed scheme as well as detuning and bandwidth tolerance of the demodulation filter are also carefully investigated. Simulation results show that the proposed FSK generation scheme is very suitable for the next-generation optical access network and optical label switching network. A potential application of our scheme in high-speed passive optical network is proposed.

A novel optical frequency-shift-keying transmitter based on polarization modulation

In this letter, we propose and experimentally demonstrate a novel optical frequency-shift-keying (OFSK) transmitter based on polarization modulation. It features data rate transparency and continuous tuning of wavelength spacing, providing great flexibility in OFSK transmitter design. The performance of the transmitter has been further experimentally characterized.

Coherent encoding of optical FSK header for all optical label swapping systems

A numerical investigation on the limits of the optical frequency shift keying (FSK) label coding technique is presented, as well as an optimization of the critical parameters involved into it. The principle of the technique concerns a typical FSK modulated label, combined with an intensity modulated (IM) payload on the same optical carrier, via four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). Simulations have been carried out for an intensity modulated nonreturn to zero (NRZ) 10-Gbs payload combined with a 625-Mbs FSK modulated header. The influence of the key parameters of the method such as the extinction ratio (ER) of the signal, the dynamic range of the FWM module and the FSK tone spacing have been investigated in combination with the system limitations, related to the propagating distance and the number of intermediate label swapping nodes. A 2R regeneration stage responsible for the label removal and reinsertion, and for the payload wavelength conversion and regeneration, has been adopted, based on a single Mach-Zender interferometer (MZI)-SOA stage. The FSK encoded label transmitter includes a compensation scheme for the removal of the residual amplitude intensity effect that FSK label causes on the IM modulated payload. A detailed numerical model has been implemented for the description of the FWM, due to its decisive role in the proposed architecture. It was found that it is possible to have successful (Q factor higher than 6 for both payload and header) transmission over five, 50-km spaced hops and assuming 10-Gbs payload with 625-Mbs header.

Optical FSK transmission with group delay compensated balance detection

A novel balance detection scheme for high-speed optical frequency-shift-keying (FSK) transmission was proposed. Fiber dispersion can be compensated by a balanced photodetector with an optical delay. 10Gbit/s optical FSK transmission over a 130km single mode fiber was demonstrated, where the FSK signal was generated by using aLiNbO3 high-speed optical FSK modulator.

High-speed optical FSK modulator for optical packet labeling

We described a novel optical label swapping (OLS) technique for optical packet systems using frequency-shift-keying (FSK) optical labeling. High-speed optical FSK signal can be generated by using an external FSK modulator consisting of four optical phase modulators. The FSK modulator was based on optical single-sideband (SSB) modulation technique, and comprised of traveling-wave electrodes for high-speed frequency switching. We demonstrate 10 Gbps FSK transmission, and simultaneous modulation by FSK and intensity modulation (IM). OLS using double-sideband modulation was also demonstrated, where this technique can be used for a bundled wavelength-domain-multiplexing (WDM) channels without using an array of pumping light sources.

10Gbit/s FSK transmission over 95km SMF using a LiNbO3 modulator

We demonstrate high-speed optical frequency-shift-keying (FSK) transmission over a 95km single-mode fiber (SMF) at 10Gbit/s using a LiNbO3 optical FSK modulator and an optical interleaver. The measured eye diagrams, bit error rate (BER) performances and optical spectrum indicate the FSK modulation is similar to zero chirp non-return-to-zero (NRZ) on-off-keying (OOK) transmission. Therefore, in view of dispersion tolerance, the FSK modulation can be treated as well as NRZ OOK.

All-optical modulation format conversion from frequency-shift-keying to phase-shift-keying

We have realized a novel optical modulation format conversion using double-sideband suppressed-carrier modulation. An optical wideband frequency-shift-keying (FSK) signal, generated by an external FSK modulator, can be directly converted into an optical phase-shift-keying (PSK) signal, where the FSK signal having two spectral components was fed to an optical intensity modulator followed by an optical bandpass filter. Optical frequency of the FSK signal was mapped into optical phase of the bandpass filter output whose phase deviation depends on a chirp of the FSK signal.We demonstrated modulation format conversion from FSK to PSK at 10 Gbps, by using a high-speed optical FSK modulator and a dual electrode Mach-Zehnder intensity modulator.

Intensity-modulated labeling and all-optical label swapping on angle-modulated optical packets

We proposed and investigated superimposing intensity-modulated labels onto high-speed angle-modulated payloads in optical label-switching packet networks. This can largely simplify the all-optical label swapping, including label extraction, processing, removal, and new label insertion. The transmission performances of 1.244-Gb/s on-off keying labels on 9.953-Gb/s optical frequency-shift keying and differential phase-shift keying payloads were investigated; and the all-optical label swapping was successfully demonstrated with low penalty.

Optical FSK/IM Signal Generation Using an Integrated Optical FSK Modulator

We demonstrate simultaneous optical modulation by frequency shift keying (FSK) and intensity modulation (IM) using a newly developed high-speed FSK modulator, for optical packet systems where payload and label signals are, respectively, in IM and FSK format. The modulator consists of four optical phase modulators, with traveling-wave electrodes to obtain high-speed frequency switching and large frequency deviation in FSK modulation.

LiNbO3 high-speed optical FSK modulator

An optical frequency-shift-keying (FSK) modulator with a pair of Mach-Zehnder structures that can switch optical frequency is developed. The operation is demonstrated at a 10 Gbit/s FSK transmission conducted on a standard single-mode fibre of 60 km, where the FSK signal is demodulated by a fibre Bragg grating.

Performance of Manchester-coded payload in an optical FSK labeling scheme

The modulation crosstalk between combined frequency-shift keying (FSK) and intensity modulation (IM) in an optical label-switching network is analyzed both theoretically and experimentally. A comparison between the performance of nonreturn-to-zero (NRZ) and Manchester-coded payload is made. It is shown that Manchester coding of the payload helps to suppress the crosstalk introduced into the optical FSK label, thus achieving better network performance than NRZ coding.

An optical FSK transmitter based on an integrated DFB laser-EA modulator and its application in optical labeling

An optical frequency-shift-keying (FSK) transmitter based on an integrated distributed feedback laser-electroabsorption modulator is proposed and demonstrated. The feasibility of its application in optical labeling is also validated by the experimental results. The generated optical signal, consisting of a 10-Gb/s intensity-modulated payload and a 312-Mb/s FSK label, can be recovered error free after transmission over 88-km standard single-mode fiber.

Data remodulation on downstream OFSK signal for upstream transmission in WDM passive optical network

Employment of optical frequency shift keying (OFSK) as the downstream modulation format in a WDM passive optical network is proposed. The upstream OOK transmitter at the ONU can be realised by remodulating the constant-intensity downstream OFSK signal power with the upstream data. Transmission and remodulation of 2.5 Gbit/s downstream and upstream signals were successfully demonstrated.

An optical FSK-based label coding technique for the realization of the all-optical label swapping

A new approach on optical label encoding for the realization of the all-optical label swapping in transparent optical packet switched networks is proposed and tested via simulation. The proposed method is based on the combination of the optical frequency shift keying (OFSK) modulated label with the on-off keying (OOK) modulated payload on the same optical carrier. The combination has been achieved by feeding the two independent optical signals, carrying the OFSK modulated label, and the OOK modulated payload, at the input of a semiconductor optical amplifier (SOA). The obtained four wave mixing at the output of the SOA combines label and payload on one carrier. The simulations have been carried out for 625-Mb/s labels and 10-Gb/s payload and for three 80-km span hops. At each hop the label was removed and a new locally generated label was loaded on the payload. The bit error rate calculations were made for both label and payload at each node, which proved the feasibility of the proposed method.