Optical SSB Modulation Scheme Based on Phase-Modulator and Vertical-Cavity-Surface-Emitting Laser

In this paper, we investigate the optical power fluctuation of the output in optical comb generator using an optical single sideband (SSB) modulator with a fiber loop. This fluctuation is caused by undesired sidebands of the SSB modulator. We show that the fluctuation can be suppressed by stabilizing the fiber loop length. In experiment, the averaged peak-to-peak power fluctuation of 23 comb outputs was suppressed from 0.86 dB to 0.13 dB.

We propose and demonstrate an optical single sideband (OSSB) modulation approach with continuously tunable optical carrier-to-sideband ratio (OCSR) theoretically and experimentally. In the proposal, one dual-parallel Mach-Zehnder modulator (DP-MZM) acts as a key component. By properly setting the modulator, three separate sub-modulators inside the DP-MZM can be used to realize the OSSB modulation, optical carrier phase-shift, and lightwave interference. By adjusting the bias voltage of one sub-modulator, the OCSR can be tuned continuously. In the experiment, the tuning range of OCSR is found to be between-20.8 dB and 23.5 dB at modulation index m=0.2. We also analyze the relationship between the OCSR and RF power after detection. It is found that with properly adjusting the OCSR, the receiver sensitivity can be greatly improved.

Using a hyperfine blocking filter based on a virtually imaged phased-array as the spectral disperser, we present a novel scheme of optical carrier-suppressed single sideband (SSB) modulation. Our experiments demonstrate sideband suppression of /spl sim/28 dB at only a 2.9-GHz offset for single subcarrier amplitude modulated at 622 Mb/s. Furthermore, the hyperfine blocking filter can be tuned for simultaneous optical SSB and strong carrier suppression to /spl sim/30 dB lower in optical power than the unsuppressed sideband.

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

In this work, we experimentally demonstrate a 100Gb/s/λ downstream transmission link for coherent passive optical networks (PONs) up to 50 km, achieving an optical power budget of 29 dB through polarization multiplexing (PolMux) of two 50 Gb/s channels using multiband carrierless amplitude phase modulation (multiCAP) and optical single side band (OSSB) modulation. Additionally, we introduce a separate PolMux 50 Gb/s link that presents an optical power budget of 38.7 dB. Both links have been achieved using a simplified polarization-demultiplexing heterodyne coherent receiver. The robustness of the system is experimentally evaluated by analyzing its response to various input states of polarization. The transmission has been accomplished using 10 GHz electrical bandwidth devices at both the transmission and receiving ends, thereby paving the way for low-cost 100G links suitable for applications such as PONs.

In this paper, a reconfigurable and tunable optoelectronic oscillator (OEO) based on the stimulated Brillouin scattering (SBS) effect is proposed and theoretically demonstrated. Based on the same structure, the OEO can generate one tunable microwave signal, two output microwave signals, or multi-frequency tunable signals. In order to obtain the carrier-suppressed double sideband (CS-DSB) signal, the single drive MZM is considered at the minimum transmission point (MITP). After passing through the tunable optical bandpass filter (TBPF), we can obtain the carrier-suppressed single sideband (SC-SSB) signal. By using the controllable SC-SSB signals, the corresponding signals are constructed. In the proposed structure, multi-pump lights are generated using carrier suppression single-sideband modulation and an optical tunable filter. As a consequence, a reconfigurable and tunable OEO can be achieved. By using one laser and an arbitrary waveform generator (AWG), multiple-frequency tunable microwave signals can be generated. The design concept and simulated results show that the proposed OEO is flexible, which can be used to offer the possibility to process multi-type microwave signals simultaneously.

Three wave mixing using a fiber ring resonator scheme is discussed, and experimental results are presented. In this scheme, an optical nonlinear medium is placed into the fiber ring laser cavity, and a semiconductor optical amplifier and a tunable optical band pass filter (TOBPF) are used as the gain medium and lasing wavelength selector. The phase-matching condition, which is necessary for efficient wave mixing, can easily be satisfied by tuning the TOBPF. Second-harmonic generation (SHG) and sum-frequency generation (SFG) were demonstrated using a LiNbO3 waveguide with a periodically domain inverted structure. Enhancements of SHG and SFG were achieved.

Repeated Bidirectional Transmission Using Two 4-Port Optical Circulators and a Bidirectional EDFA without Isolators

A microwave frequency shift keying optoelectronic oscillator (FSK-OEO) based on an optical single-sideband (OSSB) modulator is proposed and experimentally demonstrated. In the proposed FSK-OEO, a dual-drive Mach-Zehnder modulator (DDMZM) is employed to implement the optical single sideband modulation through the 90° phase shift method. By appropriately setting the amplitude of the coding signal applied to the DC port of the DMZM, a FSK microwave signal is generated. In the experiment, 9.995/10.004 GHz and 10.371/11.014 GHz microwave FSK signals were successfully generated by using the proposed OEO scheme. This scheme can generate high-frequency and low-phase-noise FSK signals without relying on high-frequency signal sources. Additionally, the pulse compression performance of the generated signals was also demonstrated.

A full-open-cavity random fiber laser with compact structure and hundreds of picometers tuning range is proposed. A tunable optical bandpass filter is used in the TRFL for spectral filtering and to choose different laser wavelengths.

In this work, a pulsed wavelength-tunable Brillouin fiber laser based on a Fourierdomain mode-locking (FDML) source with a repetition rate of 4.2 kHz is presented. The tunable Brillouin laser is formed by a fiber-ring cavity (for the Stokes signal amplification) within a primary fiber-ring cavity for generating an FDML signal. The primary cavity is formed by an erbium-doped fiber amplifier and a fiber Fabry-Perot filter (FFP-F) as the gain medium and the tunable optical bandpass filter, respectively. A spectral laser tuning range of 2.54 nm centered in 1531 nm was achieved by adjusting the offset voltage of the FFP-F, while a variation, from 0.282 to 0.462 nm, on the Brillouin linewidth of the laser was achieved by setting the amplitude of a modulation signal applied in the FFP-F. A laser pulsewidth of 6.50 μs was measured, and an output power of -7 dBm was achieved.

A tunable optical band-pass filter using an optically active, optically biaxial crystal is proposed. In a biaxial crystal, the direction of the optical axis generally depends on the wavelength. This filter capitalizes on this property and the optical activity. The filter contains a crystal sandwiched between a polarizer and an analyzer which are set in a crossed-Nicol position. The central wavelength can be selected by changing the direction of the light propagation in the crystal by rotating the crystal.

We present a new, alternative approach to realize a wavelength swept light source with no fundamental limit to sweep speed. Amplified spontaneous emission (ASE) light alternately passes a cascade of optical gain elements and tunable optical bandpass filters. We show that for high sweep speeds, the control signal for the different filters has to be applied with a defined, precise phase delay on the order of nanoseconds, to compensate for the light propagation time between the filters and ensure optimum operation. At a center wavelength of 1300 nm sweep rates of 10 kHz, 100 kHz and 340 kHz over a sweep range of 100 nm full width and an average power of 50 mW are demonstrated. For application in optical coherence tomography (OCT), an axial resolution of 12 microm (air), a sensitivity of 120 dB (50 mW) and a dynamic range of 50 dB are achieved and OCT imaging is demonstrated. Performance parameters like coherence properties and relative intensity noise (RIN) are quantified, discussed and compared to the performance of Fourier Domain Mode Locked (FDML) lasers. Physical models for the observed difference in performance are provided.

We propose a technique for the generation of broadband optical single sideband modulated signals. The technique is based on optically processing an optical double sideband signal using stimulated Brillouin scattering effect. An unwanted sideband suppression over 40 dB in a broadband range from 50 MHz to 20 GHz is experimentally demonstrated. In addition, we apply the generated optical single sideband signal for the spectral characterization of polarization dependent parameters of optical components. The experimental characterization of the polarization dependent loss and the differential group delay of a phase-shifted fiber Bragg grating is performed in order to demonstrate the feasibility of the technique.

In the paper, we proposed a simple method to generate two millimeter-wave (MMW) signals for radio-over-fiber (RoF) systems. Firstly, we utilized two cascaded dual-drive Mach-Zehnder modulators (DD-MZMs), both biased at the maximum transmission bias point (MATBP), to implement frequency octupling. And then, a wavelength division multiplexing demultiplexer (WDM Demux) is followed to filter out the −4 order optical carriers of the second DD-MZM's output to enable an optical single side-band (OSSB) modulation by only modulating the baseband data onto the −4 order optical carrier. On the other hand, the +2 order optical carrier of the first DD-MZM's output is filtered out based on an optical splitter (OS) and an optical rectangle band-pass filter (ORBPF). After that, the +2 and the −4 order optical carriers are combined to be transmitted in an identical fiber path. Finally, a 45 GHz and a 60 GHz MMWs were generated simultaneously with a 7.5 GHz local oscillator (LO), by self-heterodyning these optical carriers in a photonic detector (PD). After 50 km single-mode fiber (SMF) transmission distances, the 45 GHz and the 60 GHz MMWs were maintaining good performance with clearly open eye diagrams and power penalties of 0.6 dB and 1.1 dB, respectively, at a bit-error-rate (BER) of 1×10−9.