Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

Photonic signal processing offers the prospect of realizing extremely high multigigahertz sampling frequencies, overcoming inherent electronic limitations. This stems from the intrinsic excellent delay properties of optical delay lines. These processors provide new capabilities for realizing high time-bandwidth operation and high-resolution performance. In-fiber signal processors are inherently compatible with fiber-optic microwave systems and can provide connectivity with built-in signal conditioning. Fundamental principles of photonic signal processing, including sampling, tuning, and noise, are discussed. Structures that can extend the performance of photonic signal processors are presented, including methods for improving the filter shape characteristics of interference mitigation filters, techniques to increase the stopband attenuation of bandpass filters, and methods to achieve large free spectral range. Several photonic signal processors, including high-resolution microwave filters, widely tunable filters, arbitrary waveform generators, and fast signal correlators, are discussed. Techniques to solve the fundamental noise problem in photonic signal processors are described, and coherence-free structures for few-tap notch filters are discussed. Finally, a new concept for realizing multiple-tap coherence-free processor filters, based on a new frequency-shifting technique, is presented. The structure not only eliminates the phase-induced intensity noise limitation, but can also generate a large number of taps to enable the achievement of processors with high performance and high resolution.

Photonic signal processing of microwave signals

The recently developed digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as $M$ -ary phase-shift keying and quadrature-amplitude modulation. Moreover, in the digital domain, we can equalize all linear transmission impairments such as group-velocity dispersion and polarization-mode dispersion of transmission fibers, because coherent detection preserves the phase information of the optical signal. This paper reviews the history of research and development related to coherent optical communications and describes the principle of coherent detection, including its quantum-noise characteristics. In addition, it discusses the role of digital signal processing in mitigating linear transmission impairments, estimating the carrier phase, and tracking the state of polarization of the signal in coherent receivers.

Fundamentals of Coherent Optical Fiber Communications

We give a tutorial review and brief summary of the present status of waveguide electrooptic modulators.

Waveguide Electrooptic Modulators

The outstanding phase-noise performance of optical frequency combs has led to a revolution in optical synthesis and metrology, covering a myriad of applications, from molecular spectroscopy to laser ranging and optical communications However, the ideal characteristics of an optical frequency comb are application dependent In this review, the different techniques for the generation and processing of high-repetition-rate (>10GHz) optical frequency combs with technologies compatible with optical communication equipment are covered Particular emphasis is put on the benefits and prospects of this technology in the general field of radio-frequency photonics, including applications in high-performance microwave photonic filtering, ultra-broadband coherent communications, and radio-frequency arbitrary waveform generation

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201300126

Optical frequency comb technology for ultra‐broadband radio‐frequency photonics

Single side-band (SSB) technologies are especially useful in optical fiber communication systems, such as higher density wavelength multiplexing and long-haul fiber transmission due to less nonlinear optical effects, because of the reduced optical power. This letter reports on the SSB modulation performance of a LiNbO/sub 3/ integrated modulator consisting of four phase modulator waveguides. Optical SSB modulation with suppressions of main carrier (-22.6 dB) and J/sub 3/ subcarrier (-18.4 dB) of a 10-GHz single-tone signal with a driving voltage of 6.3 V/sub p-p/ was demonstrated. The total insertion loss was 10.6 dB.

Single side-band modulation performance of a LiNbO 3 integrated modulator consisting of four-phase modulator waveguides

High-speed control of lightwave using electrooptic (EO) effect is investigated in this paper. Agile optical frequency shift can be achieved by optical single-sideband (SSB) and frequency-shift-keying (FSK) modulators, where high-speed optical phase-shift-keying (PSK) signals can also be generated by using FSK/SSB modulators. We also describe ultrahigh extinction ratio optical intensity modulation (IM) technique for two-tone lightwave signals with high spurious suppression, which is useful for photonic microwave and millimeter-wave generation. In addition, we investigated high-order optical sideband generation techniques: quadruple dual-sideband suppressed carrier (QDSB-SC) modulation and reciprocating optical modulation (ROM). Sub-tetrahertz signals can be obtained from lightwaves with high-order sidebands

High-Speed Control of Lightwave Amplitude, Phase, and Frequency by Use of Electrooptic Effect

Wavelength-tunable ultra-flat optical frequency comb generation is demonstrated using only a conventional Mach-Zehnder modulator that is asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. A 10 GHz-spaced frequency comb with a 10 dB bandwidth of 230 GHz was experimentally generated. In addition, 50 nm widely wavelength tunable operation was achieved.

Widely wavelength-tunable ultra-flat frequency comb generation using conventional dual-drive Mach-Zehnder modulator

A hermetically packaged x-cut LiNbO/sub 3/ optical single-sideband modulator is presented, which successfully performs a carrier-suppression ratio over 25 dB with an RF driving voltage of 8 V/sub p-p/ at 10 GHz.

Masayuki Izutsu

Papers

Single side-band modulation performance of a LiNbO 3 integrated modulator consisting of four-phase modulator waveguides

High-Speed Control of Lightwave Amplitude, Phase, and Frequency by Use of Electrooptic Effect

Widely wavelength-tunable ultra-flat frequency comb generation using conventional dual-drive Mach-Zehnder modulator

X-cut lithium niobate optical single-sideband modulator

Direct measurement of chirp parameters of high-speed Mach–Zehnder-type optical modulators