Tunable superlattice p-i-n photodetectors: characteristics, theory, and application

Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response

Electro-optic dual-comb interferometry over 40-nm bandwidth

Dual-comb interferometry is a measurement technique that uses two laser frequency combs to retrieve complex spectra in a line-by-line basis. This technique can be implemented with electro-optic frequency combs, offering intrinsic mutual coherence, high acquisition speed and flexible repetition-rate operation. A challenge with the operation of this kind of frequency comb in dual-comb interferometry is its limited optical bandwidth. Here, we use coherent spectral broadening and demonstrate electro-optic dual-comb interferometry over the entire telecommunications C band (200 lines covering ~ 40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per spectral line). These results offer new prospects for electro-optic dual-comb interferometry as a suitable technology for high-speed broadband metrology, for example in optical coherence tomography or coherent Raman microscopy

Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments

We experimentally investigate mutual information and generalized mutual information for coherent optical transmission systems. The impact of the assumed channel distribution on the achievable rate is investigated for distributions in up to four dimensions. Single channel and wavelength division multiplexing (WDM) transmission over transmission links with and without inline dispersion compensation are studied. We show that for conventional WDM systems without inline dispersion compensation, a circularly symmetric complex Gaussian distribution is a good approximation of the channel. For other channels, such as with inline dispersion compensation, this is no longer true and gains in the achievable information rate are obtained by considering more sophisticated four-dimensional (4D) distributions. We also show that for nonlinear channels, gains in the achievable information rate can also be achieved by estimating the mean values of the received constellation in four dimensions. The highest gain for such channels is seen for a 4D correlated Gaussian distribution

Phase-sensitive fiber-optic parametric amplifiers and their applications

The basics and recent progress in nonlinear fiber-based phase-sensitive parametric amplifiers is discussed. In addition, their potential use as in-line amplifiers, resulting in significant link performance improvement potential, is highlighted

Optical bandgap engineering in nonlinear silicon nitride waveguides

Silicon nitride is awell-established material for photonic devices and integrated circuits. It displays a broad transparency window spanning from the visible to the mid-IR and waveguides can be manufactured with low losses. An absence of nonlinear multi-photon absorption in the erbium lightwave communications band has enabled various nonlinear optic applications in the past decade. Silicon nitride is a dielectric material whose optical and mechanical properties strongly depend on the deposition conditions. In particular, the optical bandgap can be modified with the gas flow ratio during low-pressure chemical vapor deposition (LPCVD). Here we show that this parameter can be controlled in a highly reproducible manner, providing an approach to synthesize the nonlinear Kerr coefficient of the material. This holistic empirical study provides relevant guidelines to optimize the properties of LPCVD silicon nitride waveguides for nonlinear optics applications that rely on the Kerr effect

Low-Power 400-Gbps Soft-Decision LDPC FEC for Optical Transport Networks

We present forward error correction systems based on soft-decision low-density parity check (LDPC) codes for applications in 100–400-Gbps optical transport networks. These systems are based on the low-complexity “adaptive degeneration” decoding algorithm, which we introduce in this paper, along with randomly-structured LDPC codes with block lengths from 30 000 to 60 000 bits and overhead (OH) from 6.7% to 33%. We also construct a 3600-bit prototype LDPC code with 20% overhead, and experimentally show that it has no error floor above a bit error rate (BER) of 10−15 using a field-programmable gate array (FPGA)-based hardware emulator. The projected net coding gain at a BER of 10−15 ranges from 9.6 dB at 6.7% OH to 11.2 dB at 33% OH. We also present application-specific integrated circuit synthesis results for these decoders in 28 nm fully depleted silicon on insulator technology, which show that they are capable of 400-Gbps operation with energy consumption of under 3 pJ per information bit

Phase-coherent lightwave communications with frequency combs

Fiber-optical networks are a crucial telecommunication infrastructure in society. Wavelength division multiplexing allows for transmitting parallel data streams over the fiber bandwidth, and coherent detection enables the use of sophisticated modulation formats and electronic compensation of signal impairments. In the future, optical frequency combs may replace multiple lasers used for the different wavelength channels. We demonstrate two novel signal processing schemes that take advantage of the broadband phase coherence of optical frequency combs. This approach allows for a more efficient estimation and compensation of optical phase noise in coherent communication systems, which can significantly simplify the signal processing or increase the transmission performance. With further advances in space division multiplexing and chip-scale frequency comb sources, these findings pave the way for compact energy-efficient optical transceivers.Comment: 17 pages, 9 figure

Building up low-complexity spectrally-efficient Terabit superchannels by receiver-side duobinary shaping

Recently, an increasing interest has been put on spectrally-efficient multi-carrier superchannels for beyond 100G. Apart from orthogonal frequency-division multiplexing (OFDM) and Nyquist wavelength-division multiplexing (WDM), another low-complexity WDM approach based on transmitter-side pre-filtering and receiver-side duobinary shaping is proposed to build up multi-carrier superchannels. This approach is referred to as receiver-side duobinary-shaped WDM (RS-DBS-WDM). Generation and transmission of a 1.232-Tbit/s 11-carrier superchannel is experimentally demonstrated. The superchannel signal can be well fit inside the passband of multiple 300-GHz reconfigurable optical add and drop multiplexers (ROADMs). In the superchannel scenario, the proposed RS-DBS-WDM is qualitatively compared with OFDM and Nyquist-WDM in terms of implementation complexity. In sum, the proposed RS-DBS-WDM approach features high transceiver analog-bandwidth efficiency, high spectral-efficiency, the absence of specific spectral manipulation, compatibility with conventional WDM technologies and coherent detection algorithms, and comparable implementation penalty

Mitigation of nonlinearities using conjugate data repetition

We investigate a time-domain implementation of generalized phase-conjugated twin waves which we call conjugate data repetition. A theory based on time-domain perturbation analysis explaining the mitigation of nonlinear effects is provided, and the concept is evaluated using numerical simulations. Compared to PM-QPSK at the same channel bit rate, the single-channel transmission reach in a conventional system with standard single-mode fiber of conjugate data repetition-QPSK is increased by approximately a factor of 2