Optical Single Sideband Modulator Without Second-Order Sidebands

Abstract

An optical single sideband modulator without generating both the −2ndand +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 secondorder 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 secondorder 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.

Photonic Techniques for Generating a Single RF Sideband With No Second Order Sidebands

“…A second order harmonic component is generated when the carrier beats with the remaining second order sideband at the photodetector. Another approach is based on a dual-parallel MZM (DP-MZM) [8]. It has the drawback of requiring a power splitter and two electrical couplers.…”

“…The structure shown in Fig. 1(a) does not generate both second order upper and lower sidebands and does not require any electrical component, which is clearly an advantage compared to the structures presented in [7] that uses a 120° coupler to split an RF signal and in [8] that involves a 90° hybrid coupler and a 180° hybrid coupler.…”

“…Hence, without the effect of chromatic dispersion, no second order harmonic component is present at the link output. However, chromatic dispersion in a long-haul fibre optic link alters the sideband phases, which causes the presence of the second order harmonic with a frequency-dependent amplitude as shown in (8).…”

“…Both the upper and lower second order sidebands are eliminated. Compared to the structures presented in [7] and [8], the DPol-DPMZM based OSSB modulator has the advantage of only a single standard electrical coupler is needed. Since the third order sideband on the same side as the wanted first order sideband is eliminated, there is no second order harmonic component generated after photodetection.…”

A 1-D Heterodyne Lens-Free Optical Phased Array Camera With Reference Phase Shifting

“…Silicon photonics fabrication processes have enabled integration of many optical elements on a single chip. On-chip high performance components such as modulators [1]- [3], grating couplers [4], [5], lasers [6], [7], and photodiodes [8], [9] in close proximity enable novel systems and architectures not practical in bench-top settings. Furthermore, the hybrid photonic-electronic integrated circuits [10]- [12] with the eventual co-integration enables new approaches not practical in either of the platforms by themselves.…”