Abstract
Optoelectronic devices which play important roles in high-speed optical fiber networks can offer effective measurement methods for optoelectronic devices including optical modulators and photodetectors. Precise optical signal modulation is required for measurement applications. This paper focuses on high-speed and precise optical modulation devices and their application to device measurement. Optical modulators using electro-optic effect offers precise control of lightwaves for wideband signals. As examples, this paper describes frequency response measurement of photodetectors using high-precision amplitude modulation and wavelength domain measurement of optical filters using fast optical frequency sweep. Precise and high-speed modulation can be achieved by active trimming which compensates device structure imbalance due to fabrication error, where preciseness can be described by on-off extinction ratio. A Mach-Zehnder modulator with sub Mach-Zehnder interferometors can offer high extinction-ratio optical intensity modulation, which can be used for precise optoelectronic frequency response measurement. Precise modulation would be also useful for multi-level modulation schemes. To investigate impact of finite extinction ratio on optical modulation, duobinary modulation with small signal operation was demonstrated. For optical frequency domain analysis, single sideband modulation, which shifts optical frequency, can be used for generation of stimulus signals. Rapid measurement of optical filters was performed by using an optical sweeper consisting of an integrated Mach-Zehnder modulator for optical frequency control and an arbitrary waveform generator for generation of a source frequency chirp signal.
Highlights
Published: 11 May 2021For high-speed optical links, external modulators are commonly used to generate broadband optical signals
This paper describes precise optical modulation techniques which can be used for device measurement
The imbalance between the two optical phase modulators can be described by a chirp parameter which is defined by ratio of parasitic optical phase change to amplitude change
Summary
For high-speed optical links, external modulators are commonly used to generate broadband optical signals. Various multilevel modulation techniques have been investigated to increase transmission capacity, where high-speed and precise lightwave control is required in optical-to-electric and electric-to-optical signal conversion [1]. Precise lightwave control is required in analog RoF systems, which would be sensitive to nonlinearity and frequency response, as well as in digital transmission systems with multilevel modulation formats. We can measure the frequency response of the photodetector, by sweeping the frequency of the signal fed to the optical modulator which generates the two-tone signal. High ER modulation is required for generation of a pure two-tone signal, so that the precise characterization of the modulator for the two-tone signal generation is very important to ensure accurate frequency response measurement. By monitoring or stabilizing the power of the optical two-tone signal, we can measure frequency responses of optical receivers and photodetectors.
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