An ultrafast testbed for the characterization of high-speed integrated photonic devices such as high-speed integrated photonic modulators and detectors was developed. A major requirement in performing successful research in this field is the availability of ultra-fast optoelectronic characterization tools that facilitate the study of ultrafast low-power devices and systems (e.g., modulators, switches, detectors).

The accompanying figure shows a schematic of the characterization testbed, which is used to measure the optical, electronic, and optoelectronic properties of an integrated photonic structure. The sample under test (SUT) is placed on a highly functional 5D stage with full positioning control over translation in three directions, rotation, and tilt. It is also monitored by a spatially designed microscope from the top that is connected to a camera to monitor different devices fabricated in the SUT (typically, 10s to 100s of devices are fabricated in a single substrate).

On the optical side, the input light from a tunable laser source (in the optical communications wavelength window of 1450-1650 nm) is coupled into an integrated photonic waveguide on a chip either from the top (through a grating) or from the side (through a butt-coupled fiber). The light in the input waveguide will go through the photonic structure and will be coupled out either from the side (to a butt-coupled fiber) or from the top (through a grating into a fiber). The output light is analyzed by an ultra-fast detector or an ultrafast oscilloscope. The testbed is capable of both input/output coupling formats with minimal modifications. By sweeping the wavelength of the input laser, the spectral characteristic of the device (e.g., resonance properties of a resonator or the transfer function of a filter) can be studied.

On the optoelectronic side, the electronic signal for modulating, tuning, or controlling the optical signal comes from a fast arbitrary wave generator (AWG) and it is applied to the photonic structure after the amplification by a 30 dBm power amplifier through the high speed (50 GHz) probes as shown. The output optical signal of the nanophotonic (or plasmonic) is measured by first amplifying the optical signal using a low-noise optical semiconductor amplifier and then detected by a high-speed (50 GHz) detector. Finally, the output signal is sampled and detected using a high-speed sampling oscilloscope (60 GS/s), which can provide time-domain and spectral information such as eye diagram and spectral transfer function of the device.

The testbed shown can also be used to characterize the electronic properties (e.g., current-voltage characteristics, resistance measurement, and capacitance measurement) of the integrated structures using the source measurement unit (SMU). Such measurements are very important in working with emerging materials such as graphene where the electronic properties (e.g., conductivity) have profound effects on the optoelectronic characteristics of the device (e.g., modulation speed of a photonic modulator). The electronic characterization is performed by using two high-speed probes for applying the desired voltage and measuring the resulting current.

The developed testbed enables the characterization of different electronic, (passive) photonic, and (active) optoelectronic properties of an integrated optoelectronic device/system.

The implemented high-speed characterization setup provides a high flexibility that can be used for different characterization configurations for different optoelectronic devices. The high flexibility of the proposed testbed, along with the ability to excite and detect the signals at very high speeds, make the proposed testbed a unique tool that can facilitate the study of several state-of-the-art integrated photonic structures that are of high demand for DoD applications. In addition, the proposed testbed can be utilized for the characterization of a large variety of electronic and photonic structures beyond integrated optoelectronic system.

This work was done by Ali Adibi Ph.D. of Georgia Tech Research Corporation for the Army Research Office. For more information, download the Technical Support Package (free white paper) below. ARL-0234

This Brief includes a Technical Support Package (TSP).
An Ultrafast Testbed for Comprehensive Characterization of Photonics, Electronic, and Optoelectronic Properties of Integrated Nanophotonic Structures

(reference ARL-0234) is currently available for download from the TSP library.

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This article first appeared in the February, 2021 issue of Aerospace & Defense Technology Magazine.

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