Matthew P. Chang

Optical Analog Self-Interference Cancellation Using Electro-Absorption Modulators

An optical analog self-interference cancellation system for radio-frequency communications is proposed and experimentally demonstrated. The system uses two electro-absorption modulators, an optical attenuator and delay, and a balanced photodetector to subtract strong self-interference from a corrupted received signal and recover a weak signal of interest. The system achieves >; 65 dB narrowband cancellation and >; 30 dB broadband cancellation across more than 40 MHz bandwidth for interference in both the 900 MHz and 2.4GHz bands. Both narrowband and broadband cancellation are frequency tunable, and can be combined with other forms of interference cancellation to achieve even higher levels of cancellation.

Temporal phase mask encrypted optical steganography carried by amplified spontaneous emission noise.

A temporal phase mask encryption method is proposed and experimentally demonstrated to improve the security of the stealth channel in an optical steganography system. The stealth channel is protected in two levels. In the first level, the data is carried by amplified spontaneous emission (ASE) noise, which cannot be detected in either the time domain or spectral domain. In the second level, even if the eavesdropper suspects the existence of the stealth channel, each data bit is covered by a fast changing phase mask. The phase mask code is always combined with the wide band noise from ASE. Without knowing the right phase mask code to recover the stealth data, the eavesdropper can only receive the noise like signal with randomized phase.

Exploring excitability in graphene for spike processing networks

We propose a novel excitable laser employing passively Q-switching with a graphene saturable absorber for spike processing networks. Our approach combines the picosecond processing and switching capabilities of both linear and nonlinear optical device technologies to integrate both analog and digital optical processing into a single hardware architecture capable of ultrafast computation without the need for analog-to-digital conversion.

WDM optical steganography based on amplified spontaneous emission noise

We propose and experimentally demonstrate a wavelength-division multiplexed (WDM) optical stealth transmission system carried by amplified spontaneous emission (ASE) noise. The stealth signal is hidden in both time and frequency domains by using ASE noise as the signal carrier. Each WDM channel uses part of the ASE spectrum, which provides more flexibility to apply stealth transmission in a public network and adds another layer of security to the stealth channel. Multi-channel transmission also increases the overall channel capacity, which is the major limitation of the single stealth channel transmission based on ASE noise. The relations between spectral bandwidth and coherence length of ASE carrier have been theoretically analyzed and experimentally investigated.

Adaptive Optical Self-Interference Cancellation Using a Semiconductor Optical Amplifier

We experimentally demonstrate an optical system that uses a semiconductor optical amplifier (SOA) to perform adaptive, analog self-interference cancellation for radio-frequency signals. The system subtracts a known interference signal from a corrupted received signal to recover a weak signal of interest. The SOA uses a combination of slow and fast light and cross-gain modulation to perform precise amplitude and phase matching to cancel the interference. The system achieves 38 dB of cancellation across 60-MHz instantaneous bandwidth and 56 dB of narrowband cancellation, limited by noise. The Nelder-Mead simplex algorithm is used to adaptively minimize the interference power through the control of the semiconductors bias current and input optical power.

An integrated analog O/E/O link for multi-channel laser neurons

We demonstrate an analog O/E/O electronic link to allow integrated laser neurons to accept many distinguishable, high bandwidth input signals simultaneously. This device utilizes wavelength division multiplexing to achieve multi-channel fan-in, a photodetector to sum signals together, and a laser cavity to perform a nonlinear operation. Its speed outpaces accelerated-time neuromorphic electronics, and it represents a viable direction towards scalable networking approaches.

Analog noise protected optical encryption with two-dimensional key space

An optical encryption method based on analog noise is proposed and experimentally demonstrated. The transmitted data is encrypted with wideband analog noise. Without decrypting the data instantly at the receiver, the data is damaged by the noise and cannot be recovered by post-processing techniques. A matching condition in both phase and amplitude of the noise needs to be satisfied between the transmitter and the receiver to cancel the noise. The precise requirement of the phase and amplitude matching condition provides a large two-dimensional key space, which can be deployed in the encryption and decryption process at the transmitter and receiver.

A Simultaneous Variable Optical Weight and Delay in a Semiconductor Optical Amplifier for Microwave Photonics

In this paper, we demonstrate how a single semiconductor optical amplifier can serve as a simultaneous variable optical weight and tunable optical delay for microwave photonics. The device weight, or power transmission, and delay can be controlled simultaneously and independently from each other by varying the input optical power and the semiconductor bias current. The dual functionality is achieved by combining the effects of slow and fast light with cross-gain modulation in the semiconductor. We experimentally demonstrate a tunable delay range of 100 ps and RF gain range of -6 to +3 dB for a 600-MHz microwave signal and show how the weight and delay of the device can be separately tuned. The delay range and bandwidth of the device are limited by the semiconductor carrier lifetime and characteristic of slow and fast light. As a simultaneous optical weight and delay, as well as a wavelength converter, a semiconductor optical amplifier operating in this manner can be a compact and versatile element in microwave photonics, radio-over-fiber, and general analog optical signal processing.

An integrated optical interference cancellation system

We present the design and simulation results for a photonic integrated circuit (PIC) that performs in-channel and broadband radio-frequency self-interference cancellation. The PIC removes interference by modeling channel effects and inverting a known interferer prior to combining it with the corrupted signal. We present key simulation results showing that the PIC can cancel extremely wideband interferers by ~20 dB. The PIC performance can be improved by reducing signal attenuation and nonlinearities. We plan to fabricate the PIC on a hybrid silicon-on-insulator III-V evanescent photonic platform.

Integrated Microwave Photonic Circuit for Self-Interference Cancellation

We present the first experimental demonstration of an integrated microwave photonic circuit for active, analog self-interference cancellation. The circuit is unique in its ability to operate in any radio frequency (RF) band from 400 MHz up to 6 GHz while not requiring any optical inputs or outputs. We focus on two topics related to the functional performance of the circuit. First, we investigate the amount of interference cancellation that can be achieved over a wide range of operating frequencies. We show that the circuit can achieve nearly −30 dB of interference cancellation across all existing frequency-division duplexed local thermal equilibrium and WiFi bands. Second, we investigate the control aspects of the integrated circuit and determine how much amplitude and phase tunability can be generated to perform active cancellation. Using dispersive techniques, the integrated circuit achieves 10 dB and 52° of independent amplitude and phase tunability, respectively, at 1.25 GHz. The range decreases with increasing frequency. We find that the sensitivity of the circuit’s cancellation performance to the control biases are 2 and 0.5 mA at cancellation depths of −40 and −50 dB, respectively. Finally, we use the integrated circuit to demonstrate adaptive interference cancellation. Our results show that an integrated solution is able to achieve a cancellation performance comparable to a discrete fiber-optic system. Additionally, it is one of the first demonstrations of an integrated microwave photonic circuit that only possesses RF inputs and outputs.