Switching response of dual-output Mach–Zehnder
modulator in channel-interleaved photonic
analog-to-digital converter
Lei Yu (于 磊), Weiwen Zou (邹卫文)*, Guang Yang (杨 光), Xinwan Li (李新碗),
and Jianping Chen (陈建平)
State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic
Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
*Corresponding author: wzou@sjtu.edu.cn
Received September 25, 2018; accepted November 1, 2018; posted online November 27, 2018
This Letter theoretically and experimentally studies the response of photonic switching in a channel-interleaved
photonic analog-to-digital converter (PADC) with high sampling rate and wide input frequency range. A figure
of merit (FoM) is introduced to evaluate the switching response of the PADC when a dual-output Mach–
Zehnder modulator (MZM) serves as the photonic switch to parallelize the sampled pulse train into two
channels. After the optimization of the FoM and utilization of the channel-mismatch compensation algorithm,
the system bandwidth of PADC is expanded and the signal-to-distortion ratio is enhanced.
OCIS codes: 060.5625, 230.0250, 250.4745, 000.4430.
doi: 10.3788/COL201816.120602.
The increasing demand for the processing of signals with
high frequency and wide bandwidth in modern scientific
research and engineering requires signal acquisition tech-
nology with high sampling speed and high resolution
[1–5]
.
There is a well-known electronic bottleneck of electronic
analog-to-digital converters (EADCs), which is essentially
limited by the timing jitter at the level of 100 fs. Besides,
the analog bandwidth of EADCs is only a few gigahertz
[6]
.
Thanks to the low timing jitter and broad bandwidth
of photonics, photonic analog-to-digital converters
(PADCs)
[7,8]
offer an alternative solution to overcome
the bottleneck faced by EADCs. The feasibility of PADCs
in breaking through the bandwidth limitation of EADCs
has been verified in radar systems
[1–4]
.
Among several schemes of PADCs, photonic sampling
and electronic quantizing analog-to-digital converters
(ADCs)
[7,8]
can achieve high sampling speed and high
resolution. A stable mode-locked laser (MLL) with low
timing jitter
[9,10]
serves as the sampling source, which guar-
antees a precise sampling time and a digitized signal with
low jitter-limited noise floor. A photonic modulator with a
wide input frequency range serves as a photonic sampling
gate to enlarge the analog input frequency range. In order
to reduce the sampling speed as well as the input
frequency range at the electronic backend, high-speed
PADC systems ought to be demultiplexed into multiple
channels
[11–15]
. To take advantage of the wide bandwidth
of photonics, an array of photonic switches can be laid
in front of the photo-diode (PD) array
[16,17]
for pho tonic
demultiplexing (i.e., channel interleaving). The electronic
backend consists of an array of parallel EADCs with lower
speed, narrower bandwidth, and higher precision, result-
ing in a wide input frequency range and a high sampling
speed, which is the product of the sampling rate of a single
EADC and the number of channels.
Bell et al. first demonstrated the photonic-switch-
based channel-interleaved PADC system to obtain 2.8 bits
effective number of bits (ENOB) with a sampling
rate of 2 GS/s
[17]
. Later, a 505 MS/s channel-interleaved
PADC system
[8]
, which includes a one-to-eight photonic
switch, was reported with the maximum ENOB of 8.2 bits,
and a calibration technique
[18]
was developed for the
suppression of channel-mismatch distortion. Up to date,
the laser sources utilized were mostly passively MLLs
(PMLLs)
[8,16–18]
. Due to the limited repetition rate of
PMLLs, this scheme cannot simultaneously satisfy the
requirements of high sampling speed and wide input
frequency range. With the development of MLLs with
higher repetition rate, we have recently investigated
the pulse shape mismatch of the sampling clock in a
channel-interleaved PADC
[15]
, which provides a flat
frequency response within a wide input frequency range.
However, the effect of the photonic switches on the
channel-interleaved PADC has not been thoroughly
studied.
In this Letter, we investigate theoretically and
experimentally the switching response of the channel-
interleaved PADC. Combined with the spectral
analysis
[7,15]
, a figure of merit (FoM) that evaluates the ef-
fect of the photonic switch in the channel-interleaved
PADC is defined, and a numerical simulation of the
impact of the FoM on the parameters of the photonic
switch is performed. In the experiment, an actively
MLL (AMLL) with high repetition rate serves as the op-
tical sampling clock, and a dual-output Mach– Zehnder
modulator (MZM) is used as the photonic switch. Under
COL 16(12), 120602(2018) CHINESE OPTICS LETTERS December 10, 2018
1671-7694/2018/120602(4) 120602-1 © 2018 Chinese Optics Letters