Broadband photonic RF quadrifilar with reconfigurable power
splitting ratio
C. Yuan
a
, E.H.W. Chan
b
, X. Wang
a,
n
, X. Feng
a
, B. Guan
a
a
Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Institute of Photonics Technology, Jinan University,
Guangzhou 510632, China
b
School of Engineering and Information Technology, Charles Darwin University, Darwin, NT 0909, Australia
article info
Article history:
Received 24 February 2016
Received in revised form
21 March 2016
Accepted 21 March 2016
Available online 28 March 2016
Keywords:
Radio frequency photonics
Microwaves
Analog optical signal processing
abstract
An all-optical 4-way photonic RF power splitter with quadrature-phase outputs is presented. It is based
on using the new power splitting and independent optical phase control function in a Fourier-domain
optical processor to split a single-wavelength phase modulated optical signal into four with the desired
optical phases at different frequencies and route them to four different output ports. It solves the large
phase error problem in the electrical quadrature-phase power dividers, and has the advantages of infinite
isolation and a reconfigurable RF power splitting ratio. Experimental results are presented that de-
monstrate a 4-way photonic RF hybrid splitter with a 3-dB operating frequency range from 10.5 GHz to
26.5 GHz, an amplitude imbalance of less than 1 dB and a phase error of less than 70.35°. The re-
configurable RF power splitting ratio of the hybrid splitter is also demonstrated experimentally.
& 2016 Elsevier B.V. All rights reserved.
1. Introduction
The splitting of an electromagnetic signal is a fundamental
signal processing function. Many applications, including optical
communication, beamforming networks and defense, require
splitting an RF signal into multiple signals with 90
o
phase differ-
ence between the neighboring outputs. For example radars in
electronic warfare systems require an IQ detector to extract both
real and imaginary parts of the reflected radar signal [1]. A 2-way
hybrid splitter can be implemented by using electrical components
such as a 90° hybrid coupler or a tapped delay Hilbert transformer
[2]. Recently various photonic approaches have been reported to
realize a 2-way hybrid splitting operation. They are either based
on a fi nite impulse response microwave photonic filter [3–5],a
ring resonator based optical all-pass filter [6], or a Fourier-domain
optical processor (FD-OP) [7]. Photonic RF hybrid splitters have the
advantages of wide bandwidth, electromagnetic interference im-
munity, and excellent isolation [8].
A 4-way hybrid splitter, which is also called a quadrifilar, splits
an RF signal into four with the phase difference of 0°,90°,180° and
270°. It has an application in a correlation receiver for demodu-
lating a quadrature phase shift keying (QPSK) signal, which re-
quires the recovered carrier to be phase shifted by 0°,90°,180° and
270° [9]. Other applications are the circularly polarized square slot
antenna array [10,11] , and the four-arm spiral antenna in a
beamforming network [12], which requires the four antenna arms
to be excited with 90° phase progression between the neighboring
arms in order to radiate circularly polarized waves. The conven-
tional way to implement the 4-way quadrature-phase power
splitting operation is to connect the outputs of a 2-way 90° hybrid
splitter with two 2-way 180° power splitters [12]. The quadrature-
phase power splitter realized using this technique can have a wide
bandwidth as broadband 90° and 180° power splitters are com-
mercially available. However, commercial broadband hybrid
splitters/couplers suffer from large phase errors. For example the
phase errors in a broadband 2-way 90° hybrid splitter [13] and a
broadband 2-way 180° power splitter [14] are 715
° and 75°
respectively. Hence the phase error of a 4-way quadrature-phase
power splitter implemented by connecting a 2-way 90° hybrid
splitter with two 2-way 180° power splitters can be as large as
7 20°. Photonics provides a solution to overcome this problem.
However, until now, there is no report on a photonic based 4-way
RF hybrid splitter.
In this paper, we present a 4-way photonic RF hybrid splitter or
a photonic RF quadrifilar (PRFQ). It is based on a new function in
an FD-OP, which splits a phase modulated optical signal into four
with the desired optical phases at different frequencies and routes
them to four different FD-OP output ports. Four RF signals with 90°
phase progression are obtained after photodetection. The PRFQ
only requires a single-wavelength laser source and has the ability
to control the splitting ratio. It also has an infinite isolation
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2016.03.060
0030-4018/& 2016 Elsevier B.V. All rights reserved.
n
Corresponding author.
E-mail addresses: txudong.wang@email.jnu.edu.cn (X. Wang),
eexhfeng@gmail.com (X. Feng).
Optics Communications 371 (2016) 93–99