Short overview on generation of MMW signals using dual injection locking

1. Brief Overview On Propsed Schemes for Generation of
MMW signals using dual injection locking
Introduction
The ever-increasing demand for data transmission capacity being driven by the emerging modern
technologies such as high-definition (HD) videos, 4K resolution videos, online gaming calls for
new research in developing the 5G mobile wireless communication systems. The existing RF
spectrum is already congested leading us to the available unlicensed bands. To access the
unlicensed bands in the Ghz region due to high attenuation in the wireless propagation a concept
which integrates wireless and fiber optics network is brought into light, the radio over fiber
technology. The advantages of ROF technology are low attenuation loss, large bandwidth, multi
operators and multiservice operations, immunity to RF interference and easy installation and
maintenance. Widespread applications of ROF technology can be introduced for satellite control,
cellular networks, WLAN, mobile broad band services.In the recent years, Intel and Samsung
has proposed two possible MMW carrier frequency of 28 Ghz and 39 Ghz that delivered data at
a bit rate of 1Gb/s or higher at a distance of 200m and 2 km consecutively. Currently the most
researched carrier frequency is 60 Ghz spectrum.
The idea of Radio over Fiber is to transport data using radio frequency by modulating the radio
signal with light and transmitting it through an optic fiber. The need for increased capacity per
unit area calls for frequencies above the 6GHz range i.e the unlicensed bands in the microwave
spectrum. There are several existing concepts of radio over fiber and they are attractive due to its
low loss and extremely wide bandwidth.
The techniques that mostly used are (i) Remote Heterodyne Detection (ii) Dual Mode Lasers
Mechanism
Remote Heterodyne Detection: Most RoF techniques rely on the principle of coherent
mixing in the photodiode to generate the RF signal .These techniques are generally referred to
as Remote Heterodyne Detection (RHD) techniques depicted in figure no. 4. While performing
O/E conversion, the photodiode also acts as a mixer thereby making it a key component in
RHD-based RoF systems. There are several ways of generating the two optical carriers for
coherent heterodyning. One approach is to use an optical phase modulator to generate several
optical side bands, and then selecting the required components. Another approach is to use two
separate laser sources. The two laser diodes are made to emit light at frequencies (wavelengths)
separated by the required microwave frequency. Using optical heterodyning, very high
frequencies can be generated, limited only by the photo detector bandwidth. Remote
heterodyning has an inherent advantage concerning chromatic dispersion. If only one of the two
optical carriers is modulated with data, system sensitivity to chromatic dispersion can be

2. reduced greatly. This is not possible in direct intensity modulation based methods, where the
two optical sidebands end up both being modulated with data. Another important attribute of
RHD is that it permits low-frequency data modulation at the head end since high-frequency
electro-optical components are not required. A further advantage of optical heterodyning is that
it is capable of producing signals with 100% intensity modulation depth. The major drawback
of RHD is the strong influence of laser phase noise and optical frequency variations on the
purity and stability of the generated RF carriers.
Dual Mode Lasers: As stated earlier the major drawback of optical heterodyning-based
techniques is the sensitivity to phase noise of the two heterodyning signals, and the dependence
of the RF beat signal on the polarization state difference of the two heterodyning carriers.
Several techniques used to improve beat signal phase noise have been described. A dual mode
laser designed to test the viability of this technique showed that direct electrical injection at a
sub-harmonic of the beat frequency was still needed in order to generate a pure mm-wave. The
main advantage of the DML approach is that it does not require complex feedback circuitry as
does the different optical injection locking methods discussed above. However, the method has
limitations regarding tenability, because of its narrow locking range.
Review
Source Wavelength Modul
ation
bandw
idth
Data rate Modu
lation
Sche
me
Wavelengths Remarks Referenc
e
1.(DWFL)
Dual w avelength
fiber
laser
980 nm
pumped LD
980/
1550 nm WDM
60 GHz OFDM 1546.96 nm
1547.48 nm
2016
[1]
2.Dual mode injection
locking of a colorless
diode
L band 1593 nm 39Ghz 36 gbits
Baseband
4 gbits
Free space
64
QAM-OFDM
1533 nm
1593 nm
Longitudinal
Mode spacing
0.57nm
2015 [2]
3.Dual parallel injection
locked Fabry-Perot
Devices
Tunable laser
source at
1543.905 nm
60Ghz Bi-directional
1.25 Gbits
at 20 Km
1543.905 2008 [3]
4.Erbium doped fiber
w ith FBGs and FP-LDs
FBGs center
w avelength
Are 1540nm and
1546.4nm
0.3 to
0.8 Thz
1540 and
1546.4 nm
2010
[4]

3. 1. In this paper they have they have used dual wavelength fiber laser approach to generate mm wave
signal in the 60 Ghz range for transmission of 5Ghz bandwidth in the ROF system. They also
designed an antenna for the purpose of wireless transmission for 5G application.
2. In this paper they used nully biased MZM to modulate incoming single mode light into a double
side band master with preserved or suppressed central carrier, the directly encoded dual mode
colorless laser diode is performed for a successful fusion between wired and wireless links to
establish a 5G MMWoF system. The dual-mode L-band optical carrier successfully delivers a
36-Gb/s OFDM data with a BER of 3.2 × 10-3 , while the stabilized 39-GHz mm-wave carrier
can provide wireless 4-Gb/s 16-QAM OFDM data with 16.6-dBSNR. The in-situ 39-GHz mm-
wave carrier can be synthesized by optically heterodyne mixing the dual-mode carrier at remote
node.
3. In this paper they proposed and demonstrated a novel scheme by using dual injection locked
Fabry Perot laser diodes. They achieved transmission performance for both baseband and 60 GHz
signal by injection locking of each sideband and direct modulation of the Fabry Perot laser diodes
respectively. They achieved bidirectional 1.25Gbps 20-km transmission distance by using
semiconductor optical amplifier.
4. In this paper they proposed a widely tunable dual-wavelength Erbium-doped fiber laser that uses
two micro-heater-integrated Fabry-Perot laser diodes(FP-LDs) and two fiber Bragg gratings
(FBGs) for tunable continuous-wave (CW) terahertz (THz) radiation. Each wavelength can be
independently tuned by using an FP-LD and an FBG. The wavelength spacing of the dual
wavelength can be continuously tuned from 3.2 nm to 9.6 nm. Continuous frequency
tuning of the CW THz radiation is also successfully achieved using an InGaAs-based photomixer
with dual-wavelength fiber laser as the optical beat source. The emitted CW THz radiation is
continuously tuned from 0.3 to 0.8 THz.
Reference:
1. https://www.nature.com/articles/srep19891
2. DOI: 10.1109/JSTQE.2015.2464276
3. DOI: 10.1109/JLT.2008.927611
4. https://doi.org/10.1364/OE.18.012291