Deployment of 1610 nm InAs/InP Quantum-dash Laser Diode in

28–50 GHz Hybrid RoF-RoFSO-Wireless Transmission System

M. Z. M. Khan

1,2

Optoelectronics Research Laboratory, Electrical Engineering Department,

King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

Center for Communication Systems and Sensing, King Fahd University of Petroleum and Minerals,

Dhahran 31261, Saudi Arabia

Keywords: Millimeter Waves, Radio-over-fiber, InAs/InP Quantum-dash Laser, L-band Optical Communication.

Abstract: In this paper, we report on our recent demonstrations on deploying mid L-band ~1610 nm quantum-dash

(Qdash) laser diode (LD) in millimeter-wave (MMW) applications. 28 and 30 GHz MMW beat-tones are

generated using a self-injection-locked (SIL) Qdash LD-based comb source (QDCS) with phase noise of ~-

120 dBc/Hz at 1MHz offset frequency. Moreover, we demonstrated transmission of these MMWs over

various channels comprising of single-mod-fiber (SMF), generally known as radio-over-fiber (RoF), free-

space-optics (FSO), known as radio-over-FSO (RoFSO), and wireless (WL) links, which are attractive

solutions for future flexible next-generation access networks (NGANs). In particular, we demonstrated

successful transmission of 28 and 30 GHz MMW modulated with analog 2 Gb/s quadrature-phase-shift-

keying (QPSK) data over hybrid 20 km SMF – 5 m FSO and 0- 6 m WL channel. Moreover, we also discussed

our very recent preliminary results of 50 GHz high-frequency generation and transmission utilizing QDCS.

In this case, we showed error-free transmission of 2 Gb/s QPSK data over 50 GHz carrier and 11.6 km SMF

– 6 m FSO and 0-1 m WL channel. This rule-changing broad multi-wavelength lasing spectrum from Qdash

LD and emission covering S- to U-band has made it a prime contender for NGANs.

1 INTRODUCTION

The unprecedented rise in the network connectivity

with smart devices (internet-of-things) and increase

in bandwidth-hungry services (high-definition video

broadcasting, gaming, etc.) is persistently pressing

the existing fiber-optic network infrastructure to

explore different last/first-mile access solutions,

which are the key bottlenecks in providing high data

rate services to the end-users. The so-called NGANs

are expected to be flexible, scalable, and possible

extendable in terms of wavelength operation and

reaching remote areas (Nesset, 2017, Uwaechia,

2020)

In this regard, MMW wireless technology has

been identified as a promising candidate for last/first-

mile access applications due to its several unregulated

MMW frequency spectrum across the world.

Furthermore, the MMW optical/wireless integration

could also realize seamless wireless integration with

the existing high-speed fiber-optic networks. This

RoF is a potential technology for distributing MMW

signals directly to the user end. In particular, hybrid

optical/wireless network infrastructures such as RoF-

WL and its integration with FSO communication, i.e.,

RoFSO has been envisioned as promising hybrid

architectures for NGANs (Ragheb, 2021, Uwaechia,

2020).

Moreover, transmitter light sources are expected

to play a crucial role in future access networks since

their performance, aggregate data rates in particular,

relies on the performance of these semiconductor

laser diodes. Besides, the proposal of extending the

wavelength operation of NGANs beyond the C-band

has positioned investigating high-performance laser

diodes in S- and L-band regimes to sustain the future

needs (Nesset, 2017). In recent years, InAs/InP Qdash

nanostructure active region based semiconductor

lasers have emerged as the prime contenders as light

transmitters, thanks to their rule-changing broad

multi-wavelength lasing spectrum and wavelength-

tunable broad gain profile covering S- to U-band

regions (Reithmaier, 2005). The capability of this

energy-efficient optical source in the C-band, and

Khan, M.

Deployment of 1610 nm InAs/InP Quantum-dash Laser Diode in 28–50 GHz Hybrid RoF-RoFSO-Wireless Transmission System.

DOI: 10.5220/0010987400003121

In Proceedings of the 10th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2022), pages 84-88

ISBN: 978-989-758-554-8; ISSN: 2184-4364

Figure 1: (a) L-I-V charactersitics of InAs/InP Qdash LD

with inset showing the free-running lasing spectrum. (b)

InAs/InP Qdash comb source (QDCS) with 33 GHz FSR.

by filtering two modes of (b) with 3and 35G Hz mode

spacing, respectively.

very recently, in the L-band (1600 nm) challenging

window by our group, in achieving green optical and

fifth-generation (5G) wireless communication and

beyond, has been underlined in literature (

Delmade,

2020,

Ragheb, 2021).

This paper provides an overview of our work in

deploying mid L-band InAs/InP Qdash LD in MMW

applications. In particular, we generated MMW beat-

tones at ~1610 nm exploiting injection-locked Qdash

LD-based comb source (QDCS) (Ragheb, 2021).

High-quality 33 and 35 GHz MMWs exhibiting low

phase noise of -120 dBc/Hz at 1 MHz offset

frequency, and radio frequency (RF) linewidths in a

few kHz range, have been realized. Moreover, 1.0

Gbaud (2 Gb/s) analog QPSK double-side-band

(DSB) modulated signal at 5 GHz intermediate

frequency (IF) has been successfully transmitted over

various hybrid channels comprised of WL, RoFSO,

and RoF sub-links. For instance, transmission over 28

GHz MMW carrier on hybrid 20 km SMF–6 m WL

and over 30 GHz MMW on 20 km SMF – 5 m FSO–

6 m WL channel demonstrated an error-free

transmission with receiver sensitivities ~3.3 and ~-3.0

dBm, respectively (Ragheb, 2021). In addition, our

very recent preliminary results of 50 GHz MMW

beat-tone generation at ~1610 nm using QDCS

displayed RF linewidth of 1.0 kHz and phase noise -

64 dBc/Hz at 1.0 kHz offset. Transmission of 1

Gbaud single-sideband (SSB) modulated QPSK over

11.6 km SMF–6 m FSO–1 m WL channel with ~-2.0

dBm receiver sensitivity further affirm quality beat-

tone generation and transmission of high-frequency

MMWs at ≥ 50 GHz from this new-class of laser

device, thus substantiating itself as a candidate light

source in NGANs.

2 QUANTUM DASH LASERS

In this work, the employed InAs/InP Qdash LD

operates in the mid L-band challenging window

emitting at ~610 nm. The bare unbonded and

unmounted chip typical L-I-V characteristics are

shown in Figure 1(a), exhibiting a threshold current

of ~100 mA. The emission bandwidth comprised

several Fabry-Perot (FP) modes within a 3-dB

bandwidth of ~8-10 nm. Unfortunately, the optical

linewidth of these modes displayed value in tens of

MHz, hence rendering their usage in coherent optical

communication. This is unlike the C-band InAs/InP

Qdash LD counterpart, where inherent passive mode-

locking has enabled phase locking of all FP modes

with a significant reduction in linewidths, in few tens

to hundreds of kHz (

Delmade, 2020, Rahim, 2019).

Unfortunately, mode-locking in L-band Qdash LD

has not been observed yet due possibly to the

unoptimized device design and growth process.

Hence, we deployed the optical injection locking

technique, particularly self-injection locking (SIL), to

realize a single-mode emission spectrum from the

Qdash LD with high spectral purity, exhibiting

optical linewidth ~45 kHz (Ragheb, 2021). Hence, to

demonstrate the possibility of employing Qdash LD

in MMW applications, we generated a comb using the

single locked mode by generating its harmonics by

phase modulating it with an RF source frequency

equal to the FSR of the comb source. In our initial

work, we utilized 33 and 35 GHz RF sources to

realize Qdash LD-based comb source (QDCS), whose

spectrum is shown in Figure 1(b), exhibiting seven

comb lines (Ragheb, 2021). Two modes are filtered

using an optical tunable bandpass filter (OBPF), thus

realizing a MMW beat-tone of desired frequency (33

0.00 0.08 0.16 0.24 0.32 0.40 0.48 0.56

0.0

0.4

0.8

1.2

1.6

2.0

1580 1600 1620 1640

-50

-40

-30

-20

Power (dBm, a.u)

Wavelength (nm)

I-V

L-I

Injection Current (A)

Voltage (V)

Output Power (mW)

1610 1611 1612

-30

-20

-10

Power (dBm, a.u)

Wavelength (nm)

Deployment of 1610 nm InAs/InP Quantum-dash Laser Diode in 28–50 GHz Hybrid RoF-RoFSO-Wireless Transmission System

or 35 GHz). Figures 1(c) and (d) show the electrical

spectrum of the unmodulated MMW carriers after

beating the two tones in a high-speed photodiode.

Both carriers exhibited low phase noise (not shown

here) of -120 dBc/Hz at 1 MHz offset frequency and

RF linewidths in a few kHz range (Ragheb, 2021).

In our very recent preliminary work, we

successfully generated a 50 GHz beat-tone via a 12.5

GHz FSR comb source where we selected the central

mode and the fourth mode along with a longer

wavelength, thus exhibiting a mode spacing of 50

GHz. It is worth mentioning that a low-frequency RF

source would be sufficient to generate high frequency

and good quality MMW carriers with this technique.

Moreover, it is to be noted that once mode-locking in

mid L-band Qdash LD is observed, then appropriate

mode-locked FP modes from the multi-wavelength

spectrum could be extracted to generate MMW beat-

tone, as has been the typical case in C-band Qdash

mode-locked lasers (MLLs). In this case, the LD

cavity length would dictate the mode spacing of the

locked emission spectrum or the FSR and essentially

controls the generated MMW carrier frequency,

which could be multiples of FSR. Furthermore,

Qdash MLL could also serve as energy-efficient light

sources since a single device could provide several

sub-carriers for MMW-WDM systems.

3 28 GHZ MMW TRANSMISSION

For the MMW transmission, the extracted dual-

modes of the QDCS, which is essentially the desired

MMW beat-tones (33/35 GHz), are then intensity-

modulated (with DSB modulation) via a Mach

Zehnder modulator (MZM). The modulating signal

was 2 Gb/s analog QPSK over an IF 5.0 GHz. Hence,

the output of the modulator includes the two optical

carriers, each exhibiting DSB modulating signal and

5.0 GHz apart from the carrier. Thus, the desired

28/30 GHz MMW carrier was achieved by beating

one of the unmodulated optical carrier with the

sideband.

This optical MMW beat-tone is transmitted over

20 km SMF and then 5 FSO channels, which was

established with two fiber collimators, before

reaching the variable optical attenuator (VOA) for

performance analysis, and high-speed photodiode to

convert the MMW beat-tone into an electrical signal.

The electrical MMW carrier is then transmitted over

a transmitting horn antenna, which is then received at

the receiver horn antenna. The distance between the

horn antennas constitutes the WL link length. The

received MMW is the amplified, frequency down-

Figure 2: Performance of DSB modulated 2 Gb/s analog

QPSK at 5 GHz intermediate frequeny over (a) 28 GHz and

(b) 30 GHz MMW carier signals employing QDCS. The

transmission channels are: (a) hybrid 20-km SMF – 0-6m

WL link and (b) 20 km SMF-5m FSO-0-2m WL link.

converted, and then demodulated in a Keysight

digitizer. More details of the experimental setup can

be found elsewhere (Ragheb, 2021). Figure 2(a)

shows the transmission performance of 28 GHz

MMW carrier over the hybrid 20 km SMF – 6 m WL.

The back-to-back (BtB) configuration, with 20 km

SMF – 0 m WL link length, is also shown for

comparison purposes. An error-free transmission

with both channels reaching forward-error-correction

(FEC) bit-error-rate (BER) limit of 3.8 ×10

-3

receiver sensitivity of ~-5.1 dBm and ~3.3 dBm is

noted between the BtB and the hybrid channel with 6

m WL link case. This corresponds to ~ 8 dB loss

through the 6 m WL link and is attributed to the fee-

space path loss (Ragheb, 2021).

For the 30 GHz MMW transmission

configuration, the hybrid channel comprises a 20 km

SMF – 5 m FSO – 2 m WL link, while identical 2

Gb/s analog QPSK over 5 GHz IF modulating signal

have been utilized. As seen in Figure 2(b), a

successful transmission is again achieved with

receiver sensitivities ~-7.3 dBm for the BtB case (i.e.,

with 0 m WL sub-link) and ~-3 dBm for the hybrid

channel, translating to ~3.7 dB loss over 2 m WL

20km SMF

5m FSO

0-2m WL

-6-5-4-3-2-101234

-4

-3

-2

BER

Optical Received Power (dBm)

-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1

-5

-4

-3

-2

-1

Optical Received Power (dBm)

(a)

(b)

0 m WL

6 m WL

20km SMF

0-6m WL

0 m WL

2 m WL

28 GHz

30 GHz

PHOTOPTICS 2022 - 10th International Conference on Photonics, Optics and Laser Technology

Figure 3: Performance of SSB modulated 2 Gb/s digital

QPSK over 50 GHz MMW carier signal employing QDCS

with 12.5 GHz FSR. The transmission channels are hybrid

11.6-km SMF – 0-1m WL link and 11.6 km SMF-6m FSO-

0-1m WL link.

distance. Again, free-space path loss has been

attributed to this received power loss when increasing

the WL link distance. It is to be noted that 28 GHz

and 30 GHz experiments were performed on different

days and hence the difference in their receiver

sensitivities under BtB configuration is reasonable

(Ragheb, 2021).

4 50 GHZ MMW TRANSMISSION

This section presents our very recent preliminary

results of a 50 GHz MMW carrier transmission

system. As mentioned in section 2, in this case, 50

GHz beat-tone was obtained by appropriately

selecting two comb lines from the 12.5 GHz QDCS.

Moreover, we separated the two modes with the help

of a 3-dB coupler and two OBPFs where only one

mode was SSB digitally modulated with 1Gbaud

QPSK data stream using MZM and then recombined

with the unmodulated optical carrier with the help of

another 3-dB coupler. The optical signal is then

transmitted over 11.6 km SMF, 6 m FSO channel and

then received by VOA for performance analysis and

then high-speed photodiode. The output of the PD is

a modulated 50 GHz MMW carrier, which is then

passed through the WL channel consisting of two

horn antennas. After receiving the electrical signal

from the horn antenna, it is amplified with a low-

noise amplifier, down-converted to an IF of 4.6 GHz,

which is then passed to the digital storage

oscilloscope (DSO) for demodulation and post-signal

processing. It is noteworthy to mention that this type

of MMW transmission system is challenging since

the two optical tones are now decorrelated due to

passing through different length fibers, thus

increasing the phase noise of the generated MMW.

Figure 3 shows the BER versus the received optical

power, measured before the PD. Again, transmission

over BtB channel configuration is also performed,

which shows receiver sensitivity of ~6.1 dBm. On the

other hand, the received sensitivity measured after

passing through the hybrid SMF-WL and SMF-FSO-

WL channels is noted to be ~-3.0 and ~-2.5 dBm,

respectively. This corresponds to a power loss of ~3

dB when the signal propagates over the 1 m WL

distance. More experimental work is in progress to

increase the QPSK data rate and WL link length while

pushing the generation and transmission of MMWs

beyond 50 GHz.

5 SUMMARY

We have summarized our recent progress of

deploying mid L-band Qdash LD in MMW

applications. In particular, we successfully generated

and transmitted 28 and 30 GHz MMW carriers overs

various hybrid channels, viz. 20 km SMF – 6 m WL

and 20 km SMF – 5m FSO – 2 m WL, with 2 Gb/s

QPSK data. Moreover, we also highlighted our very

recent preliminary results of pushing the generated

MMW frequency to 50 GHz employing a system with

increased phase noise. Nevertheless, a successful

transmission for 2 Gb/s QPSK data is achieved over

11.6 km SMF – 6 m FSO – 1 m WL channel.

ACKNOWLEDGEMENTS

This work was supported by Deanship of Research

Oversight and Coordination, via Center for

Communication Systems and Sensing, King Fahd

University of Petroleum and Minerals, grant no.

INCS2103.

REFERENCES

Nesset, D. (2017). PON roadmap. Journal of Optical

Communications and Networking, 9(1), A71-A76.

Uwaechia, A. N., and Mahyuddin, N. M. (2020). A

comprehensive survey on millimeter wave

communications for fifth-generation wireless networks:

Feasibility and challenges. IEEE Access, v8, p. 62367-

62414.

Rahim, M., Zeb, K., Lu, Z., Pakulski, G., Liu, J., Poole, P.,

Song, C., Barrios, P., Jiang, W. and Zhang. (2019).

Monolithic InAs/InP quantum dash dual-wavelength

DFB laser with ultra-low noise common cavity modes

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2

EVM (%)

Received Optical Power

(

dBm

)

Deployment of 1610 nm InAs/InP Quantum-dash Laser Diode in 28–50 GHz Hybrid RoF-RoFSO-Wireless Transmission System

for millimeter-wave applications. Optics Express,

27(24), 35368-35375.

Delmade, A., Browning, C., Verolet, T., Poette, J., Farhang,

A., Elwan, H.H., Koilpillai, R.D., Aubin, G., Lelarge,

F., Ramdane, A. and Venkitesh, D. (2020). Optical

Heterodyne Analog Radio-Over-Fiber Link for

Millimeter-Wave Wireless Systems. Journal of

Lightwave Technology, 39(2), pp.465-474.

Ragheb, A. M., Tareq, Q., Alkhazraji, E., Esmail, M. A.,

Alshebeili, S., & Khan, M. Z. M. (2021). Extended L-

Band InAs/InP Quantum-Dash Laser in Millimeter-

Wave Applications. Photonics, 8(5), p. 167.

Reithmaier, J.P., Somers, A., Deubert, S., Schwertberger,

R., Kaiser, W., Forchel, A., Calligaro, M., Resneau, P.,

Parillaud, O., Bansropun, S. and Krakowski, M. (2005).

InP based lasers and optical amplifiers with wire-/dot-

like active regions. Journal of Physics D: Applied

Physics, 38(13), p.2088.

PHOTOPTICS 2022 - 10th International Conference on Photonics, Optics and Laser Technology