Recently, dual mode lasers proved to be interesting sources for radio frequency generation at millimeter wave frequency and beyond, to be used in photonic RoF systems. As the optical modes can eventually be correlated, such sources associate the simplicity of heterodyning technique with the frequency stability. Still, most architectures require active frequency control loop to reach communication requirements to limit frequency drift, and reduce the phase noise of the generated carrier. In this communication, we propose the use of a free running dual mode laser integrated on glass for radio frequency generation. The device is fabricated on an ion-exchanged co-doped Erbium Ytterbium substrate to emit in the C-band. We demonstrate that this device is able to generate an ultra-narrow spectrum radio-frequency carrier, reaching 600Hz spectral linewidth without control loop nor thermal stabilization. As a proof of concept, the device proposed in this work produces a radio frequency at 6.1 GHz which has been evaluated as an electrical carrier in radio transmission experiments. Data rates of several Gbps using complex modulation formats such from BPSK to 64QAM have been successfully tested. The results are compliant with communications standards requirements, validating the use of such a source in Radio over Fibre (RoF) systems. This paper first presents the glass dual-mode laser design, followed by the characterization of the generated carrier to finally present the radio over fiber results.
In this work, we propose the realization of two single mode distributed feedback (DFB) lasers emitting at 1.5μm with ultra-narrow linewidths, co-integrated on a co-doped Erbium Ytterbium IOG1<sup>1</sup> glass substrate. The beating note of these two lasers on a fast photodiode is used to generate mm-wave signals. Each laser is composed of a waveguide fabricated by ion exchange with a Bragg grating etched on the top. In order to set a precise value of the mm-wave frequency, the emission wavelength of both DFB lasers must be accurately fixed. This is achieved by controlling the laser’s waveguide design. The beating produced between these lasers generates mm-wave signals from GHz to THz. The co-integration helps to enhance the beating quality by reducing fluctuations between the two lasers. Lasers are first studied independently: their optical power, linewidth and relative intensity noise are characterized. Finally, the beating signal quality is estimated through the characterization of the produced electrical spectrum.
The comparison of relative intensity noise (Rin) shows improved performances, for quantum dash laser (QD)
compared to the ones of bulk medium structures. We introduced a statistical measurement through a coupling
parameter that reveals the impact of strong damping on the competition between modes or the so-called partition
noise. The existence of a strong damping in QD laser prevents the relaxation frequency from being observed
in the coupling parameter, which makes the noise to appear as if the laser lines were inhomogeneous. However
the method also enables the characterization of the coupling strength between modes, showing again differences
between QD and bulk structures.
We propose in this communication an experimental study of the relaxation oscillations behavior in mode-locked
lasers. The semiconductor self-pulsating laser diode is composed by two gain sections, without saturable absorber.
It is made of bulk structure and designed for optical telecommunication applications. This specific device
allows two different regimes of optical modulation: the first one corresponds to the resonance of the relaxation
oscillations and the second one, to the mode-locking regime at FSR value. This singular behavior leads us to
characterize the self-pulsations which are coexisting in the laser and to describe two regimes of output modulation:
the first one appears thanks to the resonance of the oscillation relaxation and the other one corresponds to the
FSR of the Fabry-Perot laser at 40 GHz.
A sensitive technique to measure the relative intensity noise of a laser is described. Such experiment is a useful
tool for laser characterizations, allowing direct measurement of physical parameters like relaxation oscillation
frequencies and damping factor. Examples of determination of such parameters are given.
Photoinscription of superstructured Bragg gratings in Er-Yb codoped fiber is a promising and cost-effective approach to
produce high-quality multi-wavelength fiber lasers for various applications like radio-over-fiber systems, fiber-optic
sensors or low-cost WDM testing source. However, a good understanding of the noise properties of the laser source is
required before these applications can be addressed. Previous modeling has shown that these devices are similar to
compact cascades of single wavelength DFB fiber lasers in which the modes at each wavelength are almost nonoverlapping
along the fiber. In this paper, we further examine the independence of each channel by performing relative
intensity noise (RIN) measurements on a multi-wavelength fiber laser, a dual-polarization fiber laser and a dualwavelength
fiber laser. In each case, we estimate the correlation between the laser lines.
From RIN measurements performed on each channel of a multi-wavelength laser, as well as on the full spectrum, we
compute an average degree of correlation between the RIN of neighboring lines and observed no correlation in most of
the cases. Moreover, each channel displays a single relaxation frequency which is different from those of the other
channels. On the other hand, we observed strong partition noise, with negative correlation, between polarization modes
of a single wavelength fiber laser. Finally, we measured the RIN of the two modes of a dual-wavelength fiber laser with
modes having a greater overlap than the multi-wavelength laser. The results show that the lines share two common
relaxation frequencies, an indication of a dynamic link between them.
A study of the Relative Intensity Noise (RIN) of an optically injected semiconductor laser is presented versus the injected power. The seeded laser is then operating from an amplifying regime towards a locking one, at the same wavelength than that of the master one. It is shown that when the Master is more coherent than the slave, a reduction of the RIN of the slave is progressively observed along with an increase of the injected power. In the converse case, no significant modification of the RIN is experimentally observed.