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Stimulated Brillouin scattering has been widely utilized to realize frequency-agile narrowband and wideband microwave photonic bandpass filters by primarily utilizing its gain response. However, most demonstrated wideband Brillouin-based filters are limited in operation due to the high-power requirements for bandwidth tailoring. We propose a novel approach to realize wideband reconfigurable, Brillouin-based microwave photonic bandpass filters employing RF interferometry and advanced phase engineering. Demonstrated filters exhibit >20 dB selectivity and >700 MHz bandwidth using only 8 dB peak SBS gain (of intrinsic linewidth 30 MHz), and total optical pump power of only ∼14 dBm. We also demonstrate frequency tunability up to 22 GHz. The filter passband has a very flat and highly linear phase response, thus exhibiting zero group delay which we have experimentally verified by propagating an RF pulse at 10.25 GHz. Furthermore, the filter does not suffer from added Brillouin noise in the passband, which is a major advance compared to conventional Brillouin-based microwave photonic sub-systems. This paper presents simulations, mathematical analysis, and experimental results of the proposed filter. The proposed filter demonstrates a pathway toward power-efficient Brillouin-based microwave photonic filters, utilizing SBS responses, in combination with phase manipulation for advanced filtering operations.

Microwave photonic phase shifters based on stimulated Brillouin scattering (SBS) offer tunable and broadband, optically controllable phase shifts. However, achieving a 360° phase shift requires a large amount of SBS gain which often exceeds the available gain and power handling capability of an integrated waveguide. A Radio Frequency (RF) interference technique has recently been utilized in an integrated silicon platform, which uses forward Brillouin scattering in a suspended waveguide to compensate for the lack of available Brillouin gain in standard silicon on insulator platforms. This interference scheme amplifies the phase shift at the expense of link performance. Here, we demonstrate and analytically model a 360° ultra-broadband phase shifter using backward SBS in both fiber and on-chip by combining SBS and RF interference. The phase enhancement scheme greatly reduces the required Brillouin gain and thus the required optical power. Additionally, the backward architecture reduces filter requirements as the residual pump reflections are simpler to remove compared to the pump in the forward Brillouin scattering case, where the pump co-propagates with the signal. The model provides a deeper insight into the properties of the interferometric phase enhancement scheme and predicts the potential trade-offs of an optimized system, showing reduced link loss at higher levels of Brillouin gain. The model also predicts the sensitivity to variations of the interferometric components. Using this technique, we have demonstrated a broadband phase shift over an ultra-broad bandwidth of 0.1 – 65 GHz, limited only by the bandwidth of the available components. Also, we demonstrate a phase enhancement factor of 10 over a bandwidth of 18 GHz in an integrated chalcogenide waveguide.

We present a unique approach for learning the pulse evolution in a nonlinear fiber using a deep convolutional neural network (CNN) by solving the nonlinear Schrodinger equation (NLSE). Deep network model compression has become widespread for deploying such models in real-world applications. A knowledge distillation (KD) based framework for compressing a CNN is presented here. The student network, termed here as OptiDistillNet has better generalisation, has faster convergence, is faster and uses less number of trainable parameters. This work represents the first effort, to the best of our knowledge, that successfully applies a KD-based technique for any nonlinear optics application. Our tests show that even by reducing the model size by up to 91.2%, we can still achieve a mean square error (MSE) which is very close to the MSE of 1.04*10−5 achieved by the teacher model. The advantages of the suggested model include the use of a simple architecture, fast optimization, and improved accuracy, opening up applications in optical coherent communication systems.

Microwave signal filtering is a fundamental and central functionality in radio-frequency (RF) systems. Underpinned by advanced integrated photonics technologies, emerging integrated microwave photonic (IMWP) filter platforms enable reconfigurable and widely tunable RF signal filtering functionalities that were unattainable using conventional electronics while also exhibiting superior features in terms of compactness, light weight, stability, low power consumption, and low latency. This paper presents a comprehensive review of the principles, architectures, and performance of IMWP filters. We highlight recent advances of IMWP filters enabled by on-chip nonlinear optics, RF-interference technology and emerging integration platforms, with an emphasis on the RF performance which is critical for their usability in real-world applications. We conclude with a perspective on future research challenges and new possibilities for IMWP filters.

In this paper, we present the benefits, limitations, architectures, and milestones of the radio-over-fiber (RoF) network for application in the fronthaul of next-generation 5G mobile networks. RoF is conceived as the fronthaul of the fiber-wireless system based on a centralized radio access network (CRAN), where a fully centralized approach shifts the signal processing from the remote radio heads (RRHs) to a baseband unit (BBU) in a central office. We present our recent advances in RoF-based fronthaul for next-generation 5G mobile networks. Furthermore, we experimentally demonstrate the spectral efficient $M$ -ary quadrature-amplitude modulation ( $M$ -QAM) technique in the wavelength division multiplexed (WDM) hybrid fiber-wireless RoF network using a directly modulated laser (DML) with a symbol rate of 250 MBd (megabaud) on two optical wavelengths. The error vector magnitudes of the overall link for 4/16/64-QAM are below the 3GPP standard for 5G.

We propose a low-cost DML-based hybrid fiber-wireless WDM radio-over-fiber transmission system for 5G fronthaul networks with resource allocation flexibility under different traffic loads and demonstrate it with a proof-of-concept experiment.

Integrated microwave photonics (IMWP) is poised to release the bottlenecks in modern wireless communication systems. The manipulation of microwave signals in the optical domain offers key advantages of broad bandwidth, reconfiguration, and fast tuning speeds. However, in current IMWP devices, there are some challenges that need to be overcome. These include the ~1 GHz frequency resolution of the IMWP functionalities, limited by the on-chip photonic functional devices' performance, which has prompted research into on-chip stimulated Brillouin scattering (SBS) to achieve sub-30 MHz signal processing capabilities. Equally important, the performance metrics including the noise figure, dynamic range, and the insertion loss, need to be improved before commercial deployment. While SBS offers significant advantages of high resolution and reconfigurability, there is potential for improved signal-to-noise ratios and, therefore, to obtain a low noise figure. In this letter, we present an overview of recent approaches for achieving high-performance IMWP functionalities, including SBS-induced noise management and the optimized MWP link configurations.

Modern fiber-optic coherent communications employ advanced, spectrally efficient modulation formats that require sophisticated narrow-linewidth local oscillators (LOs) and complex digital signal processing (DSP). Self-coherent optical orthogonal frequency-division multiplexing (self-CO-OFDM) is a modern technology that retrieves the frequency and phase information from the extracted carrier without employing a LO or additional DSP. However, a wide carrier guard is typically required to easily filter out the optical carrier at the receiver, thus discarding many OFDM middle subcarriers that limit the system data rate. Here, we establish an optical technique for carrier recovery, harnessing large-gain stimulated Brillouin scattering (SBS) on a photonic chip for up to 116.82 Gbit·s−1 self-CO-OFDM signals, without requiring a separate LO. The narrow SBS linewidth allows for a record-breaking small carrier guard band of ∼265 MHz in self-CO-OFDM, resulting in higher capacity than benchmark self-coherent multi-carrier schemes. Chip-based SBS-self-coherent technology reveals comparable performance to state-of-the-art coherent optical receivers while relaxing the requirements of the DSP. In contrast to on-fiber SBS processing, our solution provides phase and polarization stability. Our demonstration develops a low-noise and frequency-tracking filter that synchronously regenerates a low-power narrowband optical tone, which could relax the requirements on very-high-order modulation signaling for future communication networks. The proposed hybrid carrier filtering-and-regeneration technique could be useful in long-baseline interferometry for precision optical timing or reconstructing a reference tone for quantum-state measurements.

Manipulating radio frequency (RF) signals in integrated photonic devices has recently emerged as a new paradigm for wireless communications, enabling high-frequency signal processing and broadband frequency agility in miniaturized photonic platforms. These advances are crucial for space and airborne applications which are weight and size sensitive. Recent progress in on-chip stimulated Brillouin scattering (SBS) using high gain has shown great potentials for RF photonic signal processing, owing to its inherent advantages of high resolution, high reconfigurability, and flexible programmability. On-chip SBS serves as a versatile and high-performance toolbox to process and manipulate the amplitude and phase of RF signals in the optical domain. In this paper, we provide a brief overview of recent advances achieved using SBS in planar waveguides, with a focus on applications requiring phase control of RF signals, including phase shifters, delay lines, and separate carrier tuning. We introduce a power-efficient scheme based on the concept of phase amplification to improve Brillouin-based phase processing capability.

In this paper, we demonstrate a self-homodyne coherent system with a significantly narrowed effective linewidth using optical carrier recovery based on stimulated Brillouin scattering (SBS), employing only coarse path length matching. The effective linewidth of the SBS-based receiver system is reduced from 75 kHz to less than 2 kHz, which is estimated by Lorentzian fitting of power spectra, and confirmed by simulation results of the tolerance window length for phase noise compensation (PNC) with different linewidth. Both experimental and numerical studies on the tracking requirements on PNC algorithms confirm effective linewidth reduction to this level, and show a 32x relaxation of the phase recovery tracking window length. This highlights the potential to significantly reduce the computational complexity of PNC even in coarsely optimized SBS-based self-homodyne coherent systems, providing an alternative to using demanding ultra-low linewidth lasers.

Signal processing using on-chip nonlinear or linear optical effects has shown tremendous potential for RF photonic applications. Combining nonlinear and linear elements on the same photonic chip can further enable advanced functionality and enhanced system performance in a robust and compact form. However, the integration of nonlinear and linear optical signal processing units remains challenging due to the competing and demanding waveguide requirements, specifically the combination of high optical nonlinearity in single-pass waveguides, which is desirable for broadband signal processing with low linear loss and negligible nonlinear distortions required for linear signal processing. Here, we report the first demonstration of integrating Brillouin-active waveguides and passive ring resonators on the same integrated photonic chip, enabling an integrated microwave photonic notch filter with ultradeep stopband suppressions of >40 dB, a low filter passband loss of

On-chip stimulated Brillouin scattering (SBS) that results from enhanced light–sound interactions, has recently demonstrated great applicability and versatility for signal generation and manipulation. Progress toward realizing fully integrated Brillouin photonic circuits is promising; however, the control and routing of on-chip optical waves requires non-reciprocal elements such as circulators, which is challenging and adds complexity. Here, a circulator-free Brillouin photonic planar waveguide circuit which eliminates the need for separate non-reciprocal elements is demonstrated. Backward inter-modal Brillouin scattering (BIBS) is used in a planar photonic integrated circuit, for the first time, to provide Brillouin processing capability in a multi-modal waveguide, conveniently allowing for the separation of counter-propagating pump and signal using passive integrated mode-selective filters. Using an As2S3–Si hybrid multi-modal photonic circuit, inter-optical-mode energy transfer with a Brillouin gain coefficient of 280 m−1W−1 is experimentally demonstrated, representing two orders of magnitude enhancement compared to conventional optical fibers. This on-chip BIBS circuit allows for independent routing of pump and signal waves, showing resilience to the cross talk. The experimental demonstrations provide an important basis for achieving fully integrated Brillouin photonic circuits without requiring on-chip circulators and fine spectral filtering, opening a new dimension for studying spatial-dependent photon–phonon nonlinear dynamics.

Stimulated Brillouin scattering has great potential for wide-wavelength-range optical carrier recovery, as it can act as a parametrically defined narrowband gain filter. However, due to the dispersion of the Brillouin frequency shift, prior demonstrations have been limited in wavelength range. Here, we demonstrate that frequency modulating the pump light for a gain filter based on stimulated Brillouin scattering enables optical carrier recovery for a broad range of input wavelengths. We demonstrate highly selective ( bandwidth) amplification for optical carriers over an 18 nm wide wavelength range in the optical communications C-band, an improvement over using an unmodulated pump. Measurements of the noise properties of these spectrally broadened gain filters, in both amplitude and phase, indicate the noise performance and SNR are maintained over a wide wavelength range. Our technique provides a potential solution for highly selective, wavelength agnostic optical carrier recovery.

High-resolution signal processing will be a key aspect in current and future communication networks in crowded spectral environments. Signal processing based on the nonlinear optical process known as stimulated Brillouin scattering (SBS) are applicable in high-performance analog signal filtering for radio frequency (RF) communications and in coherent optical communication systems for carrier amplification. To meet the requirements of small size, low weight, and low power, the development of chip-based devices is critical. In this paper, we present an overview of on-chip SBS demonstrations of RF bandpass and bandstop filter functionalities with large frequency tuning and reconfigurability from tens of MHz to almost 0.5 GHz, applicable in RF communications. We also present our recent results on chip-based SBS filtering for optical communications. While traditionally SBS has been deemed to be incompatible with phase-sensitive communications, these latest results highlight the viability of SBS-enhanced high-capacity digital communication networks. We finally discuss the limitations of SBS filtering and also present some strategies to overcome them.

We report a silicon nitride chip-based radio-frequency photonic notch filter with an unprecedented performance including an RF gain of 8 dB, a record-low noise figure of 15.6 dB, and a spurious-free dynamic range of 116 dB·Hz2/3, with a stop band rejection of 50 dB. This level of performance is achieved by using on-chip resonators’ unique phase responses, and thorough optimizations of the photonic link. These record results will potentially stimulate future implementations of integrated microwave photonic subsystems for real-world applications.

Optical frequency comb lines with poor carrier to noise ratio (CNR) are significantly improved by Brillouin amplification using its extreme narrow bandwidth gain to suppress out of band noise, enabling higher quality signal modulation. Its application to spectral lines of narrow 10 GHz pitch and poor CNR is shown to suppress the otherwise strong phase distortion caused by poor CNR after encoding with 96 Gb/s DP-64-QAM signals and restore the bit error rate (BER) to below the limit for standard forward error correction (FEC). This is also achieved with the required frequency shifted optical pump for amplification obtained by seeding it from the comb itself, sparing the need for lasers and frequency locking. Simultaneous CNR improvement for 38 comb lines is also achieved with BER restored to below the FEC limit, enabled by a multi-line pump that is pre-dispersed to suppress its spectral distortion from the Kerr effect in the gain medium. Carrier performance at minimum BER shows minimal noise impact from the Brillouin amplifier itself. The results highlight the unique advantage of Brillouin gain for phase sensitive communications in transforming otherwise noisy spectral lines into useful high quality signal carriers.

Integrated microwave photonics has strongly emerged as a next-generation technology to address limitations of conventional RF electronics for wireless communications. High-resolution RF signal processing still remains a challenge due to limitations in technology that offer sub-GHz spectral resolution, in particular at high carrier frequencies. In this paper, we present an on-chip high-resolution RF signal processor, capable of providing high-suppression spectral filtering, large phase shifts and ns-scale time delays. This was achieved through tailoring of the Brillouin gain profiles using Stokes and anti-Stokes resonances combined with RF interferometry on a low-loss photonic chip with strong opto-acoustic interactions. Using an optical power of

We report a silicon nitride RF photonic notch filter with unprecedented performance including 8 dB of RF gain, record-low noise figure of 15.6 dB, and spurious-free dynamic range of 116 dB while achieving an ultra-deep rejection of beyond 50 dB in the stopbands., Presented as a post deadline paper at CLEO Pacific Rim 2017

Integrated silicon microwave photonics offers great potential in microwave phase shifter elements, and promises compact and scalable multi-element chips that are free from electromagnetic interference. Stimulated Brillouin scattering, which was recently demonstrated in silicon, is a particularly powerful approach to induce a phase shift due to its inherent flexibility, offering an optically controllable and selective phase shift. However, to date, only moderate amounts of Brillouin gain has been achieved and theoretically this would restrict the phase shift to a few tens of degrees, significantly less than the required 360 degrees. Here, we overcome this limitation with a phase enhancement method using RF interference, showing a 360 degrees broadband phase shifter based on Brillouin scattering in a suspended silicon waveguide. We achieve a full 360 degrees phase-shift over a bandwidth of 15 GHz using a phase enhancement factor of 25, thereby enabling practical broadband Brillouin phase shifter for beam forming and other applications., Comment: \copyright 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved

We present a high link-performance multi-band microwave photonic filter based on stimulated Brillouin scattering (SBS) loss responses. The bandpass filter response is formed by suppressing the out-of-band signal using multiple broadened SBS loss responses, which avoids introducing additional noise in the passband. The low-noise SBS bandpass filter is implemented in an optimized high-performance MWP link, which enabled the demonstration of filter functionalities with a low noise figure, reconfigurability, and high resolution. A noise figure of 18.9 dB is achieved in the passband with a filter bandwidth of 0.3 GHz at a central frequency of 14 GHz, with a link gain of −13.9 dB and a spurious free dynamic range of 106 dB.Hz2/3. Bandwidth reconfiguration from 0.1 GHz to 1 GHz and multi-bandpass responses are also demonstrated.

PbSe quantum dots (QDs) were grown in high-refractive-index low-melting-temperature lead-phosphate glass. The lowest energy exciton transition of the QDs was tuned over a wide range within the infrared spectral region (0.93-2.75µm) by a controlled heat treatment. The measured QD radius ranged between 2 and 5.3nm, with a time (t) dependence of t0.29 for long dwelling times during the heat treatment, indicating that the QD growth mechanism tends to follow Lifshitz-Slyozov-Wagner theory. The QD saturable absorber behavior at 1.2µm had a measured saturation fluence of ~2.1µJ/cm2.

A novel technique to create a lossless and tunable RF photonic bandstop filter with an ultra-high suppression is demonstrated using the combination of an overcoupled optical ring resonator and tailored stimulated Brillouin scattering gain. The filter bandwidth narrowing is counterintuitively synthesized from two broad optical resonance responses. Through a precise amplitude and phase tailoring in the optical domain, the RF filter achieves a minimum insertion loss (0 dB), a high isolation (50 dB), and a tunable 3 dB bandwidth (60-220 MHz) simultaneously with wide frequency tunability (1-11 GHz). This ultra-low loss RF filter paves the way toward broadband advanced spectrum management with low loss, high selectivity, and improved signal-to-noise ratio.

Fabrication, characterization, and laser performance of an Yb:Lu₂O₃ planar waveguide laser are reported. Pulsed laser deposition was employed to grow an 8 µm-thick Yb-doped lutetia waveguide on a YAG substrate. X-ray diffraction was used to determine the crystallinity, and spectroscopic characterization showed the absorption and emission cross-sections were indistinguishable from those reported for bulk material. When end-pumped by a diode-laser bar an output power of 7.4 W was achieved, limited by the available pump power, at a wavelength of 1033 nm and a slope efficiency of 38% with respect to the absorbed pump power.

This work was supported in part by the U.K. Engineering and Physical Sciences research Council under Grants EP/H035745/1, EP/L021390/1, and EP/J008052/1. We report on progress in the field of integrated mode-locked waveguide lasers with an emphasis on compact monolithic designs producing picosecond and femtosecond optical pulses at multi-GHz repetition rates. Postprint

We report on the growth and initial characterization of pulsed laser deposited Yb:YAG. When used as a planar waveguide laser slope efficiencies of at least 34% are observed for a 45% reflectivity output coupler.

In this letter, we present the use of monolayer graphene saturable absorbers to produce Q-switched and Q-switched mode-locked operation of Yb and Yb:Er-doped phosphate glass waveguide lasers, respectively. For the 1535-nm-wavelength Yb:Er laser, the Q-switched pulses have repetition rates up to 526 kHz and contain mode-locked pulses at a repetition frequency of 6.8 GHz. The measured 0.44-nm bandwidth should allow pulses as short as $\sim 6$ ps to be generated. Maximum average output powers of 27 mW are obtained at a slope efficiency of 5% in this mode of operation. For the 1057-nm-wavelength Yb laser, Q-switched pulses are obtained with a repetition rate of up to 833 kHz and a maximum average output power of 21 mW. The pulse duration is found to decrease from 292 to 140 ns and the pulse energy increase from 17 to 27 nJ as the incident pump power increases from 220 to 652 mW.

An Yb:Lu2O3 planar waveguide laser fabricated by pulsed laser deposition has reached an output power in excess of 7W, with a slope efficiency of 38%, end-pumped by a diode bar.

A 1.94 GHz CW modelocked ytterbium-doped bismuthate waveguide laser is presented. The waveguide was fabricated using the ultrafast laser inscription technique. Pulse energy of 30.9 pJ and pulse duration of 1.1 ps are inferred from the spectral width.

We present an ion-exchanged Yb-glass waveguide amplifier, seeded by an ion-exchanged Yb-glass waveguide laser, demonstrating a gain of as high as 10 dB. We also present multi-GHz, mode-locked waveguide lasers and discuss the development of a fully integrated high-power, multi-GHz waveguide source.

A diode-pumped Er,Yb:glass waveguide laser, Q-switched mode-locked using a graphene saturable absorber is presented. Mode-locked pulses at a repetition rate of 6.8 GHz are achieved at an output power of 27 mW and a wavelength of 1535 nm.

We demonstrate passively mode-locked Yb3+-doped glass waveguide lasers in a quasi-monolithic configuration with a maximum pulse repetition frequency up to 15.2 GHz. A semiconductor saturable absorber mirror (SESAM) is used to achieve stable mode-locking around 1050 nm with pulse durations as short as 811 fs and an average power up to 27 mW. Different waveguide samples are also employed to deliver pulses with repetition rates of 4.9 GHz, 10.4 GHz and 12 GHz with an average power of 32 mW, 60 mW and 45 mW, respectively. The group velocity dispersion control in the cavity is provided by changing the gap between the SESAM and the waveguide end-face to facilitate a soliton mode-locking regime. (C) 2013 Optical Society of America Publisher PDF

We report a passively mode-locked, diode-pumped waveguide laser operating in the 1.5µm spectral region using a quantum dot SESAM as the saturable absorber element. A repetition rate of up to 6.8GHz and an average power as high as 30mW is obtained during mode-locked operation. Minimum pulse duration of 2.5ps is produced at a wavelength of 1556nm. The repetition rate of the source was tuned by more than 1 MHz by changing the pump power, demonstrating a possible route towards integrated pulse repetition rate stabilisation.

Recently, we have demonstrated the first passively mode-locked Yb:glass channel waveguide laser operating with a repetition rate of 4.9 GHz. In this work we report the pulse repetition frequency as high as 15.2 GHz from a diode-pumped Yb:glass waveguide laser which produces a pulse duration of 811 fs with an output power of 27 mW at around 1047 nm.

Solid-state lasers operating in the eye-safe region near 2 micron are of considerable interest owing to various application areas such as remote sensing, spectroscopy and LID AR. Thulium-based gain media have several attractive features including a broad emission bandwidth, a broad absorption band near 800 nm that can be diode pumped and the possibility of obtaining a quantum efficiency of up to 200% due to the process of cross-relaxation. Guided-wave devices can offer additional advantages of compactness and integration, as well as lower thresholds and high slope efficiencies if low propagation losses can be obtained. Such devices, when combined with integrated saturable absorber elements, can also be passively modelocked to generate femtosecond pulses with multi-GHz repetition rates [1].

Summary form only given. RbTiOPO4 (RTP) belongs to the KTiOPO4 (KTP) family of crystals and has similarly useful nonlinear optical properties. In addition, RTP allows higher doping of rare-earth elements, such as Yb3+, when compared to KTP, a 2 times larger damage threshold than KTP, a very large electro-optic coefficient, a low dielectric constant and high chemical stability, which makes these materials very interesting for active photonics applications. In particular, Yb3+-doped RTP exhibits a broad fluorescence spectrum that has been exploited to demonstrate ultrafast operation, with pulses as short as 155 fs being generated [1]. Recently, planar waveguiding has been demonstrated in an (Yb3+, Nb5+):RTP film grown by liquid phase epitaxy [2], opening the possibility of planar integrated devices based on this highly functional material.Channel waveguides based on this thin-film technology would be of considerable interest for realising, for example, compact ultrafast lasers with GHz repetition rates [3] with applications in optical frequency metrology, optical sampling and biological imaging, or self-frequency-doubled lasers for visible laser sources. In this work we discuss the reactive ion etching (RIE) of RTP and the process optimisation to fabricate single-mode channel waveguides for lasing application around 1 micron. A 200-nm layer of chromium (Cr) was deposited on a number of RTP substrates grown by the top-seeded solution growth method (TSSG), after which it was photolithographically patterned to give a Cr mask with waveguide features of widths 1 μm to 10 μm. The masked substrates were etched in an OPT Plasmalab 80 plus RIE system (Oxford Instruments) with an RF frequency of 13.56 MHz. SF6 and Ar were used to etch the substrates in order to study the interplay between chemical and physical etching processes, respectively. The gas flow rates, gas pressures and RF power were systematically varied to get a good balance between etch rate and RMS surface roughness. The dependence of the etch rate and surface roughness on each parameter is shown in figure 1. Based on these graphs the optimum conditions were chosen to be: RF power of 250 W, gas pressure of 40 mTorr and gas flow rate of 10 sccm for both SF6 and Ar (giving a total gas flow rate of 20 sccm). A 6-μm-thick (Yb,Nb): RTP thin-film was grown on an undoped RTP substrate by liquid phase epitaxy and then etched for 135 minutes with the optimised conditions. It was then end polished to give a 6-mm-long waveguide. An SEM image of the end face of a 9.8-μm-wide channel is shown in the inset of figure 1. The sidewall angle was measured to be 63° and the etch depth was 1.4 μm. Waveguiding experiments were carried out by end-fire coupling a 981nm fiber-coupled single-mode laser diode into the channels. The output was found to be single-mode, with 1/e2 mode diameters measured to be 16.4 μm and 8 μm in the x and y directions respectively and is in good agreement with the simulated values of 15.2 μm and 6.8 μm.

Continuous wave laser action around 1.9 µm has been demonstrated in a Tm3+ - doped germanate glass channel waveguide laser fabricated by ion-exchange. Laser action was observed with an absorbed power threshold of only 44 mW and a slope efficiency of up to 6.8% was achieved. Propagation loss at the lasing wavelength was measured and found to be 0.3 dB/cm. We believe this to be the first ion-exchanged Tm3+-doped-glass waveguide laser.

We present the fabrication of single-mode rib waveguides in (Yb,Nb):RbTiOPO4 ((Yb,Nb):RTP) by reactive ion etching (RIE) with a combination of SF6 and Ar gases. The influence of the gas pressure, RF power and gas ratio on the etch rate and surface quality was studied to optimize the etching of RTP. Optimized parameters were used to fabricate rib waveguides in a (Yb,Nb):RTP film, grown by liquid phase epitaxy, with an etch rate of 10 nm/min. Channel waveguide propagation was demonstrated for the first time in an RIE etched (Yb,Nb):RTP rib structure.

PbSe quantum dots (QDs) were grown in high-refractive-index low-melting-temperature lead-phosphate glass. QDs with various sizes ranging from 2 nm to 5.3 nm were grown by controlling the growth parameters, heat-treatment temperature and time. The corresponding room-temperature exciton absorption was tuned within the infrared region from 0.93 µm to 2.75 µm. Photoluminescence was measured for samples with absorption peaks above 0.95eV. Real time quantum dot growth was demonstrated by monitoring the evolution of exciton absorption with temperature and time duration. As a demonstration of the use of QDs in laser applications, the saturation fluence (Fsat) of one of the QDs was evaluated and found to be ~2.1 µJ/cm2 at 1.2 µm.

In this work, we demonstrate 3-level laser operation in a Yb,Gd,Lu:KYW waveguide laser fabricated by combination of liquid phase epitaxy and Ar+ ion beam milling. Laser emission was observed at 981 nm with an absorbed threshold power of 23 mW and a slope efficiency of 58% without the use of any mirrors. With an HR/6%T cavity, the threshold was reduced to 13 mW. The output was single mode with beam radii of 4.8 µm and 3 µm in the in-plane and out-of-plane direction respectively. Laser emission was also observed at 999.8 nm with a threshold of 8 mW by using mirrors favouring the 999.8 nm transition and forming an HR/5%T cavity.

In this paper, we present a diode-pumped, solid-state waveguide laser operating near 1550 nm that is passively mode-locked using a quantum-dot SESAM. A fundamental repetition rate of up to 6.8 GHz with an output power of 30 mW was achieved during mode-locked operation. Pulse durations as short as 2.5 ps were measured at a repetition rate of 4.8 GHz. Fine control of the of the repetition rate was demonstrated by varying the pump power and a tuning range of up to 1 MHz was demonstrated.

In the microwave domain, signal interference bandstop filters with high extinction and wide stopbands are achieved through destructive interference of two signals. Implementation of this filtering concept using RF photonics will lead to unique filters with high performance, enhanced tuning range and reconfigurability. Here we demonstrate an RF photonic signal interference filter, achieved through the combination of precise synthesis of stimulated Brillouin scattering (SBS) loss with advanced phase and amplitude tailoring of RF modulation sidebands. We achieve a square-shaped, 20-dB extinction RF photonic filter over a tunable bandwidth of up to 1 GHz with a central frequency tuning range of 16 GHz using a low SBS loss of ~3 dB. Wideband destructive interference in this novel filter leads to the decoupling of the filter suppression from its bandwidth and shape factor. This allows the creation of a filter with all-optimized qualities.

This research was funded through Engineering and Physical Sciences Research Council grants EP/H035745/1 and EP/H038035/1. We report on the first demonstration of a passively mode-locked, diode-pumped, monolithic Yb:glass channel waveguide laser that incorporates a semiconductor saturable absorber mirror. Stable and self-starting mode-locking is achieved in a Fabry-Perot cavity configuration producing a pulse repetition rate up to 4.9 GHz. The shortest pulse duration of 740 fs is generated with 30 mW of average output power at a center wavelength of 1058 nm. A maximum output power of 81 mW is produced during mode-locking with corresponding pulse duration of 800 fs. Publisher PDF

Fabrication, characterization, and laser performance of an Yb:Lu2O3 planar waveguide laser are reported. Pulsed laser deposition was employed to grow an 8 µm-thick Yb-doped lutetia waveguide on a YAG substrate. X-ray diffraction was used to determine the crystallinity, and spectroscopic characterization showed the absorption and emission cross-sections were indistinguishable from those reported for bulk material. When end-pumped by a diode-laser bar an output power of 7.4 W was achieved, limited by the available pump power, at a wavelength of 1033 nm and a slope efficiency of 38% with respect to the absorbed pump power.

In this paper we present a passively Q-switched Yb:Y2O3 waveguide laser using evanescent-field interaction with an atmospheric-pressure-chemical-vapour deposited graphene saturable absorber. The waveguide, pumped by a broad area diode laser, produced an average output power of 456 mW at an absorbed power of 4.1 W. The corresponding pulse energy and peak power were 330 nJ and 2 W, respectively. No graphene damage was observed, demonstrating the suitability of top deposited graphene for high-power operation.

In this paper we present the fabrication and characterization of rib waveguides made on (Yb,Nb):RbTiOPO4/RbTiOPO4 epitaxial layers. Liquid phase epitaxy (LPE) was used to grow planar thin films followed by Ar+ ion milling for surface rib fabrication. Here, we report the detailed fabrication procedure and characterization of the ribs. The study reveals good optical confinement and that type II second harmonic generation inside the rib was obtained, showing the generation of green light at 570 nm.

We demonstrate frequency redshifting and blueshifting of dispersive waves at group velocity horizons of solitons in fibers. The tunnelling probability of waves that cannot propagate through the fiber-optical solitons (horizons) is measured and described analytically. For shifts up to two times the soliton spectral width, the waves frequency shift with probability exceeding 90% rather than tunnelling through the soliton in our experiment. We also discuss key features of fiber optical Cherenkov radiation such as high efficiency and large bandwidth within this framework.