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The measurement of distance plays an integral part in many aspects of modern societies. In this paper an integrated mode-locked laser on a chip is used for distance measurement based on mode-resolved interferometry. The emission from the on-chip source with a repetition rate of 2.5 GHz and a spectral bandwidth of 3 nm is coupled into a Michelson interferometer. The interferometer output is recorded as a spectral interferogram, which is captured in a single camera image. The images are analyzed using Hilbert transform to extract the distance. The distance derived shows a deviation of 6 \mum from the reference, for a distance up to 25 mm. We also demonstrate interferometry with repetition frequency sweep which can also be used with the source. Performance is expected to be better in the near future with the rapid developments in the field of on-chip laser sources which are demonstrating larger spectral widths and coherence lengths.

Low-excess-loss arrayed waveguide gratings are enabled by unique application of deep UV lithography in InP integrated photonics through reduced feature sizes and, more specifically, well-resolved inter-waveguide gap dimensions. Submicrometer wafer-flatness is shown to be required to achieve the critical dimension uniformity better than 10 nm on 3-in substrates. Arrayed waveguide grating devices were fabricated and the effect of inter-waveguide gap scaling on the excess losses was measured and compared to simulations. Excess losses down to 0.15 dB were demonstrated to be lower than predicted with the 2-D simulations. The tapering of the etch depth inside the gaps due to the lag effect of the etch process may explain the improvements.

Foundry services for photonic integration enable access to such technologies and facilitate fab-less businesses models. The technologies are sufficiently mature for proof-of-concept demonstrators, advanced prototypes, and two-medium small-volume production. Further improvement of the technology processes behind those services requires extensive research and development efforts in order to advance the foundry offerings and assure scalability, process control, and the yield required for volume production. A high-level automation of test and assembly processes in the PIC manufacturing chain is essential to improve statistical process control and scalability of all processes. These allow for early known-good-die identification, optimization of fabrication process window, improved yield, and volume production. In this paper we propose a standardized approach to chip layout that supports automated test and assembly processes already at the design phase. Moreover, we describe a modular test software framework based on open standards. Within this test framework, standard file formats for chip, equipment, and measurement description, and the open file formats for storage and exchange of data are described. This test framework is a part of the openEPDA initiative and enables test automation, user-defined testing, data analysis, exchangeability, and traceability across the full manufacturing chain from design to product.

We report a novel type of monolithically integrated tunable semiconductor laser. The tuning is achieved by three intracavity Mach–Zehnder interferometers, realized in passive waveguides and using voltage-controlled electro-optic phase modulators requiring only four control voltages. The potential of the design is demonstrated by a realized laser system that shows an optical linewidth of 363 kHz, output power of 3 mW, and a record tuning range of 74.3 nm. Such a continuous wavelength span is in excess of any monolithic semiconductor laser reported up to date. Precision of the tuning mechanism is demonstrated by a scan over a 0.89-GHz-wide absorption line of acetylene. The laser design is suitable for a number of applications, including gas spectroscopy, telecommunication, and optical coherence tomography. The laser has been fabricated in a multi-project wafer run on an indium phosphide-based generic photonic foundry platform and demonstrates the potential of these technology platforms.

Picosecond-pulse III-V-on-silicon mode-locked lasers based on linear and ring extended cavity geometries are presented. In passive mode-locked operation a 12 kHz -3dB linewidth of the fundamental RF tone at 4.7 GHz is obtained for the linear cavity geometry and 16 kHz for the ring cavity geometry. Stabilization of the repetition rate of these devices using hybrid mode-locking is also demonstrated.

RF frequency downconverters are of key importance in communication satellites. Classically, this is implemented using an electronic mixer. In this paper we explore the use of photonic technology to realize the same functionality. The potential advantages of such an approach compared to the classical microwave solutions are that it is lighter weight, has lower power consumption and can be made smaller if photonic technology is used. An additional advantage is the fact that the optical local oscillator (LO) reference can easily be transported over longer distances than the equivalent LO signal in the microwave domain due to the large bandwidth and low loss and dispersion of optical fiber. Another big advantage is that one can envision the use of short pulse trains as the LO - starting off from a sinusoidal RF reference - in order to exploit subsampling. Subsampling avoids the need for high frequency LO references, which is especially valuable if a downconversion over several 10s of GHz is required. In this paper we present the operation principle of such a photonic frequency downconverter and describe the performance of the developed micro-photonic building blocks required for this functionality. These micro-photonic building blocks are implemented on a III-V semiconductor-on-silicon photonic platform. The components include a micro-photonic hybridly modelocked laser, a 30GHz electroabsorption modulator and an intermediate frequency (1.5GHz) photodetector.

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (

In this paper, we present the detailed characterization of a semiconductor ring passively mode-locked laser with a 20 GHz repetition rate that was realized as an indium phosphide based photonic integrated circuit (PIC). Various dynamical regimes as a function of operating conditions were explored in the spectral and time domain. A record bandwidth of the optical coherent comb from a quantum well based device of 11.5 nm at 3 dB and sub-picosecond pulse generation is demonstrated.

In this study, we provide an experimental assessment of a quantum dash Fabry–Perot´ mode-locked laser for all-optical clock recovery using data streams at 40, 80, 160, and 320 Gb/s. The data streams at 80, 160, and 320 Gb/s are phase coherent signals featuring no spectral component at 40 GHz. The 40 GHz recovered optical clock signal is characterized in terms of phase noise, timing jitter, dynamic power range, and wavelength dependence for the different data rates. Our experiments demonstrate a recovered optical clock signal from a 320 Gb/s data stream with a timing jitter of 94 fs and wavelength detuned by 23 nm. In addition, the performance of the optical time division multiplexing receiver at 80 and 160 Gb/s data signals employing the recovered clock as a demultiplexing control signal and as a clock for the bit-error-rate tester (BERT) is evaluated by bit error rate measurements on the demultiplexed data signals.

Optical sensing offers unrivalled precision with real-time monitoring, but the complexity in implementing the optical sources has so far limited deployments to high value measurement systems. Innovations in photonic integration are beginning to enable breakthroughs in terms of cost, size and performance. Integrated sources and readouts can be created with large-scale semiconductor wafer production techniques. InP integrated photonics is able to combine best-in-class components including the lasers and amplifiers within one photonic chip. The chip-scale integration of complete circuits enables on-chip stabilisation and environmental corrections for further advances in measurement precision and at lower power consumption.

We present our recent work on the realization of III-V-on-silicon mode-locked lasers and integrated nonlinear waveguides for the realization of integrated frequency combs.

Monolithic integration of four widely tunable extended cavity lasers suitable for gas detection is presented. Each laser features a precise, grid-less tuning mechanism with a low-linewidth, single-mode output over a wide wavelength range of 74nm.

The authors present the design and characterization of a novel integrated two-section discrete mode index patterned diode laser source. The two slotted regions etched into the laser ridge waveguide are formed in the same fabrication step as the ridge, thus avoiding the requirement for complex lithography and regrowth steps. The laser is encased in a temperature-controlled butterfly package, which simplifies the static and dynamic measurements. Initial static characterization of this two-section laser shows that the injection, from the master laser to the slave laser, enhances the slave's emission side-mode suppression ratio from 30 dB to over 50 dB and its relative intensity noise is reduced from about -129.3 dB/Hz to -142.6 dB/Hz. Subsequent dynamic characterization then shows that the modulation bandwidth of the laser can be improved via injection to about three times the inherent free-running bandwidth. Hence, optical injection from master section into slave section enables the improvement of various parameters, which makes this two-section device attractive as a transmitter in optical communication systems.

The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to

For the first time we demonstrate an anti-colliding mode-locked laser implemented on a III-V-on-silicon platform. In passive mode-locked operation a 1.7kHz 3dB linewidth of the fundamental RF tone at 4.83GHz is obtained.

A review is given of a number of lasers in a form of photonic integrated circuits realized on InP substrate using a generic integration approach. The potential of these photonic circuits lies in their compactness, low power consumption, and significant reduction of fabrication cost by realization in generic foundry runs. Generic integration platforms offer the possibility of realizing functionally advanced photonic circuits using combinations of just a few standardized and parameterized building blocks. This vibrant field opens new doors to innovative product development for SMEs as well as curiosity-driven research.

Experimental and simulation work, presented in this letter, demonstrates for the first time how the monolithic integration of two single-mode lasers in a master-slave configuration, can substantially increase the achievable bit rate of a direct modulation adaptively modulated optical orthogonal frequency-division multiplexing (AMO-OFDM) system. The Levin-Campello algorithm is applied to select the OFDM bit and power loading scheme used for each system configuration. Improvement in terms of data throughput due to injection is measured for several transmission distances with the improvement in performance presented in terms of error vector magnitude per OFDM subcarrier.

A passively mode locked extended cavity quantum well ring laser at 1.58 µm with repetition rate of 2.5 GHz in the form of a photonic integrated circuit is presented. The device is realized using InP based active-passive integration technology. The 33mm long cavity contains gain, saturable absorption and passive waveguide sections as well as a phase shifter sections to enable fine tuning of the spectral position of the lasing modes. Passive mode-locked operation and with wavelength tuning of the laser modes are experimentally demonstrated. This laser is the lowest reported repetition rate for a monolithically integrated ring laser.

Using monolithic integration technology we have designed and fabricated tunable lasers in the 1.5 µm region with a demonstrated tuning range of 60 nm and single mode operation. This performance is achieved using intracavity tunable Mach-Zehnder interferometers that use voltage controlled phase modulators. In this paper we will discuss design considerations and advantages of such tunable lasers.

Spectral phase control of optical pulses is often required to generate short pulses, and an important application of a pulse shaper is spectral chirp/dispersion (pre-) compensation. In this paper, we present the pulse shaping/compression capability of a monolithically integrated optical pulse shaper. Chip fabrication has been carried out in a standardized generic photonic integration platform which is available in the framework of European FP7 project EuroPIC. A key capability of this platform is the active-passive integration scheme which allows direct integration of active components such as semiconductor optical amplifiers (SOAs) with passive elements such as arrayed waveguide gratings (AWGs) and phase modulators (PMs) on a single photonic chip.

We present the first 320Gb/s all-optical clock recovery by exploiting single Quantum Dash MLL to generate 40GHz synchronized optical clock pulse with 71fs timing jitter. 320Gb/s all-optical demultiplexing operation with 1dB BER penalty was demonstrated.

We experimentally investigate the locking/unlocking dynamics of a mode-locked QDash laser diode for packet-based clock-recovery applications. Results show 20 ns locking times for the passively and externally synchronized mode-locking mechanisms.

A wavelength tunable optical comb is generated based on the gain-switching of an externally seeded Fabry-Pérot laser diode. The comb consists of about eight clearly resolved 10 GHz coherent sidebands within 3 dB spectral envelope peak and is tunable over the entire C-band (1530 to 1570 nm). The optical linewidth of the individual comb tones is measured to be lower than 100 kHz, and the RIN of the individually filtered comb tones (-120 dB/Hz) is shown to be comparable to the entire unfiltered comb (-135 dB/Hz). Besides, expansion of the tunable gain switched comb is achieved with the aid of an optical phase modulator, resulting in near doubling of the number of comb tones.

A novel and cost effective long reach PON downlink scenario is proposed employing a multi-carrier transmitter and pilot tone aided direct detection at the receiver. Error free performance with QPSK and 50km transmission is presented.

In this paper, a detection scheme based on four wave mixing in a semiconductor optical amplifier (SOA) is used to measure the frequency and bandwidth of the optical terahertz beat-tone signal generated by a passively mode locked semiconductor laser. Two signals from external cavity lasers are injected into an SOA, which acts as a local oscillator at their detuning frequency. The device under test is a passively mode locked laser with a beat-tone frequency in the terahertz spectrum. Its optical signal is injected in the SOA, which also acts as a frequency mixer. The frequency and linewidth of the terahertz signal are then measured by retrieving the intermediate frequency detected by a low bandwidth photodiode and an electrical spectrum analyser.

We present a linear self-referenced measurement of the spectral amplitude and phase of a free-running quantum-dash modelocked laser diode. The technique is suitable for measuring optical signals with repetition rates up to 100 GHz. In contrast to many other linear techniques it requires no external electronic clock synchronized to the signal under test. Using this method we are able to compensate for the intracavity dispersion of the diode to demonstrate 500 fs pulses at a repetition rate of 39.8 GHz. We also use the technique to characterize the dependence of the diode’s intracavity dispersion on the applied current.

Beat-tones at 40-GHz from a QDash-ML laser under 10 to 160 Gb/s optical injection are analyzed. A FWHM linewidth less than 8 Hz is obtained regardless of the rate of injected data stream.

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.

Performance improvement of a directly modulated 10 Gb/s OFDM system by optical injection of monolithically integrated lasers is shown experimentally over differing fibre lengths. The modulation and optical injection is performed using monolithically integrated Discrete Mode lasers. It is shown that optical injection with this device reduces third order inter-modulation distortion by up to 10dB and this results in an improvement in system performance from above a forward error correction BER threshold of 1 × 10(-3) to significantly below it.

An all-optical approach based on nonlinear interactions inside a semiconductor optical amplifier for measuring the THz beat-tone of a passively mode-locked laser is proposed. This novel approach can be applied to beat-tones in the range from GHz to few THz.

A narrowband terahertz signal generated by a uni-travelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry-Perot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. All components involved in this experiment operate at room temperature. The terahertz signal at a frequency of 372 GHz is recorded, and the linewidth is 17 MHz. The linewidth and the tunability of the emitted terahertz wave are analyzed, as a function of the laser bias.

A bulk semiconductor optical amplifier (SOA) utilizing a multi-contact biasing method is characterized as a function of the bias current supplied to each section Firstly, amplified spontaneous emission spectra and characteristic light-current profiles are analyzed. Single-pass gain and noise figure of the SOA are then assessed by injecting a continuous wave input beam. Finally, the amplification of a 10 Gb/s (215-1) long pseudo random bit sequence signal is analysed. The obtained results, particularly at a bias condition of 90mA-50mA-10mA, reveal the potential of this device as a low noise figure in-line amplifier.

Timing-jitter measurements in optically generated subpicosecond pulses by a quantum-dash passively mode-locked semiconductor laser as a function of the bias current are reported. All the measurements are retrieved from a second-harmonic-generation frequency-resolved optical gating system. A decreasing trend in the pulse width and the associated timing jitter is found with the bias current. Additionally, the optical and mode-beating linewidths are analyzed in terms of both the mode wavelength and the bias current. From our results, we can conclude that once the optical modes are phase locked, the optical linewidth associated to every individual longitudinal mode of the device under test does not have a significant impact on the mode-beating signal on neither the pulse width nor its respective timing jitter.

Wave-mixing at 370-GHz in a SOA and FP semiconductor laser is investigated by using a FROG-system. A comparison of the optical time-fluctuations measured at their output stresses the importance of a resonant cavity in THz-signals generation from semiconductor optical devices.

International audience; A narrowband terahertz signal generated by a unitravelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry–Pérot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. A terahertz signal at a frequency of 372 GHz, featuring a linewidth of 17 MHz is recorded by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this experiment operate at room temperature. The linewidth and the frequency of the emitted terahertz wave are analyzed, along with their dependency on dc-bias conditions applied to laser diode.

An experimental analysis on the quality of 40-GHz radio-frequency signals generated by various passively mode-locked semiconductor lasers is addressed. The analysis is performed considering the frequency linewidth of 40-GHz optically generated signals and the number of longitudinal modes selected by the cavity of each laser under study. Four of these devices are multi-quantum wells InAlGaAs Fabry–Perot lasers. They have been engineered to exhibit a specific number of longitudinal modes: 4, 5, 10, and 22 modes, respectively. Another device under test is a bulk distributed Bragg reflector laser exhibiting 3 lasing modes. The last device under study is a quantum-dash Fabry–Perot laser characterized by 40 lasing modes. From our experimental results it appears that, regardless the nature of the device cavity and active media, the strength of the passively mode-locked mechanism might be enhanced with the number of longitudinal modes oscillating into the laser cavity, allowing a reduction in the frequency linewidth.

A technique to measure a terahertz wave generated by spectrum tailored Fabry–Pérot lasers (FP) is assessed. A dc-biased and 25 °C temperature controlled FP is probed by a continuous wave signal, tuned at 20 nm away from its lasing modes. With a 0.02 nm resolution optical spectrum analyzer (OSA), the terahertz generated signal frequency is measured from the interval between the probe and its side-band modulations. The terahertz waves emitted by these FPs are measured at 370±5 GHz and at 1.157±0.005 THz, respectively, within a precision set by our OSA. The origin of the terahertz wave is due to passive mode-locked through intracavity four-wave-mixing processes.

We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Pérot based device with shallow grooves implemented on its p-side to engineer the longitudinal mode spectrum. The laser is dc-biased and temperature controlled at 298 K. The main two modes are separated by 3 nm at 1550 nm with a side-mode-suppression ratio of 25 dB. Using a frequency resolved optical gating, evidence of mode beating at 373 GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690 GHz.

In this paper we present some characterizations of passively mode-locked semiconductor lasers. These lasers are multimode and they exhibit a modulation of their output power even though they are DC-biased. The modulation frequency corresponds to their free-spectral range. We demonstrate their potential: for generation of ultra-fast modulation for THz wave generation at room temperature without any direct modulations applied, in the radio frequency range they synchronise their modulation to the bit-rate of an incoming signal used for clock extraction. Therefore these devices can be used for all-optical clock recovery.

Multimode semiconductor lasers under certain DC bias conditions generate electromagnetic waves from the beating between the longitudinal lasing modes. The frequency of those waves is directly related to the free spectral range of the involved modes. Our recent experimental work is carried out on slotted Fabry-Perot lasers with mode separation of 330 GHz. The devices are at room temperature biased at 3 times the threshold current. Using a bolometer coupled to an FT-IR interferometer we are able to observe radiation at 660 GHz, in the terahertz range.

Although self pulsating (SP) lasers are DC biased, they feature a modulation of the output power. For the results presented in this paper, the SP frequency corresponds to the frequency spacing between longitudinal modes or its second harmonic. The performances of both a 40 GHz self pulsating distributed Bragg reflector laser and of a 660 GHz slotted laser are presented. For the first laser, the radio frequency (RF) signal was analysed on electrical spectrum analyser and its linewidth was smaller that the sum of the main optical modes, proving a passive modelocking of the mode phases. For the slotted laser, a bolometer interfaced to a FT IR spectrometer is used for the terahertz (THz) detection. A signal 10 times larger than the noise level was measured with this set up. Both lasers have demonstrated to be an easy solution to produce RF or THz signal generator.

A compact and fabrication-tolerant integrated remotely tunable optical delay line is proposed for millimeter-wave beam steering and is fabricated in an InP generic foundry. The proposed delay line is based on a spectrally cyclic-arrayed waveguide grating feedback loop. Its major features include the tolerant architecture with reduced chip size, and bi-directional operation with simplified remote tuning. Moreover, its cyclic feature guarantees further cascaded operations either for 2D radio beam steering or for high-resolution delay generation. The experimental results show less than 6.5-dB insertion loss of the integrated delay line. Five different delays from 0 to 71.6 ps are generated with less than 0.67-ps delay errors.

A mode-locked extended cavity quantum well ring laser at 1.58 μm with a repetition rate of 2.5 GHz in the form of a photonic integrated circuit is presented. The device is realized using InP-based active-passive integration technology. The 33 mm long cavity contains gain, saturable absorption, and passive waveguide sections as well as phase shifter sections to enable fine tuning of the spectral position of the lasing modes. Passive and hybrid mode-locked operation, along with the wavelength tuning of the laser modes, are experimentally demonstrated. In the passive mode-locking regime, a beat signal at the fundamental round trip frequency with a 3 dB bandwidth of 6.1 kHz is produced on a fast photo diode.

Mode-locked fiber and solid state lasers have played an essential role in several scientific and technological developments. The integration of mode-locked lasers on chips could enable their use in a wide range of applications. The advancement of semiconductor mode-locked laser diodes has been going on for several decades, but has recently seen the development of novel devices based on generic InP and III-V-on-silicon photonic integration platforms. These photonic integration platforms enable the use of standardized components and low-loss waveguides within the laser cavity, allowing for the design of advanced extended cavities. In this manuscript we give a review of these novel devices and compare their performance.

Linewidth narrowing of the radio frequency beat-tones and the optical-modes is experimentally investigated in a ∼40 GHz quantum-dash mode-locked laser diode subject to optical injection of 10 GHz pulses. In comparison to the 75 kHz linewidth exhibited by the beat-tones in passive mode-locking conditions, a remarkable reduction to less than 8 Hz is achieved when the laser is under optical injection. From this beat-tone signal, an integrated root-mean-square timing jitter of 64 fs is calculated. In addition, a quadratic profile of the optical linewidth with the wavelength is observed in active locking, reaching a minimum of 1:7 MHz for the longitudinal modes around 1530 nm and progressively increasing to 37:4 MHz for modes at 1525 nm.

We report first demonstration of quantum dash mode-locked laser based open-loop optical clock recovery of 160 Gb/s RZ-OOK after 52 km transmission with 102 fs timing jitter 40 GHz clock and 2 dB BER penalty.