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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.

An array of monolithic wide-tunable lasers is integrated using selective area growth to shift the bandgap of their gain section. A gap-free tuning is demonstrated from the combination of the tuning ranges of the lasers, and single-mode operation is verified.

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.

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.

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.

Progress on the development of a long wavelength (∼2 µm) generic monolithic photonic integration technology on indium phosphide substrate and a novel concept of a tunable laser realized as a photonic integrated circuit using such technology are presented. Insights into the development of active and passive waveguide structures which are used to define a limited set of on-chip functionalities in the form of building blocks will be given. A novel tunable laser was proposed and designed using such predefined set of basic building blocks. The laser geometry features an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers in a nested configuration. The photonic integrated circuit chip was fabricated within the first long wavelength multi-project wafer run. The experimental evaluations of the fabricated device show a record tuning range of 31 nm around 2027 nm and successful measurements of a 0.86 GHz wide absorption line of carbon dioxide. These results provide a demonstration of a fully functional photonic integrated circuit operating at wavelengths that are much longer than those in the typical telecommunication windows as well as the use of indium phosphide based generic photonic integration technologies for gas sensing applications.

The performance of integrated planar waveguide mode locked lasers can be enhanced using the available photonic integration platform technology in indium-phosphide. Extended cavity mode locked oscillators including DBR mirrors and phase modulators can be realized at telecom wavelengths to improve performance and control over the device. Integrated pulse shapers and special amplifiers can be used to improve the output properties further.

A novel operation mode field reconfigurable DBR laser is designed, realized and investigated experimentally. With different controlling of the same hardware, a shared-cavity six-section DBR laser diode can be flexibly configured to operate as a continuous wave or a pulsed wave laser.

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.

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.

Wavelength tunability of an all-optical clock recovery operation based on a quantum-dash mode-locked Fabry-Perot laser diode is experimentally investigated. Synchronization of the device to the injection of 40-Gb/s nonreturn-to-zero (NRZ) incoming data is assessed by analyzing both the carrier-to-noise ratio and the linewidth of the 40-GHz beat-tones measured at the mode-locked laser output. Under optical injection, beat-tone linewidths below 10 Hz are measured. Recovered clock pulses featuring a width of 1.6 ps are obtained irrespective of the wavelength detuning between the laser spectra and the optical carrier of the incoming data stream.

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.

A tunable laser operating from 2015 – 2040 nm realized as a monolithic InP photonic integrated circuit is presented. The laser uses an intracavity tuning mechanism based on parallel asymmetric Mach-Zehnder interferometers with electro-refractive modulators. The device is intended for a single line gas spectroscopy and was designed and fabricated using a generic integration technology platform.

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.

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.

Optical frequency comb sources (OFCS) have recently attracted a lot of interest due to wide ranging applications such as optical arbitrary waveform generation [1], photonic microwave signal generation [2], optical signal processing [3] and multi-carrier spectrally efficient transmission techniques with the sub-channel spacing equal to the symbol rate of each sub-channel [4]. OFCS with good spectral flatness, stability and low linewidth are highly desirable for such applications. One of the conventional approaches used in realizing a comb source is based on mode-locked semiconductor and fibre lasers [5]. Although this technique can generate multi-carrier signals spanning over a wide bandwidth, it inherently suffers from cavity complexity and does not offer the free spectral range (FSR) tunability since the comb line spacing is fixed by the cavity length of the laser. Moreover, the optical linewidth of the individual comb lines can be relatively large (several MHz) preventing higher order (or low baud rate) advanced modulation formats to be imposed. Another technique that has been reported entails the use of a single, cascaded or dual drive Mach-Zehnder modulators (MZM) to generate the phase correlated optical frequency comb [6]. Although this technique provides a relatively flat optical comb, the large insertion loss of the modulator coupled with the modulation efficiency can prove prohibitive. The extra optical component also adds to the cost and complexity of the transmitter, rendering this technique unsuitable for short reach applications.

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.

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.

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.

Generation of sub-picosecond pulses by a dc-biased passively mode-locked Fabry-Perot laser is demonstrated. By using a tunable band-pass filter, it is observed that the width of the generated pulses decreases in direct proportion to the optical modes emitted by the laser. Furthermore, performing a passive compression by a piece of single mode fiber, we demonstrate the generation of 720 fs pulses by this type of mode-locked Fabry-Perot laser.

Generation of narrow microwave signals produced from the mode beating of a DBR laser is presented. The application of this process to the cw-THz wave generation is also demonstrated using a slotted FP laser.

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.

Characterizations of passively mode-locked semiconductor lasers will be presented in following paper. These lasers are able to operate in multimode regime and to exhibit a modulation of output power even though they are DC-biased. A frequency of the modulation corresponds to their free-spectral range associated with optical longitudinal modes. Some potential applications for devices of that type will be disclosed: in THz frequency range for terahertz wave generation at room temperature without any direct modulations applied, in the radio frequency range ability to synchronise their modulation to the bit-rate of an incoming signal makes them suitable for all-optical clock extraction.

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 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.

An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal (and therefore, the beat-tone signal) are resolved by using a photodiode and an electrical spectrum analyzer.

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.