Top PDF Optical devices using an external cavity semiconductor laser

Optical devices using an external cavity semiconductor laser

Optical devices using an external cavity semiconductor laser

A dual-mode optical device selectively operative in signal generation and amplification modes is disclosed herein. The dual-mode device includes a body of semiconductor material having opposed from and rear facets. During operation in the amplification mode, light is input through the front facet and is amplified within the body of the optical gain material. An at least partially optically reflective surface is positioned a first

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Performance Analysis on a Dual External Cavity Tunable Laser ECTL Source

Performance Analysis on a Dual External Cavity Tunable Laser ECTL Source

This paper presents the diffraction effects on the performance of a dual external cavity tunable laser source, whose external cavities are constructed by micro electro mechanical systems (ME- MS). One of the main problems in these structures is the optical diffraction as the emitting surface of the laser diode is usually quite limited in the transverse directions. The emitted beam diffracts rapidly in the air and only a small amount of light is coupled back to the source that usually limits the tuning range of the source. Device characteristics such as tuning range, wavelength shift and sensitivity are evaluated. New expression is used and multiple reflections inside external cavities are considered. The simulation results have shown that single external cavity has limited tuning range. It is shown that multiple reflections have significant effect in our model. To get a better en- gineering for the dual ECTL dimensions, diffraction effects must be taken into account.
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Femtosecond synchronously in-well pumped vertical-external-cavity surface-emitting laser

Femtosecond synchronously in-well pumped vertical-external-cavity surface-emitting laser

The autocorrelation of the laser pulse was also recorded and considerable variations again observed in the − 4 µm to +4 µm region. The autocorrelation traces and spectra in this detuning range are shown in Fig. 2(b). As the laser cavity was shortened from +4 µm to 0 µm, the FWHM of the autocorrelation first narrowed from 12 ps to 6.4 ps, then quickly broadened to about 14 ps and finally decreased to 5 ps again. In the positive detuning region, a strong coherent spike was present in the autocorrelation function [11, 21]. From 0 µm to − 4 µm, the autocorrelation width narrowed continuously from 5 ps to 2 ps. Further cavity shortening only resulted in a drop of gain seen by the laser pulse and corresponding reduction in output power. The spectral bandwidth of the pulses generated around the optimal position was around 7 nm with a time-bandwidth products ranging from 7 to 17.5. Synchronously pumped mode- locked lasers are often observed to display a Lorentzian pulse shape [23] with a theoretical time-bandwidth product of 0.22. Thus, our measurements indicate strong chirping of the pulse. By recording the pulse width after passing the laser output through a 10 cm long glass rod with a dispersion of ~100 fs/nm the sign of the chirp was found to be different on the two sides of the position where the spectral bandwidth was broadest (+1 µm). The pulse generated with a shorter cavity was up-chirped while it was down-chirped with a longer cavity. This agrees well with the observations for the synchronously barrier pumped VECSELs [9–11] and the qualitative features of this can be understood from the model for the GVD of synchronously pumped VECSELs [12]. For negative cavity detunings the frequency chirp is relatively small and negative (dominated by SPM via optical pumping) resulting in the observed clean spectra with narrow bandwidth. The notable feature of the broad, chirped pulse on the positive displacement side around +1 µm is caused by the strong chirp near the peak of the gain, where the SPM is most strongly affected by gain saturation.
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Continuous wave room temperature external ring cavity quantum cascade laser

Continuous wave room temperature external ring cavity quantum cascade laser

Measurements taken prior to the laser receiving AR coatings gave a pulsed threshold current of the “as cleaved” FP QCL of 400 mA. After the AR coating, the optical feedback from the facets was reduced to the extent that the laser no longer operated as a free running pulsed laser device up to the roll over current of ~700 mA. Initially, the ring cavity QCL was aligned and tested in the pulsed regime (~10 µs long pulses) before a dc driving current was introduced. The absence of optical feedback means alignment of the ring cavity must be performed using the very weak λ ~ 5.25 µm electroluminescent emission. By using the MCT detector and an additional red diode laser, we were able to develop a careful step by step procedure for the ring cavity alignment. The pulsed threshold current of the AR coated QCL, when operating inside the ring cavity, is 360 mA. Such a greatly reduced threshold current indicates a high level of external feedback and suggests that a well aligned system can exhibit high collection/coupling efficiencies. Based on the value of the threshold current, the feedback from the ring cavity is estimated to be over 30 % for each facet.
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Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry

Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry

Spectral characterisation by laser-feedback interferometry. In our experiment a QCL emitting at ~2.25 THz was used as the laser source (see Methods). Radiation from the front facet of the device was collimated and relected back to the laser cavity using a planar mirror, as shown in Fig. 1 (box A). Two wire grid polarisers were positioned in the external cavity to provide control over the level of OF to the laser; rotation of the second of these polarisers through an angle θ relative to the axis of the irst results in a power attenuation factor of cos 4 θ in double-pass, enabling a range of feedback parameters to be achieved from C ≈ 0 (no feedback) to C ≈ 1.5. To perform spectral analysis using LFI the feedback parameter was set to C ≈ 0.6, ensuring operation in the regime of weak feedback such that the spectral characteristics of the solitary laser dominate over those of the external cavity.
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Optical Design Of Dilute Nitride Quantum Wells Vertical Cavity Semiconductor Optical Amplifiers For Communication Systems

Optical Design Of Dilute Nitride Quantum Wells Vertical Cavity Semiconductor Optical Amplifiers For Communication Systems

To illustrate the relation between VCSOA gain and its bandwidth, (4) and (5) were used to obtain the gain bandwidth using different top Bragg mirrors. The equation is mainly restricted by the line-width of the Fabry-Perot modes and it used to understand the amplifier properties of the VCSOA device in reflection mode. In high reflectivities, a net gain is demonstrated where the device start lasing, while in low reflectivities, a higher carrier density and wider gain amplifier bandwidth is obtained. However if the reflectivity is too low, there will not be enough signal pass gain. The amplifier gain bandwidth is usually measured from the optical width of the gain spectrum at the full-width half-maximum (FWHM). Amplifier bandwidth versus peak reflection gain for 24- periode bottom mirrors and various top mirrors reflectivities are shown in Fig. 7 It’s clear from the figure that the amplifier bandwidth in reflection mode decreases as the peak reflection gain increases. The higher reflectivity allows for high gain and lower amplifier bandwidth. The small bandwidths are advantageous for optical filter to reduce the signal noise, while the larger bandwidths are desirable for devices used in applications with multiple channels.
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Mode referencing of an external cavity diode laser for continuous frequency stabilization

Mode referencing of an external cavity diode laser for continuous frequency stabilization

The ability to stabilize the emission from a diode laser to a reference frequency is of great importance for many appli- cations including optical telecommunications, injection locking of high-power lasers, and spectroscopic based studies. 1–4 However, depending on the type of device in- volved, control of the frequency-stabilizing mechanism may vary in complexity. For example, some widely tune- able sources with multisection architectures, such as the sampled-grating distributed Bragg reflector 共 SG-DBR 兲 la- ser, require several current sources to drive the device, and very precise manipulation of these is required to control and stabilize the output emission wavelength. 5 This situa- tion is similar to that pertaining to the external cavity diode laser 共ECDL兲, where the emission wavelength is controlled by both injection current to the laser and a voltage to a piezoelectric transducer 共PZT兲, which controls the position of the external grating. 6 ECDLs have long been a source of great interest due to their wide wavelength tuning capabil- ity, high output power, and, of course, the narrow linewidth available with an external cavity. 7,8
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Femtosecond synchronously mode-locked vertical-external cavity surface-emitting laser

Femtosecond synchronously mode-locked vertical-external cavity surface-emitting laser

A synchronously mode-locked 980 nm VECSEL has been reported. Detailed studies of the laser characteristics as a function of pump duration and cavity tuning were performed showing the potentials as well as the limitations of the synchronous pumping approach for mode- locking. The output pulses had duration of 10-40 ps for ps as well as for fs pumping. This indicates strong chirping due to the optical pumping-induced carrier generation and due to SPM by gain saturation. These processes were analyzed in some detail. Chirp compensation was effectively achieved by using either a grating-pair or a fiber. Nearly transform-limited pulses with duration of a few hundred femtoseconds with peak power ranging from 300 W to 1.3 kW were obtained. Thus it appears that synchronous pumping might be useful to provide ultrashort pulse sources at repetition rates of about 100 MHz in spectral regions which cannot be accessed directly by other sources (mainly the Ti:Sapphire laser). Our results demonstrate that it is not necessarily beneficial to use very short pump pulses, but that the performance will stay about the same till the 10 ps range. We mention that it appears to be interesting to reconsider this issue in conjunction with the recently introduced technique of in-well pumping [24], where the dynamics of the gain build-up is expected to be faster. Obviously, more efficient techniques for external pulse compression or intracavity dispersion would be helpful in order to overcome the massive chirping present in these devices.
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How the carrier momentum influences the polarization properties of a vertical-cavity semiconductor laser

How the carrier momentum influences the polarization properties of a vertical-cavity semiconductor laser

By taking carrier momentum into account, we present an extension of the commonly used model that describes the polarization properties of vertical-cavity surface-emitting lasers ~ VCSEL’s ! . We study how this modifies the polarization dependence of the gain saturation, and introduce the role of the crystalline symmetry of the semiconductor material. On a macroscopic level we show that a limited number of parameters is sufficient to describe fully the polarization properties of the VCSEL. On a microscopic level we show how the magnitudes of these parameters are determined by the dependence of the interband-transition dipole matrix element on the relative orientation of the carrier momentum and optical polarization. It turns out to be essential that the component of the carrier momentum in the plane of the quantum well is non-negligible. Furthermore, the relaxation rates of the carrier momentum and carrier spin are crucial in determining the magnitude of the polarization effects. Inclusion of the carrier momentum changes the interpretation of experimental results on the polarization of VCSEL’s, and makes it possible to understand experimental results that were until now unexplained. @ S1050-2947 ~ 99 ! 02201-5 #
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Inducing tunable single-mode operation of Fabry-Perot semiconductor laser coupled with very-short cavity with selective optical feedback

Inducing tunable single-mode operation of Fabry-Perot semiconductor laser coupled with very-short cavity with selective optical feedback

Subjecting semiconductor laser to external optical feed- back induces variety of changes in the laser output, ran- ging between linewidth narrowing to coherence collapse, and from stable CW operation or period-1 oscillations with low noise to chaotic dynamics with noisiest levels [1–15]. An experimental study of the so-called ‘regimes of feedback’ and the associated characteristic dynamics of semiconductor lasers was undertaken by Tkach and Chaprylyvy [15]. The distance between the laser facet and the external reflector plays a significant role in de- termining the nature of the response of semiconductor lasers to optical feedback as pointed out in [9, 13, 16]. When the external cavity formed between the laser front facet and external reflector is long enough, the laser out- put is mainly chaotic and could exhibit low-frequency fluctuations [17]. As the length decreases, the laser
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Wavelength controlled external cavity laser with a silicon photonic crystal resonant reflector

Wavelength controlled external cavity laser with a silicon photonic crystal resonant reflector

While one of the most appealing technologies for Si PIC is the Silicon-On-Insulator platform, one of the elements not yet widely available in it is an efficient electrically pumped laser directly integrated in Si or other group IV elements. The use of III-V materials as gain elements the preferred solution to this issue. However, compatibility challenges and lattice mismatch makes this a difficult task. One approach to overcome such challenges is the use of direct wafer bonding for the heterogeneous integration of III-V elements on SOI-based systems [6]. An alternative solution is the formation of External-Cavity (EC) lasers by the use of external reflectors based on Si and Reflective Semiconductor Optical
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Semiconductor Optical Amplifier (SOA) Fiber Ring Laser and Its Application to Stress Sensing

Semiconductor Optical Amplifier (SOA) Fiber Ring Laser and Its Application to Stress Sensing

The SOA-fiber ring laser has been developed and as the application to stress sensing by introducing a photoe- lastic material in the cavity the beat frequency changed as applying pressure proportionally. In the present laser phase difference is generated by birefringence which is reciprocal effect in the ring cavity. Since birefringence is induced by many phenomena such as electromagnetic field, pressure, and temperature, etc., sensors utilizing the present fiber ring lasers are expecting to detect such physical quantity in a frequency domain.

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Time-Domain Travelling-Wave Model for Quantum Dot Based Vertical Cavity Laser Devices

Time-Domain Travelling-Wave Model for Quantum Dot Based Vertical Cavity Laser Devices

dephasing rate increases, which will result in more reduction in gain as Eq. (2) indicates. Moreover, the temperature rise enhances the escaping rate of carriers that will result in a reduction in the population inversion term (i.e., (2ρ − 1)) which is considered as another reduction in gain. There are other effects of temperature rise which are not taken into consideration in this work, such as thermal lensing effect which means the effect of temperature rises on the refractive index. In addition, temperature rise affects the energy gap of cavity materials (i.e., GaAs, InGaAs, and InAs) which results in a red shift of the lasing wavelength. It is known that in semiconductor laser, the peak gain wavelength is temperature dependent; however, QD based semiconductor laser enjoys, theoretically, stable emission wavelength since its transition energy is nearly unaffected by the changes of the operating conditions [5, 17]. So, we have neglected temperature-wavelength dependence in this work.
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External cavity diode lasers and non linear optical frequency conversion in spectroscopic applications

External cavity diode lasers and non linear optical frequency conversion in spectroscopic applications

wide wavelength range for the device. Both single and double passing of the pump beam resulted in successful operation. By double passing the OPO, a lower threshold power was obtained, increasing the variety of pump sources available for this type of device. The threshold requirements for an OPO relax with shorter pump wavelengths so it is conceivable that for the violet OPO the threshold would be lower than 21mW, which is an output power that is attainable by a violet diode laser such as those characterised in Chapter 5. In addition, double passing the pump further restricts the number of potential oscillation conditions, thus providing a more stable output. The development of the DRO system was attempted in order to obtain a source of continuous, stable tunable laser radiation of frequency and wavelength that is, with certain restrictions,user selectable. It was discussed earlier that the DRO is more prone to discontinuous frequency output than other cavity configurations. There has been extensive theoretical and experimental work carried out on the tuning of bire- fringently phase matched (BPM) DROs [12, 5, 6]. However, as yet, these phenomena have not been investigated for quasi-phase matched DROs. Lindsay [9, 13] exam- ined these issues theoretically by modelling the tuning and stability behaviour of the DRO system described in this chapter. Based on experimental observations, Mathcad modelling and comparisons with the predicted and actual observed behaviour of BPM DROs, it appears that there are factors involved in the stability and tuning that are typical to quasi-phase matched materials (in the initial case periodically poled lithium niobate (PPLN).
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Optical phase-lock loops using semiconductor lasers

Optical phase-lock loops using semiconductor lasers

If the loop delay time is kept at 0.5ns the system would require lasers with a maximum summed linewidth of 7MHz (500MHz filter bandwidth assumed) for a modified first order loop or 6MHz for a second order loop. Such a loop would be difficult, although possible, to realise with commercially available DFB lasers, but should be straight­ forward with current tuned external cavity lasers [Mellis 88]. The recently reported monolithic tunable lasers with sub-MHz linewidths [Kotaki 89] should permit use of the OPLL offset frequency generation scheme in future systems. The tuning speed restrictions of plasma effect tuning, as used in most tunable semiconductor lasers, can be modelled, approximately, by adjusting/^. To overcome this problem multi section lasers [Yamazaki 85] or even reverse bias tuned quantum well structures [Cai 89] could be used as slave lasers.
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Spin induced gigahertz polarization oscillations in vertical-cavity surface-emitting laser devices

Spin induced gigahertz polarization oscillations in vertical-cavity surface-emitting laser devices

remove an elliptical beam shape and then passes a polarization control composed of a linear polarizer and a quarter wave plate. After this the pulse width is extended to 3 ps because of the dispersion from the single mode fiber. The polarization of the pulses can be precisely adjusted to any desired circular or linear polarization by the polarization control. The laser beam with the desired polarization is focused on the VCSEL surface nearly vertically. An extra half wave plate is used to eliminate the polarization distortion caused by two reflecting mirrors. The output emission is polarization and time resolved by a polarization analyzer and streak camera system. The electrically pumped VCSEL is operated near threshold and the average power of optical excitation was 150 mW.
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Simulations of a Novel All Optical Flip Flop Based on a Nonlinear DFB Laser Cavity Using GPGPU Computing

Simulations of a Novel All Optical Flip Flop Based on a Nonlinear DFB Laser Cavity Using GPGPU Computing

to electronics domain and vice versa, which reduces complexities and increases processing speed. All-optical flip-flop based on coupled laser diodes is investigated in [2]. All-optical flip-flop based on micro ring lasers is shown in [3]. Low power all-optical flip-flop based on a micro disk laser diode is fabricated and tested in [4]. An all optical flip-flop based on a single distributed feedback semiconductor laser is implemented in [5], and it requires also a holding beam. A device based on vertical cavity semiconductor optical amplifier that requires a holding beam is shown in [6]. Another device based on active multi-mode interference laser diode is described in [7]. All optical flip-flop based on bistable laser diodes is discussed in [8] [9].
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GaInNAs based Hellish vertical cavity semiconductor optical amplifier for 1 3 μm operation

GaInNAs based Hellish vertical cavity semiconductor optical amplifier for 1 3 μm operation

A VCSOA can be simply described as a vertical cavity surface emitting laser (VCSEL) operating in the linear regime below threshold, with a reduced number of top DBR layers. However, in this article, a novel VCSOA based on the Hellish structure as an alternative to con- ventional VCSOAs is investigated [7]. Hellish devices utilise the transport of non-equilibrium carriers parallel to the layers. Spontaneous emission of ultra bright Hell- ish structures has been demonstrated [8,9]. VCSEL operation was achieved by addiction of DBR layers [10-13]. That design is adapted in this study to make a GaInNAs-based Hellish-VCSOA structure, which differs from the conventional VCSEL by the reduced number of top DBR layers [14]. The structure is designed to operate in the 1.3-μm wavelength region via electrical pumping.
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GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 mu m operation

GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 mu m operation

A VCSOA can be simply described as a vertical cavity surface emitting laser (VCSEL) operating in the linear regime below threshold, with a reduced number of top DBR layers. However, in this article, a novel VCSOA based on the Hellish structure as an alternative to con- ventional VCSOAs is investigated [7]. Hellish devices utilise the transport of non-equilibrium carriers parallel to the layers. Spontaneous emission of ultra bright Hell- ish structures has been demonstrated [8,9]. VCSEL operation was achieved by addiction of DBR layers [10-13]. That design is adapted in this study to make a GaInNAs-based Hellish-VCSOA structure, which differs from the conventional VCSEL by the reduced number of top DBR layers [14]. The structure is designed to operate in the 1.3-μm wavelength region via electrical pumping.
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Steady State Behavior of Semiconductor Laser Diodes Subject to Arbitrary Levels of External Optical Feedback

Steady State Behavior of Semiconductor Laser Diodes Subject to Arbitrary Levels of External Optical Feedback

This paper investigates the steady-state behavior of a feedback laser with arbitrary feedback levels by means of the ITW model. It may be considered as an extension of the works of Langley et al. [12] and Spencer et al. [16]. We provide additional information about the physical insight into a compound laser system and discuss the similarities and the differences between the ITW and LK models. In Section 2, steady-state solutions will be de- rived for the external cavity modes and compared with previous work. In Sections 3 and 4, a detailed quantita- tive comparison between the ITW and LK models will be made and the rigorous condition will be given, under which the ITW model will be simplified to the LK model. Finally, Section 5 will summarize our conclusions.
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