Effect Of Optical Feedback Research Articles

High external feedback resistance of laterally loss-coupled distributed feedback quantum dot semiconductor lasers

External optical feedback effects on quantum dot (QD) laterally loss-coupled (LLC) distributed feedback (DFB) lasers are reported for the first time in this letter. The critical external feedback ratio that causes coherence collapse of the QD DFB is measured to be -14 dB. No spectral broadening at this feedback level is observed within the 0.06-nm resolution of the optical spectrum analyzer (OSA). Self-homodyne measurements also confirm that the rebroadened linewidth of the QD DFB under -14-dB feedback is still much smaller than the feedback-free linewidth. Under 2.5-Gb/s modulation, eye-diagram measurements show that the signal-to-noise ratio starts to degrade at a feedback ratio of -30 dB in the QD LLC-DFB, about 20 dB higher than a typical quantum-well DFB at the same output power and extinction ratio.

Characteristics of Light Emission by Ballistic Electron Excitation in Nanocrystalline Silicon Device Formed on a p-Type Substrate

It is demonstrated that planar light emission by ballistic electron excitation is observed in a nanocrystalline porous silicon (nc-PS) device fabricated on a p-type silicon substrate and occurs in a similar way to the case of n-type substrate. The device is composed of a semitransparent thin Au film, an organic fluorescent film, the nc-PS layer, a p-type Si substrate and an ohmic back contact. When a positive bias voltage higher than 20 V is applied to the Au top contact, the diode uniformly emits green light. The light intensity sharply increases with increasing bias voltage. The measured luminescence band coincides well with the original photoluminescence spectrum of the deposited fluorescent material. A hysteresis is observed in the current-voltage and the corresponding luminescence-voltage characteristics. These optoelectronic properties suggest that the light emission is based on excitation of a fluorescent film by ballistic electrons generated in the nc-PS layer. The observed hysteresis is due to an optical feedback effect by which photoexcited electrons in the nc-PS layer participate in the ballistic transport and subsequent impact on the fluorescent film. The present result is useful for applications to functional planar light-emissive devices.

Analysis for the self-mixing interference effects in a laser diode at high optical feedback levels

Based on the study of the self-mixing interference effects at different optical feedback levels, a model is presented in terms of the threshold condition of a compound cavity laser. This model considers the optical feedback effect on the real and imaginary parts of the complex refractive index of the laser active medium and the asymmetric external cavity effect. Complex waveforms experimentally observed at high feedback levels can be interpreted well by this model. Theoretical and experimental results show a potential increase in the resolution of the displacement measurement at a high optical feedback level or misalignment condition.

How to launch 1 W into single-mode fiber from a single 1.48-μm flared resonator

The operation of 1.48-/spl mu/m flared resonators is thoroughly studied, both experimentally and theoretically: the accurate determination of threshold condition as a function of geometrical and material parameters, the study of emission spectra and astigmatism variations as a function of optical power level allow us to better understand the may these devices operate. The origin of modal distortion is then analyzed, and an original solution is proposed to increase the single-transverse-mode power at high injection level: it is shown that implanting the multiple-quantum-well active layer with protons efficiently enhances the filtering capability of the overall structure, and particularly that of the ridge waveguide, by bringing additional lateral absorption losses. The explanation of the filtering mechanism is successfully confirmed by simulations using the beam-propagation method. This technique finally allowed more than 1.3 W of continuous wave (CW) diffraction-limited power at 6 A. Low-modal-gain structures were then realized to reduce modal optical absorption in the implanted structures with a view to maintaining a high external efficiency and a reduced vertical divergence. Finally, a three-lens coupling system was designed and the effects of optical feedback minimized so as to obtain a very high coupling efficiency: with an improved laser design, 1.12 W of CW power were then coupled into single-mode fiber at 6.6 A, which represents 65% of the power emitted by the laser chip.

Integrated Surface Emitting Laser Arrays with Flat-Tip Microprobes for the Near-Field Optical Data Storage

ABSTRACTCurrent optical data storage is challenging to increase its memory capacity and data transfer rate for realizing high-quality image and rapid service in the coming digital, multimedia and network era. To actualize more effective and simple data storage, a novel parallel near-field optical system has been proposed using vertical cavity surface emitting laser (VCSEL) microprobe arrays. The new parallel optical system is based a multibeam recording head consisting of a VCSEL array with apertures of nanometer size as a near-field wave exit. We have developed some candidates for the parallel recording head, including the direct aperture formation on the VCSEL emitting surface and the preparation of microprobe arrays with flat-tip structure. The new flat-tip microprobe array has advantages for improving the optical efficiency and stabilizing the contact head system with optical media since it is prepared from semiconductor materials of high refractive index. Silicon nano-aperture probe array has been prepared successfully with the aperture size of 150 to 500nm using micro-fabrication techniques. We have also investigated the integrated microprobe array by the direct fabrication of flat-tip probes on the substrate of bottom emitting VCSEL arrays. Finally the reading mechanism has been studied theoretically using a finite difference time domain (FDTD) simulation and an optical feedback effect of semiconductor lasers for the integrated microprobe VCSEL array. We believe this nano-aperture VCSEL probe array is sufficiently effective to be applied to the parallel recording head for the near-field optical data storage of a high data capacity and fast transfer rate.

New SNOM sensor using optical feedback in a VCSEL-based compound-cavity

Today, most near-field nanoprobes consist of specially processed optical fibres, which are difficult to fabricate with high reproducibility and in large number. To overcome this handicap, we propose a miniaturised near-field sensor. One of the novelties is to use the optical feedback properties of a vertical-cavity surface-emitting laser (VCSEL) cavity as an active principle of detection. The other novelty is that the architecture of a compound-cavity VCSEL with a GaAs micromachined tip, offering a nanometer-scale resolution of near-field probes, constitutes the first tentative to miniaturise an SNOM microscope. First, we investigate the effects of external optical feedback on the threshold and spectral characteristics of VCSELs. Second, theoretical analysis and experimental evidence demonstrate the practicability of VCSEL feedback as a detection principle for SNOM microscopy. Finally, we propose a compact architecture of an SNOM sensor with a microtip integrated on top of the VCSEL and report the preliminary results of fabrication of the integrated device.

Analysis of the linewidth of a grating-feedback GaAlAs laser

Effects of external optical feedback from a reflection grating on the linewidth of a GaAlAs semiconductor laser operating at 780 nm are investigated. Accurate linewidth measurements as a function of the laser frequency tuning have been performed by applying the self-homodyne technique with a short delay line. A realistic coupled-cavity model, which incorporates the frequency-dependent reflection from the grating, is used to explain the measured data. The agreement between the theoretical and experimental results was found to be good.

研究速報 : Monolithically Integrated Diode Laser Detection System for Scanning Near-Field Optical Microscopy (SNOM) : Study of the Optical Feedback Effect in VCSELs

The early eighties have witnessed a revolution in the perception of physical phenomena with the bith of a new generation of imag- ing systems based on the detection of non-radiating fields such as the scanning tunnelling microscope (STM) and the atomic force microscope (AFM). The scanning near field optical microscope (SNOM) is the latest of this family and is based on the detection of tunnelling photonsl. We propose to fabricate a semiconductor inte- grated nanoprobe which will further enhance the capabilities of this instrument.

Iodine-stabilized diode laser at 633 nm: effects of optical feedback

The frequency of a diode laser has been stabilized to the hyperfine spectrum of molecular iodine at 633 mm. A frequency stability and a (day-to-day) reproducibility of 4/spl times/10/sup -12/ and 5/spl times/10/sup -11/, respectively, were obtained. In particular, we have investigated the effect of optical feedback on the locking point frequency of the stabilized diode laser. Optical feedback can cause amplitude variations and harmonic distortion of the frequency modulation of the diode laser and, subsequently, cause a significant shift of the locking point of the laser. The optical feedback is shown to have undesired effects even at very small (7/spl times/10/sup -10/) levels.

Effect of strong optical feedback on vertical-cavity surface-emitting lasers

An analysis is performed of the effects of strong optical feedback on the characteristics of single-transverse mode VCSEL's. Consideration is given to the cases of short (1.5 cm) and long (15 cm) external cavities. When the laser is operated well above threshold in a short external cavity with high reflectivity, a strong dependence on the accumulated external cavity phase is observed. Stable operation is found for an optimum phase while for other values of the phase, chaotic dynamics is observed. Such behavior is not seen near threshold where the laser output is stable for any accumulated phase. For the longer external cavity the influence of the phase term is found to be insignificant: chaotic behavior is seen in the output over a wide range of operating currents.

Feedback-induced chaos and intensity-noise enhancement in vertical-cavity surface-emitting lasers

We investigate numerically the effects of optical feedback on the intensity noise of vertical-cavity surface-emitting lasers (VCSEL’s) under single-mode and two-mode operations. Our model includes transverse effects such as carrier diffusion and spatial hole-burning. Results indicate that the relative-intensity noise is relatively unaffected at low feedback levels except for a narrowing and enhancement of the relaxation-oscillation peak. At higher feedback levels, the VCSEL ceases to operate continuously, and its output becomes chaotic, following a period-doubling or a quasi-periodic route depending on the feedback level and the length of the external cavity. In the chaotic regime, the relative-intensity noise is enhanced by more than 20 dB. The critical feedback level at which the VCSEL output becomes chaotic depends on whether the laser operates in one or two transverse modes and how strongly these transverse modes are coupled through spatial hole-burning.

The effects of external optical feedback on the power penalty of DFB-LD modules for 2.5Gbs−1 optical transmission systems

We report the effects of external optical feedback on the power penalty of commercial distributed feedback laser diode (DFB-LD) modules for 2.5Gbs−1 optical transmission systems. External optical feedback presented to the DFB-LD modules causes the excitation of external cavity modes, resulting in increased relative intensity noise (RIN) and intensity noise ripples at low frequency region below 500MHz. For a 10−10 bit error rate (BER), the minimum power penalty is as much as 1.25dB for a feedback ratio of −8.8dB. An excess power penalty of 0.5dB per 3dB increase in the feedback ratio was also empirically obtained. We suggest that optical isolators in 2.5Gbs−1 DFB-LD modules used in conventional optical transmission systems or WDM systems must have a peak isolation ratio of better than 54.5dB, instead of the previously recommended 30dB, for negligible power penalty induced by external optical feedback.

Optical feedback effects on the spectral linewidth of semiconductor laser sensors using self-mixing interference

The spectral characteristics of a semiconductor laser are significantly affected by optical feedback in the active cavity of the diode. In this paper, the influence of weak optical feedback on the linewidth is examined and a new relationship proposed. Feedback-induced changes in the power spectral density are also determined by a theoretical analytical model, in good agreements with experiments. These results are then discussed for sensing applications using self-mixing interference, as the maximum range of distance and displacement sensors can be limited by half the coherence length of the laser diode modified by the optical feedback.

Comparison of the effects of nonlinear gain and weak optical feedback on the dynamics of semiconductor lasers

The influence of nonlinear gain and optical feedback on the dynamics of single-mode semiconductor lasers are numerically investigated based on the Lang and Kobayashi model. It is well known that the nonlinear gain tends to stabilize the dynamics, while the optical feedback tends to increase the instabilities. In this paper, we study the behavior of the attractors when the feedback level k and the gain saturation coefficient /spl epsi/ vary and show that the effects of these parameters are surprisingly opposite. For example, we find that the route to chaos that the external cavity modes follow for increasing k is reversed for increasing /spl epsi/ in an almost identical manner. When the feedback increases the modes follow the usual quasi-periodic route and turn into torus. If k continues to increase, the torus become chaotic attractors as the result of several period-doubling bifurcations or a third Hopf bifurcation. Further increase of k causes the chaotic attractors to lose stability, Contrarily, if the value of the parameter /spl epsi/ is increased, the attractors recover their stability and reverse the route becoming simple torus again. If /spl epsi/ is increased further, the torus reverse the quasi-periodic route and turn into stable modes again. We also find that on the contrary to k, the parameter /spl epsi/ enhances the stability region of an attractor. We show that the feedback level above which a limit cycle emerges from a stable mode, the feedback level above which a torus emerges from a limit cycle, and the feedback level above which a chaotic attractor loses stability are all increasing functions of /spl epsi/.

Effects of optical feedback on static and dynamic characteristics of vertical-cavity surface-emitting lasers

We present a numerical study of the effects of optical feedback on the static and dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) under both single-mode and two-mode operations. Our model includes transverse effects such as carrier diffusion and spatial hole burning (SHB) and is therefore capable of including gain-saturation-induced coupling among transverse modes. For short external cavities (/spl sim/30 /spl mu/m), optical feedback can completely suppress higher-order transverse modes. For relatively long external cavities (/spl sim/1 cm), VCSELs follow a period-doubling route to chaos. Numerical results show that multimode VCSELs exhibit self-pulsations at higher feedback levels compared with the single-mode case.

Analysis for relative intensity noise of optoelectronic integrated device by heterojunction phototransistor and laser diode

Analysis for relative intensity noise (RIN) is an important consideration for the optimum design of system performance in most of the optical communication systems. Monolithic integration of optical and electronic devices leads to new characteristics such as internal electrical and optical feedback among the components. This will also affect the noise performance of the device. A quantitative analysis for the RIN performance of an optoelectronic integrated device composed of a laser diode (LD) and a heterojunction phototransistor (HPT) is presented. We consider effects of the internal optical feedback from the LD to the HPT, and of avalanche multiplication in the device. It is found that the internal optical feedback improves the RIN of the device, especially near the threshold.

Effect of optical feedback on the noise properties of vertical cavity surface emitting lasers

Noise properties of vertical cavity surface emitting lasers (VCSELs) subject to optical feedback are investigated via calculations of the relative intensity noise (RIN) and turn-on delay jitter for the device. It is shown that, despite their high facet reflectivities, VCSELs have a similar sensitivity to conventional edge emitting laser diodes towards optical feedback.

Effect of optical feedback on fast modulated semiconductor lasers

The authors have studied the numerical response of a singlemode semiconductor laser under modulation of the injection current in the presence of optical feedback for different external cavity lengths. They have restricted the experiment to the nonreturn-to-zero modulation scheme and a modulation frequency of 10 Gbit/s. Observations are made that for short cavities (a few millimetres) the eye diagram aperture and the frequency chirp depend strongly on the phase of the reinjected field. Conversely, for cavity lengths of a few centimetres (pig-tail sizes) neither the eye aperture nor the frequency chirp are appreciably affected by the feedback.

Effect of optical feedback on high-dynamic-range Fabry-Perot laser optical links

The effect of optical backreflection is measured on a 450-MHz optical link using a commercial Fabry-Perot laser without an isolator. With a low backreflection photodetector, the dynamic range of the Fabry-Perot link is comparable to a link with a high-linearity distributed feedback laser. With a standard photodetector, the dynamic range is 13 dB lower.

Influence of external optical feedback on polarization switching in [formula omitted] lasers

Optical feedback effects on the emission properties of 1.3 μm InGaAsP InP ridge waveguide lasers were studied experimentally for both dc pumping and current modulation. The laser diodes used in our experiments showed a current-induced transition from TM to TE polarization without external feedback. At external optical feedback, the current for the onset of TM/TE transition droped by 25 mA and multiple TM/TE switching was observed over a large current interval. The dynamic response of the external-cavity laser to current pulses of various width was found to depend sensitively on the fine tuning of the external cavity length, resulting in TM/TE oscillations of 2 or 10 GHz, respectively, in the case of 2 ns current pulses. The physical mechanism responsible for the observed behaviour is discussed.