Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.

External optical feedback effects on semiconductor injection laser properties

The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

Optical fiber sensor technology

The effect of external optical feedback on the linewidth of a single-mode injection laser is considered theoretically. A set of three rate equations with Langevin noise sources is used to obtain the power spectrum. If the high-frequency structure in the power spectrum is ignored, the line shape is Lorentzian and exhibits broadening or narrowing depending on the external-cavity phase shift. Particular attention is paid to the line narrowing after including the effect of carrrier-induced index changes.

Line narrowing in a single-mode injection laser due to external optical feedback

Injection locking of AlGaAs double-heterostructure (DH) lasers was studied with respect to locking bandwidth, required power, and coherence. The relation of the locking bandwidth versus the ratio of locked laser power to injected power was consistent with the classical analysis on injection locking phenomena reported by Adler [2]. The measured maximum locking bandwidth was 5.8 GHz when the locking gain was 18 dB. A maximum gain of 40 dB was observed with a 500 MHz locking bandwidth. The power increase in the injected mode agrees well with theoretical values calculated with the van der Pol equation. The interference pattern was observed between an injecting beam and a locked laser beam. Visibility was the same as that obtained by the interference between forward and backward emitted beams in an identical free-running laser. Spurious mode suppression was observed when a single-frequency optical power is injected into an RF-modulated laser. Single longitudinal mode operation was obtained at a sufficiently high injecting level.

Injection locking in AlGaAs semiconductor laser

The evolution of optical interferometers into extreme resolution large dynamic range sensors implemented in a guided wave form is discussed. The design and performance of fibre optic interferometric sensors optimised for specific periodic and quasi-steady-state measurands such as rotation, magnetic field, temperature, etc., are described.

https://iopscience.iop.org/article/10.1088/0022-3735/18/12/001/pdf

Monomode optical fibre interferometers for precision measurement

Fluctuations in injection laser output intensity and spectrum caused by light reflected from an optical system are investigated theoretically and experimentally. The theoretical analysis is accomplished by applying the semiclassical theory to an injection laser, and introducing an optical feedback term. It is shown that light reflected from a near-field region causes power deviation and an oscillating wavelength shift. It is also shown that reflected light from a far-field region changes laser light spectrum and introduces frequency noise components in laser output power.

T. Kanada

Papers

Injection laser characteristics due to reflected optical power