The measured linewidth of the lasers is 500 khz at 2 mw laser output, while the linewidth power produc tion of a conventional solitary laser diode is about 150 mhz. Compared to lasers with uniform bragg gratings, devices fabricated with a. Introduction standard model of a semiconductor laser kinetic equ is there a linewidth theory for semiconductor lasers. Subkhz quantum linewidth semiconductor laser on silicon chip. A theory of the spectral width of a singlemode semiconductor laser is presented and used to explain the recent measurements of fleming and mooradian on algaas lasers. Further linewidth reduction beyond the reported here would be possible if, according to eq. Pdf investigation of the linewidth enhancement factor in. It is used in applications ranging from retinal photother apy for diabetes, lithography, and pumping of other lasers.
A laser system includes a semiconductor laser having a laser driver coupled thereto. Tunable semiconductor lasers continue to be in just about everyones list of important components for future fiber optic networks. Optical feedback locking of semiconductor lasers pro vides a powerful means for stabilizing the frequency and nar rowing the linewidth of diode lasers. Pdf linewidth enhancement factor of semiconductor lasers. Lasers argon and krypton ion lasers similar to the henelaser the argon ion gas laser is pumped by electric dis charge and emitts light at wavelength. Theory of the linewidth of semiconductor lasers ieee. Absorption of laser light at the surface leads to heating. Highcoherence semiconductor lasers based on integral highq. Aside from the advantages in size, cost and complexity, sls cover a broad spectral range and may easily be modulated at rates up to several gigahertz. This novel grating geometry is analyzed and simulated to extract the optimal design parameters in terms of intracavity field distribution. Compact narrowlinewidth integrated laser based on a low.
Tutorial on narrow linewidth tunable semiconductor lasers. To increase the photon number in the dmld we increased the laser cavity length to m and increased the front facet coating to 30% with the back facet coated at 95%. Jun 15, 2016 this phaseamplitude coupling is a key feature distinguishing semiconductor lasers from any other type of lasers and is responsible for a much broader linewidth in semiconductor lasers. Linewidth enhancement factor of semiconductor lasers. Monolithic linewidth narrowing of a tunable sgdbr laser. The linewidth enhancement factor is a parameter quantifying the amplitudephase coupling in a laser, which increases the emission linewidth e. We also need expressions for the light coming out of the laser. Wide temperature range 0 linewidth in semiconductor lasers is proportional to the ratio of the spontaneous emission noise to the total photon number in the laser cavity.
Long coherence length lasers are needed for precise 20 pm to 5 nm measurements of the optical path difference. This value is 30 times greater than can be explained by existing theories. We discuss the status of the schawlowtowneslaxhenry stlh theory of laser linewidth in the instance of semiconductor injection lasers. Rp photonics encyclopedia linewidth, bandwidth, laser. The wavelength spacing of the longitudinal modes varies slowly, and if the laser operates at approximately 1550 nm, the longitudinal modes are separated by about 1. There is a need to develop more accurate methods to characterize ultranarrow laser linewidth and frequency noises. The need for narrow spectral linewidth and stable wavelength emission is growing. An output of the semiconductor laser is optically coupled to an input of an optical splitter that provides outputs including or coupled to a first branch having a first branch fiber coupled to a feedback reflector which provides a cavity boundary that defines a passive secondary cavity for the semiconductor. Linewidth evolution in semiconductor lasers throughout. This optical tech nique can reduce laser linewidths by more than a factor of 1o00, thus achieving linewidths of a few kilohertz.
Osa design of chirpedcoupling sidewall bragg gratings for. In this paper, we report the design and first measurements of a new generation of monolithic lasers incorporating multiple. Frequency noise of semiconductor lasers is important for several reasons. Linewidth shows a continuous transition and tends asymptotically on either side to schawlowtownes inverse power behaviours. The measured linewidth of the lasers is 500 khz at 2 mw laser output, while the linewidthpower produc tion of a conventional solitary laser diode is about 150 mhz. Narrow linewidth semiconductor lasers are expected to be a key technology in nasas stellar interferometry missions to search for planets around nearby stars. Linewidth reduction of semiconductor lasers using feedback. They found the linewidth to be inversely proportional to power and to have a value of 114 mhz at 1 mw per facet. Only the photons that leave the cavity from the mirrors constitute useful output. In a small current zone at threshold warping of the linewidth is observed. Pdf a detailed experimental and theoretical investigation on the evolution of linewidth avi function of injection current for different structures. Introduction the most important property of lasers not captured by semiclassical theories, which treat the. Osa large linewidth reduction in semiconductor lasers. Laser linewidth in a typical single transversemode hene laser at a wavelength of 632.
The 3db linewidth of the sgdbr laser prior to locking was 80 mhz, which was mainly dominated by large 1f noise at low frequencies. Spectral linewidth of semiconductor lasers springerlink. A chirpedcoupling sidewall bragg grating is proposed to mitigate the nonlinear effects that deteriorate the linewidth in dfb lasers operating at a high power and current regime. Henry stlh theory of laser linewidth in the instance of semiconductor injection lasers.
Buus, linewidth broadening factor in semiconductor lasersan overview, ieee j. By investigating semiconductor laser frequency noise profiles we show that carrier induced frequency noise plays an important role in system. Article effective linewidth of semiconductor lasers for coherent optical data links miguel iglesias olmedo 1,2, xiaodan pang 3, richard schatz 1, oskars ozolins 3, hadrien louchet 2, darko zibar 4, gunnar jacobsen 1,3, idelfonso tafur monroy 4. The linewidth characteristic of gas lasers has been calculated in the transition region from. Experimental support of the standard theory is also questionable. The type of noise which contributes to the linewidth is alternately called phase noise, frequency noise, or fm noise. Recently, there has been significant interest in assembling semiconductorgainchipswithlong external cavities toreduce the laser linewidth. Pdf linewidth evolution in semiconductor lasers throughout. A simple and effective approach to semiconductor laser linewidth narrowing via mutual injection locking is proposed and demonstrated in both short and long delay regimes.
At injection levels i below threshold i linewidth of semiconductor lasers for coherent optical data links miguel iglesias olmedo 1,2, xiaodan pang 3, richard schatz 1, oskars ozolins 3, hadrien louchet 2, darko zibar 4, gunnar jacobsen 1,3, idelfonso tafur monroy 4 and sergei popov 1 1 optics division, royal institute of technology, electrum 229, kista se16440, sweden. The enhanced linewidth is attributed to the varia tion of the real refractive index n with carrier density. A detailed experimental and theoretical investigation on the evolution of linewidth avi function of injection current for different structures of semiconductor lasers has been undertaken. The linewidth enhancement factor of semiconductor lasers. Henry, theory of the linewidth of semiconductor lasers, ieee j. These feedback elements use bragg gratings formed by periodic variation of the refractive index with a resonate optical reflector. The relevance of the linewidth enhancement factor is discussed based on its physical and practical significance.
Laser linewidth theory was pioneered by schawlow and townes 1 and further developed in 2 and 3. The present invention is a method and apparatus for creating a narrow linewidth hybrid semiconductor laser using siliconoxide and siliconeoxynitride based external feedback elements. Compact narrow linewidth integrated laser based on a lowloss silicon nitride ring resonator brian stern,1,2 xingchen ji,1,2 avik dutt,1,2 and michal lipson2, 1school of electrical and computer engineering, cornell university, ithaca, new york 14853, usa 2department of electrical engineering, columbia university, new york, new york 10027, usa corresponding author. After locking the linewidth was 3 mhz, showing a 27x improvement in linewidth. The semiconductor diode laser sl has a number of properties that make it a desirable light source for spectroscopy.
Rp photonics encyclopedia linewidth enhancement factor. These feedback elements use bragg gratings formed by periodic variation of the refractive index with a. Dependence of the linewidth enhancement factor on the wavelength of emission in ingaasp multiquantum well semiconductor lasers a si592 b si590 c 51588 d sl593 e si591 dependence of the linewidth enhancement factor on the band gap of the well barrier in ingaasp multiquantum well semiconductor laser. Modulatable narrowlinewidth semiconductor lasers time and. Is there a linewidth theory for semiconductor lasers. Semiconductor lasers are subject to damage from a number of causes. On the other hand, the laser linewidth from stabilized lowpower continuouswave lasers can be very narrow and reach down to less than 1 khz. Semiconductor laser, linewidth enhancement factor, laser linewidth, laser dynamics, optical feedback. Narrow spectral linewidth an overview sciencedirect topics. Simulation results of interferometric sensing systems are also presented, taking into account both the intensity and phase noise of the laser.
Recently, there has been significant interest in assembling semiconductorgainchipswithlong external cavities toreduce the. Effective linewidth of semiconductor lasers for coherent. This means the line narrowing ratio in 17 is about 150, which roughly agrees with the calculated value 200 from 1 1. Traditionally, monolithic iiiv semiconductor lasers have not demonstrated the narrow linewidth, with the best lasers in the tens of kilohertz, and most lasers in the megahertz range. Thermally insensitive determination of the linewidth.
What narrowlinewidth semiconductor lasers can do for defense. Semiconductor lasers an overview sciencedirect topics. We find that using the technique of optical feedback locking, to narrow semiconductor linewidths, does not sacrifice the ability to modulate the lasers frequency via. Dfb lasers, threshold gain, photon lifetime, and longitudinal mode frequencies of dfb lasers. Fy 1introduction laser linewidth theory was pioneered by schawlow and townes 1 and further developed in 2 and 3.
Ece 5330 lectures notes and handouts cornell ece open. At the same pump offset as the spacer hybrid lasers, the control laser exhibits a linewidth of nearly. Measurement of linewidth enhancement factor of different. Theory of the linewidth of semiconductor lasers ieee xplore. Narrow linewidth and stable wavelength emission under different operating and temperature conditions is critical for diode lasers used in solidstate laser and fiber laser p. The linewidth of a laser diode is typically in the megahertz region, but it can also be reduced to a few kilohertz, e. To understand the intensity noise and the laser linewidth the. Results from roundrobin measurements in cost 288 action. Narrow linewidth s coherence length of more than a factor of. Highpower subkhz linewidth lasers fully integrated on silicon. Improved rate equations for external cavity semiconductor. Low noise semiconductor lasers are useful in many areas such as coherent communications, rf photonics, and coherent sensing. Yariv, theory of gain, modulation response, and spectral linewidth in algaas quantum well lasers, ieee j.
The performance of a narrowlinewidth semiconductor laser subjected to vibrations is characterized. The linewidth spectrums have been overlaid and are shown in fig. But even the manufacturers face a challenge on accurately measuring the linewidth of such lasers. Pdf effective linewidth of semiconductor lasers for. Introduction semiconductor ring lasers srls are attractive devices because they can be fabricated without the need for cleaved facet mirrors, offering the possibility to be monolithically integrated with other optoelectronic devices. The high q of the lasers reported here enables linewidths. In semiconductor lasers, the linewidth is due to intrinsic noise. Us20020037025a1 hybrid narrow linewidth semiconductor.