GB2296813A - Laser apparatus for producing pulsed light - Google Patents
Laser apparatus for producing pulsed light Download PDFInfo
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- GB2296813A GB2296813A GB9426331A GB9426331A GB2296813A GB 2296813 A GB2296813 A GB 2296813A GB 9426331 A GB9426331 A GB 9426331A GB 9426331 A GB9426331 A GB 9426331A GB 2296813 A GB2296813 A GB 2296813A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/0625—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/06209—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in single-section lasers
- H01S5/06216—Pulse modulation or generation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
- G02F1/3534—Three-wave interaction, e.g. sum-difference frequency generation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
- H01S3/082—Construction or shape of optical resonators or components thereof comprising three or more reflectors defining a plurality of resonators, e.g. for mode selection or suppression
- H01S3/0823—Construction or shape of optical resonators or components thereof comprising three or more reflectors defining a plurality of resonators, e.g. for mode selection or suppression incorporating a dispersive element, e.g. a prism for wavelength selection
- H01S3/0826—Construction or shape of optical resonators or components thereof comprising three or more reflectors defining a plurality of resonators, e.g. for mode selection or suppression incorporating a dispersive element, e.g. a prism for wavelength selection using a diffraction grating
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0601—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium comprising an absorbing region
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
- H01S5/0658—Self-pulsating
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
- H01S5/125—Distributed Bragg reflector [DBR] lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
- H01S5/4031—Edge-emitting structures
- H01S5/4068—Edge-emitting structures with lateral coupling by axially offset or by merging waveguides, e.g. Y-couplers
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
Abstract
The apparatus comprises a self-pulsating laser diode 2 and a non-linear optical medium 8 which converts the frequency of the light from the laser to a second frequency, preferably doubling the frequency. Light of a third frequency from a second self-pulsating laser diode (20) may be mixed with the light from laser diode 2 to provide sum or difference frequencies. Each laser diode may include a grating along at least part of the laser cavity or an external grating. The diodes may be operated in the self-pulsating mode by reverse or zero biassing a portion of the laser cavity, or, if the diode has an electrical contact split into two or more regions, by injecting different currents into each region. <IMAGE>
Description
AN APPARATUS FOR PRODUCING LIGHT
The present invention relates to an apparatus for producing light. Such an apparatus is suitable for producing a relatively intense light and can be used to produce a blue light.
W.P.Risk, W.J.Koziovsky, W.Lenth and S.D.Lau, "Generation of 425nm light by waveguide frequency doubling of a GaAIAs laser diode in an extended-cavity configuration", Compact blue-green lasers OSA Topical meeting, Feb 2-4, 1993, disclose the generation of blue light from a diode laser by frequency doubling infra-red radiation. The laser was formed with an extended cavity such that the laser light passed through a periodically poled potassium tri-phosphate waveguide having a period of 4i,m and a length of 4.5mm. The light was directed onto a diffraction grating operated in a retro-reflecting mode so as to reflect light back towards the laser gain element via the waveguide. A conversion efficiency of approximately 1 1% was observed.
Efficient frequency doubling is typically achieved by quasi-phasematching in a waveguide formed in a non-linear material. This imposes severe constraints on the range of wavelengths that can be efficiently doubled. In the above reference the natural spectrum of the laser was controlled by a grating structure.
U.Simon, C.E.Miller,C.C.Bradley, R.G.Hulet, R.F.Curl and F.K.Tittel, "Difference-frequency generation in AgGaS2 by use of a single-mode diode laser pump sources", Optics letters, Vol 18, No13, 1062-1064, July 1993, describe mixing two sources to generate a difference frequency.
Light from commercially available laser diodes emitting 10.1 and 1.93 mW of power at 690 and 808nm, respectively, was focused into AgGaS2 crystal and 3.3nW of radiation at approximately 2115cm l ( > 4730nm) which corresponds to the difference frequency between the two sources was observed.
The generation of blue light pulses having a duration of approximately 29 picoseconds using a laser having a switched gain has been reported by J.Ohya, G.Tohmon, K.Yamamoto, T.Taniuchi and M.Kume,
Generation of picosecond blue light pulse by a frequency doubling of a gain switched GaAIAs laser diode having saturable absorber", J Quantum
Electron, Vol 27, No 8, 2050-2059, 1991. However this system requires an external high frequency electrical signal to produce the modulation and does not aim to produce high power pulses.
According to a first aspect of the present invention, there is provided an apparatus for producing light, comprising a first self-pulsating laser diode for producing a first light having a first frequency, and a non-linear optical medium for converting the first light into a second light having a second frequency different to the first frequency.
It is thus possible to provide an apparatus which is capable of producing light using non-linear frequency conversion. The conversion efficiency may be higher than that provided by prior art systems using continuous wave light sources of the same average power. The term "self-pulsating" is understood by those in the art to exclude mode locking.
The device may be used with only a single light source so as to act as a second harmonic generator.
Advantageously the apparatus may further comprise a second self pulsating laser diode for producing a third light having a third frequency, the third light being arranged to mix with the first light within the nonlinear optical medium. The second frequency may be arranged to be a sum of the first and third frequencies. Alternatively, or the second frequency may be arranged to be a difference of the first and third frequencies.
The or each laser diode may be operated in a self pulsating mode by reverse biasing or zero biasing a portion of a laser cavity thereof. The zero or reversed biased portion may act as a saturable absorber. In a two laser arrangement, the lasers may be synchronised by having their respective saturable absorbers electrically connected together.
Alternatively the or each laser diode may have an electrical contact split into two or more regions for injecting current into a laser cavity thereof, and different currents may be supplied to each of the contacts so as to cause self pulsation of the laser diode. Such an arrangement is described by M.Möhrle, U.Feiste, J.Hörer, R.Molt and B.Sartorus, "Gigahertz selfpulsation in 1 .Sijm wavelength multisection DBF lasers", IEEE Photonics technology letters, Vol 9, No 9, September 1992.
Advantageously the or each laser diode may cooperate with an external grating for providing feedback to the or each laser diode. The grating may be positioned such that a transit time for light to travel from a laser cavity of-the laser to the grating is substantially equal to half an inter pulse interval of the laser. Such an arrangement gives the minimum increase in the duty cycle of the laser. Alternatively the or each laser diode may include a grating along at least part of a laser cavity thereof.
Additionally or alternatively the or each laser diode may comprise a pair of laser cavities coupled together by lateral coupling, longitudinal coupling or evanescent coupling. The or each laser diode may be a Y laser. The laser cavities may have different cavity lengths (either physically or effectively) and hence have slightly different mode spacings.
The cavities are coupled together so that only those modes common to both cavities are propagated. The composite cavity has a mode spacing significantly larger than the individual cavities. Only one of the modes of the composite cavity falls within the gain bandwidth of the cavity and is propagated. The effective length of cavities having the same physical length may by adjusted by the inclusion of regions having different refractive indices. The variation in refractive index may be achieved by varying the electrical drive conditions.
The second frequency may be produced using birefringent phase matching in a non-linear medium or by means of the Cerenkov effect within a wave guide containing a non-linear medium. A discussion of the Cerenkov effect in the context of non-linear optics is to be found in a paper by M.P. De Micheli, "Second harmonic generation in 'Cerenkov configuration' ",Guided wave nonlinear optics, Vol 214, 147-168, 1991 edited by D.B.Ostrowsky and R.Reinisch. Alternatively the non-linear medium may be arranged as a quasi-phased matched periodic structure as described by F. Laurell, "Stable blue second harmonic generation in a
KTP waveguide with a diode laser in an external cavity", Electronics letters, vol. 29, No.18, 1629-30, 1993. The frequency conversion may occur within a narrow acceptance bandwidth, for example within a bandwidth of 5nm. For example, a 5mm long potassium titanylphosphate (KTP) waveguide fabricated by ion-exchange techniques can be made with a period A of approximately 4pm and can exhibit a phase matching wavelength of approximately 850nm and an acceptance bandwidth of less than 1 cm.
According to a second aspect of the present invention there is provided a narrow band self-pulsating laser comprising first and second coupled laser cavities, the cavities having different but overlapping modal spacings and the first cavity being arranged to operate in a self-pulsating mode.
The cavities may be longitudinally or laterally disposed with respect to one another. In the case of laterally arranged cavities, the cavities are arranged in sufficiently close proximity such that the evanescent field of one cavity has a significant value within the other cavity. In a further arrangement, the cavities may be arranged such that they share a common region. Such an arrangement may be implemented as a Y laser.
Preferably the self-pulsating cavity has a portion with a respective contact. The portion may be reverse biased in use so as to act as a saturable absorber. The second cavity may be arranged as a Fabry-Perot cavity.
According to a third aspect of the present invention, there is provided a narrow band self-pulsating laser, comprising a laser cavity arranged to operate in a self-pulsating mode and a grating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity.
The present invention will further be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a frequency doubler constituting a first embodiment of the present invention;
Figure 2 is a graph showing an enhancement factor versus input current for various levels of reverse bias within an absorber region of a laser diode;
Figure 3 is a schematic diagram of an apparatus constituting a second embodiment of the present invention that can be used to form sum or difference between the frequencies of two input light sources;
Figure 4 is a schematic diagram of a self pulsating laser diode and a representation of the spectral output thereof;;
Figure 5 is a schematic diagram of a self pulsating laser diode including a grating for controlling the output thereof, and the figure further shows a representation of the spectral output of such an arrangement;
Figure 6 schematically illustrates two longitudinally coupled laser cavities cooperating to form a semiconductor laser diode;
Figure 7 schematically illustrates two laterally coupled laser cavities cooperating to form a semiconductor laser diode; and
Figure 8 schematically illustrates two laser cavities coupled to form a Y laser.
The second harmonic generator shown in Figure 1 has a self pulsating laser diode 2 arranged to supply light to a first lens 4. The light collected by the first lens 4 is then focused by a second lens 6 towards a non-linear optical element 8.
The laser diode 2 is a 2mm long graded index separate confinement heterostructure (GRINSCH) ridge waveguide laser diode with a contact to a p-type semiconductor thereof divided into three sections, 10, 12 and 14. The construction of a GRINSCH laser is known and is described by
C. Harder, P.Buchmann and H.Meier, "High power ridge waveguide
AlGaAs GRIN-SCH laser diode", Electronics letters Vol 22, No 20 p10811082, 1986 and is incorporated herein by reference. The laser material is GaAs and AlGaAs and the laser emits light at 856nm. The central section 12 is approximately 200ism long and is reverse biased so as to form a saturable absorber region within the semiconductor and consequently to induce self pulsation (also known as self-Q-switching or sustained self pulsation) within the laser diode 2.The repetition frequency of the pulses depends upon the carrier dynamics within the laser and is not simply related to the length of the laser cavity. Typically the self-pulsation frequency is of the order of 1GHz. The laser typically has an inverse duty cycle of six.
The non-linear optical element 8 is a bulk crystal of lithium triborate (LBO). Such a crystal material has a phase matching bandwidth of 10nm. This bandwidth is greater than the spectral bandwidth of the laser diode 2, thereby allowing harmonic generation of the full spectral output of the laser.
The non-linear material frequency doubles the light incident thereon. In such a doubling conversion, the peak power of the frequency doubled light is proportional to the square of the peak power of the input light, i.e. the light from the laser 2. Duty cycling of the laser results in the pulses having a higher peak power than would be available from a continuous wave laser operating at the same time averaged power dissipation. If the inverse duty cycle of the laser 2 is N and the average output power thereof is PaV, then the peak power p of the frequency doubled light is P2 < "p (PaV . N)2 and consequently the average power of the frequency doubled light is increased by a factor of N.
A duty cycle enhancement factor can be defined as the ratio of the conversion efficiency of producing frequency doubled light using a duty cycled laser compared to the conversion efficiency using a continuous wave laser of the same average power. Figure 2 illustrates how enhancement factor varies with respect to reverse bias of the region 12 and input current supplied to the laser 2. It is observed that enhancement factors in excess of six times can be achieved.
As illustrated in Figure 3, light from a second laser 20 may be directed towards the non-linear medium 8. The light may be directed by a third lens 22 towards a beam combiner 24, such as a polarising beam combiner. The non-linear medium effectively mixes the lights from the two lasers together and consequently generates output lights at the sum and difference frequencies of the input lights (i.e. the light supplied from the first and second lasers 2 and 20). The lasers can be synchronised by connecting their saturable absorbers together. The current drawn by the saturable absorber region varies during the pulsation cycle of the laser depending upon the photon density within the cavity. This current fluctuation gives rise to a periodic voltage change at the saturable absorber electrode. Thus connecting the saturable absorber regions of each laser tends to synchronise the lasers.
Many of the more efficient frequency doubling schemes can only frequency double light having a narrow and predefined spectral range.
Such a range is typically narrower that the output spectrum of the laser.
Figure 4 schematically illustrates the output spectrum of a self pulsating laser diode. Figure 5 schematically illustrates the output spectrum of the same laser having feedback from a grating 30. The grating 30 is a blazed grating and is ruled with 1200 lines per millimetre. The grating is inclined at the Littrow angle so that the first diffracted order from the grating is retro-reflected towards a facet 34 of the laser cavity. A lens 32 is provided to direct light from the laser cavity towards the grating 30 and to focus the retro-reflected light into the laser cavity.
The laser typically pulsates at 1GHz giving a pulse separation in air of 30cm. For optimum operation, the grating 30 is positioned at half the pulse separation from the laser facet 34.
The laser shown in Figure 5 may be used in place of the lasers shown in
Figures 1 or 3 so as to produce a narrower bandwidth system.
To achieve relatively efficient second harmonic generation, the nonlinear medium 8 may be a periodically domain inverted waveguide formed within LiTaO3. The domain inverted structure for quasi-phase matching in the region of 850nm has a phase matching bandwidth of 1 .2A. Without feedback from the grating 30, the spectral width of the laser diode is approximately 4nm. Thus very little light would be converted. With the grating feedback, the spectral width of the laser is reduced to approximately lA. Thus all the light can fall within the phase matching bandwidth resulting in a much higher conversion efficiency.
Furthermore, adjustment of the angle between the grating and the laser cavity allows the laser wavelength to be fine tuned to match that wavelength at which the non-linear medium exhibits a peak in
conversion efficiency.
The grating 30 may be formed by a periodically refractive index modulated wave guide and may be fabricated within the non-linear material 8. Alternatively a grating in the form of a distributed feedback grating or distributed Bragg reflector may be formed within all or a portion of the length of laser diode so as to limit the laser to a single mode of operation. The construction of a distributed Bragg reflector within the non-linear material is described by W.P.Risk and S.D.Lau, "Distributed Bragg reflection properties of segmented KTP waveguides",
Optics letters, vol 18, No 4, p272-274, 1993.
As a further alternative, each or either of the lasers 2 and 20 may be a coupled cavity device as shown in Figures 6 to 8. In each case the laser comprises two cavities having slightly different mode spacings. The cavities are optically coupled together such that only those modes common to both cavities are propagated. The composite cavity has a significantly larger mode spacing than either of the individual cavities.
Typically only one mode of the composite cavity falls within the gain bandwidth of the laser medium and is amplified.
The device in Figure 6 comprises first and second laser cavities 40 and 42 coupled in series. The first cavity 40 is configured as a self pulsating laser diode and has an effective length L1. The second cavity is configured as a simple Fabry-Perot cavity and has an effective length L2 slightly different from the length L1. The cavities are separated by a gap of a few microns formed by fabricating a thick back contact on the device and then cleaving the device to separate the cavities slightly or by in-situ facet etching. The cavities may have the same physical length, but the inclusion of the saturable absorber within the self pulsating laser diode cavity gives rise to a difference in effective lengths by virtue of a change of refractive index within the saturable absorber region.
The device shown in Figure 7 has first and second cavities 44 and 46 arranged side-by-side. The first cavity 44 is configured as a self pulsating laser diode and has a saturable absorber formed therein having a different refractive index from the gain sections of the cavity. Thus the effective length of the first cavity 44 is varied from that of the second cavity 46 by the inclusion of the saturable absorber. The second cavity is configured as a simple Fabry-Perot cavity. An evanescent optical field of each one of the laser cavities has a significant value in the other cavity. This coupling allows a single common mode to propagate within both cavities.Lateral coupling of the cavities is a particularly advantageous arrangement since it allows the facets of the laser cavities to be formed by cleaving and without the expense and complication of ion-beam etching required to fabricate cavities of different lengths on the same semiconductor substrate.
The device shown in Figure 8 is a Y-laser. A basic structure of the Y laser is described by O.Hildebrand, M.Schilling, W.ldler, D.Baums,
G.Laube and K.Wünstel, "The integrated interferometric Injection laser (Y-laser): one device concept for various system applications",
Proceedings of ECOC91, Paris, France, Vol 2 invited papers, Talk
Tu.A5.1,pp39-46, 1991. The Y laser described herein is a modification of the device described by Hildebrand et al. The Y laser has a "Y" shaped active waveguide region 50. An electric contact is formed over the waveguide 50 and is segmented into four electrodes 52, 54, 56 and 58. Each electrode is arranged to supply (or remove) current from an associated region of the waveguide 50. The "Y" layer can be considered as two cavities which are strongly coupled by virtue of sharing a common gain region.Only modes that are common to both cavities are allowed to propagate. The cavities are arranged to have unequal optical path lengths so that the mode spacing of the coupled cavities is greater than the mode spacing of each individual cavity. In use, only one mode of the coupled cavities should fall within the gain bandwidth of the laser medium, thereby enabling the laser to operate in a single mode.
A saturable absorber 12 is formed in one arm of the "Y", i.e. under electrode 52 as illustrated. As before, the presence of the saturable absorber alters the effective length of the cavity containing the saturable absorber. Alternatively the saturable absorber may be formed in a region common to both cavities, for example, under electrode 58. If the saturable absorber is situated in a common region, the cavities can be made to have different mode spacings by supplying different currents via electrodes 52 and 54. The position of the saturable absorber may be freely chosen. The length of the saturable absorber is approximately 10% of the length of the cavity.
First ends of the cavities are adjacent an highly reflecting facet 60, whereas the output of the laser is delivered via an anti-retlecting facet 52.
It is thus possible to provide an apparatus for frequency changing laser light. The use of a self-pulsating laser to generate blue light can reduce the power consumption and hence heat dissipation compared to continuous mode lasers to achieve a given light output power.
Claims (27)
1. An apparatus for producing light, comprising a first self pulsating laser diode for producing a first light having a first frequency, and a nonlinear optical medium for converting the first light into a second light having a second frequency different to the first frequency.
2. An apparatus as claimed in claim 1, in which the second light has a frequency double that of the first light.
3. An apparatus as claimed in claim 1 or 2, further comprising a second self-pulsating laser diode for producing a third light having a third frequency, the third light being arranged to mix with the first light within the non-linear optical medium.
4. An apparatus as claimed in claim 3, in which the second frequency is a sum of the first and third frequencies.
5. An apparatus as claimed in claim 3, in which the second frequency is a difference of the first and third frequencies.
6. An apparatus as claimed in any one of the preceding claims in which the first or each laser diode includes a grating along at least part of a laser cavity thereof.
7. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode is operated in a self pulsating mode by reverse biasing a portion of a laser cavity thereof.
8. An apparatus as claimed in any one of claims 1 to 6, in which the first or each laser diode is operated in a self pulsating mode by zero biasing a portion of a laser cavity thereof.
9. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode has an electrical contact split into two or more regions for injecting current into a laser cavity thereof, and in which different currents are supplied to each of the contacts so as to cause the first or each laser diode to self pulsate.
10. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode further comprises an external grating for providing feedback to the first or each laser diode.
11. An apparatus as claimed in claim 10, in which a transit time for light to travel from a laser cavity of the laser to the grating is substantially equal to half an inter pulse interval of the laser.
12. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode comprises a pair of laser cavities coupled together, one of the cavities being arranged to operate in a self pulsating mode.
13. An apparatus as claimed in claim 12, in which the cavities are arranged longitudinally.
14. An apparatus as claimed in claim 12, in which the cavities are arranged laterally and coupled together by evanescent coupling.
15. An apparatus as claimed in claim 12, in which the first or each laser diode is a Y laser.
16. An apparatus as claimed in Claim 3, in which each of the first and second lasers has a respective saturable absorber region and a saturable absorber electrode for biasing the saturable absorber region, the saturable absorber electrodes of the first and second lasers being electrically connected together.
1 7. A narrow band self-pulsating laser diode, comprising first and second coupled laser cavities, the cavities having different but overlapping mode spacings and the first cavity being arranged to operate in a self-pulsating mode.
18. A laser as claimed in Claim 17, in which the first and second cavities are arranged longitudinally.
19. A laser as claimed in Claim 17, in which the first and second cavities are arranged laterally and coupled together by evanescent coupling.
20. A laser as claimed in Claim 17, in which the first and second cavities share a common region.
21. A laser as claimed in Claim 20, in which the laser is a Y laser.
22. A narrow band self-pulsating laser diode, comprising a laser cavity arranged to operate in a self-pulsating mode and a grating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity.
23. A laser as claimed in Claim 22, in which the grating is separate to the laser gain medium.
24. A laser as claimed in Claim 22, in which the grating and the laser gain medium are fabricated on the same substrate.
Amendments to the claims have been filed as follows 1. An apparatus for producing light, comprising a first self pulsating laser diode for producing a first light having a first frequency, and a nonlinear optical medium for converting the first light into a second light having a second frequency different to the first frequency.
2. An apparatus as claimed in claim 1, in which the second light has a frequency double that of the first light.
3. An apparatus as claimed in claim 1 or 2, further comprising a second self-pulsating laser diode for producing a third light having a third frequency, the third light being arranged to mix with the first light within the non-linear optical medium.
4. An apparatus as claimed in claim 3, in which the second frequency is a sum of the first and third frequencies.
5. An apparatus as claimed in claim 3, in which the second frequency is a difference of the first and third frequencies.
6. An apparatus as claimed in any one of the preceding claims in which the first or each laser diode includes a grating along at least part of a laser cavity thereof.
7. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode is operated in a self pulsating mode by reverse biasing a portion of a laser cavity thereof.
8. An apparatus as claimed in any one of claims 1 to 6, in which the first or each laser diode is operated in a self pulsating mode by zero biasing a portion of a laser cavity thereof.
9. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode has an electrical contact split into two or more regions for injecting current into a laser cavity thereof, and in which different currents are supplied to each of the contacts so as to cause the first or each laser diode to self pulsate.
10. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode further comprises an external grating for providing feedback to the first or each laser diode.
11. An apparatus as claimed in claim 10, in which a transit time for light to travel from a laser cavity of the laser to the grating is substantially equal to half an inter pulse interval of the laser.
12. An apparatus as claimed in any one of the preceding claims, in which the first or each laser diode comprises a pair of laser cavities coupled together, one of the cavities being arranged to operate in a self pulsating mode.
13. An apparatus as claimed in claim 12, in which the cavities are arranged longitudinally.
14. An apparatus as claimed in claim 12, in which the cavities are arranged laterally and coupled together by evanescent coupling.
15. An apparatus as claimed in claim 12, in which the first or each laser diode is a Y laser.
1 6. An apparatus as claimed in Claim 3, in which each of the first and second lasers has a respective saturable absorber region and a saturable absorber electrode for biasing the saturable absorber region, the saturable absorber electrodes of the first and second lasers being electrically connected together.
1 7. A narrow band self-pulsating laser diode, comprising first and second coupled laser cavities, the cavities having different but overlapping mode spacings and the first cavity being arranged to operate in a self-pulsating mode.
18. A laser as claimed in Claim 17, in which the first and second cavities are arranged longitudinally.
19. A laser as claimed in Claim 17, in which the first and second cavities are arranged laterally and coupled together by evanescent coupling.
20. A laser as claimed in Claim 17, in which the first and second cavities share a common region.
21. A laser as claimed in Claim 20, in which the laser is a Y laser.
22. A narrow band self-pulsating laser diode, comprising a laser cavity arranged to operate in a self-pulsating mode and a gating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity.
23. A laser as claimed in Claim 22, in which the grating is separate to the laser gain medium.
24. A laser as claimed in Claim 22, in which the grating and the laser gain medium are fabricated on the same substrate.
25. A narrow band self-pulsating laser diode, comprising a laser cavity arranged to operate in a self-pulsating mode and a grating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity, wherein the grating and the laser gain medium are fabricated on the same substrate, and the grating is spatially separated from the laser gain medium.
26. A narrow band self-pulsating laser diode, comprising a laser cavity arranged to operate in a self-pulsating mode, wherein the cavity has an end facet formed from a grating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity.
27. A narrow band self-pulsating laser diode, comprising a laser cavity arranged to operate in a self-pulsating mode and a grating for retroreflecting light of a predetermined wavelength to a laser gain medium within the laser cavity, wherein the grating and the laser cavity are arranged such that the transit time for light to travel from the laser cavity to the grating is substantially equal to half the inter pulse interval of the laser.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9426331A GB2296813B (en) | 1994-12-29 | 1994-12-29 | An apparatus for producing light |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9426331A GB2296813B (en) | 1994-12-29 | 1994-12-29 | An apparatus for producing light |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9426331D0 GB9426331D0 (en) | 1995-03-01 |
| GB2296813A true GB2296813A (en) | 1996-07-10 |
| GB2296813B GB2296813B (en) | 1998-09-09 |
Family
ID=10766670
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9426331A Expired - Fee Related GB2296813B (en) | 1994-12-29 | 1994-12-29 | An apparatus for producing light |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2296813B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1570555A2 (en) * | 2002-10-22 | 2005-09-07 | Inplane Photonics, Inc. | Kink free operation of pump lasers having diffraction grating for providing wavelength stabilization |
| WO2008142210A1 (en) * | 2007-05-22 | 2008-11-27 | Epicrystals Oy | Light emitting array |
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| EP0322847A2 (en) * | 1987-12-28 | 1989-07-05 | Canon Kabushiki Kaisha | Second harmonic wave generating device having active layer and second harmonic wave generating layer on same substrate |
| EP0383943A1 (en) * | 1988-09-01 | 1990-08-29 | Seiko Epson Corporation | Light emitting device and method of producing the same |
| WO1991005386A1 (en) * | 1989-09-28 | 1991-04-18 | 3I Research Exploitation Limited | Nonlinear optical device |
| GB2252867A (en) * | 1991-01-07 | 1992-08-19 | Amoco Corp | Self-doubling laser. |
| US5164956A (en) * | 1991-10-21 | 1992-11-17 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Multiperiod-grating surface-emitting lasers |
| WO1993016514A1 (en) * | 1992-02-14 | 1993-08-19 | Optronics Ireland | Frequency changing of light signals |
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1994
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| EP0322847A2 (en) * | 1987-12-28 | 1989-07-05 | Canon Kabushiki Kaisha | Second harmonic wave generating device having active layer and second harmonic wave generating layer on same substrate |
| EP0383943A1 (en) * | 1988-09-01 | 1990-08-29 | Seiko Epson Corporation | Light emitting device and method of producing the same |
| WO1991005386A1 (en) * | 1989-09-28 | 1991-04-18 | 3I Research Exploitation Limited | Nonlinear optical device |
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| US5164956A (en) * | 1991-10-21 | 1992-11-17 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Multiperiod-grating surface-emitting lasers |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1570555A2 (en) * | 2002-10-22 | 2005-09-07 | Inplane Photonics, Inc. | Kink free operation of pump lasers having diffraction grating for providing wavelength stabilization |
| EP1570555A4 (en) * | 2002-10-22 | 2006-01-11 | Inplane Photonics Inc | Kink free operation of pump lasers having diffraction grating for providing wavelength stabilization |
| WO2008142210A1 (en) * | 2007-05-22 | 2008-11-27 | Epicrystals Oy | Light emitting array |
| US7660500B2 (en) | 2007-05-22 | 2010-02-09 | Epicrystals Oy | Light emitting array |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2296813B (en) | 1998-09-09 |
| GB9426331D0 (en) | 1995-03-01 |
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| Date | Code | Title | Description |
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| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20071229 |