WO2006103643A1

WO2006103643A1 - A semiconductor laser device and a method for fabricating a semiconductor laser device

Info

Publication number: WO2006103643A1
Application number: PCT/IE2006/000022
Authority: WO
Inventors: Canice Gerard O'brien; Woon-Ho Seo; Guan-Hong Wu; John Francis Donegan
Original assignee: College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin
Current assignee: College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin
Priority date: 2005-03-30
Filing date: 2006-03-30
Publication date: 2006-10-05
Anticipated expiration: 2007-09-30

Abstract

A heterostructure self-pulsating laser device (1) comprising an active layer (5) with first and second cladding layers (6, 7) on respective opposite sides of the active layer (5) is grown on an n-substrate (2) of indium phosphide, the second cladding layer (7) being grown on the substrate (2), the active layer (5) being grown on the second cladding layer (7), and the first cladding layer (6) being grown on the active layer (5). A current blocking layer (12) is formed in the first cladding layer (6) and divides the first cladding layer (6) to form a distal cladding layer (15) and a proximal cladding layer (16) adjacent the active layer (5). A channel (14) defined by the current blocking layer (12) confines the current in the first cladding layer (6) and determines the width of the active light generating area of the active layer (5). The first and second cladding layers (6, 7) and the current blocking layer (12) are of grown doped indium phosphide. The first cladding layer (6) is doped to be a p-type layer and the second cladding layer (7) and the current blocking layer (12) are doped to be of n-type. The level of dopant in the current blocking layer (12) is approximately ten times greater than the level of doping in the first cladding layer (6) in order to establish an effective refractive index step in the lateral direction of the active layer (5) in order to confine light generated in the active layer (5). A continuous wave operating laser device is also described.

Description

"A semiconductor laser device and a method for fabricating a semiconductor laser device"

The present invention relates to a semiconductor laser device of the type commonly referred to as a heterostructure laser device, and in particular, though not limited to a semiconductor laser device for producing light of wavelength in the range of 1 ,250nm to 1 ,610nm. The invention also relates to a semiconductor self-pulsating laser device for producing pulsed light of wavelength in the range of 1 ,250nm to 1 ,610nm, although the invention is not limited to a self-pulsating laser device. The invention also relates to a method for fabricating a semiconductor laser device.

Self-pulsating laser devices of heterostructure construction are known, for example, such a self-pulsating laser device is disclosed in PCT Published Application Specification No. WO 01/78205. In general, such self-pulsating laser devices are suitable for producing light pulses of wavelength in the range of 650nm to 800nm.

Optical communications require laser light pulses of wavelength in the range of 1 ,250nm to 1 ,610nm, at pulse widths in the ultra-short pulse range of from 8 picoseconds to 32 picoseconds. The shorter pulses of the order of 8 picoseconds are required to be produced at a repetition rate of the order of 40GHz, while the longer pulses of the order of 32 picoseconds are required to be produced at a repetition rate of the order of 10GHz. Indeed, present trends would indicate that optical communications requirements will shortly require light pulse repetitive rates of up to 160GHz, and this will require a repetitive light pulse signal of pulse width of the order of 2 picoseconds. In general, it is difficult to produce self-pulsating laser devices which produce light of wavelength in the range of 1,250nm to 1,610nm, and pulses of ultra-short duration of the order of 8 picoseconds to 32 picoseconds with a required consistent repetition rate. Thus, in order to produce pulsed light signals suitable for use in optical communications systems, continuous wave operating lasers are used which produce a continuous laser signal, and the continuous laser signal is passed through a modulator for converting the output into the required pulsed format. However, a problem with producing pulsed signals in this manner from a continuous wave operating laser is that the systems are sensitive to feedback, and modulators are relatively expensive.

A further problem with heterostructure semiconductor laser devices which operate in the wavelength range of 1 ,250nm to 1 ,61 Onm, irrespective of whether the semiconductor laser device is a self-pulsating laser or a continuous wave operating laser, is the difficulty in achieving the necessary effective refractive index profile in order to confine the light generated in the active layer of the device. In one construction of a laser device, in order to achieve the necessary refractive index profile, a cladding layer is formed over the active layer, and a current blocking layer is formed within or above the cladding layer. The materials of the cladding layer and the current blocking layer are different in order to achieve the necessary refractive index profile. Commonly the current blocking layer is formed of a quartemary material, and the cladding layer may also be a quartemary material. The production of heterostructure semiconductor laser devices with such cladding layers and current blocking layers adds to the complexity, and indeed the cost of such structures, as well as leading to difficulties in their production.

There is therefore a need for a semiconductor laser device which addresses at least some of the problems of prior art semiconductor laser devices which operate to produce light of wavelength in the range of 1 ,250nm to 1 ,61 Onm.

The present invention is directed towards providing a semiconductor laser device suitable for producing light of wavelength in the wavelength range of at least 1 ,250nm to 1 ,61 Onm, and the invention is also directed towards providing a method for fabricating such a semiconductor laser device.

According to the invention there is provided a semiconductor laser device comprising: an active layer, a first cladding layer located on one side of the active layer for accommodating a pumping current to the active layer, and a current blocking layer located in the first cladding layer and dividing the first cladding layer to form a distal cladding layer spaced apart from the active layer and a proximal cladding layer adjacent the active layer for distributing current to the active layer, the current blocking layer defining a current confining channel extending therethrough through which the first cladding layer extends for accommodating the pumping current through the first cladding layer from the distal cladding layer to the proximal cladding layer, wherein the first cladding layer and the current blocking layer comprise a grown doped binary semiconductor material, the first cladding layer being of one of a first and a second conductivity type, the current blocking layer being of the other of the first and second conductivity type, the respective conductivity types of the first cladding layer and the current blocking layer being determined by respective dopants in the grown doped binary semiconductor material, and the refractive index of the current blocking layer being determined by the concentration of the dopant in the current blocking layer, and the concentration of the dopant in the current blocking layer being greater than the concentration of the dopant in the first cladding layer in order that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer an effective refractive index profile for confining light generated in the active layer in response to a pumping current.

In one embodiment of the invention the concentration of the dopant in the current blocking layer is of the order of ten times greater than the concentration of the dopant in the first cladding layer.

In another embodiment of the invention the grown doped binary semiconductor material of the first cladding layer and the current blocking layer comprises an indium phosphide (InP) composition.

In one embodiment of the invention the first conductivity type is a p-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the first conductivity type is selected from one or more of the following dopants: cadmium, zinc, and magnesium.

In another embodiment of the invention the second conductivity type is an n-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the second conductivity type is selected from one or more of the following dopants: sulphur, selenium, and tellurium.

Preferably, the concentration of the dopant in the first cladding layer is in the range of 1x10¹⁷cm^~3 to 1x10¹⁸cm^~3. Advantageously, the concentration of the dopant in the first cladding layer is of the order of 7x10¹⁷cm^"3.

Preferably, the concentration of the dopant in the current blocking layer is in the range of 1x10¹⁸cm^"3 to 1x10¹⁹cm^"3. Advantageously, the concentration of the dopant in the current blocking layer is of the order of 8.5x10¹⁸cm^~3.

Ideally, the concentrations of the dopant in the proximal cladding layer and the distal cladding layer are similar.

In one embodiment of the invention a second cladding layer is located on the opposite side of the active layer to the side on which the first cladding layer is located, and the second cladding layer is of conductivity type similar to the conductivity type of the current blocking layer. Preferably, the second cladding layer is of grown doped binary semiconductor material similar to the binary semiconductor material of the first cladding layer and the current blocking layer. Advantageously, the concentration of the dopant in the second cladding layer is of an order substantially similar to that of the concentration of the dopant in the first cladding layer.

In one embodiment of the invention the concentration of the dopant in the second cladding layer is in the range of 1x10¹⁷cm^"3 to 1x10¹⁸cm^"3. Preferably, the concentration of the dopant in the second cladding layer is of the order of 1x10¹⁸cm-³.

In one embodiment of the invention the first cladding layer is doped to be of the first conductivity type.

In another embodiment of the invention the active layer comprises at least one quantum well layer with a pair of barrier layers, the barrier layers being located on respective opposite sides of the quantum well layer. Preferably, the quantum well layer comprises a quartemary alloy composition. Advantageously, three of the constituents of the quartemary alloy composition of the quantum well layer are gallium, indium and arsenide.

In one embodiment of the invention one of the constituents of the quartemary alloy composition of the quantum well layer is aluminium.

In another embodiment of the invention the quartemary alloy composition of the quantum well layer comprises Al_xGa_yln_zAs, where (x + y +z) is equal to one, and to produce light of wavelength of the order of 1 ,310nm, x is equal to 0.134, y is equal to 0.338 and z is equal to 0.528.

Alternatively, one of the constituents of the quartemary alloy composition of the quantum well layer is phosphide.

In one embodiment of the invention the quartemary alloy composition of the quantum well layer comprises ln_xGa_(1-X)AsyP₍i_-y), where x is less than one and y is less than one, and in order to produce light of wavelength of the order of 1 ,31 Onm, x is preferably equal to 0.85, and y is preferably equal to 0.58.

In another embodiment of the invention each barrier layer comprises a quarternary alloy composition.

In one embodiment of the invention three of the constituents of the quarternary alloy composition of each barrier layer are gallium, indium and arsenide.

In another embodiment of the invention one of the constituents of the quarternary alloy composition of each barrier layer is aluminium.

In another embodiment of the invention the quarternary alloy composition of each barrier layer comprises Al_xGa_yln_zAs, where (x + y + z) is equal to one, and to produce light of wavelength of the order of 1 ,31 Onm, x is equal to 0.278, y is equal to 0.198 and z is equal to 0.524.

Alternatively, one of the constituents of the quarternary alloy composition of each barrier layer is phosphide.

In one embodiment of the invention the quarternary alloy composition of each barrier layer comprises ln_xGa₍i-χ₎ASyP_(1-y₎, where x is less than one and y is less than one, and to produce light of wavelength of the order of 1 ,310nm, x is preferably equal to 0.85, and y is preferably equal to 0.31.

Preferably, the active layer comprises a plurality of quantum well layers with one barrier layer disposed between adjacent pairs of the quantum well layers, and advantageously, the quarternary alloy compositions of the respective quantum well layers are similar.

In one embodiment of the invention the quarternary alloy compositions of the respective barrier layers are similar. Preferably, the outer two barrier layers are wider than the barrier layers disposed between the respective quantum well layers.

In one embodiment of the invention the active layer is adapted for producing laser light of wavelength in the range of 1 ,250nm to 1 ,610nm.

In another embodiment of the invention the width of the current confining channel defined by the current blocking layer is adapted to confine the current in the first cladding layer so that the laser device acts as a continuous wave operating laser device. Preferably, the width of the current confining channel defined by the current blocking layer is greater than 2 microns. Advantageously, the width of the current confining channel defined by the current blocking layer lies in the range of 2 microns to 10 microns. Ideally, the width of the current confining channel defined by the current blocking layer is approximately 5 microns.

Alternatively, the width of the current confining channel defined by the current blocking layer is adapted to confine the current in the first cladding layer to the extent that the laser device acts as a self-pulsating laser device for producing repetitive pulses of light. In one embodiment of the invention the width of the current confining channel defined by the current blocking layer does not exceed 2 microns. Preferably, the width of the current confining channel lies in the range of 1 micron to 2 microns. Advantageously, the width of the current confining channel defined by the current blocking layer is of the order of 1.4 microns.

Preferably, the active layer, the first cladding layer and the current blocking layer are adapted for producing the light as repetitive light pulses.

Advantageously, the concentration of the dopant in the current blocking layer is greater than the concentration of the dopant in the first cladding layer to the extent that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer a time varying effective refractive index profile for confining the light pulses generated in the active layer in response to the pumping current.

The invention also provides a method for fabricating a semiconductor laser device of the type comprising: an active layer, a first cladding layer located on one side of the active layer for accommodating a pumping current to the active layer, and a current blocking layer located in the first cladding layer and dividing the first cladding layer to form a distal cladding layer spaced apart from the active layer and a proximal cladding layer adjacent the active layer for distributing current to the active layer, the current blocking layer defining a current confining channel extending therethrough through which the first cladding layer extends for accommodating the pumping current through the first cladding layer from the distal cladding layer to the proximal cladding layer, wherein the method comprises forming the first cladding layer and the current blocking layer by growing a doped binary semiconductor material with the first cladding layer being of one of a first and second conductivity type, and the current blocking layer being of the other of the first and second conductivity type, determining the respective conductivity types of the first cladding layer and the current blocking layer by respective dopants in the grown doped binary semiconductor material, and determining the refractive index of the current blocking layer by the concentration of the dopant in the current blocking layer and setting the concentration of the dopant for the current blocking layer at a concentration greater than the concentration at which the dopant is set for the first cladding layer in order that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer an effective refractive index profile for confining light generated in the active layer in response to a pumping current.

In one embodiment of the invention the doped binary semiconductor material is grown on the active layer to form the proximal cladding layer of the appropriate one of the first and second conductivity types, and the doped binary semiconductor material is grown on the proximal cladding layer to form the current blocking layer of the appropriate one of the first and second conductivity types and is etched to form the current confining channel, and the doped binary semiconductor material is then grown on the etched current blocking layer to fill the etched channel and to form the distal cladding layer of the appropriate one of the first and second conductivity types. Preferably, an etch stop layer is grown on the proximal cladding layer prior to growing of the doped binary semiconductor material to form the current blocking layer. Advantageously, the current confining channel is formed by etching the current blocking layer to the etch stop layer.

In one embodiment of the invention the etch stop layer comprises an alloy composition of gallium, arsenide and phosphide, and preferably, the etch stop layer is grown on the proximal cladding layer.

The advantages of the invention are many. A particularly important advantage of the invention is that the semiconductor laser device according to the invention is a relatively simple and non-complex structure, which may be constructed to operate as a continuous wave operating laser device or as a self-pulsating laser device, and in particular, is suitable for operating at wavelengths within the range of 1 ,250nm to 1 ,610nm, and furthermore, when operating as a self-pulsating laser device is capable of producing pulsed light of pulse width as low as 2 picoseconds at a repetition rate of 10GHz of consistent pulse width and at a consistent repetition rate. In particular, the semiconductor laser device according to the invention can be readily easily fabricated with readily available production processes. These advantages are in particular achieved by virtue of the fact that the first cladding layer and the current blocking layer are formed from a binary material, and in particular, are formed from identical binary materials, the only difference being in the doping. Furthermore, by forming the first cladding layer and the current blocking layer as grown doped binary semiconductor materials, the growing process is a relatively straightforward process and there is no need for subsequent doping of the first cladding layer and the current blocking layer after the layers have been grown, by, for example, ion implantation, diffusion or other doping methods.

A particularly important advantage of the invention is achieved by virtue of the fact that the effective refractive index profile required is achieved by doping the current blocking layer to a level greater than the doping level to which the first cladding layer is doped. This produces a relatively simple and straightforward arrangement whereby the effective refractive index profile for confining the light generated in the active layer is achieved. Since the effective refractive index profile is achieved by the level of doping of the current blocking layer relative to that of the first cladding layer, there is no need for the current blocking layer to be of a more complex material than a simple binary material, and since the effective refractive index profile is achieved by the relative doping levels between the current blocking layer and the first cladding layer, the current blocking layer can be of an identical binary material to that of the first cladding layer.

Thus, the semiconductor laser device according to the invention has many advantages over and above semiconductor laser devices known heretofore.

Additionally, by appropriately selecting the dimensions of the semiconductor laser device according to the invention, and in particular, by appropriately selecting the width of the channel formed through the current blocking layer, the semiconductor laser device according to the invention may be produced as a self-pulsating laser device or a continuous wave operating laser device.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, which are given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic transverse cross-sectional end elevational view of a self-pulsating laser device according to the invention, and Fig. 2 is a plot of the effective refractive index profile plotted against distance in the lateral direction across the active layer of the self-pulsating laser device of Fig. 1 illustrating how the effective refractive index profile may be altered by altering the refractive index of a current blocking layer of the laser device of Fig. 1.

Referring to the drawings, there is illustrated a heterostructure semiconductor self- pulsating laser device according to the invention, indicated generally by the reference numeral 1. The structure of the self-pulsating laser device 1 is particularly suitable for producing a pulsed light signal of wavelength in the range of 1 ,250nm to 1 ,610nm of light pulses of width as low as 2 picoseconds at a repetition rate of up to 10GHz, and the wavelength of the light pulses is determined by the construction of the laser device 1 as will be described below. The self-pulsating laser device 1 comprises a plurality of layers which are grown on a substrate 2, which in this embodiment of the invention is indium phosphide, and is doped to be of one of a first conductivity type and a second conductivity type, and in this case is doped to be of the second conductivity type, which in this embodiment of the invention is n-type. An active layer 5 within which the light pulses are generated is clad on its respective opposite sides by a first cladding layer 6 and a second cladding layer 7. A first electrical contact layer 9 is formed on the first cladding layer 6, while a second electrical contact layer 10 is formed on the underside of the substrate 2 for facilitating pumping of the active layer 5 with a continuous pumping current.

A current blocking layer 12 is formed in the first cladding layer 6 and defines a current confining channel 14 for confining current in the first cladding layer 6 for in turn defining the active width of the active layer 5 within which the light pulses are generated. The current blocking layer 12 divides the first cladding layer 6 into a distal cladding layer 15, and a proximal cladding layer 16 adjacent the active layer 5, which acts as a current spreading layer for distributing current from the current confining channel 14 to the active layer 5. The current confining channel 14 extends in the longitudinal direction of the laser device 1 , which in Fig. 1 extends into the page. The transverse direction of the laser device 1 , namely, the direction in which the layers of the laser device 1 are built up, is the X direction, while the lateral direction of the active layer 5 is the Y direction, see Fig. 1.

The first and second cladding layers 6 and 7 and the current blocking layer 12 are all grown from a doped binary semiconductor material, and the binary semiconductor material in this case is indium phosphide. The indium phosphide binary material from which the first and second cladding layers 6 and 7 and the current blocking layer 12 are grown is identical, and the proportions of indium and phosphide are equal. The second cladding layer 7 is grown on the substrate 2 and is grown from the doped binary material which is doped with sulphur to produce the second cladding layer 7 to be of the second conductivity type, namely, n-type. The level of the sulphur dopant in the doped binary material from which the second cladding _f layer 7 is grown is 1x10¹⁸cm^"3 to produce the second cladding layer 7 with a refractive index of 3.1987. The active layer 5, which will be described in more detail below, is grown on the second cladding layer 7.

The first cladding layer 6 is grown on the active layer 5, and initially, the proximal cladding layer 16 of the first cladding layer 6 is grown on the active layer 5. The doped binary material from which the proximal cladding layer 16 is grown is doped with cadmium to produce the proximal cladding layer 16 to be of the first conductivity type, namely, p-type, and is doped to a level of 7x10¹⁷cm^'3, so that the refractive index of the proximal cladding layer 16 is 3.207.

After the proximal cladding layer 16 has been grown, a thin etch stop layer 18 of approximately 0.01 microns is grown on the proximal cladding layer 16 to act as an etch stop layer during etching of the current confining channel 14 in the current blocking layer 12. The etch stop layer 18 is an alloy composition of indium, gallium, arsenide and phosphide, and may be doped to be p-type or left undoped.

The current blocking layer 12 is next grown on the etch stop layer 18, and the doped binary semiconductor material of the current blocking layer 12 is doped with sulphur to produce the current blocking layer 12 to be of the second conductivity type, namely, n-type. The binary semiconductor material of the current blocking layer 12 is doped with the sulphur to a level of the order of 8.5x10¹⁸cm^"3 to produce the current blocking layer 12 with a refractive index of 3.167. On completion of the growing of the current blocking layer 12, the current blocking layer is patterned, and the current confining channel 14 is etched through the current blocking layer 12 down to the etch stop layer 18.

The current confining channel 14 is then filled with the doped binary semiconductor material by growing and the distal cladding layer 15 of the first cladding layer 6 is then grown over the current blocking layer 12 and the filled channel 14. The doped binary semiconductor material of the channel 14 and the distal cladding layer 15 is doped with cadmium to the same level, namely, 7x10¹⁷cm^"3, as that of the proximal cladding layer 16, thus producing the filled channel 14 and the distal cladding layer

15 to be of refractive index of the order of 3.207.

The depths to which the first and second cladding layers 6 and 7 are grown can range from 0.5 microns to 2.0 microns. The current blocking layer 12 can be grown to a depth in the range of 0.5 microns to 1.0 microns. The proximal cladding layer

16 should be grown to a depth in the range of 0.02 microns to 0.2 microns. The distal cladding layer 15 can then be grown to a depth to bring the total depth of the first cladding layer 6 to the depth in the range of 0.5 microns to 2.0 microns.

The width W of the channel 14 in the current blocking layer 12 in this embodiment of the invention is 1.4 microns in order to provide the necessary current confinement in the first cladding layer 6 to produce the light in the active layer 5 as pulsed light. However, the width W of the channel may be in the range of 1 micron to 2 microns, and it is believed that within this range the laser device would act as a self-pulsating laser for producing repetitive light pulses. The pulse width and the repetition rate of the light pulses generated by the self-pulsating laser device 1 is determined by the value of the pumping current applied to the laser device 1 through the first and second electrical contact layers 9 and 10. The higher the current, the shorter will be the pulse width, and the higher will be the repetition rate. The threshold current in order to produce lasing is in the range of 20 to 40 milliamps, and the self-pulsating laser device 1 may be operated at pumping currents up to four times the threshold value.

The first electrical contact layer 9 is grown on the distal cladding layer 15 from a doped alloy composition of indium, gallium and arsenide with a doping level of 1x10¹⁹cm^'3 to be of p-type in order to produce a good electrical contact. The second electrical contact layer 10 is a gold metal alloy layer and is deposited on the substrate 2 to produce a good ohmic contact with the binary material, namely, indium phosphide, of the substrate 2.

The refractive indices of the current blocking layer 12 and the first cladding layer 6 including the distal and proximal cladding layers 15 and 16 and the filled current confining channel 14 are determined by the doping levels to which the binary material of the respective layers are doped, and the doping levels are selected for producing an effective refractive index profile in the lateral direction across the active layer 5 during lasing, which in turn produces an effective time varying refractive index step in the lateral direction of the active layer 5 during each light pulse emission for confining the light generated in the active layer 5, as will be described below.

In accordance with the invention once the refractive indices of the first cladding layer 6 and the current blocking layer 12 have been determined by the respective doping levels to which the binary material of the respective layers have been doped, the material and the construction of the active layer 5 is selected, firstly, to provide light pulses of the desired wavelength, and secondly, so that the refractive index of the active layer 5 is greater than the refractive index of the first cladding layer 6 by an amount of from 0.2 to 0.4 in order to confine the light within the active layer 5 during lasing.

In this embodiment of the invention the self-pulsating laser device 1 is to produce pulsed light of wavelength of 1 ,310nm, and the active layer 5 is of quantum well construction and comprises a plurality of quantum well layers, in this case six quantum well layers, with alternate barrier layers located between the quantum well layers and an outer barrier layer between the active layer 5 and each of the adjacent first and second cladding layers 6 and 7. Each quantum well layer is of a quaternary alloy composition of aluminium, gallium, indium and arsenide, the composition of which is Al_o.i₃₄Ga_o.₃₃₈lno.₅₂₈As, and each barrier layer is of a quaternary alloy composition of aluminium, gallium, indium and arsenide, the composition of which is Alo.₂₇₈Ga_o.ig₈lno.₅₂₄As. Each quantum well layer is of width of 6nm in the transverse direction of growing of the layers of the laser device 1 , and each barrier layer which is located between adjacent pairs of quantum well layers is of width of 10nm in the transverse direction of the self-pulsating laser device 1. Accordingly, the active layer 5 is suitable for producing light pulses of wavelength of 1 ,310nm. Additionally, in order to effect a low lasing threshold, a strong optical confinement is achieved by forming the two outer barrier layers of the active layer 5 to be wider in the transverse direction than the other barrier layers of the active layer 5. In this embodiment of the invention the width in the transverse direction of the two outer barrier layers is 32nm. This produces a separate confinement heterostructure which includes the quantum well layers and the barrier layers and in this embodiment of the invention the width of the active layer 5 including the two outer barrier layers is of the order of 150nm.

The quantum well layers of the active layer 5 have a refractive index of 3.530, and the barrier layers of the active layer 5 have a refractive index of 3.365. Accordingly, with the refractive indices of the first cladding layer 6, the current blocking layer 12 and the active layer 5 so arranged, an effective time varying refractive index profile in the lateral direction of the active layer 5 is developed, which in turn produces an effective time varying refractive index step in the lateral direction of the active layer 5 which varies during each light pulse emission from a maximum value of 6x10^"3 at the commencement of each light pulse emission, to a minimum value of 3x10^'3 at the end of each light pulse emission.

In Fig. 2 the effective refractive index step at the commencement of a light pulse emission is illustrated for three doping levels of the current blocking layer 12. The effective refractive index is plotted on the Y-axis of Fig. 2 against the lateral position in the lateral direction across the active layer 5, which is plotted on the X-axis. The lateral position zero on the X-axis corresponds to the centre of the active region of the active layer 5 in the lateral direction defined by the current confining channel 14 within which lasing occurs, and the refractive index steps on respective opposite sides of the zero position correspond with the opposite sides of the active region of the active layer 5 which is defined by the current confining channel 14. The curve A of Fig. 2 illustrates the effective refractive index profile in the lateral direction across the active layer 5 at the commencement of a light pulse emission when the current blocking layer 12 is doped as described with reference to Fig. 1 to a doping level of 8.25x10¹⁸cm^"3 to produce a refractive index of the current blocking layer 12 of 3.167.

The curves B and C of Fig. 2 show how the effective refractive index profile in the lateral direction across the active layer 5 at the commencement of a light pulse emission may be varied by varying the level of doping in the doped binary material of the current blocking layer 12, while at the same time keeping the levels to which the second cladding layer 7, the first cladding layer 6 and its component distal and proximal cladding layers 15 and 16 the same as the self-pulsating laser device 1 described with reference to Fig. 1, and also keeping the active layer 5 the same as that of the self-pulsating laser device 1. The curve B of Fig. 2 represents the effective refractive index profile in the lateral direction across the active layer 5 at the commencement of a light pulse emission when the current blocking layer 12 is doped to a level of 4x10¹⁸cm^"3 to produce the current blocking layer 12 with a refractive index of the order of 3.180. The curve C represents the effective refractive index profile in the lateral direction across the active layer 5 when the current blocking layer 12 has been doped to a level of 3x10¹⁹cm^"3 to produce the current blocking layer 12 with a refractive index of 3.130. Thus, the higher the level to which the current blocking layer is doped, the greater will be the effective refractive index step. However, due to material limitations the maximum level to which the current blocking layer when of the binary material indium phosphide could be doped in practice is 3x10¹⁹cm^"3. In use, an EMF is applied across the first and second electrical contact layers 9 and 10, the value of which develops a pumping current sufficient to produce lasing, and the EMF is then set at a value to produce the light pulses of the desired pulse width and repetition rate. Current from the first electrical contact layer 9 flows through the distal cladding layer 15 of the first cladding layer 6 and is channelled through the current confining channel 14 into the proximal cladding layer 16 where the current is directed into the active layer 5 in a relatively confined active region, which is beneath and defined by the current confining channel 14. Initially, at the commencement of each light pulse emission, the effective refractive index step in the lateral direction of the active layer 5 is high, typically of the order of 6x10^"3, see curve A of Fig. 2. The pumping current causes holes from the first cladding layer 6 and electrons from the second cladding layer 7 to combine in the confined active region of the active layer 5 within the effective refractive index step to produce stimulated emission from carriers, and when the carrier density in the confined active region of the active layer 5 is sufficiently high, lasing commences when all losses have been overcome. As more carriers enter the confined active region of the active layer 5, and the carrier density in the confined active region of the active layer 5 continues to increase, the effective refractive index step decreases, thereby allowing the optical field to extend laterally from the confined active region of the active layer 5. When the optical field has extended laterally to a stage that the losses can no longer be overcome, lasing ceases. At that stage, the optical field again contracts into the confined active region of the active layer 5, and the effective refractive index step increases, and the next light pulse cycle commences.

A continuous wave operating laser device, which is substantially similar to the laser device 1 , may be produced by altering the width W of the current confining channel 14 while maintaining the first and second cladding layers 6 and 7, the current blocking layer 12, as well as the active layer 5 and the other layers of the device 1 similar to those of the self-pulsating laser device 1 described with reference to Fig. 1 , as well as maintaining the materials and doping levels similar. By producing the laser device with a current confining channel 14 of width W of greater than 2 microns, and typically, 5 microns, the laser device operates as a continuous wave operating laser device, and produces continuous light of wavelength of 1 ,31 Onm. However, it is believed that a continuous wave operating laser device according to the invention could be produced with a current confining channel 14 of width W in the range of 2 microns to 10 microns, and with the layers of the laser device similar to the layers of the self-pulsating laser device 1 of Fig. 1.

While the active layer 5 of the self-pulsating laser device and the continuous wave operating laser device have been described as comprising quantum well layers and barrier layers, each of a quarternary alloy composition comprising aluminium, gallium, indium and arsenide, it is envisaged that the quantum well layers and the barrier layers of the active layer 5 of both the self-pulsating laser device and the continuous wave operating laser device may comprise an alloy composition of indium, gallium, arsenide and phosphide. In order to produce light of wavelength of 1 ,31 Onm, the width of the quantum well and barrier layers in the transverse direction of the laser devices would be similar to those of the self-pulsating laser device described with reference to Fig. 1, and the composition of the quantum well layers would be lno.85Gao.₁5Aso.5sPo.₄₂, and the composition of the barrier layers would be

I no.85Gao.15ASo.31 Pθ.69-

Needless to say, it will be readily understood by those skilled in the art that to produce light of other wavelengths in the range of 1 ,250nm to 1 ,61 Onm, the alloy compositions will be appropriately varied, as will the widths of the quantum well and barrier layers in the transverse direction of the laser device. Indeed, one of the advantages of the invention is that once the refractive indices which can be obtained from the grown doped binary semiconductor material of the first cladding layer and the current blocking layer is known, the materials and construction of the active layer to produce light of the desired wavelength, and to have the appropriate refractive index in order to produce the necessary effective refractive index step in the lateral direction of the active layer can be readily determined. Needless to say, it will also be appreciated that while the continuous wave laser device for producing continuous light of wavelength of 1 ,31 Onm, which has also been described, has been described as being of substantially similar construction to the self-pulsating laser device with the exception of the width W of the current confining channel, it will similarly be appreciated that by appropriately selecting the materials and construction of the active layer, a continuous wave laser device can be produced to produce continuous light of any desired wavelength.

Furthermore, it is envisaged that other suitable quarternary alloy compositions of the quantum well layers and the barrier layers of the active layer may be used besides those described.

While the active layer of the laser devices have been described as being of quantum well construction, it is envisaged that the active layer may be provided of other suitable constructions, for example, the active layer may be of quantum dot construction. The advantage of producing the self-pulsating laser with an active layer of quantum well or quantum dot construction is that quantum wells and quantum dots have a lower non-radiative Auger coefficient and intervalence band absorption coefficient, giving lower carrier losses, and therefore lower optical losses in the laser structure. Lower losses are particularly important for lasers operating in the infrared range of 1 ,250nm to 1 ,610nm, as they have much larger Auger and intervalence band coefficients than aluminium gallium arsenide laser devices, which emit light near 800nm. It is also envisaged that the active layer of the laser devices which have already been described may be constructed of bulk material.

It is also envisaged that quantum well layers and barrier layers of alloy compositions other than quarternary materials may be used, for example, quantum well layers and barrier layers of binary material, ternary materials, etc. may be used.

While, as discussed above, the wavelength of the laser devices described can be selected by appropriately selecting the material or materials of the active layer and the construction of the active layer, it will be appreciated that the wavelength of the pulsating and continuous light produced by the laser devices may be selected by appropriately selecting the size of the quantum dots where the active layer includes quantum dots. Needless to say, the quantum well layers of the quaternary material can be provided of varying widths in the transverse direction to change the wavelengths of the pulsed light, for example, by changing the emission from 1 ,250nm to 1 ,610nm. Ideally, this would be done within a single quaternary alloy material.

While the laser devices have been described for producing light pulses of wavelength of 1 ,310nm, as mentioned above, by suitably selecting the material and width of the quantum well layers of the active layer, or the material and size of the ^• quantum dots, where the active layer is provided as comprising quantum dots, laser devices according to the invention may be produced for producing light pulses or continuous light of other desired wavelengths. In particular, the wavelength of the light pulses or the continuous light can be extended to 1 ,610nm to cover the lowest loss point in optical fibre.

While the first and second cladding layers and the current blocking layer have been described as being formed from a grown doped semiconductor binary material which is indium phosphide, any other suitable grown doped semiconductor binary materials may be used, for example, gallium arsenide or zinc selenium.

While the first cladding layer has been described as being a p-type layer, it is envisaged that if the second cladding layer were produced as a p-type layer, the first cladding layer would be produced as an n-type layer, and the current blocking layer would then be produced as a p-type layer. This will be readily apparent to those skilled in the art.

While the active layers of the self-pulsating laser device and the continuous wave operating laser device have been described as comprising a plurality of quantum well layers and a plurality of barrier layers, in certain cases, it is envisaged that the active layer may comprise only one single quantum well layer, and two barrier layers, one on either side of the quantum well layer.

Claims

1. A semiconductor laser device comprising: an active layer, a first cladding layer located on one side of the active layer for accommodating a pumping current to the active layer, and a current blocking layer located in the first cladding layer and dividing the first cladding layer to form a distal cladding layer spaced apart from the active layer and a proximal cladding layer adjacent the active layer for distributing current to the active layer, the current blocking layer defining a current confining channel extending therethrough through which the first cladding layer extends for accommodating the pumping current through the first cladding layer from the distal cladding layer to the proximal cladding layer, wherein the first cladding layer and the current blocking layer comprise a grown doped binary semiconductor material, the first cladding layer being of one of a first and a second conductivity type, the current blocking layer being of the other of the first and second conductivity type, the respective conductivity types of the first cladding layer and the current blocking layer being determined by respective dopants in the grown doped binary semiconductor material, and the refractive index of the current blocking layer being determined by the concentration of the dopant in the current blocking layer, and the concentration of the dopant in the current blocking layer being greater than the concentration of the dopant in the first cladding layer in order that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer an effective refractive index profile for confining light generated in the active layer in response to a pumping current.

2. A semiconductor laser device as claimed in Claim 1 in which the concentration of the dopant in the current blocking layer is of the order of ten times greater than the concentration of the dopant in the first cladding layer. 3. A semiconductor laser device as claimed in Claim 1 or 2 in which the grown doped binary semiconductor material of the first cladding layer and the current blocking layer comprises an indium phosphide (InP) composition.

4. A semiconductor laser device as claimed in any preceding claim in which the first conductivity type is a p-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the first conductivity type is selected from one or more of the following dopants: cadmium, zinc, and magnesium.

5. A semiconductor laser device as claimed in any preceding claim in which the second conductivity type is an n-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the second conductivity type is selected from one or more of the following dopants: sulphur, selenium, and tellurium.

6. A semiconductor laser device as claimed in any preceding claim in which the concentration of the dopant in the first cladding layer is in the range of 1x10¹⁷cm^"3 to 1x10¹⁸Cm^"3.

7. A semiconductor laser device as claimed in any preceding claim in which the concentration of the dopant in the first cladding layer is of the order of 7x10¹⁷cm^"3.

8. A semiconductor laser device as claimed in any preceding claim in which the concentration of the dopant in the current blocking layer is in the range of 1x10¹⁸cm^'3 to 1x10¹⁹cm^"3. 9. A semiconductor laser device as claimed in any preceding claim in which the concentration of the dopant in the current blocking layer is of the order of

8.5x10¹⁸Cm^'3.

10. A semiconductor laser device as claimed in any preceding claim in which the concentrations of the dopant in the proximal cladding layer and the distal cladding layer are similar.

11. A semiconductor laser device as claimed in any preceding claim in which a second cladding layer is located on the opposite side of the active layer to the side on which the first cladding layer is located, and the second cladding layer is of conductivity type similar to the conductivity type of the current blocking layer.

12. A semiconductor laser device as claimed in Claim 11 in which the second cladding layer is of grown doped binary semiconductor material similar to the binary semiconductor material of the first cladding layer and the current blocking layer.

13. A semiconductor laser device as claimed in Claim 12 in which the concentration of the dopant in the second cladding layer is of an order substantially similar to that of the concentration of the dopant in the first cladding layer.

14. A semiconductor laser device as claimed in Claim 13 in which the concentration of the dopant in the second cladding layer is in the range of 1x10¹⁷cm^"3 to 1x10¹⁸cm^"3.

15. A semiconductor laser device as claimed in Claim 14 in which the concentration of the dopant in the second cladding layer is of the order of 1x10¹⁸cm-³.

16. A semiconductor laser device as claimed in any preceding claim in which the first cladding layer is doped to be of the first conductivity type. 17. A semiconductor laser device as claimed in any preceding claim in which the active layer comprises at least one quantum well layer with a pair of barrier layers, the barrier layers being located on respective opposite sides of the quantum well layer.

18. A semiconductor laser device as claimed in Claim 17 in which the quantum well layer comprises a quartemary alloy composition.

19. A semiconductor laser device as claimed in Claim 18 in which three of the constituents of the quartemary alloy composition of the quantum well layer are gallium, indium and arsenide.

20. A semiconductor device as claimed in Claim 18 or 19 in which one of the constituents of the quartemary alloy composition of the quantum well layer is aluminium.

21. A semiconductor laser device as claimed in Claim 20 in which the quartemary alloy composition of the quantum well layer comprises Al_xGa_yln_zAs, where (x + y +z) is equal to one.

22. A semiconductor laser device as claimed in Claim 21 in which x is equal to 0.134, y is equal to 0.338 and z is equal to 0.528.

23. A semiconductor device as claimed in Claim 18 or 19 in which one of the constituents of the quartemary alloy composition of the quantum well layer is phosphide.

24. A semiconductor laser device as claimed in Claim 23 in which the quartemary alloy composition of the quantum well layer comprises ln_xGa_(1-X)AsyP_(1-y), where x is less than one and y is less than one. 25. A semiconductor laser device as claimed in Claim 24 in which x is equal to 0.85, and y is equal to 0.58.

26. A semiconductor laser device as claimed in any of Claims 17 to 25 in which each barrier layer comprises a quarternary alloy composition.

27. A semiconductor laser device as claimed in Claim 26 in which three of the constituents of the quarternary alloy composition of each barrier layer are gallium, indium and arsenide.

28. A semiconductor laser device as claimed in Claim 26 or 27 in which one of the constituents of the quarternary alloy composition of each barrier layer is aluminium.

29. A semiconductor laser device as claimed in Claim 28 in which the quarternary alloy composition of each barrier layer comprises Al_xGa_yln_zAs, where (x + y + z) is equal to one.

30. A semiconductor laser device as claimed in Claim 29 in which x is equal to 0.278, y is equal to 0.198 and z is equal to 0.524.

31. A semiconductor laser device as claimed in Claim 26 or 27 in which one of the constituents of the quarternary alloy composition of each barrier layer is phosphide.

32. A semiconductor laser device as claimed in Claim 31 in which the quarternary alloy composition of each barrier layer comprises ln_xGa_(1-X)AsyP₍i_-y), where x is less than one and y is less than one.

33. A semiconductor laser device as claimed in Claim 32 in which x is equal to 0.85, and y is equal to 0.31. 34. A semiconductor laser device as claimed in any of Claims 17 to 33 in which the active layer comprises a plurality of quantum well layers with one barrier layer disposed between adjacent pairs of the quantum well layers.

35. A semiconductor laser device as claimed in Claim 34 in which the quarternary alloy compositions of the respective quantum well layers are similar.

36. A semiconductor laser device as claimed in Claim 34 or 35 in which the quarternary alloy compositions of the respective barrier layers are similar.

37. A semiconductor laser device as claimed in any of Claims 34 to 36 in which the outer two barrier layers are wider than the barrier layers disposed between the respective quantum well layers.

38. A semiconductor laser device as claimed in any preceding claim in which the active layer is adapted for producing laser light of wavelength in the range of 1 ,250nm to 1 ,610nm.

39. A semiconductor laser device as claimed in any preceding claim in which the width of the current confining channel defined by the current blocking layer is adapted to confine the current in the first cladding layer so that the laser device acts as a continuous wave operating laser device.

40. A semiconductor laser device as claimed in Claim 39 in which the width of the current confining channel defined by the current blocking layer is greater than 2 microns.

41. A semiconductor laser device as claimed in Claim 39 or 40 in which the width of the current confining channel defined by the current blocking layer lies in the range of 2 microns to 10 microns.

42. A semiconductor laser device as claimed in Claim 41 in which the width of the current confining channel defined by the current blocking layer is approximately 5 microns.

43. A semiconductor laser device as claimed in any of Claims 1 to 38 in which the width of the current confining channel defined by the current blocking layer is adapted to confine the current in the first cladding layer to the extent that the laser device acts as a self-pulsating laser device for producing repetitive pulses of light.

44. A semiconductor laser device as claimed in Claim 43 in which the width of the current confining channel defined by the current blocking layer does not exceed

2 microns.

45. A semiconductor laser device as claimed in Claim 43 or 44 in which the width of the current confining channel lies in the range of 1 micron to 2 microns.

46. A semiconductor laser device as claimed in Claim 46 in which the width of the current confining channel defined by the current blocking layer is of the order of 1.4 microns.

47. A semiconductor laser device as claimed in any of Claims 1 to 38 and 43 to 46 in which the active layer, the first cladding layer and the current blocking layer are adapted for producing the light as repetitive light pulses.

48. A semiconductor laser device as claimed in any of Claims 43 to 47 in which the concentration of the dopant in the current blocking layer is greater than the concentration of the dopant in the first cladding layer to the extent that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer a time varying effective refractive index profile for confining the light pulses generated in the active layer in response to the pumping current.

49. A method for fabricating a semiconductor laser device of the type comprising: an active layer, a first cladding layer located on one side of the active layer for accommodating a pumping current to the active layer, and a current blocking layer located in the first cladding layer and dividing the first cladding layer to form a distal cladding layer spaced apart from the active layer and a proximal cladding layer adjacent the active layer for distributing current to the active layer, the current blocking layer defining a current confining channel extending therethrough through which the first cladding layer extends for accommodating the pumping current through the first cladding layer from the distal cladding layer to the proximal cladding layer, wherein the method comprises forming the first cladding layer and the current blocking layer by growing a doped binary semiconductor material with the first cladding layer being of one of a first and second conductivity type, and the current blocking layer being of the other of the first and second conductivity type, determining the respective conductivity types of the first cladding layer and the current blocking layer by respective dopants in the grown doped binary semiconductor material, and determining the refractive index of the current blocking layer by the concentration of the dopant in the current blocking layer and setting the concentration of the dopant for the current blocking layer at a concentration greater than the concentration at which the dopant is set for the first cladding layer in order that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer an effective refractive index profile for confining light generated in the active layer in response to a pumping current.

50. A method as claimed in Claim 49 in which the doped binary semiconductor material is grown on the active layer to form the proximal cladding layer of the appropriate one of the first and second conductivity types, and the doped binary semiconductor material is grown on the proximal cladding layer to form the current blocking layer of the appropriate one of the first and second conductivity types and is etched to form the current confining channel, and the doped binary semiconductor material is then grown on the etched current blocking layer to fill the etched channel and to form the distal cladding layer of the appropriate one of the first and second conductivity types.

51. A method as claimed in Claim 50 in which an etch stop layer is grown on the proximal cladding layer prior to growing of the doped binary semiconductor material to form the current blocking layer.

52. A method as claimed in Claim 51 in which the current confining channel is formed by etching the current blocking layer to the etch stop layer.

53. A method as claimed in Claim 51 or 52 in which the etch stop layer comprises an alloy composition of gallium, arsenide and phosphide.

54. A method as claimed in any of Claims 51 to 53 in which the etch stop layer is grown on the proximal cladding layer.

55. A method as claimed in any of Claims 49 to 54 in which the concentration of the dopant in the current blocking layer is of the order of ten times greater than the concentration of the dopant in the first cladding layer.

56. A method as claimed in any of Claims 49 to 55 in which the grown doped binary semiconductor material of the first cladding layer and the current blocking layer comprises an indium phosphide (InP) composition.

57. A method as claimed in any of Claims 49 to 56 in which the first conductivity type is a p-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the first conductivity type is selected from one or more of the following dopants: cadmium, zinc, and magnesium.

58. A method as claimed in any of Claims 49 to 57 in which the second conductivity type is an n-type conductivity, and the dopant in the grown doped binary semiconductor material to produce the grown doped binary semiconductor material to be of the second conductivity type is selected from one or more of the following dopants: sulphur, selenium, and tellurium.

59. A method as claimed in any of Claims 49 to 58 in which the concentration of the dopant in the first cladding layer is in the range of 1x10¹⁷cm^"3 to 1x10¹⁸cm^"3.

60. A method as claimed in Claim 59 in which the concentration of the dopant in the first cladding layer is of the order of 7x10¹⁷cm^"3.

61. A method as claimed in any of Claims 49 to 60 in which the concentration of the dopant in the current blocking layer is in the range of 1x10¹⁸cm^"3 to 1x10¹⁹crτf³.

62. A method as claimed in Claim 61 in which the concentration of the dopant in the current blocking layer is of the order of 8.5x10¹⁸cm^'3.

63. A method as claimed in any of Claims 49 to 62 in which the concentrations of the dopant in the proximal cladding layer and the distal cladding layer are similar.

64. A method as claimed in any of Claims 49 to 63 in which a second cladding layer is located on the opposite side of the active layer to the side on which the first cladding layer is located, and is of conductivity type similar to the conductivity type of the current blocking layer.

65. A method as claimed in Claim 64 in which the second cladding layer is grown on a semiconductor substrate, and is of grown doped binary semiconductor material- similar to the binary semiconductor material of the first cladding layer and the current blocking layer.

66. A method as claimed in Claim 65 in which the concentration of the dopant in the second cladding layer is of an order substantially similar to that of the concentration of the dopant in the first cladding layer.

67. A method as claimed in Claim 65 or 66 in which the concentration of the dopant in the second cladding layer is of the order of 1x10¹⁸cm^"3.

68. A method as claimed in any of Claims 64 to 67 in which the active layer is grown on the second cladding layer.

69. A method as claimed in any of Claims 49 to 68 in which the first cladding layer is doped to be of the first conductivity type.

70. A method as claimed in any of Claims 49 to 69 in which the active layer comprises at least one quantum well layer with a pair of barrier layers, the barrier layers being located on respective opposite sides of the quantum well layer.

71. A method as claimed in Claim 70 in which the quantum well layer comprises a quartemary alloy composition.

72. A method as claimed in Claim 71 in which three of the constituents of the quartemary alloy composition of the quantum well layer are gallium, indium and arsenide.

73. A method as claimed in Claim 71 or 72 in which one of the constituents of the quartemary alloy composition of the quantum well layer is aluminium.

74. A method as claimed in Claim 71 or 72 in which one of the constituents of the quarternary alloy composition of the quantum well layer is phosphide.

75. A method as claimed in any of Claims 70 to 74 in which each barrier layer comprises a quarternary alloy composition.

76. A method as claimed in Claim 75 in which three of the constituents of the quarternary alloy composition of each barrier layer are gallium, indium and arsenide.

77. A method as claimed in Claim 75 or 76 in which one of the constituents of the quarternary alloy composition of each barrier layer is aluminium.

78. A method as claimed in Claim 75 or 76 in which one of the constituents of the quarternary alloy composition of each barrier layer is phosphide.

79. A method as claimed in any of Claims 45 to 74 in which the active layer is adapted for producing laser light of wavelength in the range of 1 ,250nm to 1 ,61 Onm.

80. A method as claimed in any preceding claim in which the width of the current confining channel defined by the current blocking layer is selected to confine the current in the first cladding layer so that the laser device acts as a continuous wave operating laser device.

81. A method as claimed in Claim 80 in which the width of the current confining channel defined by the current blocking layer is greater than 2 microns.

82. A method as claimed in Claim 80 or 81 in which the width of the current confining channel defined by the current blocking layer lies in the range of 2 microns to 10 microns.

83. A method as claimed in Claim 82 in which the width of the current confining channel defined by the current blocking layer is approximately 5 microns. 84. A method as claimed in any of Claims 49 to 79 in which the width of the current confining channel defined by the current blocking layer is selected to confine the current in the first cladding layer to the extent that the laser device acts as a self- pulsating laser device for producing light as repetitive pulses of light.

85. A method as claimed in Claim 84 in which the width of the current confining channel defined by the current blocking layer does not exceed 2 microns.

86. A method as claimed in Claim 84 or 85 in which the width of the current confining channel defined by the current blocking layer is in the range of 1 micron to 2 microns.

87. A method as claimed in Claim 86 in which the width of the current confining channel defined by the current blocking layer is approximately 1.4 microns.

88. A method as claimed in any of Claims 49 to 79 and 84 to 87 in which the active layer, the first cladding layer and the current blocking layer are adapted for producing the light as repetitive light pulses.

89. A method as claimed in any of Claims 84 to 88 in which the concentration of the dopant in the current blocking layer is greater than the concentration of the dopant in the first cladding layer to the extent that the respective refractive indices of the first cladding layer and the current blocking layer define with the refractive index of the active layer a time varying effective refractive index profile for confining the light pulses generated in the active layer in response to the pumping current.