DE10258475B4 - Optical semiconductor amplifier - Google Patents

Abstract

optical Semiconductor amplifier (10) for amplifying an optical input signal (pin) with a on a semiconductor substrate (100) arranged optical amplification area (20) and a Pumplaser (60) for generating an optical pumping shaft for the optical gain range (20), wherein the pump laser (60) and the gain region (20) are so on the semiconductor substrate (100) are arranged, that the pump shaft (80) parallel to the substrate surface spreads and into the reinforcement area (20), characterized in that the pump laser (60) the reinforcement area (20) and between the reinforcement region (20) and the Pumplaser (60) each isolation trenches (340, 350) are present, the reinforcement area (20) electrically separate from the pumping laser (60).

Description

The The invention relates to a semiconductor optical amplifier the features according to the preamble of claim 1

The reinforcement in semiconductor optical amplifiers, also called semiconductor optical amplifier (SOA), is dependent on the optical power density in the gain region of the semiconductor amplifier in Boost operation. The dependence the reinforcement from the optical power density is caused by substantially two processes: First, there is a nonlinear suppression of gain whose time constant is in the range of about 10 femtoseconds. Furthermore there is one opposite slower process, which is the charge carrier density in the gain region changed and essentially by radiative and non-radiative recombination, in particular Auger recombination, and diffusion of charge carriers is determined. The time constant of radiative and non-radiative recombination processes and those of the diffusion process are on the order of a few nanoseconds.

The physical processes in semiconductor amplifiers are described in the publication "The Gain Decompression Effect and Its Application to Very Fast Wavelength Conversions" (JH Chen et al., IEEE Photonics Technology Letters, Vol. 9, No. 6, June 1997, pp. 755-). Accordingly, as the power density in the semiconductor amplifier increases, the optical gain decreases because the excited carriers available for amplification decrease faster by recombination than they are replenished by current injection, thus resulting in the amplification of optical signals, especially at very high data rates in the range of 10 Gbit / s and more so-called bit-pattern effects. These bit-pattern effects cause the contrast - ie the on / off ratio - of the digital signals is not constant over time, but of the last bit amplified Depending on the optical signal, the transmission quality can be significantly reduced and sic h increase the bit error rate. Under certain circumstances, bit error rates (BER) of 10 ^-9 can no longer be maintained. It is therefore necessary to work with a semiconductor optical amplifier, which provides a largely independent of the optical power density and temporally constant optical gain in the operating range.

So far, various methods have been used to stabilize the optical gain in semiconductor amplifiers:
One of these methods is to provide pumping optical energy of a separate pump laser and to couple them in the direction of propagation of the optical input signal to be amplified and / or in the opposite direction to the optical input signal to be amplified via an optical fiber and associated couplers in the gain range. This method is described in the document "Improvement of Cascaded Semiconductor Optical Amplifier Gates by Using Lightning Injection" (Jianjun Yu and Palle Jeppesen, IEEE Journal Lightwave Technol., Vol. 19 No. 3, May 2001, pp. 614-623). explained.

A Another previously known method is the active semiconductor layer of the semiconductor optical amplifier at the same time for the operation of a VCSEL laser (VCSEL: vertical cavity surface emitting laser) to use. The optical output power of the VCSEL laser will be there - like also usual with VCSEL lasers - in relation to on the substrate surface of the semiconductor substrate is emitted in the vertical direction. The light of the VCSEL laser penetrates into the "over" the VCSEL laser arranged gain region of the Semiconductor amplifier and acts there as an optical pump power. An optical semiconductor amplifier with An integrated VCSEL pump laser is named under the product name LOA (LOA: linear optical amplifier) sold by the company Genoa.

From the US 5,436,759 As the closest prior art, an optical amplifier is known in which an optical signal to be amplified is coupled into an optical amplification medium along an optical axis.

From the EP 0 463 569 B1 a semiconductor optical amplifier is known in which the light generated by two lasers is coupled via a waveguide and a coupler in optical fibers.

From the US 6,043,929 For example, an adiabatic waveguide amplifier is known which has tapered regions.

Of the The invention is based on the object, one for high data rates specify suitable semiconductor optical amplifier, which is particularly simple and therefore cost-effective finished.

to solution This object is the characterizing features of claim 1 intended. Advantageous embodiments of the optical according to the invention Semiconductor amplifier are in dependent claims specified.

Thereafter, it is provided that the pump laser and the gain region on the Halbleitersub strat are arranged such that the pump shaft propagates parallel to the substrate surface and radiates into the gain region. The pump laser crosses the gain region and between the gain region and the pump laser isolation trenches are present, which electrically separate the gain region of the pump laser.

One essential advantage of the optical semiconductor amplifier according to the invention to see that the pump laser and the gain area next to each other on the semiconductor substrate, so not "stacked", are arranged as in the second of the above-explained previously known semiconductor amplifier with vertical VCSEL structure of Case is. Thus, you can the pumping current for the pump laser and the injection current for the amplification area separately from each other can be adjusted so that the optical gain of the gain range and separately controls the optical pump energy of the pump laser and can be controlled.

One Another significant advantage of the semiconductor amplifier according to the invention is to see that this is very easy to manufacture, because of Pump laser and gain area integrated on one and the same semiconductor substrate. additional separate connection components between the pump laser and the gain region, such as separate optical couplers, etc., are in the inventive semiconductor optical amplifier - in contrast For example, to the first of the above-known prior art semiconductor amplifier with separate pump laser - not required.

Especially space-saving and thus advantageous can be designed the semiconductor amplifier, if the reinforcement area and the pump laser side by side on the semiconductor substrate are arranged so that the pump shaft directly into the gain region irradiates.

The Irradiation of the pump shaft of the pump laser in the gain range should be at a given angle to the propagation direction the optical input signal in the gain range; there is for reasons the space savings a predetermined angle in the range between 30 ° and 90 ° to the propagation direction, in particular preferably of about 90 ° to the propagation direction, recommended. Especially at about vertical or preferably perpendicular angle between the propagation direction of to be reinforced optical signal and the pump light is a particularly high efficiency while pumping achieved at the same time high space savings.

Instead of an immediate coupling of the pump shaft from the pump laser in the gain range the coupling of the pump shaft can also be done indirectly; it will therefore considered advantageous if the gain region and the pump laser over at least a waveguide are connected on the semiconductor substrate is arranged.

Out establish The space savings on the semiconductor substrate, it is advantageous viewed when the gain range and the waveguide arranged to irradiate the pump shaft to each other are that the pump shaft at a predetermined angle to the propagation direction of the optical input signal in the amplification area. Especially space saving is the arrangement then, if the predetermined angle in a range between 30 ° and 90 ° or preferably about 90 °.

Around to achieve a high pumping power in the waveguide area is considered advantageous if the at least one waveguide integrated in an optical resonator.

Around to achieve that the irradiation area - or the effective range - the pump shaft in the reinforcement area preferably is great it is considered advantageous if the waveguide in the connection area to the reinforcement area is tapped.

in the With regard to a high pumping power of the pump laser, it is advantageous viewed when the end faces of the pump laser have a high refractive index jump, so that the Pump wave the pumping area or the pump laser as possible can not leave. This is how it is the pump wave reflects at a high refractive index jump at the end surfaces.

Instead of a "mirroring" of the end surfaces with The help of a high refractive index jump can advantageously also be a "mirroring" through a λ / 4-layer package take place, in particular by a λ / 4-layer package consisting of silicon and aluminum oxide layers. A mirroring is beyond advantageously also possible by a metal layer; the metal layer should be be advantageously isolated to avoid short circuits.

Especially easy and thus inexpensive can be realize the pump laser, if it has a Fabry-Perot structure.

Should however, the pump shaft is as small as possible have optical bandwidth, so it is considered advantageous if the pump laser has a DFB structure (DFB: distributed feedback) having.

A particularly cost-effective Fabrication of the semiconductor optical amplifier can then be achieved if at least one active layer of the gain region at least also forms an active layer of the pump laser. In such an embodiment of the semiconductor optical amplifier can be namely the number of layers to be deposited on the semiconductor substrate reduce or minimize, because at least one separated Layer at the same time for the reinforcement area and also for the pump laser is used.

in the Regard as possible low injection currents for the gain range or as far as possible low pumping currents for the Pump laser, it is considered advantageous if the gain range and / or the pump laser has quantum well (QW) and / or quantum dot (QD) layers. Quantum well and quantum dot layers call due to the they caused charge carrier bundling a particularly high charge carrier density in the active layer of the pump laser or the amplification area resulting in a particularly high efficiency of the pump laser or of the amplification area is reached.

Around to enable that the deposited active layers also for other components than the gain range and the pump laser can be used, it will be beneficial viewed when the gain range and / or the pump laser two or more quantum Well and / or Quantum dot layer types has. So then, for example Components such as electroabsorption modulators or photodiodes on the Integrate substrate on the active layers of the pump laser or the gain range fall back can.

Incidentally, will considered beneficial when the pumping energy of the pump laser is set to match the transparency energy of the gain region equivalent. With such a pumping energy is in fact as possible fast "recovery" of optical amplification in the gain range of the amplification area reached.

Especially at high optical output powers of the semiconductor optical amplifier considered it advantageous if several pump lasers perpendicular to Propagation direction of the optical input signal arranged in the gain region are.

to explanation of the invention show:

1 a semiconductor optical amplifier without isolation trenches according to the invention to illustrate the technical environment

2 the semiconductor amplifier according to the 1 the semiconductor amplifier 3 according to the 1 in cross section,

4 A first embodiment of a semiconductor optical amplifier according to the invention, with isolation trenches,

5 A second embodiment of a semiconductor optical amplifier according to the invention,

6 A third embodiment of a semiconductor optical amplifier according to the invention,

7 A fourth exemplary embodiment of a semiconductor optical amplifier according to the invention,

8th A fifth embodiment of a semiconductor optical amplifier according to the invention and

9 a diagram from which the optimum control of a pump laser can be read off.

In the figures are for identical or comparable or similar components for the better understanding identical reference numerals used.

The 1 to 3 show a semiconductor optical amplifier 10 without isolation trenches This shows the 1 the semiconductor amplifier 10 in the plan view, the 2 the semiconductor amplifier 10 in cross-section along the section line AA and the 3 the semiconductor amplifier 10 in section along the section line BB. The three 1 to 3 will now be described together.

One recognizes in the 1 to 3 an optical amplification area 20 in which one in the semiconductor amplifier 10 irradiated optical input signal pin is amplified. The optical input signal Pin is for this purpose at one with an anti-reflection layer 35 non-reflective coupling point 30 in the reinforcement area 20 irradiated. At one with another anti-reflection layer 45 non-reflective decoupling point 40 The amplified input signal as output signal Pout leaves the semiconductor optical amplifier 10 ,

At a predetermined angle α, which is preferably 90 °, is relative to the gain region 20 or to the direction of propagation 50 of the optical input signal Pin a pump laser 60 arranged. The pump laser 60 so crosses the gain area 20 forming an overlap area 70 , The from the pump laser 60 generated pump waves propagate perpendicular to the input optical signal Pin; the direction of propagation 80 the pump shaft is indicated by an arrow.

The pump laser 60 is at its two end faces each with a reflective layer 90 Mistake. In this reflection layer 90 it may be a layer that due to a refractive index jump at the interface "pump laser 60 / Air "has a reflective effect 90 also be formed by a metal layer or by one or more λ / 4-layer packages, each consisting of silicon and aluminum layers or the like.

At the pump laser 90 according to the 1 to 3 it is a Fabry-Perot laser.

The Sign "⨂" indicates in the figures Furthermore indicating the direction of propagation of light perpendicular to the plane of the drawing into shows; there is a circle with a point in the center of the circle indicates that the propagation direction is perpendicular to the plane of the drawing lies and points out of this.

The 2 and 3 show the layer structure of the semiconductor optical amplifier 10 in detail. One recognizes a semiconductor substrate 100 on which a buffer layer 110 is deposited. On the buffer layer 110 There is an MQW (MQW: Multiple Quantum Well) layer package 120 , which consists of a plurality of quantum well layers, which are not shown in detail for the sake of clarity.

On the MQW layer package 120 is an MQD (Multiple Quantum Dot MQD) layer package 130 deposited, which consists of a plurality of quantum dot (QD) layers. The individual QD layers are for the sake of clarity in the 2 and 3 also not shown in detail.

The semiconductor optical amplifier 10 thus has two different types of layers, namely a QD layer type and a QW layer type. Instead, the semiconductor amplifier 10 also have two different QD layer types or MQD layer types or two different QW layer types or MQW layer types.

An unstructured cover layer 140 is located on the MQD layer package 130 ; this unstructured cover layer 140 is provided with a cover layer structured, for example, by an etching step 150 provided on a metallization layer 160 rests. The metallization layer 160 forms electrical contacts 170 for the pump laser 60 and an electrical contact 180 for the reinforcement area 20 ,

On the bottom surface of the semiconductor substrate 100 is also a ground contact 190 or a return contact attached.

The direction of propagation 50 of the optical input signal Pin and the propagation direction 80 the pump shaft is in the 2 and 3 also marked.

The width b of the gain range 20 should preferably be between 2 and 3 microns. The length L1 of the pump laser 60 should preferably be 10 to 500 microns. The width B of the pump laser 60 may be 20 to 200 microns.

The Length L2 of the amplification area is preferably in a range between 50 and 1000 microns.

The 4 shows a first embodiment 300 for a semiconductor optical amplifier according to the invention. The semiconductor optical amplifier 300 according to the 4 has a pump laser 60 with two Bragg grids 320 and 330 on. The pump laser thus forms a DBR pump laser.

In contrast to the semiconductor amplifier according to the 1 to 3 is the semiconductor optical amplifier 300 with trenches 340 and 350 Mistake. The trenches 340 and 350 separate the gain area 20 electrically from the pump laser 60 ; visually, on the other hand, are the trenches 340 and 350 largely transparent. The trenches 340 and 350 can be formed for example by ion implantation or anti-reflective recesses.

Incidentally, the structure of the semiconductor optical amplifier according to the 4 the semiconductor amplifier according to the 1 to 3 , so that - as far as the embodiments match - in the 4 the same reference numerals are used as in the 1 to 3 ,

The 5 shows a second embodiment 400 for a semiconductor optical amplifier according to the invention. The pump laser 60 is in this second embodiment with an integrated grid structure 410 provided so that the pump laser 60 forms a so-called DFB (DFB: Distributed Feedback) laser. Incidentally, the semiconductor amplifier 400 with isolation trenches 340 and 350 provided and corresponds to the extent of the first embodiment according to the 4 ,

In the 6 is a third embodiment 500 for an optical according to the invention Semiconductor amplifier shown. One recognizes in the 6 that the end faces 510 and 520 of the semiconductor substrate 100 in the area of the coupling point 30 and in the area of the decoupling point 40 not perpendicular to the propagation direction 50 of the optical input signal Pin, but instead have an angle β, which deviates slightly from 90 °. The advantage of such a tilt angle is to be seen in the fact that due to the unavoidable residual reflection of the two antireflection layers 35 and 45 reflected backlight can react less on the respective upstream optical components, as would be the case at an angle β of exactly 90 °.

In the 6 In addition, two more pump lasers can be used 530 and 540 detect their pump waves also perpendicular to the gain range 20 of the semiconductor optical amplifier 500 radiate. With the three pump lasers 60 . 530 and 540 For example, they may be DBR lasers, as in the 6 through the grids 550 is indicated. Instead, it is also possible to use DFB lasers and / or Fabry-Perot lasers.

In the 7 is a fourth embodiment of a semiconductor optical amplifier according to the invention 600 shown. The semiconductor amplifier 600 has several, for example a few tens, pump laser 610 . 620 and 630 on. Each of these pump lasers has two pump zones each 610 ' . 610 '' . 620 ' . 620 '' . 630 ' . 630 '' on. The pumping zones of each pump laser are in each case via two taped waveguides 640 and 650 connected with each other. The waveguides 640 and 650 show in the connection area 660 and 670 to the reinforcement area 20 each have a larger waveguide width than in the connection area 680 and 690 to the respective pumping zone.

Due to the Auftaperung becomes a larger overlap area 70 (see 1 ), whereby a better efficiency in pumping is achieved.

The width of the tapered waveguide is in the area of the connection 680 . 690 to the pumping zones approx. 2 to 3 μm and in the connection area 660 . 670 to the reinforcement area 20 about 5 to 200 microns.

In the 8th is a fifth embodiment of a semiconductor optical amplifier according to the invention 700 shown. It can be seen that the gain range 20 in amplifier sections 710 . 720 and 730 is divided. Each of these amplifier sections 710 . 720 and 730 can be individually controlled due to the segmentation.

In the 8th In addition, it is shown that the pump laser 740 with respect to the gain range 20 need not be arranged symmetrically; Also asymmetrical arrangements are possible and possibly for individual requirements - such as space limitations on the semiconductor substrate 100 - advantageous.

In the 9 a diagram showing the optical gain in the gain region is shown 20 of the semiconductor optical amplifier. The optical amplification is applied above the photon energy and thus indirectly above the wavelength. One recognizes in the 9 in that the optical amplification decreases with increasing photon energy and becomes "negative" as of an energy value E 2. For photon energies greater than E 2, the amplification range is 20 So no more reinforcing, but dampening.

The maximum optical gain is in the diagram according to the 9 achieved at a photon energy E1. By an arrow 800 is shown in the diagram that increases with increasing injection current in the gain region 20 the gain curve shifts towards higher transparency energies E2. The pump lasers should preferably be driven in the optical semiconductor amplifier according to the invention so that they emit pump waves with a photon energy corresponding to the transparent energy E2, because then a particularly rapid "recovery" of the optical gain in the gain range 20 is achieved, which in turn is favorable for high data rates.

10

Semiconductor amplifier

20

gain range

30

coupling point

40

decoupling point

50

propagation direction

60

pump laser

70

overlap area

80

propagation direction the pump shaft

90

reflective layer

100

Semiconductor substrate

110

buffer layer

120

MQW layer packet

130

MQD layer packet

140

unstructured topcoat

150

structured topcoat

160

metallization

170

contacts for the pump laser

180

Contact for the gain range

190

mass contact

300

Semiconductor amplifier

320 330

Bragg grating

340 350

isolation trenches

400

Semiconductor amplifier

410

integrated lattice structure

500

Semiconductor amplifier

510 520

faces

530 540

Further pump laser

550

grid

600

Semiconductor amplifier

610 620, 630

pump laser

610 ', 610' '

pump zones

620 ', 620' '

pump zones

630 ', 630' '

pump zones

640, 650

getaperte waveguides

660 670

lands to waveguides

680, 690

lands at pump laser

700

Semiconductor amplifier

710 720, 730

amplifier sections

740

pump laser

800

arrow

Claims (19)

Optical semiconductor amplifier ( 10 ) for amplifying an optical input signal (pin) with a semiconductor substrate ( 100 ) arranged optical amplification area ( 20 ) and a pump laser ( 60 ) for generating an optical pump wave for the optical amplification region ( 20 ), wherein the pump laser ( 60 ) and the amplification area ( 20 ) on the semiconductor substrate ( 100 ) are arranged so that the pump shaft ( 80 ) propagates parallel to the substrate surface and into the gain region ( 20 ) einstahlt, characterized in that the pump laser ( 60 ) the amplification area ( 20 ) and between the reinforcement area ( 20 ) and the pump laser ( 60 ) each isolation trenches ( 340 . 350 ) are present, the gain area ( 20 ) from the pump laser ( 60 ) electrically disconnect. A semiconductor optical amplifier according to claim 1, characterized in that the gain region ( 20 ) and the pump laser ( 60 ) are arranged side by side so that the pump shaft directly into the gain region ( 20 ). A semiconductor optical amplifier according to claim 2, characterized in that the gain region ( 20 ) and the pump laser ( 60 ) are arranged to each other such that the pump shaft at a predetermined angle (α) to the propagation direction ( 50 ) of the optical input signal (pin) into the gain region ( 20 ). An optical semiconductor amplifier according to claim 3, characterized characterized in that the predetermined angle (α) is between 30 ° and 90 °, and preferably about 90 °. A semiconductor optical amplifier according to claim 1, characterized in that the gain region ( 20 ) and the pump laser ( 610 . 620 . 630 ) in each case via at least one waveguide ( 640 . 650 ) connected to the semiconductor substrate ( 100 ) is arranged. Optical semiconductor amplifier according to claim 5, characterized in that the at least one waveguide ( 640 . 650 ) at a predetermined angle (α) to the propagation direction ( 50 ) of the optical input signal (pin) in the gain region ( 20 ) is arranged. An optical semiconductor amplifier according to claim 6, characterized characterized in that the predetermined angle (α) is between 30 ° and 90 °, and preferably about 90 °. Optical semiconductor amplifier according to one of the preceding claims 5 to 7, characterized in that the at least one waveguide ( 640 . 650 ) is integrated in an optical resonator. Optical semiconductor amplifier according to one of the preceding claims 5 to 8, characterized in that the at least one waveguide ( 640 . 650 ) in its connection area ( 660 . 670 ) to the reinforcement area ( 20 ) expands. Optical semiconductor amplifier according to one of the preceding claims, characterized in that the end faces ( 90 ) of the pump laser ( 60 ) have a high refractive index jump. Optical semiconductor amplifier according to one of the preceding claims 1 to 9, characterized in that at least one of the end faces ( 90 ) of the pump laser ( 60 ) has a λ / 4-layer package, in particular formed by silicon and Aluminiumoxydschichten, or an insulated metal layer. Optical semiconductor amplifier according to one of the preceding claims, characterized in that the pump laser ( 60 ) is a Fabry-Perot laser. Optical semiconductor amplifier according to one of the preceding claims 1 to 11, characterized in that the pump laser ( 60 ) is a DFB laser. Optical semiconductor amplifier according to one of the preceding claims, characterized in that at least one active layer ( 120 . 130 ) of the amplification area ( 20 ) at least one active layer of the pump laser ( 60 ). Optical semiconductor amplifier according to one of the preceding claims, characterized gekenn records that the gain range ( 20 ) and / or the pump laser ( 60 ) at least one quantum well and / or quantum dot layer ( 120 . 130 ) having. A semiconductor optical amplifier according to claim 15, characterized in that the gain region ( 20 ) and / or the pump laser ( 60 ) two or more different types of layers ( 120 . 130 ), each of which is quantum well and / or quantum dot layer types. Optical semiconductor amplifier according to one of the preceding claims, characterized in that the pump energy of the pump laser ( 60 ) is set to match the transparency energy (E2) of the gain region (E2) 20 ) corresponds. Optical semiconductor amplifier according to one of the preceding claims, characterized in that a plurality of pump lasers ( 610 . 620 . 630 ) are present, each perpendicular to the propagation direction ( 50 ) of the optical input signal (pin) in the gain region ( 20 ) are arranged. Optical semiconductor amplifier according to one of the preceding claims, characterized in that end faces ( 510 . 520 ) of the semiconductor substrate ( 100 ) at least in the region of the coupling point ( 30 ) of the optical input signal (pin) a tilt angle to the propagation direction ( 50 ) of the optical input signal (pin) slightly deviates from a right angle.