JP2006505117A - Optical amplifier - Google Patents

Abstract

An optical amplifier (200) has an input means (117) for receiving an input optical signal, a beam generation means (101) for generating a pump beam, and a waveguide for receiving an optical signal from the input means and a pump beam from the beam generation means. Means (113), the waveguide means (113) absorbing and receiving the received pump beam used to drive the waveguide means (113) to perform stimulated emission. The optical signal is arranged to be amplified using stimulated emission, and the beam generating means (101) is a vertical cavity surface emitting laser.

Description

  The present invention relates to optical amplifiers and, more particularly, to multi-port optical amplifiers that use arrays of vertical cavity surface emitting lasers (VCSELs) and other components to provide dynamic pumping. The present invention has utility in, but not limited to, optical communication networks, photonic systems, photonic signal processors, and dense optical computer networks.

  The description of the background procedure is intended only to facilitate an understanding of the present invention. It will be appreciated that this description is not an admission or admission that any referenced material was part of common general knowledge in Australia on the priority date of the application.

  Along the path of an optical communication system, optical signals are attenuated by optical fibers and other optical components through which these optical signals travel. Optical amplifiers are their signals in wide area networks, local area networks, cable TV distribution, computer interconnection, and anticipated new fiber-to-the-home applications. Amplification is an important element because it is independent of transmission bit rate and data format.

  A semiconductor optical amplifier (SOA) has the advantage of small dimensions. However, the semiconductor optical amplifier has several gains and bandwidth limitations, including low saturation output power, high noise figure, high non-linearity, and performance dependent on polarization. There is an inconvenience. On the other hand, rare earth doped fiber amplifiers such as erbium doped fiber amplifiers (EDFAs) can provide performance in excess of 40 dB and small noise figure. These features include very low polarization sensitivity, high output power (size of about +37 dBm) and wide bandwidth (up to 80 nm).

  A rare earth doped fiber amplifier operates on the same principle as a laser, which is optical amplification by stimulated emission. This fiber amplifier is driven by another light source (pump) to excite an active additive (rare earth element) in one of its absorption bands. Rare earth ion electrons are pumped to an excited metastable state. The success of fiber amplifiers doped with rare earths is mainly due to their long metastable radiation lifetime. This allows the large inversion distribution necessary to obtain a large gain (so that almost all ions are in a metastable excited state rather than a ground state). Rare earth doped fiber amplifiers can be used for both 1.3 μm and 1.55 μm optical communication windows. For example, a rare earth element praseodymium doped fluoride fiber can amplify a 1.3 μm signal, while a rare earth element erbium doped silica-based fiber can amplify a 1.55 μm signal. . Current silica-based EDFAs require long lengths of several meters to obtain efficient gain performance. Phosphate glasses doped with high concentrations of erbium have recently emerged. This glass makes it possible to reduce the size of the optical amplifier to such an extent that the planar waveguide technology can be used. Using this new glass composition, a few centimeter waveguides can perform as much signal amplification as current amplifiers of about 10 meters in length.

  Future dynamic optical networks will consist of multiple nodes combined by a number of different optical fiber links to transfer optical signals to each other. In a dynamic optical network, each signal is directed by a different group of optical components, and the amount of attenuation performed by each signal component is different. To overcome this problem, there is a need for a cost effective and separately amplifying means for optical signals arriving at nodes in a multi-port network. Current EDFAs do not meet market requirements for low cost, high performance, efficient power management, and standards. Although discrete fiber amplifiers can operate at high bit rates, their effectiveness is limited because they are large and expensive. For example, erbium-doped fiber amplifiers currently allow tens of millions of simultaneous telephone conversations between continents and under the ocean on a single fiber optic cable. However, due to their high price, they are only economical for long-distance systems, meaning that their large dimensions cannot be easily integrated with other devices. A dramatic reduction in the price of high performance optical amplifiers with multiple ports will have a major impact on the design scheme and the realization of access to future metropolitan and optical networks.

According to the present invention, an amplifier for an input optical signal is provided. This amplifier
An input means for receiving an input optical signal;
Beam generating means for generating a pump beam;
Waveguide means for receiving the optical signal from the input means and the pump beam from the beam generating means;
With
The waveguide means is arranged to absorb the received pump beam used to drive the waveguide means to perform stimulated emission and amplify the received optical signal using stimulated emission;
The beam generating means is a vertical cavity surface emitting laser.

  The amplifier preferably further comprises routing means for receiving the input optical signal from the input means and the pump beam from the beam generating means and routing the received input optical signal and pump beam to the waveguide means.

  This routing means preferably comprises a glass or sapphire substrate.

  This routing means preferably includes collimating and focusing means. The collimating / focusing means is preferably composed of an array of microlenses or, alternatively, a diffractive optical element.

  This amplifier preferably further comprises monitoring means for monitoring the power of the optical signal and the pump beam. This monitoring means is preferably an array of two-dimensional photodetectors.

  The vertical cavity surface emitting laser is preferably an integrated circuit integrated with an array of photodetectors.

  The input means preferably has a multi-port configuration, in particular an array of optical fibers.

  The waveguide means preferably has a multi-port configuration with an array of optical fibers.

  The fibers in the fiber lay are preferably either core-pumped or cladding-pumped.

  The array is preferably composed of erbium-doped aluminosilicate fibers or praseodymium-doped fluoride fibers.

  The vertical cavity surface emitting laser preferably operates in a lateral single mode. Alternatively, the vertical cavity surface emitting laser operates in multimode.

  The vertical cavity surface emitting laser is preferably arranged with an external cavity resonator.

  The amplifier further includes first detection means for detecting a pump beam signal, and a processor to which a pump beam monitoring signal is sent from the first detection means in response to the detected pump signal. Preferably, a control signal for controlling the pump beam generating means can be generated in response to the signal.

  The first detection means is preferably an array of photodetectors integrated on a semiconductor chip.

  The amplifier further includes second detection means for detecting the input signal beam, and the input monitoring signal is sent from the second detection means to the processor and received by the processor in response to the detected input signal. Preferably, it is operable to generate a control signal for controlling the beam generating means in response to the inputted input monitoring signal and the pump beam monitoring signal.

  This second detection means is preferably an array of photodetectors.

In a preferred embodiment, the optical amplifier is
An optical substrate having a top surface and a bottom surface and two side surfaces extending between the top surface and the bottom surface so that the cross section of the substrate is square;
An input fiber lay for providing an incident beam and a doped fiber lay for an output that are aligned with each other and coupled to each side;
An array of vertical cavity surface emitting lasers (VCSEL) generating a pump beam and a top photodetector array arranged in series closest to the top surface;
A bottom photodetector aligned with the array of VCSELs and the top photodetector array and arranged closest to the bottom surface;
A beam splitting bottom surface that sends most of the incident beam to the output doped fiber array and reflects a small portion of the incident beam back to the bottom photodetector array, and a pump beam to the output doped fiber array. A routing element disposed in the substrate at an angle of 45 ° with respect to a side surface having a reflective top surface that reflects to
A processor that adjusts the power level of the pump beam in response to the power level detected by the top and bottom photodetector arrays so that the gain of the optical amplifier can be selectively controlled.

  This preferred embodiment eliminates free space beam propagation and allows the optical amplifier to be smaller.

  The optical amplifier preferably further includes an array of input microlenses etched into the optical substrate to collimate the incident beam.

  The optical amplifier preferably further includes an array of output microlenses etched into the optical substrate to couple the incident beam and the pump beam to the output doped fiber array.

  The bottom photodetector array is preferably a flip chip bonded to an optical substrate.

  The VCSEL array is preferably a flip chip combined with an Ultra-Thin Semiconductor (UTS) chip that integrates the top photodetector array.

  The doped fiberlay for output is preferably a fiberlay doped with erbium.

  The optical substrate is preferably composed of a glass or sapphire substrate.

According to another aspect of the invention, a method is provided for controlling the optical gain of an optical amplifier including at least one fiber optic amplifier and a pump source. This method includes
Measuring the power of the pump beam generated by the pump source and obtaining a first signal indicative thereof;
Measuring the power of the input optical signal and obtaining a second signal indicative thereof;
Evaluating a signal gain based on the measured input signal power and the pump power to obtain a third signal indicative of the difference between the measured signal gain and the desired signal gain;
Processing the first, second and third signals, and in response to the processed first, second and third signals, generating a pump source drive current profile;
Controlling the generation of a drive current profile to obtain a desired output power for the pump beam.

  This method uniquely integrates separately controlled pump sources, drive components, and motion components to provide variable optical gain that dynamically compensates for optical losses in multiport fiber optic systems. There is an advantage of providing an integrated high power multi-port optical amplifier. The preferred embodiment of the present invention reduces complexity and requires less power than most current systems.

  The present invention will now be described, by way of example only, with reference to the accompanying drawings.

  1A and 1B illustrate the principle of optical amplification in an erbium-doped optical fiber amplifier (EDFA) 1. FIG. FIG. 1A is a schematic diagram of an EDFA, and FIG. 1B is an energy level diagram for the EDFA of FIG. 1A.

The basic energy diagram of an EDFA is very similar to a three level laser system. By providing photons with a pump wavelength λ _p (usually 980 nm), erbium electrons are excited to the excitation level (ie, the energy of the electrons is increased). This excited electron then undergoes a non-emissive transition (ie, a small loss of energy) to a metastable level with a long emission lifetime of about 10 ms. Photons at the wavelength λ _{s of the} signal (usually around 1550 nm) are amplified by stimulated emission, and as in the laser, the emitted photons then excite other radiation, increasing the signal photons exponentially. Because of the long lifetime of metastable radiation, high quantum efficiency and low noise figure are obtained. If the lifetime of the metastable radiation is short, the electrons are relieved very rapidly, which means that more photons are spontaneously emitted, thus increasing spontaneous noise. Also, more input pumps are required to maintain the electrons in a metastable state.

  The EDFA 1 requires a pump laser 2 of 880 nm, a coupler 3 that couples the laser beam from the pump laser 2 with the laser beam 4 of the input signal and guides it to one fiber 5, and an EDFA 1 that is an amplification medium. In some cases, an optical fiber (not shown) is used after the EDFA 1 to filter the amplified spontaneous emission noise.

An optical fiber can propagate several wavelengths. Erbium ions (Er ³⁺ ) have quantum levels that are excited to emit in the 1550 nm band. This band is the wavelength at which power loss is minimized with most silica-based fibers. This gives erbium ions the ability to amplify signals at wavelengths where high quality amplifiers are most needed. The EDFA can be excited by either 800 nm or 980 nm. Both of these wavelengths are not the wavelengths used for signal wavelengths, although silica-based fibers can propagate without significant loss. Since these wavelengths are sufficiently far from the signal wavelength of 1550 nm, the pump beam and the signal beam 4 can be easily separated. Erbium can also be excited by 1480 nm photons, but this is generally undesirable. The reason is that both the energy pumping process and the stimulated emission by the signal occur in the same energy band, thereby causing interactions that reduce the efficiency of the EDFA and increase the noise of the amplifier.

Another important property for using erbium in EDFAs is that erbium is quite soluble in silica, so it is easy to dope erbium into a mixture for making silica-based fibers, and Al ₂ By using a co-dopant such as O ₃ , GeO ₂ —Al ₂ O ₃ or P ₂ O ₅ , the solubility of the erbium compound in the silica mixture can be greatly increased, The characteristic of the EDFA can be improved. For example, GeO ₂ —Al ₂ O ₃ can be used to almost double the time until the excited erbium relaxes, thereby almost doubling the quantum efficiency of the EDFA.

  One drawback of EDFAs is that the EDFA gain varies with the wavelength of the signal, which creates problems in many wavelength division multiplexing (WDM) applications. This can be solved by using special optical passive filters designed to compensate for EDFA gain changes.

  FIG. 2 illustrates the basic principle of the optical amplifier 100 of the present invention. In this description, a plurality of inputs and outputs are described. That is, a multiport amplifier is described. However, it should be noted that the present invention applies to one or more inputs and / or one or more output systems.

  The multi-port optical amplifier 100 includes an input fiber array 10 for propagating an input signal beam connected to an input fiber collimator array 11. The input fiber collimator array 11 converts an input signal beam into a collimated beam 12. The VCSEL array 14 generates an array of pump beams 15 perpendicular to the direction of the signal beam. The pump beam 15 and the collimated signal beam 12 are combined using a WDM beam combiner 13. The combined beam 16 output from the combiner 13 is then coupled via a fiber focuser array 17 to an output array 18 of rare earth doped fibers. The gain of each output port of the fiber lay 18 is controlled by the size of the VCSEL pump beam 15 coupled to that particular port. The amount of pump power coupled to an output port can be adjusted by adjusting the current driving the appropriate portion of the VCSEL array 14 associated with that particular output port.

  Note also that in a free space multiport optical processor (eg, an optical switch), the optical signal is essentially converted to a free space beam for parallel processing. After processing, the light beam undergoes various attenuations. This requires later optical amplification and equalization. From FIG. 2, combiner 13, VCSEL array 14, and fiber lay 18 can be integrated with a free space multiport optical processor to combine pump beam 15 and signal beam 12, thereby providing multiport amplification and (VCSEL). It can be seen that the gain can be controlled (by controlling the power).

  Having described the basic principle of the optical amplifier of the present invention, the idea of pumping an EDFA using a VCSEL as a pump source will now be described with reference to FIG.

  As can be seen from FIG. 3, the VCSEL 20 is used as a pump. The VCSEL 20 generates a diverging light beam 21. In practice, the divergence angle is less than 5 °. A VCSEL microlens 22 is integrated with the VCSEL 20 to collimate the beam 21 of the VCSEL. The VCSEL 20 is a flip chip combined with an ultra-thin semiconductor (UTS) chip 24. This ultra-thin semiconductor chip 24 is integrated with the photodetector monitor 23 to monitor the power of the pump beam from the VCSEL 20. The UTS chip 24 is bonded to a glass substrate 25 and one edge 29 of the glass substrate 25 is cleaved at 45 ° with respect to the direction of the beam 21 of the VCSEL. This edge 29 allows the VCSEL beam 21 to undergo total internal reflection after entering the edge 29. The outer surface of the edge 29 is coated with an antireflection coating. The wavelength of the anti-reflection coating is such that a free space input signal beam 26 incident on the edge 29 from the horizontal direction (ie, perpendicular to the VCSEL beam 21) passes through the glass substrate 25 and combines with the VCSEL beam 21. Selected as Since the microlens 27 is etched directly into the glass substrate 25 and the focal length and position of the microlens 27 are optimized, the VCSEL beam 21 and the input signal beam 26 enter the core of the EDFA 28. In the EDFA 28, the pump beam is absorbed and the signal beam is amplified.

  The VCSEL beam 21 emitted from the VCSEL 20 is efficiently coupled to the doped optical fiber 28. The coupling efficiency of the VCSEL 20 to the EDFA 28 is maximized by optimizing the position and focal length of the integrated VCSEL microlens 22. The coupling efficiency of the input signal beam 26 to the EDFA 28 is maximized by optimizing the position and focal length of the integrated glass microlens 27.

  Several lens manufacturers (eg, Edmund Scientific, Newport) are now selling anti-reflective coatings that significantly reduce reflection losses for various wavelengths in optical communications. The gain of the EDFA is proportional to the power intensity of the pump beam coupled into the EDFA 24. For this reason, the intensity of the VCSEL beam 21 coupled to the EDFA 28 can be adjusted to obtain an arbitrary gain by controlling the intensity of the pump beam coupled to the EDFA 28. In order to achieve maximum pumping efficiency, the doped fiber length is optimized to provide the maximum possible small signal gain at the maximum available VCSEL pump power. One VCSEL 20 and EDFA 28 have been described above with respect to FIG. However, in preferred embodiments of the invention, VCSEL arrays and EDFA arrays can be used.

  Currently, a 980 nm VCSEL array can generate more than 100 mW of optical power for each VCSEL element. For a 64-port doped EDFA fiberlay, if the pump coupling efficiency is 70%, then a pump output of 70 mW can be coupled to each output port (ie, to a port of the EDFA array). When the length of the doped fiber in the array is optimized and the optical signal output is small (<-10 dBm), obtain an optical signal output of 13 dBm or more over the C band (1530-1560 nm) of optical communication Can do. An EDFA with a flattened gain and an EDFA with a clamped gain, such as those available on the market, can be used in the present invention.

  As described above, an array of VCSELs and EDFAs can be used. FIG. 4 illustrates an embodiment of an optical amplifier 100 of the present invention that uses such an array.

  The optical amplifier 100 ″ includes a 2D input fiber array 30 with a 2D input micro lens array 31. The micro lens array 31 is glass for collimating the input signal beam 34 from the input fiber array 30. Directly etched into the substrate 32. The glass substrate 32 has a V-groove shape 41 with the left edge 33 cleaved at 45 ° and coated with an anti-reflective coating, and most of the input signal beam 34 is transferred to the glass substrate 32. The low-power monitoring signal beam 35 is reflected toward the flip-chip photodetector array 40 to pass through, while monitoring the input signal beam, as will be described in more detail later. The photodetector array 40 is a pump photodetector array (for monitoring the power of the pump beam). (Not shown) and joined to the UTS chip 60 attached to the glass substrate 32. The right edge 36 of the V-groove 41 is also cleaved at 45 ° perpendicular to the left edge 33. This right edge 36 is also reflected. Coated with a protective coating to allow the signal beam 34 to pass through with minimal reflection, V-groove 41 can be free space or any index matching glass.

  Alternatively, the glass substrate 32 can be replaced with a sapphire substrate. Sapphire has attractive properties that make it a demanding material that can be processed into any shape, including precise dimensional tolerances and lens etching with special surface treatments.

  A microlens array 37 is provided at the output portion of the glass substrate 32. This microlens array 37 is used to focus the signal beams 34 and couple them into the output port of the EDFA array 38 and is etched directly onto the glass substrate 32. In another embodiment, the microlens arrays 31 and 37 can be replaced by diffractive optical element type relays. The EDFA array 38 is composed of a rare earth-doped fiber collimator waveguide (either erbium-doped aluminosilicate or praseodymium-doped fluoride). The fiber can be either core excitation or cladding excitation.

  A 2D VCSEL array 50 is used to input the pump beam 39 to various ports of the EDFA array 38. The pitches of the VCSEL array 50, the input microlens array 31, the photodetector array, the output microlens array 37, the input fiber array 30, and the EDFA array 38 must be the same.

  The VCSEL array 50 can operate in a lateral single mode, where the fibers of the EDFA array are core pumped. In another embodiment, the VCSEL array 50 can operate in multimode for the fibers of the cladding pumped EDFA array.

  In another embodiment, an external cavity resonator (not shown) may be used with the VCSEL array 50 to increase the effective diameter efficiency and increase the loss discrimination force between lateral modes. it can.

  The detected signal beam and pump beam powers are sent from the respective photodetector arrays to the electronic processor 46 via a detection signal power bus 42 and a detection pump output bus 44. This processor 46 is operable to predict the required pump output (to obtain the desired gain of the EDFA) and to generate drive current 48 for the various VCSEL elements of the VCSEL array 50. When the VCSEL array 50 operates in the active region, the relationship between the output pump power and the input drive current is linear. This means that one multiplication operation and addition operation are required to predict the required drive current for the VCSEL. When the signal power is small, the gain of the EDFA can be calculated from the pump power by a simple formula. However, in situations where the signal is large, the gain of the EDFA depends nonlinearly on the output of the input signal and the output of the pump beam. This requires complex iterative algorithms and storage media to accurately predict the required VCSEL drive current for the EDFA gain target.

In particular, a method for controlling the gain includes measuring the power of the pump beam generated by the VCSEL array 50 using a photodetector array integrated in the UTS chip 60 and obtaining a first signal indicative thereof. Measuring the output of the input optical signal using the photodetector array 40 and obtaining a second signal indicative thereof. The processor 46 then evaluates the gain of the signal based on the measured input signal power and the pump power to obtain a third signal indicative of the difference between the measured signal gain and the desired gain. Can work. Thus, if there is a difference between the measured signal gain and the desired gain, the corresponding third signal value will be non-zero and the VCSEL required to maintain the desired signal gain. The increase in current can be calculated. That is, if the power of the input signal changes by ΔS, the corresponding third signal is the difference between the desired gain and the measured gain, ie _ΔG = G _desired −G _measured . The algorithm uses the corresponding third signal to calculate the corresponding VCSEL current increase ΔI required to return the gain to the desired value.

  Thus, the processor 40 processes the first, second and third signals and generates a drive current profile for the VCSEL array 50 in response to the processed first, second and third signals. Still further, the generation of a drive current profile can be controlled to operate to achieve the desired output power for the pump beam.

  In another embodiment shown in FIG. 5, the signal monitoring photodetector array 125 was used in FIG. 4 except that it was a flip chip coupled to an optical substrate so that it could be parallel to the VCSEL array 101. The same idea is used. This scheme eliminates free space beam propagation and makes the device more practical. The optical signal in the fiber is collimated by a microlens array 119 etched directly into the optical substrate. A small portion (<5%) of the coated signal beam 121 is reflected by a 45 ° coated edge 122 and photodetected by a flip chip coupled to a signal monitoring photodetector array 125. The majority of the signal beam is coupled to the output erbium-doped fiber port via the output microlens array 115 etched directly into the optical substrate. The scheme for coupling and monitoring the pump beam into the output EFD port is similar to the scheme described in the previous section and extinguished in FIG.

  Since this optical amplifier 200 has large output power and low noise, a large number of optical amplifiers having a large number of channels at a high bit rate can be cascaded. Furthermore, a high level of electronic and optical integration for efficient automatic gain control by software can be performed. A digital control system featuring an easy-to-use interface and command set can be realized. Amplifier integration is achieved using standard +5 VDC and GND power lines and an RS-232C interface.

The features and advantages of the preferred embodiment of the multi-port optical amplifier 200 described above can be summarized as follows.
• High number of ports: 64 or more input / output amplifier ports • High output power: Combine pump power of 70 mW or more into the core of the doped fiber for each output, thereby reducing 30 mW Signal power exceeding can be brought about.
Low noise figure: By using an appropriate pump wavelength (980 nm), the noise figure can be reduced as a result (about 3 to 6 dB).
Gain flattening possible: Gain flattening filter can be integrated with doped fiber to flatten gain over the entire band.
Variable gain: Individual port gains can be adjusted separately to accommodate a wide range of fiber span lengths and optical network element losses. Using the method described above, the amplifier can be configured by simple software instructions.
Signal and pump monitoring: Built-in monitoring can be performed by the combined photodetector array 125 and the photodetector array for the pump beam integrated in the UTS chip 108.

  Mass production: An amplifier according to a preferred embodiment of the invention is suitable for mass production.

  Throughout this specification, where the context does not require a different meaning, the term “comprising” or variations thereof is meant to include the complete or group of completeness presented, but any other It should be understood that it is not meant to exclude complete or complete groups.

  Various modifications can be made within the scope of the present invention.

1A and 1B are diagrams schematically illustrating the concept of a rare earth-doped fiber amplifier. FIG. 2 is a diagram schematically illustrating a multiport optical amplifier. It is a figure which illustrates roughly pumping of EDFA using VCSEL by this invention. It is a figure explaining the structure of the two-dimensional (2D) optical amplifier used for the amplifier of this invention. FIG. 6 schematically illustrates a second embodiment of a 2D optical amplifier structure in which one 45 ° edge is used to route the signal and the pump beam.

Claims (32)

An input means for receiving the input optical signal;
Beam generating means for generating a pump beam;
An optical amplifier comprising: an optical signal from the input means; and a waveguide means for receiving a pump beam from the beam generating means,
The waveguide means may be adapted to absorb the received pump beam and operate to amplify the received optical signal using stimulated emission, the pump beam being guided. Used to drive waveguide means to perform stimulated emission,
The beam generating means is an optical amplifier which is a vertical cavity surface emitting laser.   Routing means for receiving an input optical signal from the input means and a pump beam from the beam generating means, and routing the received input optical signal and pump beam to the waveguide means. The optical amplifier according to claim 1, further comprising:   The optical amplifier according to claim 2, wherein the routing means comprises a glass or sapphire substrate.   4. An optical amplifier according to claim 2, wherein the routing means includes collimating and focusing means.   The optical amplifier according to claim 4, wherein the collimating and focusing means includes a microlens array.   The optical amplifier according to claim 4, wherein the collimating and focusing means includes a diffractive optical element.   The optical amplifier according to claim 1, further comprising monitoring means for monitoring power of the optical signal and the pump beam.   8. An optical amplifier according to claim 7, wherein the monitoring means is a two-dimensional photodetector array.   9. The optical amplifier according to claim 8, wherein the vertical cavity surface emitting laser is an integrated circuit integrated with the photodetector array.   The optical amplifier according to claim 1, wherein the input means has a multi-port structure.   The optical amplifier according to claim 10, wherein the input means comprises an array of optical fibers.   The optical amplifier according to claim 1, wherein the waveguide means has a multiport structure.   The optical amplifier of claim 12 wherein the waveguide means comprises an array of optical fibers.   The optical amplifier of claim 13, wherein the fibers in the optical fiber array are core pumped or cladding pumped.   15. An optical amplifier according to claim 13 or 14, wherein the optical fiber array comprises an erbium-doped aluminosilicate fiber or a praseodymium-doped fluoride fiber.   The optical amplifier according to claim 1, wherein the vertical cavity surface emitting laser operates in a lateral single mode.   The optical amplifier according to claim 1, wherein the vertical cavity surface emitting laser operates in a multimode.   The optical amplifier according to claim 1, wherein the vertical cavity surface emitting laser is arranged with an external cavity resonator. First detection means for detecting a pump beam signal; and a processor to which a pump beam monitoring signal is sent from the first detection means in response to the detected pump signal;
19. An optical amplifier according to any of claims 1 to 18, wherein the processor is operable to generate a control signal for controlling the pump beam generating means in response to the pump beam monitoring signal.   20. The optical amplifier according to claim 19, wherein the first detection means is an array of photodetectors integrated on a semiconductor chip.   And further comprising second detection means for detecting the input signal beam, wherein the input monitoring signal is sent from the second detection means to the processor in response to the detected input signal, the processor 21. An optical amplifier according to claim 19 or 20, wherein is operable to generate a control signal for controlling the beam generating means in response to the received input monitoring signal and the pump beam monitoring signal.   The optical amplifier of claim 21, wherein the second detection means is an array of photodetectors. An optical substrate having a top surface and a bottom surface and two side surfaces extending between the top surface and the bottom surface, the substrate having a square cross section;
An input fiber lay for providing an incident beam and a doped fiber lay for an output that are aligned with each other and coupled to the side surfaces;
An array of vertical cavity surface emitting lasers (VCSELs) that generate a pump beam and a top photodetector array arranged in series closest to the top surface;
A bottom photodetector aligned with the array of VCSELs and the top photodetector array and arranged closest to the bottom surface;
A beam splitting lower surface that sends a majority of the incident beam to the output doped fiber array and reflects a small portion of the incident beam to the bottom photodetector array; and the pump beam for the output. A routing element disposed in the substrate at an angle of 45 degrees relative to a side surface having a reflective top surface that reflects to the doped fiber array;
A processor for adjusting the power level of the pump beam in response to the power level detected by the top and bottom photodetector arrays so that the gain of the optical amplifier can be selectively controlled. An optical amplifier characterized by.   24. The optical amplifier of claim 23, further comprising an array of input microlenses etched into the optical substrate to collimate the incident beam.   25. The output microlens array according to claim 23 or 24, further comprising an array of output microlenses etched into the optical substrate to couple the incident beam and the pump beam to the output doped fiber array. Optical amplifier.   26. An optical amplifier as claimed in any one of claims 23 to 25, wherein the bottom photodetector array is a flip chip coupled to the optical substrate.   27. The optical amplifier according to any one of claims 23 to 26, wherein the VCSEL array is a flip chip coupled to an ultra thin semiconductor (UTS) chip that integrates the top photodetector array.   28. The optical amplifier according to any one of claims 23 to 27, wherein the output doped fiber ray is an erbium doped fiber ray.   The optical amplifier according to any one of claims 23 to 28, wherein the optical substrate is made of a glass or sapphire substrate. A method for controlling the optical gain of an optical amplifier including at least one fiber optic amplifier and a pump source, comprising:
Measuring the power of the pump beam generated by the pump source to obtain a first signal indicative of the power;
Measuring the power of the input optical signal and obtaining a second signal indicative of said power;
Evaluating a signal gain based on the measured input signal power and the pump power to obtain a third signal indicative of a difference between the measured signal gain and a desired signal gain. When,
Processing the first, second and third signals, and generating a pump source drive current profile in response to the processed first, second and third signals;
Controlling generation of a drive current profile to obtain a desired output power for the pump beam.   An optical amplifier fully described above with reference to the accompanying drawings.   A method for controlling the optical gain of an optical amplifier as fully described above with reference to the accompanying drawings.

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