Abstract:
An optical block includes a first surface that receives light entering the optical block, a second surface through which the light exits the optical block, and a reflector that reflects light from the first surface towards the second surface. The reflector includes a textured surface that scatters or absorbs some of the light received from the first surface to attenuate the light exiting the optical block through the second surface.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to optical blocks. More specifically, the present invention relates to an optical block with a modified surface. 
         [0003]    2. Description of the Related Art 
         [0004]    Good modulation characteristics of high-transfer-rate data include having high and uniform contrast between the “on” (digital 1) and “off” (digital 0) states. To achieve good modulation characteristics, it is often necessary to operate a laser in an optical system that generates the high-transfer-rate data at a current well above the laser threshold current, which can generate an excessively large amount of light transmitted through an optical fiber. High optical power levels in an optical fiber can cause detector saturation in a receiver and/or induce signal distortion through optical nonlinearities. Thus, it is desirable to attenuate the amount of light before it enters the optical fiber. 
         [0005]    To attenuate the light before entering into an optical fiber, it is known to use an optical attenuator in the optical path of the light. If the optical path includes an optical block, then it is known to use an optical block made from different materials with different attenuation characteristics, e.g., 1 dB, 2 dB, etc. It is also known to use an in-line optical attenuator. For example, a thin-film on a glass substrate or a bulk absorptive attenuator can be used in the optical path. It is also known to defocus the light before it enters the optical fiber. These techniques have the disadvantage that all channels must have the same attenuation and cannot adapt to part-to-part variations. In addition, for bidirectional transceivers that include both transmit and receive channels in the same optical block, it can sometimes be difficult with these techniques to only attenuate the transmitter channels, which is desired so as to not reduce the sensitivity of the receiver channels. 
         [0006]    Adding an attenuator increases the part count and adds cost and complexity. Multi-channel devices can require multiple attenuation blocks with different attenuation levels. Defocusing the light to decrease the coupling into an optical fiber can result in the excitation of undesirable cladding modes. Defocusing the light can increase the mechanical adjustment range required to achieve the desired degree of attenuation. If the optical fibers are arranged in an optical fiber ribbon, then the attenuation of each optical fiber cannot be individually adjusted because all the optical fibers are mechanically linked. Thus, there is a need for a method and apparatus that can reduce the transmitted light to an appropriate level without adding additional components or mechanical complexity and that can attenuate the transmitted light on a channel-by-channel basis. 
       SUMMARY OF THE INVENTION 
       [0007]    To overcome the problems described above, preferred embodiments of the present invention provide an optical block that provides attenuation in an optical path, transmitter power monitoring, and variation in the attenuation between channels. 
         [0008]    An optical block according to a preferred embodiment of the present allows for the attenuation to be actively performed, while monitoring optical power transmitted through an output optical fiber. A fraction of the transmitter power that is not coupled into the output optical fiber can be coupled into a photodetector, which can be used for transmitter power monitoring. Transmitter power monitoring is useful in determining the operational status of the transmitter over its lifetime. The attenuation can be customized for each channel in a multi-channel device. 
         [0009]    According to a preferred embodiment of the present invention, an optical block includes a first surface that receives light entering the optical block, a second surface through which the light exits the optical block, and a reflector that reflects light from the first surface towards the second surface. The reflector includes a textured surface that scatters or absorbs some of the light received from the first surface to attenuate the light exiting the optical block through the second surface. 
         [0010]    The textured surface preferably includes at least one of dimples, dots, and scratches. The dots are preferably made of material with an index of refraction that matches or substantially matches an index of refraction of the optical block. 
         [0011]    The optical block is preferably a molded optical block. Preferably, the textured surface includes defects formed by a molding process or a surface modification process. 
         [0012]    According to a preferred embodiment of the present invention, an optical engine includes a substrate, a laser mounted to the substrate, an optical block according to one of the various preferred embodiments of the present invention, and an optical fiber that receives light from the second surface of the optical block. The light received by the first surface of the optical block is generated by the laser. 
         [0013]    The optical engine further preferably includes a photodetector that detects light scattered by the textured surface. The optical engine preferably includes multiple channels. Preferably, at least two optical channels have different attenuation levels, or the textured surface scatters the same amount of light for each channel of the multiple channels. 
         [0014]    According to a preferred embodiment of the present invention, a method of attenuating light in an optical engine includes providing an optical engine with a substrate; a laser mounted to the substrate; an optical block including a first surface that receives light entering the optical block from the laser, a second surface through which the light exits the optical block, and a reflector that reflects light from the first surface towards the second surface; and an optical fiber that receives light from the second surface of the optical block; determining a current provided to the laser, measuring optical power in the optical fiber, and texturing a surface of the reflector until the optical power measured in the optical fiber is reduced to a predetermined level to form a textured surface. 
         [0015]    The textured surface preferably includes at least one of dimples, dots, and scratches. The dots are preferably made of material with an index of refraction that matches or substantially matches an index of refraction of the optical block. 
         [0016]    The method further preferably includes molding the optical block. The textured surface preferably includes defects formed during the molding of the optical block. 
         [0017]    The textured surface is preferably formed from laser processing. Preferably, the laser is a pulsed laser and has an emission wavelength that is absorbed in the optical block. The laser processing preferably includes scanning the laser across the reflective surface. 
         [0018]    The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is an exploded view of optical engine that can be used with the preferred embodiments of the present invention. 
           [0020]      FIG. 2  is a cross-sectional view that shows an optical path of the optical engine shown in  FIG. 1 . 
           [0021]      FIG. 3  is a cross-sectional view of a portion of an optical engine according to a preferred embodiment of the present invention. 
           [0022]      FIG. 4  is top view of a molded optical structure. 
           [0023]      FIG. 5  shows a portion of a molded optical structure with a textured area on a reflector surface according to a preferred embodiment of the present invention. 
           [0024]      FIG. 6  is a flowchart diagram showing a method of achieving the proper attenuation level in all channels of an optical engine according to a preferred embodiment of the present invention. 
           [0025]      FIG. 7  is a cross-sectional view of a portion of an optical engine according to a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    The preferred embodiments of the present invention can be used in any application where the amount of optical power coupled into an optical fiber needs to be attenuated by an adjustable amount, including, for example, in an optical engine at an end of an active optical cable. 
         [0027]    An optical engine is a device that performs optical-to-electrical conversion or electrical-to-optical conversion. For a receiver, the optical engine provides optical-to-electrical conversion; for a transmitter, the optical engine provides electrical-to-optical conversion; and for a transceiver, the optical engine provides both optical-to-electrical conversion and electrical-to-optical conversion. In a transceiver, the receiver and transmitter component are preferably separated to reduce cross-talk. 
         [0028]    The optical engine typically includes electro-optical (EO) components connected to a substrate. The optical engine can also include a molded optical structure (MOS) or optical block that connects to the substrate and to optical fibers of an optical cable. Instead of optical fibers, any suitable optical waveguide can be used. The MOS provides an interface with the substrate at a position adjacent to the EO components. Optical paths through the MOS between the EO components and the optical fibers can include a lens system and a reflecting surface. The reflecting surface bends the light path, which can make aligning and mounting the optical fibers easier. The lens system controls the beam sizes, which can ensure good coupling efficiency between the various elements in the optical path. The optical engine can include a plurality of channels, each channel including an associated optical path. The optical engine can include a receive side and transmit side, and each side can include a plurality of channels. 
         [0029]    The optical engine can be used in numerous computer connector systems including, for example: QSFP(+), CX4, CX12, SFP(+), XFP, CXP active optical cables; USB, CIO active optical cables; MDI, DVI, HDMI, Display Port, UDI active optical cables; PCIe x1, x4, x8, x16 active optical cables; SAS, SATA, MiniSATA active optical cables. 
         [0030]      FIG. 1  is an exploded view of a portion of optical engine  100 , and  FIG. 2  shows an optical path  150  through the optical engine  100 .  FIGS. 1 and 2  in this application are similar to FIGS. 2 and 7 in U.S. Pat. No. 8,923,670, the entire contents of which are hereby incorporated herein by reference. The optical engine  100  includes a substrate  102 , EO components  104  connected to the substrate  102 , MOS  110  connected to the substrate  102 , and optical fibers  112  connected to the MOS  110 . The optical engine  100  is suitable for use with either single mode or multimode optical fibers. 
         [0031]    A channel is defined by a single path along which signals are transported, i.e., transmitted and/or received.  FIGS. 1 and 2  show a channel that includes an optical fiber  112 , an optical path  150 , an EO component  104 , and a trace  103 . A transmitting channel includes electrical signals that are inputted to the optical engine  100  at the edge of substrate  102 , that propagate along the trace  103 , that are converted to optical signals in the EO component  104 , and that continue to the optical fiber  112 . A receiving channel includes optical signals that are inputted to the optical engine  100  at the optical fibers  112 , that are converted to electrical signals in the EO component  104 , and that propagate along the trace  103  to the edge of the substrate  102 . 
         [0032]    The EO components  104  include, but are not limited to, laser diodes or laser diode arrays for a transmitting channel and photodetectors or photodetector arrays for receiving channels. The laser diode can produce either a single- or multi-transverse-mode output beam. The laser diode converts an electrical current into light. A laser diode can be, for example, a vertical-cavity surface-emitting laser (VCSEL), but other electrical-to-optical converters could also be used. The photodetector converts received light into a current. Any suitable photodetector can be used. The EO components can be electrically connected to traces  103  on the substrate  102  using either wire bonds or flip-chip techniques. 
         [0033]    The MOS  110  is preferably connected to the substrate  102  at a position adjacent the EO components  104 . The MOS  110  includes a lens system  120  that focuses and directs light from the optical fibers  112  onto the EO components  104  and/or focuses and directs light from the EO components  104  into the optical fibers  112 . The MOS  110  can be made of a single injection-molded optical component or any other suitable device. 
         [0034]    The MOS  110  includes grooves  114  that align and secure the optical fibers  112  in the MOS  110 . It is possible to use structures other than grooves  114  to align the optical fibers  112 . The grooves  114  can be V-shaped grooves or any other suitably shaped grooves. Each of the grooves  114  receives and aligns a corresponding optical fiber  112  in the MOS  110 . A pressure plate  130  secures the optical fibers  112  in the grooves  114 . The MOS  110  can include a strain-relief section  116  that extends beyond the grooves  114 . Epoxy  118  can be used to secure the optical fibers  112  to the strain relief section  116 . Grooves  114  allow assembly techniques in which the optical fibers  112  are held in a clamp and stripped, cleaved, passively aligned, and permanently attached to the MOS  110  in a single operation. 
         [0035]    The MOS  110  can include one or more optical paths  150  through the MOS  100 . Each optical path  150  preferably includes a first lens  126  positioned at a first end of the optical path  150  and a second lens  122  positioned at a second end of the optical path  150 . The first and second lenses  122 ,  126  preferably collimate the light. The second lens  122  is adjacent to the optical fibers  112  and the first lens  126  is adjacent to the EO components  104  but is not so limited. Each optical path  150  further includes a reflector  124  positioned between the first lens  126  and the second lens  122 . The reflector  124  redirects light so the optical path is bent. The bend in the optical path can be approximately 90°, but this is not a requirement. The reflector  124  can use total internal reflection (TIR) to reflect all or substantially all of the incident light. The reflector can also use a reflective film applied to the MOS  110 . Using a reflective film eliminates the angular constraints required of a TIR surface. Either or both of the first lens  126  or the second lens  122  can have no optical power, i.e. they are a flat surface. 
         [0036]    Each optical path  150  includes a second section  151  and a first section  152 . The second section  151  includes a second lens  122  at a second end of the second section  151  and a reflector  124  at a first end of the second section  151 . The second lens  122  can be adjacent to the optical fibers  112 , but is not so limited. The first section  152  includes the reflector  124  at a second end of the first section  152  and a first lens  126  at a first end of the first section  152 . 
         [0037]    The MOS  110  can include a component cavity  162  that creates an enclosed space between the planar surface of the substrate  102  and the MOS  110  for the EO components  104  mounted on substrate  102 . 
         [0038]    The substrate  102  can be any suitable substrate, including, for example, an organic substrate (e.g., FR4) or a ceramic substrate (e.g., Alumina). The substrate  102  can include electrical traces  103  that are used to route electrical data signals. The EO components  104  can include EO converters, and the semiconductor chips  106  can include, for example, analog chips, that drive the EO converters. The semiconductor chips  106  electrically drive the EO converters and can include, for example, a laser diode driver for the laser, and a trans-impedance amplifier (TIA) for the photodetector. The components of the optical engine  100  can be surface-mounted one the same side of the substrate  102  using standard semiconductor assembly processes. 
         [0039]    A riser  108  can be connected to the substrate  102 . The riser  108 , which can be formed from metallic or ceramic compositions, for example, serves as a planar mechanical reference for receiving and aligning the EO components  104  and the MOS  110 . The riser  108  is also used to conduct heat generated by the EO components  104  and/or the semiconductor chips  106  to one or more side or edge regions  109  of the optical engine  100 . 
         [0040]    The optical engine  100  can be manufactured using single-sided, surface-mount component assembly along with a two-step alignment process. The EO components can be bonded on the substrate  102  relative to fiducial marks by a precision die bonder. The EO components  104  for receiving channels and transmitting channels can be aligned and bonded precisely relatively to each other. The MOS  110  is aligned and bonded precisely relatively to the EO components  104 . The MOS  110  includes grooves  114  for precise alignment of the optical fibers  112 , and the optical fibers  112  are passively placed in the grooves  114  and attached to the MOS  110 . In this manner, the optical fibers  112  are directly attached and aligned to the MOS  110 . 
         [0041]    For transmitting channels, the electrical signal coming from the electrical interface is preferably routed and wirebonded from the substrate  102  to a laser diode driver. The laser diode driver is preferably wirebonded to the laser diodes. For receiving channels, the electrical signal coming from the photodetector is preferably wirebonded to the TIA. The TIA is preferably wirebonded to the substrate  102  that route the electrical signals to the electrical interface. These components can be mounted using any suitable technique, including being flip-chip mounted. 
         [0042]    Instead of or in addition to using an open cavity  160 , the reflector  124  can be modified to attenuate the amount of light that enters the optical fiber  112 . For example, the reflectivity of the reflector  124  can be reduced by defeating, spoiling, or degrading the surface of the reflector  124 . Reduction of the surface reflectivity can be achieved by roughening, scratching, dimpling, or in some manner providing a fine pitched mechanical texture to the surface of the reflector  124 . The textured surface on the reflector  124  is generally formed only on transmitting channels where attenuation of the optical power in the optical fiber is desired. The reflector  124  on receiving channels can remain untextured. 
         [0043]      FIG. 3  shows a cross-section of a portion of optical engine  100 . A laser  105  can be mounted on substrate  102 . The laser  105  can be any suitable laser including a VCSEL. The laser  105  can include one or more individual laser emitters. The laser  105  can provide a modulated optical signal suitable for very high bandwidth signal transfer down an optical channel. The laser  105  generates a light beam that follows the optical path  150 . A first lens  126  can be provided on a surface of the MOS  110 . The first lens  126  can collimate or focus the light emitted by the laser  105 . The reflector  124  preferably includes a textured surface so that some light is scattered or absorbed (scattered light is labeled as  111  in  FIG. 3 ) while some light is specularly reflected (reflected light follows the optical path  150 ) towards the optical fiber  112  (not shown in  FIG. 3 ). The light can be reflected because of total internal reflection or an optical coating applied to the surface of the reflector  124 . A textured surface is defined as a surface with deliberately formed defects that degrade the optical quality of the surface. Roughening a surface or applying a pattern of light absorbing or scattering dots are non-limiting examples of forming a textured surface. 
         [0044]    Optionally, a photodetector  107  can be mounted on the substrate  102  or some other location. In  FIG. 3 , alternative positions for the photodetector  107  are shown on the substrate  102  and above the reflector  124 . But any suitable location can be chosen based on the spatial distribution of the scattered light  111  by the textured surface of the reflector  124 . Some of the scattered light  111  can be directed toward the photodetector  107  such that the photodetector  107  samples a portion of the light emitted by the laser  105 , which can be used for transmission (TX) monitoring so that the laser power level can be verified and/or adjusted during operation of the optical engine  100 . The photodetectors  107  can be used in transmitting channels with a laser  105  as shown in  FIG. 3  and can be used in receiving channels with a photodetector. In a receiving channel, the photodetector  107  could be a lower bandwidth, higher sensitivity photodetector that detects lower speed signals that the TIA does not output. 
         [0045]    The MOS  110  can include features to isolate the individual channels from each other. For example, slits can be formed in the MOS  110  between the channels and filled with a light absorbing material. The amount of light reaching the photodetector  107  will be substantially proportional to the emitted laser power. It will also be substantially proportional to the optical power transmitted through the optical fiber  112  because the fraction of scattered light from the reflector is independent of the incident power level. 
         [0046]      FIG. 4  shows a top view of the MOS  110 . The MOS  110  includes a reflector  124  that directs light into an array of optical fibers  112 . The MOS  110  shown in  FIG. 4  preferably includes twelve grooves  114  that can be used with twelve optical fibers  112  (not shown in  FIG. 4 ), and thus potentially twelve high-speed optical channels.  FIG. 5  shows an example of a textured pattern on the surface of the reflector  124 . The textured pattern can be uniform or substantially uniform, within manufacturing tolerances, over the intersection region  113  where the optical path  150  intersects with the surface of the reflector  124 . The textured pattern can be an array of dimples  115  as shown in  FIG. 5 . The dimples  115  can be formed by laser marking or some other suitable method. The size of the dimples  115  in  FIG. 5  has been exaggerated for clarity. Any number of dimples  115  can be used. There can be tens, hundreds, or thousands of dimples  115  on the surface of the reflector  124 . The size and/or the number of dimples  115  can be adjusted to control the fraction of scattered light  111 . Increasing the number of dimples  115  and making the dimples  115  larger tends to increase the amount of scattered light  111 . The dimples  115  can be formed in a regular array, or the dimples  115  can be formed randomly to reduce possible patterns in the scattered light  111  from interference effects. 
         [0047]    The textured surface of the reflector  124  can be made using a laser machining process, although other methods can be used. In the laser machining process, a laser is directed and optionally focused on the surface of the reflector  124 . Application of the laser to the surface of the reflector  124  results in a spatially localized, mechanical, physical, or chemical alteration of the surface of the reflector  124 . This alteration in the surface of the reflector  124  degrades the specularly reflectivity of the surface of the reflector  124 . Preferably, the textured surface covers or substantially covers, within manufacturing tolerances, the intersection region  113 . Covering the entire intersection region  113  allows a uniform or substantially uniform reduction in the specularly reflected light, without impacting its spatial distribution. The coupling tolerances to the optical fiber  112  are thus not impacted by the texturing; only the magnitude of the specularly reflected light is impacted. It is also possible that the desired level of attenuation can be reached by selectivity degrading the reflector  124  over only a portion of the intersection region  113 . 
         [0048]    The surface of the reflector  124  can be modified by any number of methods. For example, lasers can be used to locally modify the reflective properties of the surface of the reflector  124 . In particular, lasers operating at ultraviolet wavelengths can be used. Pulsed lasers based on Q-switching or fiber amplifiers converted to UV wavelengths in the vicinity of 355 nm using nonlinear optical processes are an example of a class of lasers that can work well for this application. Carbon dioxide lasers operating around 10 μm can also be useful. Both the UV and 10-μm-wavelength lasers are strongly absorbed by the optical quality plastic of the MOS  110 . The pulse length of these lasers can be in the nanosecond or microsecond range, but this is not a requirement. 
         [0049]    Alternatively, dots can be placed on the surface of the reflector  124 . The dots can be absorptive, transparent, or translucent. The dots can be made from a material with an index of refraction that matches or substantially matches the index of refraction of the MOS  110  such that light is transmitted with little or no reflection through the surface of the reflector  124  into the dot. The light can then be absorbed in the dot, scattered in the dot, or reflected and refracted off the dot&#39;s rear surface. Each of these mechanisms can attenuate the light coupled into the optical fiber  112 . The dots can be placed using ink-jet printing techniques, but this is not a requirement. 
         [0050]    Mechanical scribing or scratching of the surface of the reflector  124  can also be used. For example, an array of sharpened pins can be pressed or dragged across the surface of the reflector  124 . The array of sharpened pins can be made using MEMS (Micro-Electronic Mechanical Systems) processing techniques, but this is not a requirement. 
         [0051]    The surface of the reflector  124  can be modified during the molding process of the MOS  110 . That is, the MOS  110  can be molded such that the surface of the reflector  124  includes spatially localized defects. These defects can scatter light, reducing the amount of light that enters the optical fiber  112 . Using MOS  110  with prefabricated defects can reduce the number of defects that need to be fabricated in an active manner, thus reducing processing time. 
         [0052]    It is possible that any optical surface, i.e., a surface either that reflects light such as reflector  124  or through which light passes such as lenses  122 ,  126 , can be modified to adjust the attenuation to a desired level. It is also possible that more than one optical surface can be modified. It is also possible to modify optical surfaces that include an optical coating. It is also possible to induce bulk scattering in the MOS  110  by creating spatially localized defects within the MOS  110 . A focus laser with ultrashort pulses, i.e., picoseconds or femtosecond pulse lengths, can be used to locally change the refractive index of the MOS  110 , but this is not a requirement. 
         [0053]    The localized modified regions can be referred to as spots, independent of how the spots are formed (laser, ink-jet, array of sharpened pins, molding, etc.). Spot sizes should be a small percentage of the overall beam size. For example, if the optical path  150  provides a 200-μm beam size on the surface of the reflector  124 , then spot sizes less than 25 μm are preferred. However, the spot size can be on the order of 1 μm, in some applications. Advantageously, a smaller spot size generally results in a more uniform attenuation of the light intensity. This makes the fraction of emitted light coupled into the optical fiber  112  independent of the spatial distribution of the emitted light. A further advantage of small spot sizes is that it provides better resolution to control the amount of light coupled into the optical fiber  112 . Many spots can be made in a millisecond, and an array of spots can be made in less than one second. 
         [0054]    The amount of scattered light can be adjusted using the method shown in  FIG. 6 . An optical engine  100  is first assembled. In step S 101 , the optical engine can be mounted on an adjustment station. The adjustment station provides the capability to both drive a laser under test and measure the light transmitted from the optical fiber associated with the laser under test. In step S 102 , a laser operating point can then be determined by finding a drive current that yields desirable modulation characteristics. As described above, this drive current can produce an excessively large optical signal level in the optical fiber. In step S 103 , the light in the optical fiber is measured. In step S 104 , the signal level in the optical fiber can be decreased by texturing the surface of the reflector. For example, the number of dimples, spots, defects, dots, or surface imperfections can be increased to increase the amount of scattered and/or absorbed light and reduce the amount of light coupled into the optical fiber. Alternatively, instead of, or in addition to, increasing the number of defects, the size or roughness of the defects can be increased to increase the attenuation level. For example, a focused laser spot can be raster scanned over the reflective surface  124 , and the optical power level in the optical fibers  112  measured. If more attenuation is required, then the laser spot can be raster scanned over the same pattern, increasing the roughness of the reflective surface  124  and thereby increasing the attenuation level. The texturing can proceed until a desired fiber transmission level is achieved. In step S 105 , a determination is made as to if all of the channels have been tested and had their respective optical power levels in the optical fibers  112  adjusted. If all the channels have not been tested (the “No” decision in step S 105 ), then in step S 106  an untested channel is selected. If all the channels have been tested (the “Yes” decision in step S 105 ), then in step S 107 , the optical engine is removed from the adjustment station. 
         [0055]    It should be appreciated that the required attenuation can differ between optical channels. In the preferred embodiments of the present invention, the attenuation level can be readily adjusted by changing the degree of texturing for each channel. This is a significant advantage over the prior art technique of using a bulk attenuator having a substantially uniform attenuation for all channels. In the preferred embodiments of the present invention, the desired attenuation in each channel can be achieved without adding an extra part, e.g., the attenuator, to the optical engine  100 . The preferred embodiments of the present invention also can eliminate the need to stock a wide variety of attenuators having different attenuation levels. Preferred embodiments of the present invention can adjust the attenuation level to more than 10 dB of the incident light. While any desired level of attenuation can be achieved, typically attenuation levels are between 2 dB and 5 dB. Using small spots can provide an attenuation resolution of 0.01 dB in each channel. But some applications may not require such fine resolution. 
         [0056]    An optical surface with a textured surface can be combined with a bulk attenuator. The bulk attenuator provides a uniform attenuation level to all channels, and then each channel can be individually optimized by texturing. This combined system has the advantage of reducing the attenuation range required from the textured surface. 
         [0057]    While the preferred embodiments of the present invention have been described in terms of a textured surface of an optical surface in an optical engine, the concepts of the preferred embodiments of the present invention can be applied more broadly. For example, any optical data transmission system requiring attenuation can use the techniques described above to attenuate an optical signal by modifying an optical surface in the optical path of the system. For example, rather than a MOS  110  transmitting light through the structure, an alternative MOS  210  can be configured to reflect light from a first surface as shown in  FIG. 7 . The light path  150  never passes through the MOS  210 . The reflective surface  124  could be curved to focus the light into the optical fiber  112 . The reflective surface  124  could be textured by focusing light through the MOS  210  such that the focus is on or in the vicinity of the reflective surface  124 . In this manner, the texturing light can modify the reflective properties of the reflective surface  124  even though the reflective surface  124  is not on an external surface of the optical engine  100 . Any of the previously described texturing methods can also be used to provide the desired level of attenuation. 
         [0058]    It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.