Indirect monitoring of semiconductor light source within a photonic package

Abstract

A photonic package includes a housing having a semiconductor light source disposed within the housing. The semiconductor light source has a first output and a second output. A reflective surface is disposed inside the housing to reflect the second output from the semiconductor light source. A photodetector is also disposed within the housing and is adapted to indirectly receive the second output of the semiconductor light source reflected off the reflective surface. As a result, interior surface of a housing of an optical transponder may be utilized to provide reflected light to a photodetector to monitor the semiconductor light source.

Description

102 106 providing a first output (shown as ref. 202 in FIG. 2). Opposite the front facet 102 106, the semiconductor light source 101 has a back facet 103 facing towards the back wall 105 providing a second output. As illustrated in FIG. 1, space within a housing of a photonic package, such as the illustrated optical transponder, can be very limited due to various components and form factor requirements (i.e., numerous components while small form factor).

In order to describe the invention, references will be made to an exemplary area 110 & 350 (an area around the semiconductor light source).

FIG. 2 illustrates indirect monitoring of a semiconductor light source by a photodetector within a photonic package, in accordance with one embodiment of the invention. Illustrated in FIG. 2 is a view of the exemplary area 110 (shown in FIG. 1). In FIG. 2, semiconductor light source 101 provides a first output 201 from the front facet 102 106. As alluded to earlier, in FIG. 2, the first output 201 may be directed towards focusing lenses 104 for focusing light to be provided to the optical fiber (not shown). Also illustrated in FIG. 2 is second output 202 from the back facet 103. Semiconductor light source 101 may be a semiconductor laser, in which case, the first and second outputs 201-202 may each be coherent laser light. Accordingly, illustrated in FIG. 2, when the second output 202 is incident on the surface or back wall 105 angularly disposed relative to the second output 202, the second output 202 may be reflected by the surface or back wall 105. The resultant illustrated as reflected light 210. In FIG. 2, the outputs 201-202 and the reflected light 210 are illustrated visually as different lights. However, it should be appreciated by those skilled in the relevant art, that the visual difference is only for ease of understanding the invention, and does not represent differences in the light.

Illustrated also in FIG. 2 is a photodetector 205 of the photonic package positioned to receive the reflected light from surface or back wall 105, in accordance with one embodiment of the invention. The photodetector 205 may be a photodiode, such as, but not limited to, p-layer, intrinsic layer, and n-layer (p-i-n) junction photodiode, an Schottky photodiode, or an avalanche photodetector. As illustrated in FIG. 2, the photodetector 205 is positioned in a coordinated manner relative to the angular surface or wall 105, such that it may receive reflected light 210 from the interior surface 105. The reflected light 210 may be received by the photodetector 205 through a window (shown as ref. 331 in FIG. 3) of the photodetector 205. Accordingly, as illustrated in FIG. 2, the window 331 of the photodetector faces angular surface or back wall 105. Additionally, illustrated in FIG. 2, the photodetector 205 is disposed on a tracing 207 to facilitate transmission of electrical signals output by the photodetector 205 responsive to the received reflected light to a processor (not shown). The photodetector 205 is adapted to produce an electrical signal responsive to the reflected light based at least on properties of the photodetector 205 such as, but not limited to, spectral responsivity, external quantum efficiency, noise, response time, dark current, and junction capacitance.

For example, the photodetector 205 may be a p-i-n junction photodiode, where spectral responsivity may be expressed as

$\begin{array}{cc}R=\frac{I}{L}& \mathrm{Equation}1\end{array}$
In Equation 1, I is amperes of current generated by the photodetector 205, and L is power of incident light, the reflected light 210, measured in watts. R is responsivity in units of amperes per watt. Furthermore, external quantum efficiency of a photodiode is its capability to convert light energy to electrical energy (i.e., electrical signals), and can be expressed as a relation to responsivity as

$\begin{array}{cc}\mathrm{EQE}\left(\lambda \right)=\frac{I\left(\lambda \right)\mathrm{hc}}{\Phi \left(\lambda \right)\mathrm{ne}\lambda },& \mathrm{Equation}2\end{array}$
where EQE (λ) is external quantum efficiency as function of wavelength, I is photocurrent (output current—dark output current) as function wavelength, h is Planck's constant, c is velocity of light, Φ is input radiant flux (power), n is index of refraction of air, e is elementary charge, and λ is wavelength of light in units of nanometers. Accordingly, the Equation 1 and Equation 2 can be utilized to form the relationship

$\begin{array}{cc}\mathrm{EQE}\left(\lambda \right)=1239\frac{R}{\lambda },& \mathrm{Equation}3\end{array}$
where R and λ, as defined earlier, are responsivity in units of amperes per watt and wavelength of light in units of nanometers, respectively.

The electrical signals may be provided to the processor wherein the electrical signals may be compared to characterization data. The characterization data may relate electrical signals from the photodetector 205 produced by reflected 210 light received by the photodetector 205 of the first output 201 of the light source 101. For example, referring to FIG. 2, characterization data may be produced by having several data points corresponding to power of light of the first output 201 from the front facet 102 106 as compared to power of light of the reflected light 210. The processor has at least access to the characterization data to facilitating calibration of the reflected light 210 by the photodetector 205. Affects, such as, but not limited to, temperature may also be accounted for during the calibration process. Accordingly, as the processor receives the electrical signals from the photodetector 205, the processor may facilitate adjustments to bias voltages of the photodetector 205 to ensure proper monitoring of the semiconductor light source 101.

As a result, a photodetector can be adapted to receive light reflected from a surface of a component disposed at the back of the semiconductor light source, housed inside a densely populated housing of an optical transponder, thereby advantageously monitoring a semiconductor light source from locations other than those that are directly behind the semiconductor light source (i.e., the photodetector is not required to be in direct path of the back output of the semiconductor light source).

FIGS. 3A-3B illustrate indirect monitoring of a semiconductor light source by a photodetector of a photonic package, in accordance with an alternate embodiment of the invention. Illustrated in FIG. 3A is a side view 300 of the housing 100 (shown in FIG. 1) with its cover 310 covering the various components within the housing 100. Commonly, the cover 310, walls (not shown) and floor (not shown) aids in forming a hermetic seal to prevent outside influences, such as, particulate, humidity, etc. In the alternate embodiment illustrated in FIG. 3A, a reflective mirror surface 301 is provided to deflect the second output 202 from the back facet 103 of the semiconductor light source 101 to an interior surface of the cover 303. Accordingly, the deflected second output 202 incidences on the interior surface of the cover 303, reflecting off the surface, and forming cover reflected light 305.

In one embodiment, the interior surface of the cover 303 may have a coating to help facilitate cover reflected light 305, such as, but not limited to, paint having a pigment of titanium dioxide (i.e., white paint).I

In one embodiment, the reflective mirror surface 301 may be a highly polished silicon mirror or a dielectric coating. In alternative embodiments, it may be a reflective sheet or stripe.

FIG. 3B is a perspective view of the exemplary area 350 illustrating an alternately adapted photodetector to receive light reflected from the interior surface of the cover 303, in accordance with the alternate embodiment of FIG. 3A. As illustrated in FIG. 3B, the alternately adapted photodetector 320 has it window 331 facing the interior surface of the cover 303 in a coordinated manner to receive the cover reflected light 305.

Alternatively, in one embodiment, the reflective mirror surface 301 may be disposed in such a manner as to reflect the second output 202 from the back facet 103 of the light source 101 to one or more other secondary reflective surfaces, such as, but not limited to, a side wall of horsing (not shown). For these embodiments, the photodetector will be adapted accordingly in a coordinated manner to receive light reflected from the alternate secondary reflective wall by positioning the receiving window of the photodetector to face the alternate secondary reflective wall.

As a result, alternate interior surfaces of a housing of an optical transponder may be utilized to provide reflected light to a photodetector adapted to receive the reflected light.

Thus, it can be seen from the above descriptions, a novel method and apparatus for indirect monitoring of a light source by a photodetector, has been described.

The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. Thus, the description is to be regarded as illustrative instead of restrictive on the invention.

Claims

1. A photonic package comprising:

a housing;

a semiconductor light source disposed within the housing, the semiconductor light source having a first output and a second output;

a first reflective surface disposed inside the housing selected from one of a side wall of the housing and an interior surface of a cover of the housing to reflect said second output;

a second reflective surface to deflect the second output to the first reflective surface; and

a photodetector disposed within the housing adapted to indirectly receive said second output of the semiconductor light source reflected off said first reflective surface.

2. The photonic package of claim 1, wherein the photonic package comprises an optical transponder.

3. The photonic package of claim 1, wherein the first reflective surface comprises an exterior surface of an elevated substrate angularly disposed relative to the second output, to reflect said second output to said photodetector.

4. The photonic package of claim 1, wherein the second reflective surface comprises a reflective mirror to angularly reflect the second output.

5. The photonic package of claim 4, wherein the first reflective surface is optically coupled to said reflective mirror to further reflect the second output to said photodetector.

6. The photonic package of claim 1, wherein the first output is provided from a front facet of the semiconductor light source.

7. The photonic package of claim 1, wherein the second output is provided from a back facet of the semiconductor light source.

8. The photonic package of claim 1, wherein the photodetector comprises a photodiode.

9. The photonic package of claim 8, wherein the photodiode comprises a p-i-n junction photodiode.

10. The photonic package of claim 1, wherein said first reflective surface comprises a reflective coating.

11. The photonic package of claim 10, wherein the reflective coating comprises paint having a pigment of titanium dioxide.

12. A method for forming a photonic package comprising:

providing a semiconductor light source to provide a first and a second output;

providing a first reflective surface to reflect the second output of the semiconductor light source, wherein said providing of a first reflective surface comprises providing a reflective interior surface to a housing of the photonic package;

providing a second reflective surface and disposing said second reflective surface in a manner such that said second reflective surface reflects said second output of the semiconductor light source to said reflective interior surface of the housing, for reflection to said a photodetector; and

adapting a said photodetector to indirectly receive the second output of the semiconductor light source reflected from the interior surface.

13. The method of claim 12, wherein said providing of a reflective surface comprises providing a substrate having an angular exterior surface, and the method further comprises disposing said substrate in a manner such that said angular exterior surface of the substrate reflects said second output of the semiconductor light source to said photodetector.

14. The method of claim 12, wherein said providing of a second reflective surface comprises of providing a mirror and disposing said mirror in a manner such that said mirror reflects said second output of the semiconductor light source to said reflective interior surface of the house housing, for reflection to said photodetector.

15. The photonic package of claim 14, wherein said at least one of said first and said second reflective surfaces comprises a mirror.

16. A photonic package comprising:

a housing;

a semiconductor light source disposed within the housing, the semiconductor light source having a first output and a second output;

a first reflective surface disposed inside the housing to reflect said second output;

a second reflective surface to deflect the second output to the first reflective surface, at least one of said first and said second reflective surfaces is selected from one of a side wall of the housing and an interior surface of a cover of the housing; and

a photodetector disposed within the housing adapted to indirectly receive said second output of the semiconductor light source reflected off said first reflective surface.

17. A method of monitoring a semiconductor light source substantially enclosed in a housing, the method comprising:

generating a light output signal from the semiconductor light source;

deflecting the light output signal from a back facet of the semiconductor light source toward an interior surface of the housing;

reflecting the light output signal from the interior surface toward a photodetector; and

receiving, at the photodetector, the light output signal reflected from the interior surface.

18. The method of claim 17, wherein said deflecting comprises deflecting the light output signal toward an interior surface selected from one of a side wall of the housing or an interior surface of a cover of the housing.

19. The method of claim 18, wherein the selected interior surface comprises a reflective surface.

20. The method of claim 17, wherein said deflecting comprises deflecting the light output signal toward an interior surface having a reflective surface.

21. The method of claim 20, wherein the reflective surface comprises a silicon mirror.

22. The method of claim 20, wherein the reflective surface comprises a reflective sheet.

23. The method of claim 20, wherein the reflective surface comprises a dielectric coating surface.

24. The method of claim 17, further comprising:

generating an electrical signal at the photodetector in response to said receiving the light output signal.

25. The method of claim 24, further comprising:

comparing, by a processor, the electrical signal to characterization data to facilitate calibration of the received light output signal by the photodetector.

26. The method of claim 25, further comprising:

facilitating, by the processor, an adjustment of a bias voltage of the photodetector in response to said comparing.