Optical modules equipped with light emitting elements such as surface emitting lasers (for example, VCSEL; Vertical Cavity Surface Emitting Laser) have been used in fiber-based optical communication.  An optical module has an optical receptacle which allows light carrying communication information emitted from the light emitting element to be incident on an end face of an optical fiber. 
Some optical modules are configured to monitor intensity and an amount of light emitted from a light emitting element for the purpose of stabilizing output characteristics of the light emitting element against temperature change and adjusting light output. 
For example, PTL 1 and PTL 2 describe a package type optoelectric converting device which includes a light emitting element and a light receiving element for monitoring.  In the package type optoelectric converting device, part of the light emitted from the light emitting element is reflected to a side of the light receiving element as monitor light by a glass window of the package.  However, when the package type optoelectric converting device described in PTL 1 and PTL 2 is driven at a high frequency, a crosstalk may occur due to an electromagnetic wave leaked from a wiring connected to the light emitting element, in which case, it is difficult to support high speed communication of 10 Gbps or higher.  Further, it is difficult to downsize an optical module which uses the package type optoelectric converting device. 
In contrast, a substrate-mounted optoelectric converting device, which has a light emitting element mounted on a circuit substrate, does not cause a crosstalk as in the package type optoelectric converting device and has an advantage that it is possible to reduce the number of parts and cost and can be downsized.  However, because the substrate-mounted optoelectric converting device does not have a glass window, it is difficult to provide a function of generating monitor light at the side of the light emitting element. 
To solve the above problems, for example, PTL 3 has proposed an optical module in which a reflecting surface for reflecting part of the light emitted from a light emitting element to a side of a light receiving element as monitor light is disposed at an optical receptacle.  This configuration realizes stable high speed communication along with monitoring of output of the light emitting element.