Optical coupling method utilizing a lensed fiber integrated with a long-period fiber grating

Abstract

A novel optical coupling scheme that uses a lensed fiber integrated with a long-period fiber grating (LPFG) is proposed. Two experiments are performed to demonstrate the validity of such a scheme in single-mode-fiber-single-mode-fiber (SMF-to-SMF) and laser-diode-single-mode-fiber (LD-to-SMF) coupling setups. The measured results show that for an appropriate lens radius the addition of a LPFG will lead to a higher coupling efficiency over a longer range of working distance than without the LPFG. Coupling efficiencies of approximately 78% and 35% are achieved for corresponding working distances of approximately 250 and 110 microm, 1-dB longitudinal tolerances of approximately 40 and 26 microm, and 1-dB transverse tolerances of approximately 7.6 and 2.6 microm for SMF-to-SMF and LD-to-SMF, respectively.

Conversion and focusing of optical fiber modes with superimposed long period gratings

“…1(a). This conversion is necessary for efficient alignment and coupling between a laser source and an optical fiber and, also, between two fibers [5][6][7][8][9]. After entering the fiber, the beam is distributed among the fiber modes.…”

“…The complex-( , ) j e x y κ 12 [5][6][7][8] assumed that the input beam is predominantly transfered into a single cladding mode (CM). For this reason, in [5][6][7][8], conventional single LPG theory [2] was applied. Ref [9] suggested a converter consisting of superimposed LPGs that couple a number of CMs and the FM.…”

“…The beam is composed by optimization of the amplitudes and phases of the first five LP 0j modes generated from the input FM. The single LPG versions of such devices have been experimentally demonstrated previously [4][5][6][7][8]. The advantage of superimposed LPGs is that they possess much broader functionality and, at the same time, can be fabricated using the standard fiber grating fabrication technology [1,3].…”

Analysis of cladding-mode couplings for a lensed fiber integrated with a long-period fiber grating by use of the beam-propagation method

“…7 Coupling schemes with a long working distance and that use an expanded-core fiber 8 or a graded-index fiber were proposed. 9,10 Recently, Chen and Wang 11,12 have demonstrated a new coupling method to obtain long working distances by utilizing a lensed fiber integrated with a long-period fiber grating ͑LPFG͒. In the scheme proposed here, light from an LD excites the fiber cladding mode that is then transferred into a fundamental core mode by the LPFG.…”

“…With the properly chosen radii of the fiber lenses, coupling efficiencies of 78% and 35% at working distances 250 and 110 m were demonstrated for fiber-to-fiber and LD-tofiber couplings, respectively. 12 Although the properties of cladding-mode couplings can be analyzed with the ABCD ray optics model, 12 the effects of fiber core cannot be properly taken into account. In this research, we use the beam-propagation method ͑BPM͒ 15,16 to investigate the field evolution through the lensed fiber with and without a core.…”